Reliability Optimization Of An Electric Bus Skeleton For Side Impact Safety And Lightweight

The body strength,stiffness,impact strength and reliability are the key aspects for the lightweight design of the commercial bus body frame.One of the critical issues by the Finite Element(FE)method to accomplish a high-efficient optimizing design is the heavy computation cost.Starting from this point,in this paper,we use a surrogate model to optimize an electric bus body frame orienting the side-impact strength and lightweight.The optimizing objectives are the total mass and side-impact invasion deformation and the performance of static strength and stiffness in bending and twist conditions are the constraints during optimization.First,an FE model is developed to perform the static strength analysis,modal analysis and side-impact strength analysis.The maximum deformation,stress distribution,modal natural frequency and vibration shape of the bus body frame in bending and torsion conditions are analyzed,and the energy and mass changes of the bus body frame in side-impact,as well as the invasion and invasion acceleration of the side protective beam are analyzed.The stiffness,strength,modal and side impact performance of the bus body frame are comprehensively evaluated.Then eleven groups of design variables were selected for optimization according to the relative sensitivity analysis for a specific area of the bus body and the design of experiment(DOE)for obtaining the sample data was carried out by the Hammersley method.The surrogate models and the constraints for optimization were built by the methods of Least Squares Regression(LSR)and Moving Least Squares Method(MLSM)and Radial Basis Function(RBF).Comparing the precision of the surrogate models developed by the three methods,the high-precision one was chosen as the optimizing model.The body structure was finally optimized through the Genetic Algorithm(GA)and the Sequential Optimization Reliability Assessment(SORA)method.After optimization,the design variables were used in the FE model for simulation and the difference between the predicted value from the surrogate model and the simulated value from the FE analysis was analyzed.After rounded for the optimized parameters of reliability,the final optimizing scheme was achieved.FE analysis reveals that the optimized bus body frame can generally satisfy the basic performance requirement.In detail,the reliability of the basic performance is100%.The peak invasion deformation around the upper and mid and down part of the side protective beam is 94.11 mm and 86.9mm and 46.43 mm,respectively,which is respectively reduced by 35.42% and 31.14% and 34.20%.The body mass has been reduced by 0.05695 t,which is 4.98% lighter than before.The surrogate model method realizes the objective of reliability optimizing design and saves the computation cost as well,which is very significant to improve the design efficiency.