Mooring force measuring method in floating body type offshore wind power generation facility

Abstract

To make it possible to measure mooring force underwater over a long period of time by solving problems at once of a conventional method for measuring tension with a sensor installed on a mooring rope.SOLUTION: In a mooring force measuring method, there are provided: a mooring rope 5 extending between a floating body 4 of a floating body type offshore wind power generation facility 1 and the sea bottom; and shape measurement means 20 for measuring a shape of the mooring rope 5. The shape of the mooring rope 5 is measured by the shape measurement means 20, and tension acting on the mooring rope 5 is estimated from the shape of the mooring rope 5. Either an underwater positioning device or an underwater sound prove device for grasping the shape of an underwater structure using sound waves is used as the shape measurement means 20, the underwater positioning device being composed of a plurality of transponders 21 fixed with space in between along the mooring rope 5 and a transceiver 22 fixed on the floating body 4 for transmitting and receiving sound waves between the transponders 21 and itself.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring a mooring force applied to a mooring line extending between a float of a floating offshore wind power generation facility and the seabed. [Background technology]

[0002] Traditionally, hydroelectric, thermal and nuclear power generation have been the main power generation methods used, but in recent years, wind power generation, which uses natural wind to generate electricity, has been attracting attention from the perspective of the environment and the effective use of natural energy. Wind power generation facilities can be installed on land or on water (mainly offshore), but in Japan, which has mountainous terrain behind its coasts, there are few plains in coastal areas where stable winds can be expected. On the other hand, Japan is surrounded by sea on all sides, and the sea has the advantage that winds suitable for generating electricity can be easily obtained and there are fewer restrictions on installation. For this reason, many proposals have been made in recent years for offshore wind power generation facilities or floating structures.

[0003] Depending on the installation method of the foundation structure, offshore wind power generation facilities can be classified into fixed-bottom types, which are installed on the seabed, such as jacket foundations and caisson foundations, floating types, which float on the surface of the sea or in the sea, such as pontoon types, which float as a float on the water surface, semi-submersible types, which float in a submerged position below the water surface, spar types, which float in an upright position like a fishing float, and semi-submersible TLP types, which are secured by tension moorings.

[0004] Fixed-bottom offshore wind power generation facilities are suitable for installation in shallow sea areas with a depth of approximately 60m or less, and floating types are considered to have a cost advantage in waters deeper than that. For this reason, technological development of floating offshore wind power generation facilities is essential in Japan, where shallow sea areas are limited.

[0005] The floats of floating offshore wind power generation facilities are moored by mooring lines such as chains that extend to the seabed. The floats are moored on the ocean for long periods of time, during which time the mooring lines are constantly and repeatedly subjected to large tensions due to the waves, tides, wind conditions, etc. This tension causes problems such as wear, corrosion, and fatigue of the links, which reduces their durability. Therefore, it is extremely important to properly understand the tensions (mooring forces) on the mooring lines, as this can lead to reduced maintenance costs, such as reduced downtime, in order to carry out preventive maintenance such as determining when to replace the mooring lines and preparing replacement parts in advance.

[0006] Known methods for measuring the tension of mooring ropes include monitoring the mooring force by inserting a load meter equipped with a strain gauge between the mooring equipment and the mooring chain or rope, as disclosed in Patent Document 1 below, and measuring the tension of the mooring lines mooring both the left and right sides near the front end of the float using a tension sensor, as disclosed in Patent Document 2 below. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 155796 / 1983 [Patent Document 2] JP 2001-1980 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, as described in the above Patent Document 1, strain gauges installed on mooring ropes have the following problems. That is, since the mooring ropes are underwater, long-term measurements become difficult due to corrosion and other factors. Although long-term measurements become possible if waterproofing measures are taken, durability becomes an issue in an environment of seawater and constant water pressure. In addition, when the applicant attached strain gauges to an actual device for testing, it became unusable within a few months.

[0009] In addition, when a spar-type float is towed to the site while lying on its side, the mooring rope is detached from the float and the float is towed while in the ocean, and the installation of the strain gauges and other equipment is also carried out in the ocean, which makes the installation technically difficult due to swaying and other factors.

[0010] Furthermore, when a strain gauge breaks down, there is a problem in that it is difficult to attach a new strain gauge to the mooring rope by gluing or welding, since the mooring rope is underwater.

[0011] On the other hand, as described in Patent Document 2, the installation of a tension sensor on a mooring rope has the following problem: Since the measurement using a tension sensor is a method in which a tension meter is clamped to the end of a chain or joint and connected to the chain, there is an issue with durability underwater, just like with measurements using strain gauges.

[0012] Furthermore, because an additional object is placed in the middle of the chain, its reliability as a mooring rope changes, and it becomes necessary to re-prove that it meets the standards of the certification agency, which creates the problem of unnecessary work.

[0013] Therefore, the main objective of the present invention is to provide a method for measuring mooring forces in floating offshore wind power generation facilities that can solve all the problems associated with the conventional method of measuring tension by installing sensors on mooring lines, and that enables the mooring forces to be measured underwater over long periods of time. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention according to claim 1 provides a floating offshore wind power generation facility comprising a mooring line extending between a float of the floating offshore wind power generation facility and a seabed, and a shape measuring means for measuring the shape of the mooring line, A mooring force measuring method for a floating offshore wind power generation facility is provided, characterized in that the shape of the mooring rope is measured by the shape measuring means, and the tension acting on the mooring rope is estimated from the shape of the mooring rope.

[0015] In the invention described in claim 1 above, rather than installing sensors such as strain gauges or tension sensors on the mooring rope to measure the tension, the shape of the mooring rope is measured by the shape measurement means, and the tension acting on the mooring rope is estimated from the shape of the mooring rope. Therefore, there are no problems with sensor deterioration or durability, as occurs when a sensor is installed, and the mooring force can be measured underwater for long periods of time.

[0016] As the present invention according to claim 2, the shape of the mooring rope is (1) There is slack in the mooring rope and the catenary cannot function properly. (2) A slack state in which a part of the mooring line on the floating body side forms a catenary and the other part is landed on the seabed. (3) The fixed anchor point of the seabed end of the mooring rope is in a tangential direction to the seabed surface. (4) A tensioned state in which the fixed anchor point at the bottom end of the mooring rope forms a certain angle with the seabed. (5) The mooring rope is in a completely straight broken state; The present invention provides a method for measuring the mooring force in a floating offshore wind power generation facility as described in claim 1, which classifies the shape of the mooring line measured by the shape measurement means into one of the five states, infers which of the five states the shape of the mooring line measured by the shape measurement means is in, and estimates the tension acting on the mooring line from a calculation formula suitable for that state.

[0017] In the invention described in claim 2, the shape of the mooring rope measured by the shape measuring means is classified into five states, and the tension acting on the mooring rope is estimated from a calculation formula suitable for these five states. This makes it possible to estimate an appropriate mooring force according to the state of the mooring rope.

[0018] The present invention as claimed in claim 3 provides a method for measuring mooring force in a floating offshore wind power generation facility as described in claim 1, in which the shape measurement means is an underwater positioning device consisting of a plurality of transponders fixed at intervals along the mooring line and a transceiver that transmits and receives sound waves between the transponders, or an underwater acoustic exploration device that grasps the shape of an underwater structure by sound waves.

[0019] In the invention described in claim 3 above, specifically, an underwater positioning device or an underwater acoustic exploration device made up of a transponder and a transceiver is used as the shape measuring means.

[0020] The present invention as claimed in claim 4 provides a method for measuring mooring forces in a floating offshore wind power generation facility as described in claim 3, in which, when an underwater positioning device consisting of the transponder and the transceiver is used as the shape measurement means, the transponder is installed within a range up to the water depth at which a diver can normally dive, and the shape of the entire mooring line is estimated from the shape of the mooring line within this range.

[0021] In the invention described in claim 4 above, when an underwater positioning device consisting of a transponder and a transceiver is used as the shape measurement means, the transponder's placement range is set to the water depth at which a diver can normally dive, and the shape of the entire mooring line is estimated from the shape of the mooring line within this range.

[0022] The present invention relates to claim 5, and provides a method for measuring mooring force in a floating offshore wind power generation facility as described in claim 3, in which, when an underwater positioning device consisting of the transponder and the transceiver is used as the shape measurement means, the transceiver is provided for each mooring line to transmit and receive sound waves between the transponder attached to the mooring line.

[0023] In the invention described in claim 5 above, in order to shorten the time required for the transceiver to communicate with the transponder and accurately measure the external forces acting on the floating body instantaneously, a transceiver is arranged on each mooring line, and sound waves are transmitted and received between the transponder attached to the mooring line. Effect of the Invention

[0024] As explained above in detail, the present invention can solve all the problems of the conventional method of measuring tension by installing a sensor on the mooring line, and can measure the mooring force underwater for a long period of time. [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a side view showing a floating offshore wind power generation facility 1 according to the present invention. [Diagram 2] 2 is a side view showing the state in which the floating body 4 is fixed by the mooring ropes 5. FIG. [Diagram 3] 2 is an enlarged view of a main portion showing the arrangement of a transceiver 22. FIG. [Figure 4] FIG. 2 is a side view showing the arrangement of the transponder 21. [Diagram 5] 2 is a side view showing the arrangement of an underwater acoustic exploration device 23. FIG. [Figure 6] This is a graph showing a catenary. [Figure 7] FIG. 2 is a side view showing a state in which the mooring rope does not function as a catenary. [Figure 8] FIG. [Figure 9] FIG. 2 is a side view showing the state in which the ends of the mooring ropes contact the seabed surface. [Figure 10] FIG. [Figure 11] FIG. [Figure 12] FIG. [Figure 13] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] [Spar-type floating offshore wind turbine 1] First, a structural example of a spar-type floating offshore wind power generation facility 1 will be described with reference to FIG.

[0027] As shown in Figure 1, the offshore wind power generation facility 1 is composed of a cylindrical floating body 4, a mooring line 5, a tower 6, and a wind turbine 7 consisting of a nacelle 8 installed on the top of the tower 6 and a number of blades 9, 9...

[0028] The float 4 is composed of a lower concrete floating structure 4A in which concrete precast cylindrical bodies are stacked in multiple layers in the height direction and each precast cylindrical body is fastened and integrated with PC steel, and an upper steel floating structure 4B connected to the upper side of the lower concrete floating structure 4A. The float 4 may be made of concrete or steel over its entire length.

[0029] Ballast materials such as water, gravel, fine aggregate, coarse aggregate, and metal particles can be charged into or discharged from the hollow portion of the floating body 4, thereby making it possible to adjust the buoyancy (draft). The charging / discharging of ballast materials is possible by employing a fluid transport method previously proposed by the applicant in JP 2012-201217 A.

[0030] The lower concrete floating structure 4A is formed with almost the same outer diameter over the entire height. On the other hand, the upper steel floating structure 4B is composed of a steel tubular body 4Ba located relatively on the lower side and a steel tubular body 4Bb located relatively on the upper side. The lower steel tubular body 4Ba has a lower portion with the same outer diameter as the concrete floating structure 4A, and is connected to the concrete floating structure 4A. The upper portion of the steel tubular body 4Ba has a truncated cone shape with a gradually narrowing diameter.

[0031] The upper steel cylindrical body 4Bb is a cylindrical body having an outer dimension that is continuous with the upper outer diameter of the lower steel cylindrical body 4Ba, and is connected to the lower steel cylindrical body 4Ba by bolts or welding, etc.

[0032] A plurality of mooring lines 5 are provided so as to moor the float 4 at two or more points, preferably three or more points. As shown in Fig. 2, one end of the mooring line 5 is moored to the float 4 at a float side anchoring point B, and the other end is connected to an anchor and fixed to the seabed at a fixed anchoring point A. In addition, in a slack state, which will be described in detail later, the mooring line 5 lands on the seabed between the fixed anchoring point A and the ground point C. The mooring line 5 is preferably made of a chain made up of many connected annular metal members, but may be made partly or entirely of wire or the like.

[0033] On the other hand, the tower 6 is made of steel, concrete or PRC (prestressed reinforced concrete), but it is preferable to use one made of steel so that the total weight is small. The outer diameter of the tower 6 and the outer diameter of the upper steel cylindrical body 4Bb are almost the same, and the outer shape is continuous in the vertical direction without any steps. In the illustrated example, a ladder 13 is provided on the top of the upper steel cylindrical body 4Bb, and a walkway scaffolding 14 is provided in the circumferential direction at approximately the boundary between the tower 6 and the upper steel cylindrical body 4Bb.

[0034] The mooring point B on the float side, which is the mooring point of the mooring rope 5 to the float 4, is set below the sea surface and at a position higher than the center of gravity G of the float 4, as shown in Fig. 1. This makes it possible to prevent the ship from coming into contact with the mooring rope 5. Also, since a resistance moment is generated around the center of gravity G of the float 4 at the mooring point B on the float side so as to prevent the float 4 from tipping over too much, the tilting attitude of the tower 6 can be appropriately maintained.

[0035] On the other hand, the nacelle 8 is a device equipped with a generator that converts the rotation of the wind turbine 7 into electricity, a controller that can automatically change the angle of the blades 9, and the like. [Method for measuring the mooring force of offshore wind power generation facility 1] A method for measuring the mooring force of the floating offshore wind power generation facility 1 according to the present invention will be described below.

[0036] The mooring force measuring method according to the present invention is provided with a shape measuring means 20 that measures the shape of the mooring rope 5. This shape measuring means 20 measures in real time the curved shape (catenary curve shape) or straight shape of the entire mooring rope 5 in the sea, which changes from moment to moment depending on the position and attitude of the floating body 4 floating on the sea surface.

[0037] Specifically, the shape measurement means 20 can be an underwater positioning device consisting of a plurality of transponders 21, 21... fixed at intervals along the mooring line 5, and a transceiver 22 fixed to the floating body 4 for transmitting and receiving acoustic waves between the transponders 21, as shown in Figures 3 and 4.

[0038] As the underwater positioning device, it is preferable to use an underwater positioning device of the USBL (Ultra Short Base Line) system. In the USBL system underwater positioning device, the transceiver 22 transmits an acoustic signal underwater, and a response signal from the transponder 21 is received by a receiving array, and the three-dimensional relative position of the transponder 21 with respect to the transceiver 22 is measured based on the distance based on the round-trip time of the acoustic wave and the phase difference of the response signal that reaches each element in the receiving array. In addition, the position (latitude and longitude) of the transponder 21 in the earth coordinates can be obtained by adding the relative position of the transponder 21 to the position (latitude and longitude) and attitude angle (tilt and direction from the horizontal) of the transceiver 22 in the earth coordinates.

[0039] In addition, in the mooring force measuring method according to the present invention, as shown in FIG. 3, the information of each transponder 21 received by the transceiver 22 is transmitted to a computer 24, and the computer 24 is provided with a calculation means for carrying out calculations. The calculation means calculates the mooring force (horizontal tension T H and vertical tension T V The method for calculating the mooring force will be described in detail later.

[0040] Another specific example of the shape measurement means 20 is an underwater acoustic exploration device 23, which is fixed to the seabed or a floating body floating on the sea surface, and grasps the shape of an underwater structure by sound waves, as shown in Fig. 5. The underwater acoustic exploration device 23 is capable of measuring the three-dimensional (3D) shape of an underwater structure, and can use, for example, an underwater 3D acoustic sonar disclosed in JP 2016-151460 A. This underwater 3D acoustic sonar rotates 45° vertically and 120° to 360° horizontally while emitting sound waves, and measures the underwater structure in 3D by capturing the reflected waves.

[0041] To explain the configuration of the underwater 3D acoustic sonar in more detail, the underwater 3D sonar has 256 acoustic sonars (hereinafter referred to as "wave receiving devices") arranged in a row in the vertical direction (up and down direction), and these 256 wave receiving devices are rotated 360° in the horizontal direction, and one wave receiving device is selected and switched from one side in turn for each rotation. This switching switches the tilt angle in the vertical direction in stages of approximately 0.1758° each, creating a state in which the underwater 3D acoustic sonar is rotating vertically.

[0042] Therefore, this underwater 3D acoustic sonar rotates 360° horizontally while switching and driving one of the 256 wave receiving devices from one side in turn for each rotation, and when the driving of all 256 wave receiving devices is finished, 256 scans with different tilt angles are completed. In addition, a unit space is cut out for each scan, and a sonar image for each unit space can be obtained. The vertical rotation is performed four times. Therefore, the scanning operation is also repeated four times, and the scan data for each time is output to the control device. Then, the control device acquires data over the entire circumference and wide range of the underwater 3D acoustic sonar based on the scan data from the underwater 3D acoustic sonar, analyzes the shape of the underwater structure in three dimensions, and outputs the analysis results to display on the screen.

[0043] The underwater acoustic exploration devices 23 are usually installed on the seabed as shown in Fig. 5, but may be installed on the side surface above the float side anchoring point B of the mooring rope 5 below the draft of the float 4 (underwater below the sea surface). When installed on the side surface of the float 4, if the horizontal exploration angle of the underwater acoustic exploration devices 23 is 120°, it is preferable to install a total of three underwater acoustic exploration devices 23 on the side surface of the float 4 at intervals of 120° so as to be able to explore the entire circumference of the float 4. In other words, when three mooring ropes 5 are installed on the float 4, the underwater acoustic exploration devices 23 are installed at positions corresponding to the respective mooring ropes 5. Although Fig. 5 illustrates the underwater acoustic exploration devices 23 on both the seabed and the side surface of the float 4, it is sufficient to install them on either one of them.

[0044] The mooring force measuring method according to the present invention measures the shape of the mooring rope 5 by the shape measuring means 20, and estimates the tension acting on the mooring rope 5 from the shape of the mooring rope 5. That is, the mooring force measuring method according to the present invention focuses on the fact that the shape of the mooring rope 5 differs depending on the external force acting on the floating body 4, and attempts to estimate the tension (mooring force) acting on the mooring rope 5 by observing the three-dimensional shape of the mooring rope 5.

[0045] The shape of the mooring rope 5 in the sea can be approximated by a catenary curve that is created when a rope with uniform linear weight density is fixed at both ends and hung down in a uniform gravitational field. The method for calculating the tension of the mooring rope using catenary theory can be the method described in "Ueda Shigeru, Shiraishi Satoru, 'Selection Method and Calculation Diagram for Optimal Mooring Chain Using Catenary Theory,' Port and Harbor Technical Research Institute Materials, Ministry of Transport, Port and Harbor Technical Research Institute, No. 379, June 1981." The method for calculating the tension of the mooring rope using catenary theory described in this material is as follows: (Method of calculating tension of mooring ropes based on catenary theory) 1. Basic formula for catenary The shape of the mooring rope 5 stretched in the sea can be approximated by a catenary if the following assumptions are made. (1) Ignore the stretch of the mooring rope 5. (2) Ignore the current force acting on the mooring line 5. (3) Ignore friction between the mooring line 5 and the seabed. (4) Vibration of the mooring rope 5 itself is not taken into consideration. (5) The weight per unit length of mooring rope 5 is constant.

[0046] Here, dragging anchor is not taken into consideration, and therefore the friction effect between the mooring rope 5 and the seabed is not taken into consideration.

[0047] The basic equation of a catenary is given by equation (1).

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[0048] Figure 2 shows the standard state of a float 4 moored by a mooring line 5. In Figure 2, point A is the fixed anchoring point on the seabed, point B is the anchoring point on the float side, and point C is the point where the mooring line 5 touches the seabed. When the float moves horizontally, points B and C also move horizontally. The symbols shown in Figure 2 represent the following quantities. S 0 : Chain length S C : Catenary part length of chain S 1 : Length of the chain lying on the seabed (ground contact length) x s : Projection length of catenary part of chain onto horizontal plane (sea bottom) h: water depth d: Floating body draft H 0 : Horizontal distance between fixed anchor point (point A) and floating anchor point (point B) V 0 : Vertical distance between fixed anchor point (point A) and floating anchor point (point B)

[0049] By the way, there are five possible states of the mooring rope 5. (1) There is slack in the mooring rope 5, and the catenary cannot function properly (Figure 7). (2) Slack state (part of the mooring line 5 on the floating body 4 side forms a catenary, and the other part is on the seabed) (Figure 8) (3) The state in which the fixed anchor point A at the end of the mooring rope 5 on the seabed side is in contact with the seabed in the tangential direction (Figure 9). (4) Tension state (fixed anchor point A at the end of the mooring rope 5 on the seabed side forms a certain angle with the seabed surface) (Figure 10) (5) Broken state (mooring rope 5 is completely straight) (Figure 11) The above five states are explained below.

[0050] 2. Calculation formula for mooring line tension (1) There is slack and the catenary does not function properly. In this state, there is slack in the mooring rope 5, and the catenary does not function properly (Figure 7). Only vertical tension acts on the floating body, and no horizontal tension acts on it. Vertical tension T V is given by equation (2). Note that H 0 The range is when equation (3) holds.

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[0051] (2) Slack state In this state, part of the mooring rope 5 forms a catenary, and the other part is on the seabed (Figure 8). The catenary equation is given by equation (4).

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[0052] The method for determining the parameter a will be shown in the next section, section 3.

[0053] Once a is determined by equation (4), the length S of the catenary part of the mooring rope 5 is C is given by equation (5).

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[0054] In addition, the horizontal tension T of the mooring rope 5 H and vertical tension T V is given by equation (6).

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[0055] (3) When the fixed anchor point is in contact with the seabed This state is when the fixed anchor point touches the seabed as shown in Figure 9. In this case, in equation (4), S C =S 0 Since this is the case,

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[0056] Therefore, the horizontal tension T of the mooring rope 5 H and vertical tension T V is calculated using equation (9).

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[0057] (4) Tension This is the state in which the floating body 4 has moved further horizontally from the state shown in Figure 9 (Figure 10). Therefore, the mooring line 5 forms a certain angle with the seabed at the fixed anchor point A. In this case, the shape of the catenary is expressed by equations (10) to (12).

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[0058] (5) Fracture state When the floating body 4 moves further horizontally from the tensioned state (Figure 10), the shape of the mooring line 5 becomes completely straight and breaks (Figure 11). At this time, the length S of the mooring line 5 0 and H 0 , V 0 There is a relationship between the horizontal tension T and the horizontal tension T as shown in Equation (14). H , vertical tension T V is given by equation (15).

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[0059] 3. How to determine the catenary parameter a (1) Slack State In the slack state, the catenary shape is given by equation (16) (see Figure 8).

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[0060] Equation (16) can be rewritten as equation (18) using equation (17).

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[0061] From the horizontal relationship, equation (19) is obtained.

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[0062] Equation (19) can be rewritten as equation (20) using equation (17).

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[0063] From the relationship of mooring line length, equation (21) is obtained.

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[0064] S c Since is expressed by equation (22), equation (21) can be rewritten as equation (23).

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[0065] Equations (18), (20), and (23) are 0 , H 0 , V 0 Given u, a, S 1 These are three-dimensional simultaneous nonlinear equations with unknowns. These are summarized in equation (24).

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[0066] The unknowns in equation (24) are solved using the Newton-Raphson method.

[0067] Incidentally, equation (16) can be transformed into equation (25).

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[0068] Here, by using the relationship between equations (20) and (22), equation (26) is obtained.

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[0069] This is equation (4) shown in 2. above.

[0070] (2) Situation of tension When in tension, the catenary shape is given by equation (27) (see Figure 10).

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[0071] Equation (27) can be rewritten as equation (30) using equations (28) and (29).

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[0072] Equations (28) and (29) can be rewritten as equations (31) and (32).

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[0073] Furthermore, equation (33) can be obtained from the relationship between the mooring line length.

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[0074] Equation (33) can be rewritten as equation (34).

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[0075] Equations (30), (31), (32), and (34) are 0 , H 0 , V 0 When is given, it is a four-dimensional simultaneous nonlinear equation with u, v, a, and H' as unknowns. These are summarized in equation (35).

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[0076] The unknowns in equation (35) are determined using the Newton-Raphson method.

[0077] Furthermore, equation (27) can be transformed into equation (36).

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[0078] This is equation (11) shown in 2. above.

[0079] In the mooring force measurement method for the floating offshore wind power generation facility 1 according to the present invention, after measuring the shape of the mooring rope 5 by the shape measurement means 20, it is determined which of the above five states the shape of the mooring rope 5 is closest to, and the tension generated in the mooring rope 5 is calculated based on the calculation formula for that state. In particular, since the tension in the extreme state affects the strength of the mooring rope 5, it is necessary to estimate the mooring force even in a non-catenary state.

[0080] [Mooring force measurement method variation 1] Below, a description will be given of a modified example of the mooring force measuring method for the floating offshore wind power generation facility 1 according to the present invention.

[0081] When an underwater positioning device consisting of a transponder 21 and a transceiver 22 is used as the shape measurement means 20, the transponder 21 may be disposed over the entire length of the mooring line 5, but since the transponder 21 is fixed to the mooring line 5 by a diver diving underwater, a method may be adopted in which the transponder 21 is disposed within a range up to the depth at which a diver can normally dive, specifically within a range up to a depth of 30 m, as shown in Fig. 12, and the shape of the entire mooring line 5 is estimated from the shape of the mooring line 5 within this range. If the shape of the mooring line 5 up to a depth of 30 m is known, the line shape of the catenary curve deeper than that can be easily estimated, including which of the above five states it is in.

[0082] [Mooring force measurement method variation 2] In the case where an underwater positioning device consisting of a transponder 21 and a transceiver 22 is used as the shape measuring means 20, a single transceiver 22 may be provided for collectively transmitting and receiving sound waves between all the transponders 21 attached to the mooring lines 5, but it is preferable to provide a transceiver 22 for each mooring line 5 for transmitting and receiving sound waves between the transponders 21 attached to the mooring line 5, as shown in Fig. 13. It takes time to communicate with many transponders 21 attached to the mooring lines 5 using a single transceiver 22 to obtain information, and there is a risk that the external force acting on the floating body 4 cannot be measured accurately instantaneously. Therefore, by allocating a transceiver 22 to each mooring line 5 and shortening the time required for processing, the external force acting on the floating body 4 can be measured accurately.

[0083] [Mooring force measurement method variation 3] After measuring the shape of the mooring rope 5 by the shape measuring means 20, a calculation means is provided which judges whether the shape of the mooring rope 5 can be approximated by a catenary curve or by another mode shape (such as a straight shape), and calculates the tension based on a calculation formula for the mooring force in the matching state of the mooring rope 5. In the case of an underwater positioning device consisting of the above-mentioned transponder 21 and transceiver 22, this calculation means is provided in the computer 24 (Fig. 3), and in the case of the underwater acoustic exploration device 23 (Fig. 5), it is provided in a computer (not shown) that receives and analyzes the data transmitted from the underwater acoustic exploration device 23.

[0084] [Mooring force measurement method variation 4] When the distribution of the tidal current velocity in the water depth direction is known, the tension generated in the mooring rope 5 can be corrected by taking into account the fluctuating component of the mooring rope 5 due to the tidal current. That is, by subtracting the effect of deformation of the mooring rope 5 due to the tidal current velocity from the shape of the mooring rope 5 measured by the shape measuring means 20 through simulation, the shape of the mooring rope 5 when it is not affected by the tidal current velocity can be estimated, and the tension of the mooring rope 5 can be calculated based on this shape. [Explanation of symbols]

[0085] Reference Signs List 1...offshore wind power generation equipment, 4...floating body, 5...mooring line, 6...tower, 7...wind turbine, 8...nacelle, 9...blade, 13...ladder, 14...walkway scaffolding, 20...shape measurement means, 21...transponder, 22...transceiver, 23...underwater acoustic exploration device

Claims

1. A mooring line extending between a float of the floating offshore wind power generation facility and a seabed, and a shape measuring means for measuring a shape of the mooring line, A mooring force measuring method for a floating offshore wind power generation facility, comprising measuring a shape of the mooring rope by the shape measuring means and estimating the tension acting on the mooring rope from the shape of the mooring rope.

2. The shape of the mooring rope is (1) There is slack in the mooring rope and the catenary cannot function properly. (2) A slack state in which a part of the mooring line on the floating body side forms a catenary and the other part is landed on the seabed. (3) The fixed anchor point of the seabed end of the mooring rope is in a tangential direction to the seabed surface. (4) A tensioned state in which the fixed anchor point at the bottom end of the mooring rope forms a certain angle with the seabed. (5) The mooring rope is in a completely straight broken state; a shape measuring means for measuring the shape of the mooring rope measured by the shape measuring means, a prediction is made as to which of the five states the shape of the mooring rope measured by the shape measuring means is in, and a calculation formula suitable for that state is used to estimate the tension acting on the mooring rope.

3. 2. A method for measuring mooring force in a floating offshore wind power generation facility as described in claim 1, wherein the shape measurement means is an underwater positioning device consisting of a plurality of transponders fixed at intervals along the mooring lines and a transceiver that transmits and receives sound waves between the transponders, or an underwater acoustic exploration device that grasps the shape of an underwater structure using sound waves.

4. A method for measuring mooring force in a floating offshore wind power generation facility as described in claim 3, wherein when an underwater positioning device consisting of the transponder and the transceiver is used as the shape measurement means, the transponder is installed within a range up to the water depth at which a diver can normally dive, and the shape of the entire mooring line is estimated from the shape of the mooring line within this range.

5. A method for measuring mooring force in a floating offshore wind power generation facility as described in claim 3, wherein when an underwater positioning device consisting of the transponder and the transceiver is used as the shape measurement means, the transceiver is provided for each mooring line to transmit and receive sound waves between the transponder attached to the mooring line.

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