bluuebunny/crossref_metadata_2025_split huggingface dataset:
Buckling and postbuckling analyses of laminated anisotropic structures
Authors: Noor Ahmed K. , Peters Jeanne M. 
Published: August 2005

AbstractA review is given of recent advances in two aspects of the numerical simulation of the buckling and postbuckling responses of composite structures. The first aspect is exploiting non‐traditional symmetries exhibited by composite structures; and strategies for reducing the size of the model and the cost of the buckling and postbuckling analyses in the presence of symmetry‐breaking conditions (e.g. asymmetry of the material, geometry, and/or loading). The second aspect pertains to the prediction of onset of local delamination in the postbuckling range and accurate determination of transverse shear stresses in the structure. The accuracy and effectiveness of the strategies developed are demonstrated by means of a numerical example.
On the analysis of the buckling behaviour of laminated composite plates and shells
Authors: Geier Bodo , Rohwer Klaus 
Published: August 2005

AbstractIn general, plates and shells out of composite laminates are more susceptible to transverse shear than those out of homogeneous isotropic material. By means of different shear flexible theories the effect on buckling and postbuckling behaviour is studied. It turns out that there is a rather limited range of plates where the transverse shear is of considerable influence. Results obtained with Mindlin‐ or Reissner‐type theories prove almost as adequate as those obtained with Reddy's theory. For the buckling analysis of shells the Kirchhoff–Love theory is precise enough. Snap‐through buckling and imperfection sensitivity appear in composite shells, too, especially if they are optimized with respect to high bifurcation buckling loads.
Finite element formulation for non‐steady‐state large deformations with sliding or evolving contact boundary conditions
Authors: Bohatier Claude , Chenot Jean‐Loup 
Published: August 2005

AbstractA method using a material description of the instantaneous configuration, valid for viscoplastic material with large deformations, is presented. In view of numerical tests which were carried out, this material formulation, associated with an implicit integration scheme which proved to be numerically accurate and reliable, is shown to be preferable.An algorithm is developed for resolution of sliding or evolving contact condition problems.
On improved hybrid finite elements with rotational degrees of freedom
Authors: Yunus Shah M. , Saigal Sunil , Cook Robert D. 
Published: August 2005

AbstractA set of three new hybrid elements with rotational degrees‐of‐freedom (d.o.f.'s) is introduced. The solid, 8‐node, hexahedron element is developed for solving three‐dimensional elasticity problems. This element has three translational and three rotational d.o.f.'s at each node and is based on a 42‐parameter. three‐dimensional stress field in the natural convected co‐ordinate system. For two‐dimensional, plane elasticity problems, an improved triangular hybrid element and a quadrilateral hybrid element are presented. These elements use two translational and one rotational d.o.f. at each node. Three different sets of five‐parameter stress fields defined in a natural convected co‐ordinate system for the entire element are used for the mixed triangular element. The mixed quadrilateral element is based on a nine‐parameter complete linear stress field in natural space. The midside translational d.o.f.'s are expressed in terms of the corner nodal translations and rotations using appropriate transformations. The stiffness matrix is derived based on the Hellinger–Reissner variational principle. The elements pass the patch test and demonstrate an improved performance over the existing elements for prescribed test examples.
Dynamic three dimensional computations for solids, with variable nodal connectivity for severe distortions
Authors: Johnson Gordon R. , Stryk Robert A. 
Published: August 2005

AbstractThis paper presents a three dimensional algorithm for dynamic Lagrangian computations for solids, with variable nodal connectivity to allow for severe distortions. The nodes are analogous to flexible spheres. When they move closer together than their equilibrium distance they generate compressive, repulsive forces. Conversely, when they move apart, they generate tensile attractive forces. Material strength effects are also included. Because a node can be affected only by its ‘neighbour’ nodes, the approach has been designated the ‘NABOR’ approach. The distinguishing feature of this technique is that it is possible to have variable connectivity. A node can acquire new neighbours, thus allowing all forms of distortion. The three dimensional NABOR algorithm has been incorporated as an option into the explicit finite element code, EPIC‐3. By using both the NABOR grid and the traditional EPIC‐3 finite element grid together, it is possible to perform Lagrangian computations for a wider range of problems.
A new method for modelling reinforcement and bond in finite element analyses of reinforced concrete
Authors: Allwood R. J. , Bajarwan A. A. 
Published: August 2005

AbstractA new method of representing the steei in finite element analyses of reinforced concrete structures is described in which the steel and the concrete are analysed separately. The forces between the steel and concrete are used In an interative method which brings the two solutions together. The method converges very rapidly and it is shown that the computational effort is principally dependent on the mesh chosen for the concrete. All the steel in a reinforced concrete structure may be easily included without affecting the layout of the concrete mesh. Results, which are given for three practical problems, include detailed steel and bond stresses for all bars.
Analysis of viscoelastic behaviour of transversely isotropic materials
Authors: Douven L. F. A. , Schreurs P. J. G. , Janssen J. D. 
Published: August 2005

AbstractIn this paper a constitutive equation to describe the mechanical behaviour of materials, reinforced with unidirectional fibres, is presented. The material behaviour of both matrix and fibres may be viscoelastic. The constitutive equation is a linear relation between the second Piola–Kirchhoff stress tensor and the Green–Lagrange strain tensor. The effective relaxation functions in the constitutive equation are composed of component relaxation functions employing the structural model of Hashin and Rosen. A two‐dimensional membrane element incorporating this constitutive equation is implemented in a finite element program. The results of several calculations are presented in order to demonstrate the possibilities of the numerical tool. One calculation concerns a square membrane with a circular hole in its centre. The effect of fibre orientation on deformation and stresses will be displayed for this structure as well as for another membrane structure.
On the modelling of scalar and mass transport in combustor flows
Authors: Nikjooy M. , So R. M. C. 
Published: August 2005

AbstractThe results of a numerical study of swirling and non‐swirling combustor flows with and without density variations are presented. Constant‐density arguments are used to justify closure assumptions invoked for the transport equations for turbulent momentum and scalar fluxes, which are written in terms of density‐weighted variables. Comparisons are carried out with measurements obtained from three different axisymmetric model combustors. The three experiments cover recirculating flow, swirling flow and variable‐density, swirling flow inside model combustors. Together, they offer wide ranging flow conditions to test the validity of the models. Results show that the Reynolds stress/flux models do a credible job of predicting constant‐density, swirling and non‐swirling combustor flows with passive scalar transport. However, their improvements over algebraic stress/flux models are marginal. The extension of the constant‐density models to variable‐density flow calculations shows that the models are equally valid for such flows. Therefore, the present results argue well for the adoption of constant‐density models for variable‐density flows until a successfully validated variable‐density model is available.
A new implementation of the force method and the optimum design of large trusses
Authors: Joseph K. T. 
Published: August 2005

AbstractAn implementation of the force method is proposed in which the forces and the displacements are simultaneously obtained by the solution of a sparse symmetric indefinite system. The matrix of coefficients is formed by just the concatenation of the element flexibility and equilibrium matrices. No computational procedure is required to generate the compatibility conditions (or the self‐stress matrix) and no partitioning of the force vector is made into a basic set and a redundant set, unlike the conventional force method. A slightly modified sparse unsymmetric system can be written in which the stresses and the displacements are the unknowns. This is used as constraints in the formulation of the minimum weight design problem for large structures under static loading conditions. A sparse generalized reduced gradient package is used as the optimizer. A class of test problems involving large truss structures is solved. The results indicate that the present implementation of the force method is better than the displacement method for the optimum design of large structures.
Virtual crack extension methods for non‐linear materials
Authors: Hellen T. K. 
Published: August 2005

AbstractThe virtual crack extension technique is a very efficient and accurate approach to fracture mechanics calculations in the numerical analysis of bodies containing cracks using the finite element method. A few variations of the technique have been described in the literature, and have been extensively used in linear elastic fracture mechanics, where good validation has frequently been available with accepted alternative solutions for standard tests. However, for non‐linear materials extra complications arise in the technique, particularly in describing material response in a compatible manner. It is shown that, using few assumptions, a very competitive virtual crack extension technique based, on a direct minimization of potential energy is available for elastic non‐linear elastic materials. Such materials can be closely approximated to elastic–plastic behaviour for monotonically increasing loads including mechanical, thermal and body force forms. The technique is described and demonstrated via examples to be in good agreement with alternative fracture parameter evaluations when evaluated in the same computer system, BERSAFE.
Free‐vibration analysis of single‐layer and two‐layer bimodular beams
Authors: Wu Jong‐Shyong , Jing Hung‐Sying , Cheng Chun‐Rong 
Published: August 2005

AbstractA method is presented for determining the natural frequencies and the corresponding mode shapes of isotropic bimodular beams at certain supporting conditions. Although only the lowest three modes of the single‐layer and two‐layer bimodular beams were studied, in principle, the method may also be used to determine higher‐mode natural frequencies and shapes of the multi‐layer beams. Numerical analysis shows that the approach is suitable for the free‐vibration analysis of clamped/free and hinged/hinged bimodular beams.
A mixed‐variable continuously deforming finite element method for parabolic evolution problems. Part III: Numerical implementation and computational results
Authors: Kececioglu Ifiyenia , Rubinsky Boris 
Published: August 2005

AbstractIn Part I of this paper,1 the conceptual framework of a rate variational least squares formulation of a continuously deforming mixed‐variable finite element method was presented for solving a single evolution equation. In Part II2 a system of ordinary differential equations with respect to time was derived for solving a system of three coupled evolution equations by the deforming grid mixed‐variable least squares rate variational finite element method. The system of evolution equations describes the coupled heat flow, fluid flow and trace species transport in porous media under conditions when the flow velocities and constituent phase transitions induce sharp fronts in the solution domain. In this paper, we present the method we have adopted to integrate with respect to time the resulting spatially discretized system of non‐linear ordinary differential equations. Next, we present computational results obtained using the code in which this deforming mixed finite element method was implemented. Because several features of the formulation are novel and have not been previously attempted, the problems were selected to exercise these features with the objective of demonstrating that the formulation is correct and that the numerical procedures adopted converge to the correct solutions.
Efficiency of group implicit concurrent algorithms for transient finite element analysis
Authors: Ortiz M. , Sotelino E. D. , Nour‐Omid B. 
Published: August 2005

AbstractThe performance of group implicit algorithms is assessed on actual concurrent computers. We show that, as the number of subdomains is increased, performance enhancements are derived from two sources: the increased parallelism in the computations; and a reduction in equation solving effort. Moreover, we show that these two performance enhancements are synergistic, in the sense that the corresponding speed‐ups are multiplied, rather than merely added. Our numerical simulations demonstrate that, if n is the number of degrees of freedom of the structure, p the number of processors used in the computations, and s ⩾ p is the number of subdomains in the partition, the net speed‐up is \documentclass{article}\pagestyle{empty}\begin{document}$ O\left({p\sqrt s} \right) $\end{document} in 2D and O(ps) in 3D, asymptotically as n/s → ∞. In particular, speed‐ups with respect to Newmark's method of \documentclass{article}\pagestyle{empty}\begin{document}$ O\left({p\sqrt s} \right) $\end{document} in 2D and O(s) in 3D are obtained on a single‐processor machine. Finally, simulations on a 32‐node hypercube are presented for which the interprocessor communication efficiencies obtained are consistently in excess of 90 per cent.
Error estimates and adaptive refinement for plate bending problems
Authors: Zienkiewicz O. C. , Zhu J. Z. 
Published: August 2005

AbstractThe Zienkiewicz–Zhu error estimator is shown to be effective in problems of plate flexure. When used in conjunction with triangular elements and an adaptive mesh generator allowing a prescribed size of elements to be developed, very fast adaptive convergence for results of specified accuracy is achieved.
Smooth postbuckling stresses by a modified finite element method
Authors: Byskov Esben 
Published: August 2005

AbstractExact postbuckling stresses usually vary fairly smoothly. Unfortunately, finite element postbuckling stresses tend to be much less well behaved. The result is that second order postbuckling constants determined by the finite element method may be highly inaccurate. The reason is that in finite element solutions transverse displacements associated with the buckling fields furnish too rapidly varying postbuckling strain contributions, while the postbuckling axial or membrane displacements contribute strain components that are sufficiently smooth, thus creating an internal postbuckling strain and stress mismatch.The present study suggests a modified finite element method that handles the problem, which is a special example of membrane locking, by introducing the postbuckling strains as independent variables. In general, the method provides rather complicated finite element expressions. However, by a suitable choice of interpolating functions, the resulting finite element equations themselves may be found to be the usual ones, and yet provide smooth postbuckling stresses and therefore good values of the postbuckling constants.
Selective refinement/derefinement algorithms for sequences of nested triangulations
Authors: Rivara María‐Cecilia 
Published: August 2005

AbstractThe construction of changing sequences of irregular and nested triangulations, based on the use of conforming refinement/derefinement algorithms for triangulations, is presented and discussed. This strategy is particularly appropriate to combine adaptivity and full multigrid algorithms for dealing with moving fronts or fluid dynamics problems. It is shown that the quality of all the triangulations iteratively generated depends only on the geometric characteristics of the initial grid. A data structure suitable to create, manage and modify series of nested triangulations as well as the main features of the DEREF prototype package are described, and numerical examples are given.
Tracing the equilibrium path beyond simple critical points
Authors: Kouhia Reijo , Mikkola Martti 
Published: August 2005

AbstractA unified presentation of some popular continuation procedures used in the non‐linear finite element analysis of structural mechanics is introduced. An extension of the elliptical constraint equation proposed by Crisfield is given. It is shown that in the proposed procedure real roots can always be obtained in solving the iterative change of the load parameter. Updated weighting factors are introduced in the constraint equation in order to get better convergence characteristics in the case when localized deformations occur. For bifurcation points a modification of Rheinboldt's branching procedure is presented. Post critical response after limit and bifurcation points is determined in some numerical examples.
A finite element methodology to predictage‐related mechanical property and structural performance changes in high performance polymers
Authors: Wadiak D. T. , Bond P. M. , Cyr N. A. , Fields S. , Ferguson G. H. , Swenson L. W. 
Published: August 2005

AbstractThe treatment of ageing processes in polymers by the finite element (FE) method is described. The development of this analytical method is motivated by the need to assess the effects of ageing on the structural performance of polymers and polymeric composites, particularly when the structures are large and expensive to replace. Also, there is a need to assess the effectiveness of corrective action options when ageing problems do occur, which can be treated by this method. The method describes the treatment of multiple, reactive chemical species in multi‐layered polymeric materials by the finite element method. Example problems featuring the simultaneous diffusion and chemical reaction are illustrated: a simple problem of binary diffusion and reaction with comparison of numerical to exact results, and the staged ageing/structural analysis of a solid rocket motor.
Dynamic modelling of skeletal systems with arbitrary mass distributions
Authors: Smith H. A. , Melosh R. J. 
Published: August 2005

AbstractThis study develops and illustrates a dynamic model for vibration analysis of rod and beam elements with arbitrary mass distributions. This arbitrary mass model represents the element shape function using a frequency dependent series that becomes exact as the number of terms in the series approaches infinity. The arbitrary mass model yields the natural frequencies and modes of elements with mass distributions which vary as continuous functions of the spanwise co‐ordinate.The arbitrary mass model, implemented using the unsymmetric formulation for vibration analysis, is illustrated in examples and compared with other dynamic models which use stepped mass representations to model the arbitrary mass distributions. Studies show that the arbitrary mass model is more computationally efficient than the stepped mass representation models, particularly when accuracy requirements are high.
Error indicators for adaptive mesh refinement in the boundary element method—a new approach
Authors: Guiggiani Massimo 
Published: August 2005

AbstractIn this paper a new approach to the development of a posteriori error indicators for the direct boundary element method (BEM) is presented. It takes advantage of a unique opportunity offered by the collocation BEM, that is the possibility of obtaining more than one numerical solution from a given boundary element mesh. Unlike other approaches, the error indicator introduced in the present paper does not require any explicit evaluation of the residual of the approximate solution. In order to test the capability of the proposed error indicators to actually control a selective mesh refinement process, an h‐adaptive refinement strategy is also described, together with the criteria for refinement and for the termination of the adaptive process. Full details on the whole numerical implementation for two‐dimensional problems are provided. In particular, there is described a direct method for the numerical evaluation of Cauchy principal value integrals. Numerical examples show that pointwise convergence is always obtained in a few steps and the final meshes look nearly as if they were designed by an expert analyst.
Application of the zienkiewicz‐zhu error estimator for plate and shell analysis
Authors: Yunus S. M. , Pawlak T. P. , Wheeler M. J. 
Published: August 2005

AbstractAn effective and efficient error estimation scheme for finite element plate and shell analysis is presented. The error estimate method proposed is applicable to all the plate and shell elements developed using either classical plate and shell or continuum mechanics theories. The global error in energy norm is computed by summing all the elemental errors. The method is well suited for adaptive mesh refinement as the error contribution for each element is known. Demonstration examples using uniform and adaptive refinement schemes for both the plate and shell analysis show the effectiveness of the method proposed.
An approach to the generation of triangular grids possessing few obtuse triangles
Authors: Deljouie‐Rakhshandeh K. 
Published: August 2005

AbstractA triangular mesh generator is presented which makes extensive use of side swapping and mesh smoothing to create a grid with few obtuse triangles. To perform the above task a data structure is presented which holds full adjacency information both for nodes and elements. It is shown how this data structure is employed in the process mesh generation, and how the methods of computational geometry such as region decomposition are used not only to decompose a complex region, but also to reflect the boundary grading into the interior the region. Algorithms are provided to show the mechanism of these processes and practical examples are given to support the approach.