Seabed energy dissipation net offshore wind power pile foundation scouring protection test method aiming at reciprocating flow and based on fluid dynamics simulation

Abstract

The invention discloses a hydrodynamic simulation-based seabed energy dissipation net offshore wind power pile foundation scouring protection test method for reciprocating flow, which comprises the following steps of: analyzing geographic characteristics of radiation sand ridge groups of south and yellow sea, and collecting and measuring sediment samples to obtain sediment data; a mathematical model of the influence of reciprocating flow, waves and tides on pile foundation scouring is established based on the fluid dynamics principle; constructing an energy dissipation network physical model; according to geographic features and sediment data, the mathematical model S2 and the physical model S3 of the energy dissipation network are used for simulation; taking a mathematical model result as a test boundary condition, carrying out a water tank test according to similar water flow movement and similar sediment movement, and carrying out the water tank test; the simulation data and the water tank test data are compared, and the pore size of the energy dissipation net, the material characteristics and the distance between the energy dissipation net and the pile foundation are adjusted according to the water tank test data; according to the method, through combination of modeling simulation and a water tank test, the pore structure and material characteristics of the energy dissipation net and the distance between the energy dissipation net and the pile foundation are optimally designed.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid dynamics experiments, and in particular to a method for testing scour protection of offshore wind power pile foundations of a seabed energy dissipation network based on fluid dynamics simulation for reciprocating flow. Background Art

[0002] Researchers face a series of challenges in protecting offshore wind turbine pile foundations from scour under reciprocating flow conditions such as ocean tides or wave-induced currents. Traditional fixed structures are susceptible to erosion in the marine environment, especially the loss of soil around the pile foundation, which may lead to instability or even collapse of the structure. Submarine energy dissipation nets, as a possible solution, aim to reduce the local flow velocity around the pile foundation by changing the flow field characteristics, thereby alleviating the scour phenomenon.

[0003] Simulation is a method of simulating fluid flow behavior through computers. For the study of offshore wind turbine pile foundations, simulation can be used to evaluate key performance indicators such as water velocity distribution under different design parameters. The energy dissipation net is usually made of flexible materials that can adapt to the unevenness of the seabed and can swing in the water flow, thereby consuming part of the energy of the water flow. It covers the key areas around the pile foundation to slow down the water flow and prevent soil erosion.

[0004] In practical applications, the fluid dynamics model needs to accurately reflect the complex marine environmental conditions. The submarine energy dissipation network must be able to work for a long time in harsh marine environments and must have good corrosion resistance and mechanical strength.

[0005] Therefore, it is necessary to improve the scour protection test method for offshore wind power pile foundation of seabed energy dissipation network based on fluid dynamics simulation for reciprocating flow in the prior art to solve the above problems. Summary of the invention

[0006] The present invention overcomes the shortcomings of the prior art and provides a scour protection test method for offshore wind turbine pile foundations of a seabed energy dissipation network based on fluid dynamics simulation for reciprocating flow, aiming to solve the problem that the protection test method in the prior art can accurately simulate the characteristics of reciprocating flow, optimize the design of the energy dissipation network, and improve its scour protection effect.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a test method for scour protection of offshore wind power pile foundation of submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow, comprising:

[0008] S1. Analyze the geographical characteristics of the radial sand ridges in the South Yellow Sea, collect and measure sediment samples, and obtain sediment data;

[0009] S2. Based on the principles of fluid dynamics, a mathematical model of the effects of reciprocating flow, waves and tides on pile foundation scour is established;

[0010] S3, according to the geographical features and sediment data, the energy dissipation network data is added to the S2 mathematical model for simulation;

[0011] S4. Build a scaled model based on the radial sand ridges in the South Yellow Sea and conduct flume tests;

[0012] S5. Compare the simulation and water tank test data, and adjust the pore size, material properties and distance from the pile foundation of the energy dissipation net according to the water tank test data.

[0013] In a preferred embodiment of the present invention, in step S1, the geographical characteristics of the radial sand ridges in the South Yellow Sea include: the distribution of sand ridges, the shape of sand ridges, the scale of sand ridges, water flow velocity, water flow direction and tidal variation patterns; the sediment data include: the particle size distribution of sediments, sediment content and sediment transport trend.

[0014] In a preferred embodiment of the present invention, in step S2, a model is established based on the Navier-Stokes equations;

[0015] The conservation of fluid mass is described by the continuity equation: Where ρ is the fluid density; u is the velocity vector of the fluid, and t is the time;

[0016] The conservation of fluid momentum is described by the Navier-Stokes equations: Among them, p is the pressure, τ is the stress tensor, and f is the external force;

[0017] Energy conservation is described by the energy equation: Where E is the total energy, k is the thermal conductivity, T is the temperature, and Φ is the power dissipated per unit volume.

[0018] In a preferred embodiment of the present invention, the boundary conditions in step S2 include: reciprocating fluid boundary conditions, wave boundary conditions and tidal boundary conditions;

[0019] Reciprocating fluid boundary conditions:

[0020] Assuming that the water flow at the inlet is uniform, a fixed velocity boundary condition is set at the inlet. The velocity inlet boundary condition is: u(t) = U0 + U tidal sin(ωt+φ), U0 is the average flow velocity, U tidal is the velocity amplitude caused by tide, ω is the angular frequency, and φ is the phase angle;

[0021] At the water outlet, the free outlet boundary condition is used to allow the fluid to flow out freely without generating reflection waves. The pressure outlet boundary condition is: Where n is the direction of the normal pointing outside the boundary;

[0022] On the pile surface and other solid boundaries, the velocity of the fluid must be equal to the velocity of the solid, and the no-slip condition: u| wall =0;

[0023] When studying erosion or deposition effects, the shear stress condition: Among them, τ w is the wall shear stress, μ is the dynamic viscosity of the fluid;

[0024] Wave boundary conditions:

[0025] Apply wave conditions involving velocity and pressure distribution at the crest and trough: η(x,t)=Acos(kx-ω′t+φ), where η is the free surface displacement, A is the wave amplitude, k is the wave number, and ω′ is the circular frequency;

[0026] Tidal boundary conditions:

[0027] The flow velocity and water level changes caused by tides are represented by a periodic function: ; where is the water level change, is the tidal amplitude, is the angular frequency of the tide, and is the phase angle of the tide.

[0028] In a preferred embodiment of the present invention, in step S3, the pore diameter of the energy dissipation net is 2-5 times the average particle size of the sediment; the pore structure shape of the energy dissipation net is one of circular pores, square pores and elliptical pores; the material of the energy dissipation net is one of polyester fiber and glass fiber reinforced plastic; the distance between the energy dissipation net and the pile foundation is 3-10 times the diameter of the pile foundation.

[0029] In a preferred embodiment of the present invention, the rows of pores of the energy dissipation net are staggered, and each row of pores is offset relative to the previous row, so that each pore is not directly below the pores in the previous row.

[0030] In a preferred embodiment of the present invention, in step S4, according to the continuity equation and momentum equation of viscous incompressible fluid, the similarity of water flow motion satisfies the similarity of gravity and the similarity of resistance:

[0031] The gravity similarity formula is Where u′ is the velocity, g is the gravitational acceleration, and L is the characteristic length; the velocity scale and characteristic length scale must satisfy u m is the experimental water flow rate, u p is the water velocity of the radial sand ridges in the South Yellow Sea, L m ,L p is the characteristic length of the experimental and South Yellow Sea radiating sand ridge groups, and the subscripts m and p represent the experimental and South Yellow Sea radiating sand ridge groups;

[0032] The resistance similarity formula is Among them, υ is the dynamic viscosity coefficient. In the experiment, it needs to satisfy Subscripts m and p denote the experimental and South Yellow Sea radiating sand ridge groups;

[0033] Water flow time scale Flow rate scale

[0034] In a preferred embodiment of the present invention, in step S4, the steps of executing the water tank test include:

[0035] S41, start the water flow, simulate the water flow environment under the action of reciprocating flow, and observe and record the transport and accumulation of sediments;

[0036] S42. Regularly check the wear status of the scale model pile foundation and energy dissipation net;

[0037] S43. Turn off the water flow, stop the experiment, organize and analyze the experimental data, and compare the effects of different energy dissipation net pore sizes, arrangements, and scale model pile foundation spacing on sediment accumulation and scale model pile foundation scour.

[0038] In a preferred embodiment of the present invention, in step S4, the sediment sample required for the experiment has a sand content of 45-49%, a silt content of 43-45%, and a clay content of 5-8%.

[0039] In a preferred embodiment of the present invention, in step S4, the water flow velocity is 0.5-0.65 m / s.

[0040] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0041] (1) Aiming at the reciprocating flow characteristics of the radial sand ridges in the South Yellow Sea, the present invention proposes a method for protecting offshore wind power pile foundations from scour by using a submarine energy dissipation net based on fluid dynamics simulation and flume test. By combining theoretical modeling, simulation and experimental verification, the pore structure, material properties and spacing between the energy dissipation net and the pile foundation are optimized to effectively reduce pile foundation scour and erosion, improve the durability and protection effect of the energy dissipation net, and provide technical guarantee for the safety and stability of offshore wind power pile foundations in complex marine environments.

[0042] (2) The present invention combines the theoretical principles of fluid dynamics with the actual design of the energy dissipation net by establishing a mathematical model in step S2 and constructing the physical data of the energy dissipation net in step S3. The mathematical model provides theoretical support, while the physical model of the energy dissipation net takes into account actual design parameters such as pore structure, material properties, and the distance from the pile foundation. This combination makes the design of the energy dissipation net more scientific and reasonable, can effectively reduce the scouring of the pile foundation in reciprocating flow, and improves the protective performance and durability of the energy dissipation net.

[0043] (3) The present invention designs the pore structure and material properties of the energy dissipation net in step S3, and combines this with the experimental data adjustment in step S5 to ensure the optimal performance of the energy dissipation net in practical applications. Through the feedback of experimental data, the pore size, material properties and spacing between the energy dissipation net and the pile foundation can be continuously adjusted to achieve the best scour protection effect. This dynamic adjustment and optimization process enables the energy dissipation net to better adapt to the changes in reciprocating flow and the characteristics of sediments, thereby improving the pertinence and effectiveness of protection.

[0044] (4) The present invention combines the simulation of step S4 with the flume test of step S4, thus achieving the complementarity between theoretical simulation and experimental verification. The simulation can predict the flow field characteristics and sediment transport under different conditions, while the flume test provides actual observation data to verify the accuracy of the simulation results. This combination not only verifies the reliability of the simulation, but also optimizes the design of the energy dissipation network through experimental data, thereby improving the actual effect of scour protection.

[0045] (5) The present invention collects the geographical characteristics and sediment data of the radiation sand ridges in the South Yellow Sea through step S1, and combines it with the fluid dynamics mathematical model established in step S2 to directly analyze the specific geographical environment and sediment characteristics of the radiation sand ridges in the South Yellow Sea, and based on these data, establishes a mathematical model that describes the effects of reciprocating flow, waves and tides on pile foundation scour. This process ensures the accuracy and pertinence of the model, so that subsequent simulations and flume tests can more realistically reflect the actual situation, thereby improving the effectiveness of the scour protection scheme. Compared with the prior art, it further achieves the effect of precise design and optimization of protective measures.

[0046] (6) The present invention realizes mutual verification and optimization of simulation and experimental data through comparative analysis in step S5, further improving the accuracy and reliability of the scour protection method. By comparing the simulation results with the water tank test data, the deviations in the simulation and their causes can be identified, and the model can be adjusted and optimized. This continuous verification and optimization process ensures the stability and effectiveness of the scour protection method in practical applications, and provides strong technical support for scour protection of submarine wind power pile foundations. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 is a method flow chart of a preferred embodiment of the present invention;

[0049] Figure 2 is a simplified diagram of a water tank test of a preferred embodiment of the present invention;

[0050] In the figure: 1. Reservoir; 2. Water pump; 3. Reciprocating flow pipe; 4. Flow control valve; 5. Energy dissipation network; 6. Test site; 7. Sediment feeding port; 8. High-resolution camera; 9. Laser scanner; 10. Scaled model pile foundation. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0053] The topography and landforms of the radial sand ridges in the South Yellow Sea are complex and varied, with sand ridges alternating with tidal channels and water depths ranging from 0 to 25 meters. The sand ridges are mostly composed of sandy sediments, ranging from several meters to tens of meters in height, hundreds of meters to thousands of meters in width, and thousands of meters to tens of kilometers or more in length. They are often distributed in patches on the seabed. The topography of the sand ridges is not fixed, but changes with the movement of seawater and the action of reciprocating currents.

[0054] The reciprocating flow is mainly formed by tidal action and is one of the important dynamic factors in the South Yellow Sea radial sand ridge group area. During the process of high tide and low tide, the direction of the tidal current changes significantly, forming a reciprocating flow. The reciprocating flow plays an important role in shaping and maintaining the landforms of the South Yellow Sea radial sand ridge group, driving the transport and redistribution of sediments in the waterway, and affecting the shape and position of the sand ridges. The reciprocating flow has significant dynamic characteristics, such as tidal velocity and flow direction changes. These dynamic characteristics have an important impact on the stability of offshore wind power pile foundations and energy dissipation nets. Under the action of reciprocating flow, the pile foundation may be subject to scouring erosion and horizontal force, and the energy dissipation net needs to have sufficient strength and durability to resist the scouring effect of the reciprocating flow. At the same time, the reciprocating flow contains a large amount of suspended matter and sediment. The pore size of the energy dissipation net and the distance from the pile foundation need to be large enough to allow fine particles to pass through, but also to avoid accumulation in front of the net, and at the same time be large enough to prevent larger particles from directly impacting the pile foundation.

[0055] In response to the above technical problems, the present invention proposes a test method for scour protection of offshore wind power pile foundations of seabed energy dissipation nets based on fluid dynamics simulation for reciprocating flow, aiming to solve the problems of reducing scour erosion of pile foundations, improving the durability and strength of energy dissipation nets, and optimizing the pore size and spacing of energy dissipation nets.

[0056] A method for testing scour protection of offshore wind power pile foundations of a submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow, comprising the following steps:

[0057] S1. Analyze the geographical characteristics of the radial sand ridges in the South Yellow Sea, collect and measure sediment samples, and obtain sediment data;

[0058] S2. Based on the principles of fluid dynamics, a mathematical model of the effects of reciprocating flow, waves and tides on pile foundation scour is established;

[0059] S3, according to the geographical features and sediment data, the energy dissipation network data is added to the S2 mathematical model for simulation;

[0060] S4. Build a scaled model based on the radial sand ridges in the South Yellow Sea and conduct flume tests;

[0061] S5. Compare the simulation and water tank test data, and adjust the pore size, material properties and distance from the pile foundation of the energy dissipation net according to the water tank test data.

[0062] In step S1, the geographical characteristics of the radial sand ridges in the South Yellow Sea include: the distribution of sand ridges, the shape of sand ridges, the scale of sand ridges, water flow speed, water flow direction and tidal change law;

[0063] Using GIS spatial analysis technology, combined with remote sensing images and seabed topography measurement data, a sand ridge distribution map was drawn, and the direction, spacing and coverage of the sand ridges were analyzed. The radial sand ridges in the South Yellow Sea radiate to the open sea in a fan shape, with a water depth of 0 to 25 meters, and the main body is distributed in the water depth range of 10 to 15 meters; the sand ridges are several meters to tens of meters high, hundreds of meters to thousands of meters wide, and thousands of meters to tens of kilometers or more long; the water flow velocity in the sea area varies significantly, and the water flow direction changes significantly with the action of the tide, forming a reciprocating flow. Observations are carried out using current meters and acoustic Doppler current profilers, and tidal flow vector diagrams are drawn to analyze the changing patterns of water flow velocity and direction; statistical analysis is performed on tidal data, and tidal amplitude and tidal cycle are calculated.

[0064] The sediment data in step S1 include: sediment particle size distribution, sediment content and sediment transport trend;

[0065] The average particle size of the sediments ranged from 1.85 to 6.5 Φ, with an average of 4.7 Φ;

[0066] The sediments of the radial sand ridges in the South Yellow Sea are mainly composed of sand, silt and clay;

[0067] In the sediments of the radial sand ridges in the South Yellow Sea, the sand content is relatively high, with an average content of 46.8%; the average content of silt is 45.2%; the average content of clay is 8.0%;

[0068] In terms of sediment transport trends, the sediments of the abandoned Yellow River Delta tend to be transported southward and northeastward, the sediments of the Yangtze River Delta are significantly transported northward, and the fine sandy sediments in the middle of the sand ridge group tend to be transported southward.

[0069] In step S2, the basic laws of fluid motion are described by using the Navier-Stokes equation or the shallow water equation as the basis of the model;

[0070] The Navier-Stokes equations are a set of nonlinear partial differential equations used to describe the motion of viscous fluids such as air or water. They are based on Newton's second law and express the principle of conservation of momentum within the fluid.

[0071] Preferably, the present application selects Navier-Stokes equations as the basis for establishing the model;

[0072] Determine the governing equations:

[0073] The conservation of fluid mass is described by the continuity equation: Where ρ is the fluid density; u is the velocity vector of the fluid, and t is the time;

[0074] The conservation of fluid momentum is described by the Navier-Stokes equations: Among them, p is the pressure, τ is the stress tensor, and f is the external force;

[0075] Energy conservation is described by the energy equation: Where E is the total energy, k is the thermal conductivity, T is the temperature, and Φ is the power dissipated per unit volume;

[0076] Define boundary conditions. For pile foundations, it is necessary to define the velocity and pressure on the boundary. Considering the characteristics of reciprocating flow, the boundary conditions reflect periodic changes. The influence of waves and tides also needs to be reflected through boundary conditions.

[0077] Reciprocating fluid boundary conditions:

[0078] Assuming that the water flow at the inlet is uniform, a fixed velocity boundary condition is set at the inlet. Considering the influence of tides and waves, this velocity is periodic, and its change over time is determined by measured data. The velocity inlet boundary condition is: u(t) = U0 + U tidal sin(ωt+φ), U0 is the average flow velocity, U tidalis the velocity amplitude caused by tide, ω is the angular frequency, and φ is the phase angle;

[0079] At the water outlet, the free outlet boundary condition is used to allow the fluid to flow out freely without generating reflection waves. The pressure outlet boundary condition is: Where n is the direction of the normal pointing outside the boundary;

[0080] On the pile surface and other solid boundaries, the velocity of the fluid must be equal to the velocity of the solid, and the no-slip condition: u| wall =0;

[0081] When studying erosion or deposition effects, the shear stress condition: Among them, τ w is the wall shear stress, μ is the dynamic viscosity of the fluid;

[0082] Wave boundary conditions:

[0083] Apply wave conditions involving velocity and pressure distribution at the crest and trough: η(x,t)=Acos(kx-ω′t+φ), where η is the free surface displacement, A is the wave amplitude, k is the wave number, and ω′ is the circular frequency;

[0084] Tidal boundary conditions:

[0085] The changes in flow velocity and water level caused by tides are represented by a periodic function: ζ(t) = H tidal sin(ω tidal +φ tidal ), where ζ is the water level change, H tidal is the tidal amplitude, ω tidal is the angular frequency of the tide, φ tidal is the phase angle of the tide;

[0086] Construct a physical model of the energy dissipation grid, including its pore structure, material properties, and spacing relationship with the pile foundation.

[0087] Energy dissipation nets are engineering facilities specially designed to reduce the impact of water flow or waves on structures such as offshore wind turbine pile foundations. They are usually installed around seabed or underwater structures and dissipate the energy of water flow through their specific pore structure and material properties, thereby protecting the structures from scouring and damage.

[0088] The pore structure of the energy dissipation net is designed based on the sediment characteristics of the radial sand ridges in the South Yellow Sea and the dynamic characteristics of the reciprocating flow. The pore size needs to be large enough to allow fine particles to pass through to avoid accumulation in front of the net, while being large enough to prevent larger particles from directly impacting the pile foundation.

[0089] In step S3, the pore diameter is set to 2-5 times the average particle size of the sediment;

[0090] The design of the pore structure shape of the energy dissipation network also affects the passage and accumulation of sediments;

[0091] The pore structure shape of the energy dissipation net is one of circular pores, square pores and elliptical pores;

[0092] Preferably, the rows of pores of the energy dissipation net are staggered, with each row of pores offset relative to the previous row, so that each pore is not directly below the pores in the previous row.

[0093] The staggered arrangement of pores can better disperse the water flow and reduce the concentration of water flow in certain areas, thereby reducing the possibility of sediment accumulation in front of the pores. Through the staggered arrangement, the water flow can be more evenly distributed on the energy dissipation network, reducing the risk of erosion caused by local high-speed water flow.

[0094] In step S3, the material of the energy dissipation net is one of polyester fiber and glass fiber reinforced plastic;

[0095] Polyester fiber has excellent corrosion resistance and is especially suitable for seawater environments. Polyester fiber has good flexibility and can effectively absorb the impact of water flow and reduce the damage of water flow to the energy dissipation net. Glass fiber reinforced plastic has very high strength and rigidity and can withstand greater water flow impact, making it suitable for energy dissipation nets in submarine environments.

[0096] In step S3, the reasonable spacing between the energy dissipation net and the pile foundation is determined according to the flow velocity and flow direction change of the reciprocating flow and the transport trend of the sediment. If the spacing is too small, the energy dissipation net may be damaged by excessive scouring force, and if the spacing is too large, the energy dissipation effect may be affected. The spacing is set to 3-10 times the diameter of the pile foundation.

[0097] In step S3, simulation is performed using FLOW-3D or CFD software;

[0098] S31. Divide the computational domain in the simulation software; ensure that the size of the computational domain is large enough to cover the entire study area and capture the flow details. Divide the computational domain and ensure that the grid size is large enough to capture the flow details, especially in the key area near the energy dissipation network, where a finer grid needs to be divided to improve the accuracy of the simulation.

[0099] S32, setting in the simulation software according to the boundary conditions defined in step S2;

[0100] S33, inputting the sediment data collected in step S1 into the simulation software;

[0101] S34. Run the simulation to observe the effects of reciprocating flow, waves and tides on pile foundations and energy dissipation nets.

[0102] FLOW-3D is a software specifically designed for free surface flow simulations and is suitable for problems involving waves, tides and sediment transport.

[0103] In step S4, when conducting the flume test, it is necessary to ensure the similarity between the model experiment and the radiation sand ridge group in the South Yellow Sea, which involves gravity similarity and resistance similarity, that is, the Froude similarity criterion and the Reynolds similarity criterion. According to the continuity equation and momentum equation of viscous incompressible fluid, the similarity of water flow motion must meet the two conditions of gravity similarity and resistance similarity.

[0104] The gravity similarity formula is Where u′ is the velocity, g is the gravitational acceleration, and L is the characteristic length; the velocity scale and characteristic length scale must satisfy u m is the experimental water flow rate, u p is the water velocity of the radial sand ridges in the South Yellow Sea, L m ,L p is the characteristic length of the experimental and South Yellow Sea radiating sand ridge groups, and the subscripts m and p represent the experimental and South Yellow Sea radiating sand ridge groups;

[0105] The resistance similarity formula is Among them, υ is the dynamic viscosity coefficient. In the experiment, it needs to satisfy

[0106] Subscripts m and p denote the experimental and South Yellow Sea radiating sand ridge groups;

[0107] Water flow time scale Flow rate scale

[0108] In step S4, the preparation for the water tank test includes:

[0109] According to the geographical characteristics and sediment data of the radiation sand ridges in the South Yellow Sea, a scaled model flume was constructed. If the geometric scale of the model is too small, the pile foundation of the scaled model will be reduced accordingly, and it will be difficult to measure the water flow changes caused by the pile foundation of the scaled model; if the geometric scale is too large, the water depth and test flow rate in the test field will be large, which will put forward higher requirements on the scope of the test site and the test water supply and return power equipment. The geometric scale of the scaled model is 1:30-35; the physical model of the flume is 60m long, 12m wide, and 0.15m deep.

[0110] The water flow in the experiment uses water from the reservoir. The water pump draws water through the reciprocating flow pipe, and the water flows. The experimental water flow reciprocates to simulate the reciprocating water flow.

[0111] Prepare the sediment samples required for the experiment, ensuring that they are consistent with the sediment characteristics of the radial sand ridges in the South Yellow Sea, with a sand content of 45-49%; a silt content of 43-45%; and a clay content of 5-8%. Add the sediment samples to the experimental field from the sediment feeding port, and use the water flow to wash the sediments toward the foundation piles;

[0112] The actual single pile foundation diameter is 0.3-0.4m, the pile center spacing is 3.5-4m, and the scaled model pile foundation is arranged in the water tank. The scaled model pile foundation size and spacing are scaled 1:30-35 according to the actual situation. The scaled model pile foundation diameter is 0.9-1.3cm, the scaled model pile foundation center spacing is 10-13.3cm, and the number of pile foundations is 8-10;

[0113] Arrange the energy dissipation net around the scaled model pile foundation. The pore size, material properties and distance between the energy dissipation net and the pile foundation are based on the data of the physical model of the S3 energy dissipation net.

[0114] The average particle size of the sediment is between 1.85 and 6.5 Φ; the pore diameter of the energy dissipation net is 2-5 times the average particle size of the sediment, and the pore diameter of the energy dissipation net is 3.7 to 32.5 Φ;

[0115] The pore structure shape of the energy dissipation net is selected from one of circular pores, square pores and elliptical pores. The material of the energy dissipation net is selected from glass fiber reinforced plastic or polyester fiber;

[0116] The distance between the energy dissipation net and the scaled model pile foundation is 3-10 times the diameter of the scaled model pile foundation, and the distance between the energy dissipation net and the scaled model pile foundation is 2.7-13cm. It is set in front of the scaled model pile foundation, behind the scaled model pile foundation, and on the right side of the scaled model pile foundation;

[0117] According to the reciprocating flow characteristics of the radial sand ridges in the South Yellow Sea, the changes in water flow velocity during high tide and low tide were simulated. The experimental water flow velocity was 0.5-0.65m / s, and real-time monitoring and adjustment were carried out through flow meters and flow control valves.

[0118] Before, during and after the experiment, use a high-resolution camera or laser scanner to record the water velocity around the pile foundation of the scale model, and the settlement and accumulation of sediments in front of and behind the energy dissipation net;

[0119] Record data such as water flow speed, direction, and tidal changes;

[0120] In step S4, the steps of executing the water tank test include:

[0121] S41. Start the water flow to simulate the water flow environment under the action of reciprocating flow; observe and record the transport and accumulation of sediments, especially the changes in sediments before and after the energy dissipation net;

[0122] S42. Regularly check the wear status of the scale model pile foundation and energy dissipation net, and adjust the water flow rate or sediment input as needed to maintain the stability of the experimental conditions.

[0123] S43. Turn off the water flow, stop the experiment, organize and analyze the experimental data, and compare the effects of different energy dissipation net pore sizes, arrangements, and scale model pile foundation spacing on sediment accumulation and scale model pile foundation scour.

[0124] Embodiment 1

[0125] A water tank test comprising:

[0126] A physical model of a water tank with a length of 60m, a width of 12m and a water depth of 0.15m was constructed, and the geometric scale of the scaled model was selected to be 1:30;

[0127] Prepare sediment samples to ensure that the sand content is 47%, the silt content is 44%, the clay content is 7%, and the average particle size is controlled at 4Φ;

[0128] The scaled model pile foundation size and spacing are scaled at 1:30. The actual single pile foundation diameter is 0.35m, so the scaled model pile foundation diameter is 1.2cm, the pile center spacing is 3.75m, so the scaled model pile foundation center spacing is 12.5cm, and the number of pile foundations is set to 9;

[0129] The pore structure of the energy dissipation net is circular pores, and the arrangement is vertically aligned;

[0130] The pore diameter of the energy dissipation net is selected to be 3 times the average particle size of the sediment, that is, 12Φ;

[0131] The material of the energy dissipation net is glass fiber reinforced plastic;

[0132] The distance between the energy dissipation net and the scale model pile foundation is set to 5 times the diameter of the scale model pile foundation, that is, 6 cm, and is arranged in front of, behind and to the right of the scale model pile foundation;

[0133] According to the reciprocating flow characteristics of the radial sand ridges in the South Yellow Sea, the experimental water flow velocity was set to 0.63 m / s, and was monitored and adjusted in real time by a current meter;

[0134] Turn on the water flow to simulate the water flow environment under the action of reciprocating flow; record the water flow velocity around the scaled model pile foundation, the settlement and accumulation of sediments before and after the energy dissipation net, and the wear status of the scaled model pile foundation and the energy dissipation net every 3 hours.

[0135] Embodiment 2

[0136] A water tank test, the same points as those in the first embodiment are not repeated here, and the difference between this embodiment and the first embodiment is that;

[0137] The pore structure of the energy dissipation net is in the shape of square pores, and the arrangement is aligned up and down;

[0138] Embodiment 3

[0139] A water tank test, the same points as those in the first embodiment are not repeated here, and the difference between this embodiment and the first embodiment is that;

[0140] The pore structure of the energy dissipation net is an elliptical aperture, and the arrangement is aligned up and down;

[0141] Embodiment 4

[0142] A water tank test, the same points as those in the first embodiment are not repeated here, and the difference between this embodiment and the first embodiment is that;

[0143] The pore structure of the energy dissipation net is circular pores, and the arrangement is staggered;

[0144] Embodiment 5

[0145] A water tank test, the same points as those in the second embodiment are not repeated here, the difference between this embodiment and the second embodiment is that;

[0146] The pore structure of the energy dissipation net is square pores, and the arrangement is staggered;

[0147] Embodiment 6

[0148] A water tank test, the same points as those in the third embodiment are not repeated here, the difference between this embodiment and the third embodiment is that;

[0149] The pore structure of the energy dissipation net is elliptical in shape and arranged in a staggered manner;

[0150] Embodiment 7

[0151] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0152] The pore diameter of the energy dissipation net is twice the average particle size of the sediment, that is, 8Φ;

[0153] Embodiment 8

[0154] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0155] The pore diameter of the energy dissipation net is 4 times the average particle size of the sediment, that is, 16Φ;

[0156] Embodiment 9

[0157] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0158] The pore diameter of the energy dissipation net is 5 times the average particle size of the sediment, that is, 20Φ;

[0159] Embodiment 10

[0160] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0161] The distance between the energy dissipation net and the scaled model pile foundation is set to 3 times the diameter of the scaled model pile foundation, that is, 3.6 cm; Example 11

[0162] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0163] The distance between the energy dissipation net and the scaled model pile foundation is set to 7 times the diameter of the scaled model pile foundation, that is, 8.4 cm; Example 12

[0164] A water tank test, the same as the sixth embodiment will not be repeated, the difference between this embodiment and the sixth embodiment is;

[0165] The distance between the energy dissipation net and the scaled model pile foundation is set to 9 times the diameter of the scaled model pile foundation, that is, 10.8 cm;

[0166] A water tank test, the same points as those in the first embodiment are not repeated here, and the difference between this embodiment and the first embodiment is that;

[0167] No energy dissipation net is set near the pile foundation of the scale model.

[0168] Test Example 1

[0169] This test example selects Example 1 to Example 6 and Comparative Example 1 to detect the water flow velocity in front, back and right of the scaled model pile foundation and the increase in sediment before and after the energy dissipation net after 24 hours;

[0170] Table 1 Effects of the pore structure shape and arrangement of the energy dissipation net on sediment and water flow

[0171]

[0172]

[0173] According to the data in the table above, the pore structure shape and arrangement of the energy dissipation net have a significant impact on the interception effect of sediment and the flow rate of water; the elliptical aperture performs best in sediment interception, especially the staggered elliptical aperture, the increase in sediment before and after the energy dissipation net is much lower than that of other experimental groups. This shows that the elliptical aperture is more effective in reducing the passage and accumulation of sediment; the water flow rate of the comparative example 1 without the energy dissipation net is the highest, indicating that the energy dissipation net plays an important role in slowing down the water flow and protecting the pile foundation from scouring.

[0174] Test Example 2

[0175] This test example selects Example 6 to Example 9 and Comparative Example 1 to detect the water flow velocity in front, behind and right of the scaled model pile foundation after 24 hours and the increase in sediment before and after the energy dissipation net;

[0176] Table 2 Effect of pore diameter of energy dissipation net on sediment and water flow

[0177]

[0178]

[0179] According to the above data, it can be obtained that when the pore diameter is 12Φ, the increase in sediment before and after the energy dissipation net is the smallest, indicating that the interception effect of the energy dissipation net is the best under this diameter; circular pores are the easiest to manufacture and the shape that can most evenly distribute water flow, which can provide better water flow smoothness and reduce local water turbulence. However, if the pores are too large, larger particles of sediment will pass through, thereby increasing the risk of impact on the pile foundation. If the pores are too small, fine particles may accumulate in front of the pores. In large-scale production, square pores are easy to manufacture. Compared with circular pores, square pores will produce higher shear stress at the edge of the pores, resulting in a decrease in the interception effect on sediments and the efficiency effect on water flow.

[0180] According to the above table, preferably, elliptical pores are selected as the pore structure shape of the energy dissipation net of the present application. The elliptical pores combine the advantages of circular pores and parallelogram pores, maintain a certain water flow smoothness, and allow a more flexible design to adapt to particles of different sizes;

[0181] Test Example 3

[0182] This test example selects Example 6, Example 10 to Example 12 and Comparative Example 1 to detect the water flow velocity in front, rear and right of the scaled model pile foundation and the increase in sediment before and after the energy dissipation net after 24 hours;

[0183] Table 3 Effect of the distance between the energy dissipation net and the scaled model pile foundation on sediment and water flow

[0184]

[0185]

[0186] According to the above data, it can be obtained that the effect of Example 6 is the best, the amount of sediment increase before and after the energy dissipation net is the least, and the water flow rate is the lowest. As the spacing increases, the amount of sediment increase increases slightly, and the water flow rate also increases, but the increase is not large, which shows that the energy dissipation net is still effective. However, when the spacing decreases, the amount of sediment increase and the water flow rate are slightly higher than those of Example 6. Due to the small spacing, the energy dissipation net is subjected to greater water flow pressure, which affects its energy dissipation effect.

[0187] In step S5,

[0188] S51, comparing the simulation results with the actual observation data of the water tank test and analyzing the differences between the two;

[0189] Flow field comparison: compare the simulated flow velocity distribution with the flow velocity distribution measured in the flume test;

[0190] Sediment transport comparison: Comparison of simulated sediment transport pathways and amounts with observations from flume tests;

[0191] The interception efficiency of the energy dissipation net Among them, Q in is the sediment transport rate before entering the energy dissipation network, Q out is the sediment transport rate after passing through the energy dissipation network, and the total amount of sediment passing through the energy dissipation network per unit time t is calculated as M = Q out ×t=Q in ×(1-E′)×t;

[0192] Sediment accumulation comparison: compare the location and amount of sediment accumulation predicted by simulations with the actual accumulation in flume tests;

[0193] S52. Based on the comparative analysis results, identify the deviations in the simulation and their causes, re-simulate using the adjusted model, and compare with the water tank test data again until the simulation results are basically consistent with the experimental data;

[0194] S53. Adjust the pore size of the energy dissipation net according to the sediment accumulation observed in the flume test to ensure that fine particles can pass through without causing large particles to directly impact the pile foundation.

[0195] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A test method for scour protection of offshore wind power pile foundations of submarine energy dissipation nets based on fluid dynamics simulation for reciprocating flow. The invention comprises: and is characterized in that; S1. Analyze the geographical characteristics of the radial sand ridges in the South Yellow Sea, collect and measure sediment samples, and obtain sediment data; S2. Based on the principles of fluid dynamics, a mathematical model of the effects of reciprocating flow, waves and tides on pile foundation scour is established; S3, according to the geographical features and sediment data, the energy dissipation network data is added to the S2 mathematical model for simulation; S4. Build a scaled model based on the radial sand ridges in the South Yellow Sea and conduct flume tests; S5. Compare the simulation and water tank test data, and adjust the pore size, material properties and distance from the pile foundation of the energy dissipation net according to the water tank test data.

2. The method for testing scour protection of offshore wind power pile foundations of a submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S1, the geographical characteristics of the radial sand ridges in the South Yellow Sea include: the distribution of sand ridges, the shape of sand ridges, the scale of sand ridges, water flow velocity, water flow direction and tidal variation law; the sediment data include: the particle size distribution of sediments, sediment content and sediment transport trend.

3. The method for testing scour protection of offshore wind power pile foundations of a submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S2, a model is established based on the Navier-Stokes equations; The conservation of fluid mass is described by the continuity equation: Where ρ is the fluid density; u is the velocity vector of the fluid, and t is the time; The conservation of fluid momentum is described by the Navier-Stokes equations: Among them, p is the pressure, τ is the stress tensor, and f is the external force; Energy conservation is described by the energy equation: Where E is the total energy, k is the thermal conductivity, T is the temperature, and Φ is the power dissipated per unit volume.

4. The method for testing scour protection of offshore wind power pile foundations of a submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow according to claim 3, characterized in that: The boundary conditions in step S2 include: reciprocating fluid boundary conditions, wave boundary conditions and tidal boundary conditions; Reciprocating fluid boundary conditions: Assuming that the water flow at the inlet is uniform, a fixed velocity boundary condition is set at the inlet. The velocity inlet boundary condition is: u(t) = U0 + U tidal sin(ωt+φ), U0 is the average flow velocity, U tidal is the velocity amplitude caused by tide, ω is the angular frequency, and φ is the phase angle; At the water outlet, the free outlet boundary condition is used to allow the fluid to flow out freely without generating reflection waves. The pressure outlet boundary condition is: Where n is the direction of the normal pointing outside the boundary; On the pile surface and other solid boundaries, the velocity of the fluid must be equal to the velocity of the solid, and the no-slip condition: u| wall =0; When studying erosion or deposition effects, the shear stress condition: Among them, τ w is the wall shear stress, μ is the dynamic viscosity of the fluid; Wave boundary conditions: Apply wave conditions involving velocity and pressure distribution at the crest and trough: η(x,t)=Acos(kx-ω′t+φ), where η is the free surface displacement, A is the wave amplitude, k is the wave number, and ω′ is the circular frequency; Tidal boundary conditions: The flow velocity and water level changes caused by tides are represented by a periodic function: ; where is the water level change, is the tidal amplitude, is the angular frequency of the tide, and is the phase angle of the tide.

5. The method for testing scour protection of offshore wind power pile foundation of submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S3, the pore diameter of the energy dissipation net is 2-5 times the average particle size of the sediment; the pore structure shape of the energy dissipation net is one of circular pores, square pores and elliptical pores; the material of the energy dissipation net is one of polyester fiber and glass fiber reinforced plastic; the distance between the energy dissipation net and the pile foundation is 3-10 times the diameter of the pile foundation.

6. The method for testing scour protection of offshore wind power pile foundations of a submarine energy dissipation network based on fluid dynamics simulation for reciprocating flow according to claim 5, characterized in that: The rows of pores in the energy dissipation net are staggered, with each row of pores offset relative to the previous row so that each pore is not directly below the previous row of pores.

7. The method for testing scour protection of offshore wind power pile foundations of submarine energy dissipation nets based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S4, according to the continuity equation and momentum equation of viscous incompressible fluid, the similarity of water flow motion satisfies the similarity of gravity and resistance: The gravity similarity formula is Where u′ is the velocity, g is the gravitational acceleration, and L is the characteristic length; the velocity scale and characteristic length scale must satisfy u m is the experimental water flow rate, u p is the water velocity of the radial sand ridges in the South Yellow Sea, L m ,L p is the characteristic length of the experimental and South Yellow Sea radiating sand ridge groups, and the subscripts m and p represent the experimental and South Yellow Sea radiating sand ridge groups; The resistance similarity formula is Among them, υ is the dynamic viscosity coefficient. In the experiment, it needs to satisfy Subscripts m and p denote the experimental and South Yellow Sea radiating sand ridge groups; Water flow time scale Flow rate scale 8. The method for testing scour protection of offshore wind power pile foundations of submarine energy dissipation nets based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S4, the steps of executing the water tank test include: S41, start the water flow, simulate the water flow environment under the action of reciprocating flow, and observe and record the transport and accumulation of sediments; S42. Regularly check the wear status of the scale model pile foundation and energy dissipation net; S43. Turn off the water flow, stop the experiment, organize and analyze the experimental data, and compare the effects of different energy dissipation net pore sizes, arrangements, and scale model pile foundation spacing on sediment accumulation and scale model pile foundation scour.

9. The method for testing scour protection of offshore wind power pile foundations of submarine energy dissipation nets based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S4, the sediment sample required for the experiment has a sand content of 45-49%, a silt content of 43-45%, and a clay content of 5-8%.

10. The method for testing scour protection of offshore wind power pile foundations of submarine energy dissipation nets based on fluid dynamics simulation for reciprocating flow according to claim 1, characterized in that: In step S4, the water flow velocity is 0.5-0.65 m / s.

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