Method for assembling a floating structure for supporting a wind turbine
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.
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 of the radial arms carrying an outer stability tower, the method comprising:
prefabricating the radial arms, central connector and at least parts of the central and outer stability towers,
pre-assembling the central connector with one arm to form a primary pre-assembly,
mounting temporary flotation devices onto the radial arms to provide additional buoyancy to the radial arms,
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 a corresponding arm on a distance less than a length of the arm.
3. The method of claim 1 , further comprising adjusting a position of each temporary flotation device axially relative to the arm to make a 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.
5. The method of claim 1 , further comprising removing the temporary flotation device after assembly of the other arms to the central connector.
6. The method of claim 1 , further comprising assembling on shore each of the radial arms 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 a 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 an assembly of each of the other arms 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 of the other arms.
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 radial arms or the temporary flotation devices to adjust the radial 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 step wherein the other arms are assembled 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 an assembly of said other arms to the primary preassembly, installation of a wind turbine mast, nacelle and blades.