Document Type
Thesis
Date of Award
9-30-1984
Degree Name
Master of Science in Mechanical Engineering - (M.S.)
Department
Mechanical Engineering
First Advisor
Michael Pappas
Second Advisor
Bernard Koplik
Third Advisor
Harry Herman
Abstract
Techniques for the improvement of procedures for large scale structural synthesis are investigated. Considerable amount of research has been devoted to structural optimization. Yet as developments continue in this area, constant improvements in structural analysis methods, most of which are computationally demanding, tax the ability of existing optimization procedures to use the most powerful of the new analysis techniques effectively. This thesis presents optimization of structures modeled by classical discretized finite elements using the direct stiffness approach. The technioue presented here utilizes a Mathematical Programming (MP) method, which is based on Zoutendijk's feasible Direction Finding Problem (DFP). Modifications on Zoutendijk's DFP were made by Pappas which resulted in an improved MP procedure called CADOP5, which forms the basis cf the optimization procedure for the scheme presented here. Modifications have been made on CADOP5 by Lee, namely a)improved treatment of upper bounds of the solution vector S. b)reduced storage requirements. It is hoped that by ircorporating the above added features to the scheme, solution to large scale structural problems can be obtained.
The objective of the work presented here is structural design optimization problems involving minimum weight design with respect to static stress and displacements constraints under several loading conditions. This scheme was tested using two classical benchmark problems viz:the ten bar stress and the ten bar deflection problems. Results obtained by the rew scheme are compared with those obtained by Fully Stressed Design (FSD) and a mixed scheme , which is a combination of FSD and Optimality Criteria. The scheme presented here solved both the benchmark problems precisely in 13 and 30 redesign cycles respectively. In comparison OPTBRZ.1, a feasible direction finding MP algorithm developed by Pappas, solved the ten bar stress and deflection problems in 15 and 25 cycles respectively. In addition to the above problems the twenty two bar problem was also attempted in this case the solution converged to670,87 (lbs.) in 79 cycles. The scheme presented here is mathematically rigorous and the above results are a testimony to this fact. It has been found that the new scheme solved the above test problems exactly however attempts to solve structures involving 200 or more members have been abortive, primarily due to insufficient memory available on the UNIVAC 80/90, VS-9 system, on which the tests were performed. For such problems it is recommended that the program be loaded on a system with at least 2MB of memory.
Recommended Citation
Alexander, Sanjay M., "Computer aided design of optimum structures" (1984). Theses. 3350.
https://digitalcommons.njit.edu/theses/3350
