An Analysis Of Interior And Exterior Sound Field Of A Diesel Engine Cylinder Head Cover Based On Smoothed Finite Element Methods

With the tightening of the international noise standard,the study on the noise characteristics of diesel engines has attracted more and more attention.In the process of diesel engine research and development,numerical simulation technique has been playing an important role.Diesel engine manufacturers hope to shorten the product development cycle and reduce the cost of the machine research and development through the noise simulation analysis and optimization of diesel engine in the early stage of research and development.However,currently used numerical simulation methods often have certain limitations: for example,finite element method(FEM)and boundary element method(BEM)can only maintain good computational accuracy when calculating low-frequency vibration and noise problems;Statistical energy method(SEA)is mainly used to calculate high frequency acoustic problems with high modal density;Due to the limitation of parameter selection,meshless method can only solve some specific acoustic problems.However,the noise frequency band of diesel engine is wide and complex,so a numerical method with good computational accuracy and high applicability in a wide frequency range should be developed to meet the research and development needs of diesel engine.By using gradient smoothing technique and mass-redistributed technique,the smoothed finite element method optimizes the stiffness matrix and mass matrix of the traditional finite element method,making the calculated numerical wave number closer to the real wave number,thus greatly improving the calculation accuracy of the traditional finite element method.In this thesis,due to the smoothed finite element methods having good performance in solving the acoustic problems,such as high computational accuracy,wide computational frequency band and wide adaptive range,the following research was conducted:Firstly,by using the five optimized traditional finite element methods: the massredistributed finite element method(MR-FEM),edge-based smoothed finite element method(ES-FEM),mass-redistributed edge-based smoothed finite element method(MRES-FEM),face-based smoothed finite element method(FS-FEM)and mass-redistributed face-based smoothed finite element method(MR-FS-FEM)to calculate the three dimensional tube model with analytical solution,the study found that MR-ES-FEM is more suitable for calculating the interior sound field problem.Secondly,the FS-FEM and ES-FEM were combined with the Dirichlet-to-Neumann(DtN)boundary condition which can truncate the infinite sound field into a limited sound field,respectively.By calculating the exterior sound field of the breathing sphere model with the analytical solutions,the feasibilities of two methods have been explored.The study found that: combine with DtN boundary of face-based smoothed finite element method(FS-FEM-DtN)is more suitable for application in numerical calculation of exterior sound field.Finally,MR-ES-FEM and FS-FEM-DtN were used to calculate the interior and exterior sound field model of diesel engine cylinder cover,and the calculated results were compared with the reference solution calculated by COMSOL Multiphysics,a mature acoustic simulation software,to verify the feasibility of applying MR-ES-FEM and FSFEM-DtN to the prediction of interior and exterior sound field in the actual diesel engine cylinder cover model.