| With the development of modern technology,developers pay more attention to the study of vehicle comfort.Consumers use vehicle comfort as an important indicator to evaluate vehicles.Vehicle NVH performance is an important indicator of vehicle comfort,and major automobile manufacturers also add The investment in the development of large-vehicle NVH,the low-frequency noise of the vehicle compartment is an important component of the vehicle NVH and seriously affects the ride comfort.The body structure is stimulated to easily cause low-frequency radiation noise,which seriously damages the cabin environment.Therefore,how to quickly find the source of low-frequency coupling noise in the car,optimize the design of the main noise-affected components,and analyze the low-frequency noise characteristics in the car,which has strong practical significance.In this paper,the finite element method is used to establish the acoustic-solid coupling finite element model of the vehicle compartment.The coupling noise of the interior structure of the vehicle is predicted and analyzed.The acoustic contribution coefficient of the panel is proposed to find out the need to optimize the plate,and the experimental design and plate optimization design are completed.A method for predicting and analyzing low-frequency noise characteristics in a vehicle and effectively reducing low-frequency noise in a vehicle compartment is formed.The main work of the thesis is as follows:(1)Establishing the finite element model of the vehicle body structure,the sound chamber of the vehicle compartment and the acoustic-solid coupling.Based on the modal theory,the modal analysis of the vehicle body structure,the acoustic modal analysis of the acoustic cavity and the modal analysis of the acoustic-solid coupling system are carried out.The analysis shows that there are many local modes in the modal structure of the vehicle body,and it is concentrated in the front door panel,the ceiling and the rear door panel;the vibration mode of the acoustic cavity mode is distinct,and the vibration mode appears strongly around the floor,the ceiling and the dash panel.The coupled system has a dense modal distribution and is easy to resonate with the vehicle components.(2)Analyze the formation mechanism of the cabin noise.The engine excitation is known.The acoustic coupling finite element method is used to predict the coupled noise of the interior structure,and the characteristics of the low frequency noise in the vehicle are analyzed.The frequency response curve of the target point in the vehicle is generallyconsistent.The main sound pressure peaks appear at frequencies of 72 Hz,134.1 Hz and183.9 Hz.The distribution of sound pressure in the vehicle is highly correlated with the vibration velocity and coupled mode of the panel.(3)The peak frequency band obtained by the analysis,combined with the 20 body panels divided by the components,calculates and analyzes the plate contribution of the target point acoustic response.It is concluded that there are many different plates with large positive contributions at the same frequency,at 72 Hz,plate No.17(door compartment door panel),No.7(car room floor middle section),No.12(The left door panel of the vehicle compartment)has a large positive contribution to the sound pressure of the two target points.The same plate is the largest positive contribution and the smallest negative contribution to the target point at different frequencies.In this paper,considering the target point weight and noise level coefficient,the board acoustic comprehensive contribution coefficient is proposed,and the board with large comprehensive contribution is calculated.There are compartment floor middle,right front door glass,cabin floor front,rear door panel,and car.The right side door panel,the rear door glass of the car room,and the front wall panel.This found a design factor for the later experimental design.(4)Using the optimal Latin hypercube design method to extract 50 sets of sample points in the design space for the thickness of the above seven plates,and calculate the body mass and the 17 th order modal frequency of the body structure in the finite element software.The sound pressure rms value of the two target points is used as the output response,and an approximate model is established based on the radial basis neural network method.Ten sets of sample points are extracted to complete the error analysis,and the error values ??are small,which indicates that the established approximate model has high precision and meets the engineering requirements,and can be optimized instead of the finite element model.(5)According to the established approximation model,the vehicle mass and the rms value of the two target points are minimized as the optimization target.The17th-order modal frequency of the vehicle body is greater than 50 Hz as the constraint condition,and the comprehensive contribution of the plate is large.The thickness of the seven plates is a design variable.Multi-objective optimization in the design space was performed using a non-dominated sorting genetic algorithm(NSGA-II)with elite strategy.The plate optimization parameters are introduced into the finite element to calculate the response and analyze the error.The response errors of the approximatemodel and the finite element model are both less than 2%,indicating that the optimization results are reliable.According to the analysis and optimization results,the rms voltage of the two target points decreased by 3.57dB(A)and 6.91dB(A)respectively.At 72 Hz,the sound pressure peaks of the two target points decreased by3.06dB(A)and 4.83dB(A)respectively.the sound pressure peaks at 134.1 Hz and 183.9Hz in the peak sound pressure band are reduced,the rms value of the overall sound pressure is reduced,the body mass is reduced by 12.167 Kg,and the coupling noise of the low frequency structure of the vehicle compartment is effectively controlled.At the same time,it also meets the requirements of lightweight body.At the same time,it is proved that the radial basis neural approximation model is established,and the reliability and effectiveness of the NSGA-II algorithm to optimize the plate thickness optimization and reduce the coupling noise scheme of the car room structure. |
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