US3764965A

US3764965A - Projector of acoustic energy

Info

Publication number: US3764965A
Application number: US00263499A
Authority: US
Inventors: Lean W Mc; S Christie
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1972-06-16
Filing date: 1972-06-16
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09

Abstract

A hydroacoustic transducer having a motor-pump unit drawing in ambient water impells the water to a chamber and through a rotary shutter unit which modulates the flow in an on-off sequence. The on-off modulated flow passes through an interposed venturi section creating a corresponding sequence of positive and negative hydraulic pressure impulses. These impulses are fed to the radiating surfaces of an acoustic-energy projector to reciprocally displace them accordingly. Having the transducer substantially filled with water renders it relatively insensitive to ambient pressure variations to ensure reliable operation irrespective of depth.

Description

McLean et a1. Oct. 9, 1973 [5 PROJECTOR 0F ACOUSTIC ENERGY 3,536,157 10/1970 Anstey 340/12 R x 3,458,858 7/1969 Wright, Jr... 340/12 R [75] Inventmsf 'f' McLean Slqney 3,275,977 9/1966 Bouyoucos 340/15 Christie, both of San Diego, Calif.

[73] Assignee: The United States of America as Primary Examiner-Benjamin A. Borchelt represented by the Secretary of the @rsjsymj Examingg- 1-1.1. Tudor Navy, Washington, D.C. Att0rney--Richard S. Sciascia et al.

[22] Filed: June 16, 1972 [21] Appl. No.: 263,499 [57] ABSTRACT A hydroacoustic transducer having a motor-pump unit drawing in ambient Water impe'lls the water to a charm" [52] US. Cl. ..340/12,181/.5 1-1, 340/8 R her and through a rotary shutter unit which modulates [51] Int. Cl. 1104b 13/00 the flow in an omoff Sequence The omoff modulated [58] Field of Search 340/8, l2, l4, 4,

flow passes through an interposed venturi section creating a corresponding sequence of positive and negative hydraulic pressure impulses. These impulses are 340/5, 15; 181/.5 A, .5 H, .5 XC, .5 R

[5 6] Refierences Cited fed to the radiating surfaces of an acoustic-energy pro- UNITED STATES PATENTS jector to reciprocally displace them accordingly. Hav- 3,376,949 4/1968 Baker et al, 131/5 ing the transducer substantially filled with water ren- 3,432,804 3/1969 Beeken 340/15 ders it relatively insensitive to ambient pressure varia- 3,392,369 7/1968 Dickie et 340/12 R tions to ensure reliable operation irrespective of 3,713,417 1/1973 Shugart 340/15 d h 3,277,437 10/1966 Bouyoucos 1 340/12 R 3,403,374 9/1968 Mellen et a1. 340/12 R X 6 Claims, 2 Drawing Figures ,5: SHUTTER IMPELLER' UNI T PMENTED BUT 9 I973 IMPELLER UNI T PROJECTOR OF ACOUSTIC ENERGY 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 therefor.

CROSS REFERENCE TO RELATED APPLICATIONS There is disclosed and claimed herein an unobvious improvement over the Hydrodynamic Transducer disclosed and claimed in the U.S. Pat. No. 3,704,443 issued Nov. 28, 1972 to Edgar N. Rosenberg.

BACKGROUND OF THE INVENTION" Most contemporary ferroelectric and magnetostrictive transducers require elaborate sealing assemblies and pressure-compensation packings or are oil filled to prevent failure especially where the transducer is to be operated at great depths. A series of noteworthy attempts to overcome the effects of varying ambient pressures are shown in a series of hydraulically actuated transducers designed by a J. V. Buoyocous and disclosed in U.S. Pat. Nos. 2,792,804, 3,143,999 and 3,275,977. These closed-system devices convert hydraulic flow into acoustic energy in response to an internally actuated valve mechanism. Even a casual inspection reveals that the Buoyocous devices are complex and, if their hydraulic systems fail or leaks occur, small particles of impurities which gain access into these systems could seriously impair their ability to function. An alternate approach employs a freelyflooded source of acoustic energy, such as that disclosed in U.S. Pat. No. 3,376,949 to B.M. Baker et al for their Water Hammer Marine Seismic Source. This device created a series of zero-pressure-overpressure impulses to ensonify the marine topography. However, a defect became apparent after prolonged operation, in that the overpressure impulses would tend to fatigue the hammers resilient radiating surface. Another mentionable advance in the evolving development of hydroacoustic transducers is disclosed in the U. S. Pat. No. 3,536,157 to N. A. Anstey entitled Underwater Sound Sources. This sound source is pulled through the water and interrupts an entrained mass of flowing water to create a series of no-pressureoverpressure impulses to project acoustic energy. While Ansteys approach eliminates a water impeller and avoids most sealing problems, from a strength-ofmaterials standpoint the repeated over-pressureunderpressure sequences may limit the useful life of this source. Furthermore, the absence of a large radiating surface raises a question as to whether or not any usable level of acoustic energy is capable of being generated and radiated. The above-identified U.S. Pat. No. 3,704,443 comes closest to providing an optimum design uneffected by changing pressures while being highly reliable due to its uncomplicated design. However, even in this design, the modulating series of off-on pressure impulses required strong helical springs to return the radiating surfaces to a normal position. There is evidence to suggest that including these helical springs interferes with the projection of the radiated signal. In all the contemporary acoustic sources, there is no provision made for driving radiating surfaces with a series of positive and negative hydraulic pressure impulses which by themselves hold the radiating surfaces between two extremes positions.

SUMMARY OF THE INVENTION The present invention is directed to providing a transducer of acoustic energy including an impeller unit for feeding impelled fluid to an interrupter unit which sequentially interrupts the flow of the fluid. A venturi section interconnecting the impeller unit and the interrupter unit hydrodynamically produces positive and negative hydraulic pressure impulses in response to the sequentially interrupted flow and a radiating surface communicating with the venturi section is bidirectionally displaced in response to the positive and negative hydraulic pressure impulses.

A prime object of the invention is to provide an improved hydroacoustic transducer.

Another object of the invention is to provide a hy droacoustic transducer feeding positive and negative hydraulic pressure impulses to radiating surfaces.

Still another object of the invention is to provide a hydroacoustic transducer freely-flooded by ambient water to thereby require no pressure compensation.

Yet another object of the invention is to provide a hydroacoustic transducer driven by a series of positive and negative hydraulic pressure impulses which function to retain the radiating surfaces between two extreme positions.

A further object is to provide a hydroacoustic transducer having an elastic radiating surface pulsating in response to positive and negative hydraulic pressure impulses.

These and other objects of the invention will become more apparent from the ensuing description when taken with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of the invention shown partially in cross section.

FIG. 2 is a schematic representation of a second embodiment of the invention also shown partially in cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, an improved projector of acoustic energy 10 is depicted schematically below the surface of a body of water with water filling all voids and cavities throughout. Being completely flooded in this manner renders the projector relatively insensitive to ambient pressure variations and substantially identical operational characteristics remain irrespective of its operational depth. An impeller unit 11 draws in the water from the surroundings through an inlet port and forcefully expels it to following elements via a section of flanged piping 12.

An improved radiation assembly 15, the exact makeup of which will be elaborated on later, receives the impelled water and channels it to a conical housing 25. The downstream wall of the housing is provided with a plurality of radially extending apertures. Journaled onto this wall, a shutter unit 26 includes a disk 26a shaped with a plurality of radially reaching slots having dimensions corresponding to the apertures in the wall. The shutter unit further includes a heavy-duty bearing for providing rotational support for the disk.

As the disk is rotated, the apertures and slots become repetitively aligned and covered to interrupt the flow of water in an on-off sequence. Creation of the modulating on-off sequence is ensured by providing a cogged belt 27 mechanically engaging the disk and being driven by a variable speed motor 28. A more thorough understanding of the mechanical configuration and coaction of the conical chamber, shutter unit and variable speed motor as they function to modulate the flow of impelled water will be gleaned from the aboveidentified US. Pat. No. 3,704,443. The only differences between this invention and the device of U. S. Pat. No. 3,704,443 is that this invention employs a cogged belt 27 for driving the disk 26a and includes a more heavy duty bearing in the shutter unit 26. Otherwise there is substantial identity between the shutter units.

Referring once again to the radiation assembly 15, its improved design enables reliable projection of lowfrequency acoustic energy by transmitting negative hydraulic pressure impulses, as well as, positive hydraulic pressure impulses to an elastic or flexible envelope 16. The envelope optionally is selected from one of a number of resilient sheets which, when filled with water assumes the configuration of an elastic sphere. As the modulated flow sequence is created by the impelled waters passing through shutter unit, the sphericallyshaped envelope pulsates responsively in a sequence of outward and inward motions. In the alternative, the envelope is selected from a an inelastic flexible material such as a tar impregnated canvas-like material tailored the same as that shown in FIG. 1. However, if an inelastic flexible material is chosen, it need be slightly underfilled with water to allow responsive outward excursions.

In either case, the envelope is suitably secured at opposite extremes around a section of piping 17 which is joined at opposite ends to flanged piping 12a and housing flange 25a. From the opposite extremes of the section of piping l, the cross-sectional area is reduced by tapering walls 18. These walls are interconnected at a region of smallest cross-sectional area 18a and, when taken with the converging tapering walls, define a venturi 19.

Since it is a well known fact that the pressure is reduced where the fluid rushes through a constricted, smallest cross-sectional area, slots 20 are provided coupling this area of reduced pressure to the envelope to draw in the envelope as fluid flows through the venturi. Thus, a plurality of slots 20 in the smallest crosssectional area of 18a of the venturi section couple and transmit negative hydraulic pressure impulses to the envelope as impelled water flows through piping l7 and shutter unit 12. Positive hydraulic pressure impulses are transmitted via the slots when the impelled water is blocked from flowing through the shutter unit. These negative and positive hydraulic pressure impulses impart responsive reciprocal displacements to the envelope in response to the interrupted water flow in the shutter unit. It has been found expedient to provide a mesh-like net 21 to prevent excessive sagging of the envelope 16 while it is being filled with water. Only onehalf of the net is shown in the drawings for the sake of simplicity.

Another embodiment of the invention is depicted in FIG. 2. Like elements are described with like reference characters to indicate their substantial identity; however, modifications in a modified radiation assembly 1511 are so fabricated to provide a more rugged energy converter. An essentially tubularly-shaped element 22 is secured at opposite lateral extremes 22a and 22b on the outer surface of section of piping 17. The tubularlyshaped element encloses the entire venturi section 19 and plurality of slots 20 to channel positive and negative hydraulic pressure impulses, created as described above, through its open opposite ends 2212.

A pair of cup-shaped dome members 23 fit down about the outwardmost portions of the open-ended tubular element and a pair of interposed annular-shaped wear strips 24 serve the purpose of sealing interior 23a as well as providing a relatively friction-free surface on which the domes rest as they undergo their reciprocal excursions. The wear strips need not provide perfect sealing since nominal leakage in either direction will not degrade the performance of this embodiment. The domes are not retained by any additional structure although a retaining ring, not shown, could be included to keep the domes on the tubular element when the transducer is idle.

The negative and positive hydraulic pressure impulses alone determine the limits of the inward and outward excursions of the domes on the tubularly-shaped element. A designer will tune the system selecting the proper flow rates, internal dimensions of the venturi section and rotational speeds for the shutter unit to create negative and positive hydraulic pressure impulses which offset each other to reciprocate the domes within preestablished limits on the tubular element.

An improved hydroacoustic transducer fabricated in accordance with the above teachings projects acoustic energy as a function of flow rate. Increasing the flow rate increaes the level of projected energy. Variation of the rotational speed of the shutter unit by the variable speed motor allows selective variation of the projected signal. Freely flooding the transducers innards renders it nonresponsive to changes in ambient pressure. Finally, the absence of structure for biasing or retaining the reciprocating surfaces, while simplifying the overall design, enables the responsive transmission of acoustic energy.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings, and, it is therefore understood that within the scope of the disclosed inventive concept, the invention may be practiced otherwise than specifically described.

What is claimed is:

1. In a transducer of acoustic energy having a motor pump unit drawing in water from the immediate surroundings for impelling the water and a rotary water chopper unit for sequentially interrupting the flow of the impelled water and for expelling the impelled water back to the immediate surroundings, an improvement therefor is provided comprising:

a venturi section provided with at least one slot interconnecting the motor pump unit and the water chopper unit for increasing the flow rate of impelled fluid therethrough creating negative hydraulic pressure impulses when said water chopper unit allows said flow of impelled fluid and positive hydraulic pressure impulses when said flow is interrupted. and

means in fluid communication with said slot for being bidirectionally displaced in response to the positive and negative hydraulic pressure impulses to project representative acoustic energy.

2. A transducer according to claim 1 in which the bidirectionally displaced means is formed of at least one panel of flexible material being outwardly and inwardly flexed upon receipt of said positive and negative hydraulic pressure impulses.

3. A transducer according to claim 1 in which the bidirectionally displaced means is an envelope of elastic material pulsating in response to said positive and negative hydraulic pressure impulses.

4. A transducer according to claim 3 in which said bidirectionally displaced means further includes a wire mesh covering for protecting the elastic envelope from envirionmental abuses and excessive said positive hydraulic pressure impulses.

5. A transducer according to claim 1 in which the bidirectionally displaced means includes,

a tubularly-shaped element in fluid communication with said slot,

a cup-shaped radiation dome coaxially disposed on said tubularly-shaped element and in fluid comm unication with said slot, and

at least one annular wear-strip interposed between said tubularly-shaped element and said radiation dome for ensuring responsive reciprocal excursions of said radiation dome in response to said positive and negative hydraulic pressure impulses.

6. A transducer according to claim 5 in which said tubularly-shaped element mounts a separate radiation dome at opposite axial extremes with a separate interposed annular wear strip for each dome for imparting simultaneous opposed reciprocal excursions in response to said positive and negative hydraulic pressure impulses.

Claims

1. In a transducer of acoustic energy having a motor pump unit drawing in water from the immediate surroundings for impelling the water and a rotary water chopper unit for sequentially interrupting the flow of the impelled water and for expelling the impelled water back to the immediate surroundings, an improvement therefor is provided comprising: a venturi section provided with at least one slot interconnecting the motor pump unit and the water chopper unit for increasing the flow rate of impelled fluid therethrough creating negative hydraulic pressure impulses when said water chopper unit allows said flow of impelled fluid and positive hydraulic pressure impulses when said flow is interrupted. and means in fluid communication with said slot for being bidirectionally displaced in response to the positive and negative hydraulic pressure impulses to project representative acoustic energy.

5. A transducer according to claim 1 in which the bidirectionally displaced means includes, a tubularly-shaped element in fluid communication with said slot, a cup-shaped radiation dome coaxially disposed on said tubularly-shaped element and in fluid communication with said slot, and at least one annular wear-strip interposed between said tubularly-shaped element and said radiation dome for enSuring responsive reciprocal excursions of said radiation dome in response to said positive and negative hydraulic pressure impulses.