結構動態研改之研究

• Main Author: 謝明憲
• Other Authors: 馬志高
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/21377839788076857268

碩士 === 國防大學中正理工學院 === 兵器系統工程研究所 === 91 === ABSTRACT In the life cycles of mechanical systems, due to the demands of customers, performance upgrades or fault corrections are usually proceeded. Therefore, the systems might be need to perform structural modifications. In additions, the weights of modern equipments are getting lighter and the operational speeds are getting faster. These will cause noise, vibration or failure problems. In general, there are two approaches to solve vibration& noise problems. One is to use proper devices to isolate the external excitations; the other is to modify the modal parameters of the mechanical systems by using the Structural Dynamics Modification (SDM) techniques. SDM has become a practical tool for improving the engineering designs of mechanical systems. It provides a very quick and inexpensive approach for investigating the effects of design modifications to a structure, thus eliminating the need for costly prototype fabrication and testing. It also has the unique advantage of working directly with data obtained either from a modal test, or from a finite element model of the structure. Once the modal properties of a structure are known, SDM, which is based on the eigenvalue modification technique, can be used to predict the dynamic effects of certain kinds of local design modifications. There are several important classes of problems that require solutions to the modal sensitivity problem. That is, given changes in a structure’s modal properties, what corresponding changes into mass, stiffness and damping properties have taken place. The effects of a local modification on the dynamics characteristics of a C-shaped bracket structure were studied numerically and experimentally in this study. The SDM method accurately represents the change in frequencies measured in the test when a stiffening rod was added to the model. Also, in this study, modal sensitivity analysis were used to search proper spring stiffness for obtaining the modes of the C-shaped bracket structure with the desired frequencies. Comparing the results of the finite element method, modal testing and SDM, it shows that the SDM is an efficient and accurate method.