### ASA 125th Meeting Ottawa 1993 May

## 2aEA3. Wave-vector filtering and flow noise reduction in finite
structures.

**Y. F. Hwang
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*David Taylor Model Basin, Carderock Div., Naval Surface Warfare Ctr.,
Bethesda, MD 20084-5000
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It has been shown in the literature that the unwanted noise voltage output
from a pressure sensing system due to the pressure fluctuations of a turbulent
boundary layer can be minimized by exploiting the wave-number filtering action
of finite hydrophones and hydrophone arrays, or by other wave-number filtering
techniques. This paper discusses the similar effect in a finite structural
panel subjected to the same excitation. However, in this case, the
corresponding output is the effective modal force per unit area that excites
the structural mode. The wave-number filtering characteristics of structural
modes as a function of flow parameters, structural dimensions, mode order
numbers, and boundary conditions are presented. The effective modal force per
unit area is evaluated as the sum of contributions from three wave-number
regions: the low-wave-number region, at and near the modal wave-number (within
the major lobe) of a structural mode; the high-wave-number region, at and near
the hydrodynamic coincident wave-number; and the intermediate wave-number
region that lies between the above two regions. The relative contributions of
the three wave-number regions are important criteria upon which further noise
reduction strategies are devised. [Work supported by ONR.]