Patent Description:
Offshore wind energy is being used on increasingly larger scale, and recent years have seen a great increase in the number of wind farms placed at sea. These wind farms of mutually electrically coupled wind turbines are generally located on the continental shelf in the sea, although there is a noticeable trend of placing such wind farms further out at sea as well. What's more, not only is the number of wind turbines placed offshore increasing, their size is also constantly increasing in an effort to increase their production capacity.

The above stated factors entail new challenges in respect of the actual placing of these offshore wind turbines on a foundation already present at sea. The foundation extends here in vertical direction and serves to bridge the distance between the seabed and the wind turbine protruding above water. For offshore wind turbines which are placed in relatively shallow water the foundation can comprise a monopile which is arranged in the seabed and extends to a position above the water surface. A lattice structure or jacket can, if desired, be applied for deeper water. A floating foundation can, if desired, be applied for even deeper water. Such a floating foundation consist of a floating body situated at or below the waterline and anchored to the seabed, for instance by means of cables. It is also possible to make use of a transition piece between the wind turbine mast and the foundation. If desired, the transition piece can be provided with superstructures such as a work platform, a jetty and other useful applications.

A frequently used method consists of manufacturing or assembling the wind turbine to the most integrated state possible on land and then transporting it to the foundation at sea on which the wind turbine is to be arranged. Installation vessels configured for this specific task are applied to be able to carry out this transport. These are however becoming increasingly bigger and are being provided with increasingly heavier lifting cranes to be able to take up the wind turbine and place it on the foundation. Jack-up installation vessels can be applied for a more stable installation at sea. Such jack-up vessels can lift themselves out of the sea on legs, making them less susceptible to the effect of waves and wind. Because installation vessels are designed specifically for transport and placing of substantially complete wind turbines, flexibility is lost.

<CIT> describes a device for offshore mounting of a wind turbine on a foundation present at sea. The described device makes it possible to perform the complete assembly of a wind turbine on the deck of a lifting platform. The completely assembled wind turbine is then placed on the foundation with a lifting crane. For assembly on the lifting platform the device comprises an upper gripping means configured to lift a coupled tower section by means of a vertical movement, and a horizontally displaceable supply structure for another tower section.

It has also been proposed to transport the wind turbine components to the foundation separately and then place these components on the foundation in a determined order. This method can facilitate the transport, but has the drawback that the placing of each component at sea takes up a great deal of time. A wind turbine does indeed generally comprise a number of tower sections, mutually stacked tower sections of which together form a wind turbine mast, a hub to be placed on the mast, and a number of wind turbine blades which are arranged in the hub. Because the number of components to be placed is greater than when a wind turbine is placed as a whole, the risk of unsafe situations increases further.

The invention has for its object, among others, to provide a device and corresponding method which at least partially prevent the above stated prior art drawbacks.

According to the invention, this object is achieved by providing a device according to claim <NUM>. The device for offshore construction of a wind turbine or arranging of components thereof on a vertically extending foundation present at sea comprises:.

In another aspect of the invention an assembly of the device and a vessel is provided. The assembly is suitable for offshore construction of a wind turbine or for arranging components thereof on a vertically extending foundation present at sea, and comprises a vessel which is provided with the wind turbine components to be arranged, these comprising a hub, one or more blades and/or one or more tower sections for forming a tower of the wind turbine, and further with a lifting means for taking up the wind turbine components; and a device according to an embodiment of the invention.

In yet another aspect of the invention a method is provided for offshore construction of a wind turbine or for arranging of components thereof on a vertically extending foundation present at sea. The method comprises of providing an assembly according to an embodiment of the invention; taking up a tower section with the lifting means and coupling it to the supply structure; moving the tower section coupled to the supply structure from outside the internal space into the internal space by displacing the supply structure and the tower section coupled thereto in horizontal direction; engaging the tower section, which was moved into the internal space, with the engaging structure; and lifting the engaged tower section in the internal space by vertically displacing the engaging structure, whereby sufficient space is created under the relevant tower section for receiving another, underlying tower section in the internal space.

According to the invention, the superstructure connected releasably to the foundation comprises an internal space which is accessible to a tower section of the wind turbine and in which the tower section, and optionally a plurality of tower sections, can be received. The internal space can extend substantially wholly between the lower surface and the upper surface of the superstructure. With the engaging structure received for vertical displacement in the internal space an engaged tower section can be moved in the internal space by a vertical displacement, this in controlled manner and relatively independently of wave movements. The superstructure does indeed form a substantially stable whole. An upward directed vertical displacement of an engaged tower section creates space for an underlying tower section to be received in the internal space. Such a tower section can be introduced into the internal space by coupling it to the horizontally displaceable supply structure outside the internal space and then displacing the supply structure horizontally from the position outside the internal space to a position inside the internal space.

With the invented device components of a wind turbine can be arranged on the foundation in accurate and safe manner and in a desired order, whereby a wind turbine can be constructed. The invention is particularly suitable for constructing a new wind turbine, but can also be used to replace a wind turbine component, particularly a tower section, which is worn or requires replacement for other reasons.

The superstructure connected releasably to the foundation provides for an increased stability during handling of wind turbine components. The superstructure further allows the construction of a desired complete wind turbine, wherein the effect of waves and wind on the structure is significantly reduced. Larger wind turbines can hereby be placed at sea under rougher conditions than was heretofore possible according to the prior art.

An embodiment of the invention is aimed at a device wherein the engaging structure is configured to lower an engaged tower section in the internal space to a position against an underlying tower section in order to couple the relevant tower section to the underlying tower section. The coupling can take place in known manner, for instance by mutually connecting corresponding flanges of the tower sections, for instance by means of a bolt connection. Other ways of connecting are however not precluded.

A suitable embodiment according to the invention provides a device wherein the engaging structure is configured to lift an engaged tower section in the internal space to a position in which the tower section protrudes above the upper surface of the superstructure. In this embodiment it becomes possible to provide a tower section thus protruding above the upper surface of the superstructure on an upper side thereof with a hub, in which wind turbine blades can then be arranged.

Another embodiment of the device is characterized in that the engaging structure is displaceable between securing positions. In these securing positions the engaging structure can be connected and fixed to the surrounding superstructure. Forces acting on the engaging structure (for instance in that a tower section is engaged by the engaging structure) are hereby transmitted to the superstructure and from there on to the foundation. The securing positions can be situated at any height of the superstructure. They can also be distributed randomly or conversely regularly over the height of the superstructure. The manner of securing can be embodied in known manner, for instance by a pin-hole connection, preferably a hydraulically driven pin-hole connection.

The displacing means for displacing the engaging structure in vertical direction can also be embodied in known manner. It is thus possible to embody the displacing means as a set of cables which is attached on an upper side of the engaging structure and is carried to winches for being taken in or payed out, which winches are for instance secured at the height of the upper surface of the superstructure. In another embodiment the displacing means comprise a rack and pinion (or toothed wheel) system, wherein a rack extends in vertical direction along an upright of the superstructure and the toothed wheel is connected to the engaging structure, for instance a toothed wheel in each corner of an engaging structure with polygonal section. It will be apparent that the invention is not limited to the stated examples and that other known embodiments of the displacing means are likewise possible.

According to another embodiment of the device, the supply structure is arranged at the position of the lower surface of the superstructure. A tower section is then displaced on an underside of the superstructure into the internal space thereof. This has the advantage that a wind turbine tower or mast can be constructed from the bottom up, wherein an upper tower section can already be provided with a hub with, if desired, a number of blades. The arranging of the hub and optionally the blades can here be carried out in controlled manner at the position of the upper surface of the superstructure.

According to yet another embodiment of the device, it is characterized in that the supply structure protrudes on either side of the superstructure in the horizontal direction. This enables a tower section to be coupled to the supply structure from the outside, in any case along a supply side of the protruding parts of the supply structure. A discharge side of the protruding parts of the supply structure, lying opposite the supply side, can for instance be used to discharge the superstructure after the construction or other work has been completed. This will be further elucidated below.

According to yet another suitable embodiment of the device, the supply structure comprises a support surface for a floor which is slidable in the horizontal direction between positions inside and outside the internal space and to which a tower section can be coupled. The support surface preferably protrudes from the superstructure on either side, making it possible to slide the floor from an outer position on the supply side to an inner position in the internal space, and on to an outer position on the discharge side of the protruding parts of the supply structure. The slidable floor can here thus be slid between three operative positions over the support surface. This latter can for instance be formed by a beam frame extending in a horizontal plane and, if desired, provided with rails over which the floor can slide or run.

In order to facilitate the arranging of a hub, and particularly of a number of blades in the hub, in an embodiment of the invention the superstructure comprises at the position of the upper surface a positioning means for a root of a wind turbine blade, wherein the positioning means is movable in the horizontal and vertical direction. The positioning means can for instance be connected to the upper surface of the superstructure via a static part. A dynamic part connected movably to the static part is movable in a horizontal plane (X, Y) and likewise in a vertical plane Z. This moveability can be embodied in known manner, for instance using hydraulic or pneumatic cylinders running between the static and dynamic part. The cylinders are preferably controlled by a hydraulic circuit in which they are received, preferably under the control of a controller. The dynamic part can be provided with a receiving surface, the geometry of which is adapted to that of the blade root to be received therein. The receiving surface can thus be a part-cylindrical receiving surface for a blade root with substantially cylindrical cross-section. If desired, the receiving surface can comprise a plurality of parts which can take up mutually differing positions, for instance to be able to move the receiving surface from an opened to a closed position.

According to the invention, the internal space of the superstructure must be accessible to a tower section or preferably to a plurality of stacked tower sections. In an embodiment this is achieved by an at least partially open side wall of the superstructure. The open side wall can extend over a part of the height of the superstructure or over substantially the whole height of the superstructure. In an embodiment the open side wall can be closed by a closing structure, such as a door.

The height of the superstructure extends from the lower surface to the upper surface of the superstructure and must in any case be at least as high as one tower section, preferably at least as high as two connected tower sections placed one on the other, still more preferably at least as high as three connected tower sections placed one on the other. The height of the superstructure is further preferably at least equal to the length of a turbine blade. A turbine blade mounted on the hub, wherein the hub is situated at the position of the upper surface of the superstructure, should preferably not come into contact with the water surface when this wind turbine blade is installed, for instance with the positioning means.

The lower surface of the superstructure is here connected to the foundation in per se known manner. The foundation generally extends partially above water, although the device can also be applied for foundations situated wholly under water.

A suitable embodiment of the device is characterized in that the superstructure comprises side walls in the form of a lattice, for instance of mutually connected uprights, beams and cross-connections. Such a superstructure is strong, stiff and light, and is less susceptible to wind forces.

The device according to the invention can advantageously be applied in an assembly which also comprises a vessel in addition to the device. Such an assembly is highly suitable for offshore construction of a wind turbine or for arranging of components thereof on a vertically extending foundation present at sea. The assembly comprises for this purpose a vessel which is provided with the wind turbine components to be arranged, these comprising a hub, one or more blades and/or one or more tower sections for forming a tower of the wind turbine, and further with a lifting means for taking up the wind turbine components. The vessel co-acts with a device according to any one of the embodiments described in this application.

This co-action is expressed in yet another aspect of the invention, wherein a method is provided for offshore construction of a wind turbine or for arranging of components thereof on a vertically extending foundation present at sea. The inventive method makes use of the assembly and further comprises the steps of:.

A substantially whole wind turbine can thus be constructed, wherein a tower section engaged with the engaging structure is lowered in the internal space to a position against an underlying tower section introduced into the internal space with the supply structure, and the relevant tower section is coupled to the underlying tower section.

Another embodiment of the invention provides a method wherein a tower section engaged with the engaging structure is lifted in the internal space to a position in which the tower section protrudes above the upper surface of the superstructure.

In some cases it may be advantageous to displace the engaging structure between securing positions and to anchor it in the securing positions with the superstructure. Forces acting on the engaging structure can then be transmitted to the superstructure and from there to the underlying foundation.

As a first step in a method according to an embodiment it is advantageous, prior to step b), to arrange an upper tower section in the engaging structure with the lifting means and thereby engage it so that the uppermost tower section protrudes above an upper surface of the superstructure, to anchor the engaging structure in a securing position, and to take the hub up from the vessel with the lifting means, arrange it on the first tower section and then secure it thereto.

In a method according to yet another embodiment, in a subsequent step at least one wind turbine blade is taken up with the lifting means and arranged with its blade root in a hub opening and secured therein. The blade root of a wind turbine blade taken up with the lifting means is here preferably engaged by a positioning means provided at the position of the upper surface of the superstructure, and the positioning means is moved in the horizontal and vertical directions in order to align the blade root with the hub opening and arrange it in the hub opening and secure it therein.

A whole wind turbine (mast, hub and blades) can be constructed in this way. According to an embodiment, a method is for this purpose provided wherein the steps b) - e) are repeated until a complete wind turbine tower of stacked and mutually connected tower sections has been constructed.

Once a complete wind turbine has been constructed, or other desired work has been carried out, in a method according to another embodiment the superstructure present around the constructed wind turbine tower can be released from the foundation, after which the superstructure is taken up with the lifting means and removed from the constructed wind turbine tower.

In order to facilitate the removal of the superstructure the superstructure is in an embodiment of the method openable by folding, and is removed in folded-open state. In another embodiment a method is provided wherein the superstructure has an open side wall and the superstructure is removed from around the wind turbine tower along the open side wall. For this purpose the open side wall preferably extends over substantially the whole height of the superstructure.

Finally, it is stated that the embodiments of the invention described in this patent application can be combined in any possible combination, and that each embodiment can individually form the subject-matter of a divisional patent application.

The invention will now be further elucidated on the basis of the following figures and description of preferred embodiments, without the invention otherwise being limited thereto. In the figures:.

Referring to <FIG>, an assembly <NUM> according to an embodiment of the invention is shown. The device <NUM> is suitable for offshore construction of a wind turbine <NUM> or for arranging of components (<NUM>, <NUM>, <NUM>) thereof on a foundation <NUM> present at sea <NUM> and extending in vertical direction <NUM>. In the shown embodiment the foundation <NUM> comprises a jacket foundation which is provided on an upper side thereof with a connecting plate <NUM> for the wind turbine. Because only an upper part of the jacket foundation <NUM> protrudes above the sea level <NUM>, only this upper part is visible. The invention is not limited to this type of foundation. The foundation can thus for instance also comprise a monopile foundation or floating foundation.

The assembly <NUM> comprises a vessel <NUM>, a deck <NUM> of which is provided with storage racks for wind turbine components (<NUM>, <NUM>, <NUM>, <NUM>) to be arranged. The wind turbine components can comprise a hub <NUM> connected to a generator <NUM>, and further one or more blades (<NUM>) and/or one or more tower sections (<NUM>-<NUM>, <NUM>-<NUM>,. ) which in assembled state form a tower or mast <NUM> of the wind turbine <NUM>. Further provided on the deck <NUM> of vessel <NUM> is a lifting means in the form of a compound lifting crane <NUM> which is configured to take up the wind turbine components (<NUM>, <NUM>, <NUM>) from deck <NUM> and carry them toward the jacket foundation <NUM>. The lifting crane <NUM> is rotatable around a vertical axis <NUM> relative to deck <NUM> via a base <NUM>. If desired, vessel <NUM> is provided with other auxiliary equipment, such as a second crane <NUM>, a helipad <NUM> and a bridge <NUM>. Vessel <NUM> can comprise a floating device (as shown), but can also be embodied as a jack-up platform (not shown) which is provided in known manner with legs which can be placed on the seabed. In this way the hull of such a jack-up platform can be brought above the sea surface, which can provide for additional stability. If desired, vessel <NUM> can be provided with a per se known swell compensation system.

The assembly <NUM> further comprises a device <NUM> according to the invention. In the embodiment shown in <FIG> the device <NUM> comprises an elongate superstructure <NUM> which extends from foundation <NUM> (the foundation being a monopile foundation <NUM> in this embodiment) in the vertical direction <NUM> between a lower surface <NUM>-<NUM> and an upper surface <NUM>-<NUM> thereof. The superstructure <NUM> is connected releasably to foundation <NUM>, for instance via the annular flange <NUM> which is fixed to foundation <NUM>, particularly to connecting plate <NUM>, with a bolt connection. As can be seen, the foundation <NUM> extends partially above water.

According to <FIG>, the superstructure <NUM> is constructed from a number of uprights <NUM> extending in vertical direction <NUM> and connected in the upper surface <NUM>-<NUM> by a U-shaped strengthening frame <NUM>. Side walls of the superstructure <NUM> are formed by strengthening ribs <NUM> which run obliquely between uprights <NUM> and form together with two uprights <NUM> a lattice structure. The add-on structure <NUM> is accessible to a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) in that a side wall thereof is kept open, i.e. is not provided with the strengthening ribs <NUM>. The open side wall lies on the open side of the U-shaped strengthening frame <NUM> and is therefore not bounded by a rib of strengthening frame <NUM>. The open side wall makes an internal space <NUM> of superstructure <NUM> accessible to a tower section (<NUM>-<NUM>, <NUM>-<NUM>,.

Situated in the lower surface <NUM>-<NUM> is a supply structure <NUM> for a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. The supply structure <NUM> comprises two support beams <NUM> extending mutually parallel in lower surface <NUM>-<NUM> and together forming a support surface for a horizontally slidable floor <NUM>. The support beams <NUM> are connected with pull rods <NUM> to uprights <NUM> of superstructure <NUM>. The floor is slidable between a position A outside the internal space and a position B lying inside the internal space <NUM>. With floor <NUM> a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) can be coupled in known manner, for instance with clamps or bolts. As can be seen in <FIG>, the support beams <NUM> - and so the support surface formed by the two as well - protrude from superstructure <NUM> on both sides. This allows floor <NUM> to be slid not only from the position A outside internal space <NUM> to the position B lying inside internal space <NUM>, but also on to a position C, lying outside internal space <NUM>, on a side of superstructure <NUM> lying opposite relative to position A. The supply structure <NUM> is configured in the described manner to move a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) coupled thereto from outside internal space <NUM> into internal space <NUM> by a horizontal displacement.

According to an embodiment shown in <FIG>, the horizontal sliding of floor <NUM> relative to support beams <NUM> can take place using a rack and pinion system (<NUM>, <NUM>). A rack <NUM> is for this purpose incorporated in both support beams <NUM> in the lower surface <NUM>-<NUM>. The rack <NUM> co-acts with a toothed wheel <NUM> which is mounted on floor <NUM>. In a suitable embodiment a toothed wheel <NUM> is arranged in each corner of the floor <NUM>, although other positions are also possible.

Superstructure <NUM> is further provided with an engaging structure <NUM> for a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ), received in internal space <NUM> for displacement in the vertical direction <NUM>. The engaging structure <NUM> is cage-like and constructed from mutually connected support beams <NUM> which together form a structural whole. Engaging structure <NUM> can have an open side which connects to the open side wall of superstructure <NUM>. In an improved embodiment (see <FIG>) the open side can comprise a lattice door <NUM>. The door <NUM> can thus form together with the rest of the engaging structure <NUM> a relatively rigid cage structure when door <NUM> is closed.

Engaging structure <NUM> is suspended from cables <NUM>, preferably of steel, which are tensioned between the strengthening frame <NUM> in upper surface <NUM>-<NUM> and the support beams <NUM> in lower surface <NUM>-<NUM> and which run through openings <NUM> made in some support beams <NUM>. Engaging structure <NUM> is further provided with strand jacks <NUM>, connected to support beams <NUM>, through which the cables <NUM> run. A strand jack comprises a hollow hydraulic cylinder provided with a central opening through which a cable <NUM> runs. The cylinder is provided at both outer ends with a clamp which can be clamped round the cable <NUM>. The string jack can climb or fall along the cable <NUM>. Climbing can for instance take place by releasing an upper clamp of the cylinder in a retracted position while a lower clamp clamps round the cable <NUM>, imparting a stroke to the cylinder (extending it) and securing the upper clamp on cable <NUM> in that position. The lower clamp is then released and the cylinder retracted, after which the lower clamp is fixed again. For falling, a reverse order is kept to. In the embodiment shown in <FIG> four strand jacks <NUM> are arranged, one on each corner point of engaging structure <NUM>. If desired, engaging structure <NUM> can be suspended from cables <NUM> with more strand jacks <NUM>. Because the strand jacks <NUM> are connected to the support beams <NUM>, a climbing or falling of strand jacks <NUM> along the cables <NUM> will also make the engaging structure <NUM> climb or fall along cables <NUM> as a whole. By clamping both clamps of the strand jacks <NUM> round cables <NUM> the strand jacks <NUM> (and so engaging structure <NUM> as well) can be secured in securing positions relative to superstructure <NUM>. The shown embodiment allows relatively great forces to be absorbed while still allowing good moveability along cables <NUM> in vertical direction. It will be apparent that other vertical moving means can be applied. It is thus possible to arrange a rack and pinion system in uprights <NUM> or to suspend the engaging structure <NUM> from cables, wherein the cables can be taken in or payed out with winches arranged on support frame <NUM> in the upper surface <NUM>-<NUM>. As further shown, guide sleeves <NUM> arranged on support beams <NUM> can provide for a better guiding of the engaging structure <NUM> along the cables <NUM>.

Engaging structure <NUM> is further provided with an engaging plate <NUM> for a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. The engaging plate <NUM> is provided on an upper side with a recess 56a in which a trunnion <NUM> arranged on an outer wall of the engaged tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) can be received. In the shown embodiment the engaging structure <NUM> is provided with two opposite engaging plates <NUM> which engage on opposite sides of the engaged tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) on a trunnion <NUM> arranged on the outer wall of the engaged tower section (<NUM>-<NUM>, <NUM>-<NUM>,. Each engaging plate <NUM> is moveable toward and away from the tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) in a horizontal direction. For this purpose hydraulic cylinders <NUM> which engage on the engaging plate <NUM> are arranged on horizontally running support beams <NUM>. In the embodiment shown in <FIG> the connection <NUM> between the hydraulic cylinders <NUM> and the support beam <NUM> is shown in broken lines for the sake of visibility. The horizontal moveability of engaging plates <NUM> serves two purposes. Firstly, tower sections (<NUM>-<NUM>, <NUM>-<NUM>,. ) with different diameters can be engaged in this way. Secondly, the engaging structure <NUM> can thus be moved along a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) without the engaging plates <NUM> coming into contact with trunnions <NUM> arranged on the outer wall of the tower section. This is because the engaging plates <NUM> can be moved further away from the outer wall of the tower section than a protrusion length 35a of the trunnions <NUM>. The protrusion length 35a is shown in <FIG>.

As can be seen clearly in <FIG>, support beams <NUM> of engaging structure <NUM> are also provided with engaging means <NUM>, placed at vertical distance 58a, for a wall part of a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. The engaging means <NUM> can be moved with hydraulic cylinders 58b from a position P1 removed from the tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) to a position P2 in which a wall part of the tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) is engaged by the engaging means <NUM>. In the shown embodiment the engaging means <NUM> are provided with two rollers 58c which can be placed against the wall part of the tower section (<NUM>-<NUM>, <NUM>-<NUM>,. These can also be rubber, plastic or metal plates. As can be seen in <FIG>, four engaging means <NUM> are connected for movement between positions P1 and P2 to the support beams <NUM>, this in two horizontal planes positioned at vertical distance 58a. The engaging means <NUM> are thus configured to hold the engaged tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) upright in that they can absorb a moment around a horizontal axis.

As shown clearly in <FIG> and <FIG>, an embodiment of device <NUM> can further be characterized in that the superstructure <NUM> comprises at the position of the upper surface (<NUM>-<NUM>) a positioning means <NUM> for a root <NUM> of a wind turbine blade <NUM>. The positioning means <NUM> comprises a lattice cage <NUM> connected via ribs <NUM> to superstructure <NUM> and provided on an upper side with a positioning plate <NUM> which is movable in X- and Y-direction. The positioning plate <NUM> can for instance be connected with hydraulic cylinders (not shown) to a fixed upper plate <NUM> of lattice cage <NUM>. Arranged on positioning plate <NUM> is an upright support <NUM>, an upper side of which is profiled in order to be able to receive a wall part of the root <NUM> of the wind turbine blade <NUM>.

The above shows that engaging structure <NUM> is configured by means of the engaging plate <NUM> and the engaging means <NUM> to engage a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) and then displace it in the internal space <NUM> in vertical direction <NUM> by means of the strand jacks co-acting with cables <NUM>. It is thus possible to lift a tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ), whereby sufficient space is created under the relevant tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) for receiving another, underlying tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) in the internal space <NUM>. This underlying tower section (<NUM>-<NUM>, <NUM>-<NUM>,. ) can for instance be moved into the internal space <NUM> by an inward sliding of the floor <NUM>. In this way a wind turbine mast can be constructed from the bottom up, as will be further illustrated below.

The different steps of an embodiment of a method for offshore construction of a wind turbine using the invented device <NUM> are illustrated in <FIG>.

Referring to <FIG>, the superstructure <NUM> is taken up with lifting crane <NUM> and placed on foundation <NUM>, and secured thereto. A first tower section <NUM>-<NUM> is then taken up with the lifting crane and moved from above into the internal space <NUM> of superstructure <NUM> and into engaging structure <NUM>, which is for this purpose secured in an upper half of the superstructure <NUM>. Two opposite trunnions <NUM> of the first tower section <NUM>-<NUM> are here moved into the recesses 56a provided on an upper side of engaging plates <NUM>. The first tower section <NUM>-<NUM> is then uncoupled from lifting crane <NUM> and the first tower section <NUM>-<NUM> rests in the engaging plates <NUM> of engaging structure <NUM>. The vertical position of engaging structure <NUM> is here high enough for an upper part of the first tower section <NUM>-<NUM> to protrude above the upper surface <NUM>-<NUM>. A hub <NUM> with generator <NUM> is then taken up from the deck <NUM> of vessel <NUM> with lifting crane <NUM> and placed on first tower section <NUM>-<NUM>, and connected here. This situation is shown in <FIG>.

A wind turbine blade <NUM> is then taken up from deck <NUM> with lifting crane <NUM> and slid with its blade root <NUM> into a hub opening 30a of hub <NUM>, and secured therein. In <FIG> two wind turbine blades <NUM> have already been connected to hub <NUM> in this manner. As shown for a third wind turbine blade <NUM>, the sliding of the blade root <NUM> into the hub opening 30a takes place via the positioning means <NUM>. For this purpose the blade root <NUM> of blade <NUM> is placed in substantially horizontal position into the upright support <NUM> with lifting crane <NUM>, wherein the blade <NUM> remains suspended in lifting crane <NUM>. The movements in the horizontal plane with the (X, Y) positioning plate <NUM> are then in any case controlled (preferably remotely) such that the root <NUM> is positioned and aligned precisely opposite hub opening 30a and is then slid therein and secured, for instance with a bolt connection. The partially constructed state shown in <FIG> thus results.

In a subsequent step a second tower section <NUM>-<NUM> is taken up from deck <NUM> of vessel <NUM> with lifting crane <NUM> and set down on the floor <NUM> of supply structure <NUM>, and coupled thereto. The coupling can for instance be done using hydraulic clamps or by means of a bolt connection. The floor <NUM> here lies outside the internal space <NUM> in the position A as can be seen in <FIG> and <FIG>. The second tower section <NUM>-<NUM> coupled to the floor <NUM> of supply structure <NUM> is then moved from the position A outside internal space <NUM> into internal space <NUM>, into the position B. According to <FIG>, this is done by sliding the floor <NUM> of supply structure <NUM> and the second tower section <NUM>-<NUM> coupled thereto in horizontal direction. Meanwhile, the first tower section <NUM>-<NUM> remains suspended in the engaging plates <NUM> of engaging structure <NUM>, as shown in detail in <FIG>.

Referring to <FIG>, the engaging structure <NUM> is lowered along cables <NUM> with the strand jacks <NUM> until a lower edge of the first tower section <NUM>-<NUM> hanging from engaging plates <NUM> comes into contact with an upper edge of the second tower section <NUM>-<NUM> coupled to floor <NUM>. The two tower sections <NUM>-<NUM> and <NUM>-<NUM> are then secured to each other, for instance by connecting corresponding flanges thereof using bolts, as shown in <FIG>. The first tower section <NUM>-<NUM> is then uncoupled from the engaging structure <NUM>. This can for instance be done by moving engaging means <NUM> into the non-engaged position P1, moving engaging plates <NUM> downward (along with the rest of engaging structure <NUM>) so that the trunnions come loose from engaging plates <NUM>, and moving engaging plates <NUM> a distance away from the wall of the tower sections <NUM>-<NUM> and <NUM>-<NUM>. This allows engaging plate <NUM> to be moved downward over the trunnion <NUM> of the second (underlying) tower section <NUM>-<NUM>.

Referring to <FIG>, the trunnion <NUM> of the second tower section <NUM>-<NUM> is then engaged with the engaging plates <NUM>. This situation is shown in more detail in <FIG> and <FIG>. Engaging means <NUM> are here in the engaged position P2.

Referring to <FIG>, the two coupled tower sections (<NUM>-<NUM>, <NUM>-<NUM>) are then moved upward in internal space <NUM> with the engaging structure <NUM> by displacing engaging structure <NUM> upward in vertical direction <NUM> using strand jacks <NUM>. This creates sufficient space under the relevant coupled tower sections (<NUM>-<NUM>, <NUM>-<NUM>) for receiving another, underlying tower section (<NUM>-<NUM>) in the internal space <NUM>. In this situation the partially formed wind turbine mast protrudes to substantial extent above the upper surface <NUM>-<NUM> of superstructure <NUM>. The engaging means <NUM> are important in keeping the partially formed wind turbine mast, which after all is not otherwise supported, upright.

Referring to <FIG>, the steps described above for the second tower section <NUM>-<NUM> are repeated for a third tower section <NUM>-<NUM>. To this end we refer to the description given above of these steps for placing the second tower section <NUM>-<NUM>. <FIG>, <FIG>, <FIG> and <FIG> here describe corresponding method steps as described in <FIG>, <FIG>, <FIG> and <FIG>.

Referring to <FIG>, the situation resulting after the above described steps is shown, wherein the wind turbine mast is constructed wholly from tower sections (<NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>) placed one on the other. The superstructure <NUM> is here still situated on foundation <NUM> and around the constructed wind turbine mast <NUM>. In order to be able to remove superstructure <NUM> the complete wind turbine mast <NUM> is lifted slightly with engaging structure <NUM>, and the floor <NUM> is moved along the support beams <NUM> of supply structure <NUM> from the position B in internal space <NUM> to the position C, lying opposite the position A (see for instance <FIG>). The wind turbine mast <NUM> is then lowered again to a position against plate <NUM>, and secured thereto.

In a final step shown in <FIG> and <FIG>, the superstructure <NUM> is released from foundation <NUM> and removed from around wind turbine tower <NUM> along the open side wall of superstructure <NUM> with lifting crane <NUM>. Door <NUM> of engaging structure <NUM> is here in folded-open state.

Claim 1:
Device (<NUM>) for offshore arranging of a wind turbine (<NUM>) or components (<NUM>, <NUM>, <NUM>, <NUM>) thereof on a vertically extending foundation (<NUM>) present at sea, comprising:
- an elongate superstructure (<NUM>) connected releasably to the foundation (<NUM>) and extending between a lower surface (<NUM>-<NUM>) and an upper surface (<NUM>-<NUM>) thereof in the vertical direction (<NUM>) from the foundation (<NUM>), wherein the superstructure (<NUM>) comprises an internal space (<NUM>) which is accessible to a tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) of the wind turbine (<NUM>) and in which the tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) can be received;
- a horizontally displaceable supply structure (<NUM>) for a tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...), wherein the supply structure (<NUM>) is configured to move a tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) coupled thereto from outside the internal space (<NUM>) into the internal space (<NUM>) by a horizontal displacement;
- an engaging structure (<NUM>), received for vertical displacement in the internal space (<NUM>), for a tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) received in the internal space (<NUM>), wherein the engaging structure (<NUM>) is configured to lift an engaged tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) in the internal space (<NUM>) by a vertical displacement, whereby sufficient space is created under the relevant tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) for receiving another, underlying tower section (<NUM>-<NUM>, <NUM>-<NUM>, ...) in the internal space (<NUM>).