Index of content:
Volume 119, Issue 5, May 2006
- STRUCTURAL ACOUSTICS AND VIBRATION 
119(2006); http://dx.doi.org/10.1121/1.2184287View Description Hide Description
The transient response of a hollow finite cylinder with radial and axial material inhomogeneity to a pulse of short duration is analyzed. The problem is solved in two steps. Radial inhomogeneity is treated first by dividing the cylinder into coaxial segments each with a constant modulus which is allowed to vary from segment to segment. Transfer matrices relating variables at the two radial interfaces of a segment combine to satisfy continuity of stress and displacement at these interfaces. The Galerkin method is then utilized to treat the general case with both radial and axial inhomogeneity adopting the eigenfunctions of the radially inhomogeneous cylinder as trial functions. Features of both static and transient responses resemble that for a weakening material along the axis: displacement increases and stress reduces in proportion to the reduction in modulus. Spatial attenuation of transient stress cannot be replicated when geometric dimensionality is reduced from 3-D axisymmetric to 2-D plane-strain.
119(2006); http://dx.doi.org/10.1121/1.2185491View Description Hide Description
In electron-acoustic (EA) detection, a periodically modulated electron beam is impinging on a sample to excite thermo-acoustic signals, and a PZTtransducer bonded on the back surface of the sample is used to detect the thermo-acoustic signals. Based on the conditions of the EA detection experiment, theoretical analyses of 3-D temperature distributions in the sample, 3-D elastic fields in the sample and piezoelectric transducer, and piezoelectric output signals of the transducer are given. Generally, the vibration modes and the electrical output signals of the transducer are hard to calculate because of the complicated structures, i.e., complicated boundary conditions, thus a finite element method(FEM) is used to simulate the electron-acoustic signals. According to the corresponding FEM model, the frequency spectra of the detected EA signals can be calculated. Meanwhile, the related experimental measurements for several homogeneous samples are carried out. Comparing the theoretical simulated results with those of the experiments, it shows that both are in good agreement with each other. Finally, using this FEM model, the dependences of the electron-acoustic signals on the thermal and elastic properties of several samples are investigated.
119(2006); http://dx.doi.org/10.1121/1.2188815View Description Hide Description
This paper is concerned with cluster control of acoustic potential energy in a cluster coupled structural/acoustic cavity using both active noise control(ANC) and active vibration control (AVC). First, fundamental characteristics of a cluster coupled cavity are discussed, intriguing phenomena being confirmed: the coupling is strictly selective; structural modes and acoustic modes interfere with each other if and only if they fall into the same cluster, and hence termed cluster coupling. It is found that acoustic potential energy is a resultant from each cluster contribution, and thus clustered acoustic potential energy in a cavity may be extracted via cluster filtering without causing observation spillover, and may also be controlled independently using cluster actuation without causing control spillover. Employing both cluster filtering and cluster actuation, an optimal cluster control law using both ANC and AVC for minimizing clustered acoustic potential energy is derived. Based upon the control law, cluster control may be achieved, enabling the implementation of a multi-SISO system that may significantly mitigate computation load, as opposed to a MIMO system, on a controller. Finally, a numerical simulation is conducted, demonstrating the cluster control effect for suppressing acoustic potential energy in the cluster coupled cavity.