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  • 1
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 13-23 
    ISSN: 1069-8299
    Keywords: mass transport problems ; error estimation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In order to make an exact estimation of discretization error for finite/infinite element methods, it is necessary to develop analytical solutions for some transient mass transport problems in infinite media. These transient mass transport problems may be viewed as the benchmark problems for the discretization error estimation of a new numerical method so that they generally have the following characteristics: (1) their initial and boundary conditions can be exactly modelled by the finite/infinite element method; (2) their solutions can be rigorously expressed in a closed form. In this paper, several of the aforementioned problems have been constructed and solved mathematically for transient mass transport problems in both 1D and 2D infinite media.
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  • 2
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    Communications in Numerical Methods in Engineering 11 (1995), S. 255-265 
    ISSN: 1069-8299
    Keywords: boundary element method ; error estimation ; hp-version ; Galerkin BEM ; numerical results ; elasticity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper investigates the convergence of the h-, p- and hp-versions of a variational symmetric boundary element method (BEM) in plane elasticity by numerical experiments. The study discusses mixed boundary value problems on polygonal domains, i.e. problems for which the exact solution is analytic except in a finite number of points. The convergence of the error in energy norm is displayed for all versions of the BEM. All results are also compared with those obtained by the corresponding finite element methods. The theoretically predicted asymptotic convergence rates for all versions of the method can be observed in the numerical experiments. A comparison of computer times is given as well.
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  • 3
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    Communications in Numerical Methods in Engineering 12 (1996), S. 581-594 
    ISSN: 1069-8299
    Keywords: acoustics ; finite element method ; error estimation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A posteriori error estimation has become very popular, mainly in linear elasticity. A robust implementation of the superconvergent patch recovery technique of O. C. Zienkiewicz and J. Z. Zhu is presented for acoustic finite element analyses: the original concepts are extended to complex variables, and both local and global behaviours of the recovery procedure and the error estimation are studied. The numerical tests confirm the improvement of the rates of convergence for the recovered solution and also show the reliability of the error estimator except at frequencies corresponding either to the analytical or to the finite element eigenfrequencies.
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  • 4
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    Communications in Numerical Methods in Engineering 13 (1997), S. 207-217 
    ISSN: 1069-8299
    Keywords: plates ; finite elements ; mixed method ; error estimation ; superconvergent patch recovery ; adaptivity ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The superconvergent patch recovery (SPR technique) has been shown to be an effective postprocessing procedure in which an improved solution is obtained based on the original finite element solution. The technique was applied to second order problems with success, but the method has not yet been studied on problems posed in mixed form. This paper demonstrates that the technique can be applied to beam and plate bending problems, characterized by fourth order differential equations. The differential equation is here written as two coupled differential equations of second order leading to a mixed finite element procedure based on approximations of the moment and displacement fields. Two elements of mixed type are handled, namely a triangular plate element with constant moment field and a rectangular element with linearly varying bending moments. Numerical examples are given to show that the postprocessed solution is more accurate and has a higher rate of convergence. © 1997 by John Wiley & Sons, Ltd.
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  • 5
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 38 (1995), S. 2325-2345 
    ISSN: 0029-5981
    Keywords: postbuckling ; plates ; perturbation methods ; FEM ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The present paper extends the finite element perturbation approach already presented for pin-jointed and framed structures15 to rectangular thin plates. Koiter's asymptotic strategy2 is coupled with a High-Continuity finite element discretization of the plate.22 The consistency of the discrete model is discussed from the kinematical and numerical points of view and several numerical tests are reported. It appears that use of the HC elements makes the perturbation algorithm insensitive to the locking phenomenon occurring in the evaluation of the postbuckling behaviour. It also allows the use of very fine discretization meshes at low computational cost.
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  • 6
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 4039-4061 
    ISSN: 0029-5981
    Keywords: finite element method ; optimal mesh ; strategy ; refinement ; error estimation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Five Adaptive Modification Strategies (AMSs) are studied as means to obtain nearly optimal meshes using an adaptive finite element modelling system based on the h-version of the FEM. These strategies include the method traditionally seem in the literature as well as four additional methods. The five strategies are tested over five numerical examples, one of them producing convergence oscillations in one example. The principal characteristic of our system is that it permits the user to control certain parameters of the adaptive process, which contributes to an improvement in the results.
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  • 7
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    Communications in Numerical Methods in Engineering 14 (1998), S. 633-645 
    ISSN: 1069-8299
    Keywords: error estimation ; boundary elements ; adaptive mesh ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A posteriori error estimation for the boundary element method is developed. The nodal error is estimated from the difference of two solutions - one from the original BEM solution, and the other from interpolation of the original solution. Based on nodal errors, a matrix analysis is carried out to calculate the corresponding errors at source points. Two formulae for estimating global percentage errors are proposed in the paper. The first formula uses nodal errors directly to estimate element error, and the second uses an integral form to calculate element error to eliminate extremely high mesh concentration near areas with singular solutions. An h-version adaptive mesh refinement is implemented to study the accuracy of the proposed error estimation. Numerical examples show that the error estimator can correctly guide mesh refinement, and a final mesh can be obtained in a few iterations. © 1998 John Wiley & Sons, Ltd.
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  • 8
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 4 (1997), S. 205-221 
    ISSN: 1070-5325
    Keywords: solid mechanics ; theory of elastoplasticity ; FEM ; scientific parallel computing ; preconditioning ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The numerical solution of non-linear problems in solid mechanics (e.g., elastic-plastic problems) may be very expensive in the case of the use of fine discretizations. There is a requirement for efficient numerical algorithms and very fast hardware. Modern parallel computers in combination with modern numerical techniques, such as the parallel preconditioned conjugate gradient method for solving large linear systems and the consequent use of a consistent linearization of the non-linear problem, may lead to a superlinear speed up in comparison with equivalent single processor machines. The authors have developed a parallel experimental computer code using both techniques. The code is used for scientific investigations in the area of the identification of mechanical material parameters of metals. © 1997 John Wiley & Sons, Ltd.
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  • 9
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    Communications in Numerical Methods in Engineering 11 (1995), S. 105-115 
    ISSN: 1069-8299
    Keywords: finite element method ; conceptual diagrams ; error estimation ; postprocessing ; teaching ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The success of the finite element method depends on the highly systematic way the analysis is built up, which means that the structure of the theoretical description and the code is transferable between different applications. It is advisable to teach the subject in such a way that this fact is fully exploited. It is a fact that most FE calculations today do not contain a check of the accuracy/quality of the solution. In the teaching of the FE method nothing is more important than the basic knowledge and understanding of the properties and behaviour of the obtained FE solution. The paper deals with the methodology in presenting the method, by use of conceptual diagrams. It also discusses the interpretation of the results from a classical FE analysis and the extraction of high quality information. Finally, error estimation and postprocessing are discussed. The detailed description of the boundary conditions is lost in the FE solution. In the postprocessing stage they should be taken into account once more.
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  • 10
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    Communications in Numerical Methods in Engineering 14 (1998), S. 381-392 
    ISSN: 1069-8299
    Keywords: porous medium ; fluid flow ; electromechanical coupling ; FEM ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We consider a coupled problem of the deformation of a porous solid, flow of a compressible fluid and the electrical field in the mixture. The governing equations consist of balance of the linear momentum of solid and of fluid, continuity equations of the fluid and current density, and a generalized form of Darcy's law which includes electrokinetic coupling. The compressibility of the solid and the fluid are taken into account. We transform these equations to the corresponding finite element relations by employing the principle of virtual work and the Galerkin procedure. The nodal point variables in our general formulation are displacements of solid, fluid pore pressure, relative velocity of the fluid and electrical potential. Derivation of the FE equations is presented for small displacements and elastic solid, which can further be generalized to large displacements and inelastic behaviour of the solid skeleton.According to this formulation we can include general boundary conditions for the solid, relative velocity of the fluid, fluid pressure, current density and electrical potential. The dynamic-type non-symmetric system of equations is solved through the Newmark procedure, while in the case of neglect of inertial terms we use the Euler method.Numerical examples, solved by our general-purpose FE package PAK, are taken from biomechanics. The results are compared with those available in the literature, demonstrating the correctness and generality of the procedure presented. © 1998 John Wiley & Sons, Ltd.
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  • 11
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    Communications in Numerical Methods in Engineering 11 (1995), S. 497-506 
    ISSN: 1069-8299
    Keywords: error estimation ; super convergent patch recovery scheme ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A comparative study of error estimators using a patch recovery scheme with those using simple nodal averaging is made for the four-noded Lagrangian quadrilateral element through two plane stress elasticity problems. It is demonstrated that error estimators using a patch recovery scheme are generally more effective and have an estimated stress field that is closer to the exact one than those using simple nodal averaging.
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  • 12
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    Communications in Numerical Methods in Engineering 14 (1998), S. 367-380 
    ISSN: 1069-8299
    Keywords: bevel gears ; instantaneous mesh stiffness ; load distribution ; FEM ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new method, namely the normal stiffness matrix along contact line (NSMACL) method, for analysing gears, is proposed. The new method uses the static coagulation technique to coagulate the global stiffness matrix of all contact teeth into a lower-order NSMACL. By adding the concert deformation condition and equilibrate condition, the relation between the torque acting on the driving gear and the load along the contact lines can be established, and the contact stress and gear tooth deformation can also be obtained. Three-dimensional (3D) highly accurate solid models of gear teeth have been established, in which the contact range and the whole finite element model can be automatically adjusted with the change of meshing process. Spur and helical bevel gears can be analysed using these models. Example models and results are presented. © 1998 John Wiley & Sons, Ltd.
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  • 13
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    Communications in Numerical Methods in Engineering 14 (1998), S. 409-418 
    ISSN: 1069-8299
    Keywords: adaptive refinement procedure ; nearly incompressible problems ; error estimation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A numerical study is carried out employing some selected 2D elements and an automatic adaptive refinement procedure for the solution of a problem involving a nearly incompressible material. For a material with Poisson's ratio close to 0·5, it is found that both hybrid elements and high-order Lagrangian triangles can be used to provide a reliable solution. Furthermore, the rate of convergence of the elements is not affected by the high value of Poisson's ratio, and a near-optimal convergence rate is achieved in all the numerical tests run. © 1998 John Wiley & Sons, Ltd.
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  • 14
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    Communications in Numerical Methods in Engineering 14 (1998), S. 963-975 
    ISSN: 1069-8299
    Keywords: cylindrical gears ; load distribution ; stress ; deformation ; stiffness ; FEM ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method, namely the normal stiffness matrix along contact line (NSMACL) method, for analysing gears is proposed. Three-dimensional (3D) finite element (FE) solid models have been established. Cylindrical gears - spur and helical, external and internal, hobbling and slotting, different parameters and materials - can be analysed using these models. Results such as load distribution along the contact lines, deformations and stiffness at any contact position, and contact stresses are presented. Calculation results show that the trend of gear tooth deformation coincides with the tested ones using the dynamic speckle photography method. © 1998 John Wiley & Sons, Ltd.
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  • 15
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    Communications in Numerical Methods in Engineering 11 (1995), S. 117-125 
    ISSN: 1069-8299
    Keywords: self similarity ; FEM ; plasticity ; crack growth ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Self-similar situations are idealized states often referred to in continuum mechanics. Such a situation is generally expected when the formulated problem only involves one significant length parameter. The state at a stationary or at a steadily moving concentrated load may be self-similar. In heat conductivity, the progressive phase transformation near a point-shaped heat source results in a self-similar situation. The problem may be non-linear and history-dependent. Thus, an incremental theory is needed, generally implying that the load has to be applied in small increments. However, at self-similarity the solutions for different loads are similar. The final solution therefore includes its own history, which may be exploited.This short communication demonstrates how an available FEM code (including many commercial codes) may be conveniently used for investigations of self-similar situations in solid mechanics. Quasistatic elastic-plastic problems are considered. The theory covers a general material behaviour including large strains and large deformations. The FEM code must allow for a user-defined material. The technique is demonstrated on a problem for an edge crack growing while the scale of yielding is large. The result is compared with calculations using a node relaxation technique.
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  • 16
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    Communications in Numerical Methods in Engineering 11 (1995), S. 149-158 
    ISSN: 1069-8299
    Keywords: FEM ; stability analysis ; algorithms ; shell structures ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The investigation of the non-linear response of shell-like structures requires insight into stability behaviour. In the paper we compare two strategies to compute singular points based on different eigenvalue problems. We show a simple algorithm to calculate critical load factors A used in engineering buckling analysis from the eigenvalues of the standard eigenvalue problem (KT - ω1) ϕ = 0. Some numerical examples illustrate the derived results and algorithms.
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  • 17
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    International Journal for Numerical Methods in Engineering 40 (1997), S. 533-550 
    ISSN: 0029-5981
    Keywords: multidisciplinary analysis ; FEM ; aeroelasticity ; aeroservoelasticity ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents details of a numerical formulation and associated general-purpose finite element (FE) software developed for the integrated aeroelastic and aeroservoelastic (ASE) analysis of complex engineering systems, encompassing such disciplines as structures, unsteady aerodynamics, and feedback controls. A linear analysis, involving panel methods for derivation of unsteady aerodynamic forces, is achieved by transforming the equations of motion from the frequency to the Laplace domain and formulating a state-space matrix relationship, the related matrices being further augmented by the analog elements such as actuators and filters as well as digital or analog controllers. For non-linear problems, FE-based structural and computational fluid dynamics (CFD) solutions are adopted for the relevant analyses.Numerical results pertaining to a number of practical problems, obtained by utilizing the associated computer program, are compared to those derived from relevant flight and wind tunnel tests as well as other analyses, and they are presented here in some detail. Such results, involving damping and frequency responses, relate to the stability characteristics of the aerospace vehicles and testify to the efficacy of the present solution procedure. © 1997 by John Wiley & Sons, Ltd.
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  • 18
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    International Journal for Numerical Methods in Engineering 40 (1997), S. 2593-2610 
    ISSN: 0029-5981
    Keywords: FEM ; BEM ; coupling ; mixed variational formulation ; Neumann series ; elasticity problems ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The Finite Element Method and the Boundary Element Method are two different structure analysis methods with a totally different numerical character. Therefore, it makes no sense to couple these two methods pointwise at the interface. In contrast to a lot of coupling strategies in the past, in this paper a method is constructed where we have coupling of the two different methods in a weak form. As a result we can analyse the given structure with two different grids independent of each other. On this account, we see that the big advantage of the proposed method is in its ablity to couple BEM and FEM. The construction of a robust and reliable numerical algorithm depends on the adaptive control of symmetry and definiteness of the coupling matrix. Therefore, we use an iterative method for solving the boundary integral equation by expanding the Calderon projector in a Neumann series. Numerical results show the preciseness and efficiency of the method. © 1997 John Willey & Sons Ltd.
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  • 19
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 1585-1606 
    ISSN: 0029-5981
    Keywords: adaptive mesh refinement ; solid transition element ; non-conforming modes ; superconvergent patch recovery ; error estimation ; neighbouring element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An automated three-dimensional adaptive h-refinement strategy using the solid transition elements with variable midside nodes at edges and faces of the element is presented. The basic behaviour of these transition elements were improved by addition of associated non-conforming modes. By introducing these transition elements, some difficulties associated with imposing displacement constraints on irregular nodes to enforce interelement compatibility in the conventional adaptive h-refinement are easily overcome. A superconvergent patch recovery technique is also extended to three-dimensional problem. Numerical examples show the effectiveness of the proposed adaptive mesh refinement scheme using transition elements.
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  • 20
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 1879-1888 
    ISSN: 0029-5981
    Keywords: FEM ; dynamics ; lumping ; acoustics ; accuracy ; convergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method for deriving hexahedral finite elements with lumped mass matrices for 3-D-problems is presented. These elements meet the theoretical conditions for high order convergence, and two numerical examples based on the 3-D scalar wave equation show that this is also the case in practice and that their accuracy is comparable to elements with consistent mass matrices.
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  • 21
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 3007-3031 
    ISSN: 0029-5981
    Keywords: postbuckling ; instabilities ; multiple modes ; perturbation methods ; thin-walled structures ; FEM ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper refers to the analysis of the postbuckling behaviour of thin-walled structures by means of an asymptotic approach based on a finite element implementation of Koiter's non-linear theory of instability.The analysis has been accomplished by using the following assumptions: (i) the structure is described as an assemblage of flat slender rectangular panels; (ii) a non-linear Kirchhoff-type plate theory is used to model each panel; (iii) HC finite elements discretization is used; (iv) linear and quadratic extrapolations are assumed for the fundamental and the postbuckling paths, respectively; (v) multimodal buckling is considered; and (vi) imperfection sensitivity analysis is performed in both multimodal and monomodal form based on the steepest- descent path criterion.Several numerical results are presented and discussed. Comparisons with numerical solution obtained by standard incremental codes are given, which show the accuracy and reliability of the proposed approach.
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  • 22
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 3235-3246 
    ISSN: 0029-5981
    Keywords: finite elements ; error estimation ; invariants ; mesh refinement ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The notion of invariants associated with differential equations introduced in Part I is used to compute consistent local errors in a finite-element analysis. The procedure is illustrated by two simple examples - a one-dimensional beam problem and a two-dimensional membrane problem. It is also shown how the computed errors may be used for adaptive mesh refinement. However, the primary intent of this paper is to introduce a new concept for calculation of local errors.
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  • 23
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    International Journal for Numerical Methods in Engineering 39 (1996), S. 3219-3234 
    ISSN: 0029-5981
    Keywords: computational mechanics ; error estimation ; invariants ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In Part I of this paper we examine the notion of invariant quantities in problems encountered in computational mechanics. These invariant quantities are then used to verify results obtained by numerical techniques. Examples in rigid-body dynamics, elastostatics and unsteady-state heat flow are presented. In Part II, we use the invariant quantities to compute consistent local errors in a finite-element analysis.
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  • 24
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 2465-2482 
    ISSN: 0029-5981
    Keywords: interface-crack ; anisotropic ; FEM ; contact ; composite ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A versatile hybrid finite element scheme consisting of special crack-tip elements and crack face contact elements is developed to analyse a partially closed interface crack between two dissimilar anisotropic elastic materials. The crack-tip element incorporates higher-order asymptotic solutions for an interfacial crack tip. These solutions are obtained from complex variable methods in Stroh formalism. For a closed interfacial crack tip, a generalized contact model in which the crack-tip oscillation is eliminated is adopted in the calculation. The hybrid finite element modelling allows the stress singularity at an open and closed crack tip to be accurately treated. The accuracy and convergence of the developed scheme are tested with respect to the known interface crack solutions. Utilizing this numerical scheme, the stress intensity factors and contact zone are calculated for a finite interface crack between a laminated composite material.
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  • 25
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 2135-2163 
    ISSN: 0029-5981
    Keywords: FEM ; h-p version ; stress intensity factors ; damage tolerance assessment ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We develop effective approaches with which complex three-dimensional components may be analysed with a high and virtually guaranteed accuracy. The main computational tool is a h-p version of FEM practically realized with the p-version program STRIPE having a mesh generator for automatic mesh refinement at edges and vertices. Use of advanced extraction methods and new theoretical approaches give exponential convergence rates for accuracies in all engineering data of interest. New methods for reliable calculation of local stresses and stress intensity data at edges and vertices to be used for fatigue dimensioning at fillets, damage tolerance assessment of three-dimensional flaws, etc., are given. A complex real-life problem is reliably analysed in order to demonstrate the practical usefulness of the procedures advocated. The technical details will be given in forthcoming papers.
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  • 26
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    International Journal for Numerical Methods in Engineering 40 (1997), S. 1413-1433 
    ISSN: 0029-5981
    Keywords: finite element method ; adaptive refinement ; shape sensitivity analysis ; error estimation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The application of the Zienkiewicz-Zhu estimator was extended to the estimation of the discretization error arising from shape sensitivity analysis using the finite element method. The sensitivity error was quantified from the sensitivity of the energy norm by using an estimator specially developed for this purpose. Sensitivity analyses were carried out using the discrete analytical approach, which introduced no additional errors other than the discretization error. In this work, direct nodal averaging was used for linear triangular elements and the SPR technique for quadratic elements in order to obtain the smoothed stress and sensitivities fields. Two examples with an exact solution are used to analyse the effectivity of the proposed estimator and its convergence with the h-adaptive refinement. © 1997 by John Wiley & Sons, Ltd.
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  • 27
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 151-174 
    ISSN: 0029-5981
    Keywords: BEM ; FEM ; air venting ; blow molding ; thermoforming ; potential flow ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We examine the three-dimensional potential flow of a fluid (air) inside a cavity as it is induced by the advancement of an isotropic homogeneous membrane (parison) of general shape. This problem is of direct relevance to the processes of blow molding and thermoforming whereby air is evacuated through a number of vents of various sizes that are optimally positioned on the surface of the mold. The membrane material is assumed to obey the Mooney-Rivlin constitutive model, and the resulting deformation field is obtained using a Galerkin based finite-element method. The flow field in the domain bounded by the inflating membrane and the cavity (mold) is obtained using the boundary-element method. The accuracies of the original finite- and boundary-element codes are assessed separately against existing numerical results and analytical solution. The coupled finite/boundary element formulation is used to examine the air flow inside a rectangular mold with an insert and through a number of vents of various sizes at each pressure step of inflation. The accuracy of the coupled method is assessed on the basis of conservation of mass of air flow. © 1998 John Wiley & Sons, Ltd.
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  • 28
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 3163-3179 
    ISSN: 0029-5981
    Keywords: shakedown ; cyclic loads ; plasticity ; FEM ; incremental analysis ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An effective method for determination of a quasi-static shakedown loading and of a steady-state response is proposed. The classical optimization problem based on Melan's theorem is suitably reformulated to meet the requirements of incremental analysis. The main attention is focused on the reduction of a computational time required for a completion of a transient elastic-plastic phase of deformation. The method differs significantly from classical incremental analyses. Here, a load cycle is approximated by the finite number of loading systems covering the cycle. Each system is then combined with a separate domain of the structure in which the load system can be treated as a dominant one. In this manner, the structure consists of parts, each of them undergoing suitably chosen one-parameter loading only. Such a modification allows us to build a set of non-linear equations for all loading systems covering the whole load cycle. As a consequence the structure can be treated as the one in which the transient plastic phase of deformation is analysed load cycle by load cycle without making load increments inside the considered cycle. Due to this innovation a significant reduction of the computational time required for the solution of the steady-state response of the structure is obtained what is illustrated on 3-D frames. © 1997 John Wiley & Sons, Ltd.
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  • 29
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 4547-4576 
    ISSN: 0029-5981
    Keywords: adaptive refinement procedure ; error estimation ; 2-D stress analysis ; performance of different 2-D elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A series of numerical tests is carried out employing some commonly used finite elements for the solution of 2-D elastostatic stress analysis problems with an automatic adaptive refinement procedure. Different kinds of elements including Lagrangian quadrilateral and triangular elements, serendipity quadrilaterals, incompatible elements and hybrid elements have been tested. It is found that for a general problem involving compressible material and when a moderate accuracy of the final solution is sought, the nine-node Lagrangian (L9) element will be the most effective element, while when an extremely accurate solution is needed, higher order Lagrangian quadrilaterals or triangles will be a suitable choice. However, if only linear elements are available, the well known 5βI linear hybrid element is the best choice. © 1997 John Wiley & Sons, Ltd.
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  • 30
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 443-472 
    ISSN: 0029-5981
    Keywords: finite element method ; error estimation ; stress recovery ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper we investigate an approach for a posteriori error estimation based on recovery of an improved stress field. The qualitative properties of the recovered stress field necessary to obtain a conservative error estimator, i.e. an upper bound on the true error, are given. A specific procedure for recovery of an improved stress field is then developed. The procedure can be classified as Superconvergent Patch Recovery (SPR) enhanced with approximate satisfaction of the interior equilibrium and the natural boundary conditions. Herein the interior equilibrium is satisfied a priori within each nodal patch. Compared to the original SPR-method, which usually underestimates the true error, the present approach gives a more conservative estimate. The performance of the developed error estimator is illustrated by investigating two plane strain problems with known closed-form solutions. © 1998 John Wiley & Sons, Ltd.
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  • 31
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 499-515 
    ISSN: 0029-5981
    Keywords: error estimation ; constitutive error formulation ; complementary solutions ; numerical methods ; finite element methods ; virtual work principle ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Most engineering problems are solved by means of numerical methods that are able to provide only approximate solutions, for which it would be extremely useful to have efficient error estimators.Upper and lower bounds for quantities of integral character, like the stored magnetic energy or the ohmic power dissipated in the domain of interest, had been clearly established along with the procedures to obtain them numerically.However, upper and lower bounds for local quantities would be of paramount interest in several fields of applications like Non-Destructive Testing or Nuclear Magnetic Resonance.We present here a procedure for the determination of upper and lower bounds of local field quantities, namely the average value of a field component in an arbitrarily small region. It is based on the introduction of an auxiliary field, and is the natural extension of the method establishing the bounds of global quantities.Our technique can be used for any linear system in stationary conditions for which a virtual work principle can be applied. Its efficiency is demonstrated with the analysis of some stationary 2D and 3D electromagnetic problems. © 1998 John Wiley & Sons, Ltd.
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  • 32
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 40 (1997), S. 3247-3277 
    ISSN: 0029-5981
    Keywords: recovery ; patch ; adaptivity ; error estimation ; robustness test ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We present in this paper a modified form of the REP gradient recovery process recently published. This new form is not only cheaper but has a much improved performance - which equals and occasionally exceeds the performance of the SPR (Superconvergent Patch Recovery) method.The comparisons are based on the robustness test originally proposed by Babuška et al. This test is described briefly in a manner suitable for those who find some aspects of modern mathematics difficult to follow.The result and comparison of the tests for various repeatable patches with regular and irregular element distribution are made with SPR and the ‘old’ form of REP and are based on the general error estimator introduced by Zienkiewicz and Zhu in 1987. © 1997 John Wiley & Sons, Ltd.
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 41 (1998), S. 127-135 
    ISSN: 0029-5981
    Keywords: renumbering ; profile ; wavefront ; matrix ; FEM ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient renumbering method for high-order finite element models is presented. The method can be used to reduce the profile and wavefront of a coefficient matrix arising in high-order finite element computation. The method indirectly performs node renumbering and involves three main steps. In the first step, nodes at corners of the elements are numbered using an existing renumbering algorithm. In the second step, elements are numbered in an ascending order of their least new corner node numbers. Finally, based on the new element numbers, both corner and non-corner nodes are renumbered using an algorithm that simulates the node elimination procedure in a frontal solution method. The method is compared to the algorithms that directly perform node renumbering. The numerical results indicate that the three-step algorithm presented here is an order of magnitude faster and the resulting renumbering produces excellent profile and wavefront characteristics of the coefficient matrix. © 1998 John Wiley & Sons, Ltd.
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  • 34
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 3969-3983 
    ISSN: 0029-5981
    Keywords: benchmark solution ; error estimation ; finite elements ; mesh optimization ; stress smoothing ; adaptive mesh refinement ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Benchmark solutions are presented for a simple linear elastic boundary value problem, as analysed using a range of finite element mesh configurations. For each configuration, various estimates of local (i.e. element) and global discretization error have been computed. These show that the optimal mesh corresponds not only to minimization of global energy (or L2) norms of the error, but also to equalization of element errors as well. Hence, this demonstrates why element error equalization proves successful as a criterion for guiding the process of mesh refinement in mesh adaptivity. The results also demonstrate the effectiveness of the stress projection method for smoothing discontinuous stress fields which, for this investigation, are more extreme as a consequence of the assumption of nearly incompressible material behaviour. In this case, lower order smoothing produces a continuous stress field which is in close agreement with the exact solution.
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 39 (1996), S. 4243-4258 
    ISSN: 0029-5981
    Keywords: distributed computing ; heterogeneous workstations ; incompressible Navier-Stokes ; FEM ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The potential for using a network of workstations for solving the incompressible Navier-Stokes equations using a finite element formulation is investigated. A programming paradigm suitable for a heterogeneous distributed workstation environment is developed and compared to the traditional paradigm employed for distributed memory parallel computers. In particular, the issues of load balancing and fault recovery are explored. Numerical results are presented for two computer configurations: (1) a homogeneous network of workstations and (2) a heterogeneous network of workstations. The superiority of the developed paradigm over the traditional paradigm employed for distributed memory parallel computers is shown in cases where a heterogeneous network of workstations is employed or when one of the workstations of the cluster is loaded by other users.
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1295-1307 
    ISSN: 0029-5981
    Keywords: energy conservation ; mesh refinement ; error estimation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: By generalizing the conservation of energy statement in classical mechanics, a useful and relatively simple approach has been developed for checking the conservation requirements in finite element analysis. By way of illustration several examples are provided from fields of stress analysis, heat transfer and fluid flow. © 1998 John Wiley & Sons, Ltd.
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