Semi-submersible floating platform for deployment of single-column semi-submersible floating foundation

Abstract

A semi-submersible floating platform (1) is configured for supporting and transporting a column structure (2), and comprises a plurality of buoyant columns (4a-c) interconnected by a support structure (5) having an adaptive opening (7) for axial and radial fastening of the column structure (2). Each column (4) comprises ballasting means (16, 17) whereby the draft may be controlled, and each column (4) comprises an active heave motion neutralization system that may be operated independently, such that the platform (1) may be maintained stable and level when handling the structure (2), for example during transit, separation and docking. A method of operating the platform involves the operation of valves (20, 22) to control the pressure inside a reservoir (12) in order to control the water level (11) in a rise canister (30) in one or more of the columns (4a-c).

Description

[0001] Semi-submersible floating platform for deployment of single-column semi- submersible floating foundation

[0002] Technical field of the invention

[0003] The invention concerns the field of semi-submersible vessels. More specifically, the invention concerns a semi-submersible floating platform as defined by the preamble of claim 1, and a method as defined by the preamble of claim 8.

[0004] Background of the invention

[0005] The present invention describes a semi-submersible floating platform with a device for stabilizing support and assisting buoyancy for a single-column semi-submersible platform - or buoy - also referred to as a spar buoy. Such spar buoys may be economically attractive as foundation for floating wind turbines. Their design is simple and they may be anchored in such a way that heave and drift movements become minimal. The disadvantage with the concept is that they need deep waters in order to float vertically and must therefore usually be towed to location floating horizontally They are then ballasted to vertical position and anchored, whereupon tower and wind turbine are arranged on top. Such offshore operations are costly, and are also dependent on favourable weather conditions.

[0006] Summary of the invention

[0007] The present invention - hereinafter referred to as the deployment platform - eliminates such extensive offshore operations. The spar buoy is towed to location in a vertical position and completely outfitted, also in shallow waters. Such platform has potential for installation of wind turbines at sea for generation of electricity with associated equipment.

[0008] The deployment platform described herein comprises a support structure with a device for securing and stabilizing the spar buoy, and three or more columns that allow sufficiently controlled submerging depth such that the attached spar buoy, following disconnection, may float independently and freely.

[0009] The invention is set forth and characterized in the main claim, while the dependent claims describe other characteristics of the invention. It is thus provided a semi -submersible floating platform configured for supporting and transporting a column structure, characterized by

[0010] - a plurality of buoyant columns interconnected by a support structure having an adaptive opening for axial and radial fastening of the column structure; - wherein each column comprises ballasting means whereby the draft may be controlled;

[0011] - wherein each column comprises an active heave motion neutralization system that may be operated independently, such that the platform may be maintained stable and level when handling the structure, for example during transit, separation and docking.

[0012] In one embodiment, the active heave motion neutralization system comprises: - a tank device configured for storing a compressed gas, such as air;

[0013] - an air reservoir inside the column;

[0014] - a rise canister arranged in, and in fluid communication with, the air reservoir, said rise canister comprising a volume that increases with increasing height and is in liquid communication with the body of water surrounding the column, such that water level inside the rise canister may move between upper and lower levels;

[0015] - wherein the tank device comprises a first valve configured for selective fluid communication with the air reservoir, whereby compressed gas may be released into the air reservoir;

[0016] - wherein the air reservoir comprises a second valve configured for evacuating gas from the air reservoir;

[0017] - control means configured for controlling at least the first valve and the second valve.

[0018] In one embodiment, the control means comprises a control system configured to receive and process data retrieved from sensors providing environmental data, and / or from sensors or devices providing operational data. The control means may comprise a machine-learning algorithm.

[0019] In one embodiment, the opening comprises one or more locking devices for releasably holding and supporting the column structure.

[0020] In one embodiment, the platform comprises three buoyant columns interconnected by the support structure in a tripod configuration. The column structure may be a spar buoy semi-submersible floating foundation comprising a fully outfitted wind power plant.

[0021] It is also provided a method of operating the platform according to the invention, whereby the first valve and the second valve are operated to control the pressure inside the reservoir in order to control the water level in the rise canister. The valves in each column may be controlled to control platform heave motion and attitude. The platform heave motion and attitude may be controlled while each column is ballasted to a desired draft.

[0022] These and other characteristics of the invention will become clear from the following description of an embodiment of the invention, given as a non-restrictive example, with reference to the attached schematic drawings.

[0023] Detailed description of embodiments of the invention

[0024] The following description may use terms such as “horizontal”, “vertical”, “lateral”, “back and forth”, “up and down”, ’’upper”, “lower”, “inner”, “outer”, “forward”, “rear”, etc. These terms generally refer to the views and orientations as shown in the drawings and which are associated with a normal use of the invention. The terms are used for the reader’s convenience only and shall not be limiting.

[0025] Figure 1 shows an embodiment of the invented deployment platform 1 floating in a body of water and carrying a spar buoy 2 and wind turbine generator 3. Furthermore, columns 4, in this case three (4a-c), extend through a deployment platform support structure 5, the waterline 6 and comparatively shallow into the sea.

[0026] Figure 2 shows the deployment platform 1 floating in the waterline 6 in a water depth suitable for deployment- here approximately 40 m - where the lower part of the spar buoy 2 and the columns 4 have approximately similar draft.

[0027] Figure 3 shows the deployment platform 1 with the spar buoy 2 together ballasted sufficiently - here e.g. above 40 m - draft where the spar buoy 2 can float stably independent of the deployment platform 1. The spar buoy 2 is retained in the deployment platform in an opening 7 having a shape complementary to the shape of a portion of the spar buoy 2. In the illustrated embodiment, the opening 7 is a U-shaped opening. Locking devices 8, here in the form of two locking skids 8, lock the spar buoy in place by pushing against the spar buoy 2 circumferential body underneath a support member 9, here a flange ring 9.

[0028] Figure 4 shows the deployment platform 1 and the spar buoy 2, but now with the locking skids 8 retracted to allow the spar buoy to escape out of the opening 7.

[0029] Figure 5 shows the deployment platform 1 and the spar buoy 2 separated and floating after the platform 1 has been pulled back

[0030] Figure 6 shows a cross section view of one of the columns 4 and part of the platform 1 structure submerged to the operational draft at waterline 6 being still water level. Reference number 29 indicates the waterline at wave trough and reference number 10 indicates the waterline at wave crest. The water level 11 in a chamber 30 (also referred to as a “rise canister”) inside the column 4 is controlled by the air pressure in an air reservoir 12. A rising wave height to level 10 will increase the water level in the rise canister 30 to level 13, and at wave trough 29 the water level in the rise canister is at level 14. Seawater from the surrounding body of water is entering through an opening 15.

[0031] Ballast water for controlling the submerged draft is contained in tanks 16 and 17.

[0032] A tank 18 which contains pressurized air is installed inside the structure. The tank 18 is fed - and continuously pressurized - from an external device or system, such as a surface service vessel - not shown - through a valve 19. A first remotely controlled valve 20 - here shown open - is configured for releasing air pressure through a pipe 21 to the air reservoir 12. A second remotely controlled valve 22 is configured for releasing pressure to the atmosphere.

[0033] Although not illustrated, it shall be understood that the platform comprises sensors for monitoring operational parameters, such as tank pressure and air reservoir pressure.

[0034] The semi-submersible deployment platform thus comprises a built-in system for maintaining constant buoyancy at varying sea levels (due e.g. to waves and tidal movement). The system provides energy-neutral generation and storage of energy in the form of superatmospheric pressure for use in predictive advanced regulation and control of heave motion neutralization (HMN). The water level 11 in the rise canister 30 is controlled by the air pressure in the reservoir 12. This pressure is controlled by manipulation of the first valve 20 - to allow a desired quantity of pressurized air from the tank 18 to flow into the reservoir 12 - and by the second valve 22 - to evacuate a desired quantity of pressurized air from the reservoir 12.

[0035] This manipulation of the first and second valves 20, 22, and hence the ability to adequately control the pressure inside the air reservoir 12 and hence the rise canister 30, may be based on real-time sensor data and / or information stored in a database. This information may obtained by machine-learning algorithms, enabling predictions as to the operation of the valves. Such algorithms and systems are per se known from DP (dynamic positioning) of ships and oil rigs, and from AHC (active heave compensated) cranes on deep subsea service vessels. Advanced software with predictive control algorithms may thus be used to control the air pressure above the water surface 11 in the rise canister 30 sufficiently in advance of the calculated vertical movement of the platform so that the movement is neutralized.

[0036] Heave motion neutralization (HMN) may thus be achieved by instant and rapid operation of the first valve 20 - for bleeding compressed air from the tank 18 and into the air reservoir 12 - and by instant and rapid operation of the second valve 22 - for bleeding compressed air from the air reservoir 12 and out into the surrounding atmosphere. The operation of these valves 20, 22 may be based on environmental data and operational data, such as ambient wind velocity, sea wave characteristics (e.g. height, frequency, direction), vessel motion (e.g. pitch, roll, yaw, heave), and global position.

[0037] Figure 7 is a schematic illustration of an embodiment of a system for controlling the valves 20, 22 (or, in general: actuators 42) in a column as described above. The figure illustrates three columns 4a-c, each having valves and actuators. This arrangement may correspond to the arrangement illustrated in figure 1, and shows how the valves in each column 4a-c vessel may be controlled independently of the valves in other columns 4a- c. Figure 7 illustrates how a control system 41 is connected to columns 4a-c and to the individual valves 20, 20 in each column. The control system 41 may be configured for receiving data from the individual column and for controlling devices in or on the column, such as the above-mentioned valves 20, 22. The control system may be arranged on a platform common to a plurality of column, or on a column itself. The control system may be arranged at a distal location, and will preferably comprise a user interface. The control system 41 is connected to environmental sensors 43 (wind, waves, etc.) and to operational sensors 44 (position, column motion, etc.). The control system may also be connected to external data and / or control devices, such as a remotely located computer or control device. The connections shown in figure 7 may be by any means known in the art, such as wire, fiberoptic cable, wireless communication, via satellite, etc.

[0038] The control system may comprise, or be connected to, computers that are configured to provide fast control actions to the actuators and valves. Such computers may incorporate machine-learning algorithms that are able to provide predictive control commands based on data obtained previously and / or on other parameters.

[0039] The heave motion neutralization system described above is useful for keeping the deployment platform 1 stable and level when handling the spar buoy 2, for example during transit, separation and docking, as the heave motion neutralization system in each column 4a-c may be controlled independently of one another.

Claims

Claims1. A semi-submersible floating platform (1) configured for supporting and transporting a column structure (2), characterized by- a plurality of buoyant columns (4a-c) interconnected by a support structure (5) having an adaptive opening (7) for axial and radial fastening of the column structure (2);- wherein each column (4) comprises ballasting means (16, 17) whereby the draft may be controlled;- wherein each column (4) comprises an active heave motion neutralization system that may be operated independently, such that the platform (1) may be maintained stable and level when handling the structure (2), for example during transit, separation and docking.

2. The platform (1) of claim 1, wherein the active heave motion neutralization system comprises:- a tank device (18) configured for storing a compressed gas, such as air;- an air reservoir (12) inside the column (4);- a rise canister (30) arranged in, and in fluid communication with, the air reservoir (12), said rise canister comprising a volume that increases with increasing height and is in liquid communication with the body of water surrounding the column, such that water level (11) inside the rise canister may move between upper and lower levels (13, 14);- wherein the tank device (18) comprises a first valve (20) configured for selective fluid communication with the air reservoir (12), whereby compressed gas may be released into the air reservoir (12);- wherein the air reservoir (12) comprises a second valve (22) configured for evacuating gas from the air reservoir;- control means (41) configured for controlling at least the first valve (20) and the second valve (22).

3. The platform of claim 2, wherein the control means (41) comprises a control system configured to receive and process data retrieved from sensors (43) providing environmental data, and / or from sensors (44) or devices providing operational data.

4. The platform of claim 2 or claim 3, wherein the control means comprises a machine-learning algorithm.

5. The platform of any one of claims 1-4, wherein the opening (7) comprises one or more locking (8) devices for releasably holding and supporting the column structure (2).

6. The platform of any one of claims 1 -5, comprising three buoyant columns (4a-c) interconnected by the support structure (5) in a tripod configuration.

7. The platform of any one of claims 1-6, wherein the column structure (2) is a spar buoy semi-submersible floating foundation comprising a fully outfitted wind power plant (3).

8. A method of operating the platform (1) as defined by any of claims 2-7, whereby the first valve (20) and the second valve (22) are operated to control the pressure inside the reservoir (12) in order to control the water level (11) in the rise canister (30).

9. The method of claim 8, wherein the valves (20, 22) in each column (4) are controlled to control platform heave motion and attitude.

10. The method of claim 9, wherein the platform heave motion and attitude are controlled while each column is ballasted to a desired draft.

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