Method for preventing scouring

Abstract

The invention relates to a method for preventing the scouring of the ground at the foot of an object placed in the flow of a fluid and to a system for implementing the method. The method consists in positioning a perforated barrier (24) at least partially around the base of the object (21) such that the perforated barrier (24) is, at least at one point, orthogonal to the direction of the flow of the fluid (22), in order to at least partially reduce the level of turbulence of the flow of the fluid (22) as it passes through the perforated barrier (24). In addition, an element (25) for stopping the fluid (22), which extends from the object (21) to the perforated barrier (24), is positioned at a height h above the ground (23) in a substantially horizontal plane or a plane substantially parallel to the ground (23), the element for stopping the fluid being a solid element.

Description

[0001] Method for preventing scouring

[0002] Scope of the invention

[0003] The present invention relates to a method and structure for preventing the excavation of particulate soil at the base of an object.

[0004] Description of the state of the art

[0005] Soil erosion at the base of objects, particularly underwater objects, is well known in the construction field. It is a specific type of erosion characterized by the localized deepening of the soil at the base of an object placed in a fluid flow. If left untreated, the object, subjected to scour at its base, risks a loss of stability that could compromise its integrity. Soils prone to scour are particulate soils, i.e., material media composed of particles that can be displaced by contact with the moving fluid. Examples of particulate soils include sand, clay, and pebbles.

[0006] A fluid is defined as a deformable material medium. The term "fluid" encompasses all liquids, gases, and plasmas. A fluid can be, for example, water, such as seawater or river water undergoing currents, or even ambient air. The flow of a fluid is characterized, at any given moment, by, among other things, its general direction, its average velocity, and its level of turbulence.

[0007] Objects subject to excavation include diverse and varied geometries such as, for example, river / ocean bridge piers, foundations on sand (such as wind turbines, antennas, photovoltaic panels, offshore platforms), underwater anchors, jack-up ship feet, submarine cables, pipelines, dock foundations, etc.

[0008] For a given object, particulate soil, and fluid, the intensity of scouring is primarily determined by the velocity and level of turbulence of the fluid flow at the base of that object. In turbulent flow, the fluid moves chaotically with eddies, transverse movements relative to the general flow direction, and oscillatory movements, as is the case with regular or irregular waves. With or without an object, friction due to the current or waves already causes overall erosion of the soil particles. When, in addition, an object obstructs the flow of a fluid, several phenomena are observed that cause scouring of the particulate soil, which are illustrated in particular in Figure 19 (Figure 4.3 of the book Scouring,

[0009] HNC Breusers & AJ Raudkivi (1991) ) with their English terminology:

[0010] • Not applicable (1) which obstructs the fluid, friction due to current (2) and / or waves can cause the displacement of soil particles (3) and generates overall erosion.

[0011] • Any object that obstructs the flow of a fluid creates a local increase in the flow velocity around its walls, which increases friction and therefore erosion.

[0012] • When a flow comes into contact with an object, part of the flow is deflected vertically downwards (4), towards the particulate soil (3). This deflection causes localized erosion around the base of the object. This erosion alters the behavior of horizontal flows, causing them to detach. This phenomenon then generates large horseshoe-shaped vortices (5), which wrap around the base of the object and accentuate the erosion of the surrounding soil.

[0013] • When the flow detaches from the object's walls, this generates even more instability, and therefore turbulence and consequently erosion. We observe the formation of wake vortices (6) which develop downstream and along the entire height of the object and which cause erosion of the particulate soil in its wake.

[0014] The concept of turbulence as used in this document therefore includes at least the state of a fluid whose flow is irregular such that at every point in space and time its properties vary randomly.

[0015] Various devices and processes have been proposed, particularly in the offshore wind energy sector, to try to eliminate the phenomenon of scouring at the base of underwater foundations. Currently, the most common method consists of depositing large pebbles all around the base of the object. In this way, the pebbles form an intermediate layer, and the fluid no longer rubs against the particulate soil. However, over time, the layer of pebbles spreads out, and thus the particulate soil reappears at the base of the object. This process is also expensive and polluting because it requires transporting a significant quantity of pebbles by ship. Furthermore, there are no solutions for dismantling the product at the end of its life. In reality, this process bypasses the problem rather than addressing its cause: namely, the increased level of turbulence near the object.The applicant therefore deemed it necessary to propose a process to reduce the level of turbulence of the fluid flow near the base of the object in order to mitigate at least part of the excavation of the particulate soil.

[0016] Solution to the invention

[0017] The invention consists of a method for preventing the excavation of particulate soil at the base of an object placed in the flow of a fluid, according to which, in order to reduce at least in part the level of turbulence of the flow of the fluid, a perforated barrier is positioned at least in part around the base of said object so that the perforated barrier is at least at one point orthogonal to the direction of the flow of the fluid and allows the passage of the fluid through it, said method being characterized in that a fluid stopping element extending from the object towards the perforated barrier is positioned in a substantially horizontal plane or substantially parallel to the ground, said fluid stopping element being a solid element.

[0018] PA? i_èr e_ _ajou_r é e

[0019] The perforated barrier is a barrier comprising openings allowing the fluid, and therefore the flow of the fluid, to pass through it completely.

[0020] The barrier has a length, a height, and a thickness, i.e., a three-dimensional structure. Its purpose is not to block the fluid flow but to reduce the level of turbulence downstream of the barrier compared to the level of turbulence upstream. The perforated barrier makes the fluid flow less turbulent, reducing turbulence by, for example, breaking larger vortices into smaller ones and dampening the fluid's transverse and oscillatory movements. The barrier tends to homogenize the flow properties.

[0021] The barrier can be positioned at least partially in the ground, on the ground, or close to the ground, for example by being suspended. In any case, it must be close enough to the ground to prevent turbulent flow from reaching the walls of the object without passing through it.

[0022] For example, the barrier can be partially buried, which allows it to be fixed to the ground.

[0023] Each opening in the barrier is designed to act as a flow-stabilizing element, reducing vortex size and dampening transverse movements. The geometry of the openings is determined by several parameters, including fluid characteristics (viscosity, density, etc.), fluid flow characteristics (average velocity, general direction, initial turbulence level, etc.), the nature of the particulate soil, the geometry of the object, and its position, etc.

[0024] The size and geometry of the openings must anticipate potential fouling during the operational life of the perforated barrier. For example, the openings must be designed with a geometric margin to prevent fouling from obstructing the perforated barrier and impairing its effectiveness.

[0025] For example, the perforated barrier includes a mesh, such as a wire mesh, grid, or net—in other words, a network of wires or bars arranged in a regular pattern, creating openings for the passage of fluid. Each opening is designed to break down larger vortices into smaller ones, and this mesh consequently reduces the level of turbulence in the fluid flow passing through it.

[0026] If the fluid flow direction is essentially fixed, the perforated barrier can incorporate a honeycomb structure facing the flow. The openings in this structure are parallel hexagonal channels, parallel to each other and to the flow direction. These hexagonal channels are arranged to force the fluid to follow straight, parallel paths, which reduces vortex size and dampens cross-flow motion. The fluid flow downstream of the honeycomb exhibits a lower level of turbulence than the fluid flow upstream.

[0027] If the fluid flow direction is essentially fixed, the perforated barrier can include capillary tubes, parallel to the flow direction, arranged to force the fluid to follow straight, parallel paths, thus reducing vortex size and dampening transverse motion. The fluid flow downstream of the capillary tubes exhibits a lower level of turbulence than the fluid flow upstream.

[0028] The barrier may consist of substantially horizontal and parallel plates or slats arranged to force the fluid to follow parallel paths, thereby reducing vortex size and dampening transverse motion. The barrier may also consist of a perforated sheet. The perforations may be of any suitable shape, arranged to force the fluid to follow parallel paths, thereby reducing vortex size and dampening transverse motion. Finally, the barrier may be a rigid 3D structure with regular or irregular porosity, in which the level of flow turbulence decreases as the fluid moves through the 3D structure. The structure's porosity is arranged to break larger vortices into smaller ones and disrupt the fluid's transverse and oscillatory motion.

[0029] The openwork barrier may include a mesh, a honeycomb structure, capillary tubes, horizontal plates, perforated sheet metal and / or a 3D structure.

[0030] If the openwork barrier is made entirely or partially of metal, its metal components can be welded, bolted, or riveted. For other materials, the assembly technique must be appropriate for the material. The barrier could, for example, be made from rope.

[0031] The geometry of the openwork barrier depends primarily on the shape of the object for which it is intended.

[0032] When the barrier is thin (mesh, wire mesh, perforated sheet metal, etc.) it is preferably arranged so as not to be in direct contact with the object, i.e. the barrier is positioned at a non-zero distance D from the object, and this at least at the point where the barrier is orthogonal to the direction of the fluid.

[0033] When the barrier is thick (honeycomb, capillary tubes, plates / slats, ...), the distance between the barrier and the object can be zero or non-zero.

[0034] The "fluid direction" here, and generally throughout the invention, refers to its local direction at the point of contact with the barrier. Indeed, the level of turbulence in the flow must be reduced, by passing through the openings, sufficiently far from the object so as not to cause the disturbance of the particulate soil at the base of the object. The distance at which the barrier must be placed depends on the dimensions.

[0035] The geometry of the perforated barrier is not necessarily a homothetic reflection of the object's contours. For example, a square object can be enclosed by a circular barrier. Similarly, a circular object can be enclosed by a polygonal barrier. Preferably, the barrier is positioned on the ground along a curve. This curve may include angles preferably less than 30°. This means that the surface of the perforated barrier does not include abrupt changes in direction to avoid creating localized excavation at the point of change. Preferably, changes in direction within the surface of the perforated barrier are less than 30°.

[0036] The term "barrier" means that it is positioned so that the fluid flow passes through it before reaching the object's contours. To this end, the barrier is positioned at least partially around the object's base so that the perforated barrier is at least at one point orthogonal to the general direction of the fluid flow. The precise positioning of the perforated barrier depends on the object's geometry and on knowledge and evolution of the fluid's general direction.

[0037] In some cases, the general direction of fluid flow is unknown or not fixed, for example at sea. The perforated barrier can then completely surround the base of the object, for example in an axisymmetric manner. The fluid then passes through the barrier before reaching the object, regardless of the general direction of fluid flow.

[0038] In other cases, the general direction of fluid flow is known and / or does not vary, for example, in a river. The perforated barrier may then only partially surround the object, and preferably extends primarily upstream of the object, i.e., around or in front of the object's faces likely to be in the direction of fluid flow. For example, it is not necessary to completely surround the foundation of a bridge located in a river where the general direction of fluid flow is known.

[0039] Preferably, the perforated barrier does not extend over the entire height of the object but only over its lower part. Indeed, its purpose is to protect the object from turbulence at ground level only.

[0040] Furthermore, the barrier is positioned at a sufficient distance from the object so that the flow turbulence level is reduced sufficiently far from the object. According to the teachings of the present invention, a person skilled in the art can calculate, based on local conditions, the optimal distance for the flow velocity to correspond to a fluid friction on the particulate soil that is below the critical erosion value.

[0041] Optionally, perforated elements can be added orthogonally to the local flow direction, between the perforated barrier and the object, to further reduce turbulence and increase efficiency. The choice of such elements depends on the object's geometry and the flow characteristics. Optionally, at least one additional perforated barrier can be positioned to further reduce fluid flow turbulence. The fluid then passes successively through the perforated barriers, which are spaced apart for a dual flow lamination effect.

[0042] Fluid stop element

[0043] To reduce the occurrence of horseshoe vortices, a fluid arresting element extending from the object towards the perforated barrier is positioned at a height h above the ground in a substantially horizontal plane or one substantially parallel to the ground. This element may cover all or part of the surface between the object and the barrier.

[0044] This stopping element is preferably sufficiently low-porosity, and preferably solid, so as to prevent the fluid flowing above it, upon impact with the object, from flowing towards the particulate soil. The fluid deflected vertically downwards is blocked by the fluid stopping element, thus preventing localized soil erosion around the base of the object. Without this erosion, horizontal flows do not stall, which limits the formation of horseshoe vortices. Consequently, the level of turbulence in the fluid flow near the base of the object is reduced, thereby decreasing the risk of erosion.

[0045] The stopping element is positioned at a height h sufficiently close to the particulate soil to minimize the size of the horseshoe vortices. Theoretically, the stopping element could be placed at the soil surface itself, i.e., h = 0. The function of blocking the downward flow would be fulfilled, and the soil would be protected. In reality, particulate soils are never perfectly flat, and a small difference in level with the stopping element could be enough to create a horizontal obstacle that would initiate erosion. In this case, the fluid would strike the stopping element horizontally and form vortices at the point of the difference in level. This is why the fluid stopping element is preferably positioned at a non-zero height h between the stopping element and the particulate soil. Thus, the fluid layers moving at ground level are not at risk of colliding horizontally with the stopping element.With this height h, a controlled space is created between the ground and the stopping element, protected from the overall downward flow that impacts the object. Furthermore, if the fluid is composed of water under oceanic conditions, the effect of waves is negligible or limited within this space. Preferably, the height h should not be too great relative to the dimensions of the object. For an excessively large height h, there would be sufficient vertical space between the stopping element and the ground for the volume of fluid between the stopping element and the ground to impact the object and create a downward flow strong enough to initiate erosion. According to the teachings of the present invention, a person skilled in the art can determine a suitable height h without undue effort. Indeed, this height depends heavily on the dimensions of the object (such as its diameter or height) as well as the characteristics of the flow (velocity, turbulence, depth, etc.).), an experimental or numerical approach makes it possible to efficiently identify the optimal parameters for each specific configuration.

[0046] Accurately determining the height h of the containment device is a delicate task, as this dimension is highly dependent on numerous parameters. It varies, in particular, according to the geometric characteristics of the object (diameter, height, shape), the flow properties (velocity, depth, turbulence, viscosity), and the nature of the particulate matter. These factors influence the local fluid dynamics and the potential formation of horseshoe vortices, making it difficult to establish a universal value for h. However, in accordance with the teachings of the present invention, a person skilled in the art, given a given object, a given flow, and a given particulate matter, is able to determine a suitable height h without undue effort.An experimental or numerical approach makes it possible to effectively adjust this dimension for each specific configuration, in order to limit the formation of vortices and reduce erosion around the base of the object.

[0047] Precisely determining the diameter or width over which the fluid containment element must extend presents a certain complexity. This dimension cannot be universally defined, as it depends on numerous parameters related to the specific configuration of the object, the flow, and the soil particles. However, in accordance with the teachings of the present invention, a person skilled in the art can determine, without undue effort, a suitable dimension using small-scale tests or tests carried out in the object's final operating environment. The containment element must have a sufficient width or diameter to prevent the fluid, deflected vertically downwards, from impacting the soil, thus avoiding localized erosion at the base of the object.In addition, the perforated barrier plays a role in the overall design of the system: the area between this perforated barrier and the object, as well as the area below the retaining element, are effectively protected against erosion. Conversely, areas outside this protection remain exposed to so-called "global" erosion, induced by the friction of the fluid on the ground. For illustrative purposes only and not as a limitation, tests carried out around a cylindrical object have shown significant effectiveness for retaining element diameters ranging from 1.4 times the object's diameter (minimum value) to a theoretical maximum value limited primarily by economic manufacturing and installation constraints. Similarly, the height of the retaining element can be effective from 0.15 times the object's diameter, although no maximum value can be generally defined.

[0048] É_l_éme rit _ d e_ _t ra riqu i_l_l is a_t i on _p o u_r _1 e s_ _vo rte x _ d_e _s i 1_1 ag e_ _ o t_i o nne 1 _)

[0049] To reduce the fluid stall turbulence, due to the object obstructing the flow, at a height higher than the perforated barrier in order to limit the formation of separation or wake vortices, a calming element can be positioned at least partially around the object, above ground level.

[0050] Similar to the perforated barrier, the calming element can include openings arranged to act as a flow stabilizer, reducing vortex size. These openings can have diverse geometries, such as those described for the perforated barrier. The calming element can, for example, include a mesh, a honeycomb structure, capillary tubes, horizontal plates, and / or a 3D structure. The total surface area of ​​the openings relative to the total surface area of ​​the calming element must be sufficiently distributed to avoid creating additional vortices and transverse movements in the fluid flow.

[0051] Alternatively, the calming element can be a solid element. In this case, the boundary layer turbulence must be increased. Indeed, a turbulent boundary layer creates more friction but is also more resistant to stall. It is this stall that causes wake vortices. For this purpose, the solid element preferably has a rough surface, i.e., one with raised features, such as the surface of a golf ball.

[0052] Preferably, the tranquilizing element is placed at a height greater than the openwork barrier.

[0053] The calming element can be an extension of the openwork barrier over at least part of the height it does not enclose. In this case, the openwork barrier and the calming element have an equivalent distance from the object's wall.

[0054] Alternatively, the tranquilizing element can be closer to or further from the object than the openwork barrier, preferably at the same distance or closer for installation reasons.

[0055] This calming element is preferably positioned at a distance from the object less than the distance between the object and the openwork barrier.

[0056] When a stopping device is used, the tranquilizing device can advantageously rely on that stopping device.

[0057] The invention also covers the installation or system for implementing the method. This system comprises a perforated barrier and a fluid stop element (25) positioned in a substantially horizontal plane in its operational position. Unlike existing systems, the method of the invention allows for a system that can be a single mechanical unit and that can be installed all at once around the walls of the object.

[0058] In an advantageous embodiment, the fluid containment element is held at a height h above the ground by supports positioned between the ground and the containment element, which minimize disruption to the flow. The perforated barrier is suspended from the containment element and is therefore not anchored to the ground or attached to the object. In this way, the structure can accommodate variations in ground level over time and remain positioned at the base of the object. Furthermore, installation of the structure around the object is simplified, as the barrier can be slid into place around it. Thus, the structure can be installed before or after the object itself. In addition, the interfaces with the object are limited, facilitating installation by several independent stakeholders during an industrial setting.Finally, the removal of the protective device is facilitated, particularly in hard-to-reach areas (at sea, in rivers, etc.). This is because the device can be manufactured as a single, mechanically independent unit, easily recoverable using conventional lifting equipment.

[0059] For example, for objects with a geometry similar to bridge piers or offshore foundations, the system can be attached to the object before installation, particularly when immediate erosion protection is required. Alternatively, the system can be placed on the ground before installation.

[0060] If the system is positioned after the object is installed, but before other components obstruct its installation, it can be fabricated as a single unit and then inserted around the object until it reaches the ground. Otherwise, if a component obstructs the system's installation, the system can be assembled in several sections around the object within a free area before being moved into its operational position.

[0061] If the system is made entirely or partially of metallic material, its metallic components can be welded, bolted, or riveted. For other materials, the assembly technique must be appropriate for the material in question.

[0062] Detailed description of the invention

[0063] The invention will now be explained in more detail, with the help of the attached drawings, on which:

[0064] Figure 1 is a block diagram of the process according to the invention;

[0065] Figure 2 is a cross-sectional view of a cylindrical object embedded in particulate soil and surrounded by a perforated barrier;

[0066] Figure 3 is a cross-sectional view of a cylindrical object embedded in particulate soil and surrounded by a perforated barrier and a stop element;

[0067] Figure 4 is a cross-sectional view of a cylindrical object embedded in particulate soil and surrounded by a perforated barrier, a stopping element and a tranquilizing element;

[0068] Figure 5 is a cross-sectional view of a cylindrical object embedded in particulate soil and surrounded by a perforated barrier, a stopping element and a tranquilizing element at an equivalent distance from the object as the perforated barrier;

[0069] Figure 6 illustrates different types of meshes;

[0070] Figure 7 represents a test on a square cross-section object embedded in particulate soil; Figure 8 represents a test on a square cross-section object embedded in particulate soil and surrounded upstream by a perforated barrier;

[0071] Figure 9 represents a test on a cylindrical object embedded in particulate soil;

[0072] Figure 10 represents a test on a cylindrical object embedded in particulate soil surrounded by a perforated barrier and a stopping element;

[0073] Figure 11 represents a test on a cylindrical object embedded in particulate soil surrounded by a perforated barrier, a stopping element and a calming element;

[0074] Figure 12 represents a test on a cylindrical object embedded in particulate soil surrounded by a perforated barrier, a stopping element and a calming element at an equivalent distance from the object as the perforated barrier; Figure 13 illustrates, from above, non-exhaustive possibilities of perforated barrier geometries;

[0075] Figure 14 is a horizontal cross-sectional view of a device according to the invention in which perforated elements are added radially between the object and the barrier;

[0076] Figure 15 is a horizontal cross-sectional view of a device according to the invention in which an additional perforated barrier is positioned around the object;

[0077] Figure 16 is a horizontal cross-section of an object and a perforated barrier placed in contact with the object;

[0078] Figure 17 is a vertical cross-section of objects surrounded and covered by a perforated barrier;

[0079] Figure 18 illustrates several typical object geometries; Figure 19 illustrates the theory of erosion of particulate soils at the base of objects placed on, or embedded in, such soil. With reference to Figure 1, a method for preventing the erosion of particulate soil at the base of an object placed in the flow of a fluid is described, in which:

[0080] A: To reduce at least partially the level of turbulence of the fluid flow, a perforated barrier is positioned at least partially around the base of said object so that the perforated barrier is at least at one point orthogonal to the general direction of the fluid flow and allows the passage of the fluid through it;

[0081] B: A fluid stop element extending from the object towards the perforated barrier is positioned in a substantially horizontal plane or substantially parallel to the ground, said fluid stop element being a solid element.

[0082] Optionally, a calming element C is positioned around the object and extends over its height.

[0083] Referring to Figure 2, a cylindrical object 21, for example a monopile for an offshore wind turbine, is driven into a particulate soil 23, for example sand. The fluid 22 is, for example, seawater, the general direction of which is not fixed over time and is represented by a wavy arrow. A perforated barrier 24 is positioned around the base of the object 21 to reduce the turbulence of the fluid 22 flow. The perforated barrier 24 comprises a wire mesh. Ideally, the mesh is made of metallic material or, if necessary, any other corrosion-resistant material when the fluid is water. To cover all possible general directions of the fluid 22 flow, i.e., 360°, the perforated barrier 24 is, for example, concentric and completely surrounds the base of the object 21.Thus, the openwork barrier 24 is at least at one point orthogonal to the general direction of the flow (represented by the thick arrow) of the fluid 22 so that the fluid 22 can pass through the openings of the mesh when it moves towards the openwork barrier 24 in order to reduce turbulence.

[0084] Referring to Figure 3, and incorporating elements from Figure 2, a stop element 25 for the fluid 22 is positioned in a substantially horizontal plane or substantially parallel to the particulate ground 23 so as to prevent the fluid 22, when it strikes the object 21, from flowing towards the particulate ground 23. The stop element 25 for the fluid 22 extends from the object 21 towards the perforated barrier 24, at a height h above the ground 23. This stop element 25 covers the entire surface between the object 21 and the barrier 24. The stop element 25 is a solid element, for example a metal plate.

[0085] Referring to Figure 4, and incorporating elements from Figures 2 and 3, a calming element 261 is positioned around object 21, above ground level 23. In this example, the calming element 261 rests on the fluid containment element 25 for fluid 22 and is closer to object 21 than the perforated barrier 24. It reduces the stall vortices of fluid 22 over virtually the entire height of object 21. To this end, the calming element 261 comprises a wire mesh. For example, here, the mesh is made of metallic material or possibly any other corrosion-resistant material.

[0086] Figure 5 illustrates an arrangement similar to that of Figure 4, except that the calming element 262 is an extension of the perforated barrier 24. The perforated barrier and the calming element 24;262 are therefore located at an equivalent distance from the object 21. Figures 6(a) to 6(c) illustrate examples of perforated barriers, in particular geometries of openings arranged to allow fluid passage. Figure 6(a) represents a mesh such as a wire mesh, grid, or net—that is, a network of wires or bars arranged regularly, creating openings for fluid passage. The mesh size is determined on a case-by-case basis according to the geometry of the object, the particulate soil, the fluid, and the flow characteristics. As an alternative to the wire mesh type, Figure 6(b) illustrates a honeycomb structure and Figure 6(c) capillary tubes.These are preferably used when the direction of flow is fixed, such as in a river.

[0087] Tests of the effectiveness of the method of the invention for the prevention of 1' af excavation

[0088] To validate the concept of the invention, various small-scale tests were carried out.

[0089] With reference to Figures 7 to 12, different variants of the device according to the invention are shown for small-scale tests, and the respective results are shown on a particulate soil after 2 hours. The device and its variants are positioned in a turbulent flow where the fluid is water. The particulate soil consists mainly of sand.

[0090] Figure 7(a) shows a cross-section of the test setup in which a square object 71, 3 cm in cross-section and 1 cm high (excluding the sand), rests on sand 73 and is placed in a water current characterized by a general direction. The object 71 is typically comparable to an anchor, for example, in a river. Figure 7(b) illustrates the areas of excavation 74 and 75 in the sand 73 after 2 hours of testing. The formation of a depression in the frontal (74) and lateral (75) areas of the object, as well as a slope 76 due to the accumulation of sand in its wake, is observed.

[0091] Figure 8(a) shows a cross-section of the test setup in which a section of wire mesh 77 is positioned in front of the square cross-section object 71 of Figure 7 at a distance of 15 mm. The wire mesh section is 50 mm long and 10 mm high and has a 1.5 mm square mesh. Figure 8(b) illustrates, from above, the results of the test after 2 hours on the particulate soil 73. It can be seen that no areas of excavation have appeared compared to Figure 7(b).

[0092] Figure 9(a) shows a cross-section of another test setup in which a cylindrical object 91, simulating a building pier, rests on a sandy soil 93 and is placed in a water current 92 characterized by a constant general direction. The object 91 is typically comparable to the monopile foundations of an offshore wind turbine. Figure 9(b) illustrates a top view of the setup after 2 hours. Significant excavation 94, 95, and 961 is observed in the frontal 94 and lateral 95 areas of the object, as well as in its wake 961.

[0093] Figure 10(a) shows a cross-section of the test setup in which a mesh 97 is positioned around the cylindrical object 91 of Figure 9. A stop element 98 is also positioned in a horizontal plane, substantially parallel to the ground plane, between the mesh barrier and the object. The stop element 98 is a solid element and is in contact with the object 91 to block and prevent the formation of horseshoe vortices at the base of the object. Figure 10(b) illustrates, from above, the results of the test after 2 hours on the particulate soil 93. Compared to Figure 9(b), it can be seen that no frontal scour zone 94 or lateral scour zone 95 appeared. Only restricted scour zones 962 in the wake of the object were formed. These are explained by the height of object 91 along which wake vortices form.

[0094] Referring to Figure 11(a), the setup shown in Figures 9 and 10 is used again, and a tranquilizing element 991 is positioned around the object on the stopping element 98. This element is almost identical in height to object 91 and has a mesh similar to that of the openwork barrier 97 placed on the ground. The tranquilizing element 991 is closer to object 91 than is the openwork barrier 97. Figure 11(b) illustrates the results of the test after 2 hours in the water current. Compared to Figure 10(b), it can be observed that the areas of scouring 962 in the object's wake have barely appeared. Only areas of scouring 963 remain, located far enough from the object to pose no danger to its integrity.

[0095] As illustrated in Figure 12, when the tranquilizing element 992 is positioned at the same distance from the object 91 as the perforated barrier 97, after 2 hours in the current, no scouring zone 963 is formed.

[0096] Figure 13 illustrates, from a top view, non-exhaustive possibilities for the geometries of openwork barriers 111, 112, 113, 114, and 115 in relation to objects with different cross-sections 101, 102, 103, 104, and 105. The geometry of the barrier is not necessarily a homothety of the object's contours. Indeed, a barrier with a circular geometry 114 can be used for an object with a square cross-section 104. Conversely, a barrier with a polygonal geometry 112 can be suitable for an object with a circular cross-section 102. Figure 14 is a horizontal cross-sectional view of a device according to the invention in which openwork elements 143 are radially added between the object 141 and the barrier 142. The main objective is to maximize the number of elements orthogonal to the local direction of the flow. These elements can contribute to the solidity of the installation, especially when the openwork barrier is a wire mesh that could be deformed by currents.

[0097] Figure 15 is a horizontal cross-section of a device according to the invention in which an additional perforated barrier 153 is positioned around the object 151 already surrounded at its base by a perforated barrier 152.

[0098] Figure 16 is a horizontal cross-sectional view of a device according to the invention in which the perforated barrier 161 is positioned in contact with the object 162. This is typically the case for a thick perforated barrier (honeycomb, capillary tubes, plates / slats,

[0099] Figure 17 illustrates objects 171 lying on the ground 173 and surrounded and covered by a perforated barrier 172. These objects are typically submarine cables, pipelines, etc. For example, in the case of a submarine cable, scouring can cause the cable to sink and generate tension that is dangerous to its integrity. The perforated barrier can, for example, be deployed at the same time as the object to prevent scouring. With reference to Figure 18, several typical object geometries are shown with respect to a flow direction 181. The figure is intended to illustrate the proportions of the object without prejudging its exact shape. The invention can be applied to a wide variety of geometries and is not limited to a wind turbine mast-type object, as illustrated in Figure 18(k).As an example, the invention can also be implemented to prevent soil erosion at the base of quays or dock foundations in port areas in contact with a fluid flow in direction 181. In this case, the fluid does not flow around a localized object, but strikes a flat surface that can be considered an infinite plane. This phenomenon can lead to significant soil erosion, and the function of the invention, namely blocking the downward flow of fluid, makes it possible to limit this effect.

Claims

Demands 1. A method for preventing the excavation of particulate soil (23) at the base of an object (21) placed in the flow of a fluid (22), according to which, in order to reduce at least in part the level of turbulence of the flow of the fluid (22), a perforated barrier (24) is positioned at least in part around the base of said object (21) so that the perforated barrier (24) is at least at one point orthogonal to the direction of the flow of the fluid (22) and allows the passage of the fluid through it, said method being characterized in that a fluid (22) stopping element (25) extending from the object (21) towards the perforated barrier (24) is positioned in a substantially horizontal plane or substantially parallel to the ground (23), said fluid stopping element being a solid element.

2. Method for preventing scouring according to claim 1, wherein to allow the passage of fluid the perforated barrier (24) comprises a mesh, a honeycomb structure, capillary tubes, horizontal plates or a 3D structure.

3. Method for preventing rummaging according to one of claims 1 or 2, wherein the perforated barrier (24) is placed so as to completely surround the base of the object (21), preferably in an axisymmetric manner.

4. Method for preventing scouring according to claim 1 or 2, wherein the perforated barrier (24) is placed so as to only partially surround the object (21), and extend mainly upstream of the object (21) with respect to the direction of flow.

5. Method for preventing rummaging according to any one of the preceding claims, wherein the perforated barrier (24) is placed so as to extend at least over the lower part of the height of the object (21).

6. Method for preventing scavenging according to any one of the preceding claims, wherein perforated elements (143) are added radially and / or orthogonally between the perforated barrier (24) and the object (21).

7. Method for preventing rummaging according to any one of the preceding claims, wherein at least one additional openwork barrier (153) is positioned around the object.

8. Method for preventing excavation according to any one of the preceding claims, wherein the stopping element (25) of the fluid (22) is placed so as to cover the entire surface between the object (21) and the perforated barrier (24).

9. Method for preventing excavation according to any one of the preceding claims, wherein the stopping element (25) of the fluid (22) is positioned sufficiently close, preferably in contact, with the object (21) to completely block the fluid which is moving towards the particulate soil (23) after having struck the object (21).

10. A method for preventing excavation according to any one of the preceding claims, wherein a tranquilizing element (261; 262) is positioned at least partially around the object (21), above ground level Tl 11. Method for preventing scavenging according to claim 10, wherein the tranquilizing element (261; 262) comprises a mesh, a honeycomb structure or capillary tubes.

12. Method for preventing scouring according to claim 10, wherein the calming element (261; 262) is a solid element having a surface comprising specific reliefs to reduce wake vortices.

13. Structure for preventing the excavation of particulate soil (23) at the base of an object (21) placed in the flow of a fluid (22), said installation comprising a perforated barrier (24) at least in part and placed around the base of said object (21) so that the perforated barrier (24) is at least at one point orthogonal to the direction of the flow of the fluid (22), said installation being characterized in that it comprises, in a substantially horizontal plane or substantially parallel to the ground (23), a stopping element (25) for the fluid (22) extending from the object (21) towards the perforated barrier (24), at a height h above the ground (23), said stopping element for the fluid being a solid element.

14. A scour prevention structure according to claim 13, wherein the perforated barrier is suspended from the fluid stop element, said fluid stop element resting on supports positioned between the ground and the stop element and said supports being arranged to minimize disruption to the flow.

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