Qi N., Cookson R.

The major obstacle to a practical structure-borne source characterization is the difficulty in acquiring and assembling the requisite source data, of which there are two components. The first is the vibration activity of the source, conventionally measured as free velocity or a blocked force spectra, at each contact and usually for more than one component of excitation. The second is the mobility (or impedance) spectra, again at each contact and for each degree of freedom. Therefore, large data sets must be acquired and processed and the acquisition of mobility data, in particular is often difficult. A simplified method of obtaining the source mobility is described where the machine or component under test is attached to a low-mobility (thick) plate. The reception plate power, along with previously measured source free velocity, gives an approximate estimate of the average effective source mobility, over the contacts. This quantity can be simply expressed as a single frequency banded value. A description is given of numerical models of reception plates systems, to achieve optimum structural dynamic performance. In particular, the reception plate is required to have a low mobility but with the high modal overlap factor. Reception plate estimates of source mobility are compared with directly measured values and the simplifying assumptions of the method are discussed.