Dissertation > Transportation > Road transport > Automotive Engineering > Automotive structural components > Travel System > Frame > Frame parts

Study of the Vehicle Front-end Structure Fast Design for Pedestrian Legform Protection

Author HuangJun
Tutor ZhouQing
School Tsinghua University
Course Mechanical Engineering
Keywords Pedestrian legform Dynamics model Energy absorption space Parametric model Space mapping
CLC U463.326
Type PhD thesis
Year 2013
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Vehicle front-end design for pedestrian impact protection has been a challenge forstructural engineers. For engineering practices during the vehicle development forpedestrian leg protection, expert experience and intuitive judgment have been mainlydepended on to conduct the tests and simulations. This study is to exploit how thevehicle front-end structures influence the pedestrian legform injury parameters, andbuild a parametric analytical model, which provides more basis in the concept designstage for balancing the requirements of styling, general layout and energy-absorberpackaging. Also, the space mapping algorithm is introduced and modified to developa more efficient optimization tool for the detail design stage, which will shorten thedevelopment period and improve the design quality.In order to provide guidance for the front-end design in the early stage of vehicledevelopment, the influence mechanism of the front-end structure design on the legforminjury parameters is analyzed. The kinetic equation of the legform movement is built.To develop a kind of approximate analytic solution of the legform injury parameters,the legform knee joint is simplified to be rigid. The finite element (FE) model isutilized to verify the correlation between the legform injury parameters and the vehiclefront-end design. Based on the approximate analytic solution, the design strategies arediscussed to prevent legform injury parameters from exceeding the standard scope.By using the FE model of legform to vehicle bumper impact, a more reasonableequation to estimate the energy absorption (EA) space is proposed, which providestheoretical support for determining appropriate space in the early stage design. Theenergy partitioning analysis indicates that about one third of the initial kinematic energyof legform was absorbed by vehicle front-end structures. A modified method forestimating EA space is proposed by introducing3parameters (energy absorbing rate,EA efficiency and effective mass). Then parametric study is conducted to statisticallydetermine values of the3parameters, and more reasonable estimation of the EA spaceis obtained.Vehicle front-end parametric model has been widely used in the variablesensitivity study related to the legform impact test. It is, however, inaccurate for traditional3-part parametric model to represent real vehicle front-end structures inlegform impact simulation. Thus, a4-part parametric model is developed based on adetailed FE model of a real vehicle front-end, in which the structure near the bumperbeam area is modeled as two parts. The4-part parametric model could better simulatethe contact force of vehicle acted on the legform.Then, space mapping algorithm is utilized to improve the efficiency of optimizingthe vehicle front-end structures. In the vehicle design for legform impact protection,detailed FE model of real vehicle is able to ensure the predicting accuracy, butcomputationally time-consuming. The optimization algorithm with the space mappingtechnique allows the designer to use a computationally efficient, but inaccurate FEmodel (coarse model) as a meta-model for predicting the optimal design of the detailedFE model. Compared to the traditional response surface optimization method, the SMbased method requires much fewer number of detailed FE model simulations, so it ismore efficient. Finally, a new vehicle front-end system consisting of trapezoidal tubesis developed, and the cross section shape parameters are optimized using the SM basedoptimization method, which demonstrated that the SM based optimization method couldsolve the problem related to the pedestrian legform protection design.

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