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  • 101
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 9 (1993), S. 713-720 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A number of improved finite-difference solutions of explicit form have been reported recently. The choice of a particular solution of these improved explicit forms is dependent on the value of the non-dimensional time step as well as whether the process involves cooling or heating. The conditions for stable operation are clarified in the paper. Two new improved solutions of implicit forms are also reported in the paper. These new solutions give better accuracy compared to the conventional Crank-Nicolson and pure implicit methods, and have unrestricted stability.
    Additional Material: 5 Ill.
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  • 102
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    Communications in Numerical Methods in Engineering 9 (1993), S. 721-727 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A direct method is proposed for the numerical solution of a wide class of symmetric block-tridiagonal systems of linear equations resulting from a finite-difference or finite-element discretization of elliptic boundary-value problems with Dirichlet boundary-value conditions on rectangular domains. The method is based on a result which generalizes the classical Cramer rule and on extensive use of the modified Chebȳshev polynomials for the formulation of the algorithm. A numerical example is provided to illustrate the validity of the proposed approach.
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  • 103
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    Communications in Numerical Methods in Engineering 9 (1993), S. 745-756 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Iterative global/local finite-element stress analysis was used to perform linear analysis of two configurations with local damage. One was a tubular joint with local debonding; the other was a fibre matrix unit cell with debonding along part of the interface. The global/local procedure was shown to be both accurate and efficient for both configurations.
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  • 104
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    Communications in Numerical Methods in Engineering 9 (1993), S. 729-743 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In a recent paper1 we presented a data structure to be used with multigrid techniques on non-homogeneously refined FEM meshes. This paper focuses on the adaptive refinement techniques used there. The error estimate is obtained from standard Taylor series. For each element we compute its efficiency in terms of the size, the norm of the second derivatives of the unknown and the parameter p, where Lp is the chosen norm. The way the norm influences the optimal mesh is studied. The number of elements to be refined at each step is such to produce a fast convergence to the optimal mesh, followed by successive homogeneous refinements. We hope that the analysis of these two subjects could be of value for people working with other (perhaps very dissimilar) adaptive refinement techniques (error estimate and data structure, for instance).
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  • 105
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    Communications in Numerical Methods in Engineering 9 (1993), S. 757-766 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A geometrically non-linear global/local technique was developed and tested. This technique uses separate global and local finite-element models. Iteration is used to enforce equilibrium between the global and local models. The results of this initial study suggest that the technique can be used to reduce both computer memory and CPU requirements.
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  • 106
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    Communications in Numerical Methods in Engineering 9 (1993), S. 785-785 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 107
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    Communications in Numerical Methods in Engineering 9 (1993), S. 773-784 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general line search concept is presented, which can be applied for the solution of non-linear equations in the presence of constraint conditions as in arc-length methods in a consistent manner.
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  • 108
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    Communications in Numerical Methods in Engineering 9 (1993), S. 767-772 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The generalized geometric programming algorithm GGP has been found to be one of the better algorithms for optimizing algebraic functions subject to algebraic constraints. The paper discusses two problems with the GGP algorithm presented by Avriel et al. (1980). The first problem is that, because of the way that constraint tolerances are checked, the checks may pass even when a constraint is violated beyond the acceptable tolerance. This problem can affect an acceleration technique suggested for the algorithm. This paper presents two possible solutions to this problem. The second problem is the algorithm's weakness in handling equality constraints. This problem seems to especially affect the ‘Phase I’ part of the algorithm, which finds a feasible solution from a random starting point. While extensions have been made to get around this limitation, no discussion on why the original algorithm has problems with equality constraints has been made. This paper discusses why the problems exist.
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  • 109
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    Communications in Numerical Methods in Engineering 9 (1993) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 110
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    Communications in Numerical Methods in Engineering 9 (1993), S. 797-803 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a filtering algorithm which corrects the results of measurements of certain physical quantities if any additional information about the measured values is known. The algorithm is very effective in one-dimensional as well as in two-dimensional problems where additional constraints are presented in the form of differential equations. For example, this technique can be used to correct the measurements of certain dynamic quantities if some information about motion of examined bodies is known. It can also be used to correct the strain field measurements if the conditions of continuity of strain field are included.
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  • 111
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    Communications in Numerical Methods in Engineering 9 (1993), S. 805-814 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A computer simulation is made of cellular convection in an anisotropic atmosphere in an attempt to more closely approximate the observed values with those obtained from mathematical models. A finite-element Galerkin technique, with Taylor approximation and Crank-Nicolson, is employed and comparisons are made with the author's earlier finite-element models of isotropic convection and with finite-difference models. It is found that postulates from physics on the effect of anisotropy on cellular atmospheric convection, with its increase in the aspect ratio, are well modelled with this finite-element technique.
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  • 112
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    Communications in Numerical Methods in Engineering 9 (1993), S. 815-824 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The use of micromechanically based constitutive equations for contact interfaces leads to technically relevant parameters to ill-conditioned finite-element equations. In the paper an augmented Lagrangian technique is employed to overcome this difficulty and to provide a good converging algorithm.
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  • 113
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    Communications in Numerical Methods in Engineering 9 (1993), S. 787-795 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The evaluation of solar pressure effects over the antenna reflectors for communication satellites is becoming more and more important, since the diameters of such devices tend to be increased. For this purpose, a statistical approach based on the Monte Carlo method has been developed, as described in this paper, within a research project of the European Space Agency (ESA). In this way, detailed simulations can be carried out easily, thus allowing for analysing different geometrical and technological solutions and for defining an adequate compromise between antenna gain and pointing control capability of the satellite.
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  • 114
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    Communications in Numerical Methods in Engineering 9 (1993), S. 825-836 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An adaptive finite-element (FE) method for the solution of two-dimensional transient dynamic problems is described. The computational domain is represented by an unstructured assembly of linear triangular elements, and the mesh adaption is achieved by regenerating the grid using an error indication procedure coupled with an automatic mesh generator. Problems involving shock and wave propagation are solved to illustrate the numerical performance of the method.
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  • 115
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    Communications in Numerical Methods in Engineering 9 (1993), S. 837-845 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents two complementary variational formulations of Trefftz-type elements wherein the piece-wise assumed displacement approximations a priori fulfil the governing differential equations over the element subdomain. The two formulations are such that either the displacement conformity or the reciprocity of the conjugate tractions is enforced at the element interfaces, one more strongly than the other. This is achieved through linking the piece-wise approximations either through an auxiliary displacement or a boundary traction frame. The two formulations concern solid mechanics and structures.Although for hybrid elements monotonic convergence in energy cannot be warranted, in practice the two presented formulations yield opposite bounds on the energy provided that the number of internal Trefftz functions is sufficiently large.
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  • 116
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    Communications in Numerical Methods in Engineering 9 (1993), S. 859-861 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 117
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    Communications in Numerical Methods in Engineering 9 (1993), S. 857-857 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 118
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    Communications in Numerical Methods in Engineering 9 (1993) 
    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 9 (1993), S. 847-856 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the BEM and FEM results have been compared in the context of 2D electromagnetic field analysis in a zoned medium with eddy current subregions. The practical problem concerning the turbogenerator end region has been discussed. The magnetic flux density over the surface of the end package and the current density in the non-magnetic pressure plate have been analysed.
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  • 120
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    Communications in Numerical Methods in Engineering 9 (1993), S. 863-871 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The design of a composite laminate involves the determination of layer thicknesses and orientation angles. The problem is posed as the optimum weight (or volume) design of composite laminates which withstand the specified loads without failure. The modified Hill-Mises or Tsai-Wu failure criterion is taken as a constraint, each layer being subjected to this criterion. The design variables considered are the layer thicknesses and orientation angles. Based on the finite-element analysis capability of composite laminates provided by NISA II, a composite laminate optimization procedure has been developed. Nonlinear optimization techniques are used to approach the optimum design of the composite laminates. Efficient design sensitivity analysis procedures are implemented based on the direct differentiation and adjoint variable methods. Example problems illustrate that the program offers an efficient and practical design tool for composite laminates.
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  • 121
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    Communications in Numerical Methods in Engineering 9 (1993), S. 883-888 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Elastic contact between a thick shell of revolution and a rigid plate in the case when the plate is brought into contact with the shell by giving a finite displacement to the plate is analysed by the finite-element method. Field-consistent higher-order strain-displacement relations with vanishing shear stresses on the surfaces are used. A finite element based on these relations is developed and used for the analysis. The contact conditions are imposed by use of the Lagrangian multipliers method, and the resulting minimization problem is solved iteratively. This procedure will lead to reduced memory requirements and computation time.
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  • 122
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    Communications in Numerical Methods in Engineering 9 (1993), S. 889-896 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An explicit formulation and a procedure for the computation of isotropic tensor-valued tensor functions is discussed. The formulation is based on a spectral decomposition in terms of second-order eigenvalue bases, which avoids the costly computation of eigenvectors. As an important result a compact structure of the fourth-order derivatives of general second-order isotropic tensor functions is presented.
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  • 123
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    Communications in Numerical Methods in Engineering 9 (1993), S. 873-881 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A simple automatic time-step control procedure is devised for use in implicit one-step time-integration schemes. First- and second-order semi-discrete systems of equations emanating from finite-element spatial discretization are considered. The varying time-step interval is controlled by the relative distance between the solution in two consecutive time steps, using the solution update formula of the time integrator under consideration. A model problem involving the vibrations of a membrane is used to demonstrate the performance of the scheme.
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  • 124
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    Communications in Numerical Methods in Engineering 9 (1993), S. 909-915 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Boundary integral equations are generally derived by employing a Cauchy Principal Value definition for the singular integral involving the derivative of the Green function. As a consequence, evaluation of this integral requires special attention, and computing the associated ‘solid angle coefficient’ can often pose difficulties. As discussed herein, these problems can be avoided by defining the integral directly, in terms of a limit to the boundary. This approach leads to a straightforward evaluation procedure.
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  • 125
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    Communications in Numerical Methods in Engineering 9 (1993), S. 917-924 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The reduction of stress concentration around a circular hole in a dynamically loaded plate by introducing auxiliary holes around the original hole is studied numerically. The solution of this plane stress problem is carried out in the Laplace transformed domain with the aid of the boundary-element method, and subsequently the time domain response is obtained by numerically inverting the transformed solution. Numerical examples are presented which demonstrate a stress reduction as high as 18 per pent by the introduction of two auxiliary holes in the loading direction for the uniaxial case.
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  • 126
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    Communications in Numerical Methods in Engineering 9 (1993), S. 897-908 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Structural models of large space structures have a substantial number of degrees of freedom (DOF) and possess semi-positive-definite stiffness matrices. The paper presents an efficient co-ordinate reduction procedure for structural dynamic analysis of large space structures. The method is based on the superposition of load-dependent Ritz vectors, which are computed in block form using a shifted stiffness matrix. Comparative transient dynamic analyses are performed on a 2803 DOF model of the space station Freedom using the load-dependent method (LDM) and the mode-displacement method (MDM) based on the superposition of eigenvectors. It is shown that the LDM is able to provide convergence of displacements with a small number of vectors. The acceleration response is found to be more sensitive to vector truncation than the displacement response. Error norms based on the representation of the dynamic load by the vector basis are developed to provide an indication of the effect of vector truncation on the structural response.
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  • 127
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    Communications in Numerical Methods in Engineering 9 (1993), S. 925-932 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Three strain recovery techniques are investigated in the framework of the mixed iterative method. The need for appropriate strain recovery for low-order elements is shown. The three techniques compared are: C-lumping, strain-smoothing and a new technique called C-splitting. It is shown that the use of C-lumping has negative effects on the convergence of the mixed iterative method. Both strain-smoothing and C-splitting deliver convergent results, but the new technique converges faster.
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  • 128
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    Communications in Numerical Methods in Engineering 9 (1993), S. 933-935 
    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 9 (1993) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 130
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    Communications in Numerical Methods in Engineering 9 (1993), S. 937-949 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: For some heterogeneous materials, it is not practical to model the microstructure directly using traditional finite elements. Furthermore, it is not always accurate to use homogenized properties. Macro elements have been developed which permit microstructure within a single element. These macro elements performed well in initial tests.
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  • 131
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    Communications in Numerical Methods in Engineering 9 (1993), S. 957-974 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper deals with the solution of the quasi-harmonic equation by the finite element method in a domain with corners on its boundary. A mapping technique, which can be used for locating the nodes of standard isoparametric elements in a subgrid (patch) of finite elements in the vicinity of a corner singularity point, is presented. The equations of the mapping are based on the analytical singular solution of the problem. Some analytical and numerical results to show the efficiency of the technique are presented.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 975-987 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An arbitrary Lagrangian-Eulerian model is described for the prediction of metal flow in a steady-state forming process. The formulation is shown to be capable of dealing with free surface and boundary friction; the coupling with thermal effects is also considered. The numerical techniques are based on the finite elements for spatial discretization of the momentum equation and on an explicit integration scheme for discretization relative to time. The mass and energy equations are integrated by a finite-volume method. Details on the application to an orthogonal cutting process are given in the final Section of the paper.
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  • 133
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    Communications in Numerical Methods in Engineering 9 (1993), S. 951-956 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A procedure was implemented to determine the optimum values for the two parameters of the Zienkiewicz three-level time schemes which could be utilized for the numerical solution of a system of ordinary differential equations. A multivariable search method was implemented to estimate optimum values for these parameters. The resultant optimum three-level time scheme produced very accurate results, satisfied physical reality, and did not produce any oscillations for the various problems that were investigated. The optimum values for the two parameters β and γ in the three-level scheme were β = 0·50005 and γ = 1·0007. A comparison was made between this optimum scheme and other existing three-level time schemes. The optimum scheme demonstrated superior results for all the problems that were analysed. However, the results of the optimization analysis produced a set of optimum parameters that were identical to the values that would reduce the general three-level time scheme into a central-difference two-level time scheme, i.e. β = 1/2 and γ = 1.
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  • 134
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    Communications in Numerical Methods in Engineering 9 (1993), S. 989-1004 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new efficient formulation of the 36 degree-of-freedom conforming shallow shell element of an arbitrary triangular shape is presented. This formulation is based on natural co-ordinates and independently assumed natural strain fields, and applied to shallow shell analysis. The 3-node element incorporates the normal displacement and its first and second derivatives plus the tangential displacements and their first derivatives at each vertex. A closed form of the element stiffness matrix is achieved. The form of the stiffness matrix derived in this formulation explicitly reveals the essence of the shallow shell theory.The presented approach results in avoiding definite integrals and matrix inversions, and permits operation with lower-order numerical matrices, which are the same for all elements. The example applications presented demonstrate that accurate predictions of stresses as well as displacements are obtained with only a few elements.
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  • 135
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    Communications in Numerical Methods in Engineering 9 (1993), S. 1005-1011 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The formulation of a straight beam element to eliminate the shear locking phenomenon is presented. The element is based on curvature so that the bending energy is fully represented, and the shear strain energy is incorporated into the formulation by the equilibrium equation. Four examples are chosen to verify the concept of the element employed and its capability of the analysis. The solutions obtained reveal that the element describes the behaviour of the straight beam quite exactly and efficiently, showing no locking and that it is also applicable to the analysis of both thin and thick straight beams.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 1013-1015 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 137
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    Communications in Numerical Methods in Engineering 9 (1993), S. 45-52 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper, based on the boundary-element technique, presents a perturbation method which can be applied to reanalysis of the eigenvalues and eigenvectors in an elastic structure. Regarding the shape changes of a structure as the perturbation of its surface nodes within the neighbourhood of the given values, this method uses the perturbation formula to obtain the eigensolutions of the modified system without solving the generalized eigenvalue problem. Finally, the authors give some sample examples to demonstrate the validity of the method.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 81-86 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 139
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    Communications in Numerical Methods in Engineering 9 (1993), S. 67-79 
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    Notes: Generalized conjugate gradient methods are often used to solve large sparse non-symmetric linear systems. Such systems often arise in the numerical solution of convection-diffusion problems. The Lanczos/Orthodir method proposed by Jea and Young suffers the roundoff error problem. In this paper a modified Lanczos/Orthodir method is considered. The modifications are based on Paige's computational procedure and on the adaptive restarting procedure. Numerical results showed that the modified Lanczos/Orthodir method is more stable than the original version. Furthermore, with the adaptive restarting scheme the method performed much better than the Lanczos/Orthomin method.
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  • 140
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    Communications in Numerical Methods in Engineering 9 (1993) 
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  • 141
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    Communications in Numerical Methods in Engineering 9 (1993), S. 111-119 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A boundary-element method is derived for determining the anti-plane displacement and stress in an inhomogeneous elastic material subjected to a time-dependent load.
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  • 142
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    Communications in Numerical Methods in Engineering 9 (1993), S. 91-102 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A numerical model of coupled heat and mass transfer in unsaturated soil, recently proposed by the authors, is used to simulate a laboratory-based experimental test. The modelling approach adopted is based on the use of the capillary potential and the temperature as independent variables. The experimental results have recently been presented in the literature by other workers. Very good correlations are obtained of both steady-state values of variables and the times required to reach steady-state conditions. The results achieved lend confidence to the numerical modelling approach proposed and extend the range of applications of the model hitherto achieved to that of a further generic soil type, namely a silt.
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  • 143
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    Communications in Numerical Methods in Engineering 9 (1993), S. 121-129 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: In this paper an algorithm for generating pure triangular or pure quadrilateral meshes for arbitrary polygonal domains is presented. The first part shows a triangulation procedure being as suitable for local mesh refinement as for local mesh coarsening. In the second part an algorithm for transformation of triangular grids to quadrilateral meshes of the same relative mesh density is introduced. Two simple strategies are shown which can easily be implemented into any existing triangulation algorithm.
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  • 144
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    Communications in Numerical Methods in Engineering 9 (1993), S. 131-137 
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    Notes: This paper examines the behaviour of various time-stepping schemes used in structural dynamic analysis when applied to models with negative stiffness. It is found that under such circumstances the accuracy of the numerical solution is greatly affected by the choice of integration parameters of the scheme. Optimal parameters for the Newmark family and the SS32 family have been investigated.
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  • 145
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    Communications in Numerical Methods in Engineering 9 (1993), S. 147-155 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper compares two formulations of Lax-Wendroff TVD methods. The basis of comparison is to the results of several test problems providing both qualitative and quantitative results. Results show that using an upwind biased limiter provides higher resolution of both smooth and discontinuous solutions from a lower amount of induced numerical viscosity. The conclusion is that a limiter should have as small a support as possible in order to limit its effects if high resolution is the object.
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  • 146
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    Communications in Numerical Methods in Engineering 9 (1993), S. 139-145 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: To obtain accurate gas-bearing lifts and moments, finite-difference and conventional finite-element techniques often require excessively large degrees of freedom. In this paper we avoid this problem by solving the compressible gas-bearing solution by the p-version finite-element method. The lubrication finite-element equation is formulated based on the weighted residual approach, and the resulting nonlinear equations are solved iteratively by the Newton-Raphson procedure. To achieve higher-order solutions the formulation utilizes the C0 hierarchical shape functions to describe the element pressure field. A numerical example is included to demonstrate the simplicity of modelling and the rapid convergence characteristics of the present p-formulation. An efficient numerical strategy, which utilizes the most recent polynomial pressure solution available as an estimate for the next higher polynomial level calculations, shows a 50 per cent reduction in the required computational effort for the low-flying Winchester air-bearing slider presented here. When compared against results obtained from conventional h-version finite-element models, the p-formulation yields better accuracy with fewer degrees of freedom required.
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  • 147
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    Communications in Numerical Methods in Engineering 9 (1993), S. 365-374 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The Richardson extrapolation method, which produces a 4th-order-accurate solution on a subgrid by combining 2nd-order solutions on the fine grid and the subgrid, is ‘completed’ - in the sense that a higher-order-accurate solution is produced on all the fine grid points.
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  • 148
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    Communications in Numerical Methods in Engineering 9 (1993), S. 387-395 
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    Notes: A p-type finite-element scheme is introduced for Navier-Stokes problems in a fully coupled stream function/vorticity formulation. The resulting coupled non-linear system is solved using a Newton iteration with incremental continuation in the Reynold's number. A biconjugate gradient (BCG) scheme in an element-by-element setting is applied to solve the linearized system at each Newton iteration. Pseudo-element block preconditioners produce a practical PBCG method, even for ill-conditioned systems arising from high-p elements in the case of Stokes flow. The problem at higher Reynolds numbers further limits p.
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  • 149
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    Communications in Numerical Methods in Engineering 9 (1993), S. 375-385 
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    Notes: It is known that the boundary-element coefficient matrices in steady-state elastodynamics are frequency-dependent. For a multifrequency run, the coefficient matrices have to be reformed at each different frequency. This procedure usually involves heavy numerical integration, and hence is very time consuming. In this paper, two interpolation schemes are initially introduced to accelerate the process of matrix reformation without sacrificing the solution accuracy. In the first scheme, the coefficient matrices are first slightly transformed and then interpolated in the frequency domain. In the second scheme, the Green function is interpolated in the spatial domain. Comparison between these two schemes both in terms of accuracy and efficiency is presented. Finally, a hybrid scheme that takes advantage of the best of both interpolation schemes is proposed. Numerical examples are given to demonstrate the three different interpolation schemes.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 397-406 
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    Notes: In the present paper numerical solutions of the one-dimensional Burger equation are obtained. The technique of finitely reproducing non-linearities introduced by Bazley is used. This technique when applied to Burger's equation gives a method where a system of non-linear ordinary differential equations is to be solved. The present method produces very accurate results in comparison to finite-difference of finite-element methods.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 407-415 
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    Notes: An efficient wave input procedure in the finite and infinite element coupled model is presented in this paper. Compared to the previous wave input method, the main advantage of the present wave input procedure lies in its computational efficiency because only a small region of the medium needs to be modelled by finite elements. The equivalence between the present wave input procedure and the previous one has been theoretically proven when a harmonic wave propagates vertically in an isotropic homogeneous elastic half-space. In addition, the accuracy of the present wave input method has been evaluated based on the solutions obtained for SH-wave, SV-wave and P-wave scattering problems in a semicircular canyon for which analytical solutions are already available.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 451-453 
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    Communications in Numerical Methods in Engineering 9 (1993), S. 427-438 
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    Notes: This paper focuses on how parameter changes in a vibration system expressed by a discrete eigenvalue problem affect vibration modes in the special case of closely spaced eigenvalues, i.e. ‘eigenvalue clusters’. For this class of problems, a perturbation analysis is developed that can be used to compute changes in eigenvalues and eigenvectors in response to small parameter changes. The analysis is applied to a 6-degree-of-freedom spring-mass system containing a single pair of closely spaced eigenvalues.
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  • 154
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    Communications in Numerical Methods in Engineering 9 (1993), S. 463-473 
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    Keywords: Engineering ; Engineering General
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    Notes: When a forging is machined to its net shape, unacceptably large distortions can occur if the final part shape is complex. Such distortions can be predicted with the application of the finite-element method. However, numerical errors associated with the finite element technique can render such predictions unreliable. This paper presents benchmark problems for verifying the accuracy of machining distortions predicted by any prospective finite-element code. Also, a comparison between two industry-standard general-purpose codes, ANSYS and ABAQUS, is presented.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 525-531 
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    Notes: The orthonormal method of integral relations (MIR) is extended to calculate wake flow problems. Two previous difficulties are overcome: (1) the non-constant integral domain is eliminated by introducing a linear transformation in the formulation; (2) the difficulty associated with determining unique orthonormal weighting functions is overcome by an iterative scheme. The new formulation is applied to calculate a wake flow. A high-order solution for N up to 4 is obtained with relative ease.
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    Communications in Numerical Methods in Engineering 9 (1993), S. 567-578 
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    Notes: A method is described whereby structured multiblock meshes can be constructed from the solution of elliptic partial differential equations and which possess the property of orthogonality close to boundaries and near orthogonality within the domain. To construct grids for viscous flow simulations which have appropriate point distributions close to solid boundaries these grids are used with point redistribution formulations. The result is high-quality grids for use with both inviscid and viscous flow simulation algorithms. Examples using the approach are given, and these include grids for single and multicomponent aerofoils and bluff bodies.
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  • 158
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 67-85 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper presents the formulation and the numerical implementation of a three-dimensional direct boundary element method for the Biot theory of poroelasticity. To avoid the need of time-stepping and volume integration, the solution is performed in the Laplace transform space. Solution in time is obtained via numerical inversion. Several examples, including the settlement of a rectangular footing and a modified Mandel problem, are examined.
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  • 159
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    Notes: Low order finite elements are of vital interest for practical applications in linear and non-linear structural analysis. The possible discretization errors, when Reissner-Mindlin shell elements with bilinear shape functions are used, and modifications to prevent these errors are presented. On some numerical examples the influence of these errors and of various modifications on the results is shown. Finally, the case of membrane locking with low order Reissner-Mindlin elements for particular assumptions concerning the base vectors and methods to prevent this locking are discussed.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 303-320 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: An efficient solution procedure for elasto-plastic analysis of Reissner-Mindlin plates has been proposed in this work. The main ingredients which render efficiency are: what appears to be an optimally tuned four-node plate element with assumed shear strains and incompatible bending modes; an elasto-plastic constitutive model given directly in terms of stress resultants; and efficient computation of plastic flow which simplifies to a solution of a single scalar equation and remaining state update computation. The performance of the element has been proved very satisfying in both elastic singularity-dominated and elasto-plastic problems.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 321-330 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The numerical solution of the Helmholtz eigenvalue problem is considered. The application of the boundary element method reduces it to that of a non-linear eigenvalue problem. Through a polynomial approximation with respect to the wavenumber, the non-linear eigenvalue problem is reduced to a standard generalized eigenvalue problem. The method is applied to the test problems of a three-dimensional sphere with an axisymmetric boundary condition and a two-dimensional square.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1299-1310 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The paper considers the elastic buckling of thick skew plates. Up to now, very little work has been done on this subject and the paper aspires to fill this gap. Based on the principle of stationary total potential energy and the recently developed pb-2 Rayleigh-Ritz method as a solution procedure, buckling solutions for skew plates of various aspect ratios, skew angles and boundary conditions are determined. The tabulation of these results, not available thus far, should be useful to designers and researchers who may use them as benchmark values to test the validity and convergence of their numerical techniques and softwares for thick plate analysis.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1311-1337 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The enhanced assumed strain (EAS) method, recently proposed by Simo and Rifai13, is used to develop new four-node membrane, plate and shell elements and eight-node solid elements. The equivalence of certain EAS-elements with Hellinger-Reissner (HR) elements is discussed. For instance, the seven-parameter element EAS-7 with 2 × 2 integration is identical to the HR-element of Pian and Sumihara2. Eight-node solid elements which are free of volumetric locking and four-node shell elements which have an improved membrane and bending behaviour, compared to the Bathe-Dvorkin shell element7, are introduced. Numerical tests for linear elastic problems show an improved performance of the EAS-elements.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1541-1562 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new approach for numerical analysis of flexible space frames subjected to impact forces is presented. The method is particularly effective in the analysis of large-amplitude vibration and dynamic stability found in extremely flexible structures.The proposed method of analysis is based on a concept of updated material frame, which allows the algorithm of handling large rotations exceeding 360° and extensions longer than 100 per cent without numerical difficulty and the need for iterations. Thus, an efficient explicit integration finite element algorithm can be adopted. The method is convenient for non-linear and inelastic material models.The basic coding procedure is similar to the popular co-rotational approach. Existing codes can be easily modified to solve transient dynamic problems. The modification steps necessary for the implementation are outlined in the paper.Several numerical examples are presented. Comparison with the standard co-rotational approach and large deformation finite element formulations, such as the updated Lagrangian approach, are presented.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1605-1607 
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1785-1787 
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1765-1783 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Four methods of implementing Morison wave-force calculations for offshore tubular-jacket structures on distributed-memory parallel hardware are presented The Morison equation is given and the method by which it is used to calculate wave forces on members of an offshore structure is briefly described. A brief background to parallel computing and a description of the transputer hardware and software available to the authors is also given. Program structure and methods of achieving parallelism are explained. A number of test runs on an example structure have been timed and the resulting speed-ups are discussed.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 523-536 
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    Keywords: Engineering ; Engineering General
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    Notes: A method for the direct computation of mean values and variances of the temperature in conduction-heated objects with random variable thermophysical properties is presented. This method is based on a Taylor expansion of the finite element formulation of the heat conduction equation and offers a powerful alternative to the computationally expensive Monte Carlo method. Both steady-state and transient problems are considered. Some example problems are solved and the results discussed. The simulations indicate that the variability of the thermophysical properties may cause a considerable variability of the temperature within the heated object. This may have important consequences on the design of heating operations in food process engineering.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2581-2605 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A novel technique is presented for the control of mapped quadrilateral and hexahedral meshes generated inside a collection of connected subregions. Target division numbers on the subregion edges are given as input. By allowing these numbers to vary, meshes can be found which satisfy both the subregion constraints imposed by the mesh patterns being employed, and the compatibility constraints on edges shared by two or more adjacent subregions. Among all such feasible solutions the optimal one is obtained by minimizing the changes to the division numbers, using an integer programming technique.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2123-2140 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: This paper addresses the formulation and discrete approximation of dynamic contact/impact initial-value problems. The continuous problem is presented in the context of non-linear kinematics. Standard semi-discrete time integrators are introduced and are shown to be unsuccessful in modelling the kinematic constraints imposed on the interacting bodies during persistent contact. A procedure that bypasses the aforementioned difficulty is proposed by means of a novel variational formulation. Numerical simulations are conducted and the results are reported and discussed.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2141-2142 
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2779-2790 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a numerical procedure for accurate determination of a limit or a bifurcation point. The method minimizes simultaneously the first and the second variations of an admissible functional or iterates to satisfy the equilibrium and the semi definite condition for the tangent stiffness matrix. It can be readily incorporated into a computer program for non-linear finite element analysis to improve its accuracy in the location of critical points.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2245-2262 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The divergence-free finite element method (DFFEM) is a method to find an approximate solution of the Navier-Stokes equations in a divergence-free space. That is, the continuity equation is satisfied a priori. DFFEM eliminates the pressure from the calculations and reduces significantly the dimension of the system to be solved at each time step. For the standard 8-node velocity and 4-node pressure DFFEM, an optimal basis for the weakly divergence-free subspace is constructed such that each basis function has non-zero support on at most nine contiguous elements. Given this basis, weakly divergence-free macroelements are constructed.
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  • 177
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2791-2804 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Analysis of forces and stresses of horizontal axis propellers and turbines has been the subject of increased interest in recent years because of the need to develop adequate analytical tools for the design and evaluation of-wind turbine rotors.Most of the structural failures of wind turbines occur in the blade root section. Hence, a three-dimensional analytical model to compute the deflection, stresses and eigenvalues in the rotor blades is proposed using bending triangular plate finite elements.Both membrane and bending stiffness are considered in deriving the element stiffness matrix. The consistent mass matrix is used in generating the overall mass matrix. Lift and drag forces created in steady wind conditions are analysed as normal and tangential forces on the blade sections at certain angles of attack. These forces are applied as boundary loads to the computer program to analyse statically and dynamically rotor blades of symmetrical aerofoil NACA 0015 series. Constant chord, tapered and twisted blades were analysed at rated and survival wind speeds.The validity of the computer program used was verified by applying it to a standard cantilever box beam using the beam theory.The results showed that maximum stresses occurred at the root of the blades for all configurations in the spanwise direction and that a tapered blade, in addition to saving material weight, diminished the stresses obtained. The twisting of the blade leads to an increase in stiffness and a decrease in the stresses.
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  • 178
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2319-2320 
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    Keywords: Engineering ; Engineering General
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  • 179
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2321-2322 
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  • 180
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    International Journal for Numerical Methods in Engineering 36 (1993) 
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  • 181
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2895-2919 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a parallel implementation of LDLT factorization on a distributed-memory parallel computer. Specifically, the parallel LDLT factorization procedure is based on a row-oriented sparse storage scheme. In addition, a strategy is proposed for the parallel solution of a triangular system of equations. The strategy is to compute the inverses of the dense principal diagonal block submatrices of the factor L, stored in a row-oriented structure. Experimental results for a number of finite element models are presented to illustrate the effectiveness of the parallel solution schemes.
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  • 182
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2877-2893 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The boundary discretization of the curl-free vector variable such as the magnetic field h and the divergence-free variable such as the surface current density k is discussed. Instead of introducing the scalar variables, the vector variables h and k are discretized by the curl-conform and the div-conform triangular edge elements, respectively. The degrees of freedom are associated with the boundary edges. In order to ensure the null curl of h and the null divergence of k, a spanning tree technique is used to identify the independent edges. The triangular edge elements contain the first-order nodal elements when expressing h or k by the scalar variables. The use of edge elements permits one to solve multiply connected problems if the independent edges are well identified, i.e. the necessary cuts are introduced in multiply connected domains. An automatic tree generation algorithm is presented. It permits one to determine automatically the additional edges on the necessary loops (cuts) of a multiply connected region. Some tree generation examples are illustrated. A numerical application to a three-dimensional multiply connected eddy current problem is reported at the end of the paper.
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  • 183
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2863-2876 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method is presented for the finite element analysis of the interaction of geometrically and materially non-linear bodies. Interaction is considered at predefined interfaces. Equations for interaction forces are assembled via static condensation, and the solution for these forces is utilized for the full analysis of the problem. An interface function using the interpolating functions is defined to maintain the equilibrium of interaction forces and the displacement compatibility at the interface nodes. The method permits large rotations and slipping as well as the occurrence of new contacts at the interfaces. Additionally, solutions can be found using high- or low-order elements and when nodes at either side of the interface are not aligned.
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  • 184
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2921-2937 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A new four-node conforming quadrilateral element (NCQ) for plate bending is Described. The element is based on an earlier free formulation due to Bergan,1,2 but extra twist variables are included to make it more accurate. The element geometry is in bilinear polynomials representation, while the displacement functions are described by slight modifications of bicubic polynomials which satisfy energy orthogonality and need not be force-orthogonal. It is shown that the coupling stiffness between the fundamental deformation modes and its higher-order deformation modes has been altered. Numerical examples indicate that the element gives a surprisingly accurate solution.
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  • 185
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2939-2954 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a method for the numerical computation of hypersingular integrals as they appear in the boundary element analysis. The proposed method is based on the finite part concept and allows for arbitrary curved boundary elements. Owing to the unknown transformation properties of finite part integrals undergoing a non-linear co-ordinate transformation, the definition formula of finite part integrals is applied prior to the transformation into the usual element co-ordinate system. The resulting integrals are regular and may be evaluated by standard Gaussian quadrature rules. The method is described in detail for the boundary integrals of two-dimensional linear elastostatics. Numerical examples are inclcded for this type of problem, but the method may easily be adapted to other two-dimensional problems.
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  • 186
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2955-2980 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents the dual hybrid-Trefftz (HT) element approach devised so as to enforce more strongly the reciprocity of boundary tractions at the element interfaces than the interelement conformity of displacements. As in the standard HT approach,1,2 a complete set of Trefftz functions is used to represent the internal displacement field of the element (and, as a consequence, the governing Navier-Lamé differential equations are a priori verified over the element). But rather than employing an auxiliary interelement displacement frame field to enforce the conformity on the internal displacements, an auxiliary boundary traction field is adopted to enforce at the element interfaces the reciprocity of tractions derived from the internal displacement field. Provided that the number of Trefftz functions is sufficiently large, this approach yields an opposite bound on the energy in comparison to the standard HT approach based on the displacement frame. As in the standard HT formulation,3 the dual HT formulation is particularly well suited for generation of highly accurate p-version elements. Although presented for solid mechanics, the formulation also holds for other problems. Numerical studies which involve comparisons of the two alternative displacement and traction frame HT element models have been performed by considering the Laplace's equation problem in two dimensions.
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  • 187
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2453-2472 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: It is well accepted that severe numerical difficulties arise when using the conventional displacement method to analyse incompressible or nearly incompressible solids. These effects are caused by the kinematic constraints imposed on the nodal velocities by the constant volume condition. In elastic-plastic analysis, these effects are due to a conflict between the plastic flow rule and the finite element discretization. Although several methods have been proposed to cope with this problem, none has been based on the appropriate choice of displacement interpolation functions to minimize the constraints. The theoretical formulation of a new six-noded isoparametric displacement finite element, which is well suited for elastic-plastic analysis of axisymmetric constrained solids by using a rational displacement interpolation function, is presented in this paper. The proposed displacement interpolation function implies that the displacement in the axial direction and the product of the displacement in the radial direction and the radius should be treated as two independent basic variables. Alternatively, the proposed displacement interpolation function can also be implemented in a conventional displacement formulation simply by using a modified shape function matrix. The suitability of the proposed formulations is first studied theoretically by assessing the number of degrees of freedom per constraint and then verified by performing numerical experiments on typical boundary value problems which involve incompressible behaviour.
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  • 188
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2501-2501 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 189
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    International Journal for Numerical Methods in Engineering 36 (1993) 
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  • 190
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2473-2499 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The understanding of the performance of the quarter-point and transition elements is of considerable importance as these singular elements are widely used in linear elastic fracture mechanics (LEFM) analyses. However, a number of issues remain unresolved although numerous investigations into their performance have been conducted. In particular is the question of optimum quarter-point element and transition element size. This study examines several aspects in relation to the size effect by performing a large number of numerical analyses on several standard problems. Interpretation of the numerical results was aided by the use of two concepts, the ‘zones of dominance’ and ‘zones of representation’. This study proposes a means of explaining the errors in stress intensity factor computation through the interaction between both types of zones. Consequently, a number of new and significant observations were made regarding the singular elements' performance. This study concludes with some recommendations for the application of these elements.
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  • 191
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2525-2544 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A unified approach is presented for establishing exact integration of the constitutive equations in elastoplasticity, assuming the total strain-rate direction to be constant. This unified approach includes all previous exact integration procedures as special cases and, in addition, some new closed-form solutions are derived for combined kinematic and isotropic hardening. Special emphasis is laid on combined kinematic and isotropic hardening for von Mises' material and on isotropic hardening for Mohr-Coulomb and Tresca materials.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2503-2523 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper addresses the performance of square elements of type Q(p) and Q′(p). (Q(p) and Q′(p) are elements of degree p, analogous to the well-known 9- and 8-noded elements for p = 2.) The performance is analysed theoretically for the class of analytic functions. Numerical experiments confirm the conclusions drawn from the theory. The computational complexity of a solution algorithm is studied using timings of the computation on an Alliant FX/8 computer. The data show that high-order elements are very effective for the considered class of solutions.
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  • 193
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 2545-2566 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The rigid-ice model of frost heave is one of the most comprehensive frost-heave models but is restricted to one-dimensional cases in its present form. In this paper, the model is extended to two-dimensional problems. The complete formulation of the partial differential equations governing heat, moisture and ice transport in freezing soils is provided. The equations are subsequently solved using the Galerkin finite element method in space and the finite difference method in time. A computer program is developed for the two-dimensional rigid-ice model. A case of freezing around chilled gas pipeline is solved and the numerical results are compared with experimental values, with good agreement between the two sets of results.
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  • 194
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 3903-3914 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A three-dimensional multilayer composite finite element method has been developed based on a composite variational functional which takes three in-plane strains εx, εx, εxy and three transverse stresses σz, σyz, σxz as the basic variables. The continuity of the transverse stresses σz, σyz, σxz across the laminate thickness is assured a priori by introducing a partial stress field parameter α which is associated with the lower and upper surfaces of a lamina in a laminate. A method has been developed to form the partial stress field based on the assumed displacement field. With this method, a three dimensional (3-D) multilayer composite finite element is formulated for stress analysis of composite laminates. A numerical example is given, which shows some advantages of this composite element.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 3915-3932 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper deals with the numerical integration of a class of rate-independent elasto-plastic models. The backward Euler scheme is used to integrate the rate constitutive relations. The non-linear equations obtained are solved by the Newton method. The consistent tangent modulus is obtained by exact linearization of the algorithm. In the case of J2 elasto-plasticity with non-linear isotropic hardening and non-linear kinematic hardening (Chaboche-Marquis model), explicit formulas are derived, without any approximations.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 3937-3956 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A kinematical algorithm is proposed in which the input is the incremental deformation gradient corresponding to an increment in motion for a time step, and the output is a constant rate-of-stretching tensor and a rotation tensor. The concept of algorithmic objectivity is discussed, with a stronger statement of objectivity than those advanced in previous works being set forth. The importance of strong objectivity is illustrated for applications in which moderately large rotation increments are to be expected. Accuracy of the proposed algorithm is discussed and illustrated with example calculations, and it is shown that the accuracy of the algorithm may be extended to arbitrary order. Also, the computational effort associated with the proposed algorithm is seen to compare favourably to that of other algorithms.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 3351-3379 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Many resequencing algorithms for reducing the bandwidth, profile and wavefront of sparse symmetric matrices have been published. In finite element applications, the sparsity of a matrix is related to the nodal ordering of the finite element mesh. Some of the most successful algorithms, which are based on graph theory, require a pair of starting pseudoperipheral nodes. These nodes, located at nearly maximal distance apart, are determined using heuristic schemes. This paper presents an alternative pseadoperipheral node finder, which is based on the algorithm developed by Gibbs, Poole and Stockmeyer. This modified scheme is suitable for nodal reordering of finite meshes and provides more consistency in the effective selection of the starting nodes in problems where the selection becomes arbitrary due to the number of candidates for these starting nodes. This case arises, in particular, for square meshes. The modified scheme was implemented in Gibbs-Poole-Stockmeyer, Gibbs-King and Sloan algorithms. Test problems of these modified algorithms include: (1) Everstine's 30 benchmark problems; (2) sets of square, rectangular and annular (cylindrical) finite element meshes with quadrilateral and triangular elements; and (3) additional examples originating from mesh refinement schemes. The results demonstrate that the modifications to the original algorithms contribute to the improvement of the reliability of all the resequencing algorithms tested herein for the nodal reordering of finite element meshes.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 3421-3439 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper the extended interior penalty methods are applied to solve the bolted joint problems of the laminated composite plates. The conventional interior penalty methods have the weak point such that the searches for optimized solution in the neighbourhood of the constraint surfaces are difficult since the values of penalty term in the infeasible domain are infinity. To improve the weak point, the extended interior penalty formulation is proposed. In this work mathematical analysis on the characteristics of the solutions is attempted and the convergence of the penalized solutions is estimated. As a numerical example, first, the case of single bolted joint is solved for a variety of lamination angles of the composite plates. The computed results are compared with the previous works and are proved to agree well. Next the problem of the two bolt holes in series and in parallel are treated in a similar manner. It is concluded that the formulations for the class of the problems by the extended interior penalty methods are mathematically sound and numerically efficient.
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  • 199
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    Notes: In this paper, a formulation is presented for the finite element treatment of multibody, large deformation frictional contact problems. The term multibody is used to mean that when two bodies mechanically contact, both may be deformable. A novel aspect of the approach advocated is that the equations governing contact are developed in the continuum setting first, before deriving the corresponding finite element equations This feature distinguishes the current work from many earlier treatments of contact problems and renders it considerably more general. In particular, the approach yields a characterization of the frictional constraint (assuming a Coulomb law) suitable for arbitrary discretizations in either two or three dimensions. A geometric framework is constructed within which both frictionless and frictional response are naturally described, making subsequent finite element discretization a straightforward substitution of finite-dimensional solution spaces for their continuum counterparts. To our knowledge, this general formulation and implementation of the frictional contact problem in a finite element setting has not been reported previously in the literature.The development includes exact linearization of the statement of virtual work, which enables optimal convergence properties for Newton-Raphson solution strategies, and which appears to be highly desirable (if not essential) for the general robustness of implicit finite element techniques. Since the theory and subsequent linearization require no limitations on the amount of deformation or relative sliding that can occur, the resulting treatment of frictional contact is suitable for a wide range of examples displaying significant non-linear behaviour. This assertion is substantiated through presentation of a variety of examples in both two and three dimensions.
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    International Journal for Numerical Methods in Engineering 36 (1993), S. 1465-1486 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An analysis procedure based on the finite element method is presented to solve moving-load problems of rigid pavements. The algorithm presented considers the dynamic pavement-aircraft interaction effects. The pavement-foundation system is modelled by thin-plate, non-conforming finite elements resting on a two-parameter elastic medium. The moving aircraft loads are represented by masses supported by a spring-dashpot system moving at a specified initial horizontal velocity and acceleration. The accuracy of the finite element program developed is verified by comparing the numerical results of a static problem with the available solution. A parametric study is conducted to determine the effects of the various parameters on the dynamic response of pavements. Emphasis is placed on identifying the influence of fictitious edge and corner forces acting on the plate due to the deformation of the soil medium outside the plate.
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