Semi-submersible floating wind turbine with T-shaped buoy

Abstract

A moored floating semi-submersible offshore wind turbine (1), the platform having at least three columns supported on two long strip-shaped underwater buoys in a T-shape, wherein one buoy (12) is perpendicular to the other buoy (11). A method for efficiently transporting a semi-submersible platform (1) to a second construction site close to a final offshore operation site after the hull components and sections are built at a first construction site, wherein the hull components and sections are assembled in a floating state at the dockside at the second construction site. At least one wind turbine device (301) or two wind turbine devices can be installed on the platform on a supporting structure (wind tower) (302). In the latter case, the platform is moored at sea using a mooring turret so that the platform faces a favorable wind direction.

Description

Technical Field

[0001] The present invention relates to an offshore semi-submersible platform capable of utilizing wind energy to produce electric energy, and an assembly and transportation method related thereto. Background Art

[0002] Semi-submersible platforms are mainly used in the exploration and production of offshore oil and gas resources. Most semi-submersible drilling platforms used to find oil and gas adopt a double-float type, that is, two long floats are used to support multiple columns to obtain the ability to move between different drilling positions, as disclosed in SE439,913 [NO159,362US4,436,050]. In recent years, semi-submersible oil and gas production platforms mostly use annular floats because annular floats have excellent structural strength properties. Among them are triangular annular floats, such as disclosed in US6,701,861; or quadrilateral / rectangular annular floats, such as disclosed in SE431,316 [NO160,249US4,498,412] and S6,015,245.

[0003] Semi-submersible platforms are well known for their good motion performance in severe sea conditions. However, in the oil and gas industry, we also know that the motion performance of semi-submersible platforms can be improved by adding horizontal plates of appropriate size to increase additional mass and motion damping, as disclosed in SE8,700,263 [NO880,277, US4,823,719].

[0004] Semi-submersible platforms are generally built in a water-filled dry dock or on land, and then launched into the water for final outfitting. Some double-floating semi-submersible platforms have their buoys and the lower part of the columns connected to them built on a slideway, then launched into the water, and then the (remaining) columns, braces, and deck structures are built on the floating buoy. In this case, the stability of the operation process is ensured by connecting the two buoys of the semi-submersible platform to avoid instability due to the high center of gravity of the semi-submersible platform during the process.

[0005] As the demand for renewable energy increases, offshore wind power is becoming an important part of the production of such clean electricity. As the offshore wind power industry develops, in order to meet the needs of developing and utilizing sea areas with more favorable wind conditions, more severe sea conditions, farther from the coast, greater water depth, etc., the advantages of floating wind turbines are also growing. However, to make floating wind power in such waters attractive, the cost of producing wind power must be maintained at an attractive and competitive level, which requires that the cost of construction, transportation, and assembly of such wind turbine platforms must be reduced compared to the current cost level.

[0006] For floating wind turbines with floating platforms (or similar devices that convert wind energy into electrical energy, such as vertical axis wind turbines), the industry has proposed different platform design schemes, such as semi-submersible platforms, Spar platforms, and tension leg platforms (TLPs), see reference [1]. Spar platforms are not very attractive because of their large draft (up to 100 meters), heavy hull structure and high cost, unless there is a deep sea area (such as a fjord) near their final installation location, where the Spar can be turned upright in the water to install the wind turbine equipment. The TLP platform disclosed in SE1850590 [WO2019 / 143,283 has the advantages of small heave, pitch and roll amplitudes. Many TLP schemes consist of a semi-submersible platform and a tension mooring system, such as disclosed in US5,197,825; while the TLP of other schemes will become unstable when not moored, so a temporary floating structure is required to be installed during towing and installation to help stabilize it. The need for complex mooring systems and the possibility of installing temporary floating structures to stabilize the towing and installation process make TLP platforms unattractive in many cases. The shortcomings and cost factors of spar platforms, TLP platforms and mooring systems make semi-submersible platforms an attractive option for floating wind power.

[0007] Regardless of the type of vessel used, towing an offshore wind power platform with installed wind turbine equipment is a complex and challenging task due to the external forces on the platform and wind turbine equipment under severe weather conditions. Therefore, it is ideal to install the wind turbine equipment in a sheltered sea area relatively close to the final work site, thereby minimizing the towing time and distance. In this case, the platform can be built near the sheltered installation site of the wind turbine equipment, or it can be transported from the construction site to a sheltered installation site near the wind turbine working sea area. The transportation of the platform from the construction site to the installation site can be done by wet towing while floating on the sea, or by dry towing on a transport ship. However, due to the size limitations of the platform and the transport ship, dry towing can often only transport one platform at a time.

[0008] There are currently a variety of three-column or multi-column semi-submersible floating wind turbine platform designs. There are three-column designs with heave damping plates, where the columns are connected by cross braces, such as Principle Power Windfloat, US9,446,822 [WO2009 / 131,826], and Dietswell Trussfloat, FR3,052,195 [WO WO2017 / 207,937]; there are also star-shaped designs, such as OO-Star, NO334,535 [WO2014 / 031,009], which uses a star-shaped float, or Gusto Tri-Floater, NL2,010,709 [WO2014163501], which uses a star-shaped deck structure; another three-column platform launched by Mitsubishi Fukushima uses a V-shaped float design, see reference [3]. There are also semi-submersible platform designs that use triangular annular floats.

[0009] The semi-submersible platforms in the above examples can only be equipped with one wind turbine. Some semi-submersible platforms can also be equipped with multiple wind turbines. A semi-submersible platform that can be equipped with two wind turbines is Enerocean's W2Power, which was originally based on NO330,058 [WO2010110671] and one has been built. Later, this model was further developed by Freia Offshore into Hexicon SE1,850,064 [WO2019 / 143,282]. Both of these dual-wind turbine platforms are three-column semi-submersibles, equipped with heave damping plates, and the columns are connected by cross braces.

[0010] A dual-wind turbine semi-submersible platform may need to follow the wind (rotate) function to align with the wind direction so that the wind turbine equipment is not affected by the slipstream of the other wind turbine blades. The technology of rotating a moored buoy around a mooring system to keep the buoy always facing the wind is widely used in the oil and gas industry and is used on production vessels, such as described in WO2017 / 174,665.

[0011] The semi-submersible platforms mentioned above have one thing in common, that is, they all need to be built and assembled in a dry dock or on land, as described in references [3] and [4]. For semi-submersible platforms that use cross braces to connect columns, the columns generally do not have independent floating stability in the upright state, and because the floating state is too low in the water, the cross braces at the lower ends of the columns often cannot be installed. Due to the low position and complex shape, it is generally impossible to use the method of underwater closure of the hull commonly used in the shipbuilding industry (such as underwater closure when the hull is lengthened) to achieve welding. An example of using a water jacket to complete the hull closure in water is disclosed in SE7,411,764.

[0012] Because of the relatively large size of semi-submersible floating wind turbine platforms, only a few dry docks can accommodate such platforms. If built on land, due to the size and weight of the platform, a large and expensive semi-submersible transport vessel (such as described in NL2,005,054), a semi-submersible launching barge, or a wide slide is required to achieve launching. Large floating docks and wide slides are scarce, especially near the installation location of the wind turbine platform. Therefore, it is often necessary to dry-tow the constructed platform with a semi-submersible vessel to the wind turbine equipment installation site near the working sea area.

[0013] The dry towing method for transporting semi-submersible floating wind turbine platforms is often limited to one platform at a time due to the size of the platform. Because the number of semi-submersible transport vessels is limited, the cost of transporting the wind turbine platform to the work site will account for a large part of the overall cost of the platform, which has become a factor affecting the competitiveness of semi-submersible wind turbine platforms.

[0014] This document focuses on the design of a semi-submersible floating wind turbine platform that can be built in several parts at a competitive construction site (shipyard), efficiently transported to the final assembly site by loading multiple platform components on a transport vessel, and assembled with limited facilities in a sheltered sea area near the final operation site. Summary of the invention

[0015] The present invention relates to the design of a semi-submersible offshore platform for producing electric energy by utilizing wind energy, and the construction, transportation and assembly methods of the platform.

[0016] More specifically, the present invention introduces a new method for arranging the underwater buoyancy of a semi-submersible floating wind turbine, so that after the wind turbine platform is built into components or sections at the construction site, multiple platforms can be transported at one time by a deck transport ship (or other types of transport ships / barges) to a favorable location close to the final operating sea area, and then the hull components or platform components / sections are assembled in water at this location into a complete wind turbine. The assembly site does not require special shipyard facilities such as dry docks, slides, launching barges, etc.

[0017] The objective of the present invention is to design an improved semi-submersible floating wind turbine and a convenient method for construction, transportation and assembly to reduce, mitigate and eliminate the challenges / deficiencies identified above in existing solutions, making the construction, transportation and assembly of the semi-submersible floating wind turbine hull more cost-effective, thereby achieving complete assembly of the platform at a location close to the final operating sea area without shipyard facilities.

[0018] The objects of the invention are achieved by the arrangement of the invention and the described construction, transport and assembly methods. In the following description / drawings, various advantages, subsequent evolutions and variants of the invention are described.

[0019] According to the present invention, a semi-submersible floating wind turbine comprises: a floating wind turbine consisting of a semi-submersible hull supported by multiple columns, wherein at least three columns have buoyancy to provide the required floating stability for the semi-submersible platform, and one or more wind energy utilization devices are installed on the supporting structure, for example, a wind turbine installed on a wind tower, each installed on the upper end of a column. The underwater hull of the platform has two long floating bodies, wherein the two ends of the first floating body support two stability columns, and the second floating body is vertically connected to the middle position of the first floating body, and the other end thereof supports the third stability column. As a result, the two floating bodies of the semi-submersible platform are horizontally connected to form a T-shape, and each end of the T supports a stability column, and more columns can be arranged along the T. The configuration of the two floating bodies does not have to be an exact T-shape, for example, the floating bodies do not have to be straight, and the intersection angle of the two floating bodies does not have to be exactly 90°.

[0020] According to a major advantage of the present invention, the two buoys have a distinct quadrilateral cross-section with two side surfaces, a bottom surface and a deck surface. A fillet (bilge) can be designed between the side surfaces and the bottom surface / deck. According to another advantage of the present invention, the two buoys have the same height so that their bottom surfaces and deck surfaces can be structurally aligned. According to another more obvious advantage of the present invention, on both sides of the end where the second buoy intersects with the first buoy, a triangular buoy structure of the same height is provided, which is connected to the other buoy and plays a role similar to a structural bracket, providing good load transfer between the two buoys.

[0021] According to another advantage of the present invention, the columns supported by the interconnected T-shaped lower buoys are also interconnected at the upper ends by upper diagonal braces, and the upper diagonal braces are partially inserted into the columns to provide good load transfer between the diagonal braces and the columns. According to another advantage of the present invention, two lower diagonal braces are interconnected with both ends of the two buoys, and the lower diagonal braces are far away from the upper diagonal braces. According to another advantage of the present invention, the two lower diagonal braces are located at the height of the decks of the two buoys.

[0022] According to another advantage of the present invention, one or more of the three stability columns are provided with vertical bulkheads aligned with the direction of the diagonal braces, so that the upper and lower diagonal braces are interconnected. These vertical bulkheads provide effective paths for load transfer between the diagonal braces and load transfer into the columns.

[0023] According to one feature of the present invention, the central positions of the three stability columns are arranged roughly in an equilateral triangle. According to another feature of the present invention, the stability columns have a circular cross-section. According to another feature of the present invention, the outer surfaces of the three stability columns extend downward to the bottom of the floating body, forming an arc surface on the outer side of the end of the floating body.

[0024] According to one embodiment of the present invention, the width of the lower buoy is substantially equal to the square root of the diameter of the stability column multiplied by 2 / 3. According to another embodiment of the present invention, the width of the first floating body is substantially equal to the diameter of the stability column supported thereon multiplied by the square root of 2 / 3. The width of the second floating body is approximately equal to half the diameter of the stability column supported thereon (B2=D2 / 2).

[0025] According to another advantage of the present invention, horizontal plates for adding additional mass and damping are provided at the bottom of both ends of the first floating body. According to another advantage of the present invention, the positions of the horizontal plates for adding additional mass and damping provided at the bottom of both ends of the first floating body are located on the same side of the center line of the first floating body close to the second floating body, so as to avoid causing a significant increase in the length of the first floating body. According to another advantage of the present invention, the position of the horizontal plate for adding additional mass and damping on the first floating body is kept at a distance from the second floating body or the triangular floating structure at least equivalent to the width B of the second floating body. According to another advantage of the present invention, a horizontal plate for adding additional mass and damping is also provided at the far end of the second floating body.

[0026] According to another advantage of the present invention, a wind energy device is installed on the vertical support structure of the semi-submersible platform, for example, a wind turbine tower is installed on the column at the end of the second floating body, that is, at the bottom end of the T.

[0027] According to one form of the invention, the semi-submersible platform floats and is moored with a catenary mooring system, such as a full anchor chain mooring system. According to another form of the invention, the semi-submersible platform floats and is moored with a tension mooring system, such as a cable mooring system, and may also use an anchor chain / cable combination at both ends of the cable.

[0028] According to another embodiment of the present invention, the semi-submersible platform is moored by a tension tendon connected to the seabed at one end, that is, the semi-submersible platform becomes a tension leg platform.

[0029] According to another advantage of the present invention, two wind energy devices are installed on the supporting structure of the semi-submersible platform, for example, a wind turbine with a wind tower structure is installed on each column at both ends of the first floating body, that is, at the top position of the T. According to another advantage of the present invention, the two wind tower structures are inclined outward and parallel to the top of the T. According to another advantage of the present invention, the two wind tower structures are connected at the top by a horizontal cross brace.

[0030] According to another advantage of the present invention, the semi-submersible platform with two wind energy devices installed is moored by a turret connected under the hull, and the platform can rotate around the turret to make the wind turbines face a favorable angle. The mooring device can be a catenary system, a tension system, or a tension leg system. According to another advantage of the present invention, the turret is located below the far end of the second floating body.

[0031] One of the objectives of the present invention is to make the construction, transportation and assembly of a semi-submersible floating wind turbine more cost-effective, thereby achieving complete assembly of the platform at a location close to the final operating sea area without shipyard facilities.

[0032] According to the present invention, the object is achieved by the construction, transportation and assembly method described in the present invention, wherein the first component of the platform is composed of a first buoy, an inner end portion of a second buoy, and columns connected to the first buoy support. Advantageously, the first component of the hull may include a triangular buoy structure at the inner end of the second buoy, and may also include an upper cross brace connected to the upper ends of the columns mentioned.

[0033] A preferred implementation of the above method is to make the second buoy have a sufficient length so that the first hull assembly can float stably in the water. This allows the first hull assembly to be prefabricated in a dry dock or on land at the construction site and to float stably in the water in an upright state after being launched.

[0034] One benefit of this method is that the outer end of the second buoy is connected to the first hull assembly to form a second assembly, which can achieve stable floating in a positive floating state. The assembly of the second assembly can be carried out at a suitable location far away from the first construction site.

[0035] Another benefit of this method is that the outer end of the second buoy is connected to the first hull assembly to form the second assembly, which can be completed by welding in the upright state in the water. The lower part of the connection can be completed in a water jacket that is drained along the weld. Alternatively, the welding can be completed in a dry dock.

[0036] In the next step of the implementation of the method, the remaining part of the semi-submersible platform is assembled to the second assembly that is stably floating in the water. The work of assembling the remaining part of the semi-submersible platform to the second assembly is preferably completed by using a dock crane when the second assembly is floating at the dock.

[0037] One advantage of this method is that after the first component is built at the first construction site, it can be transported to the second construction site where the second component is assembled.

[0038] The above method can be described in another way: a method of assembling the semi-submersible platform of the present type, the method comprising: combining a first assembly of the hull with an outer end of a second floating body to form a second hull assembly. The first assembly comprises a first floating body, two stabilizing columns, an inner end of the second floating body of length "L" capable of ensuring that the first assembly is basically stably floated, and the remaining outer end of the second floating body can also be basically stably floated.

[0039] An implementation of the method includes: before docking, making the outer ends of the first assembly and the second buoy float in the water in a substantially stable upright manner and maintaining the same draft and trim so as to achieve docking.

[0040] An implementation of the method includes: the first component and the outer end of the second float are connected by docking the outer end of the second float with the inner end of the second float.

[0041] In one implementation of the method, the first assembly and the outer ends of the second buoy are connected by welding.

[0042] In one implementation of the method, the welding of the lower part of the connection portion can be completed in a closed water jacket arranged along the weld and drained of water.

[0043] In one implementation of the method, the second component is stably floated upright in the water, and the remaining part of the semi-submersible platform is built on the second component to form a complete platform.

[0044] In one implementation of the method, after the first component is constructed at a first construction site, it can be transported to a second construction site for assembling a second component.

[0045] Another implementation of the method is that, because the first assembly can be stably upright, the first assembly is transported from the first construction site to the second construction site by a semi-submersible transport vessel in a floating manner.

[0046] One advantage of the present method is that a plurality of first components arranged in pairs can be loaded and transported on a deck transport ship, with the two first components in a pair arranged opposite to each other, with the inner end of the second float in one component pointing to the other component, and the inner ends of the second floats in the two components lying side by side, which can save the space occupied by each pair of first components on the transport ship.

[0047] In another implementation of the method, the outer end of the second float is fixed above the first assembly for transportation, which can further reduce the space it occupies on the transport ship. In an advantageous implementation of the method, the outer end of the second float has a sufficient length L so that it can be fixed above the first assembly while the first assembly can still maintain a stable upright floating state in the water.

[0048] The transport of the underwater parts of the hull (with or without the columns) can of course be carried out in other ways. One alternative is to arrange the hulls, which have not yet been assembled, in a different form than described above. Another alternative is to assemble the underwater parts of the hulls before transport. Regardless of the method used, it is certainly advantageous to arrange the underwater parts of the hulls in pairs on the transport vessel to reduce the space required, which can allow the transport vessel to transport multiple pairs of lower hulls at a time.

[0049] Therefore, the present invention is related to a transportation method, that is, two underwater hulls of at least two semi-submersible platforms are transported from a first construction site to a second construction site by a ship similar to a semi-submersible transport ship, and the arrangement direction of the two underwater components is: the first buoy is arranged along the transverse direction of the transport ship, that is, across the longitudinal axis of the transport ship; and the second buoy part of the component or the second buoy part connected to the first buoy points to another direction (for example, approximately parallel to the longitudinal axis of the transport ship). The components of the two underwater hulls are arranged oppositely, and the second buoy in one component points to the first buoy in the other component.

[0050] In one embodiment of the present invention, the second buoys in the two first components retain their full length and are connected to the relevant first buoys, the two components are staggered along the length of the transport ship, and the second buoy in one component is arranged side by side along the second buoy in the other component.

[0051] Therefore, related to this implementation type is a situation in which multiple T-shaped underwater hulls are already combined before transportation, that is, one component in a pair of combinations is arranged "head to toe" with another component, and the second buoy of one of them is arranged side by side with the other second buoy.

[0052] In another implementation, the two second buoys of the two underwater hulls are each divided into two parts, one of which is connected to the corresponding first buoy, and the other forms an independent part. The two underwater hulls are arranged in opposite directions in the following manner: the second buoy connected to the first buoy of one underwater hull protrudes toward the second buoy connected to the first buoy of the other underwater hull. The independent parts of the two underwater hulls are respectively arranged on both sides of the inner ends of the two second buoys connected to the corresponding first buoys.

[0053] Therefore, this situation is based on the T-shaped hull being incompletely assembled before transportation, that is, during transportation, only the inner end of the second floating body is connected to the first floating body, and the remaining part of the second floating body forms an independent outer end.

[0054] In the above two methods, the components of a pair of underwater hulls are preferably connected to each other to form a transport assembly that can stably float upright. For example, a portion of the second float forms an independent outer end, and the first float and the second float or float member are connected to form a transport assembly that can stably float upright.

[0055] In another version, the first and second underwater hulls are loaded with the first buoy arranged transversely across the longitudinal axis of the transport vessel. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The following detailed description and drawings are helpful for a more complete understanding of the present invention. These drawings are schematic diagrams and are not a complete description of the present invention:

[0057] Figure 1 A semi-submersible platform with three stabilizing columns realized according to the present invention is shown, wherein a wind energy utilization device is installed on one of the stabilizing columns.

[0058] Figure 2 It indicated Figure 1 A top view of the embodiment shown, wherein the wind energy utilization device is not shown.

[0059] Figure 3 A semi-submersible platform realized according to the present invention is shown, in which a wind energy utilization device is installed on an independent column.

[0060] Figure 4 A semi-submersible platform with three stability columns realized according to the present invention is shown, and two wind energy utilization devices are respectively installed on the inclined support structure above the two columns.

[0061] Figure 5 It indicated Figure 4 A top view of the semi-submersible platform is shown.

[0062] Figure 6 It indicated Figure 4 The semi-submersible platform shown has connected horizontal cross braces installed at the upper ends of two wind turbine support structures (wind towers).

[0063] Figure 7 An enlarged view of a stability column is shown, with the outer surface of the column not shown to show the internal vertical bulkhead.

[0064] Figure 8 Schematic diagram of the first hull assembly and the outer end of the second buoy, which is one implementation of the recommended construction method.

[0065] Fig. 9 It shows a schematic diagram of underwater assembling of the first hull assembly and the second buoy by welding in the water jacket, and other components will be built on the second hull assembly.

[0066] Fig.10 The stowage arrangement of a pair of first hull assemblies is shown.

[0067] Fig.11 The outer end of the second buoy is shown loaded onto the first buoy of the first hull assembly.

[0068] Fig.12 The transport structure shows six semi-submersible platform hulls, which are formed into a transport structure in pairs, wherein the first buoys of the two first hull assemblies are parallel to each other, and the inner end of one of the second buoys points to the inner end of the other second buoy. Two second hull assemblies are arranged between the two first buoys, wherein the outer end of the second buoy is parallel to the first buoy, and one is arranged on each side of the inner end of the second buoy.

[0069] Fig.13 It shows the arrangement of transporting four underwater hulls at a time, with the hulls loaded in pairs in a "head-to-foot" manner, with two second buoys arranged side by side, and the two first buoys located at both ends of the two second buoys. DETAILED DESCRIPTION

[0070] The following is a more complete description of examples of implementations of the present invention in conjunction with the accompanying drawings. However, the present invention has many implementations, and the following examples do not constitute a limitation on the implementations of the present invention. These examples are intended to make this disclosure more thorough and complete, so as to fully introduce the scope of the present invention to relevant persons. The references of the numbers in the legends also remain consistent throughout the text.

[0071] Figure 1 2 shows a semi-submersible platform floating in water (e.g., in seawater) in a semi-submerged state, with the draft represented by the water plane 2. A wind turbine device 301 is installed on the platform to generate electricity using wind energy. The wind turbine device 301 can be a horizontal azimuth axis wind turbine or a vertical axis wind turbine. The wind turbine device is installed on a supporting structure (e.g., a wind tower or a mast tower) 302.

[0072] The underwater hull of the semi-submersible platform 1 is composed of two long floating bodies, one of which is a floating body 12 (the second floating body) perpendicular to the other floating body 11 (the first floating body). The inner end of the second floating body 12 is connected to the middle length of the first floating body 11. Figure 2 See, its shape is like a T, wherein the first floating body 11 is the "top of the T", and the second floating body 12 is the "post of the T".

[0073] The following description of the direction of the semi-submersible platform 1 will use some marine terms, for example, the first floating body 11 is arranged transversely at the stern "A"; the second floating body 12 is arranged longitudinally, and its outer end constitutes the bow "F" of the platform 1. Based on the preference for the definition of direction, the above direction can also be said in reverse, depending on the mooring direction of the platform determined according to the most favorable wind direction at sea.

[0074] Based on the above-mentioned floating body arrangement, in many aspects, the semi-submersible platform 1 is symmetrical along the longitudinal center line of the second floating body 12 .

[0075] The buoys 11 and 12 are buoyant, and the ballast tanks are separated by bulkheads and equipped with a ballast system, which allows the semi-submersible platform to adjust the draft, trim and heel through the ballast system. These tanks can also be used as cabins for other purposes. It is recommended that the buoys 11 and 12 adopt a rectangular cross-section with square corners or rounded corners / bilges, and have the same depth / height to achieve effective transfer of loads between the bottoms of the two buoys and between the decks.

[0076] Two triangular prism structures 131 providing buoyancy are arranged at the junction of the buoy 11 and the buoy 12, i.e., at the inner angle formed by the two sides of the inner end / stern of the buoy 12 and the buoy 11, so as to play a role similar to that of a structural bracket to improve the structural load transfer between the two buoys. The triangular prism structure 131 has the same depth / height as the buoy.

[0077] Three stability columns 201, 202, 203 are supported by the underwater hull and connected to each other, protruding from the waterline 2. One stability column 201 is arranged at the outer end of the second buoy at the bow "F" of the semi-submersible platform 1, and the other two stability columns 202 and 203 are arranged at the two outer ends of the first buoy, namely, at the starboard stern and the port stern of the semi-submersible platform 1, respectively.

[0078] The buoyancy columns 201, 202, 203 have buoyancy, providing sufficient waterline area and moment of inertia for the semi-submersible platform 1, and the interior thereof is divided into the well-known ballast tanks, void tanks, and passages leading to the floating body by vertical watertight bulkheads and horizontal girders.

[0079] The horizontal cross-section of the stable buoyancy columns 201, 202, 203 can be a relatively advantageous circular shape, or a rectangular shape with square or rounded corners, or a triangle, etc. The three columns can be arranged vertically or inclinedly.

[0080] The stabilizing buoyancy columns 201, 202, 203 have the same cross-sectional diameter "D" and are arranged to form an equilateral triangle 291, so that the semi-submersible platform has the same moment of inertia and initial stability height in the longitudinal and lateral directions on the waterline plane 2.

[0081] The present invention is Figure 1 In the illustrated implementation, the outer surfaces of the stabilizing buoyancy columns 201, 202, 203 extend downward to the bottom of the floating bodies 11, 12, forming rounded ends at the outer ends of the two floating bodies.

[0082] The stability and buoyancy columns 201, 202, 203 are interconnected at the top or close to the top by horizontal cross braces 241, and one cross brace is connected between every two stability and buoyancy columns. These horizontal cross braces 241 can be circular in cross section, or can be other forms such as I-beams or box sections. It is best that the cross braces can partially extend into the columns so that good load transfer can be achieved between the cross braces 241 and the stability and buoyancy columns 201, 202, 203.

[0083] The present invention is Figure 1 In the embodiment shown, the first buoy 11 and the second buoy 12 are connected by two lower cross braces 141, one end of the cross brace is connected to the two outer ends of the first buoy 11, and the other end of the cross brace is connected to the outer end of the second buoy 12. The lower cross brace is much lower than the upper cross brace 241. Figure 1In the figure, two lower cross braces 141 are located below the decks 113 and 123 of the two buoys 11 and 12. The function of the lower cross brace 141 is to provide lateral strength for the second buoy 12. This design benefits the structural strength when the wind turbine equipment 301 is subjected to lateral wind along the semi-submersible platform 1. From the perspective of strength and fatigue, the lower the horizontal lower cross brace 141 is arranged, the better, and its position should also be above the waterline position when the semi-submersible platform is assembled to facilitate welding operations, as described below. By arranging the horizontal lower cross brace 141 below the decks 113 and 123 of the buoys 11 and 12, its connection position can be avoided from the joint position between the buoys 11 and 12 and the stability buoyancy columns 201, 202, and 203.

[0084] At the two outer ends of the first floating body 11, horizontal plates 118 are provided near the bottom of the floating body to increase the additional mass and motion damping. Figure 1 In the embodiment of the invention shown, these horizontal plates are mounted on the same side close to the second buoy, which does not significantly increase the length of the first buoy 11 / overall width of the semi-submersible platform 1. Reducing the overall width of the semi-submersible platform 1 is beneficial to meet the transportation requirements of certain transport ships.

[0085] In such Figure 1 In the embodiment of the present invention shown, a horizontal plate 128 for increasing additional mass and motion damping is provided at the outer end of the second buoy 12, i.e., the bow of the semi-submersible platform 1, near the bottom of the buoy. The horizontal plate 128 is made into a continuous circular plate around the end of the second buoy, and the horizontal plate can also be divided into several pieces, leaving several gaps in the middle, for example, when it is necessary to avoid conflicts with mooring cables.

[0086] Figure 1 The mid-horizontal azimuth axis wind turbine 301 is installed on a supporting structure 302 , such as a structural wind tower (or mast tower) installed on a bow stabilizing buoyancy column 201 .

[0087] The semi-submersible 1 is moored by a well-known catenary or tensioned mooring system. In another version, the semi-submersible 1 is moored by tension tendons, thereby becoming a tension leg (TLP) platform. These mooring systems are well known in the oil and gas industry for semi-submersibles and are further described below or in the accompanying drawings. There are several methods for attaching the mooring lines / tendons to the semi-submersible, which will not be described in detail here.

[0088] exist Figure 3 In another embodiment of the semi-submersible platform 1, the wind turbine equipment 301 and its supporting structure (wind tower) 302 are located on an independent column 221 specially provided for supporting the wind turbine equipment. The independent column can be buoyant or non-buoyant. By installing the wind turbine equipment on the independent column 221, the structural load on the stable buoyant column 201 can be reduced.

[0089] The independent column 221 is supported by one of the floating bodies 11 and 12, and can also be connected to other buoyant stability columns through the upper cross brace 241.

[0090] Figure 3 Another type of horizontal lower cross brace 141 is also shown, the center of which is flush with the buoy decks 113, 123. This type is more advantageous when the semi-submersible platform 1 has limited displacement / large draft during assembly. This type of horizontal lower cross brace 141 can be combined with other implementation types of the semi-submersible platform 1, and Figure 3 There is no necessary connection between the independent columns 221 shown.

[0091] Figure 4 Another embodiment of the semi-submersible platform 1 is shown, where two wind turbines 301 are installed on a structure (wind tower) 302 supported by two columns at the stern "A" of the platform. The two wind turbines can be installed in a fixed direction parallel to the longitudinal direction of the semi-submersible platform, and can be aligned with a favorable wind direction through the platform, that is, follow the wind.

[0092] In order to make the semi-submersible platform 1 follow the wind, a mooring turret 401 is installed below the bow stability column 201, and a mooring cable is connected below the mooring turret, so that the semi-submersible platform can rotate around the mooring turret. It is a well-known method in the offshore oil and gas industry to make the floating device follow the wind by mooring the turret, so the turret and mooring will not be described in detail here.

[0093] By installing the wind turbine device toward the semi-submersible platform 1 in a fixed direction with the wind, the changing wind force will mainly act in the longitudinal direction of the semi-submersible platform. Therefore, it is more advantageous to increase the longitudinal stability / initial stability height / moment of inertia than in the transverse direction. To this end, the bow buoyancy stability column 201 can have a larger waterline area / diameter than the stern buoyancy stability columns 202 and 203, and the distance between the two columns is increased, so that the three stability buoyancy columns are arranged as follows: Figure 5 Isosceles triangle 292 is shown.

[0094] like Figure 4 and Figure 5 As shown, the supporting structures (wind towers) of the two wind turbines are tilted outward in the transverse direction, parallel to the centerline of the first floating body 11. This can increase the distance between the two wind turbines and increase the wind torque of the semi-submersible platform 1 rotating around the mooring turret 401.

[0095] exist Figure 5 In the illustrated implementation of the lower hull of the semi-submersible platform, since the lower buoy 12 and the bow stabilizing column 201 are subjected to relatively small lateral forces, the underwater hull is not provided with a horizontal lower cross brace, and the second buoy 12 is relatively narrow.

[0096] Figure 6 It represents a Figure 4 The same semi-submersible platform 1 is shown, but the top ends of the two wind turbine equipment support structures 302 are connected by a horizontal cross brace 291. The horizontal cross brace 291 can reduce the static bending moment in the wind turbine equipment support structure 302.

[0097] Figure 7 An enlarged view of the stern starboard stability buoyancy column 202 after removing the outer plate is shown. There is a vertical bulkhead 212 inside the column that is aligned with the horizontal upper cross brace and the horizontal lower cross brace and points to the center of the column. This vertical bulkhead is preferably extended to the bottom of the floating body to provide efficient structural load transfer between the two cross braces, the stability buoyancy column, and the floating body 11. Such vertical bulkheads are also provided in the stability buoyancy columns 201 and 203.

[0098] Figure 8-Figure 11 The preferred construction, transportation and assembly method of the semi-submersible platform 1 is shown.

[0099] Figure 8 The first hull assembly 10 and the outer end 14 of the second floating body are shown in FIG. The first hull assembly is composed of the first floating body 11, two stern stabilizing buoyancy columns 202 and 203, an upper cross brace 241 between the columns, a triangular floating body structure 131, the inner end 13 of the second floating body, a short interface connecting the lower cross brace 141, and the upper cross brace 241 (if any).

[0100] like Fig.10 As shown, the inner end 13 of the second float should have a sufficient length L to ensure that the first hull assembly 10 can stably float upright. The size of the outer end 14 of the second float should also enable this part to float stably. The inner end 13 of the second float and the outer end 14 of the second float (not shown) in the first hull assembly 10 should be provided with a watertight bulkhead 126 near the interface.

[0101] The first hull assembly 10 and the second buoy outer end 14 are intended to be constructed at a first construction site (i.e., a shipyard) and then transported to a second construction site, i.e., a port near the final operation site of the floating semi-submersible wind turbine. The dimensions of the first hull assembly 10 and the second buoy outer end 14 should take into account that they may float in the water, such as floating on the dockside of the second construction site.

[0102] Fig. 9 A method of assembling a semi-submersible platform 1 is shown. The first hull assembly 10 and the second buoy outer end 14 float in a body of water 2, such as seawater near a pier. Because both are constructed watertight, they can float in the body of water 2, with the buoy deck away from the water surface.

[0103] The first hull assembly 10 and the second buoy outer end 14 are controlled by ballast to achieve the same draft and trim, and are positioned according to the combined relationship. A guide device (not shown) known in the shipbuilding industry can be used for positioning. A closed water jacket 50 is installed at the interface J between the first hull assembly 10 and the second buoy outer end 14.

[0104] The closing water jacket 50 is a structure that is preferably buoyant in water and has sealing devices (not shown) on both sides of the interface area "J" and on the contact surfaces of the float bottom 121 and the float side 122. The closing water jacket forms a watertight chamber by sealing. By discharging seawater, the closing water jacket and the interior of the second float at the interface area "J" are filled with air.

[0105] This allows the joint "J" to be welded in a dry environment, connecting the first hull assembly 10 and the second buoy outer end 14 to form the second hull assembly 20. After painting the joint "J", the closing water jacket is filled with water and removed from the second hull assembly, for example, the closing water jacket is disassembled into two pieces, and then the second hull assembly 20 floats in the water as a structure.

[0106] The rest of the semi-submersible platform 1, such as the bow stabilizing buoyancy column 201 and the two upper cross braces 241 connecting it to the other two buoyancy stabilizing columns on the original first hull assembly 10, are preferably assembled using a dock crane. After that, the semi-submersible platform 1 is ready to install the wind turbine equipment 301 and the supporting structure 302 (see Figure 1 , 3 , 4).

[0107] As described above, a more advantageous implementation of the present invention is that the components of the semi-submersible platform, including the first hull assembly 10, are transported to the second construction site for assembly after being constructed at the first construction site. The two construction sites may be far apart, for example, located in two countries, but the second construction site is preferably as close as possible to the sea area where the floating semi-submersible wind turbine is finally operated.

[0108] Therefore, this method requires that the hull components be transported from the first construction site to the second construction site. To reduce the cost of such transportation, an advantageous way is to use a semi-submersible transport vessel to transport these components, which can load and unload the first hull assembly by a well-known floating method.

[0109] It is important to load as many hulls as possible on one ship to reduce transportation costs. Fig.10 A more advantageous loading method is shown which can reduce the space required on the transport vessel.

[0110] Because of the favorable shape of the first hull module 10, the two hull modules can be loaded in pairs, with one second pontoon inner end portion 13 facing the other first hull module 10, and the two second pontoon inner end portions 13 arranged side by side.

[0111] Therefore, the arrangement of the first hull assembly 10 should make the distance between the horizontal plate 128 on the first buoy 11 for adding additional mass and motion damping and the inner end 13 of the second buoy or the triangular buoy structure 131 (if any) greater than "B", that is, the width of the corresponding second buoy.

[0112] A plurality of hull assemblies are loaded in pairs on a transport ship, with two first hull assemblies arranged opposite to each other to form a pair, with the inner end of one second buoy facing the other first hull assembly, and the inner end of the two second buoys arranged side by side. This enables a transport ship to transport multiple pairs of first hull assemblies at a time.

[0113] exist Fig.11 In an advantageous embodiment shown, the outer end 14 of the second buoy 12 can be loaded onto the first buoy 11 of the corresponding first hull assembly 10. This can further reduce the space it occupies on the transport vessel.

[0114] Fig.12 and Fig.13 Two different ways of using a transport vessel to transport multiple pairs of underwater hulls from a first construction site to a second construction site are illustrated.

[0115] Fig.12 The transport structure shows six semi-submersible platform hulls, wherein the hulls 1, 1a form a transport structure in pairs, wherein the first buoys 11, 11a of the two first hull assemblies 10, 10a are parallel to each other, and the inner end 13, 13a of one of the second buoys points to the inner end of the other second buoy. Two second hull assemblies 20, 20a are arranged between the two first buoys, wherein the outer end 14, 14a of the second buoys is parallel to the first buoys 11, 11a, and one is arranged on each side of the inner end 13, 13a of the second buoy.

[0116] and Fig.12 An example of this is shown where the T-shaped underwater hull is not fully assembled before transport, i.e., only the inner end 13, 13a of the second buoy 12, 12a is connected to the first buoy 11, 11a during transport, with the remainder of the second buoy forming a separate outer end member 14, 14a.

[0117] Fig.13 It shows an example of transporting four underwater hulls at a time in which the T-shaped underwater hulls have been assembled before transportation, with the hulls 1, 1a loaded in pairs in a "head-to-foot" manner and two second buoys 12, 12a arranged side by side, and the two first buoys 11, 11a located at both ends of the two second buoys.

[0118] like Fig.12As shown, each of the two underwater hulls 1 and 1a is split into a first assembly 10 and 10a, and a second assembly 20 and 20a, wherein the first hull assembly is composed of the inner end 13, 13a of the first floating body 11, 11a and the second floating body 12, 12a, and the length of the inner end L should enable each first hull assembly 10, 10a to achieve a substantially stable positive float. The two first hull assemblies 10, 10a are arranged so that the two first floating bodies 11, 11a are substantially parallel, and the two buoyant inner ends 13, 13a are collinear and opposite.

[0119] The second hull assembly 20, 20a is arranged between the two first hull assemblies, wherein the second buoy outer end portion 14, 14a is substantially parallel to the two first buoys 11, 11a, and the two second assemblies are respectively located on both sides of the second buoy inner end portion 13, 13a.

[0120] The two first hull assemblies 10, 10a and the two second hull assemblies 20, 20a are assembled together to form a transport assembly 30 that can stably float upright.

[0121] like Fig.13 In the arrangement of the two underwater hulls shown, the second buoy 12 of one hull 1 is arranged in parallel in the opposite direction along the second buoy 12a of the other hull 1a, and the two first buoys 11, 11a are located at both ends of the two second buoys.

[0122] exist Figure 12-13 In the example shown, two underwater hulls or two first hull modules 10 / 10a, of which two first buoys 11 / 11a are arranged in a transverse direction across the longitudinal line of the transport vessel.

[0123] The above-mentioned various forms do not limit the implementation forms of the present invention, and the present invention can be implemented in various forms as follows. For example, the upper cross brace 241 and the lower cross brace 141 are still connected to the stability and buoyancy columns 201, 202, and 203. However, the stability and buoyancy columns 201, 202, and 203 do not have to be arranged vertically from the floating body according to the conventional form, but can be arranged obliquely.

[0124] The terms used in this document are intended to illustrate specific examples and are not intended to limit the present invention. Unless the context otherwise indicates, when the singular "a", "the", etc. are used in this document, the plural form is also included. In addition, when the words "comprise", "include", etc. are used in this document to describe certain features, integers, steps, operations, elements, and / or components, it does not exclude that other features, integers, steps, operations, elements, and / or components may also be included.

[0125] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as those known in the industry related to the present invention. In addition, unless otherwise specified, the terms used in the text should be consistent with the context and the understanding of the industry, and should not be understood as an idealized or overly literal meaning.

[0126] The foregoing describes the principles of the present invention, the recommended examples and the method of assembly. However, this description is a demonstration rather than a limitation of the present invention, and it should not be understood that the present invention is limited to the above examples. In addition to the specific description herein, the present invention can also be implemented by combining the different features in the various examples and methods.

[0127] Legend number list

[0128] 1: Offshore semi-submersible platform

[0129] 2: Water / seawater waterplane

[0130] 10: First hull assembly

[0131] 11: First floating body

[0132] 12: Second floating body

[0133] 13: The inner end of the second float

[0134] 14: The outer end of the second float

[0135] 20: Second hull assembly

[0136] 30: Transport combination

[0137] 50: Close the water jacket

[0138] 111: Bottom of the first floating body

[0139] 113: First floating deck

[0140] 115: Circular part of the outer plate of the first buoy

[0141] 118: Horizontal plate with added mass and motion damping

[0142] 121: Bottom of the second floating body

[0143] 122: Side of the second floating body

[0144] 123: Second floating deck

[0145] 125: Circular part of the outer plate of the second buoy

[0146] 126: Second buoy watertight bulkhead

[0147] 128: Horizontal plate with added mass and motion damping

[0148] 131: Triangular floating structure

[0149] 141: Lower horizontal brace

[0150] 201: Stable Floating Column

[0151] 202: Stable Floating Column

[0152] 203: Stable Floating Column

[0153] 212: Vertical bulkhead in column

[0154] 221: Independent column

[0155] 241: Upper horizontal brace

[0156] 291: Equilateral triangle

[0157] 292: Isosceles triangle

[0158] 301: Wind turbine equipment / wind energy utilization device

[0159] 302: Fan equipment support structure

[0160] 303: Horizontal brace

[0161] 401: Mooring turret

[0162] 500: Transport Ship

[0163] A: Stern

[0164] B: Float width

[0165] D: column diameter

[0166] F: Bow

[0167] J: Interface between the inner and outer ends of the second buoy

[0168] L: Length of the inner end of the second buoy

[0169] T: shape of the underwater hull / float

Claims

1. A semi-submersible platform (1) positioned in water, which utilizes wind energy to produce electrical energy, the semi-submersible platform (1) comprising: A submersible underwater hull, Three or more columns (201, 202, 203) supported and interconnected by the underwater hull and protruding above the water surface, when the semi-submersible platform (1) is positioned in the water: At least three of the above columns (201, 202, 203) are stable floating columns. At least one wind energy utilization device (301) is installed on a support structure (302) located on a column (201, 202, 203). Features: The underwater hull is composed of a first floating body and a second floating body (11, 12) in a long strip shape; The two ends of the first floating body support and connect the lower ends of two stability columns (202, 203); The second floating body (12) is substantially perpendicular to the first floating body (11) and is connected to the middle of the length of the first floating body; The outer end of the second floating body (12) supports and is connected to the lower end of the third stability column (201), and the outer end of the second floating body (12) is opposite to the intersection end of the first floating body. The first floating body and the second floating body (11, 12) are in the shape of a letter "T" in a horizontal plane, wherein a stabilizing column (201, 202, 203) is arranged near each of the three ends of the "T" shape. The first hull assembly (10) is connected to the outer end of the second buoy (12) to form a second hull assembly (20), wherein the first hull assembly is composed of a first buoy (11), two stabilizing columns (202, 203), and a buoyant inner end (13) of the second buoy (12), wherein the length (L) of the buoyant inner end (13) of the second buoy should be able to enable the first hull assembly (10) to float stably, and the size of the outer end of the second buoy (12) should also be able to enable it to float roughly stably.

2. The semi-submersible platform (1) according to claim 1, characterized in that: Its two buoys (11, 12) have a generally quadrilateral cross-section, having two side surfaces, a bottom surface and a deck surface.

3. The semi-submersible platform (1) according to claim 2, characterized in that: Its two floats (11, 12) have approximately equal heights at their junction.

4. The semi-submersible platform (1) according to claim 3, characterized in that: A triangular floating structure (131) having approximately the same height as the two floating bodies (11, 12) is arranged on both sides of the intersection of the second floating body (12) and the first floating body (11).

5. A semi-submersible platform (1) according to any one of the preceding claims, characterized in that: The top ends of the columns (201, 202, 203) are connected by an upper cross brace (241), and the cross brace extends into the interior of the columns.

6. The semi-submersible platform (1) according to claim 5, characterized in that: The first floating body (11) and the second floating body (12) are connected via two lower cross braces (141), one end of the cross brace is connected to the two outer ends of the first floating body (11), and the other end of the cross brace is connected to the outer end of the second floating body (12), and the position of the lower cross brace is much lower than the upper cross brace (241).

7. The semi-submersible platform (1) according to claim 6, characterized in that: The two lower cross braces (141) are located at the deck height of the two floating bodies (11, 12).

8. The semi-submersible platform (1) according to claim 6, characterized in that: Each column (201, 202, 203) is provided with a vertical bulkhead (212) aligned with the lower cross brace (141) and connecting the upper cross brace (241) and the lower cross brace (141).

9. The semi-submersible platform (1) according to claim 1, characterized in that: The centers of the three stabilizing and buoyant columns (201, 202, 203) roughly form an equilateral triangle.

10. The semi-submersible platform (1) according to claim 1, characterized in that: The three stabilizing buoyant columns (201, 202, 203) have a circular cross section.

11. The semi-submersible platform (1) according to claim 10, characterized in that: The outer surfaces of the three stabilizing buoyancy columns (201, 202, 203) extend downward to the bottoms of the two floating bodies (11, 12), forming a circular end at the outer ends of the floating bodies.

12. The semi-submersible platform (1) according to claim 11, characterized in that: The width of the first and second buoys (11, 12) is substantially equal to the diameter of the stabilizing buoyancy column (201, 202, 203) multiplied by the square root of 3 / 2 (B = D *√ 3 / 2).

13. The semi-submersible platform (1) according to claim 11, characterized in that: The width of the first floating body (11) is approximately equal to the diameter of the stability column (202, 203) supported thereon multiplied by the square root of 3 / 2 (B1 = ), and the width of the second floating body (12) is approximately equal to half the diameter of the stability column (201) supported thereon (B2 = D1 / 2).

14. The semi-submersible platform (1) according to claim 1, characterized in that: Horizontal plates (118) for adding additional mass and motion damping are located at the bottom of both ends of the first floating body (11).

15. The semi-submersible platform (1) according to claim 14, characterized in that: Horizontal plates (118) for adding additional mass and motion damping at both ends of the first floating body are installed on the same side of the first floating body (11) that is close to the second floating body, so that the horizontal plates (118) for adding additional mass and motion damping will not significantly increase the length of the first floating body (11).

16. The semi-submersible platform (1) according to claim 15, characterized in that: The distance between the horizontal plate (118) on the first floating body (11) for adding additional mass and motion damping and the second floating body (12) or the triangular floating body structure (131) should be at least equal to the width of the second floating body (12).

17. The semi-submersible platform (1) according to claim 1, characterized in that: Near the outer end of the second floating body (12), a horizontal plate (128) is installed to increase additional mass and motion damping.

18. The semi-submersible platform (1) according to claim 1, characterized in that: A wind energy utilization device (301) is installed on a vertical support structure on one of the two columns (201, 221), and the column may be a stable floating column.

19. The semi-submersible platform (1) according to claim 18, characterized in that: The platform (1) floats under a catenary mooring system.

20. The semi-submersible platform (1) according to claim 18, characterized in that: The platform (1) floats under mooring by a tensioned mooring system.

21. The semi-submersible platform (1) according to claim 18, characterized in that: The platform (1) is moored by a tension tendon mooring system, one end of the tension tendon is connected to the seabed.

22. The semi-submersible platform (1) according to claim 1, characterized in that: Two wind energy utilization devices (301) are installed on a support structure (302) on stable buoyancy columns (202, 203) located at both ends of the first floating body (11).

23. The semi-submersible platform (1) according to claim 22, characterized in that: The two support structures (302) are inclined outward in opposite directions and are substantially parallel to the center line of the first floating body (11).

24. The semi-submersible platform (1) according to claim 23, characterized in that: The upper ends of the two supporting structures (302) are connected by a horizontal cross brace (303).

25. The semi-submersible platform (1) according to any one of claims 19 to 21, characterized in that: The mooring system is connected to a mooring turret, and the semi-submersible platform can rotate around the turret to make the wind energy utilization device (301) face a favorable wind direction.

26. The semi-submersible platform (1) according to claim 25, characterized in that: The turret is located below the outer end of the second floating body (12).

27. A method for assembling a semi-submersible platform (1) designed according to any one of the above claims, the method comprising: The first hull assembly (10) is connected to the outer end of the second buoy (12) to form a second hull assembly (20), wherein the first hull assembly is composed of a first buoy (11), two stabilizing columns (202, 203), and a buoyant inner end (13) of the second buoy (12), wherein the length (L) of the buoyant inner end (13) of the second buoy should be able to enable the first hull assembly (10) to float stably, and the size of the outer end of the second buoy (12) should also be able to enable it to float roughly stably.

28. The method according to claim 27, comprising: Before connection, the outer ends (14) of the first hull assembly (10) and the second buoy (12) are positioned in the water body (2) to achieve substantially stable upright floating and maintain substantially the same draft and trim, so as to facilitate docking.

29. The method according to claim 27 or 28, wherein the first hull assembly (10) is connected to the outer end (14) of the second buoy (12) by docking the outer end (14) of the second buoy (12) with the buoyant inner end (13) of the second buoy (12).

30. The method of claim 27, wherein the first hull assembly (10) is connected to the outer end (14) of the second buoy (12) by welding.

31. The method according to claim 30, wherein the welding of the lower end of the joint is performed in a closed water jacket (50) arranged along the joint and drained of water.

32. The method according to claim 27, wherein the second hull assembly (20) floats stably in the water, and the remaining components of the semi-submersible platform (1) are constructed on top of the second hull assembly (20) to form a complete semi-submersible platform (1).

33. The method according to claim 27, wherein the first hull component (10) is constructed at a first construction site and then transported to a second construction site to assemble the second hull component (20).

34. A method for transporting at least two underwater hulls of a semi-submersible platform (1) based on claim 1 from a first construction site to a second construction site by a sea vessel (500), wherein the first buoys (11) of the two first hull assemblies are arranged in one direction, and the inner end (13) of at least the second buoy (12) connected to the first buoy (11) is arranged in a direction substantially perpendicular to the arrangement direction of the first buoy (11), and the two underwater hulls are opposite to each other so that the inner end (13) of the second buoy (12) of one of the hulls points to the first buoy (11) of the other underwater hull, and vice versa.

35. The method according to claim 34, wherein the two second buoys (12) of the two underwater hulls are each divided into two parts, wherein the inner end (13, 13a) is connected to the corresponding first buoy (11, 11a), and the other part forms an independent outer end (14, 14a), and the two underwater hulls are arranged in opposite directions in the following manner: the inner end (13) of the second buoy connected to one underwater hull protrudes toward the inner end (13a) of the second buoy connected to the other underwater hull, and the outer ends (14, 14a) of the independent parts of the two underwater hulls are respectively arranged on both sides of the two inner ends (13, 13a) connected to the corresponding underwater hulls.

36. The method of claim 35, wherein the buoys and buoy components of the two underwater hulls are connected to form a transport assembly (30) that can stably float upright.

37. The method according to any one of claims 34 to 36, wherein the two underwater hulls are arranged on the transport vessel in the following manner: the two first buoys (11, 11a) are arranged across the longitudinal axis of the vessel.

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