Marine structure and method

Abstract

The present invention provides an offshore structure comprising a jacket structure comprising at least one floating body element having a first buoyancy and at least one linear guide sleeve for supporting a functional element underwater, and a substructure comprising a counterweight structure having a second buoyancy and at least one leg extending through the at least one guide sleeve and having a lower end connected to the counterweight structure and an upper end provided with a stop element, wherein the at least one leg is movable through a corresponding guide sleeve between a towing position in which the stop element is separated from the guide sleeve and the guide sleeve allows linear movement of the at least one leg relative to the support structure, and an operational position in which the stop element engages a corresponding opposing element of the guide sleeve and the at least one leg is fixed relative to the at least one guide sleeve.

Description

[Technical field]

[0001] Floating offshore structure and method for installing a floating offshore structure The present invention relates to a floating offshore structure and to a method for installing a floating offshore structure The offshore structure may for example be a base for a wind turbine. [Background technology]

[0002] Traditionally, offshore wind turbines are installed on foundations resting on the seabed in relatively shallow water. Water depths of 40-50m are usually considered the limit for such gravity-based foundations placed on the seabed.

[0003] DE 2457536 A1 discloses an offshore structure comprising a floating base, a separate floater and a work deck, the base and floater being lowered to the seabed using a winch or crane system to form a foundation.

[0004] US Patent No. 4,451,174 discloses a platform with a foot structure having a number of watertight compartments that are controllably ballasted by seawater between a floating, unballasted state that allows the platform to float during transportation, and a ballasted state that is fixed at the location of use. The foot structure rigidly supports a single central column that extends through a central opening in the deck, and the deck is movably supported on the column. A number of jack-up feet are mounted on the deck to move the deck along the columns relative to the foot structure. During transportation of the mobile offshore platform, the deck is lowered to a position adjacent to the foot structure with the platform floating solely on the foot structure. During installation of the platform, the buoyancy of the deck is used to provide stability and buoyancy. The base is lowered or pushed down to the seabed using a winch or crane system to form a gravity-based foundation.

[0005] U.S. Pat. No. 4,627,767 discloses an offshore structure comprising a base, a separate floater and a deck structure, the base being lowered to the seabed with ballasting, the separate floater being used to ensure stability during descent and connected to the base and deck using a winch or crane system to form a jack leg.

[0006] WO 2010 / 085970 discloses an offshore structure comprising a base, a separate floater and a deck structure, where the base is lowered to the seabed with ballasting and the separate floater is used to ensure stability during descent and is connected to the base and deck using a winch or crane system to form a jack leg.

[0007] A drawback of the above mentioned offshore structures is that the various buoyancy elements for providing buoyancy and stability during the lowering of the base are or need to be connected longitudinally with the lifting or jacking system. The effect of this connection is that all elements will exhibit the same wave induced heave motion, reducing their ability to withstand wave induced forces and motions during installation. This system also results in high dynamic loads due to waves and requires additional costs for the installation and procurement of the lifting system.

[0008] Another drawback of the present offshore structure is that it is relatively unstable when the base is sunk into the seabed. Temporary floating means, i.e. floating means that are removed from the offshore structure after installation, may be provided to increase stability during installation. However, providing temporary means involves additional steps during installation, increasing costs.

[0009] However, in many areas around the world, there is not enough available offshore area with suitable water depths, for example up to 50m, to deploy offshore wind power to the desired extent, so alternatives such as floating foundations for wind turbines may be required.

[0010] A variety of different floating foundation concepts can be used offshore, traditionally used by the oil industry and potentially also suitable for wind turbines. The three main concepts are the spar buoy, the semi-submersible, and the tension leg platform (TLP). Each of these main concepts has its advantages and limitations.

[0011] A spar buoy maintains stability from deep water drafts combined with ballast. It is the simplest floating foundation concept and typically consists of a simple air-filled floating tube that is held vertically in the water by ballast at the bottom. When properly dimensioned, a spar buoy can support the weight and load of a large wind turbine while maintaining a nearly vertical position. Typically, the only function of the mooring lines is to maintain position and prevent drifting. Some spar buoy designs attempt to achieve the additional benefits of taut mooring lines, but these designs have not yet been field tested. The spar buoy concept is simple and inherently attractive.

[0012] However, the draft poses a major challenge during the installation and transportation phase. Due to sea movements, it is generally considered infeasible to install wind turbines on floating foundations under marine conditions at the final installation site, and therefore floating wind turbines are usually installed on quays, using land-based cranes, or in refuge waters using floating cranes. Spar buoys generally have a draft greater than 50m, and in some designs greater than 100m. This effectively prevents the installation of wind turbines using land-based cranes on quays. Therefore, wind turbines are usually installed on spar buoy floating foundations in refuge waters, e.g. deep fjords, using floating cranes.

[0013] While in some countries, such as Norway, it is fairly easy to find refuge areas of sufficient depth to allow wind turbines to be installed by floating cranes, in many regions around the world such protected waters of sufficient depth are not available. Moreover, even if such refuge areas of sufficient depth are available, the presence of ridges or shallows in the transportation route between the installation site and the desired offshore location often effectively prevents such protected waters from being utilized for turbine installation. These limitations caused by the deep draft of the spar pose significant challenges for the spar buoy concept.

[0014] One solution for installing the turbine by means of a spar buoy floater is to install the turbine while the spar buoy is in an inclined position, e.g. in a substantially horizontal position. WO 2010 / 018359 discloses an installation method based on a substantially horizontal orientation of such a spar buoy, where the substantially horizontal position is maintained by attaching a temporary buoyancy device connected to the bottom of the spar buoy. With this arrangement, the turbine can be installed in a substantially horizontal position at the quay by means of an onshore crane. After towing to the desired offshore position, the spar buoy is brought to its final vertical position by gently disengaging the temporary buoyancy device.

[0015] WO 2013 / 048257 discloses another installation method based on a substantially horizontal orientation of the spar buoy, where the substantially horizontal position is maintained by connecting the spar buoy to an auxiliary buoyancy device, where a rotary coupling is arranged to allow changing the orientation of the spar buoy and the wind turbine attached to the spar buoy. The orientation can be changed from substantially horizontal to a desired position during installation and towing of the turbine. After towing to the desired offshore location, the spar buoy can be brought to its final vertical position by pivoting the rotary coupling.

[0016] The methods disclosed in WO2010 / 018359 and WO2013 / 048257 essentially assume that the wind turbine can be placed in a generally horizontal orientation. However, this is generally not possible for wind turbines above a certain size. Critical pieces of equipment used in wind turbines, such as controller housings, transformers, etc., are only suitable for a normal vertical orientation. In addition, some of the structural components need to be larger in size to accommodate gravity loads when tilted. Lubricants, coolants, and other fluids pose special challenges, and bearings, gearboxes, hydraulics, and expansion tank seals need to be specially designed to allow for a generally horizontal orientation. Given the industry's move to larger turbine heights, exceeding 100m tall, these spar buoy installation methods are effectively inadequate.

[0017] Semisubmersible floating foundations derive stability from a large surface area at moderate draft, combined with ballast that ensures a relatively low centre of gravity. Although the semisubmersible concept is not as simple as the spar buoy concept, it has the advantage of a shallow draft. The shallow draft allows turbine installation at the quay and towing to offshore locations using a shore crane. Semisubmersible concepts typically include mooring lines to maintain position and prevent drifting. The relative simplicity of the semisubmersible concept is inherently attractive. However, stability is a concern. Considerable heel can occur during turbine operation due to the relatively large lateral forces acting on the turbine rotor.

[0018] WO 2009 / 131826 discloses an arrangement in which the heeling angle during turbine operation can be reduced by a ballast control system. A set of pumps and valves is attached to the floating foundation and is used to redistribute the ballast water between the three main columns that form the foundation's stabilizing body. The overturning moment generated by the large lateral forces acting on the turbine rotor can be countered by the opposing overturning moment generated by the mobile ballast due to the redistribution of the ballast water. The arrangement disclosed in WO 2009 / 131826 has obvious drawbacks. Firstly, the introduction of active sensor and pump systems introduces a new level of complexity, which essentially contradicts the basic principle that unmanned offshore structures should have as few active systems as possible, due to the accessibility challenges. Secondly, since the volumes that need to be redistributed can reach hundreds or even thousands of tons, the balance system is semi-static, with time constants typically of the order of minutes, even when very large pumps are used. As a result, it is not possible to balance the transient changes in overturning moment generated by the large lateral forces acting on the turbine rotor.

[0019] US Patent No. 8,118,538 discloses an alternative method of reducing the heeling angle due to the overturning moment generated by the large lateral forces acting on the turbine rotor during turbine operation. A counterweight is attached some distance below the floating platform and essentially acts as a keel. In a further embodiment, the counterweight is connected to adjustable anchor lines and is also used to tension these lines.

[0020] Thus, both spar and semi-submersible systems present challenges.

[0021] WO 2017 / 157399 proposes a floating wind turbine consisting of a hull, a wind turbine mounted on the hull, and a counterweight suspended below the hull by a counterweight suspension means. It also discloses a method for installing the floating wind turbine consisting of a hull, a wind turbine mounted on the hull, and a counterweight suspended below the hull by a counterweight suspension means. The static and dynamic response of the floating foundation can be adjusted before installation by a combination of i) ballasting the counterweight buoyancy tank, ii) ballasting the hull, and / or iii) adjusting the installation depth of the counterweight.

[0022] A drawback of the method and floating wind turbine of WO 2017 / 157399 concerns the suspension means. The counterweight requires a large number of wires or cables to stabilize the counterweight, to keep the weight in its position and to prevent or limit twisting. Offshore, said wires or cables typically result in increased maintenance requirements and unplanned outages. In a relatively low-margin business such as individual wind turbines, maintenance and unplanned outages result in prohibitive operating costs and make the structure economically unviable.

[0023] U.S. Patent No. 9,499,240 describes a substructure having at least one first buoyancy chamber disposed under a single leg to provide a first buoyancy and a float element having at least one second buoyancy chamber to provide a second buoyancy, the first buoyancy being sufficient to keep the substructure afloat, the at least one first buoyancy chamber being ballastable to reduce the buoyancy of the leg, the second buoyancy being sufficient to keep the float element afloat, the at least one second buoyancy chamber being ballastable to reduce the buoyancy of the float element, the float element having a substantially vertically oriented passageway extending through the float element and surrounding the leg in a substantially horizontal plane, The present invention discloses a substructure comprising: a floating element, a floating element and a passageway forming a linear guide for guiding linear vertical movement of the floating element relative to the substructure, the passageway enabling wave-induced movement relative to each other in a substantially vertical direction; the legs are movable from a pre-installation position to an installation position by moving the legs substantially downwardly relative to the floating element, and during a second part of the downward movement of the legs towards and / or in the installation position, the at least one buoyancy chamber is positioned substantially below the wave zone to substantially reduce a heave effect on the at least one first buoyancy chamber, and during at least the second part of the downward movement of the legs, the weight of the complete substructure is borne by the legs.

[0024] US Patent No. 9,499,240 focuses on and is optimized for gravity-based applications.

[0025] WO 2018 / 150064 discloses a floating spar structure for large offshore wind turbines formed by a lower triangular caisson made of reinforced concrete and an upper triangular caisson made of metal that supports the shaft of the wind turbine and is joined by three liftable columns placed at its corners. The structure is a spar platform since it operates based on the lowering of the centre of gravity of the assembly, but it also has a semi-submersible component since the platform has three floats at waterline level that increase its righting moment.

[0026] The drawbacks of the method and floating wind turbine of WO 2018 / 150064 relate to the semi-submersible components embodied by floats in the waterline to improve the righting moment. The floats in the assumed waterline induce wave loads, resulting in excessive movements and accelerations, which reduces 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 radially by compressing it directly against the leg. This leads to relatively large local stresses in each leg, which in turn significantly reduces the capacity of the system.

[0027] WO 2013 / 083358 discloses a floating wind farm comprising a buoyant body adapted to be submerged in water and to support an equipment unit extending above the water, and a ballast element connected to the buoyant body via at least one spacer structure. Guide means in the buoyant body are adapted for movable interaction with the at least one spacer structure, such that the ballast element and the buoyant body are movable relative to each other. The buoyant 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.

[0028] The buoyant body and spacer structures of WO 2013 / 083358 are relatively bulky and therefore require significant amounts of structural materials such as steel and concrete, making the construction relatively complex and capital intensive. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] German Patent No. 2457536 [Patent Document 2] U.S. Pat. No. 4,451,174 [Patent Document 3] U.S. Pat. No. 4,627,767 [Patent Document 4] International Publication No. 2010 / 085970 [Patent Document 5] International Publication No. 2010 / 018359 [Patent Document 6] International Publication No. 2013 / 048257 [Patent Document 7] International Publication No. 2009 / 131826 [Patent Document 8] U.S. Pat. No. 8,118,538 [Patent Document 9] International Publication No. 2017 / 157399 [Patent Document 10] U.S. Patent No. 9,499,240 [Patent Document 11] International Publication No. 2018 / 150064 [Patent Document 12] International Publication No. 2013 / 083358 Summary of the Invention [Problem to be solved by the invention]

[0030] It is an object of the present invention to provide an alternative floating offshore structure which avoids at least one or more of the disadvantages of the prior art. [Means for solving the problem]

[0031] Aspects of the invention are set out in the accompanying claims.

[0032] The present disclosure provides a jacket structure for supporting a functional element in water, the jacket structure comprising at least one floating body element having a first buoyancy and at least one linear guide sleeve; a substructure comprising a counterweight structure having a second buoyancy and at least one leg extending through the at least one guide sleeve and having a lower end connected to the counterweight structure and an upper end provided with a stop element; The at least one leg is movable through a corresponding guide sleeve between a towing position in which the stop element is clear of the guide sleeve and the guide sleeve allows linear movement of the at least one leg relative to the support structure, and an operational position in which the stop element engages a corresponding opposing element of the guide sleeve and the at least one leg is fixed relative to the at least one guide sleeve.

[0033] In one embodiment, the jacket structure comprises a fixing mechanism for fixing the at least one leg relative to the support structure when in the operational position.

[0034] In one embodiment, the fixation mechanism comprises one or more sets of wedges, where a wedge portion of each set is connected to an outer surface of the at least one leg and a second wedge portion of each set is connected to an inner surface of a corresponding guide sleeve.

[0035] In one embodiment, the marine structure comprises a linear guide system integrated into the at least one guide sleeve, the linear guide system may comprise ridges distributed along a 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.

[0036] In one embodiment, the counterweight structure includes an adjustable weight that provides buoyancy when in the towing position and that pushes the marine structure downward when in the operational position.

[0037] In one embodiment, the functional element includes a wind turbine.

[0038] In one embodiment, the counterweight structure surrounds the lower end of the at least one leg.

[0039] In one embodiment, the at least one guide sleeve includes a brake for limiting movement of the at least one leg relative to the corresponding at least one guide sleeve.

[0040] In one embodiment, the offshore structure comprises a plurality of legs, each leg being surrounded by the at least one floating body element.

[0041] In one embodiment, when in the operational position, the first buoyant force exceeds the residual gravitational force of the offshore structure including the depressed counterweight structure to keep the offshore structure afloat.

[0042] In one embodiment, the offshore structure includes at least one propulsion device for positioning the offshore structure in the water.

[0043] In one embodiment, the counterweight structure includes a first valve for passing water and a second valve connected to a pump for pumping gas into and out of the counterweight structure.

[0044] In one embodiment, the pump is positioned above the water surface and is connected via a tube to the second valve, allowing air to be pumped in and out of the counterweight structure.

[0045] In one embodiment, the pump and the tubing are removable such that the pump and the tubing can be removed when the offshore structure is in the operational position.

[0046] According to another aspect, the present disclosure provides a method of installing an offshore structure, the method comprising: a jacket structure for supporting a functional element underwater, the support structure comprising at least one floating body element having a first buoyancy and at least one linear guide sleeve; a substructure comprising a counterweight structure having a second buoyancy and at least one leg extending through the at least one guide sleeve and having a lower end connected to the counterweight structure and an upper end provided with a stop element; providing an offshore structure, the at least one leg being movable through a corresponding guide sleeve between a towing position in which the stop element is clear of the guide sleeve and the guide sleeve allows linear movement of the at least one leg relative to the support structure, and an operational position in which the stop element engages a corresponding opposing element of the guide sleeve and the at least one leg is fixed relative to the at least one guide sleeve; Follow these steps: moving the at least one leg to the towing position by reducing the weight of the counterweight structure; moving the offshore structure to a near shore assembly location; placing the structural element on the support structure; towing the marine structure to a predetermined offshore location; increasing the weight of the counterweight structure, thereby moving the at least one leg downward to the operational position and immersing the at least one floating body element until the stop element engages a corresponding counter element of the at least one guide sleeve; and fixing the at least one leg relative to the at least one guide sleeve.

[0047] In one embodiment, the method includes anchoring the floating marine structure to the bottom of the water using one or more anchor lines.

[0048] In one embodiment, in said operational position, said counterweight structure floats below the wave zone.

[0049] In one embodiment, in the operational position, the weight of the counterweight structure is increased to submerge the at least one body element.

[0050] In one embodiment, the body element is immersed at least below the mean wave height at the predetermined offshore location, hi a preferred embodiment, in operational conditions, the body element is fully immersed.

[0051] Reducing wave loads on the structure is a major advantage of the spar-type structure of the present disclosure. The balance between righting moment and relatively low wave loads is achieved by positioning one or more of the operational floating body elements below the prevailing wave zone. The righting moment is achieved by a counterweight structure, which achieves the required righting moment by setting the center of gravity of the system well below the center of buoyancy of the system.

[0052] In one embodiment, increasing the weight of the counterweight structure includes flooding at least one buoyancy chamber in the counterweight structure using a first valve for passing water and a second valve connected to a pump for pumping gas in and out of the counterweight structure. Flooding at least one buoyancy chamber in the counterweight structure may include controlling a pressure differential across the walls of the counterweight structure to remain within a predetermined range. The predetermined range may be + / - 1 bar, more preferably + / - 0.5 bar.

[0053] By controlling the pressure difference during the lowering of the counterweight structure, less strong or structural material is required. The cost savings from the reduced amount of material outweighs the cost of the pressure balance system. An additional benefit is the reusability of the pressure balance system components, which significantly reduces the cost of projects where multiple systems are installed. The typical number of systems per project ranges from 10-60 systems. Projects here are typically for wind farms. [Brief description of the drawings]

[0054] Reference is made to the figures of the accompanying drawings, which are schematic in nature and may not necessarily be drawn to scale. Like reference numerals indicate like parts. In the accompanying drawings: [Figure 1-1] FIG. 1A shows a schematic side view of an embodiment of an offshore structure according to the present disclosure. [Figure 1-2] FIG. 1B shows a schematic top view of the embodiment of FIG. 1A. [Figure 1-3] Figure 1C shows a side view of the embodiment of Figure 1B along line AA. Figure 1D shows a side view of the embodiment of Figure 1B along line BB. [Diagram 2] 2A and 2B show schematic side views along lines AA and BB, respectively, of another embodiment of a marine structure according to the present invention (see FIG. 1B). [Diagram 3] Figures 3A and 3B show cross-sectional side views of the locking mechanism of Figure 7A in a disengaged position and an engaged position, respectively. [Figure 4-1] 4A-4D show cross-sectional top views of respective embodiments of linear guide mechanisms of the marine structure of the present disclosure. [Figure 4-2] 4A and 4B show cross-sectional top views of respective embodiments of linear guide mechanisms of the marine structure of the present disclosure. [Figure 5-1] 5A-5B show schematic side views of an offshore structure illustrating successive steps of an embodiment of the apparatus for installing the floating offshore structure. [Figure 5-2] 5C-5D show schematic side views of an offshore structure illustrating successive steps of an embodiment of the apparatus for installing the floating offshore structure. [Figure 5-3] 5A-5E show schematic side views of an offshore structure illustrating successive steps of an embodiment of the apparatus for installing the floating offshore structure. [Figure 5-4] FIG. 5F shows a perspective view of an embodiment of the present floating offshore structure in an operational position. [Figure 6] FIG. 6 shows a side view of yet another embodiment of an offshore structure according to the present invention. [Figure 7] 7A-7C show different steps of an embodiment for installing the marine structure of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] 1 shows an embodiment of an offshore structure 1 according to the present disclosure. The offshore structure 1 comprises a support structure 2 and a sub-structure 3.

[0056] The support structure 2 includes one or more body elements 10. The support structure 2 is sometimes referred to as a jacket structure. The one or more body elements 10 include one or more openings 12. The openings 12 may extend into or be integral with a guide sleeve 14. The guide sleeve 14 may extend a predetermined distance above the one or more body elements 10.

[0057] The jacket structure may comprise several structural elements 16, 18, 20 to connect one or more floating body elements 10 to the main deck 22. The main deck 22 allows to attach an upper structure, which may be a wind turbine. The structural elements 16, 18, 20 may be, for example, columns or pylons. The structural elements 16-20 may be made of a quality metal, typically steel, that is typically able to withstand corrosion and provide structural strength as required. The structural element 16 is a ramp that extends between the pylon 20 and one of the sleeves 14. The element 18 may be arranged horizontally connecting each sleeve 14.

[0058] At least one floating body element 10 of the jacket structure 2 may comprise a first buoyancy means 24. The buoyancy means 24 may comprise one or more chambers 26. The chambers 24 may be filled with air or water, making it possible to adjust the first buoyancy provided by the at least one floating body element 10. The first buoyancy provided by the at least one floating body element 10 is typically sufficient to at least hold the jacket structure 2 aft. The first buoyancy chambers 24 may be ballasted, for example by the introduction of water, concrete or other material, to reduce the first buoyancy to a level required to control the draft of the jacket structure 2.

[0059] With reference to Figure 1B, the at least one float element 10 may include multiple float elements. For example, each sleeve 14 may be connected to or comprise a separate float element 10. The float elements may have any suitable shape. As shown in Figure 1, the float element 10 may be cylindrical, circular in top view. The buoyancy chamber 26 within the float element may be cylindrical as well. The float element 10 may be constructed from any suitable material, such as steel or concrete.

[0060] The substructure 3 includes one or more legs 30. The substructure may include, for example, one, two, three, or four legs. The legs are typically tubular and rigid. The lower ends of the legs 30 may be connected to a counterweight structure 32. The upper end of at least one leg 30 extends through the opening 12 and the sleeve 14.

[0061] The substructure 3 may have adjustable weight or adjustable buoyancy. Here, the substructure 3 may include a second buoyancy means. The second buoyancy means may typically comprise one or more chambers 34, 36 that may be filled with air, water or another suitable substance. The first chamber 34 may be included in the counterweight structure 32. Optionally, a second chamber 36 may be included in one or more of the legs 30, typically at or near their lower ends.

[0062] As shown in FIG. 1A, the counterweight structure 32 may be a barge-like structure. The counterweight may be, for example, square or circular in top view (see FIG. 1B). The counterweight 32 may encircle all of the legs 30 as shown in FIG. 1A. As shown in FIG. 1A, the counterweight may be elongated in side view. The counterweight may include at least one weight element 38. The weight element may be a slab of concrete or a similar relatively heavy, dense material. The counterweight structure 32 may be fabricated using concrete and / or steel, for example, steel-reinforced concrete.

[0063] In a practical embodiment, the counterweight structure may be substantially circular and may include a central moonpool or opening. The counterweight may be donut shaped. One or more legs 30 may be substantially circular. The legs may be connected to the top surface of the counterweight structure.

[0064] The air chambers 34, 36 provide and allow adjustment of the buoyancy of the substructure 3. The buoyancy of the substructure 3 may be referred to herein as the secondary buoyancy. In one embodiment, the air chambers 34, 36 of the substructure 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 body of water 50, typically the sea or ocean, where the marine structure is placed for operation. For example, as shown in FIG. 5A, the second valve 42 may be connected via a suitable tube 44 to a control unit and / or a pump 46 located above the water surface 50. The tube 44 may be a flexible hose of a suitable material, typically including rubber or a similar elastomer. The pump 46 and hose 44 may be removably connected to the valve 42, and the hose and pump may be removed once the marine structure 1 is placed at a predefined offshore location and in its operational position. The transition from the assembled position to the operational position allowing the towing of the structure is described herein below. The elimination of the pump and hoses allows for cost savings on the pump unit, while allowing for a relatively precise control of the buoyancy of the counterweight 32. The latter allows for precise control of the upward and downward movements of the counterweight 32 in the water 50. The control of the buoyancy is, for example, significantly more precise than in prior art systems, where the air injection into the buoyancy chambers of the present substructure is connected to the surroundings via the legs, without the use of valves or control mechanisms.

[0065] The positive buoyancy provided by the combination of the chambers 34, 36, when filled with air, may be sufficient to keep the marine structure 1 afloat. This allows the entire structure 1 to float on the counterweight structure 32 during the transport phase, for example, as seen in FIG. 5A. The counterweight structure 32 can then act and behave as a barge. The second buoyancy means 34, 36 can be ballasted, for example, by replacing the air with water, concrete, or another substance. The increase in weight, and the corresponding decrease in the second buoyancy, can be precisely controlled to the extent that the substructure 3 starts to sink. The counterweight 32 now becomes negatively buoyant and acts as a counterweight.

[0066] The guide sleeves 14 comprise a linear guide system for the corresponding legs 30 extending through the respective sleeves. The linear guide system allows linear movement of the legs relative to the corresponding sleeves 14. In its simplest form, the linear guide system consists of an inner surface of the guide sleeve, e.g. cylindrical, for guiding an outer surface of the respective legs, which may be cylindrical. The guide system may comprise various elements for facilitating movement of the legs relative to the corresponding guide sleeves 14, such as one or more of rollers, bearings (such as linear ball bearings), rails, or slides. One embodiment is described below with respect to FIG. 4.

[0067] The structure 1 may include a positioning system 60, allowing controlled positioning of the legs 30 relative to the sleeve 14. Here, the upper end of one or more legs 30 may be provided with a stop element 62. The corresponding sleeve 14 may be provided with a counterbalance element 64 for capturing the stop element. The stop element and / or counterbalance element may include a flange or shoulder extending outwardly relative to the respective leg or sleeve. As will be explained in more detail in conjunction with Figs. 5A-5E, the marine structure of the present disclosure may be adjusted between a towing or assembly position and an operational position. In the towing position, at least one leg 30 is moved upward through the corresponding guide sleeve 14, and the stop element 62 is away from the corresponding counterbalance element 64. See, for example, Fig. 5A. The linear movement of the leg relative to the sleeve allows the substructure 3 to sink into an operational position relative to the jacket structure 2. In the operational position, see, for example, Fig. 1 or Fig. 5E, the stop element 62 engages the corresponding counterbalance element 64 of the guide sleeve.

[0068] The disclosed embodiment introduces tangential loads to one or more legs. Radial loads are avoided or at least significantly reduced. FIG. 4A shows a guide system with elements 72 and 74 and positioning system 60. FIG. 4B shows a guide system with elements 72 and 74, positioning system 60, and brake system 90 (elements 92, 94, 96, and 99). During the lowering of each leg, the load transfer from the sleeve to the leg is performed from member 72 to member 74. Member 74, which acts only in the tangential direction of each leg, further transfers the load to each leg 30. Thus, the capacity of each leg and of the guide system is significantly increased. The latter allows to handle larger loads while reducing the amount of structural material required. Member 60 transfers the load only when the device is in operation.

[0069] 2A and 2B, the body elements 10 may be designed to have alternative shapes and sizes. For example, the marine structure 1 of the present disclosure may comprise a single body element 10 that surrounds all of the legs 30.

[0070] Optionally, the sleeve 14 may be integrated into the body element 10 as a wall of the opening 12, which passes through the body element 10, where the buoyancy chamber 26 and the associated centre of buoyancy are below the waterline and preferably below the local mean wave height when the system is in operational condition.

[0071] The positioning system 60 may comprise flanges or stop elements 62, 64 as mentioned above. Alternatively or additionally, the positioning system 60 may comprise at least one stop element 62 connected to at least one leg 30 adapted to cooperate with an upper surface 66 of at least one floating body element 10. Said upper surface 66 may be provided with suitable reinforcement or structural support to be able to provide the necessary reaction forces. Here, the structural support may comprise, for example, a flange or shoulder structure.

[0072] 3A and 3B, the positioning system 60 may comprise a set of wedge-shaped elements, such as elements 62a, 64a and 62b, 64b, respectively. The stop element 62 may include wedges 62a, 62b. The counterbalancing element 64 may include wedges 64a, 64b. The wedge-shaped structures 62a, 62b are connected to the exterior of the leg 30. The opposing wedge-shaped structures 64a, 64b are connected to the interior of the corresponding sleeve 14 or opening 12. The wedges are sized to allow the wedges 62b and 64a to pass each other during the lowering of the leg 30. In the operational position, as shown in FIG. 3B, a set of wedges, such as wedges 62a and 64a and wedges 62b and 64b, are engaged and locked together to form a connection point between the leg 30 and the sleeve 14. The respective forces on the surfaces of the wedge-shaped elements may be such that the connection between each wedge of each pair forms a bond. The above described bond may be referred to as a cold weld. In theory, cold welds may fail, but in practice, the force between the opposing parts of each pair provides a durable, long-lasting bond. This force is due to the gravity of the substructure 3 due to the weighted counterweight 32. The wedge-shaped elements may comprise a suitable material such as a durable rubber material such as EPDM, or a similar relatively hard elastomer, or steel.

[0073] 4A shows an exemplary embodiment of a linear guide system included in the sleeve 14. Here, the sleeve 14 or the leg 30 may include one or more rails 72. The rails 72 may extend longitudinally along at least a portion of the surface of the respective sleeve or leg. The other portion, i.e. the leg or the sleeve, may include one or more nooks or protrusions 74. The rails 72 guide and direct the movement of the nooks 74. As a result, the movement of the nooks and the parts to which they are attached, such as the leg, is restricted to longitudinal linear movement. Rotation is prevented by the rails 72.

[0074] In one embodiment, the linear guide system shown in Figure 4A may have alternative configurations. For example, member 74 shown in Figure 4A may be a rail. Member 72 may be a protrusion, slide, or rail that can slide along the exterior of rail 74.

[0075] One or more of the legs and / or sleeves may include a guide system as illustrated in FIG. 4A. Typically, all sleeves may be provided with a guide system. The legs and sleeves described above may include multiple guide systems distributed around the circumference of the leg or sleeve. Multiple positioning systems 60 may be similarly distributed around the circumference of the leg or sleeve. While any number of guide and / or positioning systems are contemplated, practical embodiments may include as few as two to four positioning and guide systems per leg or sleeve.

[0076] 4B, a braking device 90 may be provided to provide a braking force between the legs 30 and the sleeve 14. This braking device 90 allows for more precise stopping or control of relative motion between the legs 30 and the sleeve 14. For example, during transportation of the marine structure 1 to an installation site, it may be desirable to ensure that no motion occurs between one or more of the legs 30 and the sleeve 14.

[0077] In one embodiment, the braking device 90 may include, for example, one or more of brake pads 92, plungers 94, hydraulic cylinders 96, hydraulic lines 98, and hydraulic pumps 99. The brake pads 92 may include rubber pads. The rubber may be a relatively robust rubber such as EPDM. The pump may be connected to a controller (not shown) to control the braking force provided by the braking device 90. Alternatives are contemplated including, but not limited to, mechanical braking using electromagnets to actuate the brake pads 92 or levers to control the brake pads. Multiple braking devices 90 may be provided. The braking devices 90 may be distributed around the circumference of the passageway 70. All of the braking devices may be controlled by the same controller and pump 99. See FIG. 4B.

[0078] The braking device 90 may be included in any of the embodiments disclosed herein and described above and below.

[0079] FIG. 5A shows the structure 1 of the invention placed on a body of water 50. An upper structure, such as a wind turbine 80 for generating electricity, may be placed on the platform 22. The wind turbine 80 may be called a wind turbine generator (WTG). The substructure 3 moves upwards relative to the jacket structure 2. Finally, the upward movement of the substructure may be limited by the upper surface of the base 32 engaging the lower surface of at least one floating body element 10. The ballast tank 34 of the counterweight structure 32 may be completely filled with gas, typically air. In this position, the buoyancy of the counterweight 32 with the tank 34 filled with air may be sufficient to lift the entire structure 1, including the upper structure 80, above the water surface. The filling and emptying of the tank 34 with air or water may be controlled via the hose 44, the pump 46, and the valves 40, 42.

[0080] The buoyancy of the counterweight 32 can be adjusted by partially replacing the air in the ballast tank 34 with a heavier than air substance 82, typically water, as shown in Figure 5B. At some point, the body elements 10 will be at least partially submerged and the buoyancy of the body elements 10 will begin to fully support the jacket structure 2.

[0081] 5C and 5D, the buoyancy of the tank 34 is further reduced by replacing the air with a heavier substance such as water. The legs 30 move downwards relative to the sleeve 14 of the jacket structure 2.

[0082] As shown in Figure 5D, downward movement of the base 3 relative to the jacket structure 2 is limited by the system 60. The buoyancy tanks 34 can be designed to be at least partially filled with air even in this position, allowing for further stabilization.

[0083] During the immersion of the counterweight structure 32, in one embodiment, the disclosed method allows to control the wall pressure difference of the counterweight structure. This pressure difference can be maintained within a predefined range. The pressure difference can be controlled, for example, using a pressure control system consisting of the first valve 40, the second valve 42, and the pump 46. The wall pressure difference of the counterweight structure 32 can be maintained, for example, on the order of + / - 1 bar, or about + / - 0.5 bar. During the step of flooding at least one buoyancy chamber in the counterweight structure 32, the wall pressure difference of the counterweight structure 32 is controlled to remain within a predefined range using the pressure control system. In practice, the wall pressure difference is minimized with respect to the surroundings. During the immersion of the counterweight structure 32, the water pressure increases. The water pressure starts at about 1 bar at the surface and increases by about 1 bar for every additional 10 m of depth. During immersion of the counterweight structure, the pressure in the buoyancy chamber of the counterweight structure increases as the water pressure increases. The pressure control system allows the pressure in the chamber 34 to be kept substantially equal to the water pressure outside the structure 32. With the structure 32 submerged in water, the pressure in the chamber 34 may be gradually increased. Here, the air pressure in the chamber 34 may be increased at a rate approximately equal to the increase in water pressure outside the counterweight structure 32, limiting the pressure difference on the walls of the counterweight while the structure 32 is lowered to the operational position. This pressure control system allows the structural strength of the walls of the counterweight structure 32 to be minimized, thereby saving material and associated costs.

[0084] Once the counterweight structure 32 reaches its operational depth, the valves of the pressure control system can be, for example, fully open, which essentially equalizes the water pressure inside and outside the counterweight structure 32. Alternatively, when the counterweight structure 32 reaches its operational depth, the valves of the pressure control system can be, for example, closed, which maintains the pressure differential at a set level while allowing some air in the buoyancy chambers to maintain the buoyancy of the counterweight structure 32 at a preferred level.

[0085] In the operational position, as shown in Figures 5E and 5F, the tank 34 can be filled with water or other heavy material up to a level where the counterweight 32 becomes negatively buoyant and sinks. The structure 32 acts as a counterweight and pulls the floating body element 10 downwards. The positive buoyancy of the floating body element 10 provides an upward force, while the weight of the ballast counterweight 32 provides a downward gravitational force. In the operational position shown in Figures 5E and 5F, the offshore structure 1 behaves as a spar, offering all the advantages in terms of stability that come from the combination of the suspended counterweight and its distance relative to the floating body element 10. In the operational position, the center of gravity of the offshore structure 1 is located below its center of buoyancy. The latter results in a spar-like behavior, making the structure inherently stable.

[0086] The position of the marine structure 1 shown in Figures 5A, 5B, and 5C allows for a limited draft by raising the counterweight structure 3 relative to the jacket structure 2. The limited draft allows the upper structure 80 to be installed in relatively shallow water, for example, in a shelter, near shore, or in a harbor. The buoyancy provided by the counterweight structure 3 can be changed from positive to negative. As illustrated in Figure 5A, when the buoyancy chamber 34 is filled with air, the counterweight structure 32 can have sufficient positive buoyancy to float and carry the entire marine structure 1, including the upper structure 80.

[0087] According to one embodiment of the present invention, in a first step the draft of the structure 1 is limited to allow the structure 1 to be placed at a selected assembly site, typically a port or a near-shore site, where near-shore may refer to a site within 100m of the shore. Depending on the available water depth at the assembly site, the draft can be adjusted to fit the available water depth, as illustrated in Figures 5A-5D.

[0088] In a second step, the upper structure 80 is placed on and connected to the platform 22. Installation can be performed using a land-based or floating crane, platform, or any available lifting means.

[0089] In a third step, the offshore structure including the upperstructure 80 is transported to a selected operating location, which may typically be relatively far offshore, where offshore may refer to distances of more than 500 m offshore. The operating location may have water depths of more than 100 m, typically up to 1 km or more.

[0090] Transportation may include towing or pushing the marine structure including the wind turbine generator 80 in an upright position to the operation location. During transportation, the draft of the marine structure can be adjusted as needed and as possible, for example using the pump 46. For example, during favorable weather conditions or during transportation through areas of shallow water depth, the draft can be limited accordingly. During transportation through areas of increased water depth, increased significant wave height, and / or (anticipated) adverse weather, the draft can be increased by decreasing the buoyancy of the counterweight 32. For example, the buoyancy of the counterweight 32 can be adjusted during transportation between the positions shown in Figures 5A-5D.

[0091] This allows the counterweight structure or substructure 3 to move in a generally vertical direction relative to the jacket structure or support structure 2. In the towing or transport position (see, for example, FIG. 5A), upward movement of the substructure 3 relative to the support structure 2 is restricted by the counterweight structure 32.

[0092] To limit trim and prevent tipping, the stability of the marine structure 1 can be adjusted by adjusting the buoyancy of the substructure 3 within a predetermined range, as illustrated in Figures 5B-5D. Increasing ballast in the tanks 34 increases the draft while lowering the center of gravity, improving stability. How, when and to what extent the buoyancy of the base 32 is adjusted may depend, for example, on weather conditions and the available water depth, during transportation and at the assembly site.

[0093] In one embodiment, in the operational position (FIGS. 5E, 5F), at least one leg 30 is fixed relative to at least one guide sleeve 14. The fixation of the legs relative to the corresponding sleeve can be fully achieved by a set of wedges of the system 60, as shown in FIG. 3B. Here, the downward movement of the wedge parts relative to each other during the transition from the assembly position to the operational position results in the respective wedge parts of each set engaging with each other. Due to the weight of the substructure and the resulting gravitational pull on the wedge parts 62a, 62b, the engagement actually provides a fixed connection point, as shown in FIG. 3B. The engagement in FIG. 3B can be considered as cold welding. Cold welding or contact welding is a solid-state welding process in which the joint is made without fusion or heating at the interface of the two parts to be welded. Unlike fusion welding, there is no liquid or molten phase at the joint.

[0094] Alternative fastening means may be used instead of or in addition to the set of wedges as shown in FIG. 3. For example, the step of fastening the leg to the sleeve may include inserting one or more locking pins through corresponding openings (not shown) that extend through both the leg and the sleeve. Although not shown, in the embodiment of FIG. 3B, this may include a transversely inserted pin that extends through both the outer and inner cylinders of the sleeve and the leg, respectively, preventing relative movement in the longitudinal direction (vertical in the figure). A rigid welded connection between the leg and the sleeve is also possible. Fastening may be achieved by a bolted connection including flanges. See for example FIG. 1A. Here, shoulders 62 and 64 may be provided with flanges that allow a bolted connection between the respective flanges. Other alternatives are also contemplated, such as, but not limited to, one or more of a pad eye and pin connection, a welded connection, etc.

[0095] 6, in another embodiment, the offshore structure 1 may comprise a single leg 30, where the platform 22 may be connected to the upper end of the single leg 30. The lower end of the leg 30 may comprise a ballastable counterweight 32 with one or more buoyancy chambers 34. The buoyancy of the counterweight 32 may be adjusted by replacing the air in the chambers 34 with a ballast material 82, such as water.

[0096] The support structure 2 comprises a body 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 foot 30. The stop element 62 may engage an upper surface 66 of the body element 10.

[0097] 7(A) shows the marine structure 1 in a shipping configuration prior to installation. The combined buoyancy, i.e. the first buoyancy provided by the floating body elements 10 and the second buoyancy provided by the unstabilized counterweights 32, is sufficient to keep the marine structure 1 floating in the water 50 at shallow water drafts. The marine structure 1 is therefore self-floating, i.e. no other means need be provided to keep the marine structure 1 floating on the sea surface at shallow water drafts.

[0098] To install the offshore structure 1 in the desired configuration, in a second step shown in Figure 7B, the counterweights 32 are ballasted by introducing ballast 82, thereby lowering the substructure 3 of the offshore structure 1. The buoyancy of the floating body elements 10 is now sufficient to keep the jacket structure 2 floating in the sea at a shallow draft.

[0099] During further lowering of the base structure 3 relative to the jacket structure 2, shown in Fig. 7C, the marine structure 1 is stabilized by the upward force provided by the floating body element 10 combined with the downward pulling force of gravity of the ballasted counterweight 32. The jacket structure 2 is submerged in water by ballasting the counterweight 32, such that the second buoyancy provided by the counterweight 32 becomes negative pressure, causing the substructure 3 to sink in water and pulling the entire marine structure downwards, as shown in Fig. 7C. The floater 10 acts as a stabilizing element, since the first buoyancy provided by the at least one floating body element 10 of the jacket structure 2 is maintained at substantially the same level.

[0100] The substructure 3 is lowered into a position such that the jacket structure 2 and the substructure 3 are connected by the connection system 60. The substructure 3 is moved substantially vertically relative to the jacket structure 2 via the passage 70.

[0101] After the jacket structure 2 and the sub-structure 3 are secured together, the buoyancy means 36 of the sub-structure 3 may be further ballasted so that the floating body elements 10 are submerged in the sea, so that the floaters 10 can be fully submerged, as shown in Figure 7C. This position, as described above, minimises wave action on the offshore structure 1 by positioning the main buoyancy 10 carrying the offshore structure 1 substantially below the wave zone.

[0102] The weight of the offshore structure 3 and the combination of the ballasted balancing weight at a lower position and the first buoyancy provided by the floating element 10 at a higher position provides a stable foundation for the offshore structure 1 even when large or tall objects such as wind turbines or cranes are placed on the offshore structure 1.

[0103] The offshore structure 1 may be held in place completely by using anchor lines 11. In alternative embodiments, additional means may be provided to hold the offshore structure at a desired position on the sea, such as a propulsion system 15 as shown in FIG. 1A. The propulsion system 15 may include one or more thrusters or similar motors. The thrusters may be automatically controlled so that the offshore structure 1 maintains a particular position within a predefined margin of error. The propulsion system may be sized such that the anchor lines 11 are not required. The propulsion system 15 may be used to counteract all environmental loads acting on the offshore system. Alternatively, such a system may be used to also or only to damp horizontal and rotational movements due to environmental dynamic loads or incidental loads generated by payloads such as wind turbines or offshore cranes.

[0104] Next, the method of lowering the base structure will be described. Figures 5A and 7A show the starting position and configuration shown in step 1. For this process, a submersion valve 40, an air vent valve 42, an air hose 44, and an air control system 46 may be provided for operation. With the air control system 46 connected to the buoyancy chamber 34, the air pressure in the chamber 34 may be preset to a small overpressure via the air hose 44 and the vent valve 42. This is done to balance the pressure difference on the outside of the base 32 with the external hydrostatic pressure at the depth of the counterweight 32.

[0105] To proceed to the second step, the flooding valve 40 is opened. Water flows into the buoyancy chamber 34 and the draft of the marine structure 1 increases. Inside the buoyancy chamber 34, pressure increases due to water intake and flooding will cease when pressure equilibrium between the exterior and interior is achieved. The air cushion above the water in the buoyancy chamber 34 balances the weight of the base structure as shown in Figures 5B and 7B.

[0106] The subsequent lowering step illustrated in Figures 5C and 5D can be performed by opening the vent valve 42 and controlling the internal pressure of the buoyancy chamber 34 using the air hose 44 and the air control system 46. By lowering the internal air pressure in the buoyancy chamber 34, ballast water flows into the buoyancy chamber 34 through at least one submersion valve 40, driven by the pressure difference over the submersion valves. The water flow increases the weight of the substructure 3, resulting in an increase in the draft of the substructure. This process is reversible by increasing the internal pressure using the air control system 46. The water can be pushed out and the draft of the substructure will decrease accordingly.

[0107] Referring to FIG. 5A, the pressure control system 46 allows the lowering or raising of the substructure 3 to be operated in a controlled and safe manner without the need for complex, expensive and dangerous mechanical lifting devices conventionally used for similar operations. Another advantage of the air control system 46 is the reduction of the design pressure loads on the exterior walls, ceiling and floor of the counterweight structure 32. The structure can be constructed of concrete or steel or a combination of the two materials. The amount of material required to resist water pressure can be significantly reduced by using the pressure control system 46 to reduce the pressure differentials on the exterior walls, ceiling and floor of the counterweight 32, even at depths underwater.

[0108] 5E or 7C, in the final step, the air control system 46 and air hoses 44 may be removed. In this position, the vent valve 42 and submersion valve 40 may be open to the sea. The internal and external pressures on the outer walls, ceiling and floor of the counterweight 32 are now perfectly balanced.

[0109] In practical embodiments, the offshore structure of the present disclosure can be dimensioned to support a wind turbine generator of any suitable shape or size. For example, the draft of the offshore structure (i.e., the maximum depth of the structure below the water surface) in its operational position may range on the order of more than 50 m up to 100 m or more. Thus, in its operational position, the structure 1 can behave like a spar structure, providing stability and preventing the upper structure 80 from tipping over due to the hanging counterweights 32.

[0110] The wind turbine generator 80 may, for example, be sized with a mast height of 50-150 m. The blades of the wind turbine generator may have a length of the order of 50-120 m. The power rating of the wind turbine generator may be of the order of 1-20 MW. The structure 1 may act as a floating foundation for wind turbines, from relatively small to the largest currently envisaged.

[0111] In practice, the marine structure of the present invention may be constructed from materials that provide adequate strength, weight, buoyancy, and sufficient life in the offshore marine environment. Offshore, corrosion resistance may be even more important than in land-based operations. The marine structure, including its upper structure, is also in fact designed to withstand high winds and large wave action. With regard to the latter, the structure of the present disclosure has the advantage of being able to control the draft through dedicated control vents such as valves 42 and 40. In its operational position, for example, see FIG. 5E, the base 32 is submerged, but the floating body element 10 may also be submerged. For added stability, the floating body element 10 may be submerged such that its upper surface is lower than a predetermined depth. The aforementioned predetermined depth may exceed the RMS wave height, significant wave height, or large wave height in the operational position.

[0112] Wave height in this specification may be the distance between the crest and trough of a wave. Significant wave height, scientifically expressed as Hs or Hsig, is a parameter for the statistical distribution of (ocean) waves. Most common waves have a lower height than Hs. This means that significant waves are encountered less frequently. However, statistically, waves much higher than significant waves can be encountered. In general, the statistical distribution of individual wave heights is approximated by a Rayleigh distribution. For example, assuming Hs is 10 meters (33 feet), statistically, 1 in 10 waves will be larger than 10.7 meters (35 feet), 1 in 100 waves will be larger than 15 meters (50 feet), and 1 in 1000 waves will be larger than 18.5 meters (61 feet). This means that waves about twice the significant wave height can be encountered. However, in rapidly changing conditions, the disparity between significant wave height and the largest individual wave can be even larger.

[0113] Other statistical measures of wave height are also widely used. The root mean square (RMS) wave height is defined as the square root of the average of all the squares of the wave heights and is approximately equal to Hs divided by 1.4.

[0114] The significant wave height may vary from one offshore location to another and may range from 5-15 m. William G. Van Dorn, in his book Oceanography and Seamanship, gives an example of the wave heights for a steady wind of 30 knots (33 mph / 53 km / h) for 24 hours with a suction range of 340 miles. In that case, 10% of all waves will be less than 3.6 feet (1 m). The most frequent wave height will be 8.5 feet (2.5 m). The average wave height will be 11 feet (3 m). The significant wave height will be 17 feet (5 m). 10% of all waves will be over 18 feet (5 m). The average wave height of the highest 10% of all waves will be 22 feet (7 m). For every 200 waves passing in about 30 minutes, there is a 5% chance of encountering a single wave over 11 meters (35 feet). For every 2600 waves that pass in about a five-hour period, there is a 5% chance of encountering a single wave over 12 meters (40 feet).

[0115] In practical embodiments, the offshore structures of the present disclosure may be sized and designed to withstand significant wave heights on the order of 10-17m. Note that Hs of 17m is the maximum significant wave height for design limitations. A system suitable to withstand Hs of 17m is the most severe design limitation. The latter makes the offshore structures of the present disclosure suitable for unrestricted worldwide operation.

[0116] The structure 1 may be designed such that when in the operational position the floating body elements 10 are immersed at least once or more than once in the operational position to a wave height, where the wave height may be selected from a significant wave height, an RMS wave height or an average wave height. Alternatively, the buoyancy of the floating body elements 10 of the structure 1 may be reduced during periods of expected adverse weather conditions to increase stability and immerse the floating body elements 10.

[0117] In practical embodiments, the marine structure of the present disclosure may be constructed using steel and concrete. For example, the support structure 2 may be made of steel. The base structure, including the legs 30, may be manufactured from concrete, potentially reinforced using steel wire mesh.

[0118] As an example, the height of the mast of the wind turbine 80 may be in the order of 100-150 m. The blades of the wind turbine 80 may have a length in the order of 70-95% of the height of the mast, for example in the order of 80-125 m. The base 32 in the operational position may have a draft of about 50-100 m, for example in the order of 60-70 m. The bottom surface of the floating body element 10 may be submerged in the order of 10-25 m, for example in the order of 15-20 m while in the operational position. The latter may be referred to as the draft of the jacket, or the draft of the support structure 2. The top surface of the floating body element 10 may be submerged in the order of 5-10 m below the water surface. The top of the support structure 2 may extend above the water surface by about 10-20 m. The counterweight 32 may be substantially circular or toroidal in shape. The counterweight structure 32 may have a diameter in the range of about 40-75 m, for example in the order of 50-60 m. The counterweight structure 32 may have a height in the range of about 5-20 m, e.g. about 10-15 m. The structure may include about three floating body elements 10. The floating body elements 10 may be substantially circular. The floating body elements 10 may have a diameter in the range of about 10-40 m, e.g. about 20-30 m, e.g. about 25 m. The legs 30 may have a diameter in the range of about 5-15 m, e.g. about 7-10 m. These dimensions are merely exemplary and in practice may be either larger or smaller. The actual dimensions may depend on the operation site, assembly site, local wave height, average weather conditions, size of the wind turbine, etc., and the structures of the present disclosure may be sized accordingly.

[0119] For example, with reference to Figure 1B, in a preferred embodiment, the jacket structure 2 and substructure 3 may be designed such that, in a top view, the center of gravity and center of buoyancy are located in the center, i.e., on the centerline. Alternatively, the center of gravity and / or center of buoyancy may be off-center.

[0120] The marine structure 1 of the present disclosure may be used as a floating base for other suitable applications such as an offshore platform, a working platform, a solar power plant, a wave energy converter, a hydrogen storage and / or conversion unit, or a meteorological mast, or the structure may be used in a multi-purpose application combining any of the aforementioned applications, for example combining a wind turbine and a wave energy converter in one marine structure 1 as disclosed herein.

[0121] The marine structure 1 of the present disclosure may be used as a wave energy converter, typically in an operational position as shown in Figure 5C. The up and down movement between the legs 30 and the sleeve 14 can be used to generate power using some kind of converter that converts mechanical energy (of the legs 30 moving relative to the jacket structure 2 by the waves) into electrical energy. Thus, when used as a wave energy converter, the legs are movable and not fixed relative to the jacket structure.

[0122] The marine structure 1 of the present disclosure may be used as a multi-purpose power plant, for example, by combining three power generation methods, such as solar power generation, wave power generation, and wind power generation, with a hydrogen energy conversion device and storage application. Thus, the system typically produces a more constant power output (called peak shaving) to the end user. The latter can significantly increase the efficiency of the installation.

[0123] The scope of the present disclosure is not limited to the above-described embodiments. Many modifications therein are possible without departing from the scope of the present invention as defined by the appended claims. In particular, combinations of features of each embodiment or aspect of the present disclosure may be made. An aspect of the present invention may be further advantageously extended by adding features described in relation to another aspect of the present invention. While the present invention has been illustrated and described in detail with reference to the drawings, such illustration and description are merely illustrative or representative.

[0124] 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 signs in the claims should not be interpreted as limiting the scope of the present invention.

Claims

1. A jacket structure comprising at least one floating element having a first buoyancy and at least one linear guide sleeve for supporting a functional element in water, A substructure comprising a counterweight structure having a second buoyancy, and at least one leg extending through the at least one guide sleeve and having a lower end connected to the counterweight structure and an upper end provided with a stop element, An offshore structure in which at least one leg is movable through a corresponding guide sleeve between a towing position in which the stop element is away from the guide sleeve and the guide sleeve is able to move linearly with respect to the support structure of the at least one leg, and an operational position in which the stop element is engaged with a corresponding opposing element of the guide sleeve and the at least one leg is fixed to the at least one guide sleeve.

2. The marine structure according to claim 1, further comprising a fixing mechanism for fixing the at least one leg portion to the support structure when the jacket structure is in the operational position.

3. The marine structure according to claim 2, wherein the fixing mechanism comprises one or more sets of wedges, the wedge portion of each set being connected to the outer surface of at least one leg portion, and the second wedge portion of each set being connected to the inner surface of the corresponding guide sleeve.

4. The marine structure according to claim 1, comprising a linear guide system incorporated into at least one of the guide sleeves.

5. The marine structure according to claim 4, wherein the linear guide system comprises raised portions distributed around the periphery of at least one guide sleeve, and corresponding nooks fitted between the two raised portions and extending from the outer surface of at least one leg portion.

6. The ocean structure according to claim 1, wherein the counterweight structure has an adjustable weight, the weight provides buoyancy when in the towing position, and the weight pushes the ocean structure downward when in the operational position.

7. The marine structure according to claim 1, wherein the functional element includes a wind turbine.

8. The marine structure according to claim 1, wherein the counterweight structure surrounds the lower end of at least one leg.

9. The marine structure according to claim 1, wherein the at least one guide sleeve is equipped with a brake for restricting the movement of the at least one leg relative to the corresponding at least one guide sleeve.

10. The marine structure according to claim 1, comprising a plurality of legs, each leg being surrounded by at least one floating element.

11. The ocean structure according to claim 1, wherein, when in the aforementioned operating position, the first buoyancy exceeds the remaining gravity of the ocean structure including the lowered counterweight structure, thereby maintaining the ocean structure in a floating state.

12. The marine structure according to claim 1, comprising at least one propulsion device for positioning the marine structure in the water.

13. The marine structure according to claim 1, wherein the counterweight structure comprises a first valve for supplying water and a second valve connected to a pump for pressurizing gas to the inside and outside of the counterweight structure.

14. The marine structure according to claim 13, wherein the pump is positioned above the water surface and connected to the second valve via a pipe, enabling the pumping of air into and out of the counterweight structure.

15. The offshore structure according to claim 14, wherein the pump and the pipe are removable so that the pump and the pipe can be removed when the offshore structure is in the operational position.

16. A jacket structure for supporting a functional element in water, comprising a support structure having at least one floating element having a first buoyancy and at least one linear guide sleeve, A substructure comprising a counterweight structure having a second buoyancy, and at least one leg extending through the at least one guide sleeve and having a lower end connected to the counterweight structure and an upper end provided with a stop element, The steps of providing an offshore structure in which at least one leg is movable through a corresponding guide sleeve between a towing position in which the stop element is away from the guide sleeve and the guide sleeve allows the at least one leg to move linearly with respect to the support structure and an operational position in which the stop element engages with a corresponding opposing element of the guide sleeve and the at least one leg is fixed to the at least one guide sleeve, The following steps: The steps include reducing the weight of the counterweight structure to move at least one leg to the towing position, The steps include moving the aforementioned offshore structure to an assembly location near the coast, The steps include: placing the structural element on the support structure, The steps include towing the aforementioned offshore structure to a predetermined offshore location, The steps include increasing the weight of the counterweight structure, thereby moving the at least one leg downward to the operating position and immersing the at least one floating element until the stop element engages with the corresponding opposing element of the at least one guide sleeve, A method for installing an offshore structure, comprising the step of fixing the at least one leg portion to the at least one guide sleeve.

17. The method according to claim 16, comprising the step of anchoring the marine structure to the seabed using one or more anchor lines.

18. The method according to claim 16 or 17, wherein, at the operational position, the counterweight structure floats below the wave zone.

19. The method according to claim 16, wherein the weight of the counterweight structure is increased at the operating position to immerse the at least one floating element.

20. The method according to claim 19, wherein the floating element is completely submerged at a predetermined offshore location, at least below the mean wave height.

21. The method according to claim 16, wherein the step of increasing the weight of the counterweight structure includes flooding at least one buoyancy chamber within the counterweight structure using a first valve for supplying water and a second valve connected to a pump for pressurizing gas in and out of the counterweight structure.

22. The method according to claim 21, wherein the step of immersing the at least one buoyancy chamber in the counterweight structure includes controlling the pressure difference on the walls of the counterweight structure to remain within a predetermined range.

23. The method according to claim 22, wherein the predetermined range is ±1 bar, more preferably ±0.5 bar.

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