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边界条件是结构进行模态分析的基础,不同的边界条件施加方式通过改变结构刚度影响结构模态参数。首先通过理论推导计算模态分析和试验模态分析的基本原理,然后对比例车体有限元模型建立5种可行的边界约束条件,计算分析知弹簧悬挂时比例车体前30阶固有频率与自由模态最大误差为0.02346%,边界条件4和边界条件5时固有频率最大误差分别为25.3386%和10.2383%,在试验模态中可用弹性悬挂模拟结构自由模态。对弹簧悬挂、弹簧杆悬挂和空簧支撑3种不同边界条件下的比例车体进行锤击模态试验分析,得出第3阶垂弯频率最大误差分别为2.545%、2.961%和4.812%,均小于误差允许值5%;利用模态判定准则(MAC矩阵)判定试验模态中结构固有频率的相关性,验证了边界条件对比例车体模态参数的影响。
Boundary conditions are the basis for the modal analysis of the structure. Different modes of application of the boundary conditions affect the modal parameters of the structure by changing the stiffness of the structure. Firstly, the basic principles of modal analysis and experimental modal analysis are deduced theoretically. Then, five feasible boundary conditions are established for the finite element model of a car body. The relationship between the natural frequency of the first 30 bodies and the natural frequency The maximum modal error is 0.02346%. The maximum natural frequency errors of boundary condition 4 and boundary condition 5 are 25.3386% and 10.2383% respectively. In the experimental mode, the elastic suspension can be used to simulate the free mode of structure. Hammer mode modal analysis of proportional body under three different boundary conditions of spring suspension, spring rod suspension and air spring support shows that the maximum error of the third-order vertical bending frequency is 2.545%, 2.961% and 4.812% respectively, Which is less than 5% of the allowable value of the error. The correlation between the natural frequencies of the test modal is determined by using the modal criterion (MAC matrix), and the influence of the boundary conditions on the modal parameters of the vehicle body is verified.