System for Offshore Power Generation

Abstract

An offshore power generating system has a buoyancy body shaped as a hull with a bow and aft end, and elongated mast extending up from the buoyancy body to the buoyancy body about a horizontal transverse axis. A rotor is supported in one end of the longitudinal mast for rotation about a horizontal axis. The buoyancy body is kept in position with the bow turning up into wind and incoming waves. Rotational support of the mast has a horizontal rotational axis through the center of gravity of the mast that lies in the center plane of the buoyancy body above the aft end when the buoyancy body lies in operational position in calm sea with the rotational axis of the rotational support of the mast orthogonal to the center plane of the buoyancy body. A method for on-board loading and commissioning of mast with installed rotor on-board a buoyancy body.

Claims

1-23. (canceled)

24. An offshore power generating system (100), comprising: a buoyancy body (110) having a shape of a hull and a length between a bow (112) and an aft end (111); an elongated mast (140) extending upwards from the buoyancy body (110) and supported on the buoyancy body (110) in a rotatable arrangement about a horizontal transverse axis (122); a rotor supported in one end of the longitudinal mast (140) for rotation about a horizontal axis oriented in the length direction of the buoyancy body (110); an arrangement for keeping the buoyancy body (110) in a position with the bow (112) turning up towards the wind and incoming waves, wherein a rotational support of the mast (140) comprises a horizontal, transversally orientated rotational axis (122) through the center of gravity of the mast (140), wherein a center of gravity of the mast (140) lies in a center plane (114) of the buoyancy body (110) vertically above the aft end (111) of the buoyancy body (110) when the buoyancy body (110) lies in an operational position in calm sea, and where the rotational axis (122) of the rotational support of the mast (140) is orthogonal to the center plane (114) of the buoyancy body (110).

25. The offshore power generating system (100) according to claim 24, wherein the center of buoyancy (112) of the buoyancy body (110) lies in a point at a length position that is no greater than 25% of the length of the buoyancy body (110) from the aft end (111) of the buoyancy body (110).

26. The offshore power generating system (100) according to claim 24, wherein the shape of the buoyancy body (110) in the horizontal plane can be circumscribed by a triangle, and the buoyancy body (110) has a maximum width at the aft end (111).

27. The offshore power generating system (100) according to claim 26, wherein the shape of the buoyancy body is defined by a compressive load on the surface in the order of 3-6 metric tons/m.sup.2 on the vertical projection of the buoyancy body (110) on the surface with a block coefficient of approximately 0.35, wherein the block coefficient is given by the formula:
CB=V/L*B*T, wherein V is an underwater volume of the buoyancy body (110), L is the length of the buoyancy body (110), B is the maximum width of the buoyancy body (110), and T is the draft of the buoyancy body.

28. The offshore power generating system (100) according to claim 24, wherein the shape of the buoyancy body (110) is defined by a draft corresponding to a significant wave height in the sea state for which it is designed.

29. The offshore power generating system (100) according to claim 24, wherein the rotor comprises a wind turbine (130) enclosed by a wind turbine housing (131) having aerodynamic properties mounted on the mast (140).

30. The offshore power generating system (100) according to claim 29, wherein the wind turbine housing (131) further comprises a water ballast tank.

31. The offshore power generating system (100) according to claim 24, wherein the mast is movable between an operating position (140a), an on-board loading and maintenance position (140b), and a survival position (140c).

32. The offshore power generating system (100) according to claim 31, wherein, in the operating position, the mast (140) with rotor and the wings of the rotor in the vertical plane form an angle a relative to a vertical plane of between 0 and 15 degrees pointing astern from the buoyancy body.

33. The offshore power generating system (100) according to claim 31, wherein, in the on-board loading and maintenance position (140b), the mast (140) and the wings (132) of the rotor are in the horizontal plane, and in survival position (140c), the mast (140) and the wings (132) of the rotor are 45-50 degrees astern from the buoyancy body relative to a vertical plane.

34. The offshore power generating system (100) according to claim 24, wherein the offshore power generating system (110) comprises one or more devices for rotating the mast (140) with wind turbine (130) between different positions (140a-c), wherein the device for rotating the mast (140) comprises one or more of rope means, winches and hydraulic cylinders on the foundation of the mast (140), the rope means comprising fiber rope, wire or chain, or hydraulic actuators for adjusting or changing the positions (140a-c) of the mast (140).

35. The offshore power generating system (100) according to claim 24, wherein the mast (140) with rotor is temporarily lockable in the operating position (140a) by a releasable restraint mechanism.

36. The offshore power generating system (110) according to claim 35, wherein the restraint mechanism comprises a plurality of hydraulically operated shear bolts arranged at the lower part of the mast foot.

37. The offshore power generating system (100) according to claim 24, wherein the mast with rotor maintains approximate operating position (140a) by one or more dampening devices (160) for maneuvering the mast (140) for compensation of the pitch motions of the buoyancy body (110).

38. The offshore power generating system (100) according to claim 37, wherein at least one of the one or more dampening devices comprises a unit for maneuvering of the mast (140), the unit for maneuvering of the mast (140) being controlled by a control unit receiving signals from sensors, wherein the control unit is configured to activate the dampening devices (160) for maneuvering of the mast (140) to maintain the mast (140) in as stable operating position (140a) as possible.

39. The offshore power generating system (100) according to claim 38, wherein the unit for maneuvering the mast (140) comprises hydraulic cylinders for compensating pitch motions of the buoyancy body (110).

40. The offshore power generating system (100) according to claim 24, wherein the device for keeping the buoyancy body (110) towards the wind comprises an anchoring system arranged at the bow (112) of the buoyancy body (110) and optionally thrusters at least at the aft end (111) of the buoyancy body (110).

41. The offshore power generating system (100) according to claim 24, where the pivotal support of the mast (140) is retained by at least one support stand (123) placed astern of the buoyancy body (100), where the support stands (123) comprise at least one leg with an aerodynamic cross section anchored in the buoyancy body (110) where the rotational support comprises a bearing housing (121) arranged on top of the support stands (123).

42. The offshore power generating system (100) according to claim 31, wherein the lower part of the mast (140) in its normal operating position (140a) is in a separate well (115) in the hull of the buoyancy body (110).

43. The offshore power generating system (100) according to claim 34, wherein the devices for rotating the mast (140) with the wind turbine (130) between different positions (140a-c) is in a separate well (115) in the hull of the buoyancy body (110).

44. The offshore power generating system (100) according to claim 42, where the well (115) comprises the restraint mechanism.

45. A method for on-board loading and commissioning of a mast (140) with mounted rotor on-board in a buoyancy body (110), comprising the steps of: placing the mast (140) with rotor in a horizontal on-board loading position (140b) on a movable rig (170) on a quay, ashore or on a floating unit on water, the buoyancy body (110) ballasted with water for receiving the mast (140) in which the buoyancy body (110) is positioned adjacent the movable rig (170); pumping out water ballast for weight transfer of the mast (140) with rotor; and rotating the mast (140) with rotor, with center of gravity in support, to different positions of the mast selected from an operating position (140a), on-board and maintenance position (140b), and survival position (140c).

46. The method according to claim 45, further comprising the steps of: engaging a plurality of hydraulically operated shear bolts with the mast foot at normal operating position (140a) of the mast (140) to lock the mast (140) in the normal operating position (140a); and moving the hydraulic shear bolts out of the engagement with the mast foot, thereby activating a plurality of hydraulic cylinders to compensate the pitching motions of the buoyancy body (110), wherein the hydraulic cylinders adjust the angular positions (160′) of the mast (140) to maintain the position of the mast (140) relative to the horizontal plane at calm sea within 2-4 degrees of the normal operating position (140a) of the mast (140) at calm sea; or moving the hydraulic shear bolts out of engagements with the mast foot to maneuver the mast (140) to a desired position of the mast (140) between the normal operating position (140a), loading and maintenance position (140b) and survival position (140c).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Embodiments of the present invention will now be described in detail, with reference to the following diagrams wherein:

[0074] FIG. 1 shows prior art of wind turbines arranged on a frame on a ship;

[0075] FIG. 2 shows schematically and in perspective one possible embodiment of a system for offshore power generation, where the system shows a buoyancy body with mounted/installed mast with a wind turbine in normal operating position;

[0076] FIG. 3A shows schematically and in perspective one possible embodiment of the buoyancy body in a normal operating state;

[0077] FIGS. 3B and 3C show schematic views of variants of a possible hull shape seen from above;

[0078] FIG. 3D shows schematically an advantageous cross section of the hull;

[0079] FIG. 4 shows schematically and in perspective a mast with a wind turbine designed for mounting on support stands;

[0080] FIG. 5 shows schematically and in perspective a truncated longitudinal section in the center plane with the mast in different positions; and

[0081] FIGS. 6A-6C shows schematically possible steps in a method for on-board loading of a mast with a wind turbine.

DETAILED DESCRIPTION

[0082] The following description of the exemplary embodiments of the present invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention or the scope of protection, as the scope of protection is defined by the person skilled in the art's interpretation of the scope of the appended claims.

[0083] Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment.

[0084] FIG. 1 shows prior art of wind turbines arranged on a frame on a ship, as mentioned in US 2007138021, showing several wind turbines 130 arranged on a frame on a buoyancy body 110 here represented by a ship. The frame or the mast 140 is supported by a bearing housing 121 on the ship forming a hinged link to the ship deck 116 and has one or more counterweights connected to the shaft. The counterweight is used to rotate the frame 120 with wind turbines 130 between a horizontal and vertical position. The ship 130 may be designed so that the counterweight is above or below the water surface 120 when the frame is in vertical position.

[0085] FIG. 2 shows schematically and in perspective one possible embodiment of a system for offshore power generation 100. The system 100 shows a buoyancy body 110 at a sea surface 150 with mounted/installed mast 140 with a wind turbine 130 in normal operating position, inclined about 9 degrees astern. The mast 140 with wind turbine 130 mounted/installed in one end of the mast 140 whereby the opposite end of the mast 140 forms a mast foot located in a well 115. The well permits a stable attachment of the mast foot, as well a protected room for equipment for maneuvering, not shown, of the mast 115. It is not open to sea, not shown in the figure, and can be filled and emptied by the bilge and ballast system of the buoyancy body. The description on FIG. 4B below gives a more detailed description of the maneuvering equipment. The mast 140 can be rotated to achieve desired positions for normal operating position, on-board loading position, maintenance position and survival position respectively, further discussed in connection with FIG. 6B below.

[0086] The mast 140 rotates about an axis of rotation 122, which is at the center of gravity of the mast 140. The mast 140 is at this point mounted/installed on bearing shafts 141, which extend on either side of the mast 140. The bearing shafts 141 of the mast 140 are supported between two bearing housings 121 mounted/installed on two support stands 123 astern of the buoyancy body.

[0087] FIG. 3A shows schematically a perspective of one embodiment of the buoyancy body 110 in a normal operating state. The buoyancy body 110 has an approximately triangular base shape with a wide stem 113 where a center of buoyancy 120 lies in a distance from the stem 113 of approximately ¼ or less of the length of the buoyancy body 110, and a contact surface with the sea 150 where the center of floatation 119 has a distance from the stem 113 of approximately ⅓ of the length of the buoyancy body 110, or less. The buoyancy body 110 is closest to the wind direction equipped with a single point anchoring system 124 known from the offshore industry. The anchoring system 124 provides for holding the buoyancy body 110 up into the wind and is preferably arranged at the bow of the buoyancy body 110, in addition, thrusters arranged at the aft end 111 of the buoyancy body can further assist keeping the buoyancy body 110 up into the wind. The buoyancy body 110 is equipped with two symmetrically positioned support stands 123 astern with legs comprising aerodynamically shaped cross sections and with shared bearing housing 121 on the top forming a rotational axis 122 for the mast 140. The bearing housings 121 are installed with a common horizontal center line 122 perpendicular to the buoyancy body's center plane 114, at a height above the deck adapted to the purpose of the support stands 123 which, among other things, may be to receive offshore structures such as masts 140 with wind turbines 130.

[0088] FIG. 3A shows two support stands 123 protruding up and are approximately perpendicular to the buoyancy body 110 and the sea surface 150 at calm sea. The support stands 123 are not limited to protrude up in this direction, each of which may also project slanted from the buoyancy body 110. Each support stand 123 is further shown to comprise of a single strut, but each of them may also be combined with one or more slanted/inclined struts for stiffening the structure.

[0089] The buoyancy body's 110 contact with the energy-rich sea surface 150 is made large enough so that an irregular and a position variable energy distribution can be integrated by the horizontal area of the buoyancy body 110, so that the energy distribution of the waves below the buoyancy body 110 can be cancelled and the buoyancy body's 110 response on the existing forces thereby are reduced.

[0090] The size of the contact surface has a low weight load per area unit, typically about 3-4 metric tonnes/m.sup.2, so that no problems with loading capacity, trim, stability and survivability will arise and will thus give the buoyancy body 110 a draft allowing docking at offshore ship yards and docking in existing dry docks. The contact surface between the buoyancy body 110 and the sea may assume different variants 10 of the base triangle where the desired location of the water line center of floatation 119 is fulfilled as shown in FIGS. 3B and 3C.

[0091] The shape of the buoyancy body 100 in the horizontal plane will influence the distribution of the buoyancy along the length L of the buoyancy body 110, which also will assume an approximate triangular shape, with the largest cross-sectional area close to the stem 113.

[0092] The sole purpose of the buoyancy body 110 is to support the wind turbine 130, and can, above the sea surface 150, instead of a conventional deck, be replaced by a super structure 116 shaped so that incoming sea is allowed to move away from the buoyancy body 110 and to excite as little motions as possible. The underwater hull 117 of the buoyancy body 110 has a shape adapted to the load of the waves upon which the super structure 116 can be shaped approximately similar to the underwater hull 117 with the keel pointing upwards, as shown in a cross section 11 in FIG. 3D. The super structure 116 takes the waves so that the hull gets less motions by the waves rolling over rather than colliding with a bow. This increases the survivability of the buoyancy body 110 by better tolerating the encounter with the waves.

[0093] The buoyancy body's 100 volume gives sufficient room for transformers, converters, rectifiers and control equipment to process the generating energy to a desired format and groups of battery for storage of energy, preferably located in the well 115 of the buoyancy body 110, other relevant, protecting locations on the deck of the buoyancy body are relevant locations.

[0094] FIG. 4 shows a mast 140 with a wind turbine 130 designed for installation on the support stands 123. The mast 140 is preferably carried out in a light-weight material with an aerodynamic cross-section 125 as shown in FIG. 4B and with a wind turbine 130 installed, with a integrated cylindrical wind turbine housing 131 arranged on the top of the mast, so that the resistance in the wind streams are minimized. The mast 140 is, approximately at half of its height, in the mass center of gravity, in the horizontal plane and perpendicular to the center plane, installed with a cylindrical support bearing shaft 141 for support in the bearing housing 121 of the support stands 123, the support bearing shaft 141 projecting preferably out on each side of the mast 140. The mast foot is installed with fixing devices for maneuvering and or dampening of the mast and the pendulum movements of the mast and possibly brake plates for that incident when lower end of the mast is submerged in water in a well at the aft part of the vessel, to reduce angular movements about the rotational axis 122 of the mast. The well 115 may be separated from the surrounding sea so that also the volume of the well contributes to the buoyancy and stability corresponding to a tank on-board the vessel. The mast 140 with the wind turbine 130 is balanced about the rotational axis 122 so that it in installed position on the buoyancy body 110, easily may be rotated to desired positions for different purposes. The well 115 may be air-filled and the dampening devices may be a suitable releasable suspension system. FIG. 5 shows a longitudinal section in the center plane with the mast 140 in different positions 140a, 140b, 140c rotated about the rotational axis in the bearing housing 121. The mast 140 in normal operational position is indicated at 140a, on-board loading and maintenance position 140b, and survival position 140c. In all these positions the mast 140 with the wind turbine 130 will keep its mass center of gravity in the rotational axis 122, whereby the maneuvering of the mast 140 to the different positions 140a, 140b, 140c can be performed with suitable, known devices. To reduce undesired angular motions in the vertical plane, which the mast can have in certain wave conditions, and that disturbs the production of the wind turbine 130, the foot of the mast 140 is connected in the vertical plane of the buoyancy body 110 with suitable passive and/or active dampening devices 160. The well 115 may also be filled with sea water so that the brake plates which may be arranged on the mast foot may further contribute to the dampening. The relative dampening of the mast 140 relative to the unit's total angular deflection can be controlled by a control unit (not shown). A plurality of hydraulic cylinders (not shown) can act as dampening means 160. These can be actuated to compensate for pitch motions of the buoyancy body 110, where the hydraulic cylinders adjust the angular position 160′ to maintain the mast 140 in position relative to the horizontal plane at calm sea corresponding to +/−2-4 degrees of the normal operating position 140a at calm sea. When the mast is in normal operating position 140a slanting/declining 9 degrees astern, the turbine housing of the wind turbine 130 is parallel to the horizontal plane, while the wings 132 of the wind turbine 130 are parallel with the vertical plane. When the buoyancy body 110 is not subjected to pitching motions, the mast 140 will temporarily be held in normal operating position 140a by releasable restraint mechanisms. These restraint mechanisms may preferably comprise one or more hydraulically operated shear bolts disposed in the well 115 at the mast foot at the lower part of the mast 140.

[0095] In the on-board loading position 140b, the mast 140 inclines a further 90 degrees astern from normal operating position 140a, the wings 132 lying parallel to the horizontal plane. In the maintenance and survival position 140c the mast 140 inclines 45-50 degrees from normal operating position 140a. Mast 140 with wind turbine 130 maintains approximately normal operating position 140a by means of one or more dampening devices 190 for maneuvering of the mast 140 to compensate for heave/pitching motions of the buoyancy body 110. The dampening devices will comprise a unit for maneuvering the mast, which is controlled by a control unit receiving signals from sensors, for example wave sensors, wind sensors, etc. The control unit will activate the dampening devices to maneuver the mast in order to maintain the mast in as stable operating position 140a as possible. The unit for maneuvering the mast may comprise hydraulic cylinders to compensate for pitching/heave motions of the buoyancy body.

[0096] FIGS. 6A-6C show on-board loading of a mast 140 with wind turbine. Mast 140 is in on-board loading position 140b on suitable movable rig 170 either in the form of a movable rig 170 floating at sea, for example a barge, or a movable rig 170 standing ashore. For preparation for on-board loading, as shown in FIG. 6A, mast 140 with wind turbine 130 with wings 132 in horizontal position on a movable rig 170 with the buoyancy body 110 ballasted and positioned adjacent the movable rig 170 for receiving the bearing shaft 141 of the mast 140 in the bearing housing 121 of the support stands 123. Weight transfer of mast 140 with wind turbine 130, as shown in FIG. 6B, is effected by pumping out water ballast. Mast 140 with wind turbine 130, balanced and with center of gravity in the bearing at the shafts 141, is rotated with suitable, known devices to the desired position, normal operating position 140a as shown in FIG. 6C.

[0097] The mast 140 with wind turbine 130 is held in normal operating position by engaging the retaining mechanism with the mast foot, whereby the retaining mechanism preferably comprises hydraulically operated shear bolts. To compensate for pitching motions of the buoyancy body 110, the restraint mechanism is brought out of engagement with the mast foot, whereby activating dampening devices, preferably comprising a given number of hydraulic cylinders, are being activated.

[0098] The mast 140 can be maneuvered by moving the retaining mechanism out of engagement with the mast foot and by known devices the mast can be maneuvered to desired mast positions; operating position 140a, on-board loading and maintenance position 140b, and survival position 140c.

TABLE-US-00001 TABLE 1 100 Offshore power generating system 110 Buoyancy body 111 Aft end 112 Bow or stern 113 Stern 114 Centre plan of the buoyancy body 115 Well 116 Super structure 117 Underwater hull 118 Forward 119 Center of floatation 120 Center of buoyancy 121 Bearing housing 122 The rotational axis 122 of the mast in the horizontal plane 123 Support stand 124 Anchoring system/point 125 Aerodynamic cross section of the mast 130 Wind turbine/rotor 131 Wind turbine hosing 132 Wing 133 The rotational axis of the wind turbine 140 Mast 140a Mast in normal operating position 140b Mast in on-board loading and maintenance position 140c Mast in survival position 141 The bearing shaft of the mast 150 Sea surface 160 Dampening devices 160′ Angular positions