Vasundara V. Varadan
Vijay K. Varadan
Res. Ctr. for the Eng. of Electron. and Acoust. Mater., Dept. of Eng. Sci. & Mech., Penn State Univ., University Park, PA 16802
An optimal design technique is used to find the optimal conditions for several parameters of an enclosure to reduce the noise radiated from an internal source. Design variables in the optimization procedure are the size and thickness of the enclosure, size and thickness of actuators, the location of actuators, and the applied voltage on the actuators. The objective function in optimal design is the total radiated sound power at far field. The practical limits of the design variables are taken as constraints. The acoustic field acts as a distributed load on the walls of the enclosure. A 3-D finite element model is used to model the walls and the PZT actuators. With an applied voltage on the actuators and with acoustic pressure loading, the velocity distribution on the outside of the walls can be found by solving the finite element equations. These are used in the Helmholtz integral representation to compute the radiated sound field to the exterior of the enclosure. The design is performed at a single frequency which may represent the dominant frequency in the noise spectrum. By comparing the initial design and the optimal design results, a noise reduction of 12--18 dB has been achieved.