Modal test methods - quality, quantity, and unobtainable

This article discusses modal test methods that can be used to better help in the building of mathematical models of complex structural systems. It takes a wide view of the term 'model.' The model of a structure could be an analytical or finite element model or a model built from experimental dynamic data, a modal model. This latter model does not use conventional equations of motion for deriving the model, but extracts the modal properties of the structure based upon the assumption that the system modal model can be described by a modal expansion. The experimentally derived models are found directly in modal space. The modal test methods discussed here are those affecting the QUALITY of the FRFs used in the estimation of modal parameters, affecting the QUANTITY of data taken to assist in the updating procedure, and using alternate vector space description of the modal problem when the modal parameters are UNOBTAINABLE via conventional modal methodologies.