Index of content:
Volume 111, Issue 4, April 2002
- STRUCTURAL ACOUSTICS AND VIBRATION 
111(2002); http://dx.doi.org/10.1121/1.1448313View Description Hide Description
The purpose of this paper is to present an experimental study of the vibrational behavior of laminated annular disks, and effects of laminations on the vibrations of the disks. The vibrations of a series of solid annular disks were calculated using the finite-element method in order to provide a basis for comparison with experimental data. An extensive range of experiments was performed on both a series of solid disks and a series of laminated disks under a range of normal clamping pressures. Based on the calculated and experimental results, it was found that the vibrational behavior of the laminated disks was dominated by that of the individual disk, of which the laminated disks were composed. Laminations had great effects on the vibrational behavior of the laminated disks and the effects depended upon the mode type, the clamping pressure, and the number of disk assembly. Laminations increased damping and reduced the amplitude of frequency response function for both the transverse modes and in-plane modes of disks. The resonant frequency of transverse modes shifted higher because of the effects of laminations. For the in-plane vibrational modes, the effects on the resonant frequency could be neglected and the resonant frequency could be considered to be a constant.
111(2002); http://dx.doi.org/10.1121/1.1456518View Description Hide Description
In this paper, a general framework is developed for determining the underlying parameters of general signal models through the application of maximum likelihood estimation theory for functions whose variables separate. This method extends previous work in sinusoidal and exponential estimation to include models with other functional bases, such as exponential functions with nonconstant amplitudes and Bessel functions. Nonuniform spatial sampling is also possible with this technique. The maximum likelihood method is applied to the identification of wave components along one-dimensional structural elements. Results are given which demonstrate the viability and accuracy of the technique estimating exponential and Bessel functionmodel parameters from noisy simulation data.
Comparison of moments and couple-generating forces near discontinuities in structural-acoustic systems111(2002); http://dx.doi.org/10.1121/1.1456515View Description Hide Description
In modeling vibration isolators in structural-acoustic systems, the isolator’s dynamic properties are often treated as acting only in the axial direction as moments are often neglected. Furthermore, the size, or scale, of the isolator is often neglected and the isolator is assumed to act at single points on the connected structures. Previous work has shown that concentrated moments can be particularly important when located near a fixed support or a structural discontinuity. This research extends that work to examine the importance of moment scale effects for a system containing a distributed structural discontinuity with its own scale. Moment scale effects are examined by determining the difference in radiated acoustic power for a simple system that is excited by a couple-generating distributed force and a concentrated moment. The distributed force produces a couple that is equivalent to the concentrated moment. As a result, only the scale is being examined. Particular interest occurs when the excitation is located near the structural discontinuity. Based on the cases studied here, moment scale is shown to be important at lower frequencies when the excitation is located near the edges of the discontinuity. At higher frequencies, any overlap of the excitation and discontinuity may warrant the need to consider moment scales.
111(2002); http://dx.doi.org/10.1121/1.1456516View Description Hide Description
A locally synthesized controller (LSC) is one that uses a local feedback signal in a noise or vibration field (VF) to synthesize the actuation signal. The global damping of a VF by available LSCs requires sensor–actuator collocation. This study presents a LSC for the global damping of a VF without requiring sensor–actuator collocation, which is important to noise control applications where a sensor may be placed away from an actuator to avoid the near field effects. It is proven that the LSC damps the entire VF instead of just a local feedback loop. This is different from other LSCs that may control local feedback loops without damping the VFs. A decentralized control law is presented here to extend the LSC to a decentralized damping system using multiple actuators.