Communications – electrical: acoustic wave systems and devices – Distance or direction finding – With towing
Reexamination Certificate
1999-06-24
2001-02-06
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Distance or direction finding
With towing
C367S020000, C367S106000, C174S101500
Reexamination Certificate
active
06185154
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to towed sonar arrays, and more particularly, but without limitation thereto, to the jacket that surrounds the acoustic equipment of such an array.
Towed sonar line arrays are deployed in the ocean for military and commercial purposes. These line arrays most commonly use thermoplastic polyurethane (TPU) in a hose-shaped envelope (known also in this art simply as a “hose”). The hose-shaped envelope contains the hydrophone elements and accompanying transmission lines of the acoustic system.
In recent years, the value of towing multiple lines at the same time has become apparent. This technique has introduced problems in the deployment of the arrays. The problems become apparent when the relativity high surface-friction TPU hoses cross over or lay in parallel contact with one another. In these circumstances, deployment can become impossible or can result in tangling of the hoses.
In military applications, some submarines have used a tube adjacent to their hull to store a single sonar line array. To deploy this array, seawater is pumped into the forwardmost end of the stowage tube, and the array is “flushed” out the aft-end of the tube along with seawater. An early attempt to replace this single line array with several smaller ones was not successful because the multiple lines, unable to move relative to one another due to the TPU hose surface friction, would lock up in the bends of the stowage tube and could not be flushed.
The geophysical (seismic) industry now tows multiple-line arrays in their search for oil. This industry has suffered problems deploying the multiple-line arrays from surface ships due to TPU hose surface friction. Current solutions in use by the oil industry are (1) adding an outer layer of polyvinyl chloride (PVC) to the TPU hose or (2) blending TPU and PVC. These combinations resulted in hose surface friction sufficiently lower than that of TPU, so that deploying multiple line arrays using typical geophysical boat deployment techniques (different from that of the submarine), is now relatively free of problems related to hose surface friction. The materials of the geophysical blends, while acceptable for their intended purposes, provide over-all performance that is less than desired for certain applications.
There is thus a need for an acoustic envelope that provides low-friction surface characteristics, while, at the same time, provides improved damping of hydrodynamically generated, array self-noise.
SUMMARY OF THE INVENTION
The invention provides a low friction surface to a hose-shaped acoustic envelope of a towed sonar array. The low friction envelope permits multiple envelopes that are in intimate, parallel contact or that arc crossed-over one another, to slide easily relative to one another, enhancing their deployment.
The hose is of a material that also provides damping of array self-noise, such as that caused by turbulent fluid flow along the hose and/or by the vibration or “strumming” of the tow cable of the array.
According to the invention, particles of a low friction material are blended with a common hose material, such as TPU. The mixture is then heat extruded into pellets and the pellets are heat extruded into a hose of desired size. The exterior surface of the resulting hose is then subject to axially aligned abrasion to both expose the particles close to the exterior surface of the hose, and to create axially aligned micro-grooves in this surface. The micro-grooves enhance the low friction performance of the envelope under both dry and wet conditions. Under wet conditions, the grooves allow water to enter and lubricate the boundary that is present. Typically these boundaries are either another hose surface or the metal or other surface of an array deployment vehicle.
An object of the invention is to provide an improved acoustic envelope for towed sonar arrays.
Another object of this invention is to provide an improved acoustic envelope for towed sonar arrays in which the envelope slides easily over similar envelopes and over acoustic array deployment surfaces.
Yet another object of this invention is to provide an improved acoustic envelope for towed sonar arrays that dampens array self noise.
These and other objects of the invention will become apparent from the following specification and claims when taken in conjunction with the accompanying drawings.
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Fendelman Harvey
Kagan Michael A.
Lipovsky Peter A.
Lobo Ian J.
The United States of America as represented by the Secretary of
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