Tendons for tension leg platforms and tension leg platforms including such tendons

Abstract

Tendons (224) are provided for the tension leg platform (202) (TLP). The TLP includes a foundation (206) connectable to the bottom (208) of the water body and a buoyant hull (216). The tendon has a length, a proximal end (223), and a distal end (225). The tendon includes a proximal end connector at the proximal end and a distal end connector at the distal end. The tendon is connectable to the hull by the proximal end connector and to the foundation by the distal end connector, and provides tensile force to the hull. The length of the tendon is at least 300 meters. The tendon includes basalt fibers for transmitting tensile force from the proximal end connector to the distal end connector.

Description

Technical Field

[0001] The present invention relates to a tendon (tension mooring cable) for a tension leg platform as recited in the preamble of claim 1 and to a tension leg platform.

Background Art

[0002] This type of tension leg platform is used as a support for offshore activities such as oil or gas production. A relatively new application currently under consideration is an offshore wind turbine.

[0003] This type of tension leg platform (TLP) is known from Patent Document 1. Patent Document 1 discloses a TLP wind turbine having a central body portion of a hollow steel structure, the central body portion including a lower axially cylindrical tubular float on which is mounted a group of upper coaxial cylindrical tubular sections, and on which is a coaxial cylindrical tubular tower of smaller cross-section. At the upper part of the tubular tower is a yaw housing carrying a conventional wind turbine. Eight horizontal steel outrigger arms are connected to the central float body portion and are uniformly radially spaced around the central float body portion, and the distal ends of the arms are interconnected by a ring of horizontal steel braces. Each carries a connection to the upper end of a respective flexible steel tether extending downward to a counterweight above the seabed. Patent Document 1 describes as a variant that the tether can be made from Kevlar (trademark). It should be noted that Patent Document 1 uses the terms "float" and "tether", whereas the present specification refers to the terms "hull" and "tendon" respectively.

[0004] TLPs provide relatively stable supports for offshore operations because they minimize the vertical motion typically induced in floating structures. However, known TLPs at greater depths have a drawback: relatively small motions at the water surface (particularly roll and pitch motions) result in relatively large rocking motions at the top of the tall working structure. Such large motions are unacceptable in certain applications. This is particularly problematic for wind turbines because they require tall towers to accommodate large rotors, while the rotors themselves can only withstand small amounts of motion.

[0005] It is the common consensus among experts in this field that TLPs are only suitable for wind turbines in relatively shallow water depths. As stated in the English Wikipedia page on “Tension Leg Platforms” (as available as of the filing date of this application), “Researchers estimate that they [TLPs with wind turbines] could operate at depths between 100 feet and 650 feet (200 m).” [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2013 / 183163-A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to solve at least one of these problems, or to provide at least an alternative. In particular, the present invention aims to provide a tendon for a tension leg platform that reduces the rolling and pitching motion of a TLP at greater water depths. [Means for solving the problem]

[0008] This objective is achieved by the tendon for the tension leg platform described in claim 1.

[0009] A tendon is designed for a tension leg platform (TLP) that includes a foundation and a buoyant hull. The foundation is connectable to the bottom of a body of water (e.g., the seabed or ocean floor). The tendon has a predetermined length, a proximal end, and a distal end. The tendon includes a proximal end connector at the proximal end and a distal end connector at the distal end. The tendon is connectable to the hull of the TLP by the proximal end connector and to the foundation of the TLP by the distal end connector, providing tensile force to the buoyant hull. The length of the tendon is at least 300 meters. The tendon includes basalt fibers for transmitting tensile force from the proximal end connector to the distal end connector.

[0010] This invention is based on the observation that para-aramid fibers (such as those commercially available under the trademark Kevlar® as described in Patent Document 1) have inherent problems when used as load-bearing fibers for relatively long tendons, even though they can theoretically provide the required strength. The problem discovered by the inventors is that relatively long para-aramid tendons exhibit excessive elongation under stress, resulting in roll and pitch movements of unacceptable magnitudes for certain applications such as wind turbines in the top-side structure of the TLP. The obvious solution would seem to be to increase the diameter of the tendon by adding more fibers, for the reason that stiffness is determined by E·A, where E is Young's modulus and A is the cross-sectional surface area. The inventors of this invention have found that increasing the diameter does not solve the problem because para-aramid fibers have nonlinear material properties and Young's modulus is not constant at relatively low stress values. Adding more fibers to the tendon for the purpose of increasing stiffness results in lower stress per fiber, and therefore results in a decrease in Young's modulus. This decrease was discovered by presenting a series of para-aramid cables with increasing diameters to the ASTM D7269 standard test and calculating the Young's modulus from the test results. The observed decrease in Young's modulus outweighed the increase in surface area, and therefore the total stiffness E·A did not reach the required value. The inventors found that basalt fibers exhibit almost none of this nonlinear effect at lower stress values. Basalt fibers already reach approximately 95% of their maximum Young's modulus at low stress values. Therefore, it is possible to add as many fibers as are needed to obtain the required stiffness. An additional advantage of basalt compared to para-aramid fibers is that tendons made from basalt fibers with comparable tensile strength are approximately 2.5 times cheaper.

[0011] It should be noted that another fiber type that can provide the strength required for tendons is ultra-high molecular weight polyethylene (UHMwPE, marketed under the trademark Dyneema®). However, the Young's modulus of this fiber type is much lower than that of basalt fibers, and on the one hand, the cost of this fiber type results in tendons costing approximately 2.8 times more than those made from basalt with the same tensile strength. The high cost of UHMwPE fibers results in the total cost of tendons under deeper water conditions being higher than the combined cost of TLP and wind turbines. Therefore, UHMwPE is not an economical solution to the problems described above.

[0012] Preferred embodiments are defined in the dependent claims and the following paragraphs.

[0013] In certain embodiments, the length of the tendon is at least 400 meters, more specifically at least 500 meters, more specifically at least 700 meters, and more specifically at least 1000 meters.

[0014] As described above, the present invention enables the use of TLP at depths exceeding 300 meters, and even up to 1000 meters. Such depths were previously impossible to achieve with conventional tendons, such as those made by Kevlar®.

[0015] In one embodiment, the basalt fibers extend parallel to each other in the longitudinal direction of the tendon.

[0016] Arranging the basalt fibers parallel to the longitudinal direction of the tendon matches the tensile load applied to the fibers during use. This ensures that the load-bearing capacity of the fibers is fully utilized, or at least close to fully utilized. In addition, providing the fibers parallel to each other reduces friction between fibers, thereby reducing fiber wear and extending the life of the tendon.

[0017] In one embodiment, the basalt fibers are not twisted.

[0018] The fibers within a rope can be twisted at several levels (i.e., within the yarn, to form sub-ropes, and by combining sub-ropes into a single rope or cable). In the context of this invention, the term "untwisted" applies to all of these levels. By providing untwisted fibers, friction between fibers is reduced. This reduces wear between fibers and therefore extends the life of the tendon.

[0019] In one embodiment, the tendon comprises a plurality of yarns. The yarns comprise basalt fibers. Each of the plurality of yarns has a length corresponding to the length of the tendon. Each yarn has a proximal yarn end connected to a proximal end connector and a distal yarn end connected to a distal end connector.

[0020] The length of the yarn corresponds to the length of the tendon; that is, the length of the yarn is substantially the same as the length of the tendon, with a difference of less than 1%. The tendon as a whole may be slightly longer than the yarn, for example, due to the end connection extending several centimeters or tens of centimeters beyond the end of the yarn.

[0021] The tendon is at least 300 meters long, in particular at least 400 meters long, more specifically at least 500 meters long, more specifically at least 700 meters long, and more specifically at least 1000 meters long. By providing yarn of the corresponding length, the tendon can be produced by the minimum fiber length compared, for example, winding the fiber between two end joints.

[0022] In one embodiment, at least one of the distal end connection portion or the proximal end connection portion includes a hollow portion having a cavity, the width of the cavity increasing toward each end of the tendon, the yarn extending into the cavity of the hollow portion and diverging inside the cavity.

[0023] At each end of the tendon, the yarns of basalt fibers diverge such that a predetermined spacing is provided between the yarns. In contrast, in most of the tendon extending between the end connection portions, the fibers are packed more closely together. The divergence of the yarns confines the yarns within the cavity of the end connection portion.

[0024] In one embodiment, the cavity includes a frustoconical shape.

[0025] The frustoconical shape closely follows the yarn as the yarn gradually spreads out in a fan shape, thus ensuring that the cavity wall stays near or even touches the outer yarns. In other words, the frustoconical cavity exactly matches the volume occupied by the diverging yarns. This means that less adhesive or resin, for example, is required to fill the cavity compared to, for example, a rectangular cavity.

[0026] In one embodiment, the cavity is filled with a matrix that fixes the diverging yarns. The yarns and the matrix form a plug that locks the yarns within the end connection portion. The matrix used to fix the diverging yarns is, for example, a resin (such as an epoxy resin).

[0027] In one embodiment, a restraining body is provided within the cavity to maintain the diverging yarns in an spaced-out state, the restraining body having a shape complementary to the shape of the cavity. In particular, a matrix, resin, or adhesive is provided to connect the yarns to the restraining body and / or the surface of the cavity, and / or to fill the remaining cavity between the diverging yarns.

[0028] For example, in embodiments with a truncated conical cavity, the restraining body has a wedge shape. In particular, the restraining body has a truncated conical or conical shape. The restraining body contributes to locking the yarns in a configuration in which they are spaced apart. In addition, since the restraining body fills part of the cavity volume, less matrix, resin, or adhesive is required to secure the yarns.

[0029] In one embodiment, the tendon is formed by extrusion molding such that the basalt yarn is bundled by a cover, particularly by a polymer cover.

[0030] The polymer may include, for example, a thermosetting polymer (such as polyvinyl chloride (PVC)). In particular, the sub-ropes are formed by drawing out multiple parallel basalt yarns arranged parallel to each other, and the sub-ropes are bundled parallel to each other to form tendons.

[0031] In one embodiment, the tendon comprises at least one yarn containing basalt fibers. The proximal end connector comprises a first thimble, and the distal end connector comprises a second thimble. The first and second thimbles are provided at both ends of the tendon. At least one yarn extends from the first thimble to the second thimble, turns around the second thimble, extends from the second thimble to the first thimble, and turns around the first thimble. In this arrangement, the yarn forms turns around the first and second thimbles, with each thimble holding a stack of multiple layers of the yarn turns.

[0032] In the context of this literature, a thimble is defined as a ring of any shape and made of any material around which at least one yarn is turned. In the context of this literature, the turning portion of the yarn can be either a semi-continuous loop or a continuous loop. The term semi-continuous loop refers to the fact that the yarn has a finite length with a distinct end, whereas in a continuous loop, the yarn has no end. Thus, in a semi-continuous loop, at least one yarn is wrapped multiple times around the first and second thimbles, forming multiple loops around these thimbles, which are not entirely continuous since the ends of the yarn are not connected to each other. Each thimble holds a stack of layers of the turning portion of at least one yarn.

[0033] In one embodiment, the adhesive is provided in at least one of the first and second thimbles, connecting at least two of the multiple layers of yarn turns in the stack of each first or second thimble, and maintaining the tangential orientation of each yarn layer relative to each other when the tendon is subjected to a load. The stack of yarn turns in each thimble engages with each thimble along a portion of the circumference of each thimble. The adhesive provided in the at least one of the first and second thimbles extends over at least a portion of the circumferential portion of each first or second thimble.

[0034] The adhesive is provided in each yarn layer in only one of the thimbles, or in only both of the thimbles and not in the yarn between the end connections along the entire length of the tendon, or in the yarn between the end connections without curing the adhesive, so that the portion of the tendon extending between the end connections remains flexible. The phrase "the adhesive is provided in at least one of the first and second thimbles" is to be interpreted accordingly in the context of this specification.

[0035] Applying adhesive to the yarn along the entire length of the tendon and allowing it to harden results in a rigid rod instead of a tendon with some degree of flexibility. For example, a tendon with some flexibility is desirable for winding up or folding it for transport.

[0036] As the yarn turns around the thimble, each thimble supports the yarn along only a portion of its circumference, while the yarn is not supported along another portion of the thimble's circumference. The adhesive extends over at least a portion of the circumferential portion of the thimble that supports the yarn. Preferably, in the portion of the end connection where the yarn is not supported by the thimble, the adhesive is not applied to the yarn.

[0037] Additionally, extra layers of yarn can include adhesive to hold those layers of yarn together within each stack. In certain examples, substantially all layers within at least one of the thimbles are held together by adhesive.

[0038] In one embodiment, the adhesive extends over only a portion of the circumferential portion. In particular, the portion is centered on the longitudinal axis of the tendon.

[0039] For example, the adhesive extends over less than 50% of the circumferential portion, for example, over less than 25% of the circumferential portion, and in particular over less than 10% of the circumferential portion. The adhesive extends over 1% or more of the circumferential portion, in particular over 2% or more of the circumferential portion, and more specifically, over 5% or more of the circumferential portion.

[0040] When a tendon is rolled up or folded for transport, the fibers on the radially outer side of the roll are stressed, while the fibers on the radially inner side of the roll are compressed. This results in a slight shift of the yarn layers relative to each other within the stack of one or both thimbles. This shifted position may remain, at least partially, after the tendon is unrolled, resulting in uneven length of the fibers, thereby resulting in uneven loading on the fibers when the tendon is loaded. Because basalt fibers have a relatively high Young's modulus, this results in some parts of the yarn receiving a lower load than planned, while others receive a higher load than planned, leading to premature failure of the yarn in the higher-loaded sections. Connecting at least two layers together using adhesive prevents relative movement of these layers and thus prevents uneven loading of the yarn on one side of the tendon to the yarn on the other side. The adhesive is applied to at least the central portion of the circumferential part of the thimble that supports the yarn, which is sufficient to prevent shifts caused by winding the tendon, while the cost of applying the adhesive only to the central portion is lower than the cost of applying it to the entire circumferential portion.

[0041] In another embodiment, the adhesive extends over the entire circumferential portion of the thimble supporting the yarn.

[0042] In addition to preventing yarn shift when winding the tendon, applying adhesive over the entire circumferential portion of the thimble supporting the yarn further prevents relative movement of these layers when subjected to load cycles. The length of the yarn within the thimble is greater in the outer layer of the yarn turning point than in the inner layer of the yarn turning point. Although this length difference is small in absolute terms from one layer to the next, it results in different elongations of the yarn under load. This is because, with respect to a given Young's modulus and cross-section of the yarn (as well as the tension in the yarn), the amount of elongation corresponds to the length of the yarn. As the tendon undergoes load cycles by repeatedly increasing and decreasing the tensile load on the thimble, the difference in elongation results in the reciprocal movement of each layer of the yarn turning point relative to the neighboring layers. This movement causes micro-abrasion of the yarn. A further failure mechanism similarly induced by the load cycle is that the longitudinal stress in each yarn layer is thimblely transmitted through the intermediate yarn layer as pressure in a radially inward direction, causing a slight compression of the yarn layer stack. This inwardly oriented pressure results in a slight compression of the intermediate layer, which in turn results in reciprocal movement of the outer yarn layer relative to the inner yarn layer, and thus results in micro-abrasion. Micro-abrasion is prevented or at least reduced by providing adhesive throughout the support area.

[0043] In another embodiment, the present invention relates to a tension leg platform according to claim 14.

[0044] The tension leg platform includes a foundation connected to the bottom of a body of water, a plurality of tendons according to any of the embodiments described above, a buoyant hull, and a topside structure, the topside structure being connected to the buoyant hull and designed to extend above the water surface of the body of water, each tendon being connected to the buoyant hull by a proximal end connection and connected to the foundation at its distal end, providing tensile force to the buoyant hull. The tendons pull the buoyant hull toward the foundation, thus increasing the displacement of the buoyant hull so that it becomes greater than the combined weight of the buoyant hull and the topside structure.

[0045] In the context of this specification, the connection of a foundation to the bottom of a body of water should be understood as any type of connection that allows the tendon to exert the required force on the TLP, including connections by form fit, friction, attraction, and gravity.

[0046] In the first example, the buoyant hull is designed to extend partially below and partially above the waterline. In the second example, the buoyant hull is designed to be entirely below the waterline.

[0047] The topside structure is connected to the hull, for example, using fastening means such as nuts and bolts, or through welding. In another example, the topside structure and the hull are connected by being formed as a single, integrated piece.

[0048] In certain embodiments, the topside structure includes a wind turbine, which includes a mast (also known as a "tower"). More specifically, the buoyant hull includes a portion of the mast (i.e., the lower portion of the mast).

[0049] In one embodiment, the buoyant hull includes one main body. In another embodiment, the buoyant hull includes a plurality of interconnected main body sections.

[0050] In one embodiment, the tendon is connected to a buoyant hull via connecting means. In particular, the connecting means includes length adjustment means. In particular, the connecting means includes fixed connecting members.

[0051] In one embodiment, the foundation includes one or more elements of a list, including anchors, piles, and counterweights.

[0052] The present invention, its effects, and advantages will be described in more detail based on schematic drawings. [Brief explanation of the drawing]

[0053] [Figure 1] This is a schematic drawing of a tension leg platform (TLP) according to a first embodiment of the present invention. [Figure 2] This is a schematic drawing of a TLP according to a second embodiment of the present invention. [Figure 3] This is a schematic drawing of a TLP according to a third embodiment of the present invention. [Figure 4] This figure schematically shows a cross-section of a tendon according to an embodiment of the present invention and a magnified detail of the said cross-section, the cross-section being taken along the line IV-IV in Figure 1. [Figure 5] This figure schematically shows a longitudinal cross-section of a tendon according to the first embodiment of the present invention. [Figure 6] This figure schematically shows a cross-section of the tendon in Figure 5 taken along line VI-VI in Figure 5, and a magnified detail of the said cross-section. [Figure 7] This figure schematically shows a longitudinal cross-section of a tendon according to a second embodiment of the present invention. [Figure 8] This figure schematically shows a cross-section of the tendon in Figure 6 taken along the line VIII-VIII in Figure 7. [Figure 9] This figure shows a tendon according to a third embodiment of the present invention. [Figure 10] This figure shows a partially decomposed cross-section of Figure 9 along line XX in Figure 12. [Figure 11] This is a detailed enlarged view from Figure 10. [Figure 12] Figure 9 is a top view of the tendon. [Figure 13] This figure shows the cross-section XIII-XIII from Figure 12. [Figure 14] This figure shows the cross-section XIV-XIV from Figure 12. [Modes for carrying out the invention]

[0054] Figure 1 shows a tension leg platform (TLP), which is shown in its entirety by reference figure 2, and it supports a wind turbine 3 comprising a mast 4, a rotor 5 with a housing and three blades, and a 15 MW generator inside the rotor housing. The 15 MW generator is designed to convert wind energy into electrical energy. The diameter of the rotor with blades in the shown embodiment is 190 meters. The TLP2 includes a foundation 6 connected to the bottom 8 of a body of water 10. In this embodiment, the foundation 6 is formed by a plurality of concrete blocks 12 (acting as counterweights), which are anchored to the seabed 8 by piles 14. The TLP2 further includes a buoyant hull 16. In the embodiment of Figure 1, the hull 16 includes a pontoon 18, which is located below the water surface 20 and the upper hull structure 22. The pontoon 18 provides buoyancy to the hull 16, for example, by an air chamber or by using a material having a density lower than that of water. Furthermore, the upper hull structure 22 of this embodiment provides buoyancy to the hull 16, for example, by including an air chamber within its vertical upright portion.

[0055] In this embodiment, the topside structure of the TLP2 is formed by a wind turbine 3 extending above the water surface 20. The rotor is located at the upper end of the mast approximately 180 meters above the sea surface 20. The wind turbine 3 is mounted on the horizontal upper portion of the hull 16, which is formed by the horizontal portion of the upper hull structure 22. The foundation 6 and the buoyant hull 16 are connected by tendons 24. The proximal end 23 of the tendon 24 is connected to the buoyant hull 16, and the distal end 25 of the tendon 24 is connected to the foundation 6 by connecting means (not shown). Figure 1 shows a tendon 24 for connecting two foundation blocks 12 to the buoyant hull 16, but it is understood that any suitable number of foundation blocks 12 and tendons 24 can be used. This embodiment includes four foundation blocks 12 at a distance of 75 meters from each other. In one variation, it is possible to use two or more tendons 24 per block 12. The tendons 24 are depicted as extending vertically. It is understood that the tendons 24 are positioned substantially vertically (for example, at an angle of up to 10°). The tendons 24 are not depicted to scale. In particular, the length of the tendons in the explanatory diagrams has been reduced to fit the tendons on the page, as indicated by the diagonal dashed lines. In reality, the tendons 24 are at least 300 meters long. In this embodiment, each tendon 24 is 1000 meters long.

[0056] Figure 2 shows a different TLP102. This TLP102 is also used to support a wind turbine 103 (only a portion of the mast of the wind turbine 103 is shown) with a rotor (not shown) having an 18 MW generator. In this embodiment, the foundation 106 is formed as a single element having a triangular shape with sides of 80 x 80 x 80 meters. The foundation 106 is anchored to the seabed 108 by its weight. For example, the foundation 106 has a chamber filled with gravel, sand, or concrete to provide it with the weight necessary to keep it on the seabed 108. The TLP102 further includes a buoyant hull 116, which includes a fully submerged pontoon 118 and a partially submerged upper hull structure including uprights 121 supporting a platform 122. Each upright 121 is mounted on one of the pontoons 118. The pontoons 118 are connected to each other via digits 119.

[0057] In the embodiment shown in Figure 2, there are three pontoons 118, but in other embodiments, it is understood that any suitable number of pontoons 118 (for example, four, six, or eight pontoons) may be provided. In another embodiment, the pontoons 118 are connected to one another in a triangular, square, hexagonal, or octagonal arrangement.

[0058] The superstructure in the form of a wind turbine 103 is mounted on a buoyant hull 116. As shown in Figure 1, the buoyant hull 116 is connected to a base 106 via tendons 124, with at least one tendon 124 per pontoon 118. The tendon 124 has a proximal end 123 connected to the hull 116 and a distal end 125 connected to the base 106. The tendon 124 in this embodiment has a length of 600 meters.

[0059] Figure 3 shows yet another embodiment of the TLP202, which is provided with a wind turbine 203 and a foundation 206. The foundation 206 is a single element, similar to Figure 2, and in this embodiment has a circular shape with a diameter of 80 meters and is connected to the ocean floor 208 by piles 214 driven into the soil, as shown in Figure 1. The TLP202 has a buoyant hull 216, which is formed as a central column 218, and the central column 218 provides buoyancy, for example, by an air chamber inside the central column 218 or by the use of a material having a density lower than that of water. The hull 216 further includes connecting means, which in this embodiment include length adjustment means (not shown) and fixed connecting members in the form of girders or arms 219, which are uniformly spaced radially around the central column 218 and connected to the central column 218. The tendons 224 connect the foundation 206 to the buoyant hull 216 via length-adjusting means and arms 219 of the hull 216, with one or more tendons 224 per arm 219. Each tendon 224 has a proximal end 223 connected to the hull 216 and a distal end 225 connected to the foundation 206. The tendons 224 have a length of 800 meters.

[0060] Figures 1 to 3 show wind turbines 3, 103, and 203 as topside structures. It is understood that within the scope of the present invention, different topside structures, such as those for oil production facilities, can be provided.

[0061] A cross-section of one of the tendons 24, 124, and 224 in Figures 1 to 3 is schematically shown in Figure 4 (not to scale). The tendon 24 contains multiple yarns 26 of basalt fibers 27. The yarns 26 are covered by a cover 28, which bundles the yarns 26 into a compact bundle and acts as a protective cover. The cover 28 includes one or more layers, for example, a coating and / or sealing tape and / or braid.

[0062] The design value for the Young's modulus of basalt is 84 gigapascals. As explained above, basalt fibers provide approximately 95% of their maximum Young's modulus at low stress values. Therefore, it is possible to add as many basalt fibers as are needed to obtain the required stiffness. Thus, the use of basalt fibers makes it possible to create tendons with the length and stiffness necessary for use in deep ocean (i.e., at a depth of at least 300 meters) with TLP.

[0063] In an embodiment with a 1000-meter-long tendon 24, the required stiffness is 35 gigawutons. This is equivalent to 0.605 m 2 This results in a tendon having a cross-section and, consequently, a diameter of approximately 88 cm. In embodiments with shorter tendons 124 and 224, the cross-section is proportionally smaller.

[0064] An additional advantage of basalt fibers is that the resulting tendons are much heavier than those made from high-performance plastic fibers. Plastic fibers (e.g., UHMwPE) even provide upward buoyancy, which increases the total load on the foundation. In contrast, tendons made from basalt fibers according to the present invention are heavier than water, which reduces the load on the foundation, resulting in a lower design load for the foundation. A tendon 24 disclosed above, having a length of 1000 meters and a diameter of 88 cm, has a weight of approximately 1200 tons. Due to this length and diameter of tendon 24, the load difference is on the order of 1000 tons. A further advantage of basalt fibers is that they exhibit virtually no creep, reducing or even eliminating the need to compensate for tendon elongation during use.

[0065] A further advantage of using basalt fibers for tendons instead of other types of fibers (such as carbon fibers and plastic fibers) is the significant cost reduction. For a good comparison, costs are compared by looking at the cost per meganewton (MN) per meter. In other words, we look at the cost to provide a tendon with a given unit stiffness per unit meter.

[0066] The cost of providing a UHMwPE fiber tendon with a length of 1 meter and a stiffness of 1 MN is 2.5 times greater than the cost of a basalt fiber tendon of the same length and stiffness. The cost of a carbon fiber tendon or a paraaramid fiber tendon (for example, those marketed under the Twaron® brand) is more than 1.6 times greater than the cost of a basalt fiber tendon.

[0067] The cost of tendons accounts for a significant portion of the total construction cost of a TLP. In fact, with respect to tendons containing carbon fiber or plastic fiber, the cost of the tendons quickly begins to exceed the cost of the platform and wind turbine as the length of the tendons increases. Typically, a TLP for a wind turbine has at least three tendons, and each tendon for a particular embodiment requires a stiffness of approximately 35 GN (giganewtons). If UHMwPE fiber tendons were used for such a platform, the cost of the three tendons would be more than four times the cost of the platform and wind turbine. The cost of carbon fiber or paraamide fiber tendons would be more than 2.8 times the cost of the platform and wind turbine. In particular, the cost of the platform and wind turbine is in the range of tens of millions of euros. Thus, it is clear that reducing the cost of tendons by using basalt fiber would lead to a significant reduction in the total construction cost of a TLP (especially with relatively long tendons (e.g., at least 300 meters, and especially 500 meters or 1000 meters)).

[0068] Figures 5 and 6 illustrate a tendon 24 according to a first embodiment of the present invention. In this embodiment, both the proximal end 23 and the distal end 25 of the tendon 24 are provided with the same end connector 30, only one of which is shown. The tendon 24 contains a bundle of yarn 26 (not drawn to scale). The bundle of yarn 26 is formed by pultrusion, in which a spool containing a number of yarns corresponding to the number of yarns 26 required for the tendon is placed on a rack, and the yarns are simultaneously unwound by pulling them from the spool. The yarns 26 are bundled together, for example, by guiding them through a screen with multiple holes, and a cover is provided by extruding a polymer (e.g., a thermosetting or thermoplastic epoxy such as polyvinyl chloride (PVC)) around the bundle. The resulting bundle of yarn 26 is then cut to the required length. The yarn 26 is bundled together in the main part of the tendon 24, but at the end connection 30, the yarn 26 diverges (i.e., gradually widens in a fan shape) inside the cavity 31 of the hollow section 32. The walls of the cavity 31 are indicated by dotted lines. The cavity 31 has a frustoconical shape that diverges toward the end of the tendon 24. The cover 28 of the tendon 24 partially extends into the hollow section 32 so that the yarn 26 is not exposed. The outer end of the hollow section 32 is provided with internal threads for connection to a threaded end cap 34, which includes an eyelet 36 for connection to the hull 16, 116, 216 or foundation 6, 106, 206 of the tendon 24TLP2, 102, 202. The ends of the yarn 26 are secured in a spaced-out configuration by the matrix filling the cavity 31 inside the hollow section 32. The matrix is ​​a resin, such as epoxy resin. For clarity in the illustration, the matrix is ​​not shown in Figure 5. The cross section in Figure 6 shows that the hollow portion 32 contains multiple yarns 26 (drawn as dots to reflect their small dimensions). The enlarged detail on the right side of Figure 6 illustrates the matrix 38 that holds the ends of the yarns 26 in their spaced-out, divergent positions.

[0069] The end connector 30 can be produced in various ways. In the first example, the yarn 26 is inserted into the hollow section 32, with its ends spaced apart, and then the cavity 31 is filled with matrix 38. After the matrix has cured, the end cap 34 is installed. In the second example, the end connector is produced by feeding a tendon 24 through the hollow section 32 (before the end cap 34 is installed), and the exposed end of the yarn 26 is placed in the mold in a divergent configuration. The mold has a shape (e.g., a frustoconical shape) corresponding to the cavity 31 inside the hollow section 32. The mold is then filled with matrix (e.g., epoxy resin) to form a plug that encloses the spaced-apart yarn ends. The tendon 24 is pulled back through the hollow section 32 until the plug is released from the mold and the molded plug fills the cavity 31. Preferably, the molded plug is then secured into the cavity 31 with an adhesive (for example, the same epoxy resin used to form the plug). Finally, the end cap 34 is installed by screwing it in.

[0070] Figures 7 and 8 illustrate a tendon 124 with an alternative end connector 130. In this embodiment, both the proximal end 123 and the distal end 125 of the tendon 124 are provided with the same end connector, but only one of the end connectors 130 is illustrated. The tendon 124 contains a bundle of yarn 126 (not drawn to scale). The yarn is bundled together within the main part of the tendon 124, but at the end connector 130, the yarn 126 diverges inside the cavity 131 of the hollow portion 132 (i.e., gradually spreads out in a fan shape). The walls of the cavity 131 are indicated by dotted lines. The cavity 131 has a frustoconical shape that diverges toward the end of the tendon 124. The cover 128 of the tendon 124 partially extends into the hollow portion 132 so that the yarn 126 is not exposed. Similar to Figure 5, the tendon 124 is inserted into the hollow portion 132, and the end of the yarn 126 is positioned to diverge inside the cavity 131 of the hollow portion 132. In this embodiment, a restraining body 140 is inserted into the hollow portion 132 to maintain the yarn 126 in its spaced-out position. The restraining body 140 has a wedge shape. In this embodiment, the shape corresponds to the shape of the cavity 131 of the hollow portion 132, and is therefore truncated cone. In the embodiments of Figures 5 and 6, the yarn 26 spreads throughout the entire volume of the hollow portion 32 (Figure 6), whereas in Figures 7 and 8, the restraining body 140 locks the yarn 126 against the inner wall of the hollow portion 132 (Figure 8). The yarn 126, the restraining body 140, and the inner wall of the hollow portion 132 are interconnected by an adhesive (not shown for clarity). One or more layers of the yarn 126 can be held between the restraining body 140 and the inner wall of the hollow portion 132. An advantage of the embodiments in Figures 7 and 8 is that less adhesive is required to secure the yarn 126 than the amount of epoxy used in the embodiments in Figures 5 and 6.

[0071] Figure 7 also shows an alternative embodiment of the end cap 134, which includes an eyelet 136 that screws into the internally threaded portion of a closing nut 142 that closes the hollow portion 132. In one modification, the end cap 134 has a fixed eyelet (for example, the eyelet 36 of the previous embodiment). In one modification of the end cap 34 of the previous version, the end cap 34 has an eyelet that screws into a closing nut (for example, the eyelet 136).

[0072] Figures 9 to 14 show a tendon 224 according to a third embodiment of the present invention. The tendon 224 has a proximal end connector 229 including a first thimble 244, a distal end connector 230 including a second thimble 246, and a plurality of yarns 226 containing basalt fibers. The first thimble 244 and the second thimble 246 are made of stainless steel and are provided at both ends of the tendon 224, each having a center 247. The plurality of yarns 226 are, in this embodiment, 24 yarns 226 of 24,000 dtex basalt fibers, all of which extend from the first thimble 244 to the second thimble 246 and turn around the second thimble 246, and extend from the second thimble 246 to the first thimble 244 and turn around the first thimble 244. Thus, each of the multiple yarns 226 forms a semi-continuous loop around the first and second thimbles. This loop is repeated multiple times, 9800 times in this embodiment. Therefore, each of the yarns 226 undergoes 9800 turns, resulting in a total of 235,000 turns in the yarn 226. Since each turn represents two yarns in cross-section, the total number of yarns in cross-section is 470,000.

[0073] Figure 10 shows in cross-section that the thimble 244 has a bearing surface 248. The thimble 244 holds a stack 249 with multiple layers 250 of the turning portion of the yarn 226. This is shown in more detail in Figure 11, which is a greatly enlarged schematic view of five layers 250 of the turning portion of the yarn 226. In the upper part of Figure 10, the stack 249 is shown in an exploded view for clarity. In reality, the entire stack 249 is held within the first thimble 244, as shown in the lower part of Figure 10. The second thimble 246 holds the same layers of the yarn turning portion 226 in the same manner and is therefore not shown in detail. Also, the enlarged drawing of Figure 11 shows that the yarn 226 each contains multiple basalt fibers 227 (shown as dots in Figure 11).

[0074] Multiple yarn layers 250 of the tendon 224 are connected to one another by an adhesive (epoxy resin 251 in this embodiment). In this embodiment, epoxy resin 251 is provided at each end connection 229, 230 to connect all the layers 250 of the yarn 226 turning portion in the stack of each thimble 244, 246, and to maintain the tangential orientation of each yarn layer 250 relative to one another when the tendon 224 is wound up for transport and subsequently subjected to load when used in a TLP (e.g., one of TLP2, 102, 202).

[0075] The cover 252 extends around the tendon 224 from the first thimble 244 to the second thimble 246, bundling all yarn turns 226 extending between the first thimble 244 and the second thimble 246 into a single compact bundle 254 at the intermediate section 256 of the tendon 224. In this embodiment, the cover 252 also covers the yarn turns 226 at the end connections 229, 230. The cover 252 causes convergence sections 258, 260 of the yarn turns 226 extending from each thimble 244, 246 to the intermediate section 256.

[0076] Figure 13 shows that the tendon 224 in the intermediate section 256 (i.e., between the end connections 229 and 230) is formed by the turning portion of the yarn 226 without any epoxy resin 251 (or any other adhesive) being present between the yarns 226, and thus the tendon 224 remains flexible.

[0077] Figure 14 is a schematic longitudinal section through the distal end connection 230. A longitudinal section through the proximal end connection 229 is similar in this embodiment and is therefore not shown in detail. It shows the inner contour 262 and outer contour 264 of the convergence section 260 of the bundle of yarn turning portions 226 as it engages with the thimble 246 and turns around the thimble 246. The yarn turning portions 226 are bundled at the intermediate section 256 and are therefore divided into two halves and diverge toward the thimble 246 so that in this embodiment they engage with the support surface 248 of the thimble 246 at an angle α of approximately 220°. The region of the support surface 248 covered by this angle is referred to as the support region 266, which is that portion of the circumference of the thimble where the yarn 226 contacts (and is supported by) the thimble 246. The support region 266 covers angle α, as indicated by the dashed line in Figure 14. Generally, the adhesive is applied over a portion 268 of the support region 266. In a preferred embodiment, portion 268 is substantially the entire support region 266. This results in the yarns 226 being interconnected within the support region 266, eliminating movement of the yarns 226 relative to one another and consequently preventing wear of the basalt fibers, which would result in premature failure of each tendon 224.

[0078] In an alternative embodiment, the epoxy resin is present within further portions of each end connection (in particular, within the entire end connection).

[0079] In an alternative embodiment, the adhesive covers less than half of the support area 268 (for example, one-third of the support area 268), as illustrated in Figure 14. The portion 268 with the adhesive is centered on the longitudinal axis 270 of the tendon 224.

[0080] The adhesive connects at least two of the multiple layers of the yarn 226, and in a preferred embodiment, substantially all of the layers of the yarn are connected by the adhesive. Connecting substantially all of the layers of the yarn turn results in a further better increase in lifespan than simply connecting two layers. In the context of this specification, substantially all of the layers of the yarn turn is interpreted as at least 80% of the layers, in particular at least 90% of the layers, and more specifically at least 95% of the layers.

[0081] In this embodiment, adhesive is not applied to the portion of the support surface 248 that does not support the turning portion of the yarn 226 (i.e., the unsupported region extending over the remaining (360°-α) degrees (for example, the remaining 140° in the example of Figure 14)).

[0082] Generally, the turning portion of the yarn engages with an angle α of the thimble's bearing surface in the circumferential direction, where α is greater than 180° and less than 360° of the circumference of the thimble's bearing surface. In one embodiment, α is greater than 200° of the thimble's bearing surface, in particular greater than 220°, and more specifically greater than 240°. In one embodiment, α is less than 340° of the thimble's bearing surface, in particular less than 320°, and more specifically less than 300°.

[0083] Several modifications are possible within the scope of the appended claims. Features of the preferred embodiments described above can be replaced by any other features within the scope of the appended claims (for example, features described in other embodiments and in the following paragraphs).

[0084] Each of the types of tendons 24, 124, and 224 described above can be used alone or in combination with other types of tendons (for example, one of the other disclosed tendons 24, 124, and 224 or one of the types of tendons not disclosed herein) in any one of the TLPs 2, 102, and 202 described above, or in other TLPs. In other words, in embodiments, TLP 102 or TLP 202 is provided with tendon 24, TLP 2 or TLP 202 is provided with tendon 124, and TLP 2 or TLP 102 is provided with tendon 224.

[0085] The tendons according to the present invention can be made from more or fewer than 10 yarns (e.g., 1 yarn, 2 yarns, or at least 5 yarns). The total number of yarn turns (i.e., the number of yarn turns and layers per layer) depends on the required strength and stiffness of the tendon, the strength of each individual yarn, and the required safety margin. The number of layers depends on the required number of yarn turns and the available width in the thimble that results in the maximum number of yarn turns in the width direction.

[0086] In one embodiment, the yarn layer in only one of the thimbles is provided with adhesive. In particular, one thimble in such an embodiment differs from the other thimble, for example, from the larger radius and / or width of each thimble, so that the adhesive is less beneficial when the load on the fibers is small.

[0087] In one embodiment, adhesive is applied to the tendons between thimbles so that the tendons between thimbles remain flexible. A tendon is considered flexible if it can be rolled up (for example, for transport). Such flexibility exists if the different layers of yarn turning points in the tendon between thimbles can shift relative to each other in its longitudinal direction. In particular, adhesive is applied to tendons extending between thimbles but is not cured, and / or the adhesive is applied to only a small portion of the tendon and cured so that the tendon as a whole remains flexible. In one embodiment, adhesive is present to connect the layers of cover around the yarn of the tendon.

[0088] In one embodiment, the tendon includes more than two thimbles. In such embodiments, at least two thimbles are present at one end of the tendon. The two thimbles at one end connection form a female end connection, and a connection to a further flexible tendon can be established by placing a male end connection between the thimbles of the female end connection.

[0089] In one embodiment, other types of resins, such as polyester resin, vinyl ester resin, or polyamide, may be used. In particular, the resin is a thermosetting polymer.

[0090] In one embodiment, the adhesive is applied to only one of the thimbles.

[0091] In one embodiment, the adhesive is applied only to one or both thimbles of the end connection and not to the convergence section of the yarn turn at the end connection.

[0092] In one embodiment, the adhesive is applied during the yarn winding process, that is, the adhesive is applied on each layer of yarn turns, or on every nth layer of yarn turns, where n is an integer, greater than or equal to 1, and less than the total number of yarn turns in the stack.

[0093] In one embodiment, the adhesive is cured by adding a curing agent (e.g., a polyamine curing agent for resins). In another embodiment, the adhesive is cured by radiation (e.g., IR radiation, UV radiation, or microwave radiation).

[0094] In one embodiment, the thimble is made from a plastic material instead of metal, or from a metal other than stainless steel (including, but not limited to, different steel alloys, aluminum alloys, magnesium alloys, and titanium).

[0095] In some embodiments, tendons are formed by pultrusion, resulting in tendons with yarn of a finite length. The pultrusion process generally involves wetting the fibers in a resin before they are covered. While this wetting results in tendons suitable for some applications, it can result in tendons that are too stiff and cannot be bent for transport. In preferred embodiments, tendons are made by dry pultrusion (i.e., without wetting the fibers before they are bundled). This ensures the mobility of the fibers relative to one another, which allows the tendons to be rolled up for transport.

[0096] In one variation, the yarn is bundled with a braided cover in addition to (or instead of) the PVC cover. In another variation, the yarn is bundled with tape (in particular, spirally wound tape) in addition to (or instead of) the PVC cover and / or the braided cover.

[0097] In one embodiment, the tendon is made from a plurality of sub-ropes, each sub-rope produced by extrusion molding of basalt yarn. The yarn in the sub-ropes is not twisted, and the sub-ropes are arranged parallel to each other (i.e., without twisting) within the tendon and are held together by a cover (for example, one or more of the covers disclosed above).

[0098] It should be noted that with respect to terms such as "fiber," "mould," and "centre," the British spelling is applied in the above specification. These terms can be replaced with the corresponding American spellings ("fiber," "mold," and "center") without altering the content of this specification. [Explanation of Symbols]

[0099] 2. Tension Leg Platform (TLP) 3. Wind turbine, topside structure 4 Mast 5 rotors 6 Basics 8 Seabed, bottom 10 Water area 12 concrete blocks 14 pile 16. Buoyant hull 18 Pontoon 20 water surface 22 Upper hull structure 23 Proximal end 24 Tendon 25 Distal end 26 yarns 27 Basalt Fibers 28 Cover 30 End connection section 31 Cavity 32 Hollow part 34 End caps 36 eyelets 38 Matrix 102 TLP 103 Wind turbine, topside structure 106 Basics 108 Seabed, bottom 110 Water area 116 Buoyant hull 118 Pontoon 119 digits 120 Water surface 121 Upright part 122 platforms 123 Proximal end 124 Tendon 125 Distal end 126 Yarn 128 Cover 130 End connection section 131 Cavity 132 Hollow part 134 End caps 136 eyelets 140 Restraint main body 142 Closing nut 202 TLP 203 Wind turbine, topside structure 206 Basics 208 Bottom, ocean floor 210 Water area 214 piles 216 Buoyant hull 218 Central Pillar 219 digits, arm 220 Water surface 223 Proximal end 224 Tendon 225 Distal end 226 Yarn 227 Basalt Fibers 229 Proximal end connection 230 Distal end connection 244 The first thimble 246 The second thimble 247 center 248 Bearing surface 249 stacks 250 Yarn Layer 251 Epoxy resin, adhesive 252 Cover 254 bundles 256 Intermediate Section 258 Convergence Section 260 Convergence Section 262 Inner contour 264 Outer contour 266 Support area 268 Part of support area 266 270 Longitudinal axis α angle

Claims

1. Tendons (24, 124, 224) for a tension leg platform (2, 102, 202), wherein the tension leg platform (2, 102, 202) includes a foundation (6, 106, 206) connectable to the bottom of a body of water and a buoyant hull (16, 116, 216), The tendons (24, 124, 224) have a predetermined length and proximal ends (23, 123, 223) and distal ends (25, 125, 225), and the proximal ends (23, 123, 223) include proximal end connectors (30, 130, 229), and the distal ends (23, 123, 223) include distal end connectors (30, 130, 230), The tendons (24, 124, 224) are connectable to the buoyant hull (16, 116, 216) by the proximal end connectors (30, 130, 229) and connectable to the foundation (6, 106, 206) by the distal end connectors (30, 130, 230) so as to provide tensile force to the buoyant hull (16), The length of the aforementioned tendon (24, 124, 224) is at least 300 meters. The tendon (24, 124, 224) is characterized in that it includes basalt fibers (27, 227) for transmitting the tensile force from the proximal end connection (30, 130, 229) to the distal end connection (30, 130, 230).

2. The basalt fibers (27, 227) extend parallel to each other in the longitudinal direction of the tendons (24, 124, 224) for the tension leg platform (2, 102, 202) according to claim 1, wherein the tendons (24, 124, 224) are the basalt fibers (27, 227) of the tendons (24, 124, 224).

3. The basalt fibers (24, 124, 224) are untwisted tendons (24, 124, 224) for the tension leg platform (2, 102, 202) according to claim 1 or claim 2.

4. The tendons (24, 124) include a plurality of yarns (26, 126) containing the basalt fibers (27), Each of the plurality of yarns (26, 126) has a length corresponding to the length of the tendon (24, 124) and has a proximal yarn end connected to the proximal end connector (30, 130) and a distal yarn end connected to the distal end connector (30, 130), the tendon (24, 124) for a tension leg platform (2, 102, 202) according to one or more of claims 1 to 3.

5. At least one of the distal end connectors (30, 130) and the proximal end connectors (30, 130) includes a hollow portion (32, 132) having a cavity (31, 131), The width of the cavity (31, 131) increases toward each end of the tendon (24, 124), Tendons (24, 124) for the tension leg platform (2, 102, 202) according to claim 4, wherein the yarn (26, 126) extends into the cavity (31, 131) of the hollow portion (32, 132) and diverges inside the cavity (31, 131).

6. The cavity (32, 132) has a frustoconical shape, and the tendons (24, 124) for the tension leg platform (2, 102, 202) according to claim 5.

7. The cavity (32, 132) is filled with a matrix (38) that secures the diverging yarn (26, 126), the tendon (24, 124) for the tension leg platform (2, 102, 202) according to claim 5 or 6.

8. A tendon (124) for a tension leg platform (2, 102, 202) according to one or more of claims 5 to 7, wherein a restraining body (140) is provided in the cavity (131) for maintaining the diverging yarn (126) in an interval-spacing arrangement, and in particular the restraining body (140) has a shape complementary to the shape of the cavity (131).

9. The tendons (24, 124) are formed by pultrusion to bundle the basalt yarns (26, 126) with a cover, particularly a polymer cover, for the tension leg platform (2, 102, 202) according to one or more of claims 4 to 8.

10. The tendon (224) comprises at least one yarn (226) containing the basalt fiber (227), The proximal end connector (229) includes a first thimble (244), and the distal end connector (230) includes a second thimble (246). The first thimble (244) and the second thimble (246) are provided at both ends of the tendon (224), The at least one yarn (226) extends from the first thimble (244) to the second thimble (246), turns around the second thimble (246), extends from the second thimble (246) to the first thimble (244), turns around the first thimble (224), and so the yarn (226) forms a turning portion around the first and second thimbles (244, 246). Each thimble (244, 246) holds a stack (249) of multiple layers (250) of the turning portion of the yarn (226), a tendon (224) for a tension leg platform (2, 102, 202) according to one or more of claims 1 to 3.

11. The adhesive (251) is provided on at least one of the first thimble (244) and the second thimble (246), and connects at least two of the plurality of layers (250) of the yarn turning portion in the stack (249) of each of the first thimble (244) and the second thimble (246) to each other, so as to maintain the tangential orientation of each yarn layer (250) relative to each other when the tendon (224) is subjected to load. The stack (249) of the yarn (226) of each thimble engages with each thimble along a portion (266) of the circumference of each thimble. The adhesive (251) provided to at least one of the first thimble (244) and the second thimble (246) extends over at least a portion (268) of the circumferential portion (266) of the first thimble (244) or the second thimble (246), a tendon (224) for a tension leg platform (2, 102, 202) according to claim 10.

12. The adhesive (251) extends over the entire circumferential portion (266) to the tendon (224) for the tension leg platform (2, 102, 202) according to claim 11.

13. The adhesive (251) extends only over the portion (268) of the circumferential portion (266), and in particular the portion (268) is centered on the longitudinal axis (270) of the tendon, the tendon (224) for the tension leg platform (2, 102, 202) according to claim 11.

14. A tension leg platform (2, 102, 202), wherein the tension leg platform (2, 102, 202) is Foundations (6, 106, 206) connected to the bottom (8, 108, 208) of the water body (10, 110, 210), A plurality of tendons (24, 124, 224) according to one or more of claims 1 to 13, Buoyant hulls (16, 116, 216) A topside structure (3, 103, 203) is connected to the buoyant hull (16, 116, 216) and is designed to extend above the water surface (20, 120, 220) of the water body (10, 110, 210). Includes, Each of the aforementioned tendons (24, 124, 224) is connected to the buoyant hull (16, 116, 216) by the proximal end connectors (30, 130, 229) and to the foundation (6, 106, 206) by the distal end connectors (30, 130, 230), and tension leg platforms (2, 102, 202) that provide tensile force to the buoyant hull (16, 116, 216).

15. The topside structure includes a wind turbine (3, 103, 203), the tension leg platform (2, 102, 202) according to claim 14.

16. The tension leg platform (2,102,202) according to claim 15, wherein the wind turbine (3,103,203) includes a mast, and the buoyant hull includes a portion of the mast.

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