Advances in Engineering Software (1978)最新文献

Improvement in understanding of the process of direct integration of the equations of motion through numerical dissipation parameter interaction is being regarded as one of the significant achievements of structural dynamics research over the past quarter century. The numerical software fraternity has extended one-step integration algorithms, emphasizing controllable approximation characteristics with respect to such factors as period elongation and amplitude decay. These studies have resulted in setting up a class of implicit, second order finite difference (FD) generic models which are unconditionally stable depending on the range of influence of the corporate parameters.

The aim of this paper is to review some of the strategems incorporating the dissipation control, and to provide representative numerical findings in beam and plate applications through a unification algorithm, which streamlines the intervention of alpha modifiers to Newmark's integration formalism by evoking a set of recurrence relations that serves to pool accessible and amendable dissipation parameters. Experience has shown that the beam and plate finite element (FE) response calculations provide considerable impetus to use Bossak's type integrator with large values of the dissipative parameter.

A procedure for implementing constraint relations among finite element nodal degrees of freedom is outlined. Rather than imposing the constraint relations on the global stiffness or mass matrix as the conventional approach, this procedure is based on the element formulation level in that the element matrices and vectors are properly converted to account for the effect of constraint relations before the global assemblage phase. Adjustment of the global matrix profile for constraint relations and matrix pivoting in equation solving are thus avoided, and the approach can be easily incorporated into existing program systems. In this paper, the theoretical treatment for the proposed procedure is given, and the software implementation aspects are also discussed.

The expression which describes the internal pressure coefficient on wind tunnels presents a high numerical instability. We present here an algorithm to avoid this instability. The results are good enough for use in common civil engineering applications.

In this paper, a FORTRAN program of BEM is established by using the ‘direct’ technique, and some good results are obtained in stress analysis of bottom outlets, which belong to a high dam of a large hydropower station situated in P.R.C. In comparison with traditional photoelastic experiment results and calculated results of FEM, it seems to us that this method is an effective technique in solving similar problems. Therefore it can be used as an important reference in engineering design. Since this method possesses advantages of saving time, high computing speed and low expense as compared with FEM, it can be provided for engineering designers to solve 2D problems of elasticity.

Initial calculations of a design of the solid rocket booster joint that failed during the shuttle tragedy showed that the design had a weight penalty associated with it. Optimization techniques were to be applied to determine if there was any way to reduce the weight while keeping the joint opening closed and limiting the stresses. To allow engineers to examine as many alternatives as possible, a system was developed consisting of existing software that coupled structural analysis with optimization which would execute on a network of computer workstations. To increase turnaround this system took advantage of the parallelism offered by the finite difference technique of computing gradients to allow several workstations to contribute to the solution of the problem simultaneously. The resulting system reduced the amount of time to complete one optimization cycle from two hours to one-half hour with a potential of reducing it to fifteen minutes. The current distributed system, which contains numerous extensions, requires one hour turnaround per optimization cycle. This would take four hours for the sequential system.

The problem under consideration involves the elastic analysis of a square plate subjected to a uniform pressure. In the first instance a square section with a central hole is considered using generalized plane strain element. The pressure is applied to the surface of a circular hole located at the centre of the section. This problem is then generalized to that of a square section with nine holes subject to internal pressure. Results involving stresses and displacements are obtained for both cases using the BEASY Boundary Element software package from Computational Mechanics Ltd. A check on the accuracy is obtained by using Lamé thick cylinder theory at selected points. The good agreement obtained gives confidence in the use of the Boundary Element method for problems of this type.

This paper discusses the development and application of a mapped type composite infinite element for modelling the response of unbounded two-phase media. The coordinate ascent mapping technique which uses conventional shape functions and the Gauss-Legendre integration method has been used for the formulation. The element is constructed such that it preserves compatibility between variations in effective stress and pore pressure. This compatibility is a basic requirement for the composite element to accurately model the two-phase media. Numerical analyses of problems with unbounded saturated media using these elements have shown considerably improved predictions compared to conventional analyses. A subroutine listing is presented to demonstrate the implementation of the element in finite element programs.

This paper presents a computer-aided engineering approach for identification of linear models from a set of frequency response data. The approach is based on a new system identification technique. The primary intention of the developed system identification technique and the associated software is to identify linear models for nonlinear systems whose input/output behaviour is characterized by their corresponding sinusoidal-input describing function models. However, the technique may also be applied to identification of linear models from experimental frequency response data. At present, the identification approach and the associated software is limited to single-output, linear, deterministic, and time-invariant systems. A computer-aided engineering environment based on the developed system identification technique has also been developed. The software is developed on a Harris-800 super-minicomputer and a Tektronix 4115B high resolution, raster, and color graphics terminal.