Identification of Time Domain Structural Responses under Operating Condition : 3rd Report, Proposition of a Modal Decomposition Method Based on the General Discription of Projection

Abstract

This paper discusses the modal decomposition of the Operating Defelction Shapes (ODSs). The ODSs offer an important contribution in the understanding of the dynamic behaviour of a system under operation. The modal decomposition can express each ODS as a linear combination of the modal modes, and have been usually done in a least squares sense. However, there are scarecely modal vectors but satisfy the orthogonal relationship. Therefore we propose that the General Discription of Projection (GDOP) is used as a tool of the modal decomposition. Moreover, we present a new model correlation technique based on the GDOP to verify the modal vectors obtained by the Finite Element Analysis, because accuracy of the modal vectors is important in the modal decomposition. These approaches are demonstrated using numerically simulated FRFs in conjunction with simulated multichannel operational response measurements. As a result, it was shown that these approaches give good clearer results compared to the ordinary modal decomposition method.