WO2004015207A1

WO2004015207A1 - Method and apparatus for the founding of an installation at the seabed

Info

Publication number: WO2004015207A1
Application number: PCT/NO2003/000268
Authority: WO
Inventors: Harald Johansen; Björn BEKKEN
Original assignee: Hammerfest Ström As
Priority date: 2002-08-13
Filing date: 2003-08-06
Publication date: 2004-02-19
Also published as: AU2003248519A1; NO20023834D0; NO320938B1

Abstract

The present invention concerns an anchoring for a post (6) to a seabed. The anchoring includes an outer tube (1) and an inner tube (3) placed inside the outer tube (1). The lower part of the post (6) is adapted for being placed in the inner tube (3) and the outer tube (1) is rigidly connected to the seabed. In one embodiment, the angle between the inner pipe (3) and the outer pipe (1) may be adjusted with an adjustment device (4). The cavity between the outer pipe (1) and the inner pipe (3) will normally be cemented when the anchoring is placed on a seabed.

Description

Method and apparatus for the founding of an installation at the seabed.

The invention concerns a foundation or base for an apparatus for the production of electric energy from ocean and river currents. Furthermore the invention concerns an anchoring of the system, and a method for the installation of the system.

Research and development relating to tidal power stations or plants for the production of electric energy has been going on for many decades. One of the advantages with tidal power plants is for instance that they, in the relation to windmills, are predictable and to a small degree dependent on the weather. Nevertheless, very few plants are built in spite of that it, on a world basis, is enormous energy resources in tidal currents. The cause is probably of an economical and - or environmental kind. These and other reasons have resulted in the development of plants that are completely placed below the ocean surface. These plants are built from modules placed on a foundation at the ocean bed. However it is a challenge to install a rigid foundation at a correct angle below the ocean surface in an economical way, because the conditions at the seabed can be difficult and varying, and because the modules that are to be founded may have considerable dimensions. The foundations must necessarily be placed in flowing bodies of water, and in some cases be installed relatively deep. The foundations are exposed to considerable mechanical loads from the flowing bodies of water and from the turbine they are meant to carry, and these loads can be fluctuating and create natural oscillations in the structure. The foundations must be able to be installed quickly because the work with the installations in many cases must be performed during the change of tide to avoid the current in the area being too strong to prevent installation.

It has previously been developed little technology within this field because plants for the production of energy from flowing bodies of water, placed on a foundation, and that are completely placed below the surface of the water, not has been widespread, and are of a newer date. The mounting of subsurface power plants has in most cases previously necessitated difficult, comprehensive and cost incentive work from divers.

An example of such a tidal plant built of modules is described in patent application NO 2001 0737, Hammerfest Strøm. This plant includes a foundation intended to be placed at the seabed, and one or more modules placed at the foundation. The modules may include a turbine, a generator for electric current, a transmission and various electrical components. These turbines are secured to a foundation that may include pillars or columns.

It has proved difficult to achieve an installation on a seabed in an enduring and cost effective way, particularly with difficult floor or seabed conditions. Bodies of water flowing around constructions of this type easily create natural oscillations in the structure, and this in turn imposes considerable requirements to the foundation. It is also a challenge to place such foundations or tower tubes at a correct angle.

Structures not extending above the surface, are favourable to reduce the disturbance and drag of the water current. Drag and disturbance in the water current may affect the turbine in an unfavourable way.

It is a purpose of the present invention to simplify installation of foundations and components for plants completely placed below the surface of the water. The invention may of course also be used as a foundation for installation of modules extending above the surface.

This is achieved with the present invention as defined in the independent claims.

The present invention provides a structure that can be founded in a simple and cost effective way with various floor or seabed conditions, and a method for installing the structure on the floor. It is a purpose with the invention to provide a structure that simplifies maintenance and replacement of components. The foundation is particularly adapted for a propeller turbine where the blades are pitch controlled to be able to twist the blades at least 180°, preferably in connection with a change of tide. Thereby the shown structure can be installed in a locked position on a carrying structure (does not need to rotated, as opposed to a windmill).

The carrying structure including the foundation may include a cable gate the transfer cable is secured to avoid fatigue fractures due to the forces from the water current.

The foundation includes preferably an anchoring pillar. In one embodiment, this may be drifted into the seabed. A reinforcement tube with a casting frame may be placed around the anchoring pillar and may be filled with concrete, and a carrying pillar may carry the housing and be secured to the anchoring pillar for anchoring the housing to the seabed.

The described components may be assembled as modules to ease installation and maintenance. During the installation, the housing with the turbine will normally represent one module and the foundation one or several other modules. In one embodiment, the foundation comprises the previously mentioned anchoring pillar, the reinforcement tube with a casting frame and the carrying pillar as separate modules.

The advantages with the modular assembly include considerably lower construction costs, the ability for stepwise building, and simplified disassembly or decommissioning.

In a method for installing the apparatus according to the invention, a stepwise installation is allowed, enabling installation in spite of large forces caused by the water current.

A foundation according to the invention is intended to be lowered down onto a seabed from a vessel. The foundation includes an outer tubing that is placed rigidly on the seabed after the founding has been performed. An inner tubing is installed inside the outer tubing. In an alternative embodiment, the inner tubing is installed after the outer tubing is placed on the seabed. The angle of the inner tubing in relation to the outer tubing, and thereby the rest of the foundation and the seabed may be adjusted with a devise intended for this purpose, such that the succeeding tower pipe or post can be placed vertically or at another desirable angle. The angular adjustment may be performed in that the lower part of the inner tube is fixed, and the upper part of the inner tube is adjusted with a suitable mechanism for this purpose. Examples of such mechanisms may include manually or mechanically operated power screws, rack and pinion drives, or hydraulic cylinders. The mechanism preferably allows adjustments about two axes, such that the angle of the inner tube can be adjusted freely.

In one embodiment, the outer tube is secured to box shaped elements by means of a truss construction or the like. The boxes may be made of a heavy material, but are preferably hollow and are filled with ballast during installation. The distance between the boxes is chosen in relation to expected load, such that the footprint of the foundation is sufficient to provide for the required stability. Following adjustment of the inner tube in relation to the outer tube, the annulus between tubes may be filled with concrete such that the tubes are stabilized in relation to each other. The diameter of the outer tubing in relation to the inner tubing is adapted such that a desired interval of adjustment in relation to the angle between the tubes and such that the annulus easily can be filled with concrete or another suitable filling material is achieved.

Following the installation of the foundation, a tower pipe or post, adapted for being attached to for instance a turbine with a housing and a generator as described, is inserted. The tower pipe includes preferably guiding cones that ensures that the tower pipe is centred in the inner tubing and is aligned parallel to this. The guiding cones are placed around the part of the tower pipe that is adapted to go into the inner tubing, and is placed such that the guiding process is facilitated, and at the same time that it is ensured that these can absorb bending moment transferred to the tower pipe. The tower pipe may furthermore include one or several keys or splines that may go into one or several slots in the tubing for correct orientation of the tower pipe, preferably in relation to a flowing direction of the flowing tidal current. Accordingly the inner tube should also be adjustable about its longitudinal axis in relation to of the direction of the current. The slot should be open towards the end of the tube with an opening that is considerably wider than the spline or key, and be tapered downwards to ease the guiding of the tower pipe and the spline. Following the guiding, the cavity or annulus between the tower pipe and the inner tubing may be cemented, or secured in any other way.

Short description of the enclosed figures:

Fig. 1a, 1b is a top view and an elevation respectively of a foundation according to an embodiment of the invention;

Fig. 2a-2c is a side elevation where an installation sequence for the embodiment shown on fig. 1 is illustrated, from left to right;

Fig. 3a-3c shows two further steps of the installation sequence from fig. 2, where fig. 3b is a top view of fig. 3a;

Fig. 4a-4c shows two further steps of the installation sequence from fig. 2 and fig.

3 where fig. 4b is a top elevation of fig. 4a; Fig. 5a and 5b shows the last two steps of the installation sequence from fig. 2, fig.

3 and fig. 4;

Fig. 6 is a side elevation of a tidal plant secured to a carrying post and a foundation according to the invention;

Fig. 7a-7d is a side elevation of an installation sequence of an another embodiment of the invention;

Fig. 8e-8g shows further three steps of the installation sequence from fig. 7; and

Fig. 9 shows an alternative embodiment of the installation shown on fig. 7 and 8.

An embodiment of the invention will in the following be described. Figure 1 shows a foundation according to one embodiment of the invention. The foundation is designed to be lowered onto a seabed from a vessel. The foundation is seen from above and from the side respectively and includes an outer tubing 1 that is connected by means of a trussed construction or a similar construction to two boxshaped elements 2. The boxes 2 may be made of a heavy material, but are preferably hollow and are filled with ballast during installation. An inner tubing 3 is installed inside the outer tubing 1. The angle of the inner tubing 3 in relation to the outer tubing 1 and thereby the rest of the foundation can be adjusted with a screw device as shown on the figure, with hydraulic cylinders, with rack and pinion drive, drive screws or in any other suitable way.

Figure 2 shows three steps during installation of the foundation with outer tubing 1 , the inner tubing 3 and the boxshaped elements 2. The steps shows from left to right, a lowering of the foundation and filling of the boxshaped elements 2 with ballast, for instance rocks, by means of a suitable vessel, and the foundation installed and completed at the seabed.

Figure 3 shows three sketchers where, figure 3a is a side elevation of a foundation placed on a seabed, that can be placed at an inclined angle for subsequent adjustment. Figure 3b is a top elevation of figure 3a and shows how the angle of the inner tubing 3 of the foundation is adjusted by means of screws, hydraulic piston/cylinders or the like 4, schematically shown as screws. The figure shows a diver adjusting the screws with wheels manually, but the adjustment may well have been performed automatically with actuators well known within the field. When the inner tube 3 is in a vertical position, it may be locked by cementing the cavity between the inner tube 3 and the outer tube 1 by means of a hose from the surface 5 as shown on figure 3c. During the installation of the foundation, it is likely that it ends up in an inclined position in relation to a true vertical position, and the outer tube 3 is accordingly not placed in a vertical position. This is why it is necessary to be able to adjust the above described angle.

Figure 4 shows three sketchers how the tower pipe is installed, where Figure 4a shows a side elevation of how the tower pipe 6 is positioned over the inner pipe 3 of the foundation. This will in most cases be more easily performed by establishing a leading or guiding wire between the surface and the foundation the tower pipe is guided down along (not shown on the figure). The tower pipe is equipped with two or several centring cones 7 at the part of the tower pipe that is to enter into the inner pipe 3 of the foundation. These cones shall ensure that the tower pipe 6 achieves the same verticality as the inner piper 3 of the foundation. Because the turbine later is to be mounted on the tower pipe 6, the tower pipe 6 must be installed at a given orientation in relation to the direction of the water flow. The inner pipe 3 is therefore equipped with an orientation slot 8 as shown on figure 4b that is a top elevation of figure 4a.

The localization of this slot in relation to the axis of the water current is observed and used to mount an orientation spline 9 on the tower pipe 6 as shown on figure 4c. During the lowering of the tower pipe 6, this orientation spline will collide with the edge of the inner tube. When this happens, the tower pipe 6 is turned until the orientation spline 9 slides into the orientation slot 8, and the tower piper 6 can be lowered to its final position. At this point the tower pipe 6 is in a correct position both with reference to verticality and orientation, and the cavity between the tower pipe 6 and the inner pipe 3 can be cemented.

Figure 5 shows an installation of a cable pipe, and that the cable is pulled in. The cable pipe 10 is secured to the tower pipe 6 and may be hinged as shown on the figure. The cable 11 to the shore may be installed in this tube either in that it is pulled into the tube, as shown on the figure, or in that the cable tube is divided and hinged, and that the cable thereby may be laid into the cable tube. The cable will normally have several integrated functions, such as power lines, signal lines and in some cases hydraulic/pneumatic lines. When installation of the cable in the cable pipe is completed, it is suspended such that the connection to the nacelle is accessible at the upper edge of the cable pipe.

Figure 6 shows a lift induced propeller turbine (1t) that is an example of an element in form of a module to generate power from flowing bodies of water that may be mounted on a foundation according to the invention. The module includes a turbine (1t) with turbine blades. The blades have an adjustable pitch to be able to be rotated at least 180° in connection with a change of current direction and are installed in a water tight capsule or housing (2t) with equipment to transform the rotation of the turbine to electrical current, including a generator, a gear or transmission and a control system. In that the turbine blades may be rotated as described, the shown construction may be mounted in a locked position on the carrying structure or the foundation (does not need to be rotated, as opposed to a windmill).

A carrying structure (3t) that carries the turbine (1t) and the capsule (2t) may also include a cable gate that a transferral cable (4t) is secured to, to avoid fatigue fracture due to the current forces. The transferral cable (4t) for the generated power stretches from the electric generator, through the water tight capsule and to a landbased plant (5t). The landbased plant (5t) transforms the generated power before it is phased in on an existing power grid.

The installation of the apparatus in relation to another embodiment of the invention is shown on figure 7 and figure 8. The installation is shown performed stepwise in the steps (a) to (g). The steps (a), (b), (c) and (d) on figure 7 shows that an anchoring post or an anchoring tube 11 first is driven into the seabed. At the outside, it is installed a combined casting frame and reinforcement tube 12. The casting frame 15 (shown as a cone) may be of various materials, including fabric that forms a conical shape when this is filled with concrete (later in the installation sequence). If the seabed masses are unstable in relation to scouring, this may be remedied by placing a rock/gravel filling 13 around the edge of the casting frame 15. The carrying foundation for turbine 1 and capsule 2 shown on figure 6 is installed inside the anchoring post 11 that is drifted into to the seabed, and is orientated in relation to the direction of the flowing current. The orientation may be achieved as defined on the figures 4a, 4b and 4c in that an orientation spline 9 is mounted on the tower pipe 6 as shown on figure 4c. During the lowering of the tower pipe 6, this orientation spline will collide with the edge of the inner tube. When this happens, the tower pipe 6 is twisted until the orientation spline 9 slides into the orientation slot 8, and the tower pipe 6 can be lowered to a final position. The steps (e), (f) and (g) on figure 8 shows that the cavity between the anchoring post 6 and the reinforcement tube 12 inside the casting frame 15 and between the carrying post 6 and reinforcement tube 12 is filled with concrete. To ensure that the tower pipe is placed at a correct angle, it may, in one embodiment, be adjusted as shown on figure 3a, 3b and 3c. The adjustment must be performed before the tower pipe is cemented. Thereafter the hinged cable gate 17 is released such that the lower part is rotated and falls towards the seabed.

Figure 9 shows a simple embodiment where the outer pipe is drifted into a seabed, and a tower pipe 6 with centring cones 7 cemented in the outer pipe.

Claims

P a t e n t c l a i m s :

1. An anchoring for a post (6) to a seabed, with a foundation comprising an outer tube (1) and an inner tube (3) placed at the outside of the outer tube (1), where the lower part of the post (6) is adapted for being placed in the inner pipe (3) and where the outer pipe (1) is rigidly connected to the seabed.

2. The anchoring for a post (6) according to claim 1 , where the angle between the inner pipe (3) and the outer pipe (1 ) may be adjusted with an adjustment device (4).

3. The anchoring for a post (6) according to claim 1 or 2, where the cavity between the outer tube (1) and inner tube (3) is cemented when the anchoring is placed on the seabed.

4. The anchoring for a post (6) according to claim 1 , where the outer tube (1 ) is secured to boxes (2), and where the boxes (2) are adapted for being filled with ballast after being placed on the seabed.

5. The anchoring for a post (6) according to claim 1 , where the lower part of the post (6) for placement in the inner pipe (6) includes a spline (9) for meshing with a slot (8) in the inner pipe (3) for the orientation of the post (6) along the longitudinal axis of the post in relation to the foundation.

6. The anchoring for a post (6) according to claim 1 , where the orientation of the inner tube (3) along its longitudinal axis may be adjusted in relation to the outer tube (1).

7. The anchoring for a post (6) according to claim 1 , where the post includes two or several centring cones (7) on the part of the tower pipe that is adapted to enter the inner pipe (3) to centre the post in the tower pipe and to ease the guidance of the post (6) into the inner pipe (3).

8. The anchoring for a post (6) according to claim 1 , where the inner pipe (3) constitutes an anchoring post (11) that is drifted into the seabed, where the outer pipe (1) constitutes a reinforcement pipe (12), where a casting frame (15) is placed around the anchoring post (12) and is filled with concrete, and where the post (6) is secured to the anchoring post (12).

9. The anchoring for a post (6) according to claim 1 , where a housing (2t) supports a turbine (2t) and where the post (6) is rigidly connected to the foundation (14), such that the housing (2t) not can be rotated in relation to the seabed.

10. The anchoring for a post (6) according to claim 1 , adapted for an apparatus assembled of modules, where these modules includes a housing (2t) with an axial

- - _. i turbine (1t) and the post (6).

11. The anchoring for a post (6) according to claim 8, comprising an anchoring post (11), a combined casting frame (15) and reinforcement pipe (12), where the casting frame (15) (shown as a cone) may be of various materials, including fabric that forms a conical shape when it is filled with concrete.

12. The anchoring for a post (6) according to claim 1 , comprising a cable gate (17) that a transferral cable (4t) is secured to, to avoid fatigue fracture due to the forces from the flowing current, where the transferral cable (4t) for the generated power from the housing and the turbine extends from an electric generator through the housing (2t) and to a landbased plant (5t),

13. A method for the anchoring of an apparatus according to claim 8, c h a r a c t e r i z e d by the following steps: drifting the anchoring post (11 ) into the seabed; tread the reinforcement pipe (12) with a casting frame (15) at the outside of the anchoring post (11); filling the casting frame with concrete; securing the carrying post (16) to the anchoring post (11); and securing the housing to the anchoring post.