bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tetrahedral mesh improvement via optimization of the element condition number
Authors: Freitag Lori A. , Knupp Patrick M. 
Published: October 2002

AbstractWe present a new shape measure for tetrahedral elements that is optimal in that it gives the distance of a tetrahedron from the set of inverted elements. This measure is constructed from the condition number of the linear transformation between a unit equilateral tetrahedron and any tetrahedron with positive volume. Using this shape measure, we formulate two optimization objective functions that are differentiated by their goal: the first seeks to improve the average quality of the tetrahedral mesh; the second aims to improve the worst‐quality element in the mesh. We review the optimization techniques used with each objective function and present experimental results that demonstrate the effectiveness of the mesh improvement methods. We show that a combined optimization approach that uses both objective functions obtains the best‐quality meshes for several complex geometries. Copyright © 2001 John Wiley & Sons, Ltd.
A canonical form return mapping algorithm for rate independent plasticity
Authors: Keavey M. A. 
Published: October 2002

AbstractA canonical form for the representation of elastic predictor radial return plasticity algorithms is presented which is deceptive in its simplicity. Iterative application of the corrector is in a form used universally in the solution of ordinary differential equations and substitution of different yield functions and state variable evolution equations is trivial. The consistency condition is maintained by an additional constraint equation via what is, in effect, a Lagrange multiplier. A consistent material Jacobian may be obtained automatically by applying partial elimination to the same set of equations. The process is numerical and requires no additional algebraic manipulation. To demonstrate the validity of such a simple technique, existing, apparently more complex, formulations are derived through the simple expedient of static condensation. As a practical example of the application of the method, a standard von Mises plasticity model is implemented and results are presented for two standard benchmarks that test quadratic convergence for large increments. Copyright © 2001 John Wiley & Sons, Ltd.
Finite element evaluation of mixed mode stress intensity factors in functionally graded materials
Authors: Kim Jeong‐Ho , Paulino Glaucio H. 
Published: October 2002

AbstractThis paper is directed towards finite element computation of fracture parameters in functionally graded material (FGM) assemblages of arbitrary geometry with stationary cracks. Graded finite elements are developed where the elastic moduli are smooth functions of spatial co‐ordinates which are integrated into the element stiffness matrix. In particular, stress intensity factors for mode I and mixed‐mode two‐dimensional problems are evaluated and compared through three different approaches tailored for FGMs: path‐independent J*k‐integral, modified crack‐closure integral method, and displacement correlation technique. The accuracy of these methods is discussed based on comparison with available theoretical, experimental or numerical solutions. Copyright © 2001 John Wiley & Sons, Ltd.
Mixed‐enhanced formulation for geometrically linear axisymmetric problems
Authors: Kasper E. P. , Taylor R. L. 
Published: October 2002

AbstractA four‐noded quadrilateral axisymmetric formulation in the context of a mixed‐enhanced method is presented. The strain field is represented by two sets of element parameters, which results in enhanced performance and coarse mesh accuracy in bending dominated problems and locking‐free response in the near incompressible limit. The mixed fields presented are such that variational stress recovery is permissible. In addition, the formulation is cast such that the mixed parameters are obtained explicitly yielding finite element arrays with the proper rank using standard order quadrature. In this paper our attention is restricted to the area of geometrically linear problems in solid mechanics. Representative simulations show favourable performance of the formulation. Copyright © 2002 John Wiley & Sons, Ltd.
A plasticity based model and an adaptive algorithm for finite element analysis of reinforced concrete panels
Authors: Pravida J. , Wunderlich W. 
Published: October 2002

AbstractThis paper deals with an adaptive finite element procedure for the analysis of plain and reinforced concrete panels in a state of plane stress. Therefore, we will present a plasticity based model for plain concrete which captures the two failure modes of concrete within one formulation. In spite of a simple formulation the model is capable to describe the different mechanisms for tensile failure as well as for compression fracture. To restrict the time discretization error and the spatial discretization error to certain tolerances, the constitutive model is embedded in an adaptive algorithm which controls the size of the incremental load steps and leads to a hierarchical mesh refinement if necessary. The application of the model will be shown by various numerical examples. Copyright © 2002 John Wiley & Sons, Ltd.
Mesh generation in curvilinear domains using high‐order elements
Authors: Sherwin S. J. , Peiró J. 
Published: October 2002

AbstractThe ability to construct suitable computational meshes is currently a significant limiting factor in the development of compact high‐order algorithms in very complex geometries. Compact high‐order algorithms such as spectral element or p‐type finite element techniques offer the potential of high accuracy if the solution is smooth and a well‐behaved mapping exists between the local sub‐domains and a standard region. In this paper we address the problem of coupling high‐order algorithms with unstructured mesh generation and CAD representation techniques. We present three complementary strategies to alleviate the problem of generation of elemental regions with singular elemental mappings. The first strategy investigates the influence of an anisometric parametric surface representation on the quality of high‐order unstructured meshes. We show that a straightforward splitting of a standard linear mesh for use in a high‐order method can lead to the generation of distorted, possibly invalid, meshes even for simple computational domains such as cubes. The second strategy uses hybrid meshes applying prismatic elements near curvilinear boundaries. In the third and final strategy we investigate the use of curvature driven surface discretization to incorporate higher‐order information about the surface into the mesh generation. Using the computational reconstruction of the arterial bypass graft as an example computational domain we demonstrate how the combination of all three strategies leads to a valid high‐order discretization of the computational domain. Copyright © 2001 John Wiley & Sons, Ltd.
Remeshing for metal forming simulations—Part II: Three‐dimensional hexahedral mesh generation
Authors: Kwak Dae‐Young , Im Yong‐Taek 
Published: October 2002

AbstractIn the present study, a hexahedral mesh generator was developed for remeshing in three‐dimensional metal forming simulations. It is based on the master grid approach and octree‐based refinement scheme to generate uniformly sized or locally refined hexahedral mesh system. In particular, for refined hexahedral mesh generation, the modified Laplacian mesh smoothing scheme mentioned in the two‐dimensional study (Part I) was used to improve the mesh quality while also minimizing the loss of element size conditions. In order to investigate the applicability and effectiveness of the developed hexahedral mesh generator, several three‐dimensional metal forming simulations were carried out using uniformly sized hexahedral mesh systems. Also, a comparative study of indentation analyses was conducted to check the computational efficiency of locally refined hexahedral mesh systems. In particular, for specification of refinement conditions, distributions of effective strain‐rate gradient and posteriori error values based on a Z2 error estimator were used. From this study, it is construed that the developed hexahedral mesh generator can be effectively used for three‐dimensional metal forming simulations. Copyright © 2002 John Wiley & Sons, Ltd.
On a wildland fire model with radiation
Authors: Asensio M. I. , Ferragut L. 
Published: October 2002

AbstractThe 2‐D simplified wildland fire model presented here is based on conservation laws and takes into account radiation as the dominant thermal transfer mechanism, as well as convection, which represents the effect of the wind and the slope. The non‐dimensional equations are obtained using the Frank–Kamenestkii change of variables. The existence of weak solutions of the non‐linear reaction diffusion problem obtained is established as a particular case of more general existence results using a compactness method. The uniqueness of the weak solution is shown for a given initial data and fixed parameters of the equations. The approximate solution is obtained using a mixed finite element method. This preserves the continuity of the flux through the inter‐element boundaries and allows to represent high gradients in the solution. Semi‐discrete error estimation is presented. The convective term is solved by a splitting technique using Godunov's method. The numerical examples show the efficiency of the algorithm in capturing the fire front, even for critical values of the parameters. Copyright © 2002 John Wiley & Sons, Ltd.
QuickTrace: a fast algorithm to detect contact
Authors: Bruneel Herman C. J. , De Rycke Igor 
Published: October 2002

AbstractQuickTrace is a new, fast contact detection algorithm. It searches for contact typically between a tool, modelled by some kind of geometrical surface facets, and deforming material. Contact is searched for at material surface points called contact nodes. A contact node is in contact with a facet when the contact node is inside of the tool and the negative outer normal on the material surface at the contact node ‘leaves’ the tool surface through that facet. When multiple facets are intersected, only the closest facet to the contact node should be considered. From this definition of contact, the penetration depth results automatically as a by‐product.In QuickTrace, the m facets of the tool are packaged in boxes that are hierarchically ordered in a search tree with an average depth of log4 m. The computational complexity for one contact search is proportional to this average depth. So, for n contact nodes the computational complexity is O(n log4 m). This places QuickTrace amongst the best performing contact detection algorithms. At the same time there are no approximations or tricks involved and the contact detection is absolutely correct. The algorithm can easily be extended to material–material or tool–tool contact. Copyright © 2002 John Wiley & Sons, Ltd.
Non‐planar 3D crack growth by the extended finite element and level sets—Part I: Mechanical model
Authors: Moës N. , Gravouil A. , Belytschko T. 
Published: October 2002

AbstractA methodology for solving three‐dimensional crack problems with geometries that are independent of the mesh is described. The method is based on the extended finite element method, in which the crack discontinuity is introduced as a Heaviside step function via a partition of unity. In addition, branch functions are introduced for all elements containing the crack front. The branch functions include asymptotic near‐tip fields that improve the accuracy of the method. The crack geometry is described by two signed distance functions, which in turn can be defined by nodal values. Consequently, no explicit representation of the crack is needed. Examples for three‐dimensional elastostatic problems are given and compared to analytic and benchmark solutions. The method is readily extendable to inelastic fracture problems. Copyright © 2002 John Wiley & Sons, Ltd.
Non‐planar 3D crack growth by the extended finite element and level sets—Part II: Level set update
Authors: Gravouil A. , Moës N. , Belytschko T. 
Published: October 2002

AbstractWe present a level set method for treating the growth of non‐planar three‐dimensional cracks.The crack is defined by two almost‐orthogonal level sets (signed distance functions). One of them describes the crack as a two‐dimensional surface in a three‐dimensional space, and the second is used to describe the one‐dimensional crack front, which is the intersection of the two level sets. A Hamilton–Jacobi equation is used to update the level sets. A velocity extension is developed that preserves the old crack surface and can accurately generate the growing surface. The technique is coupled with the extended finite element method which approximates the displacement field with a discontinuous partition of unity. This displacement field is constructed directly in terms of the level sets, so the discretization by finite elements requires no explicit representation of the crack surface. Numerical experiments show the robustness of the method, both in accuracy and in treating cracks with significant changes in topology. Copyright © 2002 John Wiley & Sons, Ltd.
A numerical upscaling method for an elliptic equation with heterogeneous tensorial coefficients
Authors: Luce Robert , Perez Sylvie 
Published: October 2002

AbstractThe aim of this paper is to develop a new numerical method to determine the effective permeability on a coarse scale level of problems with strongly heterogeneous tensorial coefficients defined on a fine scale. This method stems from a primal–dual mixed formulation and the upscaled permeability is obtained by imposing the continuity of the numerical flux across the lines of discontinuities. Moreover, a finite volume scheme is built to numerically solve elliptic equations with this kind of coefficients. Finally, the method is illustrated by several numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd.
An improved unsteady, unstructured, artificial compressibility, finite volume scheme for viscous incompressible flows: Part II. Application
Authors: Malan A. G. , Lewis R. W. , Nithiarasu P. 
Published: October 2002

AbstractIn Part I of this paper, a preconditioned artificial compressibility scheme was developed for modelling laminar steady‐state and transient, incompressible flows for a wide range of Reynolds and Rayleigh numbers. In this part, several examples of laminar incompressible problems are solved and discussed. The influence of various AC parameters on robustness and convergence rates are assessed for a complex category of problems. It is shown that the scheme developed in Part I is an accurate, robust and easy to use method for solving incompressible laminar flow problems over a wide range of flow regimes. Copyright © 2002 John Wiley & Sons, Ltd.
Sandwich shell finite element for dynamic explicit analysis
Authors: Tabiei Ala , Tanov Romil 
Published: October 2002

AbstractThe contribution of this paper consists of new development of transverse shear stresses through the thickness and finding an expression for the critical time step for explicit time integration of layered shells. This work presents the finite element (FE) formulation and implementation of a higher‐order shear deformable shell element for dynamic explicit analysis of composite and sandwich shells. The formulation is developed using a displacement‐based third‐order shear deformation shell theory. Using the differential equilibrium equations and the interlayer requirements, special treatment is developed for the transverse shear, resulting in a continuous, piecewise quartic distribution of the transverse shear stresses through the shell thickness. Expressions are developed for the critical time step of the explicit time integration for orthotropic homogeneous and layered shells based on the developed third‐order formulation. To assess the performance of the present shell element, it is implemented in the general non‐linear explicit dynamic FE code DYNA3D. Several problems are solved and results are presented and compared to other theoretical and numerical results. Copyright © 2002 John Wiley & Sons, Ltd.
Modelling three‐dimensional piece‐wise homogeneous domains using the α‐shape‐based natural element method
Authors: Cueto E. , Calvo B. , Doblaré M. 
Published: October 2002

AbstractIn this paper, the application of the natural element method (NEM) to the numerical analysis of two‐ and three‐dimensional piece‐wise homogeneous domains is presented. The NEM differs from other meshless methods in its capability to accurately reproduce essential boundary conditions along convex boundaries. The α‐shape‐based extension of this method (α‐NEM) generalizes this behaviour to non‐convex domains, enables us to construct models entirely in terms of the initial cloud of points and allows us to simulate material discontinuities in a straightforward manner. In the following sections, simple and effective algorithms are presented for the construction of α‐shapes in domains composed of various materials. Examples are presented in two‐ and three‐dimensional cases in the context of linear elastostatics showing good performance even with the simple numerical quadrature used. Copyright © 2002 John Wiley & Sons, Ltd.
Derived data structure algorithms for unstructured finite element meshes
Authors: Waltz Jacob 
Published: October 2002

AbstractA set of derived data structure algorithms for unstructured finite element meshes is presented. Both serial and parallel algorithms are described for each data structure. Colouring groups for the elements are used to facilitate parallelization on shared memory architectures. Scaling studies indicate that the parallel algorithms are most efficient when the number of elements per processor is on the order of 106 or higher, and overall efficiencies of 60–70% are achieved down to 0.5×106 elements per processor. Although the meshes under consideration are tetrahedral, the algorithms are general in nature and can be extended to arbitrary element types with minimal effort. Copyright © 2002 John Wiley & Sons, Ltd.
An algorithm coupling the OSRC and FEM for the computation of an approximate scattered acoustic field by a non‐convex body
Authors: Antoine X. 
Published: October 2002

AbstractThis paper describes a new formulation to solve the acoustic scattering problem by a non‐convex structure. The presented hybrid algorithms connect the on‐surface radiation condition method to accelerate the calculations with a two‐dimensional finite element method to treat the non‐convex part of the domain. This allows the problem of truncating the computational domain to be overcome. The variational formulations associated with a Dirichlet or a Neumann boundary condition are considered. Finally, we give some numerical results on a model test case to illustrate the improvement of accuracy of the new algorithm compared to a pure OSRC approach. Copyright © 2002 John Wiley & Sons, Ltd.
Adaptive moving mesh methods for simulating one‐dimensional groundwater problems with sharp moving fronts
Authors: Huang Weizhang , Zheng Li , Zhan Xiaoyong 
Published: October 2002

AbstractAccurate modelling of groundwater flow and transport with sharp moving fronts often involves high computational cost, when a fixed/uniform mesh is used. In this paper, we investigate the modelling of groundwater problems using a particular adaptive mesh method called the moving mesh partial differential equation approach. With this approach, the mesh is dynamically relocated through a partial differential equation to capture the evolving sharp fronts with a relatively small number of grid points. The mesh movement and physical system modelling are realized by solving the mesh movement and physical partial differential equations alternately. The method is applied to the modelling of a range of groundwater problems, including advection dominated chemical transport and reaction, non‐linear infiltration in soil, and the coupling of density dependent flow and transport. Numerical results demonstrate that sharp moving fronts can be accurately and efficiently captured by the moving mesh approach. Also addressed are important implementation strategies, e.g. the construction of the monitor function based on the interpolation error, control of mesh concentration, and two‐layer mesh movement. Copyright © 2002 John Wiley & Sons, Ltd.
A new variable‐order singular boundary element for two‐dimensional stress analysis
Authors: Lim K. M. , Lee K. H. , Tay A. A. O. , Zhou W. 
Published: October 2002

AbstractA new variable‐order singular boundary element for two‐dimensional stress analysis is developed. This element is an extension of the basic three‐node quadratic boundary element with the shape functions enriched with variable‐order singular displacement and traction fields which are obtained from an asymptotic singularity analysis. Both the variable order of the singularity and the polar profile of the singular fields are incorporated into the singular element to enhance its accuracy. The enriched shape functions are also formulated such that the stress intensity factors appear as nodal unknowns at the singular node thereby enabling direct calculation instead of through indirect extrapolation or contour‐integral methods. Numerical examples involving crack, notch and corner problems in homogeneous materials and bimaterial systems show the singular element's great versatility and accuracy in solving a wide range of problems with various orders of singularities. The stress intensity factors which are obtained agree very well with those reported in the literature. Copyright © 2002 John Wiley & Sons, Ltd.
Hyaluronan expression in differentiated thyroid carcinoma
Authors: Böhm Jan , Niskanen Leo , Tammi Raija , Tammi Markku , Eskelinen Matti , Pirinen Risto , Hollmen Sinikka , Alhava Esko , Kosma Veli‐Matti 
Published: October 2002

AbstractThe extracellular polysaccharide hyaluronan (HA) controls cell migration, differentiation, and proliferation, and is supposed to contribute to the spreading of several human cancers. Little is known about the role of HA in the development and progression of differentiated thyroid carcinoma (DTC). The expression and prognostic value of HA were therefore evaluated in 204 consecutive patients with DTC. A biotinylated affinity probe specific for HA was applied to paraffin‐embedded tumour samples to assay the expression of HA in carcinoma cells and in intra/peritumoural stroma. In a majority of the samples, a high percentage (≥90%) of normal thyroid follicle epithelial cells were HA‐positive. This high percentage was also found in 80 (47%) papillary carcinomas, but only in seven (21%) follicular carcinomas (p=0.004). Age (>60 years) of the patients was significantly associated with a low percentage of HA‐positive cancer cells (p=0.013). Cancer cell‐associated HA correlated significantly with the percentage of cells expressing total CD44 and its isoforms containing exons v3 and v6 (r=0.223–0.289, p<0.001 for all). The tumour stroma was always positive for HA. Stromal staining intensity did not differ markedly between papillary and follicular carcinomas. A strong stromal HA staining intensity was related to distant metastases (p=0.044), high pTNM stage (p=0.024), old age (>60 years) (p=0.043), and cancer‐related mortality (p=0.001). In a log‐rank univariate survival analysis, strong stromal HA staining intensity was related to DTC mortality (p=0.0007). Cancer cell‐associated HA expression did not significantly correlate with patient survival. In Cox's multivariate survival analysis, age (>60 years, p=0.0164), gender (p=0.0251), and pTNM stage (p=0.0121) were significant independent prognostic factors for DTC‐related death. These results suggest that strong stromal HA staining intensity is related to progression and unfavourable outcome in DTC patients, while the clinical factors remain more powerful in predicting DTC‐related death. Copyright © 2001 John Wiley & Sons, Ltd.