WO2012121607A1

WO2012121607A1 - Offshore foundation for installation on the seabed and method for installation of the offshore foundation

Info

Publication number: WO2012121607A1
Application number: PCT/NO2012/050012
Authority: WO
Inventors: Trond LANDBØ; Niklas NORMANN
Original assignee: Vici Ventus Technology As
Priority date: 2011-03-10
Filing date: 2012-02-02
Publication date: 2012-09-13
Also published as: NO20110369A1; NO332557B1

Abstract

Offshore foundation and a method for an installation of a foundation on the seabed 25 with mounted deck equipment 20, preferably for wind turbines or oil and gas. The foundation 1 comprises at least three cells 3 and at least one tower 13 preferably arranged centrically between the cells 3. The at least three cells 3 are arranged with the internal sliding bucket cells 6, which in an extended condition during the installation of the foundation 1 on the seabed 25 protrudes up through the water line 26 and in a submerged condition is arranged within the at least three cells 3.

Description

Offshore foundation for installation on the seabed, and method for installation of the offshore foundation

The present invention is related to an offshore platform, and a method for installation of the foundation on the seabed, with mounted deck equipment, primarily for wind turbines or oil and gas, as the foundation comprises at least three cells and at least one tower tower preferably arranged centrically between the cells.

Specifically, the foundation consists of at least one tower (cylinder / cone) with a wider foundation design in the bottom. One objective of such foundations is to be able to assemble a foundation and deck equipment (top side) close to the shore, to tow complete units to the offshore location and install when ballasting. The foundation is preferably of the type mono-tower gravity foundation or a skirt piled foundation, a "volume foundation" preferably built with concrete or steel that is self-floating in all the temporary floating phases. These foundations often have a lower limit for water depths, in which one may obtain stability in floating phases without the use of aids. This is particularly a challenge if you want a full assembly of the foundation and topside / wind turbine close to the shore. A known solution to obtain floating stability for mono-tower foundations is to make use of temporary buoyancy in the form of separate buoyancy tanks mounted on the structure prior to installation, and dismantle these after the foundation has been put in place. The latter in order to avoid these tanks being subject to large wave loads. Such temporary floating bodies will lead to costly naval operations both before and after the installation.

Another known solution is to mount permanent buoyancy tanks which are to remain after the installation, but which then will have the disadvantage that they significantly incur additional wave loads which the structure will have to be able to withstand throughout its service life.

One goal of the present invention is to provide a design that has the full stability in all floating phases, including installation at the field, at water depths that are normally too shallow to obtain such stability for this kind of foundations. Another goal is that the above-mentioned stability has to be achieved in a manner that does not require costly naval operations before and after installation, and which does not incur large wave loads during operation.

A further goal is that the construction or the offshore foundation should be removable from the seabed in a manner that is simple and cost effective.

The aims of the present invention are achieved by an offshore foundation for installation on the seabed with mounted deck equipment, preferably for wind turbines or oil and gas, as the foundation comprises at least three cells and at least one tower preferably arranged centrically between the cells,

characterized in that the at least three cells are arranged with the internal sliding bucket cells in an extended state during the installation of the foundation on the seabed protrude up through the water line, and are arranged within the at least three cells in a submerged condition.

Preferred embodiments of the offshore foundation are further elaborated in claims two to nine inclusive.

Further, the objectives of the present invention are achieved by a method for installing an offshore foundation with mounted deck equipment, preferably for wind turbines or oil and gas, as the foundation comprises at least three cells and at least one tower preferably arranged centrically between the cells,

characterized in that the at least three cells are arranged with internal sliding bucket cells, where the upper area of the bucket cells is positioned above the waterline during installation and immersion of the foundation to the seabed as the air is trapped in the cavities of the bucket cells, formed between the internal wall and the top surface of the bucket cells and the water surface or the foundation plate, and after installation of the foundation on the seabed the air in the cavity is released out, and water is filled in, whereby the bucket cells is lowered into the cells.

One preferred embodiment of the invention will hereinafter be explained with reference to the figures, where

Figure 1 shows an offshore foundation with attached deck equipment, according to the invention,

Figure 2 shows a plan view through the section 2-2 in Figure 1 ,

Figure 3 shows a detail of a bucket cell of the offshore foundation in Figure 1 and Figure 2,

Figures 4a-h show the offshore foundation in a stepwise phase from the

construction until it is installed on the seabed,

Figure 5 shows the offshore foundation with mounted deck equipment and with an alternative embodiment of the bucket cells,

Figure 6 shows a plan view through section 2-2 of Figure 5, and

Figure 7 shows a detail of the alternative bucket cell of the offshore foundation in

Figures 5 and 6.

With particular reference to Figures 1 , 2 and 3, an offshore foundation 1 is shown. The foundation 1 comprises at least three cells 3 and at least one tower 13 preferably arranged centrically between the cells 3. Deck equipment 20, in the form of a wind turbine, is mounted on the tower 13. The cells 3 are arranged with the internal sliding bucket cells 6, which in an extended condition upon installation of the foundation 1 on the seabed 25 protrude up through the water line 26, where they in a submerged condition are arranged within the at least three cells 3.

With particular reference to Figure 3, the sliding bucket cells 6 are shown as cylinders with an upper top plate 7 and a lower outer peripheral flange design 8. The cells 3 are arranged with an internal upper ring joist 4 which implies that, when the sliding bucket cells 6 are in an extended state, they will bump into and stop at the internal upper ring joist 4.

Bucket cells 6 can be arranged with a valve 1 1 for discharge or introduction of air, respectively, out of or into the cell cavities of the bucket formed between the inner cell wall and the top surface 9, 10 of bucket cells and the water surface 16.

Bucket cells 6 can be made of steel or concrete, or a combination of these materials and other suitable materials.

Bucket cells 6 can also be arranged with at least one telescoping part in the form of at least a cylinder jacket at the outside of the internal bucket cell 6.

Figures 4a-4h show a stepwise build-up of the offshore foundation 1 until it is ballasted and installed on the seabed 25.

Figure 4a shows the cells 3 with the internally arranged gliding bucket cells 6 in a floating state.

Figure 4b shows the complete offshore foundation 1 with the tower 13 mounted. Figure 4c shows the ballasting and embedding of the offshore foundation as the gliding bucket cells 6 are in a partially extended state.

Figure 4d shows ballasting until the bucket cells are in an extended condition, in which the lower outer peripheral flange design 8 bumps into against the internal upper ring joist 4 The exterior water line 26 and the internal water surface 16 are here shown. The cavity, which is enclosed by the water surface 16 and the internal cell wall and the top surface 9, 10 of bucket, is filled with air, and the cells 3 are filled with water.

Figure 4e shows the filling of solid ballast for transportation of a foundation 1 to the site where the installation is to take place.

Figure 4f shows the ballasting of the offshore foundation 1 when mounting on the deck equipment 20.

Figure 4g shows deballasting of the offshore foundation 1 with mounted deck equipment 20 upon transportation to the installation site.

Figure 4h shows an offshore foundation installed at the seabed 25. After installation, valve 1 1 is opened and the air in the bucket cells 6 is released, such that they sink down into the cells 3. Extra ballast 27 is also shown added into the lower tower area of the offshore foundation.

With reference to figures 5, 6, and 7, the offshore foundation 1 is shown in an alternative embodiment. Here also, the foundation 1 comprises the three cells 3 and one tower 13 being centrically arranged between the cells 3. With particular reference to Figure 6, it is here shown that the foundation has a somewhat different design compared with the embodiment discussed in Figures 1 , 2 and 3. Furthermore, with reference to Figure 7, the sliding bucket cell 6 is arranged with a lower foundation plate 14. The sliding bucket cell is also arranged with a second valve 12, which will be located below the external waterline 26 after installation of the foundation 1 on the seabed 25. The alternative embodiment of the sliding bucket cells 6, with both the upper top plate 7 and the lower foundation plate 14, results in a very favorable stabilizing effect for the offshore foundation 1 . An internal waterline is avoided in the bucket cells 6, and you do not have to take into account that the air inside the bucket cells 6 is being compressed, which affects both the stability and requires feeding of pressure as the draft is changed. This alternative embodiment of the bucket cells 6 results in that bucket cells 6 become dense, and must therefore be equipped with a second valve 12 located below the external waterline 26 after installation of the foundation 1 on the seabed 25. The second valve 12 may be opened to the sea, such that water can be filled into the bucket. The aforementioned valve 1 1 arranged in the upper part of the bucket cell 6 is used for evacuation of air when the bucket cells 6 is filled with water and for pumping the air when they are to be emptied of water.

The offshore foundation 1 obtains full stability in all floating phases, including the installation at the field. This is obtained by use of the sliding bucket cells 6 (preferably in steel, but concrete and other materials may be used), which runs through the water line, and significantly increases the moment of inertia of the water level. The construction according to the invention results in achieving full effects of the bucket cells during installation, and that these disappear into the foundation structure after installation in order to avoid increased wave loads. It does not require that you actively control the buoyancy of the bucket cells 6. It is the trapped air that raises the gliding bucket cells 6 or the cylinders above the waterline at all times, and lift them until the lower outer peripheral flange design 8 stops against the internal upper ring joist 4 in the cells 3 The gliding bucket cells 6 will then serve as fixed buoyancy bodies until the foundation 1 has been placed on the seabed 26. After installation has been completed, the valve 1 1 is opened and the air in the bucket cells 6 is released, such that they sink into the cells 3.

Any removal of the offshore foundation 1 will occur in the reverse order; you will then pump air into the gliding bucket cells 6 until they rise above the water line 26 and stops against the ring joist 4. You will then be able to raise the foundation 1 by pumping water out of the central chamber and the tower 13. Then the offshore foundation can be towed ashore and be dismantled into their respective parts.

In the demonstrated embodiment of the offshore foundation 1 , the cells 3, or the box, are approximately half the water depth and the buckets 6 with a similar height, so they just protrude up during the installation. At deeper waters, these bucket cells may have an additional jacket of steel cylinder on the outside, extra telescopic joints, which allow for that the box height is reduced to about one-third of the water depth, and the bucket cell 6 and the additional cylinder jacket have similar heights such that the bucket cell protrudes up through the water line 26.

Claims

120510/[RADGIVER] PATENT CLAIMS

1. Offshore foundation (1 ) for installation on the seabed (25) with mounted deck equipment (20), preferably for wind turbines or oil and gas, as the foundation (1) comprises at least three cells (3) and at least one tower (13) preferably arranged centrically between the cells (3),

characterized in that the at least three cells (3) are arranged with the internal sliding bucket cells (6) in an extended state during the installation of the foundation (1) on the seabed (25) protrude up through the water line (26), and are arranged within the at least three cells (3) in a submerged condition.

2. Offshore foundation (1 ) according to claim ^characterized in that the sliding bucket cells (6) are cylinders with an upper top plate (7) and a lower external peripheral flange design (8), and the at least three cells (3) are arranged with an internal upper ring joist (4) whereby the lower external peripheral flange design bumps into the internal upper ring joist when the gliding bucket cells (6) are in an extended state.

3. Offshore foundation (1) according to claims 1 or 2,

characterized in that the sliding bucket cells (6) are arranged with a valve (11) for discharge or introduction of air, respectively, out of or into the cavities of the bucket cells, formed between the inside of the cell wall and the top surface (9, 10) of the bucket cells and the water surface (16).

4. Offshore foundation (1 ) according to any of the preceding claims, characterized in that the sliding bucket cells (6) are further arranged with a lower bottom plate (14).

5. Offshore foundation (1 ) according to claim 4, characterized in that the sliding bucket cells (6) are arranged with a second valve ( 2) located below the external water line (26) after installation of the foundation (1) at the seabed (25).

6. Offshore foundation (1 ) according to any of the preceding claims,

characterized in that the sliding bucket cells (6) are made of steel.

7. Offshore foundation (1) according to any of claims 1 - 5,

characterized in that the sliding bucket cells (6) are made of concrete.

8. Offshore foundation (1) according to any of preceding claims,

characterized in that the sliding bucket cells (6) are arranged with at least a telescopic joint, in the form of at least a cylinder jacket on the outside of the internal bucket cell (6). ,

9. Method for installing an offshore foundation (1 ) with mounted deck equipment (20), preferably for wind turbines or oil and gas, as the foundation (1 ) comprises at least three cells (3) and at least one tower (13) preferably arranged centrically between the cells (3),

characterized in that the at least three cells (3) are arranged with internal sliding bucket cells (6), where the upper area of the bucket cells is positioned above the waterline (26) during installation and immersion of the foundation (1) to the seabed (25) as the air is trapped in the cavities of the bucket cells, formed between the internal wall and the top surface (9, 10) of the bucket cells and the water surface (16) or the foundation plate (14), and after installation of the foundation (1) on the seabed (25) the air in the cavity is released out, and water is filled in, whereby the bucket cells (6) is lowered into the cells (3).