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  • 1995-1999  (737)
  • 1995  (737)
  • Engineering General  (737)
  • Nuclear reactions
  • 101
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 497-506 
    ISSN: 1069-8299
    Keywords: error estimation ; super convergent patch recovery scheme ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A comparative study of error estimators using a patch recovery scheme with those using simple nodal averaging is made for the four-noded Lagrangian quadrilateral element through two plane stress elasticity problems. It is demonstrated that error estimators using a patch recovery scheme are generally more effective and have an estimated stress field that is closer to the exact one than those using simple nodal averaging.
    Additional Material: 8 Ill.
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  • 102
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 479-490 
    ISSN: 1069-8299
    Keywords: Modal reaction method ; modal participation factor ; support motion ; discrete system ; modal equivalent mass ; quasi-static decomposition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient method, called the modal reaction method, for calculating the modal participation factors for support motion problems is proposed. It is found that modal reactions at supports proportionally describe the magnitudes of the modal participation factors. Thus, the modal participation factor for support motion problems can be calculated very efficiently, saving more than 99 per cent, for the given example with 640 degreees of freedom, of the CPU time compared with using the popular quasistatic decomposition method.
    Additional Material: 6 Ill.
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  • 103
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 491-495 
    ISSN: 1069-8299
    Keywords: plate bending ; similar triangles ; scaling matrix ; stiffness and mass matrices ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: It has been noticed that the stiffness and mass matrices of a triangular plate bending element can be generated from the known stiffness and mass matrices of a similar triangular element making use of scaling matrices. This could be used to advantage in solving problems involving large degrees of freedom if the structure could be discretized into similar triangles. The idea is extended to study the free vibration of a square plate clamped on all edges with a square central cutout.
    Additional Material: 2 Ill.
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  • 104
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 507-513 
    ISSN: 1069-8299
    Keywords: Dynamic stiffness ; Timoshenko beams ; vibrations ; shear deformations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The Timoshenko beam model incorporates the effect of shear deformations and rotary inertia in the vibration response of beams. For constant cross-section beams it was shown that the effect is dependent on the aspect ratio of the beams, and for beams with large ratio the effect is small. In this work exact vibration frequencies for variable cross-section beams are found using the dynamic stiffness matrix approach. An example is given and compared with known results of beams with various taper ratios.
    Additional Material: 4 Ill.
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  • 105
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 545-546 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 106
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 525-534 
    ISSN: 1069-8299
    Keywords: space-time finite elements ; generalised Galerkin scheme ; sub-spaces discretisation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method is presented to evaluate space-time finite element matrices in a general 4D context. Unlike the classical Jacobian-based ‘textbook’ approach, the method described herein uses curvilinear gradient operators to properly handle finite elements having fewer local dimensions (i.e. two or three) than the global embedding domain. This unconventional, but powerful, method is described in details and is illustrated by an application simulating 4D pure convection in a curved diverging-converging flow field.
    Additional Material: 4 Ill.
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  • 107
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 515-524 
    ISSN: 1069-8299
    Keywords: integral equations ; scattering ; parallel processing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Electromagnetic and acoustic scattering from bodies many wavelengths long presents some of the largest computational problems, with costs scaling with the fourth to sixth power of incident frequency. Parallel processing offers one contributory route to the increase in computational power required for such analyses. The paper presents a parallel implementation of the integral formulation of the transient wave equation. It is demonstrated that it is the repeated evaluation of far field effects which is the dominant cost, and that with appropriate domain partitioning this process can be parallelised very effectively. Results for scattering problems comprising up to 1658 nodes are presented, evaluated on 64- and 128-processor systems.
    Additional Material: 6 Ill.
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  • 108
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 535-544 
    ISSN: 1069-8299
    Keywords: partial differential equations ; heat equation ; finite differences ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a new finite difference solution for the 3D non-linear heat equation. This solution is based on the approach of making finite difference substitutions into the solution of the partial differential equation, rather than into the partial differential equation itself, which is the classical approach. Numerical results show that the new FD equation is approximately ten times more accurate than the classical solutions.
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  • 109
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 110
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 547-548 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 111
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 563-573 
    ISSN: 1069-8299
    Keywords: constraints ; boundary conditions ; rigid inclusions ; inextensibility ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Constraints arise naturally in the context of rigid inclusions, incompressibility, inextensible fibres and deformed finite elements. Typical methods for handling constraints in the governing matrix equation include Lagrange multipliers, penalty weights and elimination of variables. Each procedure has a particular undesirable feature. Proposed here is an approach in which each constraint is handled directly and sequentially through a modification of the rows and columns of the governing matrix and force vector. Positive definiteness, symmetry and the dimensions of the matrix remain unchanged. Elementary examples involving both the static and dynamic response of a bar are given to illustrate the procedure.
    Additional Material: 4 Ill.
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  • 112
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 549-562 
    ISSN: 1069-8299
    Keywords: plate problem ; Reissner-Mindlin ; finite elements ; hierarchic elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The focus of the present work is directed towards the construction of a family of special finite elements for the numerical solution of the Reissner-Mindlin plate problem. The model describes the deformation of a plate when transverse shear deformation is taken into account. The model is widely used for thin to moderately thick plates. Despite its simple formulation, the numerical approximation is not straightforward. When standard low-order finite elements are used for the approximation the solution degenerates very rapidly for small thickness (locking phenomenon). To overcome such behaviour, non-standard formulations of the problem are usually combined with low-order finite elements to weaken or possibly eliminate the locking of the numerical solution.In recent years high-order finite elements have been introduced and successfully applied in several fields. Previously we have constructed a family of hierarchic high-order finite elements to solve the Reissner-Mindlin problem in its plain formulation. The locking was strongly reduced but was still active for very thin plates. Meanwhile some mixed-interpolated finite elements have been developed and shown to be locking free. In this paper we combine the two approaches, namely, the hierarchic high-order elements and the mixed-interpolated elements. The result is a family of special finite elements that exhibits both properties of convergence and robustness.
    Additional Material: 9 Ill.
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  • 113
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 575-584 
    ISSN: 1069-8299
    Keywords: Laplace's equation ; boundary integral ; Fourier series ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Laplace's equation in two dimensions can be solved by a boundary integral method which imposes the required consistency relation between the boundary function and its outward normal gradient. Rather than incorporating this into a standard boundary element approach for the Dirichlet problem, the known boundary function and the unknown boundary gradient are here expressed as truncated Fourier series expansions. The consistency relation then becomes an algebraic relation between expansion coefficients, whose matrix entries can be found by appropriate applications of the fast Fourier transform. This is solved for the boundary gradient coefficients; the solution can then be evaluated at any interior point. Numerical experiments explore the effect of the truncation level, and indicate that reasonable accuracy can be attained without needing a prohibitively large number of Fourier coefficients.
    Additional Material: 6 Ill.
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  • 114
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 597-606 
    ISSN: 1069-8299
    Keywords: Mindlin-Reissner (MR) plate theory ; finite strip (FS) method ; finite element (FE) method ; boundary layer (BL) effects ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The Mindlinn-Reissner finite strip method is used to study in a qualitative manner boundary layer effects_in uniform and variable-thickness plates with rectangular and curved planforms.
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  • 115
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 585-595 
    ISSN: 1069-8299
    Keywords: CFD ; transonic flows ; von Mises coordinates ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new formulation is proposed for two dimensional transonic potential flow calculations. The present approach takes advantage of both streamfunction and potential function formulations. A modified form of the partial differential equations and simplified boundary conditions are derived. Numerical examples show that a reliable method has been developed, capable of calculating highly transonic potential flows.
    Additional Material: 6 Ill.
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  • 116
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    Communications in Numerical Methods in Engineering 11 (1995), S. 619-627 
    ISSN: 1069-8299
    Keywords: post processing ; node patch ; element patch ; superconvergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Methods to calculate improved postprocessed stresses in elements for the superconvergent patch recovery technique are developed. Based on improved stresses on node patches, the improved element stresses are obtained by using weighting of patch solutions from different patch assembly points. An alternative method is to directly calculate the element stresses for an element patch based on weighted information. Numerical examples show that the performances of the two procedures are of about the same quality.
    Additional Material: 9 Ill.
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  • 117
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    Communications in Numerical Methods in Engineering 11 (1995), S. 607-617 
    ISSN: 1069-8299
    Keywords: multiple-edge crack problem ; singular integral equation approach ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The complex potential for a single-edge crack problem of an elastic half-plane is proposed. The complex potential is obtained by distributing the dislocation density along the crack configuration, and satisfies the traction-free condition along the boundary of the half-plane. The multiple-edge crack problem of an elastic half-plane can be considered as a superposition of many single-edge crack problems. Bearing this in mind, a singular integral equation for the multiple-edge crack problem is formulated, where the distributing dislocation density serves as the unknown function and the traction applied on the crack faces serves as the right-hand side in the resulting integral equation. A semi-open quadrature rule is used to solve the singular integral equation. Several numerical examples are given. The ‘shadow effect’ is observed, which means the stress intensity factor at a crack tip is negligible if the crack is placed in some particular ‘shadow area’.
    Additional Material: 8 Ill.
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  • 118
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    Communications in Numerical Methods in Engineering 11 (1995), S. 629-629 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 119
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    Communications in Numerical Methods in Engineering 11 (1995), S. 631-632 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 120
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    Communications in Numerical Methods in Engineering 11 (1995), S. 630-630 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 121
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Type of Medium: Electronic Resource
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  • 122
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    Communications in Numerical Methods in Engineering 11 (1995), S. 633-641 
    ISSN: 1069-8299
    Keywords: laminate theory ; global-local superposition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Combining a high-order shear deformation theory and a layerwise theory, a laminate theory of zigzag type is presented. Like the high-order shear deformation theories, the number of independent variables of the present theory is independent of layer number. The numerical efficiency is thus guaranteed. Similar to the layerwise theories, the in-plane displacement components vary from layer to layer. Hence, the imposition of continuity conditions of interlaminar shear stresses on the laminate interfaces becomes possible. Consequently, the accuracy of displacement and stress components can be improved. Numerical studies on composite laminates made of alternate sequences based on 0° and 90° layers are performed. It can be concluded that the present theory gives accurate in-plane displacement and stress for 6-layer, 19-layer and 32-layer laminates. Its predictions on transverse displacement, transverse shear stress and transverse normal stress seem to be gradually improved as the number of alternate layers increases.
    Additional Material: 8 Ill.
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  • 123
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    Communications in Numerical Methods in Engineering 11 (1995), S. 643-653 
    ISSN: 1069-8299
    Keywords: finite strips ; structural analysis ; shear walls ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new finite strip for the analysis of 2D elastic problems is presented. Displacement in each of the two in-plane directions is interpolated by a set of computed shape functions in the longitudinal direction and, as usual, standard 1D Lagrangian shape functions in the transverse direction. Unlike all other finite strips, the unknown parameters of the present finite strip are represented by the physical displacement variables at nodal points. Furthermore, C0-continuity is maintained across the boundaries between adjacent strips. Deep beams with geometric discontinuity can be treated in a standard finite element manner. Several numerical examples are given to demonstrate its accuracy in analysing deep beams and shear walls.
    Additional Material: 8 Ill.
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  • 124
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    Communications in Numerical Methods in Engineering 11 (1995), S. 665-674 
    ISSN: 1069-8299
    Keywords: boundary element method ; multiple reciprocity ; brinkman flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper we apply the boundary element multiple reciprocity method to the Brinkman equation, showing that the technique yields an incomplete series representation of the corresponding fundamental solution, incompleteness that is due to a weakness in the way the method is usually applied. For the present case an additional integral relation is found that makes the series complete. Unfortunately, the relation is particular to this problem and cannot be generalized in a simple way. The result found in this work suggests that in multiple reciprocity it is necessary to have an extra relation in integral form to define the missing terms in the series representation. This extra relation has to yield zero contribution for cases when the multiple reciprocity method gives the complete series representation.
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  • 125
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    Communications in Numerical Methods in Engineering 11 (1995), S. 655-664 
    ISSN: 1069-8299
    Keywords: 3D solids ; large displacement ; elastic deformation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A geometrically non-linear version of the well known 8-node Wilson brick element is presented. The element is based on a sound variational formulation and the modified method of incompatible modes, which are shown to render quite a satisfying, locking-free performance in some challenging large displacement problems.
    Additional Material: 5 Ill.
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  • 126
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    Communications in Numerical Methods in Engineering 11 (1995), S. 683-690 
    ISSN: 1069-8299
    Keywords: frictional contact ; BEM ; mathematical programming ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The contact condition is described as a linear complementarity form with penalty parameters. Based on the boundary element discretization, a mathematical programming method for elastic contact problems with friction is presented. This method avoids the tiresome iterative procedures used in previous work and, if there is no unloading, only one incremental step is necessary for a solution. Two examples are given to demonstrate the correctness and effectiveness of the method.
    Additional Material: 7 Ill.
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  • 127
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    Communications in Numerical Methods in Engineering 11 (1995), S. 675-681 
    ISSN: 1069-8299
    Keywords: blow-up ; method of fundamental solutions ; BEM ; thin plate spline ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A numerical method based on the method of fundamental solutions, thin plate spine interpolation and monotone iteration is devised to find the minimal solution of the steady-state blow-up problem. The method of fundamental solutions requires neither domain nor boundary discretization and results in high accuracy and efficiency. For illustration, critical values of the Frank-Kamenetskii parameter are given for different geometrical boundaries in the two-dimensional case.
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  • 128
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    Communications in Numerical Methods in Engineering 11 (1995), S. 713-714 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 129
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    Communications in Numerical Methods in Engineering 11 (1995), S. 691-701 
    ISSN: 1069-8299
    Keywords: electrostatic simulation ; charge density ; potential theory ; MEMS ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Computing the charge density on the surfaces of conductors is fundamental to many electrostatic applications. Difficulties arise in two-dimensional simulation due to the O(log|r|) potential. Fully understanding the 2D potential problem, and reasonably connecting the mathematical formulation with physical interpretation, are key to handling this difficulty properly. In the absence of these factors it is easy for one to propose an ill-posed problem. In this paper, a complete investigation of potential theory, from 3D to 2D, is made for computing charge density on the surfaces of conductors. Various integral formulations are derived - these are applicable in different situations. It is shown that, in general, the electrostatic potential need not be finite valued at infinity for 2D problems. Numerical examples for the 2D case are constructed to show that the formulations are consistent. Criteria for choosing the most appropriate formulation for a given problem are suggested.
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  • 130
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    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 131
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    Communications in Numerical Methods in Engineering 11 (1995), S. 703-712 
    ISSN: 1069-8299
    Keywords: non-linear structural analysis ; incremental-iterative solution ; conjugate gradient-like method ; arc length algorithm ; snap-through ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A special incremental-iterative solution method for non-linear finite element structural analysis including snap-through is presented. As an alternative to the direct solution methods, a special iterative strategy along with the pseudoload method is employed within each Newton-Raphson iteration step. Two new developments concerning the pseudoload method and the special iterative strategy, which were originally conceived and applied for the non-linear analysis of shells of revolution using a semi-analytical method, are presented. Firstly, the underlying principles of the method are utilized in solving general non-linear structural mechanics problems. Secondly, the capability of the method is enhanced for tracing the load-displacement curve beyond the critical load by integrating the arc length method. Special modifications are proposed to handle situations with a non-positive-definite tangential stiffness matrix. Numerical examples with snap-through and snap-back phases in the load-deflection path are presented to demonstrate the applicability and accuracy of this approach. Results obtained from this numerical study verify the usefulness of this method as an alternative to the conventional direct methods or iterative methods of solving linearized equations in an incremental non-linear analysis.
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  • 132
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    Communications in Numerical Methods in Engineering 11 (1995), S. 727-733 
    ISSN: 1069-8299
    Keywords: eddy currents ; finite element method ; equivalence ; uniqueness ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new variational problem corresponding to a three-dimensional eddy-current boundary-value problem is treated in the paper. The equivalence between the variational problem and the boundary-value problem is proved, and so is the uniqueness of the solution. These form the foundation of the H - Ψ method.
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  • 133
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    Communications in Numerical Methods in Engineering 11 (1995), S. 735-741 
    ISSN: 1069-8299
    Keywords: unbounded domain ; artificial boundary ; finite elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Exact non-local boundary conditions are derived and used on an artificial boundary to solve the two-dimensional Laplace and Helmholtz equations in an unbounded domain. The artificial boundary is chosen to be an ellipse, as opposed to previous works which employed circular boundaries. The use of elliptic artificial boundaries enables one to enclose slender obstacles very efficiently, especially in the case of Laplace's equation.
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  • 134
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    Communications in Numerical Methods in Engineering 11 (1995), S. 715-725 
    ISSN: 1069-8299
    Keywords: transient ; heat transfer ; inverse Laplace transforms ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We present a new procedure for the numerical calculation of the transient response of systems characterized by partial differential equations in several space variables and time. The procedure is based on: (i) spatially discretizing the system, (ii) deriving an equivalent circuit for each volume element, (iii) applying a time Laplace transformation and obtaining an admittance matrix, (iv) writing the expressions for the Laplace transforms of the desired variables according to Cramer's determinant rule, (v) interpreting the determinants as generalized eigenvalue problems, (vi) obtaining the proper eigenvalues of the system (poles and zeros), and (vii) finding the time-dependent solutions by ‘trivial’ inverse Laplace transformations. Although the procedure proposed applies to many partial differential equations (fluid flow in porous media, conductive heat transfer with convection, pressure tests in oil wells, electrical conduction, etc.), in the paper we illustrate the procedure in detail for a conduction heat transfer system (nine nodes). The procedure presented is much more efficient numerically than the direct numerical integration (in space and time) of the ruling PDE, or than solutions which require ‘standard’ numerical inverse Laplace transformation after matrix inversion.
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  • 135
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    Communications in Numerical Methods in Engineering 11 (1995), S. 757-763 
    ISSN: 1069-8299
    Keywords: Newton-Raphson method ; curvature ; line search algorithm ; non-linear problem ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A numerical method for finding the roots of any function is developed. This method considers a circle using the concept of curvature instead of the tangential line in the Newton-Raphson method. The compared results between the proposed method and the Newton-Raphson method are listed. The proposed method has a wider convergent region of initial points and finds more proper solutions than the Newton-Raphson method. In particular, the paper proposes that the curvature method is replaced by the modified Newton method discussed by Ralston in dealing with multiple roots.
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  • 136
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    Communications in Numerical Methods in Engineering 11 (1995), S. 743-756 
    ISSN: 1069-8299
    Keywords: analytical and numerical combined method (ANCM) ; free vibration ; forced vibration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The free vibration and the forced dynamic responses of a uniform cantilever Timoshenko beam carrying any number of concentrated masses, translational and rotational springs and subjected to various external loadings are studied by means of the analytical-and-numerical-combined method (ANCM), where the locations and the magnitudes of the masses, springs and loadings are arbitrary. First of all, the (exact) closed-form solutions for the natural frequencies and the normal mode shapes of the ‘unconstrained’ Timoshenko beam (without carrying any concentrated elements) are determined; then the eigenvalue equation for free vibration analysis and the equation of motion for forced vibration analysis of the ‘constrained’ Timoshenko beam (carrying the prescribed concentrated elements) are derived analytically by applying the expansion theorem and the mode superposition methodology; finally the approximate natural frequencies and mode shapes of the ‘constrained’ Timoshenko beam and its dynamic responses due to external excitations are calculated numerically. It is found that the ANCM presented in the paper has the advantages of both the pure analytical method (to be able to save computing time) and the pure numerical method (to be able to solve various practical problems).
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  • 137
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    Communications in Numerical Methods in Engineering 11 (1995), S. 765-774 
    ISSN: 1069-8299
    Keywords: spectral methods ; Chebȳshev collocation ; Galerkin collocation ; boundary layer equations ; preconditioned minimum residual ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A comparison is made between the performance of the (aliased) Chebȳshev collocation method (CM) and the more recent Galerkin collocation method (GCM), which is a least-squares collocation method, in solving the laminar, incompressible, steady boundary-layer equations, which are parabolic in nature. An iterative procedure based on the preconditioned residual minimization method has been used. It is shown that the GCM is superior to the CM on several counts. Unlike the CM, the GCM minimizes the residual uniformly over the entire domain. The global accuracy of the solution is found to be higher in the GCM, at lower grid resolutions. The method also achieves much higher convergence rates. Unlike in the collocation method, the final residual values obtained in the GCM are good indicators of the level of accuracy achieved in the solution. It is highly likely that these results will be repeatable in other systems of parabolic partial differential equations.
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  • 138
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    Communications in Numerical Methods in Engineering 11 (1995), S. 789-790 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 139
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    Keywords: Engineering ; Engineering General
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  • 140
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    Communications in Numerical Methods in Engineering 11 (1995), S. 791-792 
    ISSN: 1069-8299
    Keywords: checkerboard patterns ; P2 - P1 discontinuous pressure elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this note we obtain the checkerboard patterns of P2 - P1 discontinuous pressure elements for the Stokes problem The results are more complete than those previously presented.
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  • 141
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    Communications in Numerical Methods in Engineering 11 (1995), S. 775-787 
    ISSN: 1069-8299
    Keywords: finite element theory ; explicit stiffness matrices ; hybrid stress method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general methodology for deriving explicit element stiffness matrices in hybrid stress formulations has recently been developed by the author. The technique utilizes special stress field transformations to eliminate the complementary energy matrix inherent to hybrid formulations, thus simplifying the stiffness definition such that an explicit evaluation can be accomplished. The elimination of numerical integration and matrix inversion results in a substantial decrease in computational cost. The methodology is applied to derive explicit algebraic expressions for the Pian-Tong hexahedral element stiffness matrix.
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  • 142
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    Communications in Numerical Methods in Engineering 11 (1995), S. 805-812 
    ISSN: 1069-8299
    Keywords: solidification ; dendritic growth ; probabilistic modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A model of solidification is developed from a statistical mechanics basis that incorporates nucleation of columnar and equiaxed grains, thermal and solute diffusion, and latent heat of the phase change. The model is applied to the solidification of austenitic steel. The dendritic growth of columnar and equiaxed grains is simulated, including the segregation of solute ahead of the solid-liquid interface. The irregular branched morphology of the solid forms in a manner analogous to dendritic morphologies that arise from constitutional undercooling in real materials. There is competition between columnar and equiaxed growth. When growing grains approach, the solute layer and the thermal field act to prevent them overlapping.
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  • 143
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    Communications in Numerical Methods in Engineering 11 (1995), S. 793-803 
    ISSN: 1069-8299
    Keywords: arc-length control ; line search ; path-following ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: When solving non-linear algebraic equations resulting from a typical finite element discretization it is quite common that the popular Newton-Raphson iteration fails to converge or requires an excessive number of iterations. To solve this problem, line searches have been proposed in conjunction with load control and quadratic arc-length control, which has proved to be highly successful. In the paper we first review a number of the most popular arc-length controls. Then we highlight the severe drawbacks associated with the coupling of the cylindrical arc-length control and line searches. Next, various other forms of arc-length controls are scrutinized in the light of this coupling. It is shown that for some of the arc-length controls such a combination is extremely simple and straightforward, yet at the same time efficient and effective. For the rest the same complications incurred for the cylindrical arc-length method remain.
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  • 144
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    Communications in Numerical Methods in Engineering 11 (1995), S. 813-820 
    ISSN: 1069-8299
    Keywords: non-circular ducts ; mapping functions ; non-Newtonian fluids ; Levenberg-Marquardt algorithm ; velocity contour values ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The problem of determination of fully developed duct flows of arbitrary shape is considered for fluids obeying various constitutive equations. A numerical method based on the transformation of the physical flow (simply connected) domain into a mapped circular domain is set up. The numerical determination of the unknown transformation between the two domains leads to knowledge of the velocities and stresses in the duct, starting from circular contour values of the velocity in the mapped computational domain. Different constitutive equations are investigated for several flow geometries. The comparisons with existing analytical solutions are found to be consistent for all the geometries tested. The method may provide a useful tool for determination, in steady flow conditions, of the flow characteristics for various types of ducts and constitutive equations.
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  • 145
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    Communications in Numerical Methods in Engineering 11 (1995), S. 821-829 
    ISSN: 1069-8299
    Keywords: rotational transformations ; anisotropic elasticity ; laminates ; constitutive matrices ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In elasticity theory involving anisotropic materials, the rotational transformation of stress, strain and constitutive relations is of major importance. Also, when these problems are represented in matrix form there are several different contracted notations used to express the stress and strain tensors as column matrices. In general, the contracted notations used lead to unnecessary complications and may lead to errors. In the paper, contracted forms which yield orthonormal rotational transformations are advocated. These transformations are illustrated for stress, strain, modulus and compliance and are also applicable for strength transformation. The gains to be made are procedural and mathematically simple, leading to easier understanding.
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  • 146
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    Communications in Numerical Methods in Engineering 11 (1995), S. 831-838 
    ISSN: 1069-8299
    Keywords: coupled system ; fluid-structural interactions ; left and right eigenvector ; natural frequency ; symmetrization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: System equations of motion for a fluid-structural coupled system are formulated and their symmetrization is presented. By using the state-variable augmentation and degree of freedom reduction technique applicable to a damped mechanical system, a new approach is proposed to transform the asymmetrical equations of motion for a coupled system into some symmetrical ones. The significance of the transformation used is discussed. The relationship is established between the left and the right eigenvectors, based on which the modal superposition method can be used in predicting dynamic responses for a general asymmetrical fluid-structural coupled system.
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  • 147
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    Communications in Numerical Methods in Engineering 11 (1995), S. 839-847 
    ISSN: 1069-8299
    Keywords: validation of FE modelling ; optical techniques ; fringe contours ; shape functions ; stress analysis ; displacement analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A novel and simple approach to plot fringe contours from finite element results that simulates the fringe thickness variation as observed in experiments is presented. The procedure does not require solution of any non-linear equation. Shape functions are used as interpolation functions to plot fringe contours from the nodal values of fringe orders. The various fringe contours one usually comes across in stress analysis are also reviewed. The program code in Turbo-Pascal employing the new algorithm is given. Stress and displacement contours at the tip of a crack in an SEN (single-edge-notched) specimen are plotted using the code developed. The fringe contours plotted correspond to those observed in experiments such as photoelasticity, holography and Moire.
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  • 148
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    Communications in Numerical Methods in Engineering 11 (1995), S. 869-870 
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    Keywords: Engineering ; Engineering General
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  • 149
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    Communications in Numerical Methods in Engineering 11 (1995), S. 849-856 
    ISSN: 1069-8299
    Keywords: conjugate gradient methods ; incompressible Navier-Stokes equations ; segregated finite volume procedure ; staggered grid ; vectorization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: PISO (pressure-implicit with splitting of operators) is an algorithm devised to solve the transient incompressible Navier-Stokes and energy equations. In that it uses separate equations for each of two pressure corrections, velocity components and transported scalars, PISO is known as a segregated solution procedure. Preconditioned, generalized conjugate gradient (GCG) methods in combination with schemes for vectorization and storage minimization are described in the paper for the purpose of solving both the symmetric and non-symmetric algebraic equation systems that result from the PISO algorithm. Of particular interest in the paper is a comparison of the present procedure with a procedure described by Chin et al. (1992) in which preconditioned conjugate gradient methods are used to solve the Jacobian matrix used in the Newton iteration of the fully coupled non-linear equations. The two methods are similar in that both techniques are based on a discretization using staggered control volumes with the power-law method for modelling advection-diffusion transport.
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  • 150
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    Communications in Numerical Methods in Engineering 11 (1995), S. 857-868 
    ISSN: 1069-8299
    Keywords: adaptive analysis ; error estimate ; mesh refinement ; finite elements ; plate bending ; computations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new mesh refinement formulation for h-adaptive solutions of linear elliptic problems is presented. The reliability of the methods employed for estimating errors and the convergence rate of the errors during an adaptive process are investigated by means of an asymptotic analysis method. The present adaptive mesh refinement strategy significantly improves adaptivity performance and has higher error convergence rates than those usually used. Numerical examples are shown to illustrate the efficiency of the method shown.
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  • 151
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    Communications in Numerical Methods in Engineering 11 (1995), S. 871-871 
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    Keywords: Engineering ; Engineering General
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  • 152
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    Keywords: Engineering ; Engineering General
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  • 153
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    Communications in Numerical Methods in Engineering 11 (1995), S. 887-897 
    ISSN: 1069-8299
    Keywords: geometrically non-linear problem ; finite elasticity ; p-version ; hp-extension ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A p-version of the finite element method and an hp-extension is applied to a geometrically non-linear model problem. Starting from a standard formulation in finite elasticity, some implementation details are outlined. The robustness and efficiency of this method, as already well known for linear problems, is demonstrated. In two numerical examples high accuracy and exponential rate of convergence in energy are shown. The method presented can be used effectively in problems where standard low-order plane strain elements fail to give accurate results.
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  • 154
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    Communications in Numerical Methods in Engineering 11 (1995), S. 911-915 
    ISSN: 1069-8299
    Keywords: adaptive finite element method ; optimal mesh ; error estimate ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the authors investigate the conditions of optimal mesh, and prove that the element errors in the optimal mesh should be identical for all existing elements. Also, it is shown that the correct mesh refinement formulations should be derived at an element level rather than the global level. Thus the element permissible errors need to be determined. The method to determine these permissible element errors is described.
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  • 155
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    Communications in Numerical Methods in Engineering 11 (1995), S. 873-886 
    ISSN: 1069-8299
    Keywords: k-∊-γ model ; turbulent intermittency ; wake ; aerofoil ; non-staggered FUM ; branch-cut ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The whole turbulent flow field around a two-dimensional aerofoil is solved with a consistent numerical method on a single-grid system and with an intermittency implemented two-equation model, namely the k-∊-γ turbulence model in elliptic form. In order to solve the numerical instability problem arising from the branch-cut in C-type grids using the non-staggered finite-volume method, a new numerical technique is proposed to guarantee the correct velocity-pressure coupling along the branch-cut. The computational results are compared with those by the standard k-∊ model and experimental data. This study demonstrates the relative simplicity of the present C-type single grid system, and the capability is assessed of the k-∊-γ equations for predicting turbulent flows consisting of both wall-free and wall-bounded regions.
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  • 156
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    Communications in Numerical Methods in Engineering 11 (1995), S. 899-909 
    ISSN: 1069-8299
    Keywords: finite element method ; non-linear shell elements ; assumed strain approach ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A quadrilateral degenerated C0 shell element is presented which relies on extensible director kinematics and which incorporates unmodified three-dimensional constitutive models. It is shown that the direct interpolation of the extensible director field causes severe locking behaviour in the case of thin shell structures. An assumed strain interpolation is proposed to overcome the thin-shell defect. Due to this modification the shell element is able to accommodate large rotations without a rotation tensor, even for very thin shells. Several large deformation examples confirm that the developed shell element is competitive with more elaborate formulations which use rotational degrees of freedom.
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  • 157
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    Communications in Numerical Methods in Engineering 11 (1995), S. 927-935 
    ISSN: 1069-8299
    Keywords: incompressible continuum ; fundamental solutions ; boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Novel fundamental solutions for elastodynamics of fully incompressible media are derived, by reason of their many applications to engineering and physical problems. It is demonstrated that, when Poisson's ratio equals 1/2, the frequency domain fundamental solutions (Stokes's solutions) are independent of the dilatational wave velocity, which tends to infinity. Consequently, dynamic problems involving incompressible materials can be rigorously analysed by the boundary element method without special difficulty. Numerical solutions to geotechnical problems of incompressible half-spaces are presented to demonstrate the applicability and accuracy of the formulations.
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  • 158
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    Communications in Numerical Methods in Engineering 11 (1995), S. 917-925 
    ISSN: 1069-8299
    Keywords: stream-tube method ; Levenberg-Marquardt method ; viscoelastic fluids ; trust region (TR) algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Numerical simulation of complex flows of viscoelastic fluids requires us to use efficient algorithms for solving the non-linear governing equations. The stream-tube analysis permits calculation of such flows by considering elementary subdomains in a mapped computational domain where the transformed streamlines are parallel and straight. The consideration of subregions leads us to use optimization procedures. The paper concerns the application of such algorithms to compute main flows in axisymmetric converging geometries, for fluids obeying memory-integral constitutive equations.
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  • 159
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    Communications in Numerical Methods in Engineering 11 (1995), S. 937-950 
    ISSN: 1069-8299
    Keywords: thermal convection ; slender multigrid ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The flow in a shallow, laterally heated air-filled cavity is investigated numerically using a primitive variable formulation of the governing equations of motion. Solutions are obtained for the entire flow field using a coupled solver combined with an FAS non-linear multigrid convergence accelerator. While care is taken to use a high-order, bounded discretization scheme for convective transport, the overall stability and efficiency of the approach is enhanced through the use of defect correction. This combination of features enables solutions to be found on extremely fine grids. Results for the flow in the end region of such cavities are compared qualitatively with the predictions of asymptotic theory for large aspect ratio, A (length:height), up to values of A higher than previously reported (A= 100); the particular case of A = 20 is considered for Rayleigh numbers in the range 103 to 108. Finally it is demonstrated how such solutions can be further enhanced by using locally refined grids in the end regions.
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  • 160
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    Communications in Numerical Methods in Engineering 11 (1995), S. 951-961 
    ISSN: 1069-8299
    Keywords: enhanced strain method ; finite elastoplasticity ; hourglassing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The stability of a class of geometrically non-linear assumed enhanced strain elements is addressed. By means of an eigenvalue analysis of element tangent stiffnesses at finitely deformed configurations, circumstances under which enhanced elements become unstable, with possible development of non-physical hourglass patterns, are identified. Insight into the influence of spurious eigenvalues on the stability of solution of finite elasticity and elastoplasticity problems is provided by simple numerical tests with a patch of elements. Results of simulations of some practical engineering problems are presented and limitations on the applicability of enhanced strain elements in the finite strain regime are discussed.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 963-964 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Keywords: Engineering ; Engineering General
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  • 163
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    Communications in Numerical Methods in Engineering 11 (1995), S. 965-970 
    ISSN: 1069-8299
    Keywords: least-square finite element ; Stokes problem ; mass conservation ; incompressible flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the simulation of incompressible flow in 2D by the least-squares finite element method (LSFEM) in the velocity-vorticity-pressure version is studied. A problem with this method is that it does not conserve mass exactly, i.e. div uh ≠ 0 exactly. In the paper a modified LSFEM is developed which enforces a near zero residual of mass conservation, i.e. div u is nearly zero at every point of the discretization. This is accomplished by adding an extra restriction in the divergence free equation through the Lagrange multiplier strategy.
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  • 164
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    Communications in Numerical Methods in Engineering 11 (1995), S. 971-980 
    ISSN: 1069-8299
    Keywords: stochastic boundary element method ; domain integration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The contributions of distributed sources to the mathematical expectations and variances of the response variables are analysed in the paper using the stochastic boundary element method. The validity and the accuracy of the particular integral approach in representing statistical properties of the domain are investigated. To this end domain integration techniques to calculate the contributions of the distributed sources and their derivatives with respect to random variables that may represent both random configuration of the domain and random material parameter are developed. Several models for the random interior are presented and their influence on the response statistics is investigated. The accuracy of the particular integral approach is demonstrated through numerical comparisons with the direct integration formulation.
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  • 165
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    Communications in Numerical Methods in Engineering 11 (1995), S. 981-993 
    ISSN: 1069-8299
    Keywords: boundary element method ; boundary geometry ; smooth modelling ; Lagrange elements ; Overhauser elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper reveals the conditions under which the approximations of the normal vector and global coordinates of interior points of two segments on a smooth contour can fail using the C1-continuous Overhauser elements. A new continuous modelling of the normal vector is developed using the standard Lagrange elements. The derivation is consistent with the assumptions employed in the boundary element method formulations of potential problems. Test numerical examples are considered in order to analyse the accuracy of the approximations based on the use of standard C0-continuous elements, Overhauser C1-continuous elements and the proposed ‘smooth’ C0 elements.
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  • 166
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    Communications in Numerical Methods in Engineering 11 (1995), S. 995-1003 
    ISSN: 1069-8299
    Keywords: bandwidth ; ordering ; finite elements ; graphs ; algorithms ; sparsity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Graph theoretical algorithms are presented for finite element nodal ordering to reduce the bandwidth of their stiffness matrices. Five different graphs are defined for representing the connectivity of FE models, and the problem of finite element nodal ordering is transformed into that of a graph nodal ordering. The efficiencies of these methods are compared through examples of two- and three-dimensional finite element models.
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  • 167
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1005-1013 
    ISSN: 1069-8299
    Keywords: infinite boundary element ; mapping ; element integration formulae ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: For elastodynamic problems in an elastic half-space, the idea of describing the displacement variation on the free ground surface outside the region being studied with the fundamental solution in a full space is presented in the paper. Then a corresponding mapped infinite boundary element is constructed for the problems of anti-plane motion. The computed results show that such an element can be applied effectively to obtain high-precision solutions.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1015-1024 
    ISSN: 1069-8299
    Keywords: localization ; volumetric locking ; pressure formulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Computation of failure mechanisms is of paramount importance for engineers assessing safety of structures. However, computation of failure loads and mechanisms presents numerical difficulties leading to wrong answers, especially in the case where failure consists in localization of plastic deformation or damage in localized zones. Here, the results depend on factors like mesh alignment and element distortion. The paper addresses the problem of designing a suitable patch test to assess element performance under localized failure. It will be shown how predictions of this test provide a reliable answer to the question of whether a particular element will or will not be suitable for such failure computations.
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  • 169
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1025-1032 
    ISSN: 1069-8299
    Keywords: flux lines ; current distributions ; magnetic inverse problem ; voltage distribution ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The display of isopotential contours is a standard technique in the interpretation of results generated by the finite element analysis of voltage distribution problems. The complementary display of the current flow or flux lines is in many ways more useful intuitively, but has not been used widely in finite element analyses. We describe a simple method for generating flux line distributions, and discuss the method as applied to the reconstruction of current distributions from magnetic field maps.
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  • 170
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1033-1038 
    ISSN: 1069-8299
    Keywords: electric field ; vector potential ; electrostatic ; electric force surface ; curve integral ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite difference algorithm for plotting the electric force surface is presented in three-dimensional electrostatic field computation. Based on the flux concept, the nodal electric flux is calculated numerically through the curve integral of the electric displacement vector which was obtained by a numerical differentiation of the nodal electric potential. This latter is calculated by a finite difference method. The electric force surface may also be plotted.
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  • 171
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1047-1048 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 172
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1039-1045 
    ISSN: 1069-8299
    Keywords: pure advection ; Lagrangian treatment ; control volume ; QUICKEST scheme ; large Courant numbers ; accuracy ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper describes a new numerical algorithm for pure advection at large Courant numbers. The DISCUS scheme uses an accurate and proven control volume algorithm (QUICKEST) within a Lagrangian treatment of advection. By being in sympathy with the information flow dictated by characteristic lines, the scheme performs exceedingly well at Courant numbers greater than one. In contrast to existing Lagrangian schemes which use the characteristics to determine the grid points from which concentrations are interpolated, in DISCUS the characteristics are used to determine the appropriate location for the control volume. The scheme is of comparable accuracy to Eulerian schemes at Courant numbers less than one, but it increasingly outperforms them as the Courant number increases. Indeed, the results reported illustrate the futility of using an Eulerian scheme at high Courant numbers.
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  • 173
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    Numerical Linear Algebra with Applications 2 (1995) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 174
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    Numerical Linear Algebra with Applications 2 (1995), S. 1-16 
    ISSN: 1070-5325
    Keywords: Boundary value problem ; Boundary element method ; Preconditioning ; Iterative method ; Parallel algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The parallel version of precondition techniques is developed for matrices arising from the Galerkin boundary element method for two-dimensional domains with Dirichlet boundary conditions. Results were obtained for implementations on a transputer network as well as on an nCUBE-2 parallel computer showing that iterative solution methods are very well suited for a MIMD computer. A comparison of numerical results for iterative and direct solution methods is presented and underlines the superiority of iterative methods for large systems.
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  • 175
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    Numerical Linear Algebra with Applications 2 (1995), S. 17-28 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The incomplete Cholesky decomposition is known as an excellent smoother in a multigrid iteration and as a preconditioner for the conjugate gradient method. However, the existence of the decomposition is only ensured if the system matrix is an M-matrix. It is well-known that finite element methods usually do not lead to M-matrices. In contrast to this restricting fact, numerical experiments show that, even in cases where the system matrix is not an M-matrix the behaviour of the incomplete Cholesky decomposition apparently does not depend on the structure of the grid. In this paper the behaviour of the method is investigated theoretically for a model problem, where the M-matrix condition is violated systematically by a suitable perturbation. It is shown that in this example the stability of the incomplete Cholesky decomposition is independent of the perturbation and that the analysis of the smoothing property can be carried through. This can be considered as a generalization of the results for the so called square-grid triangulation, as has been established by Wittum in [12] and [11].
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  • 176
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    Numerical Linear Algebra with Applications 2 (1995), S. 79-83 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 177
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    Numerical Linear Algebra with Applications 2 (1995) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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  • 178
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    Numerical Linear Algebra with Applications 2 (1995), S. 29-49 
    ISSN: 1070-5325
    Keywords: Backward error ; Conditioning ; Matrix equations ; Riccati equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper, a new backward error criterion, together with a sensitivity measure, is presented for assessing solution accuracy of nonsymmetric and symmetric algebraic Riccati equations (AREs). The usual approach to assessing reliability of computed solutions is to employ standard perturbation and sensitivity results for linear systems and to extend them further to AREs. However, such methods are not altogether appropriate since they do not take account of the underlying structure of these matrix equations. The approach considered here is to first compute the backward error of a computed solution X̂ that measures the amount by which data must be perturbed so that X̂ is the exact solution of the perturbed original system. Conventional perturbation theory is used to define structured condition numbers that fully respect the special structure of these matrix equations. The new condition number, together with the backward error of computed solutions, provides accurate estimates for the sensitivity of solutions. Optimal perturbations are then used in an iterative refinement procedure to give further more accurate approximations of actual solutions. The results are derived in their most general setting for nonsymmetric and symmetric AREs. This in turn offers a unifying framework through which it is possible to establish similar results for Sylvester equations, Lyapunov equations, linear systems, and matrix inversions.
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  • 179
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    Numerical Linear Algebra with Applications 2 (1995), S. 85-85 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 180
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    Numerical Linear Algebra with Applications 2 (1995), S. 51-77 
    ISSN: 1070-5325
    Keywords: Arnoldi procedure ; Spread and condensed eigenvalues ; Eigenvalue translations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The paper considers a possible approach to the construction of high-quality preconditionings for solving large sparse unsymmetric offdiagonally dominant, possibly indefinite linear systems. We are interested in the construction of an efficient iterative method which does not require from the user a prescription of several problem-dependent parameters to ensure the convergence, which can be used in the case when only a procedure for multiplying the coefficient matrix by a vector is available and which allows for an efficient parallel/vector implementation with only one additional assumption that the most of eigenvalues of the coefficient matrix are condensed in a vicinity of the point 1 of the complex plane. The suggested preconditioning strategy is based on consecutive translations of groups of spread eigenvalues into a vicinity of the point 1. Approximations to eigenvalues to be translated are computed by the Arnoldi procedure at several GMRES(k) iterations. We formulate the optimization problem to find optimal translations, present its suboptimal solution and prove the numerical stability of consecutive translations. The results of numerical experiments with the model CFD problem show the efficiency of the suggested preconditioning strategy.
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  • 181
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    Numerical Linear Algebra with Applications 2 (1995), S. 395-397 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 182
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    Numerical Linear Algebra with Applications 2 (1995), S. 347-361 
    ISSN: 1070-5325
    Keywords: finite elements ; multilevel methods ; optimal order preconditioners ; newest vertex mesh refinement ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The application of some recently proposed algebraic multilevel methods for the solution of two-dimensional finite element problems on nonuniform meshes is studied. The locally refined meshes are created by the newest vertex mesh refinement method. After the introduction of this refinement technique it is shown that, by combining levels of refinement, a preconditioner of optimal order can be constructed for the case of local refinement along a line. Its relative condition number is accurately estimated. Numerical tests demonstrating the performance of the proposed preconditioners will be reported in a forthcoming paper.
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  • 183
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    Numerical Linear Algebra with Applications 2 (1995) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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  • 184
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    Numerical Linear Algebra with Applications 2 (1995), S. 399-399 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 185
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    Numerical Linear Algebra with Applications 2 (1995), S. 431-445 
    ISSN: 1070-5325
    Keywords: order cone ; order unit ; K-monotone operator ; Barrier element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: An abstract version of the well known Barrier Lemma is presented and some of its generalizations are shown for bounded linear and some unbounded densely defined linear monotone operators in some partially ordered Banach spaces. K-monotonicity of generally unbounded operators is characterized. Some applications of constructing error bounds for approximately solving equations governed by bounded linear operators are established.
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    Numerical Linear Algebra with Applications 2 (1995), S. 363-393 
    ISSN: 1070-5325
    Keywords: Peaceman - Rachford procedure ; domain decomposition ; nonconforming finite element spaces ; parallel processing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This paper presents a general method to associate the operator splitting for the Peaceman - Rachford procedure with a decomposition of the domain in problems arising from finite element discretization of partial differential equations. The algorithm is provably convergent without any symmetry requirement. Moreover, this method possesses the significant advantage of making the linear systems of the Peaceman - Rachford iteration block diagonal and therefore perfectly appropriate for parallel processing. Not only is sparsity not affected but a reduction of the bandwidth occurs. In fact, for appropriate choices of nonconforming finite element spaces, this method makes directly possible elementwise processing. This option remains available in general for higher-dimensional problems by applying the splitting algorithm recursively. Practical implementation requires nothing more than the standard finite element assembly procedure and some bookkeeping to relate a few different orderings of the nodes. In addition to all these attractive features, the method is rapidly convergent and remains highly competitive even when used on a serial machine.
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  • 187
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    International Journal for Numerical Methods in Engineering 38 (1995) 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 188
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 371-397 
    ISSN: 0029-5981
    Keywords: Helmholtz equation ; least squares ; Galerkin method ; Fourier analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper a Galerkin least-squares (GLS) finite element method, in which residuals in least-squares form are added to the standard Galerkin variational equation, is developed to solve the Helmholtz equation in two dimensions. An important feature of GLS methods is the introduction of a local mesh parameter that may be designed to provide accurate solutions with relatively coarse meshes. Previous work has accomplished this for the one-dimensional Helmholtz equation using dispersion analysis. In this paper, the selection of the GLS mesh parameter for two dimensions is considered, and leads to elements that exhibit improved phase accuracy. For any given direction of wave propagation, an optimal GLS mesh parameter is determined using two-dimensional Fourier analysis. In general problems, the direction of wave propagation will not be known a priori. In this case, an optimal GLS parameter is found which reduces phase error for all possible wave vector orientations over elements. The optimal GLS parameters are derived for both consistent and lumped mass approximations. Several numerical examples are given and the results compared with those obtained from the Galerkin method. The extension of GLS to higher-order quadratic interpolations is also presented.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 469-488 
    ISSN: 0029-5981
    Keywords: finite elements ; substructuring ; static condensation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes and analyses the implementation of two static condensation algorithms used to exploit the regular patterns created by two schemes of regular mesh substructuring. Computer resources required by the implementation are assessed in terms of the number of multiplications, the total CPU time, the core and the disk storage requirements. It is discovered that, when implemented for the regular mesh substructuring, the newly proposed condensation algorithm is generally more cost effective than the one proposed by Han and Abel, and modified for the regular mesh substructuring by the present authors.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 451-467 
    ISSN: 0029-5981
    Keywords: finite element ; control volume ; timber drying ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Drying is a process which involves heat and mass transfer both inside the porous material, where a phase change in moisture occurs from the liquid to the gaseous state, and in the external boundary layer of the convected hot dry air, which heats the porous medium. The equations which govern this process consist of three tightly coupled, highly non-linear partial differential equations for the unknown system variables of moisture content, temperature and pressure. Due to the inherently complex boundary conditions and intricate physical geometries in any practical drying problem, an analytical solution is not possible. In order to obtain a transient drying solution it is necessary to resort to a numerical technique. The numerical solution techniques which were employed in this research were the finite element method and the control volume method. The transient numerical results were compared and contrasted for two timber drying problems, first, at a dry bulb temperature of 50°C, and secondly, at 80°C, both cases being below the boiling point of water.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 523-524 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 509-522 
    ISSN: 0029-5981
    Keywords: Laplace transform ; finite element ; viscoelastic beam ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The quasi-static and dynamic responses of a linear viscoelastic beam are solved numerically by using the hybrid Laplace transform/finite element method. In the analysis, the Timoshenko beam theory, which includes the transverse shear and rotatory inertia effect and conventional beam theory, are used to solve this problem. The temperature field is assumed to be constant and homogeneous and that the relaxation modulus has the form of the Prony series. In the hybrid method, the Laplace transform with respect to time is applied to the coupled equations and the finite element model is developed by applying Hamilton's variational principle without any integral transformation. The numerical results of quasi-static and dynamic responses for the models of Maxwell fluid and three parameter solid types are presented and discussed.
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    International Journal for Numerical Methods in Engineering 38 (1995) 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 529-529 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 531-548 
    ISSN: 0029-5981
    Keywords: fuzzy set ; finite element ; plasticity ; geotechnical ; reliability index ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, an elastoplastic analysis based on fuzzy mathematics and using finite element method will be described. The Drucker-Prager yield criterion and the elasto-plastic matrix are fuzzified for the non-linear analyses which adopt the initial stress method for the solution. A numerical example is given to illustrate the possible variations in the displacements and the extent of plastic zones at the discrete membership functions. A reliability index of a membership grade based on the concept of non-probabilistic entropy is also proposed.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 583-606 
    ISSN: 0029-5981
    Keywords: micro polar continuum ; FE-technology ; localization computations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The 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.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 607-629 
    ISSN: 0029-5981
    Keywords: Time-domain BEM ; time integrals ; viscoelasticity ; modified Simpson's rule ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents an accurate and efficient method for the treatment of time integrals in time-domain boundary integral equations for viscoelastic problems. First, the integral equations in space and time are derived for linear viscoelastic and thermo-viscoelastic problems. Then various quadrature rules are discussed for the computation of time integrals. A modified Simpson's rule is proposed as an effective integration scheme. The proposed procedure requires a small computational effort and it is applicable even in time-domain boundary element analysis of many different problems. Numerical results of example problems show the accuracy and effectiveness of the proposed method.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 1597-1610 
    ISSN: 0029-5981
    Keywords: multi level ; non-linear solution ; FAS ; multigrid ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We 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.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 1655-1679 
    ISSN: 0029-5981
    Keywords: smooth particle hydrodynamics ; wavelets ; elastic-plastic large deformation ; tensile instability ; correction function ; aliasing control ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper explores a Reproducing Kernel Particle Method (RKPM) which incorporates several attractive features. The emphasis is away from classical mesh generated elements in favour of a mesh free system which only requires a set of nodes or particles in space. Using a Gaussian function or a cubic spline function, flexible window functions are implemented to provide refinement in the solution process. It also creates the ability to analyse a specific frequency range in dynamic problems reducing the computer time required. This advantage is achieved through an increase in the critical time step when the frequency range is low and a large window is used. The stability of the window function as well as the critical time step formula are investigated to provide insight into RKPMs. The predictions of the theories are confirmed through numerical experiments by performing reconstructions of given functions and solving elastic and elastic-plastic one-dimensional (1-D) bar problems for both small and large deformation as well as three 2-D large deformation non-linear elastic problems. Numerical and theoretical results show the proposed reproducing kernel interpolation functions satisfy the consistency conditions and the critical time step prediction; furthermore, the RKPM provides better stability than Smooth Particle Hydrodynamics (SPH) methods. In contrast with what has been reported in SPH literature, we do not find any tensile instability with RKPMs.
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    International Journal for Numerical Methods in Engineering 38 (1995), S. 1721-1738 
    ISSN: 0029-5981
    Keywords: probabilistic analysis ; optimization ; safety index ; structural reliability ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The 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.
    Additional Material: 6 Ill.
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