Floating platform for wind turbine

Abstract

The invention relates to a floating platform (10) for supporting a tower (1) with a wind turbine (2) for harnessing wind energy. The floating platform (10) comprises a floating element (11) and an adaptive mooring system for automatically achieving a substantially vertical alignment of the tower (1) at different wind speeds. The adaptive supporting system comprises a mooring rope (21) coupled to the floating platform (10) and configured for fixing said mooring rope (21) via a ground anchor (50) to the ground (101), a cantilever beam (25) with a proximal end (24) attached to the floating platform (10) and a distal end (26), the mooring rope (21) being coupled to the distal end (26), and a weight (22) coupled to said mooring rope (21) and being positioned below the cantilever beam (25), wherein a variable position of the weight (22) with respect to the cantilever beam (25) supports a compensation of forces from the wind acting on the wind turbine (2) such that the orientation of the tower (1) is substantially vertical.

Description

[0001] New PCT Application

[0002] XELLANTEC GmbH

[0003] Vossius Ref.: AJ4222 PCT-0 S5

[0004] Floating Platform for Wind Turbine

[0005] Technology of the present Invention

[0006] The present invention relates to a floating platform for harnessing wind energy.

[0007] 5 Preferably, the present invention relates to a floating offshore power installation with a tower and a wind turbine.

[0008] More specifically, the present invention proposes the development of a mooring system for a floating platform for harnessing wind energy which, because of its particular arrangement, reduces the number of required mooring ropes to one, allows the platform to always be oriented

[0009] 10 towards the wind and preferably intrinsically supports that the tower is substantially vertical under different wind conditions.

[0010] Background

[0011] One of the major challenges in the technical field of floating offshore wind turbines is the mooring because it has a major impact on several determining factors of the whole platform like material consumption, wind harvesting efficiency, complexity, installation effort, maintenance expenses. The mooring of floating wind platforms has to bring up the counter force for considerable wind forces acting on the wind turbine from virtually any direction. It is further preferred that the mooring has to get along the tidal range and the significant heave movements of the platform at high waves.

[0012] 20 One of the most widespread approaches for the mooring of prior art systems is the use of three ropes or chains which are mounted to the platform, which have a fixed length and which are fixed to the seabed using one ground anchor for each rope / chain. The length of these ropes / chains must be considerably longer than the water depth in order to keep the tension in a reasonable range. In many cases a part of their length rests on the seabed among other reasons

[0013] 25 with regard to a length reserve for the tidal range and heave movements. This implies that they can be dragged over the sea ground with an impact on the flora. Furthermore three ground anchors have to be fixed to the seafloor in precise positions to each other and the length of the ropes becomes a more and more determining factor with rising water depth. Such platforms are known, for example, from EP 2 727 813 and EP 3 548 740. These floating platforms are among the few which are already in operation in wind farms.

[0014] The present invention improves this by reducing the required number of ropes / ground anchors to preferably only one rope / chain with a corresponding ground anchor. Furthermore, the rope of the present invention is preferably under a constant tension thus never touching the seabed and intrinsically getting along tide ranges and heave movements.

[0015] The floating platform described in EP 3 548 740 Bl is based on a spar buoy working principle which has several advantages but is very susceptible to yaw movements. These movements have a negative impact on the wind harvesting efficiency. Moreover, the yaw movements are stressing the mooring ropes due to their mounting quite close to the vertical yaw axis resulting in a short lever. EP 3 548740 Bl introduces a solution how to reduce this effect by a control system acting on the blades of its wind turbine whereby the blades' angle of attack has to be changed once per turn. This effort results in a reduction but there is still a considerable yaw movement left, not to mention the complexity.

[0016] The present invention also solves this problem of unwanted yaw movements intrinsically by the special construction such that preferably no additional regulation controllers are required, which are complex and require high operational reliability. Thus, based on the mechanical design of the floating platform of the present invention, yaw movements can be reduced or substantially prevented so that there is no deterioration in wind harvesting efficiency. Furthermore, the present invention further provides an advantage that there are preferably no additional stresses for the mooring system.

[0017] A further challenge is to keep the tilt angle of the tower and the turbine working on top of the tower as low as possible because this also causes a deterioration of the wind harvesting efficiency. A large tilt angle furthermore effects considerable additional stresses on the tower due to the huge weight of the turbine on top of the tower. This problem does not exist in ground fixed solutions because all forces are absorbed by the foundation. Floating platforms, however, have to deal with potentially high wind forces acting on the turbine in a height of 100m and more above the water surface, causing a high pitch torque because the counter force can only be applied in the vicinity of the water surface resulting in a very long lever. Platforms based on a spar buoy working principle have to use a huge ballast that can be at 10.000 tons or even far more to keep the tilt angle in an acceptable range. The semi-submersible platform as shown in EP 2 727 813 uses three floatation columns arranged in a mutual distance of around 50m from each other. In order to keep the tower substantially upright, a water ballast can be pumped between these columns to compensate the wind forces. Furthermore, this kind of platform requires a considerable amount of steel for the widespread structure. The present invention solves these disadvantages by a less complex reliable mechanism, enabling much more lightweight platforms and thus a considerably better CO2 footprint of the platform itself.

[0018] It has advantages to have a floating wind harnessing platform that aligns with the direction of the wind as a whole. This also eliminates highly stressed bearing and servo mechanism between the tower and the turbine. The present invention also provides the advantage that the tower and the entire platform can be optimized towards the unified direction of the acting forces so that the amount material can be reduced and CO2 footprint can be improved.

[0019] A self-aligning platform is known from WO 2016 / 083634 but the mooring is realized with a conventional three line approach.

[0020] It is an object of the present invention to alleviate or overcome the above-mentioned drawbacks of known prior art systems.

[0021] Summary

[0022] The subject-matter of the present invention is defined by the features of the independent claims. Further preferred embodiments of the present invention are defined in the dependent claims.

[0023] In particular, the present invention relates to a floating platform configured for supporting a tower with a wind turbine for harnessing wind energy. The present invention also relates to a floating offshore wind power installation with a floating platform of the present invention which further comprises a tower and preferably also a wind turbine. Since the floating platform is configured to support a tower with the wind turbine and is also configured to be moored, the following description also refers to a support or mooring / anchoring system of the present invention.

[0024] The floating platform of the present invention comprises a floating element, which has preferably enough buoyancy such that the tower with the wind turbine is located above a water surface. In particular, a large part of the tower should be above sea level to ensure that the wind turbine works properly. In other words, a person skilled in the art will understand that a small part of the lower part of the tower could be below sea level.

[0025] The floating platform further comprises an adaptive mooring system for different wind speeds, wherein said adaptive supporting system comprises at least one mooring rope, preferably exactly one rope, coupled to the floating platform and configured for fixing said mooring rope via a ground anchor to the ground. The floating platform further comprises at least one cantilever beam with a proximal end mounted / fixed to the floating platform and a distal end, which is preferably a "free end". The mooring rope is preferably mounted next to the distal end. According to a preferred embodiment, a single rope is already sufficient. A person skilled in the art will understand that the single rope referred to may comprise a plurality of individual ropes attached in series to one another and / or forming a Y shape at one end of the rope. One advantage of a single rope is that only one ground anchor is needed.

[0026] The adaptive mooring system according to the present invention preferably provides the effect that the tower is supported towards a substantially vertical alignment, even for different wind speeds. For instance, substantially vertical means that the wind turbine is held in a position which allows harnessing of wind energy with preferably low degradation of the efficiency. In particular, substantially vertical may related a ±1°, ±3°, ±4°, ±5°, ±7°, ±10° from the vertical directions which is preferably defined by the gravitational force.

[0027] Said adaptive supporting system preferably comprises at least one weight, in the following also called compensation weight, coupled to said at least one mooring rope, wherein the weight achieves that i) the floating platform is positioned substantially vertically above the ground anchor if no wind acts on the wind turbine and that ii) the floating platform is positioned as further away from the anchor as the force of the wind acting on the wind turbine increases.

[0028] For the adaptive mooring system, it is preferred that the at least one weight automatically varies its relative position with respect to a longitudinal direction of the cantilever beam to support a compensation of forces from the wind acting on the wind turbine such that the orientation of the tower is supported to be substantially vertical. In other words, it is preferred that the position of the weight is variable, dynamical and preferably adaptive. A first end of the mooring rope is preferably configured to be fixed to the ground anchor, and a second end of the mooring rope may be fixed to the floating platform in the vicinity of the proximal end of the cantilever beam or the tower. According to an embodiment of the present invention, the rope may be alternatively or additionally fixed to the at least one (additional) weight and / or fixed to a lifting block / pulley block connected between the weight and the distal end of the cantilever beam. Preferably, the mooring rope is guided between its first and second ends by a deflection means, wherein the deflection means comprises preferably at least a pulley, wherein said pulley is preferably mounted next to the distal end of the cantilever beam.

[0029] It is further preferred that said compensation weight is mounted to the floating platform by a direct mounting rope, which has preferably a fixed length and may be also called fixed length direct mounting rope. Said direct mounting rope comprises a first end which is preferably fixed to the floating platform in the vicinity of the proximal end of the cantilever beam and / or the tower and the other end of the direct mounting rope is fixed to the weight.

[0030] The compensation weight may be also coupled slidably to the mooring rope, preferably via a pulley, wherein an optional stopper fixed to the mooring rope between the end of the mooring rope fixed to the floating platform and the weight achieves that the weight can be located below the cantilever beam distally from a middle position of the cantilever beam. A person skilled in the art understands that a single pulley or pulley means may be provided, wherein a pulley or pul ly means may also comprise a plurality of pulleys. The floating platform may further comprise a direct mounting rope, wherein a first end of the direct mounting rope is fixed to the floating platform in the vicinity of the tower and the other end of the direct mounting rope is fixed to the weight, which achieves that the weight can be located below the cantilever beam proximal from a middle position of the cantilever beam.

[0031] Preferably, a first end of an auxiliary rope is fixed to the mooring rope at a position distally from the deflection means (pulley), preferably at a branch point / rope splitter, and the second end of the auxiliary rope is fixed to an additional tension weight whose movement is primarily in vertical direction.

[0032] Preferably, the auxiliary rope acts on the mooring rope in such a way that the mooring rope is under additional tension between the splitter and the ground anchor. The auxiliary rope may be guided by one or more auxiliary pulleys where preferably at least one auxiliary pulley is mounted in the vicinity of the distal end of the cantilever beam.

[0033] The thickness of the mooring rope is preferably larger than the thickness of the auxiliary rope.

[0034] The position of the compensation weight with respect to the cantilever beam is preferably set or determined by an actual length of the mooring rope between the distal end of the cantilever beam and the ground anchor, wherein the actual (effective) length of the mooring rope changes dynamically based on the actual wind speed.

[0035] An angle between a horizontal surface of the sea, i.e., the sea surface without waves, and a linear fit of the mooring rope is preferably between 0° and 10° at no wind or light wind and preferably between 35° and 45° at high wind speed. According to the present invention, light wind is in the order of magnitude < lm / sec whereas strong wind has preferably an order of magnitude between lOm / sec to 15m / sec.

[0036] According to the present invention, it is preferred that the position of the compensation weight regulates the "actual" length of the mooring rope between the distal end of the cantilever beam and the ground anchor. In other words, the actual length of the mooring rope is determined by the interaction between the wind force and the rope force caused by the compensation weight(s).

[0037] It is further preferred that the compensation weight achieves that the floating platform is positioned substantially vertically above the ground anchor if now wind or only light wind acts on the wind turbine, whereas the floating platform is positioned as further away from the anchor as the force of the wind acting on the wind turbine increases.

[0038] It is further preferred that the mooring rope and optionally the auxiliary rope is / are limited to a range which ensures that they are not running into their respective mechanical limitation stop by limiting the wind force acting on the wind turbine preferably by setting a suitable work angle of the rotor blades. In other words, by rotating the angles of the individual rotor blades of the wind turbine, the respective force on the upper end of the tower can be enhanced or reduced. A floating offshore wind power installation of the present invention preferably comprises an additional control unit which is configured to regulate said angles of the rotor blades, e.g., to reduce the acting force acting on the upper end of the tower and thereby avoiding the mechanism with the rope and auxiliary rope does not run into mechanical limits, such that undesirably stresses on the anchor and / or the mounting points of the rope to the platform / cantilever beam can be avoided or reduced.

[0039] According to a further preferred embodiment, a power cable, for transporting the generated electrical power, is provided between the floating platform and the ground. The power cable is preferably guided along the rope and preferably so long such that there is always sufficient slack of the power cable. Preferably, the power cable is longer than the rope.

[0040] The floating platform according to present invention preferably achieves that the floating platform can be fixed to the ground via the (single) rope, such that the floating of the floating platform is provided in such a manner that the front face of the wind turbine is directed against the wind direction.

[0041] It is preferred that the cantilever beam extends substantially horizontally beyond a vertical line of the tower, wherein the cantilever beam preferably extends substantially horizontally beyond a vertical line of the tower by a length which is at least 1 / 3 of the height of the tower. It is further preferred that the angle between the cantilever beam and a tower mounted to the floating platform is between 70° and 110°, preferably between 80° and 100°, approximately 90°, preferably exactly 90°.

[0042] It is preferred that the mooring rope is a steel chain, steel cable or a synthetic rope, preferably with some buoyancy, or a composite of a steel cable and a synthetic rope. For instance, the rope may comprise nylon rope and / or Kevlar®.

[0043] The present invention also relates to a floating offshore wind power installation with a floating platform and a tower with a wind turbine.

[0044] Brief description of the Figures

[0045] Preferred embodiments of the present invention are further elucidated below with reference to the figures. The described embodiments do not limit the present invention.

[0046] Fig. la shows a preferred embodiment of a floating platform of the present invention at relative strong wind and relative light wind.

[0047] Fig. lb shows an embodiment similar to Fig. la at three different wind speeds, without power cable for clearness. Fig. lc shows the triangle of forces principle of the single rope mooring.

[0048] Fig. Id shows relevant torques acting on the floating platform.

[0049] Fig. 2 shows a preferred embodiment of the present invention for an installation deeper water using a lifting block and an additional tension weight.

[0050] Fig. 3 shows an alternate embodiment of the present invention using an additional pulley at the compensation weight and a stopper.

[0051] Fig. 4 shows a more detailed view of the ground anchor of the present invention.

[0052] Fig. 5 shows the principle of the turbine torque compensation.

[0053] Detailed description of the Invention

[0054] For a better understanding of the floating platform of the present invention, a plurality of different embodiments illustrated in the drawings will be discussed in further detail.

[0055] In particular, Fig. la shows a first embodiment of a floating platform 10 of the present invention in a complete arrangement with a tower 1 and a wind turbine 2 at a relative strong wind (left side of the figure) and the same arrangement at a lower wind speed, wherein the wind speed is indicated by the size of the arrow 5. The platform 10 in Fig. la has the working principle of a buoy, meaning, the buoyancy force is above the center of gravity thus effecting an upright position if no wind forces are applied. When harnessing wind energy, the wind interacting with the turbine 2 effects a considerable force primarily in the direction of the wind, whose counterforce is created by mooring the platform to the sea floor using a mooring rope 21 (in the following also called rope) whose one end or end region is connected to a ground anchor 50. On the platform side, the rope 21 is preferably coupled to the platform 10 over at least one pulley 27 which is located next to or at a distal end 26 of a cantilever beam 25, wherein the proximal end 24 of this cantilever beam 25 is rigidly connected to the platform 10.

[0056] In the following, the directions will be also described with reference to a rectangular coordinate system, with the Z-axis pointing against the gravitational force, i.e., the tower extends vertically upwards along the Z-axis. The elongated cantilever beam points in the X-axis and the x- and y-axis together span a plane that, under idealized conditions, i.e., without waves, defines the surface of the sea or is parallel to the surface of the see (see, for example, Fig. lb).

[0057] Moreover, the terms yaw, roll, pitch are used in this application as understood by a person skilled in the art. In particular, a yaw rotation is a movement around the yaw axis of a rigid body that changes the direction it is pointing, to the left or right of its direction of motion. Preferably, the Z-Axis is the yaw axis; swivels left and right. A roll rotation means pivots side to side (rotation around X-axis) and pitch rotation (rotation around Y-axis): tilts forward and backward.

[0058] The other end of the rope 21 is preferably connected to a compensation weight 22 which sets the rope 21 under a continuous tension. The compensation weight 22 is preferably connected in addition to one end of a direct mounting rope 34 whose other end is preferably connected to the platform 10, preferably next to or in the vicinity of the vertical axis of the tower 1. This arrangement has the effect that the compensation weight 22 can move towards the distal end 26 of the cantilever beam 25 when the wind force 5 increases, because the section of the rope 21 between the weight 22 and the distal end 26 becomes shorter when the section of the rope 21 between the ground anchor 50 and the distal end 26 of the cantilever beam 25 becomes longer. The length of the rope 21 is fixed and the pulley 27 enables an exchange of the respective section lengths.

[0059] Fig. lc illustrates the working principle of the single rope mooring based on a triangle of forces. The determining force is the wind force acting on the turbine (X-axis). This force has its counterpart in the horizontal force component of the rope tension. If there is no wind force, this force component is zero, effecting that the tension force of the rope is pushing the rope 21 into a substantially vertical direction (Z-axis), meaning the angle a between the rope 21 and the earth's surface (which is assumed to be horizontal, i.e., 90° with respect to the gravitational force) is 90°. The distal end 26 of the cantilever beam 25 is preferably located substantially above the ground anchor 50 and the distance between the distal end 26 of the cantilever beam 25 and the ground anchor 50 is minimal. The tension force of the rope 21 is a fraction of the weight force of the compensation weight 22 which is determined by the position of the compensation weight 22 between the proximal end 24 and the distal end 26 of the cantilever beam 25. When the wind force 5 increases and consequently the wind counterforce increases, the angle a will decrease with the relationship [wind counterforce] a = arccos ( — - — — )

[0060] [rope tension] until the equilibrium has been reached. Therefore the system is inherent stable. In the case of the highest expected wind force 5, the compensation weight 22 is basically underneath the distal end 26 of the cantilever beam 25 and its whole weight force is held by the rope 21 resulting in a rope tension force of substantially the same magnitude.

[0061] There is preferably a length reserve of the rope 21 foreseen before running into a hard mechanical limitation in order to avoid stresses on the platform 10, the ground anchor 50 and / or particularly on the rope 21. The wind force 5 acting on the turbine 2 is preferably limited to a value by the turbine's wind adaptation mechanism that ensures that this reserve is not underrun even under conditions like wind blasts or waves.

[0062] As illustrated in Fig. Id, the increasing wind force 5 effects an increasing distance between the distal end 26 of the cantilever beam 25 and the ground anchor 50 and consequently the weight force of the compensation weight 21 is applied closer to the distal end 26 of the cantilever beam 25 which effects an increasing torque 131 on the platform 10 which is directed in the opposite direction of the torque 130 effected by the wind force 5. The increasing torque 130 created by an increasing wind force 5 interacting with the turbine 2 effects an increasing pitch angle 120 of the platform 10, the increasing torque 131 created by the compensation weight 22 moving towards the distal end 26 of the cantilever beam 25 will compensate a relevant part of the torque 130 created by the wind force 5 and thus will counteract to an increase of the pitch angle 120 of the platform 10 as shown in Fig. Id. As a result, tower 1 is essentially upright or vertical. A person skilled in the art will be able to tune the variety of parameters, e.g., mass of weight 22 etc., to achieve a sufficient force compensation based on a respective set influencing factors.

[0063] Fig. 5 illustrates how the wind dependent mechanism of the weight 22 as described above can be used to generate an overlaid torque 70 to compensate the considerable wind dependent torque 71 of the turbine. The wind is interacting with the rotor of the turbine 2 resulting in a rotational movement of the rotor which is connected to a generator which transforms the mechanical energy to electrical energy. The mechanical energy calculates with the formula P = M * (JO

[0064] (P: generated power, M: torque by the rotor, oo: angular velocity of the rotor).

[0065] Regarding the low angular velocity of the rotor and the magnitude of the power output, very high torques 71 are required which can be in the range of 20MNm with a 15MW turbine. The torque 71 effects an inclination of the tower 1 around the roll axis (X-axis) which is defined or substantially parallel to the longitudinal axis of the cantilever beam 25. The compensation of the wind induced torque 71 is effected by an opposite roll compensation torque 70 which is generated by having a fixing point 28 of the direct fixing rope 34 in a suitable horizontal distance from the roll axis of the floating platform 10 and a biasing weight 72 on the opposite side of the roll axis. When there is no wind or light wind and thus a small wind induced torque 71, the weight 22 is closer to the fixing point 28 and therefore in a larger distance to the roll axis of the floating platform 10, resulting in a torque around the roll axis. The biasing weight 72 on the opposite side of the roll axis generates a counter torque around the roll axis and it is dimensioned in a way to compensate the torque of the weight 22 resulting in a roll compensation torque 70 which is substantially 0 in the low wind case. In the case of a stronger wind force 5 the weight 22 is closer to the distal end 26 of the cantilever beam 25 and thus also closer to the longitudinal axis of the cantilever beam 25 and thus closer to the roll axis of the floating platform 10. The roll compensation torque 70 is now substantially effected by the biasing weight 72. The roll compensation torque 70 works in the opposite direction of the wind induced torque 71 and has preferably substantially the same magnitude as the wind induced torque 71 resulting in a reduced inclination of the tower around the roll axis. For reasons of clearness the elements which connect the fixing point 28 and the biasing weight 72 to the platform 10 have been left out.

[0066] It is a further advantage of this embodiment that the rope 21 between the distal end 26 of the cantilever beam 25 and the ground anchor 50 intrinsically has a safe distance from the weight 22 to avoid getting entangled with each other. This can be seen in Fig. lb. In particular, at strong wind, the weight 22 is closer to the distal end 26 but the rope 21 between the distal end 26 of the cantilever beam 25 and the ground anchor 50 has, e.g., an angle of about 45°. At low wind, the rope 21 has a steeper angle, e.g., of about 90° but the weight 22 is pulled away from the rope 21 with the help of the direct fixing rope 34. Due to the fact that the substantially horizontal wind force 5 is applied in a horizontal distance of approximately the length of the cantilever beam 5 from the application point of the substantially horizontal counter force coming from the tension of the rope 21 at the distal end 26 of the cantilever beam 25 and the fact that the platform 10 is swimming on the surface of the water 100 and the absence of further relevant forces, the platform will intrinsically align with the direction of the wind. Therefore a rotating joint is preferably not necessary between the wind turbine 2 and the tower 1 as it would be the case in a non self-aligning platform type.

[0067] There can be yaw movements, caused e.g. by wind blasts acting asymmetrically on the wind turbine 2. The constellation of the present invention based on a cantilever beam 25 will preferably inherently reduce the yaw movements of a platform, particularly a platform working based on a spar buoy principle. The direction of the yaw torque is approximately around the vertical axis of the tower 1. The cantilever beam 25 offers a lever to effectively apply a counter torque with the help of the tension of the rope 21 which is pulling by physical nature the cantilever beam 25 in a direction where it is in line with it and thus acting against yaw movements. Moreover, yaw movements do not stress the mooring rope 21 compared to the prior art mooring of spar buoy based platforms where the mooring ropes are fixed considerably closer to the vertical axis of the tower 1. In these prior art platforms the yaw movement is limited by the mooring ropes having a hard run into the mechanical limiting stop at a shorter lever, which produces even higher forces. Countermeasures provided by a blade angle regulation of the turbine can reduce this effect only to a certain extent. The floating platform of the present invention does preferably not have a hard limiting stop and thus no relevant additional stress on the mooring rope 21 caused by yaw movements.

[0068] The rope 21 is preferably made of a synthetical material that has preferably a specific weight close to the one of sea water to compensate the weight with the lift. The relevance of this effect increases with the water depth due to the inherent length of the rope. A rope made of steel with a length of a kilometer or more would require considerable countermeasures against sag.

[0069] The floating platform 10 preferably comprises a cable 40 for the transport of the generated electrical energy to the seabed 101 where it is connected to the long-range transmission cabling system. The cable 40 is preferably primarily guided along the rope 21 until a cable branch point 41. The distance of this branch point 41 from the ground anchor 50 is preferably less than the minimum distance between the distal end 26 of the cantilever beam 25 and the ground anchor 50. The cable 40 is preferably fixed to the platform 10 at the cable fixing point 42. The length of the cable 40 between the cable fixing point 42 and the cable branch point 41 is preferably longer than the maximum distance between the points 41 and 42 to an extent that the cable 40 has enough sag to avoid high longitudinal tensions in the cable 40. The position of the cable fixing point 42 at the platform 10 is preferably chosen in a way that there is no infringement possible with the compensation weight 22. Regarding longitudinal tension forces, the specific weight of the cable 40 is preferably slightly higher than the one of sea water, preferably in an order of magnitude of 20%. The specific weight is preferably not lower than the one of sea water to ensure an appropriate sag.

[0070] Fig. 2 relates to a similar embodiment as shown in Fig. 1. Similar to Fig. 1, a tower 1 with a wind turbine 2 is mounted to the floating platform 10 to achieve a positioning of the wind turbine which allows harvesting of wind energy. This embodiment is preferably used at water depths > 400m. The delta length of the rope 21 between low wind and strong wind increases proportionally with the water depth and is, for example, 166m at 400m water depth and a strong wind angle of 45°. This delta length is acting in relation to the length of the cantilever beam 25 regarding the wind strength dependent positioning of the compensation weight 22. A too big ratio of these lengths makes this more and more difficult. To overcome this, a lifting block 30 may be put between the compensation weight 22 and the distal end 26 of the cantilever beam

[0071] 25 in order to reduce the delta length between the compensation weight 22 and the distal end

[0072] 26 of the cantilever beam 25 by the ratio of the lifting block 30. The bigger the water depth is, the bigger the ratio of the lifting block 30 is chosen. However, the tension force of the rope 21 is reduced by the ratio of the lifting block 30. The tension of the rope 21 is required regarding the counter force for the wind force 5 acting on the turbine 2. This would require increasing the compensation weight 22 by the factor of the lifting block, what would be in contradiction to function of the weight 22 of generating an appropriate counter torque to keep the tower 1 in a substantially upright position. This conflict of objectives is solved by splitting the common rope 21 with the help of a rope splitter 36 into the rope acting on the lifting block and an auxiliary rope 32 being preferably connected to an additional tension weight 31. Said auxiliary rope 32 is preferably connected to the additional tension weight 31 over auxiliary pulleys 35, preferably one at the distal end 26 of the cantilever beam 25 and one preferably at the proximal end 24 of the cantilever beam 25 in order to avoid tangling. The additional tension weight 31 is working preferably in a vertical direction resulting in a constant force in the magnitude of its weight force to the common rope 21. The size and / or mass of the additional weight 31 is preferably dimensioned in a manner that supplements the lacking force coming from the rope 21. A person skilled in the art will be able to tune the variety of parameters as appropriate based on a respective set influencing factors.

[0073] Fig. 3 shows an alternate embodiment of the present invention using an additional pulley at the compensation weight 22 and a stopper.

[0074] Fig. 4 shows an example for a preferred embodiment of a ground anchor 50, in this case a gravity anchor. The ground anchor 50 serves to fix the floating platform 10 to the seabed 100 and preferably to connect the cable 40 with a backbone power grid 45. The ground anchor 50 must be able to provide the counterforce to the force coming from the rope 21. The force vector of the rope 21 can be between an angle of 0°, meaning vertical and an angle of around 55° against the vertical axis, whereby any horizontal angle is possible. The grounding mass of the gravity-based ground anchor 50 is preferably a sufficient multiple of the highest expectable forces coming from the rope 21 to make sure it cannot be dislocated. The cable 40 is preferably guided along the rope 21 with the help of cable fixing elements 43. If the rope 21 is made of synthetical material, it has a higher expansion coefficient compared to the cable 40 which has a core of metal. To overcome this, the cable fixing elements 43 are preferably located in a suitable distance and the length of the section of the cable 40 in between is longer or equal compared to the length of the section of the rope 21 in between at maximum tension. A person skilled in the art will be able to define a suitable distance between the cable fixing elements 43 based on a variety of parameters like the bending behaviour of the cable 40, the expansion coefficient of the rope 21 or the characteristics of the cable fixing elements 43. There can be use cases where it is necessary to have a swivel 52 in order to avoid a twisting of the cable 40 and the rope 21. The cable 40 and the rope 21 are preferably fixed to the swivel 52. The swivel 52 is preferably mechanically fixed to the ground anchor 50 and has preferably sliding contacts to transmit the electrical power from the cable 40 to the seabed fixed backbone power grid 45. The swivel may be turned by an electrical servo motor which is preferably supplied and controlled over additional cable cores in the cable 40. The mechanical stresses to the bearing of the swivel 52 can be expected to be only a fraction compared to a swivel between a tower 1 and a wind turbine 2 which is necessary in the case of a non self-aligned floating platform 10. In this case with the swivel between the tower and the wind turbine, the swivel may bear the many hundred tons weight of the wind turbine and in addition all dynamic loads and torques caused by the wind, the wind blasts and the movements of the platform caused by the waves of the water surface 100 whereas the bearing of the swivel 52 of the ground anchor 50 has to bear the quite uniform forces coming from the rope 21 which are expected to be in an order of magnitude below 2MN.

[0075] Gravity-based ground anchors require medium to hard soil conditions. Where this is not the case, other anchoring solutions like suction piles can be used. The working principles of the ground anchor 50 as described above will not be substantially affected.

[0076] List of reference signs

[0077] 1 tower

[0078] 2 wind turbine

[0079] 5 wind force arrow (size is increasing with the wind force)

[0080] 10 floating platform

[0081] 11 floating element

[0082] 21 rope, mooring rope, chain, steel cable

[0083] 22 weight, compensation weight

[0084] 24 proximal end

[0085] 25 cantilever beam

[0086] 26 distal end

[0087] 27 deflection means, pulley

[0088] 28 fixing point of the auxiliary rope

[0089] 30 lifting block, pulley block, hoist, pulley block mechanism

[0090] 31 additional tension weight

[0091] 32 auxiliary rope

[0092] 33 direct mounting rope

[0093] 34 direct fixing rope

[0094] 35 auxiliary pulley 36 rope splitter

[0095] 37 common rope

[0096] 38 stopper

[0097] 39 pulley

[0098] 40 cable

[0099] 41 cable branch point

[0100] 42 cable fixing point

[0101] 43 cable fixing element

[0102] 45 backbone power grid

[0103] 50 ground anchor

[0104] 52 swivel

[0105] 70 roll compensation torque

[0106] 71 wind induced torque

[0107] 72 biasing weight

[0108] 100 water surface

[0109] 101 seabed

[0110] 120 pitch angle

[0111] 130 torque effected by the wind force

[0112] 131 torque effected by the compensation weight

Claims

Claims1. A floating platform (10) for supporting a tower (1) with a wind turbine (2) for harnessing wind energy, the floating platform (10) comprising: a floating element (11); an adaptive mooring system for different wind speeds, said adaptive supporting system comprising: a mooring rope (21) coupled to the floating platform (10) and configured for fixing said mooring rope (21) via a ground anchor (50) to the ground (101), a cantilever beam (25) with a proximal end (24) attached to the floating platform (10) and a distal end (26), the mooring rope (21) being coupled to the distal end (26); a weight (22) coupled to said mooring rope (21), wherein the weight (22) achieves that i. the floating platform (10) is positioned substantially vertically above the ground anchor (50) if no wind acts on the wind turbine (2); and ii. the floating platform (10) is positioned as further away from the anchor (50) as the force of the wind acting on the wind turbine (2) increases.

2. The floating platform of claim 1, wherein a variable position of the weight (22) with respect to a longitudinal direction of the cantilever beam (25) supports a compensation of forces from the wind acting on the wind turbine (2) such that the orientation of the tower (1) is substantially vertical.

3. The floating platform of claim 1 or 2, wherein a first end of the mooring rope (21) is configured to be fixed to the ground anchor (50), and a second end of the mooring rope (21) is fixed to the floating platform (10) in the vicinity of the tower (1),ii) fixed to the weight (22), iii) fixed to a lifting block / pulley block (30) connected between the weight (22) and the distal end (26) of the cantilever beam (25), or iv) wherein said mooring rope (21) is guided between the first end and the second end by a deflection means (27), preferably a pulley, mounted next to the distal end (26) of the cantilever beam (25).

4. The floating platform according to claim 3, option ii), wherein said weight (22) is fixed to the floating platform (10) by a direct mounting rope (33), wherein a first end of the direct mounting rope (33) being preferably fixed to the floating platform (10) in the vicinity of the tower (1) and the other end of the direct mounting rope (33) being fixed to the weight (22).

5. The floating platform according to claim 3, option i), wherein the weight (22) is coupled slidably to the mooring rope (21), preferably via a pulley (39), wherein an optional stopper (38) fixed to the mooring rope (21) between the end of the mooring rope (21) fixed to the floating platform and the weight (22) achieves that the weight (22) can be located below the cantilever beam (25) distally from a middle position of the cantilever beam (15).

6. The floating platform according to claim 5, further comprising a direct mounting rope (33), wherein a first end of the direct mounting rope (33) being fixed to the floating platform (10) in the vicinity of the tower (1) and the other end of the direct mounting rope (33) being fixed to the weight (22), which achieves that the weight (22) can be located below the cantilever beam (25) proximal from a middle position of the cantilever beam (15).

7. The floating platform according to any of the preceding claims, wherein a first end of an auxiliary rope (32) is fixed to the mooring rope (21) at a position distally from the distal end (26), preferably at a branch point / rope splitter, and the second end of the auxiliaryrope (32) is fixed to an additional tension weight (31) whose movement is primarily in a vertical direction.

8. The floating platform according to claim 7, wherein the auxiliary rope (32) acts on the mooring rope (21) in such a way that the mooring rope (21) is under additional tension between the splitter (36) and the ground anchor (50).

9. The floating platform according to claim 7, wherein the auxiliary rope (32) is guided by one or more auxiliary pulleys (34) where at least one of the auxiliary pulleys (34) is mounted in the vicinity of the distal end (26) of the cantilever beam (25).

10. The floating platform according to claim 7 or 8, wherein the thickness of the mooring rope (21) is larger than the thickness of the auxiliary rope (32).

11. The floating platform according to any of the preceding claims, wherein the position of the weight (22) with respect to the cantilever beam (25) is set / determined by an actual length of the mooring rope (21) between the distal end (26) of the cantilever beam (25) and the ground anchor (50), wherein the actual length of the mooring rope (21) changes dynamically based on the actual wind speed.

12. The floating platform according to any of the preceding claims, wherein an angle between a horizontal surface of the sea and a linear fit of the mooring rope (21) is between 0° and 10° at no wind or light wind and preferably between 35° and 55° at high wind speed.

13. The floating platform according to any of the preceding claims, wherein the position of the weight (22) regulates the actual length of the mooring rope (21) between the distal end (26) of the cantilever beam (25) and the ground anchor (40).

14. The floating platform according to any of the preceding claims, wherein a. the vertical projection of the movement of the weight (22) to a plane parallel and below the horizonal sea level forms a straight line which is substantially below the cantilever beam (25); orb. the vertical projection of the movement of the weight (22) to a plane parallel and below the horizonal sea level forms a straight line which is angled by an angle between 5° and 40°; preferably between 5° and 30°, preferably between 5° and 20°, preferably between 10° and 20° with respect to the cantilever beam, wherein said angled orientation results in a compensation of a roll movement which is preferably based on the rotation of the wind turbine and / or a biasing weight (72) which is preferably provided for compensation of a roll movement of the platform due to the rotation of the wind turbine.

15. The floating platform according claim 14, wherein the cantilever beam (25) extends along an X-axis and defines together with a perpendicular Y-axis the water surface or a surface parallel to the water surface, wherein a biasing weight (72) or a center of gravity (72) of the platform (72) is offset along the Y-axis, wherein the projected movement of the weight (22) is located in the XY-plane with Y-coordinates with a different sign.

16. The floating platform according to any of the preceding claims, wherein a power cable (40), for transporting the generated power, is provided between the floating platform (10) and the ground (101), said power cable (40) being guided along the rope (21) and being so long such that there is always sufficient slack of the power cable (40), wherein the cable (40) is preferably longer than the rope (21).

17. The floating platform according to any of the preceding claims, wherein mooring the floating platform via the single rope (21) ensures that the front face of a wind turbine (2) mounted on the floating platform is always directed against the wind direction, even wind direction changes.

18. The floating platform according to any of the preceding claims, wherein the mooring rope (21) is a steel chain, steel cable or a synthetic rope or a composite of a steel cable and a synthetic rope.

19. A floating offshore wind power installation with a floating platform according to any of the preceding claims, further comprising a tower (1) with a wind turbine (2).

20. The floating offshore wind power installation according to claim 19, where the power installation comprises a control unit configured to adjust the work angle of the individual rotor blades to the wind turbine, to reduce the maximum force acting on the upper port of the tower such that the mooring rope (21) and optionally the auxiliary rope (32) is / are limited to a working range is not running into their respective mechanical limiting stop.

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