Research On Improved Equivalent Static Loads Method And Its Application In Crash Topology Optimization Of Vehicle Structure

Title:Research on Improved Equivalent Static Loads Method and its Application in Crash Topology Optimization of Vehicle Structure Major:Automobile Engineering Advisor:Prof.Haitao Min and Prof.Tianfei MaWith the continuous increase of car ownership,energy saving and safety have become major challenges for car development.Vehicle lightweight technology and structural crashworthiness design have also become an important technical means to meet current challenges.Considering the contradiction and competition between lightweight design and structural crashworthiness,scholars and research institutions at home and abroad generally hope to apply the structural crash topology optimization method to conceptual design of automobile products to achieve the goal of lightweight design of automobile structure to meet the requirements of crashworthiness at the same time.However,as one of the most complex optimization problems,the structure crash topology optimization is a typical structural nonlinear dynamic response topology optimization problem and there is no effective optimization method at present.The equivalent static loads method for structure optimization(ESLSO)has been widely studied and applied,because it can make full use of the high efficiency advantage of linear topology optimization and the calculation advantage of existing commercial software.However,there are still some problems to be solved,such as computational efficiency and numerical stability,in solving the topology optimization problem under large deformation and crash condition.In this paper,to solve the problems of high calculation cost,low optimization efficiency and unstabllity existing in the ESLSO method in solving the crash topology optimization considering large deformation nonlinear problems,the calculation method of improved equivalent static loads and a corresponding crash topology optimization method are proposed,and the superiority of the improved method is verified by a simple structural design example.On this basis,the proposed method is extended to the topology optimization design of the key structure of the front-end system of a pure electric vehicle under the frontal crash condition,as well as,an effective optimization design method of vehicle structure lightweighting and crashworthiness is established.The proposed method improves the crashworthiness and lightweight level of vehicle structure,verifies the engineering practicability of the proposed method,and provides a new idea and practical method for the crashworthiness and lightweight design of vehicle structure.The main research work and conclusions are as follows:(1)In this paper,the research status of crash topology optimization at home and abroad is reviewed from two aspects of method research and application research.On this basis,the characteristics and shortcomings of the existing research are analyzed and summarized,based on which the main work and content of this paper are proposed,and the contents of each chapter are arranged.(2)In this paper,the whole process and related theories of the ESLSO in solving crash topology optimization are described in detail.Then,the problems and shortcomings of the ESLSO are summarizeed in solving the crash topology optimization problems of large deformation crash,and the causes of these problems and deficiencies are analyzed in depth.This forms a theoretical foundation for the improvement of equivalent static loads method.(3)The equivalent static loads is improved based on the model reduction theory,and a calculation method of reduced order equivalent static load and a crash topology optimization method based on reduced order equivalent static loads are proposed to solve the problems of high calculation cost and low optimization efficiency of the ESLSO method in large deformation crash conditons.This method retains all the advantages of the equivalent static loads method and avoids the equivalent static loads acting on all nodes and the whole model participating in the crash analysis and topology optimization,so the calculation cost of crash topology optimization is effectively reduced and the optimization efficiency is improved.(4)The equivalent static load is improved based on the idea of linear limit analysis and energy principle,and a calculation method of equivalent linear static loads and a crash topology optimization method based on the equivalent linear static loads are proposed to solve the problems of numerical instatbility of the ESLSO method in large deformation crash conditons.This method can realize the adaptive scaling of the equivalent linear static loads,which can guarantee the topology optimization of the structure under equivalent linear static loads always keep in the linear range,and further effectively improves the numerical stability of structural crash topology optimization.Finally,the method is applied to the optimization design of a crashbox structure under the large deformation crash condition,which extends the application scope of topology optimization method and verifies the effectiveness of the method.(5)The FE simulation model of a pure electric vehicle front-end system under frontal crash condition is established,and the correctness and reliability of the model are verified by real vehicle crash test.Through the crash analysis of the model,the key structures that affect the safety of frontal crash are determined,and the crashworthiness and existing problems of these structures are analyzed carefully.Then,an effective optimization design method of vehicle structure lightweight and crashworthiness is established by synthetically applying two kinds of structural crash topology optimization methods based on the improved equivalent static loads proposed in this paper.The method is applied to the crash topology optimization of key structures to realize the crashworthiness and lightweight optimization design.Finally,the optimized key structures are integrated into the original front-end crash system through the reconstruction of the FE model,forming the optimized front-end system frontal crash model,and the effectiveness of the optimized structure and the engineering application value of the proposed optimization method verified through the crash simulation under the same condition.The results show that the maximum deformation can be reduced by 13.3%,while the mean crash force and the efficiency of crash force can be increased by 15.51% and 7.89% respectively.The results show that the proposed topology optimization method based on the improved equivalent static loads can effectively balance the lightweight and crashworthiness of the structure,save computing resources and improve the numerical stability,which provides a new idea and practical method for the crashworthiness and lightweight design of the vehicle structure.The structure optimization design method established in this paper effectively solves the technical problems of structural crashworthiness and lightweight design,and provides an effective technical path for lightweight and crashworthiness design of vehicle structure.