流固耦合振动的组合模态综合法

本文提出了流固耦合振动一种新的计算方法——组合模态综合法。该方法建立在流体-固体有限元组成的杂交子结构模型基础上.对流体子结构采用约束模态(静力变换模态),同固体子结构的两种模态——模综超元法中的动力变换模态和Craig的固定界面模态进行组合,以组合模态作为广义坐标对流固杂交子结构的运动方程进行变换获得两种形式的计算方法。本方法中采用了先装配流体子结构后装配固体子结构的技巧,从而消除了流体元的全部自由度和固体子结构的全部内自由度,仅保留固体子结构对接边界自由度,使最后计算特征值的矩阵阶数保持与结构中的模态综合超单元法及Craig法的阶数完全相同,大大减少了计算机时。 通过曲弯曲板元和平面膜元的组合板元构成的立体方盒结构以及三维矩形有限元的流固耦合振动计算,获得了与P.C.Chowdhury用整体有限元计算及光测实验一致的数值结果。

COMPOSITE MODAL SYNTHESIS FOR FLUIDSTRUCTURE COUPLING VIBRATION

A novel calculation method-composite modal synthesis method-is developed for fluid-structure coupling vibration. On the basis of hybrid substructure modal composed of fluid and solid substructure, this method combines bound mode(i. e. static transformative mode), which is applied to fluid substructure, with structure mode, which are treated as the following two modes, i. e. ( 1 ) Dynamic transformation mode given by the supe-relement modal synthesis method and( 2 )Craig' s fixed interface boundary mode, and transforms motion equations in two different ways for hybrid fluid-structure substructures by using the composite mode as the generalized coordinate. By applying the technique of first assembling fluid substructure and then assembling solid substructure, the method can eliminate all degrees of freedom of fluid element and all internal degrees of freedom of solid substructure while only maintain interfacing boundary degrees of freedom for solid substructure. The subsequently calculated matrix of the eigen value retains the same order with achievable by the superelement modal synthesis method and Craing's normal(principal) mode method, thus resulting in great reduction of computer time.This method has been applied for the calculation of the fluid-structure coupling vibration of a cubic rectanguler box composite plate elements of both curved elements and plane film elements, and for the finite elements of a three-dimensional rectangular body, and has given identical numerical results with integrated finite element method and experimental results of optical measurement testing.This method is especially applicable to the calculation of ship fluid-structure coupling vibration which features large amount of fluid-structure interfacing degrees of freedom and small amount of structural interfacing degrees of freedom, as well as to calculation problems of the same kind of offshore structure and other engineering structures. Compared with con ventional calculation method for fluid-structure coupling vibration, it is of practical significence and economic effectiveness.