NL2011873C2

NL2011873C2 - Motion compensation system, hoisting device, floating marine structure, fixed marine structure.

Info

Publication number: NL2011873C2
Application number: NL2011873A
Authority: NL
Inventors: Naxin Zhang; Johan Albert Commandeur; Wilhelmus Coenradus Johannes Jozephus Woldring
Original assignee: Gustomsc Resources B V
Priority date: 2013-11-29
Filing date: 2013-11-29
Publication date: 2015-06-01
Also published as: WO2015080584A1

Abstract

Method for compensating relative motions of a lifting gear (6) of a lifting device (2) connectable to a load (20), wherein the lifting device comprises a reeving system (3) with at least one hoisting rope (4), comprising, connecting a linkage mechanism (12) of the motion compensation system (10) to the hoisting rope; actuating the linkage mechanism to impart displacement of the hoisting rope in a direction substantially transverse of a rope main loading direction, to impart movement of the lifting gear to compensate relative motion of the lifting gear.

Description

Title: Motion compensation system, hoisting device, floating marine structure, fixed marine structure

The invention relates to a motion compensation device.

Motion compensation devices are known and are typically applied for compensation of relative motion between a fixed and a moving structure and/or between two moving structures. Typically, relative motions occur during offshore operations, for example when lifting or lowering a load from a floating marine structure to a fixed marine structure and vice versa, or for example when lifting or lowering a load from one floating marine structure to another floating marine structure. During these operations, at least one of the structures is moving, usually under influence of environmental conditions, such as wind, waves, swell etc, causing relative motions between the two structures. Relative motions are also present during for example a drilling operation from a floating marine structure. The drilling string is to be lowered and controlled with respect to the fixed sea bottom. Relative vertical motions occur between the floating drilling structure moving e.g. due to waves or swell. For example, when lifting a load from a floating vessel onto a fixed offshore structure, such as a platform, the relative motions may impart the lowering of the load onto the platform. Or for example, when lifting a load from the fixed platform onto a floating vessel, e.g. a feeder vessel, the relative motions between the vessel and the platform may make the lowering of the load onto the feeder vessel difficult.

Relative motions may also occur for example during dredging operations, wherein the floating dredging vessel moves with respect to the fixed sea bottom during the dredging operation.

The relative motions, in particular the vertical relative motions, also called the heave motions, restrict the offshore operations. It is known to provide a heave compensator, drilling string compensator or dredging compensator to reduce the relative motions during the operations, in particular to reduce the relative motions of an end of the operational device, such as the lifting hook of a hoisting device or the dredging head of the dredging vessel or the drilling head of a drilling string of a drilling vessel. A conventional heave compensator comprises usually an active part and a passive part, both parts are arranged as hydraulic cylinders, either integrated or provided as separate units. The passive part provides for storing and retrieving most of the energy during compensating of the heave motions. The active part is required for system losses, non-linearity, load variations and/or load control. The active part typically is activated by a motion reference unit which detects the relative motions and controls the active part based on the detected relative motions to control the elevation of the end of the operational device. Per most industry practices, the distribution between the active part and the passive part is around 20/80, the active part provides about 20% of the compensational energy, while the passive part provides for about 80% of the compensational energy.

The conventional heave compensation system is integrated in the loop of the hoist reeving of a hoisting device. By extending and/or retracting of the cylinders, the elevation of the lifting hook of the hoisting device is controlled. A drawback of this conventional hydraulic cylinder heave compensation system is that it is a rather heavy and bulky system that is integrated in the hoist reeving. To install such a system the existing reeving needs to be demounted first and then re-reeved through the new system. Once it is installed it is thus difficult to remove. Since it is integrated within the hoist reeving system, it is also subject to very large force, namely the hoisting forces or a portion of that depending on the reeving. The conventional heave compensation system becomes relatively massive and complex when subjected to relatively heavy loads and/or relatively large heave motions. Sometimes it is difficult to allocate sufficient space on the lifting device to install such a conventional system. .

Another drawback is that the pressure of the passive hydraulic cylinder need to be set according to the load. To make an adjustment of the pressure takes normally considerable time and could reduce the operational availability of e.g. the hoisting device. In particular for offshore operations for which repetitive adjustment of the load weight occurs, such as wind turbine installations, this adjustment of the passive part can significantly increase the installation time.

Further, the active hydraulic cylinder part may require significant power and/or a cooling system.

There is a need to provide for a motion compensation system that obviates at least one of the above mentioned drawbacks. In particular, a motion compensation system that is removable and/or increases the operational availability may be aimed for.

Thereto, the invention provides for a motion compensation system according to claim 1.

By providing a motion compensation system according to the invention with an actuation mechanism and a separate linkage mechanism, the motion compensation system can be easily mountable and removable to a lifting device, such as a crane or a drilling lifting device or a dredging lifting device. For example, the motion compensation system may be removed from the lifting device if it is not required for a special job, or to be temporarily used on another lifting device. Once required, the motion compensation system can be installed back to the lifting device. So, a motion compensation system according to the invention is more suitable to be installed onto a lifting device as part of a refitting or upgrading program for the lifting device, since it requires no re-reeving and less modification works. The motion compensation system can also be put onto a lifting device when required. Thus, a single motion compensation system can be used on more than one lifting device sequentially. Providing a separate linkage mechanism that is connectable between the actuation mechanism and the hoisting rope, the motion compensation system according to the invention is separate from the hoisting rope and is not integrated in the hoist reeving as the prior art systems are.

By imparting displacement to the hoisting rope in a direction substantially transverse to the rope main loading direction, the lifting gear is moved as well. By imparting the transverse displacement, it may be sufficient to impart a relatively small movement to induce sufficient displacement of the lifting gear to compensate for at least part of the relative motions. Inducing a displacement in a direction substantially transverse is understood to be a displacement in a direction between 45 degrees and 135 degrees with respect to the rope main loading direction. This is contrary to the prior art devices that induce movement of the hoisting rope in line with the rope main loading direction.

However, to minimize the required displacement, a transverse direction or substantially transverse direction is preferred, preferably a direction between 70 degrees and 130 degrees, more preferably between 60 degrees and 120 degrees with respect to the rope main loading direction. An optimal movement would be in a direction 90 degrees with respect to the rope main loading direction, whereas in practice this angle may deviate, ± 40 degrees or ± 30 degrees or ± 20 degrees or ± 10 degrees, depending on the actual configuration and/or built-in situation. A rope main loading direction may be considered to be the main direction of the hoisting rope section comprising the linkage mechanism connection between adjacent reeving elements, such as pulleys or sheaves etc, i.e. the direction from one reeving element to a next reeving element. For example, if the hnkage mechanism connection is at a hoisting rope section parallel to a boom of the lifting device with a pulley near one end of the boom and another pulley near an opposite end of the boom, then the rope main loading direction there may be parallel to the boom. For example, if the linkage mechanism connection is at the hoisting rope section between the upper hoisting block and the lifting hook as lifting gear, then the rope main loading direction may be the direction from the hoisting block to the lifting hook, which may be approximately vertical.

Also, the hnkage mechanism connection is considered to be a physical connection at the position where the linkage mechanism is connected to or coupled to the hoisting rope. The linkage mechanism connection may be estabhshed by a pulley or by a wheel or by a sheave, etc.

Since the motion compensation system is independent from the reeving system of the lifting device, the motion compensation system can be provided lighter and less complex. Maintenance of such a system is also easier. In theory, the motion compensation system does not receive the lifting load in addition to the relative motions, since the lifting load, in theory, passes to the existing hoist reeving system. The hnkage mechanism can be connected to the hoisting rope at various positions. The actual connection between the linkage mechanism and the hoisting rope is referred to as the linkage mechanism connection.

For example the heave compensation system may be arranged on or near the boom, and the linkage mechanism may be a linkage frame such as a lever or an arm or a multi-bar hnkage frame that is arranged for connection to the hoisting rope. Upon actuation of the actuation mechanism, the linkage mechanism is operated by the actuation mechanism to move the hoisting rope in a direction mainly transverse to the rope main loading direction of the section of the hoisting rope to which the linkage mechanism is connected. By this transverse movement of the hoisting rope, which requires a relatively small force compared to the lifting force, the connected lifting gear, such as a lifting hook, is moved vertically as well and thus relative motion may be compensated. For example, the linkage mechanism may be connected to the section of the hoisting rope, with increased number of falls if necessary, running from the hoisting winch to the top of an A-frame of the lifting device, the lifting device then may run mainly vertical while the linkage mechanism may induce mainly horizontal movement of the hoisting rope which movement leads to movement of the lifting gear e.g. a lifting hook at the end of the hoisting rope. In this embodiment the linkage mechanism such as a linkage frame may be a lever arm that at one end is connected to the hoisting rope and at another end is connected to the actuation mechanism.

Advantageously, a wire rope is provided to couple the actuation mechanism to the linkage mechanism. By providing a wire rope, that is mountable to the lifting device separate of the hoisting ropes, this provides more flexibility in mounting the motion compensation system to the lifting device. For example, the actuation mechanism can be positioned remote from the linkage mechanism, e.g. the actuation mechanism may be positioned on the slewing platform and the linkage mechanism may be positioned to connect to the hoisting rope near the end of boom with the wire rope coupling the actuation mechanism with the linkage mechanism. The actuation mechanism can be mounted near the linkage mechanism, in view of compactness, or can be installed e.g. on the slewing platform or elsewhere on the hoisting device where there is space available. Also, by providing a wire rope, which can be reeved around one or more pulleys, the force on the linkage frame and thus the hoisting rope can be altered with respect to the actuation force of the actuation mechanism. Also, it may make it easier to remove at least a part of the motion compensation system, e.g. removing the wire ropes and the linkage mechanism to use elsewhere.

The actuation mechanism can be an active winch or a hydraulic or pneumatic cylinder etc. The actuation mechanism may be any type of actuator suitable for moving the linkage mechanism, for example by inducing shortening or lengthening of the wire rope, e.g. by spooling in or spooling out of the wire rope. By shortening or lengthening of the wire rope, the linkage mechanism connection of the linkage frame with the hoisting rope is being displaced in a direction mainly transverse to the rope main loading direction.

In another embodiment, the hnkage mechanism may be a multibar frame, having at least four bars or more. Typically, the four bars of the linkage frame are hingedly connected to each other, such that the connections between two adjacent bars form a hinge joint as a corner of the linkage frame. Where the corners of the multi-bar linkage frame connect to the hoisting rope, a linkage mechanism connection is established. Advantageously to a four-bar linkage frame is by moving one of the hinge corners, at least two other hinge corners move as well. Depending on the configuration of the four-bar linkage frame, e.g. a diamond frame, the two other corners may move in opposite direction with respect to each other and in transverse direction with respect to the corner that is being moved. Advantageously, the four-bar linkage frame is mounted between two more or less parallel falls of a multi-fall reeving system, such that two opposite hinge corners connect to two sides of the multi-fall reeving system. Also, each of the parallel falls may be a fall string itself comprising multiple falls as well. The multi-bar linkage frame typically is a spatial structure to connect to each of the falls of the fall string at one side, e.g. comprising multiple pulleys or sheaves, and also to connect to each of the falls of the fall string at the opposite side, e.g. comprising multiple pulleys or sheaves.

For example, the four-bar linkage frame can connect between two sides of falls of the multi-fall hoisting ropes, e.g. for the section of the hoisting rope between an upper hoisting block and a lower hoisting block with a lifting gear such as a lifting hook. This section of the hoisting rope may be of multi-falls mainly running vertically. The rope main loading direction for this section may thus be the vertical direction. The four-bar linkage frame may be positioned between two sides of hoisting ropes, one corner may be connected to the lifting device, two opposite corners may be connected to the respective hoisting ropes and one corner is free. The free corner may be moved in vertical direction e.g. by means of the wire rope, thus inducing a transverse movement, i.e. substantially in horizontal direction, of the opposite corners connected to the hoisting rope such that at the connection with the linkage frame, the hoisting rope is displaced in a direction transverse, e.g. approximately horizontal, to the rope main loading direction, e.g. approximately vertical. The imparted movement on the hoisting rope may deviate somewhat from the transverse direction, depending on the actual configuration and/or built-in situation, for example when not all four bars are equal in length. A deviation of ±20 or ±30 or ±40 degrees may thus be possible.

Typically, the control system of the actuation mechanism is connected to a motion reference unit. The motion reference unit is known in the art and is a measurement unit receiving signals from motion detectors and calculating the required relative motions. Based on the motions, the control system gives a control signal to the actuation mechanism to provide for a controlled movement of the linkage mechanism. For example, when the actuation mechanism is a winch, the relative motion is used to determine the amount of wire rope to be spooled in and/or out. For example, when the actuation mechanism is a hydraulic cylinder, the relative motion is used to determine the amount of extension or retraction of the cylinder.

Advantageously, the motion compensation system further comprises a passive part for storing and retrieving energy during lifting and/or lowering, in addition to the active part. The active part may be actively controlled, such as a hydraulic cylinder, or a pneumatic cylinder etc. In view of the rather heavy loads that typically may be hoisted, compensating the full relative motion in an active way involves a large amount of energy during hoisting and a large amount of energy to be destroyed during lowering of the hoisted load. This results in an active actuation mechanism which is rather heavy and requires large power. Thereto, most of the energy during compensation of the relative motion is being stored and retrieved by a passive part. Such passive part can be of a mechanical spring, a compressed gas, or a raised ballast weight containing potential energy.

The passive part may be a ballast weight that may be movable up and down. The passive part may be part of the reeving system as is the passive hydraulic cylinder in a conventional heave compensator. The passive part may also be separate from the reeving system and may be part of the wire rope system according to the invention. It is noted that the passive part movable up and down can be considered as an invention on its own.

Advantageously, the ballast weight is movable up and down along guide rails that can be mounted on the lifting device. The guide rails can also be mounted at a different, position, for example next to the lifting device. Advantageously, the ballast weight has an adjustable weight depending on the load to be lifted or to be lowered. In a preferred embodiment, the ballast weight can be a water tank. Such a water tank can be easily emptied and/or filled to adapt the weight of the ballast weight to the load. Alternatively, the ballast weight can comprise blocks of concrete assembled in a modular way, such that by removing and/or adding one or more concrete blocks the weight can be adjusted.

The hydraulic system as in the conventional heave compensation system, containing active part and passive part, can be used to provide the actuation force to the linkage mechanism. In an advantageous embodiment, the passive part can be locked for decoupling the passive part from the motion compensation system which can be advantageous for approaching a load with an empty lifting hook or other types of lifting gear. Providing a raised bahast weight as passive part of the actuation mechanism may be considered to be an invention on its own.

The invention further relates to a lifting device comprising a motion compensation system. According to the invention, the lifting device can be equipped with a motion compensation system when required. After use, the motion compensation system, or at least a part thereof, can be removed from the lifting device e.g. to be used on another lifting device. The motion compensation system, or at least a part thereof, is thus removable mounted on the lifting device.

The invention further relates to fixed or floating marine structures comprising a lifting device with a motion compensation system according to the invention. The fixed or floating marine structure can be used for offshore lifting or dredging or drilling or subsea mining, etc. The fixed or floating marine structure can be a vessel, or a barge, or a jack-up, or a semi-submersible, or a pontoon, or a platform, etc. Many variants are possible.

Further advantageous embodiments are represented in the subclaims.

The invention will further be elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention.

In the drawings:

Figure la shows a schematic representation of a marine structure with a lifting device comprising a first embodiment of a motion compensation system according to the invention with an actuation mechanism and a linkage mechanism;

Figure lb shows a schematic representation of the lifting device of Figure la comprising an at least partly multi-fall reeving system;

Figure 2a shows a schematic representation of a lifting device comprising a second embodiment of a motion compensation system according to the invention with an actuation mechanism and a linkage mechanism;

Figure 2b shows a schematic representation of the lifting device of Figure 2a comprising an at least partly multi-fall reeving system;

Figure 3 shows a schematic representation of a lifting device comprising a third embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a linkage mechanism;

Figure 4 shows a schematic representation of a lifting device comprising a fourth embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a linkage mechanism;

Figure 5 shows a schematic representation of the principle of the motion compensation system according to the invention for a multi-fall reeving system;

Figure 6 shows a schematic representation of a lifting device comprising a fifth embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a linkage mechanism;

Figure 7 shows a schematic representation of a lifting device comprising a sixth embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a hnkage mechanism with a raised ballast weight as passive part;

Figure 8 shows a schematic representation of a lifting device comprising a seventh embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a hnkage mechanism with a raised ballast weight as passive part;

Figure 9 shows a schematic representation of a lifting device comprising an eighth embodiment of a motion compensation system according to the invention with an actuation mechanism, an additional wire rope and a hnkage frame with a passive part and with an additional hookup configuration; and

Figure 10 shows a schematic perspective view of an embodiment of a hnkage mechanism according to the invention mounted to a multi-fall reeving system.

It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limited example. In the figures, the same or corresponding parts are designated with the same reference numerals.

Figure la shows a schematic representation of a marine structure 1 provided with a lifting device 2, here a crane, with a base platform 2a mounted on a deck la of the marine structure 1 via a foundation structure 2b. The lifting device 2 is used for lifting and/or lowering a load 20 to and/or from another marine structure, not shown here. The base platform 2a is a part of the lifting device 2 and provides spaces for various equipment required by the lifting device 2. For a revolving crane this platform 2a may be called the slewing platform.

The marine structure 1 here comprises the deck la supported by legs lb. The marine structure 1 is here shown as a fixed structure being installed in a water environment with water surface lc, but can be a floating structure as well. The other marine structure, to or from which the load is brought, not shown here, can be a floating marine structure such as a vessel or a barge or a SPAR or a TLP or a semi-sub, or a fixed marine structure such as a jack up or a platform. .

The lifting device 2 is provided with a reeving system 3 arranged along the lifting device 2 between a hoisting winch 5 and a lifting gear 6.

The reeving system 3 comprises at least one hoisting rope 4 running between the hoisting winch 5 and the lifting gear 6. The lifting gear 6 is here embodied as a lifting hook 6 to connect to a load 20. The lifting gear 6 can also be provided as a member to connect to drilhng strings or dredging strings.

The load 20 can be attached to the lifting gear 6 to be lifted and/or lowered. The hoisting winch 5 spools in and/or out the hoisting rope to lift and/or lower the lifting gear 6. The hoisting rope 4 is guided along the lifting device 2 via well-known pulleys, not shown in the schematic drawings. Also, the hoisting rope 4 can comprise multiple, parallel ropes, well known by the person skilled in the art. For simplicity’s sake, the hoisting rope 4 in the drawings is presented as a single rope, but multiple parallel ropes may be understood to be applicable as well.

Typically, the hoisting device 2 comprises an arm 7, such as a boom jib, to which one or more hoisting blocks 8 are attached. A hoisting block attached to the arm 7, is referred to as an upper hoisting block 8. Further, a lower hoisting block 9, with the lifting gear 6, is provided and between the upper hoisting block 8 and the lower hoisting block 9, the hoisting rope 4 is provided. The hoisting rope 4 can be provided as a single fall hoisting rope between the upper hoisting block 8 and the lower hoisting block 9, or as a multi-fall hoisting rope. These configurations are known in the art of lifting devices.

When lifting and/or lowering a load from a fixed marine structure to a floating marine structure or vice versa, or between two floating marine structures, one marine structure is moving with respect to the other marine structure, e.g. due to environmental influences such as waves or swell and there is relative motion between the two marine structures and thus between the load and the target marine structure. These relative motions, in particular the relative vertical motions, also called heave motions, such as wave induced motions, may restrict the hoisting operation and may make the hoisting operation more difficult and/or more complex.

To, at least partly, compensate the relative motions, a motion compensation system 10 is provided. The motion compensation system 10 is here mounted to the lifting device 2. The motion compensation system 10 can be removable mountable to the lifting device 2, or can be fixedly mountable to the lifting device 2. For example, the motion compensation system 10 can be mounted to the lifting device 2 during on-site activities, but can be removed and stored during transport to/from the offshore site, e.g. during transport from yard to/from offshore site or during transport between subsequent offshore sites. Also, when multiple lifting devices are present on the marine structure, the motion compensation system 10 may be used for one operation on a first lifting device and for another operation on a second lifting device. Advantageously, the motion compensation system 10 or at least a part thereof is removable mountable on the respective lifting device.

The motion compensation system 10 comprises an actuation mechanism 11 and a linkage mechanism 12 couplable to the actuation mechanism 11. In use, as shown in the embodiment of Figure la, the linkage mechanism 12 is connected to the actuation mechanism 11 at a first end 12a and to the hoisting rope 4 at an opposite second end 12b. Where the end 12b connects to the hoisting rope 4, a linkage mechanism connection 13 is obtained. The linkage mechanism 12 is here embodied as an arm 12 between the first end 12a and the second end 12b.

The actuation mechanism 11 is separate from the hoisting winch 5 and only imparts movement of the linkage frame 12. By moving the linkage frame 12, the hoisting rope 4 is moved locally, at the linkage mechanism connection 13 with the linkage frame end 12b, preferably in a direction at least partly transverse to a rope main loading direction H. The rope main loading direction H is understood to be the main direction along which the hoisting rope 4 is reeved at a section 21 of the reeving system 3 containing the linkage mechanism connection 13. By imparting a, relative small, displacement in a direction at least partly transverse to the rope main loading direction H, the hoisting rope 4, the lower hoisting block 9 is being moved up or downwards in reaction to and/or in anticipation of relative motions.

By providing a motion compensation system 10 that is separate from the hoisting rope 4 of the lifting device 2, the actuation mechanism 11 can be smaller than the hoisting winch 5. Since the actuation mechanism 11 only needs to impart movement of the hoisting rope 4 and does not need to overcome the lifting force to move the lower hoisting block, as in conventional motion compensator systems that are integrated in the hoist reeving system.

Advantageously, the actuation mechanism 11 comprises an active part 11a and a passive part lib. The passive part is arranged for storing and retrieving energy during hoisting and/or lowering, while the active part is arranged for imparting the active motion on the hoisting rope 4. By providing a passive part, instead of compensating the relative motion fully in an active way, a part of the relative motion can be compensated in a passive way, thereby rendering the required active energy smaller and thus the active part smaller. The active part and the passive part are typically coupled to each other. Actuation mechanisms comprising an active part and a passive part are well-known by the person skilled in the art. For example, such an actuation mechanism may comprise a hydraulic cylinder as active part 11a and a gas accumulator lib as passive part, as schematically represented in Figure la. When a piston rod of the hydraulic cylinder extends, a passive oil compartment is moved thereby reducing the total passive gas volume, which in turn increases the force acting on the piston, and vice versa. An hydraulic actuation mechanism 11 may be similar to a conventional hydraulic motion compensator system, albeit, according to the invention, it is separate from the hoisting reeving and not integrated with the hoisting reeving and thus can be smaller than the hoisting winch. In the context of this disclosure, the actuation mechanism 11 is understood to comprise an active part 11a with or without a passive part lib.

In the embodiment shown in Figure la, the actuation mechanism 11 is arranged at or on a platform associated with the lifting device 2. The actuation mechanism 11 is preferably mounted onto a mounting surface 2a such as a slewing platform or a main winch platform or any other platform away from the boom. Alternatively, as shown in Figure 2a or Figure 2b, the actuation mechanism 11 can be mounted on a hoisting arm, such as a boom 7, which is possible when the complete motion compensation system 10 is sufficiently compact with respect to dimensions and weight that it fits onto the boom. Alternatively, mounting the cylinders on the crane arm, e.g. the boom, and using then lines via the boom to another location where e.g. the passive part, such as a gas accumulator is positioned, may also be possible. The lines may be hydraulic fines when using a gas accumulator as passive part.

As in conventional motion compensator systems, the active part is controlled by a motion reference unit. The motion reference unit detects the relative motions and/or receives input from detection means regarding the relative motions. The motion reference unit further determines the actuation force and/or actuation motion required to compensate at least some of the relative motion.

In Figure 2a as well, the linkage mechanism 12 is embodied as an arm 12 between the first end 12a and the second end 12b. When the actuation mechanism 11 is actuated, the arm 12 moves and displaces the linkage mechanism connection 13 in a direction transverse to the rope main loading direction H. In the embodiment of Figure 2a, the rope main loading direction H is the direction of the section 21 of the reeving system 3 containing the linkage mechanism connection 13.

The embodiments of Figure la and Figure 2a may require substantial displacement at the linkage mechanism connection 13 in case the reeving system 4 contains multiple falls. To reduce the displacement the section 21 of the reeving system 3 containing the linkage mechanism connection 13 can be made as a multi-fall section. Figure lb and Figure 2b provide examples of such a multi-fall section 21. The linkage mechanism 12 of the motion compensation system 10 is here schematically represented as an arrow R indicating the direction of the displacement to be imparted in a direction transverse to the main hoisting rope direction H of the section 21.

In an advantageous embodiment, as shown in Figure 3 and Figure 4, the motion compensation system 10 further comprises a wire rope 14 that, in use, connects the actuation mechanism 11 with the hnkage mechanism 12, here an arm 12. The first end 12a of the linkage frame 12 connects to the wire rope 14, while the second end 12b of the hnkage frame 12 connects to the hoisting rope 4 to move the hoisting rope 4 locally at the linkage mechanism connection 13 in a direction at least partly transverse to the main hoisting rope direction H. The wire rope 14 is independent of the reeving system 3.

By providing a wire rope 14, independent of the reeving system 3, a greater flexibility in mounting and/or removing of the motion compensator system 10 can be obtained. Also, by providing the wire rope 14, and more in particular, by reeving the wire rope 14 along one or more pulleys 15, a further reduction in the dimensions and/or weight of the actuation mechanism 11 can be obtained, which may be advantageous with respect to installation and/or storing of the motion compensation system 10. Similar to the embodiments shown in Figures lb and 2b, the embodiments of Figure 3 and Figure 4 can be provided with a multi-fall section 21 to reduce the imparted displacement at the connection point 13.

The linkage frame 12 can be a single bar frame, such as the arm as for example shown in Figures 1-4. The bar can be a straight bar or a curved bar or an angled bar, many variants are possible. The bar frame may act as a lever frame when mounted to the wire rope 13 at the first end 12a and to the hoisting rope 4 at the second end 12b. The bar frame 12 may be connected to the hoisting rope 4 at any position of the hoisting reeving.

In an advantageous embodiment, the linkage frame 12 is connected to the hoisting rope 4 at the part 4a of the hoisting rope between the upper hoisting block 8 and the lower hoisting block 9, the general principle of which is shown in Figure 5. Figure 5 does not show the linkage frame, but the linkage frame is schematically represented with arrows R. When a multi-fall hoisting rope section 4a is provided, the linkage frame R can advantageously be mounted in between approximately parallel falls 4al, 4a2 of the multi-fall hoisting rope section 4a. In Figure 5, the linkage mechanism is schematically drawn as an arrow R showing the direction of the displacement to be imparted on the linkage mechanism connections 13, more or less transverse to the main -loading direction H. The main loading direction H is the intended hoisting direction of the hoisting rope 4 at the section 21 containing the linkage mechanism connections 13. Here, the section 21 of the reeving system 3 is the same as the multi-fall section 4a of the reeving system 3 connecting to the lifting gear 6. Here, the main loading direction H is the direction between the upper hoisting block 8 and the lower hoisting block 9, i.e. in vertical direction. The displacement to be imparted in the direction R is therefore in horizontal direction. By imparting a displacement in a direction R transverse to the rope main loading direction H, a displacement of the lifting gear 6 can be obtained to compensate and/or anticipate on relative motions of the lifting gear 6.

The linkage mechanism can be for example a T-bar frame, not shown in the figures, of which one end is connected to the wire rope 14 and both other ends of the T-bar frame are connected to the falls 4al and 4a2 respectively providing the linkage frame connection. The ends of such a T-bar frame providing the linkage frame connection move the falls 4a 1 and 4a2 apart from each other at the hnkage frame connection and are preferably pivoting with respect to each other. By actuating one end of such a T-bar frame, both other ends may move to and/or from each other thereby moving the linkage frame connections to and/or from each other as well, thus imposing an up and/down movement on the lower hoisting block 9 to compensate at least part of the relative motions.

In another example, shown in Figure 6, the linkage frame 12 may be a four bar linkage frame. The four bar linkage frame 12 is, in use, mounted between the falls 4a 1, 4a2 of the multi-fall section 4a of the hoisting rope 4 between the upper hoisting block 8 and the lower hoisting block 9. The four bar hnkage frame 12 comprises four bars that are hingedly connected to each other, thus providing four corners as hinge joints.

In the embodiment of Figure 6, the linkage frame 12 is shown located near the upper hoisting block 8, but alternatively, the linkage frame 12 can be located near the lower hoisting block 9 as well. The geometry of the four bar linkage frame 12 resembles here a diamond shape having four corners 12a, 12bl, 12b2 and 12c and four bars 16a, 16b, 16c, 16d which are hingedly connected with respect to each other. The four corners 12a, 12b 1, 12b2, 12c are arranged as a hinge between adjacent bars. It is advantageous to have the four bars 16a, 16b, 16c, 16d approximately the same length, in which the actuation force at corner 12a is almost constant when it moves up and down. Other variants having the four bars different lengths or pair wise approximately the same lengths are also possible.

The linkage frame 12 is connected via the wire rope 14 with the actuation mechanism 11. The first end 12a of the linkage frame 12 is connected to the wire rope 14, while other ends, the corners 12b 1 and 12b2 are connected to the hoisting rope 4 and form the hnkage frame connections 13a 1 and 13a2 respectively. With the fourth end, corner 12c, the linkage frame 12 is mounted to the upper hoisting block 8. By movement of the wire rope 14, the corner 12a is moved up and/or downwards, such that, due to the pivoting arrangement, the corners 12b 1 and 12b2 are moved towards and/or away from each other. By moving the corners 12b 1 and 12b2 towards and/or away from each other, the falls 4al and 4a2 of the multi-fall rope section 4a are moved more or less apart from each other, thus the lower hoisting block 9 is moved up or down.

The main hoisting direction H can be understood to be the main direction between the upper hoisting block 8 and the lower hoisting block 9 with the lifting hook 6, which here typically will be approximately vertical. By moving the corners 12b 1 and 12b2 towards and/or away from each other, the linkage frame connections 13al and 13a2 move in a direction substantially transverse to the main hoisting rope direction H, for example in a direction mainly horizontally sideways.

By providing the motion compensation system 10 separate from the hoisting rope reeving 3, a smaller actuation force may be sufficient, to impart motion on the lifting gear 6 to compensate at least partly the relative motion.

Figure 6 gives a two-dimensional schematic representation of a marine structure 1 with a lifting device 2 according to the invention. The linkage frame 12 is here shown as a two-dimensional structure as well, having hinge corners 12a, 12bl, 12b2, 12c providing for planar movement. A real structure will typically be a three-dimensional structure, e.g. each fall 4al, 4a2 may be a fall string comprising multiple parallel hoisting ropes.

The linkage frame 12 may then be connected to each hoisting rope of the fall string at both sides of the multi-fall section 4a, thus implying that the linkage frame is a three-dimensional structure as well. However, the hinged corners provide for planar motion also of the three-dimensional structure. The hinged corners allow for a single degree of rotational freedom of motion. An embodiment of a spatial three-dimensional linkage frame is shown in Figure 10.

Figure 7 shows a motion compensation system 10 with a four bar linkage frame 12 mounted between the falls 4al, 4a2 of the multi-fall hoisting rope section 4a of the hoisting rope. The actuation mechanism 11 is here mounted remote from the linkage frame 12, and is connected to the linkage frame 12 with the wire rope 14. The wire rope 14 is, according to the invention, independent from the reeving system 3, as in the other embodiments. In the embodiment of Figure 7, the passive part lib of the actuation mechanism 11 is provided by a raised ballast weight that can move up and down and that, contrary to the prior art is independent from the hoisting reeving system 3 as well. The ballast weight lib is only connected to the wire rope 14 and as such provides potential energy for the actuation of the linkage frame 12 to compensate for relative motion.

Instead, of gas accumulator as passive part, the passive part may be provided as a raised ballast weight, which can move up and down, to store and retrieve potential energy as passive energy, as is shown in Figure 7. Providing a ballast weight lib as a passive part, which separate from the hoisting reeving, can be understood to be an invention on its own. As shown in Figure 7, the raised ballast weight can move up and down along guide rails. Here, the guide rails are mounted on the lifting device. According to the invention, the ballast weight is part of the wire rope and is independent from the reeving system. The active part 11a of the actuation mechanism 11 may be provided by an active winch.

In the embodiment of Figure 8, the wire rope 14 comprises two parts 14a, connected to the active part 11a of the actuation mechanism 11, and 14b connected to the linkage frame 12. By reeving the wire ropes 14a, 14b around pulleys 15, the actuation force may be reduced further to limit, the size and weight of the active part 11a and/or the passive part lib. The active part 11a is here schematically represented as an active winch 11a, but can be a hydraulic cylinder or any other actuation mechanism. In the embodiment of Figure 8 it is also shown that the wire rope 14b is attached to the corners 12c and 12a to be sheaved over a pulley 15a at the end 12a so the force in the wire rope 14b may be reduced more to obtain a similar displacement of the corner 12a.

The embodiment shown in Figure 9 mainly corresponds with the embodiment shown in Figure 8, while in Figure 9 an additional configuration for hook-up operation is shown. During hook-up, the load is not yet connected to the lifting hook 6, using the energy of the passive part lib is too much for an empty lifting hook 6. In such a situation, the passive part lib is preferably temporarily disconnected and kept stationary. After the load is hooked on, the passive part lib is then connected to contribute to the passive energy for compensating at least partly the relative motions.

Figure 9 shows an embodiment of such a releasing/locking mechanism, also called hook-up configuration 19 comprising a block 17 movable engaged in a housing 18 and connected with wire ropes 14a and 14b. The movable block 17 may move up and down in the housing 18, e.g. sliding or via rails or guides, etc. In a hook-up situation, the ballast weight is disconnected from the motion compensation system 10, for example by being braked or locked. During hook-up, the passive part of the compensation energy is provided by the block 17, which is much smaller than the ballast weight lib. When a load is hooked up on the lifting hook 6, more passive energy may be required to compensate for relative motion, e.g. during lifting of the load. Then the passive weight lib is reconnected to the motion compensation system, e.g. be removing the braking action and/or removing the locking action, the block 17 may then be positioned at an upper end of the housing 18.

Figure 10 shows a schematic perspective view of a linkage frame 12 mounted to a reeving system 3. The linkage frame 12 is a spatial three-dimensional structure mounted between a right fall string 4a 1 and a left fall string 4al. Each fall string 4al, 4a2 comprises multiple hoisting ropes 4 as well and the linkage frame 12 is connected to each hoisting rope 4, as can be seen in Figure 10. Sheaves 22 are provided to connect to each of the hoisting ropes 4. The linkage frame 12 is here arranged near the upper hoisting block 8 between the upper hoisting block 8 and the lower hoisting block 9 of the section 4a of the hoisting reeving system 3. The lifting gear 6, here a lifting hook 6, is connected to the lower hoisting block 9. The linkage frame 12 is here a multi-bar linkage frame 12 comprising at least four bars hingedly connected to each other allowing for one degree of rotational motion between adjacent bars. In Figure 10 can be seen that the additional wire rope 14 is independent of the hoisting reeving 3 and is connected to the linkage frame 12 for actuating the linkage frame 12. The actuation mechanism 10 is not shown in Figure 10. In Figure 10, four hoisting ropes 4i, 4ii, 4iii, 4iv, are shown, such that a relatively large load may be hoisted which are splitted beyond the sheaves 22 to improve load bearing capacities of the reeving system 3.

The invention is explained in the above example by means of a crane as a hoisting device. The hoisting device can of course also be a hoisting device that holds a drilling string or a dredging head. The reeving system of such a hoisting device can then be arranged between the hoisting winch or hoisting cylinder and the lifting gear, e.g. the hook of the drilling string or dredging head. The motion compensation system provided is similar to the ones described above. According to the invention a linkage mechanism can be provided that connects to the hoisting rope to impart a substantially transverse motion to the hoisting rope at the linkage mechanism connection with respect to the rope main loading direction. An actuation mechanism is coupled to the linkage mechanism to actuate the linkage mechanism. According to an aspect of the invention a wire rope independent of the reeving system can be provided to connect the actuation mechanism with the linkage mechanism.

Many variants will be apparent to the person skilled in the art. The invention is not limited to the above shown examples. The invention is explained by means of a hoisting device, but the motion compensator system is equally well suitable as a drilling string compensator or a dredging compensator. All variants are understood to be comprised within the scope of the invention defined in the following claims.

List of numbers 1 marine structure la deck lb legs lc water surface 2 lifting device 2 a lifting device platform 2b foundation structure 3 reeving system 4 hoisting rope 4a, 4a 1, 4a2 falls 4i, 4ii, 4iii, 4iv hoisting ropes 5 hoisting winch 6 lifting gear 7 boom 8 upper hoisting block 9 lower hoisting block 10 motion compensation system 11 actuation mechanism 11a active part of actuation mechanism lib passive part of actuation mechanism 12 linkage mechanism/linkage frame 12a first end of linkage mechanism 12b, 12bl, 12b2, 12c second end of linkage mechanism 13 linkage mechanism connection on hoisting rope 14, 14a, 14b wire rope 15, 15a, 15b pulleys 16, 16a, 16b, 16c, 16d bars 17 block 18 housing 19 hook-up configuration 20 load 21 section of reeving system comprising linkage mechanism connection 22 sheaves of linkage frame H hoisting rope main loading direction R schematic representation of hnkage mechanism

Claims

A motion compensation system adapted for mounting on a lifting device, comprising a locking system with at least one hoist rope, comprising a lifting tool for connection to a load, for compensating for relative movements, in particular for relative vertical movements, wherein the motion compensation system is a drive mechanism and a coupling mechanism comprises for connection to the hoist rope at a coupling mechanism connection, wherein, during use, the driving mechanism is coupled to the coupling mechanism and the coupling mechanism is connected to the hoisting rope at the at least one coupling mechanism connection, before, during use, transferring to driving force of the driving mechanism via the coupling mechanism to the hoist rope to move the hoist rope locally at the coupling mechanism connection in a direction which is substantially transverse to a rope-main loading direction to effect displacement of the lifting tool n to compensate for relative movement.

A motion compensation system according to claim 1, wherein the coupling mechanism comprises a coupling frame which is adapted for connection to the hoist rope at the at least one coupling mechanism connection.

A motion compensation system according to claim 2, wherein the coupling frame comprises a multi-rod coupling frame.

A motion compensation system according to claim 3, wherein the rods of the coupling frame are hinged to each other.

A motion compensation system according to claim 3 or 4, wherein the coupling mechanism comprises a four-rod coupling frame, the four rods of which are hingedly connected to each other to form a diamond-shaped coupling frame.

A motion compensation system according to any one of the preceding claims, further comprising a connecting rope, independent of the shearing system, for connection between the driving mechanism and the coupling mechanism for transferring the driving force via the connecting rope.

A motion compensation system according to any one of the preceding claims, comprising an active part for active compensation of relative movements and a passive part for storing and retrieving energy from lifting and / or lowering.

The motion compensation system of claim 7, wherein the passive member comprises a ballast weight that is movable up and down.

A motion compensation system according to claim 7 or 8, further comprising a locking mechanism for uncoupling the passive part of the system during hooking up of a load or releasing a load.

A motion compensation system according to any one of the preceding claims, further comprising a motion reference unit, adapted to detect relative movements, to control the drive mechanism.

11. Lifting device comprising a locking system with at least one hoist rope comprising a lifting tool for connection to a load, the lifting device comprising a movement compensation system for compensating for relative movements comprising a drive mechanism and a coupling mechanism connected to the hoisting rope at a coupling mechanism. that, during use, to transfer driving force from the driving mechanism via the coupling mechanism to the hoist rope to locally move the hoist rope at the coupling mechanism connection in a direction that is substantially transverse to a rope-main loading direction.

12. Lifting device as claimed in claim 11, wherein the coupling mechanism is at least partially releasably connected to the hoist rope.

The lifting device of claim 11 or 12, wherein the motion compensation system further comprises a connecting rope connecting the drive mechanism to the coupling mechanism, the connecting rope being separate from the hoist rope.

14. Lifting device as claimed in any of the claims 11-13, wherein the shearing system comprises a plurality of parallel hoist ropes, wherein the coupling mechanism is adapted for connection to each hoist rope.

15. Lifting device as claimed in any of the claims 11-14, wherein the coupling mechanism comprises a multi-rod coupling mechanism with a hinged connection between at least two rods.

16. Lifting device as claimed in claim 15, wherein the coupling mechanism comprises a four-rod coupling mechanism which is arranged between two opposite hoist ropes of multi-fall hoist ropes.

17. Lifting device as claimed in any of the claims 11-16, wherein the coupling mechanism is arranged near an upper pile driver of the lifting device.

A fixed maritime structure comprising a lifting device according to any one of claims 11 - 17.

A floating maritime structure, comprising a lifting device according to any one of claims 11 - 17.

20. Dredger provided with a motion compensation system according to one of claims 1-10 and / or with a lifting device according to one of claims 11-17.

An offshore drilling structure provided with a motion compensation system according to one of claims 1-10 and / or with a lifting device according to one of claims 11-17.

22. Method for providing a motion compensation system on a lifting device comprising a mooring system with at least one hoist rope comprising a lifting tool for connection to a load, the method comprising: - provided with a motion compensation system according to any one of claims 1-10; - connecting the coupling mechanism to the hoist rope at the coupling mechanism, and - placing the drive mechanism to cooperate with the coupling mechanism to transfer, during use, driving force from the drive mechanism via the coupling mechanism to the hoist rope.

The method of claim 22, further comprising: - providing a connecting rope, independent of the shearing system, to connect the drive mechanism to the coupling mechanism.

24. Method for compensating for relative movements of a lifting tool of a lifting device connectable to a load, the lifting device comprising a locking system with at least one hoist rope, provided with a movement compensation system according to one of claims 1 to 10; - connecting a coupling mechanism of the motion compensation system to the hoist rope; - driving the coupling mechanism to effect displacement of the hoist rope in a direction substantially transverse to a rope-main loading direction.

The method of compensating for relative movements according to claim 24, further comprising - driving the motion compensation system during hooking, lifting or releasing a load.

26. A method for compensating for relative movements according to claim 24 or 25, further comprising - provided with a connecting rope, independent of the locking system, to connect the drive mechanism to the coupling mechanism.

The method of any one of claims 24 to 26, further comprising - compensating for the relative movements during a dredging operation, or a drilling operation or a subsea mining operation.