System and method for connecting a service vessel and a floating support structure

Abstract

The invention describes a system and a method for connecting a service vessel (1) and a floating support structure (2) for a wind turbine (3). The service vessel comprises an aft coupling section (5) and vessel contact means (6), that can be lifted by elevation means, positioned on the aft coupling section (5), upward and downward between a higher contact position and a lower free position. The floating support structure (2) comprises a central coupling space (7) capable of receiving the aft coupling section (5) and support structure contact means (8) for interacting with the vessel contact means (6) when the aft coupling section (5) is centrally positioned in the coupling space (7) and the vessel contact means (6) are moved upward. The vessel contact means (6) are positioned at an altitude below the support structure contact means (8) when the vessel contact means (6) are at the lower free position.

Description

[0001] Title: System and method for connecting a service vessel and a floating support structure

[0002] Description

[0003] Field of the invention

[0004] The invention relates to off-shore wind energy, more specifically to a system for coupling a service vessel with a floating support structure and enabling them to move as one structure.

[0005] Background

[0006] Off-shore wind is a growing energy source that will be a part of the future energy mix. Due to the remote location relative to onshore sites suitable for maintenance and repair it is desirable to be able to do all the maintenance and repair on the off-shore location, eliminating the need for floater disconnection for towing to shore. Prior art resolved heavy maintenance operations by disconnecting and towing the floater assembly and wind turbine to port. This is an expensive and very time-consuming solution and will involve detaching both anchoring systems and electrical cables before towing the wind turbine to an on-shore site.

[0007] Fred Olsen 1848 AS resolves the issue of heavy maintenance by simply mounting a crane on the support structure of the wind turbine. This will be time consuming and require a purpose designed support structure as shown on their homepage: https: / / www.fredolsenl 848.com / technologies / floating-maintenance-solution / . Fred Olsen also describes an alternative solution on their home pages: https: / / www.fredolsenl 848.com / news / fred-olsen-1848-is-developing-a-complete-o- m-solution-and-operational-procedure-for-mai or-component-exchange-that-is- optimized-for-the-floating-foundation-brunel / . Here a jack-up barge is contacting its feet to pontons of the floating structure of the wind turbine and jack the barge up above the water thus eliminating relative movement of the barge and the floating structure. A problem with this solution is that the pontoons must be strengthened and that the jack-up process takes a long time.

[0008] Heavy maintenance operations may be required for key large components, such as gear boxes and even the complete RNA (Rotor Nacelle Assembly). It is a challenge to provide the required lifting capacity in areas where jack up vessel cannot be used due to the water depth. In addition, the relative motion between the crane and the floating support structure complicates the crane operations. It is an object of the invention to provide a system and a method for connecting a service vessel and a wind turbine structure offshore in deep waters, enabling the service vessel is able to perform all service operations on site.

[0009] Summary of the invention

[0010] In one aspect of the invention it is described a system for connecting a service vessel and a floating support structure for a wind turbine. The service vessel comprises an aft coupling section, vessel contact means positioned on the aft coupling section and elevation means coupled to the vessel contact means at one end and to a deck of the service vessel at an opposite end. The vessel contact means and the elevation means are configured to move the vessel contact means upward and downward between a higher contact position and a lower free position. The floating support structure comprises a central coupling space capable of receiving the aft coupling section of the service ship and support structure contact means positioned on a top side of the coupling space for interacting with the vessel contact means when the aft coupling section is centrally positioned in the coupling space and the vessel contact means are moved upward. The vessel contact means are positioned at an altitude below the support structure contact means when the vessel contact means are at the lower free position and the vessel contact means contacts the support structure contact means before reaching the higher contact position.

[0011] In an embodiment of the invention the support structure contact means comprises strengthened sections and the vessel contact means comprises support fenders configured to receive the strengthened sections.

[0012] In yet an embodiment of the invention the support structure contact means comprises strengthened sections and the vessel contact means comprises support cribs configured to receive the strengthened sections thereon.

[0013] In yet an embodiment of the invention the elevation means comprises ballast tanks positioned above a waterline having large exit hatches for quick deballasting and ballast tanks positioned below the waterline having large intake hatches for quick ballasting.

[0014] In yet an embodiment of the invention elevation means comprises one or more elevation tables having the vessel contact means positioned on top.

[0015] In yet an embodiment of the invention the vessel contact means contacts the support structure contact means in at least three positions, wherein a line between the at least three positions enclose a point of gravity (G). In yet an embodiment of the invention the support structure comprises two transverse floating front units connected to each other by means of a horizontal transverse section interconnecting the two transverse floating front units above a waterline, the horizontal transverse section comprises a mid-point, an aft longitudinal section and an aft floating unit connected to the mid-point by means of the aft longitudinal section above the waterline, thus forming the central coupling space between the floating units and the aft floating unit.

[0016] The support structure may comprise three main sections each comprising a horizontal part above a water line and a vertical part, directly or indirectly connected to the respective horizontal parts and oriented in a vertical plane in common with the respective horizontal parts. The vertical parts may provide buoyancy to the floating support structure. The support structure may further comprise a transition piece for joining the three main sections in a central region. The coupling space may be positioned below the three horizontal parts and between the vertical parts.

[0017] In yet an embodiment of the invention the system further comprises a wind turbine connected on top of the floating support structure and wherein a point of gravity (G) of the combined structure of the wind turbine and support structure is positioned vertically above a central line (L) of the central coupling space.

[0018] In another aspect of the invention it is described a method for connecting a service vessel and a floating support structure for a wind turbine by means of system described above. The method comprises the following steps:

[0019] A: positioning the vessel contact means in the lower free position,

[0020] B: maneuvering the aft coupling section of the service vessel into the central coupling space of the floating support structure to a position where the vessel contact means are able to interact with the support structure contact means, and C: elevating the vessel contact means to a higher contact position for interacting with the support structure contact means.

[0021] In an embodiment of the invention step C comprises lifting the vessel contact means further upward to allow a portion of the weight of the floating support structure to rest on the vessel contact means.

[0022] In an embodiment of the invention step B comprises use of a dynamic positioning system for accurate maneuvering the aft coupling section 5 of the vessel into the central coupling space 7 of the support structure

[0023] Brief description of the drawings The following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where the same reference number in different drawings represent the same feature:

[0024] Fig. la shows a service vessel and an embodiment of a floating support structure joined together.

[0025] Fig. lb shows a service vessel and an alternative embodiment of a floating support structure j oined together.

[0026] Fig. 2 shows an embodiment of the service vessel.

[0027] Fig. 3 a and b shows an embodiment of the floating support structure including the coupling space from above and from the front, respectively.

[0028] Fig. 3c and 3d shows an alternative embodiment of the floating support structure including associated coupling space from above and from the front respectively.

[0029] Fig. 4a shows the service vessel and an embodiment of the floating support structure lined up for coupling.

[0030] Fig. 4b shows the service vessel and an alternative embodiment of the floating support structure lined up for coupling.

[0031] Fig. 5 shows an embodiment of the elevation means comprising elevation tables.

[0032] Fig. 6 shows an embodiment of the elevation means comprising hydraulic pistons.

[0033] Fig. 7 shows an embodiment of the vessel contact means comprising support fenders and damping cushions.

[0034] Fig. 8 shows an embodiment of the vessel contact means comprising cribs and elevation means in the form of ballasting tanks.

[0035] Fig. 9 shows an embodiment of the elevation means comprising pairs of lifting arms joined in their top ends

[0036] Fig. 10 shows wire connectors and wires for strengthening of the connection between the floating support structure and service vessel

[0037] Detailed description

[0038] The invention describes a system for connecting a service vessel 1 and a floating support structure 2 for a wind turbine 3 as shown in fig. l a and b. The system is intended to merge the service vessel and the floating support structure into one structure with regards to movements caused by wind and waves. Although, the initial contact between the service vessel and floating support structure still requires a weather window the present invention will allow heavy maintenance operation to take place once connection has been made. The extra weight and extra width and length obtained by the combined structure may also stabilizes the combined structure.

[0039] The system comprises a service vessel 1 and a floating structure 2 for a wind turbine. An embodiment of the service vessel 1 is shown in fig. 2 and two alternative embodiments of the floating support structure 2 is shown in fig 3 a and b and fig. c and d respectively. The service vessel comprises an aft coupling section 5 configured to interact with a central coupling space 7 of the floating support structure 2. As indicated in fig. 4a and b the Service vessel moves into the coupling space 7 and then lifts the floating structure with sufficient force to remain in stable contact with floating structure in the prevailing weather conditions. The lifting can be done in many different ways and some examples will be described in this text. In most embodiments the aft coupling section 5 is the aft part of the service vessel 1.

[0040] The aft coupling section 5 of the service vessel 1 comprises vessel contact means 6 positioned on the aft coupling section as seen in fig. 2. The vessel contact means is in direct or indirect contact with elevation means 10, which is able to move the vessel contact means 6 upward and downward between a higher contact position and a lower free position. The elevation means 10 may be automatically compensated to counteract relative motion between the floating support structure and the service vessel during connection. Preferably large side and rear fenders 29a and b are positioned on the side and rear of the service vessel respectively as seen in fig. 2.

[0041] In an advantageous embodiment the service vessel is provided with a Dynamic Positioning system (DP system) to ease the maneuvering of the service vessel into the coupling space. The DP system may be based on positioning points connected to the floating support structure or based on GPS signals. Many such systems are on the market and will not be described in greater detail.

[0042] The central coupling space 7 of the service vessel 1 is configured for receiving the aft coupling section 5 of the service ship 1 as seen in fig. 3a - d. For this purpose support structure contact means 8, indicated in fig. 5, are positioned on the floating support structure on a top side 9 of the coupling space 7 for interacting with the vessel contact means 6 when the aft coupling section 5 is centrally positioned in the coupling space 7 and the vessel contact means 6 are moved upward towards the higher contact position. In some embodiments the support structure contact means 8 will simply be the shape of the upper side of the coupling space 7, which may be reinforced to handle the weight of the floating support structure resting on the vessel contact means.

[0043] The altitude above sea level of the different interacting features on the vessel and floating support structure 2 are of great importance. The vessel contact means 6 of the service vessel 1 must be positioned at an altitude below the support structure contact means 8 when the vessel contact means 6 are at the lower free position. Their difference in altitude must also allow for some degree of wave action when the aft contact section 5 enters the coupling space 7. When the elevation means 10 are activated the vessel contact means 6 must be able to contact the support structure contact means 8 before reaching the higher contact position.

[0044] Generally, the coupling space 7 is free for obstacles to a depth below the deepest draft of the service vessel 1 and in the space between the water surface and the contact means.

[0045] After contact between vessel contact means 6 and support structure contact means 8 has been made, the elevation means must continue the upward movement until sufficient weight has been transferred from the buoyant parts of the floating structure 2 to the support vessel 1 . When a given measure of weight has been transferred to the service vessel 1 the combined structure of the service vessel and floating support structure will behave as one structure as long as forces from waves, wind and other external sources stay below a threshold mainly determined by the given measure of weight and the nature of the vessel contact means 6 and the support structure contact means 8. Generally, more weight transferred to the support vessel will enable the combined structure to withstand stronger forces from bigger waves and stronger winds.

[0046] Transfer of weight from the floating support structure 2 to the to the service vessel 1 will cause a change in the distribution of forces acting on the floating support structure. The support structure contact means 8, in some embodiments, comprise strengthened sections 27 as indicated in fig. 4 and 5. The embodiment of the vessel contact means shown in fig. 5 and fig. 7 comprises support fenders 11 configured to receive the strengthened sections 27 of the support structure contact means 8. The support fenders 11 may have a shape matching the shape of the floating support structure, for instance a rounded recession matching a tubular shape of a tubular of the floating support structure. The embodiment shown in fig. 5 also shows a damping cushion 15 on each side of the support fender, which may comprise an inflatable function. The damping cushion 15 will touch the support structure contact means first and provide a damping effect when wave action causes the vessel contact means to crash into the floating support structure before a stable contact has been established. In an embodiment seen in fig. 8 the vessel contact means 6 comprises support cribs 12 configured to receive the strengthened sections 27 of the support structure contact means.

[0047] The elevation means 10 may have many embodiments and in an embodiment indicated in fig. 8 the elevation means 10 comprises high ballast tanks 19 positioned above the waterline having large exit hatches for quick deballasting and low ballast tanks 28 positioned below the water line having large intake hatches for quick ballasting.

[0048] In an embodiment shown in fig. 5 the elevation means 10 comprises one or more elevation tables 13 having the vessel contact means 6 positioned on top. In a preferred embodiment the elevation means comprises both ballasting tanks 19, 28 and elevation tables.

[0049] In an embodiment shown in fig. 6 the elevation means 10 comprises a plurality of hydraulic pistons 16 connected to support structure contact means 8 in the form of strong point connectors 18 connected to the hydraulic pistons 16 strong points 17. A notable difference from the embodiments of the vessel contact means 6 describing support cribs 12 or support fenders 11 is that the hydraulic pistons 16 and strong point connectors 18 interacting with the strong points 17 may be configured to maintain contact with the floating support structure also when external forces, like waves, would have lifted the support structure from the aft coupling section if there were no hydraulic piston 16 to hold it down.

[0050] In order to strengthen the coupling between the service vessel and the floating support structure a number of wires 25 may be attached to the aft coupling section 5 and to wire connectors 26 on the floating support structure as indicated in fig. 10. This may be an option when lifting heavy items from the wind turbine to the service vessel. The nacelle may have a weight of 800 tons and would cause the service vessel to loose contact with the floating support structure if the nacelle is taken off the wind turbine and placed on the service vessel and the weight transferred from the support structure to the service vessel is less than 1600 tons. Clearly, such an operation may only be done in fair weather and will probably have a rather narrow weather window, but when comparing a week of waiting with detaching the wind turbine from anchor and electrical cables and then towing the wind turbine to shore a narrow weather window is acceptable.

[0051] Conceivably the wires 25 may in one embodiment constitute the elevation means 10. The wires 25 may be fastened to the aft coupling section 5 and the floating support structure 2 and when tightened with winches the vessel contact means 6 are moved to the higher contact position providing contact between the vessel contact means and the support structure contact means.

[0052] In another embodiment shown in fig. 9 the elevation means comprises pairs of lifting arms 20 connected together in their top ends, wherein their lower ends are running in guiding tracks 21 and is elevated by a wire system below deck pulling the lower ends towards each other to rise their top ends.

[0053] In an embodiment the vessel contact means 6 contacts the support structure contact means 8 in at least three positions, wherein a line between the at least three positions encircles the point of gravity of the wind turbine and floating support structure as indicated in fig. 4.

[0054] Figure 3a and 3b shows an embodiment of the support structure 2, which comprises two transverse floating front units 30a, b connected to each other by means of a horizontal transverse section 31 above the water. Furthermore an aft floating unit 32 is connected to a mid-point 33 of the horizontal transverse section 31 by means of a horizontal aft longitudinal section 34 above water, thus forming a central coupling space 7 between the floating units 30a, 30b and 32 for receiving the aft coupling section 5 of the service vessel 1. Obviously other constructions are possible. Instead of three buoyant units there might be four or five or the floating support structure may be shaped as a catamaran and the coupling space may be located between the two hulls of the catamaran. However, we note that the three-legged version shown in fig. 3 a and 3 c shows the best rating when evaluating stability achieved per tons of steel and the tubular shape of the transverse section and the aft longitudinal section are able to be lifted by the service vessel without much extra strengthening.

[0055] The point of gravity G of the combined structure of the wind turbine 3 and support structure 2 is preferably positioned vertically above a central line L of the coupling space 7 as indicated in fig. 3a. It is an advantage to have the contact points between the vessel and the support structure at a high level because the mass of the support structure below the contact points will have a stabilizing function.

[0056] Fig. 3 c and d shows a preferred embodiment of the support structure 2 from above and from the side. The support structure comprises three main sections 35a, 35b, 35c each comprising a horizontal part 36 above a water line and a vertical part 37, directly or indirectly connected to the respective horizontal parts 36 and oriented in a vertical plane in common with the respective horizontal parts 36. The vertical parts 37 provide buoyancy to the floating support structure 1 . The support structure further comprises a transition piece 15 for joining the three main sections 35a, 35b, 35c in a central region and providing a solid base for a wind turbine tower. The coupling space 7 is positioned below the three horizontal parts 36 and between the vertical parts 36. Preferably, the vertical parts is positioned in respective corners of a equidistant triangle and the coupling space comprises the expanse of a rectangular cuboid positioned through a side of the mentioned triangle and extending backward in a direction at a right angle to the mentioned side until touching a vertical part (36) opposite of the mentioned side as seen in fig 3c.

[0057] The embodiment shown in fig. 3c and 3d have the advantage that, due to the symmetry of the structure, the point of gravity and buoyance of the support structure coincides with the point of gravity of the combined structure and three alternative coupling spaces are provided enabling the operators to choose the coupling space most convenient according to weather conditions. Furthermore, it is possible for the operator to move the crane closer to tower as compared to the embodiment shown in fig. 3a and 3b.

[0058] The invention also describes a method for connecting a vessel and a floating structure for a wind turbine by means of the system described above. The method comprises the following steps:

[0059] A Positioning the vessel contact means 6 in a lower free position.

[0060] B Maneuvering the aft coupling section of the service vessel 1 into the central coupling space 5 of the floating support structure 2 to a position where the vessel contact means 6 are able to interact with the support structure contact means 8.

[0061] C Elevating the vessel contact means 6 to a higher contact position for interacting with the support structure contact means 8.

[0062] In an embodiment of the method step C comprises lifting the vessel contact means 6 further upward to allow a portion of the weight of the support structure to rest on the vessel contact means 6.

[0063] In an embodiment step C may comprise first lifting the elevation tables until the vessel contact means 6 touches the support structure means 8 and then emptying the high ballasting tank 19.

[0064] Preferably step B comprises use of a dynamic positioning system for accurate maneuvering the aft coupling section 5 of the vessel into the central coupling space 7 of the support structure.

[0065] Preferably, the aft coupling section 5 is able to perform a quick escape from the coupling space 7 in case of sudden weather changes or other imminent threats. By filling the low ballasting tanks 28 the service vessel will be able to disconnect with the floating support structure in a matter of minutes because in most embodiments it is only the weight of the support structure resting on the aft coupling section 5 that holds the two structures together. If connectors of a locking kind are used they should have a freeing mode for quick release in case of emergencies.

[0066] References

[0067] 1 Service vessel

[0068] 2 Support structure

[0069] 3 Wind turbine

[0070] 5 Aft coupling section

[0071] 6 Vessel contact means

[0072] 7 Central coupling space

[0073] 8 Support structure contact means

[0074] 9 Top side of central coupling space

[0075] 10 Elevation means

[0076] 11 Support fenders -High deformation support means

[0077] 12 Support cribs

[0078] 13 Elevation tables

[0079] 14 Crane

[0080] 15 Damping cushions -Low deformation support means

[0081] 16 Hydraulic pistons

[0082] 17 Strong points

[0083] 18 Strong point connector

[0084] 19 Ballasting tanks

[0085] 20 Lifting arms

[0086] 21 Guiding tracks

[0087] 22 Anchor lines

[0088] 23 Rotor blades

[0089] 24 Nacelle

[0090] 25 Wire connectors

[0091] 26 Wire

[0092] 27 Strengthened section

[0093] 28 Lowl7 ballasting tanks

[0094] 29a and b Side and rear fenders

[0095] 30a, b Transverse floating units

[0096] 31 Horizontal transverse section

[0097] 32 Aft floating unit

[0098] 33 Mid-point of horizontal transverse section

[0099] 34 Aft longitudinal section

[0100] 35 a, b and c Three main parts

[0101] 36 Horizontal part

[0102] 37 Vertical part

Claims

Claims1. System for connecting a service vessel (1) and a floating support structure (2) for a wind turbine (3), wherein the service vessel (1) comprises: an aft coupling section (5), vessel contact means (6) positioned on the aft coupling section (5), elevation means (10) directly or indirectly coupled to the vessel contact means (6), wherein the vessel contact means (6) and the elevation means (10) are configured to move the vessel contact means (6) upward and downward between a higher contact position and a lower free position, wherein the floating support structure (2) comprises: a central coupling space (7) capable of receiving the aft coupling section (5) of the service ship (1), and support structure contact means (8) positioned on a top side 9 of the coupling space (7) for interacting with the vessel contact means (6) when the aft coupling section (5) is centrally positioned in the coupling space (7) and the vessel contact means (6) are moved upward, and wherein the vessel contact means (6) are positioned at an altitude below the support structure contact means (8) when the vessel contact means (6) are at the lower free position and the vessel contact means (6) contacts the support structure contact means (8) before reaching the higher contact position.

2. System according to claim 1, wherein the support structure contact means (8) comprises strengthened sections (27) and the vessel contact means (6) comprises support fenders (11) configured to receive the strengthened sections (27).

3. System according to claim 1, wherein the support structure contact means (8) comprises strengthened sections (27) and the vessel contact means (6) comprises support cribs (12) configured to receive the strengthened sections (27) thereon.

4. System according to any one of the preceding claims, wherein the elevation means (10) comprises:ballast tanks (19) positioned above a waterline having large exit hatches for quick deballasting and ballast tanks (19) positioned below the waterline having large intake hatches for quick ballasting.

5. System according to any one of the preceding claims, wherein the elevation means (10) comprises one or more elevation tables (13) having the vessel contact means (6) positioned on top.

6. System according to any one of the preceding claims, wherein the vessel contact means (6) contacts the support structure contact means (8) in at least three positions, wherein a line between the at least three positions enclose a point of gravity (G).

7. System according to any one of the preceding claims, wherein the support structure (2) comprises: two transverse floating front units (30a, b) connected to each other by means of a horizontal transverse section (31) interconnecting the two transverse floating front units (30a, b) above a waterline, the horizontal transverse section (31) comprises a mid-point (33), an aft longitudinal section (34) and an aft floating unit (32) connected to the mid-point (33) by means of the aft longitudinal section (34) above the waterline, thus forming the central coupling space (7) between the floating units (30a, b) and the aft floating unit (32), and wherein the coupling space is positioned below the horizontal transverse section and the aft longitudinal section and between the two transverse floating units and the aft floating units.

8. System according to any one of the preceding claims 1-6, wherein the support structure (2) comprises: three main sections (35a, 35b, 35c) each comprising: a horizontal part (36) above a water line, a vertical part (37), directly or indirectly connected to the respective horizontal parts (36) and oriented in a vertical plane in common with the respective horizontal parts (36), wherein the vertical parts (37) provide buoyancy to the floating support structure (1), and a transition piece (15) for joining the three main sections (35a, 35b, 35c) in a central region, andwherein the coupling space (7) is positioned below the three horizontal parts (36) and between the vertical parts (36).

9. System according to any of the preceding claims, wherein the system further comprises a wind turbine (3) connected on top of the floating support structure and wherein a point of gravity (G) of the combined structure of the wind turbine (3) and support structure (2) is positioned vertically above a central line (L) of the central coupling space (7)10. Method for connecting a service vessel (1) and a floating support structure (2) for a wind turbine (3) by means of a system according to any one of claims 1 -7, the method comprising the steps:A: positioning the vessel contact means (6) in the lower free position, B: maneuvering the aft coupling section (5) of the service vessel (1) into the central coupling space (7) of the floating support structure (2) to a position where the vessel contact means (6) are able to interact with the support structure contact means (8), andC: elevating the vessel contact means (6) to a higher contact position for interacting with the support structure contact means (8).

11. Method according to claim 9, when dependent on claim 2 or 3, wherein step C comprises lifting the vessel contact means (6) further upward to allow a portion of the weight of the floating support structure (2) to rest on the vessel contact means (6).

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