Selection of Reference Locations for Modal Testing

Abstract

In frequency response function (FRF) estimation for modal testing, determining reference locations, namely exciting positions or exciting directions, is one of the most important subjects. If a suitable reference location is not selected, it is difficult to extract the correct structural modes from the FRF database of the system. In this paper, a method for processing estimated FRF data to select appropriate response locations is proposed. This method is based on an evaluation of the squared norm functions of FRF vectors, which are estimated by single-input multiple-output vibration testing. In this FRF estimation, the exciting locations are moved, and the squared norm functions corresponding to the exciting locations are obtained. The best input location for maximizing the Euclidean norm of a response vector or that for minimizing the angle between a certain eigenmode and the response vector can be found by comparing of these functions. The validity of the method was discussed on the basis of the results of examples applied to a numerical structural model and to a real structure. This implies that the proposed method is a practical one for selecting reference locations for modal testing in a short period of time.