Floating structures and mooring systems for offshore wind turbines
The described mooring system with inclined tendons and multiple seabed anchors addresses the issues of motion and cost in offshore wind turbines, enhancing stability and energy output while reducing expenses.
Patent Information
- Application Number
- JP2025533632
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-22
- Filing Date
- 2023-12-15
- Publication Date
- 2025-12-11
AI Technical Summary
Existing offshore wind turbine mooring systems, particularly tension leg platforms, suffer from structural motions that reduce energy production and are costly due to the need for extensive support structures or complex floating systems.
A mooring system using inclined tendons with varying connection points and angles, anchored by multiple anchors on the seabed, providing stability with a limited number of tendons made of high-strength materials, ensuring reduced motion and cost-effectiveness.
The system achieves enhanced stability and reduced motion, thereby improving energy production and lowering installation costs for offshore wind turbines.
Smart Images
Figure 2025540350000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a floating structure for an offshore wind turbine, more precisely to the subsea configuration and mooring of the floating structure on the seabed. [Background technology]
[0002] For the installation of offshore wind units, which comprise a turbine and a support connected to the seabed, it is well known to use a support structure, such as a jacket structure. Such a support structure rests on the seabed and is fixed to the ground using anchoring devices. The support structure extends above the sea surface to accommodate the wind turbine mast. Generally, this support structure is made in one piece, and the greater the depth, the higher the support structure must be. However, this solution is expensive.
[0003] Another solution for installing offshore wind units is to use floating structures moored to the seabed with mooring lines. This solution requires the use of floating technology. The structure of a floating offshore wind unit is as follows: a turbine corresponding to a rotor nacelle assembly (RNA) comprising blades, a hub and nacelle, and a tower; a floating substructure corresponding to the floating structure supporting the turbine; a station keeping system corresponding to the mooring lines and anchors, allowing the system to remain in place; It can be subdivided as follows:
[0004] The different types of floating substructures can be distributed in different families, for example barges, semi-submersibles, spars, tension leg platforms (TLP) or keels. The particularity of the tension leg platform system (TLP) is that the station keeping system (SKS) with mooring lines and anchors not only prevents structural drift but also ensures the stability of the floating structure by tensioning the mooring lines, also called tendons.
[0005] Tension leg platform systems are already known from offshore oil and gas operations, and tension leg platform systems used in oil and gas operations all include one or more tendon bundles that remain in a vertical position when static. With the tendons in a vertical configuration, the platform always remains in a vertical position (i.e., there is no pitch or roll movement).
[0006] However, even though tension leg platform systems reduce the motion of the floating structure compared to other mooring systems, motions can still be observed, and these motions reduce the performance and energy production of the offshore wind unit compared to moorings with supports connected to the seabed. Summary of the Invention [Problem to be solved by the invention]
[0007] One object of the invention is to provide an improved, inexpensive mooring system for offshore wind turbines. [Means for solving the problem]
[0008] To this end, the invention relates to a floating structure comprising a tensioned mooring system, which is intended to moor and stabilize the floating structure to the seabed, preferably for an offshore wind turbine, The tension mooring system comprises at least three independent anchors arranged on the seabed and at least two tendons connected to the floating structure for each anchor, the tendons of the same anchor having different connection points with the floating structure, such that each tendon of the same anchor is inclined at an angle of 30° to 60° with respect to an imaginary vertical axis centered on the anchor, and the connection points of the tendons on the floating structure are arranged on an inner imaginary circle; The tendons are made of a material with a Young's modulus of 50 GPa or more. The tendons are attached to anchors at anchorage points located on an outer imaginary circle that is coaxial with the inner imaginary circle and has a diameter greater than or equal to the inner imaginary circle.
[0009] Two adjacent tendons of two adjacent anchors may have a common joint point on the floating structure.
[0010] Two tendons of the same anchor can have the same inclination with a virtual vertical imaginary axis centered on the anchor's mooring point.
[0011] Two tendons of the same anchor can have an angle of up to 45° relative to each other.
[0012] The anchoring points may have a regular distribution on the outer imaginary circle.
[0013] The tendon joint points on the floating structure may have a regular distribution on the inner imaginary circle.
[0014] The anchor may be permanently sealed to the seabed.
[0015] The present invention also relates to a method for installing a floating structure, preferably for an offshore wind turbine, said method comprising the steps of: Placing at least three anchors on the seabed and attaching at least two tendons to each anchor on dedicated mooring points, the mooring points being arranged on an outer imaginary circle; towing the floating structure at a location above an anchor location; - connecting tendons to the floating structure at dedicated connection points and tensioning said tendons, said connection points being located on an inner imaginary circle that is coaxial with and has a diameter smaller than or equal to the outer imaginary circle; Includes:
[0016] Regarding the installation method, two adjacent tendons of two adjacent anchors can have a common connection point with the floating structure.
[0017] Regarding the installation method, the joint points of tendons of the same anchor can be arranged on the floating structure so that the two tendons of the same anchor have the same inclination with respect to an imaginary vertical axis centered on the mooring point of the anchor.
[0018] Regarding the installation method, two tendons of the same anchor can have an angle of up to 45° relative to each other after connection on the floating structure.
[0019] Regarding the installation method, the anchoring points can be arranged in a regular distribution on an outer imaginary circle.
[0020] Regarding the installation method, the tendon joint points on the floating structure can be arranged in a regular distribution on the inner imaginary circle.
[0021] With regard to the installation method, the anchor may be permanently sealed onto the seabed during the step of placing the anchor on the seabed. [Brief explanation of the drawings]
[0022] Further characteristics and advantages of the invention will become apparent from the following description, given by way of non-limiting example with reference to the accompanying drawings, in which:
[0023] [Figure 1] 1 is a side view of a schematic diagram of an offshore wind unit according to a first embodiment of the present invention; FIG. [Figure 2]FIG. 2 is a top view of the schematic diagram of the offshore wind unit of FIG. 1. [Figure 3] FIG. 10 is a top view of a schematic diagram of an offshore wind unit according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a top view of a schematic diagram of an offshore wind unit according to a third embodiment of the present invention.
[0024] In these figures, like elements have like reference numerals. The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference pertains to the same embodiment or that a feature applies only to a single embodiment. Individual features of different embodiments can be combined or interchanged to provide other embodiments. DETAILED DESCRIPTION OF THE INVENTION
[0025] 1 shows a floating structure 3, which can be designed to receive wind turbines 4 or other structures such as, for example, electrical substations for wind farms. The floating structure 3 comprises a tension mooring system 5 intended to moor and stabilize the floating structure 3 to the seabed Sb. The floating structure 3 preferably floats between two bodies of water below the sea surface Sl.
[0026] The tension mooring system 5 comprises at least three independent anchors 53 placed on the seabed Sb and at least two tendons 52 connected to the floating structure 3 for each anchor 53. Each tendon 52 of the same anchor 53 has a different connection point 31 with the floating structure 3. This configuration causes the tendons 52 of the same anchor 53 to be inclined about an imaginary vertical axis C centered on the anchor 32. This inclination is comprised between 30° and 60° in order to constrain all degrees of freedom of the floating structure 3.
[0027] The tendons 52 connect the junction points 31 to mooring points 51 on the anchors 53, which are preferably points passing through the vertical axis C. In addition, in order to constrain all degrees of freedom of the floating structure 3, the tendons 52 have a Young's modulus of 50 GPa or more. The tendons 52 can then be made from rigid materials such as steel, highly elastic synthetic materials such as HMPE (High Modulus Polyethylene), aramid, or carbon, either alone or in combination with these materials.
[0028] The anchors 53 may be, for example, steel piles driven into the seabed, drilled dans grouted piles driven into the seabed, or other means used in the area of offshore wind turbines, such as, for example, suction buckets. Preferably, the anchors 53 are permanently sealed onto the seabed Sb to ensure stability and mooring of the floating structure 3.
[0029] As shown in Figure 2, the connection points 31 of the tendons 52 on the floating structure 3 are located on an inner imaginary circle A. The center of this inner imaginary circle A is preferably the relative center of the floating structure 3, where it is intended to place, for example, the mast of the turbine 4.
[0030] Tendons 52 are attached to anchors 53 at anchorage points 51. These anchorage points 51 are located on an outer imaginary circle B that is coaxial with the inner imaginary circle A. The diameter of the outer imaginary circle B may be larger than (see Figure 2) or equal to (see Figure 3) the diameter of the inner imaginary circle A.
[0031] This mooring arrangement provides excellent stability for the floating structure 3, especially with regard to pitch or roll movements of the floating structure 3. Furthermore, by using a limited number of tendons 52, costs remain controlled and reduced.
[0032] If the outer imaginary circle B has a larger diameter than the inner imaginary circle A, as shown in Figure 2, the tendons 52 are directed laterally downward and outward from their junction points 31 as they descend towards their mooring points 51, and also directed outward from a vertical line below the floating structure 3 as they descend towards their mooring points 51. This configuration is particularly advantageous for further increasing the stability of the floating structure.
[0033] If the outer imaginary circle B and the inner imaginary circle A have equal diameters, then the tendons 52 will be directed downward and laterally (along the imaginary cylinder associated with the imaginary circles A, B) below their junction points 31 as they descend towards their anchoring points 51, as shown in FIG.
[0034] The diameter of the outer imaginary circle B is calculated to be the optimum between the inclination angle, the tension and the length of the tendon 52. This configuration allows the cost to be reduced by limiting the length of the tendon 52.
[0035] Two adjacent tendons 52 of two adjacent anchors 53 may have a common connection point 31 with the floating structure 3. A common connection point 31 means that the connection points 31 of these adjacent tendons 52 of two adjacent anchors 53 are located in the same area of the floating structure 3, separated by a minimum distance imposed by assembly constraints.
[0036] The two tendons 52 of the same anchor 53 may have the same inclination with respect to an imaginary vertical axis C centered on the mooring point 51 of the anchor 53, as shown in Figure 1. This allows the tension balance between these tendons 52 and the entire floating structure 3. The anchor 53 is then placed on the seabed equidistant from two adjacent joint points 31 to which these two tendons 52 are attached.
[0037] In order for the entire floating structure 3 to have excellent stability, the mooring points 51 of the tendons 52 and anchors 53 preferably have a regular distribution on the outer imaginary circle B as shown in FIGS.
[0038] In addition, in order to ensure that the entire floating structure 3 has excellent stability, the joint points 31 of the tendons 52 on the floating structure 3 preferably have a regular distribution on the inner imaginary circle A.
[0039] In the example of Figures 1 to 3, the floating structure 3 has a triangular shape and comprises only three joints 31 and, consequently, three anchors 53. It is also possible to imagine floating structures 3 having different shapes, with more joints 31, more anchors 53 and more tendons 52. Figure 4, for example, shows a square floating structure 3, with four joints 31 and four anchors 53 at each corner of the square. Other shapes are also possible.
[0040] The present invention also relates to a method for installing a floating structure 3 designed to receive a wind turbine 4 .
[0041] The installation method comprises a first step of placing at least three anchors 53 on the seabed Sb and attaching at least two tendons 52 to each anchor 53 on a dedicated mooring point 51. As mentioned above, the mooring points 51 are located on the outer imaginary circle B. As mentioned above, the center of the outer imaginary circle B is preferably the relative center of the floating structure 3, where, for example, the mast of the turbine 4 is located. If the tendons 52 are, for example, metal chains or metal cables, they can be placed directly on the seabed Sb while waiting for the next step of the installation method. If the tendons 52 are, for example, synthetic cables, underwater buoys can be used to prevent the tendons 52 from being placed directly on the seabed Sb while waiting for the next step of the installation method.
[0042] During this first step of placing the anchor 53 on the seabed Sb, the anchor 53 is advantageously permanently sealed onto the seabed Sb.
[0043] Still during this first step, anchors 53 may be placed so that the mooring points 51 are arranged in a regular distribution on the outer imaginary circle B.
[0044] The installation method includes a second step of towing the floating structure 3 in place above the location of the anchors 51 .
[0045] The installation method includes a third step of connecting the tendons 52 to the floating structure 3 on their dedicated connection points 31. As mentioned above, the connection points 31 are located on an inner imaginary circle A that is coaxial with the outer imaginary circle B. The inner imaginary circle A has a diameter smaller than or equal to the outer imaginary circle B.
[0046] During this third step, the tendon 52 is also tensioned. Various methods for tensioning the tendon 52 are possible.
[0047] A first method may be to first connect the tendons 52 to the floating body structure 3 at their joints 31 and then tension the tendons 52 by known means.
[0048] A second method may be to submerge the floating structure 3, e.g., with ballast, to a first depth in order to connect the tendons 52. After the tendons 52 have been connected, the floating structure 3 is raised to a shallower depth, e.g., by emptying the ballast and tensioning the tendons 52.
[0049] During this third step, two adjacent tendons 52 of two adjacent anchors 53 may have a common connection point 31 with the floating structure 3. The connection points 31 of the tendons 52 of the same anchor 53 may be arranged on the floating structure 3 so that the two tendons 52 of the same anchor 53 have the same inclination with respect to an imaginary vertical virtual axis C centered on the mooring point 51 of the anchor.
[0050] Still during this third step, two tendons 52 of the same anchor 53 may be arranged so that they have an angle of up to 45° relative to each other after connection on the floating structure 3. The joint points 31 of the tendons 52 on the floating structure 3 may also be arranged in a regular distribution on the inner imaginary circle A.
Claims
1. A floating structure (3) comprising a tension mooring system (5), said tension mooring system (5) intended to moor and stabilize said floating structure (3) to a seabed (Sb), preferably for an offshore wind turbine, the tension mooring system (5) comprises at least three independent anchors (53) arranged on the seabed (Sb) and at least two tendons (52) connected to the floating structure (3) for each anchor (53), wherein each tendon (52) of the same anchor (53) has a different connection point (31) with the floating structure (3), so that the tendons (52) of the same anchor (53) are inclined at an angle of 30° to 60° with respect to an imaginary vertical axis (C) centered on the anchor (53), and the connection points (31) of the tendons (52) on the floating structure (3) are arranged on an inner imaginary circle (A); The tendon (52) is made of a material having a Young's modulus of 50 GPa or more; The tendon (52) is attached to the anchor (53) on the mooring point (51) located on an outer imaginary circle (B) that is coaxial with the inner imaginary circle (A) and has a diameter greater than or equal to the inner imaginary circle (A).
2. 2. The floating structure (3) according to claim 1, wherein two adjacent tendons (52) of two adjacent anchors (53) have a common joint point (31) on the floating structure (3).
3. 3. The floating structure (3) according to claim 1 or 2, wherein the two tendons (52) of the same anchor (53) have the same inclination with respect to the imaginary vertical axis (C) centered on the mooring point (51) of the anchor (53).
4. The floating structure (3) according to any one of claims 1 to 3, wherein the mooring points (51) have a regular distribution on the outer imaginary circle (B).
5. The floating structure (3) according to any one of claims 1 to 4, wherein the connection points (31) of the tendons (52) on the floating structure (3) have a regular distribution on the inner virtual circle (A).
6. The floating structure (3) according to any one of claims 1 to 5, wherein the anchor (53) is permanently sealed on the seabed (Sb).
7. A method for installing a floating structure (3) preferably for an offshore wind turbine, said installation method comprising the steps of: - Placing at least three anchors (53) on the seabed (Sb) and attaching at least two tendons (52) to each anchor (53) on dedicated mooring points (51), said mooring points (51) being located on an outer imaginary circle (B); - towing the floating structure (3) at a location above the anchor (51) location; - connecting the tendons (52) to the floating body structure (3) on dedicated joints (31) and tensioning the tendons (52), the joints (31) being located on an inner imaginary circle (A) that is coaxial with the outer imaginary circle (B) and has a diameter smaller than or equal to the outer imaginary circle (B); Including, installation methods.
8. 8. The installation method according to claim 7, wherein two adjacent tendons (52) of two adjacent anchors (53) have a common joint point (31) with the floating structure (3).
9. 9. The installation method according to claim 7 or 8, wherein the joint points (31) of the tendons (52) of the same anchor (53) are arranged on the floating structure (3) so that the two tendons (52) of the same anchor (53) have the same inclination with respect to an imaginary vertical axis (C) centered on the mooring point (51) of the anchor (53).
10. 10. The installation method according to any one of claims 7 to 9, wherein the two tendons (52) of the same anchor (53) have an angle of at most 45° relative to each other after connection to the floating structure (3).
11. The installation method according to any one of claims 7 to 10, wherein said anchoring points (51) are arranged in a regular distribution on said outer imaginary circle (B).
12. The installation method according to any one of claims 7 to 11, wherein the connection points (31) of the tendons (52) on the floating structure (3) are arranged in a regular distribution on the inner imaginary circle (A).
13. The installation method according to any one of claims 7 to 12, wherein the anchor (53) is permanently sealed on the seabed (Sb) during the step of placing the anchor (53) on the seabed (Sb).