US3908790A

US3908790A - Sonar dome window damping and application procedure

Info

Publication number: US3908790A
Application number: US501511A
Authority: US
Inventors: Jr Howard Neile Phelps; Jr Daniel Dinsmore
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1974-08-29
Filing date: 1974-08-29
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

A bow mounted steel sonar dome has a steel plating mounted on a rigid trusswork of circular rods and flat bars. Acoustically transparent damping tiles of graphite filled polymeric composite are mounted on the inside of the steel plating in a manner to prevent the entrapment of air between the plating and the damping tiles. Each damping tile has a plurality of tapered holes to allow any entrapped air between the steel and damping tile to collect in an adhesive slug that develops in the hole during manufacture.

Description

United States Patent Phelps, Jr. et al.

1 1 Sept. 30, 1975 1 1 SONAR DOME WINDOW DAMPING AND APPLICATION PROCEDURE [751 Inventors: Howard Neile Phelps, Jr., Coventry,

R.l.; Daniel Dinsmore, Jr., East Lyme, Conn.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: Aug. 29. 1974 1211 Appl. No.: 501,511

52] U.S. Cl. 181/198; 181/175; 340/8 D Int. C1. A47B 81/06; G10K 11/00 [58] Field 01Search..... 181/198, 175 33 G 33 GE, 181/33 R; 340/8 D [56] References Cited UNITED STATES PATENTS 2,884,084 4/1959 Sussman 1. 181/175 3.038551 6/1962 McCoy et all i t 181/198 3,120,875 2/1964 Graner 4. 181/198 3.136.380 6/1964 McCoy et al. 181/198 3,421,597 H1969 Blau et a1 181/33 R 3,647.022 3/1972 Meyer et a1 181/33 G FOREIGN PATENTS OR APPLlCATlONS 611,318 10/1948 United Kingdom 340/8 D Primary E \aminerStephen .1. Tomsky Attorney, Agent, or FirmRiehard Si Sciascia; Arthur A. McGill; Prithvi C. Lall {57] ABSTRACT A bow mounted steel sonar dome has a steel plating mounted on a rigid trusswork of circular rods and flat bars. Acoustically transparent damping tiles of graphite filled polymeric composite are mounted on the in side of the steel plating in a manner to prevent the entrapment of air between the plating and the damping tiles. Each damping tile has a plurality of tapered holes to allow any entrapped air between the steel and damping tile to collect in an adhesive slug that develops in the hole during manufacture.

4 Claims, 5 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of5 3,908,790

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US. Patent Sept. 30,1975 Sheet 2 of5 3,908,790

US Patent Sept. 30,1975 Sheet4 0f5 3,908,790

U.S. Patent Sept. 30,1975 Sheet 5 of5 3,908,790

SONAR DOME WINDOW DAMPING AND APPLICATION PROCEDURE STATEMENT OF GOVERNMENT INTEREST 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 therefore.

BACKGROUND OF THE INVENTION The present invention generally relates to sonar systems and more particularly to a means for reducing sonar dome deterioration due to external coating and structural fatigue failures.

Since the introduction of steel bow-mounted sonar domes into the Navy Fleet the above mentioned failures have frequently occurred. These failures cause increased sonar self-noise levels, fouling of the dome exterior and water leakage in the domes. In fact, most domes of the type involved are left uncoated on the outside due to the inability of antifoulant coatings to remain on the steel; thus, the domes corrode and foul. The seriousness of the dome problem was first recognized in 1962, shortly after the first two AN/SQS-26 ships started to use their sonars. In 1964 investigations found that the basic cause of the domes problem was due to acoustic excitation of the dome by the sonar. This caused extremely large vibration levels within the domes.

Two types of vibratory motion to be considered when analyzing the response of domes to acoustic excitation are the forced motion, which generates the desired transmitted signal. and the free or reverberant motion, which generates scattered sound.

Measurements were conducted to confirm the theory of the reason behind the dome failures. Acceleration levels were measured on the window area of a four foot by four foot sonar dome section constructed the same as a full scale AN/SOS-26 sonar dome. The acceleration levels varied from 70 to 470 peak gs at various points on the dome window when the dome section was acoustically excited by a nine element AN/SQS-26 sonar array. From the experiment, it was determined that the plate accelerations are the sum of the reverberant field and forced field accelerations. When the two fields are inphase the maximum total plate acceleration is approximately three times larger than the forced plate acceleration. However, when the reverberant and forced field are not inphase, the resultant acceleration at some points can be considerably less than the forced field acceleration. The plate acceleration levels in an undamped steel ribbed sonar dome such the AN/SOS-26 dome increase the overall dome transmis sion loss by approximately 1 dB. Additional transmission losses result from nonspecular scattering of energy by the dome when excited by the reverberant velocity field on the dome window. These high window acceleration levels also cause paint coating failures.

SUMMARY OF THE INVENTION Accordingly it is a general purpose and object of the present invention to provide an improved sonar dome window. It is a further object to reduce the total window acceleration by a reduction in the reverberant ac celerations caused by the trusswork. Another object is to provide a window capable of being withstanding higher source levels prior to the onset of dome window cavitation. Other objects are the production of a dome window wherein, the flow induced component of self noise is considerably reduced. coating failures are prevented and fatigue failures due to acoustic excitation are eliminated.

The above objects are accomplished in accordance with the present invention by providing a sonar dome having rigid trusswork as its frame. A plurality of special composite damping tiles are affixed to the interior of the dome in a manner to provide the above objects while being transparent to transmitted radiation along a predetermined axis. In addition the construction is such that entrapped air problems are obviated by the use of an air free tile application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view ofa typical sonar dome adaptable for use with the present invention;

FIG. 2 is an interior view of the sonar dome of FIG. 1 prior to installation of the damping tiles;

FIG. 3 is a view of a typical damping tile used in the interior at the sonar dome of FIG. 1;

FIG. 4 shows the installation of the damping tile of FIG. 3; and

FIG. 5 shows the tile of FIG. 3 after installation.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figures and particularly to FIG. I there is shown a sonar dome 10. The dome 10 shown is in AN/SQS-23 bow dome and is typical of a dome 10 that may be utilized in the present invention. The dome 10 has a base 12 and lifting ring 14. The skin or steel plating 16 of the dome l0 SI'IIOWI'I is constructed of A inch thickness HY- steel plating.

FIG. 2 shows a portion of the interior of the dome 10 with its rigid trusswork 17. The trusswork 17 is comprised of a plurality of circular rods 18. Flat bars may be used in place of the rods 18, particularly in the area of the interior skin 16. FIG. 3 shows a typical damping tile 22 prior to its insertion in the system. The tile 22 is a graphite or carbon black filled polymeric composite accoustically transparent damping tile such as MIL- P-23653 Class 2 plastic damping tiles having cavitation resistance. The tile 22 has a plurality of tapered holes 24 whose use will be explained later.

The method of applying the tiles 22 to the rearward surface of the plating 16 is best shown with reference to FIG. 4. The entire interior surface of the plating I6 is sandblasted to obtain a surface roughness of 1.5 to 2.5 mils. A film thickness of a maximum of .5 mils of a wash primer is then sprayed over the sand blasted area. Four coats of a moisture curing polyurethane with each coat having a thickness of about 2.7 mils is then applied over the primer. From /2 to 6 hours must lapse between coats. At least 4 days must lapse after the final coat of polyurethane before the damping tile installation can begin. Each damping tile 22 having a dimensions of approximately 12 inches by 12 inches by inch thick has 9 to 16 tapered holes drilled through it so that the top of the hole has a diameter of about 1 /8 inch and the bottom of the hole has a diameter of about /8 inch. The purpose ofthe tapered holes is to allow any entrapped air between the steel plating l6 and damping tile 22 to collect in an adhesive slug that develops in the hole during the curing process. Each tile 22, to be inserted between the trusswork l7 must be cut to fit each individual panel to be damped. The tile should cover the metal surface to within /2 inch of the welds and not extend over any welds.

The damping tiles 22 have an adhesive epoxy applied to them to bond the tiles 22 to the steel plating 16. Prior to application of the adhesive, the interior surface of dome and the tile 22 surface must be clean and dry. In applying the tiles 22 to the plating 16 a'lternate panels should be clamped in checkerboard pattern. After the adhesive has cured on these panels, the remaining panels should be damped. An even coat of adhesive should be smoothly trowelled on both the steel plating 16 surface and the tile 22 surface. All entrapped air in the adhesive layers must be worked out. The coated tile 22 is then pressed firmly against the center of the panel.

As shown in FIG. 4 a thin sheet of polyethylene 30 is next placed over the tile 22. An inflatable installation bag 32, slightly larger in surface area than the tile 22 is placed over the tile 22 with the polyethlene sheet 30 between the tile 22 and the inflatable installation bag 32. Next a steel plate 34 is placed over the installation bag 32. The plate 34 has an aperture 36 in the center to allow an air valve 38 on the installation bag 32 to extend therethrough. A plurality of clamps 40 that are adjustable in length are then inserted between the edge of the outer circular rods and the steel plate 34 thus clamping the assembly in place. The inflatable installation bag 32 is then inflated to a pressure of approximately PSIG. The pressure is maintained on the tile for at least 12 hours permitting the adhesive to cure. After the curing of the adhesive, the pressure is released and all of the installation equipment is removed.

Referring now to FIG. 5, there is shown at this time adhesive plug 42 formed within a hole 26 of the damping tile 22. The adhesive plugs 42 formed contain entrapped air that has flowed into the holes 26 of the tile 22. These plugs 42 are snapped out by means ofa screw driver or other sharp instrument providing an air free tile application. The procedure is then repeated for each panel 22 to be applied. The opening 44 shows the appearance of hole 26 after removal of plug 42.

There has therefore been shown an improved sonar dome 10 having reduced sonar dome window vibrations, increased dome window cavitation threshold, reduced fatigue failure and other improvements. The method of making the device shows an air free method of applying tiles 22 under a constant pressure to the inner surface of the skin 16 of dome 10.

It will be understood that various changes in the details, materials, steps and arrangement of parts, which have been made herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principal and scope of the invention as expressed in the appended claims.

What is claimed is:

l. A sonar dome comprising:

a shell enclosure;

a rigid trusswork connected to the interior of said shell enclosure; and

a plurality of damping tiles affixed to the interior surface of said shell with each tile having a plurality of apertures.

2. A sonar dome according to claim 1 with each said tile apertures having a wider diameter at the end away from said shell than at the end proximate said shell.

3. A sonar dome according to claim 2 wherein said tiles comprise graphite filled polymeric composite.

4. A sonar dome according to claim 3 wherein said tiles comprise carbon black material.

Claims

1. A sonar dome comprising: a shell enclosure; a rigid trusswork connected to the interior of said shell enclosure; and a plurality of damping tiles affixed to the interior surface of said shell with each tile having a plurality of apertures.