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SMALL SUBS PROVIDE BIG PAYOFFS for SUBMARINE STEALTH
by CDR David M. Fox, USN
Have you ever looked at your submarine’s propeller, perhaps during your last dry docking, and wondered, “Why is it shaped like that?†Or maybe you’ve wondered just how someone decided on the shape of the bow, or the sail, or other external parts of the hull.
The answer, of course, is that the configuration of these components was chosen specifically to allow your ship to go fast and employ its sonar effectively while remaining as stealthy as possible. Making submarines quiet, efficient, and effective is our main mission at the Navy’s Acoustic Research Detachment (ARD) at Bayview, Idaho. As an integral part of the Navy’s Research, Development, Test and Evaluation (RDT&E) community – namely, the Carderock Division, Naval Surface Warfare Center under the Naval Sea Systems Command – we execute this mission by operating large-scale submarine models on three ranges in Lake Pend Oreille, Idaho. A fourth range is used to pull submarine towed arrays behind a 60-foot surface vessel to evaluate array self noise using recording equipment on the towing vessel.
Why is the Navy in North Idaho of all places, 350 miles from the nearest ocean? Mostly, to take advantage of the conditions in Lake Pend Oreille. The largest lake in Idaho and the fifth deepest in the United States, Pend Oreille offers a virtually ideal venue for acoustic testing. First, it is deeper than 1,000 feet over an area exceeding 26 square miles, and its flat mud bottom minimizes sound reflection. A low level of particulates in the water results in minimal reverberation and scattering, and its ambient sound level is less than the ocean at Sea State Zero more than one fourth of the time. Moreover, the lake’s water temperature remains at 39.5 degrees Fahrenheit below 300 feet all year, maximizing the repeatability of test results over time. Finally, at eight miles long by three to six miles wide, the testing volume is more than adequate.
While it is clear why the Navy takes advantage of the ideal conditions at Lake Pend Oreille, a more significant question might be why the Navy needs to use large-scale models to test submarine technology at all? The simple answer is cost. We can do model testing here at a fraction of the expense of using full-scale, operational submarines out in the fleet, while the large scale of our models (1/5 size and up) yields performance characteristics in the lake that closely match those of full-scale submarines at sea. Since this quality of data cannot be obtained in small-scale model testing, our large models and large model operating ranges are vital to validating submarine stealth technology. ARD plays a key role in developing submarine stealth by serving as one element of a sequential process in which the RDT&E community validates new technology. This approach – shown in the accompanying sidebar – has been pursued by NAVSEA and the Carderock Division for more than forty years, resulting in the quietest and most capable Submarine Force ever.
Submarine Model Range Facilities at ARD
We have several separate ranges in the lake to test various aspects of submarine sound quieting. The Buoyant Vehicle Test Range (BVTR) measures the noise produced by hydrodynamic flow over the bow and forward section of a submarine, while not masking it with the sound of propulsion or other onboard machinery. By using buoyancy to propel the model upward – like a cork – we avoid having to equip it with a propulsion system.
Operation of the BVTR is very simple. We use a shore-based winch to tow a buoyant submarine model (typically 1/5 the size of an SSN) to the bottom of the lake, stern first. A barge moored above and to the side of the range is used to control test operations, and hydrophones and accelerometers onboard the model are used to measure flow noise and operational data. After the model is hauled to the bottom and its motion settles out, we trip a release, and 15,000 to 25,000 pounds of buoyancy accelerate the model to the surface. As it nears terminal velocity, we have a window of four to six seconds to record the resulting flow noise. Near the end of the run, the stern planes are automatically shifted to dive, forcing the model to pitch over and ascend gently to the surface.
The BVTR has been used to determine the optimal shape, material, coating, mounting scheme, and overall design of the bow dome on every class of nuclear submarine since the USS Sturgeon (SSN-637) class. Modern sonars are much more efficient because of these experiments, since flow noise and its interference as background noise have been significantly reduced.
We use the Intermediate Scale Measuring System (ISMS) to test static (non- mobile) models. The newest of our ranges, ISMS consists of a 1,000-foot diameter submerged, horizontal circular hydrophone array, with an associated submerged sound projector array. We use a shore-based winch to haul the model to the center of the array (at a depth of about 500 feet), where it remains suspended for the duration of the test. The model is attached to a handling platform at the end of the haul-down cable, and operators can position it to present any desired aspect to the projector array. The ISMS can be used to measure the target strength of a submarine hull (that is, how effectively it re-radiates sound from a source not on the model) and how much sound is radiated into the water from a piece of machinery operating onboard. The data recording and processing equipment is on shore in Bayview, and is connected to the range 14 miles away by fiber-optic cables.
Finally, the Large Scale Vehicle (LSV) Range uses large, un-manned, autonomous submarine models to evaluate propeller noise, structural acoustics (overall hull structural vibration), wake production, and maneuvering and powering. In operation since 1987, the range itself consists of three distinct parts]http://www.chinfo.navy.mil/navpali....th.html[/url]
by CDR David M. Fox, USN
Have you ever looked at your submarine’s propeller, perhaps during your last dry docking, and wondered, “Why is it shaped like that?†Or maybe you’ve wondered just how someone decided on the shape of the bow, or the sail, or other external parts of the hull.
The answer, of course, is that the configuration of these components was chosen specifically to allow your ship to go fast and employ its sonar effectively while remaining as stealthy as possible. Making submarines quiet, efficient, and effective is our main mission at the Navy’s Acoustic Research Detachment (ARD) at Bayview, Idaho. As an integral part of the Navy’s Research, Development, Test and Evaluation (RDT&E) community – namely, the Carderock Division, Naval Surface Warfare Center under the Naval Sea Systems Command – we execute this mission by operating large-scale submarine models on three ranges in Lake Pend Oreille, Idaho. A fourth range is used to pull submarine towed arrays behind a 60-foot surface vessel to evaluate array self noise using recording equipment on the towing vessel.
Why is the Navy in North Idaho of all places, 350 miles from the nearest ocean? Mostly, to take advantage of the conditions in Lake Pend Oreille. The largest lake in Idaho and the fifth deepest in the United States, Pend Oreille offers a virtually ideal venue for acoustic testing. First, it is deeper than 1,000 feet over an area exceeding 26 square miles, and its flat mud bottom minimizes sound reflection. A low level of particulates in the water results in minimal reverberation and scattering, and its ambient sound level is less than the ocean at Sea State Zero more than one fourth of the time. Moreover, the lake’s water temperature remains at 39.5 degrees Fahrenheit below 300 feet all year, maximizing the repeatability of test results over time. Finally, at eight miles long by three to six miles wide, the testing volume is more than adequate.
While it is clear why the Navy takes advantage of the ideal conditions at Lake Pend Oreille, a more significant question might be why the Navy needs to use large-scale models to test submarine technology at all? The simple answer is cost. We can do model testing here at a fraction of the expense of using full-scale, operational submarines out in the fleet, while the large scale of our models (1/5 size and up) yields performance characteristics in the lake that closely match those of full-scale submarines at sea. Since this quality of data cannot be obtained in small-scale model testing, our large models and large model operating ranges are vital to validating submarine stealth technology. ARD plays a key role in developing submarine stealth by serving as one element of a sequential process in which the RDT&E community validates new technology. This approach – shown in the accompanying sidebar – has been pursued by NAVSEA and the Carderock Division for more than forty years, resulting in the quietest and most capable Submarine Force ever.
Submarine Model Range Facilities at ARD
We have several separate ranges in the lake to test various aspects of submarine sound quieting. The Buoyant Vehicle Test Range (BVTR) measures the noise produced by hydrodynamic flow over the bow and forward section of a submarine, while not masking it with the sound of propulsion or other onboard machinery. By using buoyancy to propel the model upward – like a cork – we avoid having to equip it with a propulsion system.
Operation of the BVTR is very simple. We use a shore-based winch to tow a buoyant submarine model (typically 1/5 the size of an SSN) to the bottom of the lake, stern first. A barge moored above and to the side of the range is used to control test operations, and hydrophones and accelerometers onboard the model are used to measure flow noise and operational data. After the model is hauled to the bottom and its motion settles out, we trip a release, and 15,000 to 25,000 pounds of buoyancy accelerate the model to the surface. As it nears terminal velocity, we have a window of four to six seconds to record the resulting flow noise. Near the end of the run, the stern planes are automatically shifted to dive, forcing the model to pitch over and ascend gently to the surface.
The BVTR has been used to determine the optimal shape, material, coating, mounting scheme, and overall design of the bow dome on every class of nuclear submarine since the USS Sturgeon (SSN-637) class. Modern sonars are much more efficient because of these experiments, since flow noise and its interference as background noise have been significantly reduced.
We use the Intermediate Scale Measuring System (ISMS) to test static (non- mobile) models. The newest of our ranges, ISMS consists of a 1,000-foot diameter submerged, horizontal circular hydrophone array, with an associated submerged sound projector array. We use a shore-based winch to haul the model to the center of the array (at a depth of about 500 feet), where it remains suspended for the duration of the test. The model is attached to a handling platform at the end of the haul-down cable, and operators can position it to present any desired aspect to the projector array. The ISMS can be used to measure the target strength of a submarine hull (that is, how effectively it re-radiates sound from a source not on the model) and how much sound is radiated into the water from a piece of machinery operating onboard. The data recording and processing equipment is on shore in Bayview, and is connected to the range 14 miles away by fiber-optic cables.
Finally, the Large Scale Vehicle (LSV) Range uses large, un-manned, autonomous submarine models to evaluate propeller noise, structural acoustics (overall hull structural vibration), wake production, and maneuvering and powering. In operation since 1987, the range itself consists of three distinct parts]http://www.chinfo.navy.mil/navpali....th.html[/url]
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