Volume 103, Issue 1, January 1998
Index of content:
- STRUCTURAL ACOUSTICS AND VIBRATION 
103(1998); http://dx.doi.org/10.1121/1.421112View Description Hide Description
A numerical study comparing the use of two structural sensing approaches for soundradiation control is performed on a baffled rectangular plate. The first sensing approach implements an array of accelerometers whose outputs are filtered to construct an estimate of the sound pressure radiated at given angles in the far field. The second method uses the same array of point sensors to estimate the net volume acceleration of the plate. Results show the improved performances of the sensor observing far-field sound radiation over a volume acceleration based on sensor.
103(1998); http://dx.doi.org/10.1121/1.421096View Description Hide Description
The structural intensity technique can directly measure and distinguish power transmissions between different structural wavetypes across a joint, and its applications are numerous in practical engineering. In this paper, a new method is proposed for the measurement of coupling loss factors (CLFs) using the structural intensity technique. An outline of the method’s theory is also given. Theoretically the proposed method gives an approximate estimation of CLFs. The approximate error depends on the ratios of the effective modal overlap factor of the receiving subsystem to the modal overlap factors of the subsystems coupled through the joint of interest. If the effective modal overlap factor of the receiving subsystem is large compared with the modal overlap factors of the coupled subsystems, the approximate error is small and negligible. A series of measurements were carried out to verify the outlined theory. The results measured on the joints with two subsystems showed that this proposed method can be used to accurately measure CLFs when the modal overlap factor of the receiving subsystem is larger than that of the source subsystem. The approximate error decreases with increasing frequency and the modal overlap factor ratio of the receiving subsystem to the source subsystem.
103(1998); http://dx.doi.org/10.1121/1.421120View Description Hide Description
A mathematical model is developed for the prediction of the forced response of finite plates to in-plane point force excitations. The model illustrates the nature of the coupling between in-plane longitudinal and in-plane shear waves and the resonant characteristics of the in-plane vibrational behavior of finite flat plates. The predicted resonance frequencies and mode shapes are compared against the finite element results and good agreement is found. The mode shapes of the in-plane vibration are depicted for frequencies below and above the first resonance frequency. It is illustrated by example that the input power due to in-plane force excitation at the in-plane resonance frequencies is at the same level as that due to out-of-plane force excitations at the flexural resonances in the same frequency band. The participation of the longitudinal and in-plane shear waves in transmitting the vibrational power and the resulting circulatory pattern of structural intensity is also presented.
103(1998); http://dx.doi.org/10.1121/1.421097View Description Hide Description
Diagrammatic multiple-scattering theory is applied to the calculation of ensemble average square responses in an infinite homogeneous plate in flexure attached to a random distribution of undamped sprung masses. This system is a prototypical example of a wave-bearing master structure with a locally reacting “fuzzy” substructure. Results for mean fields were obtained in an earlier work. Here it is found that fluctuations away from the mean are weak if the spectral and areal number density of sprung masses is great. A radiative transfer equation is found to govern the flow of energy on time scales greater than the inverse of the frequency, and a diffusion equation is found to govern the flow of energy at times greater than the dwell time of energy in the substructure. The diffusion rate is very slow if the dwell time in the substructure is long. The effect of true damping on these results is discussed.