DEVICE AND METHOD FOR MARINE TOWER STRUCTURE
A tower structure (1) for use in a body of water, comprising a hollow outer section (2) with a first end (4) equipped with an opening. An inner section (3) is telescopically accommodated in the cavity of the outer section (2) and is telescopically movable in the outer section (2) from a position in which essentially the whole of the inner section is accommodated in the outer section to a position in which a length of the inner section projects above the first end of the outer section. The inner section comprises a plurality of chambers (6, 6′) fluid-connected via ducts (10′) and openings (9), and where at least one chamber is fluid-connected via at least one duct (10) to a source for a ballasting fluid (8), whereby the chambers (6) can selectively be filled with ballasting fluid.
The invention relates to structures for the support of installations above a water surface, where the structures rest on the bottom below the water surface. More specifically, the invention relates to an arrangement and a method for a marine tower structure as disclosed in the preamble of the attached claims. The invention is directed in particular to the support of wind turbines, radar installations and other devices that are to be positioned above the water surface, and especially at a certain height above the water surface.
It is obvious to those of skill in the art that the uppermost section of the structure that supports the device such as the wind turbine (hereafter referred to as “the tower”) must be a slender structure in order to keep the environmental loads (wind, waves and current) to a minimum and so as not to come into conflict with the actual device, e.g., is the blades of the wind turbine as they rotate. A particular challenge in offshore installations is that the tower must be dimensioned to take up operating and environmental loads without the tower moving to any appreciable degree or being subjected to undesirable vibrations.
Characteristic natural features which affect the technical solution of typical tower structures close to shore or in small water depths are:
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- 1. Unfavourable conditions for foundation work (uneven/sloping seabed, inhomogeneous seabed masses, earth and seabed properties which require foundation work using piles driven into the seabed (usually the most expensive solution for foundation work).
- 2. Design wave loads are of substantial size and affect the whole structural component that is below the water surface, i.e., more or less right down to the seabed.
Known solutions are based on a concept where the lower part of the structure is given a fixed foundation on the seabed and then an upper part, typically in the form of a circular-cylindrical tower, is transported to the site, lifted onto and secured to the pre-installed lower part.
An example of a known tower structure for a wind turbine is shown in JP2003206852, where a lattice structure has a cross-sectional shape of an equilateral triangle. The structure has a relatively slender upper portion, whilst it is substantially wider further down and below the water surface. The structure is fixed to the seabed using piles.
Furthermore, JP20040002819 shows a relatively slender tower resting on a submerged platform that is fixed to the seabed by piles. JP2006037397 teaches a method for the installation of a tower of the monopile type by means of piling, where the method comprises the use of a jack-up rig equipped with a mobile crane. Moreover, US 2006/0222465 and WO 2006/004417 teach tower structures where the lower part is a lattice structure of the type used in connection with oil installations (“jacket”) and the upper part of the tower (typically from above the water surface) is a slender, tubular structure.
Of the prior art, GB A 2 265 905 teaches an offshore tower structure according to the preamble of claim 1.
All prior art solutions have a number of drawbacks, as for example:
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- 1. The towers must be transported to the site (often on barges) in two or more parts, and assembled in-situ.
- 2. Assembly and installation call for large (and costly) crane vessels.
- 3. Low values for permitted wave height and wind speed limit time periods in which efficient assembly and installation can be done.
- 4. Foundation work on the seabed is, as a rule, costly, piles that are driven into the seabed must often be used, and expensive ground surveys must often be carried out at a substantial depth below seabed level.
- 5. The installation often calls for work at great heights.
- 6. Removal after end of service life is demanding and requires specialised equipment.
There is therefore a need for an arrangement and a method that can remedy these and other defects of the prior art.
Thus, according to the invention there is provided a tower structure for use in a body of water, comprising a hollow outer section having a first end equipped with an opening, wherein an inner section is telescopically accommodated in the cavity of the outer section through the opening in the said first end and is telescopically movable in the outer section from a position in which essentially the whole of the inner section is accommodated in the outer section to a position in which a length of the inner section projects out above the first end of the outer section, characterised in that the inner section comprises a plurality of chambers fluid-connected via ducts and openings, and where at least one chamber is fluid-connected via at least one duct to a source for a ballasting fluid, whereby the chambers can selectively be filled with ballasting fluid.
According to the invention, there is also provided a method for installation of the tower structure, characterised by the steps of
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- a) inserting the inner section (3) into the outer section (2) and placing the connected sections floating, essentially horizontally, in a body of water having a water surface (21);
- b) filling a selection of chambers (6′) with a ballasting fluid via ducts (10, 10′);
- c) closing inlet valves (13) for ballasting fluid and pressurising the chambers (6, 6′) using a gas;
- d) towing the structure in the body of water to an installation site;
- e) opening an inlet into and preferably also an outlet out of the lowermost part (5) to give the tower a tilt which then causes the ballasting fluid originally in ballast chamber (6′) to flow to and collect in the lowermost part of the inner section (3), whereby the tower structure (1) is made to rotate in the body of water and the second end (5) of the outer section moves towards a substructure (15) on the bottom below the body of water;
- f) raising the tower structure to an almost vertical position in the body of water, the second end of the outer section being supported by the substructure (15) on the bottom;
- g) by means of gas pressure, displacing all or a predetermined amount of the ballasting fluid out of the inner section and the outer section, whereby the inner section moves relative to the outer section so that a portion of the inner section extends a distance beyond the first end of the outer section, preferably above the water surface (21);
- h) locking the inner section and the outer section in relation to one another.
The invention seeks to solve most of the negative features of today's technology, especially those associated with transport and installation of the structure (including its removal after the end of its service life). Transport and installation constitute a substantial proportion of the total costs of the structure.
The invention remedies some of the defects of the prior art in that:
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- 1. A large proportion of the installation work can be done on shore.
- 2. All transport work and most of the installation work offshore is done primarily with the aid of a towing vessel.
- 3. The foundation work is simplified and does not require that parts of the substructure penetrate so deep into the seabed. This goes a long way towards eliminating the need for costly specialist equipment and expensive ground surveys at substantial depths below the seabed.
- 4. The foundation work is fairly independent of uneven or sloping seabed.
The inventive solution resides in the design of the tower that is composed of two almost equally long sections (an outer section and an inner section) which are assembled telescopically. For transport and installation, the inner section is mounted within the outer section, which makes it practically possible to transport and install towers of substantial size. Once the assembled tower is at the installation site and secured in a vertical position, the inner (uppermost) section is extended out of the outer (lowermost) section until the inner section is secured in position and held by the outer section.
The extension of the inner section can advantageously be done by means of an interaction of natural forces, i.e., gas expansion on pressure drops and buoyancy, which will be described in more detail below. An especially advantageous utilisation is obtained if the tower is built separately, i.e., without any device/support that holds the tower in a vertical position when installed and during use of the tower, and that the building of the tower is carried out in a horizontal position (as opposed to an upright position). Then an advantageous method is obtained.
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- 1. Building and assembly in a horizontal position (on shore, a barge and the like).
- 2. Transfer to floating position, still horizontal. When constructed on shore, the tower can usually be launched directly into the water, e.g., by means of sliding or lifting. When constructed on a barge, or if other circumstances so dictate (e.g., maritime aspects of the construction site), the tower is transported in a horizontal position on a barge to a suitable unloading site.
- 3. The towing is carried out with the tower floating to the offshore installation site
- 4. The lowermost (outer) section of the tower (still in retracted position) is run to a pre-installed substructure and then raised.
- 5. The tower is moved to the vertical position and secured.
- 6. The inner section is pushed out of the outer section until fixing has been engaged/carried out.
The inventive solution of the tower comprising two almost equally long sections that are assembled telescopically can also be used in solutions where the tower is held in a vertical position and secured to the seabed in another way than by means of stays. By way of example, the tower can be integrated in a lattice structure that is designed and provided with a foundation in a known way. Transport to the installation site can s be done as a tow in water with the structure either horizontal or upright. Such a solution will often require the use of several buoyancy elements (separate/reusable or integrated). If the structure is towed upright, the buoyancy elements can be simplified in that the equipment for the gravity transfer of the ballast water is not necessary.
The invention will now be described with the aid of the attached figures, where like reference numerals designate like parts.
The device according to the invention comprises a tower structure (hereafter referred to as tower) 1 which comprises a hollow, preferably tubular outer section 2 with a first end 4 which is open and a second end 5 which is closed. Inside the cavity of the outer section 2 there is inserted an inner, preferably tubular section 3 through the said first end 4. The inner section 3 can thus move telescopically inside the outer section 2 in a way that will be described in more detail below.
It is anticipated that these operations from the start of the submersion of one of the end to the seabed until erection of the tower can begin will take two to six hours. It is desirable that during this time all ballast water moves and collects in the lower end of the inner section 3. The practical check that all water has shifted as desired is by the s position in the water that the tower has assumed, namely its angle and thus the length that is under water. Since it is not possible to get the water back into the chambers once submersion has started, the submersion equipment (wires and winch on the towing/installation vessel) must be dimensioned for unintended shifting of all ballast water before the lowermost part of the tower has been put down on a substructure on the seabed. It is obvious that the tower cannot sink by accident, except in the improbable case of significant damage to the well-protected upper section.
Filling with ballast water is done after the tower has been fully fabricated and transferred into a floating position in a body of water. Ballast water is filled through pipe 10 and the displaced air flows out of the chambers through the openings 9 and out of the inner section 3 through pipe 11 into the atmosphere. After the desired amount of ballast water has been filled into the chambers 6′, the pipe 10 is closed by the valve 13 and the whole inner section is pressurised with gas. The gas is forced in through pipe 11 until desired pressure has been reached and the pipe is closed by valve 12. Both water and gas pipes are protected against emissions in that the pipe terminations are plugged and/or enclosed in a structural protection means.
In the lower end of the inner section 3 there is located an outlet 14 for ballast water that is to be discharged in order to allow the pushing out of section 3 from section 2 to be carried out. In addition to remote controlled valves, the opening of this valve can be done using a mechanical connection between the valve and the second end of the buoyancy element which, when the element is rotated in the water (e.g., in connection with installation of a structure as discussed above), will be above the water surface and thus easily accessible. These solutions are known to those of skill in the art (valves that open with the aid of electrical or acoustic signals; alternatively, valves or plugs may be used which open with the aid of a pulling device connected to the second end of the buoyancy body, or hydraulically; one of the solutions may be a backup for the other).
An embodiment of the inner section 3 is also described in a Norwegian patent application filed by the same applicant as in this case, and filed on the same date as this patent application.
The cables 18 can be mounted at the same height as connections between the outer section 2 and the inner section 3 and in this way a favourable absorption of the forces between the two sections is obtained. The broken line shows the area in which the outer section 2 overlaps the inner section 3, and locations for devices 24 which fasten the sections together (as described above).
The next phase is shown in
As the tow boat begins to pull on the reconnected wire to the upper part of the tower, the tower begins to rotate to approximately a vertical position in the water, as shown in solid lines in
The tensioning must be done in two or more successive rounds to get the tower vertical and to obtain the desired tension in the cables that is decisive for the dynamics of the whole system when it is subjected to dynamic loads. This situation with ready tensioned cables is shown in
In the next phase the inner section 3 of the tower 1 is pushed out by buoyancy. This is shown in principle in
The erection of the assembled tower shown in
The element 39 consists of two cylindrical tanks 40, each of them located on each side of the outer section 2 as shown in
Transport and installation of anchors and substructure can advantageously be done by a towing vessel.
Submersion to the seabed is done in two steps. In the first of these, the anchor 19 is transferred from a floating position to a position in which it hangs in the lowering wire under the stem of the towing vessel. This is done by admitting seawater into the ballast chamber in the anchor which results in the buoyancy of the anchor gradually decreasing and the anchor going under the water surface and moving downwards in an almost circular path (shown in
Free flow of ballast water into the anchor was initiated in that the hose 48 was released and the whole hose with its open end 49 put in the water, which led to seawater beginning to flow in. When a certain amount of water was inside, the anchor left the surface 21 and the cover 43, because of its buoyancy, was floating on the surface and ready to be secured for re-use. The cable part 33 is held slack during this phase so that unduly large loads are not mobilised therein. After the anchor has assumed a steady position under the stern of the towing vessel, it is winched down to the seabed. At a small height above the seabed, positioning is effected in that distance line 51 is tensioned to obtain desired distance from the preinstalled substructure and is then moved in a circular path to the correct orientation in the horizontal plane. The anchor is subsequently set down on the seabed, the lowering line 32 is disconnected by tilting the end eye 46 out of position from the trunnion 44. The lower cable part 33 is brought into the desired position so that it is not an obstacle for the last operation in the installation of anchors which are ballasted with solid ballast, e.g., rock, iron ore, concrete blocks. This operation is done independent of the installation of anchors, but in the time period before the installation of the tower.
The arrangement and method according to the invention are particularly suitable for water depths in the range of about 25 metres to about 100 metres.
Claims
1-6. (canceled)
7. A tower structure for use in a body of water, said tower structure comprising:
- a hollow outer section having a first end defining an opening; and
- an inner section telescopically accommodated in a cavity of said outer section through said opening in said first end, said inner section being telescopically movable in said outer section from a first position in which the whole of said inner section is accommodated in said outer section, to a position in which a length of said inner section projects exteriorly of said first end of said outer section, said inner section having a plurality of chambers fluidly connected via ducts and openings, and wherein at least one of said chamber is fluid-connected via at least one of said ducts to a source for a ballasting fluid, wherein said chambers are selectively fillable with said ballasting fluid.
8. The tower structure according to claim 7, wherein said inner section is equipped with at least one outlet out of at least one of said chambers, through which said ballasting fluid can selectively be filled in a cavity at a second end of said outer section.
9. The tower structure according to claim 7, wherein said inner section and said outer section comprise support and locking means for locking said inner and outers sections in a desired position in relation to one another.
10. The tower structure according to claim 7 further comprising a second end of said outer section is configured for connection to a substructure placed on a bottom below a body of water.
11. The tower structure according to claim 10, wherein said substructure defining a recess in a top portion thereof, said recess being formed to receive said second end of said outer section.
12. The tower structure according to 10, wherein said substructure having a skirt adapted to penetrate the bottom of the body of water.
13. The tower structure according to claim 7 further comprising a buoyancy element connectable to said outer section.
14. The tower structure according to claim 13, wherein said buoyancy element includes a member that is a removably connectable with a member on said outer section.
15. The tower structure according to claim 7, wherein said inner section is supported against said outer section by a plurality of rollers.
16. A tower structure system comprising:
- a hollow outer section having a defined internal cavity, a first end defining an opening, and a closed second end;
- an inner section telescopically accommodated in said cavity of said outer section through said opening in said first end, said inner section being telescopically movable in said outer section from a first position in which the whole of said inner section is accommodated in said outer section, to a position in which a length of said inner section projects exteriorly of said first end of said outer section, said inner section having a plurality of chambers fluidly connected via ducts and openings, and wherein at least one of said chamber is fluid-connected via at least one of said ducts to a source for a ballasting fluid, wherein said chambers are selectively fillable with said ballasting fluid; and
- a substructure placed on a bottom below a body of water, said substructure defining a recess adapted to receive and support said second end of said outer section.
17. The tower structure according to claim 16, wherein said inner section is equipped with at least one outlet out of at least one of said chambers, through which said ballasting fluid can selectively be filled in a cavity at said second end of said outer section.
18. The tower structure according to claim 16, wherein said inner section and said outer section comprise support and locking elements for locking said inner and outers sections in a desired position in relation to one another.
19. The tower structure according to 16, wherein said substructure having a skirt adapted to penetrate the bottom of the body of water.
20. The tower structure according to claim 16 further comprising a buoyancy element connectable to said outer section.
21. The tower structure according to claim 20, wherein said buoyancy element includes a member that is a removably connectable with a member on said outer section.
22. The tower structure according to claim 16, wherein said inner section is supported against said outer section by a plurality of rollers.
23. The tower structure according to claim 16 further comprising at least one anchor element having an upward open box placed on the bottom of the body of water, at least on ballast chamber, an attachment device fixed to said open box, and a skirt adapted to penetrate into the bottom of the body of water, wherein a cable is connectable to said attachment device and said outer section.
24. A method for installation of a tower structure in a body of water, said method comprising the steps of:
- a) providing a tower structure comprising: a hollow outer section having a first end defining an opening; and an inner section telescopically accommodated in a cavity of said outer section through said opening in said first end, said inner section having a plurality of chambers, fluid-connected via ducts, and openings, and wherein at least one of said chamber is fluid-connected via at least one of said ducts to a source for a ballasting fluid;
- b) inserting said inner section into said outer section;
- c) placing said inner and outer sections floating, essentially horizontally, in a body of water having a water surface;
- d) filling a selection of said chambers of said inner section with said ballasting fluid via said ducts;
- e) closing inlet valves for said ballasting fluid and pressurizing said chambers of said inner section using a gas;
- f) towing said tower structure in the body of water to an installation site;
- g) opening an inlet into and an outlet out of a lowermost part of said outer section to give said tower structure a tilt which then causes said ballasting fluid in said chamber to flow to and collect in a lowermost part of said inner section, whereby said tower structure is made to rotate in the body of water and said second end of said outer section moves towards a substructure on a bottom below the body of water;
- h) raising said tower structure to a near vertical position in the body of water, said second end of said outer section being supported by said substructure on the bottom;
- i) displacing, by means of gas pressure, a predetermined amount of said ballasting fluid out of said inner section and said outer section, whereby said inner section moves relative to said outer section so that a portion of said inner section extends a distance beyond said first end of said outer section above the water surface; and
- j) locking said inner section and said outer section in relation to one another.
25. The tower structure according to claim 24, wherein said tower structure is raised into said near vertical position in the body of water with the aid of an external buoyancy element.
Type: Application
Filed: Jun 12, 2008
Publication Date: Jun 17, 2010
Inventor: Karel Karal (Oslo)
Application Number: 12/601,084
International Classification: E02D 11/00 (20060101); E02D 5/22 (20060101);