A floatable renewable energy platform

Abstract

A floatable renewable energy platform is provided that includes a superstructure containing one or more substantially horizontal, above wave structural support members. The superstructure is supported by a plurality of floats interconnected by the structural members, and the platform is configured to provide an air gap in the range of 10 m to 30 m between the surface of the static body of water and the structural members.

Description

[0001] The present invention relates generally to renewable energy, and in particular, though not exclusively, to floating platforms for carrying renewable energy collectors / converters.

[0002] Renewable energy is energy derived from renewable resources that are naturally replenished over human timescales.

[0003] Renewable resources include sunlight, wind, water movement, and geothermal energy.

[0004] This application claims priority to GB2300235.5 and GB2301458.2, the contents of which are incorporated herein by reference. Background Technology

[0005] Floating energy harvesters, such as floating wind turbines, require a stable floating platform to mount the harvester (e.g., the turbine).

[0006] like Figure 1 As shown (Source: Report prepared by Frazer Nash for the UK Department for Energy Security and Net Zero), there are four common designs for floating wind platforms. These designs are based on structures used in the oil and gas industry. Each of the four platform designs follows different design principles to achieve the desired stability and low motion response levels in wind and waves.

[0007] • Spar type - Stability is achieved through a deep draft and a low center of gravity.

[0008] • Barge type - has the stability characteristics of a regular barge or vessel.

[0009] • Semi-submersible type - Its design aims to achieve low motion response in waves by arranging the natural cycles of heave, roll, and pitch to be longer than the typical wave cycle. Its underwater shape is also designed to minimize vertical wave forces and motion during critical wave cycles.

[0010] • Tension leg type - achieves stability and low sag response in waves through a taut vertical chain.

[0011] This invention is a novel universal design for floating platforms based on different principles, designed to provide advantages for suitable mid-deep water offshore locations and environments. Summary of the Invention

[0012] Aspects and embodiments of the present invention relate to a floating platform for supporting equipment, such as renewable energy devices (including wind turbines that generate electricity from wind flow).

[0013] The floating platform can include one or more design features that enable the platform to be constructed, installed, and operated more cost effectively than existing designs.

[0014] One aspect of the invention provides a floatable renewable energy platform comprising a superstructure containing one or more substantially horizontal structural support members above the wave, the superstructure being supported by a plurality of floats interconnected by the structural members, and the platform being configured to provide an air gap in the range of 10m to 30m between the water surface and the structural members.

[0015] Another aspect provides a permanently moored self-floating renewable energy platform comprising a plurality of floats interconnected by horizontal structural members that are always above the wave action and direct wave forces, and have an air gap of 10m to 30m between them and the water surface (possibly determined by the wave climate for which the platform is designed).

[0016] The superstructure can include a combination of horizontal, vertical, and inclined structural members.

[0017] Some embodiments include spaced-apart bow and stern floats, resulting in a wave-like pitch response amplitude operator in head seas. The platform can include spaced-apart floats 100m to 300m apart to produce two or more frequencies in the range of 4 to 12 seconds of operating wave period at which wave excitation forces or moments are out of phase, thus resulting in zero excitation forces and responses at that frequency, as evidenced by the wave-like pitch or heave response amplitude operator in head seas in that range of operating wave period.

[0018] Some embodiments relate to the shape of the floats.

[0019] In some embodiments, the shape of the floats is configured to reduce bending loads in the horizontal structural members.

[0020] Some embodiments provide floats that are rotational bodies.

[0021] Some embodiments encompass having the axis of the rotational body at the level of the horizontal structural members.

[0022] Some embodiments provide floats (which can or can not be rotational bodies) that place wave forces at the level of the horizontal structural members in low steepness waves of a particular wavelength.

[0023] Some embodiments include floats having a wet-hull form that is the shape of a rotational body with its axis horizontal and at right angles to the longitudinal axis of the float.

[0024] Some embodiments include a float shape that aims to reduce the bending loads in the horizontal structural members by placing the axis of rotation at the neutral axis and point of action of the main structural members connected to the float.

[0025] In some embodiments, a mooring device is provided on the bow float. The mooring device can be connected to the float by way of a yoke, for example in the form of a rigid frame or equivalent chain, suspended and hinged at the level of the neutral axis of the horizontal structural members connected to the float.

[0026] The length of the float can be greater than its width. Some embodiments are configured as floating wind turbines. The floating wind energy platform can include spaced-apart stern floats beneath one or more wind turbines, and a bow float.

[0027] The platform can be configured to have a natural period of pitch, heave, and optionally roll, of less than 10 seconds, and a longitudinal metacentric height of more than one kilometer.

[0028] Some embodiments have a rated power of more than 5 MW and are configured to operate with a draft of less than 7 m.

[0029] The floats and / or structural members can be made, for example, of composite materials.

[0030] The floats and / or structural members can be made of fiberglass reinforced plastic (FGRP).

[0031] The floats and / or structural members can be made, for example, of conventional shipbuilding materials, including steel, aluminum, and concrete.

[0032] The structural members can be formed as lattice structures. The chords and cross-braces in the structural members can be airfoil cross-sections to reduce direct aerodynamic loads.

[0033] In some aspects and embodiments, the platform has a substantially flat collapsed configuration and an upright configuration.

[0034] The platform can include a plurality of structural members that contain hinges.

[0035] Some embodiments can be configured to fold flat down to the level of the horizontal structural members between the floats in a deck chair fashion, with multiple hinges depending on the arrangement of the structural members.

[0036] Some aspects and embodiments provide a platform configured as a floating wind turbine and including one or more wind turbines.

[0037] The platform can be equipped with one or more thrusters to control heading. Adding a thruster on the aft float enables the windage effect to be controlled. This is desirable because vessels with windage effect moorings are prone to "fish tail" instability in deep water, which can be stabilised by the platform. It can also be used to set the heading exactly into the wind if this is advantageous to reduce the loads on the turbine blades, particularly in survival conditions where the turbine is stopped. Alternatively, it can be used to set the heading exactly into the wave if this is advantageous to reduce the transverse wave loads on the float. Finally, it can be used in calm conditions to rotate the wind turbine completely around the vertical axis, thus unwinding the power cable to the seabed. This eliminates the need for an expensive electrical swivel joint.

[0038] Such a stable platform has uses in other applications where a stable platform is required in waves, for example floating solar panels.

[0039] In some embodiments, the platform is configured as a floating wind turbine and includes one or more wind turbines.

[0040] Another aspect provides a floatable renewable energy platform having a generally flat collapsed configuration and an erected configuration.

[0041] The platform can be moved between the generally flat collapsed configuration and the erected configuration.

[0042] The platform can be provided with floats. The floats can be interconnected by structural members located above the action of the waves.

[0043] Other aspects and embodiments are listed below.

[0044] 1) A floating wind turbine designed according to principles (a)-(c): a) increase the hydrostatic roll and pitch stiffness so that the natural roll and pitch periods fall well within the range of typical wave periods; b) reduce the platform draft so that the resonant roll and pitch motions are well damped by wave radiation; and c) choose the float length so that the vertical wave forces acting on the float cancel each other out along its length in the wave periods that excite the platform's roll resonance.

[0045] 2) A floating wind turbine incorporating hinges so that it can be collapsed flat like a deck chair, enabling assembly at a lower level (e.g. on a construction barge), thus minimising the need for high hook height cranes and allowing the entire floating wind turbine to be assembled on a sheltered anchorage on a construction barge.

[0046] 3) A floating wind turbine with a floating body shaped as a body of revolution around an axis of revolution, which is horizontal and at right angles to the longitudinal axis of the floating body. The axis of revolution is located at the neutral axis and the point of action of the main structural members connected to the floating body. This reduces the bending moments transmitted to the structural members.

[0047] 4) A floating wind turbine with propellers to control its heading.

[0048] 5) A floating platform with natural pitch and heave periods below 10 seconds and a metacentric height above one kilometer.

[0049] 6) A floatable renewable energy platform designed based on one or more of the following: a) Increased hydrostatic heave and pitch stiffness to minimize the pitch angle under wind loads by having a metacentric height in excess of one kilometer (high heave, pitch and roll stiffness can also be achieved by tension leg mooring as in some oil drilling platforms and floating wind turbines - these are not included in this invention). Large ballast systems are usually not required to counteract wind induced pitch, which is a significant advantage. High heave and pitch stiffness means that the natural heave and pitch periods fall well within the range of typical wave periods. At high wind speeds, this design feature is very advantageous to the wind turbine control system which attempts to limit the power during gusts by reducing the wind loads on the turbine. The pitch motion of the platform appears to the turbine control system as a gust: reducing the wind loads in this case corresponds to negative pitch damping. This can lead to dangerous pitch dynamic instabilities. Therefore, it is very advantageous to have a short natural pitch period for the platform, just like a land based wind turbine tower. b) Reduced draft of the platform so that the resonant heave and pitch motions are well damped by wave radiation. Shallow draft floats are used. c) "weather vane effect" mooring similar to that of a single point moored FPSO (floating production storage and offloading) (and some other floating wind turbines) so that the platform is primarily facing into the wind and waves, and the wind turbines on the platform are running downwind. d) The float length is made larger than the width, like a ship, and is pointed into the waves. The mooring is located on the bow float (rather than on the stern float below the turbines). e) The float length is chosen so that the vertical wave forces acting on the floats cancel each other out along their length (for example, the float length is chosen to be approximately equal to the wavelength) within the wave periods that excite the platform pitch resonance (platform pitch direction = float pitch direction). This will further reduce the resonant roll and pitch motions. The following equation L = 2π x (1 + Cm) x D gives the float length L. Here Cm is the heave added mass coefficient of the float, and D is the draft of the float. f) The float spacing is chosen to be very wide, typically many float lengths. This will produce a "corrugated" pitch, heave and surge RAO in head seas because at some wavelengths the wave forces on the bow and stern floats are in opposite directions, while at other wavelengths they are in the same direction. Overall, the motions in waves are reduced, which is a significant advantage. g) The floats are interconnected by structural members that are always above water. This eliminates direct wave loads on the members, which can otherwise be a major design issue. Therefore, the structural members can be lightweight lattice structures like crane booms. They and the floats can be made of composite materials (for example, fiberglass reinforced plastic (FGRP)) instead of steel, thereby reducing the cost and weight of the platform. To reduce direct air dynamic loads, the chords and cross braces in the structural members can have airfoil cross sections.h) Integrating hinges at the ends of some of the structural members, so that the platform can fold flat like a deck chair. This allows the entire floating wind turbine to be assembled on a sheltered anchorage on a construction barge. i) Because the horizontal structural members are at some distance from the still water level, as mentioned above, the horizontal wave loads acting on the floating body can act quite far below it, creating bending loads in the structural members. This can be a major design problem. By shaping the floating body so that the horizontal wave loads acting on it are at the same level as the neutral axis (usually the centreline) of the structural members, the bending loads can be greatly reduced. The simplest such floating body shape is a sphere, with its centre at that level (of course, only the wet surface of the body needs to have this shape). Another floating body shape with this property is any right-left symmetrical body of revolution, with its axis parallel to the wave crests and at the same level as the centre of the sphere. To reduce the bending loads as described, they do require the wave to travel from bow to stern (in nautical terms, "head on") but this will usually be the case because of the "weather cocking" of the mooring described above. Other floating body shapes can be designed to produce zero bending loads in head on waves of low steepness and specific wavelengths using diffraction programs (see reference 1, chapter 4) or other methods; this can be sufficient. j) Another design feature is to add a propeller to the stern floating body so that the windage effect can be controlled. This is desirable because a vessel with a windage mooring device is prone to "fish tail" instability in deep water, so that the platform heading can be stabilised. It can also be used to set the heading exactly into the wind if this is advantageous to reduce the loads on the turbine blades, especially in survival conditions with the turbine stopped. Alternatively, it can be used to set the heading exactly into the wave if this is advantageous to reduce the transverse wave loads on the floating body. Finally, it can be used in calm conditions to rotate the wind turbine completely around a vertical axis, so that the power cable to the seabed is unwound. This eliminates the need for an expensive electrical swivel joint.

[0050] 10) A floating wind turbine with a propeller to control its heading, as described herein.

[0051] 11) A floating wind turbine, etc., with natural pitch and heave periods below 10 seconds and metacentric heights in excess of one kilometre.

[0052] 12) A floating wind turbine or the like with a rated power higher than 5 MW and an operating draft lower than 7 m.

[0053] 13) A floating wind turbine or the like with a floater length given by the equation in (e).

[0054] 14) A floating wind turbine or the like with a wide-spaced floater, resulting in a "corrugated" pitch RAO, as described in (f).

[0055] 15) A floating wind turbine or the like with a floater interconnected by structural members above the wave action, and both advantageously made of FGRP, as described in (g).

[0056] 16) A floating wind turbine or the like that can fold flat like a deck chair, as described in (h).

[0057] 17) A floating wind turbine or the like with a floater shape aimed at reducing the bending loads in the horizontal structural members, as described in (i).

[0058] 18) A floating wind turbine or the like with a propeller to control its heading, as described in (j).

[0059] The different aspects and embodiments of the invention can be used individually or together.

[0060] Other specific and preferred aspects of the invention are set out in the accompanying independent and dependent claims. The features of the dependent claims can be combined with the features of the independent claims as appropriate and can be combined in combinations not explicitly set out in the claims. Each aspect can be implemented independently of the other aspects, or in combination with one or more of the other aspects. BRIEF DESCRIPTION OF DRAWINGS

[0061] The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, wherein:

[0062] Figure 1 General design for existing floating wind platforms;

[0063] Figure 2 Floating wind turbine platform formed according to one embodiment;

[0064] Figure 3 Figure 2 Side view of the platform, showing the air gap;

[0065] Figure 4 Typical corrugated pitch RAO in head sea;

[0066] Figure 5 ​Floating platform folded flat for construction or maintenance;

[0067] Figure 6 Platform in erected state Figure 5

[0068] Figure 7 Floating turbine folded / erected by means of crane

[0069] Figure 8 Floating turbine folded / erected using built-in winch

[0070] Figure 9 Platform with shaped floating body to minimize bending loads in structural members; and

[0071] Figure 10 Mooring yoke, pivoted with mooring lines around a bearing shaft.

[0072] The description of the example embodiments is sufficient to enable one of ordinary skill in the art to practice and use the systems and processes described herein. It is important to note that embodiments can be practiced with various modifications and changes so as to cover all of the bases falling within the scope of the claims. It is therefore important that the embodiments be considered in a descriptive sense only and not for purposes of limitation.

[0073] Thus, although the embodiments can be modified and varied, and be embodied in various alternative forms, specific embodiments thereof are shown in the drawings and herein described in detail. It is therefore not intended that the application be limited to the particular forms disclosed. Rather, any modifications, equivalents, and alternatives falling within the scope of the appended claims should be included.

[0074] In the drawings and detailed description, elements of example embodiments are, where appropriate, denoted by like reference numerals.

[0075] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that the terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0076] In the following description, all directional references (e.g., upper, lower, radial, and axial) are used with respect to the orientation of the figures, and are not to be construed as limitations.

[0077] Definitions of technical terms (e.g., roll and pitch) are found in reference 1. DETAILED DESCRIPTION

[0078] The present application relates to a new generic design for floating wind platforms. A typical example of such a generic design is shown in Figure 2 .

[0079] ​It has a floatable renewable energy platform 10 comprising a superstructure containing one or more substantially horizontal structural support members 20 positioned to avoid wave impact. The superstructure is supported by a plurality of floats 30 interconnected by structural members, and the platform is configured to provide an air gap in the range 10m to 30m between the surface of the water and the structural members.

[0080] In this embodiment, there is one bow float 30a and two stern floats 30b, 30c.

[0081] In this embodiment, there are three horizontal support members 20a, 20b, 20c arranged in a substantially triangular configuration, and three upright columns (the columns can be substantially vertical or for example substantially inclined) 40a, 40b, 40c, collectively providing a substantially triangular pyramid-shaped superstructure. The superstructure supports a wind turbine 50.

[0082] The air gap below the superstructure is shown in Figure 3 . It is chosen so that even in the most extreme conditions, a wave crest will not impact the structural members. The size of the air gap can be calculated from wave climate statistics at the platform site, by standard procedures.

[0083] The spacing between the bow float 30a and the stern floats 30b, 30c is in the range 100m to 300m, depending on the wave environment. By spacing the floats in this way, at certain frequencies the wave forces and moments acting on the floats are out of phase, resulting in zero excitation force over a number of wave periods in the typical operating wave period of 4 to 12 seconds. This is evident in the corrugated nature of the motion response amplitude operator shown in Figure 4 . This reduces hull motions which can be detrimental to structural integrity and energy production.

[0084] Figures 5 to 8 A floatable renewable energy platform 110 formed according to another aspect is shown. The platform 110 has a substantially flat collapsed configuration Figure 5 and an erected configuration Figure 6 .

[0085] The collapsed flat configuration can be useful for rapid installation of the wind turbine and blades, and requires the least of high hook height cranes.

[0086] In this embodiment, the main structural members have a lattice structure. The hinges in the platform 110 are shown in Figure 7 and Figure 8 . They can equally be located in any other position which allows the structure to collapse flat like a deck chair. For example, the hinges can be located at the other end of the longest structural members.

[0087] As Figure 7 illustrated, platform 110 requires two cranes to lower it into the collapsed position and to raise it into the erected position. For large wind farms, the cost of such cranes can be negligible, as the folding / erecting operation is fast, so a pair of cranes is sufficient for the entire wind farm construction and maintenance. However, for small wind farms, it can be more cost effective to provide a built-in winch function on the platform, as Figure 8 illustrated. The winch can then raise and lower the turbines by itself. The additional structure required is very light compared to the turbines, so it can be erected with small cranes, hoisted from points on the structure members close to the hinges.

[0088] Platform 210 formed according to another embodiment is illustrated in Figure 9 .

[0089] The longitudinal metacentric height of platform 210 exceeds one kilometer to minimize the pitch angle under wind load. Platform 210 is configured with two wind turbines and includes spaced-apart stern floats below the wind turbines, and a bow float. The floats are interconnected by structure members that are always above water.

[0090] The platform is moored with a "weather vane effect" mooring similar to that of a single point moored FPSO (and some other floating wind turbines), so that the platform is primarily facing into the wind and waves, and the wind turbines on the platform are running downwind. The mooring is located on the bow float (rather than on the stern floats below the turbines).

[0091] In this embodiment, the mooring is provided on the bow float. The bow mooring can take the form of a rigid frame yoke or equivalent chain structure, suspended and hinged at the level of the neutral axis of the horizontal structure members connecting the float, as Figure 10 illustrated.

[0092] The structure members are lattice structures, like crane booms. The chords and cross-braces in the structure members can be airfoil cross-sections. The structure members and floats are made of fiberglass reinforced plastic (FGRP).

[0093] Because the horizontal structural members are at some distance from the water surface, as described above, the horizontal wave loads acting on the float can act quite far below it, resulting in bending loads in the structural members. This can be a major design issue. By shaping the float so that the horizontal wave loads acting on it are at the same level as the neutral axis of the structural members (usually the centreline), the bending loads can be greatly reduced. The simplest such float shape is a sphere, with its centre at this level (of course, only the wet surface of the float needs to have this shape). Another float shape with this property is any left-right symmetric body of revolution, with its axis parallel to the wave crests and at the same level as the centre of the sphere.

[0094] Such types of floats (e.g. biconic floats) are shown in Figure 9 To reduce the bending loads as described, they do require that the waves travel from the bow float to the stern float (in nautical terms, "head seas"), but this will usually be the case due to the "weather vane effect" of the mooring. Other float shapes can be designed to produce zero bending loads in head seas of low steepness and specific wavelengths using diffraction programs (see e.g. reference 1, chapter 4) or other methods.

[0095] In Figure 10 the bow float also carries loads from the mooring. By means of a mooring yoke as shown, these loads can also be made to act horizontally on the structural members. Such a yoke has previously been used on the Pelamis wave energy machine, but there its function was quite different, helping to damp the roll motion rather than preventing structural bending. In devices such as floating wind turbines, it has the additional advantage of increasing the effective mooring length, allowing operation in shallower waters.

[0096] While the illustrative embodiments of the application have been disclosed in connection with the preferred embodiments of the application, it will be apparent to those skilled in the art that various amendments and modifications of the application can be made without departing from the scope of the application as defined by the appended claims and their equivalents.

[0097] References

[0098] 1. Faltinsen, O. M. 1990. Sea loads on ships and offshore structures. Cambridge University Press

Claims

1. A floating renewable energy platform, comprising: The superstructure comprises horizontal structural members positioned above the waves, the superstructure is supported by a plurality of floating bodies interconnected by the structural members, and the platform is configured to provide an air gap ranging from 10 m to 30 m between the still water surface and the structural members. The floating bodies have a wet hull form that is a rotating body shape, the axis of rotation of the rotating body being horizontal and perpendicular to the longitudinal axis of the floating body, and the rotating body being rotatable about the axis of rotation.

2. A permanently moored floating renewable energy platform, comprising: Multiple floating bodies are interconnected by horizontal structural members that are positioned above wave action and direct wave forces during use. The platform is configured to have an air gap of 10 to 30 m between the structural members and the still water surface. The floating bodies have a wet hull form that is a rotating body shape with a horizontal axis perpendicular to the longitudinal axis of the floating body, and the rotating body is rotatable about the axis of rotation.

3. The platform according to claim 1 or 2, comprising the spaced-apart floats, spaced 100m to 300m apart.

4. The platform according to claim 1 or 2, wherein the float is configured to reduce bending loads in the horizontal structural member by setting the axis of rotation at the neutral axis and point of action of the main structural member connected to the float.

5. The platform according to claim 1 or 2, wherein a mooring device is provided on the bow float.

6. The platform according to claim 1 or 2, having a mooring device on the bow float, the mooring device being connected to the float by a yoke, the yoke being in the form of a rigid frame or an equivalent chain, suspended and hinged at the level of the neutral axis of the horizontal structural member connected to the float.

7. The platform according to claim 1 or 2, wherein the length of the float is greater than its width.

8. The platform according to claim 1 or 2, configured as a floating wind turbine, and comprising spaced-apart stern floats located below one or more wind turbines, and a bow float.

9. The platform according to claim 1 or 2, comprising three horizontal support members and three columns, the three horizontal support members being arranged in a triangular configuration, and the three columns collectively providing a triangular pyramid-shaped superstructure.

10. The platform according to claim 1 or 2, having a longitudinal centering height of more than one kilometer.

11. The platform according to claim 1 or 2, with a rated power of more than 5MW, and configured for an operating draft of less than 7m.

12. The platform according to claim 1 or 2, wherein the float and / or the structural member is made of composite material.

13. The platform according to claim 12, wherein the float and / or the structural member is made of glass fiber reinforced plastic.

14. The platform according to claim 1 or 2, wherein the float and / or the structural member is made of one or more of the following materials: steel, aluminum, and concrete.

15. The platform according to claim 1 or 2, comprising the structural member formed as a lattice structure.

16. The platform according to claim 15, wherein the chords and cross braces in the structural members have airfoil cross sections to reduce direct aerodynamic loads.

17. The platform according to claim 1 or 2, wherein the platform has a flat folding structure and an upright structure.

18. The platform of claim 17, wherein the platform comprises a plurality of the structural members including hinges.

19. The platform of claim 17, configured to fold down and flatten to the level of the structural members between the floats in a reclining manner, having a plurality of the hinges depending on the arrangement of the structural members.

20. The platform according to claim 1 or 2, equipped with a thruster to control its heading.

21. The platform according to claim 1 or 2, configured as a floating wind turbine and comprising one or more wind turbines.

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