THE RELATIONSHIP BETWEEN FINITE ELEMENT ANALYSIS AND MODAL ANALYSIS

The properties and techniques of Modal Analysis and of Finite Element Analysis are identified, together with the present advantages and shortcomings of both methods. The interrelationship between these techniques is described, and the contributions of modal analysis to efficient finite element analysis are reviewed. It is noted that the term modal analysis is used to describe, a) a test procedure for obtaining structural data, b) an analytical procedure for efficient solution of structural dynamics problems, and c) the same solution procedure for rotordynamics analysis. Four case histories are included which describe the joint use of modal analysis and finite element analysis to diagnose and confirm the results obtained in selected practical problems of structural analysis. During the past ten years, the rapid development of specialized test equipment and efficient numerical methods for modal calculation of structures has revolutionized vibration analysis. The purpose of this article is to discuss the interrelationship between the various modal methods and finite element analysis. Certain limitations, which affect the results attained by each procedure, are identified, and the restrictions, which these limitations impose on modal analysis and its application are discussed. The extent to which modal analysis and finite element analysis can be coordinated into an effective diagnostic procedure for vibration analysis is demonstrated by several case histories. Some definitions to clarify the terminology of this subject are discussed in the following section.