Disconnectable mooring system

Abstract

A disconnectable mooring system for a semi-submersible floating structure at sea. The disconnectable buoy has a plurality of mooring lines including a buoy chain between a mooring chain and the buoy. The mooring chain and the buoy chain are connected via a three-way mooring connector, wherein the third connection is configured to pull the mooring connector to a mooring point on the structure. In a first configuration, the buoy is disconnected and supports the mooring chain to be pulled in for recovery at a shallow. In a second configuration, the mooring lines are pulled in via the mooring connector, thereby providing the structure with a deployed mooring, wherein the buoy chain remains as a catenary between the buoy and the mooring point.

Description

Technical Field

[0001] The present invention relates to mooring systems for semi-submersible floating structures at sea, and particularly, but not exclusively, to detachable mooring systems for floating offshore wind turbines. Background Technology

[0002] Wind power is a recognized and widely used renewable energy source. Offshore locations are now being sought for wind turbines because they offer higher wind energy output and fewer space constraints compared to those located onshore. The first offshore wind turbines were built on monopile foundations buried in the seabed. The use of jackets was developed; these jackets are foundations constructed similarly to steel grating structures typically resting on four piles, as they are more robust than foundations at greater depths and for certain types of subsurface rock. Compared to jackets, floating offshore wind turbines (FOWTs) are now used to access deeper waters and reduce construction costs.

[0003] FOWTs are expected to disassemble at multiple points during their service life. This is particularly true due to the increased size and height of the turbines, resulting in greater movement at the nacelle level and complicating major repairs at sea. This is further complicated by the fact that the water is often too deep for jack-up cranes anchored to the seabed, necessitating the use of floating crane vessels. Movement at the top of the crane of a floating crane is significantly greater than that of a jack-up crane. When the turbine is attached to the shroud, this movement is significantly less or negligible because the shroud is anchored and secured to the seabed.

[0004] Figures 1a and 1c illustrate the prior art of a typical arrangement of a multi-post semi-submersible FOWT on its deployed moorings. Figure 1a shows the semi-submersible platform 4 connected to mooring cables 20a, which are anchored to anchors on the seabed. This deployed mooring arrangement allows each mooring cable to be individually connected to the equipment and held in a fixed heading at every turn. For clarity, only three mooring cables are shown; however, in design, up to six to nine mooring cables are typically required. The dynamic power cable riser 10 is shown as a wave-dipping profile with buoys 12. Figure 1b The arrangement is shown in a front view.

[0005] Detail 1c shows a typical arrangement for pulling the mooring cable from the top of the column using a winch 13, which steers around a pulley 14 and passes through a female connection arrangement 15 on the semi-submersible platform. The winch is connected to the end of the mooring connector 16, and the winch cable is disengaged when fully engaged.

[0006] A range of types of mooring connectors exist that can be used as existing technologies; therefore, the designs shown are for illustrative purposes only.

[0007] This arrangement is typical not only in semi-submersible platforms but also in a range of other moored floating structures and vessels.

[0008] The disadvantage of these arrangements is that separating and reconnecting offshore FOWTs is a lengthy and costly operation, as they typically have three to nine mooring cables and, typically, two dynamic power cables. Connecting the mooring cables and power cables involves individually positioning, measuring, lifting, and connecting the end of each cable to the FOWT. During this time, the FOWT must be held in place by a tugboat. Hook-up can be a long and difficult process, especially in deep water or if the area is congested with platforms, ships, or other floating structures and their moorings. The traction of the dynamic power cables is performed after the mooring hook-up is completed, and the cable hook-up itself can be lengthy, with the risk of damage.

[0009] Other floating vessels (such as ships) use turret mooring systems for single-point mooring (SPM), where the mooring line reaches a center point, and the ship rotates around that center point via a swivel. Turret mooring systems are typically used in harsher environments where the load on the mooring system can be reduced by allowing the ship to yaw or face the windward side. US2007 / 0264889 discloses a detachable underwater turret buoy that provides single-point mooring (SPM) for a ship. The buoy has a mooring attachment point in a radius significantly smaller than the ship's width and much smaller than its length, and the buoy is pulled in and secured to the ship. The turret is stationary relative to the ground, and the ship changes its bearing around the turret in response to the rotation of wind, waves, and currents.

[0010] WO2016069636 discloses a detachable buoy system for FOWT. In this system, power cables are supported by buoys, while mooring lines are connected in a standard, deployed mooring arrangement, detached from the buoys and individually connected to each post. A disadvantage of this arrangement is that the power cables must hold the detachable buoy in place when it detaches, but not damaged by its movement. Furthermore, the weight of the cables limits the size of the buoys in deep water and presents limitations in offshore operations.

[0011] Since each corner of a semi-submersible floating structure can be separated by 50m to 150m, using diving turret buoys of such a large size is impractical. Current detachable turret buoy designs would only connect to a single point on the semi-submersible platform, and therefore the asymmetrical structure would likely rotate around this point, twisting the mooring components and cables around each other unless swivels are incorporated, which significantly increases cost and complexity. If swivels are incorporated, the semi-submersible platform changes orientation with the wind, thus interfering with the swivels located on the turbine nacelle to orient the blades toward the optimal course.

[0012] Therefore, the object of the present invention is to provide a detachable mooring system for semi-submersible floating structures at sea, which eliminates or mitigates one or more disadvantages of the prior art. Summary of the Invention

[0013] According to a first aspect of the present invention, a detachable mooring system for a semi-submersible floating structure at sea is provided, comprising:

[0014] A buoy, comprising a connecting structure and components separate from the structure;

[0015] Multiple mooring lines;

[0016] Each mooring cable includes a mooring chain having a first end that is attached to an anchor on the seabed;

[0017] At least one mooring line also includes a buoy chain, a first end of which is connected via a mooring connector to a second end of the mooring chain, and the second end of the buoy chain is connected to a buoy;

[0018] In use: In the first configuration, the buoy is separated from the structure, and the buoy chain supports the mooring chain, thereby preventing the mooring connector from contacting the seabed; and

[0019] In the second configuration, the buoy is connected to the structure, and the mooring chain is pulled into the mooring point on the structure via the mooring connector to tension the mooring chain, thereby providing the structure with an extended mooring element, wherein the buoy chain is in the form of a catenary.

[0020] In this way, mooring chains can be arranged from the mooring points around the structure in the same pattern as the deployed mooring elements. The advantage is that each mooring chain is also attached to a detachable buoy and therefore only needs to be pulled in from shallow water depths. Although the term "chain" is used, it should be understood that it can refer to rope, cable, or cord element or any element that forms part of a standard mooring line.

[0021] Preferably, the device used to connect and disconnect the detachable buoy from the structure is non-rotatable. In this way, the mooring system prevents the structure from changing orientation with the wind and is less expensive than other turret buoy systems.

[0022] Preferably, in this second configuration, mooring tension on the buoy is applied from no more than one side of the buoy. In the presence of a buoy chain, no tension is applied from the mooring lines to the buoy, as the tension is instead applied to the mooring point. In this embodiment, all mooring lines include buoy chains. In this way, no mooring tension is applied to the buoy.

[0023] At least one mooring line may be present, wherein the second end of the mooring element is directly connected to the buoy, and this mooring line provides mooring tension to the buoy. Preferably, only one such mooring line exists on the buoy. Alternatively, multiple such mooring lines may exist, but they are all connected to the buoy only on one side. In this way, mooring tension is applied to the buoy from a first direction. Multiple such mooring lines may be located on one side of the buoy and provide mooring tension in an arc of less than 180 degrees. More preferably, the arc is less than or equal to 130 degrees. The arc may be less than or equal to 90 degrees. The arc may be less than or equal to 45 degrees. Preferably, two mooring lines consisting only of mooring chains exist. Environmental forces act on the buoy only via the mooring element on one side of the buoy.

[0024] Preferably, the mooring connector is a tee connector that provides a first connection to the mooring chain, a second connection to the buoy chain, and a third connection for connecting to a mooring point on the structure.

[0025] In one embodiment, the third connector provides a mating connector for connection to a winch or other similar pulling device. In this way, the third connector is identical to prior art devices for connecting and pulling the mooring line in a second configuration. The mooring chain and connector for the third connector may be collinear with a second connector perpendicular to the first and third connectors. Alternatively, each connector provides a pivot such that the mating connector will occupy a position according to the tension applied at each connector. In this way, the mooring line can be pulled using known methods.

[0026] The mooring line, including at least one buoy chain, may further include a second mooring chain having a first end connected to an anchor on the seabed and a second end connected to a mooring connector. Additionally, at least one mooring line includes a buoy chain, and may further include a third mooring chain having a first end connected to an anchor on the seabed and a second end connected to a mooring connector. In this way, a single buoy chain and mooring connector can be used to pull multiple mooring chains into the mooring point. It should be understood that the mooring connectors will be either four-way connectors or five-way connectors.

[0027] More than one mooring chain can be attached to a single anchor on the seabed. In this way, mooring cables from a single anchor can be located at different mooring points on the structure.

[0028] In use, the buoy is fully submerged in both the first and second configurations. The buoy can be attached to the underside of the structure. The underside can be the keel. In this way, the buoy can be considered as a plug located below the structure and attached to any column base or center point of the structure. The buoy will have dimensions much smaller than the structure itself. Alternatively, in use, the buoy can be partially submerged in both the first and second configurations. The buoy can be clamped to the side of the structure. The buoy can be clamped to a column of the structure. Single-column, mast-mounted floating structures are particularly suitable for buoys clamped to the side. In this way, the buoy always pierces the water surface upon separation, making it easily identifiable when the structure surfaces for mooring. The buoy's position in the water can be controlled by the length of the mooring cable calculated for weight and depth, or by the buoy's ballast.

[0029] Preferably, the buoy chain is lighter than the mooring chain. Lighter gauge chains can be selected for the buoy chain because they do not bear tension when the structure is moored.

[0030] Preferably, the buoy also includes connectors for cables. The cables can be used to transmit electrical or communication signals. The buoy may also include connectors for risers. Flexible risers can be used to transport fluids or gases. In this way, the power cables and / or risers can be internally hooked to internal components or top-side facilities on the structure. More preferably, a manifold is provided on the buoy. In this way, continuity between two or more risers can be achieved when the buoy is separated. This is particularly advantageous for floating offshore wind applications, where breaks in the circuit would otherwise occur when the ends of the cables are laid separately on the seabed.

[0031] Preferably, the floating semi-submersible structure is a multi-post floating semi-submersible structure. In this way, mooring points can be located on each post, although a post may alternatively have a buoy attached to it. However, any floating structure with a large size that causes a change of orientation with the wind direction, such as a ship, vessel, barge, or mast, can be considered. Preferably, the floating semi-submersible structure also supports a wind turbine.

[0032] Multiple buoys may be attached to the floating semi-submersible structure, with buoy chains connecting them together. In this way, if cables / dynamic risers are required across the structure, the buoys can be positioned at any location, where the buoys maintain their relative positions when in their initial configuration.

[0033] According to a second aspect of the present invention, a method for mooring a semi-submersible floating structure at sea is provided, comprising the following steps:

[0034] Provide a separable mooring system according to the first aspect;

[0035] Connect the buoy to the structure;

[0036] Pull the mooring connector into the mooring point on the structure to tension the mooring chain on each mooring cable, which also includes a buoy chain;

[0037] And this causes the mooring cables to spread out around the structure.

[0038] The method may include fully or partially submerging the buoy. In step (b), the buoy may be attached to the underside of the structure or clamped to one side of the structure.

[0039] The method may include further steps of separating the detachable mooring system from the semi-submersible floating structure at sea. The separation steps may include releasing the detachable mooring system in a controlled manner by lowering the mooring lines and buoys using a winch or other methods known in the art. Alternatively, the separation steps may include releasing the detachable mooring system via an emergency release method, wherein the mooring connectors and buoys fall to their equilibrium depth under gravity. This has the significant advantage of allowing for rapid separation of the mooring system, while the mooring components, buoys, and cables remain in a safe configuration ready for effective reconnection. Attached Figure Description

[0040] In the following description, the drawings are not necessarily drawn to scale. Certain features of the invention may be shown enlarged to scale or in a slightly schematic manner, and for clarity and brevity, some details of conventional elements may be omitted. It should be fully appreciated that the different teachings and features of the embodiments discussed below can be used individually or in any suitable combination to produce the desired results.

[0041] Therefore, the accompanying drawings and descriptions are intended to be illustrative rather than restrictive. Furthermore, the terminology and wording used herein are for descriptive purposes only and should not be construed as limiting the scope of protection.

[0042] Different embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0043] Figure 1a Figure 1b Figure 1c is an illustration of a mooring system for a semi-submersible floating structure at sea, based on the prior art;

[0044] Figure 2a , Figure 2b Figure 2c is an illustration of a mooring system for a semi-submersible floating structure at sea, shown in a second configuration according to an embodiment of the present invention;

[0045] Figure 3a , Figure 3b Figure 3c is an illustration of a first configuration according to an embodiment of the present invention. Figure 2a , Figure 2b A diagram of the mooring system in Figure 2c;

[0046] Figures 4a to 4f It shows that Figure 2a The steps in Figure 2c for connecting the mooring system from the first configuration to the second configuration;

[0047] Figure 5a Figure 5b Figure 5c and Figure 5d It shows Figure 2a , Figure 2b And the buoys in the mooring system of Figure 2c;

[0048] Figure 6a and Figure 6b This is an illustration of a mooring system for a semi-submersible floating structure at sea, shown in a second configuration according to a further embodiment of the present invention.

[0049] Figures 7a to 7e Further embodiments of the mooring system according to an embodiment of the present invention are shown;

[0050] Figure 8a , Figure 8b and Figure 8c A further embodiment of the mooring system according to an embodiment of the present invention is shown;

[0051] Figure 9a and Figure 9b A further embodiment of the mooring system according to an embodiment of the present invention is shown;

[0052] Figure 10a , 10b 10c illustrates a single-column semi-submersible structure with a buoy connected to the side of the structure according to an embodiment of the invention; and

[0053] Figure 11a and Figure 11b This is an illustration of a mooring system for a semi-submersible barge-shaped floating structure at sea, according to an embodiment of the present invention. Detailed Implementation

[0054] First, refer to the embodiments according to the present invention. Figure 2a Figure 2c shows the mooring system, generally indicated by reference numeral 11, which is connected to the semi-submersible floating structure 4 at sea. The system 11 includes buoys 24 and mooring lines 20a to 22c with buoy chains 22b and 22c.

[0055] In Figure 2, the semi-submersible floating structure 4 is a three-post semi-submersible structure, situated and floating in the sea, interrupting the waterline 2. Although a three-post semi-submersible structure is shown, the semi-submersible floating structure can be any floating structure supporting the wind turbine 6. Multi-post semi-submersible platforms are typically selected as shown in the prior art Figures 1a to 1c. Buoys 24 are connected to the underside of the outer posts or keel of the semi-submersible platform 4, and mooring cables 20a to 20c are connected to the semi-submersible platform 4 via buoys 24.

[0056] Figure 2a An arrangement similar to the prior art shown in Figures 1a-1c is illustrated, wherein the turbine 6, the semi-submersible platform 4, and the mooring cables 20a-20c are of the same size. In the plan view, there are few obvious differences except for the additional mooring cables or “buoy cables,” which we will refer to as buoy chains 22b and 22c below the semi-submersible platform 4. Mooring cable 20a is a mooring chain anchored at a first end to the seabed 21 and connected to a buoy 24 at a second end. Mooring cable 20a is known in the art, and although called a mooring chain, it can be a chain, rope, cord, or any other similar cable used for anchoring in a mooring system. Mooring cables 20b and 20c are also mooring chains, also anchored at a first end to the seabed 21. At the second end, they are connected to a mooring connector 18, which in turn connects to buoy chains 22b and 22c. Again, although referred to as mooring links or buoy chains, these can be chains, cables, ropes, cords, or any other similar cords used for anchoring in a mooring system. The other end of buoy chains 22b, 22c is connected to buoy 24. Mooring connector 18 is a tee connector because, in addition to connecting to mooring chains 20b, 22c and buoy chains 22b, 22c, it also has a prior art connection for pulling the mooring cable from the top of the post using winch 13, turning it around pulley 14, and passing it through the female connection device 15 on the semi-submersible platform 4 at mooring points 25b, 25c.

[0057] Figure 2b A front view of the same arrangement is shown, wherein mooring cable 20a is connected to a detachable buoy 24, which is connected to the keel of a semi-submersible platform in a column. Mooring cables 20b and 20c are connected to the semi-submersible platform at mooring points 25b and 25c; however, an additional buoy cable 22b is shown as a connection point from the buoy to the semi-submersible platform for the main mooring cables, or mooring points 25b and 25c.

[0058] Detail 2c shows that the mooring connector 18 has a different design for connecting the "buoy line" or buoy chains 22b, 22c. The winch, pulley, and pull-in mechanism of the female connector remain essentially unchanged, with connector 18 mating with a receiver at the structural mooring point. Mooring chain 20 will bear the environmental load on the semi-submersible platform via connector assembly 15 / 18, and buoy chains 22b, 22c will be suspended to buoy 24 in a slack catenary configuration. In this figure, the buoy chain is shown as smaller than the mooring chain because it does not bear a large environmental load in use.

[0059] Buoy 24 can be easily attached / detached from the semi-submersible hull and supported by moorings 20 and power cables 10 in deeper water; however, the requirement for rotation is avoided by controlling the course of the semi-submersible platform 4. Furthermore, when the buoy is pulled into the keel of the structure, if the top of the buoy is above the water level, or if the internal compartments can be made waterproof, the power cables can be connected to the structure's electrical system without any handling of the dynamic power cables, representing a significant safety improvement along with cost reduction.

[0060] When connected to structure 4, buoy 24 transmits mooring loads from a limited directional arc, typically only from mooring cables 20b and 20c connected within this arc. Therefore, buoy 24 experiences mooring tension only from one direction, i.e., mooring cable 20a is directly connected to the seabed 21. When mooring chains 20b and 20c are pulled into mooring points 25b and 25c on structure 4 via mooring connector 18, the mooring load on cables 20b and 20c is directly borne by structure 4, and buoy chains 22b and 22c are redundant. As mooring chains 20b and 20c are pulled in to tension mooring cables 20a to 20c, the semi-submersible platform 4 is moored in the same deployed mooring arrangement as in the prior art (Figures 1a to 1c).

[0061] Moorings 20b and 20c and buoy chains 22b and 22c will be continuous cables with connectors between each section, each section itself connecting to the semi-submersible platform 4 at mooring points 25b and 25c.

[0062] Figure 3 illustrates the arrangement of the now-separated buoys 24 in a submerged state before or after the arrival of the semi-submersible platform 4. The separated buoys 24 can be considered as the first configuration of the mooring system 11, and the buoys 24 connected to the structure 4 (such as...) Figure 2a (As shown in Figure 2c) is considered the second configuration.

[0063] Figure 3a The first configuration is shown in a plan view in a separated state, including buoy 24 and mooring lines 20a to 20c. Mooring lines 20b and 20c are connected to the buoy via "buoy lines", that is, via buoy chains 22b and 22c and mooring connectors 18b and 18c.

[0064] Figure 3b The arrangement is shown in a front view, which shows buoy 24 lowered into the water to avoid passing over the ship's keel. Mooring cable 20b is in a similar catenary configuration to buoy cable 22b, and therefore the arrangement is stable in the water without the need to lower any mooring cables or power cables to the seabed 21.

[0065] Detail 3c shows connector 18 in its detached state within the mooring catenary and rotated approximately 90 degrees from its connection orientation. By making the connections of mooring chains 20b, 20c and buoy chains 20b, 20c to mooring connector 18 pivotal, each can rotate relative to the other, mooring connector 18 can be rotated to change the angle between the connected elements. Buoy chain 22 is shown in a smaller specification because it only bears the weight of mooring cable 20 and the seabed environmental forces on the detachable buoy 24. By reducing the size of the buoy chain, this also reduces the buoyancy required by the detachable buoy 24, thereby further reducing costs.

[0066] Therefore, when buoy 24 is disconnected, it allows support for all mooring cables 20a to 20c by being directly connected to buoy 20a or supported via short "buoy" chains 22b and 22c, which are redundant when the semi-submersible platform 4 is fully connected.

[0067] When disconnected from a semi-submersible platform, the buoyancy required to keep the mooring cables and power lines in the water is reduced due to lower pretension by introducing an additional length of "buoy chain" into the mooring cable chain.

[0068] Now refer to the attached diagram. Figures 4a to 4f It shows a typical procedure in which buoy 24 is pulled into semi-submersible platform 4 and each mooring cable 20b, 20c is connected to the structure to achieve a permanent mooring state. Figures 4a to 4f The method of connecting buoy 24 and mooring lines 20a to 20c to the semi-submersible platform 4 is shown. For clarity, the dynamic riser 10 is not shown and only two mooring lines are shown in the sketch; however, the same method is generally used when there are more than two mooring lines (e.g., 3, 6, 8, 9, 12, 15 or 16).

[0069] Figure 4aA buoy 24 is shown below the semi-submersible platform 4, with a winch 34 on one of the posts, the winch cable passing through the post and connected to the buoy 24 below the keel. A mooring cable 20a is connected to the seabed anchor and the buoy. A mooring cable 20b is connected to the seabed anchor via a mooring connector 18b and to a buoy chain 22b. The buoy chain 22b is connected to the buoy 24. To support the docking operation, a support vessel 30 is positioned nearby, and the support vessel 30 has a backup remotely operated vehicle (ROV) 32.

[0070] Figure 4b The buoy 24 is shown being pulled into the semi-submersible platform 4. The mooring cable 20a is now under slightly higher tension and is connected to the semi-submersible platform 4 via the buoy 24.

[0071] Figure 4c The repositioned winch 34 is shown to allow the mooring component to be pulled into the semi-submersible platform. The winch cable 36 has been lowered from the winch to the vicinity of the mooring connector 18b. An ROV 32 from the support vessel 30 is used to connect the winch cable to the mooring connector 18b to allow pull-in into the semi-submersible platform 4.

[0072] Figure 4d The diagram shows the winch rope 36 connected to the mooring connector 18b and the initial pull into the semi-submersible platform 4. As the winch rope 36 is pulled in, the tension in the mooring cable 20b increases and the tension in the buoy chain 22b decreases. At this point, the angle of the mooring connector 18b becomes more vertical. That is, it moves from the position shown in Figure 3c to the position shown in Figure 2c.

[0073] Figure 4e The mooring connector 18b is shown near its final position. At this point, most of the tension is on the mooring cable 20b and the pulled-in winch rope 36, while the buoy chain 22b is suspended slack. The angle of the mooring connector 18b has now exceeded the vertical direction and is close to its final connection angle. One of the key features of this arrangement is that the angle of the mooring connector 18b can be oriented relatively easily relative to the pulled cable, making it easier not only for the winch rope to connect to the seabed but also avoiding the need for the anchor to be maneuvered by the vessel with high force to assist in the connection. This significantly reduces dependence on high tension and vessel position, and offers significant advantages in reducing operational risks and fuel consumption.

[0074] Figure 4fThe mooring connector 18b is shown, pulled into the semi-submersible platform and engaged at mooring point 25b, ready to disconnect the pulled-in winch cable. The winch cable and winch can now be repositioned to other mooring cables for connection. Upon completion of the mooring cable hooking, the dynamic risers (multiple dynamic risers) can be pulled short within the structure from the top of the buoy to their final position, or connected to the shipboard system without any further pull-in, thus completing the mooring and riser hooking.

[0075] The system and method of this invention advantageously demonstrate that mooring lines and risers can be pulled in from shallow water depths instead. Therefore, the pulling operation is relatively short and eliminates the need for retrieval from the seabed, which can be a lengthy process accompanied by the risk of mooring line twisting, restricted navigation, and maintaining clearance from other subsea infrastructure. Consequently, the required winch size and rope length are much smaller.

[0076] Compared to picking each mooring cable from the seabed, load transfer is more gradual and controllable. All mooring cables are already under tension, roughly in their final bearing, without twisting, and off the seabed, allowing the vessel greater freedom to perform pull-in maneuvers in its course. Typically, it must be precise regarding the pull-in position.

[0077] After mooring is completed, the cables or risers already attached to the buoy can be hooked inside and onto the top side facility. Cables can transmit power, communication signals, etc., while risers can transmit fluids, gases, or other cables.

[0078] It should be recognized that the mooring system 11 can be detached, allowing the arrangement to be switched from the second configuration (see...). Figure 2a (Refer to Figure 2c) Return to the first configuration (see Figure 2c) Figure 3a (See Figure 3c). This separation can be achieved by controlling the release of the winch in a manner known to those skilled in the art. However, in this invention, there is an opportunity to make the mooring system 11 an emergency / overspeed separation from the system by remotely releasing the cables / rises and mooring equipment from the connector of the mooring system. The sudden release of the mooring lines and buoys will cause the mooring lines to fall into the water under gravity to their equilibrium position, becoming the first configuration arrangement, without any mechanical descent device.

[0079] With minimal vessel movement and minimal or no handling of long mooring cables to / from the seabed, hooking and disconnecting operations are significantly shorter and safer, thus reducing the risks and costs associated with hooking and disconnecting FOWTs.

[0080] Now refer to Figures 5a to 5b. Figure 5d An embodiment of a detachable buoy is shown, illustrating the configuration of mooring lines and dynamic riser / power cables when detached from the keel of a semi-submersible platform.

[0081] Figure 5a illustrates the detachable buoy described above, where six mooring lines demonstrate how gaps are typically achieved between adjacent buoy chains 22c to 22f. Buoy 24 is circular with a shortened conical shape. The larger diameter buoy 24, operating on an arc of approximately 120 degrees, provides additional buoyancy to the heavier mooring lines 20a and 20b, which consist only of mooring chains, and provides attachment points for buoy chains 22c and 22f. The mooring chains of mooring lines 20a and 20b are directly connected to the buoy structure. The buoy chains for 22c and 22d, together with 22e and 22f, are further spaced to minimize the risk of collision.

[0082] Figure 5b The buoy is shown in a perspective view, wherein a dynamic riser 10 enters the underside of a buoy 24 with a bending reinforcement 28 to control curvature. The dynamic riser 10 passes through the buoy 24 to reach the upper section, where the dynamic riser can be suspended on top of the I-tube 26. Figure 5c shows the buoy 24, the dynamic riser 10, and the mooring lines 20a, 20b, as well as the buoy chains 22c to 22f from below.

[0083] Figure 5d The buoy is shown in cross-section, from which two risers 10a, 10b enter two I-tubes 26a, 26b to connect together in the manifold assembly 17 to a third riser 10c. The connection between the third riser 10c and the buoy 24 is achieved via connector 19, which is typically intended as a waterproof seal to protect riser 10c when the buoy is lowered into the water. Thus, the power or fluid cables within risers 10a, 10b are connected and protected from breakage during deployment or disengagement. Although two risers 10a, 10b are shown, it should be appreciated that similar connections can be made via manifold 17 for any number of risers and power or fluid cables.

[0084] Figure 6 illustrates an alternative embodiment in which buoy 24 is connected to the underside of the central column or keel of the semi-submersible platform 5, and all mooring cables 20a to 20c are connected to the semi-submersible platform 5 via buoy 24. Figure 6a The semi-submersible platform 5 is shown above. Figure 6b The side elevation with the mooring system 11 fully visible is shown. Buoy 24 is connected to the central post 7 of the semi-submersible platform, and therefore, is located directly below the wind turbine 6 (which facilitates the connection of the power cable 10), a less desirable position for the mooring cable connectors. Therefore, mooring cables 20a to 20c each have buoy chains 22a to 22c and are pulled into mooring points on remote posts, as previously referred to herein. Figures 4a to 4fAs described. When buoy 24 is connected to floating structure 5, buoy chains 22a to 22c are under minimum tension. In the disengaged state, the buoy chains will support the mooring cable via the connector, as... Figure 3a As shown in Figure 3c. In this embodiment, there is no mooring tension applied to buoy 24 from any direction.

[0085] Figures 7a to 7e This arrangement demonstrates how two mooring lines are connected to a single buoy chain and mooring connector.

[0086] Figure 7a and Figure 7e An arrangement of a mooring system in a first configuration according to a further embodiment of the invention is shown. In this arrangement, multiple pairs of mooring chains 20b, 20e and 20c, 20f engage with each other at mooring connector 18. In this respect, each pair also shares a single buoy chain 22b, 22c. This arrangement reduces the number of mooring connectors and buoy chains and further reduces the system's hook-up time. Although two mooring chains are shown connected to each mooring connector, there can be three or more mooring chains. Different numbers of mooring chains can also be present on any connector.

[0087] Figure 7b and Figure 7c The illustration shows typical details of the arrangement of the engagement points of the mooring chains 20b, 20e with the mooring connector 18b, an alternative design using the mooring connector 18b, which includes a triplet 23 that allows for movement of the mooring chains across multiple independent planes. Figure 7d illustrates the arrangement with... Figure 7c The same arrangement and view show the mooring connector 18 being pulled to the mooring point 25 on structure 4.

[0088] See now Figures 8a to 8c This paper illustrates two alternative embodiments of a mooring system using multiple buoys for rapid hook-and-drop, according to a further embodiment of the invention. These arrangements may be preferred when cables / rises need to enter different posts on a semi-submersible platform.

[0089] Figure 8a A plan view is shown of three separable buoys 24a, 24b, 24c connected together by three buoy chains 22a, 22b, and 22c. Each buoy also has mooring chains 20a, 20b, 20c connected to seabed anchors. In this embodiment, the mooring point is on a replaceable buoy. The buoy chains are slightly longer than the distance between each buoy so that when connected to a semi-submersible platform, the buoy chains remain slack, but when all buoys are separated, the buoy chains hold the buoys in an underwater array, thus resisting the horizontal component of tension in the mooring cables.

[0090] Figure 8bThe connection arrangement is shown in a front view, with buoy chain 22b slackly suspended between buoys 24a and 24b. This view is identical in the other two front views of the semi-submersible platform.

[0091] Figure 8c The illustration demonstrates the use of only two buoys, where the position of buoy 24c is replaced by a connector between the two buoy chains 22b and 22c and the mooring chain 20c. This connector can be a mooring connector as shown in Figure 3. Only three mooring lines are shown in this illustration; if a larger number (such as six) is used, mooring lines 20e and 20f can be directly connected to buoys 24b and 24a, respectively.

[0092] These additional buoys eliminate the need to pull in mooring cables when they are already connected to the structure. This use of more than one buoy is particularly advantageous when two power cables are located at different positions on a semi-submersible platform.

[0093] Figure 9a and Figure 9b Alternative mooring arrangements are shown that allow two mooring chains 20a, 20b; 20c, 20d; 20e, 20f to share a single anchor 40a, 40b, 40c, respectively. In the case of multiple FOWTs, arrangements allowing for a further four mooring chains are shown, as illustrated by two pairs of moorings 20g, 20h connected to other FOWTs.

[0094] The mooring system 11 has a wide angle between the mooring chains 20a, 20b; 20c, 20d; 20e, 20f attached to each post, and therefore the mooring connector 18 can be connected to a single mooring chain or to two adjacent mooring chains 20a, 20f, such as... Figure 9b As shown in the diagram. This arrangement demonstrates a very high efficiency in minimizing the installation cost of the anchors, and reduces the duration and risk of hooking to a significantly lower level.

[0095] Figure 10a , Figure 10b and Figure 10c A single-pillar floating structure 42, which may be referred to as a mast, is shown, with a buoy 44 alternatively attached to the side of the pillar. In this arrangement, the buoy is "horseshoe-shaped" to allow the structure to be maneuvered into position and the buoy is mechanically attached to the structure. The principle of the buoy-to-side connection can be similar to that used for semi-submersible multi-pillar structures. Due to the draft of the structure, a preferred safety feature is that the buoy has a section 46 that penetrates the water surface to identify its position and the entry point of the mast. There is no requirement to pull the buoy vertically, as it is primarily a horizontal connection between the buoy and the structure, although some ballast capacity of the buoy is carefully designed to allow for fine adjustment of the buoy's drag and draft.

[0096] Figure 10b The diagram shows an electric cable 10 connected to a buoy 44 and raised above the waterline via a vertical pipe 46. This avoids the need to pull the electric cable vertically and allows for connections in a dry section above the waterline. Navigational aids such as lights and shapers are intended to be mounted on the top of the pipe to notify other surface users of seabed obstacles.

[0097] Figure 10c An alternative arrangement was demonstrated, in which the buoy extends above the waterline. This arrangement would allow for close visual observation of the buoy and structure pairing process, thereby improving the safety of connection and disengagement operations.

[0098] Mooring cables 20a to 20f are shown connected to buoys, allowing structural loads to be transferred via the buoys. Alternatively, the mooring cables can be pulled to hull connectors having the mooring connectors and buoy chain arrangements shown in Figure 2c or Figure 7d. This mooring point to the hull can be above or below the buoy.

[0099] Figure 10b The mooring connectors 25c and 25d shown are attached to the structure above the buoy, with the buoy chains 22c and 22d suspended vertically and slack.

[0100] Figure 10c A mooring connector 25b is shown, illustrated as a structure attached below a buoy, with the buoy chain 22b suspended vertically and slack. This arrangement offers the structural advantage of minimal separation force between the buoy and mast when the mooring cable 20b is environmentally loaded, and a force that pushes the mast into the buoy when the mooring cables 20c and 20b are environmentally loaded.

[0101] Figures 11a to 11b An alternative embodiment is shown in which buoy 24 is connected to the side of barge 5, wherein mooring cable 20a is directly connected to the buoy. Mooring cables 20b and 20c are connected to the structure using connectors 25a and 25b, and are therefore connected to the buoy using buoy chains 22a and 22b, respectively. In this configuration, riser 10 can be connected at the surface deck level; however, a lower-side connection can be achieved in the same way, as shown in Figure 2.

[0102] The main advantage of this invention is that it provides a detachable mooring system for semi-submersible structures at sea, which combines the convenience of "turret" buoys with the desired fixed-course deployment mooring configuration.

[0103] A further advantage of the invention is that the buoy (capable of supporting the power cable) has no rotating or swivel bearings and does not bear environmental loads or only bears loads on one side. Furthermore, if the internal components into which the buoy is pulled can be made impermeable or above the external water level, and electrical or fluid continuity can be provided between each riser or cable, the arrangement can be designed for direct handling of submarine cables.

[0104] A further advantage of the invention is that by suspending the mooring cable away from the seabed buoy and rotating the connector clockwise by approximately 90 degrees to present it at the desired angle, the seabed buoy can be pulled into position within the semi-submersible structure via the connector in the upper portion of the mooring cable, the connector being pulled upwards into the mating connector. Therefore, the pulling-in operation does not require a support tugboat to exert considerable effort to assist in the pulling-in, but is instead completed gradually and in a more controlled manner.

[0105] A further advantage of the invention is that the layout of the mooring system is adapted to its own rapid separation by remotely controlling the release of mooring lines and buoys, reducing the need for personnel on board, while still keeping the mooring components, buoys and risers ready for rapid reconnection.

Claims

1. A detachable mooring system for a semi-submersible floating structure at sea, comprising: A buoy, the buoy comprising a connection to the structure and a device detached from the structure; Multiple mooring lines; Each mooring cable includes a mooring chain having a first end that is attached to an anchor on the seabed; At least one mooring line also includes a buoy chain, a first end of which is connected to a second end of the mooring chain via a mooring connector, and the second end of the buoy chain is connected to the buoy; In use: In the first configuration, the buoy is separated from the structure, and the buoy chain supports the mooring chain, thereby preventing the mooring connector from contacting the seabed; and In the second configuration, the buoy is connected to the structure, and the mooring chain is pulled into the mooring point on the structure via the mooring connector to tension the mooring chain, thereby providing deployment to the structure, wherein the buoy chain is a catenary.

2. The detachable mooring system according to claim 1, wherein, In the second configuration, the mooring tension on the buoy is applied in no more than one direction.

3. The detachable mooring system according to claim 1 or 2, wherein, In at least one mooring cable, the second end of the mooring chain is directly connected to the buoy, and the at least one mooring cable is located on one side of the buoy such that the mooring cable provides mooring tension to the buoy from one side.

4. The detachable mooring system according to claim 1 or 2, wherein, All of the mooring lines mentioned include buoy chains.

5. The detachable mooring system according to any one of the preceding claims, wherein, The mooring connector is a tee connector that provides a first connection to the mooring chain, a second connection to the buoy chain, and a third connection for connecting to the mooring point on the structure.

6. The detachable mooring system according to claim 5, wherein, The third connector provides a mating connector for connection to the pull-in device.

7. The detachable mooring system according to claim 6, wherein, Each connector provides a pivot, such that the mating connector will occupy a position according to the tension applied at each connector.

8. The detachable mooring system according to any one of the preceding claims, wherein, The at least one mooring line also includes a buoy chain, and the at least one mooring line further includes a second mooring chain having a first end connected to another anchor on the seabed and a second end connected to the mooring connector.

9. The detachable mooring system according to any one of the preceding claims, wherein, More than one mooring chain is connected to a separate anchor on the seabed.

10. A detachable mooring system according to any one of the preceding claims, wherein, The buoy is fully submerged in both the first configuration and the second configuration.

11. The detachable mooring system according to claim 10, wherein, The buoy is connected to the lower side of the structure.

12. The detachable mooring system according to any one of claims 1 to 9, wherein, The buoy is partially submerged in both the first and second configurations.

13. The detachable mooring system according to claim 12, wherein, The buoy is clamped to the side of the structure.

14. The detachable mooring system according to any one of the preceding claims, wherein, The buoy chain is lighter than the mooring chain.

15. A detachable mooring system according to any one of the preceding claims, wherein, The buoy also includes connectors for power cables or any flexible riser for conveying fluids or gases.

16. The detachable mooring system according to claim 15, wherein, The manifold assembly is configured as part of the buoy to allow electrical or fluid connections between two or more risers when detached from the structure.

17. A detachable mooring system according to any one of the preceding claims, wherein, The semi-submersible floating structure is a multi-column floating semi-submersible structure.

18. A detachable mooring system according to any one of the preceding claims, wherein, The semi-submersible floating structure supports the wind turbine.

19. A detachable mooring system according to any one of the preceding claims, wherein, The aforementioned semi-submersible floating structure is a single-column floating semi-submersible structure.

20. A detachable mooring system according to any one of the preceding claims, wherein, There are multiple buoys attached to the semi-submersible floating structure at sea, and there is a buoy chain that connects multiple pairs of buoys together.

21. The detachable mooring system according to claim 19, wherein, The mooring cable is permanently attached to the buoy at the side of the monopole floating semi-submersible structure that enters the body of the buoy.

22. The detachable mooring system according to claim 6, wherein, The pulling device is a winch.

23. A method for mooring a semi-submersible floating structure at sea, comprising the following steps: (a) Providing a separable mooring system according to any one of claims 1 to 22; (b) Connect the buoy to the structure; (c) Pulling the mooring connector into the mooring point on the structure to tension the mooring chain on each of the mooring lines, the mooring lines also including buoy chains; and (d) This causes the mooring cable to unfold around the structure.

24. The method for mooring a semi-submersible floating structure at sea according to claim 23, wherein, The method includes the further step of separating the detachable mooring system from the semi-submersible floating structure at sea.

25. The method for mooring a semi-submersible floating structure at sea according to claim 24, wherein, The further step of detaching the detachable mooring system is to release the mooring lines and the buoy to a balanced position in the water under the influence of gravity.

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