Counterweight for semi-submersible floater of offshore wind turbine and installation method thereof

Abstract

The present invention relates to a counterweight (2) for a semi-submersible floater for an offshore wind turbine, configurable to sink or float, the counterweight (2) comprising a main counterweight structure (4) formed of a material that sinks when immersed in water, and a plurality of airbags (6, 6') removably attached to the main structure so as to float the counterweight when inflated. The present invention also relates to a method for installing such a counterweight.

Description

[Technical Field]

[0001] The present invention relates to the general field of semi-submersible floats for offshore wind turbines with pendulum counterweights, and more particularly to counterweights used to ensure the stability of such floats. [Background technology]

[0002] The purpose of an offshore wind turbine is to harness the energy of the wind to generate electricity through a turbine and generator. There are two main types of offshore wind turbines: bottom-fixed wind turbines, which are installed on the seabed (typically at shallow depths of less than 50 m), and floating wind turbines, which have the advantage that they can be constructed on land and installed in areas where the seabed depth is typically greater than 50 m.

[0003] The floating wind turbine to which the present invention relates comprises a turbine generally formed by a motor having several rotating blades with a horizontal axis and a generator coupled to the motor, the motor and the generator being fixed to the upper end of a vertical mast (or pylon), the lower end of which is attached to a floating support structure.

[0004] There are several main families of floating support structures for offshore wind turbines: semi-submersible floaters, submersible floaters with tension cables (tension leg platforms (TLPs)), SPAR (single point anchor reservoir) type floaters, barge-type semi-submersible floaters, and semi-submersible floaters with pendulum counterweights.

[0005] Semi-submersible floats are the most common type of float currently in use. They consist of a steel or concrete base with three (or four) cylindrical columns connected by a metal structure, forming a roughly tripod shape. The stability of the structure is ensured by a counterweight that allows part of the base to be submerged. These structures are characterized by their large size and shallow draft.

[0006] Reference may be made to US Pat. No. 5,629,799, which describes a semi-submersible floating structure and a method for installing a wind turbine equipped with such a floating structure. In this document, the counterweight consists of a basket capable of receiving ballast material. In practice, this basket is transported empty to the installation zone of the wind turbine and is then gradually filled with ballast material in order to tension the ballast links connecting the basket to the floating support structure. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2019 / 106283 Summary of the Invention

[0008] The object of the present invention is to propose an alternative counterweight structure for semi-submersible floating bodies of offshore wind turbines. According to the present invention, this object is achieved by a counterweight for a semi-submersible floater for an offshore wind turbine, configurable to a submerged or floating state, the counterweight comprising a main counterweight structure formed of a material that sinks when immersed in water, and a plurality of airbags removably attached to the main structure so as to float the counterweight when inflated.

[0009] The counterweight according to the invention is notable in that it is made of a material that sinks but can be made to float using airbags. In particular, since the counterweight can be made to float, it is much easier to tow it to the installation site of the offshore wind turbine. In particular, it is not necessary to use an offshore crane to install the counterweight.

[0010] The main structure may be formed from concrete, steel, or composite materials. The main structure may have a cylindrical or polyhedral shape with a plurality of sides to which the airbag is detachably attached. In this case, the main structure may have a hexagonal prism shape.

[0011] The present invention also relates to a method for installing a counterweight as defined above, said method comprising the steps of: securing the airbag in a deflated state to the main structure at the dock; inflating the airbag to float the counterweight before launching; launching the counterweight in a floating state; Towing the counterweight to the offshore wind turbine installation site; connecting a lower counterweight of the semi-submersible floating body of the offshore wind turbine via tendons; and lowering a counterweight below the semi-submersible float to generate tension in the tendon and apply a downward force to the semi-submersible float, in any order.

[0012] The method may also include towing a floating counterweight to an installation site for the offshore wind turbine separately from towing the semi-submersible float of the offshore wind turbine, and then connecting tendons pre-installed on the float to the counterweight.

[0013] Alternatively, the method may include deploying and connecting a submerged counterweight with tendons below the floating body, and then towing the counterweight and floating body to the installation site of the offshore wind turbine.

[0014] Alternatively or additionally, the method may include connecting a pre-installed tendon to the floating body to the floating counterweight, then deploying a towing line including the tugboat, the floating body and the floating counterweight, and then towing the assembly to the installation site of the offshore wind turbine.

[0015] Preferably, the counterweight is lowered below the semi-submersible float gradually using ballast chains, followed by gradually deflating an airbag, which may then be detached from the main structure after being deflated. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a perspective view of a counterweight according to an embodiment of the present invention. [Figure 2] FIG. 2 is a side view of the counterweight of FIG. 1. [Figure 3] FIG. 10 is a perspective view of a counterweight according to another embodiment of the present invention. [Figure 4] FIG. 4 is a side view of the counterweight of FIG. 3. [Figure 5] 10A-10C show an example of towing a counterweight according to the present invention for installation. [Figure 6] The next step is shown where the counterweight is lowered below the float for installation. [Figure 7] The next step shows the removal of the airbag from the counterweight below the float for installation. [Figure 8] 1 is a diagram of an installed offshore wind turbine including a floating body with a counterweight according to the present invention; FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention relates to the general field of semi-submersible floats for offshore wind turbines. The stability of these floats is ensured by a counterweight 2 as shown in Figures 1 and 2. In accordance with the present invention, the counterweight 2 can be configured to sink (hereinafter referred to as the "sinking state") or float (hereinafter referred to as the "floating state") The counterweight 2 includes a main counterweight structure 4 formed from a material that sinks when immersed in water.

[0018] For example, the main counterweight structure 4 may be formed from concrete, steel, or composite materials. A plurality of airbags 6 are removably attached to the main counterweight structure 4 so that when the airbags inflate, they lift the counterweight. An airbag is a cushion formed of a flexible membrane or flexible shell (as opposed to a rigid element).

[0019] Furthermore, as shown in Figures 1 and 2, this main counterweight structure 4 may have a polyhedral (in this case hexagonal) geometric shape having a number of sides 4a to which the airbag 6 is removably attached.

[0020] More specifically, two airbags 6 are mounted on each side 4a of the main counterweight structure 4. Additionally, a number of additional airbags 6' are mounted on the top surface 4b of the main structure 4.

[0021] It is noted that the upper surface 4b of the main structure 4 also comprises a number of pad eyes 8 which allow for the attachment of ballast links (not shown) which connect the counterweight to the semi-submersible float.

[0022] Alternatively, as shown in Figures 3 and 4, the structure 4' of the main counterweight 2' may have a cylindrical geometric shape with a peripheral surface 4'a to which the airbag is removably attached (not shown in Figures 3 and 4).

[0023] As previously mentioned, the top surface 4'b of the main structure 4 also includes a number of pad eyes 8 for attaching ballast links. An example of a method for installing a counterweight according to the present invention will be described with reference to FIGS.

[0024] In this example installation method, the counterweight 2 is intended to ensure the stability of the floating body 10 of the wind turbine 12, which may be ballastable or non-ballastable, for example by having a structure similar to that described in WO 2019 / 106283.

[0025] In the initial stage of the method, which takes place at the dock, a deflated air bag 6 is attached to the main structure of the counterweight 2. The air bag is then inflated to keep the counterweight afloat before launching.

[0026] As shown in Figure 5, this floating counterweight 2 is connected to the bottom of the float 10 by tendons (not shown in Figure 5), and after launching, it is towed to the installation site of the offshore wind turbine by two tugboats 14, which are connected to the counterweight by ballast chains 20 and to the float by towing cables 16.

[0027] Thereafter, the counterweight 2 is gradually lowered below the floating body 10 (FIG. 6), for example by gradually letting out the ballast chain 20 from the tugboat and / or gradually deflating the airbag 6.

[0028] Once the airbag is deflated, it can be detached from the counterweight 2. Tension occurs in the tendon 18 connecting the counterweight to the floating body 10, and a downward force acts on the floating body.

[0029] An anchor line 30 may then be connected to the float 10 to hold the float 10 in place and the ballast chain may be disconnected from the tug (Figure 8). Alternatively, the ballast chain may be permanent.

[0030] It should be noted that in this example installation method, the counterweight is deployed and connected by tendons in a submerged position below the float, and then the counterweight and float are towed to the installation site of the offshore wind turbine.

[0031] Alternatively, the floating counterweight may be towed to the installation site of the offshore wind turbine separately from the towing of the semi-submersible floater of the offshore wind turbine, in which case tendons pre-installed on the floater are connected to the counterweight following the towing step.

[0032] Alternatively, tendons pre-installed on the floater can be connected to a floating counterweight, after which a towing line consisting of a tug, floater and floating counterweight can be deployed, and the assembly can then be towed to the offshore wind turbine installation site.

Claims

1. A counterweight (2; 2') for a semi-submersible float (10) of an offshore wind turbine (12) that can be configured to sink or float, the counterweight comprising: a main counterweight structure (4; 4') formed of a material that sinks when immersed in water; and a plurality of airbags (6, 6') removably attached to the main structure so as to float the counterweight when inflated.

2. Counterweight according to claim 1, wherein the main structure (4; 4') is made of concrete, steel or composite material.

3. 3. The counterweight according to claim 1 or 2, wherein the main structure has a cylindrical or polyhedral shape with a plurality of sides (4a; 4'a) to which the airbag is detachably attached.

4. The counterweight according to claim 3 , wherein the main structure has a hexagonal prism shape.

5. A method for installing a counterweight according to any one of claims 1 to 4, comprising the steps of: Fixing the airbag (6, 6') in a deflated state to the main structure at the dock; Inflating the airbag to float the counterweight (2; 2') before launching it into the water; launching the counterweight in a floating state; towing the counterweight to an installation location of the offshore wind turbine; connecting the counterweight below the semi-submersible floating body (10) of the offshore wind turbine via a tendon (18); and, in any order, lowering the counterweight below the semi-submersible body to tension the tendon and exert a downward force on the semi-submersible body.

6. 6. The method of claim 5, comprising towing the floating counterweight to an installation site of the offshore wind turbine separately from towing the semi-submersible floating body of the offshore wind turbine, and then connecting the tendon pre-installed on the floating body to the counterweight.

7. 6. The method of claim 5, comprising deploying and connecting the counterweight in a submerged state below the floating body with the tendon, and then towing the counterweight and the floating body to an installation site for the offshore wind turbine.

8. 6. The method according to claim 5, comprising connecting the tendon pre-installed on the floating body to the floating counterweight, then deploying a towing line comprising a tugboat (14), the floating body (10) and the floating counterweight (2; 2'), and then towing the assembly to an installation site of the offshore wind turbine.

9. 9. The method according to any one of claims 5 to 8, wherein lowering the counterweight below the semi-submersible body is performed gradually using a ballast chain (20) and then by gradually deflating the airbag.

10. 10. The method of claim 9, wherein the airbag is detached from the main structure after being deflated.

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