JP2014510665A - Buoyancy device with special mooring system - Google Patents

Abstract

The present invention relates to a buoyancy device comprising a mooring system having at least two mooring lines (3a) and at least two anchors (31) on the seabed (9), and a float (20). Each mooring line is coupled to one anchor, and each mooring line has a first portion (32) having a first metal chain and / or cable connected to the anchor via a first end. , Including at least one elastic rope, connected to the second end of the first portion via the first end and connected to the float connection point (C) via the second end A second portion called an elastic portion (33), and the elongation of the elastic portion (33) under a load condition (ε _c ) is 4.0 × 10 ^{−3 to} 10.0. It is between x10 < ^-3 > m / kN.

Description

  The present invention relates to a buoyancy device having a float and a mooring system for fixing the float to the seabed. More specifically, the present invention relates to a buoyancy device for a wind turbine that functions as a buoyancy body for an offshore wind turbine device, wherein at least one wind turbine is attached to a float.

  Prior art buoyancy devices have a float and a mooring system for securing the float to the seabed. The buoyancy device includes a mooring line, each mooring line being coupled to a seabed anchor and including a first chain that is connected to the anchor through a first end. And a second portion including at least one elastic rope connected to the second end of the first portion via the first end and to the float connection point via the second end. And an elastic part.

  Mooring lines, including elastic ropes that are typically manufactured from synthetic fibers, are used in the field offshore, and they are more durable than conventional mooring lines composed of metal chains and / or cables. And it shows an effective substitution possibility. Compared to conventional mooring lines, the use of elastic ropes makes it possible to obtain more flexible anchor characteristics, thus a curve representing the tension of mooring lines due to float drift in relation to its reference position In addition, it is possible to prevent an excessive drift from appearing. The elastic rope can alleviate the movement of the float.

  In this type of system, in order to prevent the elastic rope from being damaged by friction, the rope must never be in contact with the seabed and thus always remain in tension. For this purpose, the elastic rope is connected to the float via a connecting cable or chain and adjusts the weight and / or spring or damper type elements, conventionally referred to as “clamp weight”, along the mooring line. It was necessary to install. For example, weight is placed at the junction of the elastic rope and the connecting chain to keep the tension of the mooring line. This weight pulls the elastic rope downward, thus reducing the angle between the mooring line and the seabed. Such weight significantly increases the cost of the mooring line, complicates the system, and increases the cost of installing and maintaining the mooring line.

  An object of the present invention is to provide a low-cost mooring system using simple components, and this system is simple in terms of installation and maintenance.

Therefore, the present invention relates to, for example, a buoyancy device for a buoyancy body of an offshore wind turbine device. The buoyancy device includes, for example, a semi-submersible float, and a mooring system for fixing the float to the seabed. Have. The mooring system has at least two mooring lines and at least two anchors on the sea floor, each mooring line being coupled to one anchor,
A first metal chain and / or cable connected to the anchor via a first end, preferably a first part having a first metal chain;
Includes at least one elastic rope and is connected to the second end of the first part via the first end and directly or indirectly to the float connection point via the second end A second portion called an elastic portion,
The elongation under the load condition (ε _c ) of the elastic part is between 4 × 10 ⁻³ to 10 × 10 ⁻³ m / kN, preferably 5 × 10 ⁻³ to 8 × 10 ⁻³ m / k. between kN.

  According to the present invention, each mooring line has an elastic part that has a special elongation under load conditions greater than the load of the elastic part of the prior art. Such special elongation characteristics of the elastic part allow weight and / or spring or damper type elements to be applied to the elastic part in order to maintain the mooring line in a tensioned configuration. Without using it, it maintains a satisfactory function in terms of tension of the mooring line due to drift of the float. This “tensioned” configuration of the mooring line is suitable to greatly enhance holding the float in place.

  Such a mooring line according to the present invention manufactured with simple components having easy offshore installation can provide a low cost mooring system.

  It can be seen that for the expected load for a given float at a given location, the new mooring system according to the present invention is lighter than prior art mooring systems. In fact, due to its modularity, the mooring system can be adjusted for the expected load by increasing / decreasing the number of elastic ropes in the elastic part of the mooring line.

  By adjusting the elasticity of the elastic part, the maximum tension of the mooring line can be reduced and the anchor can be prevented from rising due to the shorter length of the first part.

  The elasticity of the elastic part can damp the movement of the float, but does not limit the primary or uncontrollable movement of the float. By adjusting the elasticity of the elastic part, the mooring line according to the present invention provides an excellent function in attenuating the movement of the float, for example, simply lifting the weight of the mooring line according to the prior art consisting of a chain Provides a better tension drift function than can be obtained by

In the present invention, elongation (ε) and elongation under load conditions (ε _c ) expressed in m / kN are defined as follows:
ε = ΔL / L ₀
Here, L ₀ is the length of the elastic part at rest, and ΔL = (L−L ₀ ) is the amount of change in the length of the elastic part.
ε _c = ε × L ₀ / F
Here, F is a reaction force or a tensile force of the elastic portion that responds to a load applied to the elastic portion.

In the case of the linear approach, the rigidity (k) of the elastic portion represented by kN is defined by the following equation.
k = F × L ₀ / ΔL = F / ε
And the elongation under the load condition (ε _c ) can be defined as follows.
ε _c = L ₀ / k

  In this specification, a range value is given as a comprehensive boundary, and this range value is included between "... to ..." or "... to ..." including the specified boundary. Is described in the format.

  In one embodiment, for each mooring line, from the first end of the first part to the sum of the water levels below the connection point of the float, which corresponds to the distance between the connection point and the projection point to the seabed. The ratio of the total length of the mooring lines, which corresponds to the distance to the projection point, is between 0.75 and 0.90, preferably between 0.78 and 0.88, more preferably 0.80. Between ˜0.85. Such a ratio defines the initial tension of the elastic part of the mooring line. The initial tension of the mooring line is defined in such a way that the elastic part is not placed on the seabed for the maximum possible movement of the float.

  According to one embodiment, for each mooring line, the ratio of the length of the first part to the length of the elastic part is between 0.05 and 0.30, preferably 0.10 to 0.25. And more preferably between 0.15 and 0.20.

  According to one embodiment, for each mooring line, the ratio of the mass of the first part to the initial tension in the mooring line is between 1 and 10 kg / kN, preferably between 1 and 5 kg / kN; More preferably, it is between 2-3 kg / kN.

  According to one embodiment, for each mooring line, the ratio of the total length of the mooring line to the distance between the connection point and the projected point on the seabed is between 3.5 and 6.5, preferably 4. It is between 5 and 5.5, more preferably between 4.8 and 5.2.

  According to one embodiment, for each mooring line, the ratio of the length of the elastic part to the total length of the mooring line is between 0.7 and 0.8.

According to one embodiment, for each mooring line, the stiffness of the elastic part is between 3 × 10 ^{4 to} 7 × 10 ⁴ kN, preferably 3.5 × 10 ^{4 to} 6.0 × 10 ⁴ kN. Between.
Here, the designated rigidity is 50% of the minimum breaking strength of the elastic portion.

Rigidity of the elastic unit according to the present invention is significantly less than the rigidity of the elastic rope which is conventionally used in the mooring system typically is between ^{10 × 10 5 kN~40 × 10 5} kN.

  According to one embodiment, for each mooring line, the linear density of the first portion is between 400 and 650 kg / m. This first part needs to prevent any lifting of the anchor. Preferably, the first part is composed of a metal chain.

  According to one embodiment, each mooring line further includes a third portion having a metal connection chain and / or a connection cable for connecting the elastic portion to the float. Metal chains and cables for connecting to the float are particularly advantageous for the very large hydrodynamic loads identified in this area that can damage the elastic rope.

  According to one embodiment, for each mooring line, the elastic part has at least two elastic ropes, and each elastic rope is connected to the second end of the first part via the first end. And connected directly or indirectly to the float via the second end, preferably indirectly via the third portion. The number of elastic ropes per elastic part depends on the environmental conditions encountered by the buoyancy device during operation.

  According to one embodiment, each elastic rope is composed of a polyester fiber rope.

  According to one embodiment, the mooring system has at least three mooring lines. The mooring system preferably has three mooring lines, but can have more than two mooring lines.

  According to one embodiment, the floats are semi-submersible with at least three cylinders and are firmly connected to each other via connecting elements. Each mooring line is preferably connected to a cylindrical body, and the connection point of the mooring line is preferably arranged at the submerged portion of the cylindrical body, for example, substantially at the lower end of the cylindrical body.

  According to one embodiment, in order to function as a buoyant body of an offshore wind turbine device, the buoyancy device further comprises at least one wind turbine attached to a float, said wind turbine preferably comprising blades Comprises a rotor having a horizontal axis of rotation, a nacelle, and a tower connected to the float.

  The mooring system is particularly suitable for buoyancy devices intended to be fixed at a relatively shallow depth of only 25 m, less than 300 m in depth, and semi-submersible with a draft in the range of 10-30 m In the float, it is particularly suitable for the application of buoyancy bodies of wind turbines at a depth of 30 to 200 m, preferably at a depth of 50 to 150 m.

  The present invention will be more clearly understood and further objects, detailed description, features and advantages thereof will be described in the following detailed description of the presently preferred specific embodiment of the present invention, with reference to the accompanying schematic drawings. It will become clearer in the process.

1 is a partial schematic perspective view of a buoyancy device according to an embodiment of the present invention. FIG. 2 is a partial side view of the buoyancy device of FIG. 1 in its reference position illustrating the mooring line of the mooring system. FIG. 2 is a side view of the buoyancy device of FIG. 1 in its reference position and a drifted position. 4 is a curve showing the drift of the buoyancy device according to the invention as a function of the tension of the mooring line. The curve showing elongation as a percentage (%) of the elastic rope of the elastic part of the mooring system as a function of the load applied to the elastic rope, expressed as a percentage of the minimum breaking strength of the elastic rope.

  In the illustrated embodiment, the buoyancy device 1 is designed to receive a wind turbine and forms a buoyancy body of the wind turbine device.

  The buoyancy body 1 of the wind turbine apparatus includes a wind turbine 10 and a semi-submersible body or float 20. The wind turbine 10 includes a blade 11, a horizontal rotating shaft hub or rotor 12, a nacelle 13, and a tower 14 in a known manner. The wind turbine includes a generator arranged in the nacelle for generating electric power from the rotational movement of the blades, frequency conversion means for converting the electric power generated by the generator into electric power having a predetermined frequency, It further includes power transforming means for boosting the voltage between the phases of the power output by the converting means to a higher voltage, for example, for boosting to a voltage of 33,000 volts.

  In the illustrated embodiment of the present invention, the float 20 has three external vertical columns 21a, 21b, 21c that are cylindrical in shape, which are perpendicular to the center of the float. Arranged at equiangular intervals around the axis and interconnected via connecting elements. The float is described, for example, in French Patent No. 1059603, entitled “Offshore wind turbine device with special semi-submersible float” filed on November 22, 2010 on behalf of the applicant. . The connecting element comprises a fully submerged horizontal lower beam or pontoons 22, an upper beam 23, also referred to as a pedestrian bridge or deck, and a central joint 24. For example, the lower pontoon 22 having a rectangular cross section is joined to the cylindrical body in pairs in a lower cross section having a larger cross section, specifically, a so-called stabilized lower pontoon 211. For example, the upper beam 23 having a rectangular cross section is disposed on the upper cross section of the cylindrical body. Each upper beam extends radially from the central axis of the float toward one of the plurality of cylinders. The three beams 23 are joined at the central axis including the joint 24. The vertical intermediate part 27 is assembled to the joint 24 to support the tower 14 of the wind turbine. Due to the enhanced structural strength and enhanced rigidity, the cylinders 21a, 21b, 21c, the pontoon 22, the beam 23, and the intermediate portion 27 connect the first support column 25 and the second support column 26. They are interconnected in a grid pattern. Alternatively, the float includes three or more external cylinders and / or comprises a central cylinder on which a wind turbine tower rests. The cylindrical body functions advantageously as a ballast tank. Preferably, the internal volume of the cylinder is partitioned to form a separate ballast tank compartment. Each pontoon may form a separate ballast tank chamber.

  At the power generation site, the wind turbine device uses submarine power to transmit the power generated by the wind turbine to the distribution network via electrical cables (not shown) called umbilical cables or dynamic cables. Connected to cable.

  The apparatus also includes a mooring system for positioning the buoyancy body of the wind turbine apparatus at the production site.

  In the illustrated embodiment, the mooring system comprises three mooring lines 3a, 3b, 3c. Each mooring line is fixed to the seabed 9 via an anchor 31 and is connected to a cylindrical body. The arrangement angle of each mooring line is about 120 °.

  Referring to FIG. 2, each mooring line is coupled to an anchor 31 on the seabed 9 and is composed of a first portion composed of a first heavy metal (weight) chain 32 and at least one elastic rope. The elastic part 33 and the connection part 34 are included.

  Anchors are composed of conventional anchors or perforated piles, or gravity anchors, for example, depending on the type of soil encountered at the installation site.

  The first weight chain 32 is connected to the anchor 31 via the first end. The elastic portion 33 is connected to the second end portion of the first weight chain via the first end portion, and the second end portion is connected to the first end portion of the connection portion 34, and the connection The second end of the part is attached to the float cylinder 21a.

  The mooring system is designed so that the drift of the buoyancy device relative to its reference position is tolerated in terms of the static and dynamic displacement capabilities of the dynamic cable, and the wind resistance stiffness provided by the mooring system is nacelle. It is specifically defined to be sufficient to enable the good operation of Drift is the static average load induced by wind turbines, static average load induced by wind acting on towers and floats, static average load induced by water flow acting on floats and mooring lines, and It is an average displacement that means a static average drift load due to waviness. In addition, the mooring system should be able to tolerate one-dimensional motion or part of two-dimensional motion induced by swells or wind turbines under extreme conditions without any restrictions. Thus, drift corresponds to average displacement due to static loads and dynamic loads induced by wind turbines and swells. All components have sufficient resistance for wind turbines and static loads induced by wind, water flow, swell drift and for dynamic loads induced by wind turbines and swells .

  The mooring system is designed for a range of 40-300 m depth. Although tension is always applied to the elastic portion, weight is always applied to the first chain.

  The first chain connected to the anchor prevents the anchor from being raised and dragged. The weight of the first chain is basically defined by the average drift load and the movement of the float in the wave. The angle of the mooring line with respect to the horizontal direction must not exceed 6 ° at the anchor.

  The elastic part is composed of a single elastic rope or a plurality of elastic ropes. In the latter case, the elastic rope is connected to the first chain via its first end and to the connection via its second end, and the elastic ropes are preferably identical. And substantially the same length. The elastic ropes are, for example, arranged or knitted adjacent to each other substantially parallel. The elastic rope is a synthetic fiber rope, preferably manufactured from polyester fiber.

Such synthetic fiber elastic ropes generally have quadratic stiffness characteristics. The elastic rope is selected such that the maximum load expected for the elastic rope including the maximum static load and the maximum dynamic load does not exceed 50% of the minimum breaking strength of the elastic rope. As an approximation, the stiffness can be considered limited to its linear component.
k = F × L ₀ / ΔL = F / ε

  For example, the elastic part is composed of two or three ropes made from polyester fibers having a diameter of about 128 mm and a minimum breaking strength of about 3850 kN, each elastic rope being a load applied to the rope. It is characterized by an elongation curve as a function of percentage (%) and, as shown in FIG. 5, expressed as a percentage (%) of the minimum breaking strength (MBS).

Each elastic rope has a stiffness of about 1.9 × 10 ⁴ kN at 50% of its minimum breaking strength. The rigidity of the elastic part composed of three elastic ropes is about 5.7 × 10 ⁴ kN, and the rigidity of the elastic part composed of two ropes is about 3.8 × 10 ⁴ kN. .

For an elastic part having a length L ₀ of about 300 meters (m) at rest, the elongation of the elastic part under load conditions is defined by the following equation based on the assumption of a linear approximation of the rigid body.
ε _c = ε × L ₀ / F = L ₀ / k

The elongation under the load condition ε _c for the elastic part composed of three elastic ropes is about 5.2 × 10 ⁻³ m / kN, and the load of the elastic part composed of two elastic ropes The elongation under condition ε _c is about 7.8 × 10 ⁻³ m / kN.

  For example, the connecting portion 34 constituted by a metal chain connection provides a strong connection between the mooring line and the metal structure of the float. This connecting chain is arranged in the submerged part of the cylinder extending below the sea surface 8 and enters, for example, a fairlead arranged at the lower end of the cylinder of the buoyancy device. The first part of the connection chain extends below the fairlead, while the second part of the connection chain extends along the cylinder and connects the mooring line to a fixing device located on the upper deck of the float To function. In this embodiment, the connection point C of the mooring line to the float corresponds to the fair lead, and the total length of the mooring line is the length of the first chain, the length of the elastic part, and the connection under the fair lead. Equal to the sum of the length of the first part of the chain.

  Referring to FIG. 2, the distance indicated by d <b> 1 is the distance between the connection point C and the projection point P, and this projection point P is a projection in the vertical direction of the connection point C on the seabed 9. In the illustrated embodiment, the connection point is located at the lower end of the cylinder, and the distance d1 corresponds to a water level below the float. The distance indicated by d <b> 2 is the distance between the projection point P and the first end of the first chain 32 connected to the anchor 31.

  In situations where there are no static and dynamic loads applied to the buoyancy device, the buoyancy device is in the reference position. At this reference position, an initial tension is applied to the elastic portion of the mooring line.

  FIG. 3 shows two of the three mooring lines of the buoyancy device, for example, mooring lines 3a and 3b. The buoyancy device indicated by the dotted line represents the drifted position of the buoyancy device when, for example, a horizontal load F is applied to the float substantially in the axial direction of the mooring line 3a. Is substantially completely absorbed by the mooring line 3a. Due to the initial tension of the mooring line, the elastic part 33 of the mooring line is never placed on the seabed 9. In particular, the mooring line does not receive a horizontal load unlike the mooring line 3b of FIG. The mooring line to which the initial tension is applied prevents mud from the sea and dirt on the elastic part due to friction on the sea floor.

For example, a mooring system is defined to have a maximum drift for a static average load of about 15 m and a maximum drift for a static and dynamic average load of about 25 m. Two examples of mooring systems are defined in Table 1 below.

The curve in FIG. 4 shows the drift of the buoyancy device of Example 2 relative to its reference position as a function of the mooring line tension (FT) when the load is at the mooring line axis and is fully absorbed. (D) is shown. For an expected static average load of about 225 tons, the drift (D _average ) is about 13.5 m and the maximum load (maximum static) expected under a durable survival condition of about 475 tons. Drift (D _max ) is about 22.5 m. It can be seen that this curve does not have a high gradient zone that reduces the risk of mooring line breakage in the event of severer environmental conditions than expected.

  The mooring line of Example 1 including an elastic part composed of two elastic ropes is assumed for a mooring system and a float for installation on the site, where the maximum load under durable life conditions is 300 In the ton range.

  For a given drift required, a reduction in tension on the mooring line can be obtained by increasing the length of the elastic part. This increase in length can be 10 to 20 times less cost than simply increasing the length of a mooring line manufactured using a chain.

While the invention has been described with reference to various specific embodiments, it is obvious that the invention is not limited to these embodiments and is within the scope of the claims of the invention. Insofar as all technical equivalents of the described means and combinations thereof are included.

Claims (14)

A buoyancy device comprising at least two mooring lines (3a, 3b, 3c) and a mooring system having at least two anchors on the seabed, and a float, each mooring line being coupled to one anchor; Each mooring line
A first portion (32) having a first metal chain and / or cable connected to the anchor via a first end;
Elasticity including at least one elastic rope, connected to the second end of the first portion via the first end and connected to the float connection point (C) via the second end A second part referred to as part (33),
The elongation under the load condition (ε _c ) of the elastic part is between 4.0 × 10 ^{−3 to} 10.0 × 10 ⁻³ m / kN.
Buoyancy device. For each mooring line (3a, 3b, 3c), the water level below the float connection point (C) corresponding to the distance (d1) between the connection point (C) and the projection point (P) to the seabed The ratio (R ₁ ) of the total length (L _T ) of the mooring line corresponding to the distance (d2) from the first end of the first part (32) to the projection point to the total of Between ~ 0.90,
The buoyancy device according to claim 1. Each mooring (3a, 3b, 3c) for the length ratio of the first portion to the length of the elastic portion _{(33) (32) (R} 2) is between 0.05 to 0.30 is there,
The buoyancy device according to claim 1. For each mooring line, the ratio (R ₃ ) of the mass of the first part (32) to the initial tension (F _P ) in the mooring line is between 1 and 10 kg / kN.
The buoyancy device according to claim 2 or 3. For each mooring line (3a, 3b, 3c), the ratio of the total length (L _T ) of the mooring line to the distance (d1) between the connection point (C) and the projection point (P) to the seabed (R ₄ ) ) Is between 3.5 and 6.5,
The buoyancy device according to any one of claims 1 to 4. For each mooring line (3a, 3b, 3c), the ratio (R ₅ ) of the length (L ₀ ) of the elastic part (33) to the total length (L _T ) of the mooring line is 0.7 to 0.8. Between
The buoyancy device according to any one of claims 2 to 5. For each mooring line, the stiffness (k) of the elastic part (33) is between 3 × 10 ^{4 and} 7 × 10 ⁴ kN.
The buoyancy device according to any one of claims 1 to 6. For each mooring line, the linear density (W ′) of the first portion (32) is between 400 and 650 kg / m.
The buoyancy device according to any one of claims 2 to 7. Each mooring line (3a, 3b, 3c) further includes a third portion (34) having a metal connection chain and / or a connection cable for connecting the elastic part (33) to the float.
The buoyancy device according to any one of claims 1 to 8. The elastic part (33) has at least two elastic ropes,
The buoyancy device according to any one of claims 1 to 9. Each elastic rope is composed of a polyester fiber rope,
The buoyancy device according to any one of claims 1 to 10. The mooring system has at least three mooring lines (3a, 3b, 3c),
The buoyancy device according to any one of claims 1 to 11. The float is a semi-submersible type having at least three cylindrical bodies (21a, 21b, 21c), and each mooring line (3a, 3b, 3c) is connected to one cylindrical body.
The buoyancy device according to any one of claims 1 to 12. In order to function as a buoyant body of an offshore wind turbine device, the buoyancy device further comprises at least one wind turbine (10) attached to the float,
The buoyancy device according to any one of claims 1 to 13.

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