TY - THES

T1 - Underwater sound radiation, reflection and absorption by a coated infinite plate with a distributed inhomogeneity

AU - Zhang, Yanni

PY - 2012

Y1 - 2012

N2 - [Truncated abstract] Attaching a signal conditioning plate (SCP) outside the elastically coated underwater structure is a common means of reducing signal degradation for a pressure sensor placed in front of the coating. However, this SCP, usually a steel plate fully covering the coating, makes the structure unnecessarily heavy and readily exposes it to active sonar sensors. This thesis addresses this problem by proposing a locally attached SCP to the coating. The objective is to examine the effects of the SCP as a distributed inhomogeneity, on the general properties of underwater sound radiation, reflection, and absorption of a coated plate, in the hope that it may provide the required local reflection without affecting the overall sound radiation and absorption of the coated plate. Waves in an infinite structure travel independently as a response to an excitation, but become coupled when meet an inhomogeneity. The finite SCP as a distributed inhomogeneity may complicate the coupling by not only scattering or reflecting structural waves, but also by adding its internal dynamics as a finite plate. To correctly describe this coupling, an analytical model is established for a fluid-loaded plate with a patch under a line force excitation and a Fredholm integral equation is resulted. Models are also presented for a fluid-loaded coated plate with a finite SCP under both a line force and plane wave excitations and a system of Fredholm integral equations are resulted for both excitations. Numerical solutions are obtained using Nyström method and the inverse wavenumber transform. As an important feature of the sound radiation, the radiated sound powers from a fluid-loaded plate with patches at different locations are compared with those of such a plate without a patch. Different from a rib stiffener, which reduces the sound power when located above the force, an attached patch can lead to increased power at certain frequencies and oscillated power with frequency.

AB - [Truncated abstract] Attaching a signal conditioning plate (SCP) outside the elastically coated underwater structure is a common means of reducing signal degradation for a pressure sensor placed in front of the coating. However, this SCP, usually a steel plate fully covering the coating, makes the structure unnecessarily heavy and readily exposes it to active sonar sensors. This thesis addresses this problem by proposing a locally attached SCP to the coating. The objective is to examine the effects of the SCP as a distributed inhomogeneity, on the general properties of underwater sound radiation, reflection, and absorption of a coated plate, in the hope that it may provide the required local reflection without affecting the overall sound radiation and absorption of the coated plate. Waves in an infinite structure travel independently as a response to an excitation, but become coupled when meet an inhomogeneity. The finite SCP as a distributed inhomogeneity may complicate the coupling by not only scattering or reflecting structural waves, but also by adding its internal dynamics as a finite plate. To correctly describe this coupling, an analytical model is established for a fluid-loaded plate with a patch under a line force excitation and a Fredholm integral equation is resulted. Models are also presented for a fluid-loaded coated plate with a finite SCP under both a line force and plane wave excitations and a system of Fredholm integral equations are resulted for both excitations. Numerical solutions are obtained using Nyström method and the inverse wavenumber transform. As an important feature of the sound radiation, the radiated sound powers from a fluid-loaded plate with patches at different locations are compared with those of such a plate without a patch. Different from a rib stiffener, which reduces the sound power when located above the force, an attached patch can lead to increased power at certain frequencies and oscillated power with frequency.

KW - Coated plate

KW - Sound scattering

KW - Sound absorption

KW - Signal conditioning plate

KW - Distributed inhomogeneity

KW - Trapped mode

KW - Fluid-structure interaction

KW - Sound radiation

M3 - Doctoral Thesis

ER -