JP3291349B2 - Sonar Baffle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a baffle for a sonar (underwater acoustic wave detector), and more particularly to a compliant baffle.

[0002]

BACKGROUND OF THE INVENTION As is well known in the art, a baffle is a device that acts as a barrier to prevent interference between sound waves in separate adjacent enclosures. In general, sonar baffles reduce unwanted acoustic noise by mechanisms such as signal rejection and / or torsional absorption or cancellation by producing an equal signal out of phase with the signal received by the baffle. Energy canceling or energy absorbing device. In the sonar system,
Baffles are typically used to block sensitive acoustic receivers from unwanted acoustic signals, commonly referred to as noise. In such systems, it is generally desirable to increase the overall response of the sonar system to the required signal by reducing the system's response to unwanted noise.

[0003] In many applications, passive sonar receiver systems, such as arrays of hydrophones, are located on a traveling hull to detect acoustic signals propagating through the ocean. Noise generated on or by a traveling hull, such as mechanical noise, hydrodynamic noise, and noise generated by the activity of the ship's crew, is typically referred to as "self-noise" and is received by the hydrophone array. The required signal may be obscured. Navigating ships, such as submarines and ships, generally have a hull composed of large metal plates mounted on bulkheads. This metal plate is easily excited to produce bending vibrations by mechanical and hydrodynamic noise on board and acts as an acoustic emitter for aqueous media. In some applications, the sonar-baffle assembly is located between a sensitive hydrophone array and the hull of a ship or submarine. The baffle minimizes acoustic energy transmitted from the hull structure by absorbing the acoustic energy in the sonar baffle and / or by reflecting the acoustic energy to the hull. Some sources of emitted noise produce a linear component spectrum that is dominated by the fundamental frequency of the process in which the noise oscillates and the associated harmonic sound components. Another source of emission noise produces a substantially continuous spectrum associated with exciting a structural member, such as a hull, to resonance.
This type of noise, sometimes referred to as high wavenumber noise, does not produce a propagating sound wave and is called evanescent in nature. Thus, this slow wave non-propagating noise is unlikely to be detected by a slightly distant indifferent listener, but overloads the output of the adjacent hydrophone array used to detect acoustic signals traveling underwater. Easy to do.

[0004] There is a wide range of sonar baffles with different sizes, shapes and material compositions that generally depend on the particular application and operating frequency.

[0005] One sonar baffle configuration used in an underwater environment is a compliant plate baffle. The compliant plate baffle typically includes a pair of flexible metal or composite plates integrally joined at each end of the plate to a ball joint hinge. This plate is
It is typically of a length selected to resonate at the frequency of the desired acoustic signal, and is generally separated by a nylon insert to attenuate the resonant acoustic signal. The hinged, flexible plate assembly is typically embedded in a rigid polymeric plastic material, such as polyurethane, for protection against saltwater corrosion. Acoustic signals entering the compliant baffle assembly easily pass through the polyurethane causing the hinged plate to resonate. While compliant plate baffles create some absorption for the incoming sound signal, compliant baffles are typically designed to cancel out the incoming sound signal. The acoustic signal entering the baffle assembly shortens the plate and then re-extends to its original shape, releasing the compression wave at the frequency of the incoming signal but causing a differential phase shift. This response generally results in a partial cancellation of the incoming acoustic signal, thereby causing a separation condition at the receiver. Due to the inherent dimensions and strength of the materials used in the construction, compliant plate baffles provide high insertion loss for unwanted acoustic signals,
It can withstand high static water pressure characteristics typical of deep sea depth. However, the cost of manufacturing a compliant plate baffle is relatively high compared to other baffle designs due to the large number of components required for each assembly.

[0006] Another baffle structure used in underwater systems is a compliant oval tubular baffle. The compliant oval tube baffle assembly includes a plurality of elliptical or oval flexible tubes, typically made of metal or composite material. A compliant oval tube baffle is a pressure or energy counteracting device that operates in the same manner as a compliant plate baffle. The compliant oval linear tube is substantially encapsulated and substantially uniformly oriented such that the minor axis of the elliptical tube substantially defines the thickness of the baffle layer. Encapsulation of the baffle assembly is generally undesirable because this process allows for the occurrence of other modes and results in absorption of the incoming signal which reduces the peak insertion loss of the device. However, encapsulation is usually required to facilitate handling of the assembly and to protect the baffle from the corrosive effects of saline and industrial solvents.

One problem with compliant oval baffles having evenly oriented oval tubes is that certain frequencies within the operating band cause the oval tubes to be known as asymmetric modes. To excite. Acoustic signals at these frequencies pass through the baffle with little attenuation. Acoustic frequency "short" due to resonance
Radlinski and Janus in "Scat"
tering by multiple grating
gs of competent tubes "(J.
Acoustic. Soc. Am. 80 (6), December 1986).

Another problem with a compliant oval tube baffle is its displacement characteristic during excitation.
ent profile). In operation, the excited oval compliant tube has a portion that compresses the surrounding medium, while the other portions of the tube simultaneously dilute the medium. In such a situation, the displacement pattern is said to have both positive and negative displacement. In the case of a compliant oval tube, in the first half cycle of excitation, the apex of the oval tube has a negative displacement, but the wide wall of the tube produces a positive displacement. This effect generally reduces the efficiency of the compliant oval tube to reflect the incoming wave. This effect also exerts another mechanical stress on the tube. The measurement of positive displacement relative to simultaneous negative displacement is called volume flow. Baffles with low volume flow have low acoustic energy and re-emit relatively little energy, and thus exhibit low insertion loss characteristics.

[0009]

In addition, because the compliant oval tubular baffle is made from a hollow continuous hollow oval tube and is not compensated, the surrounding stresses due to hydrodynamic pressure can be large. These stresses are related to the bending stiffness properties of the tube and its shape.

[0010] Both compliant tube baffles and compliant plate baffles have another problem that reduces the efficiency of attenuation of small size bending wavelength noise. This inefficiency is associated with the large size of the compliant device with respect to the evanescent wavelength. Short wavelengths of bending noise appear almost transparent to much larger compliant tubes and plates.

Yet another baffle that is widely used when lightweight, small size, easy to assemble and maintain and requires low cost is a porous (void) elastomer, or so-called "air / rubber" baffle. The air / rubber baffle generally has a structure that includes a sheet of energy absorbing material, such as rubber, having a configuration of closely packed air hole pockets disposed within each sheet. The diameter of the air hole pocket is predetermined to limit the transmission of unwanted acoustic waves entering the baffle. Although air / rubber baffles produce insertion losses of the order of magnitude for costly and heavy compliant plate baffles, their simplicity of design is popular and is used in many applications.

One problem with air / rubber baffles is their relative inefficiency at the ocean floor where high hydraulic conditions exist. The problem of hydraulic loading is not specific to sonar baffles and generally changes the operating characteristics of many components (eg, transducers) used in sonar systems. For air / rubber baffles
These high pressure conditions may compress the energy absorbing sheet to such an extent that it no longer absorbs the acoustic energy that enters it, or, in very rare cases, air such that unwanted acoustic signals propagate to the baffle without attenuation. The shape of the hole pocket can be physically changed.

Furthermore, air / rubber baffles are generally unsuitable for use in environments where underwater explosions can occur.
In such situations, very high dynamic hydraulic pressure conditions result in pressure levels that exceed the strength capacity of the elastomeric material. Generally, air hole cavities create cracks in the material that cause it to fill with water, resulting in inoperable sonar baffles.

In the applications described above, the sonar baffle assembly is located between the hydrophone array and the hull structure. In this type of application, the compliant plate / baffle assembly is typically positioned directly below the hydrophone array to take advantage of the high insertion loss characteristics, but with a porous elastomeric baffle or compliant oval wire The tube baffle is positioned adjacent and around the compliant plate and baffle assembly.

[0015]

SUMMARY OF THE INVENTION In accordance with the present invention, a baffle includes a hollow cylindrical tube having a length and having an end and a longitudinal slot extending the full length of the tube. The baffle further includes means for sealing the tube gap and means for sealing the end of the tube. With such an arrangement, the longitudinal slots provide the air-filled baffle with a lower resonant frequency than an unslotted tube of the same shape, while at the same time having smaller dimensions made with fewer parts than a conventional compliant baffle. Provide baffles.

In accordance with yet another aspect of the present invention, a baffle assembly includes a plurality of adjacent aligned hollows each having a length, an end, and a longitudinal slot extending the length of the tube. Including tubes. The baffle assembly further includes means for sealing a gap in each of the plurality of tubes and means for sealing an end of each of the plurality of tubes. Such an arrangement provides a low frequency baffle assembly having a small thickness and a large insertion loss for small wavelength hull folding waves. Further, the baffle assembly can be used on ocean floors where high hydraulic conditions exist.

According to a further feature of the present invention, the baffle assembly has a plurality of panels. Each panel has a plurality of hollow cylindrical tubes, each having a length, an end, and a longitudinal slot extending the full length of the tube. Preferably, the plurality of tubes are aligned adjacently, and the slots of the plurality of tubes are randomly arranged with respect to one another. Each panel further includes a pair of end covers located at the ends of each tube pair;
A rubber seal disposed in each slot of the hollow tube. The rubber seal further has a looped portion that extends into the tube slot to provide a water tight seal to the inside of the tube while allowing the tube to expand and contract when subjected to incoming waves. With such an arrangement, by using a cylindrical tube with slots, the sonar-baffle assembly offers reduced thickness and increased insertion loss and bandwidth characteristics. Further, the irregular orientation of each slot of the plurality of cylindrical tubes does not increase the thickness of the baffle assembly or significantly alter other properties of the baffle.
Eliminate or at least substantially eliminate the effects of the asymmetric mode.

The above features of the invention, as well as the invention itself, will be better understood from the following detailed description of the drawings.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there is shown a portion of a submarine 10 in which a conformal hydrophone array 12 is disposed within a shaping plate 14 and over a portion of a submarine hull 16. Hydrophone array 12 and submarine hull 1
And a sonar baffle assembly 1 having a plurality of cylindrical compliant tube baffle panels 20 therebetween.
8 are arranged.

In operation, a highly sensitive hydrophone
The element array 12 is used to receive an acoustic signal propagating to the ocean. Sonar baffle assembly 18 provides an acoustic barrier between hydrophone array 12 and submarine hull 16 to minimize unwanted acoustic signals generated by the navigating submarine from being received by array 12. . Generally, rails (not shown) are welded to the hull 16 to mount the cylindrical compliant tube baffle panel 20 in applications where the baffle assembly is offset from the hull and the array.

Referring now to FIG. 2, a plurality of cylindrical compliant tube baffle panels 20 'are shown positioned directly on the hull 16' of a submarine or ship. The baffle assembly so mounted provides a barrier to acoustic signals generated within the submarine. Vibrations caused by onboard machinery and propellers are easily transmitted into the hull and re-emitted into the ocean medium, where such vibrations can be detected by enemy listening devices.

3 and 4, a cylindrical compliant tube baffle 22 is shown to include a generally thin walled tube 23 made of a resilient material. Suitable materials include glass composites, polymer plastics, or metals such as aluminum. The choice of material is generally related to the depth of the ocean in which the baffle will be used. As is well known to those skilled in the art, water pressure increases with depth in the ocean and may compress the cylindrical tube to a degree that reduces its ability to absorb acoustic energy entering it. For applications where such high hydraulic conditions exist, relatively rigid materials such as metal or glass composites are required. These cylindrical compliant tube baffles 22 can be used at significantly greater depths than porous elastomeric baffles and can have the same depth capability as other larger compliant tube baffles.

Tube 23 has a slot 24 disposed along the entire length of the tube and a membrane seal 26 disposed on the slot to provide a watertight seal for the slot. Further, the end of each tube is sealed with an end cover (cap) 28 or plug for preventing water from entering the inside of the tube 23. Seal 26 and end cover 28 provide a tube filled with air and are generally made of rubber impregnated fibers or other materials that are highly impermeable to water. The membrane seal 26 and end cover 28 are made of epoxy,
In this example, Magn of Chamblee, Georgia, USA
Magna, a product of Olia Plastics
tube 2 using a water-impermeable adhesive such as bond55-3.
3 fixed. In applications where the baffle is used at very deep ocean depths, the cylindrical compliance tube is pressurized or "pre-conditioned" with air or other suitable gas such that the high water pressure characteristic of such depths is neutralized. "Filled". The end cover has raised rib handles 29 for engaging parts of the panel housing, such as rails.
including. Configurations using such end covers are discussed below with respect to FIG.

In operation, an acoustic signal entering the cylindrical tube baffle 22 causes the C-shaped hollow tube 23 to vibrate.
This hollow tube has a resonance frequency that is approximated by the following relationship: F = (h / 50a ² ) √ (E / ρ) where h is the wall thickness (cm) a is the radius to the neutral axis of the pipe (cm) E is the elastic modulus of the pipe material (gm / cm) sec ² ) ρ is the density of the tubing (gm / cm ³ ) The cylindrical hollow tube 23 has a unique point of zero displacement called a node at a position opposite the slot 24. The cylindrical compliance tube 23 acts like a tuning fork with two equal cantilevered arms. That is, the displacement of the portion of the tube adjacent to the node is smaller than the displacement of the portion of the tube adjacent to the slot.

The cylindrical tube 23 with the slots 24 is significantly smaller in cross section than either the compliant oval tube or the compliant plate device used at comparable frequencies, and therefore has to be removed from the hull of the ship or submarine. It is quite effective in producing pressure cancellation of small folded wavelength noise.

Slot 24, in addition to lowering the resonant frequency of the tube, provides a discontinuous cylinder that greatly reduces the stress of the inner membrane within the tube. Reducing these film stresses significantly increases tube compliance.

Referring now to FIG. 4, the cylindrical compliant tube 23 is shown to include a roll seal 26 'located on a slot 24 in the tube 23. The roll seal 26 'has a loop 27 with a U-shaped cross section extending radially downward with respect to the slot 24. roll·
The seal 26 'provides a watertight seal inside the tube and allows for circumferential expansion and contraction of the tube relative to the tube end cover (FIG. 3). Loops 27 of substantially circular cross section
Reinforced, water-impermeable materials, such as reinforced rubber, composite plastics or metals, which are flexible and have sufficient tensile strength to resist pulling, are suitable. The roll seal 26 'is made of the above-mentioned Magnabond 55.
Tubing 2 using a water-impermeable adhesive such as -3 epoxy
Fixed to 3. Another embodiment for providing a roll seal to tube 23 is disclosed in K.K., filed Dec. 20, 1988, assigned to the assignee of the present invention. D. Rolt and P.M. F. Flanagan, pending US patent application Ser.
No. 86,689, "Sound Reinforcing"
Seal for Slotted Acoustic
c Transducers can be adapted from those provided for cylindrical transducers.

Referring now to FIG. 5, a cylindrical compliant tube baffle panel 20 is shown to include a plurality of cylindrical compliant tubes 22. A plurality of tubes are positioned adjacent to each other to provide a panel of cylindrical compliant tubes. Generally, it is desirable that the tube be unencapsulated to allow for contact with the transmission medium. In such an arrangement, the baffle provides better attenuation for the incoming sound signal. The de-encapsulation is generally contained within an enclosure covering. In this example,
The tube is shown housed in an open cage frame 30. The frame includes a plurality of rails 32 extending over and fixed to both ends of the frame. The rails 32 generally have slots (not shown) to allow the raised rib handles (FIG. 3) of the end covers of the compliance tubing to slide into the slots of each rail 32. In general, it is desirable to have adjacent tubes at relatively close intervals to produce relatively large insertion losses over a given area. Spacers may be required to provide proper separation between adjacent tubes. Alternatively, the outer diameter of the end covers is selected to be larger than the tube diameter such that the end covers of adjacent tubes contact each other without inhibiting movement of the tubes.

In applications requiring increased insertion loss levels, a plurality of parallel rails 32
Can provide a stacked configuration of cylindrical compliance tube baffles.

The effect of the asymmetric mode, which is commonly excited by the symmetrical arrangement of both the conventional compliant oval tube and the slotted cylindrical or oval compliant tube baffle according to the invention, has the effect of the tube. It is believed that the irregular orientation substantially eliminates it. But,
Because of its shape, the irregular orientation of conventional compliant oval tubes provides a baffle assembly of substantial thickness. This disadvantage also exists with the slotted oval tube of the present invention. However, since the cylindrical tube baffle is circular in cross section, the orientation of the individual slots in the cylindrical compliant tube baffle can be randomly directed without changing the thickness of the baffle assembly. it can.

In other applications, the baffle panels provide a general ease of handling and storage and are lossless to protect the cylindrical compliant tubing from the corrosive effects of seawater and port contaminants. It is required that the tubes be sealed with an elastomer or other suitable material.

Referring now to FIG. 6, a cross-sectional view of the cylindrical compliant tube baffle panel 20a
4 are shown to include a plurality of cylindrical compliant tubes 22 having slots 4 and the same but smaller cylindrical compliant tubes 22 'having slots 24'. In general,
It is desirable to have a baffle assembly with a packed cylindrical compliant tube that provides the greatest amount of insertion loss for a given area. In such applications, a cylindrical compliant tube 22 'having a relatively small cross section perimeter may be replaced by a cylindrical tube 22 having a relatively large perimeter.
Alternatively, or as shown, alternate layers of tubes having different diameters may be nested. Cylindrical compliant tubes 22, 22 'are shown, in this example, disposed within open cage frame 30 and supported within the frame by a corresponding number of rails 32, 32', respectively.

Having described the preferred embodiment of the invention, it will be apparent to one skilled in the art that other embodiments incorporating the concepts of the invention may be used. Therefore, it is believed that the invention is not to be limited to the disclosed embodiments, but only by the spirit of the appended claims.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a sonar wide aperture hydrophone array system with a split cylindrical compliant tube baffle assembly disposed between a hydrophone array and a hull.

FIG. 2 is a partially broken perspective view showing a cylindrical compliant pipe baffle assembly disposed on a hull.

FIG. 3 is a partially cutaway perspective view showing a cylindrical compliance type tube and a gap seal.

FIG. 4 is a cross-sectional view of a portion of the cylindrical compliant tube taken along line 4-4 of FIG.

FIG. 5 is a partially broken perspective view showing the assembled split cylindrical compliant tube baffle array.

FIG. 6 is a cross-sectional view illustrating a portion of another embodiment of a cylindrical compliant tube baffle array.

[Explanation of symbols]

 Reference Signs List 10 submarine 12 hydrophone array 14 shaping plate 16, 16 ′ hull of submarine 18 sonar / baffle assembly 20 cylindrical compliance type tube baffle panel 22, 22 ′ cylindrical compliance type tube baffle 23 cylindrical hollow tube 24, 24 'slot 26 membrane seal 26' roll seal 27 U-shaped cross section loop 28 end cover 30 open cage frame 32, 32 'rail

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Peter F. Flanagan Rhode Island, USA 02920, Apple House Drive, Cranston 27 (56) References JP-A-4-174109 (JP, A) JP-A-1-138592 (JP, A) JP-A-3-96700 (JP, A) JP-A-62-284278 (JP, A) JP-A-7-505705 (JP, A) European Patent Application Publication 447797 (EP) , A 2) European Patent 615900 (EP, B1) US Patent 5,220,535 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S ⁷ /52-7/64 G01S 15/00-15 / 96 G10K 11/16

Claims (9)

(57) [Claims] A panel (2) consisting of compliant tube baffles (22, 22 ') aligned adjacent to each other.
A baffle assembly (30) comprising 2a) wherein each baffle (22, 22 ') comprises a hollow tube (23) and comprises means (28) for closing said tube (23). The hollow tube (23) of each compliance-type tube baffle has a longitudinal slot (24) extending the entire length of the tube, and is provided with means (26) for sealing said slot (24); Mold tube baffle (22, 2
2 ') are a first plurality of tube baffles (22) having a first circumferential tube (23) and a second plurality of tube baffles (22) having a second circumferential tube (23). '), Wherein the first circumference is greater than the second circumference. 2. Each baffle (22, 22 ') closes each end of said tube in the form of a pair of end covers (28) located at each end of said tube (23). 2. The baffle assembly according to claim 1, wherein said baffle assembly includes means for performing the following. 3. A means for sealing said slot (24) comprises a flexible membrane (2) disposed in said slot (24).
Baffle assembly according to claim 1, characterized in that it comprises a watertight barrier to the interior of the tube (6). 4. A baffle assembly according to claim 3, wherein said flexible membrane (26 ') has a loop-shaped portion (27) extending into said slot (24). 5. The baffle assembly according to claim 1, wherein each tube is cylindrical with a circular cross section. 6. The baffle assembly according to claim 4, wherein said flexible membrane is a rubber seal. 7. A slot (2) in said tube (22, 22 ').
Baffle assembly according to any of the preceding claims, wherein 4) are arranged randomly with respect to each other. 8. A baffle assembly according to claim 1, wherein said tube is encapsulated in an elastomeric material. 9. The pipe has the following formula: f = (h / 50a ² ) √ (E / ρ) where h = wall thickness (cm) a = radius to the neutral axis of the pipe (cm) E = tube material modulus ^{(gm / cm sec 2) ρ} = is characterized in that it has a resonant frequency approximated by the relationship of the density of the tube material (gm / cm ^3), the baffle assembly of claim 5, wherein the.