Experimental evaluation method and system for scouring protection of offshore wind power single pile foundation

Abstract

The invention relates to the technical field of offshore wind power single pile foundation scour protection, in particular to an experimental evaluation method and system for offshore wind power single pile foundation scour protection, and the method comprises the steps: obtaining a pile foundation simulation model through an offshore pile foundation structure and sea condition environment simulation, arranging a biological reef model around the pile foundation simulation model according to a set configuration, the flow field characteristics of interaction of the biological reef and the pile foundation are obtained through a fixed bed hydrodynamic characteristic test, scouring parameters are measured through a movable bed scouring anti-skid verification test, and accordingly, the sand washing protection effect of the biological reef is quantitatively analyzed and evaluated, and the configuration characteristics of the biological reef are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of scour protection for offshore wind power monopile foundations, and in particular to an experimental evaluation method and system for scour protection for offshore wind power monopile foundations. Background Art

[0002] Pile foundations are widely used as supporting structures in bridge and marine engineering. While bearing the loads of the superstructure, these pile foundations also face a complex and changing hydrodynamic environment, including the impact of currents and waves. Because the pile foundations block the flow field, surrounding sediment is easily carried away, causing localized scouring. This scouring not only reduces the bearing capacity of the pile foundations but also may expose attached pipelines, posing safety risks to the engineering structure. Therefore, implementing appropriate protective measures to address scouring around pile foundations is crucial for maintaining the long-term safety and stability of engineering structures.

[0003] Bioherms, artificial structures designed to improve the aquatic environment and promote fishery development, have recently been used to protect pile foundations from scour. By placing bioherms around pile foundations, they effectively reduce the impact of water on the surrounding sediment, thereby protecting the safety and stability of the piles. However, practical application of bioherm scour protection technology still faces numerous challenges.

[0004] First, existing reef configuration designs often prioritize ecological benefits, such as providing fish habitats and improving water quality, but lack methods for optimizing reef layout from the perspective of scour mechanisms. This results in reefs not being ideal for scour protection in practical applications.

[0005] Secondly, there is currently a lack of quantitative assessment methods for the effectiveness of bioherms for scour protection around pile foundations. This makes it difficult to compare the advantages and disadvantages of different bioherm configurations or arrangements, limiting the further development of bioherm scour protection technology.

[0006] Furthermore, the experimental process for verifying the effectiveness of bioherms for scour protection is also plagued by numerous challenges. Because it's impossible to exhaustively consider all possible arrangements of multiple bioherms around pile foundations, the traditional method of determining the optimal arrangement relies solely on trial-and-error experiments. This approach is inefficient and struggles to guarantee reliable results.

[0007] Finally, conducting large-scale dynamic bed scour experiments to verify the effectiveness of reef scour protection requires a significant amount of manpower, material, and financial resources. Furthermore, the lack of clear experimental procedures and standards can easily increase errors during the experiment, affecting the accuracy of the experimental results.

[0008] In summary, existing bioherm scour protection technologies still face many challenges in practical applications. It is necessary to develop a systematic approach to optimize the layout design of bioherms, improve the scour protection effect, and reduce the cost and time of experimental verification. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide an experimental evaluation method and system for scour protection of offshore wind power single pile foundations, so as to solve the technical problems of low efficiency and poor effect of traditional bio-reef scour protection arrangement methods.

[0010] The purpose of the present invention is achieved by the following technical solutions: In a first aspect, the present invention provides an experimental evaluation method for scour protection of an offshore wind turbine monopile foundation, comprising: According to the offshore pile foundation structure and sea conditions, simulation is performed according to the set ratio to obtain a pile foundation simulation model; Arrange the reef model around the pile foundation simulation model according to the set configuration; Using the fixed-bed hydrodynamic characteristics test, a fixed-bed test was conducted on a simulation model of a pile foundation with bioherms to obtain the flow field characteristics of the interaction between the bioherms and the pile foundation. Using the moving bed scour and anti-slip verification test, a scour test was conducted on a pile foundation simulation model with bio-reef layout, and the scour parameters were measured. The sand scouring protection effect of the reef was quantitatively analyzed and evaluated based on the flow field characteristics and scouring parameters of the reef, and the configuration characteristics of the reef were obtained based on the quantitative analysis and evaluation results.

[0011] As a further improvement of the present invention, the simulation is performed according to a set ratio based on the offshore pile foundation structure and the sea conditions to obtain a pile foundation simulation model, which specifically includes: Set up a water tank, arrange the sand bed in the water tank according to the actual sea conditions, and determine the target seawater flow rate according to the Froude criterion; The pile foundation is simulated according to a set ratio to obtain a pile foundation model, and the pile foundation model is fixed on the sand bed in the center of the water tank; Start the water pump, fill the water tank with water to the set depth, open the water pump and the water tank inlet and outlet, gradually increase the flow rate, measure the flow rate after the water flow stabilizes, and repeatedly adjust the water pump power and gate opening until the water depth and flow rate meet the target seawater flow rate.

[0012] As a further improvement of the present invention, the bioherm model is arranged around the pile foundation simulation model according to a set configuration, specifically including: the configuration of the bioherm model includes a triangle, a hemispherical shape, and a frame square shape.

[0013] As a further improvement of the present invention, a fixed bed hydrodynamic characteristic test is performed on a pile foundation simulation model with a bioreef arrangement, specifically including: A pile foundation and a reef model were placed in a fixed-bed water tank. Particle image velocimetry was used to measure the flow field around the piles. This flow field information included downwelling in front of the piles, lateral velocity gradients, flow field differences inside and outside the reef, and edge scour. Key sections are selected for two-dimensional flow field analysis to generate velocity distribution maps, identify high velocity areas and vortex structures, and obtain flow field characteristics; key sections include at least: upstream of the pile, side of the pile, inside and outside the reef body, and outside the reef group.

[0014] As a further improvement of the present invention, a fixed bed hydrodynamic characteristic test is performed on a pile foundation simulation model with a bioreef arrangement, specifically including: A pile foundation and a reef model were placed in a fixed-bed water tank. Particle image velocimetry was used to measure the flow field around the piles. This flow field information included downwelling in front of the piles, lateral velocity gradients, flow field differences inside and outside the reef, and edge scour. Key sections are selected for two-dimensional flow field analysis to generate velocity distribution maps, identify high velocity areas and vortex structures, and obtain flow field characteristics; key sections include at least: upstream of the pile, side of the pile, inside and outside the reef body, and outside the reef group.

[0015] As a further improvement of the present invention, in the step of the fixed bed hydrodynamic characteristics test, the experimental system used includes a laser, a camera and a control computer; After the laser is moved to the section to be measured, keep the laser on and adjust the camera position and focal length to make the tracer particles clearly imaged; When the flow field in the water tank stabilizes, an external control computer is used to control the camera to take pictures, obtaining a series of tracer particle distribution images and realizing two-dimensional measurement of the flow field.

[0016] As a further improvement of the present invention, a scouring test is conducted on a pile foundation simulation model with a bio-reef arrangement using a moving bed scouring and anti-slip verification test, specifically including: Pile foundations and bio-reef models were laid out in the sand bed flume, and the scouring environment was simulated by adjusting the water flow parameters to achieve a balanced state. The current scour depth and width are measured, and the protection effect is quantified by dimensionless parameters; the scour depth is expressed as: l / l 0; Scour width is expressed as: s / s 0; in, l 0 and s 0 is the washout data of the unprotected control group, l is the scour depth, and s is the scour width.

[0017] As a further improvement of the present invention, the sand scouring protection effect of the bioherm is quantitatively analyzed and evaluated based on the flow field characteristics of the bioherm and the scouring parameters. The evaluation index of the protection effect of the scouring parameters specifically includes: the scouring depth reduction rate, the scouring width reduction rate, and the adaptability of the bioherm; The scour depth reduction rate is obtained according to the scour depth; and the scour width reduction rate is obtained according to the scour width.

[0018] As a further improvement of the present invention, a quantitative analysis and evaluation of the sand scouring protection effect of the bioherm is conducted based on the flow field characteristics and scouring parameters of the bioherm, including analysis of key sections in the fixed bed hydrodynamic characteristics test, specifically including: The upstream section of the pile foundation is used to analyze the downwelling flow and wake vortex morphology; Side sections of pile foundations to assess lateral scour; Internal sections of bioherms are used to observe flow field differences; Reef edge section, used to detect edge scour effects.

[0019] As a further improvement of the present invention, the arrangement of bioherms is optimized based on the quantitative analysis and evaluation results to obtain the best protection plan; the optimization of the arrangement of bioherms specifically includes: The frame square bioreefs are arranged in combination with the hemispherical bioreefs. The frame square bioreefs are evenly arranged around the pile foundation to form a closed circle. The hemispherical bioreefs are evenly arranged on the outside of the corresponding frame square bioreefs upstream of the pile foundation as a buffer. In a second aspect, the present invention provides an experimental evaluation system for scour protection of offshore wind power monopile foundations, which is used to implement the above-mentioned experimental evaluation method for scour protection of offshore wind power monopile foundations, including: The model simulation module simulates the offshore pile foundation structure and sea conditions according to the set ratio to obtain a pile foundation simulation model; The bioherm layout module arranges the bioherm model around the pile foundation simulation model according to the set configuration; The fixed-bed test module uses the fixed-bed hydrodynamic characteristics test to conduct fixed-bed tests on a pile foundation simulation model with bioherms, and obtain the flow field characteristics of the interaction between the bioherms and the pile foundations; The moving bed test module uses the moving bed scour and anti-slip verification test to conduct scour tests on a pile foundation simulation model with bio-reef layout, and measures scour parameters; The test evaluation module quantitatively analyzes and evaluates the sand scouring protection effect of the bioherm based on the flow field characteristics and scouring parameters of the bioherm, and obtains the configuration characteristics of the bioherm.

[0020] The beneficial effects of the present invention are as follows: the present invention provides an experimental evaluation method for scour protection of offshore wind power single pile foundations. Through the experimental evaluation method, the configuration of the reef can be optimized to better adapt it to the actual marine environment, thereby improving the scour protection effect of the offshore wind power single pile foundation. Effective scour protection can extend the service life of the pile foundation, reduce the maintenance and replacement costs caused by scour, and improve the economic benefits of offshore wind power projects. Strengthening scour protection can reduce the risk of pile foundation failure due to scour, thereby enhancing the overall safety of offshore wind power projects. By improving the safety and economy of offshore wind power projects, it helps to promote the sustainable development of the offshore wind power industry and contribute to the utilization of clean energy.

[0021] Furthermore, a water tank of appropriate size was selected based on actual ocean conditions. The tank should be able to simulate ocean conditions such as water depth, currents, and waves. A sand bed was arranged in the tank, and the material and particle size of the sand bed should be similar to sediments in actual ocean environments to ensure the authenticity of the simulation. The target seawater flow rate was determined based on the Froude criterion. The Froude criterion is used to simulate fluid dynamics and ensure the similarity between the model and the prototype. The arrangement of the sand bed in the tank and the fixing method of the pile foundation model simulated the stress conditions of the pile foundation in an actual ocean environment, improving the authenticity and reliability of the simulation.

[0022] Furthermore, PIV technology enables intuitive visualization of the flow field distribution around pile foundations and bioherms, generating detailed velocity distribution maps. Analysis of flow field characteristics allows assessment of the protective effectiveness of bioherms, such as reduced scour, lowered flow velocity, and weakened eddies. Analysis of flow field characteristics can also optimize bioherm design, such as by adjusting their shape, size, position, and arrangement. By conducting fixed-bed hydrodynamic tests and using PIV technology to measure and analyze the flow field of a pile foundation simulation model with bioherms, we can gain a deeper understanding of the impact of bioherms on the flow field around the pile foundation, assess their protective effectiveness, and optimize their design. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 This is a flow chart of an experimental evaluation method for scour protection of an offshore wind power monopile foundation in an embodiment of the present invention; Figure 2 Schematic diagram of the overall arrangement of different types of bioherms in an embodiment of the present invention.

[0025] FIG3( a ) is a schematic diagram of a fixed bed hydrodynamic characteristics experiment in an embodiment of the present invention.

[0026] FIG3( b ) is a schematic diagram of a cross-sectional measurement of a fixed bed hydrodynamic characteristics experiment in an embodiment of the present invention.

[0027] Figure 4 It is a schematic diagram of a moving bed scour protection test in an embodiment of the present invention.

[0028] Figure 5 It is a schematic diagram of the measurement points for evaluating the scour protection effect in the fixed bed hydrodynamic characteristics test in an embodiment of the present invention.

[0029] FIG6( a ) is a flow field distribution diagram around an unprotected pile foundation in an embodiment of the present invention.

[0030] Figure 6 (b) is a flow field distribution diagram around the pile foundation under the frame square fish reef protection in an embodiment of the present invention Figure 6 (c) is a flow field distribution diagram around the pile foundation under the triangular fish reef protection in an embodiment of the present invention FIG6( d ) is a flow field distribution diagram around the pile foundation under the hemispherical fish reef protection in an embodiment of the present invention.

[0031] Figure 7 1 is a graph showing the particle size distribution of experimental sand in an embodiment of the present invention.

[0032] FIG8( a ) is a diagram showing a scouring and anti-skid verification test of a moving bed under scouring at 0.2 m / s in an embodiment of the present invention.

[0033] FIG8( b ) is a diagram showing a scouring and anti-skid verification test of a moving bed under scouring at 0.25 m / s in an embodiment of the present invention.

[0034] FIG8( c ) is a diagram showing a scouring and anti-skid verification test of a moving bed under scouring at 0.3 m / s in an embodiment of the present invention.

[0035] Figure 9 It is an optimized layout design diagram in an embodiment of the present invention.

[0036] Figure 10 This is the best protection scheme arrangement diagram in the embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] The technical solutions of the present invention will be described clearly and completely below with reference to the accompanying drawings and specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0039] Example 1 like Figures 1 to 10 This embodiment provides an experimental evaluation method for scour protection of offshore wind turbine single pile foundations. By combining fixed-bed hydrodynamic characteristics experiments with moving-bed scour verification experiments, particle image velocimetry (PIV) is used to obtain flow field information under the interaction between different bioherm configurations and pile foundations. This method accurately assists in optimizing the overall bioherm arrangement and efficiently implements a reliable overall design for bioherm scour protection. The following is a specific implementation method.

[0040] First, simulation is performed according to the set proportions based on the offshore pile foundation structure and sea conditions to obtain a pile foundation simulation model.

[0041] Specifically, a water tank is set up, the sand bed in the water tank is arranged according to the actual sea conditions, and the target seawater flow rate is determined according to the Froude criterion; The pile foundation is simulated according to a set ratio to obtain a pile foundation model, and the pile foundation model is fixed on the sand bed in the center of the water tank; Start the water pump, fill the water tank with water to the set depth, open the water pump and the water tank inlet and outlet, gradually increase the flow rate, measure the flow rate after the water flow stabilizes, and repeatedly adjust the water pump power and gate opening until the water depth and flow rate meet the target seawater flow rate.

[0042] In this embodiment, according to the actual sea conditions, the flow velocity, model length and width, and water depth are scaled down according to the Froude criterion (the recommended scale is ≥1:50), and the experimental model is manufactured and arranged.

[0043] The bioherm model is arranged around the pile foundation simulation model according to the set configuration. The configuration of the bioherm model in this embodiment includes triangle, hemispherical, and frame square. The arrangement is as follows Figure 2 As shown. The reef model is made of acrylic.

[0044] The fixed-bed hydrodynamic characteristics test was used to conduct a fixed-bed test on a simulation model of a pile foundation with bioherms to obtain the flow field characteristics of the interaction between the bioherms and the pile foundation.

[0045] Specifically, a pile foundation and a bioherm model were placed in a fixed-bed water tank, and particle image velocimetry was used to measure the flow field information around the pile. The flow field information included downwelling in front of the pile, lateral velocity gradient, flow field differences inside and outside the bioherm, and edge scour flow field. Key sections are selected for two-dimensional flow field analysis to generate velocity distribution maps, identify high velocity areas and vortex structures, and obtain flow field characteristics; key sections include at least: upstream of the pile, side of the pile, inside and outside the reef body, and outside the reef group.

[0046] In the steps of the fixed bed hydrodynamic characteristics test in this embodiment, the experimental system used includes a laser, a camera, and a control computer; 3. A laser is arranged on the lower side of the water tank and a high-speed camera is arranged on the side (as shown in the left figure) to perform two-dimensional PIV measurements of the flow field around the model.

[0047] After the laser is moved to the section to be measured, keep the laser on and adjust the camera position and focal length to make the tracer particles clearly imaged; When the flow field in the water tank stabilizes, an external control computer is used to control the camera to take pictures, obtaining a series of tracer particle distribution images and realizing two-dimensional measurement of the flow field.

[0048] In addition, the density of the model in this embodiment needs to be as close as possible to the actual engineering material to simulate the behavior of real reefs, and can be manufactured by concrete injection molding or 3D aluminum alloy printing.

[0049] The moving bed scour and anti-slip verification test was used to conduct a scour test on a pile foundation simulation model with bio-reef layout, and the scour parameters were measured.

[0050] Specifically, pile foundations and bio-reef models were laid out in a sand bed flume, and the scouring environment was simulated by adjusting the water flow parameters to achieve a balanced state. The current scour depth and width are measured, and the protection effect is quantified by dimensionless parameters; the scour depth is expressed as: l / l 0; Scour width is expressed as: s / s 0; in, l 0 and s 0 is the washout data of the unprotected control group, l is the scour depth, and s is the scour width.

[0051] The sand scouring protection effect of the reef was quantitatively analyzed and evaluated based on the flow field characteristics and scouring parameters of the reef, and the configuration characteristics of the reef were obtained based on the quantitative analysis and evaluation results.

[0052] First, the sand scouring protection effect is evaluated based on the flow field characteristics of the bioherm. As shown in Figure 3, this mainly includes the analysis of the key sections in the fixed bed hydrodynamic characteristics test, including: The upstream section of the pile foundation is used to analyze the downwelling flow and wake vortex morphology; Side sections of pile foundations to assess lateral scour; Internal sections of bioherms are used to observe flow field differences; Reef edge sections, used to detect edge scour effects Secondly, the scour parameters are evaluated. The evaluation index of the protective effect of the scour parameters includes: the reduction rate of scour depth, the reduction rate of scour width, and the adaptability of the reef; The scour depth reduction rate is obtained according to the scour depth (1- l / l 0); Scour width reduction rate is obtained based on the scour width (1-s / s 0).

[0053] Example 2 As a preferred embodiment in Example 1, this embodiment specifically includes the following steps.

[0054] According to the given reef and pile foundation configuration, a model is made in a certain proportion (such as 3D printing), and the size of the reef is the same as the diameter of the pile foundation.

[0055] Specifically, to accommodate the differing requirements of fixed-bed and moving-bed experiments, two sets of experimental models were constructed. For fixed-bed experiments, PIV experiments required the use of transparent materials, and acrylic was chosen for economical processing. For moving-bed experiments, the model density needed to be as close as possible to actual engineering materials to simulate the behavior of real reefs. Concrete injection molding or 3D aluminum alloy printing was recommended.

[0056] The experiment was conducted by placing fish reefs in a 3×3 tightly encircled pattern around the pile foundation. The experiment was divided into two parts: The flow velocity field u after the interaction between the reef and the pile foundation is obtained by using the fixed bed hydrodynamic characteristics experiment; The scour experiment was carried out using the moving bed scour protection verification experiment to measure the dimensionless scour depth s / s0 and the dimensionless scour width l / l0.

[0057] In this example, fixed-bed hydrodynamic characteristics experiments were conducted in a large experimental flume. The experimental layout is shown in Figure 3(a). A rectifier was installed at the upstream inlet, a water depth gauge was attached to the sidewall, a continuously adjustable gate was installed at the end, and a flow meter was installed on the injection pipe. The pile foundation and reef model were fixed to the center of the flume via a connecting plate.

[0058] The specific steps of the fixed bed hydrodynamic characteristics experiment include: Due to the symmetry of the experimental model layout, flow field measurements only need to be performed on a single side of the pile foundation. Four sections (I, II, III, and IV, highlighted in green) were selected for measurement, as shown in Figure 3(b). After the experiment, the images were post-processed using the PIVlab open-source toolkit in Matlab software, followed by data integration and plotting using Python, resulting in a complete cross-sectional flow field map. Section I: This helps to understand the downwelling upstream of the pile foundation and the vortex pattern downstream; Section II: This passes through the side of the pile foundation and can reflect the degree of lateral scour; Section III: This passes through the interior of the upstream, midstream, and downstream reefs, facilitating the understanding of the flow field differences between the inside and outside of the reefs; Section IV: This section, located at the outermost edge of the reef complex, can examine the scour at the reef edges.

[0059] The moving bed scour protection test was carried out in a test flume with a sand bed. The experimental arrangement is as follows: Figure 4 As shown in the figure, the flume uses an external water pump to generate a constant water flow. A flow regulation section exists upstream, with a gate at the end to adjust the water depth. The experimental sand flume is filled to the same level as the flume floor. The test section features a plexiglass wall with a water depth gauge to facilitate observation and data collection. An electromagnetic flowmeter is installed upstream of the pile to measure single-point incoming flow velocity.

[0060] Before the moving bed scour protection test begins, several sets of experiments of varying lengths are conducted to determine the time required for scour to reach equilibrium. Subsequent operating conditions assume that scour has reached equilibrium. The specific steps for the moving bed scour protection test are as follows: (1) Fill the test soil to the plane elevation and preliminarily level the soil surface; (2) Start the water pump and fill the water tank to a certain depth. At this time, due to the high flow rate during water injection, a certain amount of scouring will occur near the pile foundation.

[0061] (3) Turn off the water pump and seal the water tank inlet and outlet, maintain a certain water depth, and then add test soil around the pile foundation and level it; (4) Handle the reef protection array with care to avoid damaging the flat soil surface; (5) Open the water pump and the inlet and outlet of the water tank, gradually increase the flow rate, and measure the flow rate after the water flow stabilizes. Repeatedly adjust the water pump power and gate opening until the water depth and flow rate meet the experimental requirements.

[0062] (6) After the test, turn off the water pump, take photos to record the damage to the protection, and measure the shape of the scour pit; (7) Repeat the above steps after cleaning the sink.

[0063] In order to quantitatively evaluate the scour protection effect of artificial reefs, the dimensionless scour depth is introduced. and dimensionless scour width As a parameter for evaluating the protection effect. 、 is the depth and width of the scour pit of the unprotected control group under a certain flow rate; 、 The depth and width of the scour pit at a certain flow rate after the bioreef is laid out at the corresponding flow rate. In particular, the side scour pit depth and width are the maximum values on both sides of the pile foundation. The schematic diagram of the measurement points is as follows: Figure 5 After removing the reef model, the depth and width of the scour pit upstream, along its sides, and downstream were measured to analyze its morphology. Immediately after the experiment, the scour pit contained a high concentration of suspended sediment, making accurate scour depth measurement difficult. Therefore, data collection was resumed after waiting approximately one hour for the water to clear.

[0064] The scour protection effect of the reef was quantitatively analyzed and evaluated by combining the experimentally obtained flow velocity u and the dimensionless scour width and depth, and the advantages and disadvantages of this reef configuration were summarized.

[0065] Based on the conclusions from step 3, adjust the reef layout around the pile foundation and repeat steps 1-3 to gain a more comprehensive and reliable understanding of the effectiveness of this type of reef for scour protection.

[0066] In addition, the fixed-bed hydrodynamic experimental model is machined from transparent acrylic material. The square dimensions of the frame are 14×14×14 cm, the triangular dimensions are 14×14×7 cm, the hemispherical diameter is 14 cm (the corresponding pile foundation model has a diameter of 14 cm), and the processing accuracy is 0.5 mm. The moving-bed scour experimental model is manufactured using a metal 3D printing process. The material is aluminum alloy with a density of 2.85 g / cm3 (slightly larger than ordinary concrete). The square dimensions of the frame are 5×5×5 cm, the triangular dimensions are 5×5×2.5 cm, the hemispherical diameter is 5 cm (the corresponding pile foundation model has a diameter of 5 cm), and the processing accuracy is 0.1 mm.

[0067] A high-speed PIV system was used to measure the two-dimensional flow field distribution around the pile foundation and bioherm during the moving bed scour and anti-skid verification test. The experimental system consists of a laser source, a high-speed camera, and a control computer. The laser is a VIASHO linear series laser with a maximum power of 15W, emitting a green light fan with a wavelength of 532nm. The high-speed camera is a Nikon-C model, capable of up to 2500 frames per second, a resolution of 2560×1600, and 50GB of solid-state memory. The laser is fixed to a guide rail below the flume, allowing the beam position to be adjusted along three axes. During the experiment, the laser is moved to the section to be measured and kept on. The camera position and focal length are adjusted to ensure a clear image of the tracer particles. After the flow field in the flume stabilizes, the camera is controlled by an external computer to take high-speed images, obtaining a series of images of the tracer particle distribution. After the experiment, the image set is exported and post-processed using the open-source PIVLab toolbox in Matlab to obtain the desired flow field distribution.

[0068] In addition, the test sand used in the dynamic bed scouring verification experiment was fine sand, and the median particle size measured by the laser particle size analyzer was 0.235 mm. The particle size distribution is as follows: Figure 7 shown.

[0069] In the final fixed-bed hydrodynamic characteristics test, the flow field distribution around the pile foundation was measured and shown in Figure 6(a)-Figure 6(d). From the perspective of scour mechanism, the scour protection effect of different reef configurations is preliminarily summarized: the frame-shaped square reef has a great blocking effect on the flow field and may have a good scour protection effect, but at the same time there is a significant lateral water flow, which may significantly expand the width of the scour pit; the triangular reef will direct the incoming flow to the sand bed, which is not conducive to scour protection; the hemispherical reef has a weaker effect on the water flow, but can better protect the sand bed it covers.

[0070] Table 1 shows the experimental conditions. Experiments 1-3 served as control experiments, retaining only the pile foundation without any scour protection measures. Experiments 4-12 served as verification experiments, deploying reefs of varying configurations. Prior to the experiment, measurements indicated that scour reached equilibrium after one hour.

[0071] Table 1: Comparison of dynamic bed scour verification experiments on reefs with different configurations

[0072] Figures 8(a)-8(c) show some of the experimental data obtained. The results of the fixed-bed experiments agree well with those of the moving-bed experiments. By incorporating the metric of reef adaptability to topographic changes, a more comprehensive assessment of the scour protection capabilities of the three reef configurations can be made. The results are shown in Table 2.

[0073] Table 2: Comparison of assessment results of reefs with different configurations

[0074] In order to improve the scour protection effect, the arrangement of the reefs was further optimized based on the evaluation results shown in Table 2.

[0075] If the frame square fish reefs can be arranged tightly, they can achieve good scour protection around the pile foundation; however, due to strong edge scour during the actual scour process, it is difficult to maintain its initial layout state as a whole, which greatly reduces the scour protection effect. Therefore, if the hemispherical fish reefs with a certain deceleration effect and weak edge scour are placed upstream of the frame square fish reefs as a buffer, the two types of biological reefs can complement each other. Figure 9 shown.

[0076] Further scour test results show that the above-mentioned combined arrangement can reduce the scour depth around the pile foundation by about 70% (30-40% in step three), achieving a good scour protection effect.

[0077] Finally, considering that scour protection under actual sea conditions needs to cope with reciprocating currents, the reefs are arranged symmetrically along the main current direction. Noting that there is still a possibility of strong edge scour on the side of the square frame, an additional row of reefs is added perpendicular to the main current direction, which can also optimize the overall adaptability of the reef to changes in the incoming current direction. The final design is as follows Figure 10 shown.

[0078] Through the above steps, a reliable arrangement of a combination of frame square and hemispherical bioherms for scour protection around pile foundations was efficiently obtained.

[0079] Example 3 This embodiment provides an experimental evaluation system for scour protection of offshore wind power monopile foundations, which is mainly used to implement the experimental evaluation method for scour protection of offshore wind power monopile foundations in Examples 1 and 2. The system includes: The model simulation module simulates the offshore pile foundation structure and sea conditions according to the set ratio to obtain a pile foundation simulation model; The bioherm layout module arranges the bioherm model around the pile foundation simulation model according to the set configuration; The fixed-bed test module uses the fixed-bed hydrodynamic characteristics test to conduct fixed-bed tests on a pile foundation simulation model with bioherms, and obtain the flow field characteristics of the interaction between the bioherms and the pile foundations; The moving bed test module uses the moving bed scour and anti-slip verification test to conduct scour tests on a pile foundation simulation model with bio-reef layout, and measures scour parameters; The test evaluation module quantitatively analyzes and evaluates the sand scouring protection effect of the bioherm based on the flow field characteristics and scouring parameters of the bioherm, and obtains the configuration characteristics of the bioherm.

Claims

1. An experimental evaluation method for scour protection of offshore wind power monopile foundation, characterized in that: include: According to the offshore pile foundation structure and sea conditions, simulation is performed according to the set ratio to obtain a pile foundation simulation model; Arrange the reef model around the pile foundation simulation model according to the set configuration; Using the fixed-bed hydrodynamic characteristics test, a fixed-bed test was conducted on a simulation model of a pile foundation with bioherms to obtain the flow field characteristics of the interaction between the bioherms and the pile foundation. Using the dynamic bed scour verification experiment, a scour test was conducted on a pile foundation simulation model with bioherms, and the scour parameters were measured. The sand scouring protection effect of the reef was quantitatively analyzed and evaluated based on the flow field characteristics and scouring parameters of the reef, and the configuration characteristics of the reef were obtained based on the quantitative analysis and evaluation results.

2. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 1 is characterized in that: The simulation is performed according to a set ratio based on the offshore pile foundation structure and the sea conditions to obtain a pile foundation simulation model, specifically including: Set up a water tank, arrange the sand bed in the water tank according to the actual sea conditions, and determine the target seawater flow rate according to the Froude criterion; The pile foundation is simulated according to a set ratio to obtain a pile foundation model, and the pile foundation model is fixed on the sand bed in the center of the water tank; Start the water pump, fill the water tank with water to the set depth, open the water pump and the water tank inlet and outlet, gradually increase the flow rate, measure the flow rate after the water flow stabilizes, and repeatedly adjust the water pump power and gate opening until the water depth and flow rate meet the target seawater flow rate.

3. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 1 is characterized in that: The bioherm model is arranged around the pile foundation simulation model according to a set configuration, specifically including: the configuration of the bioherm model includes a triangle, a hemispherical shape, and a frame square shape.

4. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 1 is characterized in that: The fixed-bed hydrodynamic characteristics test was used to conduct a fixed-bed test on the pile foundation simulation model with bio-reef arrangement, specifically including: A pile foundation and a reef model were placed in a fixed-bed water tank. Particle image velocimetry was used to measure the flow field around the piles. This flow field information included downwelling in front of the piles, lateral velocity gradients, flow field differences inside and outside the reef, and edge scour. Key sections are selected for two-dimensional flow field analysis to generate velocity distribution maps, identify high velocity areas and vortex structures, and obtain flow field characteristics; key sections include at least: upstream of the pile, side of the pile, inside and outside the reef body, and outside the reef group.

5. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 4 is characterized in that: In the steps of the fixed bed hydrodynamic characteristics test, the experimental system used includes a laser, a camera and a control computer; After the laser is moved to the section to be measured, keep the laser on and adjust the camera position and focal length to make the tracer particles clearly imaged; When the flow field in the water tank stabilizes, an external control computer is used to control the camera to take pictures, obtaining a series of tracer particle distribution images and realizing two-dimensional measurement of the flow field.

6. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 1 is characterized in that: The scour test of the pile foundation simulation model with bio-reef arrangement was carried out using the moving bed scour and anti-slip verification test, which specifically includes: Pile foundations and bio-reef models were laid out in the sand bed flume, and the scouring environment was simulated by adjusting the water flow parameters to achieve a balanced state. The current scour depth and width are measured, and the protection effect is quantified by dimensionless parameters; the scour depth is expressed as: l / l 0; Scour width is expressed as: s / s 0; in, l 0 and s 0 is the washout data of the unprotected control group, l is the scour depth, and s is the scour width.

7. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 6 is characterized in that: Quantitatively analyzing and evaluating the sand scouring protection effect of the bioherm based on the flow field characteristics and scouring parameters of the bioherm. The evaluation index of the scouring protection effect specifically includes: scouring depth reduction rate, scouring width reduction rate, and bioherm adaptability. The scour depth reduction rate is obtained according to the scour depth; and the scour width reduction rate is obtained according to the scour width.

8. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 4 is characterized in that: Based on the flow field characteristics and scour parameters of the bioherm, a quantitative analysis and evaluation of the bioherm's sand scour protection effect was conducted, including analysis of key sections in the fixed bed hydrodynamic characteristics test, specifically: The upstream section of the pile foundation is used to analyze the downwelling flow and wake vortex morphology; Side sections of pile foundations to assess lateral scour; Internal sections of bioherms are used to observe flow field differences; Reef edge section, used to detect edge scour effects.

9. The experimental evaluation method for scour protection of offshore wind power monopile foundation according to claim 3 is characterized in that: It also includes optimizing the arrangement of bioherms based on the quantitative analysis and assessment results to obtain the best protection plan; the optimization of the arrangement of bioherms specifically includes: The frame square bioreefs are arranged in combination with the hemispherical bioreefs. The frame square bioreefs are evenly arranged around the pile foundation to form a closed circle. The hemispherical bioreefs are evenly arranged on the outside of the corresponding frame square bioreefs upstream of the pile foundation as a buffer.

10. An experimental evaluation system for scour protection of offshore wind power monopile foundations, used to implement the experimental evaluation method for scour protection of offshore wind power monopile foundations according to any one of claims 1 to 9, characterized in that: include: The model simulation module simulates the offshore pile foundation structure and sea conditions according to the set ratio to obtain a pile foundation simulation model; The bioherm layout module arranges the bioherm model around the pile foundation simulation model according to the set configuration; The fixed-bed test module uses the fixed-bed hydrodynamic characteristics test to conduct fixed-bed tests on a pile foundation simulation model with bioherms, and obtain the flow field characteristics of the interaction between the bioherms and the pile foundations; The moving bed test module uses the moving bed scour and anti-slip verification test to conduct scour tests on a pile foundation simulation model with bio-reef layout, and measures scour parameters; The test evaluation module quantitatively analyzes and evaluates the sand scouring protection effect of the bioherm based on the flow field characteristics and scouring parameters of the bioherm, and obtains the configuration characteristics of the bioherm.

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