Research On Simplified Modeling And Optimal Design Of A Bus Bearing Structure Based On PBM Method

Structure design includes two stages: detailed design stage and conceptual design stage.The traditional structure design relatively pays more attention to the detailed design, most ofthe time and energy is spent on structure improvement and size optimization of this phase.In fact, the early stage of the design is also very important. If the simplified model whichreflects the performance of the structure is built in the initial stage, it could be analyzed andoptimized using CAE analysis method and optimization algorithm. This will guide thefollowing design, avoiding repeated modifications during the detailed design stage, savingtime and improving efficiency.The PBM structure simplified modeling method was studied in this paper. The mainbearing structure of a half-integral bus was simplified using the PBM simplified method. Onthe basis of the simplified model, the multi-objective structure optimization was carried out.At the beginning of the structure design, concrete cross section usually can’t beobtained, and there is no detailed geometric model. In order to analyze and optimize thestructure in this stage, a simplified method must be found. This method should be able toexpress the mechanical characteristics of the structure without the constraint of the crosssection shape. The PBM structure simplified method was studied in this paper, and the beamstructure was mainly researched. The beam structure was simplified as beam element whichwas defined by four section parameters considering the stiffness characteristics of thestructure. The four section parameters included the area of the section, moment of inertia intwo directions and the torsion constant. They were acquired through the displacement andangle of the known structure under the condition of tension, torsion and bending. Arbitrarybeam component was simplified using the PBM method. The displacement of the simplifiedmodel and detailed model under the same constraint and load was compared, and themaximum error was only3.455%. So the feasibility of the simplified method was verified. A half-integral bus body was studied in this paper. The main bearing structure wassimplified using the PBM method. The main bearing part of the half-integral bus waschassis, so the beam structures of carling and the luggage of the chassis part were simplified.The basic properties of original model and simplified model were compared including thestrength, stiffness and low order modal, and the errors can satisfy the requirements of theprecision in the early stage of design. So the validity of the simplified model was proved.The simplified body model was optimized aiming at multiple targets. The actualstructural design usually was not a single objective optimization, but a multi-objectiveoptimization. These goals were more likely to conflict with each other, so a balance ofmultiple targets must be found. In this paper, the body was optimized in order to improvethe bending, torsion stiffness and the first order torsion frequency, and the maximum stressin braking and cornering condition was restrained. The design variables were chosenthrough the sensitivity analysis. From all the parameters of the simplified beam elements ofthe chassis part, four design variables which were sensitive to all the three objectivefunctions were chosen. In order to save time and avoid a lot of simulation calculations,polynomial response surface method was used to establish the approximation model of theobjective and constraint function. The error of the approximation model was analyzed, andthe result showed that the R2and Radj2were very close to1, so the model could fit well tothe response. Finally, the simplified model was optimized aiming at multiple targets usingthe NSGA-II genetic algorithm. The three objective functions were all improved to a certainextent and the Pareto optimal solutions were obtained.The structural optimization method on the basis of the PBM simplified model provideda feasible way for the structure improvement in the early stage of design. It could beexplored and improved to make the structure optimization really run through the wholeprocess of structure design.