Research And Software Secondly Development Of Topological Optimization For Frame Structures Based On Stress Globalization

For the excellent characteristic of transmitting force and its simple structure, theframe structures are widely adopted in engineering practice. Structure analysis cancheck or even modify the engineering design. However, it can not provide satisfactoryresults. To improve the design we need to optimize the structure. Under the conditionof specific requirements of practical engineering, structure optimization can save thecost of the project. So it has important engineering significance and theoretical value.Stress constraints are the principal consideration for the structure optimization.For the local characteristics of stress, stress constraints are generally transformed tomovable lower limits of design variables with the full stress criterion. However, stressconstraints and other constraints can not be taken into account at the same time by thisprocess. Based on stress globalization method, stress constraints can be transformedinto one constraint, which can be solved simultaneously with other constraints in thesame optimization model. The stress globalization idea is firstly applied for framestructures optimization in this paper. The main contents researched in this paper are asfollows.(1) Based on the ICM (Independent Continuous Mapping) method presented byProf. SUI Yunkang, different filter functions of element stiffness and element weightare introduced to change the0-1type discrete topological variables into continuoustopological variables between0and1, thus a topological optimization model of framestructures is built with stress and displacement constraints and structure weight asobject.(2) Numerical experiments are taken to determine the approximate functionrelationship between allowable stress and allowable strain energy. According to thisexperiential formula, the allowable strain energy is determined. According to therelationship among the maximum stress, allowable stress and allowable strain energy,the allowable strain energy is adjusted in the iteration. The maximum stress iscontrolled to fit the stress constraints. The examples comparison between stressglobalization method and full stress criterion showed that stress globalization methodcan control maximum stress much more accurately.(3) With weak material element method, the material elastic modulus is modifiedaccording to the value of topological design variables in the process of iteration. Thedistribution of material elastic modulus has great impact on the optimizationefficiency and results. In this paper, two, three and continuous types of material arerespectively adopted in the numerical experiments. Compared the optimization resultsand efficiency for above various cases, it is shown that the distribution of materialelastic modulus is more discrete, the optimization is more efficient and the result ismore accurate.(4) Based on above optimization theory and arithmetic, with MSC.Nastransoftware as the structural analysis solver and MSC.Patran software as developingplatform, the topological optimization software of frame structures with globalizationof stress constraint is accomplished. The interface with new menu and form is added on MSC.Patran, and the optimization module for data exchanging and model solvingis implemented.