GB2589641A

GB2589641A - Buoyant platform

Info

Publication number: GB2589641A
Application number: GB1917915.9A
Authority: GB
Inventors: Foster Graham
Original assignee: Marine Power Systems Ltd
Current assignee: Marine Power Systems Ltd
Priority date: 2019-12-06
Filing date: 2019-12-06
Publication date: 2021-06-09
Also published as: GB201917915D0

Abstract

A buoyant offshore renewable energy system platform with a framework 30 with at least three vertexes and at least one mooring member. Each of the vertexes has at least one mooring member 60 and 65, and a buoyancy member 70 which has a number of buoyancy units and a renewable energy convertor 90. The converter may be a wave or tidal converter and the framework may have a wind turbine (100 figure 2). The platform may have upper 40 and lower 50 portions where the upper portion remains above the surface of the water. The mooring may be attached to the centre of the buoyancy units and the number of buoyancy members and vertexes may be equal. The framework may have an equal number of non-buoyant vertexes to buoyant vertexes.

Description

BUOYANT PLATFORM

Field of the Invention

The present invention relates to a buoyant offshore renewable energy system mounting platform.

Background to the Invention

In recent years, there has been increased emphasis on the need to exploit renewable energy so that it significantly contributes to global energy production. A combination of government targets, media representation of the issues associated with non-renewable energy sources, and ever increasing energy costs have all created a powerful driving force for the development of renewable energy systems.

Negative impacts of fossil fuels on the environment are well known, as are the problems and high costs associated with nuclear energy. Harnessing of the huge natural abundance of renewable energy on the other hand is constrained merely by our capability of capturing and supplying it at an economically viable price.

One potential renewable energy source is wave power -an abundant and consistent energy resource available in all of the world's large oceans and seas. Another is wind power, with wind speeds being higher and more consistent over oceans and seas compared to land.

For these reasons, offshore platforms providing means to mount renewable energy 25 devices which harness wave and/or wind power are required.

Adequate buoyancy to support the heavy offshore platform, good stability of the platform and means to mount the renewable energy devices to the platform are required. Problems with known offshore platforms include a failure to successfully provide the above. Known offshore platforms have potential for further improvement.

Summary of the invention

According to a first aspect of the invention, there is provided a buoyant offshore renewable energy system mounting platform for positioning a renewable energy convertor in a body of water, the body of water comprising a surface and a bed. The platform comprising: a framework comprising at least three vertexes; and at least one mooring member for positioning the platform relative to the surface and bed of the body of water. Each of the at least three vertexes having; at least one mooring member and a buoyancy member, the buoyancy member comprising a plurality of buoyancy units; wherein at least one of the buoyancy members comprises a renewable energy to convertor.

Preferably, the renewable energy convertor is a wave energy convertor system.

Preferably, the renewable energy convertor is a tidal turbine.

Preferably, the framework comprises a lower portion and an upper portion, the lower portion being arranged, in use, below the surface of the body of water and the upper potion arranged, in use, so as to remain above the surface of the body of water.

Preferably, the upper portion of the framework comprises a wind turbine.

Preferably, the buoyancy member comprises two buoyancy units.

Preferably, the at least one renewable energy convertors are orientated by the plurality of buoyancy units to face the same direction.

Preferably, the plurality of buoyancy units are proximate each other.

Preferably, the plurality of buoyancy units have a combined centre of buoyancy that is 30 the centre of buoyancy of a buoyancy member.

Preferably, the at least one mooring member is attached to the platform in close proximity to the centre of buoyancy of each of the two or more buoyancy units in the horizontal plane. More preferably, the at least one mooring member is also attached to the platform in close proximity to the position of the centre of buoyancy of each of the two or more buoyancy units in the vertical plane.

Preferably, the vertexes are at horizontal extents of the framework.

Preferably, the at least three vertexes are aligned in a horizontal plane.

Preferably, the number of the buoyancy members and the number of the at least three vertexes is equal.

Preferably, the at least three vertexes are substantially equidistant from a central axis of the framework and substantially equispaced around the central axis of the framework.

Preferably, the framework comprises at least three non-buoyant vertexes, the number of at least three non-buoyant vertexes being equal to the number of the at least three vertexes Preferably, the wave energy convertor (WEC) comprises a power take off convertor with an orbiting absorber and lever arm. More preferably, the WEC comprises a cylindrical absorber with four lever arm Power Take Off (PTO) units arranged with two lever arm PTO units on top of each buoyancy tank.

Detailed Description

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 depicts a perspective view of the platform in accordance with the present 30 claimed invention, in use, wherein each buoyancy member comprises a wave energy convertor system; Figure 2 depicts a perspective view of an alternative embodiment of the platform of Figure 1, in use, wherein each buoyancy member comprises a wave energy convertor system and an upper portion of a framework of the platform comprises a wind turbine; Figure 3 depicts a perspective view of a further alternative embodiment of the platform of Figure 1, in use, wherein each buoyancy member comprises a tidal turbine; Figure 4a depicts a top view of a vertex of a framework of the platform of Figure 1, in use, deconstructed such that the renewable energy convertor is not shown; and Figure 4b depicts a perspective view of a vertex of a framework of the platform of Figure 1, in use, deconstructed such that the renewable energy convertor is not shown.

With reference to Figure 1, there is illustrated an embodiment of the offshore platform 10 of the present claimed invention, in use, tethered to a bed 20 of a body of water. A portion of the platform 10 remains above a surface 25 of the body of water.

The platform 10 comprises a framework 30. The framework comprises an upper portion 40, which remains above the surface 25 of the body of water, and a lower portion 50 20 which remains below the surface 25 of the body of water. In alternative embodiments, all of the framework 30 remains below the surface 25 of the body of water in use.

The lower portion 50 of the framework 30 comprises a triangular base such that there are three distinct vertexes below the surface 25 of the body of water. Each vertex is equidistant from the central point of the triangle and each vertex is equispaced about the central point of the triangle, such that the base has the shape of an equilateral triangle. The framework 30 also comprises a central podium, which extends vertically upwards from the central point of the triangular base. The top section of this podium comprises the upper portion 40 of the framework 30, which extends above the surface 25 of the body of water. The podium is aligned with the central axis of the framework and is symmetrical about the central axis of the framework.

The upper portion 40 of the framework 30 may be used as an access point for the platform 10. Additionally, electrical, control and/or communication equipment may be housed on the upper portion 40, such that the equipment is not required to be suitable for prolonged submersion in the body of water.

Each vertex of the framework 30 comprises a pair of mooring members 60, 65 and a buoyancy member 70. In other embodiments, it is envisaged that one or a plurality of mooring members 60, 65 may be employed. The mooring members 60, 65 may comprise a mooring line, rope, chain or other suitable mooring means.

The mooring members 60, 65 tether the platform 10 to the bed 20 of the body of water or to other fixing means. In this way the mooring members 60, 65 prevent unwanted overturning, drifting, sinking or rising of the platform 10. The mooring members 60, 65 extend from each vertex of the framework 30 to the bed 20 of the body of water. On each vertex, an inner mooring member 60 extends vertically downwards to the bed 20 of the body of water. The outer mooring member 65 extends away from the framework 30 to the bed 25 along a horizontal line parallel to the axis where the vertex meets the central axis of the framework 30. Each pair of mooring members 60, 65 on each vertex has a complimentary pair on each other vertex. As such, the contact points these outer mooring members 65 make with the bed 25 form an equilateral triangle and all vertexes are in the same horizontal plane, parallel to the surface 25 of the body of water.

Additionally, the mooring members 60, 65 may comprise anchoring means that are fixed or removably retained in the bed 20 of the body of water. In this way the anchoring means assist in the mooring of the platform 10 to the bed 20.

Each buoyancy member 70 comprises two buoyancy tanks 80, such that there are six tanks 80 in total. Each tank 80 is filled with a gas, such as air or nitrogen, such that the tank 80 is less dense than water. The buoyancy tanks 80 provide a buoyant force upwards towards the surface 25 of the body of water. In some embodiments, it is possible to monitor and control the buoyant force provided by the buoyancy members 70, for example by removing or adding gas or fluid into the buoyancy tanks 80. It is appreciated that alternative buoyancy means may be employed which provide this buoyant force.

In use, tension is held in the mooring members 60, 65 due to the buoyant forces acting on the platform 10. The downwards gravitational pull of the platform 10 is exceeded by the upwards buoyant force of the platform 10. The buoyancy member's 70 provide the predominant upwards buoyant force to the platform 10.

The body of water, and other internal and external sources, will subject the platform 10 to numerous forces and moments, in use. It is desirable for the platform 10 to remain stable in use so that, for example, toppling of the platform 10 does not occur. Tension in the mooring members 60, 65 allows the three vertexes of the framework 30 to return to a horizontal plane, parallel to the surface 25 of the body of water after the platform 10 is subjected to forces and moments. In this way, the mooring members 60, 65 assist in stability of the platform 10.

In the embodiment illustrated, each buoyancy tank 80 is identical. Both buoyancy tanks 80 sit proximate to each other on the vertex of the framework 30. Each buoyancy tank 80 sits on either side of the vertex, symmetrically about the axis where the vertex meets the centre of the triangular base. Each pair of tanks 80 are braced to the framework 30 in a way such that relative motion of each tank 80 to the other is minimised. In this way, the structural behaviour of the two tanks 80 is similar to that of a single, larger tank, and the behaviour of the pair of tanks 80 can be effectively modelled as that of a single unit. The tanks 80 have a combined centre of buoyancy.

The tanks 80 are cylindrical and the longitudinal axis of each tank 80 is vertically upwards. In this way, the tanks 80 are less prone to toppling and rotating when subject to internal and external forces and moments given the shorter moment arm (lateral axis) of the tanks 80. It should be understood that other tank 80 geometries and shapes are envisaged.

The presence of more than one tank 80 provides the advantage that if damage or failure occurs in one tank 80, such as loss of buoyancy, at least one additional tank 80 remains on the vertex. This ensures the buoyancy of the overall platform 10 is not entirely compromised when failure of a tank 80 occurs. By ensuring each vertex has at least one additional buoyancy tank 80, the platform 10 is less prone to overturn or sink upon failure of a buoyancy tank 80, as a buoyant force is still being provided at every vertex.

This reduces the likelihood of damage to or loss of function of the platform 10. Repair or replacement of the compromised tank 80 can then be undertaken to rebalance the platform 10.

Each buoyancy member 70 comprises a wave energy convertor system(WEC) 90. The 10 WEC 90 may comprise a point absorber, an oscillating wave surge absorber, a submerged pressure differential absorber or another form of WEC technology.

The WEC 90 is connected to both buoyancy tanks 80. The WEC 90 is mounted above the buoyancy tanks 80, such that, in use, the WEC 90 sits between the buoyancy tanks 80 and the surface 25 of the body of water. In this way the WEC 90 does not interfere with the mooring members 60, 65. The WEC 90 is mounted centrally above the tanks 80, such that the longitudinal axis of the WEC 90 is parallel to the axis between the centre of each tank 80.

Any reasonable means for connecting the WEC 90 onto or proximal to one or both of the tanks 80 is envisaged, such as permanent or removable connection, rigid or deformable levers, lines or chains, or direct mounting on the tanks 80. Additionally, a connection between the WEC 90 and the framework 30 is envisaged. Components associated with converting energy from the WEC 90 may be mounted on or within the tanks 80 or on the framework 30.

Each WEC 90 is identical. In alternative embodiments, the WECs 90 may be nonidentical. The WEC 90 is cylindrical with a longitudinal axis parallel to the surface 25 of the body of water. Each WEC 90 may rotate fully or partially about the longitudinal axis of the WEC 90. The WEC 90 is orientated such that its longitudinal axis is horizontal and parallel to the surface 25 of the body of water. In this way, the WEC 90 is aligned with the direction of current or flow of the water in the body of water. The angle the longitudinal axis of the WEC 90 makes with the surface 25 of the body of water and/or the angle the longitudinal axis of the WEC 90 makes with the framework 30 may be altered, such that the orientation of the WEC 90 is optimal for wave energy conversion purposes.

Each WEC 90 is orientated identically on each vertex. Alternatively, the orientation of each WEC 90 relative to each other WEC 90 is different, such that the capturing of wave energy is improved in each application.

Consideration may be taken to reduce the platform 10 weight such as to reduce the gravitational pull of the platform 10 towards the bed 20 of the body of water is preferential.

Turning now to Figures 2 and 3 of the platform of the present invention, in the following description similar numerals will be used for similar parts of each embodiment of the present invention.

Figure 2 depicts an embodiment of the present invention, wherein the platform 110 further comprises a turbine 100. The turbine 100 is mounted on the upper portion 140 of the framework 130, such that the turbine 100 remains above the surface 125 of the body of water, in use. The turbine 100 is mounted vertically upwards, perpendicular to the surface 125 of the body of water.

The buoyant force provided by the buoyancy members 170 is such that the considerable weight of the turbine 100 is supported. In this embodiment, reducing the platform 110 weight to reduce the gravitational pull of the platform 110 towards the bed of the body of water is preferential.

In this embodiment, multiple forms of renewable energy convertors are present on the platform 110: a turbine 100 and WECs 190.

Figure 3 depicts an embodiment of the present invention, wherein each buoyancy member 270 of the platform 210 comprises a tidal energy convertor (TEC) 290, for example a tidal turbine. Each TEC 290 may have an orientation that is fixed relative to the framework 250. Alternatively, each TEC 290 is able to yaw to face the direction of the current.

Figures 4a and 4b depict the present claimed invention, with no renewable energy convertors shown. The buoyancy tanks 280 are spaced apart and symmetrically on the vertex about the axis where the vertex meets the central axis of the framework 330.

C indicates the combined centre of buoyancy of the buoyancy tanks 380. The centre of buoyancy point C is the effective point at which the buoyant force B from the tanks 380 act. The mooring members 360, 365 are attached to the framework 330 at a mooring point M. The mooring point M is the point at which the tension forces T from the mooring members 360, 365 act on the framework 330. The buoyant force B acts vertically upwards. The tension forces T act through the mooring members 360, 365.

The mooring point M and the centre of buoyancy C of the buoyancy tanks 380 are the same. In this way, the mooring point M and the centre of buoyancy C are in the same horizontal and vertical planes.

As the buoyant force B and tension forces T act at the same point (the centre of buoyancy C and the mooring point M), no moment from the buoyant force B and tension forces T acts on the platform 310. Such moments are disadvantageous as they can cause high structural loads and hinder platform stability. It is appreciated that a moment will result due to each individual buoyant force from each tank 380, however, each tanks 380 proximate position to the other of the pair of tanks 380 on the framework 380 reduces this moment.

In a further embodiment of the present invention, the platform comprises two vertexes, such that the vertexes are in a line parallel to the surface of the body of water. In this way, the buoyancy members are horizontally spaced apart from each other.

Further embodiments within the scope of the present invention may be envisaged that have not been described above, for example, there may be any combination of renewable energy convertors on the platform including, but not limited to, WECs and TECs. One, multiple or all vertexes may comprise a renewable energy convertor. The platform may comprise a number of non-buoyant vertexes which do not comprise buoyancy members. These non-buoyant vertexes may be aligned in the same horizontal plane as the buoyant vertexes, or in an offset plane. These non-buoyant vertexes may comprise renewable energy convertors. The framework may comprise a single body piece or may be assembled form a number of pieces. The invention is not limited to the specific examples or structures illustrated.

Claims

Claims 1 A buoyant offshore renewable energy system mounting platform for positioning a renewable energy convertor in a body of water, said body of water comprising a surface and a bed, said platform comprising: a framework comprising at least three vertexes; and at least one mooring member for positioning said platform relative to said surface and bed of said body of water; each of said at least three vertexes having; at least one mooring member and a buoyancy member, the buoyancy member comprising a plurality of buoyancy units; wherein at least one of said buoyancy members comprises a renewable energy convertor.
2. The platform of claim 1, wherein said renewable energy convertor is a wave energy convertor system.
3. The platform of claim 1, wherein said renewable energy convertor is a tidal turbine.
4 The platform as claimed in any one preceding claim, wherein said framework comprises a lower portion and an upper portion, said lower portion being arranged, in use, below the surface of said body of water and said upper potion arranged, in use, so as to remain above said surface of said body of water.
5. The platform of claim 4, wherein said upper portion of said framework comprises a wind turbine.
6. The platform as claimed in any one of the preceding claims, wherein said buoyancy member comprises two buoyancy units.
7 The platform as claimed in any one preceding claim, wherein said at least one renewable energy convertors are orientated by said plurality of buoyancy units to face the same direction.
8. The platform as claimed in any one claims 6 or 7, wherein said plurality of buoyancy units are proximate each other.
9. The platform as claimed in any one of claims 6, 7 or 8, wherein said plurality of buoyancy units have a combined centre of buoyancy that is the centre of buoyancy of a buoyancy member.
10. The platform of claim 9, wherein said at least one mooring member is attached to the platform in close proximity to the centre of buoyancy of each of said two or more buoyancy units in the horizontal plane.
11. The platform of claim 10, wherein said at least one mooring member is attached to the platform in close proximity to the position of the centre of buoyancy of each of said two or more buoyancy units in the vertical plane.
12 The platform as claimed in any one of the preceding claims, wherein said vertexes are at horizontal extents of said framework
13. The platform as claimed in any one of the preceding claims, wherein said at least three vertexes are aligned in a horizontal plane.
14. The platform as claimed in any one of the preceding claims, wherein the number of said buoyancy members and the number of said at least three vertexes is equal.
15. The platform as claimed in any one of the preceding claims, wherein said at least three vertexes are substantially equidistant from a central axis of said framework and substantially equispaced around said central axis of said framework.
16.The platform as claimed in any one of the preceding claims, wherein said framework comprises at least three non-buoyant vertexes, said number of at least three non-buoyant vertexes being equal to the number of said at least three vertexes.