Low Frequency Vibro-acoustic Characteristics Analysis And Multi-objective Optimization Of Interior Noise For An Automotive Body

With the continuous improvement of the automotive performance, more and more people pay attention to ride comfort. The NVH characteristics of the automobile is an important evaluating indicator for the ride comfort, which has attracted great attention from both automotive manufacturers and researchers. The low frequency noise in the car is mainly derived from the vibration of the body structure. Therefore, it is particularly important to analyze the vibration characteristics of the body structure and to effectively control the low frequency noise.In order to effectively reduce the low frequency noise in the car, the research is combined with the cooperative project. Taking a car as the studied object, the car structural-acoustic coupling mode is carried out for the frequency response analysis. The vibration characteristics of different damping structure is discussed. The laying position and area of damping layer is determined according to the modal strain energy method. Then,multi-objective optimization is conducted to reduce the vehicle interior noise.First of all, the finite element model of body in white structure was established, and the modal analysis was conducted. The finite element model of the enclosed vehicle body was built based on the body in white model, and the validity of the model was performed by experimental modal analysis. The car acoustic finite element model was established, and its modal analysis was performed based on the finite element model. The finite element models of the body structure and acoustic cavity were coupled to obtain the structural-acoustic coupling model. The frequency response analysis of the vehicle was presented under the different conditions. The sound pressure levels at the driver’s right ear and the right rear passenger’s ear positions were compared with the experimental results. The comparison shows the validity of the structural-acoustic coupling model.Then, the dynamic characteristic analysis method of damping composite structure was introduced for the further study of the damping application in the low noise control of the automotive body. The finite element modeling methods were studied for both free damping structure and constrained damping structure, respectively. Besides, the effects of different structural parameters on the vibration characteristics were analyzed. Both kinds of damping composite structural were compared based on the effect of energy dissipation. According to the modal strain energy of some key body structures, larger areas of modal strain energy were extracted and arranged the damping layers. Comparing the sound pressure responses between the new scheme and the original scheme, it is proved that the method based on modal strain energy is effective and feasible.Eventually, in order to determine optimum thicknesses of the key body structures with laying damping composite structures, the approximation model related damping thickness and the root mean square of the driver’s ear sound pressure level was established through latin hypercube design. The prediction accuracy was analyzed and compared for the approximate response surface model, Kriging model and RBF(Radial Basis Function) neural network model. Multi-objective optimization of the vehicle interior noise was conducted by using the genetic algorithm based on the RBF neural network approximation model. According to the optimization results, the damping composite structure was applied on the car body structure.The comparison of sound pressure level response at driver’s ear location before and after optimization was made under the different conditions. It shows that the vehicle interior low frequency noise is reduced and the environment of the vehicle interior noise is improved effectively.