Variable-length constant-tension mooring system and method

Abstract

The invention discloses a variable-length constant-tension mooring system and method for a floating type offshore structure, and the system comprises a variable-length constant-tension mooring theoretical normal form, i.e., when a floating body horizontally shifts from an initial balance position, the tension of a mooring cable in the mooring system is kept at a constant value, and the tension of the mooring cable in the mooring system is kept at a constant value; meanwhile, the physical length of the mooring rope between the floating body mooring point and the seabed anchor point is allowed to change along with the change of the horizontal deviation of the floating body; the invention discloses a shared single-anchor variable-length constant-tension mooring system and method. The shared single-anchor variable-length constant-tension mooring system comprises a self-installable shared concrete gravity anchor located on a seabed, a plurality of mooring cables / chains with constant tension and variable lengths and a plurality of corresponding constant-tension fair lead devices connected to a floating body. A multi-anchor variable-length constant-tension mooring system comprises a plurality of anchors symmetrically arranged on a seabed, a plurality of corresponding mooring cables / chains with constant tension and variable length and a corresponding constant-tension fair lead device connected to a floating body.

Description

Technical Field

[0001] The present invention relates to a technology in the field of marine engineering, and in particular to a variable-length constant-tension mooring system and method. Background Art

[0002] With the increasing demand for offshore wind power generation, offshore wind power technology is developing from shallow waters to deep waters, and there is an increasing demand for large-scale deployment of large wind turbines supported by floating foundations in waters with a depth of more than 60 meters. Over the past decade, dozens of innovative floating offshore wind power platform concepts have emerged. In contrast, the theory and technology of mooring systems for floating offshore structures have not made significant progress in decades. The existing mooring system concepts and technologies have been developed for offshore oil and gas production over the past 70 years.

[0003] Currently, these traditional mooring system technologies are being used for floating offshore wind platforms. However, there are very significant differences between the two industries. Existing mooring system concepts are mainly designed for large independent and extremely expensive floating oil and gas platforms installed in deep waters (300 to 3,000 meters) far from the coastline (more than 200 kilometers away). They are customized and not cost-sensitive. On the other hand, for offshore wind power development, floating offshore wind power platforms are usually deployed in relatively shallow waters (60 to 300 meters) close to the coastline (within 50 kilometers), with 50 to 100 platforms, designed for large-scale commercial offshore wind farms, standardized, and cost-sensitive.

[0004] In addition, the use of traditional mooring systems usually covers hundreds of square kilometers of ocean space, which brings unprecedented technical, environmental, commercial and supply chain challenges to the emerging floating wind power industry. At present, there are three main concepts of traditional mooring systems, namely catenary, tension (or semi-tensioned) leg and tension leg. All existing mooring system concepts are based on a default traditional mooring theory of "constant length variable tension". This theory assumes that the physical length of the mooring cable between the mooring point on the floating body (such as the fairlead) and the anchor point on the seabed is constant. This does not include the linear or nonlinear stretching of the mooring cable / chain under tension. When the floating body is horizontally offset from its equilibrium position under the action of sea wind and wave loads, the tension of the mooring cable changes with the displacement of the floating body.

[0005] For the "constant length variable tension" mooring system, the tension of the mooring cable is dynamic in nature because the sea wind and wave loads are dynamic. Under the action of highly dynamic typhoon wave loads, as the displacement of the floating body increases, the tension of the mooring cable usually increases exponentially, and the mooring cable is tightened and stretched to its entire physical length 10 degrees until the tension exceeds the limit value and the mooring cable is finally broken. At present, this traditional "constant length variable tension" mooring theory is regarded as the theoretical basis of the design system of offshore floating structure mooring systems. At the same time, it is also the theoretical root of the technical challenges faced by all mooring systems in terms of dynamic peak ultimate tension, fatigue and long-term reliability of mooring cables / chains. At present, catenary mooring is the most widely used mooring system concept for offshore floating body positioning. When a floating body is horizontally offset from its equilibrium position, the catenary shape of its mooring cable provides the required compliance 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 length of mooring line / chain consisting of heavy steel chain lying flat on the seabed, which results in zero vertical forces acting on the anchor, allowing the use of a low-cost dragging anchor.

[0006] However, the main disadvantages of the existing catenary mooring are: 1) the coverage area on the seabed is large, which has a great impact on the marine environment; 2) for deep water 20 sea areas, the catenary system is too heavy and the cost is too high; 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 extreme horizontal deviation of the floating body, so its positioning ability is not very effective in shallow water. For example, for a floating wind power platform installed at a water depth of about 60 to 100 meters, the maximum horizontal deviation of the platform will usually exceed 30% of the water depth when the catenary mooring is used. Since the dynamic tension of the mooring cable increases exponentially with the increase of the horizontal deviation of the platform, it poses a great 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, so the cost is also very high. In summary, there are many technical deficiencies in the existing mooring system theories and concepts. The existing mooring system concepts and technologies that simply adopt traditional floating oil and gas platforms are far from meeting the dual challenges of high cost and high environmental impact of mooring systems faced by today's floating wind power industry. As offshore floating wind power technology enters the stage of commercial large-scale application, the market urgently needs a new mooring system concept and technical solution with low cost, low environmental impact and higher safety. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a variable-length constant-tension mooring system and method.

[0008] The present invention is achieved through the following technical solutions:

[0009] The present invention relates to a variable length constant tension mooring method for a floating offshore structure. When a floating offshore structure, i.e. a floating body, is horizontally deflected from an initial equilibrium position under the action of an external load, the internal tension of a mooring cable in its mooring system is fixed by a constant tension fairlead device connected to the floating body, and at the same time, the physical length of the mooring cable between a mooring point on the floating body and an anchor point on the seabed changes with the change of the horizontal displacement 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 floating body returns to the initial equilibrium position, while the physical length of the mooring cable returns to the initial length, and the internal tension of the mooring cable remains unchanged.

[0011] Furthermore, when constructing a numerical model of a mooring cable in a floating body and its 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 close to infinitely when the tension increases very slightly, so that when the floating body is horizontally offset from its initial equilibrium position under the action of an external load, the length of the mooring cable is obtained based on the straight-line distance between the anchor pile and the corresponding constant tension fairlead device, while ensuring that the internal tension of the mooring cable is always equal to its initial tension, thereby achieving numerical simulation of the constant tension physical phenomenon of 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 fairlead devices connected to the floating hull.

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

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

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

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

[0017] The self-installation includes: assembling the concrete gravity anchor at the dock and being in a floating state; wet-tow the concrete gravity anchor to the offshore wind farm by a tugboat; injecting ballast water into the empty compartment to make the entire concrete gravity anchor sink to the seabed; during the sinking process, the lower cone head of the concrete gravity anchor is embedded below the mud surface of the seabed under the action of gravity, completing the self-installation process. When the floating hull is horizontally offset from the initial equilibrium position under the action of external force, the internal tension of each mooring cable in its shared single anchor constant tension mooring system is fixed to a constant value, and 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 change of the horizontal offset of the floating hull, and the effective length of some mooring cables becomes longer and some becomes shorter, thereby 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 the initial equilibrium position, the effective length of each mooring cable is restored to the 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: a plurality of anchor piles located on the seabed and a plurality of corresponding mooring cables / chains with constant tension, a floating hull and a plurality of constant tension mooring system subsystems.

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

[0020] The plurality of anchor piles on the seabed are evenly arranged on the seabed and extend outward and downward in geometric symmetry with the floating hull as the center. The horizontal distance from each anchor pile to the constant tension fairlead device on the corresponding floating hull is usually set to about 50% of the water depth.

[0021] One end of each of the plurality of mooring cables / chains is connected to a corresponding constant tension fairlead device, and the other end is connected to a corresponding anchor pile located on the seabed.

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

[0023] The present invention further relates to a multi-anchor variable-length constant-tension mooring method, in which when a floating hull is horizontally offset from an initial equilibrium position under the action of an external force, the internal tension of each mooring cable in the multi-anchor constant-tension mooring system is fixed at a constant value, and at the same time, the effective length of each mooring cable, that is, the physical length of the mooring cable between a mooring point on the floating hull and an anchor point on the seabed, changes with the change of the horizontal offset of the floating hull, wherein the effective length of the mooring cable connected to the anchor away from the floating hull becomes longer, and the effective length of the mooring cable connected to the anchor close to the floating hull becomes shorter, thereby 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 the initial equilibrium position, the effective length of each mooring cable returns to the initial length, and the internal tension of each mooring cable remains unchanged. Technical Effects

[0024] The present invention breaks through the traditional "constant length and variable tension" mooring theory and proposes a new "variable length and constant tension" mooring theory.

[0025] Secondly, based on this new mooring theory, two new mooring systems and methods are proposed for offshore floating structures, namely, the shared single-anchor variable-length constant-tension mooring system and the multi-anchor variable-length constant-tension mooring system disclosed in the present invention.

[0026] Third, the shared single-anchor constant tension mooring system of the present invention occupies an area on the seabed only the size of an anchor pile, and the volume of seawater disturbed by the mooring system from the seabed anchor pile to the surface float is very small, so the adverse effects on the marine environment and marine life are also very small. Fourth, the cost of the shared single-anchor variable-length constant tension mooring system of the present invention is more than 50% lower than that of the traditional multi-anchor catenary mooring system. Fifth, compared with existing conventional mooring systems (including catenary, tension leg and tension leg), the maximum tension (static tension + dynamic tension) of the mooring cable in the variable-length constant tension mooring system of the present invention is much smaller. In theory, the tension of the mooring cable / chain in the constant tension mooring system of the present invention has only the static part, and its dynamic part is zero, which greatly improves the safety, reliability and fatigue life of the mooring system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a three-dimensional effect diagram of the present invention;

[0028] Figure 2 It is a two-dimensional schematic diagram of the present invention;

[0029] Figure 3 It is a schematic diagram of the horizontal displacement of the floating body of the present invention;

[0030] Figure 4 It is a schematic diagram of the self-installable concrete shared gravity anchor of the present invention;

[0031] Figure 5 It is a schematic diagram of a multi-anchor variable-length constant-tension mooring system of the present invention;

[0032] Figure 6 It is a schematic diagram of the horizontal displacement of the floating body of the multi-anchor variable-length constant-tension mooring system of the present invention;

[0033] In the figure: 1 shared single anchor variable length constant tension mooring system, 1A multiple anchor variable length constant tension mooring system, 2 floating hull, 4 upright wind tower, 6 wind turbine nacelle, 8 wind turbine blades, 10 constant tension fairlead device, 12 mooring cable / chain, 12L left side mooring cable / chain, 12R right side mooring cable / chain, 20 shared single anchor, 21 shared gravity anchor body, 22 shared gravity anchor upper structure, 23 shared anchor head pipe structure, 24 shared anchor head connecting ear plate, 25 shared anchor head connecting inner plate, 26 shared gravity anchor lower cone head, 30 anchor pile, 101 water surface, 201 seabed / seabed, 301 wind load, 302 wave load, 401 mooring system restoring force. DETAILED DESCRIPTION

[0034] like Figure 1 and 2 As shown, a shared single anchor constant tension mooring system 1 involved in this embodiment includes: a floating hull 2, an upright wind tower 4 supporting the top of the floating hull 2 ​​above the water surface 101, a wind turbine cabin 6 located at the top of the wind tower 4, and wind turbine blades 8 connected to the wind turbine cabin 6.

[0035] The shared single anchor constant tension mooring system 1 comprises: at least three constant tension fairlead 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 .

[0036] The mooring cable / chain 12 is made of conventional steel cable, steel chain, polyester cable or nylon cable or a combination thereof.

[0037] The shared single anchor 20 uses a self-installable concrete gravity anchor, and also uses a traditional suction anchor pile or a driven anchor pile; 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, the intersection of the vertical centerline of the floating hull 2 ​​and the seabed 201.

[0038] The multiple mooring cables / chains 12 are evenly arranged in geometric symmetry, and 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 15 to a corresponding constant tension fairlead device 10 on the floating hull 2 ​​.

[0039] The constant tension fairlead device 10 is an active constant tension variable length device, a passive constant tension variable length device or a semi-active constant tension variable length device connected to the mooring point of the floating vessel system, and 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 hull 2 ​​and the shared single anchor 20 on the seabed 201) according to the change of the horizontal deviation of the floating hull 2 ​​under a preset constant tension.

[0040] Although there is no application in mooring systems yet, existing constant tension variable length devices used in other fields include constant tension winches (active) and top tensioners (passive) controlled by servo motors.

[0041] like Figure 3 As shown, taking a simplified two-dimensional mooring system of two mooring cables / chains as an example, when the floating hull 2 ​​is horizontally offset from its initial equilibrium position under the action of wind load 301 and wave load 302, the constant tension fairlead device 10 in the shared single anchor constant tension mooring system 1 changes 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) while keeping the internal tension of the mooring cables / chains 12L and 12R at a constant value.

[0042] When the floating hull 2 ​​is horizontally displaced from its initial equilibrium position to the right in the figure 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 ​​becomes shorter, and the horizontal component of its tension becomes smaller. At the same time, the length of the mooring cable / chain 12R connected to the right side of the floating hull 2 ​​becomes longer, and the horizontal component of its tension becomes larger. The resulting horizontal resultant force of the tension of the entire mooring system is greater than zero and is directed to the left, that is, a horizontal restoring force 401 of the mooring system is generated, which is opposite to the direction of the external forces of wind load 301 and wave load 302, and the absolute value is equal, thereby achieving a dynamic balance of the horizontal displacement of the floating hull 2. When the external forces of 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 and returns to the initial equilibrium position.

[0043] The magnitude of the restoring force 401 of the mooring system can be obtained by calculation based on the internal constant tension value of the mooring cables / chains 12L and 12R and the magnitude of the horizontal displacement value of the floating hull 2.

[0044] In actual application, 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.

[0045] When numerically simulating the shared single anchor constant tension mooring system 1 by software modeling, the initial tension of the mooring cables / chains 12L and 12R can be set to the constant tension value, and at the same time, the elastic modulus of the mooring cables / chains describing their material properties is set to infinitesimally small, such as 0.00001, close to zero, that is, the mooring cables can be stretched nearly infinitely when the tension increases very slightly. When the floating hull 2 ​​is horizontally offset from its initial equilibrium position under the action of wind load 301 and wave load 302, the length of the mooring cables / chains 12L and 12R can be obtained based on the straight-line distance between the shared single anchor 20 and the corresponding constant tension fairlead device 10, while keeping the internal tension of the mooring cables / chains 12L and 12R always equal to their initial tension, thereby realizing the numerical simulation of the physical phenomenon of "constant tension".

[0046] like Figure 4 As shown, the shared single anchor 20 of 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 is connected to a shared anchor head tubular structure 23, a plurality of mooring cable connecting ear plates 24 are connected to the upper end of the shared anchor head tubular structure 2, a plurality of connecting inner plates 25 are located inside the shared anchor head tubular structure 23, and a lower cone head structure 26 is connected to the bottom of the shared gravity anchor body 21 and embedded in the soil of the seabed 201.

[0047] The weight of the entire shared single anchor 20 in water is greater than the sum of the tensions of all mooring cables / chains connected to the shared anchor head connecting lug 24, and a certain safety factor is left, and its value is generally between 1 and 2.

[0048] The shared gravity anchor body 21 is a concrete structure. The concrete gravity anchor body 21 has a plurality of internal hollow spaces to provide buoyancy so that the entire concrete gravity anchor floats on the water.

[0049] The shared single anchor 20 has a self-installation function, which is achieved through the following methods and installation processes:

[0050] The first step is to provide buoyancy during assembly at the dock so that the entire shared single anchor 20 floats on the water.

[0051] The second step is to wet-tow the shared single anchor 20 to the offshore wind farm location by a tugboat;

[0052] The third step is to inject ballast water into the empty compartment to make the entire shared single anchor 20 sink to the seabed;

[0053] In the fourth step, the shared gravity anchor lower cone head 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.

[0054] like Figure 5As shown, this embodiment includes a multi-anchor constant tension mooring system 1A, a floating hull 2, an upright wind tower 4 supporting the top of the floating hull 2 ​​above the water surface 101, a wind turbine cabin 6 located at the top of the wind tower 4 and wind turbine blades 8 connected to the wind turbine cabin 6; the multi-anchor constant tension mooring system 1A includes: at least three anchor piles 30 located on the seabed 201 and corresponding three mooring cables / chains 12 with constant tension.

[0055] The mooring cable / chain 12 is made of conventional steel cable, steel chain, polyester cable or nylon cable, or a combination of the above cables / chains.

[0056] In other cases, 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 fairlead devices 10; and a floating hull 2, wherein the floating hull 2 ​​has an upper structure supporting wind turbines 4, 6, 8 above the waterline 101 and a lower structure at a mooring point below the waterline 101 to which the constant-tension fairlead devices 10 are connected.

[0057] The anchor pile 30 is in the form of a driven pile, a suction anchor or other anchor piles with sufficient vertical capacity, and also adopts the self-installable concrete gravity anchor described above according to this embodiment.

[0058] Each mooring cable / chain 12 is connected at one end to a corresponding constant tension fairlead device 10 and at the other end to a corresponding anchor pile 30 located on the seabed 201 .

[0059] The plurality of anchor piles 30 are evenly arranged on the seabed 201 in a geometrically symmetrical manner with the floating hull 2 ​​as the center, and each mooring cable / chain 12 extends outward and downward from the floating hull 2 ​​to a corresponding anchor pile 30 on the seabed 201 .

[0060] The horizontal distance from each anchor pile 30 to the constant tension fairlead device 10 on the corresponding floating hull 2 ​​is generally about 40% to 50% of the water depth.

[0061] Specifically, the setting of the position of each anchor pile 30 is based on the maximum allowable horizontal displacement of the floating hull 2 ​​.

[0062] When the floating hull 2 ​​is horizontally offset from its initial equilibrium position, the constant tension fairlead 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.

[0063] The constant tension fairlead device 10 is an active constant tension variable length device, a passive constant tension variable length device or a semi-active constant tension variable length device connected to a mooring point below the waterline 101 of the floating hull 2.

[0064] Existing constant tension variable length devices used in other fields include constant tension winches and top tensioners.

[0065] like Figure 6 As shown, taking a simplified two-dimensional mooring system of two anchor piles and two mooring cables / chains as an example, when the floating hull 2 ​​is horizontally offset from its initial equilibrium position under the action of wind load 301 and wave load 302, the constant tension fairlead device 10 in the multi-anchor constant tension mooring system 1A of the present invention changes the effective length of the mooring cables / chains 12L and 12R while maintaining the internal tension of the mooring cables / chains 12L and 12R at a constant value.

[0066] When the floating hull 2 ​​is horizontally offset from its initial equilibrium position toward the right in the figure under the action of wind load 301 and wave load 302, the floating hull 2 ​​is offset away from the left anchor pile 30L, resulting in the effective length of the mooring cable / chain 12L connected to the left side of the floating hull 2 ​​becoming longer and the horizontal component of its tension becoming larger. At the same time, the floating hull 2 ​​is offset close to the right anchor pile 30R, resulting in the length of the mooring cable / chain 12R connected to the right side of the floating hull 2 ​​becoming shorter and the horizontal component of its tension becoming smaller.

[0067] The horizontal resultant force of the tension of the entire mooring system generated thereby is greater than zero and is directed to the left, i.e., a horizontal restoring force 401 of the mooring system is generated, which is opposite to the direction of the external forces wind load 30 and wave load 302 and has the same absolute value, thereby achieving a dynamic balance of the horizontal displacement of the floating hull 2.

[0068] When the external forces wind load 301 and wave load 302 disappear, the floating hull 2 ​​moves to the left under the action of the mooring system restoring force 401 and returns to the initial equilibrium position.

[0069] The magnitude of the restoring force 401 of the mooring system can be obtained by calculation based on the internal constant tension value of the mooring cables / chains 12L and 12R and the magnitude of the horizontal displacement value of the floating hull 2.

[0070] In actual application, the final setting of the internal constant tension value of the mooring cable / chain 12 depends on the maximum dynamic external load wind load 301 and wave load 302. When the shared single anchor constant tension mooring system 1A is numerically simulated by software modeling, the initial tension of the mooring cables / chains 12L and 12R can be set to the constant tension value, and at the same time, the elastic modulus of the mooring cables / chains describing its material properties is set to infinitely small, such as 0.00001, close to zero, that is, the mooring cable can be stretched nearly infinitely when the tension increases very little. In this way, when the floating hull 2 ​​is horizontally offset from its initial equilibrium position under the action of wind load 301 and wave load 302, the length of the mooring cables / chains 12L and 12R can be obtained according to the straight-line distance between the anchor piles 30L and 30R and the corresponding constant tension fairlead device 10, and the internal tension of the mooring cables / chains 12L and 12R is always kept equal to its initial tension, thereby realizing the numerical simulation of the physical phenomenon of "constant tension".

[0071] Compared with the shared single anchor constant tension mooring system 1 of the present invention, the cost of the multi-anchor constant tension mooring system 1A of the present invention may be a little higher, and the impact on the marine environment is also a little greater. However, compared with the traditional catenary mooring system, the cost of the multi-anchor constant tension mooring system 1A of the present invention is still much lower, and the impact on the marine environment is also much smaller. At the same time, the multi-anchor constant tension mooring system 1A of the present invention may have better flexibility in application than the shared single anchor constant tension mooring system 1 of the present invention in certain specific occasions.

[0072] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A variable length constant tension mooring method for a floating offshore structure, characterized in that: When a floating offshore structure, i.e. a floating body, is horizontally deflected from its initial equilibrium position under the action of external loads, the internal tension of the mooring cable in its mooring system is fixed by a constant tension fairlead device connected to the floating body, and 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 change of the horizontal deviation 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 floating body returns to the initial equilibrium position, while the physical length of the mooring cable returns to the initial length, and the internal tension of the mooring cable remains unchanged.

2. The variable length constant tension mooring method according to claim 1 is characterized in that: When constructing the numerical model of the floating body and its mooring cables, i) setting the initial tension of the mooring line to a constant tension value; ii) The elastic modulus of the mooring cable is set to be close to infinitesimal, that is, the mooring cable can be stretched close to infinitely when the tension is increased very slightly, so that when the buoy is horizontally displaced from its initial equilibrium position under the action of external load, the length of the mooring cable is obtained according to the straight-line distance between the anchor pile and the corresponding constant tension fairlead device, while ensuring that the internal tension of the mooring cable is always equal to its initial tension, thereby realizing the numerical simulation of the constant tension physical phenomenon of the mooring system.

3. A shared single anchor variable length constant tension mooring system, characterized in that: include: 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 fairleads connected to the floating hull, wherein: The shared single anchor is a self-installable concrete gravity anchor, suction anchor pile or driven anchor pile. The mooring rope / chain is steel cable, steel chain, polyester rope or nylon rope or a combination thereof. The constant tension fairlead device is an active constant tension variable length device, a passive constant tension variable length device or a semi-active constant tension variable length device connected to a mooring point below the waterline of a floating hull.

4. The shared single anchor variable length constant tension mooring system according to claim 3 is characterized in that: One end of each mooring cable / chain is connected to the constant tension fairlead device on the corresponding floating hull, and the other end is connected to a shared single anchor fixed on the seabed, which is located at the geometric center of the constant tension mooring system on the seabed, that is, the intersection of the vertical centerline of the floating hull and the seabed; multiple mooring cables / chains are arranged geometrically symmetrically with the shared single anchor as the center, and the internal tension of the mooring cables / chains is a constant value.

5. The shared single anchor variable length constant tension mooring system according to claim 3 or 4, characterized in that: The self-installable concrete gravity anchor comprises: 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 is connected to a shared anchor head tubular structure, A plurality of mooring cable connection ear plates are connected to the upper end of the shared anchor head tubular structure, and a plurality of connection inner plates are located inside the shared anchor head tubular structure. A lower cone structure is embedded in the seabed soil.

6. The shared single anchor variable length constant tension mooring system according to claim 5 is characterized in that: The self-installable concrete gravity anchor further comprises: Multiple internal hollow spaces provide buoyancy, allowing the entire concrete gravity anchor to float on the water; The self-installable system includes: In the first step, the concrete gravity anchor is assembled at the dock and is in a floating state; The second step is to wet-tow the concrete gravity anchor to the offshore wind farm location by a tugboat; The third step is to inject ballast water into the empty tank to make the entire concrete gravity anchor sink to the seabed; The fourth step is that during the sinking process, the lower cone head of the concrete gravity anchor is embedded below the mud surface of the seabed under the action of gravity, completing the self-installation process.

7. A shared single anchor variable length constant tension mooring method according to any one of claims 3 to 6, characterized in that: When the floating hull is horizontally offset from the initial equilibrium position under the action of external force, 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 change of the horizontal offset of the floating hull. The effective length of some mooring cables becomes longer and some becomes shorter, thereby 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 the initial equilibrium position, the effective length of each mooring cable returns to the initial length, and the internal tension of each mooring cable remains unchanged.

8. A multi-anchor variable length constant tension mooring system, characterized in that: include: A plurality of anchor piles located on the seabed and a plurality of corresponding mooring cables / chains with constant tension, A floating hull and Multiple constant tension mooring system subsystems; The constant tension mooring system subsystem comprises: an anchor pile fixed on the seabed, a mooring cable / chain and a corresponding constant tension fairlead device connected to the floating hull.

9. The multi-anchor variable length constant tension mooring system according to claim 8, characterized in that: A plurality of anchor piles located on the seabed are evenly arranged on the seabed in a geometrically symmetrical manner extending outward and downward with the floating hull as the center, and the horizontal distance from each anchor pile to the constant tension fairlead device on the corresponding floating hull is usually set to 50% of the water depth; Each of the plurality of mooring cables / chains has one end connected to a corresponding constant tension fairlead device and the other end connected to a corresponding anchor pile located on the seabed; The internal tension of the mooring line / chain is a constant value.

10. A multi-anchor variable length constant tension mooring method according to the system of claim 8 or 9, characterized in that: When the floating hull is horizontally deviated from the 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, and 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 change of the horizontal deviation of the floating hull, wherein the effective length of the mooring cable connected to the anchor away from the floating hull becomes longer, and the effective length of the mooring cable connected to the anchor close to the floating hull becomes shorter, thereby generating a mooring system restoring force; When the external force disappears, the floating hull returns to its initial equilibrium position under the action of the restoring force of the mooring system, the effective length of each mooring cable returns to its initial length, and the internal tension of each mooring cable remains unchanged.

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