Hydrodynamic Stabilizing Device

Abstract

A configuration for high speed deployment and recovery of cable-suspended underwater devices makes use of a swivelable tail or shroud. The device shown is a generally cylindrical underwater sonar transducer having a comparatively flat or blunt frontal surface entering the water and a tapered configuration near the upper or cable-suspended end and having a spaced frustoconical shroud or tail structure. The means of attachment of the cable to the body of the transducer includes a connector supporting the shroud and having a swivelable joint. A spring in the body is calibrated to hold the connector tightly against the body during descent, thereby holding the shroud firmly in place; but this spring yields under the greater force required to draw the transducer up out of the water, permitting an axial displacement of the connector and releasing the tail or shroud to permit the body to swivel relative to the shroud. Since the shroud always maintains its alignment relative to the end of the cable, perturbations affecting the body will always be damped out, causing the body to trail the shroud and cable, and ascent is as smooth and fast as the descent.

Description

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.

BACKGROUND OF THE INVENTION

There are a number of devices which are designed to be lowered into the water a substantial distance and retrieved from the water and for which it is desirable that this be accomplished in a relatively short time. In applications involving underwater mapping or searching, a premium is placed on being able to cover a substantial area in a minimum of time. In such operations it is conventional for the transducers used to be lowered at the end of a cable and retrieved by winding in the cable by means of a hoist mechanism. Where it is necessary to operate at considerable depths, it is apparent that an appreciable amount of time must be involved in the lowering and raising operation. Many of the underwater transducer mechanisms presently in use have a roughly cylindrical configuration of considerable diameter relative to their length and are really designed more for sonar effectiveness than with hydrodynamic considerations in mind. With operation at greater depths, however, the time involved in getting the transducer to the operating depth and in returning it to the accompanying seaborne or airborne vehicle may be substantially in excess of the time the transducer is in operating position. Thus, the rate of descent and ascent of the transducer has a very direct bearing on the number of locations to which it may be moved in a given period of time and, therefore, upon the area which it may cover.

While efforts have been made to design structures having relatively good stability through the water in one direction, such structures are usually unstable when towed at any substantial speed in the opposite direction. Frequently a tail shroud or group of tail fins is attached as a means of assuring stable operation in one direction. If such a device is lowered into the water at high speed, it normally must be retrieved at a relatively low speed. Some underwater devices have used inverting structure requiring the resetting of a snatch-line mechanism and/or involving high drag in one direction with severe cable fatigue.

A design with good hydrodynamic characteristics for towing in both directions is shown in U.S. Pat. No. 3,375,488 in the name of R. M. Bridges et al. (common assignee). In this configuration, an elongated tubular transducer element is supplied with fins at the lower end and a comparatively large diameter shroud at its upper end. Receiving transducers are contained in the large diameter shroud and the transmitting elements, which are of smaller diameter, are carried on the main body and are displaced axially from the shroud to avoid interference between the transmitting and receiving elements. This axial displacement has resulted in elongating the element to a degree which is unacceptable for some applications. The large diameter tail-mounted shroud, which is somewhat thick because of the transducer elements, inposes significant drag, and therefore loads the cable heavily when the transducer is being retrieved from the water.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an underwater device with a shroud according to my invention;

FIG. 2 is a sectional view of the upper part of the device of FIG. 1 showing the relative positions of its parts as it descends into the water;

FIG. 2A shows a part of a structure similar to that of FIG. 2 but with an additional damping structure; and

FIG. 3 is a sectional view of the structure of FIG. 2 with the parts displaced to the positions they assume when when the device is being pulled out of the water.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, an elongated, generally cylindrical object 10, such as an underwater transducer, is suspended from a cable 12 which is connected to the transducer 10 through a connecting structure 14. Structure 14 has integrally fastened thereto by means of a plurality of radial fins 16 a tail section in the form of a shroud 18 which is generally frustoconical in shape but which may be slightly curved and which is spaced away from an inwardly tapering portion 20 of the body to permit the surrounding medium, normally sea water, to flow between surface 20 and the inside of shroud 18. The transducer 10 has a relatively flat nose surface 22 in conjunction with rounded shoulders 24. The curvature of the rounded shoulders 24 is normally in the nature of a two-to-one ellipse, and the flat end section 22 will typically constitute approximately 85 percent of the diameter of the transducer 10. It has been determined that the blunt configuration with rounded shoulders is preferable to an ogival configuration since it is as effective on descent and provides much more stability on ascent. It will be appreciated by those skilled in the art that the transducer 10 will normally include a plurality of piezoelectric elements for transmitting and receiving acoustic signals along with electronic circuits for driving the transmitting transducers and for receiving signals appearing at the receiving transducers. The signals processed by the electronic means are typically carried by means of conductors forming parts of cable 12 to an associated vehicle from which the transducer is suspended. Such a vehicle will normally include winch means for reeling the cable 12 in and out as desired.

FIG. 2 shows a sectional view of the device of FIG. 1 with the lower portion removed and the upper part enlarged to show details of the stabilizing structure of my invention. From this view it will be appreciated that the body 10, as it curves toward the top along surface 20, terminates in a flat end section 26. Located within the upper part of transducer 10 and along its axis are a first chamber 28, a bore 30, and a second chamber 32. Positioned within chamber 28 and anchored to its lower wall, as shown herein, is a spring 33 which has its opposite end attached to a generally cylindrical member 34 which includes a stop portion 36. At the upper or opposite end of part 34 is an extension forming part of a U-joint or swivel joint 38. The U-joint 38 might also be a ball and socket joint which will permit its parts to tilt a given number of degrees in any direction around the axis of the vehicle but will not permit them to rotate relative to each other. The opposite part of U-joint 38 constitutes an extension of the connector section 14 through which is attached the radially extending fins and the shroud 18. Connector 14 includes a flared section 40 and a tapered section 42 which cooperates with a shoulder 44 to assure that the tapered section 42 is centered relative to the shoulder 44.

FIG. 2A shows a modification of the device of FIG. 2 including the chamber 28 with springs 33, a portion of the bore 30 and the member 34 movable within bore 30. In this modification, however, the stop member 36 has been converted to a piston 46 containing a bleed 48. The chamber 28, in this instance, will normally be supplied with a working fluid which can be transferred from one side to the other of piston 46 only at a rate controlled by the area of bleed 48. In this manner, effective damping the movement of member 34 is provided.

FIG. 3 shows the device of FIGS. 1 and 2 in the position which it assumes as the transducer 10 is being pulled out of the water. The parts are the same as those shown in FIG. 2 and have the same numerals. In this view the cable 12 is exerting an upward force on the remaining structure including the spring 33 which causes spring 33 to be elongated and to permit member 34 to bottom out against stop 36. This permits significant axial displacement of the connecting structure 14, causing the flared portion 40 and the tapered portion 42 to be pulled away from surface 26. In addition to the increase in cable tension on ascent, other uncaging means could be used such as a direct servo acting on an electric signal. With the skirt structure 40 pulled away from surface 26, as shown, the connector assembly including the shroud 18 may move independently of the body 10, permitting the body 10 to swivel an amount limited by the dimensions of the parts but which may be at an angle as shown in FIG. 3. In the case of an actual structure like that shown in FIGS. 1, 2, and 3, an angle of approximately 15.degree. was found sufficient. With the tail or shroud structure 18 uncaged as described, the shroud structure or tail responds to the movement of the cable in a very stable fashion such that the cable always turns the tail in a direction to counteract any directional error the body may acquire. The body 10, although it may respond to unbalancing forces to the degree of being displaced from the direction of the cable as shown in the phantom outline, must always move back in line with the movement of the cable and the shroud 18. Experiments have shown that when a structure like that of FIG. 1 is pulled by the cable through the water at high speed and the shroud 18 is solidly fastened to the body 10, the action of the structure is to flop wildly, sometimes reaching an attitude nearly perpendicular to the direction of pull of cable 12. Since any unstable movement of the body 10 is not transmitted through to disorient the shroud 18 relative to the direction of pull of cable 12, this movement is rapidly damped out and the ascent is essentially as rapid and as smooth as the descent.

The use of the damping structure shown in FIG. 2A is entirely optional and may not be required for many applications. In the case of a sonar transducer, tests showed that a substantial amount of noise was generated by oscillation and vibration of the parts, both upon striking the water initially and upon terminating the descent into the water. The damping structure of FIG. 2A substantially avoids the generation of this noise.

While the present invention has been described in connection with an underwater transducer, it will be appreciated that the stabilizing structure shown may be useful for many elongated devices of different cross-sectional configurations which may be lowered into the water and retrieved from the water at high speed. One such application might be that of an oceanographic sounding device which would be dropped into the water to select shallow samples of the ocean bottom and return them to the surface. A structure of this type may be used with certain types of anchors which need to be deployed and retrieved quickly.

Claims

I claim:

1. A stabilizing structure for a generally cylindrical object to be rapidly lowered into a body of water and retrieved therefrom at the end of a cable comprising:

connecting means fastening said cable to said object,

a shroud having a generally frustoconical configuration attached to said connecting means with its smaller diameter end oriented upwardly toward said cable, said shroud being spaced from said cylindrical object,

a bore in the end of said object and a surface on said connecting means adapted to seat against said bore, said connecting means also having an extension forming part of a swivel joint,

an axially movable member having an extension forming part of said swivel joint, and

resilient means fastened to said object and to said axially movable member normally urging said surface on said connecting means against its seat, but permitting said connecting means to be unseated under the cable force exerted upon ascent to permit said object to swivel relative to said shroud.

2. A stabilizing structure for a generally cylindrical object to be rapidly lowered into a body of water and retrieved therefrom at the end of a cable,

a connecting structure fastening said cable to said object,

a shroud having a generally frustoconical configuration attached to said connecting structure with its smaller diameter end oriented upwardly toward said cable, said shroud including a plurality of radially extending ribs spacing said shroud from said connecting structure and said object,

a bore in the end of said object nearest said cable with a surface of said connecting structure adapted to seat against said bore, said connecting structure having an extension at one end forming part of a swivel joint,

an axially movable member having an extension forming part of said swivel joint, and

a resilient member fastened to said object at one end and to said axially movable member at its other end and normally urging said conical member against said tapered bore, but permitting said connecting structure to be unseated under the cable force exerted upon ascent to permit said object to swivel relative to said shroud.

3. A stabilizing structure for a generally cylindrical object as set forth in claim 2 wherein said swivel joint is a universal joint which permits said object to swivel in any direction relative to said shroud but not to rotate relative to said shroud.

4. A stabilizing structure for a generally cylindrical object as set forth in claim 2 wherein said object includes a cylindrical chamber, a working fluid in said chamber, said resilient means is positioned in said chamber, said axially movable member includes a piston reciprocable in said chamber and bleed means are incorporated in said piston for damping movement of said piston.

5. A stabilizing structure for a generally cylindrical object as set forth in claim 2 wherein said connecting means includes a tapered surface which centers itself relative to said bore when cable force is reduced significantly below the level required for ascent of said object.

6. A stabilizing structure for a generally cylindrical object as set forth in claim 3 wherein said object is significantly tapered at the end nearest said cable and is of straight cylindrical configuration over approximately 85 per cent of its diameter with rounded shoulders at the opposite end.

7. A stabilizing structure for a generally cylindrical object as set forth in claim 6 wherein said rounded shoulders are formed in a configuration using a two-to-one ellipse.

8. A stabilizing structure for objects of generally cylindrical configuration but tapered at one end to be lowered into the water and lifted out of the water at the end of a cable at high speed, said structure comprising

a first chamber positioned in said structure along its axis near its tapered end,

a second chamber coaxial with said first chamber and including a bore extending to the surface of said structure at its tapered end,

a bore coaxial with said chambers and positioned therebetween,

a movable member axially movable in said bore having an enlarged diameter portion extending into said first chamber functioning as a stop against one end of said chamber and including a spring retainer and having an extension forming part of a pivot joint at its opposite end in said chamber,

a spring in said first chamber fastened to said spring retainer and to the opposite wall of said first chamber,

a conical member adapted to seat in said first named bore having an extension forming the mating part of said pivot joint,

a shroud of the configuration of a truncated cone with its smaller diameter end oriented upwardly toward said cable positioned near the tapered end of said structure and spaced therefrom,

a support structure fastened to said conical member, including a plurality of radially extending arms extending from the inside surface of said shroud to said support structure, and

cable attaching means for connecting said cable to said support structure,

said spring being calibrated such that on descent into the water, spring tension holds said conical member tightly against its seat on said first named bore, but on ascent the cable force exceeds the spring force, permitting said conical member to disengage from said bore and said structure to swivel relative to said shroud.