ON PROPER ORTHOGONAL CO-ORDINATES AS INDICATORS OF MODAL ACTIVITY

Proper orthogonal decomposition (POD) is applied for examining modal activity. The extraction of proper orthogonal modal co-ordinates (POCs) is outlined. The proper orthogonal values (POVs) are the mean squared values of the POCs. The number of POVs above the noise floor provides a bound on the number of significant modes based on POVs above the noise floor. The ideas are illustrated on a linear cantilevered beam experiment. The displacement ensembles are obtained by processing six strain measurements. Coherent proper orthogonal modes (POMs) and POVs above the noise floor together confirm that six active modes are detected in the system. The distribution of modal components in POCs is discussed. The characteristics of the POMs, POVs and POCs are then examined in the presence of added noise.