Simulation And Improvement On Acoustic Performance Of Intake System Based On Noise Source Identification And Accurate Modeling

In recent years,with the population increasing year by year,bus becomes an indispensable part in people's daily life.It is of great practical significance to control the bus's interior and exterior noise.The interior and exterior noise can be controlled by the following means.First,acoustic testing and analysis are conducted.Then,signal analysis method is applied to accurately identify and reasonably evaluate the noise source.Finally,feasible improvement scheme is put forward according to the vehicle problems.A medium bus's air inlet radiated noise and interior noise is on a relatively high level.Aiming at solving the problems above,acoustic simulation and analysis of air intake system are conducted and mufflers are designed correspondingly.Then the air inlet radiated noise and the interior noise in the target frequency ranges are reduced.Firstly,based on comprehensive consideration of partial coherence analysis and spectrum analysis on road test,as well as interior acoustic cavity modal analysis,frequency characteristics are concluded where the inlet noise has the largest influence on interior noise.Then the mechanism,control method and acoustic prediction method of intake system noise is stated in detail.The structure characteristics of engine intake system is studied.And then the dynamic characteristic of air filter is researched by conducting structural modal testing.Also,the absorbent performance of filter is obtained by absorption coefficient testing.And the numerical method is concluded to calculate the acoustic properties of porous absorbent material.Then the experiment method is studied to obtain absorbent material's rate of flow resistance.Furthermore,the acoustic characteristic of perforated tube is analyzed and the transfer admittance matrix is calculated.Applying finite element method,the acoustic model of air intake system is established.And then,a method,comparing the simulated transmission loss(TL)of air intake system and the power spectrum of air inlet noise under idle speed condition,is used to verify the accuracy of the model.Combined with the road testing result and the simulated TL of air intake system,mufflers are designed to reduce the intake system noise in the objective frequency ranges.The TL of the improved air intake system reaches 24.7dB on average in frequencies between 250Hz and 440Hz.Finally,the results of road test indicate that the mufflers can effectively reduce the radiated noise from air inlet and vehicle interior noise.