Measuring the structural intensity and force distribution in plates

Identifying the sources of vibration in a structure and the energy exchange between structure elements is an important issue in vibration and noise control. Several formulations for the structural intensity have been presented in the past, but little is said about implementing the formulations using measured data. In this paper two structural intensity formulas based on different assumptions are compared, and practical issues of implementing the calculations of the structural intensity using k-space analysis are discussed. A force distribution, calculated from Mindlin's plate motion equations, is shown to be; an additional tool to locate vibration sources. Since the calculation of both the structural intensity and the force distribution require the use of fast Fourier transforms (FFT), numerical difficulties arise that are solved by signal processing techniques such as windowing and filtering. The influences of the windowing and the filtering on the calculation of the structural intensity and the force distribution are described. Results show that windowing and filtering are needed to obtain reasonable results of the structural intensity and the force distribution from measurement data; however they may remove useful information. (C) 1996 Acoustical Society of America.