Mooring rope for tension mooring floats

Abstract

The present invention aims to provide a tension mooring rope for a tension mooring floating body that can equalize the tension generated in each tension mooring rope without adjusting the length of each tension mooring rope of each mooring rope bundle supporting the tension mooring floating body, and prevents resonance with the sea wave period. The above problem is solved by a mooring rope for a tension mooring float that connects a connecting part (5b) formed on the tension mooring float and a seabed mooring part (9) fixed to the seabed (103), and is configured such that tension is generated in the tension mooring rope (7) by the buoyancy generated in the tension mooring float (5) by being connected by the tension mooring rope (7), and the tension mooring float (5) is configured to be maintained in a tension mooring state. The tension mooring rope (7) is configured such that a low-strength mooring rope (7b), which has low elongation stiffness calculated by multiplying the longitudinal elastic modulus and cross-sectional area of ​​the rope material, and a high-strength mooring rope (7a), which has high elongation stiffness compared to the low-strength mooring rope (7b), are connected through a connecting part.

Description

Technology Field

[0001] The present invention relates to a mooring rope for a tensioned moored floating body, and more specifically, it is possible to equalize the tension generated in each mooring rope without adjusting the length of each mooring rope in each mooring rope bundle that moores and supports the tensioned moored floating body. In addition, the present invention relates to a mooring rope for a tensioned moored floating body in which resonance caused by the period of sea waves and the vibration period generated by a wind turbine is prevented. Background Technology

[0002] Traditionally, wind power generation facilities were primarily installed on land. However, on land, obstacles such as forests and buildings blocked the wind, turbulence was prone to occur, and wind speeds were often unstable.

[0003] Accordingly, a plan to install wind power generation facilities offshore has been proposed. Offshore, there are no obstacles that block wind, such as forests or buildings; turbulence is less likely to occur compared to land; and stable, large winds are frequently generated. Therefore, installing wind power generation facilities offshore can be seen as enabling more stable wind power generation and the supply of large amounts of electricity compared to land-based facilities.

[0004] When installing wind power generation facilities offshore, structures are required to support the power generation equipment (windmills and generators). Such structures include bottom-mounted types, which are fixed to the seabed and extend to the surface where windmills and generators are mounted, and floating types, which consist of a floating body moored to the seabed by mooring cables and on which windmills and generators are mounted.

[0005] Floating systems have the advantage of being able to be installed in deeper waters than bottom-mounted systems. Since deep waters are generally located away from the coast, they are advantageous in that wind conditions are good and wind power generation can be carried out stably. In particular, floating systems are advantageous for Japan because the surrounding waters are deeper than those of other countries.

[0006] Floating structures include catenary mooring structures, which maintain their position by loosely connecting a seabed mooring facility and a floating body with mooring ropes.

[0007] In addition, as described in Patent Document 1, there is also a Tension Leg Platform (TLP) that forcibly pulls a floating body down by a mooring rope to submerge a portion of it underwater, and maintains its position by generating tension in the mooring rope through the buoyancy of the floating body.

[0008] Since the position of the float is maintained by the tension of the mooring rope, the tensioned mooring float is advantageous compared to the catenary mooring system in that it facilitates the miniaturization of the float and also provides high stability through the tension state of the mooring rope. Prior art literature

[0009] Patent Document 1: Japanese Patent Publication No. JP 2023-124020 The problem to be solved

[0010] A tensioned moored floating body is moored and supported by installing multiple sets of mooring rope bundles, each consisting of multiple mooring ropes, on each column constituting the floating body. For each mooring rope in each mooring rope bundle, a steel wire cable made of a material that is resistant to elongation and has high tensile strength may be used.

[0011] In each mooring rope bundle of a column, it is necessary for tension to be applied evenly to each mooring rope. If the tension is not even, some mooring ropes will not be subjected to tension or will only have weak tension, while others will be subjected to excessively strong tension, resulting in uneven loading on each mooring rope. This can lead to damage to the mooring ropes or supporting structures subjected to uneven loading, and also cause problems with durability.

[0012] In order to equalize the tension generated in each mooring rope, it is necessary to adjust the length of each mooring rope using large winch equipment, etc.

[0013] However, using large winch equipment results in an increase in the weight of installations on the floating structure, necessitates making the floating structure itself larger, and leads to higher manufacturing costs.

[0014] As a configuration that eliminates the need for equipment to adjust the length of the mooring rope, one can consider measuring the depth to the top of the pile foundation that secures the lower end of the mooring rope to the seabed in advance on-site, and determining in advance the required length of the mooring rope by determining the distance from the mooring rope mounting part on the floating body side, which secures the upper end of the rope, to the top of the pile foundation. The mooring rope is manufactured to the required length on land, and its upper end is secured by the mooring rope connection part on the floating body side, while its lower end is secured by the top of the pile foundation.

[0015] However, the length of the mooring rope includes various errors such as measurement errors when measuring the depth to the top of the pile foundation, manufacturing errors when making the mooring rope, and thermal expansion and contraction due to temperature changes. Therefore, simply making the mooring ropes to the required length in advance is not enough to equalize the tension generated in each mooring rope.

[0016] Meanwhile, one can consider manufacturing mooring ropes using materials with low tensile strength (softness), such as polyester ropes, and allowing the error to be absorbed by the elongation of the rope itself.

[0017] However, if mooring ropes are fabricated using materials with low stiffness, the spring constant k of the mooring rope decreases, and the natural frequencies of the vertical and roll-pitch directions characteristic of tensioned mooring floating bodies decrease, raising concerns that vertical resonance caused by the vibration period of the wind turbine and roll-pitch resonance caused by the period of sea waves may occur.

[0018] If resonance occurs with the ocean wave period and the vibration period caused by the wind turbine, there is a risk of damage to mooring cables or support structures, and durability issues may also arise.

[0019] Accordingly, the objective of the present invention is to provide a mooring rope for a tensioned mooring floating body that can equalize the tension generated in each mooring rope without adjusting the length of each mooring rope bundle supporting the tensioned mooring floating body, and also prevents resonance with the wave period and vibration period caused by the wind turbine.

[0020] In addition, other problems of the present invention are clarified by the following description. means of solving the problem

[0021] The above problem is solved by each of the following inventions.

[0022] 1.

[0023] A mooring rope for a tension mooring floating structure that connects a connection part formed on a tension mooring floating structure supporting a wind power generation facility offshore and a seabed mooring part fixed to the seabed,

[0024] The aforementioned connecting part and the aforementioned seabed mooring part are connected by the aforementioned tension mooring rope, thereby generating tension in the aforementioned tension mooring rope by the buoyancy generated in the aforementioned tension mooring floating body, and the aforementioned tension mooring floating body is configured to be maintained in a tension mooring state.

[0025] The aforementioned tension mooring rope comprises a low-stiffness mooring rope with low elongation stiffness, calculated by multiplying the Young's modulus and cross-sectional area of ​​the rope material, and a high-stiffness mooring rope with higher elongation stiffness compared to the aforementioned low-stiffness mooring rope, which are connected through a connector.

[0026] The aforementioned mooring material of the aforementioned low-rigidity mooring rope is a resin rope, and the aforementioned high-rigidity mooring rope is a steel wire cable composed of multiple steel wires bundled together, and

[0027] The above-described tension mooring rope is characterized in that, when the elongation strength of the above-described resin rope is set to 1, the elongation strength of the above-described steel wire cable is 2 to 5 times the elongation strength of the above-described resin rope.

[0028] 2.

[0029] A mooring rope for a tension mooring floating structure that connects a connection part formed on a tension mooring floating structure supporting a wind power generation facility offshore and a seabed mooring part fixed to the seabed,

[0030] The aforementioned connecting part and the aforementioned seabed mooring part are connected by the aforementioned tension mooring rope, thereby generating tension in the aforementioned tension mooring rope by the buoyancy generated in the aforementioned tension mooring floating body, and the aforementioned tension mooring floating body is configured to be maintained in a tension mooring state.

[0031] The aforementioned tension mooring rope consists of a low-rigidity mooring rope and a high-rigidity mooring rope, which has higher elongation stiffness compared to the aforementioned low-rigidity mooring rope, connected through a connector.

[0032] The aforementioned low-rigidity mooring rope is a resin rope, and the aforementioned high-rigidity mooring rope is a steel wire cable composed of multiple steel wires bundled in parallel.

[0033] A mooring rope for a tensioned mooring floating body, characterized in that the aforementioned tensioned mooring rope has a length of at least 50% of its total length as the aforementioned high-rigidity mooring rope.

[0034] 3.

[0035] The aforementioned resin rope is a polyester rope formed by preparing multiple sub-ropes by twisting multiple polyester wires together and binding the multiple corresponding sub-ropes in parallel.

[0036] 4.

[0037] The aforementioned tension mooring floating body is characterized by having at least three hollow columnar columns extending in the vertical direction arranged to form a triangular shape in a planar plane, three upper beams connecting each of the three aforementioned columns above the sea surface, and three lower beams connecting below the sea surface, and having a wind power generation facility supported on one of the aforementioned columns, and a mooring rope for a tension mooring floating body as described in 1 or 2 above. Effects of the invention

[0038] According to the present invention, since a material with low elongation stiffness is used in a part of each mooring rope of each mooring rope bundle that moores and supports a tensioned mooring floating body, the tension generated in each mooring rope can be evenly distributed by the elongation of the part with low stiffness without adjusting the length of each mooring rope, and high durability can be realized by preventing damage to the mooring rope or support structure due to uneven loading on each mooring rope.

[0039] In addition, according to the present invention, since there is no need to adjust the length of each mooring rope, there is no need to use large winch equipment, and the weight of the installation on the floating body is reduced, making it possible to miniaturize the floating body itself and reduce manufacturing costs.

[0040] Furthermore, according to the present invention, compared to the case where only materials with low elongation stiffness are used for the entire mooring rope, the spring constant of the mooring rope is large and the natural frequency is high, so resonance of the vibration period caused by the sea wave period and the wind turbine is prevented, and damage to the mooring rope or support structure due to resonance is prevented, thereby enabling high durability. Brief explanation of the drawing

[0041] FIG. 1 is a front view showing an offshore wind power generation facility equipped with a tension mooring floating body using a mooring rope for a tension mooring floating body according to an embodiment of the present invention. FIG. 2 is a perspective view showing the tension moored floating body of FIG. 1, (A) is a perspective view showing the tension moored floating body seen from one side, and (B) is a perspective view showing the tension moored floating body seen from the other side. Figure 3 is a side view of the mooring rope for the tension mooring floating body of Figure 1. Figure 4 is a cross-sectional view of a mooring rope (high-rigidity mooring rope) for a tensioned mooring floating body of Figure 1. Figure 5 is a graph showing the relationship between the length of the low-stiffness mooring rope and the combined elongation amount in the mooring rope for the tension mooring floating body of Figure 1. Figure 6 is a graph showing the relationship between the length of the low-stiffness mooring rope and the composite spring constant in the mooring rope for the tension mooring floating body of Figure 1. Specific details for implementing the invention

[0042] Preferred embodiments of the present invention will be described below.

[0043] FIG. 1 is a front view showing an offshore wind power generation facility (1) equipped with a tension mooring floating body using a tension mooring rope for a tension mooring floating body according to an embodiment of the present invention.

[0044] As shown in FIG. 1, the offshore wind power generation facility (1) is configured to include a wind power generation facility (3), a tension leg platform (TLP) (5) (hereinafter referred to simply as a platform) on which the wind power generation facility (3) is mounted, a tension mooring rope (7) with its upper end fixed to the tension leg platform (5), and a seabed mooring section (9) with its lower end fixed to the seabed.

[0045] The mooring rope for the tension mooring float of the present embodiment is a tension mooring rope (7) that forcibly pulls down the tension mooring float (5) carrying the wind power generation facility (3) so that a part of it is submerged underwater, and maintains the tension mooring float (5) in a predetermined position by the tension generated by the buoyancy of the tension mooring float (5).

[0046] [Wind Power Generation Equipment]

[0047] The wind power generation facility (3) is a power generation facility that converts wind into electricity, and as shown in FIG. 1, it is equipped with a tower (31), a nacelle (33), a boss (35), and a blade (37). In this embodiment, the wind power generation facility (3) converts wind into electricity by rotating the blade (37) and the boss (35) by wind power, and by rotating the rotor of the generator connected to the boss (35) due to this rotational force.

[0048] The tower (31) is a supporting column that supports the entire wind power generation facility (3) and is a column-shaped structure that extends in the vertical direction. The external shape of the tower (31) is preferably a cylindrical shape or a conical shape with a diameter that widens toward the bottom, but is not particularly limited as long as strength capable of supporting the entire wind power generation facility (3) is obtained. The lower end of the tower (31) is connected and supported to a flange portion (5a) provided by a column (51) installed on the upper surface of the part of the tension mooring floating body (5) exposed above the sea surface (101).

[0049] The nacelle (33) is a hollow structure containing a generator, installed at the top of the tower (31), and has a spindle shape with a horizontal axial direction. The nacelle (33) and the top of the tower (31) are connected by a rotating mechanism that allows the nacelle (33) to rotate around a vertical axis. The nacelle (33) is directed toward the axial direction of the boss (35) in the direction where the wind pressure is strongest.

[0050] Inside the nacelle (33), a power transmission shaft that transmits the rotational force of the boss (35), a speed increaser (gearbox, etc.) connected to the power transmission shaft, a brake that stops the power transmission shaft in case of emergency (typhoon, etc.) or inspection, and a generator with a rotor connected to the power transmission shaft are installed.

[0051] The boss (35) is a cylindrical member that supports the blade (37) and is coaxially connected to the tip of the power transmission shaft. The boss (35) is rotatable with the horizontal direction as its central axis and is located at the horizontal tip of the nacelle (33).

[0052] The blade (37) is a blade of a windmill that converts wind power into rotational power, and a plurality of blades are installed protruding from the outer circumference of the boss (35) in the diameter direction of the boss (35). In this embodiment, three blades (37) are installed protruding at equal intervals along the circumferential direction of the boss (35). When the blade (37) receives wind, it rotates together with the boss (35) around the boss (35). As the boss (35) rotates, the rotor of the generator rotates, and power generation is achieved.

[0053] The electricity generated by the generator is transmitted to land via uninhabited undersea transmission cables.

[0054] [Tension Moored Floating Body]

[0055] FIG. 2 is a perspective view showing the tension moored floating body of FIG. 1, FIG. 2(A) is a perspective view showing the tension moored floating body seen from one side, and FIG. 2(B) is a perspective view showing the tension moored floating body seen from the other side.

[0056] The tension mooring float (5) is a float that supports the wind power generation facility (3). As shown in FIG. 1, the tension mooring float (5) is floated on the sea and the wind power generation facility (3) is mounted on the part above the sea surface (101). The tension mooring float (5) has a sealed hollow section inside, so that the specific gravity of the entire outer shape becomes less than 1, allowing it to float on the sea.

[0057] Additionally, as shown in FIG. 2, the tension moored floating body (5) is provided with at least three hollow columnar columns extending in the vertical direction, arranged to form an approximate equilateral triangle shape when viewed in a plane. Also, as shown in FIG. 1 and FIG. 2, columns (52) and columns (53) are connected by upper beams (bracing) (54) above the sea surface and by lower beams (pontoons) (57) below the sea surface (101). Likewise, columns (51) and columns (52) are connected by upper beams (bracing) (55) and lower beams (pontoons) (59), and columns (51) and columns (53) are connected by upper beams (bracing) (56) and lower beams (pontoons) (58).

[0058] In the example shown, the column (51) is provided with a flange portion (5a) and configured to support the wind power generation facility (3).

[0059] In the illustrated example, the columns (51, 52, 53) are hexagonal prisms, and in the case of a modified hexagonal shape with a portion protruding in the plane, the shape of the columns is shown. The shape of the columns is not limited to this, and may be a regular hexagon, a pentagon, or a circular shape in the plane.

[0060] The upper beam (54, 55, 56) is in the shape of a square prism in the illustrated example, but is not limited thereto and may be in the shape of a cylinder or may be formed as a truss structure.

[0061] In this embodiment, the tension mooring float (5) may be equipped with a ballast tank not shown inside each of the three columns (51, 52, 53). The buoyancy and draft of the tension mooring float (5) can be adjusted by supplying and draining ballast water to and from the ballast tank. When installing the tension mooring float (5), the buoyancy can be reduced to facilitate the attachment of the tension mooring rope (7).

[0062] Additionally, FIG. 1 shows an example in which a total of nine connection parts (5b) are installed in three sets of three locations each on each column (51, 52, 53) of a tension mooring floating body (5). The upper end of a tension mooring rope (7) is connected to each of these connection parts (5b). The lower end of these tension mooring ropes (7) is connected to the seabed mooring part (9) on the seabed side, thereby connecting the tension mooring floating body (5) to a plurality of seabed mooring parts (9) which are mooring facilities on the seabed (103).

[0063] Accordingly, tension is generated in the tension mooring rope (7) by the buoyancy of the tension mooring float (5), and as a result, the tension mooring float (5) is maintained in a fixed position. That is, when the entire tension mooring float (5) is submerged in water, the buoyancy acting in the opposite direction (upward) to gravity is greater than the gravity acting downward, so the tension mooring float (5) attempts to rise to a position where buoyancy and gravity are balanced. This is because buoyancy is generated in proportion to the volume of the part of the tension mooring float (5) submerged below the sea surface. The tension mooring rope (7) maintains the tension mooring float (5) at a depth where the buoyancy of the tension mooring float (5) becomes greater than gravity.

[0064] In this state, since the buoyancy of the tension moored floating body (5) is prevented by the tension mooring rope (7), the forced buoyancy of the tension moored floating body (5), which is a buoyancy greater than gravity, is applied to the tension mooring rope (7). Tension is generated in the tension mooring rope (7) to which the forced buoyancy is applied, and a tension mooring state is established. In the tension mooring state, the tension moored floating body (5) is maintained in a fixed position by the tension generated in the tension mooring rope (7).

[0065] In this embodiment, even if there is a rise or fall in the sea level (change in seabed depth) due to tides, tension is generated in the tension mooring rope (7) within a predetermined range and the tension mooring state is maintained.

[0066] [Underwater Mooring Section]

[0067] The seabed mooring section (9) is the upper part of the pile foundation constructed on the seabed (103) in this embodiment. The seabed mooring section (9) is a mooring facility on the seabed (103) and maintains the tensioned mooring floating body (5) in a predetermined position through the tensioned mooring rope (7). The seabed mooring section (9) is equipped with a connecting part, such as a hook or ring, to which the lower end of the tensioned mooring rope (7) is connected.

[0068] The seabed mooring section (9) has a structure that is not pulled out from the seabed (103) by the tensile force applied from the tension mooring rope (7) when maintaining the position of the tension mooring floating body (5) by forced buoyancy, and other known mooring facilities may also be used if they are corrosion-resistant so as not to easily corrode underwater. Specifically, gravity anchors, pile anchors, suction anchors, etc. may be used. In this embodiment, since the length of the tension mooring rope (7) is not adjusted, any method that can securely fix the position of the lower end of the tension mooring rope (7) is sufficient and is not particularly limited.

[0069] In this embodiment, nine seabed mooring units (9) are installed for one offshore wind power generation facility (1). The nine seabed mooring units (9) are arranged in sets of three and are installed on the seabed in the vertical direction of each column (51, 52, 53) of the tension mooring floating body (5), and a total of three sets of seabed mooring units (9) are installed.

[0070] In this embodiment, three connection sections (5b) are installed on each of the columns (51, 52, 53), and the upper end of the tension mooring rope (7) is fixed to the connection section (5b) on the tension mooring floating body side, and a number of seabed mooring sections (9) equal to the number of connection sections (5b) are installed on the seabed in a vertical direction from the connection section (5b). A total of three sets of mooring rope bundles, each consisting of three tension mooring ropes (7), are fixed to the connection section (5b) and the seabed mooring section (9). Accordingly, the upper end of the tension mooring rope (7) is fixed to the connection section (5b) installed on the tension mooring floating body (5), and the lower end of the tension mooring rope (7) is fixed to the seabed mooring section (9), and the tension mooring floating body (5) is moored and maintained.

[0071] In this embodiment, the number of seabed mooring sections (9) and the number of tension mooring ropes (7) can be appropriately set within a range that allows the tension applied from the tension mooring ropes (7) to be distributed so that the tension mooring floating body (5) is not pulled out from the seabed (103) when the tension mooring floating body (5) is maintained in a predetermined position by forced buoyancy. For example, for one offshore wind power generation facility, six seabed mooring sections (9) and six tension mooring ropes (7) can be used to moor and maintain the tension mooring floating body (5) by three sets of mooring rope bundles, each consisting of two tension mooring ropes (7).

[0072] [Tension Mooring Rope]

[0073] The tension mooring rope (7) is a mooring rope connecting the tension mooring float (5) and the seabed mooring section (9), and the tension mooring float (5) is kept in a tension mooring state by the tension generated by the buoyancy of the tension mooring float (5), thereby maintaining the tension mooring float (5) in a predetermined position.

[0074] Figure 3 is a side view of the mooring rope for the tension mooring floating body of Figure 1.

[0075] The tension mooring rope (7) of the present embodiment is formed by connecting a high-rigidity mooring rope (7a) made of a material with high elongation strength and a low-rigidity mooring rope (7b) made of a material with low elongation strength in series by means of a connector (7c), as shown in FIG. 3. The connector (7c) is a mechanism that connects the upper end of the high-rigidity mooring rope (7a) and the lower end of the low-rigidity mooring rope (7b), and various shapes such as a hook shape or a ring shape can be used, and its configuration is not particularly limited. The tension mooring rope (7) has strength that does not yield or break due to tension generated by the buoyancy of the tension mooring floating body (5), and corrosion resistance that does not easily corrode underwater.

[0076] Figure 4 is a cross-sectional view of a mooring rope (high-rigidity mooring rope) for a tensioned mooring floating body of Figure 1.

[0077] In this embodiment, the high-rigidity mooring rope (7a) is a steel wire cable as shown in FIG. 4, and the steel wire cable has a plurality of wires (galvanized steel wires) (71a) arranged in parallel, and the outer circumference of these wires is covered by a protective layer (70a). In this embodiment, the high-rigidity mooring rope (7a) has, for example, about 200 to 400 wires and a covering diameter, for example, about 100 mm to 200 mm.

[0078] In the present embodiment, the illustrated example shows a plurality of wires bundled in parallel, but is not limited thereto, and if the plurality of wires are bundled, they do not have to be in parallel.

[0079] The low-rigidity mooring rope (7b) is preferably a resin rope. The material of the resin rope may be polyamide, polyester, etc. Polyamide may be, for example, nylon 6, nylon 66, nylon 11, nylon 12, etc. The resin rope is preferably a polyester rope. The polyester rope is made of wires (for example, polyester strands ( An example can be given in which multiple sub-ropes made by twisting )) are bundled in parallel, a sand filter is wound around them, and the outer surface is covered with a protective layer. An example of the protective layer is one made by weaving or braiding polyester wires.

[0080] In this embodiment, the low-rigidity mooring rope (7b) may have a diameter of, for example, about 280 mm.

[0081] In this embodiment, in the example of FIG. 1, a low-rigidity mooring rope (7b) is mounted on the connection part (5b) on the floating body side and a high-rigidity mooring rope (7a) is mounted on the seabed mooring part (9) on the seabed side, but the low-rigidity mooring rope (7b) may be mounted on the seabed mooring part (9) on the seabed side and the high-rigidity mooring rope (7a) may be mounted on the connection part (5b) on the floating body side.

[0082] These tension mooring ropes (7) allow for the easing of length precision requirements during installation and the avoidance of resonance of the tension mooring floating body (5) to be achieved simultaneously.

[0083] The requirement for length precision during installation refers to the allowable range of length error, and a relaxation of the precision requirement means that the allowable range of error is wide. As mentioned above, in one set (three) of tension mooring ropes (7), it is necessary for tension to be evenly generated in each tension mooring rope (7). If there is a large error in the length of each tension mooring rope (7), the long tension mooring rope (7) will not generate tension or will only generate weak tension, and the short tension mooring rope (7) will generate excessively strong tension, causing uneven loads on each tension mooring rope (7), and there is a risk that the short tension mooring rope (7) or the supporting structure will be damaged due to excessive tension, and problems with durability will also occur.

[0084] In the tension mooring rope (7) of the embodiment, if the error in length is within the allowable range, the low-rigidity mooring rope (7b) of the short tension mooring rope (7) is extended, so tension is generated in the long tension mooring rope (7), and excessively strong tension is not generated in the short tension mooring rope (7).

[0085] The resonance of the tension moored floating body (5) is, as described above, caused by vibrations according to the rated rotational speed of the wind turbine in the vertical direction, and also by the wave period in the roll-pitch direction.

[0086] Resonance with the wave period can occur when the spring constant k of the tension mooring rope (7) is small and the natural frequency F0 (Hz) of the roll and pitch direction system is low. It can also occur in the vertical direction.

[0087] In this embodiment, there are cases where a large wind turbine (10 MW or more) is supported by a TLP. In such cases, resonance between the vertical direction and the rotation period of the wind turbine, and resonance between the roll-pitch direction and the wave period become a problem.

[0088] The tension mooring rope (7) of the present embodiment is a hybrid mooring rope consisting of a low-rigidity mooring rope (7b) and a high-rigidity mooring rope (7a) connected through a connector (7c), regardless of the rotational period according to the specifications of the installed windmill, so the elongation stiffness can be arbitrarily changed. Accordingly, the axial stiffness and natural period of the mooring rope, which are in a proportional relationship with the elongation stiffness, can also be changed, and as a result, resonance can be avoided. For example, wave periods often have a high frequency of occurrence of periods of 4 to 5 seconds or more to about 20 seconds, and it is necessary to set the natural period differently from the wave period with such high frequency of occurrence. Since the tension mooring rope of the present invention is a hybrid mooring rope as described above, the natural period can be changed by arbitrarily changing the stiffness. Accordingly, the natural period in the roll-pitch direction can be set to 4 seconds or less, so resonance with the wave period can be prevented.

[0089] For the tension mooring rope (7) of the embodiment, the normal tension (4,900 kN (500 tons)) generated per unit, the total length (50 m), the elongation strength (661,500 kN) of the polyester rope (low-rigidity mooring rope (7b)), and the elongation strength (2,142,000 kN) of the steel wire cable (high-rigidity mooring rope (7a)) are shown in Table 1 below. In addition, elongation strength is the product of the Young's modulus (Young's modulus) of the rope material and the cross-sectional area. Table 1 shows an example in which the high-rigidity mooring rope (7a) has an elongation strength at least three times that of the low-rigidity mooring rope (7b).

[0090] In the tension mooring rope (7) of the present invention, when the tension stiffness of the low-stiffness mooring rope (7b) is set to 1, the tension stiffness of the high-stiffness mooring rope (7a) is preferably in the range of 2 to 5 times. By forming a tension mooring rope (7) in this range, the requirement for installation precision and the avoidance of resonance caused by wave cycles or vibrations of windmills can be achieved simultaneously.

[0091] Mooring conditions of tension mooring ropes and elongation stiffness of each material

[0092] Normal tension acting per mooring rope 4,900 kN Total length of the mooring cable 50 m Polyester rope tensile strength (low-strength mooring rope (7b)) 661,500 kN tensile strength of steel wire cable (high-strength mooring rope (7a)) 2,142,000 kN

[0093] As described above, it has been explained that the reduction of installation precision requirements and the avoidance of resonance caused by wave cycles or wind turbine vibrations can be achieved through the ratio of the elongation stiffness of the low-stiffness mooring rope (7b) and the high-stiffness mooring rope (7a) in the tension mooring rope (7). Furthermore, the reduction of construction and installation precision requirements and the avoidance of resonance with wave cycles can also be achieved through the length ratio of the low-stiffness mooring rope (7b) and the high-stiffness mooring rope (7a) in the tension mooring rope (7). Below, an embodiment according to the length ratio of the low-stiffness mooring rope (7b) and the high-stiffness mooring rope (7a) will be described.

[0094] FIG. 5 is a graph showing the relationship between the length of the low-rigidity mooring rope and the combined elongation amount in the mooring rope for the tension mooring floating body of FIG. 1. The relationships shown in FIG. 5 and FIG. 6 represent the case where the low-rigidity mooring rope (7b) and the high-rigidity mooring rope (7a) shown in Table 1 are used.

[0095] As shown in FIG. 5, the length of the low-rigidity mooring rope (polyester rope) (7b) for a total length of 50 m is the horizontal axis, and the elongation of the tension mooring rope (7) when the low-rigidity mooring rope (7b) and the high-rigidity mooring rope (7a) are connected is shown when an axial force of 4,900 kN is applied. In addition, if the low-rigidity mooring rope (7b) at the left end is 0 m, it means that the entire length is the high-rigidity mooring rope (7a), and conversely, if the 50 m at the right end is the entire length is the low-rigidity mooring rope (7b).

[0096] In FIG. 5, the greater the proportion of the low-rigidity mooring rope (7b), the greater the elongation of the tension mooring rope (7). For example, as illustrated in the example, if the total length of the tension mooring rope is 50 m and elongation of 200 mm or more is required in the tension mooring rope (7) to alleviate the requirements for construction and installation precision, the requirements for construction and installation precision can be alleviated by making the length of the low-rigidity mooring rope (7b) 17 m or more.

[0097] Figure 6 is a graph showing the relationship between the length of the low-stiffness mooring rope and the composite spring constant in the mooring rope for the tension mooring floating body of Figure 1.

[0098] As shown in FIG. 6, the length of the low-rigidity mooring rope (polyester rope) (7b) is the horizontal axis, and the result of the composite spring constant when the low-rigidity mooring rope (7b) and the high-rigidity mooring rope (7a) are connected is shown.

[0099] In FIG. 6, as the proportion of low-rigidity mooring ropes (7b) is small and the proportion of high-rigidity mooring ropes (7a) is large, the composite spring constant increases non-linearly. For example, if a spring constant of 20,000 kN / m or more is required to avoid resonance between the wave period and roll-pitch motion of a tensioned mooring floating body (5) as illustrated, the resonance between the wave period and roll-pitch motion can be avoided by making the length of the low-rigidity mooring ropes (7b) 25 m or less.

[0100] As described above, from the examination of the elongation amount and spring constant of the tension mooring rope (7), when the total length of the tension mooring rope (7) is 50 m, the length of the low-rigidity mooring rope (7b) is set to a range of 17 m to 25 m (34% to 50%), thereby allowing for the easing of installation precision requirements and the avoidance of resonance of the tension mooring floating body (5) to be achieved simultaneously.

[0101] In this embodiment, when the water depth is deep and the total length of the tension mooring rope (7) becomes longer, the natural frequency F0 (Hz) of the tension mooring floating body (5) is lowered. In this case, to avoid resonance with the sea wave period, the proportion of the high-rigidity mooring rope (7a) can be increased compared to the case where the total length of the tension mooring rope (7) is 50 m. In this embodiment, regarding the requirement for construction and installation precision as the proportion of the high-rigidity mooring rope (7a) increases, since the high-rigidity mooring rope (7a) also extends in proportion to the total length, the requirement for construction and installation precision can be eased even if the proportion of the high-rigidity mooring rope (7a) is increased.

[0102] From the above, as the water depth increases and the total length of the tension mooring rope (7) increases, the desirable length of the low-rigidity mooring rope (7b) decreases (the ratio also decreases). Therefore, since the ratio of the high-rigidity mooring rope can be set to be longer (the ratio also increases) as the water depth increases, the length of the low-rigidity mooring rope can be shortened. In this embodiment, when the total length of the tension mooring rope (7) is longer than 50 m, it is preferable that the high-rigidity mooring rope (7a) has a length of 50% or more of the total length of the tension mooring rope (7).

[0103] Meanwhile, in the embodiment shown in FIGS. 5 and 6, when the water depth (distance from the seabed mooring section to the connection section of the floating body) is about 50 m, the ratio of high-rigidity mooring rope (7a) and low-rigidity mooring rope (7b) in the tension mooring rope (7) is shown, but when the water depth becomes shallow, the ratio of high-rigidity mooring rope (7a) may be reduced and the ratio of low-rigidity mooring rope (7b) may be increased.

[0104] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the embodiments. Those skilled in the art can derive various modifications and improvements within the scope of the technical concept of the present invention, and such modifications and improvements are also included in the present invention. Explanation of the symbols

[0105] 1: Offshore wind power generation facility 3: Wind power generation facilities 31: Tower 33: Nasel 35: Boss 37: Blade 5: Tension moored float 5a: Flange section 5b: Connection part 51, 52, 53: Column 54, 55, 56: Beam 57, 58, 59: Pontoon 7: Tension mooring rope 7a: High-rigidity mooring rope 70a: Protective layer 71a: Small wire 7b: Low-rigidity mooring rope 7c: Connector 9: Underwater mooring section 101: Sea level 103: Underwater

Claims

Claim 1 A mooring rope for a tensioned mooring floating body that supports a wind power generation facility on the seabed, connecting a connecting part formed on the tensioned mooring floating body and a seabed mooring part fixed to the seabed, wherein the connecting part and the seabed mooring part are connected by the tensioned mooring rope, thereby generating tension in the tensioned mooring rope by the buoyancy generated on the tensioned mooring floating body, and configured to maintain the tensioned mooring floating body in a tensioned mooring state; wherein the tensioned mooring rope comprises a low-rigidity mooring rope with low elongation stiffness calculated by multiplying the Young's modulus of elasticity of the rope material by its cross-sectional area, and a high-rigidity mooring rope with higher elongation stiffness compared to the low-rigidity mooring rope, connected through a connector; wherein the rope material of the low-rigidity mooring rope is a resin rope, and the high-rigidity mooring rope is a steel wire cable composed of multiple steel wires bundled together; and wherein, when the elongation stiffness of the resin rope is set to 1, the elongation stiffness of the steel wire cable is 2 to 5 times the elongation stiffness of the resin rope. Mooring rope. Claim 2 A mooring rope for a tension mooring floating body that connects a connecting part formed on a tension mooring floating body supporting a wind power generation facility on the sea and a seabed mooring part fixed to the seabed, wherein the connecting part and the seabed mooring part are connected by the tension mooring rope, thereby generating tension in the tension mooring rope by the buoyancy generated on the tension mooring floating body, and configured such that the tension mooring floating body can be maintained in a tension mooring state, wherein the tension mooring rope is configured such that a low-rigidity mooring rope and a high-rigidity mooring rope having higher elongation rigidity than the low-rigidity mooring rope are connected through a connector, wherein the low-rigidity mooring rope is a resin rope, and the high-rigidity mooring rope is a steel wire cable composed of multiple steel wires bundled in parallel, and wherein the length of the high-rigidity mooring rope is at least 50% of the total length of the tension mooring rope. Claim 3 A mooring rope for a tensioned mooring floating body, characterized in that, in claim 1 or 2, the resin rope is a polyester rope formed by preparing a plurality of sub-ropes composed of a plurality of polyester wires twisted together and binding the plurality of sub-ropes in parallel. Claim 4 A mooring rope for a tension mooring floating body according to claim 1 or 2, wherein the tension mooring floating body comprises at least three hollow column-shaped columns extending in the vertical direction arranged to form a triangular shape in a planar plane, and comprises three upper beams connecting each of the three columns above the sea surface and three lower beams connecting below the sea surface, wherein the wind power generation facility is supported on one of the columns.

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