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  • Engineering General  (448)
  • 1985-1989  (448)
  • 1980-1984
  • 1987  (448)
  • 101
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 2315-2325 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, we extend the concept of a grading function, as introduced by Carey and Dinh2 in a one-dimensional context, to curved contours. We then apply the idea to adaptive grid redistribution for a boundary element method to solve a model boundary value problem. Numerical results are included for a potential problem to demonstrate the effect of the redistribution scheme on the solution and the geometry of the domain.
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  • 102
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 289-300 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The presented solver uses the Crout L-U decomposition method. Disk memory space requirements are reduced to an absolute minimum and disk input-output is spectacularly limited. Very extensive pivoting improves numerical accuracy and stability. Experimental test runs prove the overall efficiency of the solver.
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  • 103
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 301-317 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A simple method is proposed in this paper for improving the performance (accuracy and convergence) of quadratic elements. In this the physical domain of the problem, as well as the constitutive relationships, are transformed globally by implementing a suitable co-ordinate transformation, and the problem is then solved in the mapped (transformed) domain using finite elements of the mapped space following the processes of the conventional FEM.Results show that the method significantly improves the performance of quadratic elements in both two and three dimensions. The mathematical implications of mapping in this way indicate that the method can also be applied for improved performance to higher-order elements if required.
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  • 104
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 319-335 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An adaptive procedure for the solution of the generalized linear eigenvalue problem within the hierarchical finite element method is described. The problem of finding for a given discretization, an upper limit eigenvalue that is accurate within a prescribed tolerance is especially studied. An error estimator is presented and a recomputational scheme for improved solutions is proposed. A numerical example is included.
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  • 105
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 337-357 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new error estimator is presented which is not only reasonably accurate but whose evaluation is computationally so simple that it can be readily implemented in existing finite element codes.The estimator allows the global energy norm error to be well estmated and alos gives a good evaluation of local errors. It can thus be combined with a full adaptive process of refinement or, more simply, provide guidance for mesh redesign which allows the user to obtain a desired accuracy with one or two trials.When combined with an automatic mesh generator a very efficient guidance process to analysis is avaiable.Estimates other than the energy norm have successfully been applied giving, for instance, a predetermined accuracy of stresses.
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  • 106
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 359-373 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new method for non-linear programming in general and structural optimization in particular is presented. In each step of the iterative process, a strictly convex approximating subproblem is generated and solved. The generation of these subproblems is controlled by so called ‘moving asymptotes’, which may both stabilize and speed up the convergence of the general process.
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  • 107
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 375-392 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a method for straightening curved interfaces arising in phase-change problems. The method works on isoparametric finite elements, performing a second transformation which maps the master element onto a new one in which the interface looks like a straight line. This allows using the current Gaussian integration technique for squares to evaluate the integrals over each phase. The method provides a better estimation of the contribution of latent heat effects to the residual vector, compared to those obtained by using the assumption that the interface is straight. Appropriate guidelines for solving the non-linear system of equations arising in this kind of problem are also given. Several numerical examples are presented to show the performance of the method.
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  • 108
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 393-417 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We consider finite element analysis of problems with discontinuous material coefficients. For applications in which the material interface crosses an element, we develop special elements with an embedded flux constraint at the interface. This new procedure is compared with the standard finite element method with interface coincident with the element boundary and with an existing method proposed by Steven.1 Supporting numerical studies are conducted and rates of convergence for the solution and interface flux are examined. Some local superconvergence behaviour is observed.
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  • 109
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 419-445 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A method of evaluating eigenvalues for any combination of the first, second and third boundary conditions of heat conduction in a plate, a solid cylinder or a hollow cylinder is described. Some general relationships between eigenvalues are derived. Based on these relationships a universal algorithm is developed. A list of a package of computer subroutines is included.
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  • 110
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 474-476 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
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  • 111
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    International Journal for Numerical Methods in Engineering 24 (1987) 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
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  • 112
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 477-495 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new finite element solution method for the analysis of frictional contact problems is presented. The contact problem is solved by imposing geometric constraints on the pseudo equilibrium configuration, defined as a configuration at which the compatibility conditions are violated. The algorithm does not require any a priori knowledge of the pairs of contactor nodes or segments. The contact condition of sticking, slipping, rolling or tension release is determined from the relative magnitudes of the normal and tangential global nodal forces. Contact iterations are in general found to converge within one or two iterations. The analysis method is applied to selected problems to illustrate the applicability of the solution procedure.
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  • 113
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 513-527 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The problems of consolidation often involve unbounded continua. The most common solution is then achieved by limiting the studied area through the introduction, at finite distance, of a boundary on which adequate conditions on the field variables are imposed. In this paper mapped infinite elements are used to model the far-field solution. Spatial discretization is hence performed on the basis of both finite and infinite elements. In two examples, solutions involving finite and infinite elements are compared with known analytical solutions and it is shown that an excellent agreement can be achieved by the use of mapped infinite elements.
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  • 114
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    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 24 (1987), S. 497-512 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In an earlier paper a method for calculation of non-linear structural response was described. The method is based on an algorithm, proposed by Bergan, including simultaneous iterations in the load and displacement spaces. A method for selective damping of solution components parallel to critical eigenvectors was proposed reducing the risk for diverging equilibrium iterations.This method is, in the present paper, shown to be related to the ‘dynamic relaxation’ approach. The method has been further studied for practical problems, and especially adapted for the analysis of plate buckling. A method for variable damping is proposed, and compared to existing methods. The conclusions are that damping, based on eigenvector projection, is an efficient way to improve the stability in the iterations, and in this an alternative to other methods for choice of optimum corrections in N-R schemes. The extra computational effort is considered worth while in cases where restarts in the calculation are not desired.In the paper, suitable criteria for reformulation of the tangential relation during iterations in a step are also discussed.
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  • 115
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 529-541 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A technique is developed and presented which improves the accuracy of the predictions for the eigenvalues of the usual first order perturbation scheme for the generalized symmetric linear algebraic eigenvalue problem. The improved method very simply replaces the usual B-norms appearing in the denominator of the expressions for the first order changes in the eigenvalues by BP-norms where BP is the perturbed B matrix. With increasing sizes for the perturbations the improved technique produces results whose accuracy approaches those of the usual second order predictions. Numerical studies are presented to support the analysis.
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  • 116
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 543-556 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Using a tanh transformation a quadrature formula for the evaluation of singular integrals is obtained. The formula has the same step length h as the formula for regular integrals derived by F. Stenger. These quadrature formulae are valid for end point singularities of any order and their error exhibits an exponential decay when the number of integrations tends to infinity.Using these formulae the solution of singular integral equations does not depend on the order of the end point singularities. Furthermore the collocation points are given by a very simple equation and, in the case of constant coefficients, by a closed-form formula.
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  • 117
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 557-567 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: When the method of lines is used for solving time-dependent partial differential equations, finite differences are commonly employed to obtain the semidiscrete equations. Usually, if the solution is expected to be smooth, symmetric difference formulae are chosen for approximating the spatial derivatives. These difference formulae are almost invariably based on Lagrange type differentiation formulae. However, if it is known in advance that periodic components of given frequency are dominating in the solution, more accurate difference formulae, based on exponentials with imaginary exponent, are available. This paper derives such formulae and presents numerical results which clearly indicate that the accuracy can be improved considerably by exploiting additional knowledge on the frequencies of the solution.
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  • 118
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 569-580 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An error analysis and an adaptive refinement scheme are developed for use with a class of least-squares finite element methods. The error indicators for the refinement procedure are based on element residuals which are calculated as part of the least-squares method. The solution scheme used in the supporting numerical studies employs an elment-by-element conjugate gradient algorithm. Consequently, storage and computation are not influenced by nodal numbering.
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  • 119
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 581-604 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A nine node shell element is developed by a new and more efficient mixed formulation. The new shell element formulation is based on the Hellinger-Reissner principle with independent strain and the concept of a degenerate solid shell. The new formulation is made more efficient in terms of computing time than the conventional mixed formulation by dividing the assumed strain fields into a lower order part and a higher order part. Numerical results demonstrate that the present nine node element is free of locking even for very thin plates and shells and is also kinematically stable. In fact the stiffness matrix associated with the higher order assumed strain plays the role of a stabilization matrix.
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  • 120
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 605-620 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes the proper external potential formulation of a cathodic protection system employed for corrosion prevention of structures in infinite electrolytes. The boundary condition associated with the mathematical formulation is not of the standard type encountered in hydrodynamic, electrostatic or heat transfer applications. The developed mathematical model is discretized by the boundary element technique, which is then solved iteratively by the Newton-Raphson method.
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  • 121
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 635-654 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: By combining discrete Kirchhoff theory with least-squares smoothed shape functions, an improved quadrilateral thin-plate bending element is derived. This element exhibits improved performance over an earlier DKQ element in predicting both displacements and stresses. Numerical examples are presented comparing the element with many other quadrilateral elements for standard test problems.
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  • 122
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 621-634 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the past the time domain solution of the wave equation has been limited to simplified problems. This was due to the limitations of analytical methods and the capacity of computers to manipulate and store ‘large’ blocks of spatial information. With the advent of ‘super computers’ the ability to solve such problems has significantly increased. This paper outlines a method for transient analysis of wave propagation in arbitrary domains using a boundary element method. The technique presented will allow the definition of a domain, the input of impedance conditions on the domain's surface, the specification of inputs on the surface, and the specification of initial conditions within the domain. It will produce a complete solution of the wave equation inside the domain. The techniques are demonstrated using a program with a boundary element formulation of Kirchhoff's equation. The elements used are triangular and compatible.
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  • 123
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 975-991 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents the development of an automatic design algorithm for gears. The criterion on which the design performance is assessed is the maximum tensile stress induced in the gear tooth fillet under service conditions. Starting from an initial set of design parameters the stresses in the gear tooth fillet are calculated. The maximum value of the stress is then expressed as a function of the design variables. By minimizing this function, the objective function, subject to both equality and inequality constraints a new set of design parameters, is produced. Iterative application of the analysis and minimization stages forms a sequence of non-linear optimization problems which converges to yield the optimal design.Finite element techniques employed to calculate accurately the stresses in the gear tooth are again used to compute the design derivatives. This process is very economical, owing to its efficient reuse of the factorized stiffness matrix.The algorithm is illustrated by its application to a spur gear tooth of involute profile. Both linear and non-linear forms of the objective function are used and a comparison made between the solutions obtained.
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  • 124
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1101-1121 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Methods for generating Pareto optimal solutions to a multicriterion optimization problem are considered. The norm methods based on the scalarization of the original multicriterion problem by using the lp-norm are discussed in a unified form and a parametrization suitable for different interactive design systems is suggested. In addition, an alternative approach which, instead of scalarization, reduces the dimension of the multicriterion problem is proposed. This is called the partial weighting method and it can beinterpreted as a generalization of the traditional scalarization technique where the weighted sum of the criteria is used as the objective function. The first of these two approaches (norm method) is very flexible from a designer's point of view and it can be applied also in non-convex cases to the determination of the Pareto optimal set whereas the latter (partial weighting method) is especially suitable for problems where the number of criteria is large. Throughout the article several illustrative truss examples are presented to augment the scanty collection of multicriterion problems treated in the literature of optimum structural design.
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  • 125
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1123-1155 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A simple, shear flexible, quadrilateral plate element is developed based on the Hellinger/Reissner mixed variational principle with independently assumed displacement and stress fields. The crucial point of the selection of appropriate stress parameters is emphasized in the formulation. For this purpose, a set of guidelines is formulated based on the following considerations: (i) suppression of all kinematic deformation modes, (ii) the element has a favourable value for the constraint index in the thin plate limit, (iii) element properties are frame-invariant. For computer implementation the components of the element stiffness matrix are evaluated analytically using the symbolic manipulation package MACSYMA. The effectiveness and practical usefulness of the proposed element are demonstrated by the numerical results of a variety of problems involving thin and moderately thick plates under different loading and support conditions.
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  • 126
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1229-1231 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
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  • 127
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    International Journal for Numerical Methods in Engineering 24 (1987) 
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  • 128
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1333-1341 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The modelling of heat transfer from a moving gaseous atmosphere by the TLM technique is described. For the case of very rapidly moving gas, results are compared with those derived from finite element analysis.
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  • 129
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1343-1354 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A procedure to generate 2D meshes of triangles in a quite general fashion allowing for local and selective mesh-refinement is presented and discussed. The grid generator is based on the iterative application of 4-triangles conforming mesh-refinement algorithms for triangulations, which are also introduced in this paper. These algorithms are modified versions of those proposed in Int. j. numer. methods eng., 20, 745-756 (1984), and they can be used for global refinement of a grid, as well as for local refinement. The grid generator works in the following way: given any initial coarse triangulation which properly defines the geometry of the problem, a set of user-defined refinement subregions Ri, i = 1,2,…, N, and an associated set of tolerance parameters hi, an irregular and conforming final triangulation is automatically constructed in such a way that the diameter of all the triangles contained in Ri is smaller than hi, i= 1,2,…, N. Moreover, all angles in the final triangulation are greater than or equal to half the smallest angle in the initial, coarse one. The refinement is propagated only to assure the conformity and smoothness of the grid, and consequently, the number of involved nodes will be minimized. The refinement of the final mesh will be determined by the subregions Ri and the parameters Ni and will be essentially independent of the initial coarse grid. The 4-triangles conforming mesh-refinement algorithms are presented and their properties discussed. The implementation of these techniques is discussed and examples of the application of the grid generator are given.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1355-1366 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Classical iterative methods when applied to the partial solution of the generalized eigenvalue problem Ax =λBx, may yield very poor convergence rates particularly when ill-conditioned problems are considered. In this paper the preconditioned conjugate gradient (CG) method via the minimization of the Rayleigh quotient and the reverse power method is employed for the partial eigenproblem. The triangular splitting preconditioners employed are obtained from an incomplete Choleski factorization and a partial Evans preconditioner. This approach can dramatically improve the convergence rate of the basic CG method and is applicable to any symmetric eigenproblem in which one of the matrices A, B is positive definite. Because of the renewed interest in CG techniques for FE work on microprocessors and parallel computers, it is believed that this improved approach to the generalized eigenvalue problem is likely to be very promising.
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  • 131
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1367-1393 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The p-method capabilities have thus far been used only in connection with the assumed displacement model elements. When such elements are used, singular points have to be isolated by one or two layers of small elements graded in a suitable geometrical progression towards singularity. This paper presents an alternative formulation which circumvents this drawback and enables excellent solution results to be obtained with uniform FE-grids. The formulation is based on the recently presented hybrid-Trefftz FE-model and makes use of optional expansion sets for various singularities or stress concentrations. Stress concentrations due to concentrated loads are also properly accounted for. It is shown that by augmenting the order of approximation over a fixed grid of such elements rapid convergence towards the accurate solution is obtained in the most efficient way.This paper summarizes the results of a preliminary study that had been undertaken to critically evaluate the potential of the new approach as a suitable basis for subsequent developments of a fully automated adaptive process.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1395-1416 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An unconditionally stable algorithm for the numerical integration of elastoplastic pressure-dependent constitutive relations is analysed in detail in this paper. The application of the method to plane stress problems, in which the out-of-plane strain component is not defined kinematically, is discussed. The tangent moduli resulting from this integration algorithm are obtained by consistent linearization of the elastoplastic constitutive equations. The algorithm is applied to Gurson's constitutive model, some one-dimensional problems are solved, and comparisons with exact solutions are made. The paper closes with a numerical study of the necking of an axi-symmetric specimen using Gurson's plasticity model to describe the constitutive behaviour of the material.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1417-1419 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1419-1419 
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    International Journal for Numerical Methods in Engineering 24 (1987) 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1421-1437 
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    Notes: The paper presents a method of calculation for the transient electromagnetic field in a steel rotor screen of a superconducting generator. Using the difference method, the spatial-temporal distributions of the electromagnetic field have been calculated as a result of solving the non-linear partial differential equation for the vector potential A (in space Ω(r, θ,t)). For the difference diagram the conditions of stability and convergence have been determined.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1611-1613 
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    International Journal for Numerical Methods in Engineering 24 (1987) 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1609-1609 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1615-1628 
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    Notes: Cost effective high precision hybrid elements are presented in a hierarchical form for vibration analysis of plates. The elements are constructed by introducing computer installed hierarchical element generator algorithms which take advantage of the exact analytical treatment of the energy integrals automatically. Additional benefits accrue from: (i) the careful selection of assumed stresses and displacements satisfying finite element requirements, and maintaining the correct stiffness rank and invariance; (ii) the ability to reduce computational costs associated with various operations and the independence with respect to element geometries, which serve to build up a methodology to handle the generation of finite elements in any general purpose finite element system efficiently. Extensive numerical studies are made to predict the natural frequencies and harmonic response of plates with different boundary conditions. Accuracy of the solutions is assessed by comparison with the well established results. The noteworthy aspects of the applications are that the proposed elements are faster than those cited previously, and show a more favourable comparison to the analytical solutions for a wider range of vibration modes by maintaining rapid convergence characteristics.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1659-1669 
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    Notes: The effect of elastic strains in the steady-state visco-elastic fluid flow under the rolling process is analysed quantitatively. Spurious oscillations in the stress deviator and pressure fields are precluded and the rate of convergence is improved when the Petrov-Galerkin method, which is based on a least-square method, is introduced into the finite element equation for the constitutive law.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1697-1709 
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    Notes: A new functional which forms the basis of an improved hybrid element formulation is proposed. The variables for the functional include stresses, strains and displacements, and the displacements and stresses are further decomposed into two parts respectively. The proposed new formulation appears to be particularly suitable for improving conforming models.Based on this formulation, a new four-node plane hybrid element Qcs6 can be developed, and the conforming element Q4 and the non-conforming Wilson element Q64 and modified Wilson element Qm6 can also be derived directly by this hybrid approach. It should be noted that more accurate stresses can be obtained from this element which utilizes the concept of two stress components.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1825-1826 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1823-1824 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1901-1920 
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    Notes: This paper describes how the theorems of structural variation may be used in finite element analysis. The efficiency of the theorems is examined and their application to structural and geotechnical problems illustrated.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2167-2181 
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    Notes: This paper presents an attempt to clarify further the nature of the overstiffness of thin curved structural elements. It follows the approach presented by Ashwell and co-workers1,2 who based their study on shape functions of arch elements. Such elements display the same stiff behaviour as complex shell elements but are simpler to study and understand. An examination of several discretizations for a two-dimensional curved beam-column element for linear elastic analysis of arches is performed. This examination and the numerical results obtained from these approximations provide a new interpretation of the artificial strains based on the mapping variables of shape functions. Two new methods to reduce the artificial stiffness of the element are proposed.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2183-2200 
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    Notes: Automating triangular finite element mesh generation involves two interrelated tasks: generatine a distribution of well-placed nodes on the boundary and in the interior of a domain, and constructing a triangulation of these nodes. For a given distribution of nodes, the Delaunay triangulation generally provides a suitable mesh, and Watson's algorithm26 provides a flexible means of constructing it. In this paper, a new method is described for automating node placement in a Delaunay triangulation by seieclive refinement of an initial triangulation. Grading of the mesh is controlled by an explicit or implicit node spacing function. Although this paper describes the technique only in the planar context, the method generalizes to three dimensions as well.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2237-2238 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2201-2215 
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    Notes: A Petrov - Galerkin finite element method for two and three-dimensional time dependent convection-diffusion equations is presented in the context of two space dimensions. The method involves perturbed weighting functions in the weighted residuals formulation, that are bilinear in space and quadratic in time and depend on two parameters which are calculated according to a local analysis for the one dimensional case. The perturbations to the weighting functions can be interpreted as an added local anisotropic balancing diffusion and an added dispersion in the direction of the convective motion. The effectiveness of the method is shown through several examples involving the convective and diffusive transport of scalar distributions in known velocity fields.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2239-2239 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2241-2252 
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    Notes: A new algorithm is presented for automatically grading meshes generated over planar triangular and quadrilateral regions using parametric mappings. Rational parametric bicubic Bézier polynomials are coupled with an element density function to concentrate elements around regions of high solution gradients.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2253-2271 
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    Notes: In this paper 8-node traction singular boundary elements are employed to represent displacement and traction variations in the vicinity of the crack front in three-dimensional geometries. The numerical procedure suggested for evaluating the singular integrals extending over these special elements is described. The efficiency and accuracy of the special elements and integration procedure are demonstrated by the results obtained in a simple test problem whose analytical solution is known. The interaction of two circular coplanar cracks embedded in an infinite medium under uniform tension loading is also analysed. Finally, the stress intensity factor variation computed for a semi-circular inner surface crack in a pressurized cylinder is presented.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2301-2313 
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    Notes: Transverse vibrations of an axially moving (travelling in its own plane) membrane submerged in ideal fluid are analysed using the FEM. The discrete equations differ from the equations of the common coupled problem in that there appear two additional inertia terms due to the convective acceleration. The effect of the density of the element mesh, the effect of the truncation distance and the effect of various lumping techniques on the accuracy of the results are studied. The FEM-results are compared with available analytical and experimental results. The agreement seems to be rather good.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2273-2299 
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    Notes: In this paper we present a Legendre spectral element method for solution of multi-dimensional unsteady change-of-phase Stefan problems. The spectral element method is a high-order (p-type) finite element technique, in which the computational domain is broken up into general (curved) quadrilateral macroelements, and the solution, data and geometry are expanded within each element in terms of tensor-product Lagrangian interpolants. The discrete equations are generated by a Galerkin formulation followed by Gauss-Lobatto Legendre quadrature, for which it is shown that exponential convergence to smooth solutions is obtained as the polynomial order of fixed elements is increased. The spectral element equations are inverted by conjugate gradient iteration, in which the matrix-vector products are calculated efficiently using tensor-product sum-factorization.To solve the Stefan problem numerically, the heat equations in the liquid and solid phases are transformed to fixed domains applying an interface-local time-dependent immobilization transformation technique. The modified heat equations are discretized using finite differences in time, resulting at each time step in a Helmholtz equation in space that is solved using Legendre spectral element elliptic discretizations. The new interface position is then computed using a variationally consistent flux treatment along the phase boundary, and the solution is projected upon the corresponding updated mesh. The rapid convergence rate and stability of the method are discussed, and numerical results are presented for a one-dimensional Stefan problem using both a semi-implicit and a fully implicit time-stepping scheme. Finally, a two-dimensional Stefan problem with a complex phase boundary is solved using the semi-implicit scheme.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2343-2356 
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    Notes: Plate and shell finite elements based upon Mindlin plate theory and evaluated by one-point quadrature are attractive because of their effectiveness for both thick and thin shells, at minimal computing cost. However, these elements are rank-deficient and must be stabilized to obtain reliable behaviour. Methods for achieving full rank of the stiffness and for stabilizing element behaviour in static analysis and in explicit dynamic calculations exist and are quite effective. This paper addresses the remaining issue of controlling spurious modes of response in vibration analysis and implicit dynamic solutions. Several alternatives for the element mass formulation are examined in detail. We show that non-physical dynamic modes present a potential problem with most mass matrix formulations, and that spurious modes other than the familiar hourglassing motion are possible. A combination of projection methods and reduced quadrature is suggested which eliminates these deficiencies and produces accurate numerical results. The remaining techniques investigated give rise to anomalous behaviour which make them unsuitable for general use.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 25-45 
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    Notes: The proposed method is the direct boundary integral equation (BIE) method applied to three-dimensional transient heat transfer analyses and to corresponding elastostatic analyses under thermal loading. The mechanical and thermal problems are decoupled. For those not familiar with the BIE method, a short survey of the basic principles is given to help them understand the mathematical treatment, which is performed in the frame of distribution theory. The tempered elementary solution of the transient heat transfer problem contains time and space variables. The numerical treatment of the thermal equation is performed analytically with respect to time and numerically with respect to space in the same way as for steady state equations. Great care is paid to space integration in order to compute the values of the kernels precisely enough on the surface and inside the volume. The computational treatments of both problems are realized in such a way as to minimize computing time. Differences between transient and steady state analyses, on the one hand, and between elastostatic analyses with and without thermal loading, on the other, are emphasized. Finally, an analytical example shows the good behaviour of the proposed method to solve singular thermal problems and an industrial example shows the accuracy of the results obtained by using the BIE method to solve three-dimensional thermo-elastic problems.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 101-115 
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    Notes: A multigrid algorithm for implementation on unstructured meshes is proposed. The algorithm uses a sequence of unnested grids and requires the development of efficient inter-grid interpolation procedures. It is demonstrated how elliptic problems can be solved in this fashion by using Jacobi smoothers.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 89-99 
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    Notes: In this paper some numerical predictions are presented for the buoyancy-driven turbulent flow and heat transfer in a large cavity using both a prescribed eddy viscosity model and a k-∊ model. The results from these models are in good agreement, although the calculations with the prescribed eddy viscosity model are considerably cheaper. The results also show the correct qualitative behaviour, but there are some differences between the predictions and the available experimental data. Possible reasons for these are discussed.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 177-202 
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    Notes: This article describes numerical modelling of heat transfer and thermoelasticity effects that are significant in thermo-optical designs of solid state slab lasers capable of high average output power. The heat equation and equations of thermoelasticity are solved simultaneously to evaluate thermal stresses and microscopic deformations in isotropic and anisotropic laser host media. An efficient dynamic alternating-direction implicit method has been developed and applied in this work to solve the steady state heat transfer and stress potential equations in two dimensions. Numerical results are presented for some problems that arise in baseline designs of experimental slab laser systems.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 231-249 
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    Notes: A mathematical model has been developed to quantify the effects of process conditions during turbulent solidification and mixing of a liquid metal jet in a confined co-flowing molten metal stream.The modelling has been split into three parts. First, a single phase model with no latent heat effects to consider the solidification potential. Secondly, a two phase model where the second phase is comprised of solid particles which solidify during mixing of the two streams. Thirdly, a two phase model where the second phase consists of the inner jet, which is assumed to break up into droplets of given size, and solid particles are allowed to form by solidification within the droplets.The results show that the thermal history (solidification path) of the solid phase formed is affected by latent heat and particle size, which implies that solidification, nucleation and jet fragmentation events should be included dynamically to ensure realistic predictions.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 285-287 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 263-270 
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    Notes: The die-swell occurring during the extrusion of a visco-elastic fluid has been extensively examined in recent years, both experimentally and numerically. These investigations have been mainly confined to isothermal flows. If the material is initially relatively cool, however, viscous heating may lead to proportionally large changes in temperature and material properties, with significant effects on die-swell. An iterative computational model is presented which describes the flow of Maxwell and Oldroyed fluids subject to the effect of temperature gradients induced by viscous heating and thermal boundary conditions. Predictions are presented for extrusion from both slit and axisymmetric dies.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 993-1014 
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    Notes: New algorithms which improve the finite element solution on a fixed mesh of the domain are developed. For this, objective functions which depend on a positive parameter to be determined are proposed. These functions lead to criteria which combine in several ways the residual of the solution, the approximation in the Euclidean norm of the value of the solution at the nodes, and the approximations in the energy and Hk norms. Some aspects of optimality are studied and, finally, numerical results are given.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1029-1029 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1079-1091 
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    Notes: This paper is concerned with a method for obtaining stresses in a rod of arbitrary cross-section subjected to combined loads of bending, shearing and torsion which are the complicated functions of time. In the first step, the analysis derives the bending moment, shearing force and torsional moment by use of a combination method of the Laplace transformation and Fourier series expansion. The transient stresses are obtained based on the two-dimensional theory of elasticity, but in which the Fourier expansion collocation procedure is applied to deal with the complex boundary shape of the cross-section. To affirm the validity of this analysis, experimental tests are also carried out for an oval rod subjected to the three combined transient loads.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1232-1232 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1233-1250 
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    Notes: A system of algorithms is presented for the computer simulation of confined unsteady flows of a compressible fluid. The methods are valid for a wide range of time scales and are applied to simulate wind tunnel acoustics, flow over a ramp and flow past aircraft cavities.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1269-1281 
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    Notes: This paper proposes a basis change strategy within the reduced gradient method for optimization under linear constraints. It ensures a non-singular basis matrix at every iteration. The same strategy can reliably be used within the generalized reduced gradient method for optimization under non-linear constraints. This method is applied to the minimum weight design of large structures under displacement and stress constraints, exploiting the sparsity of the constraint Jacobian matrix.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1251-1267 
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    Notes: In order to study problems on fluid-structure interaction, we have used a mixed formulation which couples the classical functional of the structure with a new variational formulation by integral equations for the fluid. This formulation has the advantage over the finite element methods of avoiding the discretization of the fluid domain. Furthermore, unlike collocation methods, the explicit calculation of the Hadamard finite part of the singular integrals is avoided. This leads after discretization by boundary finite elements to a small and symmetrical algebraic system.Typical examples are presented that demonstrate the efficiency of this variational formulation by studying the sound transmission through a baffled plane structure and through a flexible panel backed by a rigid cavity. These include the calculation of the transmission loss factor and the determination of which modes dominate the noise transmission. Good agreement is obtained between numerical results and analytical results found in the literature.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1283-1296 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A least-squares variational procedure for first-order systems of differential equations and an approximate formulation based on finite elements are developed. Error estimates, a condition number bound and analysis of weighting factors are given. Steepest descent and conjugate gradient solution procedures are examined, and an appropriate preconditioner constructed which is demonstrated to yield rapid convergence and to be insensitive to problem size. Numerical studies of rates of convergence for a test problem are given.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1297-1303 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Chorin's random vortex method is used to predict the growth of a large-scale coherent vortex structure in the early stages of the development of turbulence in a two-dimensional co-flowing shear layer. The numerical algorithm has been simplified to such an extent that the numerical analysis can be performed on a microcomputer. The numerical solution exhibits the same early turbulent instabilities and vorticity pairings as found in recent flow-visualization experiments. In addition the results are in reasonable agreement with experimental measurements of mean velocity, root mean square fluctuations and Reynolds stresses. One could thus test the shear layer sensitivity to initial conditions and the upsteam boundary conditions.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1439-1450 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: A simplified procedure is presented for the analysis of sea water intrusion in unconfined aquifers. It involves the finite element method with a residual flow procedure which combines transformation of the salt water zone into the fresh water zone that has the same pressure distribution as that of the salt water. This procedure avoids simultaneous solutions of governing differential equations for both flow and mass transport. Numerical results are compared with laboratory observations.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1451-1459 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Sparse matrices composed of a central band and augmented dense rows and columns are becoming prevalent in the numerical solution of a large class of boundary and initial-value problems. A Fortran Subroutine ARROW is presented for the LU decomposition and solution of linear equation systems with such a structure. The computational speed of the program is compared in MFLOPS (millions of floating point operations per second) to the LINPACK benchmark for the solution of a dense linear system and is found to be of comparable speed on both supercomputers and minicomputers. Use of the Basic Linear Algebra Subroutines (BLAS) available on most machines significantly enhances the speed of ARROW.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1461-1477 
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    Keywords: Engineering ; Engineering General
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    Notes: A new kind of finite element is presented in this paper which is designed to work efficiently for bodies that are either prismatic or ‘quasi-prismatic’ in shape. Quasi-prismatic shapes are those which can be obtained from prismatic shapes by mere distortion. The element which is formulated in this paper may be coupled with other types of three-dimensional elements to allow the modelling of structures which are only partially prismatic or which have prismatic shapes within them. The element allows for a variety of boundary conditions, yet yields meshes which are easy to generate. The performance of this element is evaluated by numerical experiments that compare its results with analytical solutions for a thick cylinder problem and a curved beam problem. The element has also been demonstrated on a turbine blade model.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1479-1497 
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    Keywords: Engineering ; Engineering General
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    Topics: Mathematics , Technology
    Notes: The mathematical modelling of the electrodeposition phenomenon leads to a linear elliptic partial differential equation subject to non-linear mixed boundary contitions. This is complicated further by the fact that the domain under consideration is evolving with time.Owing to the nature of the mathematical model, the boundary element method is a very efficient numerical technique for the solution of such problems. The authors report their numerical simulation of the above problem which also has applications in the cathodic protection systems for corrosion prevention.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1499-1508 
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    Keywords: Engineering ; Engineering General
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    Notes: A simple formulation of a nine d.o.f plane triangle is achieved by the assumed-stress hybrid approach. The element has two translations and the rotation about a normal to the plane as d.o.f. at each node. Performance of the element is shown to be good. A device for softening overly-stiff elements is found to be effective and is suggested as a widely applicable method of improving the behaviour of hybrid elements. A particularly simple form of the element, herein called the CST Hybrid, appears to be the best performer.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1509-1532 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An algorithm for stable and accurate computations of stresses in finite element thermo-elastic-plastic and creep analysis of metals is presented. The effective-stress-function algorithm solves the governing equations of the inelastic constitutive behaviour by calculating the zero of the appropriate effective-stress-function: a functional relationship which involves as unknown only the effective stress. The derivation of the effective-stress-function for thermo-elasto-plasticity conditions, including creep, for 2-D and 3-D analysis is presented, and the algorithmic steps of the stress solution are discussed. For use in the stiffness matrix a tangent material stress-strain relationship is evaluated consistent with the effective-stress-function algorithm. The solution of some demonstrative problems shows the effectiveness of the solution procedure.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1541-1550 
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    Keywords: Engineering ; Engineering General
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    Notes: In finite element computations of magnetic fields, the boundary condition n × h = 0 is usually enforced on walls made of a material ofgreat permeability. We purport here to question the validity of this approximation. It is shown how this condition stems from a suitable passage to the limit (when the ratio of permeabilities μ0/μ tends to zero), provided a condition of topological nature (‘no loops’) is fulfilled. What to do when this condition does not hold is discussed.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1551-1562 
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    Notes: A finite element method for computing the resultant magnetic field arising from a given source field in the presence of a magnetic material of variable permeability is described; in this method finite element approximations to the scalar potential of the resulting field and the magnetic susceptibility, in the region occupied by the magnetic material, are determined from the non-linear integral equation for the scalar potential and the constitutive susceptibility relation, using a collocation scheme.The method is used to compute the shielding effect of a thin rectangular plate of variable permeability on a given source field. The plate is subdivided uniformly into brick elements; the resulting translational invariance of the integrals required in the calculations is exploited to achieve major computational savings.A consequence of the thinness of the plate is that the calculation of the requisite integrals by analytic methods leads to considerable loss of accuracy by differencing; this difficulty is overcome by using a scheme which combines both analytic and quadrature techniques.The resulting system of non-linear algebraic equations is solved by Powell's hybrid method; an efficient scheme for calculating an initial approximation to the Jacobian, which utilizes the structure of the equations, is presented.The results of the calculations are discussed.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1563-1579 
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    Topics: Mathematics , Technology
    Notes: The development of a general curved triangular element based on an assumed displacement potential energy approach is presented for the analysis of arbitrarily laminated thick shells. The associated laminated shell theory assumes transverse inextensibility and layerwise constant shear angle. The present element is a quadratic triangle of C0-type in the curvilinear co-ordinate plane, which is then mapped onto a curved surface. Convergence of transverse displacement, moments, stresses and the effect of two Gauss quadrature schemes also form a part of the investigation. Examples of two laminated shell problems demonstrate the accuracy and efficiency of the present element. Comparison of the present LCST (layerwise constant shear-angle theory) based solutions, with those based on the CST (constant shear-angle theory) clearly demonstrates the superiority of the former over the latter, especially in the prediction of the distribution of the surface-parallel displacements and stresses through the laminate thickness.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1581-1591 
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    Notes: The so-called finite element-difference method introduced in References 1 and 2 yields a continuous stress field by finite difference operations and finite element interpolations. In the present paper, applications of the method to vibration problems are discussed. The inverse iteration procedure is modified for this method. Numerical results show that the accuracy of solutions depends strongly on the type of finite difference operator chosen: for reliable and accurate solutions in modal analysis problems, element internal strains must be included in the strain field used to compute nodal forces associated with element deformations.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1593-1608 
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    Notes: For most practical purposes, the central-difference scheme (CDS) would be ideal only if it were unconditionally stable. It is a simple and second-order scheme which is easy to implement. It does not introduce any second-order ‘diffusion’ like truncation error. However, for grid Peclet numbers larger than 2, the CDS leads to over- and under-shoots and is unstable. This paper presents a method, called CONDIF, which eliminates this undesirable feature of the CDS. It modifies the CDS by introducing a controlled amount of numerical diffusion based on the local gradients. The numerical diffusion can be adjusted to be negligibly low for most problems.CONDIF has been used to solve a number of test problems which have been widely used for comparative study of numerical schemes in the published literature. For all these problems the CONDIF results are significantly more accurate than those obtained from the hybrid scheme when the Peclet number is very high (→∞) and the flow is at large angles (→45 degrees) to the grid. In general the computational effort for CONDIF is comparable (within 20 per cent) to that for the hybrid scheme. However, in one instance the rate of convergence was found to be significantly slower.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1645-1658 
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    Keywords: Engineering ; Engineering General
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    Notes: A finite-element discretization of a layered stratum is considered. The response to a time-harmonic load at a single node is calculated. For all practical purposes, the result is obtained in closed form in the case of two dimensions (line load) while the Fast Fourier Transform is employed in the three-dimensional problem (point load).
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1629-1644 
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    Notes: This paper contains the formulation of a space-time Sinc-Galerkin method for the numerical solution of the parabolic partial differential equation in one space dimension. The space-time adjective means that the Galerkin technique is employed simultaneously in time and space. Salient features of the method include: exponential rate of convergence, ease of assembly of the discrete system, a global approximation and the ability to handle singular problems. Two methods of solution for the discrete system are offered and numerical results for test problems, selected from the literature, are included.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 1849-1863 
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    Notes: Galerkin's method is applied to random operator equations. Appropriate Hilbert spaces are defined for random functions and solutions are projected into these spaces, allowing the first- and second-moment properties of the solution to be calculated. An equivalent energy-based approach similar to the Rayleigh-Ritz method is developed, from which a stochastic finite element technique is derived. Several one- and two-dimensional example problems are solved and the results discussed.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2327-2341 
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    Keywords: Engineering ; Engineering General
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    Notes: As a first step toward developing a finite element formulation that can model coupling among extensional, bending and torsional behaviour of beams, a new method is proposed to properly represent the warping of arbitrary cross-sections. The basic approach is to introduce a small warping displacement superimposed over flat cross-sections of a shear-flexible beam in a deformed configuration. Numerical tests involving simple isotropic beams undergoing a small elastic displacement demonstrate the validity of the new approach. The present approach can be extended to composite beams as well as isotropic beams experiencing a large deflection or finite rotation.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2357-2366 
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    Notes: This paper presents a method for determining the second order sensitivity matrix and logarithmic sensitivity functions in the frequency domain. The procedure described is applicable to any discrete and viscously damped mechanical system.A definition of the second order logarithmic sensitivity function has been proposed. The examples shown indicate that logarithmic sensitivity functions of the second order preserve the qualitative character of first order sensitivity functions and are more sensitive to changes of system parameters. The influence of large parameter changes on second order sensitivity functions has also been investigated.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2367-2388 
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    Notes: Arch dams can be conveniently analysed by the finite element method. For dam-fluid interaction problems, the fluid domain may be more conveniently handled by the boundary element method as a substructure first before connecting to the dam substructure. The added-mass matrix calculated from the fluid domain is symmetrized and lumped first so that the banded and symmetrical characteristics of the finite element method are retained. In the boundary element formulation, a mirror image method and quadratic elements are used for computational efficiency and accuracy. The strong singular terms are handled by using a solution which satisfies the governing equation and the free surface boundary condition. Infinite boundary conditions at the upstream of the reservoir can be reasonably approximated from the fundamental solution with accurate results, if the interior pressure distribution in the fluid domain is neglected. Numerical solutions on hydrodynamic pressure distribution and the natural frequencies of the dam-reservoir system with various water levels are obtained and compared with available analytical and experiment results.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2389-2411 
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    Notes: A new shell element, which is free from serious locking problems and which does not possess hourglass modes, is proposed. Solutions obtained with this element exhibit good convergence and are satisfactorily insensitive to mesh distortion. The element also exhibits good convergence for plates with variable thickness. This element is based on the use of assumed covariant strains which are obtained from the covariant strain field defined with respect to the element natural co-ordinate system. Only the linear version for thin shell cases is considered. The element performance is tested by application to several standard plate and shell problems. A problem involving variable thickness is also presented.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2429-2430 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 2413-2427 
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    Notes: In this investigation the postbuckling response of plane frames consisting of a large number of crooked bars is achieved by means of an efficient method based on non-linear kinematic stability analysis. The entire formulation of the non-linear equilibrium equations presented in matrix form is implemented by the computer program NLSRF (Non-Linear Stability of Rod Frames). Critical loads and critical displacements are obtained through a direct computation by using the additional stability condition resulting from the vanishing of the stability determinant.The efficacy of the method proposed herein is demonstrated by a three-storey single span frame.
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    International Journal for Numerical Methods in Engineering 24 (1987) 
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 47-57 
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    Notes: A moving finite element method that calculates the transient temperature distribution, the density distribution and the stress distribution during the sintering cycle has been developed. Coupled two-dimensional axisymmetric energy, continuity and stress equilibrium equations along with a constraint, specifying the direction of the initial material velocity, are solved in a Lagrangian co-ordinate system. The nodes move at the same speed as the material and therefore the convective terms in the differential equations drop out. At every time step, the energy equation is solved, and the computed temperatures are then used to find the densification rate. In two-dimensional problems, the continuity equation is not sufficient to calculate the two components of material velocity. Here, it is assumed that the diffusion caused by the density gradient is the driving force. This implies that the velocity vector of the material is perpendicular to the lines of constant density. Therefore, the combination of the diffusion and continuity equations will generate the initial sintering strains. The elastic stress equilibrium equations are then solved using the thermal and initial sintering strains as the driving forces. As a result, the final shape of the material and the stresses are determined.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 59-73 
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    Keywords: Engineering ; Engineering General
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    Notes: This paper describes practical experiences in dealing with non-linearities in temperature field calculations. First the use of the load vector for representing the heat radiation on the outer surfaces is reported. However, if there are also additional non-linearities in the conductance matrix, then it may happen that because of possible counteractions of the non-linearities no convergence is achieved, at least with the direct iteration. Therefore it is more appropriate to put the radiation terms into the conductance matrix where the other non-linearities, such as temperature dependent thermal conductivity and natural convection also appear. It is shown how the Newton-Raphson iteration can be applied in an easy way. In the case of temperature dependent heat sources the load vector also needs to be considered. The appropriate special measures are described.
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    Notes: It is argued that ‘sifting’ phenomena, in which fragments of fluid subjected to larger body forces move through those subjected to smaller body forces, are prevalent in turbulent flows, and that they can be simulated by means of mathematical methods which have been developed for two-phase flows.A connection with Prandtl's mixing-length theory is established; and it is deduced from the success of that theory for shear flows that there must exist a source term in the normal-to-wall-velocity equations which is proportional to the gradient of along-the-wall velocity. This term is then included in the two-fluid-model equations.Solutions of the equations are presented for a turbulent Couette flow in which the heating of one of the walls and the presence of a gravitational field can cause ‘sifting’ phenomena to become dominant. The friction and heat-transfer coefficients, and the profiles of velocity and temperature, are computed and discussed, for flows both with and without buoyancy influences.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 75-87 
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    Notes: During the propagation of a hydraulically induced fracture in a porous material, fluid leak-off occurs from the fracture to the formation. Conduction and convection of heat also take place, owing to the large difference between the fluid injection temperature and that of the reservoir. The paper describes a quasi-two-dimensional heat transfer model coupled with a filtration model. It is then coupled into different coupled fracture propagation models (two-dimensional and quasi-three-dimensional).The rheological characteristics of the fracturing fluid are temperature-dependent with a sharp breakdown. The fluid diffusion model combines cake growth at the fracture face with two-fluid flow in the formation. Temperature profiles along the fracture and the formation are computed during fracture propagation.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 117-128 
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    Notes: A new finite element method is presented. This new method contains several novel features including a streamline upwind formulation for the advection terms and equal order interpolations for all variables: velocities, pressure, temperature and other fluid properties. This new formulation uses an iterative solution method greatly reducing the computer storage requirements. The validity of the new finite element method was tested on both a natural convection problem, a thermally driven cavity, and a forced convection problem, a heated cylinder in cross-flow. The predicted results compared favourably with a benchmark solution for the cavity and an empirical correlation for the cylinder in cross-flow.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 141-157 
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    Keywords: Engineering ; Engineering General
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    Notes: We have developed a versatile finite element approach to analyse stresses and displacements induced in thermally thinned and thickened geological structures. Material and geometric non-linearities form an important aspect of the finite element simulation. The changes in geometry are incorporated by a multipoint constraint procedure. The method takes into account temperature-dependent variations in rheological properties of the medium, including the presence of a brittle-ductile transition. We illustrate the application of the method for specific geophysical problems associated with the temperature history of the earth's crust at continental margins of the Atlantic type.
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    International Journal for Numerical Methods in Engineering 24 (1987), S. 129-140 
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    Notes: The two-dimensional Navier-Stokes equations, suitably amplified to include the effects of chemical reactions and turbulence, are discretized by employing a finite-volume technique. A weighted upwind/central differencing scheme, the weight depending on the grid Peclet number, is used for the convection terms. Velocities are calculated on staggered grids. The source terms are treated in a quasi-implicit manner by combining linearization of these terms with an ICE procedure providing a time-advanced pressure. The effect of turbulence is included through the eddy-viscosity concept by solving equations for turbulent kinetic energy and its rate of decay. Combustion is modelled by an equation for mass fraction of fuel containing a fuel consumption term based on mixing-limited combustion.The resulting code, called FLACS-ICE, is employed in simulating the influence of confinement on flame acceleration in premixed, stoichiometric propane-air mixtures. Calculations are performed for large (425m3), medium (35m3) and small scale (0·0036m3) vessels. Satisfactory agreement with experimental data, published by Solberg1 is obtained. Some limitations of the code are also pointed out.
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