METHOD FOR ASSEMBLING A FLOATING STRUCTURE FOR SUPPORTING A WIND TURBINE

Abstract

A method for constructing a wind turbine concrete floater including a central connector from which radial arms extend, the central connector carrying a central stability tower, and each arm carrying an outer stability tower. The method includes prefabricating the arms, central connector and at least parts of the stability towers, pre-assembling the central connector with one arm to form a primary pre-assembly, mounting temporary flotation devices onto the arms to provide additional buoyancy to them, floating the primary preassembly and floating the other arms of the floater, and assembling offshore said primary preassembly with said other arms.

Claims

1. A method for constructing a wind turbine concrete floater comprising a central connector from which radial arms extend, the central connector carrying a central stability tower, and each arm carrying an outer stability tower, the method comprising: prefabricating the arms, central connector and at least parts of the stability towers, pre-assembling the central connector with one arm to form a primary pre-assembly, mounting temporary flotation devices onto the arms to provide additional buoyancy to them, floating the primary preassembly and floating the other arms of the floater, assembling offshore said primary preassembly with said other arms.

2. The method of claim 1, wherein each temporary flotation device extends along the corresponding arm on a distance less than the length of the arm.

3. The method of claim 1, further comprising adjusting the position of each temporary flotation device axially relative to the arm to make the longitudinal axis of the arm horizontal.

4. The method of claim 1, wherein each temporary flotation device is substantially a U-shape in cross section, with two legs extending downward and an upper base resting on the arm, and preferably retractable corbels at the lower end of the legs, the flotation devices preferably comprising two symmetrical parts assembled offshore over the corresponding arm.

5. The method of claim 1, further comprising removing the temporary flotation device after assembly of the other arms to the connector.

6. The method of claim 1, further comprising assembling on shore each arm with a corresponding outer stability tower or a part thereof.

7. The method of claim 1, further comprising assembling on shore the central stability tower on the corresponding arm or a part thereof.

8. The method of claim 1, further comprising providing a protection fender system between the primary preassembly and the other arms to avoid shocks between them during the assembly of each other arm to the central connector, and wherein the protection fender system is progressively disarmed until concrete-to-concrete contact is obtained between the central connector and each other arm.

9. The method of claim 8, wherein the protection fender comprises an inflatable fender.

10. The method of claim 1, further comprising water ballasting the arms and/or the flotation devices to adjust the arms at a same level before assembly.

11. The method of claim 1, further comprising approaching the other arms to the central connector using pulling cables and guiding devices.

12. The method of claim 1, further comprising activating a temporary clamping system keeping the other arms in fixed relationship to the central connector while said other arms are assembled to the central connector.

13. The method of claim 12, wherein the assembly of the other arms to the central connector comprising: activation of inflatable joints between the central connector and at least one of the other arms to create a chamber at the junction, pumping water out of the chamber, reinstating post-tensioning ducts connections in recesses formed during onshore construction, pouring non-shrink mortar in the recesses, post-tensioning tendons threaded in said ducts.

14. The method of claim 1, further comprising after completion of the assembly of said other arms to the primary preassembly, installation of a wind turbine mast, nacelle and blades.

15. A system comprising: a concrete floater comprising at least three radial arms fixed to a central connector, additional flotation devices each configured to be mounted on a corresponding arm and serving to provide additional buoyancy during off shore assembly of at least two arms to a primary preassembly of another arm with the central connector, each additional flotation device preferably comprising retractable lower corbels and two symmetrical parts to be assembled over the corresponding arm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a partial and schematic perspective view of an exemplary embodiment of a floating structure in accordance with the invention,

[0047] FIG. 2 shows in isolation the main arm of the structure,

[0048] FIG. 3 shows the arm of FIG. 2 after assembling the towers on the main arm,

[0049] FIG. 4 shows in isolation one of the secondary arms,

[0050] FIG. 5 shows in isolation the other secondary arm,

[0051] FIG. 6 shows a buoyancy device mounted on a corresponding arm,

[0052] FIG. 7 shows the floating structure equipped with the buoyancy devices after assembly of the arms,

[0053] FIG. 8 is a partial and schematic view of a flotation device mounted on a corresponding arm,

[0054] FIGS. 9A and 9B are partial and schematic longitudinal sections of the secondary arm and central connector during the assembly operation, with the waterline shown in dash line,

[0055] FIG. 10 is a partial and schematic top view of the connector and arm after contact between each other, and

[0056] FIG. 11 is a partial and schematic view in section of the interface between the connector and secondary arm.

DETAILED DESCRIPTION

[0057] FIG. 1 shows a floater 1 made in accordance with the invention.

[0058] The floater 1 is shown before the wind turbine mast, nacelle and blades are assembled thereon.

[0059] The floater 1 comprises a central connector 2 to which three arms 3, 4 and 5 are attached.

[0060] The arms extend radially outward from the connector 2.

[0061] The arms 3, 4 and 5 are hollow and can be water ballasted. Diaphragm walls (not shown) may be inserted inside the hollow structure of each arm, for trim and/or heel ballasting.

[0062] Though the floater shown has three arms, the invention applies to floaters having more arms, for example four arms.

[0063] The arms 3, 4 and 5 are arranged in a star configuration, and their longitudinal axes extend at 120° from each other.

[0064] The three arms 3, 4 and 5 together with the central connector 2 form a platform 6 that supports outer stability towers 7.

[0065] The central connector 2 carries a central stability tower 9. This central stability tower 9 is also configured for supporting the mast (not shown) of the wind generator.

[0066] These towers 7 and 9 are intended to be submerged only partially (for stability of the full floating structure) and provide stability to the platform 6. The arms are designed to be fully submerged but may be partially submerged only when under construction or assembly.

[0067] Each outer stability tower 7 is situated near the distal end 11 of the corresponding arm.

[0068] In the example shown, the outer stability towers 7 are interconnected only via the arms 3, 4 and 5 and connector 2, and the floater comprises no strut connecting the outer towers 7 to the central tower 9. However, in variants (not shown), the floater may comprise additional means connecting the outer towers 7 to the central tower 9 and/or the outer towers 7 together.

[0069] The platform 6 is made of reinforced post-tensioned concrete. The stability towers 7 and 9 are preferably made of reinforced post-tensioned concrete, but in variants are made of steel boxes, to meet stability constraints for example.

[0070] In accordance with the invention, parts of the floater 1 are made on shore and assembled offshore.

[0071] The onshore prefabrication activities are preferably as follows: [0072] Construction of the arms 3, 4, and 5 at dedicated stations.

[0073] The arms can be identical and built as a cast in-situ single piece or as an assembly of precast sections, joined using either cast in-situ reinforced concrete stitches or temporary post-tensioning over match-cast epoxy glued joints. To ensure perfect contact during assembly, the end of each arm that will be connected to the central connector 2 may either be match-cast with the central connector 2 or incorporate a match-cast section. [0074] Construction of central connectors 2 at dedicated stations. Each face 12 of the central connector 2 intended to be in contact with a corresponding face 13 of an arm 3, 4 or 5 may incorporate a precast match-cast section in case the arms are not match-cast against these faces. The central connector and/or the arms may comprise short match cast sections with either plain rubber joint or inflatable joint to be injected with cementitious grout; FIG. 11 described below shows an example of such joint 80. [0075] Construction of outer stability towers 7 and central stability tower 9 in the form of precast rings or half rings reassembled using post-tensioning or cast in situ with sliding formwork.

[0076] The central connectors 2 and arms 3, 4 and 5 are provided with ducts (not shown) for inserting tendons that will be post-tensioned after assembly of the platform 6.

[0077] The onshore assembly sequences are preferably as follows: [0078] Transfer of one arm (for example the arm 3 as shown) and the central connector 2 to an assembly station and connection of the two using possibly temporary post-tensioning. Such a primary preassembly 21 of the arm 3 and central connector 2 is shown in isolation in FIG. 2. [0079] Transfer of the components forming the central stability tower 9 and a corresponding outer stability tower 7 to the assembly station and assembly of the tower 9 onto the arm 3 and connector 2 of the primary preassembly 21, as shown in FIG. 3. The central and/or outer stability towers can also be cast in situ with using sliding formwork. In a variant, stability towers are assembled to the corresponding arms after load-out and float-off of the arms. [0080] Transfer of the two other arms 4 and 5, and of the components forming the corresponding outer stability towers 7 to the assembly station and connection to the arms, forming two secondary preassemblies 22 and 23 shown in FIGS. 4 and 5 respectively. In variants (not shown), the outer stability towers 7 are built or assembled onto the corresponding arms, after these arms have been loaded out. [0081] Transfer to storage of the primary assembly 21 and secondary preassemblies 22 and 23, for load-out. The load-out out may be carried out using a relatively short quay area since only the primary preassembly 21 and secondary preassemblies 22 and 23 are to be loaded out. The load-out vessel or lift may be relatively small thus releasing a major constraint on the port requirements and making a worldwide deployment less onerous. [0082] Before being loaded-out the primary preassembly 21 and the secondary preassemblies 22 and 23 are fitted with additional flotation devices 30 as shown in FIG. 6. In a variant, the devices 30 are mounted on the primary assembly and secondary arms offshore.

[0083] Each flotation device 30 may have the structure shown in FIG. 8, having substantially a U-shape in cross section, with two legs 31 extending downward and an upper base 32 resting on the arm. Each leg 31 may be provided with a retractable lower corbel 33, which extends under the arm to retain the device 30 on the arm.

[0084] The flotation device 30 may be made in two symmetrical parts 30a and 30b, connected by a transverse connection system 110 such as bolt/nut system or any other appropriate fixation system. Each part 30a or 30b may be initially floating independently, and connected over the corresponding concrete top slab arm 100. The upper base 32 may be a steel structure.

[0085] In a variant (not shown), the flotation device is made of side stability floaters with eccentricity, connected with floater arms and a central connection piece fastened onto the corresponding concrete arm top slab for example.

[0086] Each device 30 extends preferably along the corresponding arm on a distance less than the length of the arm, and its position can be adjusted axially to provide trim.

[0087] The connector 2 and secondary arms 4 and 5 are equipped with a guiding system 50 as shown in FIG. 10, such as a male element 51 and a female element 52 configured for interacting with the male element before the end face of the secondary arm 4 or 5 contacts the corresponding face of the connector 2.

[0088] The male element 51 preferably presents a tapered shape and the female element 52 an opening with opposite surfaces converging toward the inside.

[0089] Once floated in the water near the quay area, the primary preassembly 21 and the secondary preassemblies 22 and 23 are preferably assembled as follows: [0090] Water ballasting of the primary-preassembly 21 and the secondary pre-assemblies 22 and 23, as well as water ballasting of the flotation devices 30, to adjust free board level as well as trim and heel angles. The arm 3 of the primary preassembly 21 and the arms 4 and 5 of the secondary pre-assemblies 22 and 23 shall be at the same level for assembly. [0091] Approaching the central connector 2 of the primary preassembly 21 and the arms 4 and 5 of the secondary pre-assemblies 22 and 23 to each other using a pulling system 40 comprising for example pulling cables 41 as shown in FIGS. 9A and 9B. In the example shown, the pulling system 40 is shown being fixed on the top slab 100 of the connector 2 and secondary arms 4 or 5, but in a variant or additionally the pulling system 40 may be provided on side walls of the connector or secondary arms. During the approach of the connector and arm, the guiding system 50 will center the approaching arm relative to the connector. [0092] Protection fender system 60, such as air-inflatable protection fender or any other suitable device, is provided between the primary pre-assembly 21 and the secondary pre-assemblies 22 and 23 to avoid shocks, as shown in FIGS. 9A and 9B; once the three preassemblies 21, 22 and 23 are in desired position one to each other, this protection fender system 60 is progressively disarmed until concrete-to-concrete contact is obtained between the central connector 2 and the arms 4 and 5, as shown in FIG. 9B. [0093] A clamping system 70, such as an hydraulic clamping system, may be provided as shown in FIG. 10, and activated to keep the primary pre-assembly 21 and the arms 4 and 5 in a fixed position relatively to each other and make the assembled floater fixed. The clamping system 70 may be connected to the connector 2 or arms 4 and 5 through attachments 71 made of concrete. [0094] As shown in FIG. 11, joints 80, such as inflatable joints that are provided between the primary pre-assembly 21 and the other arms 4 and 5 enable sea water present inside the chamber 81 created at the junctions to be pumped out. [0095] Post-tensioning ducts connections 91 in recesses 90 formed during onshore construction are re-instated, and non-shrink mortar 92 is poured in the recesses 90. A concrete joint is thus cast in situ after removal of the water from recesses 90. [0096] Strands are threaded and the tendons made of these strands are post-tensioned. [0097] Ballast compartments are emptied, [0098] The additional flotation devices 30 are disconnected and the complete floater 1 is transferred to quay and docking for remaining works (for example concrete floater compliance tests, installation of mechanical devices, installation of wind turbine mast, nacelle and blades, pre-commissioning). [0099] The floater 1 may then be undocked and towed to a harbor storage station.