Compression element for mooring components

Abstract

A compression element (80) for a mooring component comprises a plurality of shell pieces (42b, 42b'). Each shell piece has a first annular portion and a second annular portion and a middle portion extending between the first annular portion and the second annular portion. The first annular portion and the second annular portion lie in a plane perpendicular to a central axis of the compression element. The maximum dimension of the first annular portion in a direction perpendicular to the central axis is greater than the corresponding maximum dimension of the second annular portion. The shell pieces are arranged along the central axis such that the first annular portion or the second annular portion of one shell piece is joined to the first annular portion or the second annular portion of an adjacent shell piece. The compression element is arranged such that, when a compressive stress causes the compression element to be compressed, the middle portion of one shell piece contacts the middle portion of an adjacent shell piece.

Description

Technical Field

[0001] The present invention relates to a compression element for mooring components, particularly for mooring components of floating structures in water. Background Technology

[0002] Floating marine structures, such as floating offshore wind turbines, can be held in place using mooring systems that connect the seabed to the floating marine structure. Typically, such mooring systems are designed to resist any movement of the floating structure away from its desired position and to generate restoring forces to return the structure to the desired position. The desired position may also include the desired orientation, wherein the mooring elements are designed to resist any or all surge, heave, sway, pitch, roll, and / or yaw movements.

[0003] There are a range of different mooring system types, such as catenary, tension, and semi-tension. All of these can utilize a range of mooring components, such as chains, synthetic ropes, counterweights, anchors, and floats. In shallow waters, catenary systems are common.

[0004] However, these mooring systems are not particularly suitable for mooring certain floating marine structures, including floating offshore wind turbines or tidal turbines, where, in addition to dynamic loads, the mooring cables are subjected to high mean background thrust loads due to turbine operation (i.e., the forces experienced by the mooring system before the application of dynamic loads, such as those exerted by mean wind or current).

[0005] With the background thrust, the structure will move to a new position (in the direction of the background thrust) until the restoring force of the mooring system (i.e., the restoring force that returns the structure to its desired position and increases as it moves further from that position) matches the background thrust. Therefore, a high background thrust results in a high restoring force from the mooring system.

[0006] Under these conditions, the stiffness of the mooring system (i.e., the force required to move the floating structure further) is typically very high, and as most mooring systems become increasingly stiff, the floating structure moves further and further from the desired location. When dynamic forces (i.e., waves) cause the floating structure to move near its new location, this thus generates very high variable loads (i.e., tension variations) on the mooring system, requiring larger and more expensive mooring components (to prevent failure).

[0007] One approach to this problem is to attempt to alter the stiffness response of the mooring cable by introducing new materials, such as those disclosed in WO 2012 / 127015. These systems function well in the absence of high background thrust. As discussed in WO 2012 / 127015, typical catenary mooring systems exhibit undesirable stress-strain behavior in rough seas due to the heavy weight of the catenary chains required to provide the desired range of motion. Such large chains impose large loads on the floating structure, subjecting the chains and the components connecting them to the structure to high levels of fatigue, thus posing a risk of chain failure.

[0008] WO 2012 / 127015 discloses an alternative mooring system comprising at least one tensioning element and at least one compression element as a proposed solution to overcome problems encountered by catenary chains.

[0009] The applicant has observed that ocean depths in the 50-100 meter range (where waves up to 20 meters are not uncommon) present particular challenges to the mooring of floating marine structures. The angle of the mooring cable between the platform and the seabed is important because it determines the proportion of restoring force required to hold the platform in place (anti-swell force = tension in the mooring cable * sine of the angle between the mooring cable and the platform). Because wave height and swell are a higher proportion of water depth, longer chains are required to suspend the platform from the seabed to provide restoring force in shallower waters compared to deeper waters.

[0010] In fiber optic mooring systems, angles are equally important because the fiber optic ropes need to be protected from impact with the seabed while simultaneously having sufficient length to allow the platform the required movement. This presents a challenge in shallow water environments where the required cable length is often a multiple of the water depth. These relatively large waves (relative to ocean depth) exert high thrust on floating marine structures, especially if the mooring system is already stiff due to high background loads. For floating offshore wind turbines (FOWTs), the background thrust generated by the turbines can easily exceed 100 tons, making the mooring system very stiff; high wave conditions can potentially drive forces exceeding 1000 tons. These enormous forces require very expensive mooring components and very costly specialized installation vessels to protect against failure. Summary of the Invention

[0011] The present invention aims to provide an improved compression element for mooring components that can be adapted to high background thrust environments.

[0012] When viewed from a first aspect, the present invention provides a compression element for a mooring component, the compression element comprising a plurality of housings (i.e., at least two), wherein each of the plurality of housings comprises a first annular portion, a second annular portion, and a central portion;

[0013] The first annular portion and the second annular portion are each located in a plane substantially perpendicular to the central axis of the compression element, wherein the maximum dimension of the first annular portion in the direction substantially perpendicular to the central axis is greater than the maximum dimension of the second annular portion in the direction substantially perpendicular to the central axis, and wherein the middle portion connects and extends between the first annular portion and the second annular portion.

[0014] The plurality of shells are arranged along a central axis such that a first annular portion of one of the shells engages with a first annular portion of an adjacent shell, or a second annular portion of one of the shells engages with a second annular portion of an adjacent shell.

[0015] The compression element is arranged such that it is compressed when compressive stress is applied to it substantially along the central axis; and

[0016] The compression element is arranged such that when the compressive stress applied to the compression element causes the compression element to be compressed by a specific proportion of its uncompressed length, the middle portion of one of the plurality of housings contacts the middle portions of the adjacent housings among the plurality of housings.

[0017] The present invention provides a compression element for inclusion, for example, as part of a mooring component in a mooring cable or system for mooring floating structures such as floating offshore wind turbines.

[0018] Each housing has a first annular portion and a second annular portion, which are joined together by a central portion. The first and second annular portions are each located in a plane substantially perpendicular to the central axis, and are therefore positioned substantially parallel to each other, for example, with respect to the central axis (e.g., which extends through the center of each of the first and second annular portions).

[0019] Preferably, the first annular portion and the second annular portion are arranged at both (axial) ends (relative to the central axis) of each housing of the compression element. The first annular portion and the second annular portion have different dimensions, wherein the maximum dimension (e.g., diameter) of the first annular portion in a direction substantially perpendicular to the central axis of the compression element is greater than the corresponding dimension of the second annular portion.

[0020] The compression element is formed of multiple shells joined together along a central axis by their respective first or second annular portions. It should be understood that the term "joined" includes the individual manufacture of these shells followed by joining, and also includes the possibility that multiple shells can be integrally formed as a single unit, with adjacent shells thus joined together by being integrally formed. For example, two adjacent shells (e.g., forming an hourglass shape) can be integrally formed together, for example, molded together, and then subsequently joined to other shells to form a larger compression element. It is also understood that because each shell can be integrally formed, the distinction between the first annular portion, the second annular portion, and the central portion can be merely conceptual.

[0021] Adjacent housings can be connected via their respective first annular portions or their respective second annular portions. However, as will be discussed, when the compression element comprises three or more housings (as is the case in some embodiments), at least one housing's first and second annular portions can both engage with the corresponding first and second annular portions of the other housings. Adjacent housings can be joined in any suitable manner; for example, they can be glued or welded together.

[0022] The central portion of each shell may optionally include a (first) shoulder portion projecting from the central portion, for example, projecting from the inner surface of the shell toward the central axis, or projecting from the outer surface of the central portion away from the central axis. The shoulder portions of the central portions may be arranged such that when the two shells are joined at their respective first or second annular portions and compressed along the central axis by compressive stress applied to the compression element substantially along the central axis, the respective (first) shoulder portions of the two shells contact each other when the compression of the compression element reaches a specific proportion of its uncompressed length, i.e., particularly the shoulder portions of the central portions. The uncompressed length is the length of the compression element in its fully uncompressed state when no compressive stress is applied to it (i.e., corresponding to the zero strain point in the stress-strain response curve of the compression element).

[0023] Those skilled in the art will understand that, because the middle portion connects the first and second annular portions, and because the maximum size of the first annular portion is greater than the maximum size of the second annular portion (e.g., the radius of the first annular portion is greater than the radius of the second annular portion), the middle portion forms an angle relative to the central axis, on average and at least at some point along its length, between the first and second annular portions. This causes the middle portion to divide the compressive stress applied along the central axis direction into stress components parallel to and perpendicular to the central axis.

[0024] The parallel component of the stress will cause deformation of the central portion based on its mechanical properties. The perpendicular component of the stress will be resisted by the circumferential stress in the first and second annular portions, for example, because any deformation in this direction will increase the diameter of the first annular portion and decrease the diameter of the second annular portion.

[0025] The angle between the central axis and the direction between the first and second annular portions (e.g., along the average path of the middle portion) can be considered a "load path" along which compressive stress acts through the contact points between adjacent shell members (because of these contact points, they are joined together at the respective first or second annular portions). The angle of this load path determines how much of the compressive stress acts perpendicular to the central axis on the annular portions and how much acts parallel to the central axis through the middle portion.

[0026] As the angle of the load path changes (due to the compression of the compression element and thus the shell), the vertical component of the stress will change, resulting in a change in the compression behavior. When the compression element is compressed, the angle changes gradually under the action of compressive stress, but when the compression element is compressed to a certain proportion of its uncompressed length, the angle will change abruptly due to the contact between the middle portions (optionally, the shoulder portions) of adjacent shells.

[0027] A compressive element having multiple shells is arranged such that when compressive stress is applied to it along the central axis, the resulting stiffness response (the slope of the stress-strain response curve) depends on the compression of the compressive element. Specifically, this response depends on a specific proportion of the uncompressed length to which the compressive element is compressed such that the middle portion of one shell contacts the middle portion of an adjacent shell. It can be seen that the contact of the corresponding middle portions (e.g., shoulder portions) alters the angle of the load path, and thus changes the stiffness response of the compressive element, for example, by providing resistance to further compression.

[0028] Therefore, it can be seen that, according to the present invention, by forming a shell having a first annular portion, a second annular portion, and a central portion (and optionally a shoulder portion) connecting them, a compression element is produced, wherein a specific compression can be selected, under which the stiffness behavior of the compression element changes. This helps the compression element to provide a high stiffness response at low thrust (compressive stress) values, for example, because the angle between the load path and the central axis is relatively small, causing the compression element to deform only a small fraction of its maximum deformation.

[0029] When the compression element is preferably formed as part of a mooring component that extends under tensile stress due to the compression of the compression element, this causes the mooring component (and therefore, for example, the mooring cable or system in which it is located) to extend by only a small amount. It is desirable that at higher thrust levels, the compression element can provide a larger amount of deformation, enabling it to provide continuous extension of the mooring cable (e.g., including the compression element).

[0030] The arrangement of the annular and central sections, for example, due to the increased angle between the load path and the central axis, also helps to provide lower stiffness at higher thrust.

[0031] For example, the behavior of the compression element of the present invention (and thus the mooring component using it) contrasts with the mooring system disclosed in WO 2012 / 127015 and other conventional mooring systems, in which the mooring component allows the mooring cable to stretch almost to its maximum length under any high background thrust experienced by the mooring cable. At such high elongation, the mooring cable is very stiff, and thus a small increase in elongation, for example, due to wave motion, now results in a large increase in tension.

[0032] Therefore, conventional mooring cables provide a less than ideal stress-strain response under conditions of high background thrust and rough seas (e.g., floating wind power platforms, floating tidal turbine platforms, environments with strong ocean currents). Because the compression of the compression element can be chosen to match the background thrust by softening the stiffness and then bringing the middle portions of adjacent shells into contact, the compression element of the present invention for mooring components suitable for offshore floating structures provides a more desirable stress-strain response. This helps allow motion above a certain point to experience lower stiffness behavior that occurs above that compression.

[0033] Compression elements can be arranged (e.g., as a result of the middle / shoulder portions contacting each other) to provide any suitable and desired stress-strain response to the compressive stress applied thereto. In one embodiment, the compression elements are arranged such that a compressive stress applied to the compression element, reaching at most a first stress value of the compressive stress, compresses the compression element by a first proportion of its uncompressed length during a first compression phase. This first proportion of the uncompressed length of the compression element is preferably smaller than a specific proportion of the uncompressed length of the compression element, wherein, in this specific proportion, the middle portions of adjacent housings are arranged to contact each other.

[0034] In this first compression stage, when a compressive stress of up to a first stress value is applied to the compression element, the compression element is subjected to (e.g., elastic) compression. Exposed to this first stress value, the compression element is compressed by a first proportion of its uncompressed length (i.e., the length of the compression element decreases by a first proportion of its uncompressed length). Preferably, the compression element exhibits an average stiffness having a first stiffness value during the first compression stage.

[0035] The first proportion of the uncompressed length can be any suitable and desired value that causes the compression element to be compressed during the first compression stage. In one embodiment, the first proportion is between 10% and 20% of the uncompressed length, for example, about 15%. Thus, when the compression element is subjected to compressive stress equal to the first stress value, preferably, the compression element is compressed to between 80% and 90% of its uncompressed length, for example, about 85% of the resultant length.

[0036] Optionally, the compression of the compression element is approximately (e.g., directly) proportional to the compressive stress experienced by the compression element up to a first value of compressive stress; that is, preferably, the stress-strain curve of the compression element is approximately linear during the first compression stage. Preferably, the slope of the stress-strain curve of the compression element is positive for all values ​​of the compressive stress up to the first stress value.

[0037] The first value of the compressive stress can be selected in any suitable and desirable manner, for example, according to the intended use of the compression element. Preferably, the compression element is arranged (e.g., manufactured) such that the first value of the compressive stress is slightly lower than the compressive stress that the compression element is expected to experience under benign conditions (i.e., low operating wind thrust, with low waves and currents). Therefore, taking into account the dynamic load around the average thrust under benign conditions, the first value of the tensile stress is the lowest load under which the mooring system using the compression element is expected to operate. The first stress value can be a considerable proportion of the average thrust, for example, at least 70%, optionally at least 80%, and further optionally at least 90%.

[0038] The initial value of the compressive stress can be determined, for example, based on the specific conditions (e.g., location) that the compressive element is expected to experience when installed in a mooring system for a floating structure (and, for example, the compressive element is manufactured and assembled accordingly). For instance, for a floating offshore wind turbine, the background thrust can be determined based on the turbine size, operating wind conditions, the number and arrangement of mooring cables, platform behavior, and benign environmental conditions. Therefore, different compressive elements for different applications (e.g., floating structures and / or environments) can be designed differently to provide different values ​​for the initial value of the compressive stress.

[0039] The compression element can be constructed in any suitable and desired manner to provide any suitable and desired response during the first compression stage. Preferably, the compression element is arranged such that the applied compressive stress acts substantially on the compression element to compress the length of the middle portion of the compression element.

[0040] Therefore, preferably, the compression element is arranged such that the annular portion of the compression element has a circumferential stress that substantially resists compressive stress in the first annular portion as a tensile force (e.g., a component of the compressive stress attempting to stretch the diameter) and in the second annular portion as a compressive force (attempting to shrink the diameter). It should be understood that the relatively high stiffness behavior in the first compression stage results in a relatively large change in the compressive stress that needs to be applied to produce a relatively small change in the length of the compression element.

[0041] Therefore, the stiffness behavior of the compressive element can depend on the compressive response of the central portion in the direction parallel to the central axis. During the first compression stage, the central portion can have relatively high stiffness, such that for a given compressive stress, the deformation of the central portion in the direction parallel to the central axis is relatively small; for example, the buckling force on the central portion is essentially resisted by its strength, resulting in relatively small changes in its shape. Since the first and second annular portions resist deformation (e.g., expansion or contraction), the central portion also resists bending (e.g., angular changes between the first and second annular portions), and therefore the angular change of the central portion (and the load path) relative to the central axis is relatively small.

[0042] The stiffness behavior of the compression element can depend on the response of the annular portion, for example, on the circumferential stress of the first and second annular portions. The annular portions can be arranged in any suitable and desirable manner to provide this response. Preferably, the annular portion defines (and thus includes) a portion of the compression element (e.g., a housing) where the inner and / or outer surfaces of the compression element (e.g., the housing) are substantially parallel to the central axis of the compression element. Preferably, the annular portion defines the end of the housing (e.g., each housing) of the compression element (in the direction along the central axis).

[0043] In one embodiment, the thickness of the first and / or second annular portions (e.g., in the radial direction, perpendicular to the central axis) is greater than the minimum thickness of the middle portion (e.g., in the direction outward from the central axis, along which the distance between the inner and outer surfaces of the middle portion is minimum) (e.g., the thickness of the middle portions adjacent to the first and / or second annular portions, respectively).

[0044] The first and second annular portions can have any suitable and desired height (in the direction parallel to the central axis). The first and / or second annular portions can have almost zero height; for example, there can be essentially no distance along the central axis between the middle portions of adjacent housing members. Preferably, the length of the middle portion (between the first and second annular portions, for example, in the direction along the load path, for example, when the compression element is not compressed) is greater than the height (and, for example, the thickness) of the first and / or second annular portions. Preferably, the thickness of the first and / or second annular portions is greater than the height of the first and / or second annular portions, respectively.

[0045] Preferably, the dimensional difference between the first and second annular portions is large enough to allow the compression element to be compressed to a combined length less than half its uncompressed length. Preferably, the maximum dimension (e.g., diameter) of the first annular portion is greater than 40% (e.g., greater than 50%) of the maximum dimension (e.g., diameter) of the second annular portion. This helps to provide suitable space for the middle portion of the compression element to bend and compress between the respective first and second annular portions, thereby allowing the compression element to be compressed to a combined length less than half its uncompressed length.

[0046] In one embodiment, the compression element is arranged such that: a compressive stress, higher than a first stress value and at most reaching a second stress value, is applied to the compression element; during a second compression phase, the compression element is further compressed by a first proportion of its uncompressed length and at most a second proportion of its uncompressed length. The second proportion of the uncompressed length of the compression element may optionally be greater than a specific proportion of its uncompressed length, at which the middle portions or (first) shoulder portions of adjacent shells are arranged to contact each other; that is, the compression element may be arranged such that the middle portions or shoulder portions of adjacent shells contact each other during the second compression phase of the compression element. During the second compression phase, the compression element exhibits an average stiffness having a second stiffness value, wherein the first stiffness value (in the first compression phase) is preferably greater than the second stiffness value. In some embodiments, additionally or alternatively, adjacent shells may be arranged to contact each other during the second phase, for example, at a contact point other than the (first) shoulder.

[0047] In the second compression stage (i.e., the response of the second segment of its stress-strain curve, under compressive stress higher than the first value of compressive stress), the compression element is compressed when a compressive stress higher than the first stress value but reaching at most the second stress value is applied to the compression element. Exposed to this second stress value, the compression element is compressed by a second proportion of its uncompressed length (i.e., the length of the compression element decreases by a second proportion of its uncompressed length).

[0048] The second proportion of the uncompressed length can be any suitable and desired value (including the first proportion) at which the compression element is compressed during the second compression phase, at which point the compression element exhibits an average stiffness with a second stiffness value. In one embodiment, the second proportion is between 40% and 50% of the uncompressed length, for example, approximately 45%.

[0049] Therefore, when the compression element is subjected to a compressive stress equal to the second stress value, preferably, the compression element is compressed to a combined length between 40% and 60% of its uncompressed length, for example, approximately 50%. Furthermore, for the compressive stress experienced in the second compression stage (i.e., the compressive stress between the first and second stress values), preferably, the compression element is compressed from 80% to 90% (e.g., approximately 85%) of its uncompressed length at the first stress value to 40% to 60% (e.g., approximately 50%) of its uncompressed length at the second stress value. Thus, during the second compression stage, the compression element can be compressed over a compression distance at least twice, and optionally at least three times, the distance of compression that occurred in the first (or pre-stretch) stage. The second proportion of the uncompressed length can be between approximately 20% and 50% of the uncompressed length. The distance the compression element is compressed over during the second stage (i.e., the distance between the first and second proportions) is greater than the distance of the first proportion, and additionally or alternatively, may be greater than the total compression distance in the third (retention) stage. Therefore, most of the length change of the compression element during compression occurs during the second (operating) stage. It should be understood that, preferably, the compression amount in the second stage is greater than the compression amount in the first stage.

[0050] Preferably, the compression of the compression element is approximately (e.g., indirectly) proportional to the compressive stress experienced by the compression element between the first and second compressive stress values; that is, preferably, the stress-strain curve of the compression element is approximately linear in the second compression stage (but its slope is less than that of the stress-strain curve in the first compression stage). Preferably, the slope of the stress-strain curve of the compression element is positive for all stress values ​​between the first and second compressive stress values.

[0051] Therefore, preferably, the slope of the stress-strain curve of the compression element is positive for all stress values ​​where the compressive stress reaches at most a second value. This helps prevent the compression element from being trapped under a particular compression (e.g., if a negative slope would exist in the stress-strain curve, or this could happen due to small variations in manufacturing).

[0052] The second value of the compressive stress can be selected, for example, in any suitable and desirable manner depending on the intended use of the compression element and mooring components. Preferably, the compression element is arranged (e.g., manufactured) such that the second value of the compressive stress is approximately equal to the compressive stress that the compression element is expected to experience under the maximum limiting state (the highest coefficient-free load that the component is expected to experience). This limiting state may occur under peak conditions during turbine operation (i.e., the maximum thrust under turbine operating environmental conditions), surviving sea states (i.e., maximum wave and wind loads, but without thrust from the operating turbine), or unexpected limiting states (i.e., the highest load experienced in the event of an unexpected event such as mooring cable breakage).

[0053] The second value of the compressive stress can be determined, for example, based on the specific conditions (e.g., location) that the mooring component is expected to experience when installed in a mooring system for a floating structure (and, for example, the compression element is manufactured and assembled accordingly). For instance, for a floating offshore wind turbine, the peak thrust can be determined based on the peak thrust expected during a 50-year return period storm under wind and / or wave conditions. Therefore, different compression elements for different applications (e.g., floating structures and / or environments) can be designed differently to provide different values ​​for the second value of the compressive stress.

[0054] As described above, in some embodiments, the middle portions or (first) shoulder portions of adjacent housings of the compression element are arranged to contact each other during the second compression phase. For example, a specific ratio of the uncompressed length when the middle portions / shoulder portions are arranged to contact each other is between a first ratio and a second ratio of the uncompressed length of the compression element. However, this specific ratio can take any suitable and desired value.

[0055] This specific ratio can be chosen to achieve the desired stress-strain response, as it is the proportion of the uncompressed length when the angle of the load path undergoes a step change. The specific ratio can also be the proportion of the uncompressed length when the compressible element begins to deform significantly under compression. As explained above, the contact between the middle portions of adjacent shell parts (e.g., shoulder portions) and the change in the angle of the load path help prevent the slope of the stress-strain curve from becoming negative.

[0056] It should be understood that before and after that specific proportion of the uncompressed length when the middle portions are in contact with each other, the stiffness response of the compression element, and indeed the value of that specific proportion itself, can be determined by a number of characteristics and parameters of the compression element, in addition to the optional shoulder portion as described above. For example, the compression element can be arranged such that during the second compression phase, the compression (and therefore the stiffness behavior) of the compression element is dominated by the deformation of the middle portion of the compression element.

[0057] The behavior of the compression element in the second compression stage can be controlled by arranging the compression element such that one or more (e.g., all) of the following occur: an increase in the maximum size (e.g., diameter) of the first annular portion, a decrease in the maximum size (e.g., diameter) of the second annular portion, and deformation (e.g., bending) of the central portion. Since these portions of the compression element are three-dimensional, complex shaping can also be used to achieve the desired result. For example, the second annular portion can be arranged to bend inward with increasing compressive stress to compress the compression element beyond a certain proportion. This helps to reduce the diameter of the second annular portion and thus allows for further compression of the compression element with further increases in compressive stress.

[0058] In some embodiments, the central portion is configured to deform (e.g., bend, rather than simply flex) relative to the first and second annular portions when the compressive stress exceeds a threshold that causes the compressive element to be compressed beyond a certain proportion. This can be achieved by arranging the first and second annular portions to be more resistant to deformation (e.g., stronger) than the central portion, for example, such that their resistance to circumferential stress deformation is greater than any resistance to circumferential stress and / or buckling deformation in the central portion. This can be achieved in any suitable and desirable manner.

[0059] In some embodiments, additionally or alternatively, the first annular portion and / or the second annular portion are configured to deform when the compressive force exceeds a threshold causing the compression element to be compressed beyond a certain proportion. For example, the first annular portion and / or the second annular portion may have circumferential stress that overcomes the circumferential stress when the compression element is compressed beyond that certain proportion. It should be understood that such a change can cause at least a portion of the central portion to rotate, for example, to bend in a direction substantially perpendicular to the central axis.

[0060] Therefore, in such an embodiment, the circumferential stress of the annular portion is exceeded, and the annular portion can then deform under the applied compressive stress. This results in a change in the stress-strain behavior of the compression element, thereby allowing the compression element to undergo a greater amount of compression for a relatively small increase in the applied compressive stress.

[0061] In one implementation, this control over the stress-strain behavior of the compressive element can be achieved by using a softer or thinner material in the annular portion (as the diameter variation caused by circumferential stress is related to the applied stress and the thickness, diameter, and material strain of the annular portion) or by changing the annular portion (e.g., its thickness) in the radial direction.

[0062] In some embodiments, the central portion has a non-uniform thickness along its length, i.e., the thickness perpendicular to the central axis varies along the central axis. In some embodiments, the central portion has a non-uniform shape, such that the thickness of the central portion parallel to the central axis varies along the central axis; for example, the shape of the central portion is bent, causing the thickness to vary along the horizontal plane.

[0063] Regardless of how the compression behavior is achieved in the second stage, preferably, the compression elements are arranged to maintain smooth deformation or bending behavior (e.g., Euler buckling) throughout the compression process of the compression elements, such as in the first, second, and / or third compression stages. This can be achieved, for example, by reducing or even avoiding any limit point instabilities in the design, which are locations where the shell structure undergoes large deformations and becomes stable in different shapes.

[0064] This instability can lead to negative stiffness at some point along the stress-strain response curve of the compressive element, causing the applied compressive stress to snap between different shell sections, resulting in some shell sections collapsing while others relax back to their original length. Because the load constantly shifts up and down, this behavior induces high fatigue in both the compressive element and the mooring system that includes it.

[0065] The stress-strain response of the compression element is preferably (substantially) non-plastic, i.e., the component is designed to be repeatedly compressed, for example, no more than a second stiffness value (i.e., during the first and second stages), where performance loss is minimal, such that when the applied tensile stress is subsequently removed, the mooring component substantially returns to its original shape.

[0066] In one embodiment, the compression element is arranged such that a second stress value, higher than the compressive stress, subjected to the compression element in a third compression stage further compresses the compression element by a second proportion greater than the uncompressed length of the compression element. During the third compression stage, the compression element exhibits an average stiffness with a third stiffness value; wherein the third stiffness value is preferably greater than the second stiffness value (in the second compression stage) and additionally or alternatively greater than the first stiffness value (in the first compression stage). Optionally, the third stiffness value is at least 50% greater than the second stiffness value. This higher stiffness helps the compression element provide a sharp increase in tension when the compression distance of the compression element is compressed beyond the second proportion.

[0067] Therefore, in this embodiment, the response of the compression element changes again to have a more rigid response than in the second stage, and optionally even more rigid than in the first stage, such that the at least one compression element undergoes very little compression in the third stage. Therefore, any further compression requires a much larger increase in the compressive stress on the compression element.

[0068] Therefore, in some embodiments, a compression element is provided such that, as the compression of the compression element increases, the stiffness changes from an initial high stiffness (first stage) to a lower stiffness (second stage) due to the deformation of the shell, and then changes back to high stiffness (third stage).

[0069] During the third compression phase, this increased stiffness response under high compression helps provide important safety features for the compression element (and mooring components that may form part of it). It helps the compression element withstand very high compressions—such as the maximum limit state (ULS) of the mooring system—while reducing the risk of damage. This situation may occur, for example, in a floating marine structure moored with multiple mooring cables, including mooring components with the compression element of this invention, and one or more of the additional mooring cables break.

[0070] In the third compression stage (i.e., the response of the third segment of its stress-strain curve under compressive stress higher than the second value of compressive stress), the compression element is compressed when a compressive stress higher than the second stress value is applied to the compression element. Exposed to this compressive stress greater than the second stress value, the compression element is compressed by a second proportion of its uncompressed length (i.e., the length of the compression element decreases by a second proportion of its uncompressed length).

[0071] As described above, preferably, the second proportion of the uncompressed length is between 40% and 50% of the uncompressed length, for example, about 45%. Therefore, the compression element is compressed by more than 40% or 50% of the uncompressed length, for example, more than about 45%, during the third compression stage (when the compression element exhibits an average stiffness with a third stiffness value).

[0072] Therefore, when the compression element is subjected to compressive stress greater than the second stress value, preferably, the compression element is compressed to at least 50% or 60% of its uncompressed length, for example at least about 55% of its combined length.

[0073] Preferably, the compression of the compression element is approximately (e.g., indirectly) proportional to the compressive stress experienced by the compression element at a second stress value higher than the compressive stress; that is, preferably, the stress-strain curve of the compression element is approximately linear in the third compression stage (but with a slope greater than that of the stress-strain curves in the first and second compression stages). Preferably, the slope of the stress-strain curve of the compression element is positive for all stress values ​​above the second stress value.

[0074] Therefore, preferably, the slope of the stress-strain curve of the compression element is positive for at most and for all stress values ​​greater than the second value. This helps prevent the compression element from being trapped under a particular compression condition (e.g., if a negative slope would exist in the stress-strain curve, or this could happen due to small variations in manufacturing).

[0075] During the third compression phase, the higher stiffness of the compression element can be selected in any suitable and desirable manner, for example, depending on the intended use of the mooring components. Preferably, the compression element is arranged (e.g., manufactured) such that during the third compression phase, the stiffness of the compression element substantially resists further compression of the compression element. This helps to provide important safety features for the compression element and the associated mooring components. For example, it helps the compression element withstand very high compression. Preferably, the tension in the compression element approaching the end of the third compression phase is approximately 1.5-2 times the maximum limit state (ULS) of the mooring system.

[0076] In one embodiment, during the third compression stage (further compression than in the first and second stages), the additional compression of the compression element is less than 10% of its uncompressed length, for example, less than 5%. Generally (i.e., cumulatively over all compression stages), preferably, the compression element is arranged to be compressed to more than 40% of its uncompressed length, for example, more than 45% of its uncompressed length, for example, more than 50% of its uncompressed length.

[0077] In some embodiments, the third compression stage of the compression element occurs due to contact between adjacent housings (e.g., the middle portion), such as at the shoulder portion as described above, or due to contact between positions different from the (first) shoulder portions of the adjacent housings. Therefore, in some embodiments, the middle portions, (first) shoulder portions (or other portions) of the adjacent housings of the compression element are arranged to contact each other in the third compression stage, for example, such that a specific proportion of the uncompressed length of the middle portions or shoulder portions arranged to contact each other is higher than a second proportion of the uncompressed length of the compression element. Therefore, in some embodiments, the second proportion of the uncompressed length of the compression element is less than or approximately equal to the specific proportion of the uncompressed length of the compression element that arranges the middle portions or shoulder portions of the adjacent housings to contact each other.

[0078] This helps to increase the stiffness of the compression element through two mechanisms during the third compression stage.

[0079] First, these contact points directly transmit the load, thereby reducing further buckling in the central section. Second, by means of the contact between adjacent shell members, the load path through the compression element is altered by reducing the angle (relative to the central axis) at which further compressive stress is applied to the compression element and by increasing the area of ​​material sharing the load.

[0080] Therefore, adjacent housings of the compression element can be arranged to contact each other in any suitable and desired manner during the third compression stage (e.g., at the beginning of that stage).

[0081] The first and / or second shoulder portions can be arranged on the central portion in any suitable and desired manner. In one embodiment, the first shoulder portion protrudes toward the first annular portion (in one direction). Preferably, the thickness of the first shoulder portion (e.g., through the housing) is greater than the thickness of the central portion adjacent to the first shoulder portion (e.g., on either side thereof).

[0082] In some embodiments, the first shoulder portion is shaped such that when the compressive stress applied to the compression element causes the compression element to be compressed by a specific proportion of its uncompressed length, the first shoulder portion (in this compression configuration) protrudes further toward the adjacent shell than any other portion of the middle portion (i.e., except for the (e.g., the first) annular portion that engages the adjacent shell). This facilitates the first shoulder portion contacting the adjacent shell before the middle portion contacts it.

[0083] To achieve this effect, during the compression phase where contact occurs between the first shoulder portions, the first shoulder portions only need to protrude further than the rest of the middle portions (e.g., along the direction of the central axis). Since the angle of the middle portions (relative to the central axis) changes during compression, the first shoulder portions only need to extend further along that direction during the compression phase where contact occurs, and not necessarily when the compression element is not under stress.

[0084] Each housing (and therefore the compression element) can be made of any suitable and desired material. Any chosen material should possess appropriate fatigue properties to allow for frequent changes in shape to be applied via wave motion. Preferably, the compression element comprises a (thermal) polymer, such as an elastomer. The spring can be formed from one or more separate polymer materials with different mechanical properties, each applied to different portions of the polymer spring such that the different portions of the spring respond differently to the same applied stress. In one embodiment, the first and / or second annular portions comprise a material that is more rigid than the material of the central portion (e.g., an elastomer). For example, the first and / or second annular portions can be made of a higher-grade or more rigid polymer (e.g., an elastomer) material.

[0085] In some embodiments, the central portion extends continuously in an azimuthal direction about the central axis. Preferably, the central portion includes a cross-sectional profile (in a plane containing the central axis) that rotates about the central axis (e.g., rotates through 360 degrees). This allows the central portion to be formed as a single (monolithic) part, for example, using a single mold, or in a single stage.

[0086] In some embodiments, the central portion is formed separately from the first and second annular portions. The central portion can then be joined together with the first and second annular portions to form a shell. For example, this allows the central portion and the first and second annular portions to be formed from different materials. However, preferably, the central portion is integrally formed with the first and second annular portions. Again, this facilitates allowing the entire shell to be formed as a single (monolithic) piece, for example, using a single mold, or in a single stage.

[0087] In some embodiments, the central portion comprises multiple discrete parts, each connected between a first annular portion and a second annular portion to form a shell. Preferably, each discrete part comprises a cross-sectional profile (in a plane containing the central axis) rotated less than 180 degrees about a central axis. This allows the central portion of the shell to be formed with less material, for example, less material than would be required to form a central portion of the same size (e.g., overall maximum size) when the central portion has a cross-sectional profile rotated 360 degrees. These smaller central portions can also be manufactured more easily, for example, by using smaller molds. Therefore, smaller central portions can be manufactured cheaper, easier, and faster than a continuous central portion.

[0088] Furthermore, the applicant has unexpectedly come to realize that, in at least the preferred embodiments, a shell comprising multiple discrete central portions can provide a stress-strain response substantially equal to that of a shell having a central portion with 360 degrees, while using less material. Preferably, each discrete central portion includes a cross-sectional profile (i.e., a shaped profile) with an azimuth angle of less than 90 degrees, for example less than 45 degrees, or for example less than 20 degrees, rotated about a central axis.

[0089] Preferably, these discrete central portions all have the same azimuth range, that is, their cross-sectional profiles are rotated by the same angle about the central axis. Preferably, the cross-sectional profiles of each discrete central portion are identical. Preferably, the plurality of discrete central portions are equally spaced from each other about the central axis (e.g., in azimuth).

[0090] Furthermore, or alternatively, in order to reduce the required material by constructing the shell from multiple parts, the applicant further recognizes that material can be removed from certain portions of the shell profile without substantially affecting the shell's stiffness response. In particular, the applicant has recognized that the shell's stiffness response can be determined substantially by the material present in the shell profile, but the thickness of this profile can vary when rotated about a central axis. Such a profile could result in very thin or no material at certain locations while still maintaining the desired overall stiffness profile.

[0091] The compression element described herein is suitable for integration into a mooring system. Therefore, according to a second aspect of the invention, a mooring system is provided comprising a mooring cable and a compression element according to a first aspect of the invention, wherein the compression element is arranged between a first segment and a second segment of the mooring cable such that the tensile stress applied to the mooring cable compressing the compression element results in an increase in the total length of the mooring system.

[0092] The invention also extends to mooring components for mooring cables or systems, wherein the mooring component includes a compression element according to a first aspect of the invention, wherein the compression element is arranged to be compressed in response to tensile stress experienced by the mooring component, wherein the compression element is arranged such that compression of the compression element causes elongation of the mooring component. The tensile stress experienced by the mooring component is converted into compressive stress, thereby subjecting the compression element to the compressive stress.

[0093] The mooring components of this invention can be components of any suitable and desired mooring cable or system, and are used for mooring any suitable and desired floating structure. A mooring system may include two or more connected mooring components, or connected at multiple points along the same length of mooring cable, for example, directly or indirectly connected to each other (i.e., in series), or may have one or more mooring cables, each including more than one mooring component (i.e., in parallel).

[0094] In one set of embodiments, the mooring component is submerged and directly or indirectly connected between the floating structure and the seabed. For example, the mooring component may be connected between the floating structure (such as a floating fish farm or a floating platform (e.g., for a floating offshore wind turbine)) and the seabed. A mooring system may include one or more mooring components, and combinations of different mooring components may be used. Typically, a mooring system includes multiple mooring cables, each of which may contain one or more mooring components according to one embodiment of the invention. The number of mooring cables and / or mooring components may be selected based on the extension required for the maximum sea state. The mooring system may be for deep-sea, tidal, or shallow-water environments. Multiple mooring components connected along the same mooring cable may be used to provide the desired extension of the mooring cable so that the mooring cable can accommodate the maximum wave height at a given mooring location. The number of components required to achieve the selected extension length will depend on the length selected for each component.

[0095] In another set of embodiments, the mooring component is connected between two (or more) floating structures. This connection can be direct or indirect. Thus, in some embodiments, the component is directly or indirectly connected between a first floating structure and a second floating structure, and optionally, the floating structures form part of an array. In such embodiments, the mooring component can respond to the motion of one floating structure by reacting to another floating structure that may have greater inertia.

[0096] In a set of preferred embodiments (e.g., when the mooring component is part of a mooring system), the mooring component is connected between the floating structure (e.g., a platform) and the seabed. In at least some embodiments, the mooring component is preferably connected between the floating structure and a mooring cable connected to the seabed. The mooring cable may include any combination of materials and mooring cable components, including high-modulus ropes (such as Dyneema®, steel wire rope), polymer ropes (e.g., polyester, nylon), chains, hooks, swivel joints, counterweights, or floats. The connection between the mooring component and the mooring cable can be direct or indirect (e.g., via an attachment joint, as described below).

[0097] In one embodiment, the mooring line comprises a catenary mooring chain. This mooring system can be used in shallow-water mooring systems, where mooring can be particularly challenging. It should be understood that embodiments of the invention are particularly well-suited when used with such a mooring line.

[0098] The compression element according to at least a preferred embodiment of the invention can be fitted into an existing mooring cable. This can be achieved by removing a section of mooring cable of approximately the same length as the compression element when subjected to compressive stress approximately equal to the background load (e.g., the uncompressed length plus 10%), attaching a first end of the compression element to a first segment of the mooring cable, and attaching a second end of the compression element to a second segment of the mooring cable.

[0099] Therefore, according to a third aspect of the invention, a method for modifying an existing mooring cable is provided, comprising removing a length of mooring cable, leaving a first segment and a second segment of mooring cable; and inserting a compression element according to the first aspect into the mooring cable by attaching a first end of a compression element to the first segment of mooring cable and a second end of a compression element to the second segment of mooring cable. All optional features disclosed herein with reference to the first and second aspects of the invention are equally applicable to this method.

[0100] For example, floating structures can include floating platforms for floating offshore wind turbines. A floating platform can be any suitable desired type of floating platform (e.g., for floating offshore wind turbines), such as a semi-submersible platform, a monopole platform, a barge platform, or a tension leg platform. The type of platform can determine the expected response of the mooring system and thus the mooring components. For example, different responses may be required depending on the water depth where the mooring components will be used, or depending on the type of platform (e.g., whether a mooring system is needed to provide stability).

[0101] The mooring component preferably includes attachment joints at one or both ends (e.g., each end) of the mooring component. The attachment joints are preferably designed and optimized for connecting the mooring component to other components in the mooring system, such as to mooring lines and anchors. They are preferably pad-eye or h-link type connectors to allow attachment to the rest of the mooring system using hooks or pins. In one set of embodiments, compression elements are connected between the attachment joints located at the ends of the compression elements. The attachment joints are preferably inelastic. The attachment joints are preferably arranged to transfer tensile stresses experienced by the mooring component (e.g., due to thrust on the mooring system) to the compression elements of the mooring component.

[0102] In one embodiment, the mooring component includes a first inner plate connected to a first annular portion or a second annular portion (i.e., at one end of the compression element) of one of the plurality of shells, a second inner plate connected to a first annular portion or a second annular portion (i.e., at the other end of the compression element) of another of the plurality of shells, a first outer plate adjacent to the first inner plate for connecting to a first portion of the mooring cable, a second outer plate adjacent to the second inner plate for connecting to a second portion of the mooring cable, a first connecting member connected to the first inner plate and the second outer plate (and, for example, extending through the second inner plate), and a second connecting member connected to the second inner plate and the first outer plate (and, for example, extending through the first inner plate).

[0103] This embodiment provides an example of how a compression element can be included in a mooring component, and for example, in a mooring cable or system, as described in a second aspect of the invention, wherein tension in the mooring cable compresses the compression element, resulting in an overall increase in the length of the mooring cable. In an alternative arrangement, the outer plate can be eliminated by attaching the attachment joint directly to the end of the connecting member extending through the inner plate.

[0104] The first and second connecting members can be provided in any suitable and desirable manner. In one embodiment, the first and second connecting members comprise a first connecting rod and a second connecting rod. Preferably, both the first and second connecting members comprise bars, such as hollow bars with a rectangular cross-section or bars with an I-beam shape. This helps to provide an arrangement that is lightweight yet still rigid and has a relatively low risk of torsion. Using an I-beam helps to provide bars that are easier to weld. Furthermore, with an I-beam, the quality of any necessary welds can be confirmed after welding. In a second embodiment, the first and second connecting members comprise first and second ropes and / or chains (e.g., rigid ropes such as steel wire or aramid). While such connecting members do not provide stiffness or torsional resistance, they do provide lighter, less costly mooring components that may be more suitable for some mooring systems.

[0105] When connecting members and connecting plates are installed in mooring components, cables, or systems, the weight of the connecting members and connecting plates connected to the compression element is a significant factor. This is because, preferably, the weight of the mooring component in the water (e.g., including the compression element, plate, and connecting members) is substantially equal to or at least as close as possible to the weight in the water of a conventional catenary mooring chain (or other mooring cable) to which the mooring component can be attached. Providing hollow bars (or I-beams) for the connecting members helps to achieve this.

[0106] In some implementations, the compression element may be heavier than the chain because it may be desirable to provide the same strength as the length of chain it replaces, even when the mooring component is extended and the compression element is compressed (e.g., up to 50% of the uncompressed length).

[0107] In one embodiment, the first and second connecting members are metallic, preferably steel. This material choice helps to provide a rigid and lightweight structure, as well as a sufficiently robust connecting member at low cost. Furthermore, in at least the preferred embodiment, the connecting member has a reduced risk of torsion, for example, due to the cross-sectional shape of the first and second connecting members.

[0108] In one embodiment, one or more (e.g., all) of the first inner plate, the second inner plate, the first outer plate, and the second outer plate include a flat ring. This helps to provide a plate that can be attached to multiple connecting members as needed and withstand the required forces while reducing the weight of these components.

[0109] In at least some implementations (e.g., when the mooring component is part of the mooring system), the mooring component is arranged close to the water surface. This helps reduce stress on the rest of the mooring system. It also helps ensure that wave or tidal movements only cause the mooring component (not the entire mooring system) to stretch.

[0110] Features of any aspect or implementation described herein may be applied to any other aspect or implementation described herein in any appropriate context. When referring to different implementations or groups of implementations, it should be understood that these implementations need not be entirely different, but may be partially identical. Attached Figure Description

[0111] Some preferred embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0112] Figure 1a A group of floating offshore wind turbines moored using mooring devices is shown;

[0113] Figure 1b It shows Figure 1a The stress-strain response of the mooring system shown;

[0114] Figure 2a A group of floating offshore wind turbines moored using mooring cables according to one embodiment of the invention is shown;

[0115] Figure 2b It shows Figure 2a The stress-strain response of the mooring system shown;

[0116] Figure 3 An example of the ideal stress-strain response of a mooring system is shown;

[0117] Figure 4 A cross-sectional view of an elastomeric compression element according to an embodiment of the present invention is shown;

[0118] Figure 5a It shows Figure 4 The appearance of the elastomer compression element shown;

[0119] Figure 5b It shows Figure 4 A cross-sectional perspective view of the elastomeric compression element shown;

[0120] Figure 5c It shows Figure 4 A cross-sectional view of the elastomer compression element shown;

[0121] Figure 5d It shows Figure 4 An exploded perspective view of the elastomer compression element shown.

[0122] Figure 6a It shows Figures 5a to 5d A perspective view of a single housing component of the elastomeric compression element shown;

[0123] Figure 6b It shows Figure 6a A sectional perspective view of a single shell component;

[0124] Figure 7 An exemplary cross-sectional profile of two adjacent shells of an elastomeric compression element is shown;

[0125] Figure 8 A series of examples are shown. Figure 7 The cross-sectional profiles of the paired shells shown are joined together to form a corrugated spring.

[0126] Figure 9 It shows Figure 8 The spring inside is compressed to approximately the beginning of the second compression phase;

[0127] Figure 10 It shows Figure 8 The spring inside is compressed to approximately the end of the second compression phase;

[0128] Figure 11 It shows Figure 8 The spring inside is compressed to a point within the third compression stage;

[0129] Figure 12 To show Figures 8-11 A graph showing the force response of a corrugated spring in a circuit.

[0130] Figure 13 Another exemplary cross-sectional profile of two adjacent shells of an elastomeric compression element is shown;

[0131] Figure 14 When adjacent shoulder parts have come into contact Figure 13 The cross-sectional profile of the shell component;

[0132] Figure 15a An example of an elastomeric compression element is shown, wherein the central portion includes multiple contour segments; and

[0133] Figure 15b It shows Figure 15a The condition of an elastic compression element under compressive force. Detailed Implementation

[0134] Floating marine structures (such as floating offshore wind turbines) typically require a mooring system that connects the structure to the seabed to maintain it in place. Implementations of mooring components for such a system will now be described.

[0135] Figure 1a A floating offshore wind turbine 1 is shown moored using a conventional chain mooring system 2. The floating offshore wind turbine 1 is shown in two different positions, representing its position before and after wind thrust is applied. The chain mooring system comprises a length of chain arranged such that one end is laid along the seabed and the other end is attached to the moored object. Horizontal arrow 3 indicates the force acting on the mooring system due to the turbine 1's movement caused by wind.

[0136] Force 3 propels turbine 1 downwind. The initial tension in the mooring cable is insufficient to resist this motion, so the platform moves. As it moves, more catenaries 2 rise from the seabed, increasing the tension in the mooring cable until an equilibrium position is reached, where the horizontal component of the tension 5 in the mooring cable balances the additional thrust caused by the wind, as shown by dashed line 4.

[0137] Figure 1b It shows the result of Figure 1a The stress-strain response curve 11 generated by the catenary mooring system 2. The x-axis 6 represents the distance x (in arbitrary units) by which the turbine has been displaced from its "neutral" position. This position is where the catenary mooring system 2 holds the turbine 1 when there is no thrust acting on the system due to wind, i.e., the position of the wind turbine 1 when the catenary chain is in position 2. The y-axis 8 represents the tension (in arbitrary units) present in the chain of the catenary mooring system. Additional wind thrust moves the platform to a new position 10, where the stiffness response of the mooring system (the additional tension required to move the platform) is much higher than in the original "neutral" position.

[0138] As can be seen from the graph, at large displacements from the "neutral" position, a small amount of wave-induced motion 7 results in very large changes in the tension experienced by the mooring system 9. This increases the dimensions required for the mooring components to not break under maximum tension. At these large displacements, such as at point 10, the system is considered to have high stiffness. This is because, under rough sea conditions, waves can cause large changes in the displacement X of turbine 1, and such stress-strain response is undesirable. This leads to huge tension peaks in the mooring system, which in turn can cause fatigue in the system and increase the likelihood of mooring cable failure.

[0139] Figure 2a A mooring system comprising a mooring component having a plurality of elastomeric compression elements is shown according to one embodiment of the invention. In this example, the elastomeric compression elements are connected along the same length of mooring cable, i.e., "in series". Turbine 1' is again acted upon by wind force 3', causing the platform to move downwind until the horizontal component of tension 5' matches the thrust of the wind. Figure 2b This is a stress-strain response curve of the mooring component. This curve shows the response curve compared to that of a conventional catenary mooring system (e.g., [missing information]). Figure 1a Compared to (as shown), the one including the mooring component Figure 2a The mooring system shown in Figure 20 provides a response curve.

[0140] Certain features of the compression element are designed to provide the stress-strain response described herein, and the thrust at the start of each stage of the stress-strain response is selected by adjusting these features to suit a particular mooring environment.

[0141] In this configuration, the compression elements are designed such that the thrust load compresses each compression element into the second compression stage, wherein the thrust load moves the turbine to... Figure 2a The position shown on the right is where the thrust load is balanced by the horizontal component of the tension in mooring cable 5'. Figure 2b As shown in the graph, at position 10', which is within the compression stage 2 (the working range of the component), the stress-strain response curve flattens out, so that changes in platform displacement 7' caused by waves, for example, only result in small changes in tension 9'.

[0142] like Figure 3 shown, than Figure 1b The example shown is a stress-strain response that is more desirable than the conventional response (also as...) Figure 2b As shown, it can be roughly divided into three independent stages. Figure 3The x-axis 36 in the figure represents stress in arbitrary units, while the y-axis 38 also represents strain in arbitrary units. This stress-strain response can be scaled to specific values ​​depending on the system intended to be included.

[0143] In the first stage 30 (at most reaching the first stress value 35), it has Figure 2b and Figure 3 The responding mooring system exhibits high stiffness. This high stiffness causes a slight extension of the mooring system to produce a significant increase in thrust. In some examples, the mooring system will not operate within this range during use because the preload and thrust loads acting on the mooring system during use will pre-compress the compression elements, causing the system to operate in the second compression phase 32. If, for some reason, the thrust load is absent and the preload is not high enough to keep the experienced tension within this second phase, the high stiffness of the components in the first phase causes the entire mooring system to behave like a conventional mooring system within this range.

[0144] In the second stage 32, above the first stress value 35 and at most the second stress value 37, the mooring system exhibits a gently sloping response curve, thus possessing lower stiffness than in the first stage 30. This is the operating range of the component, and the first value is selected based on turbine thrust and pretension, as described above, while the second value 37 is selected based on the maximum limiting state. In this second stage 32, changes in the platform location away from the anchor (e.g., due to waves) will result in a small but noticeable increase in the tension of the mooring cable, and vice versa. If the response in the second stage 32 of the stress-strain response curve is too flat, a small increase in the wind thrust applied to the platform will result in a large increase in the elongation of the mooring cable, leaving very little elongation available to cope with wave motion.

[0145] In the third stage 34 of the stress-strain response curve, above the second stress value 37, the mooring cable elongates considerably. In this third stage 34, the mooring cable again exhibits high stiffness, causing a small elongation of the mooring system to result in a significant increase in thrust. This design ensures the platform is held within the target sway (distance from the "neutral" position) and that components can withstand unexpected loads.

[0146] The applicant has designed a polymer mooring component according to at least a preferred embodiment of the invention, which has specific design features intended to implement various stages 30, 32, and 34 of the stress-strain curve. These different features will be described in more detail below.

[0147] According to at least a preferred embodiment of the invention, the stress-strain profile achieved by polymer mooring components provides numerous benefits to the mooring system. It reduces the risk of failure during impact loading, thus lowering maintenance and insurance costs; it allows the use of smaller components to provide the same performance as much larger mooring chains, thereby reducing component and deployment costs; and it also reduces operating costs due to the need for less infrastructure maintenance.

[0148] Figure 4 A cross-sectional view of an elastomeric compression element 40 according to an embodiment of the present invention is shown. Figure 5a It shows Figure 4 The appearance of the elastomer compression element 40 shown. Figure 5b It shows Figure 4 The diagram shows a cross-sectional perspective view of the elastomeric compression element 40. This cross-sectional view shows a portion of the outer surface cut away to reveal the internal structure. Figure 5c It shows Figure 4 The diagram shows a cross-sectional view of the elastomer compression element 40. This cross-sectional view shows the front half of the element cut off. Figure 5d It shows Figure 4 The exploded perspective view of the elastomeric compression element shown shows that the polymer spring is assembled from eight identical individual polymer shells.

[0149] Figure 4 , Figure 5a , Figure 5b , Figure 5c and Figure 5d The elastomeric compression element 40 in the illustrated embodiment includes four corrugated or convolute elements arranged end-to-end along a single axis, comprising a total of eight shells. Four steel rods are arranged through the middle of the corrugated elements, parallel to the central axis along which the corrugated elements are arranged. Figure 4 From this angle, since one steel rod is in front of another, only three steel rods 44a, 44b, and 44c are visible. Two of these steel rods, 44a and 44b, are each attached to a first outer plate 46a at their first end and to a second inner plate 48b at their second end. The second inner plate 48b is attached to the end of the corrugated section. The other two steel rods 44c are similarly attached between the second outer plate 46b and the first inner plate 48a. Each of the steel rods 44a, 44b, and 44c comprises an I-beam.

[0150] The elastomeric compression element 40 can be incorporated into the mooring cable by attaching the outer sides of the respective outer plates 46a, 46b to segments of the mooring cable. The ends of these segments of the mooring cable can then contact the seabed, for example, via an anchor, while the end of another segment of the mooring cable can be connected to a floating body to be moored, such as a floating offshore wind turbine.

[0151] Due to the arrangement of the inner and outer plates 46a, 46b, 48a, 48b, when the tension in the cable increases, each of the first outer plate 46a and the second outer plate 46b is subjected to tensile forces along the axis of the corrugated member and away from the corrugated member. These tensile forces are indicated by arrows 41 and 41'. Due to these tensile forces, the inner end plates 48a and 48b each exert inward compressive forces on the corrugated member, as indicated by force arrows 43 and 43'.

[0152] Each corrugated element comprises two halves, also referred to as “shells” 42a, 42a', 42b, 42b', 42c, 42c', 42d, and 42d'. Each of these shells is substantially identical. The shells can be joined together by a variety of feasible methods, including welding. Alternatively, the corrugated elastomeric compression element can be formed as a single piece. Figure 5d As shown Figure 4 An exploded perspective view of the elastomer compression element 40 is shown. The elastomer compression element 40 is... Figure 5d The image is displayed in a "magnified" format, making each shell appear separate and allowing the steel rod to be seen through the gaps between adjacent shells.

[0153] Figure 6a It shows Figures 5a to 5d The individual shell 42a of the elastomer compression element 40 shown is in the second compression stage (i.e., compressed to...). Figure 3 A three-dimensional diagram of stress values ​​above 35. Figure 6b It shows Figure 6a The cut perspective view of a single shell 42a is shown. Figure 6b The sectional perspective view shown illustrates the thickness profile of the shell material.

[0154] The applicant has recognized that various features of the shell profile contribute to, for example Figure 3 The three stages 30, 32, and 34 shown are as will be described below. The desired stress-strain response can be achieved by adjusting various parameters of the shell or compressive element; the examples given below are intended to be illustrative and not limiting.

[0155] Figure 7 The diagram shows the cross-sectional profiles of two adjacent shells 42b, 42b' of an elastomeric compression element according to an embodiment of the present invention in an uncompressed state. For clarity, dashed line 78 indicates the separation between the upper shell 42b and the lower shell 42b'. Figure 7 As shown. Because a series of such housings (i.e., compression elements) can be formed as a whole, this distinction may be merely conceptual.

[0156] Each housing member 42b, 42b' includes a first outer annular portion 74, 74' and a second inner annular portion 72, 72', wherein a middle portion 76, 76' extends between them. Housing members 42b, 42b' are constructed by means of... Figure 7 The shell profile shown is rotated 360 degrees around the central axis 70 to form the shape shown. Figure 7 It is formed by the bilaterally symmetrical outline shape shown.

[0157] One or both of the first outer annular portions 74, 74' and the second inner annular portions 72, 72' can be reinforced. For example, these annular portions 72, 72', 74, 74' can be thicker than the central portions 76, 76' of the shell, and / or they can be made of a polymer material of a higher grade or harder than the central portions 76 of the shell.

[0158] Figure 8 A series of such shell members 42b, 42b' are shown, which are joined together to form a corrugated element of the elastic element of the mooring component. Figure 8 In the middle, the corrugated element 80 (also called the corrugated part) is in an uncompressed state, that is, 0% compression when no load is applied to the corrugated element 80. The compression stage of the corrugated element 80 will be referred to below. Figure 9 , Figure 10 and Figure 11 as well as Figure 12 The response curve is used to describe it.

[0159] Figure 12 This is a graph showing the response of the bellows 80 to compressive forces. The x-axis shows the displacement in millimeters, while the y-axis shows the resistance generated by the bellows 80 in kilonewtons (kN). Figure 8 This indicates compression at point 90, which is 0% compression of the corrugated part at point 80.

[0160] Figure 9 The cross-sectional profiles of two adjacent shell members 42b and 42b' are shown, which are in a partially compressed state, i.e. Figure 12 Point 92 on the curve graph. The partial compression state of shell parts 42b and 42b' roughly corresponds to... Figure 3 The first stress value 35 shown marks the beginning of the second compression phase. In these exemplary corrugated elements 80, this occurs at approximately ( Figure 8 (As shown, the uncompressed length) under 10% compression. From Figure 8 and Figure 9 The comparison clearly shows that the shell parts 42b and 42b' of the corrugated part 80 during the first compression stage (i.e. from) Figure 8 The layout is compressed to Figure 9 The arrangement of the elements essentially retains its shape, therefore, during initial compression, including those with... Figure 7The compression element 80 of the shell members 42, 42' with the cross-sectional profile shown will deform very little. This can be achieved, for example, by selecting a suitable material stiffness.

[0161] When the shells 42b and 42b' are joined together to form the corrugated part of the elastomeric compression element of the mooring component, the relative distances of the annular portions 72, 72', 74, 74' (the joint of shells 42b and 42b') with respect to the central axis 70 define the load path 77. It is along this path 77 (for a given shell) that the compressive force 79 applied to the elastomeric compression element is transmitted. This is because... Figure 7 The load path 77 shown forms a relatively small angle with the central axis 70, thereby causing the compression element to... Figure 7 This occurs due to the relatively high stiffness of the structure shown. This stiffness response can... Figure 3 (and Figure 12 This can be seen from the steep slope of the stress-strain response curve shown in the figure.

[0162] As the compressive force acting on the compression element increases, the shells 42b and 42b' bend (around the first outer annular portions 74 and 74' and the second inner annular portions 72 and 72'). As the compression of the compression element increases, the angle of the load path 77 relative to the central axis 70 increases. This is achieved by adopting and passing through the change from the first stage 30 to the second stage 32 of the stress-strain response curve (e.g., Figure 3 As shown in the figure, the slope of the stress-strain response curve decreases as the stiffness of the compressive element decreases. This can also be seen in... Figure 12 This can be seen in the specific response curve plot. This relatively small slope of the stress-strain response curve persists in the second stage 32 until the second stress value 37 is reached, as shown below. Figure 10 As stated above. Figure 10 The cross-sectional profiles of two adjacent shell members 42b and 42b' under compression are shown, roughly corresponding to Figure 12 Point 94 in the middle. Therefore, Figure 10 The diagram shows the compression state of the bellows 80 approximately at the end of the second compression stage 32. From Figure 10 As can be seen, some adjacent shell parts 42b, 42b' have just begun to contact the adjacent outer sides of their respective middle portions 76, 76'. This results in a sharp increase in the stiffness of the corrugated part 80, and therefore in Figure 12 A significant increase in slope occurs after point 94 on the curve. Specifically, the contact between the outer surfaces of the middle portions 76 and 76' of adjacent shell members 42b and 42b' alters the load path 77 to reduce the angle between the load path 77 and the central axis 70. This produces... Figure 12 The curve shows an increase in stiffness.

[0163] Further compression exceeding this compression value further increases the contact between adjacent shell parts 42b, 42b', such as Figure 11 As shown. Figure 11 The corrugated part 80 is shown to be approximately in Figure 12 The compression at value 98 is shown on the graph. It can be seen that this contact provides a load path 77 approximately parallel to the central axis 70, resulting in high stiffness. This high stiffness under significant compression ensures that the bellows can withstand the thrust values ​​present under the maximum limit state (ULS) of the mooring system.

[0164] Additionally or alternatively, some or all of the characteristics of the response curves implemented herein can be achieved by including one or more shoulder portions on the shell. As described above, the shoulder portions are essentially a more prominent thickening of a portion of the shell extending in a direction away from the shell.

[0165] An example of this type of shell is as follows: Figure 13 As shown.

[0166] Figure 13 The cross-sectional profiles of two adjacent shells 142b, 142b' of an elastomeric compression element according to another embodiment of the present invention are shown. For aid of understanding, dashed line 178 shows the separation between the upper shell 142b and the lower shell 142b', as... Figure 13 As shown. Because a series of such housings (i.e., compression elements) can be formed as a whole, this distinction may be merely conceptual.

[0167] Each shell member 142b, 142b' includes a first outer annular portion 174, 174' and a second inner annular portion 172, 172', wherein a central portion 176, 176' extends between them. Shell members 142b, 142b' are formed by rotating the shell profile 360 ​​degrees about a central axis 170, as shown below. Figure 13 As shown, thus forming as Figure 13 The shape shown is a bilaterally symmetrical outline.

[0168] Each central portion 176, 176' includes a respective inner shoulder portion 102, 102', which protrudes from the inner surface of the central portions 176 and 176' toward the first outer annular portions 74 and 74'. The contact between adjacent shoulder portions 102, 102' can produce a third stage of the response curve in a manner similar to that described above. The contact between adjacent shoulders 102, 102' is as follows... Figure 14As shown. Alternatively, the shoulder portions 102, 102' can be arranged to contact at any desired point during the stress-strain response curve to help provide the desired response curve. A plurality of such shoulders can be provided on the inner and / or outer surfaces of the shell members 42b, 42b', and can be provided in both the annular portion and the central portion.

[0169] As described above, shells 42b, 42b', 142b, and 142b' are formed by rotating the shell outlines shown in the figure by 360 degrees around the central axes 70 and 170, thereby forming a solid of revolution.

[0170] Alternatively, the housing may include multiple profile segments, each profile segment being formed by rotation of a certain finite angle causing the illustrated profile to rotate only less than 180 degrees about axis 70. In this latter case, the multiple profile segments are then joined to a first outer annular portion 74, 74', 174, 174' and a second inner annular portion 72, 72', 172, 172'. Each annular portion 72, 72', 74, 74' extends (and is therefore continuous) 360 degrees. An example of such a configuration is as follows: Figure 15a and 15b As shown.

[0171] Figure 15a An example of an elastomeric compression element is shown, wherein the central portion comprises multiple profile segments that join at the top and bottom circumferences. The applicant has recognized that, in order to provide the desired nonlinear response curve, these portions must be at least partially rotated components of the described shell profile by at least a minimum angle; otherwise, the shell's response profile will resemble that of a beam, failing to exhibit the desired nonlinear response. Figure 15b It shows Figure 15a The deformation of an elastic compression element when subjected to compressive force.

[0172] Those skilled in the art will understand that the invention has been described by way of describing one or more specific embodiments, but the invention is not limited to these embodiments; many variations and modifications can be made within the scope of the appended claims.

Claims

1. A compression element for a mooring component, the compression element comprising a plurality of housings, wherein, Each of the plurality of housings includes a first annular portion, a second annular portion, and a central portion; The first annular portion and the second annular portion are each located in a plane substantially perpendicular to the central axis of the compression element, wherein the maximum dimension of the first annular portion in a direction substantially perpendicular to the central axis is greater than the maximum dimension of the second annular portion in a direction substantially perpendicular to the central axis, and wherein the middle portion connects the first annular portion and the second annular portion and extends between the first annular portion and the second annular portion. The plurality of shells are arranged along the central axis such that a first annular portion of one of the shells engages with a first annular portion of an adjacent shell, or a second annular portion of one of the shells engages with a second annular portion of an adjacent shell. The compression element is arranged such that it is compressed when compressive stress is applied to it substantially along the central axis; and The compression element is arranged such that when the compressive stress applied to the compression element causes the compression element to be compressed by a specific proportion of its uncompressed length, the middle portion of one of the plurality of housings contacts the middle portions of the adjacent housings.

2. The compression element according to claim 1, wherein, The compression element is arranged such that the annular portion of the compression element has circumferential stress, which substantially resists the tensile components of the compressive stress acting on the first annular portion and the compressive components acting on the second annular portion.

3. The compression element according to claim 1, wherein, The thickness of the first annular portion and / or the second annular portion is greater than the minimum thickness of the middle portion.

4. The compression element according to claim 1, wherein, The length of the middle portion is greater than the height of the first annular portion and / or the second annular portion.

5. The compression element according to claim 1, wherein, The thickness of the first annular portion and / or the second annular portion is correspondingly greater than the height of the first annular portion and / or the second annular portion.

6. The compression element according to claim 1, wherein, The maximum size of the first annular portion is more than 40% larger than the maximum size of the second annular portion.

7. The compression element according to claim 1, wherein, The first annular portion and / or the second annular portion are configured to deform when the compressive stress exceeds a threshold, wherein the threshold is a value that causes the compression element to be compressed beyond the specific proportion.

8. The compression element according to claim 1, wherein, The middle portion is configured to deform when the compressive stress exceeds a threshold, wherein the threshold is a value that causes the compression element to be compressed beyond a specific proportion.

9. The compression element according to claim 1, wherein, The central portion has an uneven thickness along its length.

10. The compression element according to claim 1, wherein, The central portion has a non-uniform shape, such that the thickness of the central portion parallel to the central axis varies along the central axis.

11. The compression element according to claim 1, wherein, The compression element is arranged such that: a compressive stress applied to the compression element, reaching at most a first stress value of the compressive stress, compresses the compression element to at most a first proportion of the uncompressed length of the compression element during a first compression phase. The compression element is arranged such that: a compression stress applied to the compression element, which is higher than a first stress value but reaches at most a second stress value of the compression stress, further compresses the compression element in the second compression stage by a first proportion of the uncompressed length of the compression element, and at most a second proportion of the uncompressed length of the compression element. Wherein, the second proportion of the uncompressed length of the compression element is less than or approximately equal to the specific proportion of the uncompressed length of the compression element, and in the case of the specific proportion of the uncompressed length of the compression element, the middle portions of adjacent housings are arranged to contact each other.

12. The compression element according to claim 11, wherein, When the stress value is not greater than the second stress value, the compression element exhibits a non-plastic response.

13. The compression element according to claim 1, wherein, Each of the plurality of shells includes a shoulder portion in its central portion that protrudes from the inner or outer surface of the central portion, wherein the shoulder portions of adjacent shells are arranged to contact each other under compression.

14. The compression element according to claim 13, wherein, The shoulder portion protrudes from the inner surface of the middle portion.

15. The compression element according to claim 13, wherein, The shoulder portion protrudes toward the first annular portion.

16. The compression element according to claim 13, wherein, The thickness of the shoulder portion is greater than the thickness of the middle portion adjacent to the shoulder portion.

17. The compression element according to claim 13, wherein, The shoulder portion is shaped such that when the compressive stress applied to the compression element causes the compression element to be compressed by a certain proportion of the uncompressed length of the compression element, the shoulder portion protrudes further toward the adjacent shell than any other portion of the middle portion.

18. The compression element according to claim 1, wherein, A first annular portion of one of the plurality of shells is welded or bonded to a first annular portion of an adjacent shell among the plurality of shells, and / or a second annular portion of one of the plurality of shells is welded or bonded to a second annular portion of an adjacent shell among the plurality of shells.

19. The compression element according to claim 1, wherein, The compression element is formed of at least two materials with different mechanical properties.

20. The compression element according to claim 1, wherein, The compression element is formed of at least one polymer material.

21. The compression element according to claim 1, wherein, The compression element is formed as a single piece.

22. The compression element according to claim 1, further comprising: A first inner plate connected to one end of the compression element, a second inner plate connected to the other end of the compression element, a first outer plate adjacent to the first inner plate for connecting to a first portion of the mooring cable, a second outer plate adjacent to the second inner plate for connecting to a second portion of the mooring cable, a first connecting member connected to the first inner plate and the second outer plate, and a second connecting member connected to the second inner plate and the first outer plate.

23. The compression element according to claim 22, wherein, The first connecting member includes a first connecting rod, rope, or chain, and the second connecting member includes a second connecting rod, rope, or chain.

24. A mooring system, comprising: Mooring cables, and The compression element as described in any one of claims 1-23, The compression element is arranged between the first segment and the second segment of the mooring cable, such that the tensile stress applied to the mooring cable that compresses the compression element results in an increase in the total length of the mooring system.

25. The mooring system according to claim 24, wherein, The compression element further includes: a first inner plate connected to one end of the compression element, a second inner plate connected to the other end of the compression element, a first outer plate adjacent to the first inner plate for connecting to a first portion of the mooring cable, a second outer plate adjacent to the second inner plate for connecting to a second portion of the mooring cable, a first connecting member connected to the first inner plate and the second outer plate, and a second connecting member connected to the second inner plate and the first outer plate, wherein the first cable segment of the mooring cable is connected to the first outer plate, and wherein the second cable segment of the mooring cable is connected to the second outer plate.

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