Index of content:
Volume 110, Issue 2, August 2001
- STRUCTURAL ACOUSTICS AND VIBRATION 
Modeling, vibration, and stability of elastically tailored composite thin-walled beams carrying a spinning tip rotor110(2001); http://dx.doi.org/10.1121/1.1377292View Description Hide Description
The problems of the mathematical modeling, eigenvibration, and stability of cantilevered thin-walled beams carrying a spinning rotor at its tip are investigated. The structure modeled as a thin-walled beam encompasses nonclassical features such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply-angle configuration inducing a structural coupling between flapping-lagging-transverse shear is implemented. The implications of combined gyroscopic effects and conservative force upon the free vibration and stability of this structural system are revealed and a number of pertinent conclusions are outlined. Among others, it is shown that the judicious implementation of the tailoring technique can yield dramatic enhancements of both the vibrational and stability behavior of the system.
110(2001); http://dx.doi.org/10.1121/1.1378353View Description Hide Description
The complex nature of noise/vibration generation and transmission in rotating machinery has made it indispensable to employ various techniques to identify the corresponding sources and paths. A theoretical approach via finite-element analysis(FEA), an experimental approach via direct measurement, and a signal processing approach via feature extraction of the measured data have all made significant contributions. Yet, there has not been much interdisciplinary effort among the three areas although their mutually complementary roles have long been recognized. In this paper, a synergetic approach is proposed to noise/vibration source and transmission path identification in order to take advantage of all the merits of the three different approaches. The proposed approach is discussed with a rotary compressor as a testbed. In the new approach, the experimentally measured sound intensity map is initially used to suggest the active radiation area, which guides us to instrument the rotary compressor at the suspected noise/vibration source positions. The collected data from the compressor is then processed to unravel the candidate source(s). Various signal processing techniques such as filtering, Hilbert transform, and fast Fourier transform are used to enhance the desired features buried in the experimental data. Finally, modal analysis via FEA and direct measurement further help to pinpoint the true source(s) and simultaneously verifies the conjecture following the experimental data processing.
110(2001); http://dx.doi.org/10.1121/1.1385566View Description Hide Description
It is shown that the smoothed spectral energy density at one point in a large complex structure may be approximated in a simple manner as proportional to the frequency-smoothed admittance at the receiver and at the source, and inversely proportional to the global modal density. Thus, the mean-square response may be estimated with little computational burden, knowing only the local properties at source and receiver and the size of the system. The approximate predictions are compared with the results of direct numerical simulations and found to be accurate except in the presence of Anderson localization.