The Prediction And Optimization Of The "Mid-frquency" Acoustic Problems On The Automobile Thin-wall Components Based On The Hybird FE-SEA Method

The prediction and simulation of mid-frequency problem in vibro-acoustic is always a challenge in the past decades. Both the deterministic method such as FEM-BEM and the statistical method such as SEA are not appropriate for the problem. As the hybrid FE-SEA method can avoid the shortcomings of using FEM or SEA separately, it can be used for predicting the mid-frequency problem efficiently and rigorously. The dissertation presented a systematic research on the mid-frequency problem in vibro-acoustic based on the hybrid FE-SEA method.Systematic study of "component level" mid-frequency problem on the thin-wall panel was performed in the dissertation. The strong couple CLF of complex structure in mid-frequency was calculated based on the Energy Flow Model and the statistical analysis was included in the method, and improved the defect of CLF calculation method using FEM only.The Insertion Loss characteristic study of sound package was conducted in mid-frequency rage under structure-borne and airborne excitation, and two engineering application conclusion were achieved. The bead and damping effect on the panel sound power radiation was studied. It was found that the bead would increase the structure-borne noise radiation but not reduce it, and the engineering application recommendation was concluded.The Sound Transmission Loss prediction was performed on the magnesium viper based on the hybrid method, and the integrated design flow including "Key Frequency Location"-"Mode Tracking"-"Critical Area Diagnosis" was proposed. Lastly, different sound packages were applied on the critical area to reduce the sound transmission around the area.The "system level" mid-frequency problem was conducted on the whole BIW of van vehicle. The hybrid modelling process was constructed, and the sound radiation variation of each body panel was conducted under different positions'excitations and sound package. Different type sound packages were applied on the specific body panel to explore the noise radiation reduction, and the engineering application conclusion was drawn.Various noise source identification experiments were carried out on the single-block diesel, and the gear-covering box was identified as the main structure-borne noise source. Two prediction models were constructed to predict the frequency response and noise radiation of the component, and the calculation results were compared between two prediction models. The topology optimization method was applied on the gear-covering box to reduce the noise radiation, and the optimized result was calibrated with the experiment values. Along with low-noise design of other components of the diesel, the SPL of the engine was reduced by 3.4dB and satisfied the requirements of national legislation. The research suggested that FEM-BEM method was efficient and the hybrid method was feasible in predicting the low-frequency structure-borne noise.The studies in this dissertation expanded the frequency range of structure-borne noise prediction which has a significant promotion for the enhancement and development of the automobile low noise and vibration design. It improves the theory and method of modern design for NVH problem on the automobile, and achieves several productions with great engineering application value.