Abstract
Traditional vibration and noise assessment criterion of vehicle body concerns mainly about modal, dynamic stiffness and transfer functions. The modal only indicates vehicle body’s inherent frequency characteristics. The dynamic stiffness indicates the vibration isolation ability of the attached points. The vibration and noise transfer functions only reference the vibration and noise transfer path when the vehicle body is excited. Therefore, all these indexes do not reflect the radiation noise performance of vehicle body. But the radiation noise in vehicle is a long-standing problem, and it interferes with vehicle quality seriously. In order to solve this problem, a method of sheet radiation stiffness based on modal shape superposition was proposed. In this method, firstly, the normal directions of elements were obtained by a program based on GWAK language. The normal directions of the nodes were obtained by average of all the elements normal directions which connected to the node. Secondly, modal shapes of the nodes were superposed by DMAP language codes. Then, the superposed modal shape was projected to the node normal direction. Finally, the reciprocal of the superposed modal displacement in the node normal direction was obtained, which indicates the radiation stiffness of millions of nodes in vehicle body. Test of the sheet radiation stiffness was established simultaneously to measure the sheet radiation stiffness. The sheet radiation stiffness results of the test were in accordance with that of the sheet radiation stiffness based on modal shape superposition, which verified the accuracy of the method of the sheet radiation stiffness analysis based on modal shape superposition. This method was used to solve a booming noise problem of a car, and the test results indicates that the booming noise gets a decrease by 5 dBA at most after the optimization by this method. It is effective to design the structure of vehicle body by the sheet radiation stiffness analysis based on modal shape superposition. The radiation stiffness performance of all the points on vehicle body can be obtained quickly and conveniently without high configuration hardware and time cost. The sheet radiation noise performance can be quantified through this new method. The sheet radiation stiffness can solve the problem that the stiffness performance of all nodes in the vehicle body cannot be obtained in the test and virtual analysis methods before and improves the vehicle’s comfort and promotes the performance of noise and vibration significantly.