To realize the lightweight structure, a car body frame conceptual design of a mini electric vehicle was performed with topology optimization and size optimization. Topology optimization was used to search load paths and size optimization was applied to model a simplified structure. Static stiffness, crash safety and free vibration conditions were considered simultaneously in both of the optimization phases. Due to the feature of conceptual design, crashworthiness cases were regarded as static stiffness ones with inertia relief analysis for a linear equivalent. The objective function in multi-objective topology optimization was defined by Compromise Programming Method in OptiStruct. Because of the characteristic of the geometry and the manufacturing constraints of profiles, the design variables in size optimization were defined as both continuous and discrete variables. The resultant structure outperforms the original one in many structure responses and most significantly, it reduces weight by 36%, which demonstrates the efficiency of the proposed method.
This paper develops a novel approach for the lightweight design of a car body frame. In this approach, the cross-sectional dimensions of a car body frame are treated as design variables. First, sampling points are created based on Latin Hypercube Sampling (LHS), and then Design of Experiment (DOE) is conducted. After that, an analysis is done to obtain those design variables affect the results most. Finally, Sequential Quadratic Programming (SQP) is utilized to solve the optimization problem while the amount of design variables is reduced according to the former analysis. The advantage of this method is that it reduces the burden of optimization algorithms and offers a practical way for the lightweight design of a car body frame.
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