Index of content:
Volume 104, Issue 6, December 1998
- STRUCTURAL ACOUSTICS AND VIBRATION 
104(1998); http://dx.doi.org/10.1121/1.423921View Description Hide Description
A simplified model, termed the flexure model, is used to analyze elastic waves in a weakly coupled periodic stack of disks bonded by thin layers of a weak polymer. Comparison with results of a more complete two-dimensional (2-D) axisymmetric model reveals the importance of axial stress and nonlinear distribution of radial displacement across the thickness. Also, in the 2-D model, it is possible to eliminate extensional modes through the thickness and inertia of the bond without compromising accuracy. In the 2-D model and for low radial wave numbers for a defined mode, its phase and group velocities can be approximated by the 1-D mass–spring model. They undergo discontinuities at the boundaries of extensional propagation zones. The flexure model reproduces the 2-D characteristic speeds but with slightly wider propagation zones and faster wavefronts.
104(1998); http://dx.doi.org/10.1121/1.423922View Description Hide Description
Optimal design of mechanical structures for vibration or noise reduction often requires finding the minima of highly nonlinear multi-dimensional functions. In this paper, genetic algorithms are introduced as a new promising tool for numerical optimization of such problems. The application presented is on the control of the vibroacoustic response of a plate carrying point-masses. Genetic algorithms have been used to determine the optimal positions of the masses on the plate. Several cases are presented, using various optimization criteria, showing the importance of selecting the most appropriate criterion.
104(1998); http://dx.doi.org/10.1121/1.423923View Description Hide Description
Active control can be applied to a vibrating structure to attenuate the acoustic radiation from the structure. In this paper, active structural acousticcontrol (ASAC) techniques are applied to a ribbed plate in order to minimize the structurally radiating sound fields. Using feedforward control strategies, multiple control forces are applied to the reinforcing beam. Modifying the structural response results in attenuation of the radiating sound fields. Cost functions are developed for the minimization of the far-field radiating sound pressure and far-field sound power. Optimization of the control system is achieved by using information on the structural coincidence conditions, and in determining the optimal error sensor location. Results demonstrate that significant reduction in the far-field sound pressure and sound power can be achieved in a large range away from the grazing angles. The effect of the control system on the structural response is also investigated.