NL2036395B1

NL2036395B1 - A vessel for monopile installation and corresponding monopile installation method

Info

Publication number: NL2036395B1
Application number: NL2036395A
Authority: NL
Inventors: Roodenburg David; Stofregen Matthijs
Original assignee: Itrec Bv
Priority date: 2023-11-30
Filing date: 2023-11-30
Publication date: 2025-06-05

Abstract

A B S T R A C T The invention relates to a vessel and corresponding method allowing to align a suspension point of a crane with a location on a monopile during monopile installation thereby improving stability of the total system during monopile installation. Fig. 2

Description

TITLE OF THE INVENTION

A vessel for monopile installation and corresponding monopile installation method

BACKGROUND OF THE INVENTION

The invention relates to the installation of monopiles as part of the installation process of wind turbines, in particular offshore wind turbines. In a known method for installing an offshore wind turbine, the foundation, in the form of a monopile, is installed first by driving the monopile into the sea bottom after which the wind turbine is installed on the monopile, either by installing the wind turbine at once as a whole or by assembling the wind turbine in parts on the monopile.

There is a trend towards larger wind turbines and a desire to install offshore wind turbines at locations with larger water depths than currently encountered. Both result in larger and heavier foundations. Hence, it is expected that soon monopiles need to be installed that are larger than 100 meters, possibly 120 meters or larger. The weight of such monopiles may be larger than 1000mt, possibly 1300mt or above.

To save time during the installation process, the use of floating vessels is preferred over jack-up type vessels. Such floating vessels typically include a lifting device such as a crane to suspend the monopile from, and a pile gripper to engage with the monopile, wherein the lifting crane and the pile gripper cooperate to lower the monopile into the sea using, amongst others, a pile gripper positioning system. Generally, the vessel further includes a dynamic positioning system to position the vessel during the lowering of the monopile.

Although the dynamic positioning system, the pile gripper positioning system and the crane all try to keep the monopile and the vessel in a desired position and/or orientation, stability issues may arise due to inherent operational limitations in the total system resulting in the vessel drifting away too much from the monopile installation site. This may result in dangerous operational situations, especially when the monopile has penetrated a seabed with a lower end thereof such that the monopile easily tilts.

SUMMARY OF THE INVENTION

In view of the above it is an object of the invention to provide a stable monopile installation method using a floating vessel.

According to a first aspect of the invention, there is provided a vessel to carry out a monopile installation method, comprising: - ahull; - a lifting device arranged on the hull and configured to lift and lower a monopile, and - a dynamic positioning system including: o an actuator system for applying forces to the vessel to position the vessel, o a vessel measurement system for measuring a position of the vessel, o a dynamic positioning control unit for driving the actuator system in dependency of a desired position and an actual position of the vessel as measured by the vessel measurement system, wherein the lifting device includes a moveable frame with a suspension point, a load connector, and one or more lifting cables extending substantially vertically between the suspension point and the load connector, and wherein the lifting device comprises a control system including: - a frame actuator system for moving the moveable frame relative to the hull, - a measurement system for determining a position of the suspension point relative to a location on a monopile suspended by the one or more lifting cables, and - a control unit configured to drive the frame actuator system in dependence of an output of the measurement system to position the suspension point above a location on a monopile during at least a portion of the monopile installation when the monopile is suspended by the one or more lifting cables.

The mentioned monopile installation method may include a plurality of phases, including but not limited to: - a suspension phase, in which the monopile is suspended from the lifting crane above water level and engaged by the pile gripper,

- a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, - aseabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, and - a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

Positioning the suspension point above a location on a monopile may include positioning the suspension point above one of the following locations on a monopile: - an upper end of the monopile, - a lower end of the monopile, - a middle section of the monopile, - a monopile section held in a pile gripper that is arranged on the vessel to engage with the monopile during monopile installation, - a monopile section at the level of the seabed during the seabed penetration phase.

The abovementioned locations on a monopile may be more specifically defined by being a center of a respective end or section of the monopile.

Stability issues typically occur during the seabed penetration phase when the lower end of the monopile has penetrated the seabed and is no longer able to move horizontally so that any vessel motion will cause the monopile to pivot when no measures are taken. In the prior art, when a vessel moves away from a monopile, the suspension point on the lifting device also moves away and the lifting forces applied by the one or more lifting cables to the monopile are no longer vertical but have a horizontal component that pulls on the monopile in a direction away from the vertical orientation of the monopile thereby contributing to the stability issues. By positioning the suspension point above a location on the monopile as described above for the first aspect of the invention, i.e. aligning the suspension point with a location on the monopile, the lifting cables remain vertical and no horizontal force is applied to the monopile, or the horizontal force that is generated is in an opposite direction than described above. Both types of improvement result in a more stable total system.

Inan embodiment, the control unit is configured to drive the frame actuator system in dependence of an output of the measurement system to position the suspension point above a location on a monopile during at least the penetration phase.

In an embodiment, the vessel further comprises a pile gripper to engage with a monopile and a pile gripper positioning system for positioning a monopile with the pile gripper.

In an embodiment, the frame actuator system is configured to move the moveable frame in two different directions, e.g. in two directions in a horizontal plane. in an embodiment, the control unit is also configured to haul in or pay out the one or more lifting cables to compensate for undesired height changes when moving the moveable frame.

In an embodiment, the moveable frame is a boom or jib and the frame actuator is configured to move the entire boom or jib.

In an embodiment, the moveable frame is pivotable up and down about a substantially horizontal pivot axis and/or rotatable about a substantially vertical rotation axis. This embodiment this combines two movements that may for instance already be available for moving the load connector during other lifting operations, e.g. by moving the boom or jib up and down and/or sideways.

In another embodiment, a rotation may be combined with a translation, e.g. using a rotatable telescopic arm comprising the moveable frame. The moveable frame can then be moved in one direction by rotation of the arm and in another direction by changing the length of the arm, i.e. elongating or shortening.

in a further embodiment, a translation in one direction is combined with a translation in another direction, e.g. using a X-Y frame or platform.

According to a second aspect of the invention, there is provided a method to install a 5 monopile, wherein use is made of a vessel comprising a dynamic positioning system and a lifting device configured to lift and lower the monopile, wherein the lifting device includes a moveable frame with a suspension point and one or more lifting cables extending substantially vertically between the suspension point and the monopile when the monopile is suspended by the lifting device, said method comprising the following steps: a. lowering a monopile towards or into a seabed while suspending the monopile using the lifting device, b. measuring a position of the suspension point relative to a location on the monopile, c. moving the suspension point to above the location on the monopile and maintaining said position relative to the location on the monopile during at least a portion of the monopile installation.

In an embodiment, the method is carried out during at least a seabed penetration phase of the monopile installation in which a lower end of the monopile penetrates the seabed.

In an embodiment, during lowering of the monopile towards or into the seabed, the monopile is engaged by a pile gripper.

In an embodiment, the vessel is a vessel according to a first aspect of the invention.

Hence, features and embodiments described in relation to the vessel according to the first aspect of the invention may be used as structural features of the vessel in the second aspect of the invention as well. Further, features and embodiments described in relation to the vessel according to the first aspect of the invention that can be respectively described in terms of method steps or equivalent functions may also be used as such in the method according to the second aspect of the invention to avoid unduly repetition of features and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting way by reference to the accompanying drawings in which like parts are indicated by like reference symbols, and in which:

Fig.1 schematically depicts a vessel according to an embodiment of the invention,

Fig. 2 schematically depicts a portion of the vessel of Fig. 1 during upending of a monopile,

Fig. 3 schematically depicts a monopile during a seabed penetration phase of a monopile installation method,

Fig. 4 schematically depicts an embodiment of a monopile installation method,

Fig. 5 schematically depicts another embodiment of a monopile installation method,

Fig. 6 schematically depicts a further embodiment of a monopile installation method, and

Fig. 7 schematically depicts yet another embodiment of a monopile installation method.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 schematically depict a vessel 200 according to an embodiment of the invention. The vessel 200 comprises a deck 201. The deck 201 provides sufficient space to store, in this case, five monopiles 202 in a horizontal orientation. The monopiles 202 are stored such that their longitudinal axes are parallel to a longitudinal axis of the vessel 200.

In this embodiment, the vessel 200 is a monohull vessel, but alternatively, the vessel could be a semi-submersible.

At a stern of the vessel 200 is provided a lifting crane 203 as lifting device. The lifting crane 203 is arranged in a center of the deck 201 seen in transverse direction of the vessel 200 to be aligned with a center of gravity of the vessel 200. On one side of lifting crane a pile gripper 1 is arranged, and on an opposite side of the lifting crane 203, a pile driving mechanism 205, alternatively referred to as a pile hammer, is arranged at a corresponding storage location.

When the vessel 200 has sailed to an offshore installation site where a monopile 202 needs to be installed into the sea bottom, a monopile 202 is positioned in a pile holder 50 of the pile gripper 1. The pile holder 50 is in this embodiment pivotable between a vertical orientation, in which it can receive a monopile in a horizontal orientation, and a horizontal orientation as shown in Fig. 1, in which it is able to guide the lowering of the monopile into the sea towards or into the sea bottom. In this embodiment, the monopile is positioned in the pile holder 50 of the pile gripper 1 while the pile holder 50 is in the vertical position.

Arms 57, 58 of the pile holder 50 are moveable between an open position to allow a monopile 202 to pass the arms 57, 58, and thus to receive the monopile, and a closed position in which the pile holder 50 (and thus the pile gripper 1) engages with the monopile 202 to limit movement in a direction perpendicular to a longitudinal axis of the monopile 202,

The pile holder 50 may be provided with a pile support 77 configured to engage with a lower end of the monopile 202. The monopile 202 can be brought into engagement by first bringing the pile support 77 into a desired position and subsequently translating the monopile along its longitudinal axis until the lower end of the monopile engages with the pile support 77. The pile support 77 is used to limit movement of the monopile 202 in a direction parallel to the longitudinal axis of the monopile 202, which is advantageous during upending of the monopile 202.

An upper end of the monopile 202 is then lifted using the lifting crane 203 with the lower side of the monopile 202 in the pile holder 50 thereby rotating the monopile 202 from a horizontal orientation to a vertical orientation. Fig. 2 shows the monopile in an intermediate oblique orientation between the horizontal orientation and the vertical orientation.

After rotating, the pile holder 50 is in the horizontal position, which may alternatively be referred to as lowering position, and the monopile 202 is located outside the contour of the vessel 202, i.e. overboard, seen from above to be lowered into the water as can be seen in Fig. 1.

Before lowering the monopile 202 into the water, the lower end of the monopile 202 needs to be disengaged from the pile support 77. The monopile 202 is in that case lifted first using the lifting crane 203 after which the pile support 77 can be moved out of the way. The monopile 202 can then be lowered into the water.

During the above operations, the vessel 200 is in floating condition, and the pile holder 50 is compensated for wave-induced motion of the vessel 200 to maintain a predetermined

X-Y location independent of the wave-induced motion of the vessel 200 by operating a pile gripper positioning system of the pile gripper 1 in wave-induced motion compensation mode.

To allow the pile gripper 1 to maintain a predetermined X-Y location, the vessel 200 must maintain its position within the working boundaries of the pile gripper 1. The vessel 200 is therefore provided with a dynamic positioning system to position the vessel 200, including maintaining or adjusting a position or orientation of the vessel 200. The dynamic positioning system includes an actuator system including for instance a multitude of thrusting modules 220 for applying forces to the vessel 200, preferably allowing to at least translate the vessel 200 in a horizontal X-Y plane and to rotate the vessel 200 about a Z-axis. The dynamic positioning system further includes a vessel measurement system 230 for measuring a position of the vessel 200, and a dynamic positioning control unit 240 for driving the actuator system in dependency of a desired position and an actual position of the vessel 200 as measured by the vessel measurement system 230.

When the monopile 202 is lowered into the water and suspended from the lifting crane 203, the lifting crane 203 may be operated in wave-induced motion compensation mode so that the monopile 202 is compensated for wave-induced motion of the vessel 200 to maintain a predetermined Z location independent of the wave=induced motion of the vessel 200. This may also be referred to as heave compensation.

To lift the upper end of the monopile 202 to rotate the monopile 202 from a horizontal orientation to a vertical orientation, the lifting crane 203 may be provided with a pile clamping device 210 comprising a clamping part 211 to clamp the upper end of the monopile 202 and a connecting part 212 allowing to connect the pile clamping device to a load connector 213 of the lifting crane 203. The connecting part 212 is able to rotate freely relative to the clamping part 211 during lifting of the upper end, i.e. during rotating of the monopile 202.

The lifting crane 203 comprises a boom 204 that is rotatable about a central mast 206 and that is pivotable up and down about a substantially horizontal pivot axis using luffing cables 207. The boom 204 may also be referred to as jib. The boom 204 includes a jib portion 204a at a free end of the boom, which may alternatively be referred to as flyjib.

The boom 204 is or includes a frame with a suspension point 204b. The lifting crane 203 further comprises a lifting system including one or more lifting cables 208 extending substantially vertically between the suspension point 204b and the load connector 213.

To position the boom 204, the lifting crane 203 comprises a frame actuator system including an actuator 209a to manipulate the luffing cables 207 and set an angular orientation of the boom 204 relative to the central mast 206 (and thus relative to a vertical), and an actuator 209b to rotate the boom 204 about the central mast 206 to set an angular orientation about a substantially vertical rotation axis defined by the central mast 206 (and thus about the vertical).

The lifting crane 203 further comprises a measurement system MS for determining a position of the suspension point 204b relative to a location on a monopile 202 suspended by the one or more lifting cable 208 as schematically indicated by the dashed arrows extending between the suspension point 204b, the monopile 202 and the measurement system MS. Output data from the measurement system MS is provided to a control unit

CU that is configured to drive the frame actuator system, in this case the actuators 209a and 209b, in dependence of the output data of the measurement system MS to position the suspension point 204b above a location on a monopile 202 during at least a portion of the monopile installation when the monopile 202 is suspended by the one or more lifting cables 208 as will be explained below in more detail. it is noted here that the control unit CU may also be connected to one or more actuators, e.g. one or more winches, that are responsible for a length of the one or more lifting cables extending between the suspension point 204b and the load connector 213.

Alternatively, or additionally, the control unit CU is connected to or part of the abovementioned heave compensation system. Operating actuator 209a will not only position the suspension point seen in plan view, but will also result in a change of the height level of the suspension point and thus the load connector 213. This may be undesired, requiring compensating for the change by hauling in or paying out of the lifting cables 208 using the corresponding actuators. However, it is also envisaged that the control unit CU and the heave compensation system work independently from each other, such that the heave compensation system automatically compensates for movement caused by the control unit CU.

By reference to Figs. 1 and 2, a portion of a monopile installation method has already been described. In more detail, a monopile installation method may include a plurality of phases, including but not limited to: - a suspension phase, in which the monopile is suspended from a lifting crane above water level and engaged by the pile gripper as for instance shown in Fig, 2 after completely rotating to the vertical orientation of the monopile, - a lowering phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile is in the water, but above the seabed, alternatively referred to as sea bottom throughout this specification, - a seabed penetration phase, in which the monopile is suspended from the lifting crane and engaged by the pile gripper, and a lower end of the monopile has penetrated the seabed, and

- a driving phase, in which the monopile is engaged by the pile gripper and driven into the seabed using a hammer or the like.

Fig. 3 schematically depicts a monopile 202 during a seabed penetration phase of a monopile installation method carried out using the vessel of Figs. 1 and 2. The monopile 202 is suspended from the lifting crane 203 using the pile clamping device 210 with clamping part 211 clamped on an upper end 202a of the monopile 202 and connecting part 212 used to connect the pile clamping device 210 to the load connector 213 of the lifting crane. Alternatively, the clamping device 210 may only include a clamping part 211 that is configured to be connected directly to the load connector 213 of the lifting crane 203.

Also shown is the jib portion 204a of the boom 204 with the suspension point 204b and the one or more lifting cables 208 that extend substantially vertically between the suspension point 204b and the load connector 213.

During the seabed penetration phase, a lower end 202b of the monopile 202 has penetrated a seabed SB, and the monopile 202 is engaged by a pile holder 50 of a pile gripper 1 for applying a force to the monopile when necessary to maintain a desired orientation of the monopile 202. In Fig. 3, the monopile 202 is depicted in the desired vertical orientation. In this situation, it is preferred that the pile gripper is not applying a net force to the monopile 202 and that the lifting crane 203 is applying a vertical suspension force to the monopile to keep the monopile 202 suspended. In such situation, it is preferred that the suspension point 204b is positioned above the monopile, in particular above a longitudinal axis 202c extending through a center of gravity of the monopile.

Figs. 4-7 are simplified schematic drawings based on Fig. 3 to depict different possible control schemes that can be used during the monopile installation method.

In all four Figs. 4-7, the monopile 202 has tilted to the right of the drawing as an example.

Compared to Fig. 3, this means that the monopile 202 has tilted away from the vessel

200. it is explicitly noted here that the amount of tilt is exaggerated for ease of explanation and will be much smaller in practice.

Referring to Fig. 4, to return to the desired orientation of Fig. 3, the vessel 200 will use the pile gripper 1 to apply a force FG in the direction of the arrow shown in Fig. 4. In Fig. 4, the control unit CU of the lifting crane 203 is configured to position the suspension point 204b above an upper end 202a of the monopile 202. in this way, the orientation of the one or more lifting cables 208 remains substantially vertical, so that no horizontal forces are applied to the upper end 202a of the monopile 202.

Compared to Fig. 3 and depending on the position of the vessel 200 relative to the monopile, the suspension point 204b can move along with the upper end 202a of the monopile 202 by appropriate adjustment of the length of the luffing cables 207 using actuator 209a. At the same time, the one or more lifting cables 208 can be hauled in or paid out to keep the load connector 213 at the same height level.

Referring to Fig. 5, similarly to Fig. 4, the vessel 200 will use the pile gripper 1 to apply a force FG in the direction of the arrow shown in Fig. 5. In Fig. 5, the control unit CU of the lifting crane 203 is configured to position the suspension point 204b above a lower end 202b of the monopile 202. In this way, the orientation of the one or more lifting cables 208 will change such that the one or more lifting cables 208 will also apply a horizontal force FL to the upper end 202a of the monopile 202 as indicated by the respective arrow in Fig. 5.

An advantage of the horizontal force FL is that it is directed in a direction towards the desired orientation of Fig. 3, thereby aiding the returning action performed by the pile gripper 1.

Figs. 6 and 7 are similar to the situation depicted in Fig. 5. The embodiment of Fig. 6 differs from the embodiment shown in Fig. 5, in that the control unit CU of the lifting crane 203 is configured to position the suspension point 204b above a middle section

202c of the monopile 202, e.g. a middle section 202c including a center of gravity of the monopile 202.

The embodiment of Fig. 7 differs from the embodiment shown in Fig. 5, in that the control unit CU of the lifting crane 203 is configured to position the suspension point 204b above a monopile section 202d that is arranged in the pile holder 50. An advantage of this embodiment is that the suspension point and the pipe holder substantially move together and thus do not deviate too much from each other.

Positioning the suspension point 204b relative to a location on the monopile 202 as described above in various possible ways requires a direct or indirect determination of the relative position of the suspension point 204b and the monopile 202.

The measurement system MS may measure parameters allowing to determine an inclination of the one or more lifting cables and/or a length of the one or more lifting cables. The embodiment of Fig. 4 has the characteristic that the orientation of the one or more lifting cables is intended to remain substantially vertical. Hence, measuring the inclination and/or the length of the one or more lifting cables may then allow to determine the relative position between suspension point and monopile location.

The embodiment of Fig. 7 has the characteristic that the suspension point is substantially above the pile holder, so that the measurement system MS may use position information from the pile holder or pile gripper to determine a relative position between suspension point and monopile location.

Although in the above examples, movement of the entire boom 204 is used to position the suspension point in one direction, it is also envisaged that a part of the boom, e.g. the flyjib 204a is pivoted up and down relative the boom 204 instead of the entire boom 204.

As less weight needs to be moved, moving the flyjib 204a only may result in a better performance of the control scheme.

Claims

CONCLUSIONS

1. A vessel (200) for performing a monopile installation method, comprising: - a hull, - a hoisting device {203} mounted on the hull and adapted to hoist or lower a monopile (202), and - a dynamic positioning system comprising: o an actuator system {220} for applying forces to the vessel to position the vessel, o a vessel measurement system {230} for measuring a position of the vessel, o a dynamic positioning control unit (240) for controlling the actuator system in dependence on a desired position and an actual position of the vessel as measured by the vessel measurement system, the hoisting device comprising a movable frame {2044} having a suspension point (204b), a load connector (213), and one or more hoist cables (208) extending substantially vertically between the suspension point and the load connector, and wherein the hoisting device comprising a control system comprising: - a frame actuator system for moving the movable frame relative to the hull, - a measuring system (MS) for determining a position of the suspension point relative to a location on a monopile suspended from the one or more hoist cables, and - a control unit (CU) adapted to control the frame actuator system in response to an output from the measuring system to position the suspension point above a location on a monopile during at least a portion of the monopile installation when the monopile is suspended from the one or more hoist cables.

2. A vessel according to claim 1, wherein the control unit is arranged to control the frame actuator system in dependence on an output from the measuring system to position the suspension point above a location on a monopile during a penetration phase in which a lower end of the monopile has penetrated the seabed.

3. A vessel according to claim 1 or 2, wherein the location of the monopile is an upper end of the monopile, a lower end of the monopile, or a middle portion of the monopile, or a monopile portion at the level of the seabed during a seabed penetration phase in which a lower end of the monopile has penetrated the seabed.

4. A vessel according to any preceding claim, further comprising a pile grab for coupling to a monopile and a pile grab positioning system for positioning a monopile with the pile grab.

5. A vessel according to claim 4, wherein the location on the monopile is a monopile section held in the pile grip.

6. A vessel according to any preceding claim, wherein the frame actuator system is arranged to move the movable frame in two directions in a horizontal plane.

7. A vessel according to any preceding claim, wherein the control unit is also arranged to retract or release the one or more hoist cables to compensate for unwanted height changes during movement of the movable frame.

8. A vessel according to any preceding claim, wherein the movable frame is a swing arm or boom and the frame actuator is arranged to move the entire swing arm or boom.

9. A method of installing a monopile using a vessel comprising a dynamic positioning system and a hoist adapted to hoist or lower a monopile, the hoist comprising a movable frame having a suspension point and one or more hoist cables extending substantially vertically between the suspension point and the monopile when the monopile is suspended from the hoist, the method comprising the following steps:

a. lowering a monopile towards or into a seabed while the monopile is suspended from the hoist,

b. measuring a position of the suspension point relative to a location on the monopile,

c. moving the suspension point above the location on the monopile and maintaining this position relative to the location on the monopile during at least a portion of the monopile installation.

10. A method according to claim 9, wherein the method is carried out during at least a seabed penetration phase of the monopile installation in which a lower end of the monopile penetrates the seabed.

11. A method according to claim 9 or 10, wherein during lowering of the monopile towards or into the seabed, the monopile is coupled to a pile gripper.

12. A method according to any one of claims 9 to 11, wherein the location on the monopile is an upper end of the monopile.

13. A method according to claim 11, wherein the location on the monopile is a portion of the monopile coupled to the pile gripper.

14. A method according to any one of claims 9 to 13, wherein the suspension point is moved by pivoting a swing arm or boom about a substantially horizontal axis and/or by rotating the swing arm or boom about a substantially vertical axis.