350:) mismatch between the bubble curtain and the seawater. Acoustic waves encountering material with a radically different speed of sound do not penetrate, but are reflected back. The speed of sound in a medium is dependent upon the square root of stiffness of a material divided by its density. In a bubble cloud, the density is most similar to that of the water, but the stiffness is that of air. The result is that the speed of sound is almost ten times slower through a cloud of bubbles in water than in water itself, and is three times slower than the speed of sound in air. Thus, sounds within the ship (or submarine) hull which would otherwise go out into the water and propagate for a long distance are reflected back into the hull and are eventually dissipated. One can experience a manifestation of these physics concepts by filling one glass with water, a second glass with carbonated water, and tapping the side of each with a spoon. The water-filled vessel will ring. The vessel with bubbles in it will "thud".
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problems. The goals of the Ship
Silencing Program are a reduction of sonar self noise over the frequency range of passive capable sonar and the reduction in the ship's radiated noise to reduce detection by enemy submarines. Self-noise is the noise generated by a ship that has an effect on its own sonar and sensors. Radiated noise is the noise generated by a ship that has an effect on other ship's sensors, especially submarines. The Masker-Prairie countermeasure systems are key elements in this program to reduce radiated noise and self-noise that are not reduced by controlling the sounds at their source or their transmission to the hull.
357:. The pressure behind the moving blade may become so low that it is less than the vapor pressure of water at that depth. This results in a water vapor bubble forming. When the bubble gets out of the low pressure area, it collapses right back into water and makes a loud noise in doing so. If, however, the trailing edge of the screw emits a small amount of air, then the cavitation bubbles have a bit of air within them. The collapse of the water vapor does not completely close the bubble, and thus little extra noise is generated.
393:) on the other hand, is fitted either near to or on the ships propellers and compressed air is pumped through small holes in the edges of the propeller. As might be expected, keeping a set of small holes clear of fouling under the surface of a ship or submarine can present a problem. On submarine installations this was prevented by running a trickle of fresh water through the system when the ship was in port. Most of the creatures that foul an ocean-going ship's hull cannot survive in fresh water.
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portion of the system is designed to silence a vessel's engine noise from detection by threat vessels and to reduce self-noise to increase the vessel's own sonar efficiency. The Masker portion typically consists of two bands fitted to the outside of the hull adjacent the vessel's engine rooms,
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Ship silencing is an important part of reducing unwanted noise, which can severely limit a naval vessel's active and passive undersea warfare capability and decrease the range or probability of detection by an unfriendly vessel. The US Navy maintains a Ship
Silencing Program to address these
294:. The Masker portion of the system is installed onto the hull of a vessel, usually near its machinery spaces. The Prairie portion of the system is designed to silence the vessel's propellers. Originally classified top secret, these systems are now used by several countries as part of their
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The use of air-bubbles and their effects upon acoustic wave propagation began to be studied systematically during the Second World War as part of a general effort to understand sound in submarine warfare. In the United States, this research effort was directed by the
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compressed air is then forced into the bands and escapes through machined perforations to create a barrier of air bubbles in the sea about the hull, thus trapping machinery noise within the hull where it is dissipated.
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In submarine use the large volume of air needed to operate the system needs to come from the surface, and therefore
Prairie-Masker can only be used when the diesel submarine is
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have found wide spread applicability in reducing noise or the damaging effect of shock waves in a variety of industry from: underwater blasting, to pile driving, to
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The noise quieting of the
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315:(NDRC) and was carried out by various US Navy laboratories. The advances made in this research were published in
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by another vessel, i.e. by a hostile submarine. Instead of hearing machinery, the ship sounds similar to rain on
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The Masker and
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cruisers of the US Navy. The system was also installed during the 1960s on a limited number of post WWII
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in 1946. Results of that study most pertinent to this discussion are found in Part IV of that volume
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Acoustic wave propagation in air-bubble curtains in water - Part I: History and theory,
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is a radiated noise reduction system fitted to some western warships, including the
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506:"Imaging of Artificial Bubble Distribution Using a Multi-Sonar Array System"
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Ho Seuk, Bae; Kim, Won-Ki; Su-Uk, Son; Joung-Soo, Park (25 November 2022).
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Information Sheet, Ship’s
Silencing Program, Information Sheet Number: 9.7,
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S. N. Domenico; Geophysics, Vol 47, No.3 (March 1982): p.345-353
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Radiated noise reduction system fitted to some western warships
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deal primarily with the United States and do not represent a
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Picture of propeller testing
Prairie installation in drydock
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Transition to
Triumph: History of the Indian Navy, 1965-1975
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The Masker portion of the system is based upon creating a
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U.S. Submarines Since 1945: An
Illustrated Design History
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A propeller based
Prairie system being tested in drydock.
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456:. Annapolis: Naval Institute Press. pp. 41, 43.
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153:. Unsourced material may be challenged and removed.
73:The examples and perspective in this article
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479:US Navy Surface Officer Warfare School, p.1
53:Learn how and when to remove these messages
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510:Journal of Marine Science and Engineering
231:Learn how and when to remove this message
213:Learn how and when to remove this message
111:Learn how and when to remove this message
601:Prairie/Masker system description at FAS
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391:acronym: propeller air-induced emission
283:modified, and later diesel submarines.
537:Hiranandani, G. M. (9 October 2017).
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151:adding citations to reliable sources
621:Equipment of the United States Navy
313:National Defense Research Committee
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34:This article has multiple issues.
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317:The Physics of Sound in the Sea
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404:frigates and such vessels as
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452:Friedman, Norman (1994).
396:A similar system called
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580:Jane's Naval Equipment
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338:Principle of operation
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543:. Lancer Publishers.
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296:antisubmarine warfare
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523:10.3390/jmse10121822
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355:cavitation
302:Background
260:frigates,
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298:systems.
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203:June 2015
89:talk page
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