Wave energy device.

Abstract

The invention relates to a wave energy recovery device comprising a structure (1) intended to float and be anchored to a seabed, in use, this structure comprising at least a first and a second wall (10, 11), one of them (10) comprising at least a first opening and a first flap (101) mounted inside said at least a first opening being rotationally movable about a first axis, so as to be able to be moved in rotation about said first axis under the effect of the wave and generate, in operation, mechanical energy, two adjacent walls of the structure being connected together by means of a float (12) to form a polygonal structure having a bottom and an upper part opposite each other, device in which the first and second walls are non-coplanar,The device also includes means for converting the mechanical energy of the shutters into electrical energy. Fig. 1,

Description

Title of the invention: Wave energy device.

[0001] The present invention falls within the general field of renewable energies and more particularly the recovery of wave energy in electrical form.

[0002] More specifically, the invention is designed to also allow, in addition to wave energy recovery, wind energy and / or solar thermal and / or photovoltaic energy recovery.

[0003] Several wave energy devices have already been proposed.

[0004] Thus, document FR2981992 describes a wave energy recovery device comprising several liquid-filled compartments. The wave creates a difference in liquid height between the compartments and a flow of liquid from one compartment to another, this flow driving a turbine.

[0005] This device is designed to float and can therefore be installed in the open sea.

[0006] However, it has the disadvantage of being of a complex design.

[0007] Document FR3102492 describes a wave attenuation device which also allows wave energy to be converted into electrical energy.

[0008] This device comprises a movable flap rotating about an axis and which can be rotated in two opposite directions under the effect of the swell. The device includes a piston which is driven in translation by the rotation of the flap and which is associated with a valve regulating the flow of hydraulic fluid displaced by the piston so as to drive a hydroelectric generator.

[0009] This device is very effective at attenuating swell, particularly due to the presence of a porous wall located downstream of the flap relative to the direction of wave propagation, but it is not primarily designed for energy recovery. Moreover, the fixed distance between the flap and the skirt necessarily limits this recovery.

[0010] Other systems are under development, including hybrid platforms designed to capture wave energy and support wind turbines. Anchoring these platforms is complex and costly. They themselves must be oversized to withstand environmental conditions. Otherwise, they are not suitable for a very wide wave spectrum.

[0011] The invention aims to overcome these drawbacks by providing a wave energy recovery device with a simple, modular, and robust structure, and whose efficiency can be easily optimized. This device will hereafter be referred to as a wave energy converter.

[0012] Another object of the invention is to provide a wave energy converter that can serve as a support structure for other energy recovery systems, such as wind turbines or photovoltaic panels.

[0013] To this end, an object of the invention is to propose a wave recovery device comprising a structure intended to float and to be anchored on a seabed, in use, this structure comprising at least a first and a second wall, one of them comprising at least a first opening and a first flap mounted inside said at least a first opening being mobile in rotation about a first axis, so as to be able to be moved in rotation about said first axis under the effect of the wave and to generate, in operation, mechanical energy, two adjacent walls of the structure being connected together by means of a float to form a polygonal structure having a bottom and an upper part opposite each other, device in which the first and second walls are non-coplanar, the device also comprising means for converting the mechanical energy of the flaps into electrical energy.

[0014] According to particular embodiments:

[0015] The second wall of this wave recovery device includes at least a second opening and a second flap mounted inside the second opening and being movable in rotation around a second axis.

[0016] The axis of a flap of the present device is substantially parallel to said background.

[0017] The means for converting the device according to the invention comprise, connected to each of the flaps of the structure, at least one piston driven in translation by said flap.

[0018] The bottom of the device according to the invention is partially closed.

[0019] The structure of the device according to the invention comprises at least three walls connected together so as to form an outer ring, said structure being closed.

[0020] At least one of said walls of the device according to the invention is solid.

[0021] Said structure comprises at least five walls connected to each other, at least four of them forming an outer ring and at least one of them being placed inside said ring.

[0022] Said structure supports at least one wind turbine and / or a photovoltaic power plant.

[0023] At least one float of said structure and / or at least one wall provided with a flap of said structure includes a box enlarged on the bottom side of said structure.

[0024] At least one of the flaps of said structure has a general concave shape, the concavity being turned towards the interior of said structure.

[0025] Other features of the invention will be set forth in the detailed description below, made with reference to the accompanying figures, given by way of example, and which respectively represent:

[0026] [Fig. 1], a schematic top view of a first embodiment of a wave energy device according to the invention, the structure of which comprises two walls;

[0027] [Fig.2], a schematic front view of a wall of the wave energy device of [Fig.1];

[0028] [Fig.3], a schematic top view of a second embodiment of a wave energy device according to the invention, comprising three walls arranged in a triangle;

[0029] [Fig.4], a schematic top view of a third embodiment of a wave energy device according to the invention, comprising nine walls forming a general triangular structure;

[0030] [Fig.5], a schematic top view of a fourth embodiment of a wave energy device according to the invention, comprising four walls arranged in a square;

[0031] [Fig.6], a schematic top view of a fifth embodiment of a wave energy device according to the invention, comprising nine walls forming a general hexagonal structure which supports wind turbines;

[0032] [Fig.7], a schematic side view along arrow VI of the device illustrated in [Fig.6];

[0033] [Fig.8], a schematic top perspective view of a sixth embodiment of a wave energy device according to the invention, comprising twelve walls arranged in a polygon;

[0034] [Fig.9], a schematic view of the wave energy converter device illustrating the means of energy conversion;

[0035] [Fig. 10],

[0036] [Fig. 11], and

[0037] [Fig. 12], illustrate side views of different variants of the shutter implementation;

[0038] [Fig. 13],

[0039] [Fig. 14],

[0040] [Fig. 15],

[0041] [Fig. 16],

[0042] [Fig. 17] illustrate side views of different embodiments of the piston(s). means of energy conversion;

[0043] [Fig. 18], a schematic side view of a variant of the wall of the structure of a wave energy device according to the invention.

[0044] In what follows, the same elements will be designated by the same reference numbers.

[0045] With reference to figures 1 and 2, in this first embodiment, the structure 1 of the wave energy device comprises two walls 10, 11 connected to each other by a float 12. These two walls make a non-zero angle with each other or, in other words, are non-coplanar.

[0046] In this example, the structure also includes a float 13 fixed to the end free of the wall 10, opposite the float 12, as well as a float 14 fixed to the free end of the wall 11, opposite the float 12. This embodiment is preferred but these two floats 13 and 14 could nevertheless be omitted.

[0047] This structure therefore has a base 15 and an upper part 16. The latter can be open or closed. Furthermore, the base 15 is preferably partially closed, for example by plates (not shown in the figures). These plates have an anti-pounding effect.

[0048] The wall 10 has an opening 100, while the wall 11 is solid. A flap 101 is mounted in the opening 100, which rotates about an axis 102 that lies in the plane of the wall 11, substantially parallel to the bottom of the structure, or substantially horizontal when the structure 1 is placed on a flat surface. This orientation has the advantage of allowing the flap to return to its original position under the action of gravity.

[0049] The opening 100 here has a rectangular shape but other shapes can be envisaged, such as that illustrated in [Fig.7].

[0050] The flap 101 is shown here in the form of a flat rectangular plate. Other shapes can be considered, particularly to take into account the shape of the plate opening. Furthermore, other profiles are illustrated in Figures 10 to 12.

[0051] Figure 2 shows that the floats 12 and 13 are fitted, on their bottom side 15, with a box 17, 18 whose cross-section is wider than that of the floats and whose height is less than this cross-section. Each box thus widens the base of a float and helps to reduce the heaving effect. However, the invention is not limited to this embodiment, and these boxes could be omitted.

[0052] Figure 3 illustrates a second embodiment in which the structure 2 of the wave energy converter comprises three walls 20, 21, 22 connected by three floats 23, 24, 25. These three walls are not coplanar and form a non-zero angle with each other in pairs. In this example, the walls are substantially identical, so structure 2 has the shape of an equilateral triangle and this angle is 60°.

[0053] This structure 2 has a base and an upper part (not referenced in the figure).

[0054] Walls 20 and 21 each have an opening (not referenced in the figure), while wall 22 is solid. In each of the openings is provided a shutter 201, 211, movable in rotation about an axis (not referenced in the figure) which extends in the plane of the wall in which it is provided and which is substantially parallel to the bottom of the structure or substantially horizontal when the structure 2 is placed on a flat support.

[0055] This structure forms an outer ring, that is to say a closed structure, unlike structure 1 illustrated in [Fig. 1] which is an open structure. From this In fact, as will be explained in more detail later in the description, resonance can be obtained inside this closed structure.

[0056] This second embodiment also includes variations. Thus, the wall 22 could have an opening fitted with a shutter and / or be solid.

[0057] In the third embodiment illustrated in [Fig.4], the structure 3 of the wave energy device comprises nine walls 30 to 38 connected to each other by six floats 39a to 39f. These nine walls are non-coplanar and form a non-zero angle with each other in pairs.

[0058] This structure 3 has a base and an upper part (not referenced in the figure).

[0059] The six walls 30 to 35 are connected to each other by the floats so as to form an outer ring in the shape of a triangle. In this example, the walls are substantially identical and each face of the triangle has two walls, the outer ring therefore having the shape of an equilateral triangle and the structure 3 is closed.

[0060] Thus, the walls 30, 31, respectively 32, 33, and respectively 34, 35 are coplanar. On the other hand, the walls 30, 31 form a non-zero angle with the walls 32, 33 and 34, 35 respectively. This angle is 60°.

[0061] Each of the six walls 30 to 35 has an opening (not referenced in the figure) in which is mounted a shutter 301 to 351, movable in rotation around an axis (not referenced in the figure) which extends in the plane of the wall in which it is provided and which is substantially parallel to the bottom of the structure or substantially horizontal when the structure 3 is placed on a flat support.

[0062] Within this outer ring, three other walls 36 to 38 are provided, which are connected to each other by means of floats 39b, 39d, and 39f. These three walls 36 to 38 are not coplanar and form a non-zero angle with each other in pairs. In this example, the walls are substantially identical, thus forming an equilateral triangle, and this angle is 60°.

[0063] These three walls 36 to 38 are solid.

[0064] This third embodiment also includes variations. Thus, one or more of the walls 36 to 38 could have an opening with or without a shutter and / or one or more of the walls 30 to 35 could be without a shutter or solid.

[0065] Figure 5 illustrates a fourth embodiment in which the structure 4 of the wave energy converter comprises four walls 40 to 43 connected by four floats 44 to 47 to form an outer ring. These four walls are non-coplanar and form a non-zero angle with each other in pairs. In this example, the walls are substantially identical, the structure 4 has the shape of a square, and this angle is 90°. This is also a closed structure.

[0066] This structure 4 has a base and an upper part (not referenced in the figure).

[0067] Each of the opposite walls 40 and 42 has an opening (not referenced in the figure) in which is mounted a shutter 401 and 421, movable in rotation around an axis (not referenced in the figure) which extends in the plane of the wall in which it is provided and which is substantially parallel to the bottom of the structure or substantially horizontal when the structure 4 is placed on a flat support.

[0068] Each of the opposite walls 41 and 43 are solid.

[0069] This fourth embodiment also includes variations. For example, one of the walls 40, 42 could be without a flap or solid. Furthermore, one or both of the walls 41, 43 could have an opening, with or without a flap. Finally, another wall (not shown in the figure) could be fixed between the floats 45 and 47 and thus be located inside the outer belt.

[0070] Figures 6 and 7 illustrate a fifth embodiment in which the structure 5 of the wave energy device comprises ten walls 50 to 59 connected to each other by seven floats 60 to 66. These ten walls are non-coplanar and make a non-zero angle with each other, two by two.

[0071] This structure 5 has a base 66 and an upper part 67. The six walls 50 to 55 are connected to each other by the floats 60 to 65 so as to form an outer ring in the shape of a regular hexagon, the walls being substantially identical. The internal angle between two adjacent walls of the outer ring is approximately 120°.

[0072] Within this outer ring, the four other walls 56 to 59 are provided, which are connected to each other via the float 66 and to the outer ring via one of the floats 60 to 65. The structure 5 is a closed structure. These four walls 56 to 59 are not coplanar and form a non-zero angle with each other in pairs. In this example, all the walls are substantially identical and the angle between two adjacent walls of the structure is 60°.

[0073] Each of the ten walls 50 to 59 has an opening. Only the openings 520 to 540 of the walls 52 to 54 and the axes of rotation 522 to 542 of the shutters 521 to 541 are shown in [Fig. 7]. In each opening, a shutter 501 to 591 is mounted, which rotates about an axis (not referenced in [Fig. 6]) that is substantially parallel to the bottom of the structure or substantially horizontal when the structure 5 is placed on a flat surface. Each axis extends in the plane of the wall in which it is located. Furthermore, [Fig. 7] shows that the axes lie in the same substantially horizontal plane when the structure 5 is placed on a flat surface.

[0074] Figure 7 shows that the floats 62 to 65 are fitted, on the bottom side 60, with a box 62a to 65a whose cross-section is wider than that of the floats and whose height is smaller than this section. Each box therefore widens the base of a float and helps to reduce the heaving effect. However, the invention is not limited to this embodiment, and these boxes could be omitted.

[0075] Openings 520 to 540 are here in the shape of an irregular hexagon, but other shapes could be considered. Each shutter is in the form of a flat plate whose contour is adapted to that of the opening.

[0076] This fifth embodiment also includes variations. Thus, one or more of the walls 50 to 59 could be without shutters or solid.

[0077] In this embodiment, the wave energy converter supports wind turbines on the upper part 67 of the structure 5. In practice, each wind turbine 600 to 660 is fixed to a float of the structure 5.

[0078] The wind turbines illustrated in Figures 6 and 7 are vertical-axis wind turbines described in document EP3426917. Compared to horizontal-axis wind turbines, they have the advantage of maintaining their performance despite the movement of the floats, even at angles of heel / pitch of up to 10°. The use of such wind turbines therefore allows for a reduction in the size and weight of the floats, and consequently, in the anchoring forces.

[0079] Figure 8 illustrates a sixth embodiment in which the wave energy converter structure 7 comprises twelve walls 700 to 711 connected to each other in pairs by twelve floats 712 to 723 to form a polygonal outer ring. Structure 7 is again a closed structure. These twelve walls are not coplanar and form a non-zero angle with each other in pairs. In this example, the walls are substantially identical, and this angle is 150°.

[0080] This structure 7 has a base and an upper part (not referenced in the figure).

[0081] Each of the twelve walls 700 to 711 has an opening (not shown in the figure). In each opening, a shutter 730 to 741 is mounted, movable in rotation about an axis (not referenced in the figure) which extends in the plane of the wall in which it is provided and which is substantially parallel to the bottom of the structure or substantially horizontal when the structure 7 is placed on a flat support.

[0082] This sixth embodiment also includes variations. Thus, one or more of the walls 700 to 711 could be without shutters or solid.

[0083] The operation of the wave energy device according to the invention will now be described with reference to [Fig. 9]. This description focuses on the device illustrated in [Fig. 2] but can be applied to all the devices described.

[0084] It should first be specified that in operation, the floats are anchored to the seabed by anchors, moorings or any other system connected by textile lines and / or chains.

[0085] Furthermore, each structure is dimensioned so that, in operation, each flap is preferably immersed to about 3 / 4.

[0086] The swell thus causes an alternating rotational movement of each flap 201, 211 of the structure around its axis. Indeed, each flap behaves like a movable barrier that creates a difference in water height between the upstream and downstream sides of the flap, and therefore a differential pressure on the height of the flap. This pressure itself creates a force that generates a moment around the axis of rotation of the flap and produces an angular velocity, and therefore mechanical energy.

[0087] Fig. 9 illustrates an example of means 8 for converting the mechanical energy of flap 201. These means can be provided for each flap, for example flap 201 of structure 2, or partially shared.

[0088] These means 8 here comprise a piston 80 driven in translation by the rotation of the flap 201, for example by means of a connecting rod 81 which connects the piston to the flap. The piston moves inside a cylinder 82 which extends vertically (or in the plane of the flap at rest). In this embodiment, the connecting rod 81 vertically connects the piston 80 to the flap 201 at rest; that is to say, in this rest position where the flap 201 is vertical, the connecting rod 81 is aligned with the piston 80 and is in the plane of the flap 201.

[0089] Other embodiments will be described with reference to Figures 13 to 17.

[0090] The piston is associated with a regulating valve 83 which regulates the flow of fluid hy The hydraulic fluid is displaced by the piston towards low- and high-pressure reservoirs 84, 85, generating a flow that drives a hydroelectric generator 86 by pressure difference. The reservoirs and the generator are connected by a hydraulic circuit. The hydroelectric generator 86 comprises a hydraulic turbine 86a connected to an electric generator 86b, which converts torque and rotation into electricity. The electrical current produced by the generator is then transmitted onshore to an electrical grid 87 or to storage facilities (not shown). It can also be consumed on-site, particularly when the device is integrated into an offshore platform.

[0091] The conversion means also include control means 88 which are capable of regulating the electrical power or voltage generated by the generator 86 according to the kinetic energy of the swell and thus the rotation of the flap. Thanks to this control, the energy extracted by the generator slows the hydraulic turbine, which increases the pressure in the hydraulic circuit and slows the pistons, thus slowing the flap. This control makes it possible, in particular, to optimize energy recovery according to the sea state.

[0092] Since structure 2 illustrated in [Fig. 3] is a closed structure, a resonance phenomenon can occur within the structure, producing an increase in This involves adjusting the amplitudes of the sea's free surface. This optimizes energy recovery. The same applies to the devices illustrated in figures 4 to 8.

[0093] To obtain such resonance, it is preferable that the structure of the device has solid walls or walls with a flap on its outer ring, walls with an opening without a flap being provided rather inside this ring (if such walls are present).

[0094] It is also noted that the wave energy devices according to the invention allow multidirectional wave recovery, while being in a fixed position, which also optimizes energy recovery while avoiding the presence of complex connectors between the export cables and the device.

[0095] Generally, in all embodiments, the upper part of the wave energy device structure can be open or closed. Furthermore, the bottom is preferably partially closed, for example by plates (not shown in the figures) which have an anti-pounding effect.

[0096] By way of illustration, the length of a wall of the device is advantageously between 20 and 100 meters. This is why the structure, and in particular its walls, can be designed to integrate energy conversion means, energy storage means, and also the various means associated with wind turbines when these are planned.

[0097] The present invention shall not be limited by the embodiments described, including those represented in the drawings or illustrated in the specifications, which are given by way of example or illustration and not by way of limitation.

[0098] The floats can be made of metal, composite fibers, concrete or any other material suitable for their functions and constraints.

[0099] Other variants of the invention may still be envisaged.

[0100] Thus, a wall may have several openings and not just one opening, each of them being fitted with a shutter.

[0101] Furthermore, the axis of rotation of a flap could have a different orientation than that previously described, for example perpendicular to the bottom.

[0102] The floats preferably have a stacked shape, and in particular the shape of a cylinder with a polygonal or elliptical round cross-section. However, the invention is not limited to this embodiment and other float shapes could be considered.

[0103] The floats may or may not be fitted with a box widening their base, as described with reference to [Fig.2] or 7.

[0104] Furthermore, as illustrated in [Fig. 18], any wall of the structure, for example wall 10, may also include, on the bottom side of the structure, a box 103 whose cross-section is wider than that of the wall and whose height is in less than this section. Each box therefore widens the base of a wall and helps to reduce the heaving effect.

[0105] A flap can be made of any material suitable for use at sea, the density of which is strictly greater than 1. Density is defined here as the ratio between the mass density of the material and the mass density of seawater. Preferably, the density is also less than 5.

[0106] A flap of the wave energy converter is not necessarily a flat plate. It may have a concave shape as illustrated in Figures 10 to 12. The flap 800 shown in [Fig. 10] has the shape of a quarter of an ellipse in side view. The flap 801 shown in [Fig. 11] has the shape of a half-ellipse in side view, while the flap 802 shown in [Fig. 12] has the shape of a spoon in side view. Other concave shapes could also be considered.

[0107] In all cases, the flap is mounted in the structure of the wave energy converter such that the concavity faces either inwards towards the structure or downstream of the wave. These particular shapes increase the amount of energy recovered from the wave.

[0108] The wave energy device can also serve as a support for other types of wind turbines, an offshore photovoltaic power plant or any other application at sea requiring a large area and energy to operate.

[0109] The piston of the wave energy conversion means can take different forms which are illustrated in figures 13 to 17.

[0110] Thus, still with reference to the flap 201 of structure 2, [Fig. 13] shows that the flap 201 is connected to two pistons 90, 91 which each slide in a cylinder 90a, 91a extending vertically (or in a plane parallel to that of the flap), the connection between the flap and each piston being obtained by means of a connecting rod 90b, 91b. In this embodiment, each connecting rod 90b, 91b horizontally connects each piston 90, 91 to the flap 201 at rest, that is to say that, in this rest position where the flap 201 is vertical, each connecting rod 90b, 91b is perpendicular to a piston 90, 91 and to the plane of the flap 201.

[0111] Figure 14 illustrates a piston 92 sliding in a cylinder 92a extending horizontally (or perpendicularly to the flap 201), the connection between the flap and the piston being obtained by means of a connecting rod 92b. In this embodiment, the connecting rod 92b connects the piston 92 to the flap 201, such that, in the rest position where the flap 201 is vertical, the connecting rod 81 is perpendicular to the piston 92 and lies in the plane of the flap 201.

[0112] Figure 15 illustrates a piston 93 sliding in a vertically extending cylinder 93a, the connection between the flap and the piston being achieved via a connecting rod 93b. In this embodiment, the connecting rod 93b connects the piston 93 to the flap 201, such that, in the rest position where the flap 201 is vertical, the connecting rod 81 is perpendicular to the piston 93 and to the plane of the flap 201.

[0113] Figure 16 illustrates the flap 201 connected to two pistons 94 and 95, each sliding within a cylinder 94a, 95a extending at an angle and symmetrically with respect to the plane defined by the flap 201, the angle between each piston and this plane being acute. The connection between the flap and each piston is achieved by means of a single connecting rod 98.

[0114] Figure 17 illustrates the flap 201 connected to two pistons 96 and 97, each sliding within a cylinder 96a, 97a extending at an angle and symmetrically with respect to the plane defined by the flap 201, the angle between each piston and this plane being obtuse. The connection between the flap and each piston is achieved by means of a single connecting rod 99.

Claims

Demands

1. Wave energy recovery device comprising a structure (1, 2, 3, 4, 5, 7) intended to float and be anchored to a seabed, in use, this structure comprising at least a first and a second wall (10, 11; 20, 21, 22; 30 to 38; 40 to 43; 50 to 59; 700 to 711), one of them (10; 20, 21; 30 to 35; 40, 42; 50 to 59; 700 to 711) comprising at least a first opening (100; 520, 530, 540) and a first flap (101; 201, 211; 301 to 351; 401, 421; 501 to 551; 730 to 741) mounted inside said at least a first opening being mobile in rotation around a first axis (102; 522,532,542) so as to be able to be moved in rotation around said first axis under the effect of the swell and generate, in operation, mechanical energy, two adjacent walls of the structure being connected together by means of a float (12; 23,24,25; 39a to 39f; 44 to 47; 60 to 66;712 to 723) to form a polygonal structure having a bottom (15; 60) and an upper part (16; 67) opposite each other, the first axis of rotation (102; 522, 532, 542) being substantially parallel to said bottom and the first flap being vertical in the rest position, device in which the first and second walls are non-coplanar, each flap behaving in operation as a movable barrier which creates a differential pressure on the height of the flap, which generates mechanical energy, the device also comprising means for converting (8) the mechanical energy of the flaps into electrical energy.;

2. Device according to claim 1 in which said second wall (21) comprises at least a second opening and a second flap (201) mounted inside the second opening and being movable in rotation about a second axis.

3. Device according to claim 2 in which the second axis of rotation is substantially parallel to said base, the second flap being vertical in the rest position.

4. Device according to any one of claims 1 to 3 in which said conversion means (9) comprise, connected to each of the flaps of the structure, at least one piston (80) driven in translation by said flap (201).

5. Device according to any one of claims 1 to 4 in which said bottom is partially closed.

6. Device according to any one of claims 1 to 3 in which said structure (2, 3, 4, 5, 7) comprises at least three walls (20, 21, 22; 30 to 38; 40 to 43; 50 to 59; 700 to 711) connected together so as to form an outer ring, said structure being closed.

7. Device according to any one of claims 1 to 6 in which at least one of said walls is solid.

8. Device according to any one of claims 1 to 7 in which said structure (3, 4, 5, 7) comprises at least five walls connected together, at least four of them (30 to 35; 40 to 43; 50 to 55) forming an outer ring and at least one of them (36 to 37; 56 to 59) being placed inside said ring.

9. Device according to any one of claims 1 to 8 wherein said structure supports at least one wind turbine and / or a photovoltaic power plant.

10. Device according to any one of claims 1 to 9 in which at least one float (12,13; 62 to 65) of said structure and / or at least one wall (10) provided with a flap of said structure comprises an enlarged box (17,18; 62a to 65a; 103) on the bottom side of said structure.

11. Device according to any one of claims 1 to 10 wherein at least one of the flaps of said structure has a generally concave shape, the concavity being turned towards the interior of said structure.

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