COMAC and CORTHOG

Where the MAC looks at the vector correlation across two modes, the Coordinate Modal Assurance Criteria (CoMAC) looks at the degree of freedom correlation across correlated mode pairs. As with MAC, there is no mass scaling involved in the CoMAC. The CoMAC (and extension to it called ECoMAC) are simple tools used to determine whether degrees of freedom are correlated to assist in the correlation process.

The Coordinate Orthogonality Check (CORTHOG) was developed as a degree of freedom correlation tool that includes mass scaling. While it is similar to CoMAC in terms of degree of freedom correlation check, it differs significantly in that CORTHOG can be used on any mode pair - not just correlated mode pairs. The CORTHOG is useful in identifying the difference between the analytical and experimental modal vectors on a mass scaled basis. Due to it's inherent formulation using the SEREP process, the basic equations can be written in terms of modal vectors and while mass scaling is included it can be shown mathematically that the system mass matrix is not need to perform the analysis offering tremendous computational advantages.

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