Methods for the maintenance and / or installation of floating offshore wind turbine towers

Abstract

The present invention relates to a method for maintaining a floating offshore structure (1) including a submersible hole (3), the method comprising the use of an auxiliary vessel (7) including at least one floating element (8), wherein the relative working depth between the submersible hole (3) and the auxiliary vessel (7) is adjusted until the auxiliary vessel (7) is in contact with the hole (3) and is supported or suspended via support points and / or suspension points (13, 13') on / from a support point (14), and the auxiliary vessel (7) and the hole (3) are integrally connected. The integral connection enables both maintenance personnel and the system itself to safely and efficiently perform maintenance, installation and / or repair work on the offshore structure (1).

Description

Technical Field

[0001] The present invention mainly relates to a method for the maintenance of marine structures, preferably for the maintenance of floating offshore wind turbine towers. Therefore, the main application field of the present invention is the civil construction industry combined with the renewable or green energy industry, more specifically, the offshore wind energy industry.

Background Art

[0002] In the field of offshore wind energy, maintenance work of wind turbines, generally called "major repairs", is economically very important and significant, and a crane is required to lift heavy components of wind turbines located at a height of about 100 meters or more up and down.

[0003] Currently, "major repair" work of offshore wind turbines with a foundation fixed to the seabed is almost always carried out by a jack-up ship, which is a ship equipped with legs that can be supported on the seabed and lift the hull from underwater. Thereby, the crane incorporated in the ship itself can work without being affected by the movement of the sea. However, these ships are, on the one hand, hindered from operating the crane due to the inevitable movement of floating wind turbines, and on the other hand, they cannot work on floating wind turbines for two reasons: the water depth at the location where floating wind turbines are used is deep and the legs of the jack-up ship cannot reach the seabed.

[0004] A possible solution to this problem is to use a system that can be actively coupled to the shaft of the wind turbine tower to be maintained, primarily by an active locking mechanism based on clamping means (see, for example, Patent Document 1, which describes this type of system in detail). Thus, when coupled by its active lock, the auxiliary maintenance system moves integrally with the wind turbine, preventing relative movement between the vessel supporting the maintenance crane and the offshore structure supporting the wind turbine. This allows the crane's operation to be used for maintenance work. However, this type of solution is only applicable to floating structures that have coupling shaft-type elements, and floating solutions exist that do not have shaft-type elements suitable for coupling. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Spanish Patent Application No. 2796978

[0006] Therefore, in the current technological field, there is a need to develop alternative maintenance methods that are particularly suitable for floating offshore structures.

[0007] This invention aims to address the above need through a novel method specifically invented for the maintenance of floating offshore wind turbine towers, which does not require active clamping means for clamping the tower shaft. [Overview of the project] [Problems that the invention aims to solve]

[0008] To overcome the limitations of the above-mentioned level of technology, an object of the present invention is to provide a method for the maintenance of floating offshore structures such as wind turbine towers. The method includes different work steps of an auxiliary vessel, which may be self-ballasted, and the system enables optimization of the above-mentioned maintenance work with respect to known systems.

[0009] More specifically, the first object of the present invention relates to a method for maintaining and / or installing an offshore structure, wherein the offshore structure is floating and includes a hole that is completely or partially submerged, and the method is One or more floating elements, A work platform located on at least one of the aforementioned floating elements, Maintenance and / or installation means for the aforementioned offshore structure, Support points on the offshore structure and hanging points from the offshore structure At least three points selected from (points), This includes operations involving auxiliary vessels.

[0010] Advantageously, the method of the present invention specifically, a) A step of selecting at least three support points on a hole in the offshore structure, b) The step of moving the auxiliary vessel while it is floating to the location where the offshore structure is located, c) The step of positioning at least a portion of the auxiliary vessel within a substantially vertical projection of at least a portion of the support points of the hole, d) Reducing the relative vertical distance between the hall and the auxiliary vessel until at least a portion of the support points is supported by at least a portion of the support points and / or at least a portion of the suspension points is suspended from at least a portion of the support points; e) The step of increasing the contact force and / or suspension force exerted by the auxiliary vessel on the support point until the downward vertical load applied by the auxiliary vessel to the hall reaches a value of more than 10 tons on average over a 10-minute period, and the auxiliary vessel and the hall are connected and can move together as a single unit in all degrees of freedom, f) A step of performing work on the offshore structure using the maintenance and / or installation means, g) The step of increasing the relative vertical distance between the submersible hall and the auxiliary vessel until the auxiliary vessel stops transmitting the load at the support point and the auxiliary vessel and the hall stop moving together as a single unit, h) The step of moving the auxiliary vessel away from the location where the offshore structure is located while it is floating, This includes performing the following actions.

[0011] Within the scope of the present invention, support points on an offshore structure and suspension points from an offshore structure are considered equivalent with respect to the object of the invention, in the sense that both represent contact points suitable for load transfer between the auxiliary vessel and the offshore structure, and as a result, both structures can be connected to increase the contact force exerted by the auxiliary vessel on the aforementioned points. However, in certain embodiments, it may be more appropriate to use some, others, or a combination of both, for example, in relation to the form or circumstances of the offshore structure.

[0012] In a preferred embodiment of the method of the present invention, the maximum horizontal distance between the support points and / or suspension points is greater than 3 meters. Similarly, the maximum horizontal distance between the support points is greater than 3 meters.

[0013] In another preferred embodiment of the present invention, the hole includes one or more ballast tanks, and step d) includes removing ballast from the ballast tanks to reduce the draft of the hole, and / or step e) includes removing ballast from the ballast tanks to increase the vertical force exerted on the hole by the auxiliary vessel, and / or step g) includes introducing ballast into the ballast tanks to increase the draft of the hole.

[0014] In another preferred embodiment of the present invention, the momentum generated by the weight of the ballast transferred to or removed from the ballast tank of the hall between steps d) and e) is substantially equal to the momentum generated by the vertical load applied by the auxiliary vessel to the hall in step e). This makes it possible to prevent or reduce the lateral tilt that the weight of the auxiliary vessel would cause to the offshore structure when it is coupled to the hall. This reduces the tilt that the supporting weight of the auxiliary vessel could impose on the offshore structure.

[0015] In another preferred embodiment of the present invention, the auxiliary vessel includes one or more ballast tanks, and step d) includes introducing ballast into the ballast tanks to increase the draft of the auxiliary vessel, and / or step g) includes removing ballast from the ballast tanks to decrease the draft of the auxiliary vessel.

[0016] In another preferred embodiment of the present invention, the auxiliary vessel includes a single floating element in the form of a barge, on which both maintenance, installation and / or repair means for offshore structures and work areas are located, the barge consisting of a single body or a set of multiple modules connected to one another.

[0017] In another preferred embodiment of the present invention, at least a portion of the suspension points of the auxiliary vessel includes a lifting means, and step d) includes activating the lifting means to reduce the draft of the auxiliary vessel, and / or step g) includes activating the lifting means to increase the draft of the auxiliary vessel.

[0018] In another preferred embodiment of the present invention, step d) includes operating the lifting means to completely remove at least a portion of the floating elements of the auxiliary vessel from the water, and / or step g) includes operating the lifting means to submerge at least a portion of the floating elements of the auxiliary vessel into the water.

[0019] In another preferred embodiment of the present invention, the floating element of the auxiliary ship forms a semi-submersible hall including three or more vertically interconnected columns that enter the waterline such that the upper part of the column remains afloat and the lower part of the column remains submerged.

[0020] In another preferred embodiment of the present invention, the step b) and / or h) includes transporting one or more components of the marine structure on the working platform of the auxiliary ship, and the floating element of the auxiliary ship provides sufficient stability while floating to withstand the weight of the components disposed on the working platform.

[0021] In another preferred embodiment of the present invention, the maintenance and / or installation means includes a crane that is at least temporarily supported on the auxiliary ship. A part of the components of the crane can be temporarily installed on the marine structure to perform installation and / or maintenance work. Similarly, the crane can be a telescopic and / or folding crane that is deployed during step f) and folded before step g) in addition to a fixed or mobile crawler-type or wheel-type land crane. Thereby, the surface of the crane exposed to wind and other adverse conditions is much less than in the case where the crane is deployed or the crane is not telescopic, so the stability of the auxiliary ship during the approach and departure stages is enhanced. Further, the maintenance means can include a mobile land crane including only an upper body having at least one jib, a counterweight, and an operating device of the crane. Thereby, the total weight to be transported is reduced, so costs are saved.

[0022] In another preferred embodiment of the present invention, the hole of the marine structure and the ballast tank of the auxiliary ship include one or more adjustable openings and / or remotely operated hatches and / or one or more pumps for removing or introducing water. The ballast tank can be operated asymmetrically to balance the weight of the auxiliary ship transmitted onto the marine structure during steps e) and f), so that the marine structure is maintained substantially vertically, providing greater stability to the entire assembly against waves or wind.

[0023] In another preferred embodiment of the present invention, at least one of the said support points and / or support points includes fixing means for forming a mechanical fixation between the support point and the support point. The method includes, after step d) and before step f), e1) engaging the fixing means to form a mechanical fixation between the support points such that both the support points and the support points cannot be separated, and includes Before step g), the method further includes e2) releasing the engagement of the fixing means so that the support point and the support point can be separated.

[0024] In another preferred embodiment of the present invention, at least one support point of the hole has a vertical axis frustoconical convex male geometry, and the support point of the auxiliary ship supported on the support point has a concave female geometry or vice versa. During step d), the frustoconical mating shape of the support point and the support point enables guiding the planar position of the auxiliary ship relative to the hole. During step e) and / or f), the mating shape of the contact between the support point and the support point enables the transmission of horizontal forces between the auxiliary ship and the hole by direct contact.

[0025] In another preferred embodiment of the present invention, steps b) and / or h) are carried out by towing by an auxiliary vessel or by the vessel's own propulsion.

[0026] In another preferred embodiment of the present invention, the auxiliary vessel includes one or more buffers or fenders, which are positioned between the auxiliary vessel and the hole in the offshore structure during one or more of steps c) to g). The buffers or fenders prevent the structure involved in the method from being damaged by any possible collision or friction.

[0027] In another preferred embodiment of the present invention, the auxiliary vessel includes at least one winch, and step c) is c1) A substep of connecting at least one cable of the winch to the offshore structure, c2) A substep in which the cable is wound up using the winch so that the auxiliary vessel gradually approaches the hall, Includes.

[0028] In another preferred embodiment of the present invention, step c) is: c3) A substep of bringing the auxiliary vessel closer to the hole until at least a portion of the buffering means or fender contacts the hole, c4) A substep of using the winch to wind up the cable in order to increase the compression applied to at least a portion of the buffer or fender located between the hole and the auxiliary vessel, Includes.

[0029] In another preferred embodiment of the present invention, during step c2), a second vessel is used to pull the auxiliary vessel in the opposite direction to the direction in which the auxiliary vessel approaches the hole, thereby maintaining at least a portion of the winch cable taut for at least part of the approach process. The second vessel is preferably a tugboat, but other types of vessels capable of exerting towing force on the auxiliary vessel may also be used.

[0030] In another preferred embodiment of the present invention, at least one support point of the auxiliary vessel includes a pneumatic fender, and step d) is d1) A substep for inflating the aforementioned pneumatic fender, d2) A substep of bringing the support point perpendicular to the support point of the hole until the pneumatic fender contacts the support point of the hole, d3) A substep of compressing and / or contracting the pneumatic fender so that as the dimensions of the pneumatic fender decrease, the support point continues to approach the support point in a controlled manner, Includes.

[0031] The use of pneumatic fenders in this embodiment of the present invention is preferred because it allows for a high level of compressibility, but other types of non-pneumatic fenders that are sufficiently flexible and / or compressible may also be used. In that case, steps d2) and d3) are maintained, while step d1) may be omitted.

[0032] Within the scope of the present invention, the term "floating marine structure" should be interpreted as any structure that can be installed or deployed in a marine environment and that can float on its own, supported by self-stabilization or auxiliary connection means such as mooring cables, to either the seabed or other structures.

[0033] Similarly, the term "submerged" applied to an element should be interpreted as meaning that the entire volume of the element remains below the waterline, and furthermore, the term "partially submerged" should be interpreted as meaning that a portion of the volume of the element remains below the waterline.

[0034] Furthermore, within the scope of the present invention, the terms “support point,” “suspension point,” and “support area” should be interpreted as meaning a support, suspension, or support area, respectively, and therefore they may include support, suspension, or support points as well as support, suspension, or support surfaces or support volumes.

[0035] Finally, within the scope of the present invention, the term “substantially” should be interpreted as meaning identical or included within a range of variation of 30%, more preferably 15%. [Brief explanation of the drawing]

[0036] The above and other features and advantages will be better understood based on preferred embodiments with reference to the detailed description of the present invention and the accompanying drawings. [Figure 1] Figure 1 schematically corresponds to the first step of the method of the present invention, in which an auxiliary vessel equipped with a foldable crane approaches an offshore structure. [Figure 2] Figure 2 schematically corresponds to the second step of the present invention, in which the relative vertical distance between the hull of the offshore structure and the auxiliary vessel is reduced. [Figure 3] Figure 3 schematically corresponds to a third step of the method of the present invention, in which an auxiliary vessel is entirely supported in or suspended in a hole of an offshore structure, and related maintenance work can be performed by a deployed crane. [Figure 4] Figure 4 shows a top view of the auxiliary vessel together with the offshore structure according to the embodiment shown in Figures 1 to 3, after the auxiliary vessel has been fully supported by the offshore structure for maintenance work on the offshore structure. [Figure 5] Figure 5 shows an illustration of an auxiliary vessel along with an offshore structure according to an embodiment of the present invention, after the auxiliary vessel has been fully supported / suspended from the offshore structure in order to perform maintenance work on the offshore structure. [Figure 6] Figure 6 shows an illustration of an auxiliary vessel along with an offshore structure according to an embodiment of the present invention, after the auxiliary vessel has been fully supported / suspended from the offshore structure in order to perform maintenance work on the offshore structure. [Figure 7] Figure 7 shows a top view of the auxiliary vessel together with the offshore structure according to the embodiment shown in Figures 1 to 3, after the auxiliary vessel has been fully supported by the offshore structure for maintenance work on the offshore structure. [Figure 8]Figure 8 shows one of the intermediate steps of the method of the present invention, more specifically, an embodiment of a maintenance task on the offshore structure by operating a crane mounted on the offshore structure after the auxiliary vessel has been fully supported on the offshore structure. [Modes for carrying out the invention]

[0037] List of reference symbols in the drawing (1) Marine structures (2) Wind turbine (3) Holes in marine structures (4) Tower or shaft (5) Water line (6) Ballast tanks in the holes of offshore structures (7) Auxiliary vessel (8) Buoys of auxiliary vessels (9) Ballast tanks of auxiliary vessels (10) Work platform of auxiliary vessel (11) Means for the maintenance and / or installation of offshore structures (11') Cranes for the maintenance and / or installation of offshore structures (12) Buffers or fenders of auxiliary vessels (12') Air fender at bearing point (13) Support points of auxiliary vessels (13') Lifting point of auxiliary vessel (14) Support points of the hull of offshore structures (15) means for securing an auxiliary vessel to an offshore structure (16) Winding means (17) Winch

[0038] A detailed description of the present invention is given below with reference to Figures 1 to 8 of this application. The foregoing description is provided for illustrative purposes only, and not limiting purposes.

[0039] Figures 1 to 4 show different elevation views (Figures 1 to 3) and plan views (Figure 4) of an offshore structure (1), preferably corresponding to an offshore tower-type wind turbine structure (2), the structure (2) further includes a hole (3) whose internal shape and volume are adapted to give buoyancy to the assembly of the offshore structure (1). In a preferred embodiment of the present invention, the hole (3) is located at the bottom of the offshore structure (1), and in other embodiments, it may be located at other locations (e.g., forming an intermediate region or integral part thereof of the tower (4) of the wind turbine (2), so that when the offshore structure (1) is floating, it is in operation, and the hole (3) is submerged in water (i.e., its entire volume is below the waterline (5)) or partially submerged. Similarly, a hole (3) in a marine structure (1) includes one or more ballast tanks (6) adapted to contain a corresponding ballast material (e.g., water) therein, thereby allowing adjustment of the working depth (draft) of the hole (3) and therefore of the assembly of the marine structure (1). Techniques for adjusting ballast in the ballast tanks (6) of a ship and, in general, techniques for adjusting ballast in a marine structure (1) are known in the art and may be based on hydraulic pumps, valves, pipes and any piping, housings and drive means for the ballast material used to empty and fill the tanks (6).

[0040] Figures 1 to 3 show a specific type of offshore structure (1) that further includes, for example, stabilizing elements suspended from a hole (3) of the offshore structure (1) by a cable. The stabilizing elements contribute to lowering the center of gravity of the offshore structure (1) and increasing its stability, but the method of the present invention is, of course, applicable to any other type of offshore structure (1).

[0041] In other alternative embodiments of the present invention (not shown), the hole (3) of the offshore structure (1) can be moored to the seabed, for example, by one or more mooring lines of fixed or adjustable length via corresponding adjustment means. In embodiments in which the length of the mooring lines is adjustable, the operating depth (draft) of the offshore structure (1) can also be changed. Thus, in the alternative embodiments, the use of the corresponding filling / discharging tank (6) is optional, but the hole (3) of the offshore structure (1) may or may not be affected by ballast.

[0042] The offshore structures (1) and holes (3) are preferably made of concrete and / or steel, at least partially, but other materials may also be used within the scope of the present invention.

[0043] In addition, to carry out the method of the present invention, it is necessary to use an auxiliary vessel (7) intended to transport workers and / or equipment necessary for installing or maintaining the offshore structure (1). In this embodiment, the auxiliary vessel (7) includes a barge-type floating body (8), but in other embodiments, it may include several floating bodies (8), such as a catamaran, trimaran, or semi-submersible vessel (7). In an alternative embodiment of the present invention, one or more of the floating bodies (8) of the vessel (7) are of a ballast-sensitive type (e.g., one or more corresponding intake / exhaust ballast tanks (9)) and may be equipped with ballast adjustment means that allows the buoyancy level of the vessel (7) to be controlled by adjusting the amount of water inside the ballast tanks (9) of the auxiliary vessel.

[0044] The ballast adjustment means of the auxiliary vessel (7) include adjustable open hatches and / or remotely operated hatches, and / or pumps for removing or introducing water or other components known in the art and commonly used in ballast adjustment or transfer systems of various types of vessels. Furthermore, in order to offset the vertical loads transmitted to the hall (3) by the auxiliary vessel (7), the ballast tank (6) of the hall (3) of the offshore structure (1) preferably includes a mechanism for transferring water to the tank on the opposite side of the hall (3) from the bearing of the auxiliary vessel (7).

[0045] The floating elements (8) can be manufactured using a variety of materials known in the art. The configuration of the floating elements (8) can also be adjusted to allow for adjustment of their overall size. The parts or modules that can be used to form the floating elements (8) can take on a variety of shapes, and their dimensions are preferably such that they can be housed in a container (the same as or smaller than the dimensions of a standard container) to facilitate transport and reuse. The modules can be mounted together to form the floating elements (8) in both planar position and height.

[0046] To perform installation or maintenance work on an offshore structure (1), the auxiliary vessel preferably includes at least one work platform (10) intended to support both the work team and the corresponding equipment, and offshore structure maintenance and / or installation means (11) which may include a fixed or deployable crane (11') (e.g., telescopic type) with adjustable height for performing maintenance or installation work on the wind turbine (2) of the offshore structure (1). The work platform (10) is preferably used for storage and / or repair of parts of the offshore structure (1) (e.g., turbine components or blades of the wind turbine (2)). In different embodiments of the present invention, the work platform (10) may be an area at a higher elevation than the floating elements (8) and / or an exempt area. Similarly, the offshore structure maintenance and / or installation means (11) may be located both on the work platform and on one or more floating elements (8), or even temporarily installed on the offshore structure (1), depending on the steps of the method being performed.

[0047] In another preferred embodiment of the present invention, the crane (11') is a mobile land crane (11') comprising an upper body formed by at least one jib, a counterweight and an operating device for the crane (11'), and an upper body including means for displacing the crane (11') by wheels and / or tracks. In a more preferred embodiment of the present invention, the auxiliary vessel (7) comprises only the upper body of the crane (11') (therefore reducing the weight). Furthermore, the lower body can be omitted because it is not necessary to move the crane 11' during maintenance procedures. In this embodiment, the auxiliary vessel 7 must include means for securing the upper body of the crane 11'.

[0048] According to the configuration described above, the auxiliary vessel (7) can be towed or displaced by its own means (self-propelled) to the offshore structure (1) where installation or maintenance work is to be performed. Similarly, for the purpose of facilitating connection to the aforementioned offshore structure (1), the vessel (7) may be equipped with a buffer (12) or impact fender configured to be installed between the vessel (7) and the offshore structure (1) during the approach or launch phase close to the connection between the vessel (7) and the offshore structure (1), thereby preventing the corresponding collisions and damages that may occur. The buffer (12) or fender may include, for example, pneumatic fenders and / or elastic elements made of a plastic material with considerable flexibility and therefore capable of absorbing or dissipating impact energy from collisions between the vessel (7) and the offshore structure (1).

[0049] Figures 5-6 refer to another preferred embodiment of the present invention in which the offshore structure (1) is a semi-submersible float comprising three round columns, and the auxiliary vessel (7) comprises a semi-submersible hull comprising four rectangular columns. The auxiliary vessel (7) includes two support points 13 and two suspension points 13'. However, in other embodiments of the present invention, various configurations can be adopted based on combinations of support points (13) and suspension points (13'). Thus, in embodiments of the present invention, the auxiliary vessel (7) may include three support points (13), in another embodiment it may include three suspension points (13'), and in yet another embodiment it may include two support points (13) and one suspension point (13'). Similarly, this embodiment of the present invention involves preparing at least three support points (14) within the hole (3) of the offshore structure (1), which can be done as part of each maintenance / installation operation for the offshore structure (1) or as a whole or in part during the manufacturing process of the hole (3).

[0050] The support points (13) / suspension points (13') are configured to be supported / suspended at the support points (14) so ​​that the auxiliary vessel (7) is mechanically connected to the holes (3) of the offshore structure (1) and, after connection, both structures can move as a whole. Furthermore, in a preferred embodiment of the present invention, the support points (13) and / or suspension points (13') are horizontally separated from each other at a distance of at least 3 meters, as are the support points (14), to ensure sufficient stability to maintain the connection between the two bodies during maintenance and / or installation work, given the normal dimensions of the offshore structure (1) involved in this type of method. Furthermore, the support points (13) and support points (14) include complementary shapes or geometric shapes to ensure a better connection between them and / or of fastening means (15), such as braces, screws, pins, anchoring, magnets, suction cups, or other means known in the art to form mechanical fastening between them, thus providing greater stability and safety. The described suspension point (13') may further include a lifting means (16) capable of acting to increase or decrease the tension therein so that the auxiliary vessel (7) can decrease or increase the vertical distance of the offshore structure (1) to the hole (3). The lifting means may include a winch, pulley, rack, rack and pinion system or any other system known in the art.

[0051] In addition to the preferred embodiments shown in Figures 5 and 6, in another preferred embodiment shown in Figure 7, the floating elements (8) of the auxiliary vessel (7) form a semi-submersible hole comprising three or more interconnected vertical columns passing through the waterline (5), with the upper parts of the columns remaining floating and the lower parts of the columns remaining submerged. This configuration provides greater stability to the auxiliary vessel (7) while simultaneously allowing for the restriction of the floating area and its movement, and facilitating the approach process for draft adjustment and connection with the offshore structure (1).

[0052] Figures 1 to 3 also show different steps of the installation and / or maintenance method of the present invention according to a preferred embodiment.

[0053] As shown in Figure 1, the auxiliary vessel (7) is heading towards the vicinity of the offshore structure (1) (specifically, an offshore wind turbine (2) equipped with a tower (4)) (by means of a tugboat, self-propulsion, etc., as described above).

[0054] Then, as schematically shown in Figure 2, the approach to the offshore structure (1) is terminated when, for example, the buffering means (12) of the auxiliary vessel (7) makes contact with the structure (1) or when the auxiliary vessel (7) is positioned close enough to the structure (1) to safely perform maintenance or installation work. In a preferred embodiment of the present invention, the approach is made by using a winch (17) included in the auxiliary vessel (7) to reduce the horizontal distance between both elements by winding up one or more cables of the winch (17) once it has been connected to the offshore structure (1). Figure 5 shows the winch (17) after the auxiliary vessel (7) has already been connected to the offshore structure (1). The winch may also be used to apply and / or maintain pressure on the fender (12) after the initial contact in order to reduce or limit the relative movement between the auxiliary vessel (7) and the offshore structure (1) during the approach process until the fender (12) of the auxiliary vessel (7) makes contact with the hole (3) of the offshore structure (1) and during steps d) and / or e).

[0055] In another preferred embodiment of the present invention, a pneumatic fender (12') provided on the support point (13) of the auxiliary vessel (7) is further used at the end of the approach, and when the pneumatic fender (12') makes contact with the support point (14), the offshore structure (1) is compressed or contracted in a controlled manner, gradually approaching the surfaces of the support point (13) of the auxiliary vessel (7) and the support point (14) of the offshore structure (1). Alternatively, other highly compressible fenders known in the art may be used instead of the pneumatic fender.

[0056] Once the approach is complete, the lower horizontal plane of the floating element (8) of the auxiliary vessel (7) is substantially contained within the vertical projection of the upper horizontal plane of the hole (3). More specifically, at least one of the support points (14) or suspension points (14') of the auxiliary vessel (7) is substantially contained within the vertical projection of at least one support point (14) of the hole. Thus, and as will be described later, once the buoyancy level of the hole (3) is sufficiently raised, at least a portion of the support (suspension) points (14, 14') will come into contact with (be suspended from) at least a portion of the support point (14). For this purpose, once the approach is complete, the buoyancy level of the hole (3) of the offshore structure (1) is adjusted to increase its working depth. Optionally, in embodiments where the auxiliary vessel (7) is also of a type that is susceptible to ballast, its ballast can also be adjusted simultaneously to reduce its working depth. In addition, in corresponding embodiments, it is also possible to adjust the draft of the auxiliary vessel (7) by acting on the lifting means (16) provided at the suspension point (13').

[0057] In all of the embodiments described above, the relative vertical distance between the hole (3) of the offshore structure (1) and the auxiliary vessel (7) is reduced by either support (support point (13) / support point (14)) or suspension (suspension point (13') / support point (14)) until force transmission occurs between the two elements. In particular, there is a transmission of vertical force such that a portion of the weight of the auxiliary vessel (7) is supported on the offshore structure (1). Thus, once support or suspension occurs, the force exerted by the auxiliary vessel (7) on the hole (3) of the offshore structure (1) increases until the latter reaches a value of 10 tons or more on average over a 10-minute period, thereby achieving an integral or nearly integral connection between the auxiliary vessel (7) and the offshore structure (1) (Figure 3). In this case, a nearly integral or integral connection is understood to mean that there is no or substantially no relative movement between the offshore structure (1) and the auxiliary vessel (7).

[0058] The integral attachment between the auxiliary vessel (7) and the offshore structure (1) allows for the elimination or sufficient limitation of relative movement between the two, enabling maintenance and / or installation means (11) of the structure (1), such as a crane (11') or its components (e.g., a wind turbine (2)), to operate safely and stably. In this context, it should be understood that certain aspects, such as the elastic deformation of materials, may result in small relative movements without falling outside the scope of the present invention.

[0059] After repair or maintenance work has been performed, one or more reverse steps are taken with respect to the above, first increasing the relative distance between the hole (3) and the auxiliary vessel (7) by ballasting the hole (3) of the offshore structure (1), and simultaneously, optionally, removing the ballast from the auxiliary vessel (7) (if including a tank (9) or ballast means) or acting on the lifting means (16) provided at the suspension point (13') to separate them again and release their integral connection. Thus, the auxiliary vessel (7) is no longer supported (not suspended) by the hole (3) of the offshore structure (1) and is floating again, so it can be towed or driven to land or to another offshore structure (1) that requires maintenance, thereby completing the method of the present invention. The reverse process corresponds to examining Figures 1 to 3 in reverse order by changing the direction of the arrows in Figure 2.

[0060] Figure 7 is a plan view and elevation view showing the configuration after an auxiliary vessel (7) has been integrally connected to an offshore structure (1) for maintenance work, according to an embodiment of the present invention. In this case, the offshore structure (1) has a wind turbine tower (4) supported by a tripod-shaped transition section supported by a hole (3) having an annular structure. There are four support points (13) supported by four corresponding support points (14) in the hole (3). The support points (14) are appropriately located in the reinforced area or larger capacity area within the hole (3) and adequately withstand the loads that occur both during the approach and connection process (steps d and e)) and during the connected state (step f). Since the support points (14) have a frustoconical shape, when the auxiliary vessel (7) is supported in the hole (3), the support points (13) can transmit not only vertical loads but also horizontal loads. Similarly, the auxiliary vessel (7) includes fenders (13') in the area of ​​the support points (14) to limit the impact forces that may occur between the approach of the two floating bodies. The fenders are preferably pneumatic and are inflated before the approach operation (step d). Once they make contact with the hole (3), they can be deflated to facilitate a more rigid contact between the support point (13) and the support point (14). Other types of foldable, non-pneumatic fenders known in the art can also be used in an equivalent manner.

[0061] Figure 8 shows the process of performing the task in an embodiment of the present invention, in which a crane (11') is placed on a marine structure (1) to perform its work, although some of the equipment for the crane's work can be left on the work platform (10).

Claims

1. A method for the maintenance and / or installation of an offshore structure, wherein the offshore structure is floating and includes a hole that is completely or partially submerged, and the method is One or more floating elements, A work platform located on at least one of the aforementioned floating elements, Maintenance and / or installation means for the floating offshore structure, At least three points selected from the support points on the offshore structure and the suspension points from the offshore structure, Including the work of auxiliary vessels, This method is a) The step of selecting support points at least three points on the hole, b) The step of moving the auxiliary vessel while it is floating to the location where the offshore structure is located, c) The step of positioning at least a portion of the auxiliary vessel within a substantially vertical projection of at least a portion of the support points of the hole, d) Reducing the relative vertical distance between the hall and the auxiliary vessel until at least a portion of the support points is supported by at least a portion of the support points and / or at least a portion of the suspension points is suspended from at least a portion of the support points; e) The step of increasing the contact force and / or suspension force exerted by the auxiliary vessel on the support point until the downward vertical load applied by the auxiliary vessel to the hall reaches a value of more than 10 tons on average over a 10-minute period, and the auxiliary vessel and the hall are connected and can move together as a single unit in all degrees of freedom, f) A step of performing work on the offshore structure using the maintenance and / or installation means, g) The step of increasing the relative vertical distance between the submersible hole and the auxiliary vessel until the auxiliary vessel stops transmitting the load at the support point and the auxiliary vessel and the hole stop moving together as a single unit, h) The step of moving the auxiliary vessel away from the location where the offshore structure is located while it is floating, A method that includes this.

2. The method according to claim 1, wherein the maximum horizontal distance between the support points and / or suspension points is greater than 3 meters, and the maximum horizontal distance between the support points is greater than 3 meters.

3. The aforementioned hole includes one or more ballast tanks, Step d) includes removing ballast from the ballast tank to reduce the draft of the hole, and / or Step e) includes removing ballast from the ballast tank to increase the vertical force exerted by the auxiliary vessel on the hole, and / or Step g) includes introducing ballast into the ballast tank to increase the draft of the hole. The method according to claim 1 or 2.

4. The method according to any one of claims 1 to 3, wherein the momentum generated by the weight of the ballast transferred to or removed from the ballast tank of the hall between step d) and step e) is substantially equal to the momentum generated by the vertical load applied by the auxiliary vessel to the hall in step e).

5. The auxiliary vessel includes one or more ballast tanks, Step d) includes introducing ballast into the ballast tank to increase the draft of the auxiliary vessel, and / or The method according to any one of claims 1 to 4, wherein step g) includes removing ballast from the ballast tank to reduce the draft of the auxiliary vessel.

6. At least a portion of the suspension points of the auxiliary vessel includes lifting means, Step d) includes activating the lifting means to reduce the draft of the auxiliary vessel, and / or The method according to any one of claims 1 to 5, wherein step g) includes activating the lifting means to increase the draft of the auxiliary vessel.

7. Step d) includes activating the lifting means to completely remove at least a portion of the floating elements of the auxiliary vessel from the water, and / or The method according to any one of claims 1 to 6, wherein step g) includes activating the lifting means to submerge at least a portion of the floating elements of the auxiliary vessel in water.

8. The method according to any one of claims 1 to 7, wherein the maintenance and / or installation means includes a crane that is at least temporarily supported on the auxiliary vessel.

9. At least one of the support points and / or support points includes a fixing means, and the method is performed after step d) and before step f), e1) A step of engaging the fixing means to form a mechanical fixation between the support point and the support point so that both the support point and the support point cannot be separated, Includes, The above method, before step g), e2) The method according to any one of claims 1 to 8, further comprising the step of disengaging the fixing means so that the support point and the support point can be separated.

10. At least one support point of the hole has a convex male shape in the shape of a frustoconical vertical axis, and the support point of the auxiliary vessel supported on the support point has a concave female shape, or vice versa. During step d), the truncated cone-shaped alignment of the support point and the support point allows the planar position of the auxiliary vessel relative to the hole to be guided. The method according to any one of claims 1 to 9, wherein, during step e) and / or f), the matching shape of the contact between the support point and the support point allows for the transmission of horizontal force between the auxiliary vessel and the hall by direct contact.

11. The method according to any one of claims 1 to 10, wherein the auxiliary vessel includes one or more buffers or fenders, and the buffers or fenders are positioned between the auxiliary vessel and the hole of the offshore structure during one or more of steps c) to g).

12. The auxiliary vessel includes at least one winch, and step c) is, c1) A substep of connecting at least one cable of the winch to the offshore structure, c2) A substep in which the cable is wound up using the winch so that the auxiliary vessel gradually approaches the hole, The method according to any one of claims 1 to 11, including the method described in any one of claims 1 to 11.

13. Step c) above is, c3) A substep of bringing the auxiliary vessel closer to the hole until at least a portion of the buffering means or fender contacts the hole, c4) A substep of using the winch to wind up the cable in order to increase the compression applied to at least a portion of the buffer or fender located between the hole and the auxiliary vessel, The method according to claim 11 or 12, including the method described in claim 11 or 12.

14. The method according to any one of claims 1 to 13, wherein during step c2), a second vessel is used to pull the auxiliary vessel in the opposite direction to the direction in which the auxiliary vessel approaches the hole, thereby maintaining at least a portion of the winch cable taut for at least a portion of the approach process.

15. At least one support point of the auxiliary vessel includes a pneumatic fender, and step d) is d1) A substep for inflating the pneumatic fender, d2) A substep of bringing the support point perpendicular to the support point of the hole until the pneumatic fender contacts the support point of the hole, d3) A substep of compressing and / or contracting the pneumatic fender so that as the dimensions of the pneumatic fender decrease, the support point continues to approach the support point in a controlled manner, The method according to any one of claims 1 to 14, including the method described in any one of claims 1 to 14.

Images