A multi-layered energy dissipation structure for preventing scour of offshore wind turbine pile foundations

Abstract

This invention relates to a multi-layered energy dissipation structure for preventing scour of offshore wind turbine pile foundations, belonging to the field of offshore wind power engineering technology. The multi-layered energy dissipation structure includes several multi-layered grate structures, which are assembled together along the circumference of the pile foundation. Each multi-layered energy dissipation structure includes several horizontally arranged perforated grate plates and a frustum for assembling the perforated grate plates; the frustum is used to connect to the pile foundation. Compared to existing scour protection structures, the multi-layered energy dissipation structure for offshore wind turbine pile foundations provided by this invention is relatively lightweight due to its hollow interior, resulting in lower transportation costs and a higher cost-effectiveness ratio. Because of its multi-segment assembly structure, it is easy to disassemble, and failed sections can be recycled, making it highly environmentally friendly.

Description

Technical Field

[0001] This invention relates to a multi-layer energy dissipation structure for preventing scour of offshore wind turbine pile foundations, belonging to the field of offshore wind power engineering technology. Background Technology

[0002] Wind energy, as an emerging clean energy source, has garnered widespread attention worldwide due to its renewable nature, high energy density, minimal impact on the marine environment, and lack of land occupation. It also possesses favorable conditions for large-scale development and promising commercial prospects. Compared to onshore wind energy resources, offshore wind energy resources offer significant advantages such as higher wind speeds, smaller vertical wind shear, and longer annual utilization periods. Consequently, offshore wind energy has become a crucial direction for wind power development in various countries globally in recent years. Pile foundations possess good stability and bearing capacity, coupled with ease of installation, making them widely used in modern marine engineering. Due to the impact of the foundation structure on marine hydrodynamics, the previously dynamically balanced external conditions of the seabed are disrupted. The balanced water flow, upon encountering the pile, flows downwards, forming a downward jet in front of the pile. This downward jet, upon encountering the seabed bottom, rises upstream, forming a horseshoe-shaped vortex. The leading edge or side of the single pile foundation is first eroded by the horseshoe vortex system, with sediment being carried to the rear of the pile by the water. The foundation's tail vortex then has a suction effect, further carrying the sediment downstream. Ultimately, scour pits form around the piles and siltation dunes form downstream of the piles, causing localized scour around the structure, reducing its foundation bearing capacity, causing uneven lateral stress, and in severe cases, even threatening the project with in-situ instability and failure.

[0003] For research on scour protection of pile foundations, different design approaches have been offered both domestically and internationally, generally falling into two main categories: active protection using external structures and passive protection methods such as post-construction rock and sand replenishment, and marine organism attachment protection. Rock and sand replenishment involves covering the seabed around the pile foundation with a thick layer of rocks and gravel to form a protective layer. However, the area around the pile foundation is relatively large, requiring a large amount of gravel and crushed stone, resulting in high engineering costs. Furthermore, targeted laying and construction in areas with strong currents is difficult, and regular replenishment and maintenance are required in the later stages of the project.

[0004] Existing pile protection structures often suppress the formation of horseshoe vortices around the pile and reduce the occurrence of buffer scouring by weakening the lateral flow. This flow-cutting method brings a series of derivative problems. Simple and lightweight structures have very limited ability to weaken the lateral water flow. Conversely, complex installation processes can lead to uneven stress on the pile during installation, which in turn affects the stability of the wind turbine. At the same time, although the diversion of the lateral water flow reduces the scouring around the pile, it exacerbates the scouring near the external structure. Over time, the protective effect of the structure will continue to decline. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide an easy-to-install, scour-resistant fixed pile foundation structure for offshore wind turbines, as well as its construction method, capable of withstanding complex marine hydrodynamics. This invention's protective structure is not only lightweight and easy to install, but also reduces the intensity of eddy currents on the sides and back of the pile, as well as the intensity of downward jets.

[0006] The present invention adopts the following technical solution:

[0007] A multi-layer energy dissipation structure for preventing scour of offshore wind turbine pile foundations includes several multi-layer grate structures, which are assembled together along the circumference of the pile foundation. The multi-layer energy dissipation structure includes several horizontally arranged perforated grate plates and a truncated cone for assembling the perforated grate plates. The truncated cone is used to join the pile foundation.

[0008] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scouring device of the present invention has a truncated cone with an arc-shaped tube-like structure, and porous grate plates are arranged from top to bottom on the outer wall of the convex surface of the truncated cone.

[0009] The axial side of the frustum is provided with a socket or groove for splicing.

[0010] The circumference of the frustum is provided with a cylindrical countersunk hole.

[0011] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention has three layers of porous grate plates in the multi-layer energy dissipation structure. The three layers of porous grate plates are semi-circular or fan-shaped. The three layers of porous grate plates extend along the horizontal plane and are arranged parallel to each other.

[0012] The radius of the porous grate plate in the three layers increases sequentially from top to bottom.

[0013] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention consists of three layers of porous grate plates arranged from top to bottom, in which the first layer is porous grate plate one, the second layer is porous grate plate two, and the third layer is porous grate plate three.

[0014] The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are arc-shaped or waist-shaped holes;

[0015] The long axis of each diversion hole is arranged transversely relative to the frustum. The long axes of each diversion hole are arranged in a straight line parallel to each other and in a group. The length of each diversion hole increases sequentially along the radial direction of the porous grate plate. Each group of diversion holes is distributed circumferentially on the porous grate plate.

[0016] The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are waist-shaped holes;

[0017] Each diversion hole is an arc-shaped waist hole with its long axis set vertically relative to the frustum. Several diversion holes are arc-shaped waist holes arranged at intervals along the surface of the porous grate plate 2.

[0018] The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are waist-shaped holes;

[0019] Each diversion hole has its long axis inclined relative to the frustum, and several diversion holes are arranged at intervals along the surface of the porous grate plate.

[0020] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention has diversion holes on the porous grate plate one, porous grate plate two, and porous grate plate three arranged alternately.

[0021] The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure described in this invention has a support rod between the porous grating plates in each layer of the multi-layer energy dissipation structure.

[0022] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention has a central hole formed inside the truncated cone, and the inner wall of the truncated cone is provided with a submarine cable hole for fixing the submarine cable; the diameter of the submarine cable hole is larger than the diameter of the submarine cable.

[0023] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scouring device of the present invention has fixed platforms on both sides of the porous grate plate three.

[0024] The connecting surface of the fixed platform is a smooth plane, and the outer side of the fixed platform is a rounded corner surface to reduce the impact of water flow.

[0025] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention has a diversion mesh structure in the holes of the porous grate plate.

[0026] The multi-layer energy dissipation structure of the offshore wind turbine pile foundation anti-scour device of the present invention has a porous grate plate at a distance of 0.3D from the seabed surface (D is the diameter of the pile column) and a width of D;

[0027] The porous grate plate, located away from the seabed, is 0.6D away from the seabed and has a width of 0.5D.

[0028] The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure of the present invention has a diversion mesh structure on the diversion holes of the porous grate plate, which is an array of multiple wave-shaped structures.

[0029] Beneficial effects

[0030] This invention provides a multi-layered energy dissipation structure for scour protection of offshore wind turbine pile foundations. Compared to existing scour protection structures, its hollow interior makes it relatively lightweight, resulting in lower transportation costs and a higher cost-effectiveness ratio. Furthermore, its multi-section assembly structure facilitates disassembly, and failed sections can be recycled, making it highly environmentally friendly.

[0031] This invention employs an external arc-shaped structure with a three-layer flow-diverting grate inside, effectively mitigating lateral flow around the wind turbine pile, back vortex, and downward jets beneath the pile. The large-sized base, slotted connection, and rivet-structured fixing design ensure excellent structural stability, enabling it to withstand various complex marine environments.

[0032] Special designs were implemented for the submarine cables leading out from offshore wind turbines to minimize fatigue damage caused by the scouring of the cable access points in the complex marine environment. Attached Figure Description

[0033] Figure 1 This is a three-dimensional schematic diagram of the complete structure of the present invention;

[0034] Figure 2 This is a three-dimensional structural schematic diagram (front view) of a single scour protection structure of the present invention;

[0035] Figure 3 This is a three-dimensional structural schematic diagram (side view) of a single scour protection structure of the present invention;

[0036] Figure 4 This is a three-dimensional structural diagram of the first layer grate plate of the present invention;

[0037] Figure 5 This is a three-dimensional structural diagram of the second layer grate plate of the present invention;

[0038] Figure 6 This is a three-dimensional structural diagram of the third layer grate plate of the present invention;

[0039] Figure 7 This is an enlarged view of the fixing platform of the present invention;

[0040] Figure 8 This is a schematic diagram of the diversion hole structure of the present invention;

[0041] The diagram includes: 1. Monopile; 2. Multi-layer hollow truncated cone; 3. Central hole; 4. Submarine cable hole; 5. Insertion hole; 6. Groove; 7. Diversion grate 1; 8. Diversion grate 2; 9. Diversion grate 3; 10. Fixing platform; 11. Threaded hole; 12. Diversion mesh; 13. Columnar countersunk hole; 14. Support rod; 15. Diversion hole. Detailed Implementation

[0042] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0043] like Figures 1 to 2 As shown, this invention provides a fixed pile foundation scour protection structure for offshore wind turbines, including a single pile 1, a multi-layer hollow frustum 2, a central hole 3, a submarine cable hole 4, an insertion hole 5, a groove 6, a diversion grate 1 7, a diversion grate 2 8, a diversion grate 3 9, a fixing platform 10, a threaded hole 11, a diversion mesh 12, a countersunk hole for a hexagonal head bolt 13, and a support rod 14. In this embodiment, the multi-layer hollow frustum has a trapezoidal pile structure in cross-section, and a disc-shaped structure in top view after splicing and fixing. The wave-facing surface of the edge of diversion grate 1 7 is sloping; the wave-facing surfaces of diversion grate 2 8 and diversion grate 3 9 are rounded and chamfered. This design allows for close contact with the seabed while improving structural stability. To facilitate machining, improve structural strength, and avoid stress concentration at the joints, the first and second layer grates are chamfered.

[0044] Preferred, such as Figure 2 ,like Figure 3 and combined Figure 7 As shown, to enhance structural stability, the multi-layered hollow frustum 2 is mutually fixed by insertion holes 5 and protrusions 6. The protrusions 6 can be inserted into the insertion hole of another multi-layered hollow frustum. A fixing platform 10 is provided at the connection of the three diversion grates 9 of the multi-layered hollow frustum 2. The fixing platform has threaded holes 11 drilled inside. After the two multi-layered hollow frustums 2 are fixed, they can be fixed with rivets to enhance structural stability. Appropriately increasing the length of the insertion holes 5 and protrusions 6 can effectively make the connection between the multi-layered hollow frustums tighter. At the same time, a columnar countersunk hole 13 for hexagonal head bolts is provided on the outer wall near the hollow hole, which can be used to firmly fix the structure to the pile column through the rivet structure.

[0045] like Figure 1 As shown: Preferably, the three-layer diversion grate can effectively weaken the downward water flow on the upstream side of the pile column, and the holes between the three layers of diversion grate are arranged in an alternating pattern. Specifically, in the three layers of porous grate plates arranged from top to bottom, the first layer is porous grate plate 7, the second layer is porous grate plate 8, and the third layer is porous grate plate 9;

[0046] The porous grate plate 7 has several diversion holes 15 arranged on its surface, and the diversion holes 15 are arc-shaped waist-shaped holes;

[0047] like Figure 4As shown: the long axis of each diversion hole 15 is arranged transversely relative to the frustum, and the long axes of each diversion hole 15 are arranged in a straight line parallel to each other. The length of each diversion hole 15 increases sequentially along the radial direction of the porous grate plate 7. Each group of diversion holes is distributed circumferentially on the porous grate plate 7. The porous grate plate 7 has several diversion holes arranged on its surface. The diversion holes are waist-shaped holes.

[0048] like Figure 5 As shown: the major axis of each diversion hole 15 is set vertically relative to the frustum of the cylinder, and several diversion holes 15 are arranged at intervals along the surface of the porous grate plate 8.

[0049] like Figure 6 As shown: The porous grate plate 39 has several diversion holes 15 arranged on its surface, and the diversion holes 15 are waist-shaped holes;

[0050] Each diversion hole 15 is inclined relative to the frustum, and several diversion holes 15 are arranged at intervals along the surface of the porous grate plate 9.

[0051] When the horizontal water flow impacts the column wall, generating a vertical downward jet, the uppermost porous grate plate 39 weakens the vertical water flow for the first time. The solid part above it initially diverts the water flow through obstruction. The vertical water flow after the initial diversion is further diverted by the diversion net on the diversion hole. At the same time, under the combined action of the holes on the grate plate and the diversion net, the diverted water flow is gathered and reaches the lower porous grate plate 28. Since the holes on the different layers of porous grate plates are staggered, the water flow gathered by the upper grate plate is diverted again. Finally, the diversion effect of multiple layers of grate plates continuously weakens the vertical downward jet. At the same time, due to the shielding effect of the porous grate plate 17 laid on the seabed, the contact area between the seabed around the column and the water flow is greatly reduced, which also inhibits the formation of horseshoe vortex system around the column, thus achieving the purpose of suppressing scour. Appropriately increasing the number of holes can more effectively divert the flow vertically and reduce the scouring of the pile shaft by the downward jet.

[0052] Preferably, the central hole of the multi-layer hollow truncated cone is the same as the outer diameter of the wind turbine monopile 1. A submarine cable hole 4 is provided next to the central hole. The laying of the submarine cable hole 4 can fix the submarine cable, which solves the problem that the submarine cable access end is prone to fatigue damage due to water circulation.

[0053] For example Figure 1 , Figure 2 , Figure 3As shown: the porous grate plate 7 close to the seabed is 0.3D from the seabed (D is the diameter of the pile, the same below), and its width is D; the porous grate plate 8 far from the seabed is 0.6D from the seabed and its width is 0.5D. Under this structural design condition, the downward vertical jet in front of the wind turbine monopile foundation pile, the flow around the sides of the monopile foundation and the intensity of the wake vortex on the back, as well as the shear stress on the seabed surface behind the monopile foundation will be reduced to the greatest extent.

[0054] like Figure 8 As shown: The diversion holes of the porous grate plate are equipped with diversion nets 12. The diversion nets are arranged in an array of wavy lines. The curved structure increases the contact area between the diversion nets and the vertical downward jet, thereby diverting and disturbing the water flow through the blocking effect, so as to weaken the water flow intensity. The diversion nets are arranged in a horizontal array as shown.

[0055] The design and assembly method of the anti-scour device for offshore wind turbine pile foundations with multi-layer energy dissipation structure in this embodiment is as follows:

[0056] The first step is to obtain the outer diameter of the wind turbine monopile foundation structure to draw the central hole; calculate the pressure threshold near the pile foundation using our own methods to determine the required screw structure parameters, and select the required anchoring structure while ensuring safety; obtain the diameter of the wind turbine submarine cable to determine the size of the submarine cable hole, and select an appropriate number of multi-layer frustum structures based on transportation and on-site installation conditions.

[0057] The second step is to calculate the self-load of different layers of diversion grates, obtain the parameters of the required support columns, design appropriate width, thickness and vertical height based on the column diameter D and the load faced by the diversion grate plate, and finally build the model using 3D modeling software such as SolidWorks to obtain the corresponding mold. According to the local sea conditions, select suitable anti-corrosion steel materials and appropriate sidewall thickness to make multiple multi-layer frustum structures and connection devices between the two components.

[0058] The third step is the assembly of the anti-scouring device. The structure is transported to the target sea area by a marine transport ship. The floating device is then bound to the structure through the holes on the platform, so that the entire structure floats on the sea surface. The bound structure is then pre-assembled next to the piles.

[0059] The fourth step is to level the seabed around the offshore wind turbine's mounting foundation;

[0060] The fifth step is to place the submarine cable next to the pile foundation, so that it passes through the submarine cable hole 4 of a multi-layer hollow truncated cone 2 from top to bottom. The multi-layer hollow truncated cone 2 is then placed flat on the sea surface in the horizontal direction until it is completely attached to the pile. Another multi-layer hollow truncated cone 2 is placed next to the previous multi-layer hollow truncated cone 2 along the wind turbine pile foundation. The two are first connected by a plug and a groove, and then pre-fixed by inserting a stud through the threaded hole 11. This process is repeated until a closed truncated cone is completely formed.

[0061] The sixth step involves connecting the device to the transport ship via ropes through the central hole, and then slowly removing the buoyancy device to allow the entire truncated cone to slowly and steadily fall vertically along the pile until it is completely in contact with the seabed.

[0062] Step 7: Fix the structure to the pile at the countersunk holes of the hexagonal head bolts, and tighten all the fixing bolts until the designed preload is reached.

[0063] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-layered energy dissipation structure for preventing scour of offshore wind turbine pile foundations, characterized in that: The anti-scouring device of the multi-layer energy dissipation structure includes several multi-layer grate structures, which are spliced ​​together along the circumference of the pile foundation; the multi-layer energy dissipation structure includes several perforated grate plates arranged horizontally to each other and a truncated cone for assembling the perforated grate plates; the truncated cone is used to join to the pile foundation. The multi-layer energy dissipation structure has three layers of porous grate plates, which are semi-circular or fan-shaped. The three layers of porous grate plates extend along the horizontal plane and are arranged parallel to each other. The radius of the porous grate plate in the three layers increases sequentially from top to bottom; The three layers of perforated grate plates arranged from top to bottom are: the first layer is perforated grate plate one, the second layer is perforated grate plate two, and the third layer is perforated grate plate three. The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are arc-shaped or waist-shaped holes; The long axis of each diversion hole is arranged transversely relative to the frustum. The long axes of each diversion hole are arranged in a straight line parallel to each other and in a group. The length of each diversion hole increases sequentially along the radial direction of the porous grate plate. Each group of diversion holes is distributed circumferentially on the porous grate plate. The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are waist-shaped holes; Each diversion hole is an arc-shaped waist hole with its long axis set vertically relative to the frustum. Several diversion holes are arc-shaped waist holes arranged at intervals along the surface of the porous grate plate 2. The porous grate plate has several diversion holes arranged on its surface, and the diversion holes are waist-shaped holes; Each diversion hole has its long axis inclined relative to the frustum, and several diversion holes are arranged at intervals along the surface of the porous grate plate.

2. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: The truncated cone is an arc-shaped tubular structure, with porous grate plates arranged from top to bottom on the convex outer wall of the truncated cone. The frustum is provided with insertion holes or grooves for splicing along its axial side. The circumference of the frustum is provided with a cylindrical countersunk hole.

3. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: The diversion holes on porous grate plate one, porous grate plate two, and porous grate plate three are arranged alternately.

4. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: In the multi-layer energy dissipation structure, support rods are provided between each layer of porous grate plates.

5. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 2, characterized in that: The truncated cone has a central hole inside, and the inner wall of the truncated cone has a cable hole for fixing the submarine cable; the diameter of the cable hole is larger than the diameter of the submarine cable.

6. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: The porous grate plate three is provided with fixing platforms on both sides of its edges; The connecting surface of the fixed platform is a smooth plane, and the outer side of the fixed platform is a rounded corner surface to reduce the impact of water flow.

7. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: The porous grate plate has a diversion mesh structure in its holes.

8. The scour prevention device for offshore wind turbine pile foundations with a multi-layer energy dissipation structure according to claim 1, characterized in that: The diversion mesh structure on the diversion holes of the porous grate plate is an array of multiple wavy linear structures.

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