Finite Element Method For Acoustic Performance Calculation Of Intake And Exhaust Silencers Of Marine Diesel Engine

The frequency of intake and exhaust noise of marine diesel engine is wide,and the structure of the intake and exhaust silencers are larger.The internal sound field is dominated by three-dimensional wave in the frequency range of concern.In order to design a good performance of the intake and exhaust silencers,a three-dimensional numerical method is usually used to calculate and analyze its acoustic characteristics.In view of the strong adaptability of finite element method,the finite element method for the characteristics of intake and exhaust silencers of marine diesel engine is studied in this paper.The intake and exhaust silencers of marine diesel engine is mainly hybrid silencer,and its wall is affixed with insulation and sound-absorbing material.In this paper,sound-absorbing material with finite thickness is equivalent to an impedance boundary condition;the finite element equation of the transmission loss of the silencer is deduced when the local action model of sound-absorbing material is used.The hybrid silencer with thinner or relatively thinner sound-absorbing material is calculated by using the global and local action models of sound-absorbing materials respectively.The difference and the calculation efficiency of these two methods are analyzed.At the same time,compared with the simulation results,the rationality of the method is verified.By changing the thickness of the sound-absorbing material,the influence of the thickness of the sound-absorbing material on the local action model is analyzed.As the diameter of the inlet and outlet of the marine diesel engine silencer is larger,the high-order mode is excited at the lower frequency,and the non-plane wave appears in the frequency range of concern for the project.The traditional method of calculating the silencer transmission loss is no longer applicable.The finite element formula of transmission loss of silencer based on the unit sound power superposition is deduced.The transmission loss of the typical silencer is calculated by the method of self-programming and duct acoustic modal method,respectively,and the rationality of the method is verified.By using the method in the paper and the traditional method,the transmission loss of the intake and exhaust silencer of the marine diesel engine is predicted,the results show that the stability of the traditionalmethod is poor when the non-plane wave is generated,while the method in the paper can greatly weaken the influence of the non-plane wave,and the stability of the method is better.In order to further verify the rationality of the finite element method in this paper,a two-load method is used to measure the transmission losses of four typical silencers.The experimental results are compared with the finite element results.