Research And Control Of Acoustic Characteristics Of Interior Sound Field In Bus

NVH performance is one of the key indicators to evaluate the ride comfort of a vehicle.The vehicle operating status are variable,and all kinds of excitation will cause the body vibration and radiate interior noise.In the study of NVH performance enhancement,the control of low frequency(20~200Hz)noise needs special attention generally.In this paper,taking a bus as the research object,the acoustic characteristics of interior sound field under external excitation is studied by means of finite element method combined with boundary element method.A concrete scheme to control low frequency interior noise is presented from the angle of optimizing the cavity geometry parameters.The results is helpful to guide the interior acoustic design in the early stage of automobile development.The main research contents are as follows:(1)According to the finite element modeling thought,the finite element models of frame、body structure、interior acoustic cavity and acoustic-structural coupling system are established respectively based on the three-dimensional model of a bus frame.(2)The modal of structure and acoustic cavity are analyzed and the dynamic characteristics is studied based on the modal analysis theory.The modal characteristics of acoustic cavity with/without seat participation are compared,and the influence of acoustic geometry parameters on acoustic modal is analyzed preliminary.In order to study the acoustic characteristics of the interior acoustic field,the modal analysis of acoustic-structural coupling model is carried out,the correlation between body、acoustic cavity and coupling system mode is studied,and frequency response of the body structure is analyzed under the condition of simulating engine excitation,then the correctness of finite element model is verified based on engine idle vibration test of the real bus.(3)The acoustic field distribution in the coupling model is studied under the condition of simulating engine excitation with broadband unit excitation force in suspension position,in order to analysis the causes of low frequency noise in the bus,the peak value、peak frequencies of the acoustic pressure level response curve are calculated.The entropy method is used to comprehensively evaluate the sound pressure level of each peak at all measure points,work as the evaluation standard of the overall acoustic environment in the acoustic cavity.The influence of different acoustic cavity geometric parameters on acoustic modes and interior acoustic field distribution are analyzed,and the design variables of acoustic cavity geometric parameters are filtered.In order to explore the acoustic characteristics of the interior acoustic field,a large number of acoustic samples are constructed by experimental design,and the corresponding acoustic response curve groups are calculated by simulation.The acoustic characteristics of the acoustic field is preliminarily explored by comprehensive scoring of the sound pressure levels at each peak frequency.(4)A generalized regression neural network(GRNN)model is established to predict the mapping relationship between geometric parameters of the acoustic cavity and comprehensive score of sound pressure level interior the bus.The objective function is to balanced minimize the peak of the acoustic pressure level corresponding to the peak frequencies in the acoustic pressure level response curve.In order to solve the non-inferior solution set after the acoustic environment optimization,the multi-objective optimization operation is carried out with the non-dominant sorting genetic algorithm(NSGA2).After the selection of the non-inferior solution set,the new acoustic samples of the optimal solution are constructed to solve the simulation results of the acoustic response.The comprehensive score of sound pressure level corresponding to the optimal solution is transformed to sound pressure level at each peak frequency.Compared with the original acoustic model,the improvement of the interior acoustic environment is verified.The result shows that the sound pressure level at the peak frequencies of the measure points are improved compared to the initial scheme,and the mean square root value of the sound pressure level is decreased 0.53~2.84dB(A).The validity of the research scheme is proved and the low frequency interior noise is controlled effectively.