Gunnar Rasmussen
G.R.A.S. Sound & Vibration aps, Skelstedet 10B, 2950 Vedbaek, Denmark
The modeling of structural behavior leads to simplified models of very often complex structures. To get a better understanding of the energy flow inside and out of the structures, the development of measurement methods is very important. Dynamic movements are associated with vibratory and acoustic energy dissipation. If the surface area is large compared to an acoustic wavelength, acoustic intensity is a good indicator of dynamic activity. If the area is small compared to a wavelength at the frequencies in question, surface measurements using the vibratory motion on the structure surface may be a good indicator. By transfer of energy between structural parts, point power measurements should be applied. Measurements may be carried out using acoustical techniques for determination of structure borne energy. The acoustical transducers used must be able to measure correctly in very reactive environments. A proper calibrated intensity probe will offer a noncontact measurement of an area, which may be small or large depending on wavelength for measurement of vectors caused by dispersed waves. The use of two accelerometers or an accelerometer and a force transducer may also be useful for detection of energy flow in a structure. Acoustic calibration of intensity probes has been improved to meet standard requirements. Calibration of accelerometers and force transducers is carried out by substitution measurements against a third transducer. Measurements on structures has found many practical applications.