Developing a Correlation Criterion (SpaceMAC) for Repeated and Pseudo-repeated Modes

One of the most important factors in the validation of a finite element model is whether the modal vectors obtained from the finite element solution match sufficiently with the modal analysis results of the part or a test prototype. Modal Assurance Criteria (MAC) (Allemang, Brown, A correlation coefficient for modal vector analysis. In: Proceedings of the international modal analysis conference, pp 110–116, 1982) is usually a very effective way to check this condition. However, in case of repeated modal frequencies and vectors, MAC can give misleading results. Hence, there is a need for a method that could indicate how well the finite element method-based estimates for the repeated modes correlate with the modal analysis modes. This work is an attempt to develop a correlation criterion between a set of repeated roots from a finite element method solution and an experimental modal analysis solution.