Adjusting the buoyancy of unmanned underwater vehicles

Patent metadata

Field	Value
Publication number	US-10464645-B2
Application number	US-201615575807-A
Country	US
Kind code	B2
Filing date	May 13, 2016
Priority date	May 21, 2015
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

A method of adjusting buoyancy of an Unmanned Underwater Vehicle (UUV) includes measuring buoyancy drift of the UUV when underwater. After docking the UUV with a subsea station, a quantity of a flowable buoyancy-adjustment material held onboard the UUV is changed by transferring that material from the station to the UUV or from the UUV to the station. A buoyancy adjustment system for a UUV includes: an onboard tank for holding a variable quantity of the buoyancy-adjustment material and upwardly-opening and downwardly-opening passageways communicating with the tank for transferring the buoyancy-adjustment material to or from the UUV. The subsea station includes: a dock for docking a UUV; a holding tank for holding the buoyancy-adjustment material; and at least one upwardly-opening or downwardly-opening passageway aligned with the dock and communicating with the holding tank for transferring the buoyancy-adjustment material to or from the docked UUV.

First claim

The invention claimed is:

1. A method of adjusting buoyancy of a UUV during a subsea mission, the method comprising:
measuring buoyancy drift of the UUV when underwater;
docking the UUV with a subsea station;
at the subsea station, changing a quantity of a flowable buoyancy-adjustment material comprising a granular solid material, a liquid, or a gas, held onboard the UUV to correct the measured buoyancy drift by transferring that material from the subsea station to the UUV or from the UUV to the subsea station, wherein the buoyancy-adjustment material is a ballast material that is negatively buoyant in seawater, and wherein when varying the quantity of buoyancy-adjustment material onboard the UUV, said material flows downwardly from the subsea station to the UUV or from the UUV to the subsea station or to the water;
undocking the UUV from the subsea station; and
continuing the mission.

2. A method of adjusting buoyancy of a UUV during a subsea mission, the method comprising:
measuring buoyancy drift of the UUV when underwater;
docking the UUV with a subsea station;
at the subsea station, changing a quantity of a flowable buoyancy-adjustment material comprising a granular solid material, a liquid, or a gas, held onboard the UUV to correct the measured buoyancy drift by transferring that material from the subsea station to the UUV or from the UUV to the subsea station, wherein the buoyancy-adjustment material is a flotation material that is positively buoyant in seawater and wherein varying the quantity of buoyancy-adjustment material onboard the UUV, said material flows upwardly from the subsea station to the UUV or from the UUV to the subsea station or to the water;
undocking the UUV from the subsea station; and
continuing the mission.

3. The method of claim 1 , comprising measuring buoyancy drift of the UUV before docking the UUV with the subsea station.

4. The method of claim 3 , comprising measuring buoyancy drift by recording an abnormal additional vertical thrust value required to keep the UUV at a constant depth.

5. The method of claim 3 , comprising measuring buoyancy drift by:
measuring a period of time required to move the UUV between different reference water depths by virtue of a level of thruster power; and
comparing the measured time period with a reference time period for moving the UUV between the reference water depths under the same level of thruster power.

6. The method of claim 3 , comprising measuring buoyancy drift by:
selecting a reference water depth for testing;
at the reference water depth, measuring and recording a first value of thruster power required to keep the UUV at the reference water depth;
using the UUV for a period of time to perform subsea tasks as part of the mission;
at the reference water depth, after said period, measuring a second value of thruster power required to keep the UUV at the reference water depth; and
comparing the first and second values of thruster power to calculate buoyancy drift over said period.

7. The method of claim 6 , wherein the UUV is substantially neutrally buoyant at the reference water depth when measuring the first value of thruster power.

8. The method of claim 7 , wherein the first value of thruster power is zero.

9. The method of claim 1 , comprising sending a signal from the UUV to the subsea station, which signal is indicative of the measured buoyancy drift.

10. The method of claim 9 , comprising transmitting said signal through the water.

11. The method of claim 9 , wherein the UUV measures buoyancy drift and transmits said signal to the subsea station automatically.

12. The method of claim 1 , comprising measuring buoyancy drift of the UUV while the UUV is docked with the subsea station.

13. The method of claim 12 , comprising measuring vertical force exerted by the docked UUV on the subsea station.

14. The method of claim 1 , comprising, after docking the UUV with the subsea station, transferring the buoyancy-adjustment material in an amount corresponding to the measured buoyancy drift.

15. The method of claim 1 , wherein the quantity of buoyancy-adjustment material onboard the UUV is adjusted autonomously without commands from surface support.

16. The method of claim 1 , triggered by an auto-diagnostic routine implemented onboard the UUV.

17. The method of claim 1 , triggered in accordance with a schedule pre-programmed into the UUV.

18. The method of claim 1 , wherein the buoyancy-adjustment material is a liquid, a gas or of granular solids.

19. The method of claim 1 , comprising, when docking the UUV with the subsea station, effecting alignment on a vertical axis between a buoyancy-adjustment material inlet of the UUV and a buoyancy-adjustment material outlet of the subsea station.

20. The method of claim 1 , comprising, when docking the UUV with the subsea station, effecting alignment on a vertical axis between a buoyancy-adjustment material outlet of the UUV and a buoyancy-adjustment material inlet of the subsea station.

21. The method of claim 1 , wherein, during transfer to or from the UUV, the buoyancy-adjustment material flows in a vertical direction determined by a difference in density between that material and the surrounding water.

22. A UUV comprising a subsea buoyancy adjustment system, the system comprising:
an onboard tank for holding a variable quantity of a flowable buoyancy-adjustment material, wherein the buoyancy-adjustment material is a liquid or a granular solid; and
at least one upwardly-opening passageway communicating with the onboard tank for transferring the buoyancy-adjustment material to or from the UUV, the at least one passageway terminating in an upwardly-facing opening on a top side of the UUV.

23. The UUV of claim 22 , further comprising a calculation subsystem configured to calculate buoyancy drift of the UUV and to record a buoyancy drift value that is indicative of the calculated buoyancy drift.

24. The UUV of claim 23 , wherein the calculation subsystem comprises: a depth sensor configured to sense water depth; a timer configured to measure a time period required to move the UUV between different reference water depths under thruster power; and a memory configured to store a reference time period for moving the UUV between the reference water depths under the same thruster power.

25. The UUV of claim 23 , wherein the calculation subsystem comprises: a depth sensor configured to sense water depth; a thrust sensor configured to measure thruster power; and a memory configured to store a value of thruster power required to keep the UUV at a reference water depth.

26. The UUV of claim 23 , further comprising a sending subsystem configured to send a signal representing the recorded buoyancy drift value from the UUV to a subsea station.

27. The UUV of claim 26 , wherein the sending subsystem is configured to transmit said signal through water between the UUV and the subsea station.

28. The UUV of claim 23 , further comprising a transfer subsystem configured to transfer an amount of buoyancy-adjustment material in accordance with the buoyancy drift value.

29. The UUV of claim 28 , wherein the transfer subsystem comprises a valve in at least one of said passageways for controlling flow of the buoyancy-adjustment material into or out of the onboard tank.

30. A subsea station comprising:
a doc

Assignees

• Subsea 7 Ltd

Inventors

• Jamieson James Andrew

Classifications

• B63G2008/002

  unmanned · CPC title

• B63G8/001 Primary

  Underwater vessels adapted for special purposes, e.g. unmanned underwater vessels; Equipment specially adapted therefor, e.g. docking stations (self-propelled or direction controlled diving chambers with mechanical link to a base B63C11/42) · CPC title

• B63G8/22 Primary

  Adjustment of buoyancy by water ballasting; Emptying equipment for ballast tanks ({conduits for emptying or ballasting on vessels in general B63B13/00;} stabilising vessels using ballast tanks B63B43/06) · CPC title

• B63G2008/008

  Docking stations for unmanned underwater vessels, or the like · CPC title

• B63G2008/004

  autonomously operating · CPC title