Floating offshore platform

Abstract

The present invention relates to a floating offshore platform, which comprises a central column, at least three peripheral columns circumferentially surrounding the central column, beams radially extending from the central column to connect the peripheral columns with the central column, and structural members spanning between each pair of adjacent peripheral columns, wherein the structural members are pre-tensioned.

Description

Technical Field

[0001] The invention relates to a floating offshore platform. Background Art

[0002] Growing concerns related to climate change have provided impetus for renewable power generation, including a potentially large market for offshore wind power. Existing large-scale construction occurs in relatively shallow waters, where the structures are fixed to the seabed. However, these technologies limit such construction to areas that are generally relatively close to the coast, have potential visual impact, and have favorable seabed conditions. In addition, fixed wind turbines often require heavy work at sea, with associated risks to workers and financial risks due to severe weather and the need for very large offshore construction vessels.

[0003] The ability to provide floating foundations for wind turbines can substantially increase the area available for offshore wind farm construction by locating these units in deeper waters, further from shore, where visual impact tends to be reduced and wind speeds are generally higher and less turbulent. In addition, these require less work at sea, as the turbines can be fully assembled at port and towed to site.

[0004] Several innovative demonstration projects have been successfully completed in recent years to demonstrate the feasibility of installing commercial-sized wind turbines on floating foundations. However, large-scale construction has not yet occurred due to the high cost of the structures that have been deployed, and the difficulty of mass-producing floaters with existing shipyards or civil engineering facilities. There is a need to reduce the size and cost of the hulls used for floating wind turbine foundations while accommodating the very large wind turbines planned for commercial-scale construction, with rotor diameters approaching 200 meters. Summary of the invention

[0005] An object of the present invention is to provide a floating offshore platform which is more economical to produce while providing substantially equal or greater stability than existing floating offshore platforms, in particular floating foundations for offshore wind turbines.

[0006] According to a first aspect, the present invention provides a floating offshore platform comprising a central column, at least three peripheral columns circumferentially surrounding the central column, beams extending radially from the central column connecting the peripheral columns to the central column, and structural members spanning between each pair of adjacent peripheral columns, wherein the structural members are pre-tensioned.

[0007] The pre-tensioning of the structural members causes a counter-pressure on the beams which deflects the beams in their slender direction towards the central column. Due to the pre-tensioning, the structural members remain in tension and the beams remain in compression during load cycles, for example, exerted by waves on the platform. This configuration of the structural members provides the beams with stiffness in the horizontal plane and thus reduces moment forces in the beams. Since the structural members and beams can be designed to primarily resist tension and compression forces, respectively, the structural members and beams can be implemented to be slimmer and lighter than conventional floating offshore platforms. Since the floating offshore platform comprises similar or identical central and peripheral columns, the stability will be largely the same as that of existing floating offshore platforms.

[0008] In an embodiment, the radially extending beams include a top beam and a bottom beam extending parallel to each other. In a further embodiment, the beams have a circular cross-section and / or an I-shaped cross-section. The beams are configured as legs in a truss configuration constructed from conventional steel segments. This is a simple steel structure that can be produced in an economical manner.

[0009] In some embodiments, the central column and / or the peripheral columns extend vertically.

[0010] In an embodiment, the perimeter columns and the structural members form a generally triangular shape, preferably an equilateral triangle shape. The triangular configuration provides a shape-stable arrangement of the perimeter columns and the structural members that is easy to manufacture.

[0011] In an embodiment, the structural member comprises a steel tube or is formed with a steel tube to transmit a high pre-tension in the structural member and the beam.

[0012] In a lightweight alternative embodiment, the structural member comprises or is formed from steel or aramid fiber anchor cables.

[0013] In an embodiment, the perimeter column comprises a connector having a channel for one end of the structural member, wherein the structural member comprises a tensioning head at the end received in the connector, and the structural member extends from the tensioning head through the channel. The tensioning head can be hooked into the connector, and then the tensioning head can be pre-tensioned.

[0014] In one embodiment thereof, the perimeter column includes one or more shims or shim plates between the connector and the tensioning head to maintain pre-tension in the structural member after the structural member has been constructed.

[0015] In an embodiment, at least one of the beams functions as a gangway to provide a passage between the central column and at least one of the peripheral columns.

[0016] In some embodiments, structural members are positioned at a height below the height of the radially extending beams and / or structural members are positioned at a height above the height of the radially extending beams to further ensure that compression of specific portions of the beams or steel segments thereof is maintained.

[0017] In an embodiment, the beams are connected to the columns using bolt connections. This is a simple connection method that can be produced in an economically advantageous manner.

[0018] Structural members extending in a common horizontal plane preferably have the same pretensioning to provide symmetry around or along their span.The pretensioning in the first set of bottom structural members and the second set of top structural members may differ from one another to differentiate between deflections in the bottom and top beams if desired.

[0019] In an embodiment, the structural members are pre-tensioned by inducing a pre-tensioning stroke thereto of 0.04% to 0.07%, preferably 0.05% of the length of the structural member. In this way, permanent deformations of the structural members will remain very small, since they operate within the elastic range. Thus, the structural members remain taut during the service life of the floating offshore platform. Due to the pre-tensioning, the structural members remain taut at all times, except during the largest waves of the strongest storms, whereby they may occasionally relax for short periods of time, such as a wave period of a few seconds at most.

[0020] In an embodiment, the beams are offset in their elongated direction towards the central column, preferably beams extending in a common horizontal plane have the same offset, thereby providing stiffness to the beams in the horizontal plane and thus reducing moment forces in the beams. The offsets in the top and bottom beams of the radially extending beams may be different from each other to further improve the stiffness of the radially extending beams.

[0021] In an embodiment, the perimeter columns include buoyancy air chambers. The air chambers provide buoyancy to the floating offshore platform at the perimeter columns. Since the perimeter columns are located at a certain distance from the central column, the additional buoyancy provides stability to the floating offshore platform.

[0022] In an embodiment, the perimeter column comprises a base, and the buoyancy air chamber opens to the sea at the base. In this way, the buoyancy of the perimeter column can be adjusted by adjusting the air level in the air chamber and thereby forcing water to enter or leave the air chamber via the base.

[0023] In an embodiment, the floating offshore platform further comprises a motion control system, the motion control system comprising a high pressure air tank for exhausting air in the open buoyancy air chamber, the high pressure air tank using an actuated valve to control the flow of air into and out of the open buoyancy air chamber and the high pressure air tank being controlled by a computer system coupled to the motion sensor. The motion control system can adjust the air level in the open buoyancy air chamber to provide a moment opposite to the moment caused by aerodynamic forces on the floating offshore platform, thereby stabilizing the floating offshore platform.

[0024] In one embodiment thereof, the high pressure air tank is formed by the airtight inner volume of one of the beams. By using the beam as an air tank, there is no need to provide an additional air tank, which saves space on the floating offshore platform.

[0025] In a further embodiment, the motion control system comprises an air compressor configured to fill the high pressure air tank. In an embodiment thereof, the motion control system comprises an inlet valve configured to control the filling of the high pressure air tank by the air compressor.

[0026] In an embodiment, the motion control system comprises an outlet valve for each open buoyancy air chamber, the outlet valve being configured for controlling the discharge of air from the high pressure air tank into the corresponding open buoyancy air chamber.

[0027] In an embodiment, the motion control system includes a release valve for each open buoyancy air chamber, the release valve connecting the open buoyancy air chamber to the atmosphere and configured to control the release of air from the open buoyancy air chamber to the atmosphere. The air compressor, inlet valve, outlet valve and release valve are conventional components that can be implemented and installed in an economically advantageous manner.

[0028] According to a second aspect, the present invention provides a floating offshore platform comprising a central column, at least three peripheral columns circumferentially surrounding the central column, and beams radially extending from the central column connecting the peripheral columns to the central column, wherein the peripheral columns include buoyancy air chambers, and wherein the offshore platform includes a motion control system, the motion control system including a high-pressure air tank that discharges air from the buoyancy air chamber, the high-pressure air tank uses an actuating valve to control the airflow entering and leaving the buoyancy air chamber, and the high-pressure air tank is controlled by a computer system coupled to a motion sensor.

[0029] The floating offshore platform according to the second aspect and its embodiments relates to the floating offshore platform according to any of the above embodiments, and therefore has the same technical advantages, which will not be described in detail herein.

[0030] The various aspects and features described and shown in this specification can be applied separately where possible. These individual aspects, in particular the aspects and features described in the presented dependent claims, can be the subject of divisional patent applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will be explained based on exemplary embodiments shown in the drawings, in which:

[0032] Figure 1A , Figure 1B and Figure 1C are isometric, side and top views of a floating offshore platform according to a first embodiment of the present invention supporting a wind turbine;

[0033] Figure 2A and Figure 2B According to Figure 1A and Figure 1B An enlarged view of a floating offshore platform of FIG. 1 with portions cut away to show some of its internal components;

[0034] Figure 3 is a detailed view of the connection between the tendons and the skirt of a floating offshore platform;

[0035] Figure 4A and Figure 4B are isometric and side views of a floating offshore platform according to a second embodiment of the present invention supporting a wind turbine;

[0036] Figure 5 A top cross-sectional view showing a perimeter column of a floating offshore platform according to a third embodiment of the present invention; and

[0037] Figure 6 is an isometric view of a floating offshore platform supporting data measurement and acquisition equipment according to a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0038] Figures 1A to 1C and FIG. 2A to FIG. 2BA floating offshore platform 1 according to a first embodiment of the present invention is shown. In this example, the offshore platform 1 supports a wind turbine 300 to form a floating wind turbine 10. The wind turbine 300 has a vertical tower 301 and a nacelle 302 on top of the tower 301, the nacelle 302 having an internal generator driven by a wind turbine rotor 303. The wind turbine rotor 303 has a hub 304 connected to the generator and, in this example, has three blades 305 radiating from the hub 304. The wind turbine 300 is capable of generating more than 1MW of electricity, currently reaching about 10MW to 12MW. For a +10MW wind turbine, the bottom diameter of the tower 301 can be between 5 meters and 10 meters. The three blades 305 can each be greater than 100 meters long. An example is a 12MW Haliade X turbine from General Electric. Other turbine designs, such as vertical axis wind turbines can also be supported by the floating offshore platform 1.

[0039] like Figure 2B As best shown in FIG. 1 , the offshore platform 1 comprises a vertical cylindrical central column 2 having a varying diameter that is approximately equal to the bottom diameter of the tower 301 at the top of the central column 2 and increases in diameter towards the bottom or keel of the central column 2. The central column 2 has a circumferential wall 3 and a bottom wall 4 defining an internal chamber 5. The central column 2 is made of steel or concrete.

[0040] In this example, the offshore platform 1 comprises three vertical stabilizers or perimeter columns 20a, 20b, 20c, which are radially arranged every 120 degrees around the central column 2. Figure 2B As best shown in , the perimeter posts 20a, 20b, 20c each comprise a first cylindrical body 21 of steel having a circumferential wall 24, a top wall 25, and an inner steel watertight planar portion 26 which in this embodiment is parallel to the top wall 25 and extends substantially halfway up the height of the perimeter posts 20a, 20b, 20c. The watertight planar portion 26 defines an inner closed air chamber 71 at the upper side and an inner open air chamber 72 at the lower side. The open air chamber 72 is open at the base or bottom edge of the circumferential wall 24 so as to be at least partially filled with water. The perimeter posts 20a, 20b, 20c comprise a horizontally extending steel skirt 27 around the bottom edge of the circumferential wall 24.

[0041] The offshore platform 1 comprises three legs 40a, 40b, 40c having the same radial length. The legs 40a, 40b, 40c are formed of tubular structural members and are arranged in a truss configuration. The legs 40a, 40b, 40c connect the central column 2 to the peripheral columns 20a, 20b, 20c. Figure 2BAs best shown in FIG. 1 , the legs 40a, 40b, 40c include a substantially horizontal top beam 45 and a substantially horizontal bottom beam 46 extending parallel to each other and interconnected with a cross member or diagonal brace 47 (if required). The top beam 45 and the bottom beam 46 are steel hollow cylindrical tubes, and the diagonal brace 47 is a steel hollow cylindrical tube with a smaller diameter. The legs 40a, 40b, 40c are connected to the central column 2 and the peripheral columns 20a, 20b, 20c by welding or by means of flanges bolted to each other to form a bolted connection.

[0042] The central column 2 comprises a vertical cylindrical top section 6 of constant diameter to which a top beam 45 is connected. The vertical cylindrical section 6 merges downwardly via a flared section or conically widened section 7 into a vertical cylindrical bottom section 8 of constant diameter to which a bottom beam 46 is connected. The central column 2 may be provided with feet, not shown, below the bottom section 8, which have a larger diameter providing additional volume. When the feet are filled with air, they help support the weight of the wind turbine 300. When the feet are filled with water, they help provide stability to the floating wind turbine 10.

[0043] The offshore platform 1 comprises six pre-tensioned elongated structural members or tendons 60a, 60b, 60c, 61a, 61b, 61c having the same length interconnected with the perimeter columns 20a, 20b, 20c. In this example, three tendons 60a, 60b, 60c interconnect the perimeter columns 20a, 20b, 20c at the skirt 27 and three tendons 61a, 61b, 61c interconnect the perimeter columns 20a, 20b, 20c near their top walls 25.

[0044] exist Figure 3Detail of the connection between tendon 61b and column 20b, particularly at skirt 27 thereof, is shown in FIG. Skirt 27 comprises an annular steel base plate 28 and a steel edge plate 29 connected thereto, the steel edge plate 29 defining a channel 37 of tendon connector 30 towards the end of tendon 61b for connection. Tendon connector 30 comprises: two pairs of parallel steel first support plates 31, two steel second support plates 32 parallel to the first support plates 31, and two reinforcements 33 made of steel plates; two pairs of parallel steel first support plates 31 extend radially on both sides of channel 37 and are connected to edge plates 29 and base plate 28; two steel second support plates 32 are connected to edge plates 29, base plate 28 and circumferential wall 24; two reinforcements 33 extend transversely to and interconnect first support plates 31 and second support plates 32. An identical or similar connector 30 is provided at the top of peripheral column 20b. It should be understood that the tendon connector 30 described above is only one example of several possible embodiments. For example, the tendon connector 30 may not be part of the skirt 27, but may be integrated into or attached to the post 20b.

[0045] The tendon 61b comprises a hollow cylindrical steel tube 62 and a tensioning head 63 at the end of the tube 62. The tensioning head 63 comprises two supports 64 which protrude from the tube 62 on opposite sides of the tube 62. The steel tube 62 of the tendon 61b extends through the channel 37 at the end and the tensioning head 63 is received in the connector 30 where it hooks behind the first support plate 31. The tendon 61b is pre-tensioned by means of a temporarily installed hydraulic cylinder 35 located at the end of the tendon 61b between the third support plate 33 of the connector 30 and the supports 64 of the tendon 61. The hydraulic cylinder 35 pushes the tensioning head 63 away from the first support plate 31 and the gap is then permanently filled with a steel shim plate 36. After the pre-tensioning of the tendon 61b, the hydraulic cylinder 35 is removed.

[0046] Each tendon 60a, 60b, 60c, 61a, 61b, 61c includes at least one tensioning head 63 at one end thereof, and each peripheral column 20a, 20b, 20c includes at least one corresponding tendon connector 30, so that each tendon 60a, 60b, 60c, 61a, 61b, 61c can be pre-tensioned. The tendons 60a, 60b, 60c, 61a, 61b, 61c may include two tensioning heads 63, one at each end of the tendon, and the peripheral column 20a, 20b, 20c may include two tendon connectors 30 corresponding to the respective tensioning heads 63. The tendons 60a, 60b, 60c, 61a, 61b, 61c may also include a forged axisymmetric head at the end opposite to the tensioning head 63, which corresponds to the connector at the other peripheral column 20a, 20b, 20c. The pre-tensioning of the tendons 60a, 60b, 60c, 61a, 61b, 61c results in inducing a back pressure in at least all the bottom beams 46 (but in this example in all beams 45, 46) which deflects the bottom beams 46 and in this example also the top beams 45 in their direction of elongation towards the central column 2. Due to the pre-tensioning in the tendons 60a, 60b, 60c, 61a, 61b, 61c, these structural members remain tensioned at all times, except during the largest waves of the most powerful storms, whereby they may occasionally become relaxed for short periods of time, such as a wave period of a few seconds at most. The tendons 60a, 60b, 60c, 61a, 61b, 61c provide stiffness to the legs 40a, 40b, 40c in the horizontal plane.

[0047] The offshore platform 1 is provided with a gangway 11 which extends around the bottom of the tower 301 and toward the top side of the peripheral columns 20a, 20b, 20c above one or more top beams 45. Alternatively, the top beam 45 is, for example, an I-beam or an H-beam, which a technician can use as a gangway for access between the central column 2 and the peripheral columns 20a, 20b, 20c.

[0048] The offshore platform 1 includes a motion control system. Figure 2BSome components of the motion control system are schematically shown in FIG. The motion control system is configured to adjust the air level in the open air chamber 72 so as to stabilize the marine platform 1 and provide a torque opposite to the torque caused by the aerodynamic force on the wind turbine rotor 303. The motion control system includes an air compressor 75, which is located in the center column 2 and is powered by the turbine electrical system. The air compressor 75 is connected to an air distribution pipe 76, which is connected to an inlet valve 77. The inlet valve 77 is connected to an airtight cabin, a high-pressure air chamber or a high-pressure air tank 82, which is the interior of the bottom beam 46 or is formed by its entire airtight internal volume. The air tank 82 is filled with 7 bar to 12 bar high-pressure air by the air compressor 75. The air compressor 75 can be configured to automatically start filling the air tank 82 when the pressure drops below a preset value. The power for running the air compressor 75 (about 100kW or less) can be provided by the turbine system. If there is insufficient wind at the site and wind turbine 300 is not producing electricity, the grid may be used to provide electricity.

[0049] The motion control system includes an automatic outlet valve 78 for each open air chamber 72, which can be controlled to release high-pressure air from an air tank 82 to an air outlet 81 at the bottom of the open air chamber 72. Therefore, with the opening of the automatic outlet valve 78, the amount of air released can be precisely controlled. An air nozzle or air outlet 81 can be added downstream of the automatic outlet valve 78 to guide the air flow toward the base of the open air chamber 72, which will generate dynamic lift. Alternatively, the air flow is directed toward the top of the open air chamber 72, and the water escaping from the open air chamber 72 causes dynamic lift through the base. The motion control system includes a ventilation line 79 in each peripheral column 20a, 20b, 20c, and the ventilation line 79 has an automatic release valve 80, which connects the top of the open air chamber 72 to the atmosphere above the top of the peripheral column 20a, 20b, 20c. The automatic release valve 80 can be controlled to open and close the ventilation line 79. The motion control system includes instruments with 6 degrees of freedom to monitor the translation and rotation of the offshore platform 1 in three vertical directions.

[0050] The motion of the offshore platform 1 is monitored by a motion control system. When the wind speed or direction changes, the floating wind turbine 10 tilts. When there is an average change in tilt, if the amount of air needs to be increased, the automatic outlet valve 78 between one or more high pressure tanks 82 and the bottom chamber 72 of the peripheral column 20a, 20b, 20c will open to connect the air in the open air chamber 72 to the sea, and / or if the amount of air needs to be reduced, one or more automatic release valves 80 controlling the atmospheric vent 79 will open. Improved rotor tilting can be achieved by the motion control system to increase power production.

[0051] Similarly, if a shutdown of the wind turbine 300 is triggered, including an emergency shutdown due to loss of grid power or any other problem causing such a turbine to respond, the air in the open air chambers 72 of the perimeter columns 20a, 20b, 20c will be regulated by opening the corresponding automatic outlet valves 78 and release valves 80. This will reduce the maximum pitch of the offshore platform 1 that is expected to occur due to such an event. The offshore platform 1 will then return to the flat keel condition until the wind turbine 300 is ready for startup.

[0052] If the sea state is high, the automatic outlet valve 78 and the release valve 80 may be opened based on the timing of the motion response to reduce the wave induced response. This will increase the ability of the floating wind turbine 10 to operate effectively in rough seas.

[0053] The motion control system can ensure that the tower 301 of the wind turbine 300 is maintained at an optimal angle for generating electricity in the wind farm. This is advantageous because most large-sized commercial wind turbines are three-bladed upwind turbines that have rotors 303 tilted upward as seen in the direction from which the wind is coming, in order to prevent the blades 305 from colliding with the bottom of the tower due to their deflection caused by aerodynamic loads. By operating the motion control system, a significant increase in the tilt angle is prevented, which would result in a reduction in wind loads and generated electricity.

[0054] In the illustrated embodiment, a first set of pre-tensioned tendons 61a, 61b, 61c interconnecting the perimeter posts 20a, 20b, 20c are disposed near the top of the perimeter posts 20a, 20b, 20c and / or at a height above the legs 40a, 40b, 40c, and a second set of pre-tensioned tendons 60a, 60b, 60c are disposed near the bottom at the skirt 27 and / or at a height below the legs 40a, 40b, 40c. Alternatively, the pre-tensioned tendons 61a, 61b, 61c interconnecting the perimeter posts 20a, 20b, 20c may be disposed only near the top of the perimeter posts 20a, 20b, 20c and / or at a height above the legs 40a, 40b, 40c. In yet another alternative embodiment, the pre-tensioned tendons 60a, 60b, 60c interconnecting the perimeter posts 20a, 20b, 20c may be provided only near the bottom at the skirt 27 and / or at a height below the legs 40a, 40b, 40c. In still other embodiments, the pre-tensioned tendons 60a, 60b, 60c interconnecting the perimeter posts 20a, 20b, 20c may be provided only near the center of the perimeter posts 20a, 20b, 20c and at a height approximately the same as the height of the legs 40a, 40b, 40c.

[0055] like Figure 2B As shown, the cylindrical top section 6 of the central column 2 matches the bottom diameter of the tower 301, whereby the cylindrical top section 6 has a top diameter D1 of 5 to 10 meters. The central column 2 can then be flared outward to reach a bottom diameter D2 of up to 20 meters at the cylindrical bottom section 8. The central column 2 and the peripheral columns 20a, 20b, 20c typically have a total height H1 of 20 to 30 meters, in this example, about 24 meters. The peripheral columns 20a, 20b, 20c have a diameter D3 of 6 to 12 meters. The watertight plane portion 26 extends at about half of the total height H1, whereby the open air chamber 72 has a chamber height H2 of 5 to 15 meters, in this example, about 9 meters. At sea, water enters the open air chamber 72 until a water depth H3 of 3 to 9 meters, in this example, about 6 meters, i.e., the water depth is lower than the chamber height H2, whereby compressed air is always present in the open air chamber 72. The tops of the central column 2 and the peripheral columns 20a, 20b, 20c may be up to 10 to 15 meters above the mean water level and the draft may vary between 10 to 15 meters.

[0056] The steel components of the offshore platform 1 are formed from S355, a marine grade low carbon steel. Higher strength steels may also be used for some components.

[0057] like Figure 1CAs shown, tendons 60a, 60b, 60c, 61a, 61b, 61c each have a length L1 of 60 to 90 meters, in this example about 73 meters. Tendons 60a, 60b, 60c, 61a, 61b, 61c have a nominal diameter D4 of 300 to 600 mm and a wall thickness of 15 to 30 mm. In some embodiments, higher strength steel can be used to apply a wall thickness of 5 to 18 mm. The length of the pre-tensioning stroke caused by the hydraulic cylinder 35 is 0.04%-0.07% of the length L of tendons 60a, 60b, 60c, 61a, 61b, 61c, in this example, 0.05% of the length L of each tendon 60a, 60b, 60c, 61a, 61b, 61c. This induces a pre-tensioning force of 200 to 300 tons in the tendons 20a, 20b, 20c, in this example about 250 tons. The pre-tensioning force in the upper tendons 60a, 60b, 60c is about the same, the pre-tensioning force in the lower tendons 61a, 61b, 61c is about the same, and the counter-pressure induced in the beams 45, 46 is about the same, giving a force symmetry around the span of the tendons 60a, 60b, 60c, 61a, 61b, 61c.

[0058] The floating wind turbine 310 is held on the station by mooring lines connected to the bottom of each perimeter column 20a, 20b, 20c by mooring line connectors that can be closed to hold the offshore platform 1 in place while the wind turbine 300 is generating electricity, or can be open if the floating wind turbine 310 needs to be towed back to shore for maintenance or decommissioning.

[0059] In the first embodiment described, the flat portion 26 divides the first cylindrical body 21 into a closed air chamber 71 and an open air chamber 72 in the vertical direction. Figure 2B As schematically shown by the middle dashed line, the first cylindrical body 21 is horizontally divided into a closed air chamber 71 and an open air chamber 72 by a vertical plate 93, wherein the closed air chamber 71 is closed by a horizontal keel plate 94 extending between the bottom edge of the circumferential wall 24 and the bottom edge of the vertical plate 93. The closed air chamber 71 is positioned closest to the corresponding legs 40a, 40b, 40c, and the air outlet 81 is positioned at the bottom of the open air chamber 72.

[0060] Figure 4A and Figure 4BA floating offshore platform 101 according to a second embodiment of the invention is shown. The offshore platform 101 supports a wind turbine 300 to form a floating wind turbine 110. Features of the floating offshore platform 101 corresponding to the floating offshore platform 1 according to the first embodiment are provided with the same reference numerals and only deviating features are described in the following.

[0061] The three perimeter columns 20a, 20b, 20c of the offshore platform 101 comprise a second cylindrical body 22 made of steel, which adjoins the first cylindrical body 21 at the side diametrically opposite to the respective legs 40a, 40b, 40c. A skirt 27 extends around the united cylindrical bodies 21, 22. The cylindrical bodies 21, 22 may also have a closed air chamber 71 and an open air chamber 72 as in the first embodiment, or one of the cylindrical bodies 21, 22, which again has a mooring line connector 99 at the far side, may have an open air chamber 71 with an air outlet 81, and the other may form a closed air chamber 71.

[0062] Figure 5 Details of a floating offshore platform 201 according to a third embodiment of the invention are shown. The offshore platform 201 supports a wind turbine 300 to form a floating wind turbine 210. Again, features of the floating offshore platform 201 corresponding to the floating offshore platforms 1, 101 according to the first and second embodiments are provided with the same reference numerals and only deviating features are described.

[0063] The three perimeter columns 20a, 20b, 20c of the offshore platform 201 include a second cylindrical body 22 and a third cylindrical body 23 made of steel adjacent to each other and both adjacent to the first cylindrical body 21 at a side diametrically opposite to the respective legs 40a, 40b, 40c. A skirt 27 extends around the united cylindrical bodies 21, 22, 23. The cylindrical bodies 21, 22 may each include a closed air chamber 71 and an open air chamber 72 as in the first embodiment, or one of the cylindrical bodies 21, 22 has an open air chamber 71 with an air outlet 81, while the other of the cylindrical bodies 21, 22 forms a closed air chamber 71. In this embodiment, the first cylindrical body 21 and the third cylindrical body 23 are closed at the bottom by the keel plate 94 to form a closed air chamber 71, while the second cylindrical body 22 is open to form an open air chamber 72 having an air outlet 81 at the bottom.

[0064] Figure 6A floating ocean platform 401 according to a fourth embodiment of the present invention is shown. In this example, the ocean platform 401 supports data measurement and collection equipment 412 to form an ocean monitoring platform. The ocean monitoring platform 410 can, for example, be configured to perform measurements and data collection of ocean meteorology (wind, waves, currents), chemical action (corrosion, ocean growth), environment (marine mammals, bird migration), biodiversity (juvenile fish density and mid-pelagic fish density), and marine aquaculture (growth rate of shellfish and algae, nutrient density) to prepare an offshore site for comprehensive construction.

[0065] The marine platform 401 includes a vertical cylindrical center column 402 having a constant diameter. The center column 402 has a circumferential wall 403, a bottom wall 404, and a top wall 409, which define an interior chamber 405, which is the main buoyancy chamber of the marine platform 401 and contains most of the equipment 412. The center column 402 is made of steel. The center column 402 may be provided with footings 428 below the bottom wall 404, which have a larger diameter to dampen the wave-induced motion of the marine platform 401. The footings 428 may provide additional volume to the center column 402, so that when the footings are filled with air, they help support the weight of the equipment 412, and when the footings are filled with water, they help provide stability to the marine monitoring platform 410.

[0066] In this example, the offshore platform 401 includes three vertical cylindrical stabilizing columns or perimeter columns 420a, 420b, 420c, which are radially arranged every 120 degrees around the central column 402. The perimeter columns 420a, 420b, 420c each include a steel first cylindrical body 421 having a steel circumferential wall 424, a top wall 425 and a bottom wall 427, which in this example extends horizontally from the bottom edge of the circumferential wall 424 to form a skirt 427. The steel circumferential wall 424, the top wall 425 and the bottom wall 427 define an internally enclosed air chamber 471.

[0067] The offshore platform 401 comprises three legs 440a, 440b, 440c having the same radial length and consisting of structural components. The legs 440a, 440b, 440c connect the central column 402 to the peripheral columns 420a, 420b, 420c. The legs 440a, 440b, 440c comprise a substantially horizontal top beam 445 and a substantially horizontal bottom beam 446 extending parallel to each other. The top beam 445 is a steel I-beam or H-beam, and the lower beam 446 is a steel hollow cylindrical tube. The legs 440a, 440b, 440c are connected to the central column 402 and the peripheral columns 420a, 420b, 420c by welding or by means of flanges, which are bolted to each other to form a bolted connection.

[0068] The offshore platform 401 includes three pre-tensioned elongated structural members or tendons 460a, 460b, 460c interconnecting the perimeter columns 420a, 420b, 420c at their skirts 427, and three pre-tensioned elongated structural members or tendons 461a, 461b, 461c. In this example, the tendons 460a, 460b, 460c, 461a, 461b, 461c are embodied as steel or aramid fiber anchor cables and may be constructed in the same manner as described above for Figures 1A to 1C The offshore platform 1 is pre-tensioned in a similar manner as described above.

[0069] In the illustrated embodiment, a first set of pre-tensioning tendons 461a, 461b, 461c of the same length interconnecting the perimeter posts 420a, 420b, 420c are disposed near the top of the perimeter posts 420a, 420b, 420c and / or at a height above the legs 440a, 440b, 440c, and a second set of pre-tensioning tendons 460a, 460b, 460c of the same length interconnecting the perimeter posts 420a, 420b, 420c are disposed near the bottom of the skirt 427 and / or at a height below the legs 440a, 440b, 440c. Alternatively, the pre-tensioning tendons 460a, 460b, 460c interconnecting the perimeter posts 420a, 420b, 420c may be disposed only near the bottom at the skirt 427 and / or at a height below the legs 440a, 440b, 440c. In yet another alternative embodiment, the pre-tensioned tendons 461a, 461b, 461c interconnecting the perimeter posts 420a, 420b, 420c may be disposed only near the top of the perimeter posts 420a, 420b, 420c and / or at a height above the legs 440a, 440b, 440c. In still other embodiments, the pre-tensioned tendons 460a, 460b, 460c, 461a, 461b, 461c interconnecting the perimeter posts 420a, 420b, 420c may be disposed only near the center of the perimeter posts 420a, 420b, 420c and at a height approximately the same as the height of the legs 440a, 440b, 440c.

[0070] The offshore platform 401 is provided with a gangway 411, which is located on the top wall 409 of the central column 402 and above the top beam 445, toward the top side of the peripheral columns 420a, 420b, 420c. The gangway 411 can be used by technicians for passage between the central column 402 and the peripheral columns 420a, 420b, 420c.

[0071] The central column 402 has a diameter of 1 meter to 3 meters, about 2 meters in this example. The central column 402 and the peripheral columns 420a, 420b, 420c generally have a total height of 5 meters to 15 meters, about 10 meters in this example. The peripheral columns 420a, 420b, 420c have a diameter of 0.5 meters to 1.5 meters, about 0.8 meters in this example. The top of the central column 402 and the peripheral columns 20a, 20b, 20c can be up to 5 meters to 9 meters above the average water level, and the draft can vary from 2 meters to 6 meters. The tendons 420a, 420b, 420c each have a length L2 of 10 meters to 20 meters, about 15 meters in this example.

[0072] The steel components of the offshore platform 1 are formed from S355, a marine grade low carbon steel.

[0073] The marine platform 401 is held on the station by at least one mooring line connected to the bottom of one of the perimeter columns 420a, 420b, 420c by means that can be closed to hold the marine platform 401 in place while the marine monitoring platform 410 is monitoring the ocean, or opened if the marine monitoring platform 410 needs to be towed back to shore for maintenance or decommissioning. Alternatively, at least one of the perimeter columns 420a, 420b, 420c includes a short length of chain or rope attached to the bottom of the perimeter columns 420a, 420b, 420c. The mooring line or mooring system can be connected to the chain or rope to hold the marine platform 401 on the station.

[0074] The ocean platform 401 includes a mast 430 on a central column 402 to carry a series of equipment and instruments, a hatch 431 for entering the central column 402, and a boat platform 432 for entering the ocean platform 401 with a ladder for climbing on board. The mast 430 is provided for communication and equipment 412 (laser radar, bird radar), antennas, etc. that need to be high or in the open air.

[0075] In this exemplary embodiment, the offshore platform 401 includes wind turbines 433 on the perimeter columns 420a, 420b, 420c and solar panels 434 arranged at the mast 430 on the central column 402. The wind turbines 433 and the solar panels 434 are electrically connected to batteries not shown. By using a combination of wind turbines 433, solar panels 434 and batteries, the offshore platform 401 has zero emissions. In some embodiments, the total power demand is equal to the capacity of approximately one wind turbine 433 (taking into account the on-site capacity utilization). When a long period of low wind speed occurs and some instruments are powered off, the solar panels 434 are sized to the minimum power requirements.

[0076] The center column 402 can have four main compartments, not shown: a ballast compartment at the base of the center column 402, which is used to maintain the desired operating draft and improve platform stability by lowering its center of gravity and increasing its metacentric height; a battery storage area, which is lowered again for weight control and is ventilated (such as with a tube passing through the top of the center column) to ensure that hydrogen or other gas formations do not accumulate; a server room where all the instruments and data boards are mounted and interfaced with the platform server, which performs aggregation of the different signals from all the instruments, assembles them, performs post-analysis as needed, and transmits the required information to shore; a storage area for tools and health, safety and environment (HS&E) equipment for visitors or maintenance technicians.

[0077] Data measurement and acquisition equipment 412 and together with ocean platform 401 can be configured to characterize the ocean in very different areas. Marine meteorology includes waves (such as using wave radar for surface mapping and accurate directionality), wind using anemometers and laser radars, currents using underwater acoustic Doppler current profilers (ADCPs), humidity using specific instruments, air temperature, water temperature, atmospheric pressure. Marine chemistry includes marine growth and corrosion, which can be monitored using visual measurements obtained on deployments or missions on specific plates and anchors that can be suspended from ocean platform 401. In addition, salinity, pH and other chemical compositions can be measured directly. Biodiversity, where ocean platform 401 can operate bird and bat radars and can have underwater acoustics to monitor marine mammal migration. Biohuts can be placed on ocean platform 401 and juvenile fish growth can be measured using both artificial diver technology and acoustics. Similarly, the presence and density of offshore pelagic fish schools around ocean platform 401 can be assessed. Marine farming, where the potential to share a leased site with local fishermen or marine farmers could have strong benefits, but knowledge of the site is important. Nutrient measurements could be performed as well as monitoring the growth of various shellfish and algae. Communications, where the marine platform 401 could be equipped with point-to-point (P2P) or other communications equipment and could be "connected". It could provide WiFi locally to the site and possibly a cell phone signal.

[0078] It should be understood that the above description is included to illustrate the operation of the preferred embodiment and is not meant to limit the scope of protection of the present invention. From the above discussion, many variations will be apparent to those skilled in the art, and these variations will still be covered by the scope of protection of the present invention.

Claims

1. A floating offshore platform comprising a central column, at least three peripheral columns circumferentially surrounding the central column, and beams radially extending from the central column to connect the peripheral columns to the central column, wherein: the beams being steel hollow cylindrical tubes, wherein the perimeter columns include buoyancy air chambers, and wherein the offshore platform includes a motion control system, the motion control system including a high pressure air tank that exhausts air from the buoyancy air chambers, the high pressure air tank controlling air flow into and out of the buoyancy air chambers using an actuated valve and the high pressure air tank being controlled by a computer system coupled to a motion sensor, and wherein the high pressure air tank is formed by an airtight interior volume of one of the beams; The floating offshore platform comprises a structural member spanning between each pair of adjacent perimeter columns, wherein the structural member is pre-tensioned and comprises or is formed from a steel tube; wherein the perimeter columns comprise a connector having a passage for one end of the structural member, wherein the structural member comprises a tensioning head at an end of the steel tube received in the connector, and the steel tube of the structural member extends from the tensioning head through the passage.

2. The floating offshore platform according to claim 1, wherein: The perimeter column includes a base, and wherein the buoyancy air chamber opens to the sea at the base.

3. The floating offshore platform according to claim 2, wherein: The motion control system includes an air compressor configured to fill the high pressure air tank.

4. The floating offshore platform according to claim 3, wherein: The motion control system includes an inlet valve configured to control filling of the high pressure air tank by the air compressor.

5. The floating offshore platform according to claim 1, wherein: The motion control system includes an outlet valve for each open buoyancy air chamber, the outlet valve being configured to control the discharge of air from the high pressure air tank into the corresponding open buoyancy air chamber.

6. The floating offshore platform according to claim 1, wherein: The motion control system includes a release valve for each open buoyancy air chamber, the release valve connecting the buoyancy air chamber to atmosphere and the release valve configured to control the release of air from the open buoyancy air chamber to atmosphere.

7. The floating offshore platform according to claim 1, wherein: The perimeter columns and the structural members form a generally triangular shape.

8. The floating offshore platform according to claim 1, wherein: The structural member is pre-tensioned by inducing a pre-tensioning stroke to the structural member, the pre-tensioning stroke being between 0.04% and 0.07% of the length of the structural member.

9. The floating offshore platform according to claim 8, wherein: The structural member is pre-tensioned by inducing a pre-tensioning stroke to the structural member, the pre-tensioning stroke being 0.05% of the length of the structural member.

10. The floating offshore platform according to claim 1, wherein: The beam is offset toward the central column in the elongated direction of the beam.

11. The floating offshore platform according to claim 1, wherein: The perimeter post includes one or more shims or shim plates between the connector and the tensioning head.

12. The floating offshore platform according to claim 11, wherein: The structural member includes a tensioning head on each end of the steel tube, and the perimeter column includes two connectors corresponding to the respective tensioning heads.

13. The floating offshore platform according to claim 1, wherein: The structural members extending in a common horizontal plane have the same pretensioning.

14. The floating offshore platform according to claim 1, wherein: The radially extending beams include a top beam and a bottom beam extending parallel to each other.

15. The floating offshore platform according to claim 1, wherein: The beam has a circular cross-section.

16. The floating offshore platform of claim 1, wherein: The central column extends vertically.

17. The floating offshore platform of claim 1, wherein: The perimeter columns extend vertically.

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