Underwater noise radiated from commercial vessels is becoming a concern for cruise vessels and work boats operating in environmentally sensitive areas. This paper assesses the primary noise sources and transmission paths controlling the vessel's signature. The relative contribution of machinery induced noise (diesel, gas turbine) and propulsor (propeller, water jet, azipod) induced noise will be highlighted. It is necessary to understand which operating conditions and systems control the vessel's signature in order to optimally design quieter ships or to abate the noise from existing ships. The effectiveness of various treatment types will be explored. A comparison will be made of the effort required to quiet a 'purpose built' research vessel such as NOAA's Fisheries Research Vessel and a commercial vessel that wants to be environmentally friendly.
With the objective of interfering with the Reynolds stress transfer of momentum to the sublayer, the loss factor is derived for turbulence dissipation by the resistive oscillation of microbubbles in the buffer layer region of a turbulent boundary layer in water. The rectilinear motion of a single bubble is examined under the influence of pressure gradients in its vicinity. It is presumed that both turbulence pressures and velocities can be represented by wavenumber-frequency spectra. Stokes drag is assumed for the bubble. The loss factor is found to be independent of the magnitudes of the fluctuating pressures and velocities. In addition to the spatial density of bubbles, the loss factor is found to depend only on a Reynolds number-like parameter involving the product of the frequency with the square of the bubble radius. The Reynolds parameter dependence has a form similar to that of a simple resonant response, although it is clear that no actual resonance is involved. With three diameters bubble spacing, the peak value of the loss factor is found to be approximately 2% at a parameter value of nine. The apparent bandwidth of the loss factor response is about one decade, suggesting that the phenomena is not “finely tuned”. For turbulence with typically large wavenumbers, very large spatial decay rates are suggested.
Facilities at AARC include an acoustic wind tunnel (AWT), a pressurized pulse tube, and a reverberant water tank. The AWT may also be used as an anechoic room. The AWT was designed primarily for the acoustic evaluation of submersible propulsors. It is large enough to use prototype hardware for an important class of such vehicles. A model afterbody with control surfaces and propulsor is submerged in an open jet surrounded by a large anechoic room. In addition to the low background noise levels and turbulence required for this duty, the AWT has a unique nose-sting model mounting arrangement that avoids the noise and flow disturbances of strut or wire supports. The pulse tube provides measurements of reflection and transmission properties of materials and coating systems samples at submergence pressures to 1000 psi and with controllable temperature. The acoustic water tank provides a highly reverberant facility useful for measurement of radiated power from submerged sources and has been used to measure radiation transfer gains by the application of reciprocity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.