Flotation Apparatus

Abstract

A spherical pressure vessel, to add buoyancy to a submersible vehicle, is designed to withstand a fraction of the maximum ambient sea pressure to be encountered. The sphere is filled with a pressurized gas and as the vehicle descends the gas is heated to increase its pressure in proportion to the absolute temperature. As the submersible ascends, the gas is cooled to decrease its pressure. The heating and cooling of the gas are so controlled that the difference between the internal gas pressure and the external pressure of the ambient sea is always within a broad safe range. Pressurization of the sphere before a descent allows attainment of a certain depth without the requirement for heating the gas.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Flotation apparatus for imparting buoyancy to submersible vehicles or the like.

2. Description of the Prior Art

Because of the high ambient sea pressures, at great depths, deep diving submersible vehicles ordinarily are built so that in the absence of special provisions they have an effective density greater than sea water. Buoyancy apparatus is generally incorporated in such vehicles to insure its ascent at the termination of a dive and in addition to attain approximate neutral buoyancy at their operating depth. The lighter the flotation apparatus, the greater its merit.

One type of buoyancy material which is used for submersible vehicles is syntactic foam, with densities in the vicinity of 40 lb./cu. ft. currently available and densities in the 35 lb./cu. ft. vicinity as current development goals. A lighter material under consideration is in the form of multi-inch diameter glass spheres embedded in a syntactic foam carrier which provides an effective density of approximately 30 to 35 pounds per cubic foot. A still lower density is attainable through the use of free glass spheres or radially oriented fiber glass spheres. However at present there is an inherent danger of sympathetic implosion propagation from sphere to sphere, with the employment of glass spheres, whether free or embedded in foam.

A liquid flotation material in use is gasoline which has a density of 44 pounds per cubic foot. In addition to the great amount of gasoline required for a dive and it unattractively high compressibility, gasoline presents a dangerous problem in handling.

Other proposals include the use of a liquidized gas as a buoyancy material by expanding the gas to equalize the pressure in the interior of a float chamber to that of the surrounding sea water. Such an arrangement is described in U.S. Pat. No. 3,112,724. The heat of the surrounding sea, or a heating means may be provided for evaporating the gas, the rate of which is controlled to maintain an equilibrium pressure and during a subsequent assent the evaporated gs is released to the surrounding sea. To eliminate the need for replenishing the liquid gas, means for recompressing the gas may be provided. Such system requires the chamber to be communicative with the ambient sea and in addition is either wasteful of liquid gas or alternatively, requires additional recompressing apparatus, which adds undesired weight to the system.

In another arrangement described in U.S. Pat. No. 3,171,376 a liquid gas is vaporized by the surrounding sea or an electric heater and the vaporized gas is conducted to a ballast chamber to expel ambient water therefrom. Such system whether utilizing a liquid gas (or a highly compressed gas) requires a change of state (or volume) and accordingly is a one time operation, or alternatively requires the extra weight of recompressing apparatus.

SUMMARY OF THE INVENTION

The flotation apparatus of the present invention includes a pressure vessel for containing a gas under pressure with one or more such vessels being utilized in conjunction with submersible apparatus such as a vehicle to impart buoyancy thereto. The pressure vessel is designed to withstand a certain differential pressure and contained within the vessel is a heating means for heating the gas to increase the pressure thereof to maintain the pressure differential within a predetermined range as the submersible descends. The pressure vessel additionally includes insulating means to insulate the inside of the pressure vessel and means for cooling the gas to reduce the pressure thereof upon ascent, to maintain the pressure differential within the prescribed range. In normal descent and ascent operations the vessel is completely closed to the ambient sea water and the gas mass and volume remain constant.

By pressurizing the vessel at the surface descent may take place to a prescribed depth without the requirment for activating the heating means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the apparatus in conjunction with a submersible vehicle.

FIG. 2 illustrates a cross-sectional view of one of the flotation devices in accordance with one embodiment of the present invention;

FIG. 3 is a temperature distribution curve;

FIG. 4 is a chart illustrating the operation of the present invention.

FIG. 5 illustrates another submersible unit which may incorporate the present invention; and

FIG. 6 illustrates a cross-sectional view of a flotation device for the use in the apparatus of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The flotation apparatus of the present invention may be utilized with a variety of submersible units such as large deep submergence submarines, submersible vehicles, cable controlled object recovery vehicles, unmanned instrumentation platforms, to name a few. FIG. 1 is illustrative and shows a submersible vehicle 10, hereinafter referred to as a submersible. The submersible includes a pressure hull 12 serving as a crew compartment, normally operative at a 1-atmosphere environment, and which includes control systems for operation of the submersible 10. An outer shell 14, open to the ambient medium e.g. sea water, is provided to afford protection to various equipment and to give the submersible a hydrodynamic shape. Not shown in FIG. 1 are various propulsion, control, battery and ballast systems.

Flotation devices 16 are provided for imparting buoyancy to the submersible and a typical flotation device 16 is illustrated in FIG. 2. The flotation device 16 includes a pressure vessel 20 which for maximum buoyancy with minimum weight, is preferably spherical.

The pressure vessel 20, hereinafter referred to as a pressure sphere, or sphere, unlike the pressure hull 12 of FIG. 1 is designed to withstand only a fraction of the maximum ambient sea pressure to be encountered. The choice of materials for the fabrication of the pressure sphere 20 may include such metals as titanium alloy 6Al- 4V, aluminum alloy 6061-T6 and steel alloy HP-9-4-20, to name a few.

The pressure sphere 20 contains a constant mass and volume of gas under pressure and is designed to withstand a certain positive and negative pressure differential of magnitude p, that is, the pressure of the gas within the sphere 20 may be p units greater than the pressure of the ambient medium outside of the sphere as measured at the uppermost portion thereof, or alternatively the pressure of the ambient medium, as measured at the lowermost portion of the sphere, may be p units greater than the internal pressure of the sphere.

The sphere 20 is designed to include an extra margin of safety, however, it may be stated that there exists a safe pressure differential range from +p to -p. The pressure of the gas within the sphere 20 is a function of its absolute temperature and to maintain the pressure differential within the prescribed range there is provided heating means for increasing the temperature, and accordingly for increasing the pressure of the gas. Although various heat exchange systems may be provided, a simple method of heating the gas is by means of an electrical resistance heating element 21 that transfers heat directly to the gas. The use of resistance heating element 21 simplifies and minimizes the type and number of penetrations required. It has no moving parts and for its weight provides an extremely high efficiency.

If the pressure sphere 20 has descended to a great depth which required the heating of the internal gas to increase the pressure thereof, then upon an ascent the gas must be cooled to decrease the pressure thereof so that the design differential pressure will not be exceeded. Accordingly, means are provided for cooling the gas for reducing the pressure thereof so that during operation of the submersible the cooling means in conjunction with a heating means maintains the pressure of the gas within the pressure sphere 20 within a certain differential pressure range with respect to the pressure of the ambient medium.

Various methods exist for cooling the gas including the use of a heat exchanger within the sphere suitably valved to the external sea water or by circulating the gas through an external heat exchanger. FIG. 2 illustrates the preferred arrangement.

Insulating means may be provided for insulating the pressure sphere 20 from the ambient medium and in the embodiment of FIG. 2 the insulating means 22 is disposed on the inside of the pressure sphere 20 and is divided into two sections, outer section 23 and inner section 24, radially spaced to define a cooling passage 26 therebetween. The determining factors for choosing a particular insulation basically, beside its ability to withstand the temperature and other conditions of its operating environment, are its density .rho. and its thermal conductivity k. The best thermal insulation theoretically has the minimum product of .rho.k for a fixed insulation weight. One such insulation which may be utilized is known as Q-Felt which is a quartz fiber material having a .rho. k factor of 3.75.

Assuming that resistance heater 21 has been activated to increase the temperature of the gas within the pressure sphere 20, there will exist a certain temperature distribution from the relatively hot central core 30, defined by the insulating means, to the relatively cool outer wall of the pressure sphere 20. This temperature distribution is graphically illustrated in FIG. 3 wherein the vertical axis represents temperature and the horizontal axis represents radius. The temperature remains at a constant value T within the core 30 and thereafter rapidly decreases due to the insulating means 22, the interstices of which, typically, contain a portion of the gas. A different temperature gradient is experienced between the inner and outer walls of the sphere 20 and the final temperature value designated T.sub.a is approximately the temperature of the cool ambient medium. Anywhere between the core 30 and the ambient medium, the temperature within the sphere 20 is less than the temperature of the core. The cooling passage 26 is located such that its position on the temperature distribution curve of FIG. 3, results in a temperature T.sub.c which is less than T and somewhat greater than T.sub.a.

Referring once again to FIG. 2, in order to effect cooling of the gas within the core 30, means are provided to communicate the core 30 with the cooling passage 26. This is accomplished by the provision of passageways 32 and 33 extending through the insulation section 24 between the core 30 and cooling passage 26 and being normally closed by means of respective movable plugs 35 and 36. Upon activation of electrically operated solenoids 38 and 39 movable plugs 35 and 36 will be moved to the dotted positions shown allowing free flow of gas between the core and cooling passage 26 to effect a reduction in gas temperature, and accordingly a reduction in gas pressure.

With the orientation illustrated and plugs 35 and 36 in the position shown dotted, there is established a convective heat flow path from the core 30 to the cooling passage 26. When the hot gas from the center of the sphere 20 flows through the passageway 32, heat is transferred to the ambient sea through section 23 of the insulation and the wall of the sphere 20. The cooled gas will then flow back to the core 30 via the lower passageway 33 thereby completing the convection circuit.

When sufficient cooling and pressure reduction has taken place, the operator may activate the solenoids to close the passageways 32 and 33 which preferably are vertically diametrically opposed. In order that the operator may properly control the heating and cooling of the gas within the pressure sphere 20, there is provided sensing means in the form of a thermal sensor 40 for providing a temperature signal, and a pressure transducer 41 for providing a pressure signal.

To avoid a possible large pressure differential across the section 24 of insulating means 22, when passageways 32 and 33 are closed, there is provided a plurality of bleed ports 43 for equalizing pressure. The bleed ports are of an extremely small diameter so that heat transfer therethrough is minimized.

Accessibility of internal components of the sphere 20, for maintenance or replacement is desirable. Accordingly, there is provided a relatively large plug or closure 50 which is threadably engage with the lower portion of the pressure sphere 20 and through which mechanical and electrical penetrations are made. Carried by the closure 50 is a valve means 53 communicative with the inside of the sphere 20 whereby the sphere may be initially charged with a constant mass of gas under pressure. The valve means 53 is communicative with the inside of the sphere 20 by means of valve passage 54 which extends into the sphere only so far as the cooling passage 26 in order to reduce heat leakage from the high temperature core 30.

A malfunction of the heating or cooling means could cause the flotation apparatus to exceed its design pressure differential. In order to obviate a consequent explosion or implosion there is provided safety valve means in the form of a safety valve 57 operable to open upon exceeding of a predetermined positive differential pressure so that gas may be expelled to the ambient sea, and safety valve 58 operable to open upon exceeding a predetermined negative pressure differential to allow the ambient sea water to enter the sphere 20. A typical submersible would normally be provided with a plurality of such spheres 20 and loss of one due to operation of safety valve 57 or 58 would not result in a catastrophic buoyance loss.

In order to prevent a possible systematic failure from affecting all the spheres carried by the submersible, the safety valve means on the pressure spheres can be set so that they are collectively operable to open at different values of pressure differential. For example, instead of having valve 58 (or 57) on each pressure sphere open at the same value of differential pressure, their settings may be staggered by increments. Alternatively a large number of spheres can be separated into groups, with the spheres in each group having the same safety valve setting, but having staggered settings from group to group.

By proper segmenting of the lower portion of insulation means 22 the internal components of the lower half of sphere 20 may be removable as a unit, with removal of the closure 50, thus facilitating maintenance or replacement.

Operation of a typical flotation device 16 is illustrated to good approximation in the chart of FIG. 4. The left-hand column of FIG. 4 represents depth; the next column depicts the sphere 20 and the pressure therein; the next column specifies the ambient pressure at the particular depth in the first column; and the last column designates the differential pressure at that depth. At the surface, represented by the depth zero, the outside pressure (gauge) is zero. The sphere 20 which is designed to withstand a pressure differential of .+-.p may be initially charged to a pressure p such that the pressure differential at the surface of the sea is +p. After descending, a depth D is reached where the ambient sea water pressure is p and consequently the pressure differential is zero since the inside of sphere 20 is maintained at pressure p. At depth 2D the ambient pressure is 2p resulting in a pressure differential of -p. It is therefore seen that with the gas initially under pressure within the sphere 20, and with a design differential pressure of .+-.p, the apparatus may descend to a depth where the outside pressure is twice the inside pressure without activation of the heating or cooling means previously described.

Descent below depth 2D, for example to depth 3D, requires the activation of the heating means to increase the pressure within the sphere 20. For example, to descend to depth 3D, where the outside pressure is 3p, the gas within the sphere 20 is heated until its pressure is 2p thereby resulting in a pressure differential of -p, within the design range. If operation well within the design range is desired, the gas within the sphere 20 from depth D down to maximum operating depth may be heated to increase the pressure within the sphere 20 to be approximately equal to the ambient pressure so that a pressure differential close to zero is maintained.

To serve as an illustrative example of an operative system, the submersible 10 of FIG. 1 may be designed to descend to maximum depth of 20,000 ft. for a 40 hour mission. For a required buoyancy of e.g. 18,000 lbs. the flotation apparatus would include 18 of the spheres such as illustrated in FIG. 2 each having a 44 inch outside diameter and fabricated of titanium alloy 6Al-4V. The gas under pressure would be helium and the design pressure differential p of the shell would be .+-. 3,000 psi (lbs. per square inch.) Maximum operating temperature would be 1,500.degree. F and the insulating means 22 would be comprised of Q-Felt insulation, 12 inches thick with section 23 being approximately 4 inches thick. Assuming that the energy for heating the resistance heater is provided by a hydrogen-oxygen fuel cell the effective density of the flotation apparatus including the apportioned weight of the fuel cell power source would be approximately 25 lbs. per cubic foot. For an operating depth less than 20,000 ft. the energy requirements would be lessened to provide an effective density of 20 lbs. per cubic foot, for example, for 12,000 ft. operation.

Another type of submersible in which the present invention finds application is the manned or unmanned submersible which is supplied with energy from a remote source. In FIG. 1, since the energy source required to heat the gas must be carried by the submersible 10 the weight of such source must be considered in computing the effective density of the apparatus. If supplied with energy from a remote source, by means of a cable for example, the effective density of the flotation apparatus may be reduced. One such submersible is illustrated in FIG. 5.

The submersible 62 is unmanned and is utilized for the lifting of large objects such as 64 from the sea bottom 65. The submersible 62 allows the inclusion of larger spheres 67 and since supplied with energy from a towing surface vessel 69, the submersible 62 has essentially a weightless power source. The remote power source, which allows for thinner insulation since heat leak loss can be tolerated and made up by supplying more energy to the heating means, coupled with the use of larger diameter spheres result in a reduction of effective density.

A typical flotation device 67 is illustrated in Sectional view in FIG. 6. The pressure vessel is in the form of pressure sphere 74 having insulating means 76 on the inner wall thereof primarily to prevent overheating of the sphere material, and is of much smaller thickness than the insulating material described in FIG. 2. Heating means in the form of a resistance heater 79 is supplied with electrical energy from a remote source to heat the gas contained within the sphere 74. As was the case with respect to FIG. 2, the various elements such as resistance heater 79, a temperature sensor 81, a pressure transducer 82 and a charging and safety valving arrangement 84 may be carried by a closure 86 threadably engaged with the lower portion of sphere 74. Valve passage 90 is communicative with the core 91 by means of bleed ports 93.

The cooling means for the arrangement of FIG. 6 includes the relatively thin layer of insulation 76, which in some arrangement may be eliminated, in conjunction with the turning off or deactivation of resistance heater 79 whereupon a heat transfer takes place through the insulation 76, through the wall of sphere 74 to the cool ambient sea water thus reducing the temperature within the sphere.

By way of example, the submersible 62 in FIG. 5 with a requirement for 20,000 lbs. of buoyancy for operation at a depth of 20,000 feet would use 4 spheres as illustrated in FIG. 6 each sphere having a 70 inch outside diameter fabricated from titanium 6Al-4V metal and designed to withstand 2,000 psi. 6 inches of Q-Felt insulation would line the walls of the sphere which would be filled with helium gas. Such an arrangement would result in an effective density of approximately 16 pounds per cubic foot.

Various modifications may be made within the spirit of the invention.

Claims

I claim as my invention:

1. Flotation apparatus for imparting buoyancy to a submersible unit capable of descending and ascending in an ambient medium, comprising:

a. a pressure vessel for containing a gas under pressure;

b. means for charging said pressure vessel with a predetermined mass of gas;

c. heating means contained within said pressure vessel for heating said gas for increasing the pressure thereof;

d. means for cooling said heated gas for reducing the pressure thereof whereby in combination with said heating means the pressure of said gas is maintained within a predetermined pressure range with respect to the pressure of the ambient medium;

e. said mass of said gas and the volume said gas remaining constant during said heating and cooling.

2. Apparatus according to claim 1 wherein:

a. said heating means is an electric resistance heating element.

3. Apparatus according to claim 1 wherein:

a. said pressure vessel is spherical.

4. Apparatus according to claim 1 which includes:

a. insulating means for insulating the interior of said pressure vessel from the surrounding ambient medium.

5. Apparatus according to claim 4 wherein:

a. said insulating means is disposed on the inside of said pressure vessel.

6. Apparatus according to claim 1 which includes:

a. safety valve means operable to open upon a predetermined exceeding of said pressure range for communicating the inside of said pressure vessel with the ambient medium.

7. Apparatus according to claim 6 which includes:

a. a plurality of other similar pressure vessels;

b. said safety valve means on said pressure vessels being collectively operable to open at different values of pressure differential.

8. Apparatus according to claim 1 wherein:

a. cooling of the gas within said pressure vessel is effected by deactivation of said heating means.

9. Apparatus according to claim 8 wherein:

a. said heating means is an electrical heating means; and which includes

b. a source of electric power remote from the submersible unit; and

c. cable means for connecting said source of power with the submersible unit for supplying said heating means with electric energy.