| The car brings great convenience to people's life.It improves the quality of life,but threats people's lives at the same time.As the car ownership soaring,more and more traffic accidents take place,which causes huge property losses to the society.The safety of car crash has become a highly focused problem in the world.The traditional way to research car crash safety is testing with real car,but this method takes more time,costs more money and has higher requirements for the equipment and test engineer.With continuous development of computer aided analysis technology as well as the collision theory is being perfected gradually,simulation design of car crash process through finite element method has come true,which greatly shortens the development period.However,car crash is a very complex process with high nonlinear dynamic character,the finite element simulation technology can't satisfy the requirement of iterative optimization calculation.Thus the optimization method of car collision safety based on the surrogate model has been developed.Aiming at the safety requirements for car crash,the multi-objective optimization design method based on surrogate model is studied on the basis of crash safety analysis and finite element model validation.The main work is as follows:(1)The simulation model of car frontal crash is established with a certain vehicle finite element model from Ford,and the grey relational degree analysis method is used to evaluate the effectiveness of the simulation results.According to the test results of frontal crash,the range analysis method is applied to find out the main plates which have large influence on the simulation result.And the density and elastic modulus of several key plates are updated using quadratic polynomial response surface model to improve the calculation precision of the crash safety simulation model.(2)The crash process is simulated in LS-DYNA with the updated model.It's found that the peak acceleration of B pillar is 35.3g,and the largest intrusion of the firewall is 138.54 mm,both of them are too large and must be optimized for the occupant's safety.The energy absorption analysis finds that 60% of the total energy are absorded by the front bumper,the front rail and other eighteen plates,which are the main plates to be optimized for crash safety optimal design.(3)Surrogate models of three objectives-the vehicle mass,the peak acceleration of B pillar and the intrudion of firewall are constructed using test point evaluation method and cross validation method,and the influence of sample size on model accuracy is studied.The results show that,with the increase of sample size,the accuracy of polynomial response surface model has an obvous trend to improve.Because the Kriging model and radial basis function model have strong fitting ability themselves,an increase in the number of sample points almost has no influence on the model accuracy.(4)The total mass of the vehicle,the peak acceleration of B pillar and the largest intrusion of the firewall are set to be the optimization objectives,the thickness of 8 plates are chosen to be the optimization variables through the range analysis method.150 groups of samples obtained by the Latin hypercube experimental design method are used to construct polynomial response surface model,Kriging model and radial basis function model.The NSGA-II optimization algorithm is applied to get the Preto solution of the target functions.The optimization results indicate that the total mass of the vehicle reduces 4.1kg,the peak acceleration of B pillar lowers 8.44% and the largest intrusion of the firewall lowers 6.03%,achieving the purpose of multi-objective optimization. |
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