Underwater structure for a floating structure of an offshore wind power plant.

Abstract

An offshore wind farm (1) comprising at least four floating structures (3) designed to receive a wind turbine (4), each floating structure (3) comprising at least three mooring cables (5', 5''), each mooring cable (5', 5'') being attached to a mooring point (51, 52, 53) arranged around the floating structure (3), the mooring cables directed inwards from the offshore wind farm (1) forming the inner mooring cables (5') of the offshore wind farm (1), the mooring cables directed outwards from the offshore wind farm (1) forming the peripheral mooring cables (5'') of the offshore wind farm (1), two adjacent floating structures (3) having at least one of their peripheral mooring cables (5'') that cross each other, and at least one of these peripheral mooring cables having a buoyancy element, relates to an offshore wind farm (1).

Description

Technical Field

[0001] The present invention relates to a subsea configuration of a floating structure for an offshore wind power plant. More precisely, the present invention relates to a subsea configuration for a floating structure fixed to the seabed for water depths exceeding 400 m.

Background Art

[0002] At a maximum depth of approximately 60 m, it is well known to use a support structure such as a jacket structure for an offshore wind turbine. Such a support structure is placed on the seabed and fixed to the ground using an anchor device. The support structure extends above the sea surface to receive the wind turbine mast. Generally, this support structure is made of one piece, and the deeper the depth, the higher the support structure must be made.

[0003] At greater depths, for example, depths exceeding 60 m, an offshore wind turbine is generally installed not on a support structure placed on the seabed, but on a floating structure moored to the seabed by mooring cables.

[0004] In an offshore wind farm, the spacing between wind turbines is governed, for example, by yield constraints due to wake effects. Therefore, two adjacent wind turbines are typically separated by 6 to 8 times the turbine rotor diameter, depending on the direction considered. For example, two adjacent wind turbines aligned in the main wind direction can be separated by 8 times the turbine rotor diameter in order to minimize wake effects and so that the wind turbine arranged behind has higher productivity. Two adjacent wind turbines not aligned in the main wind direction can be placed closer to each other, for example, separated by 6 times the turbine rotor diameter, in order to maximize the density of wind turbines in the offshore wind farm. While navigating in deeper waters, for example, waters deeper than 400 m, it is more difficult to maintain such a wind farm layout due to the installation area of the mooring system. In addition to layout constraints, standard mooring configurations in deep sea imply longer mooring cables, which means higher costs. In order to promote the development of offshore wind energy in these areas, cheaper solutions need to be developed, specifically for the subsea array for the mooring configuration.

[0005] Standard mooring configurations typically require a minimum pattern of 1.4× water depth to 1.8× water depth. In deep sea, these mooring installation areas can be adapted by considering the orientation of different floating structures between adjacent wind turbines in order to avoid collisions between mooring cables. However, this results in a very complex and congested layout and requires additional engineering effort due to the different floating structure orientations to be studied. In order to reduce costs, mooring layouts based on interconnected anchors (between adjacent mooring cables) are known. However, this solution cannot be considered in very deep waters where the mooring cables will cross before reaching the optimized location for this interconnected fixed point.

[0006] Solutions for mooring configurations based on common mooring cables have been developed, for example, using a shared fixed point on the seabed, as described in Chinese Patent No. 210653580, or using a shared fixed point on a common floating buoy, as described in Chinese Patent No. 111071400. However, these solutions provide a very low restoring load to the floating structure when the floating structure moves from its equilibrium position due to external loads, and then result in a very high offset. These very high offsets pose problems for the mooring cables themselves and for other equipment connected to the floating structure, such as cables between electrical arrays.

[0007] One object of the present invention is to provide an enhanced and inexpensive mooring configuration for an offshore wind turbine adapted for depths exceeding 400 m and having a narrow installation area.

[0008] For this purpose, the present invention is an offshore wind power plant comprising at least four floating structures designed to receive a wind turbine, each floating structure comprising at least three mooring cables, each mooring cable being attached to a mooring point disposed around the floating structure, the mooring cables directed inward from the offshore wind power plant forming inner mooring cables of the offshore wind power plant, and the mooring cables directed outward from the offshore wind power plant forming peripheral mooring cables of the offshore wind power plant. Two adjacent floating structures have at least one of the peripheral mooring cables of the floating structures that cross each other, and at least one of these peripheral mooring cables comprises a buoyancy element, relating to an offshore wind power plant.

[0009] Only one of the intersecting peripheral mooring cables may comprise a buoyancy element to pass above the other peripheral mooring cables.

[0010] The intersecting peripheral mooring cables may have a common junction point above the seabed, the buoyancy element being a peripheral underwater buoy moored to the seabed, the common junction point being attached to the peripheral underwater buoy, and this peripheral underwater buoy comprising at least one additional mooring cable connecting the peripheral underwater buoy to a mooring point on the seabed.

[0011] The peripheral subsea buoy may comprise two additional mooring lines, each additional mooring line being aligned with a peripheral mooring line attached to the peripheral subsea buoy.

[0012] Three adjacent floating structures may have at least one of the inner mooring lines of the floating structures having a common junction point above the seabed, the common junction point being attached to a subsea buoy moored to the seabed.

[0013] The attachment point of the mooring line to the subsea buoy may be arranged below the subsea buoy.

[0014] The subsea buoy is moored to the seabed using a flexible tether and may have a height limited by the seabed.

[0015] The subsea buoy may be arranged at least 50 m above the seabed.

[0016] The floating structures may be arranged such that the mooring lines form a hexagonal pattern.

[0017] At least one peripheral mooring line - has a first segment that may be attached to the floating structure, - has a second segment that may be attached to the seabed, - and has at least one intermediate segment formed of an elastomeric material and attached to the first segment.

[0018] The intermediate segment of the peripheral mooring line can provide a maximum elongation exceeding 100% of the remaining length of the intermediate segment, preferably exceeding 300%.

[0019] The intermediate segment may exhibit a minimum breaking strength greater than 18 MPa, preferably greater than 25 MPa.

[0020] The intermediate segment may exhibit a minimum breaking load greater than 400 t, preferably greater than 1200 t.

[0021] The intermediate segment exhibits a creep of less than 20%, preferably less than 10%.

[0022] The intermediate segment may exhibit a cumulative length of less than 40 m, preferably less than 15 m.

[0023] The intermediate segment is the following, namely - natural rubber, - thermoplastic elastomer, - polychloroprene, and - hydrogenated nitrile butadiene rubber, and may be made of a single material selected from these.

[0024] The intermediate segment may be directly connected to the surrounding underwater buoy.

Brief Description of the Drawings

[0025] Further features and advantages of the present invention will become apparent from the following description given as a non-limiting example with reference to the accompanying drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0026] In these figures, the same elements are given the same reference numerals. The following implementation forms are examples. This specification refers to one or more embodiments, but this does not mean that each reference relates to the same embodiment or that the features apply only to a single embodiment. The individual features of different embodiments can also be combined or exchanged to provide other embodiments.

Embodiments for Carrying Out the Invention

[0027] FIG. 1 shows an offshore wind farm 1 comprising at least three floating structures 3 each designed to receive a wind turbine 4. Each floating structure 3 comprises at least three mooring cables 5', 5'' for mooring the floating structure 3 to the seabed. Each mooring cable 5 is attached to mooring points 51, 52 arranged around the floating structure 3. The mooring cables 5', 5'' can be arranged in a "Y" shape around the floating structure 3 to maintain the floating structure 3 in any direction on the sea surface (see FIG. 2). The lengths of the mooring cables 5', 5'' depend on the inclination of the mooring cables and the water depth.

[0028] The mooring cables directed inward from the offshore wind farm 1 (towards the center or inside of the wind farm defined by the surrounding floating structures 3) form the inner mooring cables 5' of the offshore wind farm 1, and the mooring cables directed outward from the offshore wind farm 1 (directed outside the wind farm) form the peripheral mooring cables 5'' of the offshore wind farm 1.

[0029] The mooring cables 5', 5'' can be made of fiber ropes or metal cables made of metal strands. Specifically, these fiber ropes can be made of polymer fibers such as polyester, nylon, or polyolefins such as polypropylene or polyethylene.

[0030] As shown in Fig. 1, at least one of the inner mooring cables 5' having a common joint 51 above the seabed Sb is shared among three adjacent floating structures 3. This common joint 51 is attached to a submerged buoy 7 moored to the seabed Sb. The fact that adjacent floating structures 3 have a common joint 51 attached to the submerged buoy 7 makes it possible to bring the adjacent floating structures 3 closer to each other. Therefore, as shown in Fig. 2, the floating structures 3 and the wind turbines 4 can be optimally separated by a distance D1, for example, about eight times the turbine rotor diameter of two floating structures 3 aligned in the main wind direction W. This distance D1 makes it possible to minimize the wake effect and enables the wind turbine 4 arranged behind to have higher productivity. Two adjacent floating structures 3 not aligned in the main wind direction W can be separated by a distance D2, for example, about six times the turbine rotor diameter, in order to maximize the density of the wind turbines 4 in the offshore wind farm 1.

[0031] Due to these distances D1 and D2 between the floating structures 3, the common joint 51 can be the point where the inner mooring cables 5' would cross each other. The depth of the submerged buoy 7 can be determined by the common joint 51 where the inner mooring cables 5' would cross each other. Therefore, the installation area of the offshore wind farm 1 becomes narrow due to its mooring configuration. Using the submerged buoy 7 requires only one mooring point instead of three mooring points on the seabed. The length of the inner mooring cable 5' attached to the submerged buoy 7 is also shortened, which makes it possible to reduce costs. This is particularly advantageous for an offshore wind farm 1 installed at a water depth of more than 400 m, for example.

[0032] The submerged buoy 7 is preferably an isobaric buoy. An isobaric buoy makes it possible to reduce the external load on the buoy installed at the final depth. An isobaric buoy means a buoy in which the internal pressure of the buoy is equal to the external pressure of the buoy, here the pressure at the depth where the buoy is located.

[0033] To minimize the constraints imposed on the subsea buoy 7, the attachment point of the inner mooring cable 5' to the subsea buoy 7 can be located below the subsea buoy 7. Therefore, the subsea buoy 7 does not need to be sized up to the minimum breaking load of the inner mooring cable 5'.

[0034] Preferably, the subsea buoy 7 is moored to the seabed Sb using a flexible tether 71 and has a height restricted by the seabed Sb. This flexible tether 71 can be any means known to those skilled in the art. For example, the subsea buoy 7 can be moored by at least one cable or chain.

[0035] Since this mooring configuration is preferably dedicated to water depths exceeding 400 m, the subsea buoy 7 is preferably located at least 50 m above the seabed Sb. More specifically, the subsea buoy 7 is preferably located at the maximum depth of 85% of the water depth. Therefore, the flexible tether 71 has a length of at least 15% of the water depth. For example, in the case of a water depth of 600 m, the subsea buoy 7 can be located at a depth of at least 500 m using a 100 m flexible tether 71.

[0036] As shown in FIGS. 1 and 2, the peripheral mooring cables 5'' are directly moored to the seabed Sb. More specifically, the peripheral mooring cables 5'' are arranged without intersecting each other and are directly moored to the seabed Sb at the mooring points 52. The peripheral mooring cables 5'' can be moored to the seabed Sb by any means known to those skilled in the art. The fact that the peripheral mooring cables 5'' are directly moored to the seabed Sb generally makes it possible to limit the lateral movement of the offshore wind farm 1, and more specifically, the array of floating structures 3.

[0037] FIG. 3 shows an offshore wind farm 1 having at least four floating structures 3. In this particular embodiment, at least one of the peripheral mooring cables 5'' of two adjacent floating structures 3 intersects each other. At least one of these peripheral mooring cables includes a buoyancy element.

[0038] According to a first embodiment not shown, only one of the intersecting peripheral mooring cables 5’’ is provided with a buoyancy element in order to pass above the other peripheral mooring cables 5’’ without contacting each other. This buoyancy element may be associated with an increase in the anchor radius. This buoyancy element can be a sleeve surrounding a portion of the peripheral mooring cable 5’’. This buoyancy element can also be directly incorporated into a portion of the peripheral mooring cable 5’’. Preferably, these two peripheral mooring cables 5’’ intersect each other at a distance of at least about 20 m.

[0039] According to a second embodiment shown in FIGS. 3 and 4, two intersecting peripheral mooring cables 5’’ have a common joint 53 above the seabed Sb. The buoyancy element can here be a peripheral subsea buoy 7’ moored to the seabed Sb, to which the common joint 53 is attached. This peripheral subsea buoy 7’ can comprise a tether 71’ (seen in FIG. 4) moored to the seabed Sb and at least one additional mooring cable 5’’’ connecting the peripheral subsea buoy 7’ to a mooring point 54 on the seabed Sb.

[0040] The additional mooring cable 5’’’ can be made of a fiber rope or a metal cable made of metal strands. Specifically, these fiber ropes can be made of polymer fibers such as polyester, nylon, or polyolefins such as polypropylene or polyethylene.

[0041] The common joint 53 can be the point at which the peripheral mooring cables 5’’ would intersect each other. The depth of the peripheral subsea buoy 7’ can be determined by the common joint 53 at which the peripheral mooring cables 5’’ would intersect each other. The length of the peripheral mooring cable 5’’ attached to the peripheral subsea buoy 7’ is also shortened, which enables cost reduction. This is particularly advantageous for an offshore wind farm 1 installed at a water depth deeper than, for example, 400 m.

[0042] Therefore, the installation area of the offshore wind farm 1 with the mooring configuration according to either the first embodiment or the second embodiment becomes narrower.

[0043] The peripheral underwater buoy 7' is preferably an isobaric buoy. An isobaric buoy makes it possible to reduce the external load on the buoy when it is installed at its final depth.

[0044] To minimize the constraints applied to the peripheral underwater buoy 7', the attachment points of the peripheral mooring cable 5'' and the additional mooring cable 5''' to the peripheral underwater buoy 7' can be arranged below the peripheral underwater buoy 7'. Therefore, the peripheral underwater buoy 7' does not need to be sized up to the minimum breaking load of the peripheral mooring cable 5''.

[0045] Preferably, the peripheral underwater buoy 7' is moored to the seabed Sb using a flexible tether 71' and has a height restricted by the seabed Sb. This flexible tether 71' can be any means known to those skilled in the art. For example, the peripheral underwater buoy 7' can be moored by at least one cable or chain.

[0046] Since this mooring configuration is preferably for water depths exceeding 400 m, the peripheral underwater buoy 7' is preferably arranged at least 50 m above the seabed Sb. More specifically, the peripheral underwater buoy 7' is preferably arranged at a maximum depth of 85% of the water depth. Therefore, the flexible tether 71' has a length of at least 15% of the water depth. For example, in the case of a water depth of 600 m, the peripheral underwater buoy 7' can be arranged at a depth of at least 500 m using a 100 m flexible tether 71'.

[0047] As shown in FIGS. 3 and 4, the peripheral underwater buoy 7' is provided with two additional mooring cables 5'''. Each additional mooring cable 5''' is preferably aligned with the peripheral mooring cable 5'' attached to the peripheral underwater buoy 7'.

[0048] As shown in FIG. 3, the floating structure 3 is preferably arranged such that the mooring cables 5', 5'' form a hexagonal pattern. In the embodiment illustrated in FIG. 3, the offshore wind farm 1 has four floating structures 3. The first tip is the floating structure 3, the two side points are the two joints 51 and 53 connected to the floating structure 3 at the first tip, and the joints 51 and 53 are attached to the respective underwater buoys 7 and 7', and the two other side points are two floating structures 3 respectively, and the second tip is the joint 53 attached to the peripheral underwater buoy 7'. In the case of a larger offshore power plant 1 having more wind turbines 4 and more floating structures 3, this second tip can also be another common joint 51 attached to the underwater buoy 7. This hexagonal pattern also enables the floating structures 3 and the wind turbines 4 to be optimally separated by a distance D1 of about eight times the turbine rotor diameter of two floating structures 3 aligned, for example, in the main wind direction W. This distance D1 makes it possible to minimize the wake effect and enables the wind turbine 4 arranged behind to have higher productivity. Two adjacent floating structures 3 not aligned in the main wind direction can be separated by a distance D2 equal to, for example, about six times the turbine rotor diameter in order to maximize the density of the wind turbines 4 within the offshore wind farm 1.

[0049] Referring to FIGS. 5 and 6, at least one peripheral mooring cable 5'' can comprise a first segment 22 and at least one intermediate segment 26 attached to the first segment 22.

[0050] The peripheral mooring cable 5'' can also comprise a second segment 24 that can be attached to the seabed Sb via a mooring point 52. The intermediate segment 26 can be arranged between the first segment 22 and the second segment 24.

[0051] In the case of a peripheral mooring cable 5'' having a common joint 53 above the seabed Sb, the second segment 24 or the intermediate segment 26 can be connected to the peripheral underwater buoy 7'.

[0052] As shown in FIG. 5, the first segment 22 can be attached to the floating structure 3.

[0053] The first segment 22 and the second segment 24 thus exhibit a significant rigidity, which is particularly greater than the rigidity of the intermediate segment 26.

[0054] In the embodiment shown in FIGS. 5 and 6, each peripheral mooring cable 5'' comprises a placement portion 30 placed on the seabed Sb and a raised portion 32 away from the seabed Sb.

[0055] However, in a deformed form, the peripheral mooring cable 5'' does not comprise a placement portion 30 on the seabed Sb, especially in the case of tension mooring.

[0056] Each intermediate segment 26 is disposed within the raised portion 32.

[0057] Each intermediate segment 26 is thus away from the seabed Sb, avoiding wear of the intermediate segment 26 due to contact 5 with the seabed Sb.

[0058] The performance of the intermediate segment 26 is not affected by its location in the raised portion 32. However, the intermediate segment 26 is preferably disposed deep enough, especially deeper than 20 m, to avoid UV exposure and limit marine growth. Preferably, the intermediate segment 26 is disposed at a depth in the deep sea, for example, exceeding 100 m.

[0059] In the embodiment shown in FIG. 5, the peripheral mooring cable 5'' comprises a unique intermediate segment 26.

[0060] The intermediate segment 26 extends longitudinally along between two end points.

[0061] The intermediate segment 26 is connected to the first segment 22 via an interface surface 34 at a first end point.

[0062] The intermediate segment 26 can be connected to the second segment 24 or to the peripheral underwater buoy 7' via another interface surface 34 at a second end opposite the first end.

[0063] In the embodiment shown in FIG. 6, the peripheral mooring cable 5'' comprises two intermediate segments 26A, 26B.

[0064] The first intermediate segment 26A is connected to the first segment 22, and the second intermediate segment 26B is connected to the second segment 24.

[0065] A connecting segment 36 is disposed between the first intermediate segment 26A and the second intermediate segment 26B. The connecting segment 36 has the same structure as the first segment 22 and the second segment 24.

[0066] In a variant not shown, the first intermediate segment 26A and the second intermediate segment 26B are directly connected to each other without the presence of the connecting segment 36.

[0067] One skilled in the art will understand that in the variant, the peripheral mooring cable 5'' can comprise three or more intermediate segments 26, for example three or four intermediate segments 26. The connecting segment 36 can be disposed between two intermediate segments 26.

[0068] Each intermediate segment 26 is formed of an elastomeric material. Specifically, the intermediate segment 26 can be made of a single material.

[0069] Accordingly, there are no other materials or mechanical components other than the elastomeric material in the intermediate segment 26. The intermediate segment 26 comprises only the elastomeric material and is disposed between two interface surfaces 34.

[0070] The intermediate segment 26 can preferably respond only to a single traction force applied by the first segment 22 and the second segment 24 in a single traction mode.

[0071] The single material constituting the intermediate segment 26 can be selected from the following, namely, natural rubber, thermoplastic elastomer, polychloroprene and hydrogenated nitrile butadiene rubber.

[0072] Advantageously, each intermediate segment 26 can be a multi-strand wire. Specifically, the intermediate segment 26 can include, for example, about 100 strands of elastomeric material braided together.

[0073] Each intermediate segment 26 can advantageously have a cylindrical shape extending between the first segment 22 and the second segment 24.

[0074] Each intermediate segment 26 can have a cumulative length of less than 40 m, advantageously less than 15 m.

[0075] Each intermediate segment 26 can have a diameter included in the range of 30 cm to 120 cm.

[0076] Each intermediate segment 26 can possibly provide a maximum elongation exceeding 100% of the remaining length of the intermediate segment 26, advantageously exceeding 300%, and even more advantageously exceeding 500%. Typically, each intermediate segment 26 can have a maximum elongation length exceeding 10 m.

[0077] The elasticity of the intermediate segment 26 can be provided by an elastomeric material that elongates when the peripheral mooring cable 5’’ is subjected to tensile stress. It makes it possible to limit the maximum tension supported by the peripheral mooring cable 5’’.

[0078] Each intermediate segment 26 can exhibit a minimum breaking strength greater than 18 MPa, preferably greater than 25 MPa. Each intermediate segment 26 can also exhibit a minimum breaking load greater than 400 t, preferably greater than 1200 t.

[0079] The intermediate segment 26 can exhibit a creep of less than 20%, preferably less than 10%. Creep is the permanent elongation from its initial length due to the stretching of the polymer. The initial length is understood to be the length at the start of the service life without load.

[0080] The peripheral mooring cable 5’’ according to the present invention can thus support the severe tension applied to the peripheral mooring cable 5’’ due to severe environmental conditions. The intermediate segment 26 allows for significant elongation. This enables more effectively compensating for the lateral movement applied to the wind power plant 1. This is even more advantageous when the inner mooring cable 5’ is connected to the underwater buoy 7.

[0081] Optionally, as can be seen in FIG. 5, each peripheral mooring cable 5’’ can comprise at least one clamp weight 40 disposed on the second segment 24. In a variant not shown, the peripheral mooring cable 5’’ has no clamp weight 40, especially in the case of a tension mooring. The clamp weight 40 allows adding some weight to the second segment 24 and increasing the catenary effect of the cable. This makes it possible to reduce the average offset of the floating structure 3 by increasing the restoring force of the cable until all the clamp weights are lifted. Another advantage of the clamp weight is the reduction of the vertical load at the anchor location when a drag embedment anchor is used.

[0082] The peripheral mooring cable 5’’ is preferably not subjected to an anti-fouling treatment.

[0083] In the conventional mooring line, marine growths are not treated. In the deep sea, polyester ropes are conventionally located deeper along the line, for example at a depth of less than 150 m, to avoid marine growths.

[0084] The peripheral mooring line 5’’ according to the present invention makes it possible to eliminate the need for antifouling treatment due to the large deformation of the intermediate segment 26 and due to the material used for the intermediate segment 26, and prevents aquatic organisms from growing up to the peripheral mooring line 5’’.

Claims

1. An offshore wind farm (1) comprising at least four floating structures (3) designed to receive wind turbines (4), each floating structure (3) comprising at least three mooring lines (5', 5''), each mooring line (5', 5'') being attached to mooring points (51, 52, 53) arranged around the floating structure (3), the mooring lines facing inward from the offshore wind farm (1) forming the inner mooring lines (5') of the offshore wind farm (1), and the mooring lines facing outward from the offshore wind farm (1) forming the outer mooring lines (5'') of the offshore wind farm (1). An offshore wind power plant (1) comprising two adjacent floating structures (3), each having at least one of the intersecting peripheral mooring lines (5'') of the floating structures (3), at least one of these peripheral mooring lines comprising a buoyancy element.

2. The offshore wind power plant (1) according to claim 1, wherein only one of the intersecting peripheral mooring lines (5'') is equipped with a buoyancy element to pass above the other peripheral mooring lines (5'').

3. The offshore wind power plant (1) according to claim 1, wherein the intersecting perimeter mooring lines (5'') have a common connection point (53) above the seabed (Sb), the buoyancy element is a perimeter underwater buoy (7') moored to the seabed (Sb), the common connection point (53) is attached to the perimeter underwater buoy (7'), and the perimeter underwater buoy (7') comprises at least one additional mooring line (5''') connecting the perimeter underwater buoy (7') to a mooring point (54) on the seabed (Sb).

4. The offshore wind power plant (1) according to claim 3, wherein the surrounding underwater buoy (7') comprises two additional mooring lines (5'''), each additional mooring line (5''') being aligned with a surrounding mooring line (5'') attached to the surrounding underwater buoy (7').

5. The offshore wind power plant (1) according to claim 3, wherein three adjacent floating structures (3) have at least one of the inner mooring lines (5') of the floating structures (3) having a common joint (51) above the seabed (Sb), and the common joint (51) is attached to an underwater buoy (7) moored to the seabed.

6. The offshore wind power plant (1) according to claim 3, wherein the attachment points of the mooring lines (5', 5'', 5'''') to the underwater buoy (7, 7') are located below the underwater buoy (7, 7').

7. The offshore wind power plant (1) according to claim 6, wherein the underwater buoy (7, 7') is moored to the seabed (Sb) using flexible tethers (71, 71') and has a height limited by the seabed (Sb).

8. The offshore wind power plant (1) according to claim 6, wherein the underwater buoy (7, 7') is positioned at least 50 m above the seabed (Sb).

9. The offshore wind power plant (1) according to any one of claims 1 to 8, wherein the floating structure (3) is arranged such that the mooring ropes (5', 5'') form a hexagonal pattern.

10. At least one perimeter mooring rope (5'') - A first segment (22) that can be attached to the floating structure (3), - An offshore wind power plant (1) according to any one of claims 1 to 8, comprising: at least one intermediate segment (26) formed of an elastomer material and attached to the first segment (22).

11. The offshore wind farm (1) according to claim 10, wherein the intermediate segment (26) of the surrounding mooring rope (5'') can provide a maximum extension of more than 100% of the remaining length of the intermediate segment (26), advantageously more than 300%.

12. The offshore wind power plant (1) according to claim 10, wherein the intermediate segment (26) exhibits a minimum fracture strength greater than 18 MPa, preferably greater than 25 MPa.

13. The offshore wind power plant (1) according to claim 10, wherein the intermediate segment (26) exhibits a minimum breaking load greater than 400 tons, preferably greater than 1200 tons.

14. The offshore wind power plant (1) according to claim 10, wherein the intermediate segment (26) exhibits creep of less than 20%, preferably less than 10%.

15. The offshore wind power plant (1) according to claim 10, wherein the intermediate segment (26) has a cumulative length of less than 40 m, preferably less than 15 m.

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