The Research Of Computational Method For Vehicle Body Structure Vibration And Noise Based On Nodal Integration

With the rapid development of automobile industry,the vibration and noise level of the vehicle has attract more and more people's concern during the past several decades.In order to shorten the research period and reduce the cost,the maturing CAE technology plays a significant role in the conceptual phase of car design.As the core module of the commercial software,the numerical methods,which include the finite element method,the boundary element method and the meshfree method,affect significantly the accuracy and efficiency of the vehicle's performance simulation.The boundary element method and the meshfree method suffer from the low computational efficiency deficiency when dealing with these practical engineering problems.Although the low-order finite element method with three-node triangular and four-node tetrahedral elements encounter the poor computational accuracy shortage,it attracting more and more researcher 's attention in recent years for its simplicity and efficiency.In order to simulate the vehicle's NVH characteristics in an effective and efficient way,this thesis present several simple plate and shell elements,acoustic elements and phononic crystal computational methods based on the gradient smoothing technique and the generalized Galerkin weak form using the unstructured mesh and the nodal integration method.The dissertation includes:(1)Plate and shell nodal integration methods are proposed for the static and free vibration analyses of vehicle body structure.Based on the Reissner-Mindlin hypothesis,a novel nodal integration method is first proposed to cure the temporal instability and improve the accuracy and efficiency of the original nodal integration.By expressing the strain gradient through the divergence theorem,a stabilization item is added into the smoothed potential energy functional of the original nodal integration,consisting of squared-residual of equilibrium equations.With the framework of Kirchhoff hypothesis,a novel computational theory,namely,solving the fourth order boundary value problem with linear interpolation functions,is further proposed in this work,which consists of relaxing the continuity requirement of trial function with the Green's theorem and converting the domain integration into boundary integration.Based on these theoretic achievements,two nodal integration methods are thus proposed to simulate the thin shell and the axisymmetric shell problems.These numerical models can be seen as good alternatives for the mechanical property simulation of vehicle structural components.(2)A class of acoustic nodal integration methods are proposed for the numerical simulation of vehicle noise prediction.The concept of constructing the integration domain based on the nodes of element is expanded in this work.For each independent element,a compacted support domain,which will be further used to reconstruct the acoustic gradient field,is established based on the element itself and its adjacent elements sharing common edges/faces.With the aid of Shepard interpolation method,a gradient-weighted finite element method is first proposed to reduce the dispersion error in computational acoustics.In order to cure the temporal instability of the original integration method and reduce the pollution error in numerical acoustics,a novel nodal integration method by considering the gradient variance items over the smoothing domain based on the Taylor mid-value theorem is proposed in this study.Both the two computational models eliminated the numerical dispersion error in computational acoustics successfully and improved the computing accuracy and efficiency of low order linear elements.(3)A series of fluid-structure interaction algorithms based on the unstructured mesh are presented for the structural-acoustic analysis of vehicle body.An edge-based smoothed triangular shell element is presented to discretize the kinematic equation for shell structure by introducing an edge local coordinate system when performing the strain smoothing operation.After combining the face-based smoothed finite element method used in three-dimensional acoustic simulation,a coupled edge-/face-based smoothed finite element model is further proposed to analyze the structural-acoustic problems in this study.At the same time,based on the previous work,a coupled structural-acoustic numerical model is constructed using the rotation-free nodal integration thin shell formulation and the gradient-weighted finite element method.The coupled equation is established through the continuity requirement between the structural displacement and the acoustic pressure on the coupling surface.These coupling numerical models can provide much more accurate results than the traditional computational methods,which laid the foundation for their further engineering application.(4)Proposed a nodal integration method for the computation of band structure and vibration transmission character of phononic crystals.As the conventional numerical methods suffer from the slower convergence speed and higher sensitivity for large contrast between two elastic parameters,a nodal integration method that combines the gradient smoothing technique and the Bloch theorem is further proposed in this work to study the propagation of elastic waves in two-and three-dimensionalinfinite periodic phononic crystals.Because the unstructured meshes are employed here to discretize the cell consisting of different materials,the discretization error can be reduced to the minimum.Besides,the vibration transmission formula for finite periodic phononic crystals using the nodal integration method is also constructed in this work.In order to further demonstrate the effectiveness of the present method for band structure calculation,some experiment are also designed in this work.The excellent results validate that the proposed algorithm can be seen as a good technical support for the application research of phononic crystals in vibration and noise reduction.