FR3122160A1 - Floating platform for the high seas and in particular a system for producing electrical energy using such a platform. - Google Patents

Abstract

Floating platform for the high seas and in particular a system for producing electrical energy using such a platform. The invention relates to a floating platform system, comprising a floating platform 2, moorings 6 and cables 12 to connect the platform to the moorings, the platform comprising a floating box 8, a bridge 9 disposed above said caisson and means 11 for holding the deck fixed to the caisson, designed to offer reduced grip to the swell and the wind, the cables being designed so that the caisson 8 is kept submerged at a depth H8 below the surface of the water 10 and the deck is kept out of the water. Figure for abstract: Figure 2.

Description

Floating platform for the high seas and in particular a system for producing electrical energy using such a platform.

The invention is in the field of maritime platforms, in particular that of platforms intended to install energy production devices on the high seas, in particular wind turbines, but not only. The invention is more particularly in the field of floating platforms.

Fixed platforms are intended for works carried out in shallow water, between five and forty meters. The descent of loads is carried out by foundations anchored in the bottom. Generally they are intended to support works of which the weight is very heavy; 12,000 tons and more for a wind turbine. The foundations made under the liquid surface are therefore important and delicate to make. Their cost is therefore high. They are also subject to forces whose direction and amplitude are variable:

- the horizontal effects of the surface wind,

- the geometric variations of the liquid surface, the swell effect.

These efforts are generally horizontal. The induced bending moment, proportional to the height of the structure, must be taken up by the foundations. This induces a significant additional cost, but also fatigue constraints of the materials that make up the structure, and a reduction in its lifespan.

Deep-sea floating platforms, also called offshore, are used in very deep areas, generally greater than forty meters, where fixed platforms, mounted on pillars resting on the seabed, are not economically viable. They avoid some of the inherent disadvantages of fixed platforms. Notably :

- their weight and that of the structures they support is balanced by the thrust of Archimedes. The problems of deep foundations and the recovery of the bending moment of embedding are therefore eliminated; And,

- floating, they follow the variations in height due to the phenomena of the tides.

However, floating platforms are subject to variations in the liquid surface in which they are immersed, in particular the effects of the swell. This can commonly reach values of fourteen meters in height, measured from hollow to crest and the inclination of the platform can then reach an angle of seventeen degrees. When such a platform carries a wind turbine, the mechanical components of the latter, in particular the blades, are strongly stressed by the swell and the variations in inclination, as are the fixings of the mast of this wind turbine on the platform.

In addition, the wind generates forces proportional to the cube of its speed and the surface exposed, that is to say the square of the length of the blades, in the case of a wind turbine. In extreme cases (100 km/h), for a length of blades equal to 40 m, these forces reach one hundred tons and more. If the mast is embedded in the ground, these forces transmitted to the mast are balanced at the level of the recess. However, in the case of offshore technology, these efforts are balanced by Archimedean thrust. It is therefore the inclination of the platform on which the mast is fixed that will balance the whole. If the platform is not sufficiently dimensioned, this can lead to the total destabilization of the whole. In all cases, these oscillations cause a loss of performance of the wind turbine, and fatigue of the resistant components.

An object of the invention is to provide an offshore platform system that is more stable and less sensitive to environmental hazards, in particular to swell and wind.

According to the invention, a floating platform system comprises a floating platform, moorings and cables for connecting this platform to the moorings, the platform comprising a floating box, a bridge arranged above the box and means to hold the deck fixed to the casing, the holding means being designed to provide a reduced grip on the elements, in particular waves and wind, the cables being designed so that the casing is kept submerged at a depth below the surface of the water and the deck is kept out of the water. Preferably, the floating box has a volume capable of generating an Archimedean thrust greater than the weight of the system.

The system can also comprise winch means for adjusting the lengths of the cables, in particular according to the tides, in particular to maintain or to adjust the depth of immersion of the caisson.

Preferably, the depth of immersion is at least equal to half of a predictable wavelength for swell. The depth of immersion is advantageously at least equal to the foreseeable amplitude for the swell.

The system may further comprise means for producing electrical energy, preferably a wind turbine mounted on the platform, even more preferably a horizontal axis wind turbine.

Embodiments and variants will be described below, by way of non-limiting examples, with reference to the appended drawings in which:

is a schematic perspective view of a system according to the invention for the production of electrical energy at sea;

is a schematic elevational view of the system of the :

is a schematic perspective view from above of a floating platform for the system of the ;

is a sectional view of the platform of the ;

is a schematic view, in elevation and in section, of a balancing system for a wind turbine equipping the system of the ;

is a schematic view in perspective and from above of a mooring device for the system of the ;

is a schematic view in perspective and in section of a pneumatic device for the production of energy, for the system of the ;

is a schematic view in elevation and in section, illustrating the operation of the pneumatic device of the ;

is a schematic top view of the platform, illustrating a distribution of bellows for the pneumatic device of Figures 7 and 8.

is a schematic perspective view from above, illustrating a variant of the system according to the invention using six deadweights; And,

is a schematic sectional view of a terrestrial variant of a device according to the invention; And,

is a schematic view similar to that of the , illustrating a horizontally sliding variant of the pneumatic device.

In the following description, the terms horizontal and vertical must be understood in a theoretical position of rest, as illustrated in figures 1 and 2, in the absence of inclination which could be due, for example, to the action swell, wind, or an ill-distributed load.

There illustrates a floating system 1 for energy production. The system comprises a floating platform 2, on which are mounted means 3, 4 for producing electrical energy. These means of production comprise a wind turbine 3 and a pneumatic device 4. As particularly illustrated in , the system 1 further comprises a set of deadweights 6 to hold the system relative to the seabed 7.

The platform 2 is substantially of revolution around a vertical axis X2, called platform axis. It comprises a floating box 8, a horizontal bridge 9 arranged high above the box 8 and struts 11 to connect between them, substantially rigidly, the box 8 and the bridge 9. The struts form a support substantially transparent to the elements, it that is to say presenting a weak resistance to swell, waves and wind.

As particularly illustrated in Figures 3 and 4, the box 8 has the shape of a cylinder section around the platform axis X2. It has a diameter D8 of between 1.2 and 1.5 times a thickness E8 measured axially, that is to say along the platform axis X2, which is substantially constant. In the example shown, the box 8 is made of reinforced concrete.

As particularly illustrated in , the platform is connected to each of the moorings 10 by a respective cable 12. In the example illustrated, each cable comprises two strands 12A, 12B; a first of the strands 12A connects the respective deadweight to the box 8, the second strand 12B connects the same deadweight to a respective winch 13 arranged on the bridge 9 of the platform. In the example shown in , the first strand 12A forms an angle A12 with a vertical axis V of an axial plane comprising the platform axis X2. Preferably, the angle A12 is between twenty and forty-five degrees, preferably close to thirty degrees.

Each deadman includes a grooved pulley 14, illustrated in , which serves as a mooring point for the platform 2. The cable is mounted on the pulley 14, so that the winch makes it possible to simultaneously modify the length of the two strands 12A, 12B of the cable 12. Thus, it is possible to adjust a distance H7 between the caisson 8 and the seabed 7. As illustrated in FIGS. 1, 2 and 8, in particular, in the floating system 1 according to the invention, dead bodies are used so that the caisson is kept submerged at a depth H8 below surface 10.

As shown in , the swell takes the form of a surface wave 100, of amplitude H100 and wavelength L100. The immersion depth H8 of the caisson is measured from a mean plane P100 of the surface wave 100. In a given place, statistically corresponds a typical amplitude H100T and a typical wavelength L100T, considered as greater than those generally encountered in this place, for example greater than 80% of the amplitudes and the wavelengths in this place. Typically, the swell can commonly reach an amplitude of seven meters. Near the surface 10, the swell causes turbulence capable of affecting the stability of the platform.

In order to limit the influence of the swell on the stability of the platform, the caisson 8 can be immersed under a depth of water H8 greater than or equal to the typical amplitude H100T, to which a safety depth HS can also be added. . Thus, we can choose H8=H100T+HS. For example, for H100T=7m and HS=5m, the casing is immersed at a depth H8=12m.

Furthermore, studies have shown that from a depth HH1 equal to half the wavelength L100, i.e. HH1=L100/2, and beyond, there is no has noticeably more swell turbulence. Thus, preferably, the height H8 is chosen greater than or equal to half a wavelength L100, that is to say: H8 ≥ L100/2.

Thus, by immersing the caisson 8, preferably to a depth H8 greater than a thickness of a local turbulence zone, the stability of the platform is increased; the "transparency" of the support 11 also limits the grip of the elements, water or wind, so that these elements do not significantly destabilize the platform. In the illustrated case of a platform supporting a wind turbine, its greater stability makes it possible to limit the fatigue of the components of the wind turbine, in particular its mast.

The platform can also be affected by the tidal phenomenon. Thus, the depth H10 of the sea, depending on the location of the platform, can vary significantly, from a few tens of centimeters to more than ten meters. In order to maintain a substantially constant depth of immersion H8, the winches 13 are used to modify the length of the cables 12; thus, the platform can be brought closer to the bottom 7 when the tide is falling, or moved away from it when the tide is rising, while maintaining a sufficient air draft H9 under the bridge 9. The control of the winches is advantageously automated. It can be defined from a digitized table of local tides and/or from a sensor making it possible to estimate an instantaneous H8 immersion depth. The sensor can, for example, be a pressure sensor or a sonar; it can be used to correct or refine tide table values.

In the example described and as particularly illustrated in , the moorings 6 are of a type that can be described as an artificial reef, that is to say designed to limit the impact on the local ecosystem. They are substantially identical to each other.

The mooring 6 illustrated in comprises a concrete block 16. The block 16 is cylindrical; it has a thickness E16, measured vertically in the position of use illustrated, and a diameter D16, measured horizontally in this same position of use. Typically we have E16=about 2m and D16=about 3.5m. The block 16 comprises holes 17 formed irregularly in the block, so as to constitute through passages or niches. These gaps serve as refuges for aquatic fauna. In the example illustrated, the holes 17 are cylindrical in shape, with a substantially horizontal axis X17 and of different diameters D17.

The deadweight 16 further comprises a tangle 18 disposed on the block 16. In the example shown, the tangle consists of tetrapod elements 19; each tetrapod comprising four beams extending in different, non-coplanar directions. The elements are arranged in a substantially random manner and entangled with each other. Thus arranged, the elements 19 constitute a refuge for the aquatic fauna and a support for the flora.

The deadman also comprises a ring 21 supported by posts 22 which connect it to block 16. The ring has substantially the same diameter as block 16. It is arranged substantially above entanglement 18. The ring and the posts form a retaining device for the tetrapod elements. A horizontal bar 23 is fixed diametrically to the ring 21. It carries the pulley 14, serving to return the cable 12.

As specified above, the system 1 is designed for the production of energy and comprises in particular the wind turbine 3. According to the invention, this wind turbine comprises a tubular mast 31 rigidly fixed to the bridge 9 and extending vertically upwards from the bridge. As particularly illustrated in FIGS. 4 and 5, a well 32 extends the mast downwards, through the deck, and as far as an underside of the box 8. The mast and the well together form a rectilinear tubular space 33 which opens towards the top at the top 31A of the mast and down at the base 8A of the box.

As particularly illustrated in , the top 31A of the mast 31 comprises a cradle 34 of which a spherical concavity 34A is oriented upwards.

The wind turbine further comprises a mobile assembly 36 comprising a propeller 37 with a horizontal axis, a nacelle 38, a rod 39, a ball joint 60 and a rocker arm 61. The nacelle 38 comprises means for transforming the wind energy into energy electric.

The ball joint 60 is provided to come to rest on the cradle 34 and cooperate with it to form a ball joint between the movable assembly 36 and the mast 31. The rod 39 extends upwards from the ball joint and it connects the nacelle and the patella between them. Of course, although represented very schematically in , the cradle may be part of a spherical bearing, that is to say cooperating with a substantially spherical ball joint, preventing any translation. A spherical bearing in particular avoids any risk of rebound of the ball joint 60 in its cradle 34.

The pendulum 61 comprises a rod 22 and a counterweight 63. The rod extends downwards from the ball joint, through the passage 33, to below the box 8. The counterweight is fixed at one end bottom of the rod, under the box. The rod and the bead are substantially aligned with each other, along an X36 crew axis. In a rest position, i.e. when the platform and the moving assembly only undergo their own weight and the Archimedes force, the assembly axis X36 coincides with the platform axis X2 . In particular under the action of the wind applied to propeller 37, the crew axis tilts. This inclination is limited by the return force of the pendulum, in particular by the action of the counterweight 63. This arrangement is particularly advantageous since, on the one hand, it eliminates the efforts of embedding the nacelle on the mast and, on the other hand, it allows a reduced section for the rod, which limits the aerodynamic disturbances downstream of the propeller 37.

As specified above, the energy production system 1 comprises, in addition to the wind turbine 3, a pneumatic device 4 for energy production.

Such a pneumatic device 4 is illustrated in FIGS. 7 to 9. It notably comprises a set of bellows 40 and two turbines 41, 42. The turbines are fixed on the bridge 9. The bellows are fixed under the bridge. They are substantially cylindrical. Their number is not imposed. In Figures 1 and 2, the set of bellows is represented by a single bellows; however, a higher number of bellows makes it possible to follow the movements of the swell more precisely, as illustrated in Fig. . In the top view of the , there are thirty-six bellows evenly distributed under deck 9.

In the example illustrated, each bellows comprises an upper plate 43, a base 44 and a deformable wall 46. The plate 43 is fixed under the bridge. The base 44 is floating, so that it can follow the vertical movements of the swell by sliding along a respective vertical guide 47, fixed relative to the deck 9. The wall 46 has a substantially cylindrical shape, around the guide 47 ; it is designed to deform like that of an accordion when the base 44 approaches or moves away from the plate 43, under the action of the swell. The wall is made of an airtight material, for example a rubber or a coated canvas, optionally reinforced with fiber, for example metal fibers. The base 44 can advantageously take the form of a concrete box, an interior volume of which is filled with polystyrene, in order to ensure its buoyancy. Preferably, the density of the base 44 of the bellows is close to the density of water.

The pneumatic device further comprises two buffer volumes 51, 52. A first buffer 51 is connected with a first turbine 41. The other buffer 52 is connected to the second turbine 42. Each bellows is connected, through the plate 43 to each of the two buffers 51, 52 by valves 53, 54 respectively. A first valve 53, connected to the first buffer, opens when the volume of the bellows increases and sucks in air. The surrounding air is sucked into the first buffer and drives the first turbine 41. The sucked air is pooled between all the bellows in the first buffer, which allows a substantially regular drive of the first turbine. The second valve 54, connected to the second buffer 52, opens when the volume of the bellows decreases and rejects air. This air is discharged into the second buffer and drives the second turbine 42, when it joins the atmosphere. The exhaled air is pooled between all the bellows in the second buffer 52 which allows a substantially regular drive of the second turbine 42.

In the example illustrated, the turbines 41, 42 are vertical axis wind turbines, of the Darrieus type, wrapped in a fairing 55. They drive one or more alternators or dynamos, which thus produce electrical energy.

We will now describe a variant of a system 1 according to the invention, in that it differs from the systems previously described, with reference to the .

In this embodiment, the platform 2 is moored to six moorings 6 of the type previously described with reference to the . The six moorings are arranged in a circle, that is to say, in the position of the , substantially regularly distributed around the platform axis X2.

The platform 2 comprises three high recovery points 71, on the edge of the bridge 9, and three low recovery points 72, on the bank of the base 8A of the box 8. They are arranged so that an axial plane passing through a point top 71 and an axial plane passing through a neighboring low point 72 together form an offset angle A7 equal to half of a similar angle between two neighboring high points. That is to say that the low points 72 are regularly offset from the high points 71 around the platform axis X1. In this example, the offset angle A7 is sixty degrees.

Each deadweight 6 is connected to the same high point 71 as one of its two immediate neighboring deadweights and to the same low point as its other immediate neighboring deadweight. This arrangement ensures greater stability of the platform relative to the seabed 7.

In addition, the moorings may include mooring points consisting of pulleys 14, as previously described. The low points 72 can also comprise pulleys, as well as at least two of the high points 71, the third high point comprising an attachment point, for one end of the cable 12, and a winch for the opposite end of the cable. The same cable 12 therefore passes successively through a high point 71, a mooring point 14 and a low point 72, from the attachment point to the winch. Thus, a single winch makes it possible to adjust the altitude of the platform above the bottom 7.

The principle of angular offset of the mooring points is also applied to the embodiment of Figures 1 and 2.

We will now describe a terrestrial variant of a system according to the invention, in that it differs from the systems previously described, with reference to the .

In this embodiment, the wind turbine comprises ball joint means 34, 60 similar to those previously described with reference to the .

Furthermore, the system 1 comprises a concrete block 80 having a buried part 81 and an annular aerial part 82, horizontally movable mounted and resting on the buried part 81. The mast 31 rests on the buried part 81 and rises through of the aerial part 82. A well 132 is formed through the buried part 81 into the ground 83, to receive therein a lower end of the balance 61, in particular the counterweight 63. Transmission means 84 articulated with the balance 61, allow the horizontal movement to be transmitted to the aerial part. The aerial part thus constitutes an inertial mass which resists the effects of the wind, generating a force against the effects of the wind which is added to the restoring force developed by the counterweight. The use of an inertial mass 82 makes it possible to reduce the length of the balance 61 and/or the weight of the counterweight. This arrangement is particularly advantageous in the case of a terrestrial system, so that it avoids or limits the digging of a well 132.

As the embedding forces are reduced by the use of a mast with a ball joint, the buried part 81 of the concrete block can have a reduced thickness E81, which limits the costs and the environmental impact of an onshore wind turbine. In particular, the concrete block can be more easily destroyed, being of a volume and a thickness much lower than those of a block necessary for the anchoring of an onshore wind turbine of the prior art.

We will now describe a variant of the platform, in that it differs from that previously described, in particular with reference to the .

In this variant, the platform 2 comprises two parts 2A, 2B. A first part 2A of the platform comprises the floating box 8. The second part 2B comprises the pneumatic device 4. The second part 2B is mounted to move horizontally, that is to say transversely to the axis of the platform X2, relative to the first part A1. The platform also includes guide and rolling means between the two parts 2A, 2B.

As in the example previously described with reference to the , the second part constitutes an inertial mass 82. The platform further comprises transmission means 84 between the balance 61 and this inertial mass 82.

Of course, the invention is not limited to the examples which have just been described. On the contrary, the invention is defined by the following claims.

It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching which has just been disclosed to them.

Thus, the term cable, used in the description, covers any type of mooring line, flexible, wired, capable of being used to connect the platform to its moorings, in particular a rope or a chain, in any appropriate material, for example steel, or composite materials.

In areas of low tidal range, provision can be made for the cable to be of constant length. In this case, it is not necessary to provide a winch on the deck or a pulley on the moorings, the cable can have a fixed length.

Also, the shapes of the different elements may vary. In particular, the platform can have a rectangular plan instead of a circular one. Thus, the corresponding floating box can be parallelepipedal; it can also be conical.

Also, a bellows may not be directly driven by the swell, but indirectly, for example by a linkage moved by a float driven by the swell. In this case, the bellows can be arranged above the bridge.

In particular in the case of a maritime platform, the swiveling means can be arranged substantially at the level of the deck of the platform, so that the mast has a low height or that there is no need for a mast.

The immersion of the box and the swiveling of the nacelle significantly reduce the forces undergone by the energy production system according to the invention, compared to the systems of the prior art. The quantities of material needed to manufacture such a platform are reduced accordingly, which significantly reduces the cost.

In addition, the stability of the moving assembly is improved. As a result, the wind turbine propeller is generally closer to a vertical plane, in a wider wind speed range. The performance of the wind turbine is therefore significantly improved by the improvements made by the invention.

Thus, a system according to the invention has all or some of the following advantages:

- reduction of the movements resulting from the deformations of the surface of the liquid, since it includes means which make it possible to immerse the caisson under the zone of turbulence of the surface of the sea, and to maintain it there;

- lowering of the center of transmission of forces due to the wind in the wind turbine; this arrangement makes it possible to reduce the moment applied to the center of gravity of the box, and therefore the cost and the impact on the environment;

- maintenance in a substantially vertical plane of the surface described by the blades of the wind turbine, without increasing the buoyancy volume necessary to balance the dead weight of the structures of the offshore assembly; this arrangement makes it possible to considerably reduce the quantities of materials used in the known systems, generally reinforced concrete or steel;

- recovery of wave energy produced by the deformation of the surface of the water body under the action of the wind;

- reduction of the sections of the disturbing masts for the flow of the wind on the blades. This increases the performance of the vertical wind turbine;

- reduction of the quantities of material necessary for the manufacture of such a platform, thanks to a better distribution of the reactions of the forces and the suppression of the movements caused by the swell, which notably reduces the cost and its environmental impact.

The pneumatic device of the offshore system allows an additional energy production estimated at approximately 4% of the energy produced thanks to an offshore electrical energy production system according to the invention.

Of course, a platform or a platform system according to the invention is not limited to a use for the production of electricity, it can comprise only a wind turbine with a horizontal axis, or only pneumatic means of energy production. Such a platform can also be used to carry dwellings or serve as a wharf or floating bridge.

Also, the pneumatic device can comprise more than two turbines, for example four or six.

Claims (6)

Floating platform system (1), characterized in that it comprises a floating platform (2), moorings (6) and cables (12) for connecting said platform to said moorings, said platform comprising a floating box (8), a deck (9) disposed above said casing and means, preferably props (11), for holding said deck fixed to said casing, the casing (8) being kept submerged at a depth (H8) below the surface of the water (10, P100) and the deck being kept out of the water. System according to Claim 1, characterized in that the floating box has a volume capable of generating an Archimedean thrust greater than the weight of the system. System according to one of Claims 1 and 2, characterized in that it comprises winch means for adjusting the lengths of the cables, in particular according to the tides, in particular for maintaining or for adjusting the depth of immersion (H8) of the box (8). System according to one of Claims 1 to 3, characterized in that the depth of immersion (H8) is at least equal to half of a predictable wavelength (L100) for swell (100). System according to one of Claims 1 to 4, characterized in that the depth of immersion (H8) is at least equal to the foreseeable amplitude (H100) for the swell (100). System according to one of Claims 1 to 5, characterized in that it comprises means for producing electrical energy, preferably a wind turbine (3) mounted on the platform (2), even more preferably a wind turbine with an axis horizontal.