Patent Application
20250206420
This application is the National Stage of International Application No. PCT/EP2023/056050, filed Mar. 9, 2023, which claims the benefit of Netherlands Application No. 2031193, filed Mar. 9, 2022, the contents of which is incorporated by reference herein.
The present invention relates to a floating marine structure and a method of installing a floating marine structure. The marine structure may be a base for, for example, a wind turbine.
Traditionally, offshore wind turbines are installed on foundations based on the sea floor in relatively shallow water. A water depth of 40 to 50 m is normally considered the limit for such gravity based foundations arranged on the sea floor.
DE2457536 discloses a marine structure with a floating base, a separate floater and a work deck where the base and floater are lowered to the sea floor to form a foundation using a winch or crane system.
U.S. Pat. No. 4,451,174 discloses a platform comprising a foot structure having a plurality of watertight compartments which are controllably ballastable with sea water between an unballasted buoyant state which allows floating of the platform during transit and a ballasted state while stationary at the use site. The foot structure rigidly supports a single central column extending through a central opening of a deck which is movably supported on the column. The deck carries a plurality of jack-up legs to move the deck relative to the foot structure along the column. During transit of this mobile offshore platform, the deck is lowered to a position adjacent to the foot structure with the platform floating on the foot structure alone. During installation of the platform, the buoyancy of the deck will be used to provide stability and buoyancy. The base is lowered or pushed down to the sea bottom using a winch or crane system to form a gravity-based foundation.
U.S. Pat. No. 4,627,767 discloses a marine structure with a base, a separate floater and a deck structure where the base is ballasted down to the sea bottom and where the separate floater is used to provide stability during lowering and being connected to the base and deck using a winch or crane system to form jacking legs.
WO2010/085970 discloses a marine structure with a base, a separate floater and a deck structure where the base is ballasted down to the sea bottom and where the separate floater is used to provide stability during lowering and being connected to the base and deck using a winch or crane system to form jacking legs.
A drawback of the marine structures described above is that the different buoyancy elements to provide buoyancy and stability during lowering of the base are connected or need to be connected in vertical sense with a lifting or jacking system. The effect of this connection will be that all elements will show the same wave induced heave motions which reduce the capability to withstand wave-induced forces and motions during installation. Also the system will introduce large dynamic loads due to wave actions and requires additional costs to install and procure the lift system. Another drawback of the marine structure is that the marine structure is relatively unstable when sinking the base to the sea floor. Temporary buoyancy means, i.e. buoyancy means which are detached from the marine structure after installation, may be provided to increase stability during installation. However, the provision of temporarily means involves extra steps during installation, increasing costs.
In many areas of the world however, there is simply not enough offshore area available with suitable water depths of—for instance—at most 50 m, for deployment of offshore wind power to the desired extent. Here, alternatives may be required, such as floating foundations for wind turbines.
A variety of different floating foundation concepts are possible for use offshore, conventionally used by the oil industry and potentially also suitable for wind turbines. The three primary concepts are spar buoys, semisubmersibles and Tension Leg Platforms (TLPs). Each of these primary concepts has its advantages and limitations.
A spar buoy maintains stability from a deep draft combined with ballast. It is the simplest floating foundation concept, typically consisting of a simple air-filled, floating tube which is kept vertical in the water by ballasting at the bottom. Suitably dimensioned, a spar buoy can support the weight and loads from a large wind turbine while maintaining a near-vertical position. Typically, the function of the mooring lines is only to maintain position and preventing drifting. Some spar buoy designs seek to achieve additional benefits from taut mooring lines; these designs have not yet been tested in practice. The simplicity of the spar buoy concept makes it inherently attractive.
However, the draft poses major challenges during the installation and transportation phases. Due to the motion of the sea it is generally not considered feasible to install wind turbines on floating foundations under ocean conditions at their final location, and therefore floating wind turbines are normally installed at quayside using land-based cranes, or in sheltered waters using floating cranes. Spar buoys generally have drafts larger than 50 m, some designs even have drafts larger than 100 m, and this effectively prevents quayside wind turbine installation using land-based cranes. Therefore, wind turbines are normally installed on spar buoy floating foundations in sheltered waters, such as deep fjords, using floating cranes.
While it is fairly easy in a few countries, such as Norway, to find sheltered waters with sufficient depth to permit wind turbine installation using a floating crane, in many parts of the world such sheltered waters with sufficient depth are not available. Furthermore, even where such sheltered waters with sufficient depth are available, the presence of ridges or shoals in the transportation corridor between the point of installation and the desired offshore locations will often effectively prevent the utilization of such sheltered waters for turbine installation. These limitations caused by the deep draft of a spar pose a significant problem for the spar buoy concept.
One solution for turbine installation with spar buoy floaters is to install the turbine while the spar buoy is in an inclined position, for instance in an almost horizontal position. WO2010/018359 discloses an installation method based on such near-horizontal orientation of the spar buoy. Here, the near-horizontal position is maintained through the attachment of a temporary buoyancy device connected to the bottom of the spar buoy. With this arrangement the turbine can be installed at quayside in the near-horizontal position using land-based cranes. After towing to the desired offshore location, the spar buoy is brought to its final, vertical position through gradual disengagement of the temporary buoyancy device.
WO2013/048257 discloses another installation method based on near-horizontal orientation of the spar buoy. Here, the near-horizontal position is maintained through the connection of the spar buoy to a supplementary buoyancy device, where the connection is arrangement with a rotary coupling device which permits the change of the orientation of the spar buoy and the wind turbine mounted on the spar buoy. The orientation can be changed from near-horizontal during turbine installation and towing to the desired location. After towing to the desired offshore location, the spar buoy can be brought to its final, vertical position through rotation of the rotary coupling.
Methods like those disclosed in WO2010/018359 and WO2013/048257 inherently assume that a wind turbine can be placed in a near-horizontal orientation. However, this is generally impossible for wind turbines exceeding a certain size. Significant parts of the equipment used in wind turbines, e.g. controller enclosures, transformers, etc. are suited for normal, vertical orientation only. In addition, some of the structural components will need to be of larger dimensions to accommodate the gravity loads when tilted. Lubricants, coolants and other fluids pose a special problem; seals in bearings, gearboxes, hydraulics, expansion tanks, will need to be of special design to allow for near-horizontal orientation. Given that the industry is moving to ever larger turbines, often exceeding 100 m height, these spar buoy installation methods are virtually unsuitable.
A semisubmersible floating foundation obtains stability from a large waterplane area at a moderate draft, in combination with ballast which ensures a relatively low centre of gravity. The semisubmersible concept is not as simple as the spar buoy concept, but it has the advantage of shallow draft. The shallow draft allows turbine installation at quayside using land-based cranes, and it allows towing to an offshore location. The semisubmersible concept typically includes mooring lines to maintain position and preventing drifting. The relative simplicity of the semisubmersible concept makes it inherently attractive. However, the stability is a concern. Considerable heel can be experienced during turbine operation due to the relatively large lateral forces acting on the turbine rotor.
WO2009/131826 discloses an arrangement whereby the heeling angle during turbine operation can be reduced with a ballast control system. The floating foundation is fitted with a set of pumps and valves that is used to redistribute water ballast between the three main columns comprising the stabilizing body of the foundation. Through redistribution of water ballast the overturning moment created by the large lateral forces acting on the turbine rotor can be offset by an overturning moment in the opposite direction created by the moveable ballast. The arrangement disclosed in WO2009/131826 has obvious disadvantages. Firstly, through the introduction of active sensor and pumping systems a new level of complexity is introduced, inherently violating the fundamental principle that due to the challenges in accessibility unmanned offshore structures should have as few active systems as possible. Secondly, since the masses that need to be redistributed are significant, measured in hundreds or thousands of tons, the balancing system will be semi-static, typically with time constants on the order of minutes even when very large pumps are used. Consequently, transient changes in the overturning moment created by the large lateral forces acting on the turbine rotor cannot be balanced.
U.S. Pat. No. 8,118,538 discloses an alternative way of reducing the heeling angle during turbine operation due to the overturning moment created by the large lateral forces acting on the turbine rotor. A counterweight is mounted some way below the floating platform, and it essentially acts as a keel. In further embodiments the counterweight is connected to adjustable anchor lines and also serves to tighten these lines.
Thus, both the spar system and the semisubmersible system pose challenges.
WO2017157399 proposes a floating wind turbine comprising a hull, a wind turbine mounted on top of the hull and a counterweight suspended below the hull by means of counterweight suspension means. A method for the installation of a floating wind turbine comprising the hull, and a wind turbine mounted on top of the hull and a counterweight suspended below the hull by means of counterweight suspension means is also disclosed. The static and dynamic response of the floating foundation can be adjusted before installation through a combination of adjustment of i) ballasting of the counterweight buoyancy tanks, ii) ballasting of the hull, and/or iii) adjustment of the installed depth of the counterweight.
Disadvantage of the method and floating wind turbine of WO2017157399 relates to the suspension means. The counterweight requires multiple wires or cables to stabilize the counterweight, to keep the weight in position and to prevent or limit torsion. Offshore, said wires or cables will typically result in increased maintenance requirements and unplanned outage. For a relatively low-margin operation such as individual wind turbines, the maintenance and unplanned outage results in prohibitive operating costs rendering the structure economically unviable.
U.S. Pat. No. 9,499,240B2 discloses a floating marine structure comprising: a sub-structure having only one leg having at least one first buoyancy chamber arranged in a lower part of the leg to provide a first buoyancy, wherein the first buoyancy is sufficient to keep the sub-structure afloat, and wherein the at least one first buoyancy chamber is ballastable to decrease buoyancy of the leg; and a float element having at least one second buoyancy chamber to provide a second buoyancy, wherein the second buoyancy is sufficient to keep the float element afloat, and wherein the at least one second buoyancy chamber is ballastable to decrease buoyancy of the float element, wherein the float element comprises a substantially vertically orientated passage extending through the float element and enclosing the leg in a substantially horizontal plane to form a linear guide to guide linear movement of the float element with respect to the sub-structure in the substantially vertical direction to allow relative wave induced motion with respect to each other in a substantially vertical direction, wherein the leg is movable from a pre-installation position to an installation position by a substantially downwards movement of the leg with respect to the float element, wherein during at least a second part of the downwards movement of the leg towards the installation position and/or in the installation position the at least one first buoyancy chamber is substantially located below a wave zone to substantially decrease heave action on the at least one first buoyancy chamber, and wherein during the at least a second part of the downwards movement of the leg, the weight of the complete sub-structure is carried by the leg.
The structure and method of U.S. Pat. No. 9,499,240B2 are focused on, and optimized for gravity based application.
WO 2018/150064 discloses a floating spar structure for large offshore wind turbines, formed by a lower triangular caisson made of reinforced concrete and by an upper triangular caisson made of metal on which the shaft of the wind turbine is supported both joined by means of three liftable columns disposed in the corners thereof. The structure is a spar platform because its operation is based on the descent of the centre of gravity of the assembly, but the platform also has semi-submersible components, since it has three floats on the waterline level that increase the restoring moment thereof.
Disadvantage of the method and floating wind turbine of WO 2018/150064 relates to the semi-submersible component embodied by the floats in the waterline to improve the restoring moment. The envisaged floats in the waterline will attract wave loading, leading to excessive motions and accelerations, that will downgrade the performance of the wind turbine. Also, the system included in the upper triangular caisson for guiding the legs transfers the load of each leg in a radial direction by direct compression against the leg. This will result in relatively large local stresses in the respective leg, which in turn will greatly reduce the capacity of the system.
WO 2013/083358 discloses a floating wind power plant comprising a buoyancy body configured for being submerged in water and supporting an equipment unit extending above water, and a ballast element connected to the buoyancy body via at least one spacer structure. Guiding means in the buoyancy body are configured for movable interaction with the at least one spacer structure such that the ballast element and the buoyancy body are movable with respect to one another. The buoyancy body has an elongated shape with a forward portion and an aft portion, and the ballast element has a corresponding forward portion and an aft portion.
The buoyancy body and spacer structure of WO 2013/083358 are relatively bulky and as a result require significant amounts of structural material, such as steel and concrete, rendering the structure relatively complex and capital intensive.
It is an aim of the present invention to provide an alternative floating marine structure obviating at least one or more of the disadvantages of the prior art.
Aspects of the present invention are set out in the accompanying description.
The disclosure provides a marine structure, comprising:
In an embodiment, the jacket-structure comprising a fixating mechanism to fixate the at least one leg with respect to the support structure when in the operating position.
In an embodiment, the fixating mechanism comprising one or more sets of wedges, one wedge part of each set of wedges being connected to an outer surface of the at least one leg, and a second wedge part of each set of wedges being connected to an inner surface of a corresponding guide sleeve.
In an embodiment, the marine structure comprises a linear guiding system, integrated in the at least one guide sleeve. The linear guiding system may comprise ridges distributed along the circumference of the at least one guide sleeve, and corresponding nooks fitting between two ridges and extending from an outer surface of the at least one leg.
In an embodiment, the counterweight structure has an adjustable weight, said weight providing buoyancy when in the towing position and said weight weighing the marine structure down when in the operating position.
In an embodiment, the functional element includes a wind turbine.
In an embodiment, the counterweight structure encloses the lower end of the at least one leg.
In an embodiment, the at least one guide sleeve is provided with a brake to limit movement of the at least one leg with respect to the corresponding at least one guide sleeve.
In an embodiment, the marine structure comprises multiple legs, each leg being enclosed by the at least one float element.
In an embodiment, the first buoyancy exceeds a gravitational force of the rest of the marine structure including the weighed counterweight structure when in the operating position, keeping the marine structure afloat.
In an embodiment, the marine structure comprises at least one thruster for positioning the marine structure in the water.
In an embodiment, the counterweight structure being provided with a first valve for passage of water, and a second valve connected to a pump for pumping gas in or out of the counterweight structure.
In an embodiment, the pump is located above the water surface and being connected to the second valve via a conduit allowing to pump air into or out of the counterweight structure.
In an embodiment, the pump and the conduit are removable to allow removal of the pump and conduit when the marine structure is in the operating position.
According to another aspect, the disclosure provides a method to install a marine structure, the method comprising the steps of:
In an embodiment, the method comprises the step of anchoring the floating marine structure to the bottom of the body of water using one or more anchoring lines.
In an embodiment, in the operating position the counterweight structure floats below a wave zone.
In an embodiment, in the operating position, the weight of the counterweight structure is increased to submerge the at least one float element.
In an embodiment, the float element is submerged at least below an average wave height at the predetermined offshore location. In a preferred embodiment, in an operating condition, the float element is entirely submerged.
Reducing wave loads on the structure provides a significant advantage of the spar type structure of the disclosure. A balance between restoring moment and relatively low wave loading is achieved by positioning the one or more float elements in the operating condition below the governing wave zone. The restoring moment is achieved by the counterweight structure, which sets the Centre of Gravity of the system well below the Centre of Buoyancy of the system, resulting in the required restoring moment.
In an embodiment, the steps of increasing the weight of the counterweight structure comprises flooding at least one buoyancy chamber in the counterweight structure using a first valve for passage of water, and a second valve connected to a pump for pumping gas into or out of the counterweight structure. The step of flooding the at least one buoyancy chamber in the counterweight structure may comprise controlling a pressure differential over walls of the counterweight structure to remain within a predetermined range. The predetermined range may be +/−1 bar, more preferably +/−0.5 bar.
By controlling the pressure difference during the lowering of the counterweight structure, the required amount of strong, or structural, material can be reduced. The cost reduction due to reduction in the amount of material outweighs the cost of the pressure balancing system. A further advantage is the reusability of the pressure balance system components, which greatly reduces the cost of projects with more than one system to be installed. Typical numbers of systems per project is in the range of 10 to 60 systems. A project herein typically relates to wind farms.
Reference will be made to the figures on the accompanying drawings. The figures are schematic in nature and may not necessarily be drawn to scale. Similar reference numerals denote similar parts. On the attached drawing sheets:
The support structure 2 comprises one or more float elements 10. The support structure 2 may be referred to as jacket-structure. The one or more float elements 10 are provided with one or more openings 12. The openings 12 may extend into, or be an integral part of, guide sleeves 14. The guide sleeves 14 may extend a predetermined distance above the one or more float elements 10.
The jacket-structure may comprise a number of structural elements 16, 18, 20 to connect the one or more float elements 10 to a main deck 22. The main deck 22 allows to attach a topside structure. The topside structure may be a wind turbine. The structural elements 16, 18, 20 may be, for instance, beams or tubes. The structural elements 16 to 20 may typically be made of a metal, typically steel, of a quality able to withstand corrosion and to provide structural strength as required. Structural elements 16 be diagonal, extending between the tube 20 and one of the sleeves 14. Elements 18 may be arranged in horizontal direction, connecting respective sleeves 14.
The at least one float element 10 of the jacket-structure 2 may be provided with first buoyancy means 24. The buoyancy means 24 may comprise one or more chambers 26. The chambers 24 can be filled with air or water, allowing to adjust the first buoyancy provided by the at least one float element 10. The first buoyancy provided by the at least one float element 10 is typically sufficient to keep at least the jacket-structure 2 afloat. The first buoyancy chambers 24 can be ballasted, for instance by introduction of water, concrete or other material, to decrease the first buoyancy to a required level to control the draft of the jacket-structure 2.
Referring to
The sub-structure 3 comprises one or more legs 30. The sub-structure may comprise, for instance, one, two, three or four legs. The legs are typically tubular and rigid. Lower ends of the legs 30 may be connected to a counterweight structure 32. Upper ends of the at least one leg 30 extend through the openings 12 and the sleeves 14.
The sub-structure 3 may have an adjustable weight or adjustable buoyancy. Herein, the sub-structure 3 may comprise second buoyancy means. The second buoyancy means may comprise one or more chambers 34, 36 allowing to be filled with, typically, air, water, or another suitable material. First chambers 34 may be comprised in the counterweight structure 32. Optionally, second chambers 36 may be included in one or more of the legs 30, typically at or near the lower ends thereof.
As shown in
In a practical embodiment, the counterweight structure may be substantially round, provided with a central moonpool or opening. The counterweight may have a doughnut shape. The one or more legs 30 may be substantially round. The legs may be connected to a top side of the counterweight structure.
The air chambers 34, 36 allow to provide and adjust the buoyancy of the sub-structure 3. The buoyancy of the sub-structure 3 may be referred to herein as second buoyancy. In an embodiment, the air chambers 34, 36 of the sub-structure 3 may be connected to a first valve 40 and a second valve 42. The first valve 40 may connect one or more of the chambers 34, 36 to the environment, typically a body of water 50, such as the sea or ocean, wherein the marine structure will be positioned for operation. As shown in, for instance,
When filled with air, the positive buoyancy provided by the combination of the chambers 34, 36 may be sufficient to keep the marine structure 1 afloat. This allows the entire structure 1 to float on the counterweight structure 32 in the transport phase, see for instance
The guide sleeves 14 are provided with a linear guiding system for the corresponding leg 30 extending through the respective sleeve. The linear guiding system allows linear movement of the leg with respect to the corresponding sleeve 14. In its simplest form, the linear guiding system is comprised of an inner surface of the guide sleeve, which is for instance cylindrical, for guiding an outer surface of the respective leg, which may also be cylindrical. The guiding system may comprise various elements to promote movement of the legs with respect to the corresponding guide sleeve 14, such as one or more of: rollers, bearings (such as linear ball bearings), rails, or slides. One embodiment will be described below with respect to
The structure 1 may be provided with a positioning system 60 allowing controlled positioning of the legs 30 with respect to the sleeves 14. Herein, an upper end of one or more of the legs 30 may be provided with a stop element 62. The corresponding sleeve 14 may be provided with a counter element 64 for catching the stop element. The stop element and/or the counter element may comprise a flange or shoulder, extending outward with respect to the respective leg or sleeve. As explained in more detail in combination with
The embodiments of the present disclosure introduce loads in tangential direction into the one or more legs. Loads in radial direction are obviated, or at least significantly reduced.
Referring to
Optionally, the sleeves 14 may be integrated in the float element 10, as walls of the openings 12. The openings extend through the float element 10. Herein, the buoyancy chambers 26 and the related centre of buoyancy are below the waterline, and preferably below the local average wave height, when the system is in the operating condition.
The positioning system 60 may comprise the flanges or stop elements 62, 64 as described above. Alternatively or in addition, the positioning system 60 may comprise at least a stop element 62 connected to the at least one leg 30, adapted to cooperate with a top surface 66 of the at least one float element 10. Said top surface 66 may be provided with suitable strengthening or structural support to be able to provide the required counterforce. Structural support herein may include, for instance, a flange or shoulder structure.
Generally referring to
In an embodiment, the linear guide system shown in
One or more of the legs and/or sleeves may be provided with a guide system as exemplified in
Generally referring to
In an embodiment, the brake device 90 may comprise, for instance, one or more of a brake pad 92, a plunger 94, a hydraulic cylinder 96, a hydraulic pressure line 98, and a hydraulic pressure pump 99. The brake pad 92 may include a rubber pad. The rubber may be a relatively robust rubber, such as EPDM. The pump may be connected to a control device (not shown) to control the braking force provided by the braking device 90. Alternatives are also possible, including but not limited to, an electromagnet to drive the brake pad 92; or a mechanical brake using levers to control a brake pad. Multiple braking devices 90 may be provided. The braking devices 90 may be arranged divided along the circumference of the passage 70. All braking devices may be controlled by the same control device and pump 99. See
The braking device 90 may be included in any of the embodiments disclosed herein, and as described herein above and below.
Buoyancy of the counterweight 32 may be adjusted by partially replacing air in the ballast tanks 34 with a material 82 heavier than air, typically water, as shown in
In subsequent steps, see
As shown in
While submerging the counterweight structure 32, in an embodiment, the method of the present disclosure allows to control a pressure differential over walls of the counterweight structure. Said pressure differential can be kept within a predetermined range. The pressure differential can be controlled using a pressure control system, for instance comprised of the first valve 40, the second valve 42 and the pump 46. The pressure differential over walls of the counterweight structure 32 can be kept within a range of, for instance, in the order of +/−1 bar, or about +/−0.5 bar. During the step of flooding the at least one buoyancy chamber in the counterweight structure 32, the pressure differential over the walls of the counterweight structure 32 is controlled using the pressure control system to remain within the predetermined range. In practice, the pressure differential over the walls is minimized with respect to the environment. While the counterweight structure 32 sinks in the water, the water pressure will increase. Water pressure increases with about 1 bar for every additional 10 m of depth, starting at about 1 bar at the surface. While submerging the counterweight structure, the pressure inside the buoyancy chambers of the counterweight structure is increased in accordance with the increasing water pressure. The pressure control system allows to keep the pressure inside the chambers 34 substantially equal to the water pressure outside structure 32. The pressure inside the chambers 34 may be gradually increased while the structure 32 sinks in the water. Herein, the air pressure in the chambers 34 can be increased at a rate about equal to the increase in water pressure outside the counterweight structure 32, limiting the pressure differential across the wall of the counterweight while the structure 32 is lowered to the operating position. This pressure control system allows to minimize structural strength of the walls of the counterweight structure 32, and as a result allows to save material and associated costs.
When the counterweight structure 32 will have reached the operating depth, the valves of the pressure control system can, for instance, be opened entirely, in effect evening the water pressure inside and outside of the counterweight structure 32. Alternatively, when the counterweight structure 32 will have reached the operating depth, the valves of the pressure control system can, for instance, be closed, keeping the pressure differential at a set level while allowing some air inside the buoyancy chambers to maintain the buoyancy of the counterweight structure 32 at a preferred level. As shown in
The positions of the marine structure 1 shown in
According to an embodiment of a method of the disclosure, in a first step, the draft of the structure 1 is limited to allow the structure 1 to be positioned in an assembly location of choice, typically a harbour or a near shore location. Near shore herein may refer to a location within 100 m from shore. Depending on available water depth at the assembly location, the draft may be adjusted within a range to match with available water depth, as exemplified in
In a second step, the top side structure 80 is placed on and connected to the platform 22. Placement can be done using a land-based or floating crane, a platform, or any available lifting means.
In a third step, the marine structure including the top side structure 80 is transported to an operating location of choice. The operating location may typically be relatively far offshore. Far offshore herein may refer to a distance exceeding 500 m offshore. The operating location may have water depths exceeding 100 m, typically up to 1 km or more.
Transportation may include towing or pushing the marine structure, including the wind turbine generator 80 in its upright position, to the operating location. During transport, the draft of the marine structure can be adjusted, for instance using pump 46, as required and possible. For instance, during favourable weather conditions or transport over areas with limited water depth, the draft may be limited accordingly. During transport over areas with increased water depths, increased significant wave height, and/or during (expected) adverse weather, the draft may be increased by decreasing the buoyancy of the counterweight 32. For instance, the buoyancy of the counterweight 32 can be adjusted during transport between the positions shown in
Thus, the counterweight-structure or sub-structure 3 can move in a substantially vertical direction with respect to the jacket-structure or support structure 2. In the towing position or transportation position (see, for instance,
To limit trim and prevent toppling, stability of the marine structure 1 can be adjusted by adjusting the buoyancy of the sub-structure 3 within a given range, as exemplified in
In an embodiment, in the operating position (
Alternative fixating means may be used, instead of or in addition to the sets of wedges as shown in
Generally referring to
The support structure 2 comprises a float element 10 having one or more buoyancy chambers 26. The positioning system 60 may comprise a stop element 62, such as a shoulder or flange extending radially outward from the leg 30. The stop element 62 may engage a top surface 66 of the float element 10
To install the marine structure 1 to the desired configuration, in a second step shown in
During further lowering of the base-structure 3 with respect to the jacket-structure 2, shown in
The sub-structure 3 is lowered in a position so that the jacket-structure 2 and sub-structure 3 are connected by means of the connection system 60. The sub-structure 3 has been moved through the passage 70 in a substantially vertical direction with respect to the jacket-structure 2.
After the Jacket-structure 2 and sub-structure 3 have been fixated with respect to each other, the buoyancy means 36 of the sub-structure 3 may be ballasted further so that the float element 10 sinks into the sea. As a result, the floater 10 may be completely submerged as shown in
The combination of the weight of the sub-structure 3 and its ballasted counterweight at a low position and the first buoyancy provided by the float element 10 at a high position provides a stable base for the marine structure 1 even if relative large or tall objects, such as wind turbines or cranes, are arranged on the marine structure 1.
The marine-structure 1 may completely be held on position by using anchor lines 11. In an alternative embodiment, extra measures may be provided to keep the marine structure on the desired position at the sea, for instance a propulsion system 15 as shown in
The lowering procedure of the base structure is now described.
To proceed to a second step, the flood valve 40 is opened. Water will flow into the buoyancy chambers 34 and the draft of the marine structure 1 will increase. Inside the buoyancy chamber 34 the pressure will increase due to the water intake to such level that the flooding will stop when a pressure balance between outside and inside is achieved. The air cushion above the water inside the buoyancy chamber 34 is now balancing the weight of the base-structure, as shown in
The next lowering steps, exemplified in
With the pressure control system 46, See
In a final step, see
In a practical embodiment, the marine structure of the disclosure can be dimensioned to support a wind turbine generator of any suitable shape or size. For instance, the draft (i.e. the maximum depth of the structure below the surface of the water) of the marine structure in its operating position may range in the order of more than 50 m, up to 100 m or more. Thus, the structure 1 in its operating position can behave like a spar structure, providing stability and preventing toppling of the top side structure 80 due to the suspended counterweight 32.
The wind turbine generator 80 may be sized up of, for instance, a mast height of 50 to 150 m. Blades of the wind turbine generator may have a length in the order of 50 to 120 m. The power indication of the wind turbine generator may be in the order of 1 to 20 MW. The structure 1 can function as a floating foundation for wind turbines ranging from relatively small to the largest wind turbines currently envisaged.
In practice, the marine structure of the disclosure may be constructed from materials providing suitable strength, weight, buoyancy, and sufficient lifetime in offshore marine environments. Offshore, corrosion resistance may be even more important than for onshore operations. Also, the marine structure including its top side structure will, in practice, be designed to withstand storm and significant wave motion. Regarding the latter, the structure of the disclosure has the advantage of controllable draft via dedicate control vents, such as valves 42 and 40. In its operating position, see for instance
Wave height herein may be the distance between the peak of a wave to a valley. Significant wave height, scientifically represented as Hs or Hsig, is a parameter for the statistical distribution of (ocean) waves. The most common waves are lower in height than Hs. This implies that encountering the significant wave is not too frequent. However, statistically, it is possible to encounter a wave that is much higher than the significant wave. Generally, the statistical distribution of the individual wave heights is approximated by a Rayleigh distribution. For example, given that Hs is 10 metres (33 feet), statistically: 1 wave in 10 will be larger than 10.7 metres (35 ft); 1 wave in 100 will be larger than 15 metres (50 ft); and 1 wave in 1000 will be larger than 18.5 metres (61 ft). This implies that one might encounter a wave that is roughly double the significant wave height. However, in rapidly changing conditions, the disparity between the significant wave height and the largest individual waves might be even larger.
Other statistical measures of the wave height are also widely used. The root mean square (RMS) wave height, which is defined as square root of the average of the squares of all wave heights, is approximately equal to Hs divided by 1.4.
Significant wave height may differ per offshore location, and may be in the range of 5 to 15 m. In the book Oceanography and Seamanship, William G. Van Dorn provided an example of what the wave heights would be if a steady 30 knots (33 mph/53 km/h) wind blew for 24 hours over a fetch of 340 miles. If so, 10% of all waves will be less than 3.6 ft. (1 m). The most frequent wave height will be 8.5 ft. (2.5 m). The average wave height will be 11 ft. (3 m). The significant wave height will be 17 ft. (5 m). 10% of all waves will be higher than 18 ft. (5 m). The average wave height of the highest 10% of all waves will be 22 ft. (7 m). A 5% chance of encountering a single wave higher than 35 ft. (11 m) among every 200 waves that pass in about 30 minutes. A 5% chance of encountering a single wave higher than 40 ft. (12 m) among every 2,600 waves that pass in about five hours.
In a practical embodiment, the marine structure of the disclosure can be dimensioned and designed to withstand significant wave height in the order of 10 to 17 m. Please note that Hs of 17 m is the highest significant wave height for design restrictions. A system suitable to withstand Hs of 17 m is the most severe design restriction. The latter will render the marine structure of the disclosure suitable for unrestricted worldwide operation.
The structure 1 may be designed such that, when in the operating position, the float elements 10 are submerged more than at least once or twice the wave height at the location of operation. Herein, wave height may be selected from significant wave height, RMS wave height, or average wave height. Alternatively, buoyancy of the float elements 10 of the structure 1 may be reduced in periods of expected adverse weather conditions, to increase the stability and submerge the float elements 10 more.
In a practical embodiment, the marine structure of the disclosure can be constructed using steel and concrete. For instance the support structure 2 can be made of steel. The base structure 3 including the legs 30 may be made of concrete, wherein the concrete is potentially reinforced using steel wire mesh.
As an example, the wind turbine 80 may have a mast height in the order of 100 to 150 m. The blades of the wind turbine 80 may have a length in the order of 70 to 95% of the mast height, or for instance in the order of 80 to 125 m. The base 32 in the operation position may have a draft of about 50 to 100 m, for instance about 60 to 70 m. The bottom side of the float elements 10 may be submerged about 10 to 25 m while in the operating position, for instance about 15 to 20 m. The latter may be referred to as the draft of the jacket or the draft of the support structure 2. A top surface of the float elements 10 may be submerged about 5 to 10 m below the surface of the water. The top of the support structure 2 may extend about 10 to 20 m above the surface of the water. The counterweight 32 may be substantially round or donut-shaped. The counterweight structure 32 may have a diameter in the order of 40 to 75 m, for instance about 50 to 60 m. The counterweight structure 32 may have a height in the order of 5 to 20 m, for instance about 10 to 15 m. The structure may comprise about three float elements 10. The float elements 10 may be substantially round. The float elements 10 may have a diameter in the order of 10 to 40 m, for instance about 20 to 30 m, for instance about 25 m. The legs 30 may have a diameter in the order of 5 to 15 m, for instance about 7 to 10 m. These sizes are exemplary only, and may in practice either be larger or smaller. The dimensions in practice may depend on the operating location, the assembly location, local significant wave height, average weather conditions, wind turbine dimensions, etc., the structure of the disclosure may be sized in accordance.
With reference to, for instance,
The marine structure 1 of the present disclosure may also be used as a floating base for other suitable applications, such as an offshore platform, a work platform, a solar power installation, a wave energy converter, a hydrogen storage and/or conversion unit or a meteo mast. Alternatively, the structure may be used for a multi-use application combining any of the mentioned applications, for instance wind turbine and wave energy converter combined on one marine structure 1 as disclosed herein.
The marine structure 1 of the present disclosure may also be used as a wave energy converter, typically at an operation position as shown in
The marine structure 1 of the present disclosure may also be used as multi-use power station by combining for instance three electricity generation methods, such as solar, wave and wind, with a hydrogen energy conversion and storage application. Thus, the system will typically produce a more constant electrical power output (called peak shaving) to end users. The latter may significantly increase the efficiency of the installation.
The scope of the present disclosure is not limited to the embodiments described above. Many modifications therein are conceivable without deviating from the scope of the present invention as defined by the appended claims. In particular, combinations of features of respective embodiments or aspects of the disclosure can be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention. While the present invention has been illustrated and described in detail with reference to the figures, such illustration and description are illustrative or exemplary only.
In the claims, the word “comprising” does not exclude other steps or elements, and “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference numerals in the claims should not be construed as limiting the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2031193 | Mar 2022 | NL | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/056050 | 3/9/2023 | WO |
