Interior Noise Control And Structural Optimization Based On Finite Element Method

The interior low frequency noise in car is important for NVH performance.With the increasing demand of consumer for comfort,the car interior noise has been paid more and more attention by the government and the automobile enterprises.Utilizing the finite element method to predict the interior low frequency noise and optimizing the structural is an effective method to avoid the problem of low frequency noise.The modal performance and acoustic performance of the body are two important aspects causing low frequency noise problem of the vehicle.The modal performance is mainly evaluated by the first-order bending and torsion modal frequency,the acoustic performance is evaluated by the acoustic sensitivity,the noise transfer function.Taking a car as the research object,the structure is optimized to improve the modal performance and interior acoustic performance.1.Establish the BIW,closures,front and rear bumper,front sub frame finite element models and assemble them into a trimmed-body model.Establish the acoustic finite element model and build acoustic-structure coupling model used in the interior noise prediction.2.Mode and stiffness of the body in white are analyzed respectively to find out the first-order bending and torsion modal,then compute the body stiffness.It is concluded that the distribution between the first torsion frequency and the first bending frequency is relatively reasonable,but the first-order torsion frequency is low and easy to couple with the engine idle frequency causing resonance.The panels that needed to optimize are selected by combining the direct sensitivity and relative sensitivity analysis.Considering the lightweight of the body in white and ensuring the original body stiffness not reduce,the first order torsion frequency and bending frequency are improved by optimizing the panel thickness.3.In order to study on the acoustic performance of the car,acoustic modal and noise transfer function are analyzed respectively and get the conclusion that there are 4 critical paths(the first exhaust lug in the Z direction,the left engine mount in the Y direction and Z direction,rear engine mount in the Z direction)need to be optimized.4.In order to find out the reason why the peak sound pressure response is beyond the target value,diagnostic analysis of 4 critical noise transfer functions is conducted,including the contribution analysis and attachment point dynamic stiffness analysis.The contribution analysis indicates that firewall,roof and front floor have the greatest influence on the interior noise,the results of the attachment point dynamic stiffness analysis indicates that lower dynamic stiffness of the left engine mount in the Z direction and the rear engine mount in the Z direction mainly caused peak sound pressure in their noise transfer functions.5.The roof is optimized by laying damping and the front floor and the firewall is improved by combination of the topography and topology optimization.According to the optimized results,the structure is redesigned by adding beads and reinforcement,laying damping.The optimization results indicate the peak sound pressure of four critical paths have been reduced effectively.Continue to utilize topology optimization method to strengthen sub frame structure,improve attachment dynamic stiffness the left engine mount in Z and rear mount in Z.Finally the noise transfer function of critical paths are all controlled in the target range.At the same time,the correction of the diagnosis analysis and optimization design are proved.