Gravity-based foundation system for the installation of offshore wind turbines and method for the installation of an offshore wind turbine foundation system

Abstract

The present invention relates to a gravity-based foundation system for offshore wind turbine installation that comprises three floating concrete bases built with self-floating concrete caissons, equipped with valves for filling them with water and emptying the water out enabling their ballasting and anchoring at their final location; a metal structure which connects the floating concrete bases by means of a connecting element to the wind turbine tower, and a metal element which connects the floating concrete bases to the wind turbine, metal element on which a docking area is installed, a maintenance platform and access stairs, and it also relates to a method of installation of the gravity-based foundation system.

Claims

1. A gravity-based foundation system for offshore wind turbine installation that comprises: three floating concrete bases built with self-floating concrete caissons, equipped with valves for filling them with water and emptying the water out enabling their ballasting and anchoring at their final location, a metal structure which connects the three floating concrete bases by means of a connecting element to a wind turbine tower of a wind turbine, and wherein the connecting element which connects the three floating concrete bases to the wind turbine tower is a metal element on which a docking area, a maintenance platform and access stairs are installed; wherein each of the three floating concrete bases comprises a lower slab which is in contact with the terrain once the system has been submerged, an upper slab, a perimeter wall and interior walls or partitions that define a first group of interconnected cells.

2. The system of claim 1 wherein the metal structure is tripod shaped.

3. The system of claim 1 wherein the metal structure is lattice shaped.

4. The system of claim 1, wherein the attachment of the metal structure to the three floating concrete bases is performed by means of mixed connecting nodes, one for each one of the three floating concrete bases, each of which comprises a concrete core and a prestressing system integrated therein.

5. The system of claim 4 wherein the metal structure comprises three inclined diagonal rods whose ends which connect to each one of the mixed connecting nodes are conical frustum-shaped.

6. The system of claim 5 wherein each one of the mixed connecting nodes further comprises a sheet metal coating externally coating the concrete core.

7. The system of claim 6 wherein each one of the mixed connecting nodes receives, via the metal coating the inclined diagonal rod, some first auxiliary rods joining together two adjacent mixed connecting nodes of each one of the three floating concrete bases and a second auxiliary rod joining each mixed connecting node to the connecting element.

8. The system of claim 7 wherein the metal coating of each one of the mixed connecting nodes has a polyhedral shape with an upper prismatic-trapezoidal-shaped area wherein one of their sides, the one that receives an inclined diagonal rod, is in turn inclined and perpendicular to the inclined diagonal rod, and a lower irregular prismatic-hexagonal-shaped area, wherein two of its vertical sides, which receive some first auxiliary rods linking together two adjacent mixed connecting nodes of each one of the three floating concrete bases, are perpendicular to said first auxiliary rods, wherein the sides, at which the inclined diagonal rod and the first auxiliary bars join, are made of sheet steel.

9. The system of claim 8 wherein the lower irregular prismatic-hexagonal-shaped area of each one of the mixed connecting nodes comprises a vertical side which is situated between the two vertical sides receiving the first auxiliary rods, wherein said vertical side receives the second auxiliary rod which joins each one of the mixed connecting nodes to the connecting element.

10. The system of claim 7 wherein the metal coating of each one of the mixed connecting nodes has a tubular shape and the concrete core is situated in its interior.

11. The system of claim 7 wherein each one of the mixed connecting nodes further comprises active anchors for transmitting forces, while the each one of the three floating concrete bases comprises passive anchors situated therein, either directly on an upper closing slab or on rigidity partitions arranged under each one of the mixed connecting nodes.

12. The system of claim 11 wherein active anchors are placed in the concrete core, comprising: transfer sheets of the strengths of the four rods which penetrate each one of the mixed connecting nodes, wherein two of them, the inclined diagonal rod and the second auxiliary bar are joined together by welding at the point of intersection of the axes of all the rods, transfer and connecting sheets of the strengths of the first auxiliary rods joining the first auxiliary rods together, and additionally, the prestressing system is also located inside each one of the mixed connecting nodes.

13. The system of claim 1 wherein each one of the three floating concrete bases comprises a group of cells not involved in buoyancy for access from the upper slab to the contact surface between the lower slab and the terrain.

14. The system of claim 1 further comprising a control system which in turn comprises a sensing subsystem, an operational control subsystem and decision-making subsystem wherein the operational control subsystem enables the coordination between the sensing subsystems and the decision-making support subsystem.

15. The system of claim 14 wherein the sensing subsystem comprises at least one of the following: a filling level sensor for the filling of the first group of interconnected cells to measure their ballasting level, inertial acceleration sensors, doppler acoustic sensors for measuring currents in the vicinity of the system and the distance to the seabed, a gyro for monitoring the roll and pitch of each one of the three floating concrete bases, relative and absolute positioning sensors, pressure sensors for the estimation of actions resulting from the interaction between the ocean flow and the system, deformation sensors for the evaluation of the number and magnitude of stress load cycles of the system through its interaction with the ocean flow and/or cyclic stresses transmitted by the wind turbine.

16. The system of claim 15 wherein the decision-making support subsystem comprises a logical device which is a first-level instrumental alarm to generate warnings to prevent exceeding the thresholds registered by the sensing subsystem, and a second-level prediction device based on a climate prediction system and on the instrumental historical records obtained by different sensors, performing a real-time control by the operational control subsystem and may be displayed on a display device; an operational control subsystem acting on the control actuators that perform the opening and/or closing of the valves for water filling and emptying and on a system of anchors and winches, to fix the position of the foundation system.

17. Method for the installation of an offshore wind turbine foundation system comprising, wherein the system comprises: three floating concrete bases built with self-floating concrete caissons, equipped with valves for filling them with water and emptying the water out enabling their ballasting and anchoring at their final location, a metal structure which connects the three floating concrete bases by means of a connecting element to the wind turbine tower, and a metal element which connects the floating concrete bases to the wind turbine, metal element on which a docking area is installed, a maintenance platform and access stairs; and wherein each of the three floating concrete bases comprises a lower slab which is in contact with the terrain once the system has been submerged, an upper slab, a perimeter wall and interior walls or partitions that define a first group of interconnected cells; and wherein the method comprises the following stages: a first transport stage wherein the foundation system is towed from a collecting and/or assembly dock to the final location by using tug boats where the three floating concrete bases are anchored, a second anchoring stage wherein the foundation system is anchored until making contact with the seabed modifying the overall buoyancy by the controlled ballasting of some groups of cells in the three floating concrete bases with the operation of valves located in said bases, and a third refloating stage in the event of dismantling or repositioning of the foundation system by evacuating the water ballast from the previously ballasted cell groups to achieve positive buoyancy of the foundation system.

18. The method of claim 17 wherein before the first transport stage there are a series of foundation system manufacturing stages comprising: a stage for the manufacturing of the three floating concrete bases at a dock of a port using a floating dock in which a steel tubular projection is left embedded to serve as the connection between the metal structure and the concrete bases, a stage for the manufacturing of the metal structure on land, a stage for the manufacturing of a connecting element that is the base of the wind turbine, a stage of joining together the metal structure and the three floating concrete bases and of welding the connecting element to the metal structure, and a stage for mounting the wind turbine onto the connector element.

Description

DESCRIPTION OF THE DRAWINGS

(1) To complete the description being made and for a better understanding of the characteristics of the invention, according to a preferred practical embodiment thereof, a set of drawings is attached as an integral part of the description, which by way of example without limiting the scope of this invention, show the following:

(2) FIG. 1Shows a perspective view of a first embodiment of the gravity-based foundation system for offshore wind turbine installation of the present invention.

(3) FIG. 2.Shows an elevation view of FIG. 1.

(4) FIG. 3.Shows a plan view of FIG. 1.

(5) FIG. 4.Shows a perspective view of a second embodiment of the gravity-based foundation system for offshore wind turbine installation of the present invention.

(6) FIG. 5.Shows an elevation view of FIG. 4.

(7) FIG. 6.Shows a plan view of FIG. 4.

(8) FIG. 7.Shows a perspective view of a first embodiment of the mixed connecting node between the metal structure and each of the floating concrete bases.

(9) FIG. 8shows a plan view of the detail of the metal structure rod connection to the mixed connecting node.

(10) FIG. 9.Shows a sectional view AA of FIG. 8.

(11) FIG. 10.Shows a sectional view BB of FIG. 8.

(12) FIG. 11.Shows a plan view of the detail of the metal structure rod connection to the mixed connecting node according to a second embodiment thereof.

(13) FIG. 12.Shows a sectional view AA of FIG. 11.

(14) FIG. 13.Shows a block diagram of the control system of the gravity-based foundation system for offshore wind turbine installation.

PREFERRED EMBODIMENT OF THE INVENTION

(15) FIGS. 1 to 3 identify the main parts comprised by the gravity-based foundation system for offshore wind turbine installation according to a first embodiment. These figures identify the following elements: Floating concrete bases (1) or hollow concrete supports, known as caissons in the field of maritime civil engineering, with an integrated valve system to allow the ballasting and de-ballasting of the base with water. Tripod-shaped metal structure (2) attaching the concrete bases to a connecting element (3) to the height of the wind turbine installation. Connecting element (3) between the floating concrete bases (1, 4) and the wind turbine. It includes a maintenance ship docking system and the stairs for access to the base of the wind turbine, as well as the system for attaching the wind turbine to the foundation.

(16) FIGS. 4 to 6 show the main parts are identified comprised by the gravity-based foundation system for offshore wind turbine installation according to a second embodiment. These figures identify the following elements: Hollow reinforced floating concrete bases (4), known as caissons in the field of maritime civil engineering, with an integrated valve system to allow the ballasting and de-ballasting of the base with water. Lattice-shaped metal structure (5) as to join the floating concrete bases (4). Connecting element (6) between the floating concrete bases (1, 4) and the wind turbine. It includes the maintenance ship docking system and the stairs for access to the base of the wind turbine, as well as the system for attaching the wind turbine to the foundation.

(17) In either embodiment, the attachment of the metal structure (2, 5) to the three floating concrete bases (1, 4) is performed by means of mixed connecting nodes (7, 27), one for each floating concrete base (1, 4), each of which comprises a concrete core (8) and a prestressing system (9) integrated therein.

(18) The metal structure (2, 5) attaching the three floating concrete bases (1, 4) to the connecting element (3, 6) comprises three inclined diagonal rods (10) whose ends (11) which connect to each mixed connecting node (7, 27) are conical frustum-shaped which enables the appropriate adjustment of the mechanical constraints.

(19) The mixed connecting node (7, 27) further comprises a sheet metal coating (12) externally covering the concrete core (8), a metal coating (12) whose primary function is to assist in the transfer and resistance to the stresses caused by the forces introduced by the inclined diagonal rods (10) in the mixed connecting nodes (7, 27), although it also acts as a closure and protection element for the concrete core (8) used, to promote durability conditions thereof and, above all, of the working conditions of the prestressing system (9) situated in the mixed connecting node (7, 27) of the metal structure (2, 5) and the floating concrete base (1, 4).

(20) The mixed connecting node (7, 27) further comprises anchors that are actively involved in the transmission of forces, while the floating concrete base (1, 4) comprises passive anchors disposed in its interior, either directly in an upper closing slab (13) or in rigidity partition walls or interior walls situated under the mixed connecting nodes (not shown).

(21) On these anchors arranged on the upper closure slab (13) or on the rigidity walls the upper closure slab (13) of the floating concrete base (1, 4)where partly prefabricatedis concreted, whereby only some sheaths with tendons inside (not shown) remain exempt, while in the case of prefabricated mixed connecting nodes (7, 27), the latter together with some sheaths, tendons and passive anchors will be placed in an approximate position during the concreting of the floating concrete base (1, 4).

(22) In a first embodiment of the mixed connecting node (7) shown in FIGS. 7 to 10, the metal coating (12) of the mixed connecting node (7) has a polyhedral-like geometric shape with an upper prismatic-trapezoidal-shaped area (14) wherein one of the sides (15), the one that receives an inclined diagonal rod, is in turn inclined and perpendicular to the inclined diagonal rod, and a lower irregular prismatic-hexagonal-shaped area (16), wherein two of its vertical sides (17), which receive some first auxiliary rods (18) linking together two adjacent mixed connecting nodes (7) of each floating concrete base (1), are perpendicular to said first auxiliary rods (18), wherein the sides (15, 17) at which the inclined diagonal rod and the first auxiliary bars join are made of sheet steel.

(23) Furthermore, at the mixed connecting node (7), a vertical side (19) of the lower irregular prismatic-hexagonal-shaped area (16) which is situated between the two vertical sides (17) that receive the first auxiliary rods (18), receives a second auxiliary rod (20) joining the mixed connecting node (7) to the connecting element (3).

(24) Therefore, in this first embodiment of the mixed connecting node (7), said mixed connecting core (7) receives, via the metal coating (12) with a tubular-like geometric shape, the inclined diagonal rod (10), the first auxiliary rods (18) linking together two adjacent mixed connecting nodes (7) of each floating concrete base (1) and the second auxiliary rod (20) joining the mixed connecting node (7) to the connecting element (3).

(25) Inside the mixed connecting node, that is, in the concrete core (8), the active anchors comprising: transfer sheets (21) of the four rods (10, 18, 20) which penetrate the mixed connecting node (7), wherein two of them, the inclined diagonal rod (10) and the second auxiliary bar (20) are joined together by welding at the point of intersection of the axes of all the rods (10, 18, 20), transfer and connecting sheets (22) joining the first auxiliary rods together,

(26) Additionally, the prestressing system (9) is also located inside the mixed connecting node (7),

(27) Once the preceding system has been placed, either on the prefabrication bench, or at the port if the mixed connecting node (7) is constructed therein, the node will then be concreted, preceded in the latter case by the concreting of a connection area between the mixed connecting node (7) and the floating concrete base (1), a connection area left as a control element with assembly and execution tolerances.

(28) The prestressing system (9) arranged inside the mixed connecting node (7) that penetrates the floating concrete base (1) is then prestressed, followed by the injection of the sheaths, and lastly the placing and welding of the metal coating (12) of the mixed connecting node (7) which encloses the concrete core (8).

(29) In a second preferred embodiment of the mixed connecting node (27), shown in FIGS. 11 and 12, the mixed connecting node (27) has a metal coating (23) with a tubular-like geometrical shape arranged around a concrete core (24), wherein the metal coating (23) is a steel pipe section open at its upper end, to enable the concreting and the placing of the other elements described in the first embodiment of the mixed node (7).

(30) The mixed connecting core (27) receives, via the metal coating (23) with a tubular-like geometrical shape, the inclined diagonal rod (10), the first auxiliary rods (18) linking together the two adjacent mixed connecting nodes (27) of each floating concrete base (1) and the second auxiliary rod (20) which connects the mixed connecting node (27) to the connecting element (3).

(31) Inside the mixed connecting node (27), that is, in the concrete core (24) the transfer sheets (21) are situated, as well as the transfer and connection sheets (22), the prestressing system (9) and the passive anchors as described above.

(32) The gravity-based foundation system for offshore wind turbine installation further comprises a control system which in turn comprises a sensing subsystem (30), an operational control subsystem (31) and a decision-making subsystem (32) during the transport, anchoring, service and refloating stages, wherein the operative control subsystem enables the coordination between the sensing subsystems and decision-making support subsystem.

(33) The sensing subsystem (30) comprises filling level sensors (33) for the filling of the first group of cells whose function is to measure their ballasting level during the towing, anchoring and refloating stages. They are preferably situated on the lower slab.

(34) The sensing subsystem (30) further comprises inertial acceleration sensors (34) preferably placed on the upper slab of the caisson, in the mixed connection nodes joining and in the connection between the connecting element of the wind turbine and the metal structure. Their function is to measure the accelerations to avoid exceeding the possible thresholds set by the turbine manufacturer during the towing and anchoring stages.

(35) The sensing subsystem (30) further comprises Doppler acoustic sensors (35) for measuring currents in the vicinity of the structure and the distance to the seabed. Its function is to monitor the hydrodynamics surrounding the structure and to control the position of each caisson relative to the seabed in the anchoring stage and to support the erosion evolution characterization during the service stage. They are located at the point where the lower slab and the perimeter wall meet.

(36) The sensing subsystem (30) further comprises a gyro (36) to monitor the roll and pitch of each of the floating concrete bases (1, 4), which are preferably arranged in the centre of each floating concrete base. Its function is to control the verticality of the system during the towing and anchoring stages.

(37) The sensing subsystem (30) further comprises relative and absolute positioning sensors (37) to locate the system during transport and for its dynamic positioning during the anchoring stage. They are arranged on top of the metal structure.

(38) The sensing subsystem (30) further comprises pressure sensors (38) for the estimation of the actions resulting from the interaction between the flow of the sea and the structure during the service stage. They are preferably arranged embedded inside the perimeter walls of floating concrete bases.

(39) The sensing subsystem (30) further comprises deformation sensors (39) that enable the estimation of the number and magnitude of stress load cycles of the system due to its interaction with the ocean flow and/or cyclic stresses transmitted by the wind turbine. They are preferably arranged at the nodes of the metal structure and at the transition point between the metal structure and the floating concrete bases.

(40) The decision-making support subsystem (32) comprises a logical device (40) which is a first-level instrumental alarm to generate warnings to prevent exceeding the thresholds registered by the sensing subsystem, and a second-level prediction device (41) based on a climate prediction system (42) and on the instrumental historical records obtained by the different sensors (33, 34, 35, 36, 37, 38, 39), performing a real-time control (43) by the operational control subsystem (31) and may be displayed on a display device (44); an operational control subsystem (31) acting on the control actuators (45) that perform the opening and/or closing of the valves (46) for water filling and emptying and on a system of anchors and winches (47), to fix the position of the foundation system, generating response scenarios for the foundation system in the short and long term.