EP2982801B1 - Offshore device with a platform and method for their foundation - Google Patents

Description

The invention relates to an offshore device according to the preamble of claim 1 and to a method for establishing an offshore device according to claim 9.

Offshore facilities are well known in the art. In this case, this is a platform with a substructure on which the platform will be built at a height above sea level. The substructure has three or more legs set up in the seabed. In order to base the legs in the seabed, one must exert on the legs individually a preload at least at the level of the maximum force to be assumed in operation under environmental loads, which presses the foot of the leg into the seabed

From the DE 27 227 47 A1 is an offshore platform known as a mobile single leg. A stabilizing diagonal bracing is not disclosed here, so that the platform with the individually movable legs withstands only lower horizontal loads, for example due to waves and underwater currents.

Furthermore, from the DE 10 2013 001188 B3 Substructures of wind turbines are known which have a framework structure. For this purpose, diagonal and horizontal braces are welded or bolted together, which give stability to the entire substructure. The diameters of the individual braces can be reduced compared to non-braced single legs. The disadvantage of this, however, is that the legs are no longer individually movable and therefore can not be individually biased. Here foundation mechanisms by suction feet, anchor piles or the like are known.

Furthermore, founding procedures from the EP 2 313 605 B1 in which a trunk body is placed by means of a lowerable substructure of four connecting legs and a fixedly connected to the connecting legs mat on a seabed.

It is an object of the invention to provide an offshore device mentioned above, which reduces the above-mentioned disadvantages. It is in a second aspect the object of the invention to provide a method which enables the establishment of an offshore facility and avoids the above-mentioned disadvantages.

In the first aspect, the object is achieved by an offshore device having the features of claim 1.

The offshore device according to the invention has a platform and at least three legs and at least one frame interconnecting the at least three legs. The at least one frame is movable along a longitudinal direction of the at least three legs relative to the platform.

According to the invention, the at least three legs are individually movable relative to the at least one frame in the longitudinal direction, and the at least one frame is arranged in a transport position laterally and / or meeresbodenabseitig the platform, the platform circumferentially and arranged in a foundation position between the platform and the seabed. The term "revolving around the platform" here means that the at least one frame in a section perpendicular to the longitudinal direction in any position along the longitudinal direction of each outer contour of the platform runs outside and thus as a ring-like structure from the transport position outside of the platform in the foundation position sea bottom side of the platform can be moved.

Horizontal distances, d. H. Distance in a cross-section perpendicular to the longitudinal direction, between adjacent legs are the same in each case at least along sections in which the at least one frame has contact with the legs. That is, the minimum distance from any point on the longitudinal axis of a leg to the longitudinal axis of a selected adjacent leg is the same. The two legs run completely linear and parallel next to each other. Two other legs may have a different, but again constant distance from each other.

At least in the section in which the at least one frame has contact with the legs, the legs have a continuous longitudinal axis. Preferably, the at least one support leg has a continuous longitudinal axis along its entire longitudinal extent.

During the relative movement of the at least one frame relative to the legs, contact points, preferably all contact points, of the platform on the respective leg change. Each leg is fastened by attaching the platform to the leg, which preferably are formed as sleeves, pushed through. The platform is moved along the leg.

The leg has along its entire longitudinal extent a longitudinal axis, which cuts the leg centrally in each horizontal cross-section, preferably in a centroid. A length of each leg between a portion of the leg on which the platform is located in the operative position on the leg and a foot of the leg on which the leg is in the operating position on the seabed is the same in the transport position and the operating position.

The offshore facility assumes the transport position during transport to the place of foundation. In the transport position, the at least three legs and the at least one frame are pulled up to the platform or even extended beyond the ocean side, whereas in the foundation position all legs are lowered onto the seabed while the platform still floats on the sea surface. In an operating position, the platform is raised from the sea to operating altitude above the sea surface.

The at least three legs and the at least one frame may form a substructure that is movable back and forth in a longitudinal direction. The offshore facility is preferably made with the substructure largely completely in a dock, and the substructure must be lowered for foundation only to the seabed.

According to the invention, the stability-imparting at least one frame is combined with the individually movable legs, whereby the leg diameter of each leg can be lowered and the legs can still be pressed deep into a seabed. The legs can be pressed with different or different preload different depths deep into the seabed.

Under a leg here are understood both solid profiles and tubular profiles and built profiles and resolved structures that extend in a vertical direction in the operating state of the offshore facility to a sea level aligned longitudinal direction. The term leg is to be understood generally and includes elongated structures on which the load of the above the sea surface arranged platform is supported.

The maximum leg load corresponds to a maximum load applied to each leg during operation of the offshore facility, theoretically taking into account Ripples and underwater currents would occur when adverse weather conditions occur, as well as adding additional loads by outwardly projecting cranes, etc. acting on the respective leg.

Each leg is loaded with a preload lying above the leg load and pushed so far into the seabed, until it comes to a standstill due to the buildup of counterforce. Thus it remains stable in position even under the most unfavorable weather conditions after the foundation.

The platform itself is preferably designed buoyant, so that the offshore facility can be dragged out of the dock and also out of the shallow water with a raised base and transported to the foundation site.

At the founding site, the legs are lowered onto the seabed until preferably all feet of the legs have contact with him. Thereafter or at the same time, the at least one frame can be lowered. It can be provided for lowering devices for the at least three legs and additionally for the at least one frame, which are preferably arranged along the platform. The lowering systems may be or at least include strand jack systems.

There are various embodiments of the invention Offhore device conceivable that allow each of the at least three legs to each load a preload.

There is preferably provided loading means for the at least three legs which load each of the at least three legs with a partial weight force of the platform, the partial weight force corresponding to the preload and above a predetermined leg load.

In one embodiment of the invention, the loading device on ballast tanks that can be filled with sea water to produce a higher weight and thus apply on each of the at least three legs at the same time a lying above the leg load partial weight force. The embodiment is provided in particular with substructures with exactly three legs.

In another embodiment of the invention, a loading device is arranged on each of the at least three legs between the respective leg and the platform, with the various distributions of the weight of the platform on the at least three legs are adjustable such that each of the at least three legs in at least one of the distributions is loaded with a preload that is above a predetermined leg load. A leg load is to be understood as a load that is mathematically determined before the offshore facility is established. This embodiment is particularly suitable for exactly four or even higher number of legs.

Conveniently, the loading device on Litzenhebersysteme. However, other types of loading devices, such as lifting devices and lifting systems, are also conceivable.

Preferably, the at least one frame has sleeves and connecting struts. The at least three legs are guided in reciprocating sleeves along a longitudinal direction of the legs, and connecting struts are relatively immovably connected to the sleeves. Connecting struts and sleeves preferably form together a truss structure. It may be at the connecting struts to diagonal struts and / or horizontal struts. Each of the at least three legs may be guided in one or more sleeves.

The at least one frame comprises exactly one frame or two or even more frames. The frames may be in contact with each other in the foundation position, but they may also be spaced apart longitudinally, for example, one of the frames may be located directly on the seabed, while another frame is provided immediately on the seabed side of the platform. Additional frames add extra stability to horizontal loads.

Conveniently, the at least one frame is formed by sleeves and connecting struts. A frame formed by sleeves and struts is preferably rigid and immovable, however, each of the at least three legs in the sleeves is individually reciprocable longitudinally relative to the at least one frame. However, the at least one frame does not have to be rigidly formed; it may also be variable horizontally in its extension, preferably adjustable, transversely to the longitudinal direction. This makes it possible to lower the frame at different legs differently wide and fast without being misjudged. Pods are generally understood to mean devices in which the leg is guided. They are adapted in an inner cross section an outer cross section of the associated leg; they can completely surround the leg completely or in sections. In particular, they can be cuff-shaped or tubular. This combines the individual mobility of the legs with the stability of the frame.

Preferably, the at least one frame is fixable in an arbitrarily predetermined position along the longitudinal direction between the seabed and the platform on the legs. The offshore device may have exactly one or more frames, which are additionally movable against each other in the longitudinal direction. The frames can be lowered from their transport position and can be fixed to the legs in any desired position along the longitudinal direction between the seabed and the platform.

In the foundation position, the slidability and the play of the legs in the sleeves can be prevented by various methods and thus the strength of the substructure can be further increased. In particular, the sleeves can be fixed by filling the gaps between leg and sleeve with grout on the leg.

Each frame preferably has exactly one sleeve per leg, but two sleeves or any larger number of sleeves are also conceivable.

Particularly preferably, the connecting struts of the at least one frame with the substructure pulled up are arranged laterally next to the platform during the transport of the offshore device.

For this purpose, the connecting struts are conveniently mounted platform outside on the sleeves, and the entire frame is chosen so large that it can accommodate the platform in its free inner cross section and the platform laterally surrounds.

Preferably, in each case a connection between each leg and the platform is provided, with the transverse loads in the respective leg are feasible. The links are open in the transport position because the at least one frame is mounted laterally adjacent to the platform and obstructs the connections between the platform and the at least three legs. At least after the foundation, the connections are conveniently closed already after the frame has been lowered.

In addition, a lifting device is provided, which can lift the platform, after the substructure is established, along the at least three legs of the substructure from the sea to operating height.

The lifting device and the loading device are conveniently identical. It can be any suitable lifting system, such as a stranded lifter system.

In its second aspect, the object is achieved by a method having the features of claim 10.

The method is particularly suitable for carrying out with one of the abovementioned offshore installations with a platform having at least three legs and at least one frame interconnecting the at least three legs, the at least one frame being movable along a longitudinal direction of the at least three legs relative to the platform is. and the at least three legs are individually movable relative to the at least one frame in the longitudinal direction. According to the invention, during transport of the offshore installation to a foundation site, the platform is laterally arranged around the at least one frame, and the at least one frame is lowered at the foundation site during formation along a longitudinal direction of the at least three legs relative to the platform in the direction of a seabed.

The substructure with the at least one frame and the at least three legs is raised during transport, and the offshore device has a shallow draft to be brought from a dock by shallow water to the foundation site.

At the place of foundation of the substructure is lowered to the seabed, preferably until the feet of all at least three legs touch the seabed.

After all at least three legs are lowered onto the seabed, each of the at least three legs is loaded with a partial weight force of the platform by means of loading means for the at least three legs, the partial weight force being above a predetermined preload.

Preferably, the at least three legs are pressed individually and / or in groups successively into the seabed and / or pressed into the seabed at different depths.

The fact that the legs are individually movable, they can be pushed to a different depths deep into the seabed, on the other hand, by some of the load devices, the weight of the platform can be distributed differently over the legs, so that by raising legs a greater part of the weight the platform is applied to the other legs, which is above the leg load and thus generates the required preload. Conversely, the platform on the other legs can be pulled up to then exercise on these legs a higher part of the weight. This method is particularly suitable for exactly four, five or any higher number of legs.

The loading devices may include ballast tanks that are filled with seawater and thus increase the weight of the platform. In this case, preferably exactly three legs are provided. In particular, the weight can be increased so far that all legs are loaded simultaneously with the preload.

During foundation or subsequently, the at least one frame can be lowered from its transport position and fixed in any given position along the longitudinal direction between the seabed and the platform on the legs. With two or more frames, the frames are movable separately in the longitudinal direction and can be fixed separately in each case in an arbitrarily predetermined position in the longitudinal direction of the legs. In particular, a frame near the bottom of the sea and another frame on the sea bottom side of the platform can be fixed in the water under the waves on the legs, thus increasing the stability of the substructure.

During the lowering of the frame, the sleeves have a game on the associated bees. The game can be taken out after the establishment by suitable procedures, in order to increase the stability further.

Fig. 1

einen ersten Schritt des erfindungsgemäßen Verfahrens, indem die Offshore-Einrichtung aufschwimmend verbracht wird,

Fig. 2

einen zweiten Schritt des Verfahrens, indem ein Unterbau abgesenkt wird,

Fig. 3

einen dritten Schritt des Verfahrens, indem vier Füße von vier Beinen des Unterbaus auf einem Meeresboden aufsetzen,

Fig. 4

einen vierten Schritt des Verfahrens, indem der Fuß eines ersten Beines in den Meeresboden eindringt,

Fig. 5

einen fünften Schritt des Verfahrens, indem alle vier Füße der vier Beine in den Meeresboden eingedrungen sind und die Plattform aufschwimmt,

Fig. 6

einen sechsten Schritt des Verfahrens, indem die Plattform mit den vier Beinen verbunden wird,

Fig. 7

einen siebenten Schritt des Verfahrens, indem die Plattform auf eine Betriebsposition angehoben wird.

The invention will be described with reference to an embodiment in seven figures, in which:

Fig. 1

a first step of the method according to the invention by floating the offshore device,

Fig. 2

a second step of the method by lowering a substructure,

Fig. 3

a third step of the process by placing four feet of four legs of the substructure on a seabed,

Fig. 4

a fourth step of the method in which the foot of a first leg penetrates into the seabed,

Fig. 5

a fifth step of the process, in which all four feet of the four legs have penetrated into the seabed and the platform is floating,

Fig. 6

a sixth step of the process by connecting the platform to the four legs,

Fig. 7

a seventh step of the method by raising the platform to an operating position.

In the FIGS. 1 to 7 an inventive method for establishing an offshore facility 1 is shown. The drawings are not to scale or true to scale.

The offshore installation 1 comprises a floating platform 2 and a substructure 9 having four legs 3a, 3b supporting the platform 2 in a foundation state, of which only the first and second legs 3a, 3b are in the FIGS. 1 to 7 can be seen, and a four legs 3a, 3b connecting frame 8 with a truss structure with diagonal and horizontal struts 4, 5 and four sleeves 6a, 6, of which also only two sleeves 6a, 6b are shown. To each leg 3a, 3b is exactly one sleeve 6a, 6b placed. Shown in the FIGS. 1 to 7 only the first and second legs 3a, 3b and the first and second sleeves 6a, 6b respectively disposed in front of and covering the third and fourth legs and the third and fourth sleeves, respectively. They are identical.

The sleeves 6a, 6b are reciprocally movable along one of the four legs 3a, 3b in a longitudinal direction L of the four legs 3a, 3b, respectively. The sleeves 6a, 6b have a small clearance on the four legs 3a, 3b. The horizontal and diagonal struts 4, 5, which are referred to together as connecting struts 4, 5, are fixedly connected to the sleeves 6a, 6b under load and therefore movable relative to the four legs 3a, 3b in the longitudinal direction L back and forth. The frame 8 forms in a top view, not shown, a rectangle or square, which is particularly stable due to the horizontal struts 5 and diagonal struts 4 against laterally acting on the frame 8, for example, generated by wave and water currents forces.

The platform 2 itself is buoyant. The combination of platform 2 and substructure 9 is buoyant. It is envisaged that in the arrangement according to Fig. 1 a number (not shown) of connections 31 a, 31 b is provided between the floating platform 2 and the substructure 9, which hold the substructure 9 on a sea surface 7. The frame 8 is arranged at the level of the platform 2 and surrounds the also square platform 2 outside and around. The frame 8 has the four sleeves 6a, 6b, wherein in each of the four sleeves 6a, 6b respectively exactly one of the four legs 3a, 3b is guided.

Seabed-side ends of the four legs 3a, 3b have widened feet 11a, 11b, so-called elephant feet. Instead of the widened feet 11a, 11b, other embodiments of the leg ends are conceivable.

The offshore facility 1 Fig. 1 is a total buoyant and can be spent with the substructure 9 raised to a selected location above a seabed 12 by means of tugs or the like.

At the selected location above the seabed 12 is according to Fig. 2 the substructure 9 lowered in the direction of the seabed 12. For this purpose, stranded wire systems or other suitable systems are selected. First, each of the legs 3a, 3b is provided with a strand lifter system (not shown). This makes it possible to lower the four legs 3a, 3b at the same time on the seabed 12. On the other hand, the frame 8 is equipped with its own Litzenhebersystem so that the frame 8 can be lowered simultaneously with all four legs 3a, 3b or offset in time to the legs 3a, 3b in the direction of the seabed 12.

The frame 8 is freely reciprocably supported by the four sleeves 6a, 6b in the longitudinal direction L to the four legs 3a, 3b, and the frame 8 therefore descends along the legs 3a, 3b down to the seabed 12. The four sleeves 6a, 6b are initially on the sea surface on the widened four feet 11a, 11b. The frame 8 is dimensionally stable during the lowering of the substructure 9.

Fig. 3 shows in a third step, the lowered to the seabed 12 substructure 9; the widened four feet 11a, 11b of the four legs 3a, 3b lie on the sea floor 12, and the frame 8 is lowered onto the widened four feet 11a, 11b along the four legs 3a, 3b toward the sea floor 12. The platform 2 floats continuously on the sea surface 7 between the four legs 3a, 3b. It is envisaged that in steps one, two or three according to Fig. 1, Fig. 2 and Fig. 3 four connections 13a, 13b are made between corners of the platform 2 and the four legs 3a, 3b which receive transverse forces and hold the platform 2 in position between the four legs 3a, 3b. In this case, the platform 2 can be arranged in the longitudinal direction L movable on the four legs 3a, 3b. The four connections 13a, 13b are initially arranged in a cuff-like manner around the four legs 3a, 3b and permit a movement of the platform 2 in the longitudinal direction L. After the platform 2 has been moved in accordance with FIG Fig. 7 is raised to the operating level, the four connections 13, 13b are solidified.

The four sleeves 6a, 6b have an extension in the longitudinal direction L which corresponds to approximately one third of the length of each of the four legs 3 a, 3 b of equal length. But there are also other lengths conceivable. Other embodiments of the frame 8 are also possible, for example by means of two sleeves 6a, 6b arranged one above the other or even more sleeves 6a, 6b per leg 3a, 3b.

In the illustrated embodiment, two adjacent sleeves 6a, 6b are connected to each other in their longitudinal direction L upper and lower ends, each with a horizontal strut 5 in a fixed position. Under "above" and "below" is here and elsewhere referred to the position relative to the seabed 12. Furthermore, two intersecting diagonal connecting struts 4 are provided between adjacent sleeves 6a, 6b, the ends of which contact ends of the horizontal struts 5, the ends being mounted together on the respective sleeve 6a, 6b.

Between each of the seabed-down portions of the four legs 3a, 3b and the platform 2 is provided a lifting device (not shown).

By operating a lifting device differently, the weight of the platform 2 is distributed differently over the four legs 3a, 3b on the widened four feet 11a, 11b, and the four legs 3a, 3b are loaded with a preload and pressed into the seabed until sufficient large opposing force is built up and stops the Eindrückbewegung.

There are so long different weight distributions on the four feet 11a, 11b performed until all four legs 3a, 3b were loaded with the preload and have penetrated under the preload in the seabed 12 and there have reached their unchangeable position in the seabed 12. The final state of the foundation is in Fig. 5 shown.

In Fig. 6 are also connections 13a, 13b shown, with which the platform 2 is connected at its corners with the four legs 3a, 3b. The connections 13a, 13b can be sleeves which can be opened and are placed around the outside of the respective four legs 3a, 3b. The connections 13a, 13b are intended to absorb horizontal loads and to prevent a relative change in position between platform 2 and substructure 9.

In a seventh process step, which in Fig. 7 is shown, the platform 2 is lifted by means of the lifting device from the sea surface 7 to operating altitude. The platform 2 is permanently fixed in the operating height. The loading devices and the lifting device can be provided in one device or in separate devices.

The inventive offshore device 1 makes it possible to use in cross-section small legs 3a, 3b, since horizontal forces on the truss structure of the frame 8 can be added and the substructure 9 is significantly stabilized by the truss structure of the frame 8. However, because the four legs 3a, 3b are still reciprocally movable in the frame 8 in the longitudinal direction L, the entire substructure 8 can be prefabricated with sleeves 6a, 6b which are adapted precisely to the outer shape of the four legs 3a, 3b and with sufficiently large clearance built as a total construction on land and to the predetermined location above the seabed 12 according to Fig. 1 be spent. There, the entire substructure 9 can be lowered, and due to the relative displaceability between the four legs 3a, 3b and the frame 8, each one of the four legs 3a, 3b or pairs of legs can be pressed into the ground. It is only the weight of the platform 2 necessary to press the four legs 3a, 3b in the seabed 12. The play between the four sleeves 6a, 6b and the four legs 3a, 3b can be removed after the foundation by various methods and so the substructure 9 even greater stability can be imparted.

LIST OF REFERENCE NUMBERS

1

Offshore facility

2

platform

3a

leg

3b

leg

4

diagonal braces

5

horizontal struts

6a

shell

6b

shell

7

sea

8th

frame

9

substructure

11a

foot

11b

foot

12

Seabed

13a

connection

13b

connection

L

longitudinal direction

Claims (15)

1. Offshore installation with a platform (2) and with at least three legs (3a, 3b) and at least one frame (8) connecting the at least three legs (3a, 3b) to one another, wherein the at least one frame (8) is movable along a longitudinal direction (L) of the at least three legs (3a, 3b) relative to the platform (2), and horizontal distances between neighbouring legs (3a, 3b) are in each case equal, at least along sections in which the at least one frame (8) has contact with the legs (3a, 3b), wherein the at least three legs (3a, 3b) are individually movable relative to the at least one frame (8) in the longitudinal direction (L), characterised in that in a transport position the frame (8) is arranged running laterally around the platform (2), and in a grounding position it is arranged between the platform and a seabed (12).
2. Offshore installation according to claim 1, characterised in that a loading device for the at least three legs (3a, 3b) is provided which loads each of the at least three legs (3a, 3b) with a partial weight force of the platform (2), and the partial weight force corresponds to a predetermined initial load.
3. Offshore installation according to one of claims 1 or 2, characterised in that the at least one frame (8) has sleeves (6a, 6b) and connecting struts (4, 5) and the at least three legs (3a, 3b) are guided in the sleeves (6a, 6b) and the connecting struts (4, 5) are connected relatively immovable to the sleeves (6a, 6b) and between each of the at least three legs (3a, 3b) and the platform (2) a loading device is arranged respectively, by which various distributions of the weight force can be set over the at least three legs (3a, 3b) so that each of the at least three legs (3a, 3b) in one of the distributions is loaded with a partial weight force which corresponds to a predetermined initial load.
4. Offshore installation according to one of claims 1 to 3, characterised by a connection in each case (13a, 13b) between each of the at least three legs (3a, 3b) and the platform (2) which is open in the transport position and closed in the grounding position, and by means of which transverse loads can be guided into the respective leg (3a, 3b).
5. Offshore installation according to one of claims 1 to 4, characterised in that the at least one frame (8) can be fixed to the legs (3a, 3b) in any predetermined position along the longitudinal direction (L) between the seabed (12) and the platform (2).
6. Offshore installation according to one of the preceding claims, characterised by a lifting device for the platform (2) along the at least three legs (3a, 3b).
7. Offshore installation according to claim 6, characterised in that the loading device comprises the lifting device.
8. Offshore installation according to one of claims 1 to 7, characterized by a removable clearance between the sleeves (6a, 6b) and the associated legs (3a, 3b).
9. Method for grounding an offshore installation (1) with a platform (2) and with at least three legs (3a, 3b) and with at least one frame (8) connecting the at least three legs (3a, 3b) to one another, wherein the at least one frame (8) is movable along a longitudinal direction (L) of the at least three legs (3a, 3b) relative to the platform (2), and the at least three legs (3a, 3b) are movable individually relative to the at least one frame (8) in the longitudinal direction (L), and horizontal distances between neighbouring legs (3a, 3b) are in each case the same, at least along sections in which the at least one frame (8) has contact with the legs (3a, 3b),
   the at least one frame (8) being arranged laterally running around the platform during transport of the offshore installation to a grounding site and
   the at least one frame (8) being lowered along a longitudinal direction (L) of the at least three legs (3a, 3b) relative to the platform (2) in the direction of a seabed (12) at the grounding site during a grounding.
10. Method according to claim 9, characterised in that each of the at least three legs (3a, 3b) is loaded by means of a loading device for the at least three legs (3a, 3b) with a partial weight force of the platform (2), and the partial weight force corresponds to a predetermined initial load.
11. Method according to claim 9 or 10, characterised in that the at least three legs (3a, 3b) are pressed individually and/or in groups successively into the seabed (12) and/or are pressed to different depths into the seabed (12).
12. Method according to one of claims 9 or 10, characterised in that ballast tanks of the platform (2) are filled with sea water in order to produce a higher weight force and thus a partial weight force corresponding to the initial load is simultaneously applied to each of the at least three legs (3a, 3b).
13. Method according to one of claims 9 to 12, characterised in that the platform (2) is permanently connected to the at least three legs (3a, 3b) by means of connections (13a, 13b) which are opened during transport and are closed at least after grounding.
14. Method according to one of claims 9 to 13, characterised in that the at least one frame (8) is fixed to the legs (3a, 3b) in any predetermined position along the longitudinal direction (L) between the seabed (12) and the platform (2).
15. Method according to at least one of claims 9 to 14, characterised in that a clearance between the sleeves (6a, 6b) and the associated legs (3a, 3b) is removed.

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