Structure and implementation method for supporting offshore facilities

Abstract

The invention relates to a structure (2) for supporting a wind turbine tower (1), the structure being provided with a housing (7) for accommodating the base of the tower (1), a main axis (Γ) defined on a platform (2) coinciding with the main axis of the tower (1), and comprising a body of constant cross section and an inner wall (8) and an intermediate wall (10) connected by inner radial ribs (11) perpendicular to the inner wall (8) and whose plane passes through the main axis (Γ), so that at the intermediate wall (10), a first connection node (12) is defined between the intermediate wall (10) and the radial ribs (11), the intermediate wall (10) and the outer wall (9) being connected by ribs (14 and 15). The structure provides an optimal force transmission. The invention also relates to methods for manufacturing, assembling and installing the structure.

Description

Technical Field

[0001] The present invention belongs to the field of offshore structures, to the construction and implementation of buildings and facilities in offshore environments. More specifically, it relates to a floating structure and a method for constructing, assembling, commissioning and disassembling a marine structure. Background Art

[0002] In this document, reference will be made to the method for marine concrete structures of the type described above, without any limitation of the scope of the invention in terms of base size, tower size (or absence of tower) and shape (triangular, rectangular, hexagonal, polygonal, circular or leaf-shaped). Furthermore, it is applicable to semi-submersible, spar and TLP floating platforms, and it is even applicable to platforms whose final position is on the seabed despite being mobile by floating.

[0003] The object of the present invention is a high performance floating platform and the description of an innovative and efficient system of construction, assembly and commissioning which entails considerable cost savings, a much shorter implementation time compared to existing platforms and maximum safety.

[0004] With regard to the terminology used in this document, emphasis is placed on the equivalence of the following terms: platform, structure and base; and on the equivalence of the following terms: wall, surface, enclosure, rib.

[0005] Marine structures embedded in the offshore environment have experienced significant growth in recent years, especially due to the huge boom in offshore wind energy that began to spread from Northern Europe throughout the world.

[0006] The culmination of this growth process will occur when the cost of offshore wind energy falls below the cost of generating it by other means, and that goal is within reach.

[0007] Basically, all large wind turbine manufacturers are developing high-power models (10, 12, even 15 MW), which require a significant increase in their size and in the actions they perform on the marine structures that support them.

[0008] However, this increase in power is precisely the key point for a reduction in energy costs, as it makes the impact of base and facility costs per installed MW much lower.

[0009] There is therefore currently an important technical challenge to develop said platforms while following an industrialization process that allows their dense construction in very different locations, preferably using local means, and reducing the logistic costs associated with their commissioning within the required time.

[0010] This means overcoming the various problems that arise with the large number of new wind turbines to be supported, such as:

[0011] 1. A reproducible construction system is needed that is able to build large platforms occupying an area of ​​approximately 50 meters in diameter and which must eventually float by some auxiliary means. Currently, there are essentially no means already built that allow this task to be carried out, since all these facilities are prepared for the manufacture of vessels with a length significantly greater than their maximum width (beam), which almost never exceeds 40m. In addition, they are scarce and expensive means, which will create a major bottleneck when wind farms need to be produced in large quantities.

[0012] 2. In the face of new large stresses, the constructed structure is required to have high structural strength, fatigue strength and impact resistance with low maintenance and excellent durability. Therefore, the construction system must provide the structure with a high degree of compactness and integrity, which can hardly be ensured by using prefabricated systems, and the joints of prefabricated systems are potential sources of possible failures.

[0013] 3. The marine structure must provide an adequate and effective response to the new major actions to which it will be subjected, yet be easily disassembled.

[0014] The structure must generate a large restoring moment which minimizes the static tilt angle during the service phase, but with low accelerations in the turbine. This also requires an inherently heavy structure which does not require additional solid ballast and thus allows it to be transferred back to port when necessary.

[0015] The most suitable way to achieve such a large weight at low cost is by using reinforced concrete following the port caisson construction technology that has been widely developed and used in Spain with excellent cost and efficiency results. The greatest difficulty is that, due to its size, it cannot be carried out at any existing floating dock.

[0016] 4. The marine structure must be completely built and assembled in port and transported to its service location by tugboats. This represents a significant reduction in cost, since it does not require the expensive and scarce auxiliary means required for the offshore installation of large new wind turbines. The construction method must be able to be carried out at low draft in order to be able to be carried out in the vast majority of existing ports and thus to distribute production and bring it closer to the installation site.

[0017] The design and manufacture of floating structures for supporting wind turbines are currently based on technologies developed by the oil and gas industry. In this way, as mentioned above, three main types of platforms can be distinguished: semi-submersibles, stilts and TLPs. These three types correspond to three systems for stabilizing the structure against external actions (wind, waves and currents):

[0018] - Buoyancy stability

[0019] - Ballasted and stabilized to lower the center of gravity

[0020] - Stabilization by mooring lines

[0021] Most platforms with floating concrete bodies are essentially circular prisms with radial internal walls coming from a core coinciding with the axis of the wind turbine. Due to their large dimensions, they are usually built from prefabricated elements, mainly in dry dock. In addition to the large costs involved in building these facilities, they have two important disadvantages that the proposed solutions do not have:

[0022] - The joints between the preforms are not integral and are therefore susceptible to failure under specific conditions.

[0023] If a leak occurs, a large portion of the base will be submerged, potentially putting it at risk.

[0024] Thanks to this construction system, the proposed structure is completely monolithic and in the event of a very serious accident, thanks to the double shell ( Figure 2a and Figure 2b ), only the surrounding small cells will be flooded.

[0025] - Patent US9120542 describes an annular floating body in which a wind turbine is arranged eccentrically on one side. This solution is technically very effective, but it presents great structural difficulties in its implementation.

[0026] The annular shape causes the wind turbine located on one side thereof to significantly bend the structure on the side arm, which, if made of concrete, will crack on its upper face, deteriorating and reducing its service life. To avoid this, in addition to requiring a large amount of steel (up to 400 kg / m3), post-tensioning cables must be arranged to compress the structure in its upper part.

[0027] On the other hand, the tower is connected to the upper face of the concrete structure by bolts which require significant anchors to locally transfer the entire bending moment generated by the wind.

[0028] This all translates into high cost concrete structures with large amounts of reinforcements, long build times and fatigue issues due to stress concentrations.

[0029] On the contrary, as has been seen, the proposed solution has almost no bending forces and distributes the loads without any type of stress concentration. Figure 2a and Figure 2b It is shown how the invention evenly transfers the forces of the tower by means of a distribution of faces, first through the radial faces and then all the way through three smaller faces reaching the periphery.

[0030] The inner pool of the ring has the problem that it hardly traps the bulk of the water contained therein, nor the bulk of the water below it. On the other hand, a great advantage of the proposed invention is that it traps both, thus significantly extending all oscillation periods and reducing accelerations.

[0031] - Patent WO2009131826 describes a metal buoy consisting of three towers with heave brackets, connected by connecting arms through which the transfer of active ballast circulates to stabilize it. This is indeed the most tested solution today, with good results. However, the proposed solution has great improvements:

[0032] - The cost of the steel required to construct it is more than twice the cost of the finished concrete in the proposal.

[0033] - The fatigue of the components, especially in the tower and the connecting arms, is very high compared to the lack of fatigue in the proposed compact concrete elements.

[0034] - Energy production must be reduced when transferring ballast and, in the proposal, it is always the maximum value that can be obtained.

[0035] - The trapped water is carried out under the heave bracket, while in the proposal it is implemented over the entire surface of the base and in the central cell.

[0036] - This structure requires maintenance of submerged metal elements and equipment, which is not required in the present invention as everything is above ground level on deck.

[0037] Patents WO2014031009 and WO2014177729 are constructed, at least in some of their construction solutions, of hollow concrete bodies linked together by arms that are also hollow and through which water passes from one to the other. Given their low initial draft, these solutions, like the previous patents, can be towed with the fully installed wind turbine and have a simple mounting system since they only use water for ballast. Since the stabilizing torque is lower than the tipping torque at maximum production (more than half of the proposal), active systems must be used for transferring ballast from some bodies to others in the event of a normal loss of power production.

[0038] However, the greatest problem of both solutions concerns the construction when it is done in concrete. One and the other both require the implementation of different hollow bodies that cannot be implemented simultaneously. Solutions have been proposed for implementation by means of pieces (towers and pontoons) linked with post-tensioning complexes, creating a series of links precisely where the greatest stresses are concentrated. This results in structures requiring a lot of maintenance and subject to a lot of fatigue.

[0039] The proposed solution solves this problem in concrete, building a compact piece without protruding elements and with unprecedented strength and durability. Summary of the invention

[0040] In order to overcome the shortcomings of the prior art, the present invention proposes a structure according to any one of claims 1 to 16 and a method according to any one of claims 17 to 22.

[0041] The proposed structure is of the "semi-submersible" type, with buoyancy stability; however, it can also be used as a column type. This latter option will require solid ballast for its installation, making its unloading more complicated and not as straightforward as a semi-submersible structure that uses only water for ballast, if it is feasible at all. It can also be used as a TLP type, but not as a preferred construction solution.

[0042] To this end, the invention consists of a concrete structure whose construction is based on the port caisson technology widely used in Spain for the construction of docks and quays. These structures are gravity-based structures, manufactured on floating docks (commonly called "caisson equipment"), which are transported to their service locations by floating. They are large reinforced concrete structures, usually parallelepiped, whose inner side consists of a series of vertical faces forming a single grid, in order to reduce its weight and provide buoyancy to the assembly. Its construction is very versatile, through the sliding formwork technology, which allows a continuous and very efficient production, and floats directly when it is built.

[0043] The proposed structure is designed so that maximum performance and minimum cost are obtained when it is built in a caisson apparatus (although it is also possible to build it in a dry dock or on a fixed platform on a quay without these advantageous performances).

[0044] It has the following characteristics:

[0045] 1. Optimal structural system

[0046] a. Excellent robustness and resistance to possible accidents

[0047] One of the advantages of the method using sliding formwork arranged in the caisson equipment is the integrity achieved in the construction. In addition to being able to compact it and guarantee its connection with the previous layer in perfect conditions, the advantage of being able to place it in the formwork in small layers is also used, removing the concrete connection.

[0048] Furthermore, this type of construction allows to manufacture very rigid structures with many faces distributing the load.

[0049] Through all this, a structure is achieved that is very resistant to atmospheric conditions and impacts, although in very specific cases of water leakage it will only flood smaller cells without having virtually any effect on the stability of the assembly.

[0050] On the contrary, in concrete floating platform solutions currently designed on the market, in order to achieve performances somewhat similar to those of caisson equipment, prefabricated elements are used, the joints of which are prone to failure and in which case the water that can be introduced can seriously compromise the integrity of the structure.

[0051] b. Stress minimization

[0052] Based on extensive knowledge of how harbor caissons work, the proposed floating structure is designed to take full advantage of their properties.

[0053] Despite the enormous forces it will be subjected to and the significant moments it must compensate for transmitted by the wind turbine, the concrete of the entire structure experiences almost no bending. The main stress on the structure is compression. This is achieved through its precise geometry and construction:

[0054] - The wind tower is not connected to the platform via a plate with bolts, which concentrates all the torsion in this area, but via simple joints that convert it into compression at the upper and lower parts of the platform, so that the stress is not concentrated at one point, but distributed throughout the embedment in a manner similar to driving piles in qualified ground.

[0055] To do this, the wind turbine tower is simply inserted into the central hole left by the structure, with its full height, until it rests on the lower plate, and the gap between them is filled with grout. In this way, it works like piling in optimal terrain, so that it requires very little driving depth, while the available height of the caisson is sufficient to guarantee stability.

[0056] The walls of the central concrete column will not absorb the pressure transmitted by the tower, but will distribute it by the large radial walls and very thick upper and lower plates that reinforce it.

[0057] - The great weight provided by all the concrete used in the platform and the increased water ballast (about 36,000t), and the metacentric height between 7 and 10m, allow a great restoring torque to be achieved, enabling it to face the maximum effects of the environment. Other less heavy solutions would have to increase the metacentric height to 15m to achieve a smaller restoring torque.

[0058] The fact that the metacentric height is not too large (less than 10 m) is important because, in addition to reducing the accelerations generated in the turbine, it also makes the separation of the forces of the structure weight and the water thrust very small (about 0.8 m for a 5° inclination) and therefore hardly generates any bending forces in the structure.

[0059] On the other hand, other solutions on the market, due to their larger metacentric height, place these forces further apart and therefore they generate significant bending stresses which must be compensated by post-tensioning the cables or by using a greater amount of steel. The present invention is clearly a semi-submersible platform with lower bending stresses.

[0060] - The arrangement of the wind turbine in the centre of the platform (unlike the previously mentioned case where the tower is off-centre) significantly reduces the bending forces experienced by its base.

[0061] - The forces exerted on the structure by the mooring lines are absorbed and distributed directly by three large main radial screens ( Fig.28 ) without local concentrations of stress. Although in the figures indicated the mooring points are located on the upper part of the face, they could also be located at an intermediate height, or even at the level of the lower plate, with the same derivation performance, depending on the applied construction solution.

[0062] - The external span of the structure is only about four meters, and the wall thickness is 50cm, making the possible bending on the same structure very small.

[0063] All of this results in a structure with many walls that distribute the load well, requires little assembly, and has no stress concentration points where fatigue can act.

[0064] c. Excellent durability and low maintenance

[0065] One of the greatest hazards of concrete structures in an offshore environment is cracking, which can increase the risk of corrosion of reinforcements.

[0066] When also subject to cyclic loading from waves and wind, fatigue may occur, which increases the problem in cells that are more exposed due to their slenderness, such as cantilevers, overhangs and towers.

[0067] In the present invention, cracking is very low because the concrete is mostly in compression. Therefore, maintenance is almost zero due to low stress and concentration in the concrete with almost no reinforcement.

[0068] Furthermore, the structure in its service position is ballasted only with water. This enables easy emptying for transfer back to port and for onshore maintenance. Furthermore, a "plug and play" system is provided for mooring and electrical connections, making the process very easy.

[0069] d. Excellent implementation speed

[0070] The fabrication of caisson equipment structures is a highly tested technology with well-proven logistics. Capable of fabricating 20,000t pieces in only 7 days.

[0071] The caisson equipment dock is transported to where it is needed and can be installed in a location that does not interfere with the daily activities of the port. Therefore, it is very versatile and can be used in almost all types of ports.

[0072] All this means high-quality implementation in record time, especially in large structures.

[0073] 2. Large amounts of water trapped in motion

[0074] Those skilled in the art know that in order to minimize turbine acceleration, the floating structure must trap most of the surrounding water as it moves, so as to increase the inertia of the assembly in heave and in pitch / roll. This increase in inertia increases its oscillation period, causing the acceleration at the mast head to decrease.

[0075] Many existing platforms already include heave plates consisting of cantilevers that abut the structure and increase the water trapped in its movement. This is a fairly effective solution, but it is limited to the width of the cantilever, which is subject to significant cyclic action causing significant fatigue to its structure.

[0076] The present invention is designed to trap as much water as possible and comprises a larger lower plate (52) having perforations in its central region (52). Figure 7 ), so that it traps water on both its lower and upper faces, because the flow rate through the gap is much slower than the movement of the component.

[0077] On the one hand, the lower plate is moved outward about two meters ( Figure 7), which constitutes a very resistant undulating plate, similar to other solutions. But the most important aspect is that the huge volume of water trapped by the assembly of the lower plate is equivalent to the hemisphere of the radius of the circle inscribed on it and connected to the water in the central cell on the outside. This entire volume requires the mass of the structure to be increased by 1 to 2 times its displacement (depending on the shape of its perimeter), that is, equivalent to the mass of the platform being double or triple its original mass.

[0078] On the other hand, existing solutions using undulating plates, usually consisting of three towers, can only increase their mass by 0.5 to 0.8 times their displacement, since they have no larger lower plates connecting them, nor internal cells connected to the outside via gaps.

[0079] 3. Low draft

[0080] The proposed platform together with the superstructure supporting it (wind turbine) has an initial draft (about 10 m), which significantly increases the availability of a quay close to the implementation site for its construction.

[0081] This allows the complete onshore installation to be carried out and towed to its location in a vertical position, with excellent vessel stability, its high natural period of rolling back and forth and low resistance to displacement.

[0082] The commissioning process of the structure is carried out simply by ballasting its cells with seawater, without the need for any additional means or special auxiliary vessels of large capacity or floating elements other than the structure itself.

[0083] The disconnection process for better maintenance in port is perfectly feasible since it is sufficient to restore 10 m of draft, considering that it is only for commissioning the ballasting with water, thus reversing the process carried out by the filling pumps.

[0084] 4. Large restoring torque

[0085] Due to the large mass of the platform, with a displacement of about 30,000 t and a high metacentric height of about 9 m (slightly different according to different alternatives), it provides a large restoring moment of 25,000 tm, which requires a static tilt angle of 5° for a 10 MW wind turbine without using variable ballast to improve it. This restoring moment is key to energy production and in the present invention it is two to three times that of other floating solutions which usually have 7,000 to 14,000 tm.

[0086] It should be noted that the displacement of the proposed structure is at least three times that of the rest of the existing platforms (which are typically between 8,000 and 10,000 t). This significant increase in weight is due in particular to its manufacture using reinforced concrete caissons, which allow for the production of high-quality structures at low cost. Achieving similar displacement in steel is not feasible due to its cost, and other existing solutions manufactured in concrete have significant construction and durability problems due to cracking.

[0087] 5. Increased Energy Production

[0088] Since the platform tilts less than five degrees in the case of a wind of 11 m / s, ie when the maximum tipping torque is applied in a 10 MW turbine, the energy production of the turbine is guaranteed at full load at all times.

[0089] Other solutions with a recovery torque of one third to one half must reduce energy production to reduce the wind until the water is transferred from some towers to others and thus compensates for the over-tilt that will occur. This process will take about half an hour each time the wind changes significantly, so that production is affected. In the event of a fault or during system maintenance, it will have to be completely interrupted.

[0090] The proposed solution also makes it possible to use this variable ballast system, not only to avoid excessive tilting, but also to quickly reduce it to a minimum. This makes it possible to fully exploit the energy of winds blowing less than 11m / s and thus significantly increase the MWh produced.

[0091] In this way, if Fig.29 As shown in the figure, every 170m 3 of water, they will expand by 7000tm, which is sufficient to optimize production. This brings about an increase of about two meters in the height of the water column for a single cell arranged at a vertex (44) ( Fig.29 ), and the water column height for the single grid arranged at the other two vertices is reduced by one meter. This process will take about 10 minutes using two 500m 3 / h pump.

[0092] Water transfer between the end cells is via a pump activated pipe (41) ( Fig.23 ) is carried out and the pump remains on deck for inspection and maintenance.

[0093] 6. Accessible maintenance of all equipment

[0094] As described above for the water transfer situation, all maintainable facilities on the platform (connections for mooring systems, electrical systems, sensors, pipes, pumps, control systems, etc.) are at deck level, always above sea level.

[0095] No metal structure remains submerged and thus requires maintenance, and furthermore, there is enough space on the deck to support any type of machinery, which facilitates maintenance of the wind turbine tower or superstructure which will always be above the ground.

[0096] 7. Low cost

[0097] Caisson concreting is the most modern, efficient and environmentally friendly technology currently used for the construction of wind and port infrastructure. This in itself brings environmental improvements, but also means savings in possible corrective measures.

[0098] Consuming less raw material resources, which, depending on the characteristics of each subject, can result in savings of 50%.

[0099] The speed of implementation not only means saving time and money, but also represents a significant reduction in pollutants compared to traditional technologies.

[0100] The low reinforcement of the proposed structure and its rapid implementation represent a cost reduction of more than 50% compared to other similar metal structures.

[0101] The proposed construction system consists of two methods, bringing huge savings both in creating small numbers of units and in mass production.

[0102] The above described features overcome the shortcomings presented by the above mentioned prior art platforms.

[0103] The present invention consists of two parts: the definition of the structure and the construction, assembly and commissioning process, aspects discussed in the section on the preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0104] Figure 1a A perspective view of a structure according to the invention is shown, which consists of a single caisson. The following list includes the basic elements of the piece:

[0105] 1. Superstructure (usually a wind tower)

[0106] 2. Base

[0107] 3. Structure that forms the base (caisson)

[0108] 4. Lower plate of caisson

[0109] 5. Caisson surface

[0110] 6. Upper plate

[0111] 7. A housing in which the base of the tower is placed.

[0112] Figure 1bA perspective view is shown of a structure according to the invention having the same basic elements except that the base is constituted by three caissons instead of one.

[0113] Figure 2a A plan view of the invention consisting of a single caisson is shown, showing the proposed structural system and the distribution of loads transmitted by the wind turbine. It consists of the following elements:

[0114] 8. Inner wall

[0115] 9. External wall

[0116] 10. Middle wall

[0117] 11. Radial ribs

[0118] 12. First connection node

[0119] 13. Mesh structure

[0120] 14. First reticular rib

[0121] 15. Second reticular rib

[0122] 16. Second connection node

[0123] 17. Internal Cell

[0124] 18. External single cell.

[0125] Figure 2b A plan view of the invention consisting of three caissons is shown, showing the proposed structural system and the distribution of loads transmitted by the wind turbine. It consists of the same elements, except:

[0126] 19. Connecting wall between caissons

[0127] 20. The mesh structure of each caisson

[0128] 8bis. Central wall section

[0129] 9bis. External wall section

[0130] 10bis. Intermediate wall section.

[0131] Figure 3a A plan view of the invention consisting of a single hexagonal caisson is shown, showing the proposed structural system and the distribution of loads transmitted by the wind turbine. Figure 2a Same components.

[0132] Figure 3bA plan view of the invention consisting of three caissons forming a hexagonal base is shown, in which the proposed structural system and the distribution of loads transmitted by the wind turbine are shown. Figure 2b Same components.

[0133] Figure 4a A cross-sectional view of the invention is shown showing the modulation of the structure and presenting a chamfered triangular base having three sides of length 7A and another three sides of length A.

[0134] Figure 4b The invention is shown in plan view showing the modulation of the structure and presenting a chamfered triangular base with three sides of length 7A and another three sides of length A. The arrangement of three highly rigid radial walls is indicated, which in the case of three caissons are double-joined walls 54.

[0135] Figure 5 Plan and cross-sectional views of the invention are shown showing the modulation of the structure and presenting a hexagonal base with six sides of length 3A.

[0136] Figure 6 A perspective view is shown indicating exterior cells that may be added to form tower 55 .

[0137] Figure 7 A bottom perspective view of the platform in both configurations is shown, with the following elements highlighted:

[0138] 50. Opening in the upper plate for inserting the bottom of the tower

[0139] 51. Opening in the center of the center cell in the upper plate

[0140] 52. An opening in the center of the center cell in the lower plate of a single caisson or triple caisson

[0141] 53. Shock absorbing tabs formed by extensions of the lower plate.

[0142] Figure 8 A plan view of an alternative embodiment of the invention is shown having a circular shape with a diameter 6A, wherein the modulation of the structure is shown.

[0143] Fig. 9 A plan view of an alternative embodiment of the invention is shown having a chamfered square shape with sides measuring 5A, showing the modulation of the structure.

[0144] Fig.10There is shown a plan view of the base construction of the present invention having three added circular cells 56 for supporting a building, substation or other facility requiring more support.

[0145] Fig.11a Shown is a perspective view of a "caisson facility" floating dock that is purpose built to build the platform in one piece.

[0146] Fig.11b A perspective view of a one-piece built platform, already with sufficient freeboard, is shown freed from an already submerged floating dock.

[0147] Fig.11c A perspective view of the platform being built as a single floating piece is shown, with concrete pouring continuing on the slip formwork.

[0148] Fig.12 A perspective view of the construction of the platform in three pieces by means of a "caisson equipment" floating dock is shown, one of the three pieces being completed and floating.

[0149] Fig.13 A perspective view of one of the caissons forming the structure is shown ready for connection of the caissons. It consists of the following components:

[0150] 21. Embedded sheath for connecting cables

[0151] 22. Side hole

[0152] 23. Waterproof joints that cushion and make the connection between caissons watertight

[0153] 24. Strengthen the ribs.

[0154] Fig.14 A perspective view of three segmented and unsegmented caissons that have been joined is shown, indicating the arrangement of hollow, preferably steel columns 25, and their corresponding closures 26, which may be of any type, such as covers, gates, butterfly valves or the like.

[0155] Fig.15 A perspective view showing the joining process of three caissons is shown, wherein three tugboats are shown approaching the caissons while pulling the cables previously inserted in the sheaths at the ends.

[0156] Fig.16 A perspective view is shown of regularised grouting 27 carried out in the chambers between the caissons formed by previously installed flashing tape.

[0157] Fig.17 A schematic perspective view of the insertion of a pin 28 into a hole in a joining wall is shown.

[0158] Fig.18 A perspective view of three linked caissons is shown, with the concrete cast area of ​​the circular lower plate 29 highlighted.

[0159] Fig.19 A perspective view of three linked caissons is shown, in which are placed internal pipes 30 to be installed for filling and emptying the cells.

[0160] Fig. 20 A perspective view of the entire base is shown, in which the following elements are presented:

[0161] 31. Pre-slab for the upper part of the caisson for its subsequent concrete pouring

[0162] 32. Air outlet pipe and valve

[0163] 33. Ballast water pipeline

[0164] 34. Anchors for mooring ropes

[0165] 35. Concrete of upper slab.

[0166] Fig.21 A perspective view is shown showing how the superstructure (wind tower) (36) is installed in the formed central gap.

[0167] Fig. 22 A perspective view is shown showing the grouting of the space left between the central circular cell and the axis of the superstructure 37 .

[0168] Fig.23 A perspective view is shown showing the ballast system consisting of the following elements:

[0169] 38. External water inlet

[0170] 39. Distribution Ring

[0171] 30. Pipes with valves for single cell ballast

[0172] 40. Pump

[0173] 41. Pipes for active ballast systems

[0174] 42. Adjustable air outlet

[0175] 43. Sliding gate for lower water connection.

[0176] Fig.24 A cross-sectional view showing the ballast system is shown with the gate of the lower gap closed.

[0177] Fig.25A cross-sectional view showing the ballast system is shown, wherein the gates of the lower gap are open when the level of the center cell coincides with the outer sides.

[0178] FIG. 26 a shows a perspective view showing the pneumatic damping system, reflecting the configuration of the internal cells when the platform is at the wave crest.

[0179] Figure 26b A perspective view showing the pneumatic damping system is shown reflecting the configuration of the internal cells when the platform is in the trough of a wave.

[0180] Fig. 27 A perspective view is shown, wherein the movement of the platform (dashed line) is presented relative to the reduction of the profile of the waves (grey area).

[0181] Fig.28 A perspective is shown in which the platform is presented in a service state.

[0182] Fig.29 Plan and cross-sectional views are shown, wherein the locations of cells for the variable ballast system 44 are presented. DETAILED DESCRIPTION

[0183] A. Description of the structure

[0184] The present invention is a floating structure for implementing buildings, installations and wind turbines in an offshore environment, distinguished by two main features:

[0185] - Structural system that is easy to manufacture, completely safe, highly resistant, with very low bending stresses, low fatigue and good durability;

[0186] - Special hydrodynamic operation, which captures large amounts of surrounding water and converts it into optimal performance for wind energy production.

[0187] The floating structure consists of a base 2 consisting of a concrete structure ( Figure 1a ) or three concrete structures ( Figure 1b ) is formed, also called a "caisson", consisting of external vertical faces and an internal pattern of internal vertical faces forming a cell 5, the caisson is closed at the bottom 4 and at the top 6 by plates, and is built using a floating dock ("caisson equipment"), which is a widely used and proven method in the implementation of docks and quays. The caisson equipment construction allows to quickly and easily implement the structure and also make it float at the end of the process.

[0188] A caisson constructed in this way is closed around its entire perimeter, is monolithic, individually well resistant, and floats stably at a reduced draft.

[0189] Anyone familiar with port construction knows what this type of structure looks like and how they are built, which usually has regularly arranged rectangular or circular internal cells. However, the present invention includes a specific design for the use it will undergo, which design significantly improves its handling performance, resistance and durability.

[0190] One of the greatest structural problems when defining a floating concrete platform supporting a powerful wind turbine is to distribute the enormous forces transmitted without concentrating stresses at any point of the base where reinforcements would have to be added significantly and where points with a high risk of fatigue and cracking would be identified.

[0191] Instead of proposing to connect the tower to the upper plate by a series of connecting bolts (as is usually done), which would concentrate stress in this area, the present invention proposes to fully insert the shaft of the wind turbine 1 into the central cell 7 up to the lower plate of the platform 4 ( Figure 1a ). It thus consists in transferring the wind-generated forces exerted by the shaft of the wind turbine on the walls of the central cell directly to the very large radial screens 11 ( Figure 2a ), which in turn are distributed over a very resistant perimeter formed by a mesh of smaller screens forming an equilateral triangular grid 13. In this way, no part of the structure is overstressed, which means safety and durability.

[0192] To this end, the present invention, in its preferred construction, consists of a base having both regular and irregular hexagonal polygonal layouts, and the cells formed by the internal vertical faces have the following characteristics:

[0193] The perimeter of the base is constituted by a grid of equilateral triangles 15 , and the triangles having sides on the outside of the base are divided by another vertical face perpendicular to their midpoint 14 .

[0194] - In the centre of the base there is a large circular cell 8 which will allow it to support the forces transmitted by the superstructure (which will mainly be a wind turbine).

[0195] - By connecting the two areas described above, a radial face 11 is arranged which connects the central cell with the inner vertices of each of the triangles on the perimeter.

[0196] Figure 2a and Figure 2b The essence of the proposed structural system is shown, where the load is distributed throughout the structure in a branching manner without any non-branching nodes. It consists of the following elements:

[0197] - an inner wall 8 defining a housing in which the base of the tower is housed

[0198] - an external wall 9 which defines the outer periphery of the body

[0199] - an intermediate wall 10, which is arranged between the inner wall and the outer wall

[0200] - Internal radial ribs 11 which connect the inner wall to the intermediate wall

[0201] - First connection node 12

[0202] - Primary mesh ribs 14, which connect the first connection node perpendicularly to the outer wall

[0203] - Secondary mesh ribs 15, which connect the first connection node to the outer wall obliquely

[0204] - In the second connection node 16, the distance between them is the distance A of the modulation structure ( Figure 4b and Figure 5 ).

[0205] Figure 2b and Figure 3b The essence of the system consisting of three caissons in the present invention is shown. It is composed of the same elements, except:

[0206] - Tie wall 19 for attaching caissons

[0207] - Central wall section (8bis)

[0208] - outer wall segment (9bis) and

[0209] - Intermediate wall section (10bis).

[0210] In both cases, the inner wall 8 forms a housing for the base of the tower 7 and in the preferred construction this inner wall will be cylindrical as it is required to support the wind turbine, but it may generally have any other polygonal based prismatic shape to accommodate other types of supports for other types of facilities or buildings.

[0211] The wall and rib configurations described previously can be classified into internal and external cells:

[0212] - The inner cell 17 is a cell formed by at least one inner wall segment, two radial ribs and an intermediate wall segment.

[0213] - The peripheral cells 18 are all other cells which are not internal and are generally composed of an external wall section, a first or second web rib and an intermediate wall section.

[0214] The grid of equilateral triangles on the perimeter forms a highly resistant enclosure for the platform. It also constitutes a double safety shell, so that any water leak that may be generated by an accidental impact will only flood very small individual cells without any impact on the whole.

[0215] It can also be seen that this system is again optimal for transmitting the forces of waves and currents towards the interior of the structure, thereby resisting them without concentrating them. The outer span of the grid is about 4m and the thickness is at least 50cm, which is much smaller than the outer span of the remaining existing concrete platforms, which are usually 8m or more and about 40cm thick. This significant difference translates into much lower bending stresses, greater resistance and fewer reinforcements.

[0216] This feature can be considered not an advantage, since other platforms can do the same thing by simply introducing more faces and increasing thickness. But in this case, it will not be implemented in other solutions, because it will add so much weight to them that they will lose stability and all other ship performances.

[0217] This means that it is possible due to the proposed branching configuration and due to the overall design of the volume and weight of the invention allowing it.

[0218] The perimeter of the base formed by a grid of equilateral triangles forms a six-sided polygon with parameter "A" being the distance between each pair of consecutive secondary nodes:

[0219] - If three edges have length A, and the other three edges have length nA, then the result is Figure 4b A chamfered triangle like in the figure.

[0220] - If the six sides are equal in length nA, then it is Figure 5 A regular hexagon like the one in .

[0221] Any other configuration of the sides is possible as long as the above structure is maintained. As a reference, it can be indicated that the module A can vary between 6 and 14 meters, and the sides of the base are 1 to 10 times A.

[0222] Another important aspect of the structural design is the three highly rigid radial walls 54 ( Figure 4b ) to achieve, by means of a low stress structure, exceptional resistance to the large movements to which it will be subjected.

[0223] As described, the platform can be made of one or three pieces. In the latter case, its connecting wall will be just three larger radial walls 54 ( Figure 4b ). This accomplishes three things:

[0224] - Double walls are larger walls with a "support" thickness of at least 1m and give exceptional stiffness to the structure, minimizing its fatigue

[0225] - Large contact surface between caissons to achieve perfect integrity in the joint

[0226] - Mooring systems can be attached to it and thus distributed without affecting the rest of the structure ( Fig. 22 )

[0227] In order to capture the special hydrodynamic operation of the large amount of surrounding water, a series of perforations ( Fig.14 ) and a pressure control valve is made in the upper plate 42 ( Fig.23 ).

[0228] As already indicated, almost all existing platforms have a heave plate, since it is an effective system for trapping as much water as possible and thus optimizing its operation, but it is only used locally in the tower and on the perimeter of the base. One of the advantages of the present invention is precisely to design the platform as a huge heave plate, which traps a lot of water below and a lot of everything above that enters the path of the central cell and the peripheral plates.

[0229] Furthermore, the opening of the lower gap in the central cell results in an increase of about one meter in the metacentric height of the platform (from 8.50m to 9.47m), and the floating surface is lowered when external water comes in. All this translates into greater stability and optimal performance for wind energy production.

[0230] In addition, it can also include an optional system, the pneumatic damping system, which enables further improvement of the platform's performance, which is of great interest in very strong seas:

[0231] The pneumatic damping system includes a pressure control valve 42 ( Fig.23 ) to restrict air inlet and outlet to the interior cell, thereby shifting the level of the interior cell relative to sea level.

[0232] a) When the platform is on the wave crest (Figure 26a), the central cell has a lower level because the restriction of the air outlet inside it slows down its filling. This means a significant reduction in the lift of the structure and therefore in the acceleration.

[0233] As time goes on, the center cell continues to fill, but out of phase with the wave.

[0234] b) When the platform is in the trough ( Figure 26b ), the central cell is already filled and can hardly be emptied because the air inlet is blocked. This means a significant reduction in the descent of the structure.

[0235] Depending on the wave conditions, the inlet and outlet of air can remain constant or can be adjusted by a control system that optimizes its operation.

[0236] Fig. 27 The reduction in the profile (grey area) relative to the waves is shown on the platform movement (dashed line).

[0237] The invention may provide other construction solutions which, although having very similar characteristics, will allow its adaptation to very different scenarios and technical means of construction:

[0238] - Some peripheral cells can rise above the deck of the base, forming towers that further increase stability. They are not always necessary, since with the base construction all the required criteria are adequately covered, and have the disadvantage of lacking a large useful deck for maintenance, since in this case only the towers will be exposed. However, the structural solution and water retention work in the same way, and even the volume of water displaced can be larger, and therefore with lower accelerations.

[0239] Figure 6 It is shown how a triangular perimeter grid allows the construction of a tower 55. As already indicated, the preferred construction is with sliding formwork in the caisson device and its construction will not have any complications since it is only necessary to continue concreting the faces corresponding to the tower.

[0240] - The platform can also have a circular layout, which has the same characteristics as previously defined, but with a perimeter triangle similar to an equilateral triangle, with the outer and inner sides in the shape of arcs ( Figure 8 ).

[0241] - The platform can also have a square layout (with chamfered corners) with the same characteristics as previously defined, but in this case divided into four prismatic concrete structures (caissons) instead of three and will be divided by its diagonals ( Fig. 9 ).

[0242] - The structure may have, in addition to the central circular cell, three other smaller cells, regularly distributed and having the same characteristics as previously defined, in order to be able to accommodate the other supports of the superstructure ( Fig.10 ). These supports will be necessary when the structure to be supported is not a wind turbine but a building, a substation or any other type of facility.

[0243] - Another option is that the structure, once towed by floatation to the service area, is completely ballasted with seawater to rest on the seabed.

[0244] - When there is no possibility of the existence of a floating dock with caisson equipment of sufficient size for the construction of the platform, it is possible to build it using prefabricated elements or using sliding formwork on a pier with a launching system or on a dry dock capable of accommodating the construction.

[0245] Some values ​​that can be used to assess a vessel's stability and its suitability for energy production are:

[0246] - Initial metacentric height = 9.47m

[0247] - Displacement = 29734t

[0248] - 5° restoring torque = 24541tm

[0249] - 10° restoring torque = 48896tm

[0250] - 20° restoring torque = 63333tm

[0251] - Expansion per 170m3 of transferred water = 7000tm.

[0252] Considering that the horizontal force exerted by the wind on the hub of a 10MW DTU turbine at maximum energy production is 150t, this will result in a destabilizing moment of 18,000tm, which gives one an idea of ​​the small inclination that the platform will experience and the consequently huge energy production.

[0253] B. Description of build, assembly, and debugging methods

[0254] The proposed build system consists of two methods:

[0255] Method 1: "One-piece build".

[0256] When it comes to large-scale production of wind farms of about 700-1000 MW, where the initial investment in building the infrastructure is divided into many units, it is profitable to build special caisson equipment floating docks with these unusual dimensions for the joint construction of the entire platform.

[0257] Method 2: "Build from three pieces"

[0258] When it comes to building a small number of units, such as prototypes or shore power supply facilities for ports or industries, and investing in a very expensive caisson equipment dock is not justified, it can be built in three pieces using existing smaller sized caissons.

[0259] Method 1

[0260] The first method is used for large-scale production and consists of four blocks:

[0261] 1. One-piece construction

[0262] 2. Install the supporting superstructure (usually a wind turbine)

[0263] 3. Debugging adapted to implementation conditions

[0264] 4. Disconnect and refloat for maintenance or removal

[0265] 1. One-piece construction

[0266] When the build volume is reasonable, a floating dock of the size required for the construction of the platform will be pre-built.

[0267] The floating dock will preferably have a platform-like shape, slightly larger in layout to save material, but can also be made rectangular by linking existing pontoons. On the required face, guides will be fixed to the seabed, which will stabilize the dock when it is ballasted with water to release the structure. Fig.11a ). It can also be stabilized by flotation using submerged towers arranged in the corners.

[0268] The build is implemented in the following phases:

[0269] - Placement of lower slab reinforcements and concreting

[0270] - Placement of sliding formwork for building vertical surfaces

[0271] - Concrete the opposite side until the structure has sufficient buoyancy to have a safe freeboard. Continue concreting on the outside of the caisson equipment.

[0272] - Ballasting the caisson equipment until the caisson is released and moored to the quay to continue the concrete pouring while floating ( Fig.11b )

[0273] - Concreting of the rest of the structure using sliding formwork while floating ( Fig.11c )

[0274] - Once the entire support of the structure has been concreted, remove the sliding formwork, place the pre-slab, and concrete the upper slab

[0275] This system allowed for a very efficient construction, being able to implement the process in just one week, leaving the fully finished structure already floating.

[0276] 2. Install the supporting superstructure (usually a wind turbine).

[0277] For the installation of wind towers, substations or structures supporting platforms, follow these steps:

[0278] - Insert the superstructure (wind tower) 36 into the created central gap ( Fig.21). This is an important innovation since it involves replacing the usual connection of the tower, which is usually implemented by means of a large flange screwed to a bolt cage embedded in the wall of the platform. This connection is highly complex, requires great construction precision and, moreover, it creates significant stress concentrations in this area. On the other hand, this solution is very simple, requires much less restrictive tolerances and distributes the loads without concentrations.

[0279] - Grout the space 37 left between the two ( Fig. 22 ). This step is similar to that usually performed for joining a monopile and a transition piece, but now used in the joining of the shaft to the platform, which allows an integral joining between the two elements.

[0280] 3. Debugging

[0281] The process consists of the following stages:

[0282] - Towing and positioning of the platform by three tugboats. The platform is moved with one or two conventional tugboats pulling it, and a third tugboat stays behind to avoid possible lateral drift during displacement. Subsequently, the same three tugboats will allow coupling to the previously installed moorings and positioning the platform in its service position.

[0283] - Ballasting with water via installed pumps

[0284] The ballast system will vary depending on the type and shape of the marine structure in question, but it will always consist of something like Fig.23 The components shown in the figure are:

[0285] External water inlet 38

[0286] Distribution ring 39

[0287] Pipe with valve for single cell ballast 30

[0288] Pump 40

[0289] Pipes for active ballast systems 41

[0290] Adjustable air outlet 42

[0291] Slide gate for lower water connection 43

[0292] Ballasting is carried out by introducing water from the inlet 38 by means of a pump 40 and from the outside via a distribution ring 39 and a pipe 30 with a valve; the central cell is filled so that when the pressure is the same as outside, the gap arranged in the lower plate can be easily opened by means of a sliding gate or the like 43 ( Fig.23 ).

[0293] The debugging method is as follows:

[0294] - Fill the center cell until the interior water level is equal to sea level.

[0295] - Opening the lower gate, thus connecting the central cell with the sea. There is also another possible construction of the invention, in which the central cell is not connected to the outside, so that the platform will not have a gap in the lower plate, and therefore this and the next point will be omitted.

[0296] - Adjustment of the upper air outlets which are needed to achieve aerodynamic damping adapted to the waves.

[0297] - Slightly fill the cell at the base 44 vertex ( Fig.29 ), for the pipeline 41( Fig.23 ) operation of the variable ballast system.

[0298] - Connecting previously pre-installed mooring ropes (plug and play). One of the most important features of the invention is its easy commissioning and removal, since it is ballasted with seawater only. Furthermore, the mooring ropes can be easily connected and disconnected with the help of only conventional tugboats. This allows bringing the platform back to port when necessary.

[0299] - Electrical connection (plug and play). In the same way, the power lines can be connected and disconnected through an underwater electrical connection hub, which is also pre-installed to enable it to be disconnected.

[0300] 4. Disconnect for maintenance or disassembly

[0301] The process consists of the following stages:

[0302] - Secure the platform using three tugboats;

[0303] - electrically disconnected and secured for subsequent use;

[0304] - disconnection of mooring lines and securing for subsequent use;

[0305] - Close the gap in the lower plate;

[0306] - emptying of ballast water from the cells by means of installed pumps or by injection of compressed air, which results in refloating of the structure;

[0307] - Tow the structure to the port.

[0308] Method 2

[0309] The second method allows the production of a small number of units and is a process similar to the previous one, with the difference that the base is constructed from three separate pieces which are then integrally connected by concreting the upper and part of the lower plate, if necessary by connecting bolts.

[0310] This method requires three specific processes:

[0311] 1. Construct the elements that make up the structure

[0312] 2. Preparation of structures for subsequent assembly of structures

[0313] 3. Assemble the previous components

[0314] The assembly, commissioning and disconnection of the superstructure (wind turbine) will be the same as in Method 1.

[0315] 1. Construct the elements that make up the structure

[0316] As described above, the greatest difficulties encountered when constructing any of the existing platforms that must support buildings, facilities or 12 or 15 Mw wind turbines are their huge size (about 50 m in diameter) and the major motions that need to be supported.

[0317] Specialized shipyards and ports currently have the means available for these purposes, such as:

[0318] - Synchronous lift (Syncrolift) and launching ramp: They will allow the platforms to be built on the quay and transported to the launching area using a rail system, spmt trailers or oversized cranes, where they can float. It is a complex system to build, but it is proposed by existing solutions. The fact is that none of these means are built using the maximum width of 50m, which is what is needed.

[0319] - Dry dock: In principle, this is the simplest system to solve the problem, but there are currently few dry docks of the required size. Therefore, it is necessary to implement a large-scale excavation in the port area and provide a series of locks and waterproofing, which will incur high additional costs.

[0320] In any case, these resources are extremely scarce and expensive, creating bottlenecks when it comes to meeting deadlines for large implementations.

[0321] Therefore, for its manufacture, it is currently necessary to pre-build specific facilities that allow the implementation of the work and allow the transport and floating of the system in the case of very high tonnage. This leads to an impact on the cost of each unit, which can be compensated in large wind farms, but will never be compensated when it comes to the manufacture of a small number of platforms.

[0322] As explained, for a concrete cast solution the ideal form of construction would be harbour caisson construction technology (using a "caisson rig") but this presents the significant problem of not "fitting" into any of the existing floating docks.

[0323] For this reason, the present invention proposes to decompose the platform into several elements which are watertight, durable and self-supporting and which can be constructed in the many transferable floating docks which exist for the construction of caissons.

[0324] For the construction of the caissons defined previously, the port caisson system will be used, by using a floating dock. Construction can also be carried out on a dry dock or on a platform on a quay, which will then float, but in all cases the concreting will be carried out using a sliding formwork system (it can be built with prefabricated flat pieces and then the joints will be concreted, but only if no other means are available).

[0325] The "caisson facility" floating dock has a perfectly designed infrastructure that raises the formwork by a system of hydraulic jacks, giving it the following great advantages: it is possible to place the concrete in small layers in the formwork, removing the concrete joints, in addition to being able to compact the concrete and ensure its connection with the previous layer in perfect conditions. In addition, once the caisson has been built, it floats in a stable manner ( Fig.12 ), which is a very important operational advantage.

[0326] This creates a great solidity and integrity in the built structure (which makes it ideal for withstanding the blows of waves and wind) and a strong resistance to accidental impacts from ships or icebergs. On the other hand, in floating concrete platform solutions currently designed on the market, in order to achieve performances somewhat similar to those of caisson equipment, prefabricated elements are used, the joints of which are prone to failure and therefore have a much lower resistance.

[0327] 2. Preparation of structures for subsequent assembly of structures

[0328] Each of the modules that make up the structure must be prepared for the subsequent connection between them. To this end, it is necessary to leave the side holes 22 (23) necessary for the introduction of the cables that connect them as a whole. Fig.13 ) and embedded in a sheath 21. The location and number of sheaths and holes will depend in each case on the stresses caused by the superstructure and the environmental conditions in which it is located. The location of the side connection holes is already provided in the arrangement of the reinforcements, but only a recess of about 5 cm is left on the face, which serves as an indication of the location of the side connection holes. Inside this cutout, when the caissons are firmly connected at their ends by cables, perforations will then be made and the gaps remaining between the faces will be completely filled with grout (this process will be explained later). Finally, the pins will be introduced to achieve the overall connection.

[0329] In some cases, if necessary, a series of sheaths can also be arranged on the inside of the lower plate or side wall for the introduction of post-tensioning cables.

[0330] like Fig.13 As can be seen in the figure, on the inner edge of the lower plate and on the outer band of the joint area, waterproof joints 23 are arranged, which allow the joint between the caissons to be sealed. In the upper part of the caisson and in the lower circular area, the necessary reinforcement ribs 24 will remain in order to create an integral joint between the caissons later when the small circles of the upper and lower plates are concreted.

[0331] In the lower plate, in the area below the central cell, a circular opening with a diameter of about two meters will be left, which will allow the passage of water to the inside.

[0332] For this purpose, hollow, preferably steel, columns 25 ( Fig.14 ) which will protrude sufficiently from its upper face so that some type of closure 26 can then be connected to close the water passage.

[0333] The closure must withstand the hydrostatic pressure present on the lower face, and this pressure will always be less than two bars, which is perfectly acceptable for sheets that are not very thick. This means that many different types of closures, covers, gates, butterfly valves, etc. can be used.

[0334] A simple solution is to Fig.14 A vertical lifting gate is shown in Figure 2, which can be remotely actuated by a small hydraulic jack to simplify its operation.

[0335] 3. Assembling the caisson

[0336] The objective of the assembly method is to carry out the operation in a reliable and safe way, thus ensuring the stability of the structure at all times and guaranteeing the solidity and integrity of the resulting structure.

[0337] The process consists of the following stages:

[0338] - Straightening of the caisson before connecting it (to keep it in a horizontal position). This consists in filling some cells of the caisson with a certain small amount of water so that the caisson floats completely horizontally.

[0339] - Approaching their joining position with tugboats. Each caisson is moored to a tugboat which will position them until they are a short distance apart, facing the faces to which they will be joined. At this point, some cables are inserted through the sheaths located at the ends, so that as they are pulled by each tugboat, they will be more tightly joined together ( Fig.15 ).

[0340] - Final approach and connection by tensioning the cables. When the caisson is already in its coupling position, it is successively tightened by means of jacks before being cut and disconnected from the tugboat.

[0341] - Regular grouting of the chambers between the caissons 27( Fig.16 ), the chamber is provided with waterproof tape 23 ( Fig.13 ) are formed between.

[0342] - Drill holes 22 in the arranged cutouts ( Fig.13 ), and insert the pin 28 into the hole made ( Fig.17 ). Since the chambers formed between the caissons 27 have been completely filled with grout, there will be no problem of water entering through the gaps, and the support between the caissons is completely regular.

[0343] - Concrete the circular lower plate 29 ( Fig.18 ). This step is very important because it creates the lower connection of the three caissons, which will provide excellent integrity to the structure and will serve as a support for the wind turbine tower. In some cases, if necessary, this connection can be supplemented with post-tensioning cables, which further strengthen the connection of the lower plate and provide it with continuity.

[0344] - Installation of internal pipes for filling and emptying the cells 30( Fig.19 ). They will allow ballasting and deballasting with seawater for commissioning, as well as for removing water in emergency situations.

[0345] - Positioning of the pre-plate 31 in the upper part of the caisson and placing of the reserve for the passage of the air outlet duct 32 and the ballast water 33 ( Fig. 20 )

[0346] - Placement of anchors 34 for mooring lines ( Fig. 20 )

[0347] - Concrete the upper slab 35( Fig. 20 ). For this purpose, a perimeter formwork will be provided to cover its edges, which is fixed to the upper part of the outer face. Another option is to increase the outer face to the edge height of the plate in the caisson device itself, so that the outer face again serves as a formwork for it.

[0348] 10MW wind turbine installation example

[0349] For the installation of a 10 MW wind turbine, the preferred construction solution consists of a polygonal base with 6 sides, 3 of which are 7A in length and 3 of which are 1A in length, forming a triangle truncated at the vertex and a 20 m column, with the following characteristics:

[0350] - Size: 65.60m in length

[0351] 56.80m Maximum width

[0352] - Dimensions of each caisson when it is made in three parts:

[0353] 61.90m Length

[0354] 18.20m maximum width

[0355] - Base height (H): 20.00m

[0356] - Maximum external span (A / 2): 4.10m

[0357] - External surface thickness (E2): 0.50m

[0358] - Internal surface thickness (E1): 0.25m

[0359] - Lower plate thickness (LI): 0.50m

[0360] - Width of undulating plate (T): 2.20m

[0361] - Upper plate thickness (LS): 0.80m

[0362] - Weight of each caisson: 8243t

[0363] - Total structural weight: 28460t.

[0364] Advantages of the present invention

[0365] The proposed construction, assembly and debugging method has great advantages over other systems performing the same functions:

[0366] 1. The present invention proposes a feasible solution in a floating dock for caisson equipment which, besides making it float at the end of the process, allows a quick and simple implementation of the structure.

[0367] 2. The ability to place the concrete in small layers in the formwork, in addition to compacting the concrete and ensuring its connection with the previous layer in perfect conditions, allows the caisson to be integral without concrete joints. This makes it a structure highly resistant to water blows and accidental impacts.

[0368] 3. The manufacture of caisson equipment structures is a highly tested technology with well-proven logistics. Ability to manufacture 20,000t parts in only 10 days. All this means high-quality implementation in record time.

[0369] 4. Due to the ease of construction, low cost and the size and resulting weight, this construction system allows the construction of platforms supporting the largest wind turbines currently designed (10 MW, 12 MW or more).

[0370] 5. Rather than being connected to the platform via a plate with bolts that support all the torsion in that area, the superstructure (usually a wind tower) is connected via simple connections that distribute the torsion throughout the structure, thus avoiding stress concentrations.

[0371] 6. The external span of the structure is approximately four meters and the wall thickness is 50cm, making the bending that could occur on the same structure very small.

[0372] 7. The forces exerted on the structure by the mooring lines are absorbed and distributed directly by three large radial faces which reinforce the structure and therefore do not affect the stresses on other faces. All this results in low reinforcement and minimized stresses.

[0373] 8. Maintenance is almost zero due to low stresses and concentrations in concrete with little reinforcement. Cracking is very small because, due to its type of structure, the concrete is mostly in compression, even if in other solutions it is in strain. The service life of the resulting structure can exceed 50 years and can allow the wind turbine to be replaced with another more powerful wind turbine after 20-25 years.

[0374] 9. The structure is completely built and assembled in port, including the superstructure (usually a wind turbine), and it is moved to its working position by floating by conventional tugboats. The low draft of the structure allows its implementation in almost any conventional port close to implementation.

[0375] 10. The anchoring process of the structure is carried out only by ballasting its cells with sea water without any additional means or auxiliary vessels.

[0376] 11. Due to its very large restoring torque and therefore minimal operating tilt, the energy production of the turbine is guaranteed to be always in full load operation without reduced ballast transfer when the wind changes (as occurs in the case of almost all other existing solutions).

[0377] 12. All facilities subject to routine maintenance are located on the deck of the platform (no submerged equipment or metal structures), which means that the task is greatly simplified.

[0378] 13. Because it is ballasted with water only, it can be easily emptied for transfer back to port and for more complex maintenance (onshore). In addition, it has a "plug and play" system for mooring and electrical connection, making the process very flexible.

[0379] 14. The construction system using caisson equipment is the most environmentally friendly system for building wind and port infrastructure, with a significant reduction in pollutants compared to traditional technologies. It is a foundation system that does not produce noise that affects marine mammals, and it can be carried out on almost all types of seabeds without changing them. It requires lower consumption of raw material resources and can lead to 50% savings depending on the characteristics of each entity.

[0380] 15. The low reinforcement required in the case of the proposed method and its rapid implementation represent a cost reduction of more than 50% compared to other similar metal structures.

[0381] 16. The construction system used generates the same savings even when producing small numbers of units, unlike current solutions which only generate savings in large production runs because they require a large infrastructure whose cost must be distributed over large production runs.

[0382] In this document, the word “comprise” and its variations (such as “include”, etc.) should not be understood in a non-exclusive sense, that is, they do not exclude the possibility that the described content includes other elements, steps, etc.

[0383] Furthermore, the present invention is not limited to the particular embodiments described herein, but comprises variations that may be made by a person skilled in the art within the scope that can be inferred from the claims, for example.

Claims

1. A structure (2) for supporting a wind turbine tower (1), said structure being provided with a housing (7) for accommodating the bottom of said tower (1) therein, a main axis (Γ) defined on a platform, said main axis coinciding with the main axis of said tower (1) when said tower (1) is accommodated in said housing (7), characterised in that: It comprises a body having a constant cross section along the main axis (Γ), in which the following are defined: - an inner wall (8) defining the housing (7) for housing the base of the tower (1); - an external wall (9) which defines the outer periphery of said body; - an intermediate wall (10) arranged between said inner wall (8) and said outer wall (9); The inner wall (8) and the intermediate wall (10) are connected by an inner radial rib (11) perpendicular to the inner wall (8), the plane of the inner radial rib (11) passing through the main axis (Γ), so that at the intermediate wall (10), a first connection node (12) is defined between the intermediate wall (10) and the radial rib (11); The intermediate wall (10) and the outer wall (9) are connected by reticular ribs, and the cross-section of the reticular ribs according to the plane perpendicular to the main axis (Γ) is a reticular structure (13), so that the first reticular ribs (14) extend perpendicularly to the outer wall (9) from the first connection node (12), and the second reticular ribs (15) extend obliquely from the first connection node (12) to the outer wall (9) relative to the first reticular ribs (14), and the second connection node (16) is defined on the outer wall (9), where the outer wall (9) and the paired second reticular ribs (15) meet; Wherein, the walls and ribs are made of concrete; The housing is a housing for seating the bottom of the tower therein by inserting grout between the bottom of the tower and the housing, The following are defined: - an inner cell (17), which is a cell formed by at least one inner wall segment, two radial ribs (11) and an intermediate wall segment; and - peripheral cells (18) are all other cells that are not internal cells; and Some of the inner cells (17) comprise upper openings (51) and lower openings (52) such that they form an aerodynamic damping system which allows the level of the inner cells (17) to be displaced relative to sea level by limiting the inlet and outlet of air from the inner cells (17).

2. The structure according to claim 1, comprising n identical bodies (3), each body being defined by: - at least two connecting walls (19) consisting of internal radial ribs and first reticular ribs, said connecting walls (19) being intended to be attached to the adjacent connecting walls (19) of said body (3), the two radial walls forming an angle α=360 / n; and - a central wall, such that the central wall constitutes the nth portion of the inner wall (8); - an outer wall segment; - connecting means between adjacent bodies (3).

3. A structure according to any one of the preceding claims, wherein: The mesh structure (13) is of Warren type with columns.

4. The structure according to claim 1 or 2, wherein: The angle between the paired second mesh ribs (15) is 60 degrees, thereby constructing a grid of equilateral triangles divided by the first mesh ribs (14).

5. The structure according to claim 1 or 2, wherein: The distance (A) between each pair of second connecting nodes (16) is comprised between 6 and 14 meters, and wherein the side measurements of said structure (2) are between 1 and 10 times said distance (A).

6. The structure according to claim 1, wherein: Some of the peripheral cells can rise above the deck of the base of the structure (2) to form a tower (55).

7. A structure according to claim 1 or 2, wherein: The groups of internal cells (17) are provided with a hydraulic communication system between them, comprising means for emptying and filling, which allow the liquid level to be adjusted, both for its anchoring and for refloating.

8. The structure according to claim 1 or 2, wherein: Each body is closed at its lower part by a lower plate (4) perpendicular to the main axis (Γ), the structure (2) comprising an upper plate (6) provided with an opening (50) for the bottom of the tower (1), the upper plate covering at least one body (3).

9. The structure according to claim 1 or 2, wherein: The housing (7) is cylindrical.

10. The structure according to claim 8, wherein The lower plates (4) protrude laterally from the respective outer walls (9) so as to configure damping tabs (53).

11. The structure according to claim 8, wherein: The lower plate (4) and the upper plate (6) are made of concrete.

12. The structure according to claim 2, wherein: The space between the connecting walls (19) is filled with grout.

13. The structure according to claim 1 or 2, wherein: The platform has a circular layout, wherein the perimeter triangle is formed as an equilateral triangle with outer and inner sides in the shape of circular arcs.

14. The structure according to claim 1 or 2, wherein: Three additional smaller circular cells are arranged, evenly distributed and positioned relative to the central circular cell and at uniform intervals therebetween to be able to accommodate other supports of the superstructure.

15. The structure according to claim 2, wherein: The connecting devices are bolts and grouting.

16. The structure of claim 12, wherein: The grouting is a low shrinkage fluid mortar.

17. A method for constructing a structure according to claim 1 by means of a floating dock, wherein The following phases are included: - Construction of a floating dock of sufficient size for building the platform; - Placing reinforcements of the lower slab and concreting on the base of the floating dock; - Place the sliding template for building the vertical faces; - Concreting of the face until the structure has sufficient buoyancy to have a safe freeboard and concreting continues outside the caisson; - ballasting the caisson equipment until the caisson is released and moored to a quay to continue concreting while floating; - Once the entire column of the structure has been concreted, the slip formwork is removed, the pre-slab is placed and the upper slab is concreted.

18. A method for constructing a structure according to claim 2 by means of a floating dock, wherein The following phases are included: - constructing a caisson on said floating dock; - preparing the structure for subsequent assembly of the structure; - manufacturing grooves for indicating the location of the perforations to be made for the insertion of pins; - inserting cables in the sheath which will be used to bring the caissons closer together; - Arrange waterproof connection part (23); - Arrange a gate (26) in the gap of the lower plate; - Assembling the structure consisting of three pieces, which includes the following stages: - straightening the caissons before coupling them to keep them in a horizontal position; - Use tugboats to approach its connection location; - Final access and connection through the cable previously inserted in the sheath at the end; - Regular grouting (27) of the chambers between the caissons; - drilling a hole in the arranged cutout (22) and inserting a pin (28) in the produced hole; - Concreting of the circular lower plate (29); - installing internal pipes (30) for filling and emptying the cells; - Positioning the pre-plate (31) in the upper part of the caisson and placing the reserves for the passage of the air outlet duct (32) and ballast water (33); - placing anchors for mooring ropes (34); - Concreting of the upper slab.

19. A method for assembling a wind turbine shaft on a structure according to any one of claims 1 to 16, comprising the following stages: - inserting the wind tower (36) into the formed central gap; - Grouting the space (37) left in between.

20. A method for commissioning a structure according to any one of claims 1 to 16, comprising the following stages: - Towing and positioning of the platform by three tugboats; - Ballasting with water via installed pumps; -Fill the center grid until the inner water level is equal to the sea level; - filling of cells located at the apex (44) of the base of the structure for operation of the variable ballast system carried out by the pipes (41); - Connect previously pre-installed mooring ropes; -Electrical connection.

21. A method for commissioning a structure according to any one of claims 1 to 16, comprising the following stages: - Towing and positioning of the platform by three tugboats; - Ballasting with water via installed pumps; -Fill the center grid until the inner water level is equal to the sea level; - opening the lower gate, thereby connecting the central cell with the sea; - Adjustment of the upper air outlets, which are required to achieve aerodynamic damping adapted to the waves; - filling of cells located at the apex (44) of the base of the structure for operation of the variable ballast system carried out by the pipes (41); - Connect previously pre-installed mooring ropes; -Electrical connection.

22. A method for unloading a structure according to any one of claims 1 to 16, comprising the following stages: - securing the platform by means of three tugboats; - electrically disconnected and secured for subsequent use; - disconnecting mooring lines and securing for subsequent use; - Close the gap in the lower plate; - emptying the cells of ballast water by means of installed pumps or by injection of compressed air, which causes the structure to refloat; - Towing said structure to the port.

23. A method for constructing a structure according to claim 1 or 2, carried out on a dry dock or on a fixed platform using prefabricated elements or using sliding formwork, the method comprising the method according to claim 17, but in this case carried out on solid ground instead of on a floating dock.

24. A method for constructing a structure according to claim 1 or 2, carried out on a dry dock or on a fixed platform using prefabricated elements or using sliding formwork, the method comprising the method according to claim 18, but in this case carried out on solid ground instead of on a floating dock.

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