The Research Of Hybrid Numerical Methods For Control Of Vibration And Noise Of Vehicle Boby Structure

In the process of rapid development of automobile industry, the automobile vibration and noise level has become an important performance index which both vehicle manufactures and consumers care a lot. The sources of vibrations and noise of vehicle are complicated and multiple. Vibration and noise formed from different mechanisms are having different frequency characteristics. The vehicle body structure noise is one of the important factors affecting the inter noise of the car. The study and control of body structure noise has practical engineering significance. In car bod y development process, the design and optimization of NV(Noise Vibration) performance of the vehicle are mainly in the early stage of whole development process. Early body developmentis very dependent on a virtual CAE(Computer Aided Engineering) techniques. Once there are some preliminary design problems, the cost of later modification is very high. CAE is the key technique to shorten the design cycle and ensure high NV performance. While numerical methods for vibration noise are the core components of CAE technology. Therefore, the importance of the accuracy and computational efficiency of the numerical simulation method of bod y design is self-evident.In this dissertation, different numerical methods for simulating different structural vibration and noise are introduced. The main characteristics of low-frequency, mid-frequency and high-frequency of different numerical methods are summarized. According to the limitation of the existing numerical methods, some newly numerical approaches are proposed.The research of this work mainly focused on four aspects of the body structure of NV characteristics. Nunmerical methods for studying vibration characteristics of the car body structure, body structure vibration and acoustic coupling, vibration and acoustic transfer loss method,vibration and radiated noise are proposed. The details are expressed as following:(1) For the body structure vibration prediction,a new smoothed finite element method(S-FEM) is proposed using hybrid smoothing operations based on nodes and edges of the mesh for static and free vibration analyses of plates governed by the Reissner-Mindlin plate theory. In the present approach, both the node-based smoothed finite element method(NS-FEM) and edge-based smoothed finite element method(ES-FEM) are utilized in a careful designed manner to overcome the shear locking. The bending strains field are smoothed by the means of gradient smoothing technique over smoothing domains constructed by element edges, while the shear strains filed is smoothed based on the combination of NS-FEM and ES-FEM with a proper weightage controlled by a coefficient. A simple formula is developed for automatic selection of the coefficient by considering mesh size and thickness of the plate. The formulations use 3-node triangular elements for easy automatic mesh creation, and linear interpolation functions are used for simplicity and robustness. For easy reference, the present technique is termed as NS+ES-FEM. The numerical examples demonstrate that the proposed method passes the shear-locking test and improves accuracy of the solution.(2) For the structural acoustic coupling problems, an edge-based gradient smoothing technique embedded with SEAis introduced to eatabish a hybrid ES-FE-SEA theory framework.The predictions of the response of the Vibro-acoustic problems in mid-frequency regime have been one of hotspotsand difficulties in academy and engineering. However, there is a broad series of mid-frequenc y Vibro-acousticproblems that are not suited to either deterministic methods or statistic methods, due to the complexity of mixed behaviors in this frequency range. According to this approach, the whole vibro-acoustic system is divided into a combination of a plate subsystem with statistic behaviors and an acoustic cavity subsystem with deterministic behaviors. The plate system is treated using the recently developed eace-based smoothed finite element method(ES-FEM), and the cavity system is dealt with using the SEA(statistical energy analysis). These two different types of subsystems can be coupled and interacted through the so-called “diffuse field reciprocity relation. The ensemble average response of the system is calculated, and the uncertainty is confined and treated in the SEA subsystems. The proposed ES-FE-SEA is verified and its features are examined by various numerical examples.(3) For the noise transmission loss predictions, the widely-used numerical modeling approaches such as the finite element method(FEM) and statistical energy analysis(SEA) often have limited applicability to the transmission loss prediction in mid-frequency range. In this paper, a novel hybrid edge-based smoothed FEM coupled with statistical energy analysis(ES-FE-SEA) method is proposed to further improve the accuracy of “mid-frequency” transmission loss predictions. The application of ES-FEM will “soften” the well-known ‘‘overly-stiff’’ behavior in the standard FEM solution and reduce the inherent numerical dispersion error. While the SEA approach deals with the physical uncertainty in the relatively higher frequency range. The plate of interest is appropriately described by an ES-FEM model, due to its relative robustness to perturbations. Its adjacent reverberation cavities are modeled b y employing the SEA approach, because of their high model density. The coupling and interaction between SEA subsystems and the FE subsystem is governed by the “reciprocity relationship” theorem. A standard numerical example for benchmarking is examined and excellent agreement was achieved between the prediction and reference results. The proposed ES-FE-SEA is then applied to the modeling a complicated engineering problem–acoustic fields on both sides of the front windshield and dash plate in a passenger car.The advantage in accuracy aspest of proposed method is finally verified by experiments(4) For the analysis of structural vibration radiated noise, in this paper, a coupled numerical method of the edge-based smoothed finite element(ES-FEM) with the fast multipole BEM(FM-BEM) is proposed to analyzestructural acoustic problems. The edge-based gradient smoothing operations are applied to “soften” the ‘‘overly-stiff’’ behavior in the standard FEM, which significantly reduces the inherent numerical dispersion error.Thenormal velocities on the surface of the structure are imposed as boundary conditions for the acoustic domainwhich is modeled using the FM-BEM for both the interior andexterior acoustic domains. Comparing with the conventional BEM, the matrix vector multiplication and the memory requirement in the FM-BEM is reduced dramatically. Thecoupled ES-FEM/FM-BEM method takes the advantages of both ES-FEM and FM-BEM, which can avoid drawbacks of the “overly-stiff” behavior in FEM and computational inefficiency in the conventional BEM. Two numerical examples are presented to verify and demonstrate the effectiveness of the combined method: one academic problem for studying in detail the accuracy and efficiency of the present method, and one application to a practical vehicle noise simulation.