US2942681A - Noise reduction device for submarines - Google Patents

Description

June 28, 1960 M. w. LINDMAN uoxsa REDUCTION .DEVICEFOR SUBMARINES Filed Aug. 29, 1957 3%?! was 395 INVENTOR v v1ZW'f/J Aka mew,

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ATTORNEYS United States Patent 2,942,681 NOISE REDUCTION DEVICE FOR Morris w. Lindman, Adelphi, Md, assignor m the United States of America as represented by the Secretary of the Navy Filed Aug. 29, 1957, Ser. No. 681,147

7 Claims. (Cl. 181-33) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to sound absorbing systems and particularly to systems for absorbing structure-borne noise.

More particularly, this invention relates to the reduction of noise transmission from submarines, minesweepers and other vessels to ambient waters.

With submarines, for example, inherently noisy machinery hereinafter referred to as noise-producing machinery, is mounted on resilient mountings which in turn are supported on the structural rings that reinforce the pressure hull of the ship. With present submarines, a large part of the structure-borne noise of the machinery is transmitted through the mounting and hence to the reinforcing rings, the pressure hull, and to ambient waters. This transmission of noise to surrounding water is extremely dangerous in that the presence of the submarine may readily be detected from the noise by known detecting devices.

Therefore, a broad object of the present invention is to reduce the transmission of structure-borne noise to ambient media.

Another object of this invention is to absorb structureborne noise.

A further object of this invention is to provide a path of highly efficient acoustical power transmission for the transmission of absorbed noise from a source to a place of absorption.

A more specific object of this invention is to provide a plurality of structural sound-transmitting paths of highly efiicient acoustical power transmission from inherently noisy machinery, and of converging such paths in a sound absorbing material.

Briefly, in applying the instant invention to the hull of a submarine, for example, a plurality of metal, noisetransmitting rings, one for each of the structural reinforcing rings, is mounted between the reinforcing rings and the interior of the pressure hull. The noise-transmitting rings are interconnected by a plurality of spaced metal bars, all of which bars converge into a single bar or rod within and spaced from the stern of the ship. The single bar is embedded within a substantial volume of sound absorbing material and is equipped with a plurality of spaced disks of various natural frequencies, which disks are loosely embedded within the sound absorbing material.

The plurality of sound-transmitting rings and the plurality of bars make up a squirrel-cage, the material of which is of higher specific acoustic impedance than that of the rest of the ships structure, thereby forming a path, or rather a plurality of paths of least resistance that converge into a single path, which single path is surrounded by a relatively thick bedding of sound absorbing material. In other words, the sound-transmitting rings 2,942,681 Patented June 28, 1960 and bars that make up the squirrel cage should be of a material such that its impedance matches the output impedance of the driver better than the impedance of the hull or casing, thereby forming a plurality of paths of highly efiicient acoustical power transmission for transmitting noise from the machinery to a concentration region remote from the machinery; a structure which conducts more vibrational energy away from the machinery than does the hull or casing. The sound-transmitting rings are insulated from the metal of the pressure hull and the bars are preferably coated with a highly dissipative material, such as a suitable plastic, to minimize their vibration between the rings and radiation to the hull.

Thus, there is provided a plurality of paths for transmitting structure-borne noise from inherently noisy machinery to a concentration area wherein the noise is smothered and suppressed in a substantial volume of sound absorbing material. As used herein, noise is intended to refer to structure-borne noise" and is not intended to include noise that is transmitted or radiated through air. The squirrel-cage of the instant invention is not intended to be, and preferably is not, a strength member for the ship.

The invention, together with the above and other obljects and advantages, is set forth in more technical detail in the following description and accompanying drawing wherein the single figure is a schematic perspective view, partly in section, of the stern or aft portion of a submarine, illustrating a preferred embodiment of the invention.

Referring now to the drawing, reference numeral 10 designates the pressure hull of a submarine, to the interior of which is securely mounted a plurality of reinforcing rings 12, only two of which rings are shown in the drawing. As is customary, various noise-producing machinery (not shown) is mounted on the reinforcing rings.

In accordance with this invention, a plurality of metal, noise-transmitting rings 14, one for each of the reinforcing rings, are mounted between the reinforcing rings and the interior surface of the pressure hull. The rings 14 are in metal-to-metal contact with the reiifiorcing rings, but are insulated by suitable means, not shown, from the pressure hull. A plurality of metal bars or straps 16 are attached to the rings 14 and converge in a region A, from which extends a single metal bar or rod 18, on which rod is located a plurality of disks 20 of various natural frequencies. The region of convergence, A, of bars 16, the rod 18 and the disks 20 are located within and spaced from the stern of the ship, which space is filled with sound absorbing material, 21, which may be a mineral wool, or glass fiber batting or the like. The sound absorbing material is confined within the stern by a partition or bulkhead 22, which partition is provided with a plurality of openings 24 for passage of the bars 16 therethrough and out of contact with the partition.

The sound-transmitting rings 14 and bars 16 that make up the squirrel-cage, and the rod 20 are each formed of the same material, a material having a higher specific acoustic impedance than that of the rest of the ships structure. The material of the squirrel cage is such that its impedance matches the output impedance of the driver (machinery) better than the impedance of the hull or casing, thereby forming a structure which conducts more vibrational energy away from the machinery than does the hull or casing. For steel ships, this material may be nickel or steel with a high nickel content. In wooden ships, such as mine sweepers, almost any non-magnetic metal may be used. So as to minimize vibration of the bars or separate elongated, rodlike metal sound conducting members 16 between the rings 14, the bars are coated with a highly dissipative plastic material, such as polyethylene or polystyrene, the latter being preferred because I of its ability to withstand somewhat higher temperature without distortion.

-Thus it is seen, in accordance with the illustrated embodiment of the invention, structure-borne noise is transmitted from inherently noisy machinery, mounted on or supported by the reinforcing rings, by the members of the squirrel-cage, to a region within the stern of the ship, wherein the noise is smothered in the sound absorbing material.

The invention is herein illustrated as applied to noiseproducing machinery of a submarine or the like. The invention may, however, be applied with equal facility to other noise-producing machinery. It should therefore be understood that the foregoing disclosure relates to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A submarine or the like comprising a metallic hull, a skeleton machinery supporting frame on the interior of said hull, sound insulating means between said frame and said hull, and sound attenuating means adjacent a terminal portion of said hull and acoustically insulated therefrom, said frame being operatively connected to said attenuating means.

2. The combination of claim 1 in which the sound attenuating means comprises a plurality of laterally spaced metal bars, each of which conducts more vibrational 4 energy away from said machinery supporting frame than does said hull.

3. The combination of claim 1 in which the sound attenuating means comprises a network of sound conducting bars and rings, and sound absorbing material encompasses the bars and rings.

4. The combination of claim 1, including a. network formed of sound conducting bars and rings, and sound absorbing material encompassing the bars and rings.

5. The combination of claim 1, which includes a central rod, a plurality of sound dissipating disks mounted in spaced relation on said rod and embedded within the sound absorbing material.

6. The combination of claim 1, which includes inherently noisy machinery disposed within said hull, a network formed of sound conducting bars and rings, and sound absorbing material encompassing said bars and rings.

7. The combination of claim 6 in which the sound absorbing material is mineral wool batting.

References Cited in the file of this patent UNITED STATES PATENTS Stewart et al Jan. 17, 1956

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