Modal decomposition of full field measurements

Abstract

Full field modal measurement techniques, such as pulsed holographic interferometry or scanning laser Doppler vibrometry, can be used to obtain operating modeshapes with high spatial content at a specific frequency. The large amount of data present in each measurement typically limits the data collection to a smaller number of frequencies, which makes these techniques undesirable for the measurement of systems with significant modal overlap. However, if a set of pointwise measurements with high spectral resolution are made in addition to the full field ones, fitting techniques can be used to obtain a spectral representation of the system in terms of modal parameters, even for the case where modal overlap takes place. In this paper a hybrid technique is developed utilizing the high spectral resolution of the pointwise techniques and the high spatial content of the full field techniques. Results are presented for measurements of a mechanical component, and the decomposition of modeshapes from deformed shapes is demonstrated.