bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improvement of the runtime behaviour of a frontal solution code
Authors: Gloos D. , Hoehn W. , Spellucci P. 
Published: August 2005

AbstractThe frontal solution method for finite element linear systems is well known to be especially useful for small and medium‐sized computing equipment. Even memory sizes from 1 to 8 MB, which are now possible, put severe space limitations on three‐dimensional calculations run on a time‐sharing system. This paper describes a programming technique which greatly increases the applicability of the frontal solution method without using the automatic paging of modern operating systems, which would result in extreme inefficiency.
OAHM: A fortran subroutine for solving a class of unsymmetric linear systems of equations
Authors: Makinson G. J. , Shah A. A. 
Published: August 2005

AbstractThe discretization, by means of the usual 5‐point difference formulae, of an elliptic partial differential equation can give rise to an unsymmetric and sparse linear system of equations in which the matrix A of coefficients is an M‐matrix such that each element in the upper/lower triangular part is greater than or equal to the respective element in the lower/upper triangular part. In other applications, dense matrices with the same property can arise. A FORTRAN subroutine called OAHM is presented for the solution of such systems which can be easily modified to deal efficiently with the sparse case. The OAHM subroutine uses a regular splitting and the convergence is therefore guaranteed.
An explicit form of the plastic matrix for a Mohr–Coulomb material
Authors: Griffiths D. V. , Willson S. M. 
Published: August 2005

AbstractAn explicit from of the plastic matrix for a Mohr–Coulomb material in two dimensions is presented. The derivation, which assumes elastic–perfectly plastic behaviour is obtained by direct differentiation of a non‐invariant expression for the Mohr–Coulomb yield function. A FORTRAN 77 subroutine is also provided.
Finite element simulation of recirculating flows with heat transfer
Authors: Polansky G. F. , Lamb J. P. , Klein D. E. 
Published: August 2005

AbstractThe finite element method was investigated as a means of simulating incompressible laminar and turbulent flow with heat transfer. Governing equations include the complete, two‐dimensional Navier–Stokes equations expressed in terms of primitive variables. The turbulent viscosity is determined by a two‐equation (k‐ϵ) model of turbulence. Both high Reynolds' number and low Reynolds' number forms of the two‐equations model were considered. The formulation was first tested in laminar recirculating flows as well as in a fully developed turbulent channel flow. The code was then applied successfully to flow past a confined backward facing step and to a backward facing ramp. Although the high Reynolds' number turbulence model was found to be incompatible with the current numerical scheme, good results were obtained using the low Reynolds' number model. Results of the current calculations are compared with experimental data and a variety of other computational results.
Numerical treatment of boundary conditions at points connecting more than two electrically distinct regions
Authors: Paulsen Keith D. , Lynch Daniel R. , Strohbehn John W. 
Published: August 2005

AbstractPoints of intersection of three or more lossy dielectric regions (i.e. tissues) often occur in anatomical cross‐sections of the human body obtained with CT‐scans. The boundary conditions for the electric and magnetic fields require special attention at these points, in contrast to points of connectin of only two tissues, thus posing a problems for numerical methods involved with calculating the electromagnetic fields in tissue. In this paper, a simple theoretical analysis, which exposes the dominant analytic behaviour near such points, is followed. The derived analytic behaviour is numerically enforced via a special basis function which is compatible with the finite element method. Results are shown which indicate that the special basis preserves the analytic behaviour while maintaining grid resolution that is typical of the overall mesh.
Concurrent iterative solution of large finite element systems
Authors: Farhat Charbel , Wilson Edward 
Published: August 2005

AbstractA general iterative algorithm for the solution of large finite element systems of arbitrary domain geometry is designed to operate efficiently on modern computers with concurrent processors. The domain is recursively and automatically subdivided into the same number of subdomains as available processors. Convergence is ensured because of the Gauss–Seidel type of iterations operated on each subdomain and corresponding interface. This subdomain iterative solution approach is compatible with the other phases of a complete concurrent finite element analysis (concurrent stiffness formation and assembly and concurrent element post‐processing), from both the data structure and computation points of view. Implementation of the resulting stratagem on MIMD computers is presented. Several examples are run on a hypercube multiprocessor to validate the proposed algorithm and assess its performance. An efficiency of 91 per cent is achieved for a problem with 16,000 degrees‐of‐freedom.
p‐adaptive boundary elements for three‐dimensional potential problems
Authors: Cerrolaza Miguel , Alarcón Enrique 
Published: August 2005

AbstractThis paper deals with the boundary element method (BEM) p‐convergence approach applied to three‐dimensional problems governed by Laplace's equation. The advantages derived from the boundary discretization and hierarchical interpolation functions are collated in order to minimize human effort in preparation of input data and improve numerical results.
Adaptive grid refinement methods for time‐dependent flow problems
Authors: Ewing Richard E. 
Published: August 2005

AbstractIn the multi‐dimensional numerical simulation of certain multi‐phase fluid flow processes, many phenomena are sufficiently localized and transient that self‐adaptive local grid refinement techniques are necessary to resolve the local physical behaviour. For large‐scale simulation problems, efficiency is the key to the choice of specific adaptive strategies. Several different types of self‐adaptive methods will be discussed and briefly compared. The differences in complexity of the data structure and efficiency of the solution techniques will be explained. Concepts for incorporating these methods in existing large‐scale simulators will also be presented. Man man‐years have been invested in developing large‐scale numerical simulators which do an excellent job of resolving most of the larger length‐scale phenomena in our production processes. Although adaptive local refinement methods are critical for many applications, most techniques which have been developed to date either cannot be incorporated in our codes or are so computationally complex that they destroy the efficiency of existing simulators. Recently, new preconditioning techniques have been developed which allow grid refinement methods to be used efficiently in exisiting codes without disrupting the basic solution process. These techniques are highly amenable to vectorization and parallelization of the algorithms. They are also a first step in allowing complex well models to be incorporated into large field‐scale codes and applications.
A geometrically nonlinear finite element analysis of wrinkled membrane surfaces by a no‐compression material model
Authors: Contri P. , Schrefler B. A. 
Published: August 2005

AbstractA total Lagrangian formulation and a continuum approach are used in a geometrically nonlinear finite element analysis of wrinkled regions in membranes. The analysis makes use of a no‐compression material model together with large out‐of‐plane displacements of the elements to simulate a problem which is in fact due to the lack of flexural stiffness. This model simulates the stress state in surface areas with distributed wrinkles better than a model where the tendency of the membrane to avoid compressive stresses is simulated only by large out‐of‐plane displacements of the elements. A distinction between single folds and wrinkled regions is introduced.
Use of quasi‐Newton methods for large strain elastic‐plastic finite element computations
Authors: Gelin J. C. , Picart P. 
Published: August 2005

AbstractIn this paper, quasi‐Newton methods are used to solve large strain elastic‐plastic problems. The governing nonlinear equations are derived from the principle of virtual work written in an updated Lagrangian manner. The constitutive equations result directly from the definition of free energy and plastic potential that involve a convex functional form. A mixed algorithm is proposed that combines the Newton‐Raphson method and modified Newton‐;Raphson method with symmetric quasi‐Newton update. The efficiency of the algorithm, measured in terms of rate of convergence and computation time is studied on numerical tests. The procedure has a very wide field of application in nonlinear elastic‐plastic analysis.
On the folding of numerically generated grids: Use of a reference grid
Authors: Castillo José E. , Steinberg Stanly , Roache Patrick J. 
Published: August 2005

AbstractWhen variational grid generation techniques are used to produce grids suitable for solving numerical partial differential equations in irregular geometries, a reference grid can be used to determine the properties of the desired grid. Grid folding is a major problem in all methods of numerical grid generation; this paper studies the use of a reference grid, in variational smoothing methods, to prevent such foldings. The effects of various types of reference grid are compared and natural reference grids are shown to prevent foldings in the examples studied. The analysis is performed for a model problem with only one free point, and is then applied for finer grids. In addition, a short description of a discrete variational method is given. The reference grid concept applies to this discrete formulation.
Free surface flow — exposing the hidden nonlinearity
Authors: Liggett James A. 
Published: August 2005

AbstractMost calculations of free surface flow use an inconsistent equation. The inconsistency comes about through the need to apply the boundary conditions on the known boundary instead of on an unknown (advanced time step) boundary. That condition represents a nonlinearity and its treatment should be made consonant with that of the other nonlinearities. Although algebraically difficult, that nonlinearity can be treated in a rational manner with the result that the accuracy is improved.
Upwind and downwind effects of numerical approximations to wave equations
Authors: Pearson Carl E. 
Published: August 2005

AbstractA wave equation such as ut + cux = 0 propagates effects downwind only, but upwind effects resulting from a numerical approximation to the equation can be equally strong. Several common numerical approximations are considered, and asymptotic effects for small timesteps are evaluated. An extension to vector equations in several variables (related to the Euler equations of computational fluid mechanics) is made.
A restarted version of a generalized preconditioned conjugate gradient method
Authors: Axelsson O. 
Published: August 2005

AbstractA generalized preconditioned conjugate gradient method for the iterative solution of a preconditioned linear system Bx = b was recently derived and analysed by the author. Here is presented a special version of it which is efficient in cases where the matrix‐vector multiplication with the given matrix is costly, as in various substructuring methods, where the matrix is usually not present in explicit form but the action of it can be computed.For a restarted version, it is shown that the residuals decrease monotonically for any nonsingular matrix B except when a certain inner product is zero. It is shown why it is advantageous to let the maximal number of search directions in each cycle be not smaller than the number of clusters of eigenvalues of B in the complex plane. An upper bound is derived for the rate of convergence of the algorithm when the clusters can be transformed to an ellipse by a polynomial mapping.
Transformation of incremental plasticity relation from defining space to general Cartesian stress space
Authors: Chan A. H. C. , Zienkiewicz O. C. , Pastor M. 
Published: August 2005

AbstractIncremental plasticity relations are frequently defined in terms of stress invariants and their related strain quantities, and in computation need to be transformed to a Cartesian co‐ordinate system. This paper indicates how much transformation can be implemented simply and consistently without redefining yield and plastic potential. Indeed, the procedure developed is applicable to the transformation between any two stress spaces.
A simple procedure for reducing numerical integration errors near singularities
Authors: Manno Vincent P. 
Published: August 2005

AbstractNumerical integration of functions near singularity points presents a challenge to even advanced quadrature algorithms. Often it would be advantageous to have a simple technique with which to test the accuracy of these estimates. One such technique is described. It consists of subtracting an integrable complementary function from the original integrand, which reduces the curvature of the function to be integrated. This allows simpler numerical integration techniques to be employed for verification. In addition, the technique can be used directly to improve the accuracy of the baseline quadrature. The method provides a means of estimating the order of the functional singularity, which may be unknown.
FEM‐FCT: Combining unstructured grids with high resolution
Authors: Löhner R. , Morgan K. , Vahdati M. , Boris J. P. , Book D. L. 
Published: August 2005

AbstractWe present the extension of flux‐corrected transport (FCT) schemes to unstructured grids. The spatial discretization is performed via finite elements. In particular, we have chosen triangular elements in two dimensions. The limiting procedure is based on Zalesak's extension to more than one dimension of the FCT schemes developed by Boris and Book. The resulting scheme, FEM‐FCT, is capable of resolving moving and stationary shocks within two elements, and several examples are given that demonstrate the accuracy attainable, even for complicated geometries.
Numerical calculation of profiles corresponding to given pressure distributions
Authors: Meyer J. P. , Mathews E. H. , Van Zyl G. P. 
Published: August 2005

AbstractThe pressure distribution over the profile of a body in fluid flow influences the forces, moments and flow separation on it. It is therefore often advantageous to design a profile in such a way that a predetermined pressure distribution is obtained over the final profile. In this paper a numerical procedure is proposed for calculating the profile corresponding to a given pressure distribution. The procedure employs a transformed version of the potential flow equation for the stream function, which makes the method very effective. Predicted profiles are verified against an analytical solution and against the profile of a NACA 0015 aerofoil. The measured pressure distribution on a calculated axisymmetrical profile is also found to compare favourably with its prescribed pressure distribution.
A new generalized conforming triangular element for thin plates
Authors: Yuqiu Long , Junqing Zhao 
Published: August 2005

AbstractThe concept of a generalized conforming element14 is used to introduce a generalized compatibility condition under constant moment, and a new version of the generalized conforming triangular element for thin plate with nine degrees of freedom is developed. The formulation is as simple as for the conventional non‐conforming element, and it can be implemented in a routine manner. By satisfying the generalized compatibility condition under constant moments, the present element can always pass the patch test, and convergence towards an exact solution is guaranteed. The element gives highly accurate results, requires fewer degrees of freedom, and is not sensitive to geometrical distortion.
A point concerning quadratic elements in two‐dimensional boundary element methods
Authors: Deb Anindya , Wang Hui‐Ching 
Published: August 2005

AbstractIn two‐dimensional boundary element methods, the use of quadratic elements for modelling geometric shape and interpolating boundary variables is quite common. For straight boundaries, an interesting indeterminancy of the normal at an end‐node may occur in the usual numerical strategy if the intermediate node lies at a distance of a quarter of the element length from that node. Inaccuracies in the values of nodal boundary stresses caused by errors in the direction cosines of normals are most easily avoided by choosing the intermediate node to lie sufficiently far away from the one‐quarter point from either end‐node.
On the imposition of a flowrate by an augmented Lagrangian method
Authors: Fortin André 
Published: August 2005

AbstractThis paper introduces an augmented Lagrangian method for the imposition of a given flowrate in the numerical simulation of problems where no a priori knowledge of the velocity profile at the inlet of the domain is availble. This method can be seen as a convenient way to generate boundary conditions consistent with the Navier‐Stokes equations when only the flowrate is known. The theoretical formulation of the problem and a numerical algorithm are presented. The efficiency of the proposed method is verified by numerical simulations.
Inviscid transonic flow over a wavy wall decaying downstream
Authors: Park Jeong‐Joo , Chang Keun‐Shik 
Published: August 2005

AbstractInviscid transonic flow over a wavy wall with either subsonic or supersonic freestream speeds is studied by solving the Euler equations numerically. The streamwise flow development through a series of shock waves and entropy production are investigated in depth. In the case of supersonic freestream, isentropy contours of both horseshoe and staircase forms are found. The limitations and validity of this inviscid rotational flow model are discussed by comparing the results with those for viscous turbulent flow calculated previously.
A consistent mass EBE algorithm for linear parabolic systems
Authors: Gladwell I. , Smith I. M. , Gilvary B. , Wong S. W. 
Published: August 2005

AbstractTo date, EBE algorithms for parabolic systems have assumed that the mass or capacity matrix may be lumped (diagonalized). An algorithm is presented in which this lumping process is not necessary. The practical implications of these alternatives are discussed.
Two‐level finite element method for plane cracks
Authors: Leung A. Y. T. , Wong S. C. 
Published: August 2005

AbstractA new method to evaluate the stress intensity factors for plates of arbitary shape by conventional finite elements is introduced. The problems of the large number of unknowns and the round‐off errors associated with fine meshes are eliminated by means of global interpolation functions. These global interpolation functions are actually the analytical solutions of the displacement patterns near the crack tips. While the analytical solutions do not satisfy the boundary conditions in general, the present method considers the boundary conditions by master nodes. Very few unknowns can predict accurate results and no unconventional finite elements are required. The stress intensity factors can be calculated from the nodal displacements of the super‐element in one go. Plates with single and double notch edges and centre crack are taken as examples. The method can be generalized to other crack problems without difficulty.
A new boundary element method coupled with FEM packages
Authors: Gangming Luo 
Published: August 2005

AbstractThe asymmetry of the stiffness matrix in the boundary element method makes the coupling of the boundary and finite element methods difficult. In the paper, the author presents a new boundary element method model in which the stiffness matrix in the model is close to symmetry. After symmetrization, the stiffness matrix can be used as an ordinary finite element type element stiffness matrix to be assembled in the total stiffness matrix. Compared with the directly symmetrized model,1,2 the model in the paper has higher accuracy.
Finite element computations for second‐order hyperbolic equations with non‐smooth solutions
Authors: Bales L. A. 
Published: August 2005

AbstractComputed discrete negative norm errors for the approximate solution of second‐order hyperbolic equations with non‐smooth solutions are presented. The numerical approximations are based on a finite element discretization in the space variable and a two‐step cosine method in the time variable. The approximate solution develops large oscillations when, for example, the solution has jump discontinuities. The error in some negative norms is small and this suggests that good accuracy may be obtained (where the solution is smooth) if smoothing operators are applied to the approximate solution. The results of applying several smoothing operators are presented.
The control of spurious modes in the 20‐noded solid isoparametric element
Authors: Kelen P. 
Published: August 2005

AbstractThe 20‐noded solid isoparametric element can be over‐stiff if a standard integration rule (such as 13, 3 × 3 × 3 or more Gauss points) is used to evaluate the stiffness matrix. Reduced integration (2 × 2 × 2 Gauss points) of the stiffness matrix often gives improved flexibility. Unfortunately, reduced integration can also predict spurious low‐energy modes in certain cases. A simple control method is suggested for the restraint of spurious modes which gives good results with the majority of practical meshes.
Convergence studies of least‐squares finite elements for first‐order systems
Authors: Carey G. F. , Shen Y. 
Published: August 2005

AbstractA least‐squares finite element method for first‐order systems describing two‐point boundary‐value problems is constructed. Comparison studies are made with the corresponding mixed Galerkin formulation for the same system. Numerical experiments on representative test problems reveal that the least‐squares method has superior convergence behaviour to the mixed method. Some superconvergence properties of the least‐squares method are identified.
A finite element algebraic closure model for turbulent separated‐reattaching flows
Authors: Olson M. D. , Zhong Qin 
Published: August 2005

AbstractThe Baldwin‐Lomax algebraic turbulence model has been modified for two‐dimensional incompressible separated‐reattaching flows. The finite element method and the modified turbulence model are combined in a new program. The streamline upwind technique is adopted to eliminate solution oscillations due to coarse element grids. A new computational procedure is adopted to reach high Reynolds numbers efficiently. Preliminary results with experimental comparisons are presented for a turbulent blockage flow problem.
The use of network theory in the finite‐element analysis of coupled thermo‐electric fields
Authors: de Alwis A. A. P. , Fryer P. J. 
Published: August 2005

AbstractA possible alternative to the conventional way of modelling heat generation in the solution of coupled electric and thermal fields is presented. The numerical method presented uses a resistance network analogy and results in a 7% saving in computing time. An analytical formulation presented saves a further 4%. This will be important in the solution of large problems.
BEM for general anisotropic 2D elasticity using particular integrals
Authors: Deb A. , Banerjee P. K. 
Published: August 2005

AbstractIn the context of the direct boundary‐element method (DBEM) for most general two‐dimensional elastostatics, new particular integrals are presented in this paper to account for inertial and centrifugal body forces, as well as for those cases of three‐dimensional behaviour where the assumption of plane strain (or stress) may remain approximately valid despite the presence of non‐zero strain (or stress) in the out‐ofplane direction. These integrals have been implemented in a general‐purpose multi‐region boundary‐element code (namely, GPBEST) and tested via examples.