Offshore platform with vertical column assembly

Abstract

The present invention aims to improve the options available for the use and installation of structures including, for example, wind turbines. An apparatus and method for installation of an offshore platform to support an installation of equipment is provided. The apparatus includes a platform configured to support the offshore equipment supported by a structure such as a modular column assembly. The modular column assembly may be comprised of a main barrel joint bundle.

Description

[Technical field]

[0001] The present disclosure relates generally to offshore structures, and more specifically to structures for supporting offshore wind turbines, oil and gas operations, desalination operations, electrical substations, or similar facilities.

[0002] In the described embodiments, there are several types of configurations that provide a stable platform for mounting offshore equipment. Many types of equipment can be supported by the structures disclosed or installed using the steps disclosed herein, but reference is made to one such example, an offshore wind turbine installation. Those skilled in the art will appreciate that other equipment can be affixed to the structures disclosed herein, and one such example is shown and should not be read off the present disclosure. [Background technology]

[0003] For offshore installations, the arrangement of piles, submerged structures, and / or platform types generally varies based on the depth of the installation. For offshore wind developments, shallow depth installations, i.e., installations less than about 50 meters, are typically fixed to the seabed by rigid structures that are anchored by piles. Examples of structures that can be used in shallow waters may include, for example, monopiles, jacket structures, jack-up installations, etc. However, the use of piles may be inconvenient due to noise pollution created during the installation of driven piles. As the water depth increases beyond approximately 50 meters, the cost of fixed structures increases rapidly. This is due to the additional material costs for the structures to withstand increased wave and current loads, as well as the significantly more expensive installation vessels required to carry out the installation. Thus, floating platforms are currently used or planned to be used in deeper waters.

[0004] In deeper waters, typically greater than 50 meters deep for wind development, floating platforms can alternatively be used. These include, for example, barges, spar buoys, tension leg platforms, semi-submersible platforms, etc. The transition depth from fixed structures to floating platforms varies depending on the local wind, wave and current, seabed conditions, and economic considerations.

[0005] Floating platforms are subject to wave and current loads, which pose challenges that require additional costs to achieve the necessary stability to support equipment such as wind turbines, or require modifications to the equipment, or reduce the operability or uptime of the equipment, or result in additional maintenance and repairs. As a result, an increase in water depth beyond 50 meters or so significantly increases installation costs, whether using traditional fixed structures or floating platforms.

[0006] The economics of the offshore wind power market require that the cost of structures or platforms be minimized. Water depths in the 50-150 meter range represent a large market opportunity because of the shortcomings of both traditional fixed and floating platform installations, and because in many locations, ideal wind farm sites, i.e., easily accessible, located near available infrastructure, and not in the public view, are found within this depth range. Such transitional water depth sites are available for installation in many offshore wind farms around the world, such as the North Sea, Baltic Sea, Celtic Sea, Irish Sea, Mediterranean Sea, US East Coast, Gulf of Mexico, Yellow Sea, Taiwan Strait, South China Sea, and Bass Strait. Because traditional fixed structures and floating platforms are not economical in the 50-150 meter range of water depths, and floating platforms do not perform as well in shallower waters, improved solutions are needed. The present invention seeks to improve the use of, and the options available for installing, structures, including, for example, wind turbines, in these transitional sites around the world. Summary of the Invention

[0007] One or more embodiments of the present invention describe a structure for supporting offshore installations including, for example, wind turbines. Those skilled in the art will recognize that other similar installations, such as oil and gas operations, desalination operations, electrical substations, or similar offshore operations, may use one or more of the embodiments of the present invention.

[0008] In further embodiments, features of specific embodiments may be combined with features of other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

[0009] The accompanying drawings, which are included to provide a further understanding, and which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosed embodiments. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows a schematic diagram of an offshore wind turbine installation according to an embodiment of the present disclosure. [Diagram 2] 1 illustrates an offshore wind turbine installation from a top view according to an embodiment of the present disclosure. [Diagram 3] FIG. 1 illustrates a schematic diagram of a wind platform having a column spring assembly according to an embodiment of the present disclosure. [Figure 4] 1 illustrates an isometric view of a compression guide member according to an embodiment of the present disclosure. [Figure 5A] FIG. 1 shows a schematic diagram of a wind platform having a lattice tower assembly according to an embodiment of the present disclosure. [Figure 5B] 5B shows an alternative embodiment of the configuration shown in FIG. 5A having multiple mooring lines attached to the upper frame structure at different locations. [Figure 6] FIG. 1 shows a schematic diagram of a wind platform having a modular assembly according to an embodiment of the present disclosure. [Figure 7]1 illustrates an embodiment of an offshore superframe structure according to an embodiment of the present disclosure. [Figure 8A] FIG. 1 illustrates a schematic diagram of a wind platform having a spudcan foundation according to an embodiment of the present disclosure. [Figure 8B] 8B shows an alternative embodiment of the configuration shown in FIG. 8A having multiple mooring lines attached to the upper frame structure at different locations. [Figure 9] FIG. 1 shows a schematic diagram of a wind platform with micropiles according to an embodiment of the present disclosure. [Figure 10] FIG. 1 shows a schematic diagram of a wind platform with inclined tension lines according to an embodiment of the present disclosure. [Figure 11] 1 illustrates an installation sequence for a wind turbine platform according to an embodiment of the present disclosure. [Figure 12] 1 illustrates an alternative installation procedure for a wind turbine platform according to an embodiment of the present disclosure. [Figure 13] 1 illustrates an alternative installation procedure for a wind turbine platform according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present disclosure relates generally to offshore structures, and more specifically to structures for supporting offshore wind turbines and similar equipment. As described herein, embodiments of the offshore structures described herein improve upon conventional offshore structure configurations, particularly in transitional sites with water depths of 50 to 150 meters.

[0012] Overall description of the structure 1 provides a schematic diagram of an exemplary configuration of an offshore installation for supporting offshore operations, in this example, a wind turbine 106, according to an embodiment of the present disclosure. In the illustrated embodiment, an upper frame structure 101 supports a wind turbine tower 102 and a wind turbine 106. In the illustrated embodiment, stays 108 provide additional support to the wind turbine tower 102. In the illustrated embodiment, the upper frame structure 101 is supported by a column assembly 110 and at least three tension lines 104. The column assembly (space frame in the embodiment shown in FIG. 1) 110 and tension lines 104 extend to a foundation 105 located on the seabed.

[0013] The tension lines 104 are tensioned to some degree so as to maintain tension at all times during operation. The number of tension lines and the degree of tension in the tension lines 104 are determined based on the water depth, turbine size, and the expected wave, current, and wind patterns experienced at the site. Tension is transferred to each tension line by its connection to a tendon attachment pouch, as discussed in more detail below. In certain embodiments, the tension lines 104 may be adjustable and / or may include adjustable sections or adjustable connections to the upper frame structure 101. The tension lines 104 have connection configurations to the upper frame structure 101 and the foundation 105. In some embodiments, the connections are shackles or flexible bearings. Those skilled in the art will appreciate that a hydraulic wedge jack system can be used to pre-tension the tension lines. In other embodiments, a rotating step shim system can be pre-installed so that the jack system can manipulate and rotate the step shim system into position without the need for hydraulics.

[0014] In certain embodiments, tension line 104 is formed by a number of tension line interjoints connected together to form a tension line joint string.

[0015] The column assemblies 110 support the weight of the upper frame structure 101, the wind turbine tower 102, and the wind turbine 106 and facilitate tensioning of the tension lines 104. The tension lines 104 resist rotation of the upper frame structure 101 due to wind loads on the turbine, thus maintaining a stable platform, which is particularly advantageous in applications supporting wind turbines or other sensitive equipment. The upper frame structure 101 is supported laterally by taut mooring lines 103. In the illustrated embodiment, the upper frame structure 101 is supported by at least three mooring cables 103. In certain embodiments, three pairs of mooring cables 103 can be used to increase yaw stiffness. In this case, each pair of mooring cables 103 is oriented with an angular separation of, for example, 60 degrees. The mooring cables resist shear forces acting on the offshore structure due to wind, waves, and currents. In the illustrated embodiment, mooring anchors 107 are used to anchor the mooring lines 103 to the seabed. In the illustrated embodiment, the foundation 105 is located on the seabed.

[0016] 2 shows an upper portion of an offshore installation supporting a wind turbine 106 according to an embodiment of the present disclosure. In the illustrated embodiment, the offshore structure is not a floating hull as vertical support is provided from below the water surface by a column assembly 110. The column assembly 110 provides compressive forces on the upper frame structure 101 according to the weight of the turbine 106, tower 102 and upper frame structure 101, as well as tension forces applied to the tension lines 104 and mooring lines 103, so that the structure is held rigid at its installation location to counter the effects of wind, waves and currents on the offshore structure, reducing accelerations and therefore mechanical and inertial loads on the turbine tower and turbine in wind turbine applications.

[0017] The illustrated embodiment minimizes the exposure of the structure to wave and current loads compared to conventional floating platforms. Advantageously, this reduces mooring and mooring anchor requirements and helps minimize environmental disturbances in wave and current conditions. Furthermore, the design provides a smaller footprint than conventional catenary-moored floating platforms due to the reduced mooring requirements, thus providing more space between offshore installations for vessel movement.

[0018] Detailed description of components A column assembly 110 is connected to the upper frame structure 101 and the foundation 105. As illustrated in FIG. 1, the column assembly 110 may be a space frame, but one skilled in the art will understand that other structures may be used. The column assembly 110 supports the weight of the turbine 106, tower 102, and upper frame structure 101 while countering the tension of the tension lines 104. A power umbilical may be installed through a tubing in the column assembly 110, entering the column assembly 110 at a point near the end of the superstructure and exiting at a point near the end of the foundation. This is advantageous because the umbilical is shielded from wave and current loads, thus reducing dynamic loads and associated fatigue damage. Alternatively, the power umbilical may be clamped to the outside of the column assembly 110 or tension lines 104.

[0019] In certain embodiments, the upper and lower ends of the column assembly 110 are connected to the upper frame structure 101 and the foundation 105, respectively, with flexible connections allowing rotation in any direction. In certain embodiments, the connections between the upper and lower ends of the column assembly 110 and the upper frame structure 101 and the foundation 105 are fixed. One skilled in the art will appreciate that fixed connections allow limited rotational freedom while maintaining axial stiffness. As will be appreciated by one skilled in the art, any combination of fixed or flexible connections may be used depending on the design requirements. Some embodiments use pin connections during operation, but may be beneficial to lock the connections during installation.

[0020] In some embodiments, for example in shallow areas, it may be beneficial to use a single large diameter pipe for the column assembly 110.

[0021] In other embodiments, up to four or five pipes may be used. One skilled in the art will appreciate that in some embodiments, the pipe diameters may range from 36 inches to 60 inches or more.

[0022] As illustrated in FIG. 3, in some embodiments, a column spring assembly 210 may be connected to the upper frame structure 101 and the foundation 105. The column spring assembly 210 is designed to resist global buckling. In certain embodiments, various composite sections may be used along its length. In the illustrated embodiment, the column spring assembly 210 includes a compression member 211 that extends from the upper frame structure 101 to the foundation 105. The compression member 211 is preloaded by tension in the tension line 104. As previously described, this preloaded compression is thereby increased to an operating state by increasing the tension on the tension line 104. The tension line 104 provides an additional constraint to the movement of the upper frame structure 101, thereby providing additional stability.

[0023] In the illustrated embodiment, the post spring assembly 210 includes at least three compression members 211. The plurality of compression members 211 are supported by buckle stops or compression member guides 212, which are discussed in more detail below.

[0024] In a particular embodiment of the post spring assembly 210, the compression member 211 is connected to an end plate on the post spring assembly 210 by a pin perpendicular to the bending plane indicated by a buckle stop or slot in the compression member guide 212, but may be connected in any number of ways that would be apparent to one of ordinary skill in the art.

[0025] 4 shows an isometric view of a buckle stop 512 according to an embodiment of the present disclosure. The buckle stops 512 allow each compression member 511 to deflect outward from the center of the assembly toward the outer portion of the guide body 524, thereby increasing the moment of area of ​​the composite section, but limit the deflection and ultimately restrain the compression members 511 laterally from one another to prevent overall buckling of the individual compression members 511, and therefore the composite post spring assembly 210.

[0026] In the illustrated embodiment, there are three compression members 511. Each compression member 511 passes through a buckle stop 512. The buckle stop 512 includes a guide slot 520 for each compression member 511. In the illustrated embodiment, a guide retainer 522 is installed on each compression member 511. The guide retainer 522 may be installed on the compression member 511 after it is positioned on the buckle stop 512 such that the guide retainer 522 may be positioned on each side of the guide slot 520 to retain the buckle stop 512 in its intended position.

[0027] Those skilled in the art will appreciate that any mechanical connection, including but not limited to buckle stops 512, may be positioned at any point between the upper frame structure 101 and the foundation 105. Those skilled in the art will appreciate that if the mechanical connection is a compression member guide, it may be advantageous to position the compression member guide equidistantly between the upper frame structure 101 and the foundation 105 to optimize buckling capacity. Those skilled in the art will also appreciate that in some cases it may be advantageous to include multiple mechanical connections positioned between the upper frame structure 101 and the foundation 105. In some embodiments, the mechanical connections are formed of standard structural grade steel, such as API 2H grade 50.

[0028] As illustrated in FIG. 5A, in some embodiments, the column assembly is a lattice tower column assembly 310. In this embodiment, straight pipes are used rather than pipes intended to deflect outward as in the embodiment of column spring assembly 210 discussed above. Similar to the column spring assembly 210 discussed above, the lattice tower column assembly 310 includes pipes 311 that extend from the upper frame structure 101 to the foundation 105. The lattice tower column assembly 310 may include braces 313. The braces 313 may be fitted to the column assembly using friction clamps. In other embodiments, diagonal braces 313 are welded to the column assembly. The braces 313 distribute shear forces within the column assembly. The braces between the pipes 311 may be in any configuration, including but not limited to horizontal, vertical, or diagonal. One skilled in the art will appreciate that the specific configuration of any braces will depend on the conditions at the installation site, the equipment to be installed on the upper frame structure 101, and other variables potentially specific to a particular location.

[0029] Those skilled in the art will appreciate that the column assemblies 110 connected to the upper frame structure 101 and foundation 105 can be of any configuration that provides sufficient strength and stability to support the weight of the system and the downward force of the tension lines 104 and tension moorings 103, and provides stability to the upper frame structure 101.

[0030] In some embodiments, the space frame, column spring assemblies, lattice tower column assemblies, pipes, or other structures connected to the upper frame structure 101 and foundation 105 may be modular. As illustrated in Figure 5A, in the case of a lattice tower column assembly 310, a plate 312 may be included to support the connections between modules and provide additional strength, which is discussed in more detail below. Alternatively, the modules of a modular column assembly may be joined together using any suitable pipe connectors.

[0031] As illustrated in FIG. 5B, an exemplary offshore installation may include lateral supports, such as mooring lines, attached to the upper frame structure at multiple different points. For example, multiple mooring lines 303 may be attached toward the outer edge of the upper frame structure 101, with each such line anchored to the seabed at a different location with respect to the lateral distance from the foundation 105. In addition, other mooring lines 303 may be attached toward the center of the upper frame structure 101, i.e., near the point where the lattice tower column assembly 310 is attached to the upper frame structure 101. One skilled in the art will recognize that for any of the embodiments disclosed herein, any number of lateral supports may be used and attached at any location, as dictated by the particular conditions of the installation site.

[0032] As shown in FIG. 6, the modular column assembly 810 may be formed by a number of prefabricated joint bundles 812, 814, 816, with mechanical connections attached at each end of the joints, so that they can be easily transported to a convenient location for final assembly of the joints prior to installation to form the assembly, or configured offshore during deployment, as discussed in more detail below. In certain embodiments, the upper and lower ends of the modular column assembly 810 are connected to the upper frame structure 801 and foundation 805 via the upper main barrel pup joint 814 and the lower main barrel pup joint 816, respectively, with flexible connections allowing rotation in any direction. In certain embodiments, the connections between the upper end of the modular column assembly 810 and the upper frame structure 801, and between the lower end of the modular column assembly 810 and the foundation 805 are fixed. One skilled in the art will appreciate that fixed connections allow limited rotational freedom while maintaining axial stiffness. As will be appreciated by those skilled in the art, any combination of fixed or flexible connections may be used depending on design requirements. In some embodiments, pin connections are used during operation, but it may be beneficial to lock the connections during installation.

[0033] In modular embodiments of column assemblies where one or more mechanical connections are positioned between the upper frame structure 101 and the foundation 105, plates 312 as illustrated in FIG. 5A can be used to stiffen the mechanical connections and restrain the individual pipes from one another. In these embodiments, the compression members or pipes extend through the plates. As will be appreciated by those skilled in the art, there may be multiple plates at different axial locations along the pipe 311 or there may be only a single plate. In certain embodiments, braces 313 (FIG. 5A) may be used to transfer shear loads between the individual pipes and act on them in a compound manner.

[0034] The tower 102 and wind turbine 106 are supported by an upper frame structure 101. In some embodiments, the upper frame structure is a tetrahedral structure with members extending from the tower. As shown in the exemplary embodiment of FIG. 7, the upper frame structure 101 has a center point 403 with multiple protruding sections 402 extending from the center point 403. In certain embodiments, each protruding section 402 of the upper frame structure 101 has a truss arrangement. The protruding sections 402 extend from the center point of the upper frame structure 101 to tendon attachment pouches 409 that hold tension for the tension lines.

[0035] In another embodiment, the upper frame structure 101 is a double plate structure with webbing between the double plates to provide the necessary strength and rigidity.

[0036] The foundation 105 supports the offshore structure or other similar structure at the base of the column assembly 110. It will be understood that the foundation 105 can be any number of structures. In some embodiments, the foundation 105 includes multiple protruding sections, similar to the protruding section 402 of the upper frame structure 101. The protruding sections of the foundation 105 connect to tension lines, similar to the upper frame tendon attachment pouches 409 of the upper frame structure 101 that connect to tension lines. In certain embodiments, the foundation 105 includes three protruding sections that connect to three tendon attachment pouches. It will be understood that the foundation 105 can have any number of protruding sections connected to the tension lines 104. In certain embodiments, the foundation 105 can be stabilized on the seabed by using weight baskets on each of the protruding sections. Separately or in addition, in certain embodiments, mud mats are included to limit the penetration of the foundation 105 into the seabed. Those skilled in the art will understand that the foundation 105 is designed such that the seabed does not need to be pre-drilled or secured.

[0037] As illustrated in FIG. 8A, the foundation may also be a central spudcan 605. The central spudcan 605 may provide the axial capacity necessary to support the weight of the equipment. In this embodiment, the tension lines 104 are separately attached to piles 608. As illustrated in FIG. 8B, similar to FIG. 5B, this embodiment, like all other disclosed embodiments, may include lateral supports such as mooring lines attached to the upper frame structure at multiple different points. For example, toward the outer edge of the upper frame structure 101, multiple mooring lines 103 may be attached, each such line being anchored to the seabed at a different location with respect to the lateral distance from the central spudcan 605. In addition, other mooring lines 103 may be attached toward the center of the upper frame structure 101, i.e., near the point where the lattice tower column assembly is attached to the upper frame structure 101. As previously mentioned, one skilled in the art will recognize that for any of the embodiments disclosed herein, any number of lateral supports may be used and attached at any location as dictated by the specific conditions of the installation site.

[0038] As illustrated in FIG. 9, in certain embodiments, the foundation 105 is anchored to the seabed by piles positioned through pile guides as an alternative to weighted baskets. In certain embodiments, a small number of large piles may be used, while in other embodiments, a larger number of micropiles 706 may be used to optimize the anchorage and design of the foundation 105. A micropiles may be positioned on each leg of the foundation so that loads are transferred to the seabed. Those skilled in the art will appreciate that the specific foundation configurations will vary from location to location as dictated by the specific conditions at the installation site. For example, a central spud can as shown in FIG. 8A may be appropriate in one location, while a micro pile as shown in FIG. 9 may be more appropriate in another location due to different conditions of the seabed.

[0039] 10, tension lines 904 may be angled to connect to foundation 105 near the center to reduce the size of foundation 105. In this case, in certain embodiments, the functions of tension lines 904 and taut mooring lines 103 may be combined such that a "tripod" of three tendons on each arm provides rotational, lateral, and torsional stiffness.

[0040] In any of the disclosed embodiments, one skilled in the art will understand that tendons may be used interchangeably with mooring lines 103, depending on location, as dictated by the particular conditions of the installation site.

[0041] As shown in the illustrated embodiment, the taut mooring lines 103 provide lateral support to the upper frame structure 101. The taut mooring lines 103 may be connected to the overhanging sections 402 at tendon attachment pouches 409 of the upper frame structure 101.

[0042] Tension mooring lines are known to those skilled in the art, and the present disclosure is not limited to any particular type or configuration of such mooring lines. In certain embodiments, segments of chain are used at each end of the mooring. In certain embodiments, the tension tethers may be synthetic materials such as HMPE or aramid. In other embodiments, the tension tethers may be steel pipes or tendons to maximize stiffness and minimize footprint.

[0043] FIG. 11 illustrates a method for installing an offshore platform according to an embodiment of the present disclosure. In particular, this method may be useful for installing smaller turbines in shallower water depths. In step 1, the upper frame structure 101 is skidded onto an installation vessel or barge with equipment, which in the illustrated embodiment is a wind turbine 106, and floated to the installation site. The installation site already includes a foundation and column assembly 110 (space frame, column spring, lattice column tower, or other arrangement). Once the installation vessel or barge is positioned on the foundation, tension lines 104 are deployed from the upper frame structure to the foundation 105 positioned on the seabed at the transition site. In step 2, the tension lines 104 are used to jack the upper frame structure 101 away from the installation vessel or barge. In the illustrated embodiment, the tension lines 104 are designed to temporarily support the upper frame structure 101 during installation. The installation vessel or barge then departs the area leaving the upper frame structure 101 above the transition site tethered to the foundations 105 via tension lines 104. In step 3, the column assemblies are lifted so that the column assemblies 110 connect with the upper frame structure. At this point, additional tension lines 104 can be deployed from the upper frame structure 101 to the foundations 105. The tension lines 104 are then tensioned.

[0044] FIG. 12 illustrates an alternative method for installing an offshore platform according to an embodiment of the present disclosure. As shown in step 1, the installation site already includes the foundation 105 and column assembly 110 (space frame or other arrangement). In step 2(a), the upper frame structure 101 and wind turbine 106 are loaded onto an installation vessel or barge. In step 2(b), the combination of the upper frame structure 101 and wind turbine 106 is floated to the installation site. In step 3, the foundation 105 and column assembly 110 are disposed below the sea surface such that the foundation 105 is raised off the seabed, with the column assembly 110 connected to both the upper frame structure 101 and the foundation 105. In step 4, the tension lines 104 are deployed from the upper frame structure 101 to the foundation 105. In step 5, tension is applied to the tension lines 104 such that the column assembly 110 is compressed. In step 6, the offshore fasteners are removed, and in step 7, the platform is raised on an elevator. Tension mooring anchors 107 are pre-installed at the installation site. In step 8, tension mooring lines 103 are installed. In step 9, the platform is lowered until the foundations 105 land on the seabed. In step 10, tension mooring lines 103 are tightened. In step 11, additional tension can be added to tension lines 104 if needed to offset the reduction in tension due to the weight of turbine 106.

[0045] In certain embodiments, a diverless subsea connection is used to connect the column assembly 110 (or other support structure) and tension lines 104 to the foundation 105.

[0046] FIG. 13 illustrates a method for installing an offshore platform according to an embodiment of the present disclosure. In particular, this method can be used for installing a modular lattice tower or other support structure having a modular configuration, as discussed above. In step 1, the foundation 105 is assembled near the wharf (or on land). For example, the foundation may be assembled on a dock. On land, the lower main barrel pup joint bundle 816 is installed on the foundation 105. In step 2, the foundation 105 is lifted and lowered offshore to the seabed. For example, the foundation 105 may be lowered to the seabed below or next to a dock. An installation vessel or barge is then floated into position above the foundation 105. The installation vessel or barge lifts the foundation 105 via the lower main barrel pup joint bundle 816. The lower main barrel pup joint bundle 816 is then secured to the installation vessel or barge. Once the lower main barrel pup joint bundle 816 is secured, the three tendon pup joints 804 are deployed to the foundation 105 and secured to the installation vessel or barge. The installation vessel or barge is then loaded with all installation equipment and moved to the wind turbine site. In step 3, the first main barrel interjoint bundle 812 is installed on top of the lower main barrel pup joint bundle 816. Further, tendon joints 806 are installed on top of each of the three tendon pup joints 804 already secured to the installation vessel or barge. The entire offshore platform assembly is then lowered. The steps in step 3 are repeated until the foundation 105 is close to the seabed. Once the foundation contacts the seabed, the tension moorings 103 are deployed. In step 4, another tendon joint 806 is installed on top of each of the three tension lines 104 such that the tension lines 104 extend above the installation deck. Temporary buoyancy / tension clamps are installed on the top of the upper main barrel joint bundle 814 and tension lines 104. Once the clamps are installed, the assembled offshore platform is then lowered and anchored to the ocean floor. The installation vessel or barge is then removed.

[0047] In certain embodiments, materials for an installation can be made from components manufactured near the installation, such as an installation in the North Sea with manufacturing in the UK. In certain embodiments, where local manufacturing capacity is limited, the installation can be made from modular components prefabricated at a low-cost location and shipped to a port near the installation for assembly. In the case of prefabricated components, the structure can be partially assembled onshore to save installation time and labor due to availability of components near the installation site minimizing the need for exotic components. Additionally, since many installation sites are near ports with standard port water depths, the assembly can be prefabricated near shore.

[0048] Additionally, these installations can be installed with standard vessels at the transition site and the towers can be installed near dock (on land), eliminating the need for expensive heavy lift crane barges and vessels. Additionally, portions of the installation on the seabed can be pre-installed prior to installation of the turbine tower sections themselves, thereby minimizing the time required for a vessel on the sea during turbine tower installation and enhancing the ability to perform multiple turbine tower installations at once.

[0049] Thus, as the offshore wind industry seeks to provide more installations at these transitional site depths, the current design is cost-competitive with fixed towers and floating solutions. The design also reduces the environmental impact compared to other known solutions. In particular, in certain embodiments, the offshore platform described in connection with Figures 1-13 above minimizes the piling requirements required to anchor the offshore platform. This reduces the amount of noise pollution and makes it suitable for shallow water applications. In addition, the illustrated embodiment minimizes the exposure of the structure to wave and current loads compared to conventional floating platforms. Advantageously, this reduces mooring and mooring anchor requirements and minimizes environmental disturbances in wave and current loading conditions. Furthermore, the design provides a smaller footprint than conventional floating platforms due to the reduced mooring requirements, thus providing more space between offshore installations for vessel movement.

[0050] It is understood that modifications may be made in the above without departing from the scope of the present disclosure. In some exemplary embodiments, the elements and teachings of the various illustrative exemplary embodiments may be combined in whole or in part in some or all of the illustrative exemplary embodiments. In addition, one or more of the elements and teachings of the various illustrative exemplary embodiments may be at least partially omitted and / or at least partially combined with one or more of the other elements and teachings of the various illustrative exemplary embodiments.

[0051] For example, any spatial references such as "upper", "lower", "top", "below", "between", "bottom", "vertical", "horizontal", "angle", "upward", "downward", "side to side", "left to right", "right to left", "top to bottom", "bottom to top", "top", "bottom", "bottom up", "top down", etc. are for illustrative purposes only and are not intended to limit the particular orientation or location of the structures described above.

[0052] In some exemplary embodiments, different steps, processes, and procedures are described as appearing as separate acts, but one or more of the steps, one or more of the processes, and / or one or more of the procedures may also be performed in a different order, simultaneously and / or sequentially. In some exemplary embodiments, steps, processes, and / or procedures may be combined into one or more steps, processes, and / or procedures.

[0053] In some exemplary embodiments, one or more of the operational steps in each embodiment may be omitted. Furthermore, in some examples, some features of the present disclosure may be employed without the corresponding use of other features. Furthermore, one or more of the above-described embodiments and / or variations may be combined in whole or in part with any one or more of the other above-described embodiments and / or variations.

[0054] Although several exemplary embodiments have been described in detail above, the described embodiments are merely illustrative and not limiting, and one skilled in the art will readily recognize that many other modifications, changes, and / or substitutions are possible in the exemplary embodiments without substantially departing from the novel teachings and advantages of the present disclosure. Therefore, all such modifications, changes, and / or substitutions are intended to be included within the scope of the present disclosure as defined in the following claims. In the claims, any means-plus-function clause is intended to encompass the structures described herein as performing the recited function, as well as structural equivalents and equivalent structures. Furthermore, it is the express intent of the applicants not to invoke 35 U.S.C. 112, paragraph 6, as to any limitation of any of the claims herein, except where the claim expressly uses the word "means" with the relevant function. At least one specification heading is required. If not applicable to the application, delete this heading section. For more information regarding specification headings, see MPEP 608.01(a).

Claims

1. An offshore installation, an upper platform having a weight and including an upper surface and a lower surface; a foundation configured to be disposed on the seabed; 1. A modular vertical column assembly comprising: Central longitudinal axis, a first end fixedly connected to the upper platform; a second end connected to the foundation; a modular vertical column assembly comprising: a first modular vertical support member extending from the first end to the second end such that the modular vertical column assembly supports the weight of the upper platform; a first plurality of tendons configured to extend from the upper platform to the foundation; and a plurality of lateral supports configured to extend from the upper platform to the seabed.

2. The offshore installation of claim 1 , wherein the modular vertical column assembly comprises a lattice tower.

3. The upper platform is center point, a first leg extending outwardly from said central point; a second leg extending outwardly from said central point; a third leg extending outwardly from the central point; The offshore installation according to claim 1 , wherein the first leg, the second leg, and the third leg are all on a first plane.

4. The offshore installation of claim 1 , further comprising a flexible connection between the first end of the modular vertical column assembly and the upper platform.

5. The offshore installation of claim 1 , further comprising a wind turbine configured to be mounted to the upper surface of the upper platform.

6. The offshore installation of claim 1 , wherein the plurality of lateral supports includes a second plurality of tendons.

7. The upper platform is The center point, at least one leg extending outwardly from the center point and having a first length; 2. The offshore installation of claim 1, wherein the foundation comprises a base having a radius less than the first length of the legs of the upper platform such that the first plurality of tendons provide lateral support to the upper platform.

8. A method for installing an offshore installation on a seabed, comprising the steps of: mounting the offshore installation on a superframe structure having a weight and including an upper surface and a lower surface; transporting the upper frame structure and the offshore equipment to an installation site; installing a foundation and a lower portion of a modular vertical column assembly on the seabed at the installation site; positioning the upper frame structure on the foundation; deploying a first plurality of tendons from the upper frame structure to the foundation; installing an upper portion of the modular vertical column assembly; lifting an end of the modular vertical column assembly into contact with the upper frame structure such that the modular vertical column assembly supports the weight of the upper frame structure and the offshore equipment; applying tension to the first plurality of tendons; attaching a plurality of lateral supports to the upper frame structure; and extending the plurality of lateral supports from the upper frame structure to the seabed.

9. 10. The method of claim 8, further comprising lifting the upper frame structure away from the installation vessel prior to lifting the modular vertical column assemblies into contact with the upper frame structure.

10. The method of claim 8 , wherein the modular vertical column assembly comprises a lattice tower.

11. The method of claim 8 , wherein the plurality of lateral supports includes a second plurality of tendons, the method further comprising applying tension to the second plurality of tendons.

12. The method of claim 8 , wherein the offshore facility comprises a wind turbine.

13. The upper platform is The center point, at least one leg extending outwardly from the center point and having a first length; 9. The method of claim 8, wherein the foundation comprises a base having a radius less than the first length of the legs of the upper platform such that the first plurality of tendons provide lateral support to the upper platform.

14. A method for installing an offshore installation on a seabed, comprising the steps of: mounting the offshore installation on a superframe structure having a weight and including an upper surface and a lower surface; transporting the upper frame structure and the offshore equipment to an installation site; installing a foundation and a lower portion of a modular vertical column assembly on the seabed at the installation site; installing an upper portion of the modular vertical column assembly; positioning the upper frame structure on the foundation; lifting an end of the modular vertical column assembly into contact with the upper frame structure such that the modular vertical column assembly supports the weight of the upper frame structure and the offshore equipment; elevating the foundation off the seabed with the modular vertical column assemblies; and deploying a first plurality of tendons from the upper frame structure to the foundation; lowering the foundation to the seabed via the first plurality of tendons; applying tension to the first plurality of tendons; attaching a plurality of lateral supports to the upper frame structure; and extending the plurality of lateral supports from the upper frame structure to the seabed.

15. The method of claim 14 , wherein the step of attaching the plurality of lateral supports to the upper frame structure is performed before the foundation is installed on the seabed.

16. The method of claim 14 , wherein the modular vertical column assembly comprises a lattice tower.

17. The method of claim 14 , wherein the offshore facility comprises a wind turbine.

18. The method of claim 14 , wherein the plurality of lateral supports includes a second plurality of tendons.

19. The upper platform is The center point, at least one leg extending outwardly from the center point and having a first length; 15. The method of claim 14, wherein the foundation comprises a base having a radius less than the first length of the legs of the upper platform such that the first plurality of tendons provide lateral support to the upper platform.

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