A New Structural Modification Method with Additional Degrees of Freedom for Dynamic Analysis of Large Systems

Abstract

Structural modification techniques are widely used to predict the dynamic characteristics of modified systems by using the information of the original and modifying systems. Nowadays, due to the increased computational power, large finite element models are regularly used. During design optimization, modifications are done on the original structure in order to meet the design requirements which require reevaluation of the dynamic response of the structure. This is a time consuming process since for each modification, the whole structure needs to be analyzed. In this study, a new structural modification method is proposed in order to decrease the computational effort during the design optimization. Proposed method uses the modal data of the original system and system matrices of the modifying structure in order to predict the modal data of the modified system which can be used for the dynamic analysis. Initially, the application of the method is presented on a lumped parameter model. Later, the proposed method is applied on a finite element model of a cantilever beam which is modified by additional systems having different number of total degrees of freedom (DOFs) and different number of connection DOFs. Modal data of the original structure and the system matrices of the modifying part are extracted from a commercial finite element software. The modal information obtained from the proposed method and the one obtained from finite element software are compared and it is observed that they are in perfect agreement if all information of the original structure is used. The effect of reduction of the original structure is as well investigated and the performance of the developed method is studied for varying the size of the modifying system. The computation time required for the determination of frequency response function is compared with other structural modification methods where significant improvement in computation time is observed.