WO2021256939A1

WO2021256939A1 - Floating windmill construction

Info

Publication number: WO2021256939A1
Application number: PCT/NO2021/050148
Authority: WO
Inventors: Bjarte Nordvik
Original assignee: Bjarte Nordvik
Priority date: 2020-06-19
Filing date: 2021-06-18
Publication date: 2021-12-23
Also published as: NO346376B1; NO20200725A1

Abstract

A floating windmill construction comprising a foundation (12) which is partially submerged in a body of water (20), where the partially submerged foundation (12) supports at least one tower (14) equipped with a windmill (16). The foundation (12) is comprising one or more outwardly extending stabiliser arms (30), where said stabiliser arm (s) (30) extend out from the foundation (12) in an area above a water surface of the body of water (20) and are comprising an upper arm (32) and a forearm (34).

Description

Floating windmill construction Field of the invention

The present invention relates to a floating windmill construction comprising a foundation which floats in a body of water, where the partially submerged foundation supports at least one tower equipped with a windmill.

The description relates to an invention within the technical field of offshore wind energy. A technical solution for stabilising a floating foundation for one or more windmills is described.

Background of the invention

To reduce pollution and to limit global warming, it is desirable to develop technology that can make renewable energy more competitive. Offshore wind is a particularly interesting resource related to renewable energy extraction. There is a great potential in utilising ocean areas, and the wind across such areas, to extract electrical energy. One challenge related to the extraction of energy from offshore wind is the cost. In order that offshore wind shall be able to be a competitive energy source, it is crucial that costs related to production, installation, operation and maintenance of offshore wind turbines are reduced. To achieve this goal, it is important to develop a new, cost-effective technology.

A large number of technical solutions have been developed for the production of wind energy offshore. Some of these are related to fixed foundations, while others are related to floating foundations. In many cases, the floating foundations are advantageous, especially for use at great ocean depths, typically above 50 metres.

At sea, an offshore wind turbine and its foundation are exposed to strong forces from wind, waves and currents. Particularly critical are the wind forces. Calculations have shown that the tilting forces which act on an offshore wind turbine will typically be 15 times as strong in the primary direction of the wind relative to a direction of 90 degrees to it. In order to prevent a wind turbine from tilting too much in harsh weather conditions at sea, it is important that the foundation is constructed to counteract tilting caused by the said forces. Disclosure of prior art

Stability against tilting is a challenge and cost driver for floating foundations, especially for floating foundations that shall be used in areas with the potential for extreme wind and wave conditions. Existing solutions to ensure stability in such areas are often large, heavy and expensive. An example of such a solution is known as "Hywind". The offshore wind solution “Hywind” includes an example of a foundation for an offshore wind turbine, where the foundation is a floating, vertical spar buoy. To counteract tilting forces when the spar buoy reaches deep into the ocean in an operational position, and it is often very heavy. The weight is largely due to the spar buoy solution's need for corrective ballast. Its size makes it expensive to manufacture and transport to a destination at sea, and it means that "Hywind" cannot be used in ocean areas of limited depth.

Alternative solutions for stabilisation include solutions with buoyancy towers that penetrate the water surface, where the buoyancy towers are mounted on a rigid, partly submerged platform and where the buoyancy forces of the device act through the buoyancy centre and through the metacenter when the device tilts.

WO2019143282A1 shows a floating windmill construction with two side by side and inclined towers attached to a common floating framework foundation which is partially submersible where the main buoyancy is located in each of its outer towers.

Reference is also made to US 2009091136 A1.

Objects of the present invention

It is an object of the invention to provide a floating windmill construction with improved stability.

In this document a technical solution is described which has advantages over the prior art for stabilising a foundation for an offshore wind turbine by counteracting tilting.

To move the stabiliser arms up in the structure and out of the water means that they are not exposed to the same influence from forces from waves as if they were to be submerged and can thus be designed accordingly. The stabiliser arms will then also not displace a volume of water, and thus have no effect on the buoyancy of the structure. It is also possible to inspect load-bearing and stabilising structures both inside and outside, as well as simplify assembly, compared with today’s solutions.

Summary of the invention

The above-mentioned objects are achieved with a floating windmill construction comprising a foundation which floats in a body of water, the partially submerged foundation supports at least one tower equipped with a wind turbine, in which said foundation is comprising one or more outwardly extending stabiliser arms, where said stabiliser arm (s) extend out from the foundation in an area above a water surface of the body of water. The stabiliser arm is comprising an upper arm and a forearm.

In some embodiments the forearm can be arranged at an angle in relation to the upper arm.

Furthermore, the forearm can be connected to the upper arm in an articulated connection or hinge connection. Alternatively, the forearm can be freely suspended from the upper arm.

The partially submerged foundation can, in one embodiment, support a first and a second tower which are positioned side by side and inclined in relation to each other, and where a first stabiliser arm of the first tower extends out in the opposite direction in relation to a second stabiliser arm of the second tower.

The first and second stabiliser arms can be attached to a shoulder shaft that runs between the first and second towers.

The partially submerged foundation can be comprising an elongated floating element which, in a forward part, has a rotatable anchoring and which, in a rear part, comprises said tower. The partially submerged element can, in some embodiments, extend behind said tower.

The elongated floating element can be arranged to float below the water surface in the body of water, where individual sections or the entire pipe can be filled with water or arranged with another type of ballast to regulate the COB and COG of the device. During tilting of the windmill construction in the body of water, the said stabiliser arms are preferably arranged to exert a directing force onto the windmill construction. The length of the stabiliser arm (s) from the device will affect the GZ “correcting arm” and thus a long stabiliser arm will be advantageous with regard to a short stabiliser arm when it comes to stability. This at the same time as the effect of the waves on the device will decrease the further from the device said stabiliser arm extends.

Said stabiliser arm (s) extend out and down from the foundation towards the water surface of the body of water, and at least during tilting of the windmill construction said stabiliser arm extends down into the body of water or is pulled out of the body of water, depending on the position of the stabiliser arm in relation to direction of the tilting. Stabiliser arm (s) are also adapted to brake and thus stabilise the movement of the windmill construction.

In the case of a free-hanging forearm, the forearm will typically have a weight which indicates that it will sink into a body of water, and thus contribute to a reduced weight which in turn contributes to a correcting force if it is immersed in a body of water when the device is tilted.

The stabiliser arms can be comprising a lower brake collar. The brake collar can be an outwardly extending circular disc situated on the outer and lower ends of the stabiliser arm.

Description of the figures

Preferred embodiments of the invention shall be described in more detail below with reference to the accompanying figures, in which:

Figures 1-3 show a first embodiment of a windmill construction according to the invention, seen in perspective, front view and top view, respectively.

Fig. 4 shows, in perspective, a second embodiment of a windmill construction according to the invention.

Fig. 5 shows, in perspective, a third embodiment of a windmill construction according to the invention.

Figure 6 shows, in perspective, a fourth embodiment of a windmill construction according to the invention. Description of preferred embodiments of the invention

The invention relates to a stabilising structure in the form of one or more stabiliser arms 30 for a foundation 12 of an offshore windmill construction. The floating windmill construction is comprising a foundation 12 which floats in a body of water 20, where the partially submerged foundation 12 supports at least one tower 14 equipped with a wind turbine or a windmill 16. The lower part of the tower 14 will naturally form part of the foundation 12, and consequently the foundation 12 is perceived to include the lower part of the tower 14. According to the invention, said foundation 12, or tower 14, is comprising one or more outwardly extending stabiliser arms 30, where said stabiliser arm (s) 30 extend out from the foundation 12 in an area above a water surface of the water mass 20.

The part of the foundation 12 that floats down in the water mass 20 can be partially filled with water or other ballast to further stabilise the windmill construction, as well as regulate the device's COB and COG.

The stabiliser arm (s) 30 can extend out or hang rigidly, adjustably or freely from the foundation 12 in such a way that a change is obtained in the part of the stabiliser arm which is immersed in the water mass 20 by tilting the windmill construction.

In figs. 1-3, the stabiliser arms 30 are rigidly attached to the foundation 12, i.e. , to the lower part of the tower 14, and where each stabiliser arm 30 is comprising an upper arm 32 attached to or equipped with a forearm 34. As shown in, for example, figs. 1 and 2, the upper arm 32 extends mainly straight out, while the forearm 34 extends downwards towards the body of water 20. In the embodiment shown, the forearm 34 is rigidly attached to the upper arm 32 via a rigid joint connection 36 so that the forearm is arranged at a fixed angle in relation to the upper arm 34. In the embodiment shown, the angle between the upper arm 32 and the forearm 34 is at a right angle, but the forearm 34 can also be inclined in relation to the upper arm 32 at any other angle.

Alternatively, the joint connection 36 can be an articulated connection or a hinge connection which allows free or regulated control of the forearm 34 in relation to the upper arm 32.

In figs. 4-6, the stabiliser arm(s) 30 are freely suspended, in the sense that the forearm 34 is freely movable in relation to the upper arm 32. The forearm 34 can be suspended from the upper arm 32 via a joint connection 36 in the form of a strut, chain, wire or the like.

By changing the part of the stabiliser arm 30 which is immersed in water, the force the stabiliser arm exerts on the windmill construction is changed. If the part increases, the force is reduced. If the part decreases, the force is increased.

The stabiliser arm 30 can typically be comprising, or consist of, a material of high density if it has a free-hanging forearm 34. It can further be advantageous if the stabiliser arm 30 is comprising, or consists of, a material which is relatively inexpensive, which is relatively environmentally friendly and/or which ably withstands harsh offshore weather conditions.

The stabiliser arm 30, i.e., more specifically the forearm 34, can further be comprising a lower collar 38 in the lower part and which, during movement in the water, gives a braking effect. The collar 38 can be in the form of an outwardly extending circular disc.

The partially submerged foundation 12 can support a first and a second tower 14 which are positioned side by side and inclined in relation to each other. Figs. 1-4 show two twin towers 14 which are attached to the partially submerged foundation 12, and where the foundation is comprising a mainly elongated and horizontally arranged floating element 40 which, in a forward part, has an anchoring point 42 for rotatable anchoring and which, in a rear part, is comprising said tower 14. A shoulder shaft 44 runs between the two towers 14 and can be connected to upper arms 32 of the stabiliser arms 30, where a first stabiliser arm 30 of the first tower 14 extends out in the opposite direction in relation to a second stabiliser arm 30 of the second tower 14.

Several other beams or struts 46 can run between the floating element 40 and the towers 14 and can function as strengtheners for the foundation and also as walkways for service personnel.

In an alternative embodiment as shown in fig. 4, the foundation 12 can be comprising two stabiliser arms 30, where each is suspended via the joint connection 36 from a shoulder shaft 44 in the form of a beam, for example firmly connected to a rigid foundation structure. The rigid shoulder shaft 44 can be said to be part of the rigid structure of the foundation and be comprising the upper arm 32. By tilting the foundation 12 with two stabiliser arms 30 in a first direction, a first of the two stabiliser arms will be raised, while the second will be lowered. When tilted in a second, opposite direction, the first of the two stabiliser arms is lowered, while the second is raised.

The upper arm 32 can be attached to the foundation/tower 12,14 in a way which causes it to extend downwards towards an ocean surface when the foundation is standing in normal position. This can be advantageous because the angle can influence whether a stabiliser arm 30 moves closer to, or farther from, a foundation centre of gravity during tilting. It can be advantageous if a stabiliser arm moves away from a centre of gravity on a side where increased torque from the stabiliser arm is desirable to stabilise the foundation against tilting, and/or it can be advantageous if a stabiliser arm moves towards the centre of gravity on a side where it is desirable with less rotating torque from the stabiliser arm to stabilise the foundation against tilting. Since the torque is given by force times the arm, it is advantageous, if it is desirable to increase the rotating torque, to increase both the force and the arm, while it is advantageous to reduce the force and arm if a lower rotating torque is desired.

In an embodiment of the invention as shown in fig.5, the foundation 12 can comprise one stabiliser arm 30 with an upper arm 32 in the form of one or more beams projecting from the foundation/tower 12,14, and with one forearm 34 freely suspended in the upper arm 32. The stabiliser arm 30 can then be suspended so that when the foundation is in a normal position, on calm seas, it is partially submerged in the body of water 20. The part of the stabiliser arm which is located below the ocean surface when the foundation is in the normal position can be 50%, 30%, 70%, below 30% or above 70%. The "part" can refer to a part of the volume of the stabiliser arm or a part of the mass of the stabiliser arm. In such an embodiment, tilting the foundation in one first direction will lower the stabiliser arm 30 so that the part that is located below the surface is increased, while tilting in a second, opposite direction will raise the stabiliser arm so that the part which is located below the surface is reduced. When the part of the stabiliser arm which is located below the surface is increased, the force which is applied to the foundation from the stabiliser arm is reduced. When the part of stabiliser arm which is located below the surface is decreased, the force which is applied to the foundation from the stabiliser arm is increased. In this embodiment form, the stabiliser arm can be suspended on one side on the foundation, at the front on the foundation, or at the rear on the foundation.

Fig. 5 shows a tower 14 which is attached to the partially submerged foundation 12, and where the foundation is comprising a mainly elongated and horizontally arranged floating element 40 which, in a forward part, has an anchoring point 42 for rotatable anchoring.

In the embodiments of the foundation where there are two or more stabiliser arms, these can be symmetrically attached to the rigid structure of the foundation, as for example shown in fig. 6. The part of each stabiliser arm 30 which, under calm conditions when the foundation/tower 12,14 are in the normal positions, is below the ocean surface can be the same for each stabiliser arm or be different. The part of one or more stabiliser arms which is located below the ocean surface can be 0%, or above 0%. The part can be 100% .

Fig. 6 shows a tower 14 which is attached to a standing and partially submerged foundation 12, and where the foundation is comprising a device 42 for rotatable anchoring.

The stabiliser arm can be in the form of a cylinder, a cone, a cube, or have any other shape which is suitable for the purpose of the stabiliser arm.

Centre of Buoyancy- COB describes the centre of gravity of the buoyancy (centre of the upwardly acting force of the device). Centre of Gravity- COG describes the centre of gravity of the facility (centre of the downward acting force of the facility). Correcting arm Distance - GZ, the longer the straightening arm, the less buoyancy needed at the end of the arm to get the same stability.

Low COG and high COB result in good stability as the «correcting arm» GZ becomes long when tilting is applied.

The windmill construction shown in fig. 6 is only equipped with one tower 14, which indicates that the "centre of buoyancy" can be a body (platform) which extends downwards in a body of water. Figs. 1-5 show a body (the floating element 40) which lies horizontally in a body of water. In the cases shown, the centre of buoyancy is close to the water mass, something which results in a high-lying COB which in turn is good for stability.

Claims

1. A floating windmill construction, comprising a foundation (12) which is partially submerged in a body of water (20), where the partially submerged foundation (12) supports at least one tower (14) equipped with a windmill (16), where the foundation (12) comprises one or more outwardly extending stabiliser arms (30), and where said stabiliser arm (s) (30) extend out from the foundation (12) in an area above a surface of the body of water (20), characterised in that said stabiliser arm (s) (30) comprises an upper arm (32) and a forearm (34) .

2. The floating windmill construction according to claim 1, characterised in that the forearm (34) is arranged at an angle in relation to the upper arm (32).

3. The floating windmill construction according to claim 1, characterised in that the forearm (34) is connected to the upper arm (32) in an articulated connection or a hinge connection (36).

4. The floating windmill construction according to claim 1, characterised in that the forearm (34) is freely connected to the upper arm (32).

5. The floating windmill construction according to claim 1, characterised in that the partially submerged foundation (12) supports a first and a second tower (14) which, in relation to each other, are placed side by side and inclined, where a first stabiliser arm (30) of the first tower (14) extends out in an opposite direction in relation to a second stabiliser arm (30) of the second tower (14).

6. The floating windmill construction according to claim 5, characterised in that the first and the second stabiliser arms (30) are attached to a shoulder shaft (44) which runs between the first and the second tower (14).

7. The floating windmill construction according to claim 1, characterised in that the foundation (12) comprises an elongated floating element (40) which, in a forward part, has an anchorage (42) for rotatable anchoring and which, in a rear part, comprises said tower (14)

8. The floating windmill construction according to claim 7, characterised in that the elongated floating element (40) is arranged to float below the water surface in the body of water (20).

9. The floating windmill construction according to claim 1, characterised in that during tilting of the windmill construction in the water mass (20), said stabiliser arms (30) are arranged to apply a correcting force to the windmill construction.

10. The floating windmill construction according to claim 1, characterised in that said stabiliser arm (s) (30) extend out and down from the foundation (12) towards the water surface of the water mass (20), and at least during tilting of the windmill construction, said stabiliser arm (30) extends down into the water mass (20) and is arranged to brake and stabilise the movement of the windmill construction.

11. The floating windmill construction according to claim 10, characterised in that said stabiliser arm (s) (30) on a lower part comprises a brake collar (38).

12. The floating windmill construction according to claim 11 , characterised in that the brake collar (38) is an outwardly extending circular disc situated on the outer and lower end of the stabiliser arm (30).