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  • Articles  (1,823)
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  • 1
    Electronic Resource
    Electronic Resource
    Assessment of some failure criteria for strongly anisotropic geomaterials (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 1-26 
    Details
    ISSN: 1082-5010
    Keywords: anisotropy ; failure criterion ; schist ; sedimentary rock ; rock joints ; laboratory testing ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is devoted to the assessment of some representative failure criteria in the framework of modelling the failure behaviour of strongly anisotropic geomaterials. Experimental data concerning the failure behaviour of a typical strongly anisotropic rock; the schist of Angers are first presented. Nine widely used failure criteria are then selected and classified into three groups, the mathematical continuous models, the empirical continuous models and the discontinuous weakness planes based models. This classification is made up according to the main assumptions and techniques used in each criterion to describe the strength anisotropy. The calibration of each one is carried out with respect to the laboratory data of Angers schist. Qualitative and quantitative comparisons between the selected criteria and with the experimental data are provided. © 1998 John Wiley & Sons, Ltd.
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  • 2
    Electronic Resource
    Electronic Resource
    A new anisotropic failure criterion for transversely isotropic solids (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 89-103 
    Details
    ISSN: 1082-5010
    Keywords: transversely isotropic material ; elliptic paraboloid failure surface ; strength differential effect ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A coordinate-free formulation of a failure criterion for transversely isotropic solids is proposed. In the three-dimensional stress space the criterion is represented by an elliptic paraboloid. The anisotropic form of the proposed criterion is based on generalization of the second invariant of the deviatoric stress and of the mean stress obtained through the introduction of a unique fourth-order tensor. For isotropic conditions, the criterion reduces to the Mises-Schleicher failure condition. It is shown that the criterion satisfactorily predicts the strength anisotropy of transversely isotropic rocks subjected to an axisymmetric stress state. The procedure for the identification of the parameters of the criterion from a few simple laboratory tests is outlined. © 1998 John Wiley & Sons, Ltd.
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  • 3
    Electronic Resource
    Electronic Resource
    A model for ageing visco-elastic tension softening materials (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 27-39 
    Details
    ISSN: 1082-5010
    Keywords: creep ; effective spring concept ; Kelvin chain model ; load bearing volume ; micromechanical model ; relaxation ; softening spring ; solidification ; tension softening ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An analytical constitutive model similar to the Kelvin chain rheological model associated with solidification theory, is developed for time-dependent tension softening of ageing materials like concrete. The stiffness of spring elements is allowed to vary with time via a function of load bearing volume fraction as in the solidification theory. The development of cracks reduces the load bearing volume fraction with time, so that the overall behaviour of springs is a softening type. A reduction in the load bearing volume with time ensures a gradual reduction in the spring stiffness without violating prescribed retardation times. In some circumstances, depending on the boundary conditions, the stress in a structure can remain unchanged over a period of time. During this period, any cracks in the structure will continue to experience an increased opening due to creep. In other parts of the structure, again depending on the boundary conditions, the crack opening displacements may remain unchanged over a period of time, so that the stress will relax over these parts of the structure. In a large concrete structure, creep and relaxation may be taking place simultaneously in different parts or in the same part but at different times. There is thus a need for a visco-elastic tension softening model for ageing concrete that will cater for both creep and relaxation. © 1998 John Wiley & Sons, Ltd.
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  • 4
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    A constitutive model coupling elastoplasticity and damage for cohesive-frictional materials (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 41-63 
    Details
    ISSN: 1082-5010
    Keywords: elastoplasticity ; damage ; bonded geomaterials ; triaxial testing ; intact and remoulded specimen ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In order to model the various phenomena which govern the mechanical response of bonded geomaterials under monotonic loadings, an elastoplastic model coupled with an elastic model with damage was developed, taking into account both the frictional and cohesive aspects of these materials. First, the principles at the base of the model are presented, as well as the physical meaning of the parameters which were used in the elastic model with damage. In order to illustrate the capabilities of the model to reproduce the mechanical behaviour of bonded geomaterials, we simulated triaxial tests on various materials: a deep cemented clay, whose heterogeneity from one specimen to another appeared mainly due to the calcium carbonate content; an assembly of sintered glass balls; and an artificially cemented sand. In this last example, various initial mean stresses allowed us to enlighten the brittle-ductile transition which was modelled by introducing the mean confining pressure in the damage evolution law. We demonstrated that the parameters of each part of the model could be adapted to reproduce the observed general trends. For weak bonds, the elastoplastic part played the predominant role, whereas for strong bonds, the elastic part with damage governed the mechanical behaviour. © 1998 John Wiley & Sons, Ltd.
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  • 5
    Electronic Resource
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    An investigation on the uniqueness of the incremental response of elastoplastic models for virgin sand (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 65-87 
    Details
    ISSN: 1082-5010
    Keywords: elastoplasticity ; sand ; constitutive modelling ; controllability ; instability ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The paper investigates the possibility of the occurrence of a multiplicity of homogeneous responses of soil specimens under the same incremental loading, and the associated non-controllability of the imposed loading path.It is shown that for non-associated elastoplastic strain-hardening constitutive laws, such a possibility exists even in the hardening regime. Only when the stiffness matrix is positive-definite is the incremental solution unique for any loading programme.A particular constitutive model is chosen and the shape of the loci of non-uniqueness is calculated for various loading programmes. It is shown that the conditions for the occurrence of a shear band and of a peak of the deviator stress in a triaxial undrained test can be seen as special cases of the theory presented. Accordingly, the so-called ‘instability line’ concept in undrained conditions is generalized. © 1998 by John Wiley & Sons, Ltd.
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  • 6
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    ALE analyses of localization in wave propagation problems (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 105-125 
    Details
    ISSN: 1082-5010
    Keywords: localization ; non-local damage ; Perzyna viscoplasticity ; mesh adaptivity ; Arbitrary Lagrangian-Eulerian technique ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The computational modelling of localization of deformation in cohesive-frictional materials must be carried out in a proper, accurate and efficient manner. A proper solution can be obtained by using an enriched material description such as a non-local damage model or Perzyna's viscoplasticity model. However, still a large number of finite elements is needed for an accurate description of the localization zone. To improve efficiency, mesh adaption is applied here by means of the Arbitrary Lagrangian-Eulerian (ALE) technique. The ALE technique must typically be applied in combination with an enriched material model. Otherwise, the use of a standard model gives a zero-width solution of the localization zone and therefore remeshing results in a continuing decrease of finite element size. Implementation of this method requires the addition of convective forces in the equations of motion, transport of the state variables and the formulation of a remeshing strategy. The remeshing strategy heavily determines the success of the ALE method. Three examples of wave propagation have been treated and it is shown that a suitable remeshing strategy in combination with an enriched material model leads to proper, accurate and efficient analyses of the localization process. © 1998 John Wiley & Sons. Ltd.
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  • 7
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    Daphnis: a new model for the description of post-localization behaviour: application to sands (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 127-153 
    Details
    ISSN: 1082-5010
    Keywords: constitutive equations ; post-localization behaviour ; large strain ; interface model ; bifurcation ; shear band ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper addresses developments on a constitutive model able to describe the post-localized behaviour of structures composed by geomaterials. The behaviour of the shear band is defined by means of a specific non-linear constitutive equation in the framework of large strain. Concept of ‘consistency’ of this model with the CLoE model from which it is derived at the onset of localization is discussed. During the post-localization regime this model evolves in a specific way by introducing the concept of critical void ratio. After some recalls about the CLoE framework and about a Rice bifurcation analysis involving CLoE models, the basic concepts of the Daphnis model are introduced. The last part of this paper is devoted to numerical results on an initially homogeneous frictionless biaxial test. The behaviour of the sample is modelled by means of a plane Mohr Coulomb model defined in the CLoE framework and its associated Daphnis model is used to characterize the specific behaviour of the shear band in the post-localization regime. © 1998 John Wiley & Sons, Ltd.
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  • 8
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    Development of a plasticity bond model for steel reinforcement (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 155-180 
    Details
    ISSN: 1082-5010
    Keywords: reinforced concrete ; bond model ; plasticity ; interface ; yield surface ; modelling ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The development of an interface, non-associative, plasticity model for bond between ribbed, steel bars and concrete is discussed. The model relates average local slip and radial dilation to average bond shear stress and radial confinement stress. The model partially accounts for the response of the damaged, finite-thickness region around the bar - the bond zone. The model is developed for standard steel bars that are initially unstrained. With simplifying assumptions, data for the components of a plasticity law are extracted from a key set of experimental results. In this paper, we emphasize the development of an expression for the yield surface for monotonic loading. While the forms of the model's components are empirically derived, they qualitatively reflect the mechanics of the mechanical interaction of ribbed bars with the adjacent concrete. A characteristic length, related to the rib pattern, helps quantify this interaction. The mechanics of the bond are difficult to characterize in a simple form, but the calibrated model only requires four physical properties and reproduces with acceptable accuracy experimental results with various levels of radial confinement stress. Model refinements are suggested for future work. © 1998 John Wiley & Sons, Ltd.
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  • 9
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    FE-Simulation of compaction and solid-state sintering of cemented carbides (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 181-205 
    Details
    ISSN: 1082-5010
    Keywords: cemented ; carbide ; finite ; element ; compaction ; sintering ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We have developed a tool for simulating the press cycle and the sintering cycle of cemented carbides. A constitutive model for compaction and tensile fracture has been implemented in the explicit FE programme LS-DYNA2D, and it has been tuned to experiments of hydrostatic compression, uniaxial strain and conventional triaxial compression. The programme simulates the complete compaction cycle in a robust manner. Friction against the tooling is properly taken into account. We have further developed a constitutive model for the stress-free solid-state sintering to also account for a mechanical stress field. The sintering model is based on physical concepts, diffusion parameters, free surface energy, dimensions of carbide grains, etc. of the constituents, and was tuned to successfully simulate the unloaded and loaded sintering of simple specimens. The models of compaction and sintering have a common set of state variables, such that after the compaction cycle, and at raising the temperature the sintering starts out with proper account of the residual stress field. Finally, the potential of the model is demonstrated by simulating the production cycle of a simple WC-Co tool piece until sintering to 75% of full density. The final geometrical shape of the specimen is compared to experimental data. © 1998 John Wiley & Sons, Ltd.
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  • 10
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    A superstable time-discrete scheme for the numerical integration of viscous constitutive equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 229-256 
    Details
    ISSN: 1082-5010
    Keywords: finite element method ; viscous constitutive equations ; time-discrete scheme ; stability ; superstability ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The general framework of the paper deals with the finite element modelling of mechanical problems involving viscous materials such as bitumen or bituminous concrete. Its aim is to present a second-order-accurate discrete scheme which remains unconditionally superstable when used for the time discretization of the linear and non-linear viscoelastic constitutive equations considered. After stating the space- and time-continuous mechanical problem we focus on the time discretization of these equations, considering three different schemes. For both of them sufficiently small values of the time step are required in order to ensure the superstability, whereas the third remains unconditionally superstable. Eventually, some numerical results are presented. © 1998 John Wiley & Sons, Ltd.
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  • 11
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    Numerical simulations of impacts using a discrete element method (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 257-276 
    Details
    ISSN: 1082-5010
    Keywords: impacts ; structural damage ; discrete element method ; dynamic loading ; scabbing ; perforation ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Impacts of rigid spherical nose shaped missiles on concrete beams are simulated with a discrete element method. The history of the structural damage of the beam is followed from the very first crushing and fracturing processes to the ultimate fragmentation step. Spalling, scabbing, penetration and perforation events are characterized and compared with real test cases of the civil engineering industry. It is found that these phenomena depend not only on the kinetic energy of the missile as predicted by some recent empirical laws but also on its momentum. This means that the dynamic impact loading time is determinant in the scabbing and perforation thicknesses. When the numerical data is plotted against the empirical rules determined from experimental data, the fit is good although the model is two dimensional. © 1998 John Wiley & Sons, Ltd.
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  • 12
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    Failure design of jointed rock structures by means of a homogenization approach (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 207-228 
    Details
    ISSN: 1082-5010
    Keywords: jointed rock masses ; stability ; failure ; yield design ; homogenization ; strength anisotropy ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Conceived as a potential alternative to the methods usually employed for evaluating the stability of jointed rock masses, the homogenization approach developed in this paper stems from the intuitive idea that, from a macroscopic point of view, a rock mass intersected by a regular network of joint surfaces may be perceived as a homogeneous continuum. The failure criterion of such an equivalent medium is theoretically determined from the knowledge of the failure conditions of the individual constituents, namely the intact rock matrix and joint interfaces. Owing to the existence of privileged material directions associated with the joint orientation distribution, this criterion turns out to be of the anisotropic frictional type, as shown by the closed-form expression obtained in the particular case of two mutually orthogonal joint sets. This criterion is then applied to the investigation of two illustrative engineering problems: the calculation of the load-bearing capacity of a shallow foundation on a jointed rock half-space and the stability analysis of an excavation. Both problems are handled by means of the kinematic method of yield design, making use of the previously determined macroscopic failure condition. The upper bound estimates thus derived appear to be significantly better than those obtained from a direct analysis in which the intact rock matrix and joints are considered separately. In spite of some limitations regarding its range of applicability, which are underlined throughout the paper, the homogenization approach may constitute an appropriate general framework for the design of densely jointed rock structures. © 1998 John Wiley & Sons, Ltd.
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  • 13
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    Experimental behaviour of fibre concrete slabs on soil (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 277-290 
    Details
    ISSN: 1082-5010
    Keywords: experimental analysis ; slabs on soil ; reinforced concrete ; steel fibres ; fracture energy ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The cracking control of plain concrete slabs on soil foundation requires the execution of joints with mechanisms of load transfer between adjacent panels. These joints increase the construction costs and, often, are the source of local damage and loss of service performance. Slabs reinforced with steel wire mesh have been used in order to increase the load-carrying capacity and to enhance the cracking control. However, the use of this conventional reinforcement increases the costs, mainly due to labour time spent on the arrangement and positioning of the reinforcement.Fibre-reinforced concrete is a recent material well fitted for applications in industrial floors on soil foundation. The cost of fibres is compensated by a faster construction process and a reduction in the number of expansion joints. The fatigue, impact and flexural strength are significantly improved when steel fibres are added to the concrete mix.The work developed aims to contribute to the on going research effort to clarify the behaviour of fibre-reinforced concrete slabs on soil foundation. For this purpose, an experimental and numerical investigation were carried out. The present article deals basically with the experimental work developed, describing the tests performed and discussing the main results obtained. © 1998 John Wiley & Sons, Ltd.
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  • 14
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    Enhanced consolidation in brittle geomaterials susceptible to damage (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 291-303 
    Details
    ISSN: 1082-5010
    Keywords: poroelasticity ; isotropic damage ; brittle geomaterials ; enhanced consolidation ; saturated geomaterials ; computational modelling ; indentation of geomaterials ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper examines consolidation behaviour of saturated geomaterials with a matrix component which is susceptible to damage. Finite-element-based computational model accounts for the alteration in both the deformability and permeability characteristics of the porous material due to damage evolution. The isotropic damage criteria governing the evolution of elastic stiffness and hydraulic conductivity parameters are characterized by the dependency of the damage variable on the distortional strain invariant. The computational procedure is utilized to evaluate the extent to which the time-dependent axisymmetric indentation behaviour of a rigid circular punch on a poroelastic half-space can be influenced by the damage evolution in the porous skeleton. © 1998 John Wiley & Sons, Ltd.
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  • 15
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    A multilayered mixed beam element in gradient plasticity for the analysis of localized failure modes (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 305-322 
    Details
    ISSN: 1082-5010
    Keywords: strain localization ; finite element ; mesh sensitivity ; regularization ; gradient plasticity ; multilayered concrete beams ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A gradient-dependent plasticity theory is applied to finite element solutions of static strain localization problems. Assuming weak satisfaction of constitutive equations, a multilayered beam finite element with a mixed character is developed. The plastic strain field is discretized in addition of the displacement field. A consistent Newton-Raphson algorithm for this approach is presented. Some examples are carried out in order to illustrate the approach and verify the performances of the element. © 1998 John Wiley & Sons, Ltd.
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  • 16
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    Sliding friction, Physical Principles and Applications by Bo N. J. Persson, Springer, Berlin, 1998 (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 365-365 
    Details
    ISSN: 1082-5010
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 17
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    Gradient-enhanced damage modelling of concrete fracture (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 323-342 
    Details
    ISSN: 1082-5010
    Keywords: concrete fracture ; computational modelling ; continuum damage mechanics ; localization ; regularization ; gradient enhancement ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Classical continuum damage theory for quasi-brittle fracture exhibits an extreme sensitivity to the fineness and orientation of the spatial discretization in finite element simulations. This sensitivity is caused by the fact that the mathematical description becomes ill-posed at a certain level of accumulated damage. The ill-posedness can be removed by the use of a gradient-enhanced damage model. In this model, higher-order deformation gradients give rise to a non-local effect, which regularizes the localization of deformation and thus renders numerical analyses mesh-objective.The mesh objectivity of the gradient-enhanced damage approach is demonstrated by the application to two concrete fracture experiments: a double-edge notched bar subjected to a uniaxial, tensile load and a single-edge notched beam under anti-symmetric four-point loading. Both the initiation and the propagation of damage can be simulated. Particularly the latter aspect calls for an appropriate definition of the strain measure which governs the evolution of damage. © 1998 John Wiley & Sons, Ltd.
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  • 18
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    On the linearization of the microplane model (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 343-364 
    Details
    ISSN: 1082-5010
    Keywords: concrete modelling ; microplane model ; anisotropic damage ; consistent linearization ; localization analysis ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The paper addresses the microplane model in the context of localization analysis. Capable of reproducing experimental results of concrete specimens, the microplane model includes anisotropic damage in a natural and conceptually simple and explicit way. However, the efficiency of former microplane implementations suffers from the expense of the solution procedure being based on the secant stiffness method. Within this paper, the macroscopic constitutive equation derived by kinematically constraining the microplane strains to the macroscopic strain tensor is consistently linearized resulting in quadratic convergence of the Newton-Raphson iteration for the equilibrium equations. A fully three-dimensional model will be presented and linearized incorporating the two-dimensional case in a natural fashion. Furthermore, the localization criterion is analysed, indicating locally the onset of localization in terms of the acoustic tensor. Several examples demonstrate the features of the microplane model in predicting the material behaviour of concrete in tension and compression as well as in shear. © 1998 John Wiley & Sons, Ltd.
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  • 19
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    A numerical study of turbulent line puffs via the renormalization group (RNG) k-∊ model (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 217-247 
    Details
    ISSN: 0271-2091
    Keywords: puffs and thermals ; turbulence modelling ; jets and plumes ; environmental fluid mechanics ; vortex flow ; added mass ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The time evolution of a line puff, a turbulent non-buoyant element with significant momentum, is studied using the renormalization group (RNG) k-∊ model. The numerical results show that the puff motion is characterized by a vortex pair flow; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless time of around 30. The added mass coefficient of the puff motion is found to be approximately unity. The predicted puff flow and mixing rate are substantially similar to those obtained from the standard k-∊ model and are well supported by experimental data. The computed scalar field reveals significant secondary concentration peaks trailing behind in the wake of the puff. The present results suggest that the overall mixing rate of a puff is primarily determined by the large-scale motion and that streamline curvature probably plays a minor role. © 1998 John Wiley & Sons, Ltd.
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  • 20
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    Grid convergence studies for the prediction of hurricane storm surge (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 369-401 
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    ISSN: 0271-2091
    Keywords: storm surge ; shallow water model ; grid convergence ; coastal ocean ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The focus of this paper is a systematic determination of the relationship between grid resolution and errors associated with computations of hurricane storm surge. A grid structure is sought that provides the spatial resolution necessary to capture pertinent storm surge physics and does not overdiscretize. A set of numerical experiments simulating storm surge generation over 14 grid discretizations of idealized domains examines the influence of grid spacing, shoreline detail, coastline resolution and characteristics of the meteorological forcing on storm surge computations. Errors associated with a given grid are estimated using a Richardson-based error estimator. Analysis of the magnitude and location of estimated errors indicates that underresolution on the continental shelf leads to significant overprediction of the primary storm surge. In deeper waters, underresolution causes smearing or damping of the inverted barometer forcing function, which in turn results in underprediction of the surge elevation. In order to maintain a specified error level throughout the duration of the storm, the highest grid resolution is required on the continental shelf and particularly in nearshore areas. The disparity of discretization requirements between deep waters and coastal regions is best met using a graded grid. Application of the graded gridding strategy to the hindcast of Hurricane Camille reinforces the necessity of using a grid that has high levels of resolution in nearshore regions and areas of complex coastal geometry. © 1998 John Wiley & Sons, Ltd.
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    Viscous oscillatory flow around a circular cylinder at low Keulegan-Carpenter numbers and frequency parameters (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 403-442 
    Details
    ISSN: 0271-2091
    Keywords: oscillating flow ; Keulegan-Carpenter number ; finite element method ; in-line force ; transverse force ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The results of a numerical study of the viscous oscillating flow around a circular cylinder at low Keulegan-Carpenter numbers (KC) and frequency parameters (β) are presented in this paper. The finite element method was used for the solution of the Navier-Stokes equations in the formulation where the streamfunction and vorticity are the field variables. The computation was conducted at Keulegan-Carpenter numbers extending up to KC=15 and frequency parameters ranging between β=6 and 100. At low values of the Keulegan-Carpenter number the flow remains symmetrical. As the Keulegan-Carpenter number is increased over a certain value which depends also on the frequency parameter, asymmetries appear in the flow which are eventually amplified and lead finally to complex vortex-shedding patterns, some of which are markedly different from those observed at higher frequency parameters. The solution revealed that although for certain values of KC and β the shedding of vortices is periodic, there also exists a complicated flow regime in which the flow is not periodic but switches between different modes in consecutive cycles of flow oscillation. For the various flow cases examined, the traces of the hydrodynamic forces are presented and the hydrodynamic coefficients and RMS values of the in-line force are compared with experimental evidence. © 1998 John Wiley & Sons, Ltd.
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    Direct numerical simulation of the amplification of a 2D temporal disturbance in plane Poiseuille flow (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 443-457 
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    ISSN: 0271-2091
    Keywords: direct numerical simulation ; 2D temporal disturbance ; plane Poiseuille flow ; finite difference method ; transient non-linear equation ; stream-function-vorticity equation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A direct numerical scheme is developed to study the temporal amplification of a 2D disturbance in plane Poiseuille flow. The transient non-linear Navier-Stokes equations are applied in a region of wavelength moving with the wave propagation speed. The complex amplitude involved in the perturbation functions is considered as the initial input of the non-linear stability equations. In this study a fully implicit finite difference scheme with five points in the flow direction and three points in the normal direction is developed so that numerical simulation of the amplification of a two-dimensional temporal disturbance in plane Poiseuille flow can be investigated. The growth and decay of the disturbance with time are presented and neutral stability curves which are in good agreement with existing solutions can be determined. The critical conditions as a function of the amplitude A0 of the disturbance are presented. Fixing the wavelength, the Navier-Stokes equations are solved up to Re=10,000 a friction factor increasing with Reynolds number is observed. The 2D non-linear behaviour of the streamfunction, vorticity and velocity components at Re=10,000 are also exhibited. © 1998 John Wiley & Sons, Ltd.
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    Effect of Reynolds number on the eddy structure in a lid-driven cavity (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 557-579 
    Details
    ISSN: 0271-2091
    Keywords: lid-driven cavity ; Taylor-Görtler-like vortices ; instabilities ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper we apply a finite volume method, together with a cost-effective segregated solution algorithm, to solve for the primitive velocities and pressure in a set of incompressible Navier-Stokes equations. The well-categorized workshop problem of lid-driven cavity flow is chosen for this exercise, and results focus on the Reynolds number. Solutions are given for a depth-to-width aspect ration of 1:1 and a span-to width aspect ratio of 3:1. Upon increasing the Reynolds number, the flows in the cavity of interest were found to comprise a transition from a strongly two-dimensional character to a truly three-dimensional flow and, subsequently, a bifurcation from a stationary flow pattern to a periodically oscillatory state. Finally, viscous (Tollmien-Schlichting) travelling wave instability further induced longitudinal vortices, which are essentially identical to Taylor-Görtler vortices. The objective of this study was to extend our understanding of the time evolution of a recirculatory flow pattern against the Reynolds number. The main goal was to distinguish the critical Reynolds number at which the presence of a spanwise velocity makes the flow pattern become three-dimensional. Secondly, we intended to learn how and at what Reynolds number the onset of instability is generated. © 1998 John Wiley & Sons, Ltd.
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    A fast algorithm to solve viscous two-phase flow in an axisymmetric rocket nozzle (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 501-517 
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    ISSN: 0271-2091
    Keywords: Multiphase ; turbulent ; finite volumes ; structured grids ; compressible flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerically fast algorithm has been developed to solve the viscous two-phase flow in an axisymmetric rocket nozzle. A Eulerian-Eulerian approach is employed in the computation to couple the gas-particle flow. Turbulence closure is achieved using a Baldwin-Lomax model. The numerical procedure employs a multistage time-stepping Runge-Kutta scheme in conjunction with a finite volume method and is made computationally fast for the axisymmetric nozzle. The present numerical scheme is applied to compute the flow field inside JPL and AGARD nozzles. © 1998 John Wiley & Sons, Ltd.
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    Non-singular direct formulation of boundary integral equations for potential flows (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 627-635 
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    ISSN: 0271-2091
    Keywords: arbitrary-order boundary element method ; non-singular formulation ; potential problems ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents a general direct integral formulation for potential flows. The singularities of Green's functions are desingularized theoretically, using a subtracting and adding back technique, so that Gaussian quadrature or any other numerical integration methods can be applied directly to evaluate all the integrals without any difficulty. When high-order quadrature formulas are applied globally, the number of unknowns can be reduced. Interpolation functions are not necessary for unknown variables in the present paper. Therefore, the present method is much simpler and more efficient than the conventional one. Several numerical examples are calculated and compared satisfactorily with analytical solutions or published results. © 1998 John Wiley & Sons, Ltd.
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    Parallel computation of atmospheric pollutant dispersion under unstably stratified atmosphere (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 677-696 
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    ISSN: 0271-2091
    Keywords: second-order closure model ; pollutant dispersion ; finite element method ; unstably stratified atmosphere ; parallel computation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Pollutant dispersion under unstably stratified atmosphere was investigated numerically using the finite element method. The effects of atmospheric stability on plume trajectory were studied using a three-dimensional second-order closure dispersion model. The numerical model was implemented using domain decomposition method and carried out using a parallel computer. The computation accelerates significantly and the size of computation can be largely increased as a result of the parallelism. A passive contaminant point source was placed at the middle of the convective boundary layer to simulate the atmospheric dispersion. The requirement of the input of dispersion coefficients in k-theory and Gaussian models was replaced with direct input of turbulence flow data. It was found that the present numerical model can predict several non-Gaussian plume behaviours and the computed results agreed well with findings from experimental observations. © 1998 John Wiley & Sons, Ltd.
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    Computation of viscoelastic cable coating flows (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 697-712 
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    ISSN: 0271-2091
    Keywords: viscoelastic ; boundary conditions ; tube tooling ; cable-coating ; finite elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A viscoelastic analysis is presented for model tube tooling, draw-down and combined geometry flows encountered in the cable coating industries. The work investigates the development of stress fields and studies the effect of varying entry flow stress boundary conditions. The analysis takes into account tube tooling and draw-down flow sections individually, and in combination. The flow behaviour of cable-coating grade low density polyethylene is studied assuming a viscoelastic, isothermal flow, and employing a Taylor-Petrov-Galerkin finite element scheme with an exponential Phan-Thien-Tanner constitutive model. © 1998 John Wiley & Sons, Ltd.
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    Numerical analysis of breaking waves using the moving particle semi-implicit method (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 751-769 
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    ISSN: 0271-2091
    Keywords: MPS ; particle method ; incompressible flow ; free surface ; breaking wave ; surf similarity parameter ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The numerical method used in this study is the moving particle semi-implicit (MPS) method, which is based on particles and their interactions. The particle number density is implicitly required to be constant to satisfy incompressibility. A semi-implicit algorithm is used for two-dimensional incompressible non-viscous flow analysis. The particles whose particle number densities are below a set point are considered as on the free surface. Grids are not necessary in any calculation steps. It is estimated that most of computation time is used in generation of the list of neighboring particles in a large problem. An algorithm to enhance the computation speed is proposed. The MPS method is applied to numerical simulation of breaking waves on slopes. Two types of breaking waves, plunging and spilling breakers, are observed in the calculation results. The breaker types are classified by using the minimum angular momentum at the wave front. The surf similarity parameter which separates the types agrees well with references. Breaking waves are also calculated with a passively moving float which is modelled by particles. Artificial friction due to the disturbed motion of particles causes errors in the flow velocity distribution which is shown in comparison with the theoretical solution of a cnoidal wave. © 1998 John Wiley & Sons, Ltd.
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    An efficient operator splitting scheme for three-dimensional hydrodynamic computations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 771-789 
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    ISSN: 0271-2091
    Keywords: three-dimensional numerical method ; hybrid method ; splitting method ; Eulerian-Lagrangian method ; shallow water equations ; sigma co-ordinate transformation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A new efficient numerical method for three-dimensional hydrodynamic computations is presented and discussed in this paper. The method is based on the operator splitting method and combined with Eulerian-Lagrangian method, finite element method and finite difference method. To increase the efficiency and stability of the numerical solutions, the operator splitting method is employed to partition the momentum equations into three parts, according to physical phenomena. A time step is divided into three time substeps. In the first substep, advection and Coriolis force are solved using the explicit Eulerian-Lagrangian method. In the second substep, horizontal diffusion is approximated by implicit FEM in each horizontal layer. In the last substep, the continuity equation is solved by implicit FEM, and vertical diffusion and pressure gradient are discretized by implicit FDM in each nodal column. The stability analysis shows that this method is unconditionally stable. A number of numerical experiments have been performed. The results simulated by the present scheme agree well with analytical solutions and the other documented model results. The method is efficient for 3D shallow water flow computations and fully fits complicated configurations. © 1998 John Wiley & Sons, Ltd.
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    A numerical simulation of hydrodynamic forces of ground-effect problem using Lagrange's equation of motion (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 725-747 
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    ISSN: 0271-2091
    Keywords: unsteady two-body interaction ; potential flow theory ; boundary-integral method ; Lagrange's equation of motion ; generalized Taylor's formula ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: On the basis of the potential flow theory, Lagrange's equation of motion is used to study the unsteady ground-effect problem. The forces and moments acting on the moving body are solved in terms of the derivatives of added masses in which the generalized Taylor's formulae are applied. The singular integral equations used to solve the surface source intensities and their derivatives are regularized by the Gauss flux theorem and are therefore amenable to the direct use of the Gaussian quadrature formula. In illustration, the condition of a prolate spheroid moving in the fore-and-aft direction at constant speed past a flat ground with a protrusion is considered. The hydrodynamic forces and moments acting on the moving spheroid are investigated systematically by varying the size of the protrusion and the cruising height of the spheroid. © 1998 John Wiley & Sons, Ltd.
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    Numerical analysis of secondary instabilities of the incompressible boundary layer flow with suction (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 811-835 
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    ISSN: 0271-2091
    Keywords: Floquet ; subharmonic ; fundamental ; secondary instability ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Based on the Euler-Maclaurin formula, a compact finite difference scheme is employed to solve a two-point boundary value problem for studying the secondary instabilities of the boundary layer flow. The parametric resonance of unstable waves is explored using the Floquet method. For both subharmonic and fundamental modes, two additional Fourier terms are added in the analysis, and the spatial growth rates are determined. The effect of suction mechanism on the secondary instability waves is also investigated. From numerical experiments, it is shown that the proposed numerical scheme is very promising. © 1998 John Wiley & Sons, Ltd.
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    Calculation of laminar flows with second-order schemes and collocated variable arrangement (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 887-905 
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    ISSN: 0271-2091
    Keywords: laminar flows ; incompressible flows ; second-order schemes ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical study of laminar flows is carried out to examine the performance of two second-order discretization schemes: a total variation diminishing scheme and a second-order upwind scheme. The former has the same form as the standard first-order hybrid central upwind scheme, but with a numerical diffusion reduced by the Van Leer limiter; the latter is based on the linear extrapolation of cell face values using the two upwind neighbors. A collocated grid arrangement is used; oscillations which could be generated by pressure-velocity decoupling are avoided via the Rhie-Chow interpolation. Two iterative solution methods are used: (i) the deferred correction procedure proposed by Khosla and Rubin and (ii) implicit treatment of the second-order upwind contribution. Three two-dimensional laminar test cases are considered for assessment: the plane lid-driven cavity, the plane backward facing step and the axisymmetric pipe with sudden contraction. Experimental data are available for the two last cases. Both the total variation diminishing and the second-order upwind schemes give wiggle-free results and can predict the flowfields more accurately than the standard first-order hybrid central upwind scheme. © 1998 John Wiley & Sons, Ltd.
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    A semi-coarsening strategy for unstructured multigrid based on agglomeration (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 927-957 
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    ISSN: 0271-2091
    Keywords: multigrid methods ; finite elements ; finite volumes ; semi-coarsening ; numerical analysis ; turbulent flows ; compressible flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Extending multigrid concepts to the calculation of complex compressible flow is usually not straightforward. This is especially true when non-embedded grid hierarchies or volume agglomeration strategies are used to construct a gradation of unstructured grids. In this work, a multigrid method for solving second-order PDE's on stretched unstructured triangulations is studied. The finite volume agglomeration multigrid technique originally developed for solving the Euler equations is used (M.-H. Lallemand and A. Dervieux, in Multigrid Methods, Theory, Applications and Supercomputing, Marcel Dekker, 337-363 (1988)). First, a directional semi-coarsening strategy based on Poisson's equation is proposed. The second-order derivatives are approximated on each level by introducing a correction factor adapted to the semi-coarsening strategy. Then, this method is applied to solve the Poisson equation. It is extended to the 2D Reynolds-averaged Navier-Stokes equations with appropriate boundary treatment for low-Reynolds number turbulent flows. © 1998 John Wiley & Sons, Ltd.
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    A three-dimensional simulation of a steady approach flow past a circular cylinder at low Reynolds number (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 1003-1022 
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    ISSN: 0271-2091
    Keywords: steady approach flow ; low Reynolds numbers ; 3D simulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The three-dimensional (3D) unsteady viscous wake of a circular cylinder exposed to a steady approach flow is calculated using a fractional-step finite-difference/spectral-element method. The calculated flow fields at Reynolds numbers of 100 (2D) and 200 (3D) are examined in detail. The flow field at Re = 100 is 2D as expected, while the flow field at Re = 200 has distinct 3D features, with spanwise wavelengths of about 3.75 cylinder diameters. The calculated results produce drag and lift coefficients and Strouhal numbers that agree extremely well with the experimental values. These 3D values at Re = 200 are in better agreement with experimental values than the results of a 2D calculation at Re = 200, which is expected. © 1998 John Wiley & Sons, Ltd.
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    Domain decomposition for the incompressible Navier-Stokes equations: solving subdomain problems accurately and inaccurately (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 1217-1237 
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    ISSN: 0271-2091
    Keywords: domain decomposition ; GCR ; Krylov-Schwarz ; incompressible Navier-Stokes ; boundary-fitted co-ordinates ; finite volume ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: For the solution of practical flow problems in arbitrarily shaped domains, simple Schwarz domain decomposition methods with minimal overlap are quite efficient, provided Krylov subspace methods, e.g. the GMRES method, are used to accelerate convergence. With an accurate subdomain solution, the amount of time spent solving these problems may be quite large. To reduce computing time, an inaccurate solution of subdomain problems is considered, which requires a GCR-based acceleration technique. Much emphasis is put on the multiplicative domain decomposition algorithm since we also want an algorithm which is fast on a single processor. Nevertheless, the prospects for parallel implementation are also investigated. © 1998 John Wiley & Sons, Ltd.
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    A general algorithm for compressible and incompressible flows. Part III: The semi-implicit form (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 13-32 
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    ISSN: 0271-2091
    Keywords: splitting ; pressure stabilization ; characteristic schemes ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this paper we consider some particular aspects related to the semi-implicit version of a fractional step finite element method for compressible flows that we have developed recently. The first is the imposition of boundary conditions. We show that no boundary conditions at all need to be imposed in the first step where an intermediate momentum is computed. This allows us to impose the real boundary conditions for the pressure, a point that turns out to be very important for compressible flows.The main difficulty of the semi-implicit form of the scheme arises in the solution of the continuity equation, since it involves both the density and the pressure. These two variables can be related through the equation of state, which in turn introduces the temperature as a variable in many cases. We discuss here the choice of variables (pressure or density) and some strategies to solve the continuity equation.The final point that we study is the behaviour of the scheme in the incompressible limit. It is shown that the method has an inherent pressure dissipation that allows us to reach this limit without having to satisfy the classical compatibility conditions for the interpolation of the velocity and the pressure. © 1998 John Wiley & Sons, Ltd.
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    Unstructured mesh procedures for the simulation of three-dimensional transient compressible inviscid flows with moving boundary components (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 41-55 
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    ISSN: 0271-2091
    Keywords: unstructured mesh ; compressible flow ; transient flow ; mesh adaptation ; moving boundaries ; Delaunay triangulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The solution of high-speed transient inviscid compressible flow problems in three dimensions is considered. Discretization of the spatial domain is accomplished by the use of tetrahedral elements generated by Delaunay triangulation with automatic point creation. Methods of adapting the mesh to allow for boundary movement are considered and a strategy for ensuring boundary recovery is proposed. An explicit multistage time-stepping algorithm is employed to advance the flow solution. A number of examples are included to illustrate the numerical performance of the proposed procedures. © 1998 John Wiley & Sons, Ltd.
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    On a multilevel approach for the two dimensional Navier-Stokes equations with finite elements (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 241-258 
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    ISSN: 0271-2091
    Keywords: multilevel algorithm ; 2D Navier-Stokes equations ; finite element ; large eddy simulations ; long time integration ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: We study if the multilevel algorithm introduced in Debussche et al. (Theor. Comput. Fluid Dynam., 7, 279-315 (1995)) and Dubois et al. (J. Sci. Comp., 8, 167-194 (1993)) for the 2D Navier-Stokes equations with periodic boundary conditions and spectral discretization can be generalized to more general boundary conditions and to finite elements. We first show that a direct generalization, as in Calgaro et al. (Appl. Numer. Math., 21, 1-40 (1997)), for the Burgers equation, would not be very efficient. We then propose a new approach where the domain of integration is decomposed in subdomains. This enables us to define localized small-scale components and we show that, in this context, there is a good separation of scales. We conclude that all the ingredients necessary for the implementation of the multilevel algorithm are present. © 1998 John Wiley & Sons, Ltd.
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    A parallel solver based on the dual Schur decomposition of general finite element matrices (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 23-46 
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    ISSN: 0271-2091
    Keywords: domain decomposition ; parallel algorithms ; finite element ; Lagrange multipliers ; projected GMRES ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A parallel solver based on domain decomposition is presented for the solution of large algebraic systems arising in the finite element discretization of mechanical problems. It is hybrid in the sense that it combines a direct factorization of the local subdomain problems with an iterative treatment of the interface system by a parallel GMRES algorithm. An important feature of the proposed solver is the use of a set of Lagrange multipliers to enforce continuity of the finite element unknowns at the interface. A projection step and a preconditioner are proposed to control the conditioning of the interface matrix.The decomposition of the finite element mesh is formulated as a graph partitioning problem. A two-step approach is used where an initial decomposition is optimized by non-deterministic heuristics to increase the quality of the decomposition.Parallel simulations of a Navier-Stokes flow problem carried out on a Convex Exemplar SPP system with 16 processors show that the use of optimized decompositions and the preconditioning step are keys to obtaining high parallel efficiencies. Typical parallel efficiencies range above 80%. © 1998 John Wiley & Sons, Ltd.
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    Large eddy simulation of temporally developing juncture flows (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 47-72 
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    ISSN: 0271-2091
    Keywords: large eddy simulation ; juncture flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Large eddy simulation (LES) results are reported for temporally developing solid-solid and solid-rigid-lid juncture flows. A MacCormack-type scheme that is second-order in time, and fourth-order in space for the convective terms and second-order in space for the viscous terms, is used. The simulations are obtained for a low subsonic Mach number. The subgrid-scale stresses (SGS) are modeled using the dynamic modeling procedure. The turbulent flow field generated on a flat-plate boundary layer is used to initialize the juncture flow simulations. The results of the flat-plate boundary layer simulations are validated with experimental and direct numerical simulations (DNS) data. In juncture flow simulations, the presence of an adjacent solid-wall/rigid-lid boundary altered the mean and the turbulent field, setting up gradients in the anisotropy of normal Reynolds stresses resulting in the formation of turbulence-induced secondary vortices. The relative size of these secondary vortices and the distribution of mean and turbulent quantities are in qualitative agreement with the experimental observations for the solid-solid juncture. The overall distribution of the mean and turbulence quantities showed close resemblance between the solid-solid and the solid-rigid-lid junctures; except for the absence of a second vortical region near the rigid-lid boundary. In agreement with the experimental observations, it was found that the normalized anisotropy term exhibited similarity when plotted against the distance from the boundary, regardless of the type of boundary, i.e. solid-wall or rigid-lid. The turbulent kinetic energy increased near the rigid-lid boundary. While the surface normal velocity fluctuations decreased to zero at the rigid-lid boundary, the other two velocity components showed an increase in their energy, which is also consistent with the experimental observations. © 1998 John Wiley & Sons, Ltd.
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    On initial, boundary conditions and viscosity coefficient control for Burgers' equation (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 113-128 
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    ISSN: 0271-2091
    Keywords: optimal control ; Burgers' equation ; data assimilation ; adjoint model ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In order to use the optimal control techniques in models of geophysical flow circulation, an application to a 1D advection-diffusion equation, the so-called Burgers' equation, is described. The aim of optimal control is to find the best parameters of the model which ensure the closest simulation to the observed values. In a more general case, the continuous problem and the corresponding discrete form are formulated. Three kinds of simulation are realized to validate the method. Optimal control processes by initial and boundary conditions require an implicit discretization scheme on the first time step and a decentered one for the non-linear advection term on boundaries. The robustness of the method is tested with a noised dataset and random values of the initial controls. The optimization process of the viscosity coefficient as a time- and space-dependent variable is more difficult. A numerical study of the model sensitivity is carried out. Finally, the numerical application of the simultaneous control by the initial conditions, the boundary conditions and the viscosity coefficient allows a possible influence between controls to be taken into account. These numerical experiments give methodological rules for applications to more complex situations. © 1998 John Wiley & Sons, Ltd.
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    A numerical study on flow through the spiral casing of a hydraulic turbine (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 143-156 
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    ISSN: 0271-2091
    Keywords: turbine ; spiral casing ; finite element method ; Galerkin weighted residual technique ; Gauss-Legendre quadrature ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Flow through the spiral casing of a hydraulic turbine was analyzed. Reynolds averaged Navier-Stokes equations were solved using a finite element method. The physical domain was divided into a number of hexahedral elements which are isoparametrically mapped onto standard cubic elements. Numerical integration for the unsteady momentum equation is performed over such hexahedral elements to obtain a provisional velocity field. Compliance with the mass conservation equation and determination of the pressure correction are accomplished through an iterative procedure. The velocity distribution inside the spiral casing corroborates the results available in literature. The static pressure at the midplane generally decreases from the outside wall towards the exit of the spiral casing. © 1998 John Wiley & Sons, Ltd.
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    Free-surface flow over curved surfaces: Part II: Computational model (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 201-213 
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    ISSN: 0271-2091
    Keywords: curved surface ; shallow water ; non-hydrostatic ; spillway ; finite element ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In Part I a detailed derivation of a more general shallow water equation set was developed via a perturbation analysis. A finite element computational model of these more general equations is now constructed and the model behavior is compared with conventional shallow water formulations applied to an outletworks flume. © 1998 John Wiley & Sons, Ltd.
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    Numerical and experimental investigation of turbulent flow in a rectangular duct (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 225-242 
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    ISSN: 0271-2091
    Keywords: turbulent flow ; non-linear turbulence modelling ; secondary flow ; rectangular duct ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Details of the turbulent flow in a 1:8 aspect ratio rectangular duct at a Reynolds number of approximately 5800 were investigated both numerically and experimentally. The three-dimensional mean velocity field and the normal stresses were measured at a position 50 hydraulic diameters downstream from the inlet using laser doppler velocimetry (LDV). Numerical simulations were carried out for the same flow case assuming fully developed conditions by imposing cyclic boundary conditions in the main flow direction. The numerical approach was based on the finite volume technique with a non-staggered grid arrangement and the SIMPLEC algorithm. Results have been obtained with a linear and a non-linear (Speziale) k-ε model, combined with the Lam-Bremhorst damping functions for low Reynolds numbers. The secondary flow patterns, as well as the magnitude of the main flow and overall parameters predicted by the non-linear k-ε model, show good agreement with the experimental results. However, the simulations provide less anisotropy in the normal stresses than the measurements. Also, the magnitudes of the secondary velocities close to the duct corners are underestimated. © 1998 John Wiley & Sons, Ltd.
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    Computations using the preconditioning BI-CGSTAB algorithm in chemical non-equilibrium problems (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 267-291 
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    ISSN: 0271-2091
    Keywords: non-equilibrium equations ; Bi-CGSTAB method ; adaptive grid ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A robust method for solving the chemical non-equilibrium Navier-Stokes equations, including all of the species conservation and energy production equations, is developed. The algorithm is embodied in a fully coupled, implicit, large block structure. Van Leer flux splitting for inviscid terms and central differencing for viscous terms in the explicit operators are applied in the numerical algorithm. The fully-coupled system is solved implicitly and the bi-conjugate gradient stable (Bi-CGSTAB) method with a preconditioner of incomplete lower-upper (LU)-factorization (ILU) is used for solving large block structure and diagonal dominate matrix equations. The computations are performed for the hypersonic inflow over blunt bodies including half cylinder, double ellipse and blunt nose. The adaptive grid constructed by moving grid method is employed to capture the shock location. Computational results in the present study are compared with other calculated data and exhibit good agreement. Convergence histories of the mean flow variables and species equations demonstrate that the fast convergent rate can be achieved by the preconditioned Bi-CGSTAB method. © 1998 John Wiley & Sons, Ltd.
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    Efficient algebraic multigrid solvers with elementary restriction and prolongation (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 317-336 
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    ISSN: 0271-2091
    Keywords: algebraic multigrid ; elementary restriction/prolongation ; minimum residual methods ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An algebraic multigrid (AMG) scheme is presented for the efficient solution of large systems of coupled algebraic equations involving second-order discrete differentials. It is based on elementary (zero-order) intergrid transfer operators but exhibits convergence rates that are independent of the system bandwidth. Inconsistencies in the coarse-grid approximation are minimised using a global scaling approximation which requires no explicit geometrical information. Residual components of the error spectrum that remain poorly represented in the coarse-grid approximations are reduced by exploiting Krylof subspace methods. The scheme represents a robust, simple and cost-effective approach to the problem of slowly converging eigenmodes when low-order prolongation and restriction operators are used in multigrid algorithms. The algorithm investigated here uses a generalised conjugate residual (GCR) accelerator; it might also be described as an AMG preconditioned GCR method. It is applied to two test problems, one based on a solution of a discrete Poisson-type equation for nodal pressures in a pipe network, the other based on coupled solutions to the discrete Navier-Stokes equations for flows and pressures in a driven cavity. © 1998 John Wiley & Sons, Ltd.
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    A volume-tracking method for incompressible multifluid flows with large density variations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 357-378 
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    ISSN: 0271-2091
    Keywords: interfacial flow ; multigrid ; surface tension ; flux-corrected transport ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical technique (FGVT) for solving the time-dependent incompressible Navier-Stokes equations in fluid flows with large density variations is presented for staggered grids. Mass conservation is based on a volume tracking method and incorporates a piecewise-linear interface reconstruction on a grid twice as fine as the velocity-pressure grid. It also uses a special flux-corrected transport algorithm for momentum advection, a multigrid algorithm for solving a pressure-correction equation and a surface tension algorithm that is robust and stable. In principle, the method conserves both mass and momentum exactly, and maintains extremely sharp fluid interfaces. Applications of the numerical method to prediction of two-dimensional bubble rise in an inclined channel and a bubble bursting through an interface are presented. © 1998 John Wiley & Sons, Ltd.
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    Numerical solution of a two-dimensional fluidized bed model (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 381-394 
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    ISSN: 0271-2091
    Keywords: fluidized bed ; hyperbolic PDEs ; Roe's method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The numerical solution of a model describing a two-dimensional fluidized bed is considered. The model takes the form of a hyperbolic system of conservation laws with source term, coupled with an elliptic equation for determining a streamfunction. Operator splitting is used to produce homogeneous one-dimensional hyperbolic systems and ordinary differential equations involving the source term. The one-dimensional hyperbolic problems are solved using Roe's method with the addition of an entropy fix. The numerical procedure is second-order in time and first-order in space. Second-order-accuracy in space is obtained using flux limiting techniques. Numerical experiments which show the development of bubbles in the bed are presented. The familiar kidney-shaped bubble, observed experimentally, is found when using the method which is second-order in space. On the same mesh, the first-order method produces bubbles which are no longer kidney-shaped. © 1998 John Wiley & Sons, Ltd.
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    Design sensitivity and finite element analysis of free surface flows with application to optimal design of casting rigging systems (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 419-442 
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    ISSN: 0271-2091
    Keywords: finite element analysis ; design sensitivity analysis ; optimization ; mold filling ; free surface ; turbulence ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A novel, fully-analytical design sensitivity formulation for transient, turbulent, free surface flows is derived and implemented in the context of finite element analysis. The time-averaged, turbulent form of the Navier-Stokes equations are solved using a mixing length model, in conjunction with the volume of fluid (VOF) method to model the free surface movement. The design derivatives of these governing equations are computed and solved to find the analytical sensitivities of the fluid position, velocity and pressure fields with respect to shape design variables. The computational efficiency produced by evaluating the sensitivities analytically is demonstrated. The design of the runner and gating system of a simple block casting is presented as an example application for using sensitivity information in design. The analytical sensitivity routine is coupled to a numerical optimizer to yield an automated method for optimal design of the casting rigging system. The results produce runner shapes which eliminate mold-gas aspiration. © 1998 John Wiley & Sons, Ltd.
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    An operator splitting algorithm for the three-dimensional advection-diffusion equation (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 461-476 
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    ISSN: 0271-2091
    Keywords: advection-diffusion equation ; operator splitting algorithm ; Holly and Preissmann scheme ; method of characteristics ; finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Operator splitting algorithms are frequently used for solving the advection-diffusion equation, especially to deal with advection dominated transport problems. In this paper an operator splitting algorithm for the three-dimensional advection-diffusion equation is presented. The algorithm represents a second-order-accurate adaptation of the Holly and Preissmann scheme for three-dimensional problems. The governing equation is split into an advection equation and a diffusion equation, and they are solved by a backward method of characteristics and a finite element method, respectively. The Hermite interpolation function is used for interpolation of concentration in the advection step. The spatial gradients of concentration in the Hermite interpolation are obtained by solving equations for concentration gradients in the advection step. To make the composite algorithm efficient, only three equations for first-order concentration derivatives are solved in the diffusion step of computation. The higher-order spatial concentration gradients, necessary to advance the solution in a computational cycle, are obtained by numerical differentiations based on the available information. The simulation characteristics and accuracy of the proposed algorithm are demonstrated by several advection dominated transport problems. © 1998 John Wiley & Sons, Ltd.
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    Non-reflecting boundary conditions applicable to general purpose CFD simulators (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 523-540 
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    ISSN: 0271-2091
    Keywords: non-reflecting boundary conditions ; numerical simulation ; compression wave ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In simulations of propagating blast waves the effects of artificial reflections at open boundaries can seriously degrade the accuracy of the computations. In this paper, a boundary condition based on a local approximation by a plane traveling wave is presented. The method yields small artificial reflections at open boundaries. The derivation and the theory behind these so-called plane-wave boundary conditions are presented. The method is conceptually simple and is easy to implement in two and three dimensions. These non-reflecting boundary conditions are employed in the three-dimensional computational fluid dynamics (CFD) solver FLACS, capable of simulating gas explosions and blast-wave propagation in complex geometries. Several examples involving propagating waves in one and two dimensions, shock tube and an example of a simulation of a propagating blast wave generated by an explosion in a compressor module are shown. The numerical simulations show that artificial reflections due to the boundary conditions employed are negligible. © 1998 John Wiley & Sons, Ltd.
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    The fundamental solution method for incompressible Navier-Stokes equations (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 565-568 
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    ISSN: 0271-2091
    Keywords: fundamental solution method ; integral equation method ; Navier-Stokes equations ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A complete boundary integral formulation for incompressible Navier-Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for the lift and the drag hysteresis associated with a NACA0012 aerofoil oscillating in pitch show good agreement with available experimental data. © 1998 John Wiley & Sons, Ltd.
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    Viscous flow with large fluid-fluid interface displacement (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 859-881 
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    ISSN: 0271-2091
    Keywords: 3D ; finite elements ; arbitrary Lagrange-Euler ; fluid-fluid interfaces ; annulus ; displacement ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The arbitrary Lagrange-Euler (ALE) kinematic description has been implemented in a 3D transient finite element program to simulate multiple fluid flows with fluid-fluid interface or surface displacements. The description of fluid interfaces includes variable interfacial tension, and the formulation is useful in the simulation of low and intermediate Reynolds number viscous flow. The displacement of two immiscible Newtonian fluids in a vertical (concentric and eccentric) annulus and a (vertical and inclined) tube is simulated. © 1998 John Wiley & Sons, Ltd.
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    Three-dimensional incompressible Navier-Stokes equations on non-orthogonal staggered grids using the velocity-vorticity formulation (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 917-943 
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    ISSN: 0271-2091
    Keywords: Navier-Stokes ; incompressible flow ; velocity-vorticity formulation ; generalized curvilinear co-ordinates ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper is concerned with the numerical resolution of the incompressible Navier-Stokes equations in the velocity-vorticity form on non-orthogonal structured grids. The discretization is performed in such a way, that the discrete operators mimic the properties of the continuous ones. This allows the discrete equivalence between the primitive and velocity-vorticity formulations to be proved. This last formulation can thus be seen as a particular technique for solving the primitive equations. The difficulty associated with non-simply connected computational domains and with the implementation of the boundary conditions are discussed. One of the main drawback of the velocity-vorticity formulation, relative to the additional computational work required for solving the additional unknowns, is alleviated. Two- and three-dimensional numerical test cases validate the proposed method. © 1998 John Wiley & Sons, Ltd.
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    Simulations of 2D and 3D thermocapillary flows by a least-squares finite element method (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 983-1007 
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    ISSN: 0271-2091
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Numerical results for time-dependent 2D and 3D thermocapillary flows are presented in this work. The numerical algorithm is based on the Crank-Nicolson scheme for time integration, Newton's method for linearization, and a least-squares finite element method, together with a matrix-free Jacobi conjugate gradient technique. The main objective in this work is to demonstrate how the least-squares finite element method, together with an iterative procedure, deals with the capillary-traction boundary conditions at the free surface, which involves the coupling of velocity and temperature gradients. Mesh refinement studies were also carried out to validate the numerical results. © 1998 John Wiley & Sons, Ltd.
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    Numerical modelling of advection-dispersion equation in a stretched curvilinear grid using the QUICKEST scheme (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1033-1052 
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    ISSN: 0271-2091
    Keywords: QUICKEST ; curvilinear grid ; advection-dispersion ; stretched grid ; suspended sediment ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A stretched version of the QUICKEST scheme for solutions of the advection-dispersion equation is presented. The scheme is accurate for large degrees of stretching, so that it can be used where large gradients are present, e.g. for the calculation of sediment in suspension close to the bed. The scheme is tested for various cases of sediment advection and dispersion in one and two dimensions. © 1998 John Wiley & Sons, Ltd.
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    Computation of internal high-speed separated flow with modified B-L and J-K models (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1053-1071 
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    ISSN: 0271-2091
    Keywords: turbulence modeling ; internal flow ; flow separation ; shock-boundary layer interaction ; finite volume method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The existence of shock-turbulent boundary layer interactions lead to very complicated flow phenomena and pose a challenge for numerical simulation. In this paper, two turbulence models, the Baldwin-Lomax (B-L) model and the Johnson-King (J-K) model, which were originally developed for simple external flow simulation, are modified to model complex high-speed internal separated flows. The full Navier-Stokes solver used in this paper is based on a cell-centered finite volume method and multistepping time marching scheme. Both implicit residual smoothing and local time stepping techniques are incorporated to accelerate the convergence rate. To ensure the numerical stability with the present explicit scheme, a point-implicit treatment to the source term in the ordinary differential equation (ODE) of the J-K model has been developed and has proved to be very effective in modeling such a complex flow. An arc-bump channel flow case has been studied. Comparisons of computed results with experimental data show that the present solver, with the modified turbulence models, predicts the shock and the flow separation very well. The J-K model is found to predict the size of the separation bubble with a higher accuracy. © 1998 John Wiley & Sons, Ltd.
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    Symmetry techniques for the numerical solution of the 2D Euler equations at impermeable boundaries (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1093-1108 
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    ISSN: 0271-2091
    Keywords: boundary conditions ; Euler equations ; finite volume ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The implementation of boundary conditions at rigid, fixed wall boundaries in inviscid Euler solutions by upwind, finite volume methods is considered. Some current methods are reviewed. Two new boundary condition procedures, denoted as the symmetry technique and the curvature-corrected symmetry technique are then presented. Their behaviour in relation to the problem of the subsonic flow about blunt and slender elliptic bodies is analysed. The subsonic flow inside the Stanitz elbow is then computed. The symmetry technique is proven to be as accurate as one of the current methods, second-order pressure extrapolation technique. Finally, for arbitrary curved geometries, dramatic advantages of the curvature-corrected symmetry technique over the other methods are shown. © 1998 John Wiley & Sons, Ltd.
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    A Navier-Stokes solver for complex three-dimensional turbulent flows adopting non-linear modelling of the Reynolds stresses (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1139-1158 
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    ISSN: 0271-2091
    Keywords: non-linear Reynolds stresses ; k-ε turbulence model ; higher-order convective scheme ; pressure correction ; direct sparse matrix solver ; incompressible duct flows ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A non-linear modelling of the Reynolds stresses has been incorporated into a Navier-Stokes solver for complex three-dimensional geometries. A k-ε model, adopting a modelling of the turbulent transport which is not based on the eddy viscosity, has been written in generalised co-ordinates and solved with a finite volume approach, using both a GMRES solver and a direct solver for the solution of the linear systems of equations. An additional term, quadratic in the main strain rate, has been introduced into the modelling of the Reynolds stresses to the basic Boussinesq's form; the corresponding constant has been evaluated through comparison with the experimental data. The computational procedure is implemented for the flow analysis in a 90° square section bend and the obtained results show that with the non-linear modelling a much better agreement with the measured data is obtained, both for the velocity and the pressure. The importance of the convection scheme is also discussed, showing how the effect of the non-linear correction added to the Reynolds stresses is effectively hidden by the additional numerical diffusion introduced by a low-order convection scheme as the first-order upwind scheme, thus making the use of higher order schemes necessary. © 1998 John Wiley & Sons, Ltd.
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    Transient finite element analysis of generalized Newtonian coextrusion flows in complex geometries (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1159-1181 
    Details
    ISSN: 0271-2091
    Keywords: coextrusion ; interfacial instability ; transient simulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A two-dimensional transient finite element model capable of simulating problems related to two-layer polymer flows has been developed. This technique represents an effective tool which can be used to study the possibility of the onset of interfacial instability in coextrusion flows, considering melt rheology as well as the fluid-geometry interaction. A code has been developed to solve the transient problem of the flow of bi-component systems of Newtonian and generalized Newtonian fluids through parallel plates and complex geometries, such as: 2:1 abrupt expansion, 2:1 (30°) expansion, 4:1 abrupt contraction and 4:1 tapered (30°) contraction. Solutions are compared with experimental data from the literature and results provided by linear stability analysis (LSA) for the case of parallel plate flows. Numerical results are in agreement with LSA results for the parallel plate geometry cases studied. The expansion geometries tend to stabilize flows in the parallel plate section downstream of the expansion. Contractions may give rise to break-up of the interface depending on the flow conditions. © 1998 John Wiley & Sons, Ltd.
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    A bore-capturing finite volume method for open-channel flows (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1241-1261 
    Details
    ISSN: 0271-2091
    Keywords: shallow water equations ; finite volume ; open channel ; hydraulic jump ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A high-resolution finite volume hydrodynamic solver is presented for open-channel flows based on the 2D shallow water equations. This Godunov-type upwind scheme uses an efficient Harten-Lax-van Leer (HLL) approximate Riemann solver capable of capturing bore waves and simulating supercritical flows. Second-order accuracy is achieved by means of MUSCL reconstruction in conjunction with a Hancock two-stage scheme for the time integration. By using a finite volume approach, the computational grid can be irregular which allows for easy boundary fitting. The method can be applied directly to model 1D flows in an open channel with a rectangular cross-section without the need to modify the scheme. Such a modification is normally required for solving the 1D St Venant equations to take account of the variation of channel width. The numerical scheme and results of three test problems are presented in this paper. © 1998 John Wiley & Sons, Ltd.
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    Large eddy simulation of the subcritical flow past a circular cylinder: numerical and modeling aspects (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1281-1302 
    Details
    ISSN: 0271-2091
    Keywords: large eddy simulation ; turbulent flow ; circular cylinder ; accuracy ; finite volume method ; subgrid scale model ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The turbulent flow past a circular cylinder (Re=3900) was computed by large eddy simulation (LES). The objective was not to investigate the physical phenomena of this flow in detail but to study numerical and modeling aspects which influence the quality of LES solutions. Concerning the numerical method, the most important component is the discretization of the non-linear convective fluxes. Five different schemes were investigated. Also, the influence of different grid resolutions was examined. Two aspects play an important role on the modeling side, namely the near-wall model and the subgrid scale model. Owing to the restriction to low Reynolds numbers in this study, no-slip boundary conditions were used at solid walls. Therefore, only the second aspect was taken into account. Two different subgrid scale models were applied. Additionally, LES computations without any subgrid scale modeling were carried out in order to prove the performance of the models. The results were evaluated by comparison with available experimental data. © 1998 John Wiley & Sons, Ltd.
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    Automatic grid generation of complex geometries in Cartesian co-ordinates (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1303-1324 
    Details
    ISSN: 0271-2091
    Keywords: grid generation ; automation ; Cartesian ; diagonal ; saw-tooth ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A method of automatic grid generation for complex boundaries in Cartesian co-ordinates is proposed in this paper. In addition to the Cartesian grid lines the diagonal segments are used for the approximations of complex geometries in Cartesian co-ordinates. A structured Cartesian grid is employed for the sake of the numerical simplicity and the potential of automatic grid generation. The automatic grid generation is achieved by this diagonal Cartesian method and the accuracy estimations of geometry approximations are given. The approximations of a few complex geometries, such as the multibody system in porous media, lake banks, grooved channels and spheres are shown and analyzed. The proposed method is verified by the numerical solutions of a rotated cavity flow. It is shown that the diagonal Cartesian method improves both the accuracy of geometry approximations and the numerical solution of a rotated cavity flow, comparing with the traditional saw-tooth method in which only Cartesian grid lines are utilized for geometry approximations. The stability and convergence of the proposed method is demonstrated. Finally, the application of the diagonal Cartesian method for the prediction of a grooved channel flow is presented. © 1998 John Wiley & Sons, Ltd.
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    Numerical prediction for laminar forced convection heat transfer in parallel-plate channels with streamwise-periodic rod disturbances (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1371-1387 
    Details
    ISSN: 0271-2091
    Keywords: heat transfer ; duct flow ; laminar flow ; boundary conditions ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A numerical study has been performed for the periodically fully-developed flow in two-dimensional channels with streamwise-periodic round disturbances on its two walls. To accurately describe the round disturbance boundary condition, a body fitted grid was used. The flow and heat transfer have been studied in the range of Reynolds number, Re=50-700, and Prandtl number Pr=0.71. The influences of disturbance parameters and Reynolds number on heat transfer and friction have been investigated in detail. Some of the solutions have been examined using both steady and unsteady finite difference schemes; and the same results have been obtained. The results show that different flow patterns can occur with different deployments of the disturbances. With appropriate configuration of the disturbances, the Nusselt number can reach a value four times greater than in a smooth channel at the same condition, with the penalty of a much greater pressure drop. On the other hand, if the disturbances are not deployed properly, augmentation of heat transfer cannot be acquired. © 1998 John Wiley & Sons, Ltd.
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    Parallel conjugate gradient performance for least-squares finite elements and transport problems (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1421-1440 
    Details
    ISSN: 0271-2091
    Keywords: parallel ; conjugate gradient ; least squares ; FEM ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this study we consider parallel conjugate gradient solution of sparse systems arising from the least-squares mixed finite element method. Of particular interest are transport problems involving convection. The least-squares approach leads to a symmetric positive system and the conjugate gradient scheme is directly applicable. The scheme is applied to both the convection-diffusion equation and to the stationary Navier-Stokes equations. Here we demonstrate parallel solution and performance studies for a representative MIMD parallel computer with hypercube architecture. © 1998 John Wiley & Sons, Ltd.
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    Simulation of gas-solid particle flows over a wide range of concentration (1998)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1441-1479 
    Details
    ISSN: 0271-2091
    Keywords: gas-solid particle flow ; dilute to dense concentrations ; two-fluid model ; kinetic theory ; control-volume finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A two-fluid model of gas-solid particle flows that is valid for a wide range of the solid-phase volume concentration (dilute to dense) is presented. The governing equations of the fluid phase are obtained by volume averaging the Navier-Stokes equations for an incompressible fluid. The solid-phase macroscopic equations are derived using an approach that is based on the kinetic theory of dense gases. This approach accounts for particle-particle collisions. The model is implemented in a control-volume finite element method for simulations of the flows of interest in two-dimensional, planar or axisymmetric, domains. The chosen mathematical model and the proposed numerical method are applied to three test problems and one demonstration problem. © 1998 John Wiley & Sons, Ltd.
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    A model for coupled mechanical and hydraulic behaviour of a rock joint (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 29-48 
    Details
    ISSN: 0363-9061
    Keywords: hydraulic behaviour ; joint ; mechanics of joint ; joint degradation ; joint elements ; interface mechanics ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Constitutive laws for rock joints should be able to reproduce the fundamental mechanical behaviour of real joints, such as dilation under shear and strain softening due to surface asperity degradation. In this work, we extend the model of Plesha to include hydraulic behaviour. During shearing, the joint can experience dilation, leading to an initial increase in its permeability. Experiments have shown that the rate of increase of the permeability slows down as shearing proceeds, and, at later stages, the permeability could decrease again. The above behaviour is attributed to gouge production. The stress-strain relationship of the joint is formulated by appeal to classical theories of interface plasticity. It is shown that the parameters of the model can be estimated from the Barton-Bandis empirical coefficients; the Joint Roughness Coefficient (JRC) and the Joint Compresive strength (JSC). We further assume that gouge production is also related to the plastic work of the shear stresses, which enables the derivation of a relationship between the permeability of the joint and its mechanical aperture. The model is implemented in a finite element code (FRACON) developed by the authors for the simulation of the coupled thermal-hydraulic-mechanical behaviour of jointed rock masses. Typical laboratory experiments are simulated with the FRACON code in order to illustrate the trends predicted in the proposed model. © 1998 by John Wiley & Sons. Ltd.
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    Field stresses around an inclined shaft (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 229-238 
    Details
    ISSN: 0363-9061
    Keywords: inclined shaft ; stress distribution ; field stress ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: In this study, the vertical overburden pressure in the vicinity of an inclined circular underground opening is defined by relation to the geometry of the medium. The stresses around the opening consisting of six components are induced by geostatic field stress. In this regard, the inclined circular opening i.e. shaft changes the original stress condition and an interrupted region develops beneath it. Three zones are defined on a plane which is perpendicular to the axis of shaft. The mathematical expressions of vertical overburden stresses at these three zones are established, respectively. The example given in appendix demonstrates the variation of radial and tangential stresses around the inclined shaft. It is seen that the stress distributions in the third zone, which includes the interrupted region, beneith the shaft display different configurations than that of those obtained by undisturbed field stresses. In the interrupted region the stresses around the shaft linearly grow up due to increasing overburden pressure by radial distance from the periphery of the shaft. At the boundary of interrupted region stresses jump to the original values induced by field stresses. © 1998 John Wiley & Sons, Ltd.
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    Elastoplastic constitutive equation of soils with the subloading surface and the rotational hardening (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 197-227 
    Details
    ISSN: 0363-9061
    Keywords: elastoplasticity ; constitutive equation ; subloading surface model ; cyclic plasticity ; soil ; rotational hardening ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The subloading surface model fulfills the mechanical requirements for constitutive equations, i.e. the continuity condition, the smoothness condition and the work rate stiffness relaxation and describes pertinently the Masing effect. The constitutive equation of soils is formulated by introducing the subloading surface model and formulating the evolutional rule of rotational hardening for the description of anisotropy. The applicability of the constitutive equation to the prediction of real soil deformation behaviour is verified by predicting monotonic and cyclic loading behaviour of sands under drained and undrained conditions and comparing them with test data. © 1998 John Wiley & Sons, Ltd.
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    Numerical analysis of soil plug behaviour inside open-ended piles during driving (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 303-322 
    Details
    ISSN: 0363-9061
    Keywords: pile driving ; open-ended piles ; plugging mechanism ; one-dimensional modelling ; stress wave propagation ; finite element analysis ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The plugging mechanism of infinitely-long open-ended piles is examined using numerical simulation of the wave propagation inside the soil plug and pile. It is shown that the key parameters for the plugging mechanism are the pile radius, the shape of the impact load, the shear wave velocity of the soil inside the pile, and the friction at the pile-soil interface. Consequently, the tendency of the pile to plug during driving can be assessed prior to the driving process by consideration of these key parameters. Existing one-dimensional models for the shaft response of open-ended piles are discussed and an improved model is presented. The differences between using one-dimensional models and finite element models to simulate the plugging process are examined. The differences are found to vary with the key parameters. Pile-in-pile and lumped-mass one-dimensional models are found to give satisfactory performance for some parameter combinations, while for others an axisymmetric finite element model must be used. © 1998 John Wiley & Sons, Ltd.
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    Elastic solutions for a transversely isotropic half-space subjected to a point load (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 425-447 
    Details
    ISSN: 0363-9061
    Keywords: closed-form solution ; transversely isotropic half-space ; Fourier transform ; Hankel transform ; rock anisotropy ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: We rederive and present the complete closed-form solutions of the displacements and stresses subjected to a point load in a transversely isotropic elastic half-space. The half-space is bounded by a horizontal surface, and the plane of transverse isotropy of the medium is parallel to the horizontal surface. The solutions are obtained by superposing the solutions of two infinite spaces, one acting a point load in its interior and the other being free loading. The Fourier and Hankel transforms in a cylindrical co-ordinate system are employed for deriving the analytical solutions. These solutions are identical with the Mindlin and Boussinesq solutions if the half-space is homogeneous, linear elastic, and isotropic. Also, the Lekhnitskii solution for a transversely isotropic half-space subjected to a vertical point load on its horizontal surface is one of these solutions. Furthermore, an illustrative example is given to show the effect of degree of rock anisotropy on the vertical surface displacement and vertical stress that are induced by a single vertical concentrated force acting on the surface. The results indicate that the displacement and stress accounted for rock anisotropy are quite different for the displacement and stress calculated from isotropic solutions. © 1998 John Wiley & Sons, Ltd.
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    Contaminant transport under variable density flow in fractured porous media (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 575-595 
    Details
    ISSN: 0363-9061
    Keywords: contaminant transport ; variable density flow ; fractures ; leakage ; dispersion ; diffusion ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A numerical model for simulating flow and transport of contaminants with variable density in fractured porous media is presented. The non-linearities arising from the density variation and the velocty-dependent dispersion terms have been handled by Picard method. It is shown that the contaminant transport in a fractured porous medium is initially dominated by fractures. However, with time increasing, the contaminant concentration in porous blocks increases, due to the leakage of contaminant from the fracture network to the porous blocks. It is also shown that the high density of contaminant has a greater effect on its transport in the fracture network than in the porous blocks. © 1998 John Wiley & Sons, Ltd.
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    Modelling of shearing behaviour of a residual soil with Recurrent Neural Network (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 671-687 
    Details
    ISSN: 0363-9061
    Keywords: recurrent neural network ; residual soil ; shear behaviour ; simulation ; prediction ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Modelling of shear behaviour of residual soils is difficult in that there is a significant variability in constituents and structures of the soil. A Recurrent Neural Network (RNN) is developed for modelling shear behaviour of the residual soil. The RNN model appears very effective in modelling complex soil shear behaviour, due to its feedback connections from an hidden layer to an input layer. Two architectures of the RNN model are designed for training different sets of experimental data which include strain-controlled undrained tests and stress-controlled drained tests performed on a residual Hawaiian volcanic soil. A dynamic gradient descent learning algorithm is used to train the network. By training only part of the experimental data the network establishes neural connections between stress and strain relations. Although the soil exhibited significant variations in terms of shearing behaviour, the RNN model displays a strong capability in capturing these variabilities. Both softening and hardening characteristics of the soil are well represented by the RNN model. Isotropic and anisotropic consolidation conditions are precisely reflected by the RNN model. In undrained tests, pore water pressure responses at various loading stages are simultaneously simulated. With a RNN model designed for a special drained test, the network is able to capture abrupt changes in axial and volumetric strains during shearing courses. These good agreements between the measured data and the modelling results demonstrate the desired capability of the RNN model in representing a soil behaviour. © 1998 John Wiley & Sons, Ltd.
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    Coupled wellbore erosion and stability analysis (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 749-769 
    Details
    ISSN: 0363-9061
    Keywords: wellbore stability ; sand erosion ; sand production ; sand prediction ; radial flow ; poroelasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper extends earlier work on sand erosion and presents an attempt to couple sand erosion to mechanical damage of rock around a wellbore. Porosity which evolves in time and space as surface erosion progresses, is chosen as the coupling parameter. Both rock elasticity and strength (cohesion) are assumed to depend on porosity in such a way that the material becomes weaker with increasing porosity. The mathematical model, consists of erosion equations, mixture flow equations and stress equilibrium equations, is solved numerically by Galerkin finite element method. Numerical results suggest that erosion, resulting in sand production, is high close to the free surface. Erosion is accompained by changes in porosity and a significant permeability increase. Erosion in the vicinity of the wellbore induces alterations in the mechanical behaviour of the medium. Weakening of rock stiffness leads to severe alteration of both effective stresses and pore pressure near the cavity. Since cohesion decreases with increasing porosity, one can also identify the time instant at which rock mechanical failure starts. © 1998 John Wiley & Sons, Ltd.
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    A numerical procedure for the analysis of the hydromechanical coupling in fractured rock masses (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 867-901 
    Details
    ISSN: 0363-9061
    Keywords: finite elements ; hydromechanical coupling ; fractured rock masses ; viscoplasticity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This work presents a finite element implementation to treat the Hydromechanical Coupling (HM) in fractured rock masses under the framework of the so-called ‘equivalent continuum’ approach. The multilaminar concept, introduced by Zienkiewicz and Pande, is used to simulate the mechanical behaviour of both the intact rock and the families of fractures. In that concept, the non-linearities in the constitutive relations are dealt by means of fictitious viscoplasticity. In the present implementation, the mechanical behaviour of the fractures is modelled by means of Barton-Bandis model. The shear stress/shear displacement/dilatancy relationship is modelled as viscoplastic and the normal stress/normal displacement as non-linear viscoelastic. Flow along fractures is considered to occur as a sequence of permanent states. The permeability tensor of the equivalent continuum is determined from the hydraulic apertures, in accordance of Barton et al. From the numerical point of view, the basic aim of the work is the implementation of an efficient scheme to solve the above described problem. This is done by designing a self-adaptive time step control, transparent to the user, which determines the highest possible time step while assuming the conditions of precision, stability and convergence. The paper presents the numerical details of such scheme together with validation/comparative examples and the results obtained on the analysis of the fractured rock foundation of a hypothetical dam. © 1998 John Wiley & Sons, Ltd.
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    The effect of interface properties on retaining wall behaviour (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1021-1033 
    Details
    ISSN: 0363-9061
    Keywords: retaining wall ; interface ; finite element ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A series of finite element analyses have been undertaken to investigate the effects of interface properties on the behaviour of a vertical retaining wall and the deformation of the ground around it. The boundary between a rigid embedded wall and the soil is modelled with zero thickness interface elements. Uniform translation of the wall has been studied. The analyses show the predicted limiting active and passive pressure on the wall are dependent on the maximum wall friction angle and are in reasonable agreement with accepted approximate analytical solutions. The limiting pressure is independent of the stiffness and dilation properties of the interface elements. The dilation properties of the interface have a significant effect on the ground surface deformation around the wall. © 1998 John Wiley & Sons, Ltd.
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    Coupled analysis of a backfill hydration test (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1-27 
    Details
    ISSN: 0363-9061
    Keywords: expansive clay ; hydromechanics ; unsaturated soils ; nuclear waste ; in situ test ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: BACCHUS2 in situ isothermal wetting experiment has been analysed by means of a coupled flow-deformation approach. Backfill material, a mixture of Boom clay powder and high density pellets, has been extensively tested in the laboratory in order to determine its hydraulic and mechanical properties. Parameters of constitutive equations were derived from this experimental data base. Two mechanical constitutive models have been used in the simulation of the ‘in situ’ experiment: a state surface approach and an elastoplastic model. Calculations have shown several features of the hydration process which help to understand the behaviour of expansive clay barriers. Predictions using both models have been compared with each other and with actual measurement records. This has allowed a discussion of the comparative mertis of both approaches and the identification of some critical parameters of backfill behaviour. Overall agreement between calculations and field measurements is encouraging and shows the potential of the methods developed to model the behaviour of engineered clay barriers in the context of nuclear waste disposal. © 1998 by John Wiley & Sons, Ltd.
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    Three-dimensional heat, moisture and air transfer in unsaturated soils (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 75-95 
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    ISSN: 0363-9061
    Keywords: three-dimensional ; heat ; moisture ; air ; transfer ; unsaturated ; soil ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A new three-dimensional numerical model of coupled heat, moisture and air transfer in unsaturated soil is presented. In particular, the model accommodates moisture transfer in the form of liquid and vapour flow and heat transfer arising from conduction, convection and latent heat of vaporization. The bulk flow of dry air and the movement of air in a dissolved state are also included. The theoretical basis of the model, the finite element solution of the spatial terms and finite difference solution of the temporal terms are briefly presented. Attention is focused on the verification of the new numerical solution. This is achieved via comparisons with independent solutions of heat, moisture and air transfer in an unsaturated soil. The physical problem considered includes the highly non-linear hydraulic properties of sand. Thermal conductivity is also included as a function of soil moisture content. Excellent correlation of results is shown thus providing confidence in the new model.The new model is also applied to a number of test cases which illustrate the need for the development of a model which can fully include three-dimensional behaviour. In particular, three applications are presented each increasing in complexity. The first application illustrates three-dimensional heat transfer. This particular application is verified against existing commercial finite element software. Subsequent applications serve to illustrate how the coupled processes of heat moisture and air transfer combine to yield three-dimensional problems even within a simple geometric domain. Visualization of three-dimensional results is also addressed. © 1998 by John Wiley & Sons, Ltd.
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    Propagation of a shear crack in a compressed plane with a circular hole (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 175-196 
    Details
    ISSN: 0363-9061
    Keywords: shear crack ; singular integral equation ; excavation ; discontinuities ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The problem of the equilibrium of a plane with a circular hole and a shear crack is considered to model failure of an excavation (borehole or circular opening) in rocks weakened by discontinuities (planes of weakness). It is assumed that sliding occurs in a part of the plane of weakness when the Mohr-Coulomb friction criterion is satisfied due to the stress redistribution caused by the excavation. The method of singular integral equations is employed to solve the boundary value problem. Geomechanical problems concerning borehole breakout and rockburst caused by fault-opening interaction are discussed. © 1998 John Wiley & Sons, Ltd.
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    Analytically computed rates of seepage flow into drains and cavities (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 277-301 
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    ISSN: 0363-9061
    Keywords: seepage ; flow rate ; drain ; tunnel ; optimization ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The known formulae of Freeze and Cherry, Polubarinova-Kochina, Vedernikov for flow rate during 2-D seepage into horizontal drains and axisymmetric flow into cavities are examined and generalized. The case of an empty drain under ponded soil surface is studied and existence of drain depth providing minimal seepage rate is presented. The depth is found exhibiting maximal difference in rate between a filled and an empty drain. 3-D flow to an empty semi-spherical cavity on an impervious bottom is analysed and the difference in rate as compared with a completely filled cavity is established. Rate values for slot drains in a two-layer aquifer are ‘inverted’ using the Schulgasser theorem from the Polubarinova-Kochina expressions for corresponding flow rates under a dam. Flow to a point sink modelling a semi-circular drain in a layered aquifer is treated by the Fourier transform method. For unsaturated flow the catchment area of a single drain is established in terms of the quasi-linear model assuming the isobaric boundary condition along the drain contour. Optimal shape design problems for irrigation cavities are addressed in the class of arbitrary contours with seepage rate as a criterion and cavity cross-sectional area as an isoperimetric restriction. © 1998 John Wiley & Sons, Ltd.
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    Dimensionless and unbiased CPT interpretation in sand (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 351-391 
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    ISSN: 0363-9061
    Keywords: cone penetration testing ; sand ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The cone penetration test (CPT) is widely used, and although initially developed as a stratigraphic logging tool its excellent repeatability and accuracy offers a benchmark quantitative test for sand in particular. A continuing difficulty, however, is that the CPT does not measure any soil property directly, so that parameters of interest must be recovered from solution of an inverse boundary value problem, which is difficult. To date most CPT interpretations in sand have been based on very limited calibration testing carried out in large chambers on a few sands from which mappings are developed. But there are differences in the CPT response from one sand to another leaving the interpretation imprecise (and arguably even speculative) because these differences remain poorly understood. In this paper we use the familiar spherical cavity expansion analogy to the CPT including large strains and a good, critical-state-based, soil model to develop a pattern of behaviour which we then compare to some of the reference chamber test data. We find that one of the issues of dispute in the empirical interpretation methods, the so-called stress-level effect, is caused by neglect of elasticity and that there are several additional parameters of first-order significance to cavity expansion in sands. More generally, we show that the difference in CPT response between various chamber sands in predicted. Our results are cast in dimensionless form and the inversion illustrates that extreme care is required in interpreting CPT data if the in situ sand state is to be determined with precision approaching that suggested as achievable by the repeatability of the CPT data itself. Aspects requiring particular care in interpreting CPT data in sand are discussed. © 1998 John Wiley & Sons, Ltd.
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    Coupled consolidation of a porous medium with a cylindrical or a spherical cavity (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 449-475 
    Details
    ISSN: 0363-9061
    Keywords: consolidation ; heat transfer ; poroelasticity ; pore pressure ; coupled fields ; Laplace transform ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a theoretical approach to analyse coupled, linear thermoporoelastic fields in a saturated porous medium under radial and spherical symmetry. The governing equations account for compressibility and thermal expansion of constituents, heat sink due to thermal dilatation of water and thermal expansion of the medium, and thermodynamically coupled heat-water flow. It has been reported in the literature that thermodynamically coupled heat-water flows known as thermo-osmosis and thermal filtration have the potential to significantly alter the flow fields in clay-rich barriers in the near field of a underground waste containment scheme. This study presents a mathematical model and examines the effects of thermo-osmosis and thermal-filtration on coupled consolidation fields in a porous medium with a cavity. Analytical solutions of the governing equations are presented in the Laplace transform space. A numerical inversion scheme is used to obtain the time-domain solutions for a cylindrical cavity in a homogeneous or a non-homogeneous medium. A closed form time-domain solution is presented for a spherical cavity in a homogeneous medium. Selected numerical solutions for homogeneous and non-homogeneous media show a significant increase in pore pressure and displacements due to the presence of thermodynamically coupled flows and a negligible influence on temperature. © 1998 John Wiley & Sons, Ltd.
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    Obituary - John R. Booker (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 421-423 
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    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: No Abstract
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    Rational approximation of stress and strain based on downhole acceleration measurements (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 603-619 
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    ISSN: 0363-9061
    Keywords: earthquakes ; stress-strain response ; downhole arrays ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Recordings from downhole accelerometer arrays offer unique insight into soil behavior and ground response during earthquakes. In this paper we present a scheme for interpolating displacement and acceleration measurements to provide approximations for subsurface shear strain and stress as continuous functions of time. Our suggested interpolating functions are constructed in such a way that the free surface boundary condition will always be satisfied and the interpolated displacement and acceleration remain finite for all depths. We also show how the functions can be adapted to represent layered soil profiles. Depending on the number of instruments in the downhole array, a truncated series of functions can be derived so that each represents a modal shape for the layered soil profile. The resulting approximations for strain and stress are considered more accurate and robust than previous approximations. © 1998 John Wiley & Sons, Ltd.
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    CASM: a unified state parameter model for clay and sand (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 621-653 
    Details
    ISSN: 0363-9061
    Keywords: state parameter ; stress-state relation ; constitutive modelling ; plasticity ; critical state ; sand and clay ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The purpose of this paper is to present a simple, unified critical state constitutive model for both clay and sand. The model, called CASM (Clay And Sand Model), is formulated in terms of the state parameter that is defined as the vertical distance between current state (v, p′) and the critical state line in v-ln p′ space. The paper first shows that the standard Cam-clay models (i.e. the original and modified Cam-clay models) can be reformulated in terms of the state parameter. Although the standard Cam-clay models prove to be successful in modelling normally consolidated clays, it is well known that they cannot predict many important features of the behavior of sands and overconsolidated clays. By adopting a general stress ratio-state parameter relation to describe the state boundary surface of soils, it is shown that a simple, unified constitutive model (CASM) can be developed for both clay and sand. It is also demonstrated that the standard Cam-clay yield surfaces can be either recovered or approximated as special cases of the yield locus assumed in CASM.The main feature of the proposed model is that a single set of yield and plastic potential functions has been used to model the behaviour of clay and sand under both drained and undrained loading conditions. In addition, it is shown that the behaviour of overconsolidated clays can also be satisfactorily modelled. Simplicity is a major advantage of the present state parameter model, as only two new material constants need to be introduced when compared with the standard Cam-clay models. © 1998 John Wiley & Sons, Ltd.
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    Limit loads for an anchor/trapdoor embedded in an associative coulomb soil (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 855-865 
    Details
    ISSN: 0363-9061
    Keywords: anchor ; trapdoor ; limit load ; cohesionless ; associative ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A methodology for determining the plane strain limit load acting on an anchor or trapdoor buried within a purely associative Coulomb soil is presented. True lower bounds derived from a family of limiting stress fields appropriate to shallow horizontal trapdoors and anchors are shown to correlate to within less than 1 percent of upper bounds available in the literature, permitting the true limit load to be almost exactly defined. The solution form alters for deeply buried anchors and trapdoors resulting in poorer correlations. Methods by which the work may be extended to cover the more practical instances of non-associative Coulomb soils are indicated but are beyond the scope of the current paper. © 1998 John Wiley & Sons, Ltd.
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    Bifurcations of thick-walled hollow cylinders of geomaterials under axisymmetric compression (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 903-919 
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    ISSN: 0363-9061
    Keywords: hollow cylinders ; diffuse mode bifurcations ; geomaterials ; non-normality ; pressure-sensitivity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper derives analytically the condition for the onset of diffuse mode bifurcations in thick-walled hollow cylinders with internal radius a, external radius b and length L under axial compression and confining pressure. The thick-walled cylindrical specimens are made of geomaterial characterized by Rudnicki's constitutive model, and the method of solution for the governing equations is the velocity potential approach employed by Chau. Numerical results show that thick-walled cylinders are stronger than thin-walled cylinders against diffuse mode bifurcations, including both buckling, axisymmetric and non-axisymmetric deformations. In contrast to the conclusion for solid cylinders (Chau), no buckling solution is found for γ = mπa / L smaller than about 0·7 under compression for a fixed and finite value of a / b (i.e. no buckling for long and slender hollow cylinders with small a / L and fixed b / a). When 0·7 〈 γ 〈 0·9, buckling is the expected first bifurcation; whereas, when γ 〉 0·9, bulging or barrelling is anticipated. The exact value of γ that excludes buckling and separates the buckling and barrelling phenomena depends on the current values of the constitutive parameters of the solid. Hollow cylinders with higher degree of anisotropy, disobeying normality flow rule, and subjected to confining pressure are more conducive to bifurcations than cylinders made of materials with isotropy, obeying normality, and subjected to no confining pressure. In addition, diffuse mode bifurcations are found possible in the pre-peak regime of the stress-strain curve. © 1998 John Wiley & Sons, Ltd.
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    Efficient solution of 3-D geomechanical problems by indirect BEM using iterative methods (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 983-1000 
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    ISSN: 0363-9061
    Keywords: geomechanics ; indirect boundary element method (BEM) ; three-dimensional (3-D) elastostatics ; iterative methods ; approximate solution ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The research herein primarily addresses to geomechanical problems of underground constructions in Mining and Civil Engineering. The problems are solved using the Indirect Boundary Element Method (IBEM). Although the geometry of the constructions themselves is usually very complicated, it will become much more complicated if we were to draw the existing joints. The computational problem therefore is how to deal with huge amount of equations and find out efficient methods of their formation and solution keeping in mind restraints of the computer memory and calculation time. Several approaches are used to enhance the performance of the Indirect Boundary Element Method. One of them deals with application of efficient equation solvers. It is shown that Krylov-type methods like CGS and GMRES with simple Jacoby preconditioning appear to be efficient and robust. In addition, adaptive integration on the boundary elements, together with diagonal dominance of equationsmake it possible to accelerate convergence of the iterative procedure. Some of the problems discussed allow a substantial reduction of matrix entries that leads to a very cheap iterative solution keeping reasonable accuracy of the results. © 1998 John Wiley & Sons, Ltd.
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    Theoretical analysis of strain response envelopes using incrementally non-linear constitutive equations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 97-132 
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    ISSN: 0363-9061
    Keywords: constitutive model ; rate-independent type ; strain response envelope ; granular material ; uniqueness ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper reviews some incrementally non-linear constitutive equations of interpolation type, and proposes a new approach to illustrate the discrepancies between different interpolation models. This approach uses the strain response envelopes, based on experimental data when restricted to triaxial plane, and the Jacobian of the constitutive equations to examine the loss of uniqueness. A new family of interpolation functions is proposed to meet the three requirements: C1-continuity of strain response envelope, correct description of experimental data, and respect of the one-to-one property. © 1998 by John Wiley & Sons, Ltd.
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    A finite-element treatment of sea ice dynamics for different ice rheologies (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 153-174 
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    ISSN: 0363-9061
    Keywords: finite-element ; sea ice pack ; rheology ; viscous-plastic ; viscous fluid ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: In this paper the effects of four different rheologies on the evolution of a large-scale sea ice pack are determined and compared. Two rheologies are of viscous-plastic form, and two are viscous fluid relations. The initial pack domain is rectangular, and the motion is driven by wind stress and resisted by ocean drag. Two adjacent edges are rigid shore boundaries, and the other two are free boundaries at open water which move during the pack motion, so that the pack domain changes in time. Two different forms of boundary conditions at the rigid shore edges are considered, which also influence the evolution. The governing equations are solved numerically using a finite-element method, and, unlike previous numerical treatments, no artificial viscosity is incorporated to stabilise the algorithm near interfaces between converging and diverging flow. Instability arises when any tensile stress is abruptly cut-off when diverging flow is initiated, and an alternative view is offered. © 1998 John Wiley & Sons, Ltd.
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    Scattering of elastic waves by a plane crack of finite width in a transversely isotropic medium (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 263-275 
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    ISSN: 0363-9061
    Keywords: non-ideal interface ; crack scattering ; domain decomposition ; collocation methods ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This work presents a numerical algorithm for solving crack scattering in a transversely isotropic medium whose symmetry axis is perpendicular to the crack surface. The crack is modelled as boundary discontinuities in the displacement u and the particle velocity v, of the stresses [κu+ζv], where the brackets denote discontinuities across the interface. The specific stiffness κ introduces frequency-dependence and phase changes in the interface response and the specific viscosity ζ is related to the energy loss.The numerical method is based on a domain decomposition technique that assignes a different mesh to each side of the interface, that includes the crack plane. As stated above, the effects of the crack on wave propagation are modelled through the boundary conditions, that require a special boundary treatment based on characteristic variables. The algorithm solves the particle velocity-stress wave equations and two additional first-order differential equations (two-dimensional case) in the displacement discontinuity. For each mesh, the spatial derivatives normal to the interface are solved by the Chebyshev method, and the spatial derivatives parallel to the interface are computed with the Fourier method. They allow a highly accurate implementation of the boundary conditions and computation of the spatial derivatives, and an optimal discretization of the model space. Moreover, the algorithm allows general material variability. © 1998 John Wiley & Sons, Ltd.
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    A practical numerical approach for large deformation problems in soil (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 327-350 
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    ISSN: 0363-9061
    Keywords: finite element analysis ; large strain ; remeshing ; integration ; penetration ; bearing capacity ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A practical method is presented for numerical analysis of problems in solid (in particular soil) mechanics which involve large strains or deformations. The method is similar to what is referred to as ‘arbitrary Lagrangian-Eulerian’, with simple infinitesimal strain incremental analysis combined with regular updating of co-ordinates, remeshing of the domain and interpolation of material and stress parameters. The technique thus differs from the Lagrangian or Eulerian methods more commonly used. Remeshing is accomplished using a fully automatic remeshing technique based on normal offsetting, Delaunay triangulation and Laplacian smoothing. This technique is efficient and robust. It ensures good quality shape and distribution of elements for boundary regions of irregular shape, and is very quick computationally. With remeshing and interpolation, small fluctuations appeared initially in the load-deformation results. In order to minimize these, different increment sizes and remeshing frequencies were explored. Also, various planar linear interpolation techniques were compared, and the unique element method found to work best.Application of the technique is focused on the widespread problem of penetration of surface foundations into soft soil, including deep penetration of foundations where soil flows back over the upper surface of the foundation. Numerical results are presented for a plane strain footing and an axisymmetric jack-up (spudcan) foundation, penetrating deeply into soil which has been modelled as a simple Tresca or Von Mises material, but allowing for increase of the soil strength with depth. The computed results are compared with plasticity solutions for bearing capacity. The numerical method is shown to work extremely well, with potential application to a wide range of soil-structure interaction problems. © 1998 John Wiley & Sons, Ltd.
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    Analysis of axial strain induced by 3-D consolidation of cohesive soils (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 495-508 
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    ISSN: 0363-9061
    Keywords: consolidation ; cohesive soil ; clay ; axial strain ; true triaxial ; finite difference method ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper presents a simplified approach for the analysis of axial strain induced by three-dimensional consolidation of cohesive soils. The axial strain is divided into a constant volume component and a consolidation component. A relevant undrained stress-strain relationship is required to determine the constant volume component. A theoretical formulation is developed for the evaluation of the consolidation component. Predictions of the axial strain accompanying true triaxial laboratory tests for a variety of stress patterns correlate sufficiently well with the measured data. The proposed method is potentially applicable in conjunction with a finite difference scheme to analyze the time-dependent response of pile groups subjected to static vertical loading. © 1998 John Wiley & Sons, Ltd.
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    A constitutive study of thermo-elasto-plasticity of deep carbonatic clays (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 549-574 
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    ISSN: 0363-9061
    Keywords: carbonatic clays ; thermo-plasticity ; nuclear waste disposal ; thermo-mechanical tests ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Argillaceous masses considered for potential nuclear waste repositories may exhibit significant space variability in their carbonate content. This may affect mechanical clay properties, such as strength or maximum apparent preconsolidation stress known to strongly depend on carbonate content. This paper investigates experimentally the dependence of thermo-hydro-mechanical behaviour of clays on carbonate content. The properties investigated are thermal strains, thermally induced over-consolidation, strength changes, destructuration, and thermally developed water pressure in undrained conditions. The experimental data are analysed in terms of a thermo-elasto-plasticity theory for clays, being an extension of Cam-clay model, modified to include the variability of the carbonatic content. © 1998 John Wiley & Sons, Ltd.
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    Uni-axial wave propagation and pore pressure generation in fluid saturated sands exhibiting irreversible compaction (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 695-720 
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    ISSN: 0363-9061
    Keywords: wave propagation ; compaction ; pore pressure generation ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The propagation of a plane load-unload pulse through a compacting sand is analysed and illustrated for both dry sand and liquid saturated sand in undrained conditions. A major feature is the interaction between the initial loading wave and the faster following unloading wave. Free draining and undrained conditions exhibit distinct qualitative and quantitative results, and the pore liquid pressure generation is a significant physical feature. Illustrations show the effects of different applied surface pulse shapes. © 1998 John Wiley & Sons, Ltd.
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    Analysis of piled rafts (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 777-790 
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    ISSN: 0363-9061
    Keywords: piles ; rafts ; finite elements ; preconditioning ; conjugate gradients ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Analysis of piled raft foundations, taking account of their full three-dimensional complexity, can be accomplished by modern finite element analysis techniques. The characteristics of the (preconditioned conjugate gradient) numerical method applied to this problem are analysed, and then the method isused in a field problem of a raft subjected to very rapidly varying loading patterns. © 1998 John Wiley & Sons, Ltd.
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    Numerical analysis of the miniature piezocone penetration tests (PCPT) in cohesive soils (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 791-818 
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    ISSN: 0363-9061
    Keywords: Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: An analytical model to simulate the penetration of the piezocone penetrometer in cohesive soils is presented here. The elasto-plastic coupled field equations of the saturated cohesive soils (given by Voyiadjis and Abu-Farsakh) is used in this analysis. The numerical simulation of the piezocone penetration is implemented into a finite element program. The analytical model is used to analyze the miniature piezocone penetration tests (PCPT) conducted at LSU calibration chambers. Simulation of the piezocone penetration is done for two cases. In the first case, the soil-penetrometer interface friction is neglected, while in the second case, the soil-penetrometer interface friction is taken into consideration. The constraint approach is used to model the soil-piezocone interface friction in which the Mohr-Coulomb frictional model is used to define the sliding potential. Analysis is done for three different soil specimens with different stress histories. The results of the numerical simulations are compared with the experimental measurements of the miniature piezocone penetration tests (PCPT) in cohesive soil specimens conducted in LSU calibration chambers. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available prediction methods. © 1998 John Wiley & Sons, Ltd.
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    Analysis of stone-column reinforced foundations (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 1001-1020 
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    ISSN: 0363-9061
    Keywords: stone-column reinforcement ; homogenisation technique ; elastoplastic analysis ; sub-iteration scheme ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: A numerical model is proposed to analyse elastic as well as elastoplastic behaviour of stone-column reinforced foundations. The stone-columns are assumed to be dispersed within the in situ soil and a homogenization technique is invoked to establish equivalent material properties for in situ soil and stone-column composite. The difficulties encountered in carrying out elastoplastic analyses of composite materials are overcome by adopting a separate yield function for each of the constituent materials and a sub-iteration procedure within an implicit backward Euler stress integration scheme. In the proposed procedure, equilibrium as well as kinematic conditions implied in the homogenization procedure are satisfied for both elastic as well as elastoplastic stress states.The proposed model is implemented in an axi-symmetric finite element code and numerical prediction is made for the behaviour of model circular footings resting on stone-column reinforced foundations. This prediction indicates good agreement with experimental observation. Finally, a new scheme in which the length of stone-column is variable is proposed and its behaviour is examined through a numerical example. © 1998 John Wiley & Sons, Ltd.
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    Heat-induced moisture transport in the vicinity of a spherical heat source (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 969-981 
    Details
    ISSN: 0363-9061
    Keywords: heat and moisture flow ; analytical solution ; transient analysis ; spherical heat source ; coupled analysis ; Green's function method ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: The present paper develops an analytical approach to the problem of heat-induced moisture movement in the vicinity of a spherical heat source embedded in an undeformable, moist porous solid of infinite extent. A transient-state distribution of temperature within the infinite medium is assumed to induce the moisture transport process. The numerical results, presented in the paper, illustrate the influence of the moisture transport characteristics on the time-dependent distribution of moisture within the porous medium. © 1998 John Wiley & Sons, Ltd.
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    An examination of the validation of a model of the hydro/thermo/mechanical behaviour of engineered clay barriers (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 49-71 
    Details
    ISSN: 0363-9061
    Keywords: unsaturated soil ; heat transfer ; moisture transfer and stress-strain behaviour ; model and validation ; Engineering ; Civil and Mechanical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: This paper focuses attention on the development of a numerical model of the hydro/thermo/mechanical behaviour of unsaturated clay and its consequent verification and validation. The work presented describes on-going collaboration between the Cardiff School of Engineering and Atomic Energy of Canada. The model development, which was carried out at Cardiff, can be described as being based on a mechanistic approach to coupled heat, moisture and air flow. This is then linked to a deformation analysis of the material within a ‘consolidation’ type of model. The whole is solved via the finite element method to yield a computer software code named COMPASS (COde for Modelling PArtly Saturated Soil). Some aspects of verification and validation of the model have been addressed in-house. However, the purpose of current AECL work is to provide an independent, rigorous, structured programme of validation and the paper will also explore the further validation of COMPASS within this context. © 1998 by John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
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