FLOATING STRUCTURE FOR SUPPORTING A MARINE WIND TURBINE

Abstract

The floating structure (20) for supporting a marine wind turbine comprises a tower (21), a float (23), and a transition element (22) between the tower (21) and the float (23). The tower (21) has a tower tubular wall (31) having a tower axisymmetric outer surface about a central axis (5) defined by a tower generatrix, the float (23) has a float tubular wall (33) and a float lower end closing wall (34), the float tubular wall (33) has a float axisymmetric outer surface about the central axis (5) defined by a float generatrix, and the transition tubular wall (32) has a transition axisymmetric outer surface about the central axis (5) defined by a curved concave transition generatrix which is tangent to the tower generatrix. The transition axisymmetric outer surface of the transition element (22) has a transition upper diameter equal than a tower lower diameter (D1) and a transition lower diameter equal than a float upper diameter (D2). At least the float tubular wall (33), the float lower end closing wall (34) and the transition tubular wall (32) are made of reinforced concrete forming together a reinforced concrete monolithic body.

Claims

1. A floating structure for supporting a marine wind turbine, the floating structure comprising a tower, a float moored to a seabed by mooring lines, and a transition element between the tower and the float, wherein: the tower has a tower frustoconical lower portion adjacent to the transition element, said tower frustoconical lower portion of the tower having a tower tubular wall having a tower axisymmetric outer surface defined by a tower generatrix about a central axis and a tower lower diameter; the float has a float tubular wall and a float lower end closing wall, said float tubular wall has a float axisymmetric outer surface defined by a float generatrix about the central axis and a float upper diameter which is greater than the tower lower diameter; the transition element has a transition tubular wall having a transition axisymmetric outer surface defined by a curved concave transition generatrix about the central axis and a transition upper diameter equal than the tower lower diameter and a transition lower diameter equal than the float upper diameter; wherein said curved concave transition generatrix is tangent to the tower generatrix; and at least the float tubular wall, the float lower end closing wall and the transition tubular wall are made of reinforced concrete forming together a reinforced concrete monolithic body.

2. The floating structure according to claim 1, wherein said curved concave transition generatrix is and arc of circumference.

3. The floating structure according to claim 1, wherein said curved concave transition generatrix is adjusted by means of two or more straight segments providing two or more frustoconical segments in the transition tubular wall.

4. The floating structure according to claim 1, wherein said reinforced concrete monolithic body has continuous longitudinal reinforcement tendons arranged along the transition tubular wall and the float tubular wall, circumferential reinforcement tendons distributed along the transition tubular wall and the float tubular wall, and a set of main circumferential reinforcement tendons clustered in a geometrical discontinuity zone comprising a meeting point of the transition tubular wall and the float tubular wall.

5. The floating structure according to claim 4, wherein the main circumferential reinforcement tendons, the circumferential reinforcement tendons and the longitudinal reinforcement tendons are pre-stressed steel tendons arranged inside sleeves embedded in the concrete monolithic body.

6. The floating structure according to claim 1, wherein the float tubular wall has a float upper end wall thickness and the transition tubular wall has a transition upper end wall thickness and a transition lower end wall thickness, said transition lower end wall thickness being equal than the float upper end wall thickness.

7. The floating structure according to claim 1, wherein the tower tubular wall is made of reinforced concrete and forms part of the reinforced concrete monolithic body together with the float tubular wall, the float lower end closing wall and the transition tubular wall.

8. The floating structure according to claim 6, wherein said reinforced concrete monolithic body has continuous longitudinal reinforcement tendons arranged along the tower tubular wall, the transition tubular wall and the float tubular wall, circumferential reinforcement tendons distributed along the tower tubular wall, the transition tubular wall and the float tubular wall, and a set of main circumferential reinforcement tendons clustered in a geometrical discontinuity zone comprising a meeting point of the transition tubular wall and the float tubular wall.

9. The floating structure according to claim 8, wherein the main circumferential reinforcement tendons, the circumferential reinforcement tendons and the longitudinal reinforcement tendons are pre-stressed steel tendons arranged inside sleeves embedded in the concrete monolithic body.

10. The floating structure according to claim 6, wherein the tower tubular wall tubular has a tower lower end wall thickness, the float tubular wall has a float upper end wall thickness and the transition tubular wall has a transition upper end wall thickness equal than the tower lower end wall thickness and a transition lower end wall thickness equal than the float upper end wall thickness.

11. The floating structure according to claim 1, wherein at least the tower frustoconical lower portion of the tower is made of metal and is connected to the concrete monolithic body by bolts.

12. The floating structure according to claim 1, wherein curved concave transition generatrix defines an arc of circumference.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be more fully understood from the following detailed description of several preferred embodiments with reference to the accompanying drawings, in which:

[0026] FIG. 1 is a diagrammatic elevation view of a floating structure according to an embodiment of the present invention in a working situation supporting a marine wind turbine;

[0027] FIG. 2 is an enlarged perspective view of detail II of FIG. 1;

[0028] FIG. 3 is a cross-sectional view taken by the plane III-III of FIG. 1;

[0029] FIG. 4 is a partial cross-sectional view taken by the plane IV-IV of FIG. 3;

[0030] FIG. 5 is a partial cross-sectional view similar to FIG. 4 but belonging to an alternative embodiment of the present invention; and

[0031] FIG. 6 is a partial cross-sectional view similar to FIG. 4 but belonging to still another alternative embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Referring first to FIGS. 1-4, the reference character 20 generally indicates a floating structure for supporting marine wind turbines according to an embodiment of the present invention. The floating structure 20 comprises a tower 21, a float 23 and a transition element 22 between the tower 21 and the float 23. In a working situation as depicted in FIG. 1, a marine wind turbine 24 is supported on top of the tower 21 and the floating structure 20 is moored to the seabed SB by mooring lines 25. The floating structure is configured such that, in the working situation, the float 23 is fully submerged in the sea, the transition element 22 is partially submerged in the sea and partially emerged, and the tower is fully emerged. The main sea level is indicated with the reference characters MSL in FIG. 1.

[0033] The floating structure 20 is hollow and has an outer revolution shape about a central axis 5. The tower 21, or at least a lower portion thereof adjacent to the transition element 22, has a frustoconical shape constituting a tower frustoconical lower portion which has a tower tubular wall 31. The tower tubular wall 31 has a tower axisymmetric outer surface about a central axis 5. The float 23 has a float tubular wall 33 and a float lower end closing wall 34. The float tubular wall 33 has a float axisymmetric outer surface about the central axis 5. The transition element 22 has a transition tubular wall 32 which has a transition axisymmetric outer surface about the central axis 5.

[0034] The frustoconical tower axisymmetric outer surface of the lower portion of the tower 31 has a tower lower diameter D1. The float axisymmetric outer surface of the float 23 is preferably cylindrical and has a float upper diameter D2. The float upper diameter D2 is greater than the tower lower diameter D1 and the transition axisymmetric outer surface of the transition element 22 has a transition upper diameter equal than the tower lower diameter D1 and a transition lower diameter equal than the float upper diameter D2.

[0035] The frustoconical tower axisymmetric outer surface of the lower portion of the tower 31 is defined by a tower generatrix, the float axisymmetric outer surface of the float 23 is defined by a float generatrix, and the transition axisymmetric outer surface of the transition element 22 is defined by a curved concave transition generatrix which is tangent to the tower generatrix. For example, the curved concave transition generatrix is and arc of circumference providing a toroid-shaped transition axisymmetric outer surface. Since the curved concave transition generatrix is not tangent to the float generatrix, there is a geometrical discontinuity zone comprising a meeting point of the transition tubular wall 32 and the float tubular wall 33.

[0036] In the embodiment shown in FIGS. 1-4, the tower tubular wall 31, the transition tubular wall 32, the float tubular wall 33 and the float lower end closing wall 34 are made of reinforced concrete forming together a reinforced concrete monolithic body. The tower tubular wall 31 has a tower lower end wall thickness, the float tubular wall 33 has an float upper end wall thickness, and the transition tubular wall 32 has a transition upper end wall thickness equal than the tower lower end wall thickness and a transition lower end wall thickness equal than the float upper end wall thickness.

[0037] The reinforced concrete monolithic body has continuous longitudinal reinforcement tendons 8 arranged along the tower tubular wall 31, the transition tubular wall 32 and the float tubular wall 33, and circumferential reinforcement tendons 7 distributed along the tower tubular wall 31, the transition tubular wall 32 and the float tubular wall 33. The reinforced concrete monolithic body further comprises and a set of main circumferential reinforcement tendons 6 clustered in the geometrical discontinuity zone comprising the meeting point of the transition tubular wall 32 and the float tubular wall 33. Preferably, the main circumferential reinforcement tendons 6, the circumferential reinforcement tendons 7 and the longitudinal reinforcement tendons 8 are pre-stressed steel tendons arranged inside sleeves embedded in the concrete monolithic body.

[0038] FIG. 5 shows an alternative embodiment similar to that described above with reference to FIGS. 1-4 with the difference that in the embodiment of FIG. 5 the curved concave transition generatrix is adjusted by means of two or more straight segments providing two or more frustoconical segments in the transition tubular wall 32. This option involves higher concentrations of stresses in the junctions of the frustoconical segments which can in turn be absorbed by means of clustered circumferential reinforcement tendons in each junction.

[0039] FIG. 6 shows still another alternative embodiment in which only the transition tubular wall 32 of the transition element 21 and the float tubular wall 33 and the float lower end closing wall 34 of the float 23 are made of reinforced concrete forming together a reinforced concrete monolithic body while the tower tubular wall 31 of the tower frustoconical lower portion of the tower 21 is made of metal and is connected to the concrete monolithic body by bolts 35.

[0040] In this embodiment of FIG. 6, the reinforced concrete monolithic body has continuous longitudinal reinforcement tendons 8 arranged along the transition tubular wall 32 and the float tubular wall 33, circumferential reinforcement tendons 7 distributed along the transition tubular wall 32 and the float tubular wall 33, and a set of main circumferential reinforcement tendons 6 clustered in a geometrical discontinuity zone comprising a meeting point of the transition tubular wall 32 and the float tubular wall 33. The main circumferential reinforcement tendons 6, the circumferential reinforcement tendons 7 and the longitudinal reinforcement tendons 8 are preferably pre-stressed steel tendons arranged inside sleeves embedded in the concrete monolithic body.

[0041] By means of using the described geometry for the transition element 22 and the float 23 and steel reinforcement tendons 6, 7, 8 for longitudinal and circumferential prestressing, a smooth transmission of the strains generated in the tower 21 to the float 23 is achieved through the transition element 22. By adopting this geometry, suitable distribution of the longitudinal and transverse stresses on the concrete is obtained, including the loads of the tower plus those loads due to the prestressing of the reinforcement tendons embedded in the concrete, whether they are longitudinal or circumferential. The state of compression provided by the main circumferential reinforcement tendons 6, the circumferential reinforcement tendons 7 and the longitudinal reinforcement tendons 8 assures durability of the floating structure throughout the entire underwater section thereof and splash zone.

[0042] In the case where the walls of the tower 21, the transition element 22 and the float 23 form together a concrete monolithic body, the longitudinal reinforcement tendons 8 correspond to the prestressing longitudinal tendons existing at the lower end of the tower 21, which have continuity to the float 23 through the transition element 22. In the case where the tower is made of metal, the longitudinal reinforcement tendons 8 start from the upper end of the concrete monolithic body adjacent to the lower end of the tower 21, which in the working situation is above the mean sea level MSL.

[0043] In addition to the structural advantages, it must be observed that the transition element 22 increases downwardly in diameter in a nonlinear manner such that it allows moving larger diameters away from the surface of the sea, where the effect of the waves is maximal, and decrease exponentially with depth, while they proportionally increase with diameter. This greatly improves the hydrodynamic response of the floating structure, being more permeable on the surface of the sea.

[0044] The shape of the transition element 22 also helps to prevent possible adverse effects in movement under severe wave conditions, where a significant part of the transition element 22 is temporarily exposed, which with the use of typical linear transition sections causes significant variations in hydrostatic rigidity, which must be compensated for in the design by means of an increase in the length of the transition section, or in the depth and/or the diameter of the float.

[0045] Furthermore, the smooth shape transition at the junction of the tower 21 and the transition element 22 allows for providing a greater radius around the tower with a minimal depth than by means of other types transition shapes, which favors the passage of ships.