Variable length constant tension mooring system and method

Abstract

A variable length constant tension mooring system and method for floating offshore structures, including a variable length constant tension mooring paradigm, in which the tension in the mooring lines of a mooring system remains constant when a floating body is displaced horizontally from an initial equilibrium position, while allowing the physical length of the mooring lines between the floating body mooring points and the seabed anchor points to vary with the horizontal displacement of the floating body; a shared single anchor variable length constant tension mooring system and method, including a self-installable shared concrete gravity anchor on the seabed, a plurality of mooring lines / ropes of constant tension variable length, and a plurality of corresponding constant tension fairleads attached to the floating body; and a multiple anchor variable length constant tension mooring system, including a plurality of symmetrically arranged anchors on the seabed, a plurality of corresponding mooring lines / ropes of constant tension variable length, and a plurality of corresponding constant tension fairleads attached to the floating body.

Description

Technical Field

[0001] This invention relates to a technology in the field of marine engineering, specifically to a variable-length constant-tension mooring system and method. Background Technology

[0002] With the increasing demand for offshore wind power, offshore wind technology is evolving from shallow to deep waters, with a growing need for large-scale deployment of floating foundation-supported wind turbines in waters deeper than 60 meters. Over the past decade, dozens of innovative floating offshore wind platform concepts have emerged. In contrast, the theory and technology of mooring systems for floating offshore structures have not progressed significantly in decades. Existing mooring system concepts and technologies have all been developed over the past 70 years for offshore oil and gas exploration.

[0003] Currently, these traditional mooring system technologies are being used for floating offshore wind platforms. However, there are significant differences between the two industries. Existing mooring system concepts are primarily designed for large, freestanding, and extremely expensive floating oil and gas platforms installed in deep waters (300 to 3000 meters) far from the coastline (over 200 kilometers). They are customized and cost-insensitive. On the other hand, for offshore wind development, floating offshore wind platforms are typically deployed in relatively shallow waters (60 to 300 meters) closer to the coastline (within 50 to 20 kilometers). There are 50 to 100 platforms in total. They are designed for large-scale commercial offshore wind farm development, are standardized, and are cost-sensitive.

[0004] Furthermore, traditional mooring systems typically cover hundreds of square kilometers of ocean space, posing unprecedented technological, environmental, commercial, and supply chain challenges to the emerging floating wind power industry. Currently, there are three main traditional mooring system concepts: catenary, tension (or semi-tension) outrigger, and tension leg. All existing mooring system concepts are based on a default traditional mooring theory of "constant length with varying tension." This theory assumes that the physical length of the mooring cable between the mooring point on the float (such as the guide) and the anchor point on the seabed is constant, excluding the linear or nonlinear stretching of the mooring cable / chain under tension. When the float shifts horizontally from its equilibrium position under the influence of wind and wave loads, the tension of the mooring cable changes with the shift of the float.

[0005] For mooring systems with "constant length varying tension," the tension of the mooring cable is inherently dynamic due to the dynamic nature of wind and wave loads. Under highly dynamic typhoon wave loads, the tension of the mooring cable typically increases exponentially with the increase in buoy displacement, stretching the cable to its full physical length by 10 degrees until the tension exceeds its limit, ultimately causing the cable to break. Currently, this traditional "constant length varying tension" mooring theory is considered the theoretical foundation for the design of mooring systems for offshore floating structures. It is also the theoretical root of the technical challenges currently faced by all mooring systems in terms of dynamic peak tension, fatigue, and long-term reliability of mooring cables / chains. Currently, catenary mooring is the most widely used mooring system concept for positioning offshore floating bodies. When a floating body shifts horizontally from its equilibrium position, the catenary shape of its mooring cable provides the required compliant displacement range and horizontal restraint restoring force through the weight of the steel chain and / or cable suspended in the water. There is usually a section of mooring cable / chain made of heavy steel chains lying flat on the seabed, which makes the vertical force acting on the anchor zero, thus allowing the use of a low-cost towed anchor.

[0006] However, the main drawbacks of existing catenary mooring systems are: 1) They cover a large area on the seabed, significantly impacting the marine environment; 2) For deep-water areas, the catenary system is too heavy and costly; 3) For shallow-water areas, due to the shallow water column, the mooring cable cannot form a sufficient catenary shape between the mooring point on the floating body and the anchor point on the seabed to limit the maximum horizontal displacement of the floating body, thus its positioning capability is not very effective in shallow water. For example, for floating wind power platforms installed in water depths of approximately 60 to 100 meters, using catenary mooring, the maximum horizontal displacement of the platform usually exceeds 30% of the water depth. Since the dynamic tension of the mooring cable increases exponentially with the increase in platform horizontal displacement, it poses a significant challenge to the design of the mooring system; at the same time, the length of the catenary mooring cable on the seabed is usually several times the water depth, thus also resulting in high costs. In summary, existing mooring system theories and concepts have many technical shortcomings. Simply adopting existing mooring system concepts and technologies based on traditional floating oil and gas platforms is far from meeting the dual challenges of high cost and high environmental impact faced by the floating wind power industry today. As offshore floating wind power technology enters the stage of large-scale commercial application, the market urgently needs a new mooring system concept and technical solution that is low-cost, has minimal environmental impact, and is safer. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, this invention proposes a variable-length constant-tension mooring system and method.

[0008] This invention is achieved through the following technical solution:

[0009] This invention relates to a variable-length constant-tension mooring method for floating marine structures. When a floating marine structure, i.e., a floating body, shifts horizontally from its initial equilibrium position under external load, the internal tension of the mooring cable in its mooring system is fixed by a constant-tension cable guide device connected to the floating body. At the same time, the physical length of the mooring cable between the mooring point on the floating body and the anchor point on the seabed changes with the horizontal shift of the floating body, thereby generating a restoring force of the mooring system.

[0010] When the external load disappears, under the action of the restoring force of the mooring system, the float returns to its initial equilibrium position, and the physical length of the mooring cable returns to its initial length, while the internal tension of the mooring cable remains unchanged.

[0011] Furthermore, when constructing the numerical model of the floating body and its mooring cable in the mooring system, the initial tension of the mooring cable is set to a constant tension value, and the elastic modulus of the mooring cable is set to be close to infinitesimal. That is, the mooring cable can be stretched almost infinitely when the tension increases by a very small amount. This allows the length of the mooring cable to be determined from the straight-line distance between the anchor pile and the corresponding constant tension guide device when the floating body shifts horizontally from its initial equilibrium position under external load. At the same time, it ensures that the internal tension of the mooring cable is always equal to its initial tension, thereby realizing the numerical simulation of the physical phenomenon of constant tension in the mooring system.

[0012] The present invention also relates to a shared single-anchor variable-length constant-tension mooring system, comprising: a single-anchor constant-tension mooring system and a floating hull, wherein: the single-anchor constant-tension mooring system comprises: a shared single anchor located on the seabed and at least three mooring cables / chains with constant tension and their corresponding constant-tension guide devices connected to the floating hull.

[0013] The shared single anchor is a self-installing concrete gravity anchor, suction anchor, or driven anchor.

[0014] The mooring cable / chain is a steel cable, steel chain, polyester cable, or nylon cable or a combination thereof.

[0015] The constant tension cable guide device is an active, passive, or semi-active constant tension variable length device that is connected to a mooring point below the waterline of the floating hull.

[0016] The self-installable concrete gravity anchor includes: a shared gravity anchor body, an upper connecting structure with its lower end connected to the gravity anchor body and its upper end connected to a shared anchor head tubular structure, multiple mooring cable connecting lugs connected to the upper end of the shared anchor head tubular structure, multiple connecting inner plates located inside the shared anchor head tubular structure, and a lower cone structure embedded in the seabed soil.

[0017] The self-installation process includes: assembling the concrete gravity anchor at the dock, where it is floating; towing the concrete gravity anchor to a windy location at sea using a tugboat; injecting ballast water into the empty compartment to sink the entire concrete gravity anchor to the seabed; during the sinking process, the lower cone of the concrete gravity anchor embeds itself below the mud surface of the seabed under the action of gravity, completing the self-installation process. When the floating hull shifts horizontally from its initial equilibrium position under the action of external forces, the internal tension of each mooring cable in its shared single-anchor constant tension mooring system is fixed at a constant value. At the same time, the effective length of each mooring cable, that is, the physical length of the mooring cable between the mooring point on the floating hull and the anchor pile point on the seabed, changes with the horizontal shift of the floating hull. Some mooring cables become longer, and some become shorter, thus generating a mooring system restoring force. When the external force disappears, under the action of the mooring system restoring force, the floating hull returns to its initial equilibrium position, the effective length of each mooring cable returns to its initial length, and the internal tension of each mooring cable remains unchanged.

[0018] The present invention also relates to a multi-anchor variable length constant tension mooring system, comprising: multiple anchor piles located on the seabed and multiple corresponding mooring cables / chains with constant tension, a floating hull, and multiple constant tension mooring system subsystems.

[0019] The constant tension mooring system subsystem includes: an anchor pile fixed to the seabed, a mooring cable / chain, and a corresponding constant tension guide device connected to the floating hull.

[0020] The multiple anchor piles located on the seabed are arranged in a geometrically symmetrical manner extending outward and downward around the floating hull. The horizontal distance from each anchor pile to the constant tension cable guide device on the corresponding floating hull is usually set to about 50% of the water depth.

[0021] Each of the multiple mooring cables / chains has one end connected to a corresponding constant tension guide device and the other end connected to a corresponding anchor pile located on the seabed.

[0022] The internal tension of the mooring cable / chain is a constant value.

[0023] This invention further relates to a multi-anchor variable-length constant-tension mooring method. When a floating hull shifts horizontally from its initial equilibrium position under the action of an external force, the internal tension of each mooring cable in its multi-anchor constant-tension mooring system is fixed at a constant value. Simultaneously, the effective length of each mooring cable—that is, the physical length of the mooring cable between the mooring point on the floating hull and the anchor point on the seabed—changes with the horizontal shift of the floating hull. Specifically, the effective length of the mooring cable connecting the anchor points farther from the floating hull increases, while the effective length of the mooring cable connecting the anchor points closer to the floating hull decreases, thereby generating a restoring force in the mooring system. When the external force disappears, under the action of the restoring force, the floating hull returns to its initial equilibrium position, the effective length of each mooring cable returns to its initial length, and the internal tension of each mooring cable remains unchanged.

[0024] Technical effect

[0025] This invention breaks through the traditional "constant length varying tension" mooring theory and proposes a new "variable length constant tension" mooring theory.

[0026] Second, based on this new mooring theory, two novel mooring systems and methods are proposed for floating structures at sea, namely the shared single-anchor variable-length constant-tension mooring system and the multi-anchor variable-length constant-tension mooring system disclosed in this invention.

[0027] Third, the single-anchor constant tension mooring system of this invention occupies only the area of ​​one anchor pile on the seabed. The volume of seawater disturbed by the mooring system between the seabed anchor pile and the surface float is very small, thus minimizing adverse impacts on the marine environment and marine life. Fourth, the cost of the single-anchor variable-length constant tension mooring system of this invention is more than 50% lower than that of traditional multi-anchor catenary mooring systems. Fifth, compared with existing conventional mooring systems (including catenary, tension leg, and tension leg systems), the maximum tension (static tension + dynamic tension) of the mooring cable in the variable-length constant tension mooring system of this invention is much smaller. Theoretically, the tension of the mooring cable / chain in the constant tension mooring system of this invention is only a static component, with zero dynamic component, thereby greatly improving the safety, reliability, and fatigue life of the mooring system. Attached Figure Description

[0028] Figure 1 This is a three-dimensional rendering of the present invention;

[0029] Figure 2 This is a two-dimensional schematic diagram of the present invention;

[0030] Figure 3 This is a schematic diagram of the horizontal offset of the float in this invention;

[0031] Figure 4 This is a schematic diagram of the self-installing concrete shared gravity anchor of the present invention;

[0032] Figure 5 This is a schematic diagram of the multi-anchor variable length constant tension mooring system of the present invention;

[0033] Figure 6 This is a schematic diagram of the horizontal displacement of the float in the multi-anchor variable length constant tension mooring system of the present invention;

[0034] In the diagram: 1 Shared single-anchor variable-length constant-tension mooring system, 1A Multi-anchor variable-length constant-tension mooring system, 2 Floating hull, 4 Vertical wind tower, 6 Wind turbine nacelle, 8 Wind turbine blades, 10 Constant-tension guide cable device, 12 Mooring cable / chain, 12L Portal mooring cable / chain, 12R Starboard mooring cable / chain, 20 Shared single anchor, 21 Shared gravity anchor body, 22 Shared gravity anchor superstructure, 23 Shared anchor head tube structure, 24 Shared anchor head connecting lug, 25 Shared anchor head connecting inner plate, 26 Shared gravity anchor lower cone, 30 Anchor pile, 101 Water surface, 201 Seabed / Seafloor, 301 Wind load, 302 Wave load, 401 Mooring system restoring force. Detailed Implementation

[0035] like Figure 1 and 2 As shown, this embodiment involves a shared single-anchor constant tension mooring system 1, which includes: a floating hull 2, a vertical wind tower 4 supporting the top of the floating hull 2 ​​located above the water surface 101, a wind turbine nacelle 6 located at the top of the wind tower 4, and wind turbine blades 8 connected to the wind turbine nacelle 6.

[0036] The shared single anchor constant tension mooring system 1 includes: at least three constant tension guide devices 10 located below the floating hull 2 ​​below the water surface 101, at least three mooring cables / chains 12 with constant tension, and a shared single anchor 20 located on the seabed 201.

[0037] The mooring cable / chain 12 is made of conventional steel cable, steel chain, polyester cable, or nylon cable, or a combination thereof.

[0038] The shared single anchor 20 is a self-installing concrete gravity anchor, or a traditional suction anchor or driven anchor; in some embodiments, the shared single anchor 20 is located at the geometric center of the mooring system 1 on the seabed 201, that is, at the intersection of the vertical centerline of the floating hull 2 ​​and the seabed 201.

[0039] The multiple mooring cables / chains 12 are arranged in a geometrically symmetrical and uniform manner. One end of each mooring cable / chain 12 is connected to a shared single anchor 20 on the seabed 201, and the other end is connected to a constant tension cable guide device 10 on the floating hull 2.

[0040] The tension constant guide device 10 is an active tension constant length variable device, a passive tension constant length variable device, or a semi-active tension constant length variable device connected to the mooring point of the floating vessel. It can change the effective physical length of the mooring cable / chain 12 (i.e., the physical length of the mooring cable / chain 12 between the mooring point 10 on the floating vessel 2 and the shared single anchor 20 on the seabed 201) according to the change of the horizontal offset of the floating vessel 2 under a preset constant tension.

[0041] Although there is currently no application in mooring systems, existing tension-constant length variable devices used in other fields include constant tension winches (active) controlled by servo motors and top tensioners (passive).

[0042] like Figure 3 As shown, taking a simplified two-dimensional mooring system with two mooring cables / chains as an example, when the floating hull 2 ​​shifts horizontally from its initial equilibrium position under the action of wind load 301 and wave load 302, the constant tension guide device 10 in the shared single anchor constant tension mooring system 1 maintains the internal tension of the mooring cables / chains 12L and 12R as constant while changing the effective length of the mooring cables / chains 12L and 12R (i.e., the physical length of the mooring cables / chains 12L and 12R between the mooring point 10 on the floating hull 2 ​​and the shared single anchor 20 on the seabed 201).

[0043] When the floating hull 2 ​​shifts horizontally to the right from its initial equilibrium position under the action of wind load 301 and wave load 302, the length of the mooring cable / chain 12L connected to the left side of the floating hull 2 ​​decreases, and its horizontal tension component decreases. Simultaneously, the length of the mooring cable / chain 12R connected to the right side of the floating hull 2 ​​increases, and its horizontal tension component increases. The resulting horizontal resultant force of the entire mooring system is greater than zero and directed to the left, generating a horizontal restoring force 401. This force is opposite in direction to the external forces wind load 301 and wave load 302, and has the same absolute value, thus achieving dynamic equilibrium of the floating hull 2's horizontal displacement. When the external forces wind load 301 and wave load 302 disappear, under the action of the mooring system restoring force 401, the floating hull 2 ​​moves to the left, returning to its initial equilibrium position.

[0044] The magnitude of the restoring force 401 of the mooring system can be calculated based on the internal constant tension values ​​of the mooring cables / chains 12L and 12R and the magnitude of the horizontal displacement value of the floating hull 2.

[0045] In practical applications, the final setting of the internal constant tension value of the mooring cable / chain 12 depends on the maximum dynamic external loads wind load 301 and wave load 302.

[0046] When performing numerical simulation of the shared single-anchor constant tension mooring system 1 using software modeling, the initial tension of the mooring cables / chains 12L and 12R can be set to the constant tension value. Simultaneously, the elastic modulus of the mooring cables / chains, describing their material properties, is set to an infinitesimally small value, such as 0.00001, close to zero. This means the mooring cables can be stretched almost infinitely with a very small increase in tension. When the floating hull 2 ​​shifts horizontally from its initial equilibrium position under the action of wind load 301 and wave load 302, the lengths of the mooring cables / chains 12L and 12R can be derived from the straight-line distance between the shared single anchor 20 and the corresponding constant tension guide device 10. This ensures that the internal tension of the mooring cables / chains 12L and 12R remains equal to their initial tension, thus achieving a numerical simulation of the physical phenomenon of "constant tension."

[0047] like Figure 4 As shown, the shared single anchor 20 in this embodiment is a self-installable concrete gravity anchor, including: a shared gravity anchor body 21, an upper connecting structure 22, the lower end of which is connected to the gravity anchor body 21 and the upper end of which is connected to the shared anchor head tubular structure 23, multiple mooring cable connecting lugs 24 connected to the upper end of the shared anchor head tubular structure 23, multiple connecting inner plates 25 located inside the shared anchor head tubular structure 23, and a lower cone structure 26 connected to the bottom of the shared gravity anchor body 21 and embedded in the soil of the seabed 201.

[0048] The weight of the entire shared single anchor 20 in the water is greater than the sum of the tensions of all mooring cables / chains connected to the shared anchor head connecting lug 24, with a certain safety factor, which is generally between 1 and 2.

[0049] The shared gravity anchor body 21 is a concrete structure. The concrete gravity anchor body 21 has multiple internal chambers to provide buoyancy, allowing the entire concrete gravity anchor to float on the water surface.

[0050] The shared single anchor 20 has a self-installation function, which is achieved through the following methods and installation process:

[0051] The first step is to provide buoyancy during assembly at the dock, allowing the entire shared single anchor 20 to float on the water.

[0052] The second step is to use tugboats to tow the shared single anchor 20 to the offshore wind farm location.

[0053] The third step is to inject ballast water into the empty compartment to sink the entire shared single anchor 20 to the seabed.

[0054] In the fourth step, the shared gravity anchor cone structure 26 of the shared single anchor 20 is embedded below the mud surface of the seabed under the action of gravity, completing the self-installation process.

[0055] like Figure 5As shown, this embodiment includes a multi-anchor constant tension mooring system 1A, a floating hull 2, a vertical wind tower 4 supporting the top of the floating hull 2 ​​located above the water surface 101, a wind turbine nacelle 6 located at the top of the wind tower 4, and wind turbine blades 8 connected to the wind turbine nacelle 6; the multi-anchor constant tension mooring system 1A includes: at least three anchor piles 30 located on the seabed 201 and three corresponding mooring cables / chains 12 with constant tension.

[0056] The mooring cable / chain 12 is made of conventional steel cable, steel chain, polyester cable or nylon cable, or a combination of the above.

[0057] In other contexts, the multi-anchor variable-length constant-tension mooring system 1A includes: at least three subsystems consisting of anchor piles 30, mooring cables / chains 12, and constant-tension guide devices 10; and a floating hull 2 ​​having a superstructure supporting wind turbines 4, 6, and 8 above the waterline 101 and a lower structure at a mooring point below the waterline 101 to which the constant-tension guide devices 10 are connected.

[0058] The anchor pile 30 mentioned above is a driven pile, a suction anchor, or other anchor pile with sufficient vertical capacity, or a self-installable concrete gravity anchor as described in this embodiment.

[0059] One end of each mooring cable / chain 12 is connected to a corresponding constant tension guide device 10, and the other end is connected to a corresponding anchor pile 30 located on the seabed 201.

[0060] The multiple anchor piles 30 are arranged geometrically symmetrically and uniformly on the seabed 201 with the floating hull 2 ​​as the center. Each mooring cable / chain 12 extends outward and downward from the floating hull 2 ​​to a corresponding anchor pile 30 on the seabed 201.

[0061] The horizontal distance from each anchor pile 30 to the constant tension guide device 10 on the corresponding floating hull 2 ​​is typically about 40% to 50% of the water depth.

[0062] Specifically, the setting of each anchor pile 30 position is based on the maximum permissible horizontal displacement of the floating hull 2.

[0063] When the floating hull 2 ​​shifts horizontally from its initial equilibrium position, the constant tension guide device 10 in the multi-anchor constant tension mooring system 1A can change the effective length of the mooring cable / chain 12 while maintaining the internal tension of the mooring cable / chain 12 at a constant value, thereby achieving constant tension and variable length of the mooring cable / chain 12.

[0064] The constant tension cable guide device 10 is an active tension constant length variable device, a passive tension constant length variable device, or a semi-active tension constant length variable device connected to the mooring point below the waterline 101 of the floating hull 2.

[0065] Existing constant tension variable length devices used in other fields include constant tension winches and top tensioners.

[0066] like Figure 6 As shown, taking a simplified two-dimensional mooring system with two anchor piles and two mooring cables / chains as an example, when the floating hull 2 ​​shifts horizontally from its initial equilibrium position under the action of wind load 301 and wave load 302, the constant tension guide device 10 in the multi-anchor constant tension mooring system 1A of the present invention maintains the internal tension of the mooring cables / chains 12L and 12R at a constant value while changing the effective length of the mooring cables / chains 12L and 12R.

[0067] When the floating hull 2 ​​shifts horizontally to the right from its initial equilibrium position under the action of wind load 301 and wave load 302, the floating hull 2 ​​shifts away from the left anchor pile 30L, resulting in an increase in the effective length of the mooring cable / chain 12L connected to the left side of the floating hull 2 ​​and an increase in the horizontal component of its tension. At the same time, the floating hull 2 ​​shifts closer to the right anchor pile 30R, resulting in a decrease in the length of the mooring cable / chain 12R connected to the right side of the floating hull 2 ​​and a decrease in the horizontal component of its tension.

[0068] The resulting horizontal resultant force of the entire mooring system tension is greater than zero and is directed to the left, thus generating a horizontal restoring force 401 for the mooring system. Its direction is opposite to that of the external forces wind load 30 and wave load 302, and their absolute values ​​are equal, thereby achieving dynamic equilibrium of the horizontal displacement of the floating hull 2.

[0069] When the external forces wind load 301 and wave load 302 disappear, the floating hull 2 ​​moves to the left and returns to its initial equilibrium position under the action of the mooring system restoring force 401.

[0070] The magnitude of the restoring force 401 of the mooring system can be calculated based on the internal constant tension values ​​of the mooring cables / chains 12L and 12R and the magnitude of the horizontal displacement value of the floating hull 2.

[0071] In practical applications, the final setting of the internal constant tension value of the mooring cable / chain 12 depends on the maximum dynamic external loads wind load 301 and wave load 302. When performing numerical simulation of the shared single-anchor constant tension mooring system 1A using software modeling, the initial tension of the mooring cables / chains 12L and 12R can be set to the aforementioned constant tension value. Simultaneously, the elastic modulus of the mooring cables / chains, which describes their material properties, is set to an infinitesimally small value, such as 0.00001, close to zero. This means that the mooring cable can be stretched almost infinitely with a very small increase in tension. Thus, when the floating hull 2 ​​shifts horizontally from its initial equilibrium position under the action of wind load 301 and wave load 302, the lengths of the mooring cables / chains 12L and 12R can be derived from the straight-line distance between the anchor piles 30L and 30R and the corresponding constant tension guide device 10, while maintaining the internal tension of the mooring cables / chains 12L and 12R always equal to their initial tension, thereby achieving numerical simulation of the physical phenomenon of "constant tension."

[0072] Compared to the shared single-anchor constant tension mooring system 1 of this invention, the multi-anchor constant tension mooring system 1A of this invention may have a slightly higher cost and a greater impact on the marine environment. However, compared to the traditional catenary mooring system, the multi-anchor constant tension mooring system 1A of this invention is still much cheaper and has a much smaller impact on the marine environment. Furthermore, in certain specific situations, the multi-anchor constant tension mooring system 1A of this invention may offer better flexibility in application than the shared single-anchor constant tension mooring system 1 of this invention.

[0073] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for mooring a floating marine structure with variable length and constant tension based on a shared single-anchor variable length constant tension mooring system, characterized in that, The shared single-anchor variable-length constant-tension mooring system includes: a single-anchor constant-tension mooring system and a floating hull. The single-anchor constant-tension mooring system includes: a shared single anchor located on the seabed and at least three mooring cables / chains with constant tension and their corresponding constant-tension guide devices connected to the floating hull. The shared single anchor is a self-installable concrete gravity anchor, comprising: a shared gravity anchor body, an upper connecting structure, the lower end of which is connected to the gravity anchor body and the upper end of which is connected to a shared anchor head tubular structure, multiple mooring cable connecting lugs connected to the upper end of the shared anchor head tubular structure, multiple connecting inner plates located inside the shared anchor head tubular structure, and a lower cone structure embedded in the seabed soil. The mooring cable / chain is a steel cable, steel chain, polyester cable, or nylon cable or a combination thereof; The constant tension cable guide device is a passive tension constant length variable device or a semi-active tension constant length variable device connected to the mooring point below the waterline of the floating hull. The aforementioned constant tension variable length device includes: a top tensioner; One end of each mooring cable / chain is connected to the constant tension guide device on the corresponding floating hull, and the other end is connected to a shared single anchor fixed to the seabed. The shared single anchor is located at the geometric center of the constant tension mooring system on the seabed, that is, at the intersection of the vertical centerline of the floating hull and the seabed. Multiple mooring cables / chains are arranged geometrically symmetrically around the shared single anchor. The internal tension of the mooring cables / chains is a constant value. The weight of the entire shared single anchor in the water is greater than the sum of the tensions of all mooring cables / chains connected to the connecting lugs of the shared anchor head, with a safety factor of 1 to 2. The variable-length constant-tension mooring method refers to the following: when a floating offshore structure, i.e. a floating body, shifts horizontally from its initial equilibrium position under external load, the internal tension of the mooring cable in its mooring system is fixed by a constant-tension cable guide device connected to the floating body. At the same time, the physical length of the mooring cable between the mooring point on the floating body and the anchor point on the seabed changes with the horizontal shift of the floating body, thereby generating a mooring system restoring force. When the external load disappears, under the action of the restoring force of the mooring system, the float returns to the initial equilibrium position, and at the same time, the physical length of the mooring cable returns to the initial length, while the internal tension of the mooring cable remains unchanged. The tension constant guide device is a passive tension constant length variable device or a semi-active tension constant length variable device connected to the mooring point of the floating vessel. Under a pre-set constant tension, the effective physical length of the mooring cable / chain changes according to the change of the horizontal offset of the floating vessel, that is, the physical length of the mooring cable / chain between the mooring point on the floating vessel and the shared single anchor on the seabed. The aforementioned constant tension variable length device includes: a top tensioner.

2. The variable-length constant-tension mooring method according to claim 1, characterized in that, When constructing the numerical model of the floating body and its mooring system, i) Set the initial tension of the mooring cable to a constant tension value; ii) Set the elastic modulus of the mooring cable to be close to infinitesimal, that is, the mooring cable can be stretched to near infinity with a very small increase in tension. This allows the length of the mooring cable to be determined from the straight-line distance between the anchor pile and the corresponding constant tension guide device when the float shifts horizontally from its initial equilibrium position under external load, while ensuring that the internal tension of the mooring cable is always equal to its initial tension. This enables numerical simulation of the physical phenomenon of constant tension in the mooring system.

3. The variable-length constant-tension mooring method according to claim 1, characterized in that, The self-installing concrete gravity anchor further includes: Multiple internal chambers provide buoyancy, allowing the entire concrete gravity anchor to float on the water surface; The self-installable feature includes: The first step is to assemble the concrete gravity anchor at the dock, where it is in a floating state; The second step is to use tugboats to wet-tow the concrete gravity anchor to the offshore wind farm location; The third step is to inject ballast water into the empty chamber to sink the entire concrete gravity anchor to the seabed. The fourth step involves the lower cone of the concrete gravity anchor embedding itself below the mud surface of the seabed under the force of gravity during the sinking process, thus completing the self-installation process.

4. A variable-length constant-tension mooring method according to any one of claims 1-3, characterized in that, When the floating hull shifts horizontally from its initial equilibrium position under the action of external forces, the internal tension of each mooring cable in its shared single-anchor constant tension mooring system is fixed at a constant value. At the same time, the effective length of each mooring cable, that is, the physical length of the mooring cable between the mooring point on the floating hull and the anchor point on the seabed, changes with the horizontal shift of the floating hull. Some mooring cables become longer and some become shorter, thus generating a restoring force of the mooring system. When the external force disappears, under the action of the restoring force of the mooring system, the floating hull returns to its initial equilibrium position, the effective length of each mooring cable returns to its initial length, and the internal tension of each mooring cable remains unchanged.

5. A multi-anchor variable-length constant-tension mooring system for implementing the variable-length constant-tension mooring method according to any one of claims 1-4, characterized in that, include: Multiple anchor piles located on the seabed and multiple corresponding mooring cables / chains with constant tension. A floating hull and Multiple constant tension mooring system subsystems; The constant tension mooring system subsystem includes: an anchor pile fixed to the seabed, a mooring cable / chain, and a corresponding constant tension guide device connected to the floating hull. The constant tension guide device is a passive tension constant length variable device or a semi-active tension constant length variable device connected to the mooring point below the waterline of the floating hull. The aforementioned constant tension variable length device includes: a top tensioner.

6. The multi-anchor variable length constant tension mooring system according to claim 5, characterized in that, Multiple anchor piles located on the seabed are evenly arranged outward and downward in a geometrically symmetrical manner around the floating hull. The horizontal distance from each anchor pile to the constant tension cable guide device on the corresponding floating hull is usually set to 50% of the water depth. Each of the multiple mooring cables / chains has one end connected to a corresponding constant tension guide device and the other end connected to a corresponding anchor pile located on the seabed. The internal tension of the mooring cable / chain is a constant value.

7. A method for multi-anchor variable-length constant-tension mooring according to claim 5 or 6, characterized in that, When a floating hull shifts horizontally from its initial equilibrium position under the action of external forces, the internal tension of each mooring cable in its multi-anchor constant tension mooring system is fixed at a constant value. At the same time, the effective length of each mooring cable, that is, the physical length of the mooring cable between the mooring point on the floating hull and the anchor point on the seabed, changes with the horizontal shift of the floating hull. The effective length of the mooring cable connecting the anchor point farther away from the floating hull becomes longer, and the effective length of the mooring cable connecting the anchor point closer to the floating hull becomes shorter, thus generating a restoring force of the mooring system. When the external forces disappear, the floating hull returns to its initial equilibrium position under the restoring force of the mooring system, the effective length of each mooring cable is restored to its initial length, and the internal tension of each mooring cable remains unchanged.

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