Numerical Simulation Of A Vehicle Exhaust System And Its Suspension Optimization

In recent years,the automobile industry has made great progress,and the demand for the quality of the car is becoming higher and higher.The improvement of the NVH performance of the car has become one of the main means to improve the quality of the car.The vehicle exhaust system is an important component connecting the engine assembly and the body floor.A well-designed exhaust system can reduce the vibration energy transferred from the engine to the body,which can suppress the vibration and noise level in the vehicle,and it also can improve its life.Therefore,the vibration analysis and optimization of the vehicle exhaust system has become an important research content in the vehicle design and development.The research is based on the engineering project for the NVH optimization of one car.According to the test of the car,it was found that the body floor vibrated obviously under the 3GWOT test conditions,which greatly exceeds the scope of the engineering standard.After investigating the whole vehicle,we found that vibration was mainly transferred from the engine to the body floor through the exhaust system.For this reason,combining the computer simulation analysis,test analysis and ISIGHT automation platform technology,and applying the reduction of the vibration from the exhaust system to the body floor as the research objective,numerical simulation of the exhaust system was implemented and the position and rigidity of the suspension of the exhaust system were also optimized based on the finite element theory,the mechanical vibration theory and the numerical analysis theory.The specific research contents are as follows:Firstly,based on the material and geometric parameters of the exhaust system,the geometric model of the exhaust system was established by CATIA software,and a reasonably simplified finite element mesh model was obtained by using the finite element analysis software HYPERMESH.The modal analysis was carried out in the free and constrained boundary conditions,and the modal frequencies and modal shapes were obtained for the two boundary conditions.Under the actual state of the vehicle,the constrained modal test was carried out to the exhaust system.Comparison between the simulation constraint mode and the experimental constraint mode has verified the correctness of the finite element model,which lays the foundation for subsequent optimization design.Then,according to the free modal parameters obtained,the mode-weighted minimum displacement nodes of the exhaust system were obtained by means of the average driving free degree displacement method.Taking these points as the potential distribution points of the suspension hook,six arrangements of the hook were put forward.The vibration characteristics of each scheme were analyzed respectively.The optimal position scheme was determined for the optimal static displacement and transfer force connected the hook and the body.Lastly,taking the transfer force peak of the 5th hook and the 11 th order mode as the optimization target,and the Z direction stiffness of 5 suspended hangers was optimized.In the optimization,based on the ISIGHT automation platform,the two order response surface mathematics model of the multi-objective optimization problem was constructed by integrating the software of OPTISTRUCT and NASTRAN.Then,the LSGRG optimization algorithm was applied to approximate the real Pareto front,and the best combination of the 5 suspension hangers was obtained.The numerical results show that the optimized transfer forces,displacements and the other indicator have reached the engineering standard,and the modal frequency of the system is also far away from the engine idle speed.The proposed research methods and results can provide guidance and theoretical reference for the design of vehicle exhaust system,which have certain practical value in engineering.