Research On The Optimization Of A Coach Structure Aimed At Improving The Rollover Safety

The high frequency of coach accidents,especially of rollover ones,had brought the most serious harm to humans,and that is why the thesis chooses coach as the object of study.Based on the rollover studies,the upper part of the coach structure is optimized,which further enhances its rollover safety,by increasing the difficulty of rollover and thus reducing the rollover probability.First of all,a finite element model is built up in this thesis,and then the fundamental performance parameter of the original coach is obtained through static performance analysis(bending mode,reverse operating mode,braking operating mode and turn operating mode)and modal analysis.Rollover simulation is carried out to analyze the parameters including the distance between the second window pillar and the surviving space at the maximum deformation,the maximum acceleration of the center of mass,as well as the angles between the side wall and the under-frame at the maximum acceleration of the center of mass and the maximum deformation.Then,previous researches focus on improving the rollover safety mainly through the optimization of the upper part of coach.But this thesis puts forward the method of lowering the height of center of mass to improve the safety,that is,to lower the overall height of center of mass by lowering the height of the coach floor based on the original mode of the coach.Rollover stimulation and contrasted analysis are carried out in this respect.From the contrasted result,we can see that with the reduction of the height of center of mass,the rollover safety of coach has been improved,and thereby the validity of the proposed method can be testified.At last,considering the surplus quantity of coach material,a multi-objective optimization towards the structure is proposed in the thesis,so as to make sure that each performance and material can be fully achieved.With the weight and the maximum acceleration of the center of mass as its objects,and with the distance between the second window pillar and the surviving space as constraint condition,the thesis chooses the thickness of six member bars that greatly affect the weight and performance of coach as its design variables,through energy analysis of the member rods when rollover occurs.In consideration of time and conditional limits and through response surface approximation mode in place of the original mode,the calculation of structure optimization is carried out.With the application of NSGA-II genetic algorithm,the thesis carries out multi-objective optimization and obtains the optimal solution set of Pareto.From the analysis result and data,we can see that,compared with the original structure,the two optimal objects,namely,the maximum acceleration of the center of mass and the weight of coach's framework have been reduced by 4.78% and 28.32% respectively,which shows that the optimization effect is good.