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  • Artikel  (289)
  • finite element method
  • 1
    Publikationsdatum: 2020-02-24
    Beschreibung: The L'Aquila earthquake (Mw 6.3) occurred on April 6th at 01:32 UTC in the Central Appennines at a depth of about 9 km and was felt all over the central Italy. The main shock was preceded by a long seismic sequence started several months before and was followed by thousands of aftershocks, some of them with Mw〉4. In this work we present a 3D Finite Element (FE) study of the co-seismic deformation field produced by the L'Aquila earthquake and investigated the slip distribution on the fault. Our approach is based on a fully 3D parametrization of the spatial domain by means of a high resolution hexahedral mesh, discretized using 20-nodes brick elements. The element horizontal size is biased from 300 m to 2-3 km using the paving meshing algorithm in combination with an appropriate adaptive sizing function. Real surface topography (500 m) and rheological heterogeneities, deduced from a vp/vs travel time tomographic model, were incorporated within the model. The seismic source has been modeled as a normal fault plane having an heterogeneous moment release. We first computed the co--seismic deformation field by a direct simulation and then the Green's functions, to retrieve the slip distribution on the fault by linear inversion of different GPS datasets. Our results show that the adoption of a realistic 3D domain has a sensible impact on the rupture slip distribution, confirming that a simple halfspace approach introduces some trade-off between domain homogeneity and source complexity.
    Beschreibung: Unpublished
    Beschreibung: San Francisco (USA)
    Beschreibung: 3.3. Geodinamica e struttura dell'interno della Terra
    Beschreibung: open
    Schlagwort(e): Fault inversion ; slip distribution ; L'Aquila earthquake ; finite element method ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: Poster session
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  • 2
    Publikationsdatum: 2019-11-04
    Beschreibung: Employing a 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We consider different source models, such as sphere, spheroid and sill, dilating in elastic media (homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera (Italy), during the 1982-1984 unrest episode. The source shape and the characteristics of the medium have great influence on the calculated gravity changes, leading to very different values for the source densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto- plastic, the resulting gravity changes exhibit a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the source ranges from ∼400 kg/m3 (super critical water) to ∼3300 kg/m3 (higher than trachytic basalts), with drastically different implications for risk assessment.
    Beschreibung: Published
    Beschreibung: 119-133
    Beschreibung: 3.6. Fisica del vulcanismo
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): Campi Flegrei ; deformation ; gravity ; finite element method ; heterogeneous medium ; 04. Solid Earth::04.02. Exploration geophysics::04.02.02. Gravity methods
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 3
    Publikationsdatum: 2017-04-04
    Beschreibung: Modeling postseismic deformation is an increasingly valuable tool in earthquake seismology. In particular, the Finite Element (FE) numerical method allows accurate modeling of complex faulting geometry, inhomogeneous materials and realistic viscous flow, appearing an excellent tool to investigate a lot of specific phenomena related with earthquakes.
    Beschreibung: Unpublished
    Beschreibung: San Francisco, CA, USA
    Beschreibung: open
    Schlagwort(e): faulting sources ; coseismic deformation ; finite element method ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: Poster session
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  • 4
    Publikationsdatum: 2017-04-03
    Beschreibung: The 26 December 2004 Sumatra-Andaman earthquake is one of the largest earthquakes ever recorded since 1900. The earthquake resulted from complex slip on the fault where the oceanic portion of the Indian Plate slides under the Eurasian Plate, by the Indonesian Island of Sumatra. The particular features of the detected quasi-static displacement field has been previously attributed to the heterogeneous distribution of moment release on the fault plane. In the present work, we use a new computational FEM strategy to model the co- and postseismic displacement field associated with the Sumatra earthquake. For the first time we can study the joint effects of sphericity and 3D mechanical and rheological heterogeneities on the investigated observables. The comparison between our synthetic results and the available deformation data allows us to ascertain if also lateral heterogeneities in the physical properties of the medium could have played a role in assessing the deformation field.
    Beschreibung: Unpublished
    Beschreibung: San Francisco, CA, USA
    Beschreibung: open
    Schlagwort(e): Sumatra earthquake ; coseismic deformation ; finite element method ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: Poster session
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  • 5
    Publikationsdatum: 2017-04-04
    Beschreibung: The ground deformation produced by a spherical overpressure source in a heterogeneous elastic and/or viscoelastic medium is investigated by numerical models based on the finite element method. Sources are assumed to be located at different depths beneath Mount Etna, Sicily, Italy, the structure of which is approximated as axially symmetric. Finite element modelling allows to incorporate in the analysis realistic features such as topographic relief and the laterally heterogeneous multi-layered structure inferred from seismic tomography. In order to avoid introducing artifacts in the solution, great care was taken to calibrate the computational domain necessary to reproduce analytical results accurately. An elastic analysis, performed initially, shows significant changes of the deformation field with respect to homogeneous half-space solutions: topography induces slight but detectable changes in the deformation field; in particular the maximum value of the vertical component is shifted away from the symmetry axis. When introducing the elastic heterogeneities, the ground deformation is found to be more confined to the proximity of the axis and its amplitude is mostly sensitive to the presence of low rigidity layers above the source. The ratio of maximum radial to vertical deformation is significantly larger for deeper sources. A further development of the model includes the study of inelastic properties assuming a Maxwell viscoelastic rheology for different layers. If the viscoelastic rheology is applied only to layers deeper than the source, the solutions are affected in different ways according to the distance of the source from the viscoelastic layer. If a viscoelastic layer is present above the source, a very large amplification (by more than 100%) of the surface deformation is predicted by the model; moreover, uplift transients are found to be followed by subsidence, without invoking any decrease in source overpressure. The most striking effects are observed when the source is embedded within a viscoelastic layer: in this case a static equilibrium configuration is not attained and, in the long term, both components of deformation reverse their signs in proximity to the axis. Furthermore, the surface deformation becomes nearly independent of source depth, in the long term. Simple physical explanations are proposed for the different cases.
    Beschreibung: Published
    Beschreibung: 89-110
    Beschreibung: 3.6. Fisica del vulcanismo
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Mount Etna ; surface deformation ; topographic effect ; finite element method ; rheological layering ; overpressure source ; 04. Solid Earth::04.03. Geodesy::04.03.08. Theory and Models
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 6
    Publikationsdatum: 2019-11-04
    Beschreibung: Employing 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We consider different source models, such as sphere, spheroid and sill, dilating in elastic media (homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera (Italy), during the 1982-84 unrest episode. The source shape and the characteristics of the medium have great influence in the calculated gravity changes, leading to very different values for the source densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto-plastic, the resulting gravity changes exhibit a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the source ranges from ∼ 400 kg/m3 (supercritical water) to ∼ 3300 kg/m3 (higher than trachytic basalts), with drastically different implications for risk assessment.
    Beschreibung: Unpublished
    Beschreibung: 1-37
    Beschreibung: 3.3. Geodinamica e struttura dell'interno della Terra
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): Campi Flegrei ; Deformation ; gravity ; finite element method ; heterogeneous medium ; 04. Solid Earth::04.02. Exploration geophysics::04.02.02. Gravity methods
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 7
    Publikationsdatum: 2019-11-04
    Beschreibung: Volcanic areas often show complex behaviour as far as seismic waves propagation and seismic motion at surface are concerned. In fact, the finite lateral extent of surface layers such as lava flows, blocks, differential welding and/or zeolitization within pyroclastic deposits, introduces in the propagation of seismic waves effects such as the generation of surface waves at the edge, resonance in lateral direction, diffractions and scattering of energy, which tend to modify the amplitude as well as the duration of the ground motion. The irregular topographic surface, typical of volcanic areas, also strongly influences the seismic site response. Despite this heterogeneity, it is unfortunately a common geophysical and engineering practice to evaluate even in volcanic environments the subsurface velocity field with monodimensional investigation method (i.e. geognostic soundings, refraction survey, down-hole, etc.) prior to the seismic site response computation which in a such cases is obviously also made with 1D algorithms. This approach often leads to highly inaccurate results. In this paper we use a different approach, i.e. a fully 2D P-wave Çturning rayÈ tomographic survey followed by 2D seismic site response modeling. We report here the results of this approach in three sites located at short distance from Mt. Vesuvius and Campi Flegrei and characterized by overburdens constituted by volcanoclastic deposits with large lateral and vertical variations of their elastic properties. Comparison between 1D and 2D Dynamic Amplification Factor shows in all reported cases entirely different results, both in terms of peak period and spectral contents, as expected from the clear bidimensionality of the geological section. Therefore, these studies suggest evaluating carefully the subsoil geological structures in areas characterized by possible large lateral and vertical variations of the elastic properties in order to reach correct seismic site response curves to be used for engineering projects.
    Beschreibung: Published
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): dynamic amplification factor ; seismic ; tomography ; pyroclastic rocks ; finite element method ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Optical and quantum electronics 32 (2000), S. 719-734 
    ISSN: 1572-817X
    Schlagwort(e): anisotropic waveguides ; finite element method ; integrated optics ; open boundary conditions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract An efficient method to model guided and leaky modes of anisotropic dielectric waveguides with arbitratry dielectric tensor ε¯¯ is presented. This method takes advantage of a particular β-formulation approach of the finite element method (FEM), leading to an optimized use of the computational resources.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Applications of mathematics 45 (2000), S. 99-129 
    ISSN: 1572-9109
    Schlagwort(e): Stokes equations ; nonstandard boundary conditions ; finite element method ; approximation of boundary
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract We investigate a finite element discretization of the Stokes equations with nonstandard boundary conditions, defined in a bounded three-dimensional domain with a curved, piecewise smooth boundary. For tetrahedral triangulations of this domain we prove, under general assumptions on the discrete problem and without any additional regularity assumptions on the weak solution, that the discrete solutions converge to the weak solution. Examples of appropriate finite element spaces are given.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1349-9432
    Schlagwort(e): near infrared spectroscopy ; diffusion equation ; finite element method ; hybrid radiosity diffusion model ; topographic imaging ; photon measurement density function
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract An accurate modelling of light propagation in the head is required to develop an algorithm to reconstruct the image of brain activity. Most previous studies have calculated the light propagation in two dimensional models because of their advantage in computation time and memory requirement over three dimensional models. However, in topographic imaging, the sensitivity distribution in the cross sections parallel to the brain surface which cannot be obtained from a two dimensional model is most important to reconstruct the image. In this study, the light propagation in three dimensional adult head models is calculated by finite element method and hybrid radiosity-diffusion method. The light propagation in the adult head is strongly affected by the non-scattering cerebrospinal fluid (CSF) layer surrounding the brain. The sensitive area is shifted toward the deeper region, and is spread around the CSF layer. The intensely sensitive region on the brain surface is broadly distributed between the source and detector. However, the sensitive region does not penetrate into the deeper part of the brain.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Archive of applied mechanics 70 (2000), S. 377-386 
    ISSN: 1432-0681
    Schlagwort(e): Key words Curved crack ; compositional profile ; thermal shock ; functionally graded material ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Summary Thermal cracking in a ceramic/metal functionally graded plate is discussed. When a functionally graded plate is cooled from high temperature, curved or straight crack paths are experimentally observed on the ceramic surface. One of the reasons that make the crack paths to differ are the thermal or mechanical conditions. In order to clarify the influence of these conditions on the crack path, the crack propagation is simulated using finite element method.
    Materialart: Digitale Medien
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  • 12
    Digitale Medien
    Digitale Medien
    Springer
    Journal of statistical physics 98 (2000), S. 813-834 
    ISSN: 1572-9613
    Schlagwort(e): conductance ; electron waveguide ; electron scattering ; random matrix theory ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We show that the S-matrix for electrons propagating in a waveguide has different statistical properties depending on whether the waveguide cavity shape gives rise to chaotic or integrable behavior classically. We obtain distributions of energy level spacings for integrable and chaotic billiards shaped like the waveguide cavity. We also obtain distributions for Wigner delay times and resonance widths for the waveguide, for integrable and chaotic cavity geometries. Our results, obtained by direct numerical calculation of the electron wave function, are consistent with the predictions of random matrix theory.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 103 (2000), S. 293-310 
    ISSN: 1573-2673
    Schlagwort(e): Cohesive crack models ; concrete ; finite element method ; fracture ; mixed mode ; numerical analysis.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A simple and efficient numerical procedure for mixed mode fracture of quasibrittle materials is shown: This technique predicts crack trajectories as well as load-displacement or load-CMOD responses. The model is based on the cohesive crack concept and uses the local mode I approach. Numerical results agree quite well with three experimental sets of mixed mode fracture of concrete beams; one from Arrea and Ingraffea, another from García, Gettu and Carol and from a nonproportional loading by the authors. In constrast to more sophisticated models, this method offers two major advantages: it requires only material properties measured by standardized methods and it can easily be implemented with general multipurpose finite element codes.
    Materialart: Digitale Medien
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 4 (2000), S. 43-56 
    ISSN: 1573-2738
    Schlagwort(e): dry friction ; finite element method ; moving contact ; photoviscoelasticity ; viscoelasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Moving contact problems in a viscoelastic body with a rigidindentor are often seen in an industrial field. An evaluation of thetime-temperature-dependent stress and strain behavior around a contactregion is required in order to make clear the fundamental mechanism ofthe local fracture and wear on the contact surface of the viscoelasticbody under moving loads with dry friction. No analyses have yet beenpublished about the stress/strain of the viscoelastic moving contactproblem with the dry friction using both an experimental and a numericalmethod. The authors discuss an experimental and a numerical model forthe analysis of not only the viscoelastic stress and strain, but alsodeformations, taking into consideration the dry friction. Animage-processing-aided photoviscoelastic technique is applied foranalyzing the principal stress and strain behavior near the contactregion. Also, a two-dimensional plane stress model which consists of aviscoelastic strip and a rigid sliding cylinder is adopted in a finiteelement analysis of the same problem. The time-dependent stress andstrain and the coefficient of dry friction are successfully evaluated byexperimental and numerical methods.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica Sinica 16 (2000), S. 254-263 
    ISSN: 1614-3116
    Schlagwort(e): microcrack ; damage healing ; microcrack splitting and spheroidization ; surface diffusion ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Based on the thermal kinetic and mass conservation, a series of controlling equations for the finite element are derived and related programs are developed to simulate the damage microcrack healing process controlled by surface diffusion. Two kinds of typical models for microcrack splitting are proposed, i.e., the grain boundary energy existing on the crack surface and residual stresses applying on the crack surface. And the conditions of microcrack splitting in the two models are given as a function of the microcrack aspect ratio. The microcrack with traction-free surfaces will directly evolve into a spheroid.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica Sinica 16 (2000), S. 374-382 
    ISSN: 1614-3116
    Schlagwort(e): contact impact ; contact search ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A new contact searching algorithm for contact-impact systems is proposed in this paper. In terms of the cell structure and the linked-list, this algorithm solves the problem of sorting and searching contacts in three dimensions by transforming it to a retrieving process from two one-dimensional arrays, and binary searching is no longer required. Using this algorithm, the cost of contact searching is reduced to the order ofO(N) instead ofO(Nlog2 N) for traditional ones, whereN is the node number in the system. Moreover, this algorithm can handle contact systems with arbitrary mesh layouts. Due to the simplicity of this algorithm it can be easily implemented in a dynamic explicit finite element program. Our numerical experimental result shows that this algorithm is reliable and efficient for contact searching of three dimensional systems.
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Journal of mathematical chemistry 27 (2000), S. 251-265 
    ISSN: 1572-8897
    Schlagwort(e): evanescent energy ; optical fibers ; single-molecule detection ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Mathematik
    Notizen: Abstract A finite element method is presented to find the propagation characteristics of an optical fiber with arbitrary cross section. This method uses a non-local boundary operator to reduce the infinite problem (open waveguide) to a bounded one. Evanescent energy in circular and square fibers of the same core area are computed and compared to show that square fibers can be effectively used in single molecule detection.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Numerical algorithms 24 (2000), S. 309-332 
    ISSN: 1572-9265
    Schlagwort(e): computational fluid dynamics ; Navier–Stokes equations ; finite element method ; finite volume method ; multigrid algorithm ; parallel computing ; 76N10 ; 76M10 ; 65M55 ; 65Y05
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract In this paper, we report on our recent efforts concerning the design of parallel linear multigrid algorithms for the acceleration of 3-dimensional compressible flow calculations. The multigrid strategy adopted in this study relies on a volume agglomeration principle for the construction of the coarse grids starting from a fine discretization of the computational domain. In the past, this strategy has mainly been studied in the 2-dimensional case for the solution of the Euler equations (see Lallemand et al. [6]), the laminar Navier–Stokes equations (see Mavriplis and Venkatakrishnan [12]) and the turbulent Navier–Stokes equations (see Carré [1], Mavriplis [10] and Francescatto and Dervieux [4]). A first extension to the 3-dimensional case is presented by Mavriplis and Venkatakrishnan in [13] and more recently in Mavriplis and Pirzadeh [11]. The main contribution of the present work is twofold: on the one hand, we demonstrate the successful extension and application of the multigrid by a volume agglomeration principle to the acceleration of complex 3-dimensional flow calculations on unstructured tetrahedral meshes and, on the other hand, we enhance further the efficiency of the methodology through its adaptation to parallel architectures. Moreover, a nontrivial aspect of this work is that the corresponding software developments are taking place in an existing industrial flow solver.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of composite materials 36 (2000), S. 459-464 
    ISSN: 1573-8922
    Schlagwort(e): composite strip ; curved structure ; bending ; geometrical nonlinearity ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract To date, bending problems for strips or plates made of composite materials with curved structure have been investigated only in the linear statement. However, in many cases, the necessity arises to investigate the corresponding bending problems in the geometrically nonlinear statement. Therefore, in the present paper, some bending problems for a composite strip with a periodically curved structure is investigated in such a statement using the exact nonlinear equations of elasticity theory in Lagrangian coordinates. The numerical results are obtained by employing the FEM with the use of the Newton-Raphson and the Modified Newton-Raphson algorithms.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of composite materials 36 (2000), S. 277-286 
    ISSN: 1573-8922
    Schlagwort(e): stability theory ; sandwich shell ; arbitrary geometry ; finite element method ; linearized problem ; geometrically nonlinear problem ; arbitrary buckling form
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract Two statements of the problem of arbitrary buckling forms (BFs) (including synphasic, antiphasic, mixed flexural, flexural-shear, and shear forms in the tangential directions) of general-form sandwich shells and two schemes of its solution by the FEM are given. The first of the schemes is based on the use of refined linear equations for determination of the precritical stress-strain state and linearized equations of neutral equilibrium with all parametric addends necessary to determine the critical loads and reveal the possible BFs. The second one uses the general geometrically nonlinear relations of elasticity theory for investigation of the whole deformation process up to buckling in terms of a modified incremental (stepwise) statement of the problem. Examples of solution of particular problems are given.
    Materialart: Digitale Medien
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    International journal of infrared and millimeter waves 21 (2000), S. 63-76 
    ISSN: 1572-9559
    Schlagwort(e): groove guide ; dominant mode ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper, the dominant mode in groove guide is analyzed by finite element method. For the guide with a shallow groove, the electric field lines (abbreviated as E lines) are perpendicular to the parallel plate, which is different from the literatures, and the dominant mode distribution is irrelevant to the groove width; for the guide with a narrow but deeper groove, the E lines are parallel to the plate region, which represents the characteristics of lower attenuation, for the guide with a deeper and wider groove, a complicated E lines are obtained. These results reveal that the dominant mode distribution in groove guide is varied, which replenish our understanding of groove guide, and the results have important values in design, manufacture, and application of groove guide.
    Materialart: Digitale Medien
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  • 22
    Digitale Medien
    Digitale Medien
    Springer
    International journal of infrared and millimeter waves 21 (2000), S. 965-977 
    ISSN: 1572-9559
    Schlagwort(e): V-groove guide ; dominant mode ; electrical lines ; finite element method ; millimeter waves
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper, the electric field lines of the dominant mode in a closed V-groove guide as well as an open one are analysed by finite element method. The results show that the electric field lines are not parallel to the parallel plate region, but perpendicular to them. Since the attenuation increase with increasing frequency when the electric field lines are perpendicular to the mental walls, the V-groove is not suitable to be used in millimeter and submillimeter wavebands, and it is can't be regarded as low-loss wave guiding structures.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    International journal of infrared and millimeter waves 21 (2000), S. 1341-1354 
    ISSN: 1572-9559
    Schlagwort(e): elliptical waveguide ; the lowest TM mode ; field patterns ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In this paper, finite element method is first used to discuss the field patterns in a hollow perfectly conducting pipe with elliptical cross section. The electrical field lines of the dominant TE mode as well as the magnetic field lines of the lowest TM mode are presented. The results are the same with literatures, and also give a correction to the field pattern of the lowest TM mode in elliptical waveguide.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Optimization and engineering 1 (2000), S. 277-304 
    ISSN: 1573-2924
    Schlagwort(e): fluid flow ; finite element method ; Navier-Stokes ; partial differential equations ; projections ; design sensitivity analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Abstract Gradient computations can be a limiting factor in algorithm efficiency and accuracy for optimization based design. In this paper, we present three parameterized flow problems and consider the evaluation of state sensitivities both theoretically and numerically. Existence and uniqueness results are given for the sensitivities of a specific group of two-dimensional Navier-Stokes problems. We then turn our attention to obtaining numerical approximations to state sensitivities. We show convergence of our numerical sensitivities using a problem having an exact solution. Next, two problems, flow around a cylinder and flow over a bump, are used to evaluate several computational schemes. In particular, a local projection scheme for improved state derivative approximations and the use of an adaptive finite element scheme are shown to be important techniques for obtaining accurate sensitivity approximations. Lastly, we evaluate the impact of these computational techniques on cost function and gradient calculation.
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  • 25
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 21 (2000), S. 579-584 
    ISSN: 1573-2754
    Schlagwort(e): influence line method ; analytical method ; finite element method ; microcirculatory dynamics ; O368 ; O242.1
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The mathematical model described in Part I was solved using “influence line method” combining analytical method and finite element method. Many important aspects of microcirculatory dynamics were analyzed and discussed. It show that interstitial fluid pressure changes its sign twice within one arteriolar vasomotion period and it is therefore not important that interstitial fluid pressure is a little higher or lower than atmospheric pressure; arteriolar vasomotion can periodically result in lymph formation and interstitial total pressure plays an important role in this procedure; local regulation of microcirculation can meet metabolic need some extent in the form of dynamic equilibrium. The property of arteriole as a “resistant vessel” and the efficiency of microvascular network as heat exchanger are also shown. These results show that the comprehensive mathematical model developed in Part I is physiologically resonable.
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 21 (2000), S. 87-94 
    ISSN: 1573-2754
    Schlagwort(e): cyclically symmetric structure ; finite element method ; stress analysis ; O175.14
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, a computational method for finite element stress analysis of a cyclically symmetric structure subjected to arbitrary loads is provided. At first, using discrete Fourier transformation technique, the complete structure is analyzed by considering only one sector with appropriate complex constraints on its boundary with the adjacent sectors. Next, an imaginary structure which is composed of two identically overlapping sectors is constructed, and that the complex constraints mentioned above can be equivalently replaced by a set of real constraints on this imaginary struture is proved. Therefore, the stress analysis of a cyclically symmetric structure can be solved conveniently by most of finite element programs.
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 21 (2000), S. 1381-1389 
    ISSN: 1573-2754
    Schlagwort(e): porous media ; viscous fluid ; dynamic response ; finite element method ; O347
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The governing equations as well as boundary and initial conditions for nonlinear dynamic response problems of viscous fluid-saturated biphase porous medium model, based on mixture theory, are presented. With Galerkin weighted residual method the corresponding nonlinear dynamic penalty finite element equation, in which the dependencies of volume fraction and permeation coefficients on deformation are included, is obtained. The iteration solution method of the nonlinear system equation is also discussed. As a numerical example, the dynamic response of a porous medium column under impulsive loading action is analyzed with the developed finite element program. The numerical results demonstrate the efficiency and correctness of the method.
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 21 (2000), S. 341-346 
    ISSN: 1573-2754
    Schlagwort(e): buckling ; composites ; delamination ; finite element method ; shells ; TB332 ; O242.21 ; O346.5 ; TG335.81
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The purpose of the present study is to develop a new finite element method for analyzing buckling of delaminated composite plates and shells. This is achieved by establishing a new finite element called the reference-surface element. By use of the compatibility condition under Mindlin assumptions, the formulation of the reference-surface element was derived from whichever plate-element or shell-element being capable of analyzing composite plates and shells. This method assures a reasonable description of displacement field and the satisfaction of compatibility conditions for delamination problem. Numerical results for linear delamination buckling of axially compressed shells are presented to validate the method.
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 21 (2000), S. 13-18 
    ISSN: 1573-2754
    Schlagwort(e): wavelet analysis ; finite element method ; nonconforming analysis ; CLC number ; O242.21
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The compactly supported wavelet basis functions are introduced into the construction of interpolating function of traditional finite element method when analyzing the problems with high gradient, and the traditional, interpolating method is modified. The numerical stability of the new interpolating pattern is discussed and the convergence of the new method is also discussed by patch test analysis. The additional freedom of the new interpolating pattern is eliminated by static condensation method. Finally, the wavelet finite element formulations based on variational principles are put forward.
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of composite materials 36 (2000), S. 373-378 
    ISSN: 1573-8922
    Schlagwort(e): finite element method ; poroelasticity ; cellular stimulation ; fracture healing
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The process of healing of fractured bone is known to be influenced by the mechanical environment and the loads exerted by physical activity of the patient or otherwise. We compute mechanical fields in the soft connective tissue of the healing fracture using Biot's poroelasticity model and a finite element (FE) method for low-frequency loading. A two-scale FE framework is used to model effects of the rough bone-callus contact surface. We look at the difference the interface roughness makes with respect to different possible mechanostimulating agents.
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Optical and quantum electronics 31 (1999), S. 1073-1084 
    ISSN: 1572-817X
    Schlagwort(e): active devices ; beam propagation method ; electromagnetic propagation ; finite element method ; photonics devices
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract A finite element beam propagation method to analyze nonlinear active optical waveguides is presented. The model takes into account the mutual coupling among the equations describing the electromagnetic field propagation and the ones governing the signal amplification due to a doped medium. The approach is able to distinguish the different behavior of Ex (quasi-TE) and Ey (quasi-TM) polarizations. The performances of nonlinear and doped couplers are analyzed in detail by varying the input power, the field polarization and the pumping scheme.
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  • 32
    ISSN: 1572-817X
    Schlagwort(e): beam propagation methods ; finite difference method ; finite element method ; integrated optics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract New 2D scalar beam propagation methods for both TE and TM polarization are presented. Both second- and fourth-order accurate schemes, in the lateral stepsize, are shown. The methods use uniform discretization and can handle arbitrary positions of interfaces between materials with different refractive indices. Either Transparent Boundary Conditions or Perfectly Matched Layers are used at the boundary of the computational window.
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Fire technology 35 (1999), S. 210-231 
    ISSN: 1572-8099
    Schlagwort(e): heat transfer ; high heat flux ; flash fire ; finite element method ; thermal protective performance ; protective clothing ; apparent heat capacity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung
    Notizen: Abstract A heat-transfer model has been developed for two common, inherently flame-resistant fabrics, Nomex® IIIA and Kevlar®/PBI, when subjected to the high heat fluxes used in bench top tests, such as the thermal protective performance (TPP) test, ASTM D 4108. The apparent heat capacity method was used to model thermochemical reactions in these materials with information from thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) tests. Also included were in-depth radiation absorption, variable thermal properties, and heat transfer across an air space from the fabric to a test sensor. The finite element method was used to solve the resulting equations. Absolute temperatures predicted by this relatively simple model fall within 4% of those measured by an infrared thermometer. Estimated times to the Stoll second-degree burn criterion are within 6% of those derived from actual tests.
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Advanced performance materials 6 (1999), S. 149-159 
    ISSN: 1572-8765
    Schlagwort(e): super plastic forming ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract FEM analysis has proved to be a powerful investigative tool capable of encompassing all the aspects that characterise an SPF process. However, despite the high potential of FEM programs they do not allow one to directly and suitably obtain the thickness of a sheet product for high deformation values, as commonly occurs in SPF processes. Many papers have been published on finite element analysis of S.P.F. process but the question of calculus accuracy in thicknesses of a sheet product has not been directly investigated. This problem has been already considered by the authors in a previous study which proposed an algorithm to determine thicknesses for a specific application. The software set up starts out with the results of the FEM modelling, keeps track of the “deformation” undergone by each element of the mesh and calculates to a good approximation the thicknesses at the end of the forming. Although the original version of the algorithm could only be used for the application studied an updated version is introduced in this study that can be used for any case. In other words, the software generates the thickness profile at the end of the analysis independently of technological set up, item shape and type of simulation (3D and 2D). The proposed algorithm was tested with reference to the superplastic forming of an item of simple geometry beginning with a thin circular plate blocked at the edges and put under constant hydrostatic pressure on one side. The test material, made superplastic by means of a series of repeated laminations, was characterised using an alternative method to the traditional tension test. The results of the experiments are in good accordance with the numerical predictions both in terms of thickness distribution and forming times.
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Numerical algorithms 21 (1999), S. 23-47 
    ISSN: 1572-9265
    Schlagwort(e): multilevel method ; stabilization ; finite element method ; additive method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Mathematik
    Notizen: Abstract There exist two main versions of preconditioners of algebraic multilevel type, the additive and the multiplicative methods. They correspond to preconditioners in block diagonal and block matrix factorized form, respectively. Both can be defined and analysed as recursive two-by-two block methods. Although the analytical framework for such methods is simple, for many finite element approximations it still permits the derivation of the strongest results, such as optimal, or nearly optimal, rate of convergence and optimal, or nearly optimal order of computational complexity, when proper recursive global orderings of node points have been used or when they are applied for hierarchical basis function finite element methods for elliptic self-adjoint equations and stabilized in a certain way. This holds for general elliptic problems of second order, independent of the regularity of the problem, including independence of discontinuities of coefficients between elements and of anisotropy. Important ingredients in the methods are a proper balance of the size of the coarse mesh to the finest mesh and a proper solver on the coarse mesh. This paper presents in a survey form the basic results of such methods and considers in particular additive methods. This method has excellent parallelization properties.
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 20 (1999), S. 1331-1341 
    ISSN: 1573-2754
    Schlagwort(e): porous media ; wave propagation ; finite element method ; O347
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract With the porous media model based on mixture theory, a finite element formulation for dynamic transient analysis of fluid-saturated two-phase porous media is presented. Time integration of the equation, deduced with penalty method, can be performed by using implicit or explicit method. One-dimensional wave propagation in column under step loading and impulsive loading are analyzed with the developed finite element program. The obtained curves of displacements, velocities, effective stresses and pore pressures against time demonstrate the existence of wave propagation phenomena, which coincide with the theoretical results.
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Journal of mathematical imaging and vision 10 (1999), S. 143-162 
    ISSN: 1573-7683
    Schlagwort(e): non-rigid medical image registration ; elasticity theory ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A parameter-free approach for non-rigid image registration based on elasticity theory is presented. In contrast to traditional physically-based numerical registration methods, no forces have to be computed from image data to drive the elastic deformation. Instead, displacements obtained with the help of mapping boundary structures in the source and target image are incorporated as hard constraints into elastic image deformation. As a consequence, our approach does not contain any parameters of the deformation model such as elastic constants. The approach guarantees the exact correspondence of boundary structures in the images assuming that correct input data are available. The implemented incremental method allows to cope with large deformations. The theoretical background, the finite element discretization of the elastic model, and experimental results for 2D and 3D synthetic as well as real medical images are presented.
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  • 38
    ISSN: 1573-6857
    Schlagwort(e): DNA bending ; DNA curvature ; DNA models ; 3D model ; finite element method ; internet server
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Bending is a local conformational micropolymorphism of DNA in which the original B-DNA structure is only distorted but not extensively modified. Bending can be predicted by simple static geometry models as well as by a recently developed elastic model that incorporate sequence dependent anisotropic bendability (SDAB). The SDAB model qualitatively explains phenomena including affinity of protein binding, kinking, as well as sequence-dependent vibrational properties of DNA. The vibrational properties of DNA segments can be studied by finite element analysis of a model subjected to an initial bending moment. The frequency spectrum is obtained by applying Fourier analysis to the displacement values in the time domain. This analysis shows that the spectrum of the bending vibrations quite sensitively depends on the sequence, for example the spectrum of a curved sequence is characteristically different from the spectrum of straight sequence motifs of identical basepair composition. Curvature distributions are genome-specific, and pronounced differences are found between protein-coding and regulatory regions, respectively, that is, sites of extreme curvature and/or bendability are less frequent in protein-coding regions. A WWW server is set up for the prediction of curvature and generation of 3D models from DNA sequences (http://www.icgeb.trieste.it/dna).
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 20 (1999), S. 739-747 
    ISSN: 1573-2754
    Schlagwort(e): neutron logging ; transport equation ; finite element method ; streamline diffusion ; O241.8
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract In this paper, a new numerical method, the coupling method of spherical harmonic function spectral and streamline diffusion finite element for unsteady Boltzmann equation in the neutron logging field, is discussed. The convergence and error estimations of this scheme are proved. Its applications in the field of neutron logging show its effectiveness.
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  • 40
    ISSN: 1573-8922
    Schlagwort(e): shells of revolution ; anisotropy ; numerical methods ; finite element method ; linear elasticity ; transverse shear
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The discussion focuses on two numerical algorithms for solving the nonlinear static problems of multilayer composite shells of revolution, namely the algorithm based on the discrete orthogonalization method and the algorithm based on the finite element method with a local linear approximation in the meridian direction. The material of each layer of the shell is assumed to be linearly elastic and anisotropic (nonorthotropic). A feature of this approach is that the displacements of the face surfaces of the shell are chosen as unknown functions, i.e., the functions which allows us to formulate the kinematic boundary conditions on these surfaces. As an example, a cross-ply cylindrical shell subjected to uniform axisymmetric tension is considered. It is shown that the algorithms elaborated correctly describe the local distribution of the stress tensor over the shell thickness without an expensive software based on the 3D anisotropic theory of elasticity.
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of composite materials 35 (1999), S. 307-314 
    ISSN: 1573-8922
    Schlagwort(e): carbon-carbon composite ; spatial reinforcement ; asymptotic averaging method ; thermoelasticity ; periodicity cell ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract A zero approximation of the asymptotic averaging method is applied to investigate the structural stresses in the structures of spatially reinforced composite materials subjected to mechanical loading and high-temperature heating. A carbon-carbon composite material reinforced with anisotropic fibers in three mutually orthogonal directions in the ratio 1∶1∶1 is considered. According to the averaging method, the local functions, namely the components of the tensors of elastic moduli and thermoelasticity in a zero approximation, must be determined by solving a set of problems for a periodicity cell. The effective thermoelastic constants of the composite are found by averaging the local functions obtained over the periodicity cell. To calculate the structural stresses in constructions, the periodic local functions and the field of macrostrains, which is obtained from the solution of the averaged boundary value problem, must be known. The problems posed for the periodicity cell are solved by the method of finite elements. The average values of the local functions and the measures of deviation from them are examined for various temperatures and volume fractions of fibers of two different cross section shapes.
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    International journal of computer vision 33 (1999), S. 29-49 
    ISSN: 1573-1405
    Schlagwort(e): non uniform multiresolution ; optical flow ; non quadratic regularization ; finite element method ; adaptive mesh ; phase portrait ; flow pattern classification ; ocean and atmospheric circulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract In this paper we define a complete framework for processing large image sequences for a global monitoring of short range oceanographic and atmospheric processes. This framework is based on the use of a non quadratic regularization technique for optical flow computation that preserves flow discontinuities. We also show that using an appropriate tessellation of the image according to an estimate of the motion field can improve optical flow accuracy and yields more reliable flows. This method defines a non uniform multiresolution approach for coarse to fine grid generation. It allows to locally increase the resolution of the grid according to the studied problem. Each added node refines the grid in a region of interest and increases the numerical accuracy of the solution in this region. We make use of such a method for solving the optical flow equation with a non quadratic regularization scheme allowing the computation of optical flow field while preserving its discontinuities. The second part of the paper deals with the interpretation of the obtained displacement field. For this purpose a phase portrait model used along with a new formulation of the approximation of an oriented flow field allowing to consider arbitrary polynomial phase portrait models for characterizing salient flow features. This new framework is used for processing oceanographic and atmospheric image sequences and presents an alternative to complex physical modeling techniques.
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 96 (1999), S. 1-15 
    ISSN: 1573-2673
    Schlagwort(e): Crack ; finite element method ; least-squares ; roller bearing ; stress intensity factors.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The three-dimensional finite element method and the least-squares method were used to find the stress intensity factors (SIFs) of a surface crack in a lubricated roller. A steel roller on a rigid plane was modeled, in which a semi-elliptical surface crack is inclined at an angle ψ to the vertical axis. A distance c is set between the crack base and the roller edge. The results indicate that the mode-I SIF reaches the maximum value when the angle θ is equal to 0° (on the roller surface), and the mode-II SIF reaches the absolute maximum value when the angle θ is near or equal to 90° (inside the roller), where θ is the angle of the semi-ellipse from 0° to 180°. The influence of mode-III SIFs in this model is minor since they are much smaller than the mode-I and mode-II SIFs. The SIFs increase greatly when the crack location approaches the uncrowned edge. At this time, a crowned profile can be used to significantly reduce the SIFs near the roller edge.
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  • 44
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 3 (1999), S. 245-261 
    ISSN: 1573-2738
    Schlagwort(e): experimental stress analysis ; finite element method ; photoviscoelasticity ; rolling contact ; viscoelasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In this paper, the authors discuss the first step in theapproach to the fundamental mechanism of small-scale local wear/fracturenear the contact surface between a viscoelastic body and a rigidtraveling roller. A rectangular viscoelastic strip made of epoxy resinwas loaded by a cylindrical hard roller moving along the upper straightedge. A convenient photoviscoelastic method using computer immageprocessing was applied to investigate the time-dependent stress andstrain around a contact region under a typical type of non-proportionalloading conditions. On the other hand, the finite element method (FEM)was used to analyze the viscoelastic stress and strain under the severalconditions. The results obtained from the two methods qualitativelycompared the time variation for the photoviscoelastic fringe patternsand the contour bands of stress/strain distribution patterns. Moreover,the time variation for principal stress differences, principal straindifferences and the directions of principal stress/strain undernon-proportional conditions, were evaluated, at which time the materialshowed remarkable viscoelastic and rubber-like properties.
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Applications of mathematics 43 (1998), S. 401-411 
    ISSN: 1572-9109
    Schlagwort(e): finite element method ; superconvergence error estimates
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract In 1995, Wahbin presented a method for superconvergence analysis called “Interior symmetric method,” and declared that it is universal. In this paper, we carefully examine two superconvergence techniques used by mathematicians both in China and in America. We conclude that they are essentially different.
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Studia geophysica et geodaetica 42 (1998), S. 61-80 
    ISSN: 1573-1626
    Schlagwort(e): tides ; cavity effect ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geologie und Paläontologie , Physik
    Notizen: Abstract The measurements of tide-induced tilts and deformations are usually performed in underground cavities (mostly man-made). Therefore, the data obtained must be debugged of the influence of the cavity itself (cavity effect) and of the effect of elastic parameter inhomogeneities in the vicinity of the point of measurement (geological effect), if they are to he presented. Since these effects are reflected as a modulation of tidal waves (in both amplitude and phase), the only way to perform this can be modelling of the strain and stress field around the cavity as precisely as possible. The finite element method (F.E.M.) seems to be a very useful tool for this purpose. To justify some conclusions in this paper, a number of numerical runs of the F.E.M. models of the tide-induced strains and stresses (in two dimensions) were performed. A higher degree of approximation (up to the value of 7) was used in these calculations. To estimate the cavity effect, the correction factors (relative changes of particular strain components due to the presence of the cavity) were determined and plotted in the cavity's close neighbourhood. The distribution of the deformation energy (and also the work of external forces) over the whole domain of interest is given, and the conclusions for subsequent error estimation are drawn. An attempt was made to compare the real tilt data to the theoretical deduced from the numerical model.
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  • 47
    ISSN: 1573-2754
    Schlagwort(e): finite element method ; quenching ; heat conduction ; phase transformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract The calculation of temperature field has a great influence upon the analysis of the thermal stresses and strains during quenching, and also upon the residual stresses and microstructure of the workpiece after quenching, too. In this paper, a 42CrMo steel cylinder was taken as an investigating example. From the TTT diagram of the 42 CrMo steel, the CCT diagram was simulated by mathematical transformation, and the volume fraction of phase constituents was calculated. The thermal physical properties were treated as the functions of temperature and the volume fraction of phase constitutents. Finally, the temperature field with phase transformation and non-linear surface heat-transfer coefficients was calculated with finite element method, and the corresponding functional of temperature was established.
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  • 48
    ISSN: 1573-1987
    Schlagwort(e): vibro-acoustics ; finite element method ; boundary element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The coupling between a cavity and a vibrating plate is written as a strong coupling where both the continuity of stresses and particle velocities at the interface are taken into account. A FEM analysis reveals an important coupling between the first mode of the plate and the cavity. The pressure distribution in the cavity shows a strong quarter of a wave length pattern indicating the influence of the first Dirichlet mode in the cavity. The vibrating plate is then excited by a turbulent flow modelled by its spectral density using the Corcos model. A comparison is made between the results obtained from a FEM and a BEM formulation. Good agreements are observed concerning the plate displacements. The comparison of the cavity sound pressure levels is less good.
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  • 49
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    Digitale Medien
    Chichester, West Sussex : Wiley-Blackwell
    Mathematical Methods in the Applied Sciences 21 (1998), S. 1637-1654 
    ISSN: 0170-4214
    Schlagwort(e): generalized Stokes equations ; incompressible flow ; least-squares ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik
    Notizen: In this paper we are concerned with a weighted least-squares finite element method for approximating the solution of boundary value problems for 2-D viscous incompressible flows. We consider the generalized Stokes equations with velocity boundary conditions. Introducing the auxiliary variables (stresses) of the velocity gradients and combining the divergence free condition with some compatibility conditions, we can recast the original second-order problem as a Petrovski-type first-order elliptic system (called velocity-stress-pressure formulation) in six equations and six unknowns together with Riemann-Hilbert-type boundary conditions. A weighted least-squares finite element method is proposed for solving this extended first-order problem. The finite element approximations are defined to be the minimizers of a weighted least-squares functional over the finite element subspaces of the H1 product space. With many advantageous features, the analysis also shows that, under suitable assumptions, the method achieves optimal order of convergence both in the L2-norm and in the H1-norm. © 1998 B. G. Teubner Stuttgart - John Wiley & Sons, Ltd.
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  • 50
    Digitale Medien
    Digitale Medien
    Springer
    Applied mathematics and mechanics 19 (1998), S. 1065-1071 
    ISSN: 1573-2754
    Schlagwort(e): finite element method ; pipe conveying fluid ; solid-fluid coupling vibration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Mathematik , Physik
    Notizen: Abstract On the basis of Hamilton principle, the equation of solid-liquid coupling vibration of pipe conveying fluid is deduced. An asymmetrical solid-liquid coupling damp matrix and a symmetrical solid-liquid coupling stiffness matrix are obtained. UsingQR method, pipe's nature frequencies are calculated. The curves of the first four orders of natural frequency-flow velocity of pipe waw given. The influence of flowing velocity, pressure, solid-liquid coupling damp and solid-liquid coupling stiffness on natural frequency are discussed respectively. The dynamic respondence of the pipes for stepload with different flow velocity are calculated by Newmark method. It is found that, with the flow velocity increased, the nature frequency of the pipes reduced, increased, reduced again and so on.
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    International journal of computer vision 26 (1998), S. 25-40 
    ISSN: 1573-1405
    Schlagwort(e): medical imaging ; adaptive meshes ; non-rigid motion ; differential geometry ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Notizen: Abstract We describe a new method for computing the displacement vector field in time sequences of 2D or 3D images (4D data). The method is energy-minimizing on the space of correspondence functions; the energy is split into two terms, with one term matching differential singularities in the images, and the other constraining the regularity of the field. In order to reduce the computational time of the motion estimation, we use an adaptive image mesh, the resolution of which depends on the value of the gradient intensity. We solve numerically the minimization problem with the finite element method which gives a continuous approximation of the solution. We present experimental results on synthetic data and on medical images and we show how to use these results for analyzing cardiac deformations.
    Materialart: Digitale Medien
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  • 52
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 2 (1998), S. 269-286 
    ISSN: 1573-2738
    Schlagwort(e): crack growth process ; finite element method ; fracture mechanic ; numerical modelling ; viscoelasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract In this paper, the effects of viscoelastic characteristics, on the creep-crack growth process are studied through a finite element approach. The general approach of an independent path integral is extended to crack propagation. Afterwards, fracture parameters are computed through a coupling process with an incremental viscoelastic formulation. Finally, numerical examples are presented in order to demonstrate the independence of the integration domain and the possibility of evaluating fracture characteristics which can be energetic (energy release rate) and local in the vicinity of the crack tip (stress and crack opening intensity factors).
    Materialart: Digitale Medien
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 93 (1998), S. 409-429 
    ISSN: 1573-2673
    Schlagwort(e): Stress intensity factor ; plate theory ; energy release rate ; finite element method ; large deflection.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The stress field near the tip of a crack in a plate subjected to membrane and bending loads and undergoing large deflections, is investigated by performing an asymptotic analysis in the context of von Karman plate theory. It is demonstrated that the character of the near tip fields is identical to those of the linear plate theory. However, the determination of the crack tip stress intensity factors requires the solution of a large deflection, and hence nonlinear, problem due to the coupling of the membrane and bending modes. This effect is illustrated through the solution of three fracture problems involving plates of simple geometries loaded by pressure, tension and shearing. In two of these problems, the energy release rate is obtained exactly. Nonlinear finite element computations are performed to obtain the stress intensity factors and energy release rate associated with tension, bending and shearing. These results are compared to the theoretical results for energy release rate and stress intensity factors.
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 94 (1998), S. 357-370 
    ISSN: 1573-2673
    Schlagwort(e): Fracture ; elastic-plastic fracture ; constraint ; two-parameter characterization ; stable crack growth ; finite element method ; remeshing.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract An investigation is performed to determine to what extent the state at a growing crack tip vicinity can be characterised by J and Q calculated from FE analyses of successively stationary crack tip positions. FE models in two-dimensionals of single edge notch bend and double edge cracked panel specimens with several different crack lengths are used to cover a range of load and constraint levels. The stress and strain fields are compared between different specimens keeping J- and Q-values equal. A remeshing technique in the commercial FE-code ABAQUS is used to enhance the efficiency of the analysis. The results show that the J-Q-theory provides reasonably accurate crack tip characterization also for growing cracks. This leads to the conclusion that FE analyses of successive stationary cracks rather than full FE propagation analyses are sufficient. The limit of validity for propagation is similar to the validation limit for the stationary case, although somewhat more restrictive.
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  • 55
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 229-240 
    ISSN: 1069-8299
    Schlagwort(e): filling of thin section ; finite element method ; surface tension ; interface element ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: An interface element to model the pressure discontinuity due to surface tension when applied to the filling of a thin section cavity is presented. The equations used to form the element matrix for the interface element are the line integral form of the continuity and momentum equations. During the development of the finite element model, the pressure difference across the free surface due to surface tension is treated as an additional traction and is applied to all element sides which form the free surface. Simple numerical examples are then presented to illustrate the technique on the filling of a rectangular thin section cavity. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 6 Ill.
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  • 56
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 135-149 
    ISSN: 1069-8299
    Schlagwort(e): multiphase immiscible flow ; deforming porous media ; fully coupled ; soil displacements ; fluid pressures ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A fully coupled numerical model has been developed which describes multiphase fluid flow through soil: namely gas, water and a non-aqueous phase liquid (NAPL) in a deforming porous media for subsurface systems. A multiphase flow model, based on the two-phase flow model of Brooks and Corey, is presented to express the dependence of saturation and relative permeability on the capillary pressure. Non-linear saturation and relative permeability functions are incorporated into a Galerkin finite element model which is subsequently used to simulate multiphase immiscible fluid flow under saturated and unsaturated conditions in porous media. The governing partial differential equations, in terms of soil displacements and fluid pressures, which are coupled and non-linear, are solved by the finite element method. Numerical implementation of the formulation is discussed, and example problems demonstrate the model and solution procedure. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
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  • 57
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 181-194 
    ISSN: 1069-8299
    Schlagwort(e): oscillating flow ; Keulegan-Carpenter number ; finite element method ; in-line force ; transverse force ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The results of a numerical study of the viscous oscillating flow around a circular cylinder at Reynolds number=200 and Keulegan-Carpenter number=20 are presented. The finite element method was used for the solution of the Navier-Stokes equations, in the formulation where the streamfunction and the vorticity are the field variables. The computation revealed a complicated flow pattern at which the flow is not periodic but switches between different modes at various oscillation cycles. The vortex shedding patterns occurring at different cycles were identified by means of numerical flow visualization. The traces of the hydrodynamic forces were derived from the solution, and the hydrodynamic coefficients of the in-line force were evaluated. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 7 Ill.
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  • 58
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Mechanics of Cohesive-frictional Materials 3 (1998), S. 229-256 
    ISSN: 1082-5010
    Schlagwort(e): finite element method ; viscous constitutive equations ; time-discrete scheme ; stability ; superstability ; Engineering ; Civil and Mechanical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 4 Ill.
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  • 59
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 9-22 
    ISSN: 1069-8299
    Schlagwort(e): finite element method ; optimal control theory ; Navier-Stokes equations ; Lagrange multipliers ; adjacent equations ; Sakawa-Shindo method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: This work presents control of vorticity for buoyancy-driven flows. The governing set of equations includes Navier-Stokes and heat transfer equations. The basic formulation for the control problem is derived using Lagrange multipliers and the Pontryagin minimum principle. Control values are found using the Sakawa-Shindo method. Control was accomplished using velocity components. Numerical examples present control of vorticity for Rayleigh-Bernard convection in an enclosed cavity for a wide range of Ra numbers. The current formulation proved reliable and fast. Optimal control was obtained and turned out to be adequate. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 997-1012 
    ISSN: 1069-8299
    Schlagwort(e): potential flow ; finite element method ; wave resistance ; absorbing boundary condition ; free surface flow ; partial discretization ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A method for computing ship wave resistance from a momentum flux balance is presented. It is based on computing the momentum flux carried by the gravity waves that exit the computational domain through the outlet plane. It can be shown that this method ensures a non-negative wave-resistance, in contrast with straightforward integration of the normal pressure forces. However, this calculation should be performed on a transverse plane located far behind the ship. Traditional Dawson-like methods add a numerical viscosity that dampens the wave pattern so that some amount of momentum flux is lost, and resulting in an error in the momentum balance. The flow field is computed, then, with a centred scheme with absorbing boundary conditions. Copyright © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 8 Ill.
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  • 61
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 14 (1998), S. 1119-1131 
    ISSN: 1069-8299
    Schlagwort(e): Reissner-Mindlin plate ; finite element method ; p version ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: We consider the finite element (FE) approximation of the Reissner-Mindlin (RM) plate model, and indicate how to design meshes that yield accurate results when the p/hp version of the standard FE method is used. These guidelines allow quantities of engineering interest to be predicted numerically with great confidence near the boundary. We illustrate this through numerical computations in the case when both boundary layers and corner singularities are present. Copyright © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 15 Ill.
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  • 62
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 403-442 
    ISSN: 0271-2091
    Schlagwort(e): oscillating flow ; Keulegan-Carpenter number ; finite element method ; in-line force ; transverse force ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 33 Ill.
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 677-696 
    ISSN: 0271-2091
    Schlagwort(e): second-order closure model ; pollutant dispersion ; finite element method ; unstably stratified atmosphere ; parallel computation ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 143-156 
    ISSN: 0271-2091
    Schlagwort(e): turbine ; spiral casing ; finite element method ; Galerkin weighted residual technique ; Gauss-Legendre quadrature ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 8 Ill.
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  • 65
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 461-476 
    ISSN: 0271-2091
    Schlagwort(e): advection-diffusion equation ; operator splitting algorithm ; Holly and Preissmann scheme ; method of characteristics ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: 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.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 507-532 
    ISSN: 0029-5981
    Schlagwort(e): adaptivity ; finite element method ; interior error estimates ; a posteriori error estimators ; hybrid interior error estimators ; pollution errors ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A hybrid error estimator using a priori interior region estimates in an a posteriori framework is presented for linear elastostatics problems in FEA. It is shown that local rates of convergence are augmented by this technique and global rates are not adversely affected. The effects of pollution for this estimator are explained and a pollution error estimator is derived using the concept of error loads. It is shown that pollution error estimation can improve the performance of both the conventional a posteriori and the hybrid techniques. A series of numerical results are presented which demonstrate the superior performance of the proposed method over previously published interior error estimation techniques. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 8 Ill.
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  • 67
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 941-953 
    ISSN: 0029-5981
    Schlagwort(e): muscle model ; numerical stress calculation ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: We present a numerical algorithm for the determination of muscle response by the finite element method. Hill's three-element model is used as a basis for our analysis. The model consists of one linear elastic element, coupled in parallel with one non-linear elastic element, and one non-linear contractile element connected in series. An activation function is defined for the model in order to describe a time-dependent character of the contractile element with respect to stimulation.Complex mechanical response of muscle, accounting for non-linear force-displacement relation and change of geometrical shape, is possible by the finite element method. In an incremental-iterative scheme of calculation of equilibrium configurations of a muscle, the key step is determination of stresses corresponding to a strain increment. We present here the stress calculation for Hill's model which is reduced to the solution of one non-linear equation with respect to the stretch increment of the serial elastic element. The muscle fibers can be arbitrarily oriented in space and we give a corresponding computational procedure of calculation of nodal forces and stiffness of finite elements.The proposed computational scheme is built in our FE package PAK, so that real muscles of complex three-dimensional shapes can be modelled. In numerical examples we illustrate the main characteristic of the developed numerical model and the possibilities of solution of real problems in muscle functioning. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
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  • 68
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1437-1451 
    ISSN: 0029-5981
    Schlagwort(e): crack ; finite element method ; J-integral ; least-squares method ; stress intensity factor ; three-dimensional ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The main purpose of this paper is to investigate the accuracy of the least-squares method incorporating the finite element method for finding three-dimensional (3-D) Stress Intensity Factors (SIFs). Numerical simulations in this paper indicate that the least-squares method can be used to calculate 3-D SIFs accurately, if three or more than three displacement or stress terms are included. The calculated SIFs of this method are independent of the maximum radius of the area from which data is included; furthermore, a very fine mesh is not necessary. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 10 Ill.
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  • 69
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1173-1191 
    ISSN: 0029-5981
    Schlagwort(e): warping ; bimoment ; Vlasov's thin-walled beam ; block stiffness matrix ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A new finite element for the analysis of thin-walled open beams with an arbitrary cross section is presented. Combining Timoshenko beam theory and Vlasov thin-walled beam theory, the derived element includes both flexural shear deformations and warping deformations caused by the bimoment. By adopting an orthogonal Cartesian co-ordinate system, one can obviate the ad hoc introduction of St. Venant stiffness. The derived block stiffness matrix is comparable but more general than the one given by earlier researchers. The versatility and accuracy of the new element are demonstrated by comparing the numerical results with the classical solutions or other numerical results available in the literature. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
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  • 70
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 1343-1390 
    ISSN: 0029-5981
    Schlagwort(e): optimal design ; design sensitivity ; direct differentiation method ; non-isothermal ; metal forming ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A new approach to process optimal design in non-isothermal, non-steady-state metal forming is presented. In this approach, the optimal design problem is formulated on the basis of the integrated thermo-mechanical finite element process model so as to cover diverse objective functions and design variables, and a derivative-based approach is adopted for conducting optimization. The process model, the formulation for process optimal design, and the schemes for the evaluation of the design sensitivity, and an iterative procedure for optimization are described in detail. The validity of the schemes for the evaluation of the design sensitivity is examined by performing a series of numerical tests. The capability of the proposed approach to deal with diverse process parameters and objective functions is demonstrated through applications to some selected process design problems. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 23 Ill.
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  • 71
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 33-50 
    ISSN: 0029-5981
    Schlagwort(e): contact problems ; material fatigue ; pitting ; fracture mechanics ; finite element method ; experiments ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A computational model for simulation of surface pitting of mechanical elements subjected to rolling and sliding contact conditions is presented. The two-dimensional computational model is restricted to modelling of high-precision mechanical components with fine surface finishing and good lubrication, where the cracks leading to pitting are initiated in the area of largest contact stresses at certain depth under the contacting surface. Hertz contact conditions with addition of friction forces are assumed and the position and magnitude of the maximum equivalent stress is determined by the finite element method. When the maximum equivalent stress exceeds the local material strength, it is assumed that the initial crack develops along the slip line in a single-crystal grain. The Virtual Crack Extension method in the framework of finite element analysis is then used for two-dimensional simulation of the fatigue crack propagation under contact loading from the initial crack up to the formation of the surface pit. The pit shapes and relationships between the stress intensity factor and crack length are determined for various combinations of contacting surface curvatures and loadings. The model is applied to simulation of surface pitting of two meshing gear teeth. Numerically predicted pit shapes in the face of gear teeth show a good agreement with the experimental observations. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 17 Ill.
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  • 72
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 561-578 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; adaptivity ; a posteriori error estimation ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The problem of finding a nearly optimal distribution of polynomial degrees on a fixed finite element mesh is discussed. An a posteriori error estimator based on the minimum complementary energy principle is proposed which utilizes the displacement vector field computed from the finite element solution. This estimator, designed for p- and hp-extensions, is conceptually different from estimators based on residuals or patch recovery which are designed for h-extension procedures. The quality of the error estimator is demonstrated by examples. The results show that the effectivity index is reasonably close to unity and the sequences of p-distributions obtained with the error indicators closely follow the optimal trajectory. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
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  • 73
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 443-472 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; error estimation ; stress recovery ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: 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.
    Zusätzliches Material: 18 Ill.
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  • 74
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    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 685-702 
    ISSN: 0029-5981
    Schlagwort(e): asymptotic postbuckling ; stability ; finite element method ; smooth stresses ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: Application of the finite element method to Koiter's asymptotic postbuckling theory often leads to numerical problems. Generally it is believed that these problems are due to locking of non-linear terms of different orders. A general method is given here that explains the reason for the numerical problems and eliminates these problems. The reason for the numerical problems is that the postbuckling stresses are inaccurately determined. By including a local stress contribution, the postbuckling stresses are calculated correctly. The present method gives smooth postbuckling stresses and shows a quick convergence of the postbuckling coefficients. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 13 Ill.
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  • 75
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 41 (1998), S. 739-757 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; crack propagation ; low cycle fatigue ; remeshing ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: An algorithm is presented which allows for fully automatic linear elastic low cycle fatigue (LCF) crack propagation calculations of mode I plane cracks in large structures by means of the finite element technique. The bulk of the algorithm consists of an automatic procedure to introduce the geometry of a plane crack with an arbitrary crack front in an existing three-dimensional (3-D) mesh. Once the K-distribution for the initial crack has been calculated, the use of the superelement technique reduces the computing time for the subsequent cycles by a factor of up to 40 or more. Two industrial examples illustrate the accuracy and effectiveness of the method. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 16 Ill.
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  • 76
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 219-236 
    ISSN: 0029-5981
    Schlagwort(e): secant and tangent stiffness matrices ; structural analysis ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: The paper presents a general and straightforward procedure based on the use of the strain energy density for deriving symmetric expressions of the secant and tangent stiffness matrices for finite element analysis of geometrically non-linear structural problems. The analogy with previously proposed methods for deriving secant and tangent matrices is detailed. The simplicity of the approach is shown in an example of application. © 1998 John Wiley & Sons, Ltd.
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  • 77
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 601-629 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; scattering problems ; open boundaries ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: An iterative procedure is described for the finite-element solution of scalar scattering problems in unbounded domains. The scattering objects may have multiple connectivity, may be of different materials or with different boundary conditions. A fictitious boundary enclosing all the objects involved is introduced. An appropriate Robin (mixed) condition is initially guessed on this boundary and is iteratively improved making use of Green's formula. It will be seen that the best choice for the Robin boundary condition is an absorbing-like one. A theorem about the theoretical convergence of the procedure is demonstrated. An analytical study of the special case of a circular cylindrical scatterer is made. Comparisons are made with other methods. Some numerical examples are provided in order to illustrate and validate the procedure and to show its applicability whatever the frequency of the incident wave. Although particular emphasis is laid in the paper on electromagnetic problems, the procedure is fully applicable to other kinds of physical phenomena such as acoustic ones. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 13 Ill.
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  • 78
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 42 (1998), S. 749-772 
    ISSN: 0029-5981
    Schlagwort(e): crack ; propagation ; remeshing ; mode-I ; three-dimensional ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: A previous article (G. Dhondt, ‘Automatic 3-D mode I crack propagation calculations with finite elements’, Int. J. Numer. Meth. Engng. 41, 739-757 (1998)) has illustrated how automatic 3-D mode I cyclic crack propagation calculations making repeated use of the finite element method can be performed for structures in which the crack plane is made up of element faces. In the present paper an automatic cutting procedure is proposed which allows the method to be applied to arbitrarily meshed structures for which the crack plane intersects the elements. New 20-node brick elements are automatically generated and a subsequent smoothing procedure improves the quality of the resulting mesh. The method is illustrated by cyclic crack propagation calculations in a specimen and an industrial component. © 1998 John wiley & Sons, Ltd.
    Zusätzliches Material: 19 Ill.
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  • 79
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1053-1068 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; variational inequalities ; contact problems ; heuristic algorithms ; nondifferential optimization methods ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: This article is devoted to the development of a new heuristic algorithm for the solution of the general variational inequality arising in frictional contact problems. The existing algorithms devised for the treatment of the variational inequality representing frictional contact rely on the decomposition of the physical problem into two sub-problems which are then solved iteratively. In addition, the penalty function method and/or the regularization techniques are typically used in the solution of these reduced sub-problems. These techniques introduce user-defined parameters which could influence the convergence and accuracy of the solution. The new method presented in this article overcomes these difficulties by providing a solution for the general variational inequality without decomposition into sub-problems. This is accomplished using a new heuristic algorithm which utilizes mathematical programming techniques, and thus avoids the use of penalty or regularization methods. The versatility and reliability of the developed algorithm were demonstrated through implementation to the case of frictional contact of an elastic hollow cylinder with a rigid foundation. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 10 Ill.
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  • 80
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 43 (1998), S. 1253-1273 
    ISSN: 0029-5981
    Schlagwort(e): finite element method ; continuum modelling ; traffic equilibrium ; user-optimal pattern ; fixed demand ; variable demand ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik , Technik allgemein
    Notizen: In this paper, we consider a city with a highly compact Central Business District (CBD), and the commuters’ destinations from the CBD are dispersed over the whole city. The street network is approximated as a continuum and commuters’ movements in the city are measured by the flow intensity, and the local travel cost depends on the location and the traffic flow intensity. We extend the continuum user equilibrium problem to deal with the case of variable demand, in which the traffic demand from any destination in the city to the CBD is assumed to be a function of both the destination location and the total travel cost to the CBD. An equivalent mathematical model is formulated and proved to satisfy the user equilibrium conditions, which is then solved by a finite element solution algorithm. Numerical examples are given to illustrate the effectiveness of the proposed method. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 11 Ill.
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  • 81
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    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 89-96 
    ISSN: 0749-159X
    Schlagwort(e): finite element method ; third-order differential equation ; Mathematics and Statistics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik
    Notizen: A splitting of a third order partial differential equation into a first-order and a second-order one is proposed as the basis for a mixed finite element method to approximate its solution. A time-continuous numerical method is described and error estimates for its solution are demonstrated. Finally, a full discretization is described based on backward Euler finite differences in time, and error estimates for the resulting approximation are established. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 89-96, 1998
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  • 82
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 213-231 
    ISSN: 0749-159X
    Schlagwort(e): cell-centered finite volume method ; convergence ; finite element method ; Mathematics and Statistics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik
    Notizen: The article is devoted to the study of convergence properties of a Finite Volume Method (FVM) using Voronoi boxes for discretization. The approach is based on the construction of a new nonconforming Finite Element Method (FEM), such that the system of linear equations coincides completely with that for the FVM. Thus, by proving convergence properties of the FEM, we obtain similar ones of the FVM. In this article, the investigations are restricted to the Poisson equation. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14:213-231, 1998
    Zusätzliches Material: 2 Ill.
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  • 83
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    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Methods for Partial Differential Equations 14 (1998), S. 679-693 
    ISSN: 0749-159X
    Schlagwort(e): least squares method ; finite element method ; Volterra equation ; Mathematics and Statistics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Mathematik
    Notizen: In this article least squares approximations to Volterra integral equations are considered, both with exact integration and with quadrature. Optimal error estimates are derived, and it is shown that the same order of convergence is obtained in both cases with only modest requirements on the quadrature rule used in the latter. The most important practical setting for least squares is the case of convolution kernels, and these are also studied in this article. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 679-693, 1998
    Zusätzliches Material: 3 Ill.
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  • 84
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 133-149 
    ISSN: 0363-9061
    Schlagwort(e): thermoporoelasticity ; thermoporoplasticity ; Laplace transform ; Stehfest algorithm ; finite element method ; Engineering ; Civil and Mechanical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geologie und Paläontologie
    Notizen: Solutions are presented for the behaviour of a layered porous space which contains a decaying heat source. Such a problem arises when high-level nuclear waste is placed in deep underground depositories in deep clayey formations of sedimentary basins. The geometry of the problem is one dimensional and the porous space is constituted by two layers: a deep low permeability layer which contains the nuclear waste disposal and a superficial layer. The solution is used to examine the effects of contrasts of permeability, thermal conductivity and specific heat capacities between the two layers on the large-scale behaviour of the porous space. Results are presented, using realistic data, for the pore pressure and temperature evolution at the heat source centre, and for the vertical displacement of the ground level. The superficial layer has no significant effects on pore pressure, temperature and stress evolution near the heat source centre. The vertical displacement of the ground level is mainly due to the thermal dilatation of the pore water, so it decreases with an increasing of permeability of the superficial layer. The solution of the time-dependent problem is carried out by applying Laplace transforms to the field variables, obtaining solutions and then using numerical methods to invert the transformed solutions. Comparisons with numerical simulations taking into account the non-linear and non-reversible behaviour of the rock mass are presented. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 8 Ill.
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  • 85
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    International Journal for Numerical and Analytical Methods in Geomechanics 22 (1998), S. 245-261 
    ISSN: 0363-9061
    Schlagwort(e): Cosserat continuum model ; equivalent continuum medium ; layered rock mass ; finite element method ; non-associative plasticity ; Engineering ; Civil and Mechanical Engineering
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geologie und Paläontologie
    Notizen: Layered rock masses can be modelled either as standard, orthotropic continua if the layer bending can be neglected or as Cosserat continua if the influence of layer bending is essential. This paper presents a finite element smeared joint model based on the Cosserat theory. The layers are assumed to be elastic with equal thickness and equal mechanical properties. All the cosserat parameters are expressed through the elastic properties of layers, layer thickness and joint stiffness. Plastic-slip as well as tensile-opening of layer interface (joint) are accounted for in a manner similar to the conventional non-associative plasticity theory.As an application, the behaviour of an excavation in a layered rock mass is examined. The displacement and stress fields given by smeared joint models based on the Cosserat continuum and the conventional anisotropic continuum approaches are compared with those obtained from the discrete joint model. The conventional anisotropic continuum model is found to break-down completely when the effective shear modulus in the direction parallel to layering is low in comparison to the shear modulus of the intact layer, whereas the Cosserat model is found to be capable of accurately reproducing complex load-deflection patterns irrespective of the differences in shear moduli. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 13 Ill.
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  • 86
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    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 26 (1998), S. 1127-1154 
    ISSN: 0271-2091
    Schlagwort(e): free surface ; transient viscous incompressible fluid ; finite element method ; VOF (volume-of-fluid) method ; adaptive grid ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The VOF method is adopted for the finite element analysis of transient fluid flow with a free surface. In particular, an adaptation technique for generating an adaptive grid is incorporated to capture a higher resolution of the free surface configuration. An adaptive grid is created through the refinement and mergence of elements. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Also, three techniques based on the VOF method are newly developed to increase the accuracy of the analysis, namely the filling pattern, advection treatment and free surface smoothing techniques. Using the proposed numerical techniques, radial flow with a point source and the collapse of a dam are analysed. The numerical results agree well with the theoretical solutions as well as with the experimental results. Through comparisons with the numerical results of several cases using different grids, the efficiency of the proposed technique is verified. © 1998 by John Wiley & Sons, Ltd.
    Zusätzliches Material: 28 Ill.
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  • 87
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    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 159-168 
    ISSN: 0271-2091
    Schlagwort(e): finite element method ; Galerkin method ; residual free bubbles ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: An overview of the unusual stabilized finite element method and of the standard Galerkin method enriched with residual free bubble functions is presented. For the first method a concrete model problem illustrates its application in advective-diffusive-reactive equations and for the second method it is shown how static condensation of residual free bubbles gives rise to mass lumping and selective reduced integration, which are viewed as numerical tricks and can now be derived by the standard Galerkin method without tricks. © 1998 John Wiley & Sons, Ltd.
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  • 88
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 139-157 
    ISSN: 0271-2091
    Schlagwort(e): hydrodynamic stability ; finite element method ; incompressible cavity flow ; Arnold's method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Numerical methods have been applied to theoretical studies of instability and transition to turbulence. In this study an analysis of the linear stability of incompressible flow is undertaken. By means of the finite element method the two-dimensional base flow is computed numerically over a range of Reynolds numbers and is perturbed with three-dimensional disturbances. The partial differential equations governing the evolution of perturbation are obtained from the non-linear Navier-Stokes equations with a slight compressibility by using linear stability and normal mode analysis. In terms of the finite element discretization a non-singular generalized eigenproblem is formulated from these equations whose solution gives the dispersion relation between complex growth rate and wave number. This study presents stability curves to identify the critical Reynolds number and critical wavelength of the neutral mode and discusses the mechanism of instability. The stability of lid-driven cavity flow is examined. Taylor-Göertler-like vortices in the cavity are obtained by means of reconstruction of three-dimensional flows. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 14 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 95-112 
    ISSN: 0271-2091
    Schlagwort(e): square columns in tandem ; finite element method ; improved BTD ; 3D computation ; aerodynamic characteristics ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Two- (2D) and three-dimensional (3D) finite element analyses for flow around two square columns in tandem arrangement were performed with various column spacings and Reynolds numbers. The computed values were compared with the wind-tunnel results in terms of the aerodynamic characteristics of the leeward column. In most 2D computations, strong vortices were formed behind the windward column, irrespective of widely changed Reynolds numbers. This was different from the experimental phenomena of equivalent spacing, so that the computed time-averaged pressure coefficients were not identical to the experimental values except when the distance between the two columns was adequately wide or narrow. On the other hand, in 3D computation, distinct differences in flow structures behind the column were observed between Reynolds numbers of 103 and 104 and the pressure coefficient in the 3D analysis with Re=104 agreed well with the experimental value. Thus, the effectiveness of 3D computations and Reynolds number effects on the flow around two square columns have been confirmed. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 17 Ill.
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  • 90
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 719-736 
    ISSN: 0271-2091
    Schlagwort(e): front tracking ; mesh adaptation ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A numerical model is developed for the simulation of moving interfaces in viscous incompressible flows. The model is based on the finite element method with a pseudo-concentration technique to track the front. Since a Eulerian approach is chosen, the interface is advected by the flow through a fixed mesh. Therefore, material discontinuity across the interface cannot be described accurately. To remedy this problem, the model has been supplemented with a local mesh adaptation technique. This latter consists in updating the mesh at each time step to the interface position, such that element boundaries lie along the front. It has been implemented for unstructured triangular finite element meshes. The outcome of this technique is that it allows an accurate treatment of material discontinuity across the interface and, if necessary, a modelling of interface phenomena such as surface tension by using specific boundary elements. For illustration, two examples are computed and presented in this paper: the broken dam problem and the Rayleigh-Taylor instability. Good agreement has been obtained in the comparison of the numerical results with theory or available experimental data. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 12 Ill.
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  • 91
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 1355-1369 
    ISSN: 0271-2091
    Schlagwort(e): viscous flow ; moving boundary ; fountain flow ; pseudo-concentration method ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: Mould filling processes, in which a material flow front advances through a mould, are typical examples of moving boundary problems. The moving boundary is accompanied by a moving contact line at the mould walls causing, from a macroscopic modelling viewpoint, a stress singularity. In order to be able to simulate such processes, the moving boundary and moving contact line problem must be overcome. A numerical model for both two- and three-dimensional mould filling simulations has been developed. It employs a pseudo-concentration method in order to avoid elaborate three-dimensional remeshing, and has been implemented in a finite element program. The moving contact line problem has been overcome by employing a Robin boundary condition at the mould walls, which can be turned into a Dirichlet (no-slip) or a Neumann (free-slip) boundary condition depending on the local pseudo-concentration. Simulation results for two-dimensional test cases demonstrate the model's ability to deal with flow phenomena such as fountain flow and flow in bifurcations. The method is by no means limited to two-dimensional flows, as is shown by a pilot simulation for a simple three-dimensional mould. The reverse problem of mould filling is the displacement of a viscous fluid in a tube by a less viscous fluid, which has had considerable attention since the 1960's. Simulation results for this problem are in good agreement with results from the literature. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 5 Ill.
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  • 92
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 27 (1998), S. 109-125 
    ISSN: 0271-2091
    Schlagwort(e): multiphase porous material ; cavitation ; water pressure ; vapour pressure ; strain localization ; finite element method ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: A model to simulate cavitation phenomena in the pores of saturated porous media is developed. Such phenomena appear in connection with pore water traction, which may be observed during strain localization in dense sand samples or in dynamic fluid-structure interaction problems where the structure is made of geomaterials. The model makes use of an isothermal two-phase flow approach. Numerical examples relating to strain localization are shown. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 9 Ill.
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  • 93
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 28 (1998), S. 633-661 
    ISSN: 0271-2091
    Schlagwort(e): free convection ; porous enclosure ; Darcian model ; wavy surface ; finite element method ; numerical study ; Engineering ; Numerical Methods and Modeling
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Maschinenbau
    Notizen: The coupled streamfuction-temperature equations governing the Darcian flow and convection process in a fluid-saturated porous enclosure with an isothermal sinusoidal bottom sun face, has been numerically analyzed using a finite element method (FEM). No restrictions have been imposed on the geometrical non-linearity arising from the parameters like wave amplitude (a), number of waves per unit length (N), wave phase (Φ), aspect ratio (A) and also on the flow driving parameter Rayleigh number (Ra). The numerical simulations for varying values of Ra bring about interesting flow features, like the transformation of a unicellular flow to a multicellular flow. Both with increasing amplitude and increasing number of waves per unit length, owing to the shift in the separation and reattachment points, a row-column pattern of multicellular flow transforms to a simple row of multicellular flow. A cycle of n celluar and n+1 cellular flows, with the flow in adjacent cells in the opposite direction, periodically manifest with phase varying between 0 and 360°. The global heat transfer into the system has been found to decrease with increasing amplitude and increasing number of waves per unit length. Only marginal changes in the global heat flux are observed, either with increasing Ra or varying Φ. Effectively, sinusoidal bottom surface undulations of the isothermal wall of a porous enclosure reduces the heat transfer into the system. © 1998 John Wiley & Sons, Ltd.
    Zusätzliches Material: 21 Ill.
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  • 94
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    Digitale Medien
    Springer
    Applications of mathematics 42 (1997), S. 147-159 
    ISSN: 1572-9109
    Schlagwort(e): magnetic field ; variational formulation ; two-sided existence and uniqueness condition ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract A special two-sided condition for the incremental magnetic reluctivity is introduced which guarantees the unique existence of both the weak and the approximate solutions of the nonlinear stationary magnetic field distributed on a region composed of different media, as well as a certain estimate of the error between the two solutions. The condition, being discussed from the physical as well as the mathematical point of view, can be easily verified and is fulfilled for various magnetic reluctivity models used in electrotechnical practice.
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  • 95
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    Springer
    Applications of mathematics 42 (1997), S. 259-277 
    ISSN: 1572-9109
    Schlagwort(e): Parameter identification ; parabolic problem ; finite element method ; Crank-Nicolson scheme
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Mathematik
    Notizen: Abstract The identification problem of a functional coefficient in a parabolic equation is considered. For this purpose an output least squares method is introduced, and estimates of the rate of convergence for the Crank-Nicolson time discretization scheme are proved, the equation being approximated with the finite element Galerkin method with respect to space variables.
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  • 96
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    Digitale Medien
    Springer
    Journal of marine science and technology 2 (1997), S. 35-51 
    ISSN: 1437-8213
    Schlagwort(e): mesh generation ; finite element method ; object oriented ; object oriented database ; parallel mesh generation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract In ship structural design, many structural analyses by the finite element method are carried out on models at several different scale levels; for example, a whole ship, cargo hold parts, and detailed structures. However, one serious problem with this design and analysis process is that the generation of the finite element models for a complex configuration is very difficult and laborious. To overcome this problem, an object oriented, finite element modeling system, MODIFY, has been developed by the authors. In this paper, the concept of the finite element modeling system and the techniques for the construction of the system are explained. First, the object oriented data structure of the system, based on the Part-Object concept, is proposed. In this concept, not only the geometry of the domain but also the analytical conditions, such as boundary conditions and material properties, and the finite element model, are represented by the object oriented data structure. By using this data structure, effective finite element model generation can be expected. Second, a mesh generation algorithm based on the frontal method is described. The original frontal method by S.H. Lo was improved for application to three-dimensional curved surfaces. A new inner node placement technique to make quadrilateral elements around stress concentrated areas is also proposed. These techniques are suitable for ship structures, and more accurate results from the finite element analysis can be expected. Moreover, the parallel mesh generation is implemented in MODIFY by using the client-server concept to accelerate mesh generation. Third, a prototype system for the automatic finite element model generation for different analysis levels is proposed. The system is based on the concept of the PD part, which is the part in the design and production stage, and automatic computing of the intersection between PD parts. The validity of this system is demonstrated by some examples.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica solida Sinica 10 (1997), S. 28-35 
    ISSN: 0894-9166
    Schlagwort(e): buckle propagation ; arrest of buckle ; beam on a nonlinear foundation ; finite element method
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Based on the dynamic governing equation of propagating buckle on a beam on a nonlinear elastic foundation, this paper deals with an important problem of buckle arrest by combining the FEM with a time integration technique. A new conclusion completely different from that by the quasistatic analysis about the buckle arrestor design is drawn. This shows that the inertia of the beam cannot be ignored in the analysis under consideration, especially when the buckle propagation is suddenly stopped by the arrestors.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Acta mechanica solida Sinica 10 (1997), S. 76-85 
    ISSN: 0894-9166
    Schlagwort(e): finite element method ; mode- II loading ; J integral
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Finite element method (FEM) has been used to analyze the stress and strain fields and the stress tri-axial levels around the tip of the crack under mode- II loading. The results show that: under mode- II loading, the direction of the maximum tensile stress and that of the maximum tri-axial levels (R o ) exist at an angle of −75. 3° from the original crack plane; the maximum shear stress andR o = 0 exist along the original crack plane. Mode- II loading experiment using BHW-35 steel at different temperatures show that there are two kinds of fracture mode, opening mode (or tensile mode) and sliding mode (or shear mode). A decrease in temperature causes the fracture mode to change from shear mode to tensile mode. For BHW-35 steel, this critical temperature is about −90 C. Actually, under any kind of loading mode (mode I . mode II , mode III or mixed mode), there always exist several kinds of potenital fracture modes (for example, opening mode, sliding mode, tearing mode or mixed mode). The effect of temperature under mode- II loading is actually related to the change of the elastic-plastic properties of the material.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Optical review 4 (1997), S. 253-260 
    ISSN: 1349-9432
    Schlagwort(e): speckle photography ; Young’s fringe ; two-dimensional Fourier transform ; finite element method ; stress intensity factor ; interface crack ; mixed mode ; displacement extrapolation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The image-processing system based on a two-dimensional Fourier transform is presented for the analysis of Young’s fringes pattern created from a double-exposure speckle photograph. The fringe spacing and orientation are determined using only one Young’s fringes pattern without any other diffraction halo patterns. The stress-intensity factors of a mixed-mode interface crack were measured by speckle photography. A compact normal and shear specimen with an interface crack was employed. This specimen enables us to carry out the experiment under various kinds of mixed-mode loading. A steel and an epoxy resin were used as dissimilar materials. The displacement along the crack lines at the free surface was measured by speckle photography. The K1 and K11 values were determined by a least squares method using displacement data along the crack lines. Three-dimensional finite element analysis was carried out on the same specimen. An accuracy of stress intensity factors obtained by the speckle photography was discussed by comparison of results obtained by the finite element analysis.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 49 (1997), S. 999-1005 
    ISSN: 1572-8943
    Schlagwort(e): DSC ; finite element method ; temperature gradients ; polymer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Differential Scanning Calorimetry is frequently used for measurements of thermal properties on all kinds of substances. The temperature lag in the samples depend on the thermal properties and the thermal contact between sample and sample holder. In the paper, we discuss the temperature distribution in samples of comparatively low thermal conductivity, such as polymers. The purpose of this study is to pinpoint the substantial temperature differences that may occur in such bad conducting samples under different conditions. The calculations of the temperature gradients have been carried out by using a finite element software package.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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