Researches On Improvement Of Evolutionary Structural Optimization (ESO)

The Evolutionary Structural Optimization(ESO)method propounded by XIE Y M,etc.in 1993 is an important method for structural topology optimization and has been widely accepted and applied after the development and improvement of 20 years.Now,some new optimization methods have been developed on the basis of ESO theory.Many of these methods,however,have some deficiencies owing to the defectiveness of ESO propounded by XIE Y M,etc.in respects of how to remove material and add it.Being aimed at the defectiveness of ESO in material removal and addition,improvement researches were made in many respects in this paper;and four sorts of improvement systems,including nine kinds of improvement methods based on ESO,were put forward by the author.These four sorts of ESO improvement systems are of controlling material removal and addition according to material efficiency grades in ESO,Periodically Expanding Frame in ESO(PEFESO);Adjusting Elastic Modulus in ESO(AEMESO),and structural optimization in Multiple Load Cases in ESO(MLCESO).These improvement researches in the paper were aimed at the defectiveness of the most basic and central optimization ideas in ESO.Therefore,optimization methods put forward in the paper are of great pertinence and widespread applicability.Being aimed at the defectiveness of ESO unable flexibly adjusting the standard of material removal and addition,two methods were put forward in the paper.One is the ESO method of removing material pro rata according to material efficiency rank,and the other is the ESO method of controlling material removal and addition according to material efficiency grade.These two methods enable ESO to make optimization easier of the structures with stress or strain changing greatly or little.Being aimed at the defectiveness of material removal and addition in the bi-direction ESO,a new Bi-direction ESO according to Material Efficiency Grades(BESO-MEG)was put forward.This method can adjust flexibly at any time the standard of adding or removing material according to specific stress.Thus,it can control better the speed of removing or adding material and enables the optimization to be made "evolutionarily".In addition,BESO-MEG is also a post-treatment of restraining effectively check format.Being aimed at the defectiveness of the higher standard of material addition and the narrower addition area in the bi-direction ESO,Periodically Expanding Frame in ESO(PEFESO)was put forward.This method lowers the standard of material addition,extends the area of material addition,and increases greatly the probability of the material being restored to structure,which has been removed mistakenly in the former optimization.PEFESO not only has completely the traditional function of the bi-direction ESO,but also improves the quality of optimization,so the former can be a better substitute for the latter.Further research was made in this paper and Periodically Expending Frame for ESO according to Material Efficiency Grades(PEFESO-MEG)was put forward.PEFESO-MEG can resolve the defectiveness of optimization relying excessively on the rejection ratio;adjust automatically at any time the speed of removing material during optimization,and therefore,further ensure optimization to be made in an evolutionary manner.Traditional ESO removes material just according to a current iteration calculation without considering the change trends of future stress.Being aimed at such a defectiveness of the traditional ESO,two ESO methods of adjusting elastic modulus in whole and in part were put forward.These two methods can find potential inefficient material through simulating the change trends of future stress of structure.They are different from the traditional method which decides inefficient material just according to one iteration calculation of certain transitional structure,so they increase the accuracy of removing inefficient material.Periodically Expanding Frame Adjusting Elastic Modulus in ESO put forward in this paper integrates the advantages of such three sorts of methods as PEFESO,controlling material removal and addition according to material efficiency grades in ESO,and adjusting material elastic modulus in ESO,thus improves systematically the defectiveness of traditional ESO method.Being aimed at the different effects of different load cases on structure optimization in multiple load cases,a method of amending rejection ratio in ESO in multiple load cases was put forward.The area of removed material after each iteration calculation in this method is determined by the weight of structural compliance or strain energy in each load case.This approach effectively resolves the structural optimization problem in multiple load cases,especially in illness load cases,and it can be directly used in the ESO of moving load or dynamic load such as an earthquake.