Research On Parametric Modeling And Modal Analysis For Frame Structure Of Car Body

Concept design of car body structure is the comprehensive optimum design procedure, which combined with body structure strength, crash safety and manufacturing process based on automobile body shape-designing. The auto-body conceptual design quality is related to the normal various functions of car body. It is a key link during the whole automobile design. To do well during the concept design phase is the key importance to shorten the whole automobile design cycle. And thus the work of repeated design can be reduced. The car body design in China and especially the car body concept design starts relatively late, although many automobile manufacture enterprises engaged in this aspect actively at present and have achieved some results, but also have certain disparity with foreign countries, especially in the development of CAE simulation date base and the accumulation of key CAE technology need to be strengthen.In the model building, our objective is to analyze the whole car body stiffness and mechanical properties, describe the details of non-key structure too particularity, it not only increases the difficulty of model building, but also makes the element dimensional of finite element mode changes greatly and influence calculation precision. To alleviate workload in a reasonable range, we often only consider the critical strictures. So we usually simplify structure. Structure simplification should fidelity to the main mechanical properties, namely demands the geometric type of every element consistent with actual structure, and aim to consistent with the dynamic characteristics of element transfer. The main structures which form the modal can be simulated by the element of with similarity mechanical properties.Body stiffness is characteristics, which reflect relationship between loads and deformation. The aim of analyzing body stiffness is control shedding deformation of car body, meanwhile guarantee car body stiffness design satisfy the requirement of car body assembly and using. Moreover, the reasonable car body stiffness design can solve the problem of body vibration very well. Based on above, before modal analysis, this paper first analyzes stiffness of the concept body under the work conditions of bending and torsion.Car body modal characteristics analysis is one of important content in car structure design and research. The dynamic characteristics of car body can be reflected by modal frequency and modal shape, especially high low of first few modal frequency directly affect its performance of NVH. While automotive driving, these are all dynamic loads, which act on various car elements, namely it is the function of time. Therefore, the corresponding displacement, stress and strain of the structure not only follow with the spatial position changing of the structure, but also follow with the temporal variation. If dynamic loads acts on the structure are smaller, it only needs static analysis. If dynamic loads acts on the structure ware larger, or not large, but its frequency is close to some natural frequency, the severe vibration of structure would occurred, thus induce very high dynamic stresses, cause strength failure or large deformation which is not allowed. In order to avoid resonance, reduce noise and ensure the safety, we need to calculate the natural frequency and the corresponding shape with the finite element method.Structure modification is often required in structure optimization, how to calculate the low-order eigenvalue is very important for improving the efficiency of the whole structure optimization. After known the research of structure modification and reanalysis in detail, this paper mainly discusses extended Kirsch combined method and matrix perturbation method, especially mainly studies matrix perturbation method.There are three main parts in the content:1) This paper introduces the detail car body, studies the principles of car body structural simplification based on the whole car body stiffness and mechanical properties, and build the detail car body model and the concept body model according to these principles. Select suitable finite-element, and simulate car body accurately as much as possible, for it is very important in finite element analysis. According to the characteristics of car body plate structure, this paper chooses the Timoshenko beam element with transverse shear, triangle thin plate element and arbitrary quadrilateral element, which belong to thin plate element, as well as spring element which simulate T joint, and derive these particularly. Based on basic steps of the finite element method and derivation process of elements, I compiled the program of building the finite element parametric model, on these basics, built the finite element parametric model, and compiled the program of static analysis, then import the model. Preparing for modal analysis, this paper analyzes stiffness of the concept body under the work conditions of bending and torsion.2) Modal characteristics analysis is one of important content in car structure design and research. Certainly, it is an indispensable part of the CAE software of the concept body. This paper analyses the process of modal analysis particularity, especially further study the key steps, which are the reduction of mathematical modal and the solution method of large-scale eigenvalue problem. Based on above theory, I compiled the program of modal analysis, which is a part in the CAE software of concept body, and research on modal analysis of the concept body model, also contrast and analyze these methods. Afterwards, test the results calculated by the soft of independent development with the mature commercial software, and verify the model.3) Structure modification is often required in structure optimization; it should be recalculated after every modification. The problem of solving large generalized eigenvalue repeated needs amazing time, and effects development progress seriously. How to calculate the low-order eigenvalue is very important for improving the efficiency of the whole structure optimization. So we study the modal reanalysis technology of structure parameters modification, mainly discuss matrix perturbation method, compile the program of modal reanalysis of structure parameters modification, and verify the efficiency and precision of it by an example.