US20100294192A1 - Buoyancy system for an underwater device and associated methods for operating the same - Google Patents
Buoyancy system for an underwater device and associated methods for operating the same Download PDFInfo
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- US20100294192A1 US20100294192A1 US12/470,279 US47027909A US2010294192A1 US 20100294192 A1 US20100294192 A1 US 20100294192A1 US 47027909 A US47027909 A US 47027909A US 2010294192 A1 US2010294192 A1 US 2010294192A1
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- bladders
- water
- chamber
- volume
- underwater device
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
- B63G8/00—Underwater vessels, e.g. submarines; Equipment specially adapted therefor
- B63G8/14—Control of attitude or depth
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
- B63G8/00—Underwater vessels, e.g. submarines; Equipment specially adapted therefor
- B63G8/14—Control of attitude or depth
- B63G8/24—Automatic depth adjustment; Safety equipment for increasing buoyancy, e.g. detachable ballast, floating bodies
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING
- B63B22/00—Buoys
- B63B22/18—Buoys having means to control attitude or position, e.g. reaction surfaces or tether
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
- B63G—OFFENSIVE OR DEFENSIVE ARRANGEMENTS ON VESSELS; MINE-LAYING; MINE-SWEEPING; SUBMARINES; AIRCRAFT CARRIERS
- B63G8/00—Underwater vessels, e.g. submarines; Equipment specially adapted therefor
- B63G8/001—Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations
- B63G2008/002—Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations unmanned
- B63G2008/004—Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations unmanned autonomously operating
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
- F28D20/02—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat
- F28D20/023—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat the latent heat storage material being enclosed in granular particles or dispersed in a porous, fibrous or cellular structure
Definitions
- the present invention relates to the field of underwater devices, and more particularly, to a buoyancy system for controlling buoyancy of an underwater device.
- An underwater glider is a type of underwater device that collects subsurface data in an observation region.
- the underwater glider is typically a torpedo shaped, winged device that moves through the water in a saw-tooth sampling pattern by changing its buoyancy.
- the underwater glider is neutrally buoyant, and typically includes a buoyancy system in its nose section.
- the buoyancy system may be based on a displacement piston. To diver the displacement piston moves water into nose section of the underwater device. This makes the underwater glider's nose heavy. To ascend, water is pushed out of the nose section by the displacement piston. This makes the underwater glider's nose lighter.
- U.S. Pat. No. 6,131,531 discloses a selectively deformable buoyancy system.
- the buoyancy system includes a housing having walls defining an interior, sealable cavity. Changing the volume of the cavity controls buoyancy.
- the cavity has an original volume when the walls are maintained at or above a preselected temperature.
- the walls are deformed at temperatures below the preselected temperature to define a volume less than the original volume.
- the housing returns to the original volume when the temperature of the walls is raised above the preselected temperature.
- Composite materials may be used as part of a buoyancy system, as disclosed in U.S. Pat. No. 4,482,590.
- implosion resistant macrospheres for use in buoyancy systems may be fabricated from synthetic foams, preferably from synthetic thermosetting polymeric resins.
- the implosion resistant macrospheres are primarily used in buoyancy devices at sea depths in excess of 4,500 feet.
- a buoyancy system comprising a chamber having a volume associated therewith, and a plurality of bladders within the volume of the chamber.
- Each bladder may contain a clathrate mixture in a liquid state.
- the chamber may include at least one opening to allow surrounding water to circulate within the volume.
- the plurality of bladders may expand based on the clathrate mixture changing from the liquid state to a solid state. This thereby increases buoyancy by allowing less water to circulate within the volume of the chamber.
- the plurality of bladders may contract based on the clathrate mixture changing from the solid state to the liquid state. This thereby decreases buoyancy by allowing more water to circulate within the volume of the chamber.
- Each bladder may comprise a water-tight enclosure so that the clathrate mixture therein does not directly contact the water.
- the clathrate mixture may comprise water and a clathrating agent.
- Each bladder may maintain a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state. Vaporization of the clathrating agents would make an underwater device with such a buoyancy system permanently buoyant. The maintained minimum pressure thus depends on the clathrating agent, since each clathrating agent has a unique dissolution pressure.
- Each bladder may comprise an elastic enclosure that expands as the clathrate mixture changes to the solid state.
- the elastic enclosure may comprise a thermally conductive material.
- the thermally conductive material advantageously allows the temperature of the surrounding water to be efficiently transferred to the clathrate mixture. As the water temperature cools, the clathrate mixture decreases density when it begins to freeze. The clathrate mixture expands as it freezes, similar to an ice cube that floats.
- each bladder expands as a result of the volume increase of the ice.
- This volume increase multiplied for the total number of bladders, causes water to be forced out of the chamber. This decreases the overall mass while displacing the same volume of water.
- the buoyancy changes.
- the same concept applies in reverse as the ice melts. The bladders will shrink and the buoyancy system will weigh more as more water is allowed to enter the chamber, and its buoyancy will change again.
- the buoyancy system may further comprise a respective spacer coupled between adjacent bladders so that the bladders are spaced apart from one another within the volume of the chamber. This advantageously helps with the transfer of heat from the water to the clathrate mixture since the water will surround each bladder, as compared to partially surrounding the bladders when they are bunched up against one another.
- each bladder may be spherically shaped to provide a greater surface area for the water to contact, thereby improving heat transfer.
- the bladders may form a three-dimensional array of bladders.
- the buoyancy system may further comprise a water permeable enclosure surrounding the plurality of bladders within the volume of the chamber.
- the water permeable enclosure advantageously prevents anyone of the bladders from escaping the chamber.
- Another aspect of the present invention is directed to an underwater device comprising a housing, and a buoyancy system carried by the housing.
- the buoyancy system may be as defined above.
- the housing and the buoyancy system may be configured so that the underwater device is an underwater glider or a sonar buoy, for example.
- Yet another aspect of the present invention is directed to a method for changing buoyancy of an underwater device comprising a buoyancy system as described above.
- the method may comprise placing the underwater device in the water, and submerging the underwater device based on the surrounding water entering the at least one opening within the chamber and contacting the plurality of bladders.
- the method may further comprise expanding the plurality of bladders based on the clathrate mixture changing from the liquid state to a solid state so that less water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device.
- the method may further comprise contracting the plurality of bladders after having been expanded, with the contracting being based on the clathrate mixture changing from the solid state back to the liquid state so that more water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device.
- FIG. 1 is a schematic block diagram of an underwater glider with a buoyancy system in accordance with the present invention.
- FIG. 2 is a schematic block diagram of a sonar buoy with a buoyancy system in accordance with the present invention.
- FIG. 3 is a block diagram of a buoyancy system, wherein each bladder therein comprises a clathrate in a liquid state in accordance with the present invention.
- FIG. 4 is a block diagram of a buoyancy system, wherein each bladder therein comprises a clathrate in a solid state in accordance with the present invention.
- FIG. 5 is a block diagram of a buoyancy system, wherein the bladders therein form a three-dimensional array of bladders in accordance with the present invention.
- FIG. 6 is block diagram of a buoyancy system, wherein a water permeable enclosure surrounds the bladders in accordance with the present invention.
- FIG. 7 is a flow chart for a method for changing buoyancy of an underwater device in accordance with the present invention.
- an underwater device 10 comprises a housing 12 , and a buoyancy system 20 carried by the housing.
- the underwater device 10 is illustrated as an autonomous underwater glider that may be used to collect subsurface data in an observation region.
- the underwater glider is neutrally buoyant, and travels through the water in a saw-tooth-sampling pattern 22 by using the buoyancy system 20 to change its buoyancy.
- the buoyancy system 20 is readily applicable to other types of underwater devices, such as a sonar buoy, for example, as illustrated in FIG. 2 .
- the buoyancy system 20 changes buoyancy of the underwater device 10 based on the use of a plurality of bladders 30 , where each bladder contains a clathrate mixture.
- the plurality of bladders 30 may also be referred to as a blister pack.
- the clathrate mixture comprises water and a clathrating agent, as will be discussed in greater detail below.
- the bladders 30 are in contact with the water, and expand or contract based on the effects of the water's temperature on the clathrate mixture. The expansion or contraction of the bladders 30 affects the buoyancy of the underwater device 10 .
- the clathrate mixture changes from a liquid state to a sold state as the underwater device 10 submerges, and from the sold state back to the liquid state as the underwater device 10 rises.
- the mixture When the clathrate mixture is in the solid state, the mixture may also be referred to as a clathrate hydrate. Transition between the liquid and solid states is based on the temperature of the water surrounding the bladders 30 .
- the sharpness of the saw-tooth-sampling pattern 22 depends on the rate of fusing the clathrate hydrate (bottom saw-tooth-sampling pattern) and on the rate of melting the clathrate hydrate (top saw-tooth-sampling pattern).
- the buoyancy system 20 comprises a chamber 24 having a volume associated therewith, and the bladders 30 are within the volume of the chamber.
- the chamber 24 includes an opening 40 facing the nose of the underwater device 10 , and allows water to flow into the chamber 24 and contact the bladders 30 .
- the chamber 24 may further include another opening 42 facing the rear of the underwater device 10 so that the water exits the chamber 24 as fresh water enters. Buoyancy of the underwater device 10 is based on the amount of water within the chamber 22 , which is based on how much of the clathrate mixture within the bladders 30 are in a liquid and/or solid state.
- the clathrate mixture comprises water and a clathrating agent.
- the clathrating agent may include, but are not limited to, methane or propane, for example.
- the clathrate agent is not limited to a single type clathrating agent.
- the bladder 30 may include more than one type of clathrating agent.
- Clathrate hydrates are crystalline compounds defined by the inclusion of a guest molecule within a hydrogen bonded water lattice.
- Gas hydrates are a subset of clathrate hydrates wherein the guest molecule is a gas at or near ambient temperatures and pressures.
- Such gasses include methane, propane, carbon dioxide, hydrogen, for example; although not all the gas hydrates are suitable for buoyancy modulation when their solidified state is denser than the liquid state (as is the case for carbon dioxide hydrate).
- the clathrate mixture changes density when it freezes. As best illustrated in FIG. 3 , the clathrate mixture is in a liquid state so that the bladders 30 are at a normal size. The bladders 30 are separated from one another when the clathrate mixture is in the liquid state. When the clathrate mixture freezes, the bladders 30 expand, as best illustrated in FIG. 4 . Instead of being separated from one another, the bladders 30 now are closer with one another when in the solid state, possibly in contact with one another.
- Each bladder 30 comprises a water-tight enclosure so that the clathrate mixture therein does not directly contact the water.
- the water-tight enclosure could be a variety of plastics or rubber compounds that are elastic enough to accommodate the expanding clathrate as it freezes, but rigid enough to prevent any leaks between the ambient water and the clathrates.
- Each bladder 30 maintains a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state.
- the clathrating agent is propane
- the bladder maintains a pressure of at least 150 psi so that the propane does not vaporize when the underwater device 10 is at the surface of the water. Vaporization of the clathrating agent would make the underwater device 10 permanently buoyant.
- the maintained minimum pressure thus depends on the clathrating agent, since each clathrating agent has a unique dissolution pressure.
- each bladder 30 comprises an elastic enclosure that expands as the clathrate mixture changes to the solid state.
- the elastic enclosure also comprises a thermally conductive material.
- the thermally conductive material advantageously allows the temperature of the water to be efficiently transferred to the clathrate mixture.
- the clathrate mixture fuses into clathrate hydrate which decreases in density as the mass expands. This is similar to an ice cube that floats.
- some clathrate hydrates become more dense than their respective clathrate mixture states, and consequently, these clathrating agents are not appropriate for use with a buoyancy system 20 .
- the propane fuses with water at about 6 degrees Celsius.
- This volume increase, multiplied for the total number of bladders 30 causes water to be forced out of the chamber 24 .
- the buoyancy increases.
- the same concept applies in reverse as the clathrate hydrate melts.
- the bladders 30 will shrink and the buoyancy system 20 will weigh more as more water is allowed to enter the chamber 24 , and its buoyancy will change again.
- the size and number of bladders 30 within the chamber 24 will vary depending on the size or volume of the chamber, as well as the intended application of the underwater device 10 . There needs to be enough bladders 30 to provide enough clathrate mixtures within the chamber 24 to effect a density change in the underwater device 10 to reverse its buoyancy. This would also depend on the volume and weight of the underwater device 10 , and the desired climb or dive rates that may be required.
- each bladder 30 may be within a range of about 1/16 to 2 inches, for example.
- the size of the chamber 24 is typically about 10 to 20% of the total volume of the underwater device 10 .
- the chamber 24 would have a volume of about 2.5 to 5 cubic feet.
- the number of bladders 30 within the chamber 24 may also compensate for failure of a certain number of bladders 30 that is expected over time. Consequently, additional bladders 30 may be included within the chamber 24 so that buoyancy can still be controlled even with the loss of a portion of the bladders 30 .
- the buoyancy system 20 may further comprise a respective spacer 32 coupled between adjacent bladders 30 so that the bladders are spaced apart from one another within the volume of the chamber 24 .
- a respective spacer 32 coupled between adjacent bladders 30 so that the bladders are spaced apart from one another within the volume of the chamber 24 .
- each bladder 30 may be spherically shaped to provide a greater surface area for the water to contact.
- the bladders 30 may be coupled together so that they form a three-dimensional array of bladders. This resembles atomic crystal structures to maximize packing of the bladders 30 within the chamber 24 .
- the buoyancy system 20 may further comprise a water permeable enclosure 50 surrounding the plurality of bladders within the volume of the chamber, as illustrated in FIG. 6 .
- the water permeable enclosure 50 advantageously prevents anyone of the bladders from escaping the chamber 24 .
- Another aspect of the invention is directed to a method for changing buoyancy of an underwater device 10 comprising a buoyancy system 20 as described above.
- the method comprises placing the underwater device 10 in the water at Block 72 .
- the water needs to have a temperature at depth that is cold enough to freeze the clathrate mixture within the bladders 30 .
- the water needs to have a temperature at the surface that is warm enough to melt the clathrate mixture within the bladders 30 .
- the underwater device 10 submerges and sinks from the surface based on the surrounding water flooding the chamber 24 and engulfing the bladders 30 at Block 74 .
- the bladders 30 then expand at Block 76 as the clathrate mixture changes from a liquid state to a solid state so that less water is circulated within the volume of the chamber 24 . This increases the buoyancy of the underwater device 10 . As a result, the underwater device 10 floats toward the surface of the water at Block 78 . The bladders 30 contact warmer water causing the clathrate mixture in the solid state to melt back into the liquid state.
- the cycle of descending and ascending is continuously repeated in Blocks 74 , 76 and 78 .
- the bladders 30 may rupture over time due to environmental causes at Block 80 .
- the bladders 30 may fail when their elastic properties become brittle over time at Block 82 .
- Yet another option for ending this cycle is to scuttle the underwater device 10 by rupturing the bladders 30 on purpose at Block 84 .
- the method ends at Block 86 .
- the blister pack approach has a significant lifecycle advantage over a piston cylinder device or a single large bladder device. Both these devices are disclosed in U.S. patent application Ser. No. 12/017,966, which is incorporated herein by reference in its entirety and is assigned to the current assignee of the present invention.
- the failure of any single bladder will have little effect on the overall performance of a buoyancy cycle. It would take a large number of bladder failures to terminate the buoyancy cycle.
- an underwater device 10 including a plurality of bladders 30 will have a longer endurance. Its performance eventually will gradually diminish as individual bladder failures accumulate over time, as opposed to the catastrophic failure that would occur with a piston cylinder device or with a large bladder device.
- the blister pack bladder approach has a significant production advantage over the piston cylinder device or the large bladder device since the bladders 30 can be more easily mass produced.
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Abstract
A buoyancy system includes a chamber having a volume associated therewith, and bladders within the volume of the chamber. Each bladder contains a clathrate mixture in a liquid state. The chamber includes an opening to allow surrounding water to circulate within the volume and contact the bladders. As the chamber is submerged in the surrounding water, the bladders expand based on the clathrate mixture changing from the liquid state to a solid state. This changes buoyancy by allowing less water to circulate within the volume of the chamber.
Description
- The present invention relates to the field of underwater devices, and more particularly, to a buoyancy system for controlling buoyancy of an underwater device.
- An underwater glider is a type of underwater device that collects subsurface data in an observation region. The underwater glider is typically a torpedo shaped, winged device that moves through the water in a saw-tooth sampling pattern by changing its buoyancy. The underwater glider is neutrally buoyant, and typically includes a buoyancy system in its nose section.
- The buoyancy system may be based on a displacement piston. To diver the displacement piston moves water into nose section of the underwater device. This makes the underwater glider's nose heavy. To ascend, water is pushed out of the nose section by the displacement piston. This makes the underwater glider's nose lighter.
- Even in view of the advances made in buoyancy systems, there is still a need to improve such systems. For example, U.S. Pat. No. 6,131,531 discloses a selectively deformable buoyancy system. The buoyancy system includes a housing having walls defining an interior, sealable cavity. Changing the volume of the cavity controls buoyancy. The cavity has an original volume when the walls are maintained at or above a preselected temperature. The walls are deformed at temperatures below the preselected temperature to define a volume less than the original volume. The housing returns to the original volume when the temperature of the walls is raised above the preselected temperature.
- Composite materials may be used as part of a buoyancy system, as disclosed in U.S. Pat. No. 4,482,590. In particular, implosion resistant macrospheres for use in buoyancy systems may be fabricated from synthetic foams, preferably from synthetic thermosetting polymeric resins. The implosion resistant macrospheres are primarily used in buoyancy devices at sea depths in excess of 4,500 feet.
- In view of the foregoing background, it is therefore an object of the present invention to provide an improved buoyancy system for controlling buoyancy of an underwater device.
- This and other objects, advantages and features in accordance with the present invention are provided by a buoyancy system comprising a chamber having a volume associated therewith, and a plurality of bladders within the volume of the chamber. Each bladder may contain a clathrate mixture in a liquid state. The chamber may include at least one opening to allow surrounding water to circulate within the volume. When the chamber is submerged in increasingly frigid surrounding water, the plurality of bladders may expand based on the clathrate mixture changing from the liquid state to a solid state. This thereby increases buoyancy by allowing less water to circulate within the volume of the chamber.
- Similarly, when the chamber ascends in the increasingly warm surrounding water, the plurality of bladders may contract based on the clathrate mixture changing from the solid state to the liquid state. This thereby decreases buoyancy by allowing more water to circulate within the volume of the chamber.
- Each bladder may comprise a water-tight enclosure so that the clathrate mixture therein does not directly contact the water. The clathrate mixture may comprise water and a clathrating agent. Each bladder may maintain a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state. Vaporization of the clathrating agents would make an underwater device with such a buoyancy system permanently buoyant. The maintained minimum pressure thus depends on the clathrating agent, since each clathrating agent has a unique dissolution pressure.
- Each bladder may comprise an elastic enclosure that expands as the clathrate mixture changes to the solid state. The elastic enclosure may comprise a thermally conductive material. The thermally conductive material advantageously allows the temperature of the surrounding water to be efficiently transferred to the clathrate mixture. As the water temperature cools, the clathrate mixture decreases density when it begins to freeze. The clathrate mixture expands as it freezes, similar to an ice cube that floats.
- Once the clathrate mixture reaches a depth in the water where it can begin forming ice, each bladder expands as a result of the volume increase of the ice. This volume increase, multiplied for the total number of bladders, causes water to be forced out of the chamber. This decreases the overall mass while displacing the same volume of water. As a result, the buoyancy changes. The same concept applies in reverse as the ice melts. The bladders will shrink and the buoyancy system will weigh more as more water is allowed to enter the chamber, and its buoyancy will change again.
- The buoyancy system may further comprise a respective spacer coupled between adjacent bladders so that the bladders are spaced apart from one another within the volume of the chamber. This advantageously helps with the transfer of heat from the water to the clathrate mixture since the water will surround each bladder, as compared to partially surrounding the bladders when they are bunched up against one another. Moreover, each bladder may be spherically shaped to provide a greater surface area for the water to contact, thereby improving heat transfer.
- The bladders may form a three-dimensional array of bladders. The buoyancy system may further comprise a water permeable enclosure surrounding the plurality of bladders within the volume of the chamber. The water permeable enclosure advantageously prevents anyone of the bladders from escaping the chamber.
- Another aspect of the present invention is directed to an underwater device comprising a housing, and a buoyancy system carried by the housing. The buoyancy system may be as defined above. The housing and the buoyancy system may be configured so that the underwater device is an underwater glider or a sonar buoy, for example.
- Yet another aspect of the present invention is directed to a method for changing buoyancy of an underwater device comprising a buoyancy system as described above. The method may comprise placing the underwater device in the water, and submerging the underwater device based on the surrounding water entering the at least one opening within the chamber and contacting the plurality of bladders. The method may further comprise expanding the plurality of bladders based on the clathrate mixture changing from the liquid state to a solid state so that less water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device. The method may further comprise contracting the plurality of bladders after having been expanded, with the contracting being based on the clathrate mixture changing from the solid state back to the liquid state so that more water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device.
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FIG. 1 is a schematic block diagram of an underwater glider with a buoyancy system in accordance with the present invention. -
FIG. 2 is a schematic block diagram of a sonar buoy with a buoyancy system in accordance with the present invention. -
FIG. 3 is a block diagram of a buoyancy system, wherein each bladder therein comprises a clathrate in a liquid state in accordance with the present invention. -
FIG. 4 is a block diagram of a buoyancy system, wherein each bladder therein comprises a clathrate in a solid state in accordance with the present invention. -
FIG. 5 is a block diagram of a buoyancy system, wherein the bladders therein form a three-dimensional array of bladders in accordance with the present invention. -
FIG. 6 is block diagram of a buoyancy system, wherein a water permeable enclosure surrounds the bladders in accordance with the present invention. -
FIG. 7 is a flow chart for a method for changing buoyancy of an underwater device in accordance with the present invention. - The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
- Referring initially to
FIG. 1 , anunderwater device 10 comprises ahousing 12, and abuoyancy system 20 carried by the housing. Theunderwater device 10 is illustrated as an autonomous underwater glider that may be used to collect subsurface data in an observation region. The underwater glider is neutrally buoyant, and travels through the water in a saw-tooth-sampling pattern 22 by using thebuoyancy system 20 to change its buoyancy. Although theunderwater device 10 is illustrated as an autonomous underwater glider, thebuoyancy system 20 is readily applicable to other types of underwater devices, such as a sonar buoy, for example, as illustrated inFIG. 2 . - As will be discussed in greater detail below, the
buoyancy system 20 changes buoyancy of theunderwater device 10 based on the use of a plurality ofbladders 30, where each bladder contains a clathrate mixture. The plurality ofbladders 30 may also be referred to as a blister pack. The clathrate mixture comprises water and a clathrating agent, as will be discussed in greater detail below. - The
bladders 30 are in contact with the water, and expand or contract based on the effects of the water's temperature on the clathrate mixture. The expansion or contraction of thebladders 30 affects the buoyancy of theunderwater device 10. - The clathrate mixture changes from a liquid state to a sold state as the
underwater device 10 submerges, and from the sold state back to the liquid state as theunderwater device 10 rises. When the clathrate mixture is in the solid state, the mixture may also be referred to as a clathrate hydrate. Transition between the liquid and solid states is based on the temperature of the water surrounding thebladders 30. The sharpness of the saw-tooth-sampling pattern 22 depends on the rate of fusing the clathrate hydrate (bottom saw-tooth-sampling pattern) and on the rate of melting the clathrate hydrate (top saw-tooth-sampling pattern). - Referring now to
FIGS. 3 and 4 , thebuoyancy system 20 comprises achamber 24 having a volume associated therewith, and thebladders 30 are within the volume of the chamber. Thechamber 24 includes anopening 40 facing the nose of theunderwater device 10, and allows water to flow into thechamber 24 and contact thebladders 30. Thechamber 24 may further include anotheropening 42 facing the rear of theunderwater device 10 so that the water exits thechamber 24 as fresh water enters. Buoyancy of theunderwater device 10 is based on the amount of water within thechamber 22, which is based on how much of the clathrate mixture within thebladders 30 are in a liquid and/or solid state. - As readily appreciated by those skilled in the art, the clathrate mixture comprises water and a clathrating agent. The clathrating agent may include, but are not limited to, methane or propane, for example. The clathrate agent is not limited to a single type clathrating agent. The
bladder 30 may include more than one type of clathrating agent. When the clathrate is in the solid state, the clathrate mixture is also referred to as a clathrate hydrate. Clathrate hydrates are crystalline compounds defined by the inclusion of a guest molecule within a hydrogen bonded water lattice. Gas hydrates are a subset of clathrate hydrates wherein the guest molecule is a gas at or near ambient temperatures and pressures. Such gasses include methane, propane, carbon dioxide, hydrogen, for example; although not all the gas hydrates are suitable for buoyancy modulation when their solidified state is denser than the liquid state (as is the case for carbon dioxide hydrate). - The clathrate mixture changes density when it freezes. As best illustrated in
FIG. 3 , the clathrate mixture is in a liquid state so that thebladders 30 are at a normal size. Thebladders 30 are separated from one another when the clathrate mixture is in the liquid state. When the clathrate mixture freezes, thebladders 30 expand, as best illustrated inFIG. 4 . Instead of being separated from one another, thebladders 30 now are closer with one another when in the solid state, possibly in contact with one another. - Each
bladder 30 comprises a water-tight enclosure so that the clathrate mixture therein does not directly contact the water. The water-tight enclosure could be a variety of plastics or rubber compounds that are elastic enough to accommodate the expanding clathrate as it freezes, but rigid enough to prevent any leaks between the ambient water and the clathrates. - Each
bladder 30 maintains a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state. For example, if the clathrating agent is propane, then the bladder maintains a pressure of at least 150 psi so that the propane does not vaporize when theunderwater device 10 is at the surface of the water. Vaporization of the clathrating agent would make theunderwater device 10 permanently buoyant. The maintained minimum pressure thus depends on the clathrating agent, since each clathrating agent has a unique dissolution pressure. - As noted above, each
bladder 30 comprises an elastic enclosure that expands as the clathrate mixture changes to the solid state. The elastic enclosure also comprises a thermally conductive material. The thermally conductive material advantageously allows the temperature of the water to be efficiently transferred to the clathrate mixture. As the water temperature cools, the clathrate mixture fuses into clathrate hydrate which decreases in density as the mass expands. This is similar to an ice cube that floats. As readily appreciated by those skilled in the art, some clathrate hydrates become more dense than their respective clathrate mixture states, and consequently, these clathrating agents are not appropriate for use with abuoyancy system 20. Once the clathrate mixture reaches a depth in the water where it can begin forming ice, eachbladder 30 expands as a result of the volume increase of the ice. - When the clathrating agent is propane, for example, the propane fuses with water at about 6 degrees Celsius. This volume increase, multiplied for the total number of
bladders 30, causes water to be forced out of thechamber 24. This decreases the overall mass while displacing the same change in volume of water. As a result, the buoyancy increases. The same concept applies in reverse as the clathrate hydrate melts. Thebladders 30 will shrink and thebuoyancy system 20 will weigh more as more water is allowed to enter thechamber 24, and its buoyancy will change again. - The size and number of
bladders 30 within thechamber 24 will vary depending on the size or volume of the chamber, as well as the intended application of theunderwater device 10. There needs to beenough bladders 30 to provide enough clathrate mixtures within thechamber 24 to effect a density change in theunderwater device 10 to reverse its buoyancy. This would also depend on the volume and weight of theunderwater device 10, and the desired climb or dive rates that may be required. - For illustrative purposes, the size of each
bladder 30 may be within a range of about 1/16 to 2 inches, for example. The size of thechamber 24 is typically about 10 to 20% of the total volume of theunderwater device 10. For anunderwater device 10 that is about 25 cubic feet in volume, thechamber 24 would have a volume of about 2.5 to 5 cubic feet. There needs to be a sufficient number ofbladders 20 to displace water from thechamber 24 so that there is an effect on buoyancy of theunderwater device 10. - The number of
bladders 30 within thechamber 24 may also compensate for failure of a certain number ofbladders 30 that is expected over time. Consequently,additional bladders 30 may be included within thechamber 24 so that buoyancy can still be controlled even with the loss of a portion of thebladders 30. - As illustrated in
FIG. 3 , thebuoyancy system 20 may further comprise arespective spacer 32 coupled betweenadjacent bladders 30 so that the bladders are spaced apart from one another within the volume of thechamber 24. This advantageously helps with the transfer of heat from the water to the clathrates since the water will surround each bladder, as compared to partially surrounding the bladders when they are bunched up against one another. Moreover, eachbladder 30 may be spherically shaped to provide a greater surface area for the water to contact. - Referring now to
FIG. 5 , thebladders 30 may be coupled together so that they form a three-dimensional array of bladders. This resembles atomic crystal structures to maximize packing of thebladders 30 within thechamber 24. Thebuoyancy system 20 may further comprise a waterpermeable enclosure 50 surrounding the plurality of bladders within the volume of the chamber, as illustrated inFIG. 6 . The waterpermeable enclosure 50 advantageously prevents anyone of the bladders from escaping thechamber 24. - Another aspect of the invention is directed to a method for changing buoyancy of an
underwater device 10 comprising abuoyancy system 20 as described above. Referring now toFIG. 7 , from the start (Block 70), the method comprises placing theunderwater device 10 in the water atBlock 72. The water needs to have a temperature at depth that is cold enough to freeze the clathrate mixture within thebladders 30. The water needs to have a temperature at the surface that is warm enough to melt the clathrate mixture within thebladders 30. Theunderwater device 10 submerges and sinks from the surface based on the surrounding water flooding thechamber 24 and engulfing thebladders 30 atBlock 74. - The
bladders 30 then expand atBlock 76 as the clathrate mixture changes from a liquid state to a solid state so that less water is circulated within the volume of thechamber 24. This increases the buoyancy of theunderwater device 10. As a result, theunderwater device 10 floats toward the surface of the water atBlock 78. Thebladders 30 contact warmer water causing the clathrate mixture in the solid state to melt back into the liquid state. - The cycle of descending and ascending is continuously repeated in
Blocks bladders 30 may rupture over time due to environmental causes atBlock 80. Similarly, thebladders 30 may fail when their elastic properties become brittle over time atBlock 82. Yet another option for ending this cycle is to scuttle theunderwater device 10 by rupturing thebladders 30 on purpose atBlock 84. The method ends atBlock 86. - The blister pack approach has a significant lifecycle advantage over a piston cylinder device or a single large bladder device. Both these devices are disclosed in U.S. patent application Ser. No. 12/017,966, which is incorporated herein by reference in its entirety and is assigned to the current assignee of the present invention.
- In the illustrated
buoyancy system 20, the failure of any single bladder will have little effect on the overall performance of a buoyancy cycle. It would take a large number of bladder failures to terminate the buoyancy cycle. By eliminating single points of failure, anunderwater device 10 including a plurality ofbladders 30 will have a longer endurance. Its performance eventually will gradually diminish as individual bladder failures accumulate over time, as opposed to the catastrophic failure that would occur with a piston cylinder device or with a large bladder device. The blister pack bladder approach has a significant production advantage over the piston cylinder device or the large bladder device since thebladders 30 can be more easily mass produced. - Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
Claims (32)
1. A buoyancy system comprising:
a chamber having a volume associated therewith; and
a plurality of bladders within the volume of said chamber, each bladder containing a clathrate mixture in a liquid state;
said chamber including at least one opening to allow surrounding water to circulate within the volume and contact said plurality of bladders, and as said chamber is submerged in the surrounding water said plurality of bladders expand based on the clathrate mixture changing from the liquid state to a solid state, thereby changing buoyancy by allowing less water to circulate within the volume of said chamber.
2. The buoyancy system according to claim 1 , wherein the clathrate mixture comprises water and a clathrating agent; and wherein the clathrating agent comprises at least one of methane, floro-methane, propane, floro-propane and hydrogen.
3. The buoyancy system according to claim 1 , wherein each bladder comprises a water-tight enclosure so that the clathrate mixture therein does not directly contact the water.
4. The buoyancy system according to claim 1 , wherein each bladder comprises an elastic enclosure that expands as the clathrate mixture changes to the solid state.
5. The buoyancy system according to claim 4 , wherein the elastic enclosure comprises a thermally conductive material.
6. The buoyancy system according to claim 1 , wherein the clathrate mixture comprises water and a clathrating agent, and each bladder maintains a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state.
7. The buoyancy system according to claim 1 , further comprising a water permeable enclosure surrounding said plurality of bladders within the volume of said chamber.
8. The buoyancy system according to claim 1 , wherein each bladder is spherically shaped.
9. The buoyancy system according to claim 1 , further comprising a respective spacer coupled between adjacent bladders so that said bladders are spaced apart from one another within the volume of said chamber.
10. The buoyancy system according to claim 1 , wherein said plurality of bladders form a three-dimensional array of bladders.
11. An underwater device comprising:
a housing; and
a buoyancy system carried by said housing, and comprising
a chamber having a volume associated therewith, and
a plurality of bladders within the volume of said chamber, each bladder containing a clathrate mixture in a liquid state,
said chamber including at least one opening to allow surrounding water to circulate within the volume and contact said plurality of bladders, and as said chamber is submerged in the surrounding water said plurality of bladders expand based on the clathrate mixture changing from the liquid state to a solid state, thereby changing buoyancy of the underwater device by allowing less water to circulate within the volume of said chamber.
12. The underwater device according to claim 11 , wherein the clathrate mixture comprises water and a clathrating agent; and wherein the clathrating agent comprises at least one of methane, floro-methane, propane, floro-propane and hydrogen.
13. The underwater device according to claim 11 , wherein each bladder comprises a water-tight enclosure so that the clathrate mixture therein does not directly contact the water.
14. The underwater device according to claim 11 , wherein each bladder comprises an elastic enclosure that expands as the clathrate mixture changes to the solid state.
15. The underwater device according to claim 14 , wherein the elastic enclosure comprises a thermally conductive material.
16. The underwater device according to claim 11 , wherein the clathrate mixture comprises water and a clathrating agent, and each bladder maintains a predetermined pressure on the clathrate mixture so that the clathrating agent does not vaporize when the clathrate mixture is in the liquid state.
17. The underwater device according to claim 11 , further comprising a water permeable enclosure surrounding said plurality of bladders within the volume of said chamber.
18. The underwater device according to claim 11 , wherein each bladder is spherically shaped.
19. The underwater device according to claim 11 , further comprising a respective spacer coupled between adjacent bladders so that said bladders are spaced apart from one another within the volume of said chamber.
20. The underwater device according to claim 11 , wherein said housing and said buoyancy system are configured so that the underwater device is an underwater glider.
21. The underwater device according to claim 11 , wherein said housing and said buoyancy system are configured so that the underwater device is a sonar buoy.
22. A method for changing buoyancy of an underwater device comprising a buoyancy system, the buoyancy system comprising a chamber having a volume associated therewith, and includes at least one opening to allow water to circulate within the volume, and a plurality of bladders within the volume of the chamber, with each bladder containing a clathrate mixture in a liquid state, the method comprising:
placing the underwater device in the water;
submerging the underwater device based on the surrounding water entering the at least one opening within the chamber and contacting the plurality of bladders; and
expanding the plurality of bladders based on the clathrate mixture changing from the liquid state to a solid state so that less water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device.
23. The method according to claim 22 , further comprising contracting the plurality of bladders after having been expanded, the contracting based on the clathrate mixture changing from the solid state back to the liquid state so that more water is circulated within the volume of the chamber, thereby changing the buoyancy of the underwater device.
24. The method according to claim 22 , wherein the clathrate mixture comprises water and a clathrating agent; and wherein the clathrating agent comprises at least one of methane, floro-methane, propane, floro-propane, and hydrogen.
25. The method according to claim 22 , wherein each bladder comprises a water-tight enclosure so that the clathrate mixture therein does not directly contact the water.
26. The method according to claim 22 , wherein each bladder comprises an elastic enclosure that expands as the clathrate changes to the solid state.
27. The method according to claim 26 , wherein the elastic enclosure comprises a thermally conductive material.
28. The method according to claim 22 , wherein each bladder maintains the clathrate mixture pressure above the vaporization pressure of the clathrating agent.
29. The method according to claim 22 , wherein the buoyancy system further comprises a water permeable enclosure surrounding the plurality of bladders within the volume of the chamber.
30. The method according to claim 22 , wherein each bladder is spherically shaped.
31. The method according to claim 22 , wherein the buoyancy system further comprises a respective spacer coupled between adjacent bladders so that the bladders are spaced apart from one another within the volume of the chamber.
32. The method according to claim 22 , wherein the housing and the buoyancy system are configured so that the underwater device is at least one of an underwater glider and a sonar buoy.
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US12/470,279 US20100294192A1 (en) | 2009-05-21 | 2009-05-21 | Buoyancy system for an underwater device and associated methods for operating the same |
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US12/470,279 US20100294192A1 (en) | 2009-05-21 | 2009-05-21 | Buoyancy system for an underwater device and associated methods for operating the same |
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US12/470,279 Abandoned US20100294192A1 (en) | 2009-05-21 | 2009-05-21 | Buoyancy system for an underwater device and associated methods for operating the same |
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CN102917946A (en) * | 2011-05-30 | 2013-02-06 | 陈家山 | Telescopic submarine |
CN102963514A (en) * | 2012-11-26 | 2013-03-13 | 上海交通大学 | Portable submarine ocean environment monitoring glider |
DE102011057091A1 (en) * | 2011-12-28 | 2013-07-04 | Atlas Elektronik Gmbh | Floatation structure for e.g. manned underwater craft, has actuator that is arranged for varying density of filling material partially filled in variable-volume chamber |
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US20160001860A1 (en) * | 2014-07-01 | 2016-01-07 | Kyushu University, National University Corporation | Ocean exploration apparatus and ocean exploration method |
CN109733573A (en) * | 2019-03-04 | 2019-05-10 | 中国船舶科学研究中心(中国船舶重工集团公司第七0二研究所) | A kind of phase transformation buoyancy regulating device using reactor waste |
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CN112278204A (en) * | 2020-11-30 | 2021-01-29 | 山东未来机器人有限公司 | Underwater operation device |
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CN112124538A (en) * | 2020-09-30 | 2020-12-25 | 中国科学院沈阳自动化研究所 | 7000 meter-level deep-Yuan underwater glider |
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