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The body strength, stiffness and crashworthiness are the key aspects for the mass reduction of the commercial bus body frame. Heavy computation cost is one of the critical problems by the finite element (FE) method to accomplish a high-efficient multi-objective optimizing design. Starting from this point, in this paper, the surrogate model method is adopted to optimize the electric bus frame to reduce the mass as possible while guaranteeing the side-impact strength. The optimizing objective comprises the total mass and side-impact intrusion while the performances of static strength and stiffness in bending and torsion conditions are chosen as the constraints in optimization. First, an FE model is developed to perform the static strength analysis, modal analysis and side-impact strength analysis. Nine groups of candidate variables are determined as the optimizing design variables by sensitivity analysis.

The traditional design optimization of the bus body frame are mainly limited to the optimization of the thickness of the parts. In this work, we perform the optimization design of the bus body frame by optimizing the sectional shape of the tube beams based on the mesh morphing technology. Several groups of finite element analysis are performed for the body frame and the sectional sizes of the rectangular tube beams of the chassis and the side structure of the body that have a greater impact on the body performance are selected for optimization. The mesh morphing technology is used to establish shape design variables for the selected tube beams, and the design variables are comprised of the length, width, and thickness of the sections of the selected tube beams. Based on the entropy weight method and the order preference by similarity to the ideal solution (TOPSIS) comprehensive weight method, the design variable with a higher comprehensive contribution is obtained.