Method for preserving wind turbine towers with auxiliary flotation systems - Patents.com

Abstract

The invention relates to a method for the maintenance of an offshore structure (2), the structure (2) comprising a wind turbine (20) and at least one vertical shaft (4). The method comprises using an auxiliary floating system (1) comprising at least one floating element (5) that remains semi-submerged due to the maintenance work of the offshore structure (2), at least one connection structure (7) connecting the system (1) to the floating structure (2), a contact element (9') and a clamping element (9'). The clamping element is fixed to the connection structure (7) intended to rigidly connect the system (1) to the shaft (4). Advantageously, due to the rigid connection, the maintenance work of the offshore structure (2) can be carried out in an efficient and safe manner for the maintenance personnel and the system involved in the work.

Description

[Technical field]

[0001] The present invention mainly relates to a method using an auxiliary floating system for the maintenance of marine towers, for example for the maintenance of offshore wind turbine towers. The main field of the application is therefore the civil construction industry, in particular the tower construction and / or foundation works and maintenance industry, combined with the environmental protection or renewable industry, in particular the marine wind energy industry. [Background technology]

[0002] In the field of offshore wind energy, wind turbine maintenance work, commonly known as "major improvement" maintenance, has huge economic impact and importance. This wind turbine maintenance work requires cranes to raise and lower heavy parts of the wind turbine, which are located at very high altitudes of about 100 meters or more.

[0003] Traditionally, "major workover" operations for offshore wind turbines are almost exclusively carried out by jack-up vessels, which are ships with legs that can be supported on the seabed to raise the vessel's hull. Thus, the cranes incorporated by the actual vessel can operate and are hardly adversely affected by the sea movements. On the other hand, these vessels are very rare and expensive, which penalizes the maintenance costs of offshore wind farms.

[0004] A very cost-effective method known in the prior art for operating cranes on offshore structures is based on using conventional land-based cranes on barges or pontoons. However, this method is not feasible for offshore wind turbines. Due to the large working height, the movement of the barge supporting the crane is increased at the end of the boom that needs to operate at a given height of the wind turbine. This makes the crane operation unfeasible even in good conditions with respect to sea states. The above mentioned problems are magnified when the support structure of the wind turbine is not fixed and is floating.

[0005] The present invention aims to overcome these limitations and drawbacks of known systems by means of a new auxiliary floating system and corresponding method of use during maintenance operations of an offshore structure, which allows to eliminate relative movements between the floating element supporting the maintenance crane and the offshore structure supporting the wind turbine on which maintenance is being performed. Summary of the Invention

[0006] In order to overcome the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a method using an auxiliary floating system for the maintenance of an offshore structure, such as a wind turbine tower, which may be floating or not, said system optimizing the above-mentioned maintenance operations with respect to known systems.

[0007] The above mentioned object is preferably achieved by a method for the maintenance of a wind turbine supported on an offshore structure, which can be floating or fixed to the seabed and comprises a shaft and / or a foundation. The invention is particularly suitable for maintenance operations of parts at a large height, preferably by crane operation. Also, by means of the invention the limitations of known barge or floating crane systems can be overcome in operations where the freedom of movement of the system is a drawback or unfavourable, e.g. in the case of operations for maintenance of wind turbines.

[0008] Advantageously, the method of the present invention includes the use of an auxiliary flotation system. The auxiliary flotation system comprises: One or more floating elements. At least one crane located on at least one of said floating elements. At least one working area for storage and / or repair of parts of said wind turbine and / or said offshore structure. At least one attachment structure for attachment to said offshore structure. The coupling structure comprises: An articulated closure ring configured to close around an element of the offshore structure, preferably a shaft or a tower, although this closure ring may also close on other elements of the foundation, without departing from the scope of the invention. A plurality of contact elements between the coupling structure and the marine structure. In a preferred embodiment, at least three contact elements are arranged at a large height and at least three other contact elements are arranged at a small height. Thus, a torque is generated between the reaction of the elements at the upper height and the reaction of the elements at the lower height. Also, a moment transfer between the coupling structure and the element of the marine structure to which it is coupled is facilitated. one or more clamping elements, the position of the contact element being adjustable, the clamping elements being configured to apply a clamping force to the marine structure by the contact element;

[0009] Preferably, the attachment structure for attachment to the marine structure takes at least three forms. The closed ring is open in an open configuration. A closed configuration in which the closed ring is closed. A clamping configuration configured such that the closure ring is closed and the clamping element applies a clamping force to the marine structure.

[0010] The method of the invention also comprises carrying out, in any order technically possible, the following steps: (a) transporting the floating auxiliary floating system relative to the location of the offshore structure; (b) bringing the auxiliary floating system closer to the offshore structure with the coupling structure in the open configuration. Step (c) of placing said coupling structure (7) in said closed configuration such that said closed ring completely surrounds said element of the marine structure. Step (d) of acting on the clamping elements in a controlled manner to place the coupling structure in the clamped configuration so that the offshore structure and the auxiliary floating system are rigidly connected in six degrees of freedom of motion (heave, fore-aft, yaw, yaw, pitch, and roll). (e) using the crane to perform maintenance work on the wind turbine and / or the offshore structure. using the working area of ​​the auxiliary floating system for storage and / or repair of components of the wind turbine and / or the offshore structure. (f) . (g) decoupling the auxiliary floating system from the offshore structure and placing the combined structure in the open configuration.

[0011] In a preferred embodiment of the method of the present invention, said auxiliary flotation system comprises a plurality of said flotation elements connected to each other and / or to said coupling structure.

[0012] In another preferred embodiment of the method of the present invention, the auxiliary flotation system comprises a single flotation element in the form of a barge; both the crane and the work area are disposed on the barge; The barge may be formed by a single body or by a series of multiple modules connected together. In this second case, the barge can be formed by special modules that are specially formed with the connecting structure to complete the barge with the required area. Conventional or commercial barge modules are connected to the connecting structure. Cost economy is achieved since the number of special elements for the system is minimized. Also, standard modules for barges known in the prior art can be used as a complement.

[0013] In another preferred embodiment of the method of the present invention, The crane is a telescopic and / or folding crane, The crane is deployed after step (d) and refolded before step (g). This capability is advantageous because it aids and / or increases the stability of the floating system when it is floating and free (i.e., not attached to an offshore structure).

[0014] In another preferred embodiment of the method of the present invention, The work area is located at least partially at a predetermined distance away from the crane that is greater than a minimum radius of the crane. The radius of action of the crane is limited not only when it is too far away, but also when it is too close. (This second case is the most limiting case for a given configuration, the crane cannot operate with elements too close to the crane.) This also imposes a minimum size on the barge. This prevents the barge from being too large, so that barge movements are difficult to avoid. The present invention considers using a "free" working area, for example on a ship or offshore structure, with a structure similar to that which a helicopter pad has. As a result, this structure can be separated from the crane without increasing the size of the barge and the waterline area. The working area is at least partially free with respect to the floating element, At least a portion of the working area is not located on the deck of the floating element. The advantage of a free platform is that by using the platform, the working area of ​​the crane can be moved away so that the platform is outside the minimum working radius without unnecessarily increasing the area of ​​the floating elements. By limiting the area, the stresses in the whole system and in the offshore structure itself can be limited in the connections between the whole system and the offshore structure.

[0015] In another preferred embodiment of the method of the present invention, The step (a) and / or the step (b) may be carried out by towing the auxiliary floatation system. This may reduce the cost of the auxiliary system. While the auxiliary floating systems described in the present invention may also be self-propelled for transport, they do not need to be self-propelled when using tugboats for the operation.

[0016] In another preferred embodiment of the method of the present invention, The flotation element comprises a hydrodynamic damping plate. The advantage of this plate is primarily its ability to limit floating motion, especially during binding steps (b) and (c) and separation step (g).

[0017] In another preferred embodiment of the method of the present invention, The flotation element may be ballast stabilized, either centrally or eccentrically. The advantage of eccentric ballast stabilization consists essentially of counterbalancing the weight of the crane when it is preferred to be eccentrically positioned. This allows the crane's working area to be appropriately spaced away, encouraging the positioning of the linkage outside the crane's minimum working radius, to prevent interference with the linkage. Eccentric ballast systems also allow for other eccentric weights, such as the weight of the linkage, to be counterbalanced.

[0018] In another preferred embodiment of the method of the present invention, The method comprises: After step (d), there is a step (j) of stabilising at least one of the floating elements with ballasting to counteract rising tides and / or destabilising at least one of the floating elements with ballasting to counteract falling tides. The coupling structure reduces the forces that need to be transmitted to maintain a solid coupling with the offshore structure during heave motion. This advantage only applies in the case of fixed offshore structures and not in the case of floating structures, since the tides will affect the offshore structure and the auxiliary floating system equally when the offshore structure to be maintained is floating. Alternatively, the coupling structure can be kept in a clamped configuration and rigidly connected during heave motion only when the crane is actuated in step (e). On the other hand, when the crane is not actuated, the coupling structure can relax the clamping force to be free to move. Thus, relative movement between the auxiliary floating system and the offshore structure during heave motion is possible to accommodate tidal changes.

[0019] In another preferred embodiment of the method of the present invention, The freeboard of the auxiliary floating system accommodates tidal changes such that tidal changes do not reduce the freeboard to less than 10 cm whilst the auxiliary floating system remains attached to a fixed offshore structure.

[0020] In another preferred embodiment of the method of the present invention, the auxiliary floating system comprising one or more approximation or anchoring cables between the auxiliary floating system and the offshore structure; The length of the cable is adjusted during the approximating step (b). These cables are generally operated by a winch, which has the advantage of allowing greater control during operation to move the auxiliary floating system closer to the offshore structure. In a preferred embodiment, the cable is anchored at one end to the offshore structure and the length of the cable is adjusted by a winch from the auxiliary floating system. The cable also has both ends anchored to the auxiliary floating system, for example partially surrounding the shaft of the offshore structure.

[0021] In another preferred embodiment of the method of the present invention, The closure ring retains sufficient internal space for coupling with an area of ​​the offshore structure that comprises a ship landing structure. During operations for docking or undocking the system with the offshore structure, interference with the ship's landing area is prevented from occurring.

[0022] In another preferred embodiment of the method of the present invention, The tightening element comprises: A lever fixed at an articulated position, said lever being rotatable relative to said articulated position. A contact element connected to the lever position. A telescoping and / or collapsible hydraulic cylinder connected to another position of the lever. By actuating the hydraulic cylinder to extend and / or retract, the lever is caused to rotate, The position and / or force exerted by the contact element may be adjusted.

[0023] In another preferred embodiment of the method of the present invention, Since the distance between the line of action of the hydraulic cylinder and the joint position is greater than the distance between the line of action of the contact element and the joint position, By effect of the lever, the force F of the hydraulic cylinder produces a force F' on the contact element which is greater than force F.

[0024] In another preferred embodiment of the method of the present invention, The method comprises: Before the step (c), (k) providing reinforcing means to the element of the marine structure to which the joint structure is joined, The contact elements enable the offshore structure to resist forces that the auxiliary floating system may impart to the offshore structure.

[0025] The system is therefore applicable not only to marine structures which are pre-configured for use with said system, but also to structures which are not pre-configured for use with said system but which are suitably reinforced to resist forces which may be transmitted by the connecting structure of the auxiliary floating system.

[0026] In another preferred embodiment, The marine structure is a monopile structure, The reinforcing means This involves completely or partially filling the interior of the monopile with concrete. This filling is preferably performed in the support area of ​​the contact element by the offshore structure and may be a complete filling or annular filling of the monopile interior at two levels that correspond to the two levels of the contact element of the connection structure. In case of a monopile with a transition between the monopile and the wind turbine tower, said reinforcing means may be attached in a similar manner to the transition. This type of reinforcement has the advantage that it is very easy to carry out in the existing structure, by simply pouring concrete, through an access hatch to the tower or another suitable access to the monopile or to the transition, thus providing a robust reinforcement in a simple and cost-effective way to the area provided for the connection of the auxiliary floating system. In other embodiments, other reinforcing means known in the prior art may be metallic or of other type and may be used without consequently departing from the scope of the invention.

[0027] In another preferred embodiment of the method of the present invention, The auxiliary flotation system comprises: means for controlling and / or monitoring the clamping force and / or position of said clamping element; and / or means for opening and closing said closed ring. The means for opening and closing the ring may, for example, comprise a hydraulic actuator having one end fixed to a central portion of the ring and the other end fixed to an outer portion of the ring, such that when the hydraulic actuator is extended it biases the outer portion to gradually close the ring and when it is retracted it exerts the opposite action to open the ring.

[0028] In another preferred embodiment of the method of the present invention, The auxiliary flotation system comprises a combination of active clamping elements and passive elements. Within the scope of the present invention, passive elements are understood to be contact elements that lack a clamping means while exerting a force on the marine structure in a passive manner, as a reaction. The use of active elements is essential to be able to adjust the clamping force of the coupling structure. On the other hand, the combination with some passive elements may reduce the number of active elements required and, as a consequence, the cost of the system.

[0029] In another preferred embodiment of the method of the present invention, The contact element comprises a support plate in contact with the marine structure and a coefficient of friction greater than 3%; Clamping of the contact element against the offshore structure creates frictional forces which result in a solid coupling between the offshore structure and the auxiliary floating system. In particular, when the closing ring surrounds the shaft of the offshore structure or other vertical element of the offshore structure, said friction is advantageous for transmitting vertical forces and for making a rigid connection during up and down movements. Thus, during step (e) of the method in which the crane operates, a large force is exerted by the clamping element between the contact element and the offshore structure, creating sufficient friction to prevent relative vertical movements. On the other hand, when the crane is not operating, said force can be reduced or moderated, so that relative vertical movements can be made with reduced friction to accommodate the tides. (This force only acts on fixed offshore structures and is not necessary for floating offshore structures, since the tides have an equally adverse effect on the offshore structure and the auxiliary floating system.)

[0030] In another preferred embodiment of the method of the present invention, the closed ring of the auxiliary flotation system includes a guard; The guard is in a position such that it contacts the marine structure during step (b) or step (c) before the contact element is activated. On the one hand, the guard is understood to be a flexible element intended to dampen shocks, for example between two vessels or between a vessel and a fixed element.

[0031] In another preferred embodiment of the method of the present invention, The crane is a mobile land crane having tracks or wheels, The mobile land crane is supported on at least one of the floating elements. The ability to use land-based cranes instead of the offshore cranes typically used for maintenance of offshore wind turbines represents significant cost economies.

[0032] In another preferred embodiment of the method of the present invention, The crane is a mobile land crane, The mobile land crane is an upper body having at least one boom, a counterweight, and equipment for operating the crane; a lower body having means for moving the crane by wheels and / or tracks, The auxiliary flotation system only comprises the upper body of the crane. The weight of the crane is therefore reduced. Also, if the crane does not need to move during the method of the invention, the lower body can be dispensed with. In this embodiment, the auxiliary floating system must comprise anchoring means for the connection of said upper body of the crane. [Brief description of the drawings]

[0033] The above and other features and advantages will become apparent from the detailed description of the invention and preferred embodiments taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 shows a plan view with the offshore structure. [Figure 2a] FIG. 2a shows a detailed view of the fastening elements of the auxiliary floating system of the present invention which are not fixed to the offshore structure. [Figure 2b] FIG. 2b shows a detailed view of the fastening elements of the auxiliary floating system of the present invention secured to the offshore structure to which the floating system is secured. [Figure 3a] FIG. 3a shows a closed ring of the system of the invention in an open configuration in a preferred embodiment. [Figure 3b] FIG. 3b shows a closed ring in the closed configuration of the system of the invention in a preferred embodiment. [Figure 4] FIG. 4 shows a first preferred embodiment of the system of the present invention applied to the maintenance of a telescoping wind turbine tower. [Diagram 5] FIG. 5 shows a diagram of a second preferred embodiment of the system of the invention, in which the floating element is configured in the form of a barge. [Figure 6] FIG. 6 shows a diagram of a second preferred embodiment of the system of the invention, in which the floating element is configured in the form of a barge. [Figure 7] FIG. 7 shows a diagram of a second preferred embodiment of the system of the invention, in which the floating element is configured in the form of a barge. [Figure 8] FIG. 8 shows a third preferred embodiment of the invention, in which the offshore structure is a monopile structure, preferably comprising reinforcing means completely or partially embedded within the monopile. [Figure 9] FIG. 9 shows a view of a second preferred embodiment of the system of the invention corresponding to FIGS. 5 to 7, in which the floating element of the system is configured in the form of a barge. [Figure 10] FIG. 10 shows a view of a second preferred embodiment of the system of the invention corresponding to FIGS. 5 to 7, in which the floating element of the system is configured in the form of a barge. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] A detailed description of different preferred embodiments of the present invention is set forth below with reference to Figures 1 to 10. The above description is provided to illustrate the claimed invention, without limiting it.

[0035] FIG. 1 shows a plan view of the auxiliary floating system (1) of the present invention together with an offshore structure (2) supporting a wind turbine (20). Said offshore structure (2) comprises a foundation (3) and a tower or shaft (4). In this embodiment, the auxiliary floating system (1) comprises at least one floating element (5). (i.e., in the example of FIG. 1, three such elements (5) are shown.) The auxiliary floating system (1) is preferably coupled to the offshore structure (2) during maintenance operations. (However, certain embodiments of the present invention may be used in other ways to install or transport the offshore structure (1) to a predetermined offshore location.)

[0036] The floating elements (5) of the system (1) are connected by connecting elements (6) (e.g. trusses or lattice jibs) to a coupling structure (7) that is preferably intended to enclose at least one element of the offshore structure (2), for example arranged around the shaft (4). The positions or areas of contact with the coupling structure (7) thus provide a means for fixing to the offshore structure (2). The floating system (1) thus retains its position during the abovementioned operations. Preferably, the coupling structure (7) forms a closed ring (8) around the shaft (4). This closed ring (8) may be circular or have any other closed shape, for example curved or polygonal.

[0037] With regard to the location or area of ​​contact between the connecting structure (7) and the marine structure (2), the system of the invention comprises one or more clamping elements (9). The contact elements and the clamping elements are fixed to the connecting structure (7) and can preferably be arranged along a closed ring (8). Said clamping elements (9) comprise active actuators, such as hydraulic cylinders. This active actuator allows, for example, the system to be (1) When the connecting structure (7) is connected to the offshore structure (2), a clamping force is generated on the offshore structure and the position of the system (1) can be fixed or to some extent fixed on the offshore structure (2). Due to the rigid attachment between the connecting structure (7) and the offshore structure (2), the relative movements between both structures can be reduced or substantially limited. In this connection, it is understood that certain aspects such as the elastic deformation of materials can result in small relative movements without departing from the scope of the invention. In any case, the rigid attachment between the connecting structure (7) and the offshore structure (2) can always limit the relative translational movements to less than 50 cm and the relative rotational movements to less than 2 degrees in the roll or pitch direction and less than 5 degrees in the yaw direction.

[0038] In a fixed-bottom foundation (3), the motion of the offshore structure (2) is substantially zero. Thereby, in terms of the connection, a stiff or semi-stiff connection is taken to mean that said motion is substantially zero both for the offshore structure (2) and the connecting structure (7). Whereas in a floating offshore structure (2), this does not occur since motion is common. In this case, a semi-stiff connection or a rigid connection is taken to mean that there is substantially zero relative motion between the offshore structure (2) and the connecting structure (7).

[0039] The clamping element (9) typically comprises an active element, such as an arm, which can be deployed by an electromechanical, hydraulic, pneumatic or similar system, so that the position of the contact element (9') can be adjusted to move closer to the offshore structure (2) until it contacts the offshore structure (2). The clamping element (9) may also comprise a passive element, configured for example as a stop to limit or prevent the movement of the offshore structure (2) with respect to the floating system (1). This passive element keeps the position of the offshore structure (2) relative to the closure ring (8) unchanged.

[0040] The system (1) of the invention may also optionally comprise a contact element (9') suitable for use during a step prior to the complete fixing of the clamping element (9) to the offshore structure (2). Said contact element (9') may or may not be provided on the clamping element (9) itself and is preferably suitable for providing a free sliding contact with the shaft (4). The contact element (9') thus allows a relative vertical movement between said shaft (4) and the auxiliary floating system (1) during a step prior to the rigid attachment of the clamping element (9) to the offshore structure (2). The coupling structure (7) thus provides a physical stop to the change in the horizontal position of the offshore structure (2) by means of the contact element (9') and limits the possible tilt that said structure may maintain (e.g. due to wind, waves, etc.) so that said structure (2) remains stable, preferably by means of a sliding contact. This allows a free movement of the offshore structure (2) substantially along a vertical axis. The free movement of the above-mentioned offshore structure (2) can be performed by sliding, rolling, caterpillar tracks or any known technique, which allows independent and sufficient free relative movement between the contact elements (9') over the surface of the shaft (4).

[0041] The contact element (9') therefore prevents and / or limits other relative movements between the auxiliary floating system (1) and the shaft (4), namely the relative horizontal movements (preferably less than 1 m), the relative rotations during roll and / or pitch movements (preferably less than 10 degrees) and the relative rotations during yaw movements (preferably less than 20 degrees). On the other hand, in the novel method of the present invention, the clamping element (9) is in charge of preventing or limiting the relative vertical movements between the offshore structure (2) and the floating system (1) during maintenance operations.

[0042] Similarly, in an embodiment of the invention, the marine structure (2) has a ship landing. The shape of the closing ring (8) can prevent interference with said ship landing. Thus, said shape can be adapted to the geometric characteristics of the marine structure (2) to facilitate fastening the system (1) and improve maintenance operations.

[0043] Figures 2a-2b show a possible embodiment of the clamping element (9). Said element comprises at least one contact element (9') coupled to a lever (10). This lever (10) can be actuated by a hydraulic cylinder (11). In this embodiment, when the coupling structure (7) closes against the shaft (4), the lever (10) is actuated until it comes into contact with said shaft (4), keeping said actuation and the lever (10) deployed until the floating system (1) is rigidly coupled to the offshore structure (2). In this embodiment, all the clamping elements (9) are in active form (in the form of levers (10) exerting a counter force by the hydraulic cylinder (11)). Alternatively, a combination of levers (10) and passive elements can be used. Said levers (10) exert a force against the passive elements by the shaft (4). In different embodiments of the invention, the actuation of the levers (10) can be performed in situ or by remote control means. Similarly, the connection between the lever (10) and the hydraulic cylinder (11) may be articulated by one or more articulation points (14).

[0044] In a possible embodiment of the invention, at least three contact elements (9') are used at a first height of the coupling structure (7) and at least three contact elements (9') are used at a second height of the coupling structure (7). The closing ring (8) is thus constituted by two support levers, improving its ability to absorb moments caused by the relative gradient between the offshore structure (2) and the auxiliary floating system (1). Similarly, said ring (8) may have different mechanisms for closing or for holding its position around the offshore structure (2), by pins, cooperating attachments, electromechanical systems or other known means.

[0045] In the embodiment of Fig. 3a-3b, the coupling structure (7) is formed by a metal lattice structure. Said coupling structure (7) also comprises an opening and closing subsystem (not shown) to facilitate its deployment and / or removal from the marine structure (2) and, optionally, one or more actuators for folding and / or unfolding the system (1) on the marine structure (2). Said actuators may be remotely actuated or not. In different embodiments, the actuators may also comprise telescopic hydraulic cylinders that can exert a force when extending and when retracting. Alternatively, the actuators may also comprise different kinds of means known in the art, such as mechanical actuators, pneumatic actuators, hydraulic actuators, haul ropes actuated by ropes, or winches, etc. The means for opening and closing the ring (8) may consist of a hydraulic actuator having one end fixed to the central part of said ring (8) and the other end fixed to the outer part. Thus, the hydraulic actuator biases the outer portion to close the ring (8) when extended, and creates the opposite effect to open the ring when retracted.

[0046] Figure 3a shows a plan view of the closed ring (8) in the open configuration. The closed ring has a central sector and two outer sectors connected to it at each articulation position. The ring in the closed configuration can be positioned by rotating the outer sectors at the articulation positions as shown in Figure 3b.

[0047] As mentioned above, the connecting structure (7) is preferably modular or adjustable, so that it can be adapted to offshore structures (2) and / or shafts (4) of different dimensions and / or characteristics, without the need to previously modify the structure (2) or provide additional means or substructures to the structure (2). For example, modules can be added to or removed from the lattice jib of the connecting structure (7) to adjust the length and distance to the shaft (4), thus preventing the shaft (4) itself from having to be modified. In an alternative or complementary manner, the position and / or dimensions of the clamping elements (9) and / or the contact elements (9') can be changed or adjusted. Thus, the same auxiliary floating system (1) can be used for the maintenance of offshore structures (2) with shafts (4) of different diameters, or shafts (4) of variable diameters, different cross sections (e.g. hexagonal or circular), or different dimensions (e.g. different center distances or diameters).

[0048] In a preferred embodiment of the system (1) of the invention, as shown in figure 1 and in a side view in figure 4, said system comprises a maintenance work crane (12), which is preferably arranged in a working area (13) of said system. The working area (13) can be located on the floating element (5) itself or on an auxiliary structure attached for that purpose. The working area (13) is likewise preferably used for the storage and / or repair of parts of the offshore structure (2), for example parts of the turbine or blades of the wind turbine (20). In different embodiments of the invention, said working area (13) can be an elevated area and / or a free area with respect to the floating element (5).

[0049] Preferably, a land-based crane (12) (understood to be a mobile commercial crane or a tracked crane commonly used in land-based construction work) is more cost-effective than using an offshore crane. A land-based crane (12) is considered as a result of the rigid coupling of the floating system (1) to the offshore structure (2) which limits the movement of the system and facilitates crane operation even at very high altitudes during maintenance work, such as occurs for example in work for maintenance of a wind turbine (20). In different embodiments, the crane (12) may be a folding and / or telescopic crane, preferably remaining folded in a step prior to the rigid coupling between the floating system (1) and the offshore structure (2) (FIG. 5). When the coupling is made, the crane can be deployed in a safe manner. Thus, maintenance work at high altitudes can be performed in a safe manner.

[0050] Figures 5-7 show a second preferred embodiment of the invention. The floating elements (5) of the auxiliary floating system (1) are assembled on a single support block in the form of a barge. Both the crane (12) and the working area (13) are arranged on the barge. Figures 5 and 6 show a front view and a plan view when the crane (12) has a telescopic boom that is folded up. This case is preferred for the situation where the auxiliary floating system (1) is floating independently and separated from the offshore structure (2) (e.g. in step (a)). During this situation, the boom and the hook of the crane (12) may have provisional elements for fixing to fixed elements of the auxiliary floating system (1) so as to mitigate possible effects of the movements of said system (1) when floating.

[0051] Likewise, in different embodiments of the invention, the floating element (5) may comprise hydrodynamic damping plates, e.g. heave plates, to reduce and damp undesirable motions caused by waves. Similarly, said floating element (5) of the system (1) may be ballast stabilized to provide an additional means for controlling the buoyancy and, consequently, the stability of the offshore structure (2). Thus, the floating element (5) may comprise one or more ballast adjustment means arranged on its submerged body (i.e. the part of the floating body submerged in contact with the water) to allow and / or control the water flow between the inside of said floating element (5) and the body of water in which it is floating. This ballast adjustment means allows an adjusted movement to modify the damping and natural frequency of the assembly in its delivery towards the offshore structure (2). The ballast adjustment means limits the tidal influence of the floating system (1) and offshore structure (2) assembly during maintenance operations. This capability is particularly advantageous in operations where the system (1) holds heavy equipment (e.g. blades of a wind turbine (20)) eccentrically, thereby changing the horizontal position. As a result of eccentrically ballast-stabilizing the floating element (5), the system can counteract the destabilizing effects of said equipment during maintenance operations prior to the step of transporting the system (1) towards a location offshore of the offshore structure (2). Similarly, the ballast means can be used as a tidal countermeasure, allowing water to be taken in or discharged from the floating element (5). This ballast can be used to counteract tidal movements when the system (1) is coupled to the offshore structure (2), for example in the maintenance of a fixed wind turbine (20).

[0052] The ballast adjustment means preferably comprise a gate with an adjustable and / or remotely operable opening, and / or a pump for removing or taking in water. The opening of the adjustable gate allows the filling height of the floating element (5) of the system and / or the water entry and exit height to be determined. In practice, this is equivalent to adjusting the effective waterline area and / or the draft. Thus, the oscillation period of said floating element (5) and / or the assembly it forms with the offshore structure (2) can be indirectly controlled during different steps of the transport or maintenance work of the offshore structure (2).

[0053] The floating element (5) can be manufactured using different materials known in the art, preferably concrete and / or metal materials. A mixed construction can also be used, with the lower part of the floating element (5) being manufactured from concrete and the rest from steel. Furthermore, precast concrete techniques can be used, similar to the methods commonly used for the construction of precast tanks.

[0054] The construction of the flotation element (5) may also be modular to adjust the overall size. The pieces or modules that may be used to form the flotation element (5) may form a number of shapes. The dimensions are therefore preferably such that they can be placed in a container (without exceeding the dimensions of a standard container) to facilitate transport and reuse. The modules may be attached to each other both at the bottom and at higher points to form the flotation element (5).

[0055] Preferably, the assembly formed by the floating element (5) and the connecting structure (7) for connecting it to the offshore structure (2) is hydrodynamically self-supporting, so that the distribution of mass and the centre of flotation of said floating element (5) and connecting structure (7) are such that when the opening and closing subsystem (10) is open (i.e. when the system (1) is separated from the offshore structure (2)), the floating element (5) is balanced in an upright position.

[0056] In another preferred embodiment of the invention, the method for preservation may comprise an additional step in which reinforcing means (15) are attached to the elements of the offshore structure (2) to which the connecting structure (7) is connected, so that the offshore structure (2) can resist the forces that the auxiliary floating system (1) may exert on it by means of the contact elements (9').

[0057] FIG. 8 shows a monopile offshore structure (2). The reinforcing means (15) preferably consists of a complete or partial filling of the interior of the monopile with concrete. This filling is preferably performed in the area of ​​contact of the contact elements (9') and may be a complete, partial or annular filling of the interior of the monopile at two levels corresponding to the two levels of the contact elements (9') of the connecting structure (7). In case of a monopile with a transition between the monopile and the offshore structure (2), said reinforcing means may be attached to the transition in a similar manner. In other embodiments, other reinforcing means known in the prior art may be of metal or other type and may be used without, as a result, departing from the scope of the invention.

[0058] In another preferred embodiment of the invention, the crane (12) is a mobile land crane having a lower body with at least one boom, a counterweight, equipment for operating the crane, and means for moving the crane by wheels and / or tracks. The auxiliary floating system (1) only comprises the upper body of the crane (12) (thus reducing the weight of the crane). Also, during the maintenance method, the crane (12) If the lower body does not need to move, the lower body can be dispensed with. In this embodiment, the auxiliary floating system (1) must be provided with anchoring means for the connection of said upper body of the crane (12). In Fig. 4 the above-mentioned embodiment is shown. In contrast to e.g. Figs. 5-7 it is shown that only the upper body of the crane is used. In Figs. 5-7 a land crane with both bodies (including the lower body with wheels) is used.

[0059] Finally, Figures 9 to 10 show different views of a preferred embodiment of the auxiliary floating system (1) of the invention, corresponding to Figures 5 to 7. The floating element (5) is configured in the form of a barge. [Explanation of symbols]

[0060] 1. Auxiliary Flotation System 2 Marine structures 3 Basics 4 Shaft 5. Floating Elements 6 Connection elements 7 Bonded structure 8. Closed Ring of Bonding Structure 9 Fastening elements 9' Contact Element 10 Lever 11 Hydraulic cylinder 12 Working crane 13 Working area 14 Joint Position 15 Reinforcement measures 20. Wind Turbines

Claims

1. A method for the maintenance of a wind turbine (20) supported on an offshore structure (2), comprising: The marine structure (2) comprises: Can be floating or anchored to the seabed, The device has a shaft (4) and / or a base (3), The method comprises: One or more flotation elements (5); at least one crane (12) located on at least one of said floating elements (5); at least one working area (13) for storage and / or repair of parts of said wind turbine (20) and / or said offshore structure (2); and at least one attachment structure (7) for attachment to said marine structure (2), The bonding structure (7) is an articulated closing ring (8) adapted to close around an element of the marine structure (2); a plurality of contact elements (9') between the coupling structure (7) and the marine structure (2); one or more active clamping elements (9), the position of which can be adjusted, the one or more active clamping elements (9) being configured to exert a clamping force on the marine structure (2) in a horizontal direction by means of the contact elements (9'); one or more passive elements combined with said one or more active tightening elements (9), The bonding structure (7) is an open configuration in which the closed ring (8) is open; a closed configuration in which the closing ring (8) is closed; a clamping configuration in which the closure ring (8) is closed and the one or more active clamping elements (9) are configured to apply a clamping force to the marine structure (2); The method comprises: In any order technically feasible: (a) transporting the floating auxiliary floating system (1) relative to the location of the offshore structure (2); (b) bringing the auxiliary floating system (1) closer to the offshore structure (2) with the connecting structure (7) in the open configuration; (c) placing said coupling structure (7) in said closed configuration such that said closed ring (8) completely surrounds the element of said marine structure (2); (d) acting in a controlled manner on the one or more active clamping elements (9) to place the coupling structure (7) in said clamped configuration so that the offshore structure (2) and the auxiliary floating system (1) become rigidly connected in six degrees of freedom of motion, namely heave, fore-aft, yaw, yaw, pitch and roll; (e) using the crane (12) to perform maintenance work on the wind turbine (20) and / or the offshore structure (2); (f) using the working area (13) of the auxiliary floating system (1) for storage and / or repair of parts of the wind turbine (20) and / or the offshore structure (2); and (g) separating said auxiliary floating system (1) from said offshore structure (2) and placing said coupling structure (7) in said open configuration.

2. 2. The method according to claim 1, characterized in that the auxiliary flotation system (1) comprises a plurality of said flotation elements (5) connected to each other and / or to the coupling structure (7).

3. said auxiliary floating system (1) comprising a single floating element (5) in the form of a barge; Both the crane (12) and the work area (13) are located on the barge; 2. The method of claim 1, wherein the barge is formed by a single body or a series of multiple modules connected together.

4. The crane (12) is a telescopic and / or folding crane, 4. The method according to any one of claims 1 to 3, characterized in that the crane (12) is unfolded after step (d) and folded again before step (g).

5. 5. The method according to claim 1, wherein the working area (13) is at least partially located at a predetermined distance from the crane (12) that is greater than a minimum radius of the crane (12).

6. said working area (13) being at least partially free with respect to said floating element (5), 6. The method according to any one of claims 1 to 5, characterized in that at least a part of the working area (13) is not located on the deck of the floating element (5).

7. 7. The method according to any one of claims 1 to 6, characterized in that step (a) and / or step (b) are performed by towing the auxiliary floating system (1) or by self-propelled transportation of the auxiliary floating system (1).

8. The method according to any one of the preceding claims, characterized in that the flotation element (5) comprises a hydrodynamic damping plate.

9. 9. A method according to any one of claims 1 to 8, characterized in that the floating element (5) can be ballast stabilized, either centrally or eccentrically.

10. 10. The method according to any one of claims 1 to 9, comprising, after step (d), a step (j) of stabilising at least one of the floating elements (5) with ballasting to counteract rising tides and / or of destabilising at least one of the floating elements (5) with ballasting to counteract falling tides.

11. 11. A method according to any one of claims 1 to 10, characterised in that the freeboard of the auxiliary floating system (1) is adapted to tidal changes such that the tidal changes do not reduce the freeboard to less than 10 cm whilst the auxiliary floating system (1) remains attached to a fixed offshore structure.

12. the auxiliary floating system (1) comprises one or more access or anchoring cables between the auxiliary floating system (1) and the offshore structure (2); 12. The method according to claim 1, wherein the length of the cable is adjusted during the approaching step (b).

13. 13. The method according to any one of claims 1 to 12, characterized in that the closing ring (8) retains sufficient internal space for coupling with an area of ​​the marine structure (2) comprising a ship landing structure.

14. The one or more active tightening elements (9) It comprises a lever (10) fixed at a joint position (14), The lever (10) is rotatable relative to the articulation position (14); The one or more active tightening elements (9) a contact element (9') connected to a position of said lever (10); a telescopic and / or collapsible hydraulic cylinder (11) connected to another position of the lever (10); By actuating the hydraulic cylinder (11) to extend and / or retract, the lever (10) is caused to rotate, Method according to any one of the preceding claims, characterized in that the position and / or the force exerted by the contact element (9') is adjusted.

15. Since the distance between the line of action of the hydraulic cylinder (11) and the joint position (14) is greater than the distance between the line of action of the contact element (9') and the joint position (14), 15. The method according to claim 14, characterized in that the effect of the lever (10) is that the force F of the hydraulic cylinder (11) produces a force F' of the contact element (9') that is greater than said force F.

16. The method comprises: Before the step (c), and further comprising a step (k) of providing reinforcing means (15) to the elements of the marine structure (2) to which the connecting structure (7) is connected, 16. The method according to any one of claims 1 to 15, characterized in that the offshore structure (2) is able to resist forces that the auxiliary floating system (1) can exert on the offshore structure (2) by means of the contact element (9').

17. The marine structure (2) has a monopile structure, 17. A method according to claim 16, characterized in that the reinforcing means (15) comprise a complete or partial filling of the interior of the monopile with concrete.

18. The auxiliary flotation system (1) comprises: means for controlling and / or monitoring the clamping force and / or position of said one or more active clamping elements (9); Method according to any one of the preceding claims, characterized in that it comprises means for opening and closing the closed ring (8).

19. The contact element (9') comprises a support plate in contact with the marine structure (2) and a coefficient of friction greater than 3%, so that 19. The method according to any one of claims 1 to 18, characterized in that tightening the contact element (9') against the offshore structure (2) generates frictional forces resulting in a solid coupling between the offshore structure (2) and the auxiliary floating system (1).

20. The closing ring (8) is provided with a guard, 20. A method according to any one of the preceding claims, characterised in that the guard is in a position such that it contacts the marine structure (2) during step (b) or step (c) before the contact element (9') is activated.

21. The crane (12) is a mobile land crane having tracks or wheels, 21. The method according to any one of claims 1 to 20, characterized in that the mobile land crane is supported on at least one said floating element (5).

22. The crane (12) is a mobile land crane, The mobile land crane is an upper body having at least one boom, a counterweight, and equipment for operating said crane (12); a lower body having means for moving the crane (12) by wheels and / or tracks, A method according to any one of the preceding claims, characterized in that the auxiliary floating system (1) only comprises the upper body of the crane (12).

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