Semi-submersible float, especially for a floating wind turbine

Description

[0001] The present invention relates to a semi-submersible float, in particular for a floating wind turbine.

[0002] The present invention also relates to a method of installing such a semi-submersible float.

[0003] As is known in itself, a semi-submersible float generally comprises a central column and at least two outer columns, each connected to the central column by a pontoon-shaped branch.

[0004] For example, the float is configured to float on a sea surface.

[0005] The floating platform defines, in particular, an operational state in which it is located at its offshore operating site and anchored to the seabed. In this state, the floating wind turbine is ready to generate electricity. Furthermore, in this state, the semi-submersible platform has a predefined draft.

[0006] Thus, in the operational state of the semi-submersible float, the central column provides buoyancy. The central column has a significant submerged volume, but this volume does not compensate for the weight of the mast, turbine, and nacelle that it supports. Consequently, the central column is subjected to a downward force, that is, a force directed towards the seabed.

[0007] The outer columns also provide buoyancy to the semi-submersible float and present a significant submerged volume.

[0008] In particular, their buoyancy exceeds their weight. Each outer column is therefore subjected to a resultant force directed upwards, that is, in the opposite direction to the seabed. This results in tensile forces in the lower slab of the central column and in that of the corresponding pontoon-shaped branch.

[0009] The pontoon-shaped branches also exhibit significant buoyancy. This results in substantial shear forces at the junction of each pontoon-shaped branch with the central column.

[0010] Furthermore, during operation, the turbine exerts a thrust on the semi-submersible float. This thrust is primarily a function of the floating wind turbine's power output and must be at least partially counterbalanced to stabilize the float.

[0011] The forces applied to the floating platform are also due to mechanical stresses induced by environmental conditions such as wind, swell, and current, whether the turbine is operating or not. This results in a dynamic amplification of these mechanical stresses when the floating wind turbine is set in motion by these environmental conditions.

[0012] It is therefore desirable to balance the forces acting on the semi-submersible float when it is in the operational state.

[0013] A semi-submersible float according to the preamble of claim 1 is disclosed in document WO2016 / 172149A1.

[0014] The invention aims to provide a semi-submersible float exhibiting particularly increased stability when in the operational state.

[0015] For this purpose, the present invention relates to a semi-submersible float, in particular for a floating wind turbine, as defined in claim 1.

[0016] In other words, in the operational state of the float, the second portion of each arm includes the ballast material while the first portion does not include such material.

[0017] According to particular embodiments, the semi-submersible float comprises one or more of the features of claims 2 to 9, taken individually or in any technically possible combination.

[0018] The invention also relates to a method for installing a semi-submersible float, in particular for a floating wind turbine, as defined in claim 10.

[0019] Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, given by way of example only with reference to the drawings which are: there figure 1 , a schematic perspective view of an example of a floating wind turbine comprising a semi-submersible float according to the invention, and the figure 2 , a schematic cross-sectional view of the semi-submersible float of the figure 1 according to the section plan II-II indicated on the figure 1 .

[0020] In this description, a quantity is substantially equal to a value V when the quantity is equal to plus or minus 10% of the value V.

[0021] A floating wind turbine 10 is shown on the figure 1 .

[0022] With reference to this figure, the floating wind turbine 10 comprises a semi-submersible float 12, at least one mast 14, a turbine 16 and a nacelle 18 supporting at least part of the turbine 16.

[0023] In the remainder of this application, the semi-submersible float 12 is referred to as "float 12".

[0024] The float 12 is configured to float on a surface S of a body of water 20, such as the surface of the sea.

[0025] Float 12 has an operational state and a non-operational state.

[0026] In the operational state of the float 12, as previously mentioned, the float 12 is located at its operating site at sea and anchored, for example, to the seabed by an anchoring device (not shown in the figures). Furthermore, in the operational state of the float 12, the floating wind turbine 10 is ready to generate electricity. It is understood that in the operational state of the float 12, the turbine 16 is either operating or not. In addition, in the operational state of the float 12, the float 12 has a predefined draft T.

[0027] The float 12 illustrated on the figure 1 is in an operational state.

[0028] In its non-operational state, the floating platform 12 is not capable of generating electricity. In this state, the platform 12 also has a predefined draft that is less than the predefined draft T of the platform 12 in its operational state. For example, a non-operational state of the platform 12 corresponds to a phase during which the platform 12 is being towed from a port to its operating site.

[0029] The float 12 comprises a central column 22 and at least two outer columns. In addition, for each outer column, the float 12 comprises a pontoon-shaped arm connecting that outer column to the central column 22.

[0030] In the example of implementation of the figure 1 , float 12 includes three external columns 24, 26, 28 and therefore, three pontoon-shaped branches 30, 32, 34.

[0031] The outer columns 24, 26, 28 are arranged in a star shape around the central column 22 and, for example, regularly distributed angularly around the central column 22. Thus, in this case, the angle between each pair of pontoon-shaped branches 30, 32, 34 is approximately equal to 120 degrees.

[0032] According to yet another embodiment, the float 12 comprises two outer columns. In this case, the central column forms the vertex of an isosceles triangle, and the two other vertices are formed, respectively, by an outer column. Furthermore, for each outer column, a pontoon-shaped branch connects the central column to that outer column.

[0033] In another embodiment, the float 12 comprises four outer columns regularly spaced angularly around the central column. Thus, the angle between two successive pontoon-shaped branches is approximately 90 degrees. Furthermore, similarly, for each outer column, a pontoon-shaped branch connects the central column to that outer column.

[0034] Each pontoon-shaped branch 30, 32, 34 defines a branch axis A, oriented from the central column 22 to the corresponding outer column 24, 26, 28. As visible on the figure 1 , a branch axis A is shown for the pontoon-shaped branch 30.

[0035] The central column 22 defines a vertical axis Z, perpendicular to the branch axis A.

[0036] In addition, each pontoon-shaped branch 30, 32, 34 defines a transverse axis B perpendicular to the corresponding branch axis A.

[0037] As seen on the figure 1 The central column 22 is designed to receive a payload. In the illustrated case of a floating wind turbine, the payload includes, in particular, the mast 14, the nacelle 18 and the turbine 16.

[0038] The central column 22 has, for example, the shape of a cylinder with a circular cross-section and a vertical axis Z. For example, the diameter D1 of the central column 22 is equal to 10 meters (m).

[0039] The central column 22 comprises a base 22A and a head 22B.

[0040] Base 22A is arranged in the extension of each pontoon-shaped branch 30, 32, 34 along the corresponding branch axis A. For example, base 22A is at least partially made of concrete.

[0041] The head 22B of the central column 22 is fixed to the base 22A. The head 22B and the base 22A are coaxial with vertical axis Z. The head 22B of the central column 22 is, for example, made of steel.

[0042] For example, the central column 22 has a height H1 along the vertical direction Z of between 30 m and 40 m.

[0043] The remainder of the description of float 12 is made with reference to the figure 2 .

[0044] In addition, in the following, the float 12 is described in relation to the central column 22, one of the outer columns 24 among the three outer columns 24, 26, 28 and the pontoon-shaped branch 30 connecting the central column 22 to this outer column 24.

[0045] Thus, each other outer column 26, 28 is analogous to the outer column 24 described below. Furthermore, each other pontoon-shaped branch 32, 34 is also analogous to the pontoon-shaped branch 30 described below.

[0046] Just like the central column 22, the outer column 24 has the shape of a cylinder with a circular cross-section and a vertical axis Z. For illustration purposes, the diameter D2 of the outer column 24 is between 9 m and 9.5 m.

[0047] The outer column 24 also includes a base 24A and a head 24B.

[0048] Base 24A is arranged in the extension of the pontoon-shaped branch 30 along the axis of branch A. For example, base 24A is at least partially made of concrete.

[0049] The 24B head is fixed to the corresponding 24A base. The 24B head and the 24A base are coaxial along the vertical Z axis.

[0050] The outer column 24 has a height H2 along the vertical axis Z of, for example, between 30 m and 40 m.

[0051] The pontoon-shaped branch 30, for example, has a parallelepiped shape, delimited by four slabs forming the faces of the parallelepiped. Thus, this branch 30 comprises a lower slab 36, an upper slab 38, and two lateral slabs 40 connecting the lower slab 36 and the upper slab 38. Only the lateral slab 40 is visible on the figure 1 .

[0052] The pontoon-shaped branch 30 is formed of a first portion 42 and a second portion 44 extending successively along the branch axis A.

[0053] The pontoon-shaped branch 30 defines a total extent E of this branch 30. The total extent E corresponds to the length of a straight line connecting the two ends of this branch 30 along the branch axis A.

[0054] For illustration purposes, this total extent E is between 20 m and 30 m.

[0055] The height H3 of the pontoon-shaped branch 30 along the vertical axis Z is, for example, between 8 m and 9 m.

[0056] The width L of the pontoon-shaped branch 30 along the transverse axis B is, for example, substantially equal to the diameter D2 of the outer column 24.

[0057] The first portion 42 extends over at least 10% of the total extent E of the pontoon-shaped branch 30.

[0058] Preferably, the first portion 42 extends over at least 20% of the total extent E of the pontoon-shaped branch and advantageously over at least 35% of the total extent E of the pontoon-shaped branch.

[0059] More precisely, the first portion 42 extends over 20% to 70%, preferably over 35% to 45%, and advantageously over approximately 40% of the total extent E of the pontoon-shaped branch 30.

[0060] In addition, the first portion 42 is hermetically isolated from the central column 22 and more specifically from the base 22A of the central column 22 as well as from the second portion 44, for example, by a hermetically sealed wall 50.

[0061] The second portion 44 also extends over at least 10% of the total extent E of the pontoon-shaped branch 30.

[0062] More specifically, the second portion 44 extends over 30% to 80%, preferably over 55% to 65%, and advantageously over approximately 60% of the total extent E of the pontoon-shaped branch 30.

[0063] The second section 44 comprises a first compartment 44A and a second compartment 44B extending successively along the axis of branch A.

[0064] The first compartment 44A has an extent E1 and the second compartment 44B has an extent E2. The extent E1 of the first compartment 44A corresponds to the length of a straight line connecting the two ends of the first compartment 44A along the branch axis A. Similarly, the extent E2 of the second compartment 44B corresponds to the length of a straight line connecting the two ends of the second compartment 44B along the branch axis A.

[0065] The ratio of the extent E2 of the second compartment 44B to the extent E1 of the first compartment 44A is, for example, between 2 and 4. More precisely, the ratio is between 2 and 3. For example, the ratio is equal to 2.5.

[0066] The first compartment 44A is hermetically isolated from the second compartment 44B, for example by a hermetically sealed wall 52. In addition, the second compartment 44B is hermetically isolated from the outer column 24 and more specifically from the base 24A of the outer column 24.

[0067] The second compartment 44B defines a total volume corresponding to the volume of the internal free space of the branch 30 delimited by the slabs 36, 38, 40, the watertight wall 52 arranged between the first and second portion 42, 44 and a wall isolating the second compartment 44B from the external column 24.

[0068] Thus, the second portion 44B forms a receiving ballast for a ballast material 66.

[0069] For example, ballast material 66 is seawater.

[0070] Alternatively, ballast material 66 includes sand, gravel and / or mud.

[0071] According to an advantageous aspect of the invention, the first portion 42 comprises an internal partition 46 dividing the first portion 42 into two parts 42A, 42B of the first portion 42.

[0072] Furthermore, the second portion 44 includes, for example, two internal partitions 54, 56 dividing the second compartment 44B into three compartment parts 58, 60, 62. In this case, the total volume of the second compartment 44B corresponds to the sum of the volumes of the internal free spaces of the three parts 58, 60, 62 of the second compartment 44B.

[0073] According to another advantageous aspect of the invention, the base 24A of the outer column 24 defines a receiving ballast for the ballast material 66.

[0074] In this case, the ballast formed by the base 24A of the outer column 24 replaces, for example, the first compartment 44A of the second section 44 of the pontoon-shaped branch 30. In other words, the second section 44 no longer has a first compartment 44A. The ballast formed by the base 24A of the outer column 24 has a total volume equal, for example, to the volume of the free internal space of this base 24A.

[0075] A method for installing a floating wind turbine float 12 in the operational state is described in the remainder of this description.

[0076] The installation method is also described in relation to the central column 22, one of the outer columns 24 among the three outer columns 24, 26, 28 and the pontoon-shaped branch 30 connecting the central column 22 to this outer column 24.

[0077] Thus, the steps of the process described in relation to the pontoon-shaped branch 30 apply in the same way to each other pontoon-shaped branch 32, 34 of the float 12.

[0078] The installation process begins once the float 12 is located on its operating site.

[0079] Initially, the first and second sections 42, 44 are devoid of ballast material 66.

[0080] The process includes a filling step during which the second portion 44 of the pontoon-shaped branch 30 is at least partially filled with ballast material 66.

[0081] More specifically, during this filling stage, 40% to 60% of the total volume of the first compartment 44A of the second portion 44 is filled with the ballast material 66. In addition, during this same stage 80% to 100% of the total volume of the second compartment 44B is filled with the ballast material 66.

[0082] The process further includes a step in which the first portion 42 of the pontoon-shaped branch 30 is left empty of ballast material.

[0083] In this example, the central column 22 and the outer column 24 are also left empty of ballast material 66.

[0084] According to another embodiment of the process, when the base 24A of the outer column 24 forms a ballast and the second portion 44 is devoid of a first compartment 44A, during the filling step, 80% to 100% of the total volume of the second compartment 44B of the second portion 44 is filled by the ballast material 66 and 40% to 60% of the total volume of the ballast of the outer column 24 is filled by the ballast material 66.

[0085] Le fait de remplir au moins en partie la deuxième portion 44 de matériau de ballastage 66 et de laisser vide de tout matériau de ballastage 66 la première portion 42 permet d'obtenir un flotteur 12 dans l'état opérationnel présentant une stabilité accrue.

[0086] The filling of the second portion 44 allows, in particular, the adjustment of the hydrostatic stiffness to which the float 12 is subjected, in order to resist the thrust of the turbine 16 of the floating wind turbine 10.

[0087] Furthermore, when the second portion 44 is filled with ballast material, the forces within the float 12 related to the structure of the float 12 itself are balanced, in particular by the adjustment of the draft.

[0088] More specifically, filling the second section 44 balances the shear and bending forces at the junction between the pontoon-shaped arm 30 and the central column 22 because the weight of the second section 44 becomes greater than the hydrostatic thrust to which it is subjected. In particular, filling 80% to 100% of the total volume of the second compartment 44B with the ballast material 66 increases the weight of the portion of the pontoon-shaped arm 30 closest to the outer column 24 in order to compensate for the significant buoyancy of the outer column 24.

[0089] Furthermore, filling the second portion 44 also has the advantage of balancing the tensile forces to which the lower slab 36 of the pontoon-shaped branch 30 and that of the central column 22 are subjected.

[0090] Furthermore, the second section 44 of the pontoon-shaped branch 30 is the portion of this branch most subject to variations in hydrostatic and hydrodynamic pressure when the wind turbine 10 tilts. Therefore, filling the second section 44 of the pontoon-shaped branch 30 reduces the pressure difference between the inside and outside of this branch. This, in turn, reduces the "membrane" effect of the slabs 36, 38, and 40 that make up the branch 30.

[0091] In the embodiment example in which the first compartment 44A is filled with ballast material, due to the filling of this first compartment 44A, the evolution of shear forces is more progressive along the pontoon-shaped branch 30 along the corresponding branch axis A.

[0092] Furthermore, when the first compartment 44A is filled with the ballast material 66, this compartment 44A exhibits a buoyancy and weight that compensate each other.

[0093] In the embodiment example in which the base 24A of the outer column 24 forms a ballast, increased stability of the float 12 is obtained by at least partially filling this ballast.

[0094] Finally, the watertight walls 50, 52 and the internal bulkheads 46, 54, 56 increase the resistance of the branch 30 to the seawater pressure to which it is subjected. Furthermore, the internal walls 54, 56 of the second compartment 44B prevent the effects of liquid hulling when the ballast material 66 is at least partially liquid.

Claims

1. A semi-submersible floater (12), in particular for a floating wind turbine (10), defining an operating state and a non-operating state, and comprising: - at least two outer columns (24, 26, 28), - a central column (22) for receiving a payload (14, 16, 18), and - for each outer column (24, 26, 28), a pontoon-shaped branch (30, 32, 34) connecting this outer column (24, 26, 28) to the central column (22) and defining a branch axis (A) oriented from the central column (22) towards this outer column (24, 26, 28), each pontoon-shaped branch (30, 32, 34) is formed by a first portion (42) and a second portion (44) that extend successively along the corresponding branch axis (A), wherein in the operating state of the semi-submersible floater (12), the second portion (44) of each branch (30, 32, 34) comprises a ballast material (66), and in that the first portion (42) does not contain any ballast material (66), and wherein each second portion (44) comprises a first compartment (44A) and a second compartment (44B) extending successively along the branch axis (A), characterized in that each one of the first portion (42) and the second portion (44) extending over at least 10% of the total extent (E) of said pontoon-shaped branch (30, 32, 34), along this branch axis (A), and, in the operating state of the semi-submersible floater (10), the volume of the ballast material (66) of each first compartment (44A) is between 40% and 60% of the total volume of this compartment (44A) and the volume of the ballast material (66) of each second compartment (44B) is between 80% and 100% of the total volume of this compartment (44B).

2. The semi-submersible floater (12) according to claim 1, wherein each outer column (24, 26, 28) comprises a ballast (24A) able to be filled with a ballast material (66), arranged in the extension of the pontoon-shaped branch (30, 32, 36) connecting the central column (22) to this outer column (24, 26, 28) along the corresponding branch axis (A), and wherein, in the operating state of the semi-submersible floater (12), the volume of the ballast material (66) of the ballast (24A) of each outer column (24, 26, 28) is between 40% and 60% of the total volume of this ballast (24A).

3. The semi-submersible floater (12) according to claim 2, wherein the volume of the ballast material (66) of the second portion (44) of each pontoon-shaped branch (30, 32, 34) is between 80% and 100% of the total volume of this portion (44).

4. The semi-submersible floater according to claim 1 or 2, wherein the ratio of the extent (E2) of the second compartment (44B) of the second portion (44) of each pontoon-shaped branch (30, 32, 34) along the corresponding branch axis (A) to the extent (E1) of the first compartment (44A) of the second portion (44) of this same branch (30, 32, 34) along the corresponding branch axis (A), is between 2 and 4.

5. The semi-submersible floater (12) according to claim 1 or 2 or 5, wherein each second portion (44) comprises at least one inner partition (54, 56) arranged in the second compartment (44B) of this portion (44), the inner partition (54, 56) dividing this compartment (44B) into at least two compartment (44B) parts (58, 60, 62).

6. The semi-submersible floater (12) according to any one of the preceding claims, wherein the second portion (44) of each pontoon-shaped branch (24, 26, 28) extends over 30% to 80% of the total extent (E) of this branch (30, 32, 34), along the corresponding branch axis (A).

7. The semi-submersible floater (12) according to any one of the preceding claims, wherein the first portion (42) of each pontoon-shaped branch (30, 32, 36) is tightly isolated from the second portion (44) of this branch (30, 32, 34).

8. The semi-submersible floater (12) according to any one of the preceding claims, wherein the central column (22) does not contain any ballast.

9. The semi-submersible floater (12) according to any one of the preceding claims, wherein the ballast material (66) comprises at least one of the materials from the following list: - seawater, - mud, - sand, - gravel.

10. A method for installing a semi-submersible floater (12), in particular for a floating wind turbine (10), the semi-submersible floater (12) defining an operating state and a non-operating state, and comprising: - at least two outer columns (24, 26, 28), - a central column (22) for receiving a payload (14, 16, 18), and - for each outer column (24, 26, 28), a pontoon-shaped branch (30, 32, 34) connecting this outer column (24, 26, 28) to the central column (22) and defining a branch axis (A) oriented from the central column (22) towards this outer column (24, 26, 28), each pontoon-shaped branch (30, 32, 34) is formed by a first portion (42) and a second portion (44) that extend successively along the corresponding branch axis (A), each one over at least 10% of the total extent (E) of said pontoon-shaped branch (30, 32, 34), along this branch axis (A), each second portion (44) comprising a first compartment (44A) and a second compartment (44B) extending successively along the branch axis (A), and wherein, the method being characterized in that it comprises the following steps for placing the semi-submersible floater (12) in the operating state: - filling the second portion (44) of each pontoon-shaped branch (30, 32, 36) at least partially with a ballast material (66), the volume of the ballast material (66) of each first compartment (44A) is between 40% and 60% of the total volume of this compartment (44A) and the volume of the ballast material (66) of each second compartment (44B) is between 80% and 100% of the total volume of this compartment (44B), and - leaving the first portion (42) of each pontoon-shaped branch (30, 32, 36) empty of ballast material.