DK201800520A1

DK201800520A1 - A method of compensating motion of a vessel for an object

Info

Publication number: DK201800520A1
Application number: DKPA201800520A
Authority: DK
Inventors: Andersen Gad Jens; Rensch-Jacobsen Filip
Original assignee: Maersk Supply Service A/S
Priority date: 2018-08-31
Filing date: 2018-08-31
Publication date: 2019-08-29

Abstract

A method of compensating motion of a vessel for an object comprises supporting the object at a first position on the object with a first adjustable arm moveably mounted to the vessel and supporting the object at a second position on the object with a second adjustable arm moveably mounted to the vessel. The method also comprises determining motion of the object with respect to at least one reference, moving the first adjustable arm and / or the second adjustable arm with respect to the vessel based on the determined motion; and compensating for relative motion between the object and the at least one reference such that the object is stable relative to the at least one reference.

Description

A method of compensating motion of a vessel for an object

The present invention relates to a method of compensating motion of a vessel for an object.

In order to reduce the dependence on limited fossil fuel resources around the world, there has been an increasing demand for renewable energy generation. One such source of renewable energy that has become increasingly reliable is wind energy generation.

Typically electricity is generated from the wind with wind turbine generators (WTG) installed in locations with a reliable prevailing wind. Some wind turbine generators have been installed on land in windy areas such as on hilltops. Wind turbine generators installed on land are also known as “onshore” wind turbine generators.

In recent times, the trend has been to install bigger and taller wind turbines. This increases the area that the blades of the wind turbine sweep through and increases the total potential energy production. In addition, by positioning the blades higher into the atmosphere, the wind blows more steadily, and the wind turbine blades are further from objects that may cause turbulent airflow.

The feasibility of the construction of onshore wind turbine generators can be affected by the local population objecting to the noise and other environmental impact. Accordingly, larger wind turbine generators can be installed in coastal waters. Wind turbine generators installed in coastal waters, the sea or deep ocean are also known as “offshore” wind turbine generators.

The complexity of installing offshore wind turbine generators is greatly increased with respect to installing onshore wind turbine generators. For example, the materials and structure of the offshore wind turbine generators must be transported to the installation site with a suitable vessel. Furthermore, the offshore wind turbine generator must be anchored securely in position.

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In this way, offshore wind turbine generator installation is typically carried out in separate stages. One current method of installation is to anchor a foundation to the seabed using a monopile foundation. This is a steel and / or concrete tube which is fixed to and protrudes from the seabed. A transition piece (TP) is fixed to the monopile foundation and the transition piece projects out of the water. The offshore wind turbine generator is then fixed to the transition piece.

WO2014/070024 discloses a method of installing an offshore wind turbine generator is using a jack-up vessel. The jack-up vessel comprises legs that extend down to and engage with the seabed. The jack-up vessel comprises a crane sufficiently tall to receive and install pre-assembled offshore wind turbine generators to the transition piece. A problem with a jack-up vessel is that not all types of seabed are suitable for receiving the extended legs which means this vessel cannot be operated in all coastal waters. Furthermore, the jack-up vessel is very sensitive to adverse weather which means operation of the jackup vessel is restricted to calm weather windows.

WO2007/091042 discloses an alternative method of installing an offshore wind turbine generator using a crane mounted on a vessel. In order to install the largest wind turbine generators, the crane must be suitably massive. Similar to a jack-up vessel, a crane mounted vessel is also sensitive to adverse weather conditions during operation. Another problem is that the vessel must not collide with the foundation or transition piece and this means that the vessel must operate at a safe distance. This means the height of the crane is increased even further so that the crane has sufficient outreach whilst the vessel is positioned at a safe distance from the transition piece.

Another alternative method of offshore wind turbine generator installation is contemplated in WO2017/055598. This discloses installing separate parts of a wind turbine generator with a crane mounted to part of the tower. The crane is initially winched onto the tower from a barge from a motion compensated foot. A problem with this arrangement is that the crane is not motion compensate during the entire transfer of the crane. In addition the cable must be preattached to the tower in order for the crane to be winched onto the tower. This

DK 2018 00520 A1 means that the vessel must be in close proximity to the foundation and transition piece because otherwise the crane will be immersed in water during the winching operation.

It is undesirable for the vessel to be in immediate proximity of the foundation piece for a protracted period of time because this increases the risk of collision of the vessel with the foundation and transition piece.

Motion compensation is described in WO2018030897 using a crane, for transferring equipment to a second vessel. However, a problem with this arrangement is that the load must be suspended underneath the crane arm. This means that the crane must always be taller that the target destination and the crane arm is unsuitable for lifting loads into confined spaces.

Embodiments of the present invention aim to address the aforementioned problems.

According to an aspect of the present invention there is a method of compensating motion of a vessel for an object comprising: supporting the object at a first position on the object with a first adjustable arm moveably mounted to the vessel and supporting the object at a second position on the object with a second adjustable arm moveably mounted to the vessel; determining motion of the object with respect to at least one reference; moving the first adjustable arm and / or the second adjustable arm with respect to the vessel based on the determined motion; and compensating for relative motion between the object and the at least one reference such that the object is stable relative to the at least one reference.

Optionally, the at least one reference is a fixed reference point.

Optionally, the at least one reference is a moving reference point.

Optionally, the compensating comprises determining the relative motion of the object with respect to the vessel.

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Optionally, the compensating comprises adjusting the position of the object with respect to the vessel in one or more directions to compensate for heave, sway, surge, roll, pitch and / or yaw motion of the vessel.

Optionally, the compensating comprises matching the movement of the object with movement of the at least one reference.

Optionally, the determining comprises receiving information from one or more sensors detecting relative motion between the object and the at least one reference.

Optionally, the object is a crane and the at least one reference point is an offshore wind turbine generator.

Optionally, the object is a container and the at least one reference point is a suspended load.

Optionally, the adjustable arms are extendable and / or pivotable with respect to the vessel.

Optionally, the adjustable arms are independently controllable.

Optionally, the first and / or the second adjustable arm comprises an actuator for rotating the object about an axis.

Optionally, the first and second adjustable arms are mounted on a motion compensated platform arranged to compensate for relative motion between the object and the at least one reference.

Optionally, the first and second arms are mounted on opposite sides of the object.

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Optionally, the centre of gravity of the object is positioned on or below a straight line between the mounting points of the first and second arms.

According to another aspect of the invention there is a vessel comprising: a first adjustable arm moveably mounted to the vessel and arranged to support an object at a first position on the object; a second adjustable arm moveably mounted to the vessel and arranged to support the object at a second position on the object; at least one actuator coupled to each of the first and second adjustable arms for moving the first and second adjustable arms with respect to the vessel; at least one sensor arranged to sense motion of the object; and a controller configured to determine motion of the object with respect to at least one reference based on received information from the at least one sensor and to send control instructions to the at least one actuator to move the first adjustable arm and / or the second adjustable arm with respect to the vessel based such that the object is stable relative to the at least one reference.

Various other aspects and further embodiments are also described in the following detailed description and in the attached claims with reference to the accompanying drawings, in which:

Figure 1 shows a side view of a vessel in the proximity of a wind turbine generator;

Figure 2 shows a schematic perspective view of a vessel;

Figure 3 shows a side view of a vessel with a crane in a first position according to an embodiment;

Figure 4 shows a close up perspective view of the vessel in a first position according to an embodiment;

Figure 5 shows a close up perspective view of the vessel in a first position according to an embodiment;

Figure 6 shows a side view of a vessel according to an embodiment;

Figure 7 shows a schematic plan view a vessel with a crane according to an embodiment; and

Figure 8 shows a flow diagram of a method of compensating motion of a vessel for an object.

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Figure 1 shows a side view of a vessel 100 in the proximity of a wind turbine generator (WTG) 102. For the purposes of clarity, the WTG 102 is not drawn to scale and the broken portions of the WTG 102 represent missing portions of the WTG 102. The WTG 102 comprises a foundation 104 anchored to the seabed 106. The foundation 104 is a steel and / or concrete tube which is fixed to and protrudes from the seabed 106. Typically the foundation 104 engages with the seabed 106, but in some embodiments the foundation can be floating where the ocean is particularly deep. In other embodiments, other types of foundation 104 can be used including, but not limited to: monopile foundations, tripod foundations, jacket foundations, space-type foundations, floating foundations and / or gravity-based structure foundations.

A transition piece (TP) 108 is fixed to the monopile foundation 104 and the transition piece 108 projects out from the surface of the water 110. The transition piece 108 comprises access ladders (not shown) for access to the WTG 102 from a boat. The transition piece 108 further comprises a platform 112 and a door 114 for internal access to the WTG 102.

The WTG 102 comprises a tower 116 which is fixed to the transition piece 108. The tower 116 can be a unitary element or can be constructed from a plurality of tower segments. A nacelle 118 is rotatably mounted on the top of the tower 116. The nacelle 118 can rotate about the vertical axis A-A of the tower 116. The nacelle 118 houses a generator (not shown) for converting the rotation of a hub 120 and blades 122 into electrical energy. There may a plurality of blades 122 connected to the hub. The generator is connected to an electrical substation via one or more cables (not shown). Access to the nacelle 118 can be achieved via an internal set of stairs (not shown).

Each of the elements of the WTG 102 is installed with the vessel 100, which will be described in further detail below.

The vessel 100 as shown in Figure 1 is a subsea supply vessel. In other embodiments the vessel is another type of vessel including but not limited to an

DK 2018 00520 A1 anchor handling tug supply (AHTS) vessel, a platform supply vessel (PSV), multipurpose support vessel (MSV), a tug boat, a barge or any other suitable vessel for installing WTGs 102.

The vessel 100 can be used for various marine operations such as anchor handling, towing, supply of offshore installations, and fire-fighting. The vessel 100 comprises one or more winches (not shown) for handling towlines and anchors of offshore installations such as oil rigs. The vessel 100 comprises an open aft portion 124 for storing and managing anchors.

In some embodiments, the aft portion 124 is used for stowing one or more parts of the WTG 102. In some embodiments, the aft portion 124 can be used to store disassembled parts 302, 304, 306 of the tower 116 (as shown in Figure 3), the nacelle 118, the hub 120 and / or the blades 122. In other embodiments, disassembled parts of the WTG 102 can be stowed on a separate vessel (not shown) such as a barge which is positioned close to the vessel 100 when the WTG 102 is being installed.

Figure 1 shows that the open aft portion 124 is clear from anchors and towlines for the purposes of clarity. The open aft portion 124 may comprise one or more cranes (not shown) fixed to the structure of the vessel 100 for lifting and moving objects. The vessel 100 can use the winch together with a towline for towing the barge or other floating structures, if required. Alternatively, the towline can be attached to a capstan or bollard secured to the deck 334 of the vessel 100 when towing the barge. The method of towing barges with a towline and vessel is known and will not be discussed in any further detail.

The vessel 100 comprises a plurality of propulsors for moving the vessel through the water. In some embodiments, the propulsors are one or more of the following: a propeller, a thruster, or an azimuth thruster. The vessel 100 can have any number or configuration of propulsors. The vessel 100 as shown in Figure 1 comprises two propellers 1002 (schematically represented in Figure 7). The propellers 1002 are both coupled to a diesel two stoke engine 1000 (schematically shown in Figure 7) or each propeller 1002 is coupled to a

DK 2018 00520 A1 separate diesel two stroke engine 1000. Alternatively, the two propellers 1002 can be driven by one or more diesel four stroke engines 1000. In other embodiments, the propulsors can be powered with a diesel electric engine with or without a direct coupling. Under normal sailing, the propellers 1002 are principally used for moving the vessel 100 in a direction towards the bow 126 of the vessel 100. When the propellers 1002 are reversed, the vessel 100 will move in a direction towards the stern 128. In some embodiments, the vessel 100 only has one propeller mounted along the centreline X-X (as shown in Figure 2) of the vessel 100.

A rudder 130 is positioned aftwards of each propeller 1002 for steering the vessel 100. The rudder 130 is used for directing a wash which is a mass of water moved by the propellers 1002. Each propeller 1002 can have a nozzle which is a hollow tube that surrounds each propeller 1002 for increasing the propulsive force of the respective propellers 1002.

The vessel 100 comprises plurality of bow thrusters 132, 134, 136 and a plurality of stern thrusters 138, 140, 142. Each of the bow thrusters 132, 134, 136 and the stern thrusters 138, 140, 142 are mounted in a tunnel 144. For the purposes of clarity, only one tunnel 144 has been labelled. The tunnel 144 is a hollow tube integral with the hull 146 of the vessel 100 and is open at both sides, e.g. port side and starboard side of the hull 146. This means a thrust force can be imparted at either side of the vessel 100. The tunnel 146 which is integral with the hull 146 of the vessel 100 maintains a compact form and reduces drag on the thrusters 132, 134, 136, 138, 140, 142 when the vessel 100 is moving forwards.

The bow thrusters 132, 134, 136 and the stern thrusters 138, 140, 142 provide a side force with respect to the vessel 100. In this way, the thrusters 132, 134, 136, 138, 140, 142 increase the manoeuvrability of the vessel 100. In some embodiments, the thrusters 132, 134, 136, 138, 140, 142 are driven by an electric motor 1004 (schematically shown in Figure 7). The electric motor 1004 is powered by a diesel engine which may be an auxiliary engine (not shown) in addition to the diesel engines 1000 driving the propellers 1002. Optionally, the

DK 2018 00520 A1 electric motor 1004 can also drive the propellers 1002. Alternatively, the electric motors 1004 can be powered from the same engine 1000 which drives the propellers 1002. Additionally or alternatively, the electric motors 1004 of the thrusters 132, 134, 136, 138, 140, 142 are powered by a battery (not shown). In other embodiments, the thrusters 132, 134, 136, 138, 140, 142 are driven by a diesel engine 1000 and gearing and linkages (both not shown) couple the engine 1000 to the thrusters 132, 134, 136, 138, 140, 142. In operation, one or more thrusters 132, 134, 136, 138, 140, 142 can generate a thrust on a side of the vessel 100. All the thrusters 132, 134, 136, 138, 140, 142 can generate a thrust on the same side of the vessel 100 or on different sides of the vessel 100.

In other embodiments, one or more of the propellers 1002 or the thrusters 132, 134, 136, 138, 140, 142 are replaced with azimuth thrusters 1006 (as shown in Figure 7). The azimuth thruster 1006 is housed in a pod and is also known as an “azipod”. The azipod 1006 is rotatable by an angle (azimuth) around a horizontal plane parallel with a main horizontal plane of the vessel 100. In this way, the azipod 1006 can direct thrust in any direction. Similar to the thrusters 132, 134, 136, 138, 140, 142, the azipods 1006 can be driven by an engine 1000 or an electric motor 1004.

Turning back to Figure 1, control of the vessel 100 is achieved by manual controls 1008 such as joysticks, helm, wheel etc. (shown schematically in Figure 7) located in the bridge 148. The bridge 148 is usually located in position such that the crew members have good visibility of the vessel 100 and the surrounding sea. The bridge 148 as shown in Figure 1 has 360 degree visibility of the sea surrounding the vessel 100. This means that crew members operating the vessel 100 can safely and easily control the vessel 100 irrespective of whether the vessel 100 is moving forwards, backwards or side to side. In other embodiments, the vessel can be autonomously controlled with a dynamic positioning module 1010 and a vessel control module 1012 (as shown in Figure 7). Use of the dynamic positioning module 1010 will be discussed in further detail together with Figure 7 below.

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Motion of the vessel 100 during operation will now be discussed in reference to Figure 2. Figure 2 shows a perspective schematic view of the vessel 100. The vessel 100 has three principle axis about which it can rotate, a longitudinal axis X-X, a transverse axis Y-Y, and a vertical axis Z-Z. Rotation about the longitudinal axis or centreline X-X of the vessel 100 is called roll. Rotation about the transverse axis Y-Y which is the perpendicular to the longitudinal axis X-X, is called pitch. Rotation about the vertical axis Z-Z is called yaw. In addition to rotational motion about the axes X-X, Y-Y and Z-Z, the vessel 100 can also experience translational motion along each of the axes. Translational motion about the longitudinal axis X-X, the transverse axis Y-Y and the vertical axis ZZ is respectively known as surge, sway and heave.

During operation of the vessel 100, motion compensation of the vessel 100 is carried out to compensate for one or more of roll, pitch, yaw, sway, surge, and heave. In order to compensate for the motion of the vessel 100, measurement of the motion of the vessel 100 is carried out by one or more sensors. Figure 2 schematically represents a pitch motion sensor, 200, a roll sensor 202, a yaw sensor 204, a surge sensor 206, a sway sensor 208 and a heave sensor 210.

In some embodiments, the sensors for detecting the motion of the vessel 100 can be accelerometers, gyroscopes, cameras, or any other suitable sensor for detecting motion of the vessel 100. In some embodiments, alternatively, or additionally the translation movement of the vessel 100 in a plane substantially parallel to the surface of the water is detected with a global positioning system (GPS) 1016 of the vessel 100. This means that the sway sensor 208 and the surge sensor 206 can optionally be omitted. The one or more sensors 200, 202, 204, 206, 208, 210 in some embodiments, can be one or more accelerometers for detecting motion in three perpendicular axes. In some embodiments, one or more sensors (not shown) can detect motion of the vessel 100 in all six degrees of freedom (roll, pitch, yaw, surge, sway, heave). The sensors 200, 202, 204, 206, 208, 210 are connected to a motion compensation module 1014. The motion compensation module 1014 determines the motion of the vessel 100 due to the wind and the waves based on the received sensor information.

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The compensating for the motion of the vessel 100 will be described in further detail below.

In addition, in some embodiments there may be one or more sensors 212 for detecting a reference. For example, the reference 214 may be the transition piece 108 of the WTG 102, or another vessel (not shown) or a load 600 suspended in the air (see Figure 6). Alternatively, the reference can be a part of another object or a beacon 400 placed on an object. The sensor 212 may be a camera or a video camera, or any other motion sensor for detecting motion of the reference 214 with respect to the vessel 100 and / or the support structure 332 described below.

Turning to Figure 3, the method of compensating motion of a vessel for an object 300 will be described in further detail. The object 300 can be any object which needs to remain stable and independent of the vessel 100 motion due to the wind and the waves. For the purposes of describing Figures 3 and 4, the object 300 is a crane 300.

In a first embodiment, compensation motion of a vessel is for a crane 300 to be transferred and mounted on a WTG 102. Figure 3 shows a side view of a vessel 100 with a crane 300 in a first position according to an embodiment. In the first position, the crane 300 is positioned at the aftmost part of the vessel 100. In the first position, the crane 300 is mounted on the deck 334 or positioned on a platform 324 mounted on the deck 334.

The crane 300 is mountable on a portion 308 of the WTG 102. The portion 308 of the WTG 102 is a first section 308 of the tower 116. The first section 308 has been installed and fixed to the transition piece 108 before the crane 300 is mounted on the WTG 102. In other embodiments, the crane 300 is mountable on other parts of the WTG 102 such as the transition piece 108 or the foundation 104.

The crane 300 comprises a crane body 310 engageable with the tower 116. In some embodiments the crane body 310 optionally comprises a first door, and

DK 2018 00520 A1 a second door (not shown) pivotally hinged to the crane body 310. The first and second doors, are arranged to move between a first position in which the doors in an open position and a second position in which the doors are in a closed position. In the open position, the crane body 310 can be positioned around the tower 116. In the closed position, the crane body 310 envelops the tower 116 and secures the crane body 310 to the tower 116. In some embodiments, as discussed below one or more other mechanisms for securing the crane body 310 to the tower 116 are additionally or alternatively used. In some other embodiments, the doors do not perform a securing function but instead when the doors are closed, the crane body 310 guides the vertical movement of the crane 300 on the WTG 102. The doors 900, 902 are actuated with hydraulic arms (not shown for clarity). The doors 900, 902 can be held together with a locking mechanism (not shown). The hydraulic arms can be connected to the vessel hydraulic system 1022.

In some other embodiments, the crane body 310 comprises a single pivotally hinged door (not shown). In other embodiments, the doors slide against the crane body. In yet other embodiments, the crane body 310 does not have doors. Optionally there is a strap or other securing mechanism which secures around the tower 116 when there are no doors.

The crane 300 comprises a boom 312 which is pivotally coupled to the crane body 310 at pivot 314. The crane 300 comprises one or more cables 316 which is coupled to a winch 318. The cable 316 is connected to yoke 320 for engaging with a load, such as a tower segment 302, 304, 306 to be lifted. The boom 312 projects laterally from the crane body 310 so that the load can be lifted clear from the crane body 310. In some embodiments, the boom 312 is optionally pivotally connected to an additional jib portion (not shown). The jib portion fixed to the boom 312 or is pivotally mounted to the boom 312 and increase the lateral reach of the crane 300.

In some embodiments, the crane 300 comprises a counterweight 322 positioned on the opposite side of the crane body 310 to the boom 312. In some embodiments, the counterweight 322 is a water filled container

DK 2018 00520 A1 suspended from the crane body 310. In this way, the counterweight 322 is emptied of water when the crane 300 is being transferred from the vessel 100 to the WTG 102. This reduces the weight of the crane 300 during the lift operation.

As mentioned previously, the crane 300 as shown in Figure 3 is mounted in a first position on the aftmost portion of the vessel 100. The crane 300 is removeably mounted on the stern 128 of the vessel 100. In some embodiments, the crane 300 is attached to the vessel 100 with quick release fixings. This means that the crane 300 can be fixed in place when the vessel 100 sails to the location of the WTG 102. Once the vessel 100 is in the proximity of the WTG 102, the crane 300 can be released from the vessel 100 and prepared for the transfer to the WTG 102. In some embodiments, the crane 300 is mounted on a moveable platform 324. The moveable platform 324 can be mounted on wheels or rails (not shown) on the deck 334 of the vessel 100. This means that the moveable platform 324 can undergo a translational movement on the deck 334 of the vessel 100. In this way, the crane 300 can be moved from a stowed position on the aft portion 124 of the vessel 100 to a transfer position at the aftmost part of the vessel 100 (as shown in Figure 3). The parts of the WTG stowed on the vessel 100 can also be mounted on moveable platforms (not shown) to move them from a stowed position to a position ready for transfer.

The crane 300 is releasably coupled to a support structure 332 arranged to suspend the crane 300 above the deck 334 of the vessel 100. The support structure 332 comprises a first adjustable arm 326 which supports the object 300 at a first position on the object 300. The support structure 332 further comprises a second adjustable arm 500 which supports the object at a second position on the object 300. The first and second adjustable arms 326, 500 are moveably mounted to the vessel 100. In some embodiments, the support structure 332 comprises a first adjustable arm 326 which is releasably engageable to a first side of the crane 300 and a second adjustable arm 500 (better viewed from Figure 4) releasably engageable to a second side of the crane 300.

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The first and second adjustable arms 326, 500 (as shown in Figure 4) are moveably mountable to the platform 324. In other embodiments, the adjustable arm 326 is moveably mounted on the vessel 100. In some embodiments, the adjustable arms 326, 500 are each pivotally mountable with first and second orthogonal pivoting joints 508. In other embodiments, the adjustable arms are mounted in ball and socket joints. In yet other embodiments, the adjustable arms 326, 500 can be moveably mounted using any suitable mechanism for permitting multiple degrees of freedom.

The adjustable arms 326, 500 are configured to pivot with respect to the longitudinal axis X-X of the vessel 100. In this way, the adjustable arms 326, 500 can increase the outreach of the crane 300 as the adjustable arms 326, 500 tends towards the horizontal.

Similarly, the adjustable arms 326, 500 are configured to pivot with respect to the vertical axis Z-Z of the vessel 100. Accordingly, as the vessel 100 experiences roll or pitch in the X-X axis or Y axis respectively due to waves, the adjustable arms 326, 500 can be moved to remain upright.

Optionally, the crane body 310 comprises one or more crane couplings 502. Figure 4 shows a first crane coupling 502 mounted on a first side of the crane body 310. The opposite side of the crane body 310 comprises a second crane coupling (not shown). The first and second crane couplings 502 are configured to mount the crane 300 to the support structure 332 during the transfer operation. In some embodiments, the first and second crane couplings 502 permit relative movement between the crane 300 and the support structure 332. In some embodiments, the crane couplings 502 permit pivotal movement of the crane 300 about the centre axis B-B of the crane couplings 502. This means that as the angle between the adjustable arms 326, 500 and the longitudinal axis X-X varies as the adjustable arms extend, the crane 300 pivots in the plane of the longitudinal axis X-X and the vertical axis Z-Z and the crane 300 remains vertical.

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In some embodiments, the first adjustable arm 326 and the second adjustable arm 500 are independently controllable. In this way, the first adjustable arm 326 can be moved with respect to the second adjustable arm 500. The relative movement between the first and second adjustable arms 326, 500 can be due to pivotal movement or extension of the telescopic arms. This means that the crane 300 can be tilted and rotated due to the relative movement between the first and second adjustable arms 326, 500. Where the first and second adjustable arms 326, 500 are independently controllable, the crane couplings 502 permit movement in more than one degree of freedom. In this way, the crane couplings 502 can be ball and socket joints or a plurality of orthogonal pivoting joints.

In some other embodiments, the crane couplings 502 only permit pivoting movement along the X-X axis. Accordingly, the relative movement of crane 300 with respect to the adjustable arms 326, 500 is constrained. Instead, the support structure 332 is mounted on a motion compensated platform 324. This means that the roll, pitch and heave can of the vessel is compensated by the platform 324. In this way, the pivoting movement of the crane 300 about axis B-B is to compensate for the change in angle of the adjustable arms 326, 500 as the adjustable arms 326, 500 extend from the first position to the second position.

Referring back to Figure 3, in some embodiments, the platform 324 is rotatable with respect to the vessel 100 about an axis parallel with the Z-Z axis of the vessel 100. Indeed, the platform 324 comprises a rotatable bearing (not shown) mounted on the deck 334 of the vessel 100. In this way, the crane 300 can slew whilst mounted to the vessel 100.

Discussion of the method installing the crane 300 on the WTG 102 will now be discussed in reference to Figures 3, 4, 7 and 8. Figure 7 is a schematic view of the components and control systems of the vessel 100. Figure 8 is a flow diagram of the method compensating motion of the vessel 100 for the crane

300.

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In order to transfer the crane 300 to the WTG 102, the crane 300 is suspended in the support structure 332. The support structure 332 will be further described in reference to Figure 4. Figure 4 shows a close up perspective view of the crane 300 mounted on the vessel 100. Figure 4 shows the adjustable arms 326, 500 are extended.

The adjustable arms 326 are telescopic and have extended from the first, transfer position as shown in Figure 3 to a second position in which the crane 300 is in a suspended position. As the adjustable arms 326, 500 extend, the crane 300 is moved closer to the tower 116. In some embodiments, the telescopic arms are hydraulically actuated. In other embodiments, the extension of the telescopic arms 326, 500 is carried out with a rack and pinion mechanism (not shown) or any other suitable mechanism. In some embodiments, the extension of the telescopic arms is controllable via a hydraulic system 1022 (as shown in Figure 7). The adjustable arms 326, 500 extend along their longitudinal axis. Optionally, the adjustable arms 326, 500 can also pivot with respect to the vessel 100.

In this way, the object, e.g. the crane 300 is supported on a first and second sides with the first and second adjustable arms 326, 500 as shown in step 1100 of Figure 8.

In the suspended position, the crane 300 is ready to be mounted on the tower 116 and can be positioned such that the crane body 310 is surrounding the tower 116. When the crane 300 is being suspended from the support structure 332, movement of the vessel 100 from the wind and the waves are exaggerated. Optionally, the boom 312 is in a horizontal position as shown in during transfer of the crane 300. Placing the boom 312 in a horizontal position can protect the crane 300 during the transfer of the crane 300 from the vessel 100 to the WTG 102. Accordingly, the doors of the crane body 310 have been closed and secured together.

Accordingly, the motion of the vessel 100 is compensated in order to keep the suspended crane stable relative to the tower 116. This means that the

DK 2018 00520 A1 movement of the vessel due to the waves and wind does not affect the position of the crane 300 with respect to the tower 116. Instead, translational movement of the crane 300 with respect to the tower 116 is due to transferring the crane 300 from the vessel 100 to the tower 116. In this way, the translational movement of the crane 300 is with respect to the tower 116 is due to the extension of the support structure 332 or from a controlled thrust of the vessel itself required to move the crane 300 closer to the tower 116.

Compensation for relative motion between the portion of the offshore wind turbine generator 102 and the vessel 100 is described in further detail with respect to Figures 7 and 8.

Turning to Figure 7, the vessel 100 comprises a plurality of different modules for controlling one or more aspects of the vessel 100. The modules may be implemented on hardware, firmware or software operating on one or more processors or computers. A single processor can operate the different module functionalities or separate individual processors, or separate groups of processors can operate each module functionality.

The vessel 100 further comprises modules for determining parameter information relating the vessel 100. Figure 7 is a non-exhaustive list of the different control modules of a vessel 100. The vessel 100 comprises a vessel control module 1012 for controlling the movement, positioning and orientation of the vessel 100 by sending instructions to the propulsors e.g. the propellers 1002, the thrusters 132, 134, 136, 138, 140, 142 and / or azipods 1006. The vessel control module 1012 can control one or more other aspects of the vessel 100 such as the motion compensation module 1014.

The vessel control module 1012 receives position information from a dynamic positioning module 1010. The dynamic position module 1010 receives positioning information from one or more inputs such as a global positioning system (GPS) 1016, global navigation satellite system (GLONASS) 1018, and a compass 1020 for determining the current position and heading of the vessel

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100. The GPS system 1016 can detect motion of the object with respect to a reference 102 as shown in step 1102.

The dynamic positioning module 1010 can receive additional positioning input information from other input sources, if required such as a WTG distance module 1026. The dynamic position module 1010 sends target position information to vessel control module 1012. The target position information received from the dynamic positioning module 1010 is position information for moving the vessel 100 from a current position to a desired target position of the vessel 100. For example, the target position information can be position information for maintaining the vessel 100 in a static position for the vessel 100 or a maintaining the vessel on a course or heading.

Additionally or alternatively, at least one beacon or 400 is placed on a surface of the WTG 102 for measuring the distance between the WTG 102 and the vessel 100 by the WTG distance module 1026. The beacon 400 can be passive and provide a surface which is better for reflecting the measurement signals e.g. light, radio waves, sound waves. In this way the beacon 400 can be made from a reflective material such as foil. In alternative embodiments, the beacon 400 can be active and send a signal to a distance sensor 1024 for measuring the distance. The distance sensor 1024 can be a laser range finder, LIDAR, a camera, radar, sonar or any other suitable sensor for measuring distance between the vessel 100 and the WTG 102. For example, the active beacon 400 can comprises a GPS detector for determining position of the WTG 102 which is sent to the distance sensor 1024. In some embodiments, the beacon 400 can be launched from the vessel 100 to the WTG 102 using a drone, cannon or any other suitable means for delivering the beacon 400 to the WTG 102. Indeed, the beacon 400 can be placed on the transition piece 108 by a person. In this way, the motion of the object 300 can be determined with respect to a reference 102 as shown in step 1104 of Figure 8.

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Additionally or alternatively, in some embodiments, the motion compensation module 1014 generates a model of the motion of the vessel over a period time based on observed vessel motion from the sensors described in reference to the embodiments shown in Figures 1 to 8. Accordingly, the generated model is a prediction of the motion of the vessel based on recent motion on the vessel. In this way, generating the model of the motion of the vessel 100 is determining motion of the object with respect to at least one reference according to step 1104 as shown in Figure 8. The motion compensation model 1014 sends control instructions to the actuators 328, 330, 504, 506 based on the vessel motion model.

In some embodiments, the WTG distance module 1026 sends target position information based on the measured distance between the WTG 102 and the vessel 100 as shown in step 1106 of Figure 8. Based on the measured distance, the WTG distance module 1026 issues a command to the dynamic positioning system to move the vessel 100 to a safe operating distance. In this way, the WTG distance sensor 1024 can provide accurate distance information to the dynamic positioning module 1010 which the dynamic positioning module 1010 may not be able to determine using only information from the GPS sensor 1016.

Accordingly, the dynamic positioning module 1010 can compensate for vessel motion due to drift from the wind and the waves. That is the sway, surge and yaw motion of the vessel 100 can be compensated with use of the thrusters and propellers.

As mentioned above, the vessel 100 can also experience motion due to roll, pitch and heave from the waves. The motion compensation module 1014 moves the support structure 332 in order to compensate for the roll, pitch and heave of the vessel 100.

The support structure 332 will be discussed in more detail with reference to Figure 4. Figure 4 shows a close up perspective view of the crane 300 mounted

DK 2018 00520 A1 on the vessel 100. Only the aft portion of the vessel 100 is shown for the purposes of clarity.

The support structure 332 is suspending the crane 300 above the deck 334 of the vessel 100. Indeed, the first and second adjustable arms 326, 500 are in the extended, second position. The doors of the crane body 310 are open so that the crane body 310 can be positioned to surround the tower 116. In comparison with Figure 3, the doors are in the closed position.

In some embodiments, the support structure 332 comprises at least one actuator for moving the suspended crane 300 with respect to the vessel 100. In the embodiment shown in Figure 4, there is a first actuator 328 and a second actuator 330 for moving the first adjustable arm 326. Similarly the second adjustable arm 500 comprises first and second actuators 504, 506 for moving the second adjustable arm 500. The actuators 328, 330, 504, 506 are configured to move the adjustable arms 326, 500 to compensate for the motion of the vessel. In some embodiments, there are any number of actuators for moving the support structure 332. The actuators 328, 330, 504, 506 are hydraulically actuated extendable pistons and are coupled to the hydraulic system 1022. In some embodiments, the actuators 328, 330, 504, 506 moved by linkages and gearing or any other suitable mechanism.

The pitch, roll and heave motion of the vessel 100 is detected using the pitch motion sensor, 200, the roll sensor 202, and the heave sensor 210. The motion compensation module 1014 receives the sensor data relating to the detected motion of the vessel 100 as shown in step 1102. The motion compensation module 1014 determines the deviation of the crane 300 due to the detected motion of the vessel from a stable crane position as shown in step 1104.

The stable crane position is a position whereby the movement of the vessel 100 due to the waves and wind does not affect the position of the crane 300 with respect to the tower 116. Instead, translational movement of the crane 300 with respect to the tower 116 is due to transferring the crane 300 from the vessel

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100 to the tower 116. In this way, the translational movement of the crane 300 is with respect to the tower 116 is due to the extension of the support structure 332 or from a controlled thrust of the vessel 100 itself required to move the crane 300 closer to the tower 116.

In some embodiments, the motion compensation module 1014 calculates the deviation from a position of the crane suspended above the vessel at a height corresponding to the position on the WTG 102 where the crane 300 is to be transferred to as shown in step 1104. On detection of deviation from a stable crane position, the motion compensation module 1014 then sends one or more instructions to the actuators 328, 330, 504, 506 to move the crane 300 back to a stable position as shown in steps 1106.

Instructions sent to actuators 328, 330 move the first adjustable arm 326 as shown in step 1108 of Figure 8. Similarly, instructions sent to actuators 504, 506 move the second adjustable arm 500 as shown in step 1110 of Figure 8.

In this way, the motion compensation module 1014 controls the actuators 328, 330, 504, 506 to keep the crane 300 fixed at a height with respect to the WTG 102 as shown in step 1112 of Figure 8.

Additionally or alternatively, the platform 324 is coupled to actuators connected to the motion compensation module 1014. Accordingly, the platform 324 can be used for loading the crane 300 and / or parts 302, 304, 306 of the WTG 102 and stabilized.

Once the crane 300 is in a stable position and in a suspended position, the crane can be transferred to a portion of the WTG 102.

During the transfer step 1104, the crane 300 is positioned such that it is orientated around the tower 116 as shown in Figure 4. Accordingly the crane

300 can be transferred and secured to the WTG 102.

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Alternatively or additionally, relative motion between the crane 300 and the reference 102 can be determined with an optical sensor 212. A camera 212 can be mounted on the crane 300. The camera 212 will detect movement of the reference 102 between successive images captured by the camera 212 according to step 1102. Accordingly, the motion compensation module 1014 can determine that the object is moving with respect to the reference because the reference is not static or substantially static in successive images captured by the camera 212. The motion compensation module 1014 determines the necessary movement of the first and second adjustable arms 326, 500 to keep the reference 102 static in the successive images captured by the camera 212 as shown in step 1106. The motion compensation module 1014 then sends control instructions to one or more of the actuators 328, 330, 504, 506 to move the first and / or second adjustable arms 326, 500 according to steps 1108, 1110.

This means that the first and second arms 326, 500 compensate for relative motion between the object and the at least one reference such that the object is stable relative to the at least one reference according to step 1112.

The method as described in reference to Figures 7 and 8 for compensating motion of a vessel for an object can be applied to any of the described embodiments in this application.

Another embodiment will now be described in reference to Figures 5 and 6. Figure 5 shows a close up perspective view of the vessel with the first and second adjustable arms 326, 500 suspending a container 510. Figure 6 shows a side view of the vessel 100.

In this way, the object is the container 510 and the method of compensating the motion is the same as previously discussed with reference to Figures 3, 4, 7 and 8.

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The container 510 comprises an open top. However, in other embodiments, the container 510 can have a lid (not shown) for sealing the container 510.

The container 510 is suitable for receiving or transferring a load 600 from another vessel and / or a static installation. Such a static installation such as an offshore oil rig 604 is shown in Figure 6. A load 600 is being suspended from a crane 602 mounted on the deck of the oil rig 604. The load 600 can be supplies, equipment, food, people or any other objects that need to be transferred between the vessel 100 and the oil rig 602.

As shown in Figure 6, the load 600 is swinging the air as represented by the arrows adjacent to the load 600.

Optionally, the container 510 comprises a camera 212 for detecting relative motion between the load 600 and the container 510. In other embodiments, any other sensor for detecting relative motion can be used, including sensors discussed with respect to the previous embodiments.

In contrast to previously embodiments, the reference, e.g. the load 600 is moving with respect to the oil rig 602. Accordingly, the motion compensation module 1014 uses the load 600 as the reference and matches the movement of the container 510 with the movement of the load 600. In this way, the adjustable arms 326, 500 move to match the swaying of the load 600. When the movement of the adjustable arms 326, 500 matches the movement of the load 600, there is no relative motion the container 510 is stable with respect to the load 600.

At this point, the adjustable arms 326, 500 can be extended further to capture the load. Alternatively, the load can be released from the crane 602.

In addition, the container 510 is coupled to at least one rotation actuator 512.

The rotation actuator 512 is coupled between the first adjustable arm 326 and the side of the container 510. One or more other rotation actuators 512 can be connected to the second adjustable arm 500. When the rotation actuator 512

DK 2018 00520 A1 moves with respect to the first adjustable arm 326, the container 510 rotates about axis B-B as shown in step 1114 of Figure 8. This can mean the object such as the container 510 can be manipulated to be positioned in confined spaces which cannot be reached by winching a load from above.

In some embodiments, the centre of gravity of the object is aligned with axis BB. This means that the container 510 will not experience a turning moment when the container 510 is rotated by the rotation actuator 512. Alternatively, the centre of gravity of the object is positioned below the rotation axis B-B of the container 510. This means that the top of the container 510 will remain facing upwards when the adjustable arms 326, 500 pivot with respect to the deck 334 of the vessel 100.

In some embodiments, the first and second adjustable arms 326, 500 are mounted to the object 300, 510 on a first side and a second side of the object 300, 510. The first side and the second side of the object 300, 510 can be opposite sides of the object 300, 510. In other embodiments, the first and the second adjustable arms 326, 500 are mountable to any two points, faces or sides of the object 300, 510.

This means that an object 510 can be compensated for motion of a vessel and motion of a reference. This is advantageously when transferring objects between vessels or a vessel and an offshore installation during rough conditions.

In another embodiment two or more embodiments are combined. Features of one embodiment can be combined with features of other embodiments.

Embodiments of the present invention have been discussed with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the invention.

Claims

Claims

1. A method of compensating motion of a vessel for an object comprising: supporting the object at a first position on the object with a first adjustable arm moveably mounted to the vessel and supporting the object at a second position on the object with a second adjustable arm moveably mounted to the vessel;

determining motion of the object with respect to at least one reference; moving the first adjustable arm and / or the second adjustable arm with respect to the vessel based on the determined motion; and compensating for relative motion between the object and the at least one reference such that the object is stable relative to the at least one reference.
2. A method according to claim 1 wherein the at least one reference is a fixed reference point.
3. A method according to claim 1 wherein the at least one reference is a moving reference point.
4. A method according to any of the preceding claims wherein the compensating comprises determining the relative motion of the object with respect to the vessel.
5. A method according to any of the preceding claims wherein the compensating comprises adjusting the position of the object with respect to the vessel in one or more directions to compensate for heave, sway, surge, roll, pitch and / or yaw motion of the vessel.
6. A method according to claim 3 wherein the compensating comprises matching the movement of the object with movement of the at least one reference.

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7. A method according to any of the preceding claims wherein the determining comprises receiving information from one or more sensors detecting relative motion between the object and the at least one reference.
8. A method according to any of the preceding claims wherein the object is a crane and the at least one reference point is an offshore wind turbine generator.
9. A method according to any of the preceding claims wherein the object is a container and the at least one reference point is a suspended load.
10. A method according to any of the preceding claims wherein the adjustable arms are extendable and / or pivotable with respect to the vessel.
11. A method according to any of the preceding claims wherein the adjustable arms are independently controllable.
12. A method according to any of the preceding claims wherein the first and / or the second adjustable arm comprises an actuator for rotating the object about an axis.
13. A method according to any of the preceding claims wherein the first and second adjustable arms are mounted on a motion compensated platform arranged to compensate for relative motion between the object and the at least one reference.
14. A method according to any of the preceding claims wherein the first and second arms are mounted on opposite sides of the object.
15. A method according to claim 14 wherein the centre of gravity of the object is positioned on or below a straight line between the mounting points of the first and second arms.
16. A vessel comprising:

DK 2018 00520 A1 a first adjustable arm moveably mounted to the vessel and arranged to support an object at a first position on the object;

a second adjustable arm moveably mounted to the vessel and arranged to support the object at a second position on the object;

5 at least one actuator coupled to each of the first and second adjustable arms for moving the first and second adjustable arms with respect to the vessel; at least one sensor arranged to sense motion of the object; and a controller configured to determine motion of the object with respect to at least one reference based on received information from the at least one 10 sensor and to send control instructions to the at least one actuator to move the first adjustable arm and / or the second adjustable arm with respect to the vessel based such that the object is stable relative to the at least one reference.