摘要:

AbstractA 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.

ISSN:0029-5981    

DOI:10.1002/nme.1620240702

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractIn 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 literatur

ISSN:0029-5981    

DOI:10.1002/nme.1620240703

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThis 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 mat

ISSN:0029-5981    

DOI:10.1002/nme.1620240704

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA 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 gi

ISSN:0029-5981    

DOI:10.1002/nme.1620240705

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractChorin'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 con

ISSN:0029-5981    

DOI:10.1002/nme.1620240706

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractConformal mapping regularizes (in the new plane) the singular stress field around the crack tip. So, conventional finite elements can be used in the transformed plane. The inverse mapping of the above elements gives another class of ‘mapped elements’. The crack‐tip mapped element is a singular element. Thus, using various elements (the ‘parent elements’) in the mapped plane we obtain an infinity of singular elements, the ‘product elements’. These singular elements are introduced naturally and have no defect, as many other singular

ISSN:0029-5981    

DOI:10.1002/nme.1620240707

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe established finite difference equations to estimate one‐dimensional transient heat flow in solids are the ‘classical’ form (explicit), and the Crank–Nicolson and ‘pure‐implicit’ forms (both implicit). They are all based on finite difference approximation to the Fourier continuity equation. To these are now added three more explicit forms: exponential linear, exponential inverse cosine and polynomial, which are based on exact solutions to the Fourier equation. The performance of each of the six equations is tested against the exact results of a well known step excitations problem (the Groeber model). The tests consist of examining (i) finite difference errors arising from a single implementation of each form at different stages in the transient cooling process, (ii) the errors that accumulate during part or all of the cooling process (both as regards any bias that is introduced, and also a measure of variance) and (iii) the run times in executing the various forms. The nondimensional time steprwas treated as the independent variable, and can be made arbitrarily large, by use of a simple time‐division procedure (otherwiser<½ for use with the classical form). It is shown that having regard to both error and run time, the polynomial form appears to be the most eff

ISSN:0029-5981    

DOI:10.1002/nme.1620240708

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe 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.

ISSN:0029-5981    

DOI:10.1002/nme.1620240709

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA 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 inInt. 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 subregionsRi,i= 1,2,…,N, and an associated set of tolerance parametershi, an irregular and conforming final triangulation is automatically constructed in such a way that the diameter of all the triangles contained inRiis smaller thanhi,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 subregionsRiand the parametersNiand 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 ge

ISSN:0029-5981    

DOI:10.1002/nme.1620240710

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractClassical iterative methods when applied to the partial solution of the generalized eigenvalue problemAx=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 matricesA,Bis 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 promisi

ISSN:0029-5981    

DOI:10.1002/nme.1620240711

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY