GB2598615A

GB2598615A - Floating support arrangement

Info

Publication number: GB2598615A
Application number: GB2013963.0A
Authority: GB
Inventors: Borgen Eystein
Original assignee: Ebtec As
Current assignee: Ebtec As
Priority date: 2020-09-04
Filing date: 2020-09-04
Publication date: 2022-03-09
Also published as: GB202013963D0; WO2022049269A1

Abstract

A floating support arrangement 1 comprises at least three support legs 2 and 39, each support leg comprising a top end for holding a load 6 and a bottom end opposite said top end comprising a float 3. The support legs are arranged relative to the load such that said support legs are under compression and tend to be forced away from each other at their bottom ends when in use. A plurality of flexible tension members 5 connect the at least three support legs at or close to said bottom ends. The tension members may be ropes, wires or chains. The floating support arrangement may be used to support a net or cage for fish farming, a marine observation room and/or a restaurant, a wind turbine or a carrier beam (28, Fig 7) for a road or railway track.

Description

Floating Support Arrangement

Technical Field

The present invention relates to a floating support arrangement, for example for carrying an offshore wind turbine generator (offshore VVTG, or OVVTG).

Background

The field of floating offshore wind remains, as of 2020, in its early days commercially, with only a handful of concepts having undergone a successful test phase with a full-scale prototype, and only a few pre-commercial floating windfarms. However, a variety of concepts for floating offshore substructures has been described and published.

W02009131826 describes a wind turbine with a tower mounted on a semisubmersible floating structure. The floating structure comprises columns, or floats, which gives the structure sufficient buoyancy to float and be stable in waves and wind. The floats are connected together with a rigid truss like structure to resist and resolve the forces transferred from the wind turbine and tower, as well as resisting the translational and rotational forces (moments) acting directly on the floats due to waves. The truss members below the surface transfer both tension and compression forces and are formed of pipes with support braces to resist the local bending moments in the pipes.

KR20110003919 describes two wind turbine rotors positioned on a shaft between an upwind oriented mast, or arm, and a downwind oriented mast, or arm, fixed to a floating foundation US2016061192 describes a wind turbine supported by an upwind oriented arm and two downwind oriented arms. At their lower ends, the arms are connected to floats and pontoons, which rigidly connect the arms together. The floats and pontoons together give sufficient buoyancy for the wind turbine to float on water. The arms are rigidly connected together by their upper ends. The floats will be subject to wave forces which will impose both translational forces and rotational forces (moments). The arms and pontoons will resist these forces and moments due to the structural continuity in the whole of the structure formed by the floats, the pontoons and the arms, which allow the entire structure to be made rigid.

W02018/234986A1 discloses a 3-leg support structure for a wind turbine, the upper ends of the legs are connected to each other at the top (apex) and the lower ends of the legs are spread apart. The lower ends of the legs are rigidly connected to each other under the water via long rigid truss beams or the like. A float to provide buoyancy is rigidly connected to each corner of the floating structure, with two of the floats positioned at the downwind side and one float at the upwind side. The apex of the legs is located above the two aft floats. A wind turbine is located near the apex of the legs with its wind rotor on the downwind side of all legs. A single point mooring which allows the floating system to freely yaw consist of tension wires grouped together and a free hanging electrical cable with an electrical and mechanical swivel located on the float at the upwind side of the floating foundation. Due to the location of the wind turbine at the aft the centre of gravity of the wind turbine will be located substantially above the two aft floats. The upwind leg will therefore be subject to both tension and compression forces in waves, as well as bending moments. The rigid beams under water will therefore also be subjected to both varying compression forces and tension forces and therefore have to be made rigid to avoid buckling. The long beams under water will be subjected to wave forces, and high bending moments will occur in these beams. In addition, the waves acting on the floats will induce both forces and moments in the floats which also call for a rigid connection to the legs and underwater beams.

For a floating support structure having three or four legs, or with even more legs, with floats, columns or pontoons or the like which provide buoyancy, hereafter denoted buoyancy members, the wave forces acting on each buoyancy member requires a strong and rigid structure. In particular, the rotational moments acting on each of the buoyancy members will attempt to rotate the buoyancy members relative to the rest of the structure it is attached to. Therefore the buoyancy members of such structures are supported by rigid beams, or alternatively with a truss system to connect the lower parts of the buoyancy members with each other under water.

Summary of the invention

Aspects of the present invention provide floating support arrangements and a method of using such arrangements to support a load, as well as a floating wind power facility and a floating bridge comprising a floating support arrangement according to the invention.

The invention will now be described by way of example with reference to the accompanying drawings.

Brief description of drawings

Fig. 1 shows a side view of a floating support arrangement 1 with support legs 2 and 39, tension members 5 positioned under water and a wind turbine comprising a wind rotor 4 and a nacelle 6; Fig. 2 shows a top view of the floating support arrangement of fig. 1; Fig. 3 shows a perspective view of a floating support arrangement 1 where the wind turbine is omitted; Fig. 4 shows a side view of the floating support arrangement 1 with an alternative support leg arrangement 2, 39 comprising structural pipes; Fig. 5 shows a side view of the floating support arrangement 1 with alternative floats 3; Fig. 6 shows a side view of a mooring arrangement; Fig. 7 shows a side view of the floating support arrangement 1 with a bridge; Fig. 8 shows a side view of the floating support arrangement 1 arranged to be sailing on water; and Fig. 9 shows a side view of the floating support arrangement 1 during installation comprising a telescopic jacking arrangement.

Detailed description

The rigidity and size of known structures attract large wave forces, especially the long underwater pontoons which are rigidly connecting the floats and arms together will be exposed to large bending moments due to the wave forces acting on the pontoons themselves. Therefore these pontoons will have to be made very strong, or be braced, in order to resist the large bending moments and will correspondingly use a considerable amount of material, typically steel, and be costly to fabricate. Furthermore, long rigid beams under water will have to be heavy in order to have sufficient strength to resist the wave forces in a harsh environment, and a correspondingly high cost.

One aim of the floating support arrangement described herein is to overcome at least some of the disadvantages of known floating support structures, which is lighter and less costly to fabricate. It is also an aim to improve the single point mooring system as well as the yaw control.

Embodiments described herein comprise an ultralight support structure for an object/load with large mass or pay load that needs to be supported in a stable manner at a large height floating on water. The load could be a wind turbine, the main carrying road beam for a bridge or any other mass or load that needs to be supported in a stable manner on water.

In a first embodiment, as shown in fig. 1, two downwind oriented support legs 39 comprising floats 3 are connected together at their upper ends at or close to a nacelle 6. An upwind oriented support leg 2 comprising floats 3 is connected to the nacelle 6 at a pivot connection 13 arranged to pivot about a horizontal axis oriented 90 degrees to the longitudinal structural neutral axis 8 of said upwind support leg 2. Said support legs 2, 39 may comprise a truss structure. A wind rotor 4 is arranged to rotate about a substantially horizontal axis, aligned with the wind direction and aligned with the centre of nacelle 6. It is understood that the wind turbine alternatively can be arranged to be operating in the opposite direction, i.e.180 degrees rotated about the vertical (yaw) axis, in which case the support leg 2 will be located downwind of the wind rotor. All longitudinal structural neutral axes 8 of said support legs' 2, 39 lower parts meet at a point 26 located substantially in the centre of said wind rotor 4, alternatively at the combined centre of mass of a wind turbine comprising the nacelle 6 and wind rotor 4, alternatively in between said centre of the wind rotor 4 and said centre of combined mass. This feature ensures that the compression forces in said support legs 2, 39 from the pay load at its apex are acting as substantially pure axial forces in the support legs; hence avoiding or reducing the bending moments in said support legs 2, 39 to a minimum level. At the upper ends of support legs 39 this will in some configurations be difficult to achieve due to geometrical constraints/clashing with the wind turbine nacelle 6. However, the upwind support leg 2 and the lower parts of support legs 39 will have the full benefit of this configuration of the neutral axes 8. The water surface is shown as 14. Tension members 5 (being e.g. wires, ropes, cables, chains or similar devices with substantially no bending stiffness) connect the support legs 2, 39 together at their lower parts, preferably at the lower ends of the floats 3. By using tension members 5 instead of a rigid structure (e.g. long beams and/or trusses), the weight and cost of the floating support arrangement 1 can be significantly reduced. A mooring line arrangement 7, preferably made from flexible rope (e.g. twisted nylon), is arranged between an anchor arrangement fixed to the seabed (not shown) and the upper part of said upwind support leg 2. By connecting the mooring line 7 at a point close to the top of the floating support arrangement 1, preferably at a point above the waterline 14 and more than half the total height of the floating support arrangement 1 above the water, the flexibility of the mooring line 7 will be increased due to its longer length than in conventional taut mooring systems. This feature makes it possible to use a flexible mooring at a smaller water depth than for known mooring systems. An adjustable bridle arrangement 42 is connected to said mooring line arrangement. Upper tension members 40 are arranged between the support legs 2, 39 above said (lower) tension members 5 to enhance the stiffness and fatigue resistance of said support legs 2, 39 in response to wave bending moments acting on the floats 3. Said floats 3 are arranged as pipes, with said floats' 3 longitudinal axes arranged to substantially coincide with the structural neutral axis 8 of the support legs 2, 39, and/or substantially intersecting the pivot point 13 where the upwind support leg 2 is connected at its top. This feature will avoid, or reduce the risk, of large torsion forces being transferred via said support legs 2, 39 to the connections at their top caused by wave action on said floats 3. Heave plates 12 are arranged at the lower ends of said floats 3 to increase heave damping.

As shown in fig. 2, the two tension members 5 which connect the upwind support leg 2 to the downwind support legs 39, each comprises a bridle comprising two bridle legs 9, 10. Each bridle leg 9, 10 is connected at two points to the support leg 2 spaced apart in the horizontal plane in order to stabilize support leg 2 against any rotation about its longitudinal axis. A transverse tension member 11 is arranged between two of the tension members 5.

In another embodiment a method to control the yaw of said floating support arrangement 1, when moored to a single anchor, is presented. As shown in fig. 3, the mooring line arrangement(s) 7 are connected to a bridle 42 comprising two bridle legs, where each of the two bridle legs is connected between said mooring line(s) 7 and the floating support arrangement 1. Each bridle leg is configured to be adjustable in length in response to a yaw misalignment signal from a control system. By reducing the length of one of the bridle legs compared to the other, the mooring line 7 will be forced horizontally to the side of an imaginary straight line 90 degrees to the wind rotor plane and coinciding with the centreline of said wind rotor disk, and therefore creating a moment arm. Hence, a yawing moment will be created due to the thrust force acting on the wind rotor multiplied by said moment arm. Said yawing moment can be used, in response to a yaw misalignment signal from a control system, to yaw the floating support arrangement 1 to re-align the wind rotor with the incoming wind.

Fig. 4 shows another embodiment comprising support legs 2, 39 in the form of structural pipes, supported by a bracing comprising two stays 15 for each of said support legs and spreader beams 16. This feature lends itself for easy fabrication with fewer welded nodes.

Fig. 5 shows an embodiment comprising floats 3 floating on the surface 14, said floats comprising a cylinder with the longitudinal axis of said cylinder arranged horizontally and aligned with said wind rotor plane, i.e. normally substantially 90 degrees to the incoming wind and waves. This feature has the advantage of all the pressure forces from waves aligned with the wind to be directed into the centreline of said cylinders. In yet another embodiment of the invention said floats comprise a substantially sphere shaped member, or flat plated member taking the approximate overall shape of a sphere. Heave damping plates 12 are configured below said cylinders or sphere like floats suspended by ropes and bridles.

In fig. 6 another embodiment of the invention is shown with a mooring arrangement comprising an anchor 24 connected to the seabed 25, a substantially torsion resistant connection comprising a lower delta plate 18 connected rotatably about a horizontal axis to said anchor at said delta plate's lower end, two mooring line arrangements 7 spread apart with its lower part connecting said lower delta plate to an upper delta plate 18, rotatably connected about a horizontal axis to a rigid hollow pipe 20 which is arranged to pass through the splash zone where the waves are most powerful, said rigid hollow pipe comprising a mechanical swivel 23 with its upper part arranged to rotate relative to said rigid hollow pipe about the longitudinal axis of said rigid hollow pipe. An upper part of said mooring line arrangements 7 in one end connected to the upper part of said mechanical swivel and in its other end connected to upwind support leg 2. A bridle 42 comprising two bridle legs adjustable in length in response to a yaw misalignment signal is connected between said mooring line arrangement(s) 7 and the upwind support leg 2 or alternatively to the tension members 5 or bridle legs 9 or 10 as shown on figure 2, or alternatively to upper support legs 40 as shown on figure 1 and 2. A cable 17 which may comprise an electrical cable and a signal cable including a fibre optic cable, is mechanically connected to each of the mooring line arrangements 7 routed from side to side in a snake like wave configuration when there is no load in said mooring line arrangements. In the case the mooring line arrangements are made up of flexible taut ropes said mooring line arrangements will stretch in order to absorb the forces from waves, current and wind. In that case, by careful geometrical consideration of said initial wave ("snake") form of said cable the wave form will be stretched partially out towards a straight line when said mooring line arrangements 7 are loaded, however never reaching the fully straight line and thus the cable 17 will not be mechanically compromised even during an extreme event. This feature will also have the benefit of pushing the two mooring line arrangements 7 away from each other, reducing the risk of them coming close and hence lose its torsion resistance, as some torsion resistance is needed to guarantee said mechanical swivel is rotating when necessary instead of twisting the mooring lines. Said cable 17 is further routed through rigid pipe 20 and passes through said mechanical swivel substantially along its axis of rotation. Finally, said cable is terminated in a power swivel assembly 22 arranged above said mechanical swivel, said power swivel assembly comprising an electrical slip ring or an electrical disconnectable circuit breaker, which may be disengaged to unwind said cable and then be re-engaged. The latter will avoid the expensive fabrication of a high voltage slip ring unit.

Fig. 7 shows an embodiment having two left side oriented support legs 39 comprising floats 3 connected together at their upper ends at or substantially close to an apex point 26. A right side oriented support leg 2 comprising a float 3 is connected to said apex at a pivot connection substantially coinciding with said apex point 26 and arranged to pivot about a horizontal axis oriented 90 degrees to the longitudinal structural neutral axis 8 of said right side support leg. Said support legs 2, 38 may comprise a truss structure. Tension members 5 (comprising e.g. wires, ropes, cables, chains or the like with substantially no bending stiffness) connect the support legs 2, 39 together at their lower parts, preferably at the lower ends of the floats 3. A mooring line arrangement 7 connected to each of said support arms, preferably taut and made from flexible rope, is arranged to be connected to an anchor arrangement (e.g. piles) fixed to the seabed (not shown). A carrier beam 28 comprising a road member for the transportation of cars, trucks or trains is suspended by bridge tension members 27 from substantially said apex point of said support legs 2, 39. Alternatively said carrier beam 28 is suspended from vertical bridge tension members 30 connected between a catenary rope 29 which is arranged between said apex 26 and adjacent support arrangements (not shown) on each side of said floating support arrangement 1 effectively forming a floating suspension bridge.

Another embodiment comprises a floating support arrangement 1 arranged to be sailing on water in response to wind forces acting on said support arrangement 1.

Fig. 8 shows a side view of the floating support arrangement 1 comprising Aerodynamic wind profiles 31 arranged on support legs 2, 39 which may be used as sails. In addition, the rotor blades of the rotor 4 are pitched substantially 90 degrees to increase the effective sail area, i.e. the rotor blades are used as sails as well. The wind profiles 31 may be arranged to rotate substantially about the longitudinal axis of each of said support legs 2, 39 in response of the direction of the incoming wind.

Hydrodynamic profiles 32 are arranged on floats 3 in order to give sideways stability during sailing, hence acting as keels. Optionally, one or several of said hydrodynamic profiles is (are) arranged to rotate about the longitudinal axis of the float(s) hence acting as rudders with adjustable azimuth angles. In that case, the wind profiles 31 on said support legs 2, 39 can be fixed and the rudders, which are arranged to rotate the full 360 degrees, will make the floating support arrangement 1 able to sail in all directions to orient the fixed wind profiles 31 on said support legs 2, 39 at an optimum angle relative to the wind, i.e. the bow direction is defined by the collective rudder orientations at any time. By proper co-ordination of the different rudder azimuth angles relative to each other, the floating support arrangement 1 will be able to turn as a normal sailing boat with a single rear rudder and a fixed keel, with the "boW' variably defined at any time depending on the azimuth angles of the hydrodynamic profiles. The heave plates 12 arranged at the lower ends of said floats 3 will preferably be positioned with their flat planes coinciding with a horizontal plane to decrease drag forces during sailing.

Another embodiment comprises a jacking system arranged to erect the support legs during the assembly of the system. The jack may be engaged close to the top of the support legs, or ideally close to the upwind support leg's pivot point at the top. Fig. 9 shows a side view of the floating support arrangement 1 during the erection. In a preferred embodiment, the wind turbine nacelle 6 is mounted rigidly to the two support legs 39 before the erection operation commences. Support leg 2 is pivotally connected to the front of the wind turbine at pivot connection 13. A telescopic cylinder 34 is arranged on the seabed 25 in its lower end and moored with at least three taut mooring lines 35 to at least three anchors 36 on the seabed. The telescopic cylinder 34 may comprise an outer support pipe of large diameter which may be partly open to the sea water, and an inner water tight piston cylinder with slightly smaller diameter with removable water inside. When the water is pumped out of said inner cylinder it, i.e. the piston, will rise due to its flotation. Two tension members 5 are connected to the upwind float 3 in one end and via sheaves 41 to two opposing floats 41 in the other ends to winches 38. Said telescopic cylinder is pushing vertically on said pivot connection until the wind turbine and support legs are lifted free from a temporary installation barge 37. The tension members 5 are simultaneously winched in to control the azimuth angle between the legs to be substantially 120 degrees before and during the erection. When the cylinder is raised to a certain height the rest of the lifting can be carried out entirely by winching in on the tension members 5 or as a combination of the two In one embodiment, the wind turbine is replaced by a dummy frame during said erection and installation phase. Once the support arms are erected using said dummy frame and the tension wires 5 are secured the wind turbine can be winched up from a barge positioned between the support legs 2, 39 by winches mounted on or close to said dummy frame at the top of the support legs 2, 39. The dummy frame will be configured so that the wind turbine will fit inside the frame when lifted up in its final position. Once the wind turbine is connected and secured to each side, i.e. to the upwind oriented support leg 2 on one side and the downwind oriented support legs 39 on the opposite side, the dummy installation frame can be unbolted and removed in smaller pieces which can be handled by a small and permanently mounted service crane. The dummy frame can later be used, even offshore, if the wind turbine needs to be decommissioned or taken to shore for repair, without having to de-rig said support legs 2, 39 In general, embodiments described herein may relate to horizontal axis wind turbines (HAVVTs) comprising at least an energy conversion unit which would normally be an electrical generator and a wind rotor with at least one blade positioned substantially at the apex of at least three support legs. At least one of the support legs is arranged to be upwind of the wind rotor (referred to as "upwind oriented support leg") and at least one support leg is arranged to be downwind of the wind rotor (referred to as "downwind oriented support leg"). The support legs are spread apart at their lower ends. Each support leg comprises a float at its lower end, rigidly connected to the rest of the support leg. By careful arrangement of sufficient mass at said apex, i.e. the mass of the wind turbine, the length of the support legs, the angle between the support legs and the shape of the floats it is possible to ensure that the legs will substantially always be in compression and always tend to be forced away from each other at their lower ends, even when the structure is exposed to large waves. The dimensions can be arranged in such a way that the moments about each individual support leg's upper end, at the connection point, is substantially always positive. Hence, the upward acting buoyancy force acting on a support leg multiplied by the horizontal arm to said support leg's upper end is larger than the mass times total acceleration (g + a) of said support leg multiplied by the arm from said support leg's centre of gravity to said support leg's upper end + the vector sum of wave forces acting on the support leg at any time multiplied by the arm about said support leg's upper end. That is, the sum of moments acting about said apex is always tending to spread the legs further apart. In this situation it is possible to connect the support legs together at their lower ends by only using a pure tension member, like a rope or wire or the like being a flexible member (i.e. the tensions members have little or no bending stiffness).

For instance, ensuring that the extreme waves at the location for which the floating wind turbine is installed has a wave length that differs from half the length between the floats will reduce the risk of the wave forces being in opposite phases at two different floats, pushing the support legs together. In addition, placing the wind turbine close to the geometrical centre between the floats in the horizontal plane will be favourable. Said tension members substantially do not transfer bending moments so any transverse wave forces acting on the tension members will not cause high bending stresses in said tension members. Said tension members can therefore be made with a small diameter, e.g. less than 0.5 m, or if using a steel wire, less than 0.3 m, for a floating support arrangement carrying a 12 MW wind turbine which attract only small wave forces and can therefore be much lighter than a rigid frame structure or a pontoon structure.

Preferably, exactly three support legs are used. The three legs form a tripod connected together at the top with pivot or ball joint connections so as to form a structure which is statically determinate. In that case the wind turbine has to be rigidly connected to at least one of the support legs in order to transfer the resolved bending moments from the wind rotor at the hub to the rest of the floating structure. In another embodiment the support legs can be rigidly connected at the top. In that case the flexibility of the support legs in bending must be large enough compared to the axial stiffness of the tension members in order to avoid too high bending stresses in the support legs.

In the case of three support legs, the support legs are preferably spread apart at substantially 120 degree angles as seen from above. The angle of the support legs against the vertical would preferably be 45 degrees +/-20 degrees to ensure that there is tension in the tension members for all environmental conditions.

The tension members are preferably arranged as far down on the support legs as possible, e.g. attached at the lower end of the floats. In order to reduce the wave induced cyclic bending moments, and therefore fatigue loading, in the support legs, a second set of upper tension members may be arranged above the first lower tension members. By having two sets of tension members above each other the wave induced moments on the support legs' lower part can be at least partially resolved which results in lower cyclic bending moments caused by the wave action being carried up along the support legs. The upper tension members may also be used to dampen vibrations in the support legs, further reducing fatigue loading in the support legs. The tension in the upper tension members relative to the lower tension members may also be tuned to optimize the structural performance and further reducing the fatigue loading along the support legs. Preferably, the pretension in the upper tension members is at least 5% of the tension in the lower tension members.

The floats on the support legs may be cylindrical with the longitudinal axis of said cylinder positioned horizontally and aligned with the wind rotor of the wind turbine (normally 90 degrees to the incoming waves). By attaching each end of said tension members on the side of each cylinders at a plane intersecting the centre of all said cylinders the integrated buoyancy and wave pressure acting on each cylinder, which will always be directed in the direction of the centre of the cylinder, will have zero moment arm. In this way the wave forces which are directed perpendicular to the cylinders, i.e. incoming waves aligned with the optimal yaw orientation for the wind turbine will be resisted substantially entirely by the tension wires without creating any substantial bending moments in the floats and support legs. In this way the support legs can be made lighter and with less material. To also include the same effect when the incoming waves are misaligned with the direction of optimum yaw orientation, for instance waves from the side, the floats may be arranged to be spherical or substantially spherical, for instance comprising several flat plates welded together in the shape and pattern of a flat plated football for easier fabrication. In such a case, waves from any direction will not create substantial moments in the support arms, other than moments caused by inertia forces in the support legs due to acceleration of the floating structure. To ensure sufficient damping in heave a heave plate can be arranged at the lower end of the floats, or optionally suspended in a cable at a depth below the floats where there is less wave action.

To control the yaw of said floating support arrangement, when moored to a single anchor, wires pulling on the mooring line arrangement in a horizontal direction can be provided in order to create an offset of the effective horizontal mooring connection point to the floating structure and the direction of the wind rotor thrust force. For example, a mooring arrangement comprising a substantially torsion resistant connection from at least one anchor on the seabed to a mechanical swivel above the anchor can be provided. A power cable for the export of energy can be routed through said mechanical swivel and terminated above said mechanical swivel in a power swivel assembly comprising a slip ring member or alternatively a circuit breaker and a plug and a rotatable member arranged to rotate at least said power cable to unwind any twist when the plug is disconnected, and then reconnect the plug and re-establish the electrical connection.

Instead of a wind turbine, the floating support arrangement can be arranged to carry a carrier beam comprising, for example, a road or railway track to form a floating bridge.

The floating support arrangement may comprise aerodynamic profiles acting as sails and hydrodynamic profiles arranged under water acting as keels and / or rudders. The floating support arrangement may then be sailing when subject to sufficient wind.

A telescopic erection system (also referred to as a telescopic jacking system) may be provided to erect the floating support arrangement. Said erection system can be used to lift the support legs close to their connection points at the top. A central water tight cylinder is placed in a support member which holds the central water tight cylinder aligned vertically while it is de-ballasted and used to force the support legs up at a height sufficient for said tension members to support the load. Thereafter said tension members can be winched in to erect the floating structure to its full height.

The floating support arrangement may comprise a net or cage for the farming of fish or any other marine life. Alternatively or in addition, the floating support arrangement may comprise a space for access to people, for example inside at least one of said floats. The space may comprise windows arranged under the waterline, said space being arranged as a marine observation room, for example a real life aquarium. The space may also comprise a restaurant.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. It will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS: 1. A floating support arrangement comprising: at least three support legs, each support leg comprising a top end for holding a load and a bottom end opposite said top end comprising a float, wherein said support legs are arranged relative to said load such that said support legs are under compression and tend to be forced away from each other at their bottom ends when in use; and a plurality of tension members connecting the at least three support legs at or close to said bottom ends, wherein said tension members are flexible.
2. A floating support arrangement according to claim 1, which comprises only three support legs.
3. A floating support arrangement according to claim 1 or 2, wherein said at least three support legs comprises an upwind oriented support leg pivotally connected to said load, and a downwind oriented support leg rigidly fixed to said load.
4. A floating support arrangement according to claim 1, 2 or 3, wherein said tension members comprise one of rope, wire and chain.
5. A floating support arrangement according to any one of the preceding claims, further comprising a set of further tension members located above said plurality of tension members and connecting said support legs.
6. A floating support arrangement according to any one of the preceding claims, wherein said float of each support leg comprises a cylinder having a longitudinal axis substantially aligned with a longitudinal structural neutral axis of said support leg.
7. A floating support arrangement according to any one of claims 1 to 5, wherein said float of each support leg comprises a cylinder having a longitudinal axis arranged substantially horizontally when in use.
8. A floating support arrangement according to claim 7, wherein said tension members are attached to the cylinders at a plane intersecting the centre of all said cylinders.
9. A floating support arrangement according to any one of claims 1 to 5, wherein said float of each support leg has a spherical shape.
10. A floating support arrangement according to any one of the preceding claims, further comprising a plurality of heave plates connected to said support legs. 10
11. A floating support arrangement according to any one of the preceding claims, further comprising a mooring arrangement for mooring said floating support arrangement to the seabed, said mooring arrangement comprising a single anchor and a mooring line connected to said anchor at one end and to one of said support legs or to a wind turbine nacelle held by said support legs at an opposite end.
12. A floating support arrangement according to claim 11, wherein said mooring line is attached to said support leg or to said wind turbine nacelle at a height above a waterline of at least 50% of a height above said waterline of said floating support arrangement when in use.
13. A floating support arrangement according to claim 11 or 12, wherein said mooring line is attached at or close to said top end of an upwind oriented support leg.
14. A floating support arrangement according to claim 11, 12 or 13, further comprising wires attached to said mooring line for controlling the yaw of said floating support arrangement.
15. A floating support arrangement according to any one of claims 11 to 14, wherein said mooring arrangement comprises a torsion resistant connection from said anchor on the seabed to a mechanical swivel above said anchor.
16. A floating support arrangement according to claim 15, further comprising a power cable for the export of energy routed through said mechanical swivel and terminated above said mechanical swivel in a power swivel assembly comprising one of a slip ring member, and a circuit breaker and a plug and a rotatable member arranged to rotate said power cable to unwind any twist when the plug is disconnected, and then reconnect the plug and re-establish the electrical connection.
17. A floating support arrangement according to any one of claims 11 to 16 wherein said mooring arrangement comprises two parallel mooring line arrangements, and wherein said floating support arrangement further comprises a cable which is intermittently mechanically connected with a clamp member to each of said mooring line arrangements, said cable being routed from side to side between said clamp members in a snake like wave configuration.
18. A floating support arrangement according to any one of the preceding claims, wherein said support legs comprise pipes supported by a bracing comprising stays attached to said support legs by support beams.
19. A floating support arrangement according to any one of claims 1 to 17, wherein said support legs comprise a truss structure.
20. A floating support arrangement according to any one of the preceding claims, further comprising aerodynamic profiles acting as sails and hydrodynamic profiles arranged under water acting as keels and / or rudders.
21. A floating support arrangement according to any one of the preceding claims, further comprising a telescopic erection system to lift the support legs, said erection system comprising a support member and a central water tight cylinder located in said support member which holds the central water tight cylinder aligned vertically, said erection system being operable to force the support legs up to a height sufficient for said tension members to support the load.
22. A floating support arrangement according to any one of the preceding claims, further comprising a net or cage for the farming of fish or any other marine life.
23. A floating support arrangement according to any one of the preceding claims, further comprising a space which comprise windows arranged under a waterline when in use, said space being arranged as a marine observation room and/or a restaurant.
24. An offshore wind power facility comprising a floating support arrangement according to any one of claims 1 to 23 and a wind turbine, wherein said wind turbine is said load supported by said floating support arrangement.
25. A floating bridge comprising a floating support arrangement according to any one of claims 1 to 23 and a carrier beam comprising a road or railway track, wherein said carrier beam is said load supported by said floating support arrangement.
26. A method of using a floating support arrangement according to any one of claims 1 to 23 to support said load.