Un-Weighted And Weighted Versions Of The Modal Assurance Criterion (MAC) For Evaluation Of Modal Vector Contamination

Modal vectors frequently have small amounts of contamination or distortion from random errors or bias errors, particularly when compared to results from modeling where normal modal vectors are the common result since damping is not included in the model. In order to understand, and possibly eliminate the contamination, tools are needed to evaluate the contamination. While the traditional modal assurance criterion (MAC) is useful, more sensitive methods are desirable. Several altered forms of MAC are reviewed for this purpose. These methods include evaluating the real part of a modal vector compared to the complex valued modal vector (rMAC), evaluating the imaginary part of the modal vector compared to the complex valued modal vector (iMAC) and evaluating the real part of a modal vector compared to the imaginary part of the modal vector (riMAC). Weighted versions of each of these evaluations are also utilized (rwMAC, iwMAC and riwMAC). These methods have shown to be very useful when evaluating modal vectors associated with close modal frequencies and suggest a need for improved processing (numerical estimation procedures for modal vectors) or ’decontamination’ (post processing procedures for modal vector sets) are required.