Tension leg platform assembly, mooring assembly and connector assembly

Abstract

A tension leg platform assembly is provided, comprising a buoyant body and a number of mooring assemblies attached thereto, which extend between the buoyant body and a fixed foundation on the seabed. Each mooring assembly comprises at least one elongate member having an upper end and an opposite lower end. At least one of said upper end and lower end by means of a connector assembly is connected to the buoyant body or the fixed foundation, respectively. Said connector assembly is provided with a first yoke which is connected to the buoyant body or fixed foundation for a rotation around a first axis which extends substantially horizontally at a first level, and a second yoke attached to the elongate member which is mounted in the first yoke for a rotation around a second axis which extends substantially perpendicularly to the first axis at a second level. The second level is further away from the upper end or lower end, respectively, of the elongate member than the first level.

Description

[0001] Tension leg platform assembly, mooring assembly and connector assembly

[0002] In a first aspect , the invention relates to a tension leg platform assembly, comprising a buoyant body and a number of mooring assemblies attached thereto , which mooring assemblies each, in an operative position of the tension leg platform assembly, extend between the buoyant body and a fixed foundation on the seabed, wherein each mooring assembly comprises at least one elongate member ( also called tendon) , such as for example a cable , chain or rope , having an upper end and an opposite lower end .

[0003] Among others , a tension leg platform assembly ( TLPa ) is used for a floating of fshore wind turbine . The TLPa may support a wind turbine generator and a wind turbine tower . Generally, the TLPa itsel f may consist of a central column and a number (mostly three ) of pontoons . The system to keep the TLPa stationary at a fixed position at sea consists of a vertical or nearly vertical set of elongate members . The buoyancy in the TLPa provides an excessive (upward) buoyancy force that keeps the tendons under pretension at all times ( also under severe weather and sea conditions ) . The pretension forces provide stability to the system and prevent slack line events ( in the tendons ) .

[0004] The use of of fshore wind is constantly growing due to an increased demand for sustainable energy . This has led to an increase of the dimensions of wind turbines , which poses challenges with regard to the mooring assemblies used for keeping the TLPa stationary ( for example as a consequence of an increase of the pretension in the tendons , the need for an increased number of tendons per tendon set ) .

[0005] In many cases the TLPa will be installed in water depths which result in relatively large excursions ( surge / sway) and rotations ( roll / pitch) . The angles ( inclination) at which the tendons extend ( relative to a vertical direction) will be increased for achieving optimi zed motions and loads in the tendons . However, inclined tendons may have a negative impact on the load sharing between parallel tendons close to each other in a tendon set .

[0006] It is an obj ect of the present invention to provide an improved tension leg platform assembly .

[0007] Thus , in accordance with the present invention, the tension leg platform assembly is characteri zed in that at least one of said upper end and lower end of the elongate member by means of a connector assembly is connected to the buoyant body or to the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is directly or indirectly connected to the buoyant body or fixed foundation for a rotation around a first axis which extends substantially hori zontally at a first level , and a second yoke which, in said operative position, is mounted in the first yoke for a rotation around a second axis which extends substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level . In many cases , the second axis also extends substantially hori zontally .

[0008] The connector assembly according to the present invention provides an optimi zed load trans fer between the elongate member ( tendon) and the buoyant body ( or fixed foundation) and is capable of allowing a load sharing between di fferent tendons ( resulting in a more equal loading of the tendons ) . The relative position between the first axis and second axis firstly has the advantage that the first axis supports the second axis under the pretension loads without the need for dedicated ( complicated and / or additional ) constructive members , and secondly results in an optimi zed load path between the buoyant body / fixed foundation and the elongate members .

[0009] In one embodiment the buoyant body and / or the fixed foundation is / are provided with two spaced primary sockets and each first yoke is provided with opposite primary shaft ends defining the first axis and mounted in the spaced primary sockets when the first yoke is positioned between the spaced primary sockets . This provides a simple , yet ef fective construction for supporting the first yoke .

[0010] Then it is possible that the first yoke is provided with two spaced arms extending between and interconnecting its opposite primary shaft ends , wherein the arms therebetween define a passage for the second yoke as well define spaced secondary sockets and that each second yoke is provided with opposite secondary shaft ends defining the second axis and mounted in the spaced secondary sockets when the second yoke is positioned between the spaced arms .

[0011] Equivalent to such an embodiment is an embodiment in which the second yoke is provided with such spaced arms between which the first yoke extends .

[0012] In such an embodiment it is conceivable that the secondary sockets comprise curved cradles which are open in a direction away from the respective at least one elongate member and which preferably are provided with removable retainer caps intended for retaining the secondary shaft ends in the respective cradles . Although not necessary for supporting the secondary shaft ends , the retaining caps provide additional safety for preventing the secondary shaft ends to j ump out of the cradles under severe conditions .

[0013] In one embodiment the second yoke and the at least one elongate member are interconnected separate parts . For example , the second yoke and the at least one elongate member may be connected through an assembly of a through-hole and a shaft extending rotatably therethrough, wherein preferably the second yoke is provided with the through-hole and wherein the at least one elongate member ends in a forked member carrying the shaft .

[0014] In another embodiment of the tension leg platform assembly according to the present invention the second yoke is defined by a shaft defining the second axis , wherein the respective end of the at least one elongate member extends in a loop-shape around the shaft ( and may be secured by a clamp or similar member ) .

[0015] As an alternative , the second yoke and the respective end of the at least one elongate member are combined into a single integral part .

[0016] In yet another embodiment , the first yoke is rotatably mounted in a U-shaped connection frame which, in the operative position of the tension leg platform assembly, is connected to the buoyant body or to the fixed foundation . The use of such a connection frame may simpli fy the process of mooring the TLPa but also is capable of protecting the first yoke ( and its bearings ) against damage during an installation process .

[0017] Then, it is conceivable that the buoyant body comprises receiving openings in which the connection frame can be introduced by a downward movement and / or wherein the fixed foundation comprises receiving openings in which the connection frame can be introduced by an upward movement . Such a downward or upward movement corresponds with the direction of the pretension forces in the elongate member ( s ) at such a location, which results in a situation in which the connec- tion frame is kept safely in the respective receiving opening, even i f no additional locking members would be provided .

[0018] In another embodiment the mooring assembly is provided with multiple elongate members , for example three elongate members arranged side-by-side in a single plane or arranged in a triangular arrangement . However, a di f ferent number and di f ferent arrangements are conceivable too .

[0019] Further, preferably both the upper end and lower end of the at least one elongate member by means of a connector assembly are connected to the buoyant body and the fixed foundation, respectively . This means that at both ends of the elongate member (near to the buoyant member and near to the fixed foundation) a connector assembly in accordance with the present invention is provided (however without implying or requiring that these connector assemblies are embodied in the same way) .

[0020] As stated previously, the tension leg platform assembly according to any of the previous claims may be of a type wherein the buoyant body comprises a central member and a number of buoyant members radiating outwardly from the central member and each having an outer end remote from the central member to which a respective one of the mooring assemblies is attached .

[0021] In a second aspect , the present invention relates to a mooring assembly intended for use in a tension leg platform assembly according to the present invention, wherein each mooring assembly comprises at least one elongate member, such as for example a cable , chain or rope , having an upper end and an opposite lower end, wherein at least one of said upper end and lower end is provided with a connector assembly intended to , in an operative position of the mooring as- sembly, be connected to the buoyant body or the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is intended to be connected directly or indirectly to the buoyant body or fixed foundation for a rotation around a first axis which, in said operative position, extends substantially hori zontally at a first level , and a second yoke which is mounted in the first yoke for a rotation around a second axis which, in said operative position, extends substantially hori zontally and substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level .

[0022] In a third aspect , the present invention relates to a connector assembly intended for use in a tension leg platform assembly according to the invention or intended for use in a mooring assembly according to the invention, wherein the connector assembly is intended to , in an operative position of the mooring assembly, be connected to the buoyant body or the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is intended to be connected directly or indirectly to the buoyant body or fixed foundation for a rotation around a first axis which, in said operative position, extends substantially hori zontally at a first level , and a second yoke which is mounted in the first yoke for a rotation around a second axis which, in said operative position, extends substantially hori zontally and substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level.

[0023] Hereinafter the invention will be elucidated while referring to the drawings, in which:

[0024] Figure 1 shows a general view of a tension leg platform assembly;

[0025] Figures 2-5 show an overview and details of a connector assembly;

[0026] Figures 6-8 illustrate the use of a connection frame;

[0027] Figures 9 and 10 show (both in a side view a. and in a bottom view b.) two different tendon attachment configurations, and

[0028] Figure 11 illustrates an alternative attachment of a tendon to a second yoke.

[0029] In a first instance referring to figure 1, an embodiment of a tension leg platform assembly 1 in general (and for two of its parts in a more detailed manner) is illustrated. The TLPa comprises a buoyant body which, in the illustrated embodiment, comprises a central member 2 (such as a column supporting a nacelle 2' of a wind turbine 2") and a number of buoyant members 3 radiating outwardly from the central member and each having an outer end 3' remote from the central member to which a respective mooring assembly 4 is attached.

[0030] Each mooring assembly 4, in an operative position of the TLPa as illustrated in figure 1, extends between an outer end 3' and a fixed foundation 5 on the seabed 5' and comprises at least one elongate member (or tendon) 6, such as for example a cable, chain or rope, having an upper end 6' and an opposite lower end 6" (best visible in the enlarged detailed illustrations) . In the illustrated embodiment the upper end 6 ' and the lower end 6" by means of a connector assembly 7 are connected to the outer end 3 ' of a buoyant member 3 and to a fixed foundation 5 , respectively . All connector assemblies 7 may be identical or may be of di f ferent construction . It is also possible that only the upper end 6 ' or only the lower end 6" is connected through such a connector assembly 7 .

[0031] Next , reference is made to figures 2-5 which show ( constitutive parts of ) a connector assembly 7 provided at an upper end of an elongate member or tendon 6 ( for connecting it to the outer end 3 ' of a buoyant member 3 ) .

[0032] Of course a similar description could be provided for a connection to a fixed foundation, as will be clear for the reader .

[0033] Said connector assembly 7 is provided with a first yoke 8 which, in an operative position of the TLPa as illustrated in figure 1 , is directly or indirectly connected to the outer end 3 ' of the buoyant member 3 for a rotation around a first axis 9 which extends substantially hori zontally at a first level .

[0034] In the illustrated embodiment the buoyant member 3 is provided with two spaced primary sockets 10 ( figure 2 ) , whereas the first yoke 8 is provided with opposite primary shaft ends 11 defining the first axis 9 and mounted in the spaced primary sockets 10 when the first yoke 8 is positioned between the spaced primary sockets 10 ( as illustrated in figure 2 ) .

[0035] The connector assembly further comprises a second yoke 12 which, in said operative position, is mounted in the first yoke 8 for a rotation around a second axis 13 which, in the illustrated embodiment , extends substantially horizontally and substantially perpendicularly to the first axis 9 at a second level (but which in alternative embodiments not illustrated also could extend in an inclined manner ) .

[0036] In a manner to be described below, the second yoke 12 is attached to the at least one elongate member / tendon 6 ( two elongate members / tendons 6 in figure 2 ) .

[0037] The second level at which the second axis ( of rotation) 13 of the second yoke 12 extends is further away from the (upper end 6 ' of the ) elongate member ( s ) 6 than the first level at which the first axis ( of rotation) 9 of the first yoke extends . This means that these axes 9 and 13 do not intersect each other ( or, in other words , do not extend in a same plane ) .

[0038] Speci fically referring to figures 3 and 4 , the first yoke 8 is provided with ( or defined by) two spaced arms 14 extending between and interconnecting its opposite primary shaft ends 11 , wherein the arms 14 therebetween define a passage 15 for the second yoke 12 . Further, the arms 14 define spaced secondary sockets 16 .

[0039] The second yoke 12 is provided with opposite secondary shaft ends 17 ( only one of which is visible in figures 2 and 3 ) defining the second axis 13 and, in the operative position, mounted in the spaced secondary sockets 16 ( see figures 2 and 3 ) when the second yoke 12 is positioned between the spaced arms 14 and extends through the passage 15 .

[0040] In the illustrated embodiment the secondary sockets 16 comprise curved cradles which are open in a direction away from the at least one elongate member 6 (here upwards ) . Preferably the cradles 16 are provided with removable retainer caps 18 ( see figures 6 and 8 ) intended for retaining the secondary shaft ends 17 in the respective cradles 16 .

[0041] Figure 5 shows an embodiment of the second yoke 12 , with at its top an opening 19 which may receive a shaft (not illustrated) defining the secondary shaft ends 17 , and at its bottom through-holes 20 used for attaching elongate members 6 . In such a case , the second yoke 12 and the at least one elongate member 6 are interconnected separate parts . For example , as illustrated in figure 2 , the upper end 6 ' of the tendons 6 may be provided with forked members 21 receiving each a shaft 22 which extends rotatably through a corresponding through-hole 20 of the second yoke 12 . As an alternative the shafts 22 may be an integral part of the second yoke 12 and be received rotatably in the forked members 21 .

[0042] As an alternative and very simple embodiment ( shown in figure 11 ) , the second yoke 12 is simply defined by a shaft 23 defining the second axis 13 , wherein the respective end of the at least one elongate member / tendon 6 extends in a loop-shape around the shaft 23 ( and may be secured by a clamp 24 ) .

[0043] It is possible too that the second yoke 12 and the upper end 6 ' or lower end 6" of the at least one elongate member 6 are combined into a single integral part ( for example welded together or otherwise manufactured as a single part ) .

[0044] Referring to figures 6- 8 , an embodiment is illustrated in which the first yoke 8 is rotatably mounted in a U-shaped connection frame 25 which, in the operative position of the tension leg platform assembly, is connected to the buoyant member 3 ( or to the fixed foundation 5 ) . The buoyant member 3 comprises receiving openings or supports 26 in which the connection frame 25 can be introduced by a downward movement ( or upward movement in case of installation at a fixed foundation 5 ) . For manipulation of the connection frame 25 it comprises hoisting eyes 27 .

[0045] The first yoke 8 with its primary shaft ends 11 may be pre-installed in receiving openings 28 of the connection frame 25 . The mooring assembly may be provided with a single tendon 6 , but also with multiple tendons , for example three tendons arranged side-by-side in a single plane and attached to a correspondingly shaped second yoke 12 as illustrated in figures 9a ( side view) and 9b (bottom view) or arranged in a triangular arrangement as illustrated in figures 10a ( side view) and 10b (bottom view) .

[0046] The invention is not limited to the embodiments described previously which may be varied widely within the scope of the invention as defined by the claims .

Claims

CLAIMS1 . Tension leg platform assembly, comprising a buoyant body and a number of mooring assemblies attached thereto , which mooring assemblies each, in an operative position of the tension leg platform assembly, extend between the buoyant body and a fixed foundation on the seabed, wherein each mooring assembly comprises at least one elongate member, such as for example a cable , chain or rope , having an upper end and an opposite lower end, characterized in that at least one of said upper end and lower end of the elongate member by means of a connector assembly is connected to the buoyant body or the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is directly or indirectly connected to the buoyant body or fixed foundation for a rotation around a first axis which extends substantially hori zontally at a first level , and a second yoke which, in said operative position, is mounted in the first yoke for a rotation around a second axis which extends substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level .2 . Tension leg platform assembly according to claim 1 , wherein the buoyant body and / or the fixed foundation is / are provided with two spaced primary sockets and wherein each first yoke is provided with opposite primary shaft ends defining the first axis and mounted in the spaced primary sockets when the first yoke is positioned between the spaced primary sockets .3 . Tension leg platform assembly according to claim 2 , wherein the first yoke is provided with two spaced arms extending between and interconnecting its opposite primary shaft ends , wherein the arms therebetween define a passage for the second yoke as well define spaced secondary sockets and wherein each second yoke is provided with opposite secondary shaft ends defining the second axis and mounted in the spaced secondary sockets when the second yoke is positioned between the spaced arms .4 . Tension leg platform assembly according to claim 3 , wherein the secondary sockets comprise curved cradles which are open in a direction away from the respective at least one elongate member and which preferably are provided with removable retainer caps intended for retaining the secondary shaft ends in the respective cradles .5 . Tension leg platform assembly according to any of the previous claims , wherein the second yoke and the at least one elongate member are interconnected separate parts .6 . Tension leg platform assembly according to claim 5 , wherein the second yoke and the at least one elongate member are connected through an assembly of a through- hole and a shaft extending rotatably therethrough, wherein preferably the second yoke is provided with the through-hole and wherein the at least one elongate member ends in a forked member carrying the shaft .7 . Tension leg platform assembly according to claim 1 , wherein the second yoke is defined by a shaft defining the second axis and wherein the respective end of the at least one elongate member extends in a loop-shape around the shaft .8 . Tension leg platform assembly according to any of the claims 1-4 , wherein the second yoke and the respective end of the at least one elongate member are combined into a single integral part .

9. Tension leg platform assembly according to claim 1 , wherein the first yoke is rotatably mounted in a U- shaped connection frame which, in the operative position of the tension leg platform assembly, is connected to the buoyant body or to the fixed foundation .10 . Tension leg platform assembly according to claim 9 , wherein the buoyant body comprises receiving openings in which the connection frame can be introduced by a downward movement and / or wherein the fixed foundation comprises receiving openings in which the connection frame can be introduced by an upward movement .11 . Tension leg platform assembly according to any of the previous claims , wherein the mooring assembly is provided with multiple elongate members , for example three elongate members arranged side-by-side in a single plane or arranged in a triangular arrangement .12 . Tension leg platform assembly according to any of the previous claims , wherein both the upper end and lower end of at least one elongate member by means of a connector assembly are connected to the buoyant body and the fixed foundation, respectively .13 . Tension leg platform assembly according to any of the previous claims , wherein the buoyant body comprises a central member and a number of buoyant members radiating outwardly from the central member and each having an outer end remote from the central member to which a respective one of the mooring assemblies is attached .14 . Mooring assembly intended for use in a tension leg platform assembly according to any of the previousclaims , wherein each mooring assembly comprises at least one elongate member, such as for example a cable , chain or rope , having an upper end and an opposite lower end, wherein at least one of said upper end and lower end is provided with a connector assembly intended to , in an operative position of the mooring assembly, be connected to the buoyant body or the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is intended to be connected directly or indirectly to the buoyant body or fixed foundation for a rotation around a first axis which, in said operative position, extends substantially hori zontally at a first level , and a second yoke which is mounted in the first yoke for a rotation around a second axis which, in said operative position, extends substantially hori zontally and substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level .15 . Connector assembly intended for use in a tension leg platform assembly according to any of the claims 1- 13 or intended for use in a mooring assembly according to claim 14 , wherein the connector assembly is intended to , in an operative position of the mooring assembly, be connected to the buoyant body or the fixed foundation, respectively, wherein said connector assembly is provided with a first yoke which, in said operative position, is intended to be connected directly or indirectly to the buoyant body or fixed foundation for a rotation around a first axis which, in said operative position, extends substantially hori zontally at a first level , and a second yoke which is mounted in the first yoke for a rotation around a second axis which,in said operative position, extends substantially hori zontally and substantially perpendicularly to the first axis at a second level and which second yoke is attached to the at least one elongate member, and wherein the second level is further away from the upper end or lower end, respectively, of the elongate member than the first level .

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