GB2544282A

GB2544282A - System for deploying a semi-submerged floating turbine

Info

Publication number: GB2544282A
Application number: GB1519817.9A
Authority: GB
Inventors: Mackie Graeme
Original assignee: OCEANFLOW DEV Ltd
Current assignee: OCEANFLOW DEV Ltd
Priority date: 2015-11-10
Filing date: 2015-11-10
Publication date: 2017-05-17
Anticipated expiration: 2035-11-10
Also published as: GB2544282B; GB201519817D0

Abstract

A device adapted to extract energy from a tidal stream of a body of water having a water line when the device is semi-submerged in the body of water, comprises at least two turbines 4, wherein the at least two turbines are mounted on a turbine support structure 3 being movable between a transport orientation and an operational orientation. In the transport orientation turbine blades of the at least two turbines are floating above the water line, and in the operational orientation the turbine blades of the at least two turbines are immersed below the water line. The support structure may also comprise at least one buoyancy structure 5 which is used to change between the transport and operation orientations by using seawater 12 and horizontal subdivisions 11 to create ballasts. The device may comprise attachment means as shown in Figure 1 for attaching the support structure to at least one mooring line 6.

Description

SYSTEM FOR DEPLOYING A SEMI-SUBMERGED FLOATING TURBINE Field of the Invention

The invention relates to a means for deploying a buoyant semi-submerged structure for supporting turbines used for the extraction of energy from tidal streams and ocean currents.

Background of the Invention

Tidal streams and ocean current can be used to generate power by placing a turbine in the flow. The turbine can either be attached to a structure that is mounted on the seabed or attached to a buoyant body that is suspended in the water column and tethered to the seabed by a mooring system. For an un-ducted turbine the energy extracted from the flow is directly proportional to the swept area of the turbine therefore it is beneficial to deploy laige diameter turbines for maximum energy extraction. These turbines have to be fully immersed in operation and therefore the diameter of the turbine dictates the overall draught (depth below the waterline) of the device.

The inventive step described below specifically relates to semi-submerged turbine support structures with streamline surface piercing buoyant stmt(s) as described in published patent number GB 2422878 and is an enhancement to the solution described in GB 2422878 in that it describes a configuration of the floating body that can be towed to the deployment site with the turbines out of the water such that the draught when launched and when being towed is much less than the normal operating draught. This much reduced launch and towing draught facilitates the building and deployment of the device from conventional port facilities with draught limitations. The innovation also permits the initial hook-up of the device to its moorings while the turbines are still out of the water thus reducing forces on the moorings during hook-up operations.

Summary of the Invention

According to the invention there is provided a device adapted to extract energy from a tidal stream of a body of water having a water line when the device is semi-submerged in the body of water, the device comprising at least one turbine, wherein the at least one turbine is mounted on a turbine support structure, the turbine support structure movable between a transport orientation and an operational orientation, wherein in the transport orientation turbine blades of the at least one turbine are above the water line, and in the operational orientation the turbine blades of the at least one turbine are immersed below the water line.

Preferably, the device is in the form of a free floating turbine support structure that is launched and towed to site in a transport orientation also referred to as a horizontal orientation with the turbine blades out of the water and which, when is at the deployment site, can be ballasted with sea water such that it rotates through approximately 90 degrees to an operation orientation also referred to as a vertical orientations such that the turbine blades are fully immersed.

Preferably, the floating structure has elements of its mooring lines referred to as mooring tails pre-attached to the structure such that they can be joined up to a pre-laid mooring system when the device arrives at the deployment site.

Preferably, the floating structure is fully connected to the upstream element of the mooring system when it is ballasted to the vertical orientation so that the upstream mooring lines can restrain the device with the turbine blades immersed in the flow.

Preferably, the tension in the connected mooring lines can be adjusted from above the waterline when the device is in its vertical orientation.

Preferably, the support structure includes at least one buoyancy chamber and wherein the support structure is moved between the transport and operational orientations by introducing ballast into or removing ballast from the at least one buoyancy chamber.

The device may comprise attachment means for attaching the support structure to at least one mooring line.

Preferably, the device comprises attachment means for attaching the support structure to at least one upstream mooring line and at least one downstream mooring line.

Preferably, the device comprises attachment means for attaching the support structure to at least two upstream mooring lines and/or at least two downstream mooring lines.

Advantageously, the attachment means provide for attachment of the or each mooring line to the support structure at two spaced apart positions thereon, with the support structure in its operational orientation, one of the attachment means capable of resisting the horizontal component of tension in the mooring line being below the water line and approximately in the same horizontal plane as the resultant horizontal drag force of the turbines and the other attachment means capable of resisting the tension in the mooring line being above the water line.

Preferably, the attachment means include fairleads.

The device may further comprise a mooring line tensioner. The mooring line tensioner may be a hydraulic ram, a winch, a capstan or a tirfor.

It is preferred that the support structure comprises one or more main struts, at least one buoyancy chamber and at least two turbine support strut.

Advantageously, the main strut is of small water plane area.

Preferably, the at least two turbine support struts each support at least one horizontal axis turbine nacelle.

Advantageously, each mooring line is attached to the main strut and the at least one buoyancy chamber.

Preferably, the at least two upstream mooring lines are attached to the at least one buoyancy chamber at separate locations and to the main strut at a common location, and wherein the at least two downstream mooring lines are attached to the at least one buoyancy chamber at separate locations and to the main strut at a common location.

Preferably, the at least two upstream mooring lines are attached to the main stmt at separate locations, and wherein the at least two downstream mooring lines are attached to the main strut at separate locations.

Preferably, the attachment means includes at least one mooring tail, the or each mooring tail attachable to a mooring line at a deployment site.

According to another aspect of the invention there is provided a method of deploying a device according to the first aspect of the invention comprising the steps of: towing the device in the transport orientation to a desired location where a pre-laid spread mooring comprising mooring line or lines upstream and downstream of the desired location is situated; holding the device in a fixed position with a first vessel positioned upstream of the device and to which the device is attached; positioning a second vessel downstream of the device to the device; using the second vessel to connect the mooring line or lines downstream of the device to the mooring tail or tails on the device; waiting for slack water or for the tide to change direction introducing ballast into the or each buoyancy chamber until the device is in its operation orientation; connecting the mooring line or lines of which were upstream of the device and after the tide direction has changed are now downstream of the device to the mooring tail or tails on the device; and releasing the second vessel.

Figure 1 shows one embodiment of the device in its operating configuration.

Figure 2 shows a section through the one embodiment of the device.

Figures 3 and 4 show the one embodiment of the device in its launch and tow-out configuration

Figures 5 and 6 show the process of connecting the one embodiment of the device to its moorings.

The device is a semi-submerged body consisting of one or more main struts (1) of small waterplane area onto which are mounted two or more turbine support struts (2) with each strut supporting one or more horizontal axis turbine nacelles (3) with blades (4). The bottom of the main strut(s) is attached to a buoyancy chamber (5) which is streamline in form (Figure 1).

Figure 1 shows an embodiment of the device in operational mode where the turbines are immersed with the main strut in the vertical orientation and the turbine support struts are close to the horizontal orientation. In this orientation the horizontal axis turbine axes of rotation are aligned with the flow. A spread mooring lines (6) attached to either end of the buoyancy chamber restrains the device in a fixed orientation to the flow.

The key innovations in the design are: 1. The geometry of the buoyancy chamber and strut(s) are configured such that in the operational mode with the mooring tethers attached the device floats with its main strut(s) is in the vertical orientation. This requires that the overall centre of gravity is below the overall centre of buoyancy which is achieved by adding ballast weight in the form of seawater (12) to compartments that are low down in the device, specifically the buoyancy chamber or lower section(s) of the strut(s) (Figure 2). The ballast spaces and other un-ballast or void spaces within the strut are created by introducing watertight horizontal subdivisions (11). 2. The device is tethered to the seabed by mooring lines (6) that are configured such that their tension can be slackened off from a fixing point above the waterline (8), normally the top deck of the main strut(s). Mooring line fairleads (9) are positioned at either end of the buoyancy chamber with the option of additional fairleads (10) where the mooring lines meet the top deck of the strut(s). The mooring tether lines pass from the fixing point at the top of the main strut(s) down the length of the strut to pass through the fairleads and then continue to the seabed anchor points. Once the moorings are tensioned from above the waterline they can be locked off at the lower fairlead positions (9) by standard commercially available wire or chain stopper arrangements (not part of this patent). 3. The geometry is configured such that when the mooring tethers are slackened off and seawater ballast (12) is evacuated from the buoyancy chamber and/or strut(s) the device will achieve a floating equilibrium position where the main strut(s) are in the near horizontal orientation and the turbine blades are above the waterline (Figures 3 and 4). The turbine nacelles (3) and the struts (2) supporting the turbine nacelles are configured with sufficient reserve of buoyancy such that when the device is de-ballasted they are partially above the waterline and act as stabilizing arms to keep the turbines out of the water. 4. When the device is initially deployed in the sea either by launching from a slipway, lifting into the water off a quayside or floated out of a flooded dry dock it will be without water ballast and will float in the horizontal attitude. The device can then be towed in the horizontal attitude to the tidal deployment site by a tug. 5. The device is to be attached to a ‘spread’ mooring (6) and (7) consisting of mooring chains, wires or ropes that are aligned into the direction of the tide with one set of moorings positioned to restrain the device in the flood tide and the second set of moorings configured to restrain the device in the ebb tide such that the two sets of moorings are spread out in approximately opposite directions. If the device is to be deployed in an ocean current then the two sets of moorings are aligned into and away from the predominant direction of the current. The individual mooring lines are buoyed off so that their ends can be readily recovered from the sea. 6. To connect the device to its spread mooring the device is first brought up to the moorings while in the horizontal attitude by an anchor handling vessel acting as a tug boat (13) connected by a towline that is attached to the forward mooring tails (7) (Figure 5). A second anchor handling vessel (14) picks up the downstream mooring lines (17) using its winch (15) or crane (16) and connects them to the aft mooring tails (6) that are pre-deployed through the fairleads (9). Once joined together the mooring tails (6) connected to mooring lines (17) are released from the second vessel (14). 7. The device is then held on station until the tide changes direction which happens approximately every six hours. Once the tide changes direction it is held by aft mooring lines which are now the upstream mooring lines. 8. The device is then ballasted by flooding the ballast chambers with seawater (12) until it orientates itself into the upright attitude with the strut(s) in the vertical or upright orientation and the turbines fully immersed with their shaft axes in the horizontal attitude (Figure 6). 9. The anchor handling vessel then connects the now downstream mooring lines (18) to the forward mooring tails (7) that are pre-deployed through the fairleads. Once joined together the mooring tails (7) joined to mooring lines (18) are released. The device is now moored fore and aft by the spread mooring. 10. A tensioning device, e g. a winch, capstan, hydraulic ram or tirfor mounted permanently or temporarily on the struts top deck, is then used to tension each mooring line in turn until the mooring lines achieves the level of pre-tension required to constrain the movement of the device when subject to environmental forces.

Claims

1. A device adapted to extract energy from a tidal stream of a body of water having a water line when the device is semi-submerged in the body of water, the device comprising more than one turbine, wherein the at least two turbines are mounted on a turbine support structure, the turbine support structure movable between a transport orientation and an operational orientation, wherein in the transport orientation turbine blades of the at least two turbine are above the water line, and in the operational orientation the turbine blades of the at least two turbine are immersed below the water line.

2. A device according to Claim 1, wherein the support structure includes at least one buoyancy chamber and wherein the support structure is moved between the transport and operational orientations by introducing ballast into or removing ballast from the at least one buoyancy chamber.

3. A device according to Claim 1 or 2, wherein the device comprises attachment means for attaching the support structure to at least one mooring line.

4. A device according to Claim 3, wherein the device comprises attachment means for attaching the support structure to at least one upstream mooring line and at least one down stream mooring line.

5. A device according to Claim 4, wherein the device comprises attachment means for attaching the support structure to at least two upstream mooring lines and/or at least two down stream mooring lines.

6. A device according to any of Claims 3 to 5, wherein the attachment means provide for attachment of the or each mooring line to the support structure at two spaced apart positions thereon, with the support structure in its operational orientation, one of the attachment means being below the water line and the other above the water line.

7. A device according to any of Claims 3 to 6, wherein the attachment means include fairleads.

8. A device according to any of Claims 3 to 7, further comprising a mooring line tensioner.

9. A device according to Claim 8, wherein the mooring line tensioner is a hydraulic ram, a winch, a capstan or a tirfor.

10. A device according to any preceding claim, wherein the support structure comprises one or more main struts, at least one buoyancy chamber and at least two turbine support strut.

11. A device according to Claim 10, wherein the main strut is of small water plane area.

12. A device according to Claim 10 or 11, wherein the at least two turbine support struts each support at least one horizontal axis turbine nacelle.

13. A device according to Claim 12, wherein the turbine comprises blades.

14. A device according to any of Claims 10 to 13 when dependent on Claim 6, wherein each mooring line is attached to the main strut and the at least one buoyancy chamber.

15. A device according to Claim 14 when dependent on Claim 5, wherein the at least two upstream mooring lines are attached to the at least one buoyancy chamber at separate locations and to the main strut at a common location, and wherein the at least two downstream mooring lines are attached to the at least one buoyancy chamber at separate locations and to the main stmt at a common location.

16. A device according to Claim 15, wherein the at least two upstream mooring lines are attached to the main strut at separate locations, and wherein the at least two downstream mooring lines are attached to the main strut at separate locations.

17. A device according to any preceding claim, wherein the attachment means includes at least one mooring tail, the or each mooring tail attachable to a mooring line at a deployment site.

18. A method of deploying a device as claimed in any of Claims 1 to 17, comprising the steps of: towing the device in the transport orientation to a desired location where a pre-laid spread mooring comprising a first set of mooring lines downstream and a second set of mooring lines upstream of the desired location is situated; holding the device in a fixed position with a first vessel positioned upstream of the device and to which the device is attached; deploying a second vessel downstream of the device to connect up the first set of mooring lines to the device; introducing ballast into the or each buoyancy chamber until the device is in its operation orientation; connecting the second set of mooring lines to the device.

19. The method of Claim 18, comprising the further step of tensioning the mooring lines by shortening their length at their termination points to the device.

20. The method of Claim 18 or 19, wherein the mooring lines of the spread mooring are provided with floatation elements and the first and second vessels pick up the mooring lines of the spread mooring and attach them to the mooring lines of the device.

21. A device adapted to extract energy from a tidal stream of a body of water substantially as shown in, and as described with reference to, the drawings.

22. A method of deploying a device adapted to extract energy from a tidal stream of a body of water, substantially as shown in, and as described with reference to, the drawings.