Process for installing an offshore tower

Abstract

Process for installing an offshore tower, specifically a substructure, which basically comprises the following steps: a) dry manufacturing a foundation comprising a block (1, 1) basically made of concrete and dry manufacturing a base section (25) of a shaft (2); b) applying said base section to said foundation block, forming a unit called the starting unit; c) moving said starting unit to the installation point of said substructure; and d) actuating in a controlled manner, first ballast valve means in such a manner that said starting unit sinks until resting on the seabed; having placed said foundation block or said starting unit in the body of water where the installation point said substructure is located.

Claims

1. A process for installing an offshore tower, particularly a substructure which includes a tower shaft basically made of concrete and a corresponding tower foundation basically made of concrete, wherein said shaft is semi-submerged in installed conditions and said foundation is submerged in installed condition; said process comprising: performing the following steps, in chronological order: (a) dry manufacturing said foundation comprising a block basically made of concrete, said foundation block being essentially hollow nd watertight and having a ballast valve means for opening a passage to the interior of said foundation block, dry manufacturing a base section of said tower shaft, and dry manufacturing one or more superposition section(s) of said shaft; (b) applying, mechanically or integrally, said base section to said foundation block in such a manner that said base section and said foundation block assume the relative position envisaged for the installed condition, said base section and said foundation block forming a starting unit; (c) moving said starting unit, in a self-floating manner, through the body of water wherein the installation point of said substructure is located up to the installation point of said substructure; (d) actuating, in a controlled manner, said ballast valve means of said foundation block so as to open a passage to the interior of said foundation block for introducing ballast in said foundation block through said passage, in such a manner that said starting unit sinks until resting on the bottom of the body of water; said process also comprises, after step (a) and before step (c), step: (e) placing said foundation block or said starting unit in the body of water where the installation point of said substructure is located; said foundation block is configured in such a manner as to have the floatability required for step (c) and/or said starting unit is configured in such a manner as to have the floatability required for step (c); said process also comprises, after step (a), step: (f) laterally applying to said foundation block and/or to said base section at least one positive auxiliary floating structure which is temporary and reusable, which remains at least partially emerged during the installation process, and guiding means comprising articulated bars joined in a fixed manner to said at least one positive auxiliary floating structure and in a sliding manner to said base section, wherein both said at least one positive auxiliary floating structure and said guiding means assist in sinking of the said foundation block and/or said base section, such that the guiding means remain emerged during the sinking thereby causing the base section to sink in, a substantially vertical position until resting on the bottom of the body of water; said process also comprises after step (a) and before step (c), step: (g) applying at least one of said superposition section(s) to said foundation block and/or to said base section and/or to said auxiliary structure(s) in a position different from the installed condition in relation to the starting unit; said process also comprises, after step (c), step: (h) disposing said superposition section(s) in said starting unit in such manner that said superposition section(s) assume the position envisaged for the installed condition in relation to the starting unit.

2. The process for installing an offshore tower according to claim 1, wherein in step (a), the dry manufacturing of said superposition section(s) includes the pre-assembly of long voussoirs having a vertical dimension larger than a horizontal dimension, until forming complete sections.

3. The process for installing an offshore tower, according to claim 1, which also comprises, after step (a) and before step (c), step: (j) applying wind turbine means to said foundation block and/or to said base section and/or to said superposition section(s) and/or to said auxiliary structure(s).

4. The process for installing an offshore tower, according to claim 3, which also comprises, after step (j), step: (k) disposing said wind turbine means in such a manner as to assume the position envisaged for the installed condition.

5. The process for installing an offshore tower, according to claim 1, which also comprises, after step (a) and before step (h), step: (l) applying lifting means for tower assembly to said foundation block and/or said base section and/or said auxiliary structure.

6. The process for installing an offshore tower, according to claim 1, wherein in step (a) said foundation block is internally divided into watertight enclosures by means of partition walls.

7. The process for installing an offshore tower, according to claim 6, wherein in step (d) the introduction of ballast in said foundation block causes spatially selective ballasting by means of distribution valve means for fluid communication with the adjacent watertight enclosures of said foundation block.

8. The process for installing an offshore tower, according to claim 7, wherein said ballast valve means and/or said distribution valve means include remote actuation means and/or predetermined automated actuation means.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and further characteristics and advantages of the invention will become evident from the following description of an embodiment of the invention, provided solely by way of non-limiting example, with reference to the accompanying drawings, wherein:

(2) FIG. 1 shows a schematic front view of an embodiment of an offshore tower which can be assembled following the installation process according to the present invention;

(3) FIG. 2 shows a schematic top plan view of a first starting unit which is being towed with superposition sections thereupon;

(4) FIG. 3 shows a schematic sectional top plan view of the internal configuration of the foundation block of the starting unit of FIG. 2;

(5) FIG. 4 shows a schematic sectional front view of the starting unit of FIG. 2 with superposition sections thereupon;

(6) FIG. 5 shows a schematic sectional front view corresponding to FIG. 3 but at a later stage of the installation, according to the present invention;

(7) FIG. 6 shows a schematic front view of a detail of the assembly of FIGS. 2 to 5, in partial cross-section;

(8) FIG. 7 shows a schematic top plan view of a second starting unit with two auxiliary floatability structures which support superposition sections and wind turbine means;

(9) FIG. 8 shows a schematic sectional top plan view of the internal configuration of the foundation block of the starting unit of FIG. 7;

(10) FIG. 9 shows a schematic sectional front view of the starting unit of FIG. 7 with two auxiliary floatability structures which support superposition sections and wind turbine means;

(11) FIG. 10 shows a schematic sectional front view corresponding to FIG. 8 but at a later stage of an installation process according to the present invention with the auxiliary flotability structure which remains at least partially emerged during the installation process;

(12) FIG. 11 shows a schematic elevational view and top plan view, both in cross-section, of a detail of the assembly of FIGS. 7 to 10, specifically the configuration of superposition sections supported by an auxiliary floatability structure of the assembly of FIGS. 7 to 10, configuration wherein said superposition sections are essentially disposed on the same axis and level, with the smaller sections inside the larger sections, hereinafter referred to as multi-layered configuration;

(13) FIG. 12 shows a schematic top plan view of an assembly of starting units having common auxiliary floatability structures;

(14) FIG. 13 shows a schematic front view of a third starting unit which is being towed, with superposition sections and means for assembling towers thereupon;

(15) FIG. 14 shows a schematic front view corresponding to FIG. 13 but at a later stage of the installation process according to the present invention;

(16) FIG. 15 shows a schematic plan view and front view of a starting unit in the floated transportation phase, with connected auxiliary floating structures and superposition sections and wind turbine means being transported over the foundation block and the auxiliary floating structures;

(17) FIG. 16 shows a schematic plan view and front view of the group showed in FIG. 15 during the ballasting process.

DETAILED DESCRIPTION OF THE INVENTION

(18) Initially referring to FIG. 1, an embodiment of an offshore wind tower 27 is shown, that is, a substructure 1, 1, 2 for supporting wind turbine means 16, susceptible of being installed by means of the installation process according to the present invention.

(19) Said tower 27 is formed by a foundation block, specifically a submerged platform 1, 1 acting as a gravity-based foundations, basically made of structural concrete, full of ballast, and a shaft 2, of the semi-submerged type, which in turn includes a plurality of sections 25, 7 mainly formed by concrete voussoirs 3, also including horizontal joints 4 and vertical joints 5 between said sections 25, 7 and said voussoirs 3, respectively. Said substructure 1, 1, 2 supports wind turbine means 16. For certain applications, not according to the invention, said substructure can comprise only the platform 1, 1 and base section 25, disposing said wind turbine means 16 directly on said base section 25.

(20) Said platform 1, 1 is dry manufactured (on land, dry docks, coastal or floating ports, or other enabled and protected coastal or maritime facilities) and configured following the installation process of the present invention in such a manner that, during installation phases prior to shaft 2 assembly, said platform 1, 1, without ballast, provides a provisional and stable floating platform which enables transport by self-floatation with the corresponding base section 25 applied thereto (said foundation platform and said base section thus forming a starting unit 1, 1, 25), to its final site.

(21) Therefore, according to the installation process according to the present invention, the voussoirs 3 that form at least some sections 25, 7 of the shaft 2 are assembled prior to transport thereof in open sea, in such a manner as to transport sections 25, 7 already pre-assembled and complete.

(22) The final assembly of the shaft 2 by successive stacking of the superposition sections 7 is generally carried out at the final site.

(23) Platform 1, 1 is substantially flat and horizontal and built of structural concrete, whether using in-situ concrete techniques or by assembling prefabricated parts or panels, or a combination of both. The plan and elevation geometry thereof may vary in accordance with specific project requirements, adopting for example significantly circumferential 1 floor plan configurations, whether with a curved or polygonal perimeter, or quadrangular 1 type configurations aimed at simplifying construction thereof, as well as other regular or irregular polygon shapes. The dimensions of the platform 1, 1 are predetermined in accordance with known techniques in such a manner that: wind tower 27 stability in installed condition is provided, thanks to its own weight and that of the ballast, and to adequate load transfer on the seabed, a platform 1, 1 is provided, having the floatability and stability required for said previous function as a provisional floating and stable platform, a starting unit 1, 1, 25 is provided, having the necessary space and resistance to transport superposition sections 7 or other necessary components and equipment.

(24) The flat morphology and large volume of the foundation platform 1, 1 allow limitation of the necessary water depths for floatation thereof, thereby reducing the operating requirements for the infrastructures that serve for manufacturing and subsequent floating thereof.

(25) FIGS. 2 to 6 relate to a first example of an offshore tower for the installation process according to the present invention.

(26) Specifically, FIG. 2 shows a starting unit 1, 25 which is being towed in a self-floating manner along the sea surface prior to sinking thereof, with superposition sections 7 disposed thereupon.

(27) FIG. 3 shows the platform 1 of FIG. 1, configured by way of a multicellular circular box, which comprises a lower slab 11, an upper slab 12 and a peripheral slab 9, as well as a plurality of straight, rigid inner ribs 10. The ribs 10 are disposed forming squares which delimit inner enclosures 13. For example, the lower slab 11 and peripheral slab 9 are executed by means of in-situ concrete, and the upper slab 12 and ribs are materialised by means of prefabricated alveolar slabs. The platform 1 comprises a circumferential rib 26 which coincides with the circumferential extension of the base section 25 and is structurally prepared for mechanically connecting to the base section 25 by means of the upper slab 12.

(28) At least one of the lower 11, upper 12 or peripheral 9 slabs has ballast valves, and at least part of said inner enclosures 13 are watertight and/or have distribution valves. These inner enclosures provide an adequate floatation volume for said function as a provisional and stable floating platform; additionally, upon reaching the installation point, controlled filling, totally or partially, with ballast (for example water 17) of all or some of these enclosures 13 by means of said ballast valves and/or said distribution valves helps to carry out the sinking operation of the starting unit, in such a manner as to correctly orient said starting unit.

(29) Remote actuation means and/or predetermined automated actuation means can be incorporated to actuate said ballast valves and/or said distribution valves. There can also be intermediate stable phases during the sinking operation, wherebetween superposition section 7 assembly phases are interspersed. To this end, different floatation configurations can be used, varying the selective filling of the inner enclosures 13. Finally, said inner enclosures can remain filled with ballast 17 in their final situation after installation in order to generate greater stabilising weight.

(30) As shown in FIGS. 2 and 4-6, at least part of the superposition sections 7 can be transported on the starting unit 1, 25, whether in their final position on said starting unit 1, 25 or, as shown, in a provisional position enabled for transporting the superposition sections 7.

(31) As shown in FIG. 5, the starting unit 1, 25 can use the internal volume of the platform 1 and also the internal volume of the base section 25 as floatation volume. In fact, the floatation of said internal volume of the base section 25 can complement or substitute the floatation of the platform 1. The platform 1 can be submerged during transport.

(32) FIG. 5 also shows that securing and anti-collision means can be disposed to aid the sinking of said starting unit 1, 25. Said securing and anti-collision means comprise arms 6 joined in a fixed manner to said superposition sections 7 and in a sliding manner to said base section 25, in such a manner that while sinking, the arms 6 move upwards through the base section 25 so as to maintain said superposition 7 sections conveniently secured to the base section 25, thereby preventing the superposition sections 7 (which are floating nearby) from drifting away and becoming dispersed and/or colliding with the starting unit 1, 25.

(33) Fastening means for provisionally securing the superposition sections 7 on said platform 1 may be disposed. As can be particularly seen in FIG. 6, in this embodiment said fastening means comprise tensioning cables 8 which secure the superposition section 7 to the platform 1 and a base 15 whereupon the superposition section 7 rests. Said tensioning cables 8 will be released before disposing said superposition sections 7 on said starting unit 1, 25 in the position envisaged for the installed condition. Preferably, said tensioning cables 8 will be released while sinking the starting unit 1, 25.

(34) In this example of a tower, said superposition sections 7 are adapted by means of internal partitioning for self-floatation and, optionally, self-overturning, in such a manner that, when not joined to the starting unit 1, 25 (whether due to being superposition sections 7 which have been transported on the starting unit 1, 25, the fastening means of which have become released, or due to being superposition sections 7 which have been transported independently to the starting unit 1, 25) these float and can be oriented.

(35) After anchoring, shown in FIG. 5, the superposition sections 7 will be raised and positioned using external assembly means (conventional and therefore not shown) for executing marine constructions.

(36) FIGS. 7 to 11 relate to a second example of an offshore tower for the process of the present invention.

(37) Specifically, in accordance with the project and stability conditions adopted for the platform 1, as shown in this example, at least two sections 25, 7 can be stacked in their final position on the platform 1 prior to transporting the assembly by floatation. Likewise, auxiliary floating structures 14 can be used, provisional and reusable, which increase platform 1 floatability and stability. These auxiliary floating structures 14 are provisionally attached and connected to said platform 1 using adequate anchoring 21 means. These auxiliary floating structures 14 also serve, in this example, to transport at least part of the superposition sections 7 and wind turbine means 16, with or without blades, thereupon. As shown in FIG. 10, this auxiliary flotability structure remains at least partially emerged during the installation process.

(38) Guiding means can also be disposed to aid the sinking of said starting unit 1, 25. As can be particularly seen in FIG. 10, said guiding means comprise articulated bars 18 joined in a fixed manner to said auxiliary structures 14 and in a sliding manner to said base section 25.

(39) As shown particularly in FIG. 11, although also included in FIG. 7, in order to transport the superposition sections 7 at least part of said superposition sections 7 can be disposed in a temporary multi-layered configuration 22, such that said superposition sections 7 are essentially disposed on the same axis and level, with the smaller sections inside the larger sections. This allows greater efficiency of the space occupied and can facilitate the assembly operation of the sections, given that it allows successive raising of the superposition sections without obstacles, whereupon the superposition section having the largest diameter and being most outwardly disposed is raised from its temporary position in each case.

(40) As shown in FIG. 12, assemblies formed by several starting units 1, 25 and auxiliary floating structures 14 common to some of said starting units 1, 25 can also be formed for transport operations by floatation. This solution allows a reduction in the number of auxiliary structures required, which can be particularly advantageous if the distance from the manufacturing point of said starting unit to the installation point of the corresponding tower is significantly high.

(41) As now shown in FIGS. 13-14, a crane 20 can be disposed on the platform 1, possibly provisional and reusable, for assembling the substructure 1, 1, 7, 25, and optionally the wind turbine means 16 or any of its constituent parts. In this case, at least part of the crane 20 mast, for example the metal jacket, can be transported already installed on the platform 1 and remain partially submerged after sinking. By way of example, as shown specifically in FIG. 14, the crane 20 is secured using means for fastening 19 to sections of the tower itself, and the crane 20 parts are provisional and reusable with the exception of a semi-submerged lower part, which is permanent for the purpose of facilitating reinstallation of the crane 20 for maintenance, repair or component replacement operations, etc.

(42) Said crane can be self-mountable, i.e. the tower can be a crane-tower, already known in other applications.

(43) FIG. 15 and FIG. 16 represent another example of an offshore foundation and tower installed following the process of the present invention. They represent the floating transportation stage and the ballasting stage respectively. The variations with respect to the example showed in FIGS. 7 to 10 are: Wind turbine means 16 are also transported in a temporary position on the auxiliary floating structures 14, together with the superposition sections 7. Wind turbine means 16 include a wind turbine nacelle which is transported on top of a superposition section 7, and a wind turbine blade which is transported directly over the auxiliary floating structure. The number of auxiliary floating structures 14 is four instead of two.

(44) Naturally, the principle of the invention remaining the same, the embodiments and construction details can widely vary with regard to those described and illustrated herein purely by way of non-limiting example, without departing from the scope of protection of the invention, as defined in the following claims.

(45) Specifically, by way of illustrative and non-limiting example, while the tower shaft has a circular cross-section in a preferred option of application, alternative polygonal cross-section geometries are also possible.