Estimation of Rotation Mode Shapes by Use of Numerical Analysis. How to Select Mode Shapes to Be Combined.

Abstract

This paper presents a procedure to estimate unmeasured rotation mode shapes of a test structure as a linear combination of those of the corresponding finite-element (FE) model. In this procedure, weighting coefficients for each mode shape combined are determined by comparing experimentally measured translation mode shapes with analytical mode shapes of the FE model. Since the accuracy of the estimated strongly depends on the selection of the mode shapes combined, a method based on the modal assurance criterion (MAC) values between experimental and analytical translation mode shapes for assessing the significance of mode shapes to be combined is proposed. The proposed method is shown to be suitable for a proper selection of mode shapes through a numerical example using a frame structure model. In addition, a practical technique to use the MAC values as the mode selection indicator under incomplete conditions of the measurements of translation mode shapes is suggested.