| In recent years,with the development of computer technology,free-form surfaces with changeable forms can be generated by using geometric modeling technology.The free-form surface grid structures have more abundant forms and better diversity,which can better express the meaning of architecture.It has been widely used in engineering practice at home and abroad.However,the free-form surface grid structures should not only meet the architectural beauty and function,but also have good mechanical performance.At present,the design steps of architectural design first and then structural design often make the free-form surface grid structures unable to ensure good mechanical performance.The previous researches on the optimization of free-form surface grid structures lack of systematic multi-objective optimization which can consider the comprehensive performance of the structure.Therefore,considering the mechanical performance,architectural aesthetics and economy of structure,establishing a perfect multi-objective optimization design theory,and then providing theoretical guidance for the engineering application of free-form surface grid structures is a very urgent topic in space structure.Based on the above background,in this paper,firstly,the hybrid multi-objective optimization algorithm based on multi-search strategy was proposed to solve the multi-objective optimization problem.Secondly,based on the hybrid algorithm,the multi-constraint and multi-objective optimization method of free-form surface grid structures was proposed,and then the multi-objective optimization research based on evaluation of comprehensive performance of grid structures was carried out,and the optimization method considering the initial prestress,joint stiffness and initial geometric imperfects of the structure was proposed;Finally,the parametric modeling of engineering structure was carried out,and the simulation optimization of engineering structure was carried out based on the proposed multi-objective optimization method.The main research work carried out is as follows:(1)The research on algorithm for solving the multi-objective optimization problem was carried out.For solving the multi-objective optimization problem,combining the advantages of traditional algorithm and evolutionary algorithm,hybrid algorithm of multi-objective optimization based on multi-search strategy with higher efficiency and better comprehensive performance was proposed,including low dimensional hybrid algorithm(LD-MOHA)and high dimensional hybrid algorithm(HD-MOHA).The 17 low dimensional multi-objective optimization problems and 6high-dimensional multi-objective optimization problems in test sets were selected.Then,based on the evaluation system of convergence,uniformity and universality of the algorithm,the effectiveness and superiority of the hybrid algorithm were verified.(2)The research on multi-constraint and multi-objective optimization method of free-form surface grid structures was carried out.The systematic multi-constraint and multi-objective optimization method of free-form surface grid structures,which including geometric model creation,multi-objective optimization problem,algorithm and constraint condition processing was established.The structural strain energy and geometric comprehensive quantitative index were taken as the optimization objective,and the multi-objective optimization of free-form surface grid structures was carried out,which verified the effectiveness and rationality of the proposed method,and verified the effectiveness and superiority of the LD-MOHA algorithm in solving the multi-objective optimization problem of freeform surface grid structures.(3)The research on multi-objective optimization of grid structures based on nonlinear analysis was carried out.Aiming at the multi-objective optimization problem with many objective functions,the integrated multi-attribute decisionmaking method was improved.Based on the nonlinear finite element analysis method,a shape optimization method,which can accurately consider the nonlinear stability of the structure was proposed,and the accuracy and superiority of the method were verified.It was verified that the HD-MOHA algorithm has higher computational efficiency and better comprehensive performance in solving practical problems.The step-by-step optimization of shape and section was carried out,which considered structural static performance,grid quality,stability and economy,and then the effectiveness of the optimization was verified.(4)The research on multi-objective optimization of grid structures considering the influence of initial state was carried out.The free-form cable supported reticulated shell was taken as the research object,the effects of initial prestress,joint stiffness and initial geometric imperfects were considered respectively.The influence of initial prestress amplitude on the multi-objective optimization results was discussed,and the joint optimization of shape and initial prestress of cable supported reticulated shells was conducted.The multi-objective considering the joint stiffness was conducted,and the influence of joint stiffness on the results of multiobjective optimization was discussed.Based on the consistent imperfect method and eigenvalue imperfect method,a multi-objective optimization method considering structural geometric imperfects was established.The effectiveness of the above multiobjective optimization methods was verified by optimization examples.(5)The research on simulation application of multi-objective optimization in practical engineering grid structures was carried out.The parametric modeling of engineering structures was carried out based on NURBS inverse mapping.Through the simulation optimization of free-form surface engineering structures with quadrilateral and triangular grids,it was verified that the multi-objective optimization method proposed in this paper can effectively improve the static performance,grid quality,stability and economy of the structure.At the same time,it was verified that the multi-objective optimization method has certain universality in engineering application. |
PDF Full Text Request