Advances in Engineering Software (1978)最新文献

This paper describes the theoretical basis of SDRC's redesign package OPTISEN for structures with frequency constraints. The use of the program is illustrated using two examples from the literature plus a realistic design example.

Engineering decision problems are characterized by a set of engineering alternatives which are evaluated with respect to a set of technical/non-technical criteria. The “importance” or “weights” of the criteria play a significant role in the decision analysis. Often experts' opinions are solicited to determine the criteria weights. This paper presents a method to find criteria weights.from expert's judgment. Theory of the method is presented and illustrated by an example. A computer program (subroutine) of the method in TURBO-PASCAL is presented in the appendix and applied to an engineering location problem from the literature. The subroutine can be easily adopted by writing a suitable main program.

Dynamic optimization problems occur often in all fields of engineering and management science. Such problems are often formulated as optimal control problems which is a generalization of the classical calculus of variation. As most of these problems cannot be solved analytically, efficient numerical methods are often found wanting. These are however difficult to devise, especially when hard constraints are involved. This paper presents a general purpose software which utilizes a unified computational approach to solve a wide range of optimal control problems subject to general constraints.

An idea of using a human-computer interactive program for an engineering design dealing with a nonlinear multisolution problem is introduced. The example shown is a program for a design of a drainage open channel. The hydraulics and geometry equations for triangular or trapezoidal ditches are to be satisfied by the ditch parameters, which are the side slopes (S_L and S_R), the depth (d) and the width of the bottom (W_b). The data are the flow rate (Q) and maximum allowable flow velocity. After W_b and one of the slopes for a nonsymmetrical ditch (S_L) are chosen by the designer, the other slope and d may be found as a solution of two nonlinear algebraic equations. Instead of trying to solve these equations, the program displays the two curves in s-d coordinate system. If the curves intersect, the designer types in the coordinates of the point of intersection. Otherwise, new curves for decreased velocity are displayed as the indicated key is pressed. The procedure may be continued until the curves intersect. The final parameters chosen by the designer are checked by the program to verify that the actual flow rate and velocity are within the required limits.

The current development of electroheating modeling and its application to metal industry are reviewed in this paper. Particular attention is given to formulating the coupled electromagnetic and induced heat transfer and fluid flow problems that arise in the metal industry. Following a brief introduction of the nature of electroheat problems, the formulation of electromagnetic, heat transfer, and fluid dynamic phenomena is presented. The numerical methods used for electromagnetic modeling including the finite element, and finite difference are then examined. Several commercially available software packages for electromagnetic modeling are also briefly assessed. Finally, the applications of these modeling efforts to the induction heating or melting problems are discussed.

The related problems of computing the separation/interference distance between two three-dimensional objects and clearance/protrusion distance between an object and a container wall occur frequently in industry. A method for computing these distances by solving appropriate optimization problems is presented. The method can treat three-dimensional objects with curved sides. The problem of optimally packing objects into a container is also discussed. The packing problem is also solved as an optimization problem The separation/interference and clearance/protrusion problems become subproblems to the packing problem. Examples are presented in the paper.

The paper describes a general framework for the spectral analysis of linear structures under stationary random excitation. The method can be implemented as a post-processor to a Finite Element programme.

The formulation is made in the frequency domain in a way which includes structures with hereditary characteristics. It uses the coupled equations of the normal mode components.

The method is illustrated by two examples. The first is used to show that the off-diagonal terms in the modal equations may sometimes be significant and that the damping must be treated carefully in the formulation. The second is concerned with the along wind response of buildings and is used as a benchmark. It is shown that in this case, which involves a fairly complicated excitation mechanism, the algorithm is very fast, and can reproduce previously published results.

The paper compares two Pascal programs that solve unsymmetric (very) sparse linear systems by applying, respectively, Gaussian elimination with partial pivoting and Gauss-Jordan reduction. The comparison involves both the CPU times and the storage requirements.