Test method for local scour of monopile composite bucket foundation under realistic wave-current conditions

Abstract

The present invention relates to a test method for local scour of a monopile composite bucket foundation under realistic wave-current conditions, comprising: acquiring basic data of a target wind farm area; determining a scale ratio and constructing a scaled physical model flume in accordance with similarity criteria; determining parameters of a first bidirectional pump, a second bidirectional pump, and a wave maker by means of adjustment and measurement; excavating a test scour zone, installing a scaled monopile composite bucket foundation, and spreading model sand; and conducting a scour test until scour equilibrium is reached, recording a scour depth and a scour extent, and converting same to prototype-scale values. The present invention allows for effective simulation of the combined action of realistic rotational tidal currents and waves in a sea area, reproducing a scour pattern consistent with the field conditions at the sea area, and thereby enabling accurate determination of the local scour status of the monopile composite bucket foundation under realistic wave-current conditions.

Description

Test method for local scour of single-column composite cylindrical foundation under actual wave and current conditions Technical Field

[0001] This invention relates to a test method for local scour of a single-column composite cylindrical foundation under actual wave and current conditions, belonging to the field of physical model test for local scour of offshore wind power foundations. Background Technology

[0002] Currently, physical model tests for localized scour of offshore wind turbine foundations are often conducted in rectangular flumes, employing generalized tidal current and wave dynamic conditions in a single direction. This generalization is reasonable for monopile structures with uniform cross-sections. However, for single-column composite cylindrical foundations with variable cross-sections, the direction of water flow significantly affects the flow around the structure, thereby altering the localized scour process.

[0003] A search revealed that patent application number 202211456477.1 and publication number CN118056954A discloses a device and method for experimental research on localized scour by rotating currents. This method simulates the localized scour near wind turbine foundations fixed on the seabed by laying bed sand after fixing a foundation model on a rotating platform. However, this technical solution does not address the impact of waves on scour. Even with the addition of wave-generating equipment, it can only generate waves in the same direction as the tidal current and cannot simulate the superposition of actual rotating currents and waves in the ocean.

[0004] Therefore, there is an urgent need to develop a technical solution that can effectively simulate the scouring patterns under the combined action of rotating tidal currents and waves in the ocean. Summary of the Invention

[0005] The main objective of this invention is to overcome the problems existing in the prior art and propose a test method for local scour of a single-column composite cylindrical foundation under actual wave and current conditions. This method can effectively simulate the superposition of actual rotating tidal currents and waves in the sea area, simulate the scour pattern that matches the actual sea area, and thus accurately determine the local scour condition of the single-column composite cylindrical foundation under actual wave and current conditions.

[0006] The technical solution of this invention to solve its technical problem is as follows:

[0007] A method for conducting a local scour test on a single-column composite cylindrical foundation under actual wave and current conditions includes the following steps:

[0008] The first step is to obtain basic data of the target wind farm area, which includes: topographic data, tide data, tidal current data, wave data, and seabed data.

[0009] The second step is to determine the geometric scale λ of the model based on the experimental conditions. LThe scale is equal to the prototype size / the model size. A scaled-down physical model water tank is constructed according to similarity conditions. The main body of the model water tank projected onto the horizontal plane is rectangular, with a circular center. The intersection of the two axes of symmetry of the rectangle, the center of the circle, and the center of the model water tank coincide. The width of the rectangle is less than the diameter of the circle, which is less than the length of the rectangle. In the model water tank, the length direction of the rectangle is the main direction of the ebb and flow tides, and the diameter direction of the circle extending along the width direction of the rectangle is the direction of the secondary waves. The model water tank has a first bidirectional pump at each end of the length direction of the rectangle and a second bidirectional pump at each end of the diameter direction of the circle extending along the width direction of the rectangle. The wave direction is determined based on the wave data obtained in the first step. Wave generators are arranged along the wave direction on the circular edge of the model water tank, and wave-dissipating structures are arranged on the circular edge directly opposite the wave generators.

[0010] The third step is to simulate the measured tidal process of the target wind farm area in the model water tank, and measure the tidal level data, tidal current data, and wave data near the center of the model water tank, according to the geometric scale λ of the model. L After conversion to the prototype quantity, it is compared with the tide level data, tidal current data, and wave data obtained in the first step; by adjusting the parameters of the first bidirectional pump and the second bidirectional pump, the comparison results of the tide level data and tidal current data are made consistent; by adjusting the parameters of the wave generator, the comparison results of the wave data are made consistent.

[0011] Step 4: Excavate the test scour area in the middle of the model water tank. The projection of the test scour area onto the horizontal plane is circular. Install a λ scale according to the geometric scale of the model at the center of the test scour area. L A scaled-down single-column composite cylindrical foundation was constructed and model sand was laid on it; in the projection on the same horizontal plane, the center of the test scour area coincided with the center of the model water tank.

[0012] Step 5: Following the parameters of the first bidirectional pump, the second bidirectional pump, and the wave generator determined in Step 3, conduct a scouring test in the model tank until scouring reaches equilibrium. Record the scouring depth and range, and measure the results according to the model's geometric scale λ. L Convert to prototype quantity.

[0013] In this method, a first bidirectional pump is used to simulate the main tide, and a second bidirectional pump is used to simulate the secondary wave, forming a rotating tidal current pattern near the center of the model tank. At the same time, a wave generator is used to simulate the waves, which can effectively simulate the superposition of actual rotating tidal currents and waves in the sea area. Finally, a scouring pattern that matches the actual sea area is simulated.

[0014] The further improved technical solution of this invention is as follows:

[0015] Preferably, in the first step, the topographic data is obtained from actual topographic measurements of the target wind farm area, including water depth; the tidal level and tidal current data are obtained from actual measurements of tidal level and tidal current by tidal level and tidal current observation stations within the target wind farm area at the same time period, including tidal current data including velocity and direction; the wave data are obtained from statistical analysis of wave data obtained from actual wave measurements by wave observation stations within the target wind farm area, including wave height, wave period, and wave direction; and the sediment data includes the median grain size d of the sediment. 50 .

[0016] More preferably, in the first step, if no tide level observation station, tidal current observation station, and wave observation station have been established in the target wind farm area, a two-dimensional tidal current and wave mathematical model of the target wind farm area is established using software, and then the tide level data, tidal current data, and wave data of the target wind farm area are obtained through model calculation.

[0017] By adopting the above preferred solution, the specific technical details of the first step can be further optimized.

[0018] Preferably, in the second step, both the first bidirectional pump and the second bidirectional pump are variable frequency bidirectional pumps; the wave generator is a pusher plate type wave generator; the wave damping structure consists of a gravel slope and a wave damping plate, and the wave damping plate is located on the side of the gravel slope away from the wave generator.

[0019] Preferably, in the second step, a gravel ramp is provided on the back side of the wave generator; a ramp extending perpendicular to the main wave direction, a flow straightening wall, and a sand collection pit are provided in front of the first bidirectional pump in sequence, and a flow straightening wall extending perpendicular to the secondary wave direction is provided in front of the second bidirectional pump.

[0020] Preferably, in the second step, the similarity conditions include water flow motion similarity conditions and wave motion similarity conditions; the water flow motion similarity conditions include:

[0021] Flow velocity ratio

[0022] Roughness ratio λ n =λ L 1 / 6 ;

[0023] Time scale

[0024] In the above equations for the similarity conditions of water flow motion, λ L The geometric scale of the model is given, and each scale is equal to the prototype quantity divided by the model quantity.

[0025] The similarity conditions for wave motion include:

[0026] The wave propagation speed is similar to λ. c =λ h 1 / 2 =λL 1 / 2 ;

[0027] The wave period is similar to λ T =λ h 1 / 2 =λ L 1 / 2 ;

[0028] The similarity of water particle motion is λ u′ =λ v′ =λ h 1 / 2 =λ L 1 / 2 ;

[0029] Wave refraction similarity is λ h =λ L ;

[0030] Wave diffraction similarity is λ l =λ L ;

[0031] Wave breaking similarity is λ h =λ L =λ H ;

[0032] Wave reflection similarity is λ h =λ L ;

[0033] In the above equations for the similarity conditions of wave motion, λ L The geometric scale of the model is given by λ. The subscripts of the other scales λ have the following meanings: l represents wavelength, h represents water depth, c represents wave speed, T represents wave period, u' represents horizontal velocity of water particles, v' represents vertical velocity of water particles, and H represents wave height. Each scale is equal to the prototype quantity divided by the model quantity.

[0034] By adopting the above preferred solutions, the specific technical details of the second step can be further optimized.

[0035] Preferably, in the third step, the parameters of the first bidirectional pump and the second bidirectional pump are adjusted using a frequency converter; the tide level data is measured using a tide gauge; the flow direction in the tidal current data is recorded by throwing paper flowers onto the water surface; the flow velocity in the tidal current data is measured using a propeller current meter; and the wave data is measured using a wave meter.

[0036] By adopting the above preferred solutions, the specific technical details of the third step can be further optimized.

[0037] Preferably, in the fourth step, the model sand should satisfy the sediment initiation similarity condition and the underwater angle of repose similarity condition; the sediment initiation similarity condition is: λ u0 =λ uIn the formula, the subscripts of each scale λ have the following meanings: u0 represents the initial velocity of sediment flow, and u represents the horizontal velocity.

[0038] The formula for the initiation velocity of sediment flow is: In the formula, u0 is the initial velocity of the sediment flow, g is the acceleration due to gravity, h is the water depth, and d is the sediment particle size, which is taken as the median sediment particle size d. 50 s=γ s / γ,γ s γ is the bulk density of sediment, and γ is the bulk density of water;

[0039] The underwater angle of repose similarity condition is as follows: the underwater angle of repose of the model sand is 0.9 to 1.1 times that of the prototype sand; the formula for the underwater angle of repose is... d represents the particle size of the sediment, and the median particle size of the sediment is taken as d. 50 .

[0040] By adopting the above preferred solutions, the specific technical details of the fourth step can be further optimized.

[0041] Preferably, in the fifth step, scour balance means that the maximum scour depth remains unchanged.

[0042] Preferably, in the fifth step, the conversion result is represented by a contour map.

[0043] By adopting the above preferred solutions, the specific technical details of step five can be further optimized.

[0044] Compared with existing technologies, this invention can effectively simulate the superposition of actual rotating currents and waves in the sea, and simulate the scour pattern that matches the actual sea area, thereby accurately judging the local scour condition of single-column composite cylindrical foundations under actual wave and current conditions. Attached Figure Description

[0045] Figure 1 is a schematic diagram of the target wind farm area in Embodiment 1 of the present invention. The figure shows the topography of the wind farm area, the location of the wind turbine pile foundation, the location of the tide level observation station, the location of the tidal current observation station, and the location of the wave observation station. In the figure, "single column composite cylinder turbine location" is the location of the wind turbine pile foundation, "current velocity station" is the tidal current observation station, "tide level station" is the tidal level observation station, and "wave station" is the wave observation station.

[0046] Figure 2 is a verification diagram of tide level and current flow in Embodiment 1 of the present invention. The figure shows the measured and experimental values ​​of (A) spring tide level, (B) current velocity, and (C) current direction.

[0047] Figure 3 is a physical model layout diagram of Embodiment 1 of the present invention. In the figure, "test scour section" refers to the test scour area.

[0048] Figure 4 is a photograph of the physical model of Embodiment 1 of the present invention. Figure A shows the overall layout, Figure B shows the side wall, and Figure C shows the gravel slope and wave-dissipating plate that play a role in wave dissipation.

[0049] Figure 5 shows the local scour morphology and contour map of Embodiment 1 of the present invention. Figure A is a photograph of the scour morphology around the scaled-down single-column composite cylindrical foundation. The left figure is a top view and the right figure is a side view. Figure B is a contour map converted into the prototype quantity. Detailed Implementation

[0050] In practical implementation, the method for local scour testing of a single-column composite cylindrical foundation under actual wave-current conditions according to the present invention includes the following steps:

[0051] The first step is to obtain basic data of the target wind farm area, including: topographic data, tide data, tidal current data, wave data, and seabed data.

[0052] The topographic data includes water depth, obtained through actual topographic measurements. Tidal and tidal current data are obtained from simultaneous measurements taken by tidal and tidal current observation stations within the target wind farm area; tidal current data includes velocity and direction. Wave data is obtained from wave measurements taken by wave observation stations within the target wind farm area, followed by statistical analysis; wave data includes wave height, wave period, and wave direction. The sediment data includes the median grain size d of the sediment. 50 .

[0053] In addition, as an alternative: if there are no tide level observation stations, tidal current observation stations, and wave observation stations in the target wind farm area, then existing software (such as Mike21, delft3d, and other existing mature software) can be used to establish a two-dimensional tidal current and wave mathematical model of the target wind farm area, and then the tide level data, tidal current data, and wave data of the target wind farm area can be obtained through model calculation.

[0054] The second step is to determine the geometric scale λ of the model based on the experimental conditions. L A scaled-down physical model of the water tank was constructed based on similar conditions.

[0055] The model water tank, projected onto a horizontal plane, is primarily rectangular with a circular center. The intersection of the two axes of symmetry of the rectangle coincides with the center of the circle. The width of the rectangle is less than the diameter of the circle, which is less than the length of the rectangle. In this model water tank, the length direction of the rectangle represents the main tidal current direction, while the diameter direction of the circle extending along the width of the rectangle represents the secondary wave direction. The model water tank has a first bidirectional pump at each end along the length of the rectangle and a second bidirectional pump at each end along the diameter direction of the circle extending along the width of the rectangle. Both the first and second bidirectional pumps are variable frequency bidirectional pumps. Each variable frequency bidirectional pump generates current in a controlled manner, creating a rotating tidal current pattern near the center of the model water tank (i.e., the center of the circle).

[0056] Based on the wave direction of the engineering area (i.e. the target wind farm area) obtained in the first step, pusher-type wave generators are arranged along the wave direction on the circular edge of the model water tank, and crushed stone slopes and wave-dissipating plates are used on the circular edge directly opposite the wave generators to dissipate waves.

[0057] In addition, a gravel ramp is provided on the back side of the wave generator; in front of the first bidirectional pump, there is a ramp extending perpendicular to the main wave direction, a flow straightening wall, and a sand collection pit; in front of the second bidirectional pump, there is a flow straightening wall extending perpendicular to the secondary wave direction.

[0058] The main similarity conditions are similarity in water flow motion and similarity in wave motion, including:

[0059] ① Similarity conditions of water flow

[0060] Flow velocity ratio

[0061] Roughness ratio λ n =λ L 1 / 6 ;

[0062] Time scale

[0063] In the above equations for the similarity conditions of water flow, each λ represents a scale of the model, and each scale = prototype quantity / model quantity, where λ L The geometric scale of the model is the preset model scale.

[0064] ② Similarity conditions for wave motion

[0065] When conducting wave physics model tests, the wave conditions in the model, such as wave propagation speed, wave period, water particle motion, wave refraction, wave diffraction, wave breaking, and wave reflection, must be similar to those of the prototype, as detailed below:

[0066] The wave propagation speed is similar to λ. c =λ h 1 / 2 =λ L1 / 2 ;

[0067] The wave period is similar to λ T =λ h 1 / 2 =λ L 1 / 2 ;

[0068] The similarity of water particle motion is λ u′ =λ v′ =λ h 1 / 2 =λ L 1 / 2 ;

[0069] Wave refraction similarity is λ h =λ L ;

[0070] Wave diffraction similarity is λ l =λ L ;

[0071] Wave breaking similarity is λ h =λ L =λ H ;

[0072] Wave reflection similarity is λ h =λ L ;

[0073] In the above equations for the similarity conditions of wave motion, λ L The geometric scale of the model is the preset model scale. The subscripts of the other scales λ have the following meanings: l represents wavelength, h represents water depth, c represents wave speed, T represents wave period, u' represents the horizontal velocity of water particles, v' represents the vertical velocity of water particles, and H represents wave height; and each scale = prototype quantity / model quantity.

[0074] The third step involves adjusting all bidirectional pump parameters using a frequency converter to simulate the measured tidal rise and fall process of the target wind farm area. This simulates the tidal level, flow velocity, and flow direction near the proposed pile foundation location (i.e., the center of the model's water tank) in the model (using the model's geometric scale λ). L The data (converted to prototype) is basically consistent with the tidal level, flow velocity, and flow direction data obtained in the first step.

[0075] The tide level was measured using a tide gauge, the flow direction was recorded by throwing paper flowers onto the water surface, and the flow velocity was measured using a propeller current meter. A wave generator was used to generate the waves obtained in the first step; wave height and period were measured using a wave meter.

[0076] Step 4: Excavate the test scour area in the middle of the model water tank. The projection of the test scour area onto the horizontal plane is circular. Install a λ scale according to the geometric scale of the model at the center of the test scour area. LA scaled-down single-column composite cylindrical foundation was constructed and model sand was laid on it; in the projection on the same horizontal plane, the center of the test scour area coincided with the center of the model water tank.

[0077] The model sand must satisfy the similarity of sediment initiation and underwater angle of repose.

[0078] ① Similarity in sediment initiation: λ u0 =λ u ,

[0079] In the above formula, the subscripts of each scale λ are: u0 represents the initial velocity of sediment flow, and u represents the horizontal velocity.

[0080] Based on the following starting velocity formula, determine the model sand particle size that satisfies the similarity of starting velocities.

[0081] In the formula, u0 is the starting flow velocity, g is the acceleration due to gravity, h is the water depth, and d is the sediment particle size, which is taken as the median sediment particle size d. 50 s=γ s / γ,γ s γ is the bulk density of the sediment, and γ is the bulk density of the water.

[0082] ②Conditions for similarity of angles of repose:

[0083] Zhang Hongwu's formula for the natural underwater angle of repose is: d represents the particle size of the sediment, and the median particle size of the sediment is taken as d. 50 Calculate the underwater angle of repose of the model sand and the prototype sand using this formula. The two angles should be similar, with a difference of no more than 10%, meaning the former is 0.9 to 1.1 times that of the latter.

[0084] Step 5: Following the parameters of the first bidirectional pump, the second bidirectional pump, and the wave generator determined in Step 3, conduct a scouring test in the model tank until scouring reaches equilibrium (i.e., the maximum scouring depth remains constant). Record the scouring depth and scouring range, and measure the results according to the model's geometric scale λ. L Convert to the prototype quantity; the result is represented by a contour plot.

[0085] The present invention will be further described in detail below with reference to the embodiments. However, the present invention is not limited to the examples given.

[0086] Example 1

[0087] This embodiment adopts the technical solution of the present invention as described above, and is specifically implemented in a wind farm in Rudong, Jiangsu Province, as a test example.

[0088] The specific details of this embodiment are as follows:

[0089] 1) For a wind farm in Rudong, Jiangsu Province, topographic information of the wind farm area was obtained, as shown in Figure 1. The single-column composite piles (i.e., wind turbine pile foundations) are mainly distributed on the north side of the area, with a water depth of 14m-17m, showing little variation. A representative water depth of h = 15m was taken. The locations of the tide level observation station, tidal current observation station, and wave observation station are shown in Figure 1. Tide level data was obtained from the tide level observation station, tidal current data (velocity and direction) from the tidal current observation station, and wave data (wave height, wave period, and wave direction) from the wave observation station. Tide level data and tidal current data (velocity and direction) from a spring tide in July 2018, measured by the tide level and tidal current observation stations, were taken from historical observation data, as shown in Figure 2. Simultaneously, based on the annual observation data from the wave observation station, the annual effective wave height H = 0.80m and period T = 3.6s were calculated. Furthermore, the median particle size d of the bottom sediment was... 50 =0.07mm.

[0090] 2) Determine the geometric scale λ of the model according to the experimental conditions at a scale of 1:60. L The model is 60m long, 13.0m wide, and 1.0m high. The length of the model is aligned with the main tidal current direction. Variable frequency bidirectional pumps are used to control the flow at both ends of the length direction, and bidirectional pumps are also used to generate flow at both ends of the width direction, thus creating a rotating tidal current pattern near the model's center. The prevailing wave direction in this area is NE, therefore a pusher-type wave generator is placed in the NE direction, and a gravel slope and wave-damping plates are used on the opposite side to dampen the waves.

[0091] 3) Adjust all bidirectional pump parameters using a frequency converter to simulate the measured tidal rise and fall process in step 1), ensuring that the tidal level, velocity, and direction near the proposed pile foundation location in the model (converted to prototype quantities using the model scale) are basically consistent with the tidal level, velocity, and direction data in step 1), as shown in the experimental values ​​in Figure 2. The simulation effect is good. Tidal level was measured using a tide gauge, flow direction was recorded by throwing paper flowers onto the water surface, and velocity was measured using a propeller current meter. Waves with H = 0.80m and period T = 3.6s, as statistically observed in step 1), were generated using a wave generator. Wave height and period were measured using a wave meter.

[0092] 4) The central area of ​​the water tank is excavated, a scaled-down single-column composite cylindrical foundation is installed, and model sand is laid to complete the final model construction. A site photo is shown in Figure 4. The model sand must meet the requirements of similar sediment initiation and similar underwater angle of repose. The median particle size d of the wind farm bottom sand... 50 =0.07mm, under water depth of 15m, the initial velocity of the sediment flow on site is approximately 0.72m / s. Velocity ratio. The initial flow velocity of the sand in the model should be: In the model, the median particle size d is selected. 50 =0.24mm wood powder is used as model sand, according to The starting flow velocity is 0.093 m / s, satisfying the starting similarity requirement. According to... The model sand's angle of repose is 25.36°, while the prototype sand's angle of repose is 24.14°, with an error of 5%, making them similar.

[0093] 5) Based on the rotating flow and wave dynamics determined in step 3), conduct scouring tests until scouring reaches equilibrium (i.e., the maximum scouring depth remains constant). Record the scouring depth and scouring range, and convert them into prototype quantities according to a geometric scale. The results are shown in Figure 5. This concludes the entire method.

[0094] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A test method for local scour of a single-column composite cylindrical foundation under actual wave-current conditions, characterized in that, Includes the following steps: The first step is to obtain basic data of the target wind farm area, including: topographic data, tidal level data, tidal current data, wave data, and seabed data. The second step is to determine the geometric scale λ of the model based on the experimental conditions. L The scale is equal to the prototype size / the model size. A scaled-down physical model water tank is constructed according to similarity conditions. The main body of the model water tank projected onto the horizontal plane is rectangular, with a circular center. The intersection of the two axes of symmetry of the rectangle, the center of the circle, and the center of the model water tank coincide. The width of the rectangle is less than the diameter of the circle, which is less than the length of the rectangle. In the model water tank, the length direction of the rectangle is the main direction of the ebb and flow tides, and the diameter direction of the circle extending along the width direction of the rectangle is the direction of the secondary waves. The model water tank has a first bidirectional pump at each end of the length direction of the rectangle and a second bidirectional pump at each end of the diameter direction of the circle extending along the width direction of the rectangle. The wave direction is determined based on the wave data obtained in the first step. Wave generators are arranged along the wave direction on the circular edge of the model water tank, and wave-dissipating structures are arranged on the circular edge opposite the wave generators. The third step is to simulate the measured tidal process of the target wind farm area in the model water tank, and measure the tidal level data, tidal current data, and wave data near the center of the model water tank, according to the geometric scale λ of the model. L After conversion to the prototype quantity, it is compared with the tide level data, tidal current data, and wave data obtained in the first step; by adjusting the parameters of the first bidirectional pump and the second bidirectional pump, the comparison results of the tide level data and tidal current data are made consistent; by adjusting the parameters of the wave generator, the comparison results of the wave data are made consistent. Step 4: Excavate a test scour area in the middle of the model water tank. The projection of the test scour area onto the horizontal plane is circular. Install a model according to the geometric scale λ at the center of the test scour area. L A scaled-down single-column composite cylindrical foundation was constructed and model sand was laid on it; in the projection on the same horizontal plane, the center of the test scouring area coincided with the center of the model water tank. Step 5: Following the parameters of the first bidirectional pump, the second bidirectional pump, and the wave generator determined in Step 3, conduct a scouring test in the model tank until scouring reaches equilibrium. Record the scouring depth and range, and measure the results according to the model's geometric scale λ. L Convert to prototype quantity.

2. A method for local scour test of a single-column composite cylindrical foundation under actual wave and current conditions as described in claim 1, characterized in that, in the first step, the topographic data is data obtained from actual topographic measurements of the target wind farm area, and the topographic data includes water depth; the tidal level data and tidal current data are data obtained from actual measurements of tidal level and tidal current by tidal level observation stations and tidal current observation stations within the target wind farm area at the same time period, and the tidal current data includes flow velocity and flow direction; the wave data are the results obtained from statistical analysis of wave data obtained from actual wave measurements by wave observation stations within the target wind farm area, and the wave data includes wave height, wave period, and wave direction; the sediment data includes the median grain size d of the sediment. 50 .

3. The method for local scour test of single-column composite cylindrical foundation under actual wave and current conditions as described in claim 2, characterized in that, in the first step, if no tide level observation station, tidal current observation station and wave observation station have been established in the target wind farm area, a two-dimensional tidal current and wave mathematical model of the target wind farm area is established using software, and then the tide level data, tidal current data and wave data of the target wind farm area are obtained through model calculation.

4. The method for local scour test of single-column composite cylindrical foundation under actual wave and current conditions according to claim 2, characterized in that, in the second step, the first bidirectional pump and the second bidirectional pump are both variable frequency bidirectional pumps; the wave generator is a pusher plate wave generator; the wave-dissipating structure is composed of a gravel slope and a wave-dissipating plate, and the wave-dissipating plate is located on the side of the gravel slope away from the wave generator.

5. A method for local scour test of a single-column composite cylindrical foundation under actual wave and current conditions as described in claim 2, characterized in that, in the second step, a gravel slope is provided on the back side of the wave generator; a slope extending perpendicular to the main wave direction, a flow straightening wall, and a sand collection pit are sequentially provided in front of the first bidirectional pump, and a flow straightening wall extending perpendicular to the secondary wave direction is provided in front of the second bidirectional pump.

6. The method for local scour test of a single-column composite cylindrical foundation under actual wave-current conditions as described in claim 2, characterized in that, In the second step, the similarity conditions include water flow motion similarity conditions and wave motion similarity conditions; Similarity conditions for water flow include: Flow velocity ratio Roughness ratio λ n =λ L 1 / 6 ; Time scale In the above equations for the similarity conditions of water flow motion, λ L The geometric scale of the model is given, and each scale is equal to the prototype quantity divided by the model quantity. The similarity conditions for wave motion include: The wave propagation speed is similar to λ. c =λ h 1 / 2 =λ L 1 / 2 ; The wave period is similar to λ T =λ h 1 / 2 =λ L 1 / 2 ; The similarity of water particle motion is λ u′ =λ v′ =λ h 1 / 2 =λ L 1 / 2 ; Wave refraction similarity is λ h =λ L ; Wave diffraction similarity is λ l =λ L ; Wave breaking similarity is λ h =λ L =λ H ; Wave reflection similarity is λ h =λ L ; In the above equations for the similarity conditions of wave motion, λ L The geometric scale of the model is given by λ. The subscripts of the other scales λ have the following meanings: l represents wavelength, h represents water depth, c represents wave speed, T represents wave period, u' represents horizontal velocity of water particles, v' represents vertical velocity of water particles, and H represents wave height. Each scale is equal to the prototype quantity divided by the model quantity.

7. A method for local scour test of a single-column composite cylindrical foundation under actual wave and current conditions as described in any one of claims 2 to 6, characterized in that, in the third step, the parameters of the first bidirectional pump and the second bidirectional pump are adjusted using a frequency converter; the tide level data is measured using a tide gauge; the flow direction in the tidal current data is recorded by throwing paper flowers onto the water surface; the flow velocity in the tidal current data is measured using a propeller current meter; and the wave data is measured using a wave meter.

8. A method for testing local scour of a single-column composite cylindrical foundation under actual wave-current conditions, as described in any one of claims 2 to 6, characterized in that, In the fourth step, the model sand should satisfy the sediment initiation similarity condition and the underwater angle of repose similarity condition; the sediment initiation similarity condition is as follows: In the formula, the subscripts of each scale λ have the following meanings: u0 represents the initial velocity of sediment flow, and u represents the horizontal velocity. The formula for the initiation velocity of sediment flow is: In the formula, u0 is the initial velocity of the sediment flow, g is the acceleration due to gravity, h is the water depth, and d is the sediment particle size, which is taken as the median sediment particle size d. 50 s=γ s / γ,γ s γ is the bulk density of sediment, and γ is the bulk density of water; The underwater angle of repose similarity condition is as follows: the underwater angle of repose of the model sand is 0.9 to 1.1 times that of the prototype sand; the formula for the underwater angle of repose is... d represents the particle size of the sediment, and the median particle size of the sediment is taken as d. 50 .

9. A method for testing local scour of a single-column composite cylindrical foundation under actual wave-current conditions, as described in any one of claims 2 to 6, characterized in that, In the fifth step, the scouring balance refers to the maximum scouring depth remaining constant.

10. A method for testing local scour of a single-column composite cylindrical foundation under actual wave-current conditions according to any one of claims 2 to 6, characterized in that, In the fifth step, the conversion result is represented by a contour map.

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