In the flexural farfield, vibrational intensity can be measured by using the cross spectrum of two accelerometer signals. However, accelerometers can mass load a structure and they can impede the process of mapping intensity over the surface. Consequently, the use of a scanning two-channel laser Doppler vibrometer was investigated for flexural intensity measurements. Results from vibrometer cross-spectral intensity measurements on a small aluminum beam are given and compared with results obtained by other (one-dimensional) approaches. An investigation was also conducted into measuring longitudinal intensity using the vibrometer in the differential Doppler mode. Results are given and comparisons made with one-dimensional longitudinal methods.
This paper presents a methodologyfor designing quiet shell structures through tie use of multiple tuned resonators. The method combines an ftite element method vibration prediction code, a boundary element methd sound power prediction code and a combined stochastic / gradient-based optfition algorithm for opttiing the locations and parameters of the tuned absorbers, A design example has been optimixed a thin shell covering a motor / gearbox. It is dernonstiated that the addition of a small amount of weight (130g, or 1.6V0of the weight of the shell) w produce substantial reductions in sound power (13 @in the targeted 1/3 octave band centered at 125 =.
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