bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory and numerics of ductile micropolar elastoplastic damage
Authors: Steinmann Paul 
Published: August 2005

AbstractThe aim of this work is to extend an isotropic elastoplastic damage concept for ductile materials within a generalized micropolar continuum framework. The underlying motivation is on the one hand to model softening behaviour by damage evolution and on the other hand to regularize the impending loss of ellipticity which results in strong mesh dependence of localization computations. To this end, the classical displacement field is supplemented by an independent rotation field to yield an enhanced continuum. For the model originally proposed by Lemaitre the damage evolution follows from a dissipation potential and the hypothesis of general associativity. Special emphasis is directed towards the numerical implementation of the constitutive model within the framework of finite element analysis of inelastic boundary value problems. To compare damage evolution and standard strain softening the results are contrasted to the outcome of an analysis with the micropolar version of the classical von Mises model. Thereby, the intriguing correspondence of strain softening and damage evolution is highlighted. Additionally, several planar micropolar finite element formulations are derived within mixed variational principles to enhance the poor performance of the standard bilinear displacement and rotation expansions used so far in the literature. The merits of these new element developments are demonstrated for the example of localization within a compression problem.
Cost‐effective staggered schemes for the numerical simulation of wave propagation
Authors: Kamel A. , Sguazzero P. , Kindelan M. 
Published: August 2005

AbstractThis paper presents a cost‐effectiveness analysis of explicit Finite Difference (FD) methods for the numerical integration of the wave equation. Formal notions of computational cost (expressed in floating point operations) and numerical dispersion error are introduced. Restricting the analysis to leapfrog timemarching, for sake of simplicity, various spatial discrete differentiators are examined. For each scheme, by minimizing the cost at a given error threshold, a cost‐effective operating poin (time sampling rate and number of gridpoints per shortest wavelength) is obtained, which is remarkably different from the stability limit. Different schemes, each operated at its cost‐effective point, are then compared. High‐order dispersion‐bounded operators, in the sense of Holberg,1 are found to be competitive with the Pseudo‐spectral (PS) method.New optimal schemes improving over the Holberg's spatial differentiators are introduced together with accurate expansions of the convolutional weights is terms of the design error threshold. It is also shown that the composition of two distinct Holberg's operators of consecutive orders, with opposite phase properties, minimizes dispersion and yields cost‐effective schemes.Numerical experiments illustrate the suitability of the new methods for large‐scale wave‐equation seismic modelling.
Bounding‐surface plasticity for non‐linear analysis of space structures
Authors: Al‐Bermani F. G. A. , Zhu K. , Kitipornchai S. 
Published: August 2005

AbstractThis paper presents a method for the non‐linear analysis of space structures subjected to static and cyclic loading. A bounding‐surface kinematic hardening plasticity model is used to simulate the hardening and hysteritic material behaviour. The model is used in conjunction with the lumped plasticity assumption coupled with the concept of a yield surface in force space. A hardening coefficient matrix which is a function of the plastic strain and the elastic stiffness matrix is introduced while the vectorial nature of the material memory parameters is maintained. This provides a smooth transition from the elastic to the plastic regime which simulates the hysteresis loops quite accurately. An updated Lagrangian formulation is used together with a predictor/corrector solution method. Several examples are presented to demonstrate the accuracy and efficiency of the method.
Extension of moment‐method solutions to vector scattering by three‐dimensional non‐linear dielectric objects in free space
Authors: Caorsi Salvatore , Massa Andrea , Pastorino Matteo 
Published: August 2005

AbstractIn this paper, we explore the possibility of applying the moment method to determine the electromagnetic field distributions inside three‐dimensional bounded non‐linear dielectric objects of arbitrary shapes. The moment method has usually been employed to solve linear scattering problems. We start with an integral equation formulation, and derive a non‐linear system of algebraic equations that allows us to obtain an approximate solution for the harmonic vector components of the electric field. Preliminary results of some numerical simulations are reported.
A new fundamental solution for boundary element analysis of thin plates on Winkler foundation
Authors: El‐Zafrany A. , Fadhil S. , Al‐Hosani K. 
Published: August 2005

AbstractThis paper introduces an efficient boundary element approach for the analysis of thin plates, with arbitrary shapes and boundary conditions, resting on an elastic Winkler foundation. Boundary integral equations with three degrees‐of‐freedom per node are derived without unknown corner terms. A fundamental solution based upon newly defined modified Kelvin functions is formulated and it leads to a simple solution to the problem of divergent integrals. Reduction of domain loading terms for cases of distributed and concentrated loading is also provided. Case studies, including plates with free‐edge conditions, are demonstrated, and the boundary element results are compared with corresponding analytical solutions. The presented formulations provide a very accurate boundary element solution for plates with different shapes and boundary conditions.
The use of bubble functions for the post‐local buckling of plate assemblies by the finite strip method
Authors: Azhari M. , Bradford M. A. 
Published: August 2005

AbstractThe finite strip displacement functions for post‐local buckling are augmented with so‐called bubble functions, which are extra modes associated with internal or nodeless degrees of freedom. A non‐linear finite strip method of analysis including bubble functions is described for the post‐local buckling of geometrically imperfect plate assemblies. It is shown that the use of bubble functions improves significantly the convergence of the method. The non‐linear finite strip method is then used to study channel and I‐section members in compression and bending.
A finite element algorithm to study creep cracks based on the creep hardening surface
Authors: Krishnaswamy P. , Brust F. W. , Ghadiali N. D. 
Published: August 2005

AbstractThis work addresses finite element (FE) modelling of creep cracks under reversed and cyclic loads in steels. A constitutive model based on the creep hardening surface developed by Murakami and Ohno has been selected for this purpose. This model is particularly accurate for describing creep under reversed and cyclic loads and requires no additional material constants. An FE algorithm for this model has been derived and implemented into a research code FVP. The algorithm is verified by comparing the numerical predictions with closed form solutions for simple geometries and loading configurations. FE predictions are compared with experimental data for a stationary crack in a compact tension specimen. The stress and strain fields in the vicinity of a crack under a sustained load are compared with those for the intermediate unloading case. Several integral fracture parameters are investigated as to their appropriateness for describing creep cracks under reversed and cyclic loads.
A successive bounding method to find the exact eigenvalues of transcendental stiffness matrix formulations
Authors: Ye Jianqiao , Williams F. W. 
Published: August 2005

AbstractAn alternative algorithm for finding exact natural frequencies or buckling loads from the transcendental, e.g. dynamic, stiffness matrix method is presented in this paper and evaluated by using the plate assembly testbed program VICONOPT. The method is based on the bounding properties of the eigenvalues provided by either linear or quadratic matrix pencils on the exact solutions of the transcendental eigenvalue problem. The procedure presented has five stages, including two accuracy checking stages which prevent unnecessary calculations. Numerical tests on buckling of general anisotropic plate assemblies show that significant time savings can be achieved compared with an earlier multiple determinant parabolic interpolation method.
Voronoi cell finite element model based on micropolar theory of thermoelasticity for heterogeneous materials
Authors: Ghosh Somnath , Liu Yunshan 
Published: August 2005

AbstractIn this paper, a new ‘Voronoi cell finite element model’ is developed for solving steady‐state heat conduction and micropolar thermoelastic stress analysis problems in arbitrary heterogeneous materials. The method is based on the natural discretization of a multiple phase domain into basic structural elements by Dirichlet Tessellation. Tessellation process results in a network of polygons called Voronoi polygons. In this paper, formulations are developed for treating these polygons as elements in a finite element mesh. Furthermore, a composite Voronoi cell finite element model is developed to account for the presence of a second phase inclusion within a polygonal element. Various numerical examples are executed for validating the effectiveness of this model in the analysis of the temperature and stress fields for micropolar elastic materials. Effective material properties are derived for microstructures containing different distributions of second phase.
Parallel performance and scalability for block preconditioned finite element (p) solution of viscous flow
Authors: Barragy E. , Carey G. F. , Van De Geijn R. 
Published: August 2005

AbstractA two‐dimensional p‐type finite element scheme for distributed parallel computation of viscous flows is developed. The approach is based on an element‐by‐element implementation of the Biconjugate Gradient Stabilized 2 iterative method coupled with a recently developed class of block preconditioners. Critical to the overall parallel performance is the parallel solution of the imbedded bilinear preconditioner. Performance results are presented for the 2‐D driven cavity incompressible viscous flow problem solved using incremental continuation in the Reynolds number on the Intel Touchstone Delta. These results are used to validate a run‐time model. The run‐time model is then used to examine the scaling properties of the method over a range of p and h.
An efficient multilevel solution scheme for large scale non‐linear systems
Authors: Fish J. , Pandheeradi M. , Belsky V. 
Published: August 2005

AbstractWe present a new approach for the fast, efficient solution of large systems of non‐linear equations arising from the finite element discretization. The proposed non‐linear solver builds on the advantages of the popular methods of solution that are currently being employed, while eliminating most of their undesirable features. It combines the well‐known BFGS method with the FAS version of the multigrid method, introduced by Brandt,1 to form a fast, efficient solution method for non‐linear problems. We present numerical performance studies that are indicative of the convergence properties as well as the stability of the new method.
Discrete crack growth analysis methodology for through cracks in pressurized fuselage structures
Authors: Potyondy David O. , Wawrzynek Paul A. , Ingraffea Anthony R. 
Published: August 2005

AbstractA methodology for simulating the growth of long through cracks in the skin of pressurized aircraft fuselage structures is described. Crack trajectories are allowed to be arbitrary and are computed as part of the simulation. The interaction between the mechanical loads acting on the superstructure and the local structural response near the crack tips is accounted for by employing a hierarchical modelling strategy. The structural response for each cracked configuration is obtained using a geometrically non‐linear shell finite element analysis procedure. Four stress intensity factors, two for membrane behaviour and two for bending using Kirchhoff plate theory, are computed using an extension of the modified crack closure integral method. Crack trajectories are determined by applying the maximum tangential stress criterion. Crack growth results in localized mesh deletion, and the deletion regions are remeshed automatically using a newly developed all‐quadrilateral meshing algorithm. The effectiveness of the methodology, and its applicability to performing practical analyses of realistic structures, is demonstrated by simulating curvilinear crack growth in a fuselage panel that is representative of a typical narrow‐body aircraft. The predicted crack trajectory and fatigue life compare well with measurements of these same quantities from a full‐scale pressurized panel test.
Hypersingular quarter‐point boundary elements for crack problems
Authors: Sáez A. , Gallego R. , Dominguez J. 
Published: August 2005

AbstractThe present paper deals with the study and effective implementation for Stress Intensity Factor computation of a mixed boundary element approach based on the standard displacement integral equation and the hypersingular traction integral equation. Expressions for the evaluation of the hypersingular integrals along general curved quadratic line elements are presented. The integration is carried out by transformation of the hypersingular integrals into regular integrals, which are evaluated by standard quadratures, and simple singular integrals, which are integrated analytically. The generality of the method allows for the modelling of curved cracks and the use of straight line quarter‐point elements. The Stress Intensity Factors can be computed very accurately from the Crack Opening Displacement at collocation points extremely close to the crack tip. Several examples with different crack geometries are analyzed. The computed results show that the proposed approach for Stress Intensity Factors evaluation is simple, produces very accurate solutions and has little dependence on the size of the elements near the crack tip.
A robust incomplete factorization based on value and space constraints
Authors: Suarjana Made , Law Kincho H. 
Published: August 2005

AbstractThis paper describes an incomplete factorization method for computing a preconditioning matrix for the conjugate gradient method. The incomplete factorization satisfies the stability requirement that the incomplete factor remains positive definite throughout the factorization. When selecting a preconditioner for the conjugate gradient method, the number of non‐zero entries to be retained in the incomplete factor should be limited so that the amount of computations involving the preconditioning matrix is minimized. This paper introduces a method to generate an effective preconditioning matrix within a predefined space. Numerical results are presented to demonstrate the effectiveness of the incomplete factor as a preconditioner for the conjugate gradient method for solving large‐scale structural engineering problems.
Structural reliability optimization using an efficient safety index calculation procedure
Authors: Wang Liping , Grandhi Ramana V. , Hopkins Dale A. 
Published: August 2005

AbstractThe objective of this paper is to conduct reliability‐based structural optimization in a multidisciplinary environment. An efficient reliability analysis is developed by expanding the limit functions in terms of intermediate design variables. The design constraints are approximated using multivariate splines in searching for the optimum. The reduction in computational cost realized in safety index calculation and optimization are demonstrated through several structural problems. This paper presents safety index computation, analytical sensitivity analysis of reliability constraints and optimization using truss, frame and plate examples.
A finite volume procedure to solve elastic solid mechanics problems in three dimensions on an unstructured mesh
Authors: Bailey C. , Cross M. 
Published: August 2005

AbstractA Finite Volume (FV) procedure is described for solving the elastic solid mechanics equations in three dimensions on an unstructured mesh, for bodies undergoing thermal or mechanical loads. The FV procedure is developed in parallel with the conventional FE Galerkin procedure so that the differences in each approach may be clearly distinguished. The matrix form of the FV procedure is described, and is implemented in parallel with the FE procedure, both for two‐dimensional quadrilateral and three‐dimensional brick meshes. The FV and FE procedures are then compared against a range of benchmark problems that test the basic capability of the FV technique. It is shown to be approximately as accurate as the FE procedure on similar meshes, though its system matrix set‐up time is twice as long for a node by node set‐up procedure.
Reliable stress and fracture mechanics analysis of complex components using a h–p version of FEM
Authors: Andersson Börje , Falk Urban , Babus̆ka Ivo , Von Petersdorff Tobias 
Published: August 2005

AbstractWe develop effective approaches with which complex three‐dimensional components may be analysed with a high and virtually guaranteed accuracy. The main computational tool is a h‐p version of FEM practically realized with the p‐version program STRIPE having a mesh generator for automatic mesh refinement at edges and vertices. Use of advanced extraction methods and new theoretical approaches give exponential convergence rates for accuracies in all engineering data of interest. New methods for reliable calculation of local stresses and stress intensity data at edges and vertices to be used for fatigue dimensioning at fillets, damage tolerance assessment of three‐dimensional flaws, etc., are given. A complex real‐life problem is reliably analysed in order to demonstrate the practical usefulness of the procedures advocated. The technical details will be given in forthcoming papers.
h‐Hierarchical adaptive boundary element method using local reanalysis
Authors: Charafi A. , Neves A. C. , Wrobel L. C. 
Published: August 2005

AbstractAn adaptive boundary element scheme is developed using the concept of local reanalysis and h‐hierarchical functions for the construction of near‐optimal computational models. The use of local reanalysis in the error estimation guarantees the reliability of the modelling process while the use of quadratic and quartic h‐hieararchical elements guarantees the efficiency of the adaptive algorithm. The technique is developed for the elastic analysis of two‐dimensional models. Numerical examples show the rapid convergence of the results with a few refinement steps.
An explicit time integration technique for dynamic analyses
Authors: Pezeshk S. , Camp C. V. 
Published: August 2005

AbstractA simple explicit solution technique for problems in structural dynamics, based on a Modified Trapezoidal rule Method (MTM) approximation of the governing ordinary differential equations, is developed. The resulting conditionally stable explicit method (MTM) can be easily implemented and is extremely simple to use. Particular attention is focused herein on the concept of numerical stability of the proposed method for a free‐vibrational response of a linear undamped Single‐Degree‐Of‐Freedom system (SDOF). To examine the effectiveness, strengths, and limitations of MTM, error analyses for the natural period, the displacement, the velocity and the associated phase angle for a free undamped simple mass–spring system are derived and compared with Modified Euler Method (MEM) and the well‐known Newmark Beta Method (NBM). Numerical examples for a SDOF system and a Multi‐Degree‐Of‐Freedom (MDOF) system are presented to illustrate the strengths and the limitations of the proposed method.
A unified parametric design approach to structural shape optimization
Authors: Zhang Wei‐Hong , Beckers Pierre , Fleury Claude 
Published: August 2005

AbstractThis paper presents a general parametric design approach for 2‐D shape optimization problems. This approach has been achieved by integrating practical design methodologies into numerical procedures. It is characterized by three features: (i) automatic selection of a minimum number of shape design variables based on the CAD geometric model; (ii) integration of sequential convex programming algorithms to solve equality constrained optimization problems; (iii) efficient sensitivity analysis by means of the improved semi‐analytical method. It is shown that shape design variables can be either manually or systematically identified with the help of equality constraints describing the relationship between geometric entities.Numerical solutions are performed to demonstrate the applicability of the proposed approach. A discussion of the results is also given:
A consistent DXDR method for elastic‐plastic problems
Authors: Kadkhodayan M. , Zhang L. C. 
Published: August 2005

AbstractThis paper proposed a new efficient method, the consistent DXDR method, for analysing general elastic‐plastic problems. Two important factors in computational plasticity, the convergence and stability, were addressed. The method was constructed through a natural combination of two vital components: the DXDR algorithm which had been proved to be a powerful equation solver developed by the authors and a stable consistent algorithm for the integration of the constitutive equations of plasticity. Numerical examples demonstrated in detail the efficiency, accuracy, and stability attainable in solving various engineering problems.
A hybrid finite element analysis of interface cracks
Authors: Lee Jin , Gao Huajian 
Published: August 2005

AbstractA versatile hybrid finite element scheme consisting of special crack‐tip elements and crack face contact elements is developed to analyse a partially closed interface crack between two dissimilar anisotropic elastic materials. The crack‐tip element incorporates higher‐order asymptotic solutions for an interfacial crack tip. These solutions are obtained from complex variable methods in Stroh formalism. For a closed interfacial crack tip, a generalized contact model in which the crack‐tip oscillation is eliminated is adopted in the calculation. The hybrid finite element modelling allows the stress singularity at an open and closed crack tip to be accurately treated. The accuracy and convergence of the developed scheme are tested with respect to the known interface crack solutions. Utilizing this numerical scheme, the stress intensity factors and contact zone are calculated for a finite interface crack between a laminated composite material.
Application of cubic Hermitian algorithms to boundary element analysis of heat conduction
Authors: Singh K. M. , Kalra M. S. 
Published: August 2005

AbstractThis paper presents the application of cubic Hermitian interpolation based finite element schemes for the time integration of the differential‐algebraic system arising in the dual reciprocity boundary element formulation of transient diffusion problems. Weighted residual procedure is used to obtain the desired recurrence relations. Numerical results presented for three representative problems involving different types of boundary conditions amply demonstrate the high accuracy of the cubic Hermitian schemes.