Abstract: In order to predict the exterior noise of the car, a new method for exterior noise prediction based on statistical energy analysis (SEA) is proposed . A SEA model is built, including 47 body substructures and exterior acoustic cavities. The modal density and damping loss factor of the regular shaped subsystems are determined by using theoretical method, and the modal density and damping loss factor of the complex structure subsystems are measured. Meanwhile, the coupling loss factors between line junction and area junction subsystems are calculated. A uniform speed of 55 km/h is determined as the computational condition, and the excitations to car body caused by vibration of powertrain mounts and random input of the road. Meanwhile, the acoustic radiation excitation of engine cabin is measured in semi-anechoic chamber. The computational fluid dynamics (CFD) model of the car is built, and the wind excitation of the exterior surface of the car is computed. Then, the exterior noise is predicted by the SEA model with all of parameters and excitations, and the prediction result is compared with the experimentation result, which shows that the error of the prediction result is less than 2 dB(A), the relative error is less than 2.7%. The proposed method for exterior noise prediction is fully validated. And the prediction method also meets the requirements of exterior noise analysis and prediction in the development and design stage of car products. Furthermore, the effects of the prediction cavity with different section and changes of the thickness of the cavity on the exterior noise prediction are analyzed. The analysis result shows that the sound pressure level of the exterior noise gradually decreases along with the increase of thickness of prediction cavity, and the prediction cavity with different section has little effect on the exterior noise prediction of the car.

Key words: Car, Coupling loss factor, Damping loss factor, Modal density, Statistical energy analysis, Vehicle exterior noise