Patent Application
20230264784
The present invention relates primarily to a floating, preferably semi-submersible, support structure for offshore windmills.
The support structure is particularly suitable for transport as modules on heavy-lift vessels over large distances and assembly of these modules in sea.
Floating support structures for offshore windmills are known in the art.
For example, patent publication US 2014/0196654 A1 discloses a floating support structure for windmills consisting of columns having stabilizing elements mounted to their ends. The columns have an inner volume for ballasting. Another type of support structure having the possibility of stabilization and ballasting is disclosed in patent publication US 2019/0061884 A1. Yet other examples of floating support structures are disclosed in patent publications U.S. Pat. No. 10,518,846 B2, WO 2014/163501 A1 and JP 2005-201194 A.
A common disadvantage for any of the known floating support structures of the above-mentioned type is that they are ill-suited for transport across large distances on vessels due to their bulky design and heavy weight.
In view of the above, it is an object of the invention to provide a floating support structure that solves or at least mitigates one or more of the aforementioned problems related to use of prior art solutions.
A particular object of the invention is to provide a floating support structure that may easily be produced in parts or modules, thereby facilitating long distance transport on suitable vessels such as semi-submersible vessels.
Another object of the invention is to provide parts or modules that may be assembled into a fully functional floating support structure of the above-mentioned type when submerged/floating in water.
Yet another object of the invention is to provide a floating support structure that may easily be towed from an assembly site to an operation site using a tugboat.
Yet another object of the invention is to provide a floating support structure that ensures sufficient robustness with respect of transfer of torque, torsion and shear forces during operation.
Yet another object of the invention is to provide a floating support structure that ensures favorable motion characteristics during operation, even in rough seas.
The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention.
In one aspect, the invention concerns a floating support structure suitable for supporting a windmill system comprising a windmill tower, a windmill nacelle and windmill blades.
The support structure comprises an aft main section comprising a horizontal aft part with a first horizontal aft end and a second horizontal aft end, a vertical aft part with a first vertical aft end at least indirectly connected perpendicular to the first horizontal aft end and a second vertical aft end, wherein the vertical and the horizontal aft parts are oriented in a common vertical aft plane, and an aft damping structure connected to the second vertical aft end. A horizontal cross-sectional area of the aft damping structure is larger than a horizontal cross-sectional area of the second vertical aft end.
The support structure further comprises a transverse main section comprising a horizontal transverse part with a first horizontal transverse end and a second horizontal transverse end, two vertical transverse parts, each having a first vertical transverse end and a second vertical transverse end, wherein the first vertical transverse ends of the vertical transverse parts are at least indirectly connected perpendicular to the first and second horizontal transverse ends, wherein the two vertical transverse parts and the horizontal transverse part are oriented in a common vertical transverse plane and two transverse damping structures connected to the second vertical transverse ends of the respective two vertical transverse parts. As for the damping structure of the aft main section, a horizontal cross-sectional area of each of the transverse damping structures is larger than a horizontal cross-sectional area of the second vertical transverse end.
The support structure further comprises a connecting flange for connecting a coupling end of the windmill tower distal to the windmill nacelle and vertically onto the floating support structure.
The second horizontal aft end of the aft main section is connected to the horizontal transverse part of the transverse main section such that the vertical aft plane is oriented perpendicular to the vertical transverse plane.
Horizontal is herein defined as the orientation perpendicular to the vertical aft part, the vertical transvers parts and perpendicular to the vertical aft and transverse planes.
In an exemplary configuration, the connecting flange is arranged on the horizontal aft part, for example at, or near, the support structure's center of buoyancy. The connecting flange has preferably a tubular shape with an inside diameter being equal or larger than an outside diameter of the coupling end of the windmill tower.
In another exemplary configuration, the horizontal aft part encloses at least one hollow volume situated adjacent to the connecting flange, wherein at least one reinforcement structure is arranged within the at least one hollow volume. An example of a reinforcement structure may be plates with suitable rigidity/strength orientated vertically and/or horizontally and fixed to the internal wall(s) representing the outer boundary of the volume(s).
In yet another exemplary configuration, each of the horizontal aft part, the vertical aft part, the horizontal transverse part and the vertical transverse parts encloses at least one hollow volume. The percentage of this or these hollow volume(s) may be 50% or more of the total volume of the respective part, more preferably 70% or more, for example 90%. If for example each part is a tube, the difference between the total volume and the hollow volume is the volume of the tube walls.
In yet another exemplary configuration, at least a section of the at least one hollow volume within the vertical aft parts and the vertical transverse parts, hereinafter called the ballast section, is filled (or may be filled) with a ballast substance, for example a liquid such as seawater, allowing regulation of the draft of the floating support structure prior to submersion, and/or during submersion, and/or after submersion, into water. Hence, the buoyancy section constitutes at least part of a draft regulator system.
In yet another exemplary configuration, the second horizontal aft end is connected at a longitudinal mid position, or near a longitudinal mid position, of the horizontal transverse part, thereby achieving a desired high symmetry of the support structure.
In yet another exemplary configuration, the second horizontal aft end of the aft main section is connected to the horizontal transverse part via a coupling structure.
In yet another exemplary configuration, the coupling structure encloses at least one hollow volume, wherein at least one reinforcement structure is arranged within this or these hollow volume(s). As described above, an example of a reinforcement structure may be plates with suitable rigidity/strength orientated vertically and/or horizontally and fixed to the internal wall(s) representing the outer boundary of the volume(s).
In yet another exemplary configuration, the aft main section further comprises a bent aft part connecting the second horizontal aft end of the horizontal aft part to the first vertical aft end of the vertical aft part. Further, the transverse main section may comprise two bent transverse parts connecting the first and second horizontal transverse ends of the horizontal transverse part with the respective first vertical transverse ends of the two vertical transverse parts. The bent aft part may in this configuration extend from the horizontal aft part at an aft angle αA relative to the horizontal plane. Similarly, the two bent transverse parts may each extend from the first horizontal transverse end and the second horizontal transverse end, respectively, at a transverse angle αT relative to the horizontal plane. Both the aft angle αA and the transverse angle αT have non-zero values and preferably equal or near equal.
In yet another exemplary configuration, the bent aft part is shaped as a frustum such as a cut cone, having its smallest cross-sectional area connected to the second horizontal aft end. Moreover, each of the two bent transverse parts is shaped as frustum having its smallest cross-section area connected to the respective first and second horizontal transverse ends.
In yet another exemplary configuration, each of the bent aft part and the two bent transverse parts encloses at least one hollow volume. The enclosed volume(s) may be 50% or more of the total volume for each part more preferably 70% or more, for example 90%. Further, at least a section of the at least one hollow volume within the bent aft part and the two bent transverse parts, hereinafter called the buoyancy section(s), is configured to be filled with, or depleted of, a buoyancy substance such as gas or liquid, allowing regulation of the buoyancy of the floating support structure when submerged in water. Hence, the buoyancy section(s) constitutes in this configuration another part of the above-mentioned draft regulator system. The gas and liquid may for example be air and seawater, respectively.
In yet another exemplary configuration, each of the horizontal aft part, the vertical aft part, the horizontal transverse part and the vertical transverse parts has a tubular shape such as a straight tube or a set of straight tubes fixed parallel to each other. In the latter case, each tube may be cut along their longitudinal direction and then joined at the cut surfaces in order to create a continuous hollow interior volume.
In yet another exemplary configuration, the floating support structure further comprises a mooring assembly comprising an aft mooring line connected to the aft main section, a first transverse mooring line connected to an end part of the transverse main section along the vertical transverse plane and a second transverse mooring line connected to the opposite end part of the transverse main section along the vertical transverse plane. Preferred locations of the ends of the mooring lines on the support structure are on the bent aft part (for the aft mooring line) and the two bent transverse parts (for the first and second transverse mooring lines) and/or at or near the connection area of the bent parts and the horizontal parts.
In a second aspect, the invention concerns a windmill facility comprising a floating support structure in accordance with the support structure described above, a windmill tower having a low end fixed to the connecting flange, a windmill nacelle fixed at a top end of the windmill tower and windmill blades rotationally coupled to the windmill nacelle. The rotational coupling may be achieved by equipping the windmill nacelle with a suitable rotational device such as a motorized swivel.
Typically, the shipyard building the aft main section and the transverse main section and the assembly site are situated at locations where towing to the location for assembly is not a suitable option. Hence, the sections should be transported on deck of vessels such as semi-submersible heavy-lift vessels. The operation of arranging the sections on the deck at the production site, and subsequent off-loading and assembly at the assembly site, is described in detail below.
Note that use of semi-submersible vessels to place the sections above the deck represents just one of several methods. An example of an alternative method may be the use of skids that allows the sections to slide from the quay onto the deck.
In a third aspect, the invention concerns a method for assembling one or more floating support structure(s) at an assembly site using a plurality of floating sections produced at a production site distal from the assembly site. An example of a production site and an assembly site may be China and Norway, respectively.
Each of the plurality of sections comprises a horizontal part and a vertical part which are connected at least indirectly to the horizontal part.
The method comprises the following steps:
The term “side-by-side” is herein defined as when the elongated sides of the horizontal parts are arranged in parallel.
An example of a low freeboard FL may for example be about 2 to 3 meters of the typical height of the main sections
In an exemplary performance of the method, step C further comprises the following step:
arranging the transport assembly onto the transport vessel where the transport assembly is kept at a predetermined high freeboard FH, being higher than the intermediate freeboard FI, by use of the draft regulator system.
When launching for transferring the assembly to a transport vessel all internal sections of the main section may be kept dry, i.e. no water-filling. An example of a high freeboard FH may for example be about 20 to 25 meters of the typical height of main sections.
In another exemplary performance of the method, the transport vessel is a semi-submersible vessel and step C further comprises the following steps:
In yet another exemplary performance of the method, step E further comprises the following steps:
Note that the term ‘horizontal’ means throughout the description parallel to the water surface at rest.
In yet another exemplary performance, the method further comprises the following step performed between step G and H:
An example of an intermediate freeboard FI may for example be about 3 to 5 meters of the typical height of the main sections.
In yet another exemplary performance of the method, each of the plurality of sections comprises a buoyancy tank arranged at positions vertically offset from the position of the one or more internal ballast tanks, and preferably higher with reference to the water surface, wherein the buoyancy tanks are permanently closed passive air-filled tanks.
In another exemplary performance of the method, the buoyancy tanks comprise a closable opening for filling or discharging the buoyancy tanks for buoyancy substance.
For this exemplary performance of the method, step H may further comprise the step of adjusting the amount of buoyancy substance in the buoyancy tank prior to, or during, the turning of each section such that stability is ensured stability during execution of step H.
In yet another exemplary performance, the method further comprises the following step:
Alternatively to step J, step I may further comprise the following steps:
a) adjusting the freeboard of the at least two sections to be interconnected by use of the draft regulator system, for vertical alignment of the at least two horizontal parts,
b) temporary interconnecting the at least two sections in final horizontal orientations by use of a first coupling device,
c) optionally adjusting the freeboard of the interconnected at least two sections by use of the draft regulator system to a predetermined operational freeboard FO being higher than the low freeboard FL, preferably such that the horizontal parts are at least partly, preferably fully, above the water surface, and
d) permanently interconnecting the at least two sections by use of a second coupling device such as welding the two parts together directly or via a coupling structure.
Step I a) and step I b) may alternatively be interchanged.
The first coupling device may for example be guide plates fixed on top of both horizontal parts to ensure correct positioning of the two sections. When the sections are in place, the guide plates may be welded together.
For step I c) the operational freeboard FO may be set equal to the intermediate freeboard FI.
The main aft section comprises a horizontal aft part with a first horizontal aft end and a second horizontal aft end and a vertical aft part with a first vertical aft end at least indirectly connected perpendicular to the first horizontal aft end and a second vertical aft end, wherein the vertical and the horizontal aft parts are oriented in a common vertical aft plane.
Further, the main transverse section comprises a horizontal transverse part with a first horizontal transverse end and a second horizontal transverse end and two vertical transverse parts, each having a first vertical transverse end and a second vertical transverse end. The first vertical transverse ends of the vertical transverse parts are at least indirectly connected perpendicular to the first and second horizontal transverse ends. The two vertical transverse parts and the horizontal transverse part are oriented in a common vertical transverse plane.
A connecting flange is arranged on either the horizontal aft part, the horizontal transverse part or a coupling structure connecting the horizontal aft part and the horizontal transverse part, more preferably on top of the horizontal aft part at or near the gravitational center point of the assembled floating support structure. The connecting flange is configured to connect to a coupling end of a vertically oriented windmill tower. Hence, it has preferably a tubular shape with an inside diameter being equal or larger that an outside diameter of the coupling end of the windmill tower.
Said mooring lines may comprise an aft mooring line connected to the aft main section, a first transverse mooring line connected to an end part of the transverse main section along the vertical transverse plane and a second transverse mooring line connected to the opposite end part of the transverse main section along the vertical transverse plane.
In yet another exemplary performance, the method further comprises the following step:
The windmill tower may constitute part of a windmill system comprising the windmill tower, a windmill nacelle connected to the other end of the windmill tower and windmill blades rotationally connected to the windmill nacelle.
In yet another exemplary performance, the method further comprises the following steps:
In yet another exemplary performance of the method, the aft main section further comprises an aft damping structure connected to the second vertical aft end, wherein a horizontal cross-sectional area of the aft damping structure is larger than a horizontal cross-sectional area of the second vertical aft end. Furthermore, the transverse main section may comprise two transverse damping structures connected to the second vertical transverse ends of the respective two vertical transverse parts, wherein a horizontal cross-sectional area of each of the transverse damping structures is larger than a horizontal cross-sectional area of the second vertical transverse end, and preferably of equal horizontal cross-sectional area as the aft damping structure.
In yet another exemplary performance of the method, each of the horizontal aft part, the vertical aft part, the horizontal transverse part and the vertical transverse parts encloses at least one hollow volume.
In yet another exemplary performance of the method, the second horizontal aft end is at step I connected at a longitudinal mid position, or near a longitudinal mid position, of the horizontal transverse part.
In yet another exemplary performance of the method, the aft main section further comprises a bent aft part connecting the second horizontal aft end of the horizontal aft part to the first vertical aft end of the vertical aft part. Further, the transverse main section may comprise two bent transverse parts connecting the first and second horizontal transverse ends of the horizontal transverse part with the respective first vertical transverse end of the two vertical transverse parts.
In yet another exemplary performance of the method, each of the plurality of sections has a tubular shape.
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.
In the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings.
With particular reference to
As best seen in
The first main section 10, hereinafter called the aft main section 10, comprises a horizontal pipe 11, a vertical pipe 12 and a transition cone 13 joining the horizontal and vertical pipes 11,12. The diameter of the pipes 11-13 should be made large enough to ensure the necessary structural strength to allow long time operation of the windmill facility 100, also in harsh weather conditions.
A damping structure 30 in form of a horizontal plate 30a is attached at the end of the vertical pipe 12 distal to the transition cone 13. The purpose of the damping structure 30 is to reduce/minimize movements of the support structure 1 due to waves and currents during offshore operation of the windmill facility 100.
The second main section 20, hereinafter called the transverse main section 20, comprises a horizontal pipe 21, two vertical pipes 22 and two transition cones 23 joining the vertical pipes 22 to each end of the horizontal pipe 21. The horizontal pipe 21 may be set up by several horizontal portions. In the particular configuration shown in
The general design of the damping structures 30, such as the horizontal cross-sectional area of the plates 30a-c relative to the cross-sectional area of the ends of the vertical pipes 12,22, can be determined by model testing and/or computer modelling.
The transfer of forces from the windmill tower 100 to the support structure 1 takes place through the connecting flange 15 which may be a bolted flange welded on top of a transfer pipe which again is welded in vertical direction to the horizontal pipe 11. The transfer pipe and the horizontal pipe 11 have preferably equal or almost equal diameters.
With particular reference to the encircled detailed drawing in
The reinforcement plates with reference numerals 15′,15″ oriented along and perpendicular to the transverse direction are welded to the inside walls of the horizontal pipe 11 of the aft main section 10 and to the connecting flange 15. Further, the reinforcement plates in the longitudinal direction with reference numeral 24′ are welded to either the horizontal pipe 21 of the transverse main section 20 or the coupling structure 24 or both. And finally, the reinforcement plates with reference numerals 11′,11″ are welded to the inside wall of the horizontal pipe 11 of the aft main section 10 only.
The reinforcement plate 15″ fixed between the transfer pipe and the inner surface of the horizontal pipe 11 ensures that the horizontal pipe 11 maintains full structural strength throughout its length also in the parts where the load is high.
Moreover, due to the reinforcement plates 11′,11″,15′,15″,24′, the forces from the connecting flange 15 are transferred into the aft horizontal pipe 11 and the transverse horizontal pipe 21.
A joint 25 joining the aft main section 10 and the transvers main section 20 is in
The two main sections 10,20 and the coupling structure 24 are illustrated in different angles in
The angle between the transverse horizontal pipe 21 and the transition cones 23 joining both ends with the transverse vertical pipes 22 is defined as αT. Likewise, the angle between the aft horizontal pipe 11 and its transition cone 13 joining the end with the aft vertical pipe 12 is defined as αA. In the configurations shown in all accompanied drawings, the angles αT, αA are equal and non-zero, typically between 30° and 60° relative to the horizontal plane.
The aft main section 10 comprises a hollow volume 18.
The transverse main section 20 comprises a hollow volume 28.
To ensure inter alia high stability during offshore operation of the windmill facility 100, the support structure 1 is equipped with ballast tanks 43,44. A specific example of a ballast tank arrangement is seen in
The ballast tanks 43,44 comprise opening valves 45 for filling and draining of ballast fluid as seen in
The ballast tanks 43,44 further comprise internal filling valves 46 for filling and draining the hollow volumes 18,28 of the aft main section 10 and the transverse main section 20 respectively. The internal filling valves 46 are configured to alternate between an open position and a closed position. The open position allows flow of a fluid or gas between ballast tanks 43,44 and the hollow volumes 18,28 of the main sections 10,20. The closed position enables the hollow volume of the main sections 10,20 to be fully sealed and for example hold a predetermined amount of ballast fluid. The internal filling valves 46 thus provide a closable opening between the ballast tanks 43,44 and the hollow volumes 18,28 of the main sections 10,20. The internal filling valves 46 are depicted in an open position.
As shown in
In the particular configuration shown in
As shown in
The specific purpose of the buoyancy tanks 41,42 will be explained in more detail below.
The complete method for production, transport, assembly and installation is described below with reference to
301. Production of main sections 10,20 constituting parts for the support structure 1.
At least one, preferably several, of the two main sections 10, 20, i.e. the aft/longitudinal main section 10 and the transverse main section 20, will be completed at a shipyard or equivalent facility. To be able to optimize the space, and thereby the transport efficiency, from the shipyard to the assembly site, the two main sections 10,20 are at this initial stage not joined together via the coupling structure 24 to form the desired support structure 1. See also
302. Locking main sections 10,20 side by side using locking structure 50
To be able to carry as many building blocks for the support structure 1 as possible in one shipping, the main sections 10,20 produced in the shipyard will be placed upside-down and locked together with a removable (non-permanent) locking structure 55 to form a transport assembly 50. The locking structure 55 may for example be a plurality of metal plates/rods extending across the main sections 10,20 as illustrated in
Relevant sizes of the transport assembly 50 may however vary dependent of the available deck space of the transport vessel 20. Examples are 2 to 6 sets, where a set consists of one aft main section 10 and one transverse main section 20.
303. Launching transport assembly 50 upside down in sea from shipyard.
Due to the locking of the main sections 10,20 with the non-permanent locking structure 55, the complete transport assembly 50 may easily be launched into sea in the up-side-down position, either from a dry deck/quay or similar, or from a launching barge.
Alternatively, the main sections 10,20 may be bundled together to form the transport assembly 50 after having been launched.
304. Regulating draft of transport assembly 50 to a predetermined high freeboard FH
The transport assembly 50 is launched in sea with no ballast in the draft regulator system 40 and the transport assembly 50 is therefore floating at a predetermined, shallow draft/high freeboard FH (see
When the draft regulator system 40 does not hold any ballast, the shallow draft achieved may also be called the maximum freeboard FM.
Alternatively, if necessary, after the launching of the transport assembly 50 in sea, the buoyancy of the transport assembly 50 may be regulated in order to ensure that the transport assembly 50 is floating at a predetermined, shallow draft/high freeboard FH (see
A preferred example of such a draft regulator system 40 may be a system within hollow volumes 18,28 of the aft main section 10 and the transverse main section 20, comprising ballast tanks 43,44. Furthermore the draft regulator system may comprise buoyancy tanks 41,42 as described above in connection with
305. Arranging transport assembly 50 on deck 203 of a semi-submersible heavy lift vessel/transport vessel 200
When in shallow draft position, the transport assembly 50 may easily be towed in position on a semi-submersed heavy lift vessel 200. The heavy lift vessel 200 is first ballasted until a vessel loading draft VL is achieved in which a vessel deck 203 is located deeper than the shallow draft of the transport assembly 50, for example 5 meters. A dedicated vessel such as a tugboat (not shown) may then tow the transport assembly 50 to a position directly above the vessel deck 203 (see
The load-on and sea-fastening will not require any assistance from e.g. floating cranes or other high cost equipment and can be completed efficiently at a minimum of time.
306. Transporting transport assembly 50 from the shipyard to an assembly site.
The transport with a semi-submersible heavy lifter vessel/transport vessel 200 can effectively be made over long distance transports, for example between China and Norway. For shorter distance transports submergible barges towed by tugs may be used.
307. Launching transport assembly 50 upside down in water from vessel 200
With reference to
308. Regulating draft of transport assembly 50 to a predetermined intermediate freeboard FI.
When the transport assembly 50 is safely secured, the draft/buoyancy is regulated until the transport assembly 50 is floating at a draft showing increased stability. A reasonable intermediate freeboard FI at this stage may be about 3 to 5 meters of a typical height of the main sections. See
As described in step 304, the draft/buoyancy of the transport assembly 50 can be regulated by filling/removing water to/from the draft regulator system 40 integrated into, and/or coupled to, the main sections 10,20.
309. Removing locking structure 55 to release each main section 10,20 one by one from the transport assembly 50.
When floating at the intermediate freeboard FI where the transport assembly 50, as well as all individual main sections 10,20 are stable in sea, the main sections 10,20 may be released, preferably one by one, from the locking structure 55, which in
When each individual main section 10,20 is floating at the intermediate freeboard (FI), the individual sections 10,20 will float stably in the water with the horizontal parts 11,21 oriented below the vertical parts 12,22
310. Regulating draft of main sections 10,20 to a predetermined intermediate freeboard FI
After the main sections 10,20 are released, the draft of the individual main sections 10,20 are regulated to a low intermediate freeboard FIL, which is lower than that of the intermediate freeboard FI of the transport assembly 50. The lower intermediate freeboard FIL, of the individual main sections 10,20 is reached by filling more water in the draft regulator system 40. The lower intermediate freeboard FIL, allows for disconnecting the main sections 10,20 from the locking arrangement 55 and to ensure stability in the water. The lower intermediate freeboard FIL, means a freeboard low enough to enable disconnection from the locking arrangement 55.
311. Assembling the support structure 1 and installing the floating windmill facility 100
311
a. Towing each set of main sections 10,20 to a dedicated turning area.
In order to start the assembling of the support structure 1, the two main sections 10,20 constituting the support structure set are towed to a location for turning that exceeds a predetermined safety distance from the other main sections 10,20 of the transport assembly 50 launched from the vessel 200.
311
b. Turning the main sections 10,20 180 degrees around a horizontal axis of rotation.
Prior to interconnecting the main sections 10,20, they must be turned from their upside-down orientation to the correct orientation in a stable and secure way. After the main sections 10,20 are towed to the location for turning, more water is filled into the hollow volumes 18,28 via the external filling valves 47 to further lower each main section 10,20 to a low freeboard FL,
Adjusting to a low freeboard FL is done to initiate the turning of the main sections 10,20. Lowering the main sections is done by operating the draft regulator system 40.
The main function of the buoyancy tanks 41,42 is first to provide instability when a main section 10,20 is floating upside down at a low freeboard FL, that is sufficient for initiating the turning of a main section 10,20 from the upside down position to the correct operational position where the horizontal parts 11,21 are oriented above the vertical parts 12,22. When floating at a low freeboard FL, the main section 10,20 will in its upside-down orientation be unstable and rotate until it reaches a stable position. The buoyancy tanks 41,42 (normally two or more for each main section 10,20) are designed with sufficient volume to give a second main function that is to give a stable floating position where the main sections 10,20 are floating with the horizontal parts 11,21 oriented above the vertical parts 12,22 and with the upper part of the horizontal parts (11,21) floating above the sea surface. The operation is repeated for the next main section 10,20. In one exemplary method the rotation may be achieved by exposing each main section 10,20 for an external force, for example from a tug boat.
When the main sections 10,20 are turned to correct orientation and floating stable next to each other, the assembly of the main sections 10,20 into the floating support structure 1 may start.
311
c. Temporary interconnecting main sections 10,20 via the coupling structure 24.
The assembly starts by orienting and positioning the aft main section 10 and the transverse main section 20 relative to each other to prepare for interconnection, for example by aid of a tug boat. The initial connection is made with the sections 10,20 floating at the draft obtained after rotation to the correct orientation. If necessary, the freeboard of the main sections 10,20 may be adjusted by use of the draft regulator system 40 to vertically align the coupling structure 24 and the end of the horizontal pipe 11.
At the final stage, preinstalled guide plates at the top of the main sections 10,20 are guiding the two sections 10,20 in correct position. The plates are then welded together to temporarily secure the sections 10,20 in order for the next phase to commence.
311
d. Regulating draft of the temporary assembly.
The next step is to pump out water from the hollow volumes 18,28 and ballast tanks 40,43,44 (and, if needed, also the buoyancy tanks 40,41,42) until the two horizontal pipes 11,21 are well above the water surface 60.
311
e. Completing support structure 1.
When the pipes 11,21 are in a dry environment (above the water surface 60), the final welding for assembling the two main sections 10,20 into the support structure 1 can be completed.
311
f. Installing additional equipment.
After the final welding, the remaining equipment such as supports 16,26,27 for mooring lines 70,70a-c and winch(es) 80 may be mounted onto the respective main sections 10,20. Any pre-installment of mooring line sections 70,70a-c may also be connected at this stage.
To avoid handling of heavy mooring line equipment during mooring at the installation site, the mooring lines 70,70a-c may be split in two segments where the upper segment can be preinstalled in the assembly site/harbor.
311
g. Positioning base end of windmill tower 101 into the support structure 1.
After the installment of the additional equipment, the lower base end of the windmill tower 101, with or without the accompanying windmill nacelle 102 and windmill blades 103, is guided and fastened to the connecting flange 15 of the support structure 1. This operation may be performed by a suitable crane located on a quay or on an installation vessel.
311
h. Regulating draft to operating draft
When all necessary equipment is in place the support structure 1 will be ballasted to a towing draft, for example to the planned operating draft. Ballast tanks 43,44 will then be closed. Adjustments of the buoyancy by filling/emptying the buoyancy tanks 41,42 may also be performed at this stage.
311
i. Towing support structure 1 with equipment to installation site.
The complete support structure 1 with equipment is towed out to the installation/operation site at the operating draft.
311
j. Mooring support structure 1 to seabed.
As mentioned above (step 311f) part of the mooring system 16,26,27 may be preinstalled before the support structure 1 arrives at the installation site. This may include segments of the mooring lines 70a-c attached to the supports 16,26,27.
Connections of mooring lines 70,70a-c at the installation site start with connecting the mooring lines 70b,c to the transverse main section 20. The transverse mooring lines 70b,c can be connected one by one after the support structure 1 has been towed to a position where these mooring lines 70b,c will have no tension.
The final stage of the mooring sequence is to connect the end of the last (aft) mooring line(s) 70a to a dynamic fixing device 16 on the aft main section 10. The term ‘dynamic’ means in this particular embodiment that the fixing device 16 allows tensioning and locking of the mooring line 70a after connection. The tensioning may be made/aided by one of the installation tugs used for anchor handling. After the desired tensioning is completed, the support structure 1 is ready for operation, optionally after additional/emptying of the ballast tanks 43,44 and/or the buoyancy tanks 41,42 to ensure correct operational draft. Advantageously, a length of the last mooring line 70a attached to the dynamic fixing device 16 is a chain 71 or the like in order to inter alia enable use of known tensioning devices as exemplified in
311
k. Pulling-in and connecting power cables.
Next phase is to pull-in and connect one or more power cables 84 to the support structure 1 using a winch system 80. A pull-in winch 81 is installed on a winch support 81, which again is fastened (releasably or permanent) to support structure 1, in order to facilitate the power cable 84 pull-in. In
With the cable 84 locked in position on the support structure 1, it will be connected to a cable arrangement on board. The pull-in winch 81 may be kept on board. Alternatively, it may be disconnected and stored more safely on land.
If more heavy service or modifications of windmill facility 100 are required, the windmill facility 100 may be towed to a suitable yard/harbor for service/upgrade, etc. Disconnection and reconnection of both the mooring system 70 and the power cable 84 does not involve any complex operations.
In the preferred embodiment, no ballast operations are required during operation at the installation site.
In the preceding description, various aspects of the system and the method according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiments, as well as other embodiments of the system and the method, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20200726 | Jun 2020 | NO | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/066031 | 6/15/2021 | WO |
