VESSEL AND A METHOD OF INSERTING A MONOPILE INTO A GUIDE

Abstract

A vessel comprises a hull and a guide for guiding a monopile. The guide is movably mounted to the hull and includes a receiving part and a closure part which is movable for creating a closed condition of the guide where the guide forms an annular body extending in a main plane and an open condition in which the guide has an opening to a space, allowing a monopile to be received in the space. A displacing device displaces the guide within the main plane. A control system controls the displacing device and such that it determines an oscillating path of a monopile relative to the hull in a direction within the main plane when the monopile and the guide are moving towards each other and the guide is in the open condition for receiving the monopile. The displacing device displaces the guide substantially synchronously with the determined oscillating path.

Claims

1. A vessel, comprising: a hull; a guide configured to guide a monopile to be driven into a seabed, which guide is movably mounted to the hull and provided with a receiving part and a closure part which is movable with respect to the receiving part for creating a closed condition of the guide in which closed condition the guide forms an annular body extending in a main plane and an open condition in which the guide has an opening to a space which is bordered by the receiving part, allowing the monopile to be received in the space via the opening; a displacing device configured to displace the guide within the main plane with respect to the hull; and a control system configured to control the displacing device, wherein the control system is configured such that the control system determines an oscillating path of the monopile with respect to the hull in a direction within the main plane when the monopile and the guide are moving towards each other and the guide is in the open condition for receiving the monopile and such that the displacing device displaces the guide substantially synchronously with the determined oscillating path in a same direction thereof.

2. The vessel according to claim 1, wherein the control system is configured such that the control system decomposes a direction in a first component which is towards the guide and away from the guide and a second component which extends transversely to the first component, wherein when the determined oscillating path is located at a first distance from the receiving part, the displacing device displaces the guide along the first and second components, whereas when the determined oscillating path is located at a second distance from the receiving part, which is larger than the first distance, the displacing device displaces the guide along the second component only.

3. The vessel according to claim 1, wherein in the closed condition, the guide is substantially circular within the main plane such that the receiving part is partly circular within the main plane.

4. The vessel according to claim 1, wherein the closure part comprises a pair of doors which are pivotally mounted to the receiving part and open in opposite directions with respect to each other in outward direction of the guide.

5. The vessel according to claim 1, wherein the displacing device is provided with linear actuators, which operate along lines of action that extend perpendicularly to each other.

6. The vessel according to claim 1, wherein the control system comprises a position sensor configured to determine an actual location of a monopile with respect to the guide so as to determine the oscillating path.

7. The vessel according to claim 6, wherein the position sensor is located at the guide.

8. The vessel according to claim 7, wherein the position sensor is located at the receiving part.

9. The vessel according to claim 1, wherein the vessel is provided with a crane configured to hoist the monopile and move the hoisted monopile towards the guide.

10. The vessel according to claim 6, wherein the control system comprises an inclination angle sensor configured to determine an actual inclination angle of the monopile.

11. The vessel according to claim 1, wherein the guide and/or the displacing device is provided with a damping device configured to mitigate collisions between a monopile and the guide.

12. The vessel according to claim 11, wherein the damping device comprises damping elements at an inner circumference of the guide.

13. The vessel according to claim 1, wherein the guide is rotatable with respect to the hull about an axis which extends perpendicularly to the main plane.

14. A method of inserting a monopile to be driven into a seabed into a guide for guiding the monopile, which guide is movably mounted to a hull of a vessel and provided with a receiving part and a closure part which is movable with respect to the receiving part for creating a closed condition of the guide in which closed condition the guide forms an annular body extending in a main plane and an open condition in which the guide has an opening to a space which is bordered by the receiving part, the method comprising: receiving a monopile in the space via the opening; in the open condition moving the monopile and the guide to each other, during which movement an oscillating path of the monopile with respect to the hull within the main plane is determined; and displacing the guide substantially synchronously with the determined oscillating path in a same direction thereof.

15. The method according to claim 14, wherein the direction is decomposed in a first component which is towards the guide and away from the guide and a second component which extends transversely to the first component, wherein when the determined oscillating path is located at a first distance from the receiving part the guide is displaced along the first and second components, whereas when the determined oscillating path is located at a second distance from the receiving part which is larger than the first distance the guide is displaced along the second component only.

16. The method according to claim 14, wherein after inserting the monopile into the guide, the closure part is closed, during which and/or after which the guide is displaced such that a counterforce is applied on the monopile in order to minimize an amplitude of the oscillating path.

17. The method according to claim 14, wherein after inserting the monopile into the guide the closure part is closed, during which and/or after which a remaining oscillating motion of the guide including the monopile is dampened.

18. The vessel according to claim 1, wherein the closure part comprises a pair of doors which are pivotally mounted to the receiving part and open in opposite directions with respect to each other in outward direction of the guide independently from each other.

19. The vessel according to claim 5, wherein the linear actuators comprise hydraulic cylinders.

20. The vessel according to claim 5, wherein the linear actuators comprise a rack and pinion system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Aspects of the invention will hereafter be elucidated with reference to the schematic drawings showing an embodiment of the invention by way of example.

[0025] FIG. 1 is a perspective view of an embodiment of a vessel.

[0026] FIG. 2 is an illustrative view of successive activities from hoisting a monopile from the vessel as shown in FIG. 1 to driving the monopile into a seabed.

[0027] FIG. 3 is an enlarged top view of a part of the vessel as shown in FIG. 1, showing a guide for guiding a monopile to be driven into the seabed.

[0028] FIG. 4 is a similar view as FIG. 3, but illustrating a different situation.

[0029] FIG. 5 is a diagram, showing actual positions of the guide and the monopile of FIGS. 3 and 4 as a function of time.

[0030] FIG. 6 is a similar view as FIG. 3, but showing the guide in a different orientation.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0031] FIG. 1 shows a floating installation vessel 1 for installing a monopile 2 in a seabed B. The installation vessel 1 has a hull 3 including an upper deck 4. A crane 5 for lifting the monopile 2 is mounted to the hull 3. The installation vessel 1 is also provided with a guide 6 for guiding the monopile 2 in its longitudinal direction during driving the monopile 2 into the seabed B.

[0032] Under operating conditions, the monopiles 2 are transported horizontally by the installation vessel 1 from a production facility to an off-shore installation site. FIG. 2 illustrates a number of successive activities at the off-shore installation site. One of the monopiles 2 is up-ended by means of the crane 5, assisted with a hinge 17, as shown in FIG. 1, that supports the monopile 2 on the deck 4, after which the monopile 2 suspends vertically from a cable 7 of the crane 3. Subsequently, the monopile 2 is received by the guide 6 and placed onto the seabed B, after which the cable 7 is separated from the monopile 2. Then, a pile driving device 8 is placed on top of the monopile 2 by the crane 5 in order to drive the monopile 2 into the seabed B. Alternatively, a split block crane is present, wherein an upper end and lower end of the monopile 2 can be lifted separately such that the crane can perform upending on its own without the hinge 17.

[0033] The guide 6 has an open condition and a closed condition. The open condition is shown in FIGS. 3 and 4. In the closed condition the guide 6 forms an annular body for enveloping a monopile 2. The annular body extends in a main plane. In this case the annular body is substantially circular and has a centerline CL. The main plane is substantially parallel to the upper deck 4 of the installation vessel 1, which is horizontal in the event of a calm sea. The guide 6 is provided with a receiving part 9 and a closure part in the form of a pair of doors 10 which open in opposite directions with respect to each other in outward direction of the guide 6. In the open condition the guide 6 has an opening which enables a monopile 2 to be inserted into a space that is bordered by the receiving part 9. The receiving part 9 in the embodiment as shown in FIGS. 3 and 4 is semi-circular. The doors 10 can be locked to each other through cooperating locking members 11. The guide 6 may have a different shape than shown in FIGS. 3 and 4, whereas the doors 10 may be replaced by a single door, for example.

[0034] The guide 6 is provided with retractable pile supports or so-called bogeys 12, which are guide arms including rollers. The bogeys 12 are moved towards the centerline CL before pile driving starts, i.e. when the monopile 2 is located in the guide 6 and the guide 6 is in its closed condition. In the open condition of the guide 6 the bogeys 12 are retracted in order to allow the monopile 2 to enter the space which is bordered by the receiving part 9 and to minimize the risk of collisions between the bogeys 12 and the monopile 2. In this case the bogeys 12 lie on an imaginary circle when the guide 6 is in the closed condition and the bogeys 12 are retracted.

[0035] The installation vessel 1 comprises a displacing device in the form of a pair of first hydraulic cylinders 13 and a pair of second hydraulic cylinders 14. The first hydraulic cylinders 13 operate along a first line of action Y and the second hydraulic cylinders 14 operate along a second line of action X which is perpendicular to the first line of action Y. The first and second lines of action X, Y extend parallel to the main plane. Consequently, the guide 6 is movable with respect to the upper deck 4 within the main plane. Alternatively, the first and second hydraulic cylinders 13, 14 may be replaced by other linear actuators such as a rack and pinion system, a winch or the like.

[0036] FIGS. 3 and 4 illustrate a desired path D which is followed by an axial centerline of the monopile 2 at the level of the main plane towards the centerline CL of the guide 6. The partly circular path D or slewing trajectory is caused by the rotating motion of the crane 5. Such a circular path D may be followed in case of a very calm sea. However, since the monopile 2 is installed from the floating installation vessel 1, the monopile 2 will oscillate due to motion of the installation vessel 1 and due to waves when a lower portion of the monopile 2 is located in the sea, in practice. This is illustrated in FIG. 2. Usually, the monopile 2 oscillates about its center of gravity which lies at a distance of, and often above, the main plane of the guide 6.

[0037] In order to prevent the guide 6 and the monopile 2 from collisions during inserting the monopile 2 into the space that is bordered by the receiving part 9 the installation vessel 1 is provided with a control system 15 for controlling the first and second hydraulic cylinders 13, 14 such that the guide 6 moves substantially synchronously with an oscillating path of the approaching monopile 2. For this reason the installation vessel 1 comprises position sensors 16 at the receiving part 9, see FIG. 3. In this case, each of the position sensors 16 covers a detection range of which the borders are indicated by broken lines in FIG. 3. Signals from the position sensors 16 are received by the control system 15. On the basis of these signals the control system 15 determines the actual oscillating path of the monopile 2 with respect to the guide 6 in the main plane when the monopile 2 is being moved towards the guide 6. The control system 15 controls the hydraulic cylinders 13, 14 such that the guide 6 is displaced substantially synchronously with the determined oscillating path of the monopile 2 in the same direction thereof. In other words the guide 6 follows the oscillating motion of the monopile 2. The position sensors 16 and the control system 15 may be configured such that a ceterline of the monopile 2 is determined. This provides the opportunity to use the centerline of the monopile 2 as a reference which should be followed by the centerline CL of the guide 6.

[0038] In the embodiment as shown in the figures, the control system 15 decomposes the determined oscillating path in a first component F which is directed towards the guide 6 and away from the guide 6 and a second component S which extends perpendicularly to the first component F, see FIG. 4. When the determined oscillating path is located close to the receiving part 9 of the guide 2, i.e. at a first distance from the receiving part 9, the control system 15 controls the hydraulic cylinders 13, 14 such that the guide 6 is displaced along both the first component F and the second component S. When the determined oscillating path is located at a greater distance from the receiving part 9, i.e. at a second distance from the receiving part 9 which is larger than the first distance, the guide 6 is displaced along the second component S only. The latter situation is illustrated in FIG. 3. The reason for this control strategy is that when the monopile 2 is approaching the guide 6 the risk of a collision between the receiving part 9 and the monopile 2 along the second component S is higher than along the first component F, whereas when the monopile 2 is close to the receiving part 9 the risk of a collision in both directions increases. Hence, the monopile 2 passes the opening of the guide 6 at maximum clearance at opposite sides thereof.

[0039] The guide 6 and/or the first and second hydraulic cylinders 13, 14 may be provided with a damping device for mitigating collisions between the monopile 2 and the guide 6. For example, the bogeys 12 may comprise damping elements (not shown).

[0040] The actions of the control system 15 are visualized in FIG. 5. This figure shows the actual positions P of the centerline CL of the guide 6 and the centerline of a monopile 2 as a function of time t. The centerline of the monopile 2 oscillates about a curve which represents the average movement of the centerline of the monopile 2 towards the guide 6. The curve is given reference sign D in order to indicate that it represents the path D as shown in FIGS. 3 and 4. At the left part of FIG. 6 it can be seen that the oscillating monopile 2 approaches the guide 6, whereas the guide 6 is still not displaced by the control system 15. At a certain moment the distance between the monopile 2 and the guide 2 becomes smaller than a predetermined value. The motion compensation can be started as soon as the monopile 2 arrives in the range of the position sensors 16. Subsequently, the guide 6 starts to follow the oscillating path of the monopile 2 within the main plane. As a consequence the monopile 2 can safely move further inside the space that is bordered by the receiving part 9 and finally, as soon as the centerline of the monopile 2 substantially coincides with the centerline CL of the guide 6 the doors 10 are closed and the bogeys 12 are extended. Then, the control system 15 may control the hydraulic cylinders 13, 14 such that the guide 6 counteracts the oscillating motion of the monopile 2 in order to stabilize the monopile 2 with respect to the hull 3. After stabilizing the monopile 2 with respect to the hull 3 the monopile 2 needs to be actively positioned with respect to the sea bottom B as it needs to be stabbed at the right target location. After that, the hoisting cable 7 may be decoupled from the monopile 2 and a pile driving device 8 can be placed on top of the monopile 2 in order to drive the monopile 2 into the seabed B.

[0041] FIG. 6 shows that the guide 6 is rotatable with respect to the hull 3 about an axis that extends perpendicular to the main plane of the guide 6. Consequently, the opening can be directed in a different direction in the open condition of the guide 6. In the situation as shown in FIG. 6 the opening is directed in a direction perpendicularly with respect to a longitudinal axis of the hull 3. Hence, the centerline CL of the guide is not located at an end of the partly circular path D of the monopile 2 towards the guide 6 such as in the conditions as shown in FIGS. 3 and 4.

[0042] The invention is not limited to the embodiment shown in the drawings and described hereinbefore, which may be varied in different manners within the scope of the claims and their technical equivalents.