Reliability-based Design Optimization Of Car Body

Weight reduction of automobiles is a fundamental approach to realize save energy,fuel economy and environmental protection.The weight reduction in body structure plays a rather important role in decreasing the weight of full vehicle,which results from the fact that body structure possesses about 40% weight of full vehicle.Due to the manufacturing process and other aspects of the uncertainties,the structural parameters of the automobile body are uncertain,and the uncertainty of these random variables directly affects the structural performance of the vehicle.Reliability-based design optimization(RBDO)is the method for the lightweight design of car body,considering the variation of sheet thickness and mechanical parameters of material caused by various kinds of uncertainties.The main research work and corresponding conclusions are listed as follows:1.The simplified geometric model of the car body was meshed and welded,and the finite element model of the vehicle body was established.The properties of the finite element model of car body were assigned and corresponding loads were applied.Then,according to the calculation method of car body stiffness under bending and torsion conditions,the static stiffness of the vehicle body could be obtained.The results showed that bending and torsional rigidity of the vehicle body met the design requirements.2.A static sensitivity analysis was performed on the vehicle body.Based on the calculation method of direct sensitivity analysis,the sensitivity analysis of the static stiffness and the vehicle’s own weight was carried out for the car body involved in the sensitivity analysis.The analysis results showed that the direct sensitivity analysis methods could not accurately identify design variables that have a large impact on weight reduction.Therefore,the relative sensitivity method was adopted.The description of relative sensitivity is the ratio of static stiffness sensitivity to self-weight sensitivity.Finally,20 body parts were identified as design variables and a preliminary lightweight design was performed in the finite element software.3.Based on the dimension reduction algorithm,reliability analysis model of the car body was established.Firstly,Using the dimension reduction algorithm,a new n dimensional function model was established to replace the original function.With the help of Taylor series and statistical moment theory,the first four order moments of the performance function were solved.The reliability of the structure could be calculated by the fourth-order moment method.Then,this method was applied to deterministically optimized car body’s bending and torsion conditions.It could be seen from the results that the bending reliability of the vehicle body satisfied the design requirements,but the torsional reliability did not meet the requirements.4.The reliability optimization model of vehicle body was established,with the minimum body mass as the objective function,and the bending and torsion reliability of the vehicle body was taken as a constraint.Aiming at the shortcomings of standard genetic algorithm and existing adaptive genetic algorithm,combined with the idea of dynamic adjustment of crossover operator and mutation operator in evolutionary process,an improved adaptive genetic algorithm was adopted.Then the improved adaptive genetic algorithm was used as the outer loop,which gave the reliability optimization process of the vehicle body.The optimization process was applied to the reliability optimization solution of the vehicle body structure,and the obtained calculation result satisfied both the reliability requirement and the weight reduction of the vehicle body.At the same time,compared with the deterministic optimization of the body bending and torsion conditions,it was found that the deterministic optimization could optimize the design of the vehicle body,but the optimized results did not necessarily meet the reliability requirements.