A method and device for measuring the PIV flow field of the incipient motion condition of accumulated sediment

Abstract

The application discloses a kind of PIV flow field measurement method and device of accumulation body sediment starting critical condition, and the device is screened and dyed with natural sand, significantly reduce its mirror surface reflection under laser irradiation, greatly improve the signal-to-noise ratio of tracer particle in PIV image.Recognition accuracy is improved, and foundation is laid for subsequent high-precision flow field measurement.Based on the two-dimensional instantaneous velocity field obtained by PIV, the distribution cloud picture and the along-the-way variation curve of shear strain rate and vertical vorticity are further deduced.These parameters can directly reflect the shear strength and vortex structure of the water flow near the slope of the accumulation body, and reveal the internal relationship between sediment starting and scour pit morphology.The design is specially aimed at the permeable accumulation body model, and the dyed sand is used to build the permeable bank slope, to simulate the penetration and flow coupling effect of water flow in the accumulation body.The key section of the slope is illuminated vertically by laser sheet, and the high-speed camera is used for synchronous acquisition, to realize the fine capture of complex flow field structure.

Description

Technical Field

[0001] This invention relates to the field of sediment testing technology, specifically to a method and apparatus for measuring the critical conditions for sediment initiation in sediment accumulation (PIV flow field). Background Technology

[0002] Braided channels often form large amounts of bank deposits due to landslides and collapses. The conditions under which sediment is moved directly affect river stability, flood control safety, and the operation of downstream hydropower stations. The key to studying the sediment movement patterns on the slopes of these deposits lies in accurately obtaining the hydrodynamic parameters of the complex three-dimensional flow field near the deposits at the moment of initiation, such as flow velocity, shear strain rate, and vorticity.

[0003] Traditional studies often rely on fixed-bed models or contact-type single-point velocity meters (such as electromagnetic current meters and ADV). Fixed-bed models cannot simulate the coupling effect of water infiltration and flow around real permeable deposits, leading to flow field distortion. Contact-type velocity measuring instrument probes can disturb the flow field, especially in the strong shear and vortex regions formed around the deposit. This interference can significantly affect the observation of the force balance of sediment particles, making it impossible to accurately capture the critical initiation state. Furthermore, single-point measurements cannot simultaneously acquire the velocity gradient, shear strain rate, and vorticity distribution within the flow field plane, which are crucial for revealing the dynamic mechanisms of sediment initiation (such as flow scouring).

[0004] Taking the Chinese patent publication number CN121008059B, "An Indoor Water Tank Sediment Initiation Velocity Measurement System and Method," as an example, this solution proposes a non-contact measurement system based on PIV technology. It acquires flow field images through an imaging unit and a laser illumination unit, and uses a data processing unit for image calibration, particle displacement calculation, and flow velocity field generation. This method can effectively obtain the cross-sectional average flow velocity in a straight water tank and is suitable for preliminary sediment initiation velocity determination.

[0005] However, this solution has the following technical limitations:

[0006] The interference from sediment reflection remains unresolved: Although the patent mentions "optimization of sediment characteristics," it does not offer a specific solution to the problem of strong specular reflection caused by mineral components such as quartz in natural sand under laser irradiation. This reflected light severely interferes with the identification of tracer particles in PIV images, reduces the image signal-to-noise ratio, and affects the accuracy of flow velocity measurement.

[0007] The data processing method is simplistic and difficult to adapt to complex flow fields: The data processing of this scheme mainly focuses on the statistical analysis of cross-sectional average velocity, using a cross-correlation algorithm with a 32×32 pixel window, which is suitable for relatively uniform flow field structures. However, for areas near the banks of sedimentary deposits with complex three-dimensional flow characteristics such as strong shear and vortices, a single average velocity analysis cannot reveal the intrinsic mechanical mechanisms of sediment initiation, such as key parameters like shear strain rate and vorticity distribution.

[0008] Unable to adapt to the flow field characteristics of permeable structures in the embankment: The test object of this system is flat bed surface sediment, and the coupling effect of the permeability of the embankment on water infiltration and flow around is not considered, making it difficult to realistically simulate the start-up process of the embankment under non-steady flow conditions.

[0009] Therefore, existing technologies lack targeted pretreatment methods, refined flow field analysis capabilities, and measurement strategies that match unsteady flow processes when studying the critical conditions for sediment initiation in permeable deposits. Summary of the Invention

[0010] The purpose of this invention is to provide a method and apparatus for measuring the PIV flow field of sediment initiation critical conditions in a sediment mass, so as to solve the problems mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a method for measuring the PIV flow field of sediment initiation critical conditions in an accumulation body, comprising:

[0012] Step 1: Pretreatment of test sediment: Sand that meets the test particle size is screened from natural river sand using a screening and dyeing device, dyed and dried for later use.

[0013] Step 2, Model Preparation and Initial Flow Field Establishment: Lay a fixed bed of sand and level it in the test section of the water tank. Use dyed sand to build a permeable pile model according to the preset geometric parameters. Pour water into the water tank until the pile is completely submerged and soak for a preset time to stabilize.

[0014] Step 3: PIV System Calibration and Debugging: Install and adjust the measurement component mounting unit so that the laser sheet on it illuminates the vertical cross-section of the accumulation slope, release tracer particles, complete the spatial calibration of the high-speed camera's shooting area through the calibration plate, and establish the mapping relationship between pixel coordinates and physical coordinates;

[0015] Step 4: Unsteady Flow Simulation: The stepped drop water level method is used to simulate the unsteady flow during flood season. Starting from the high water level, the tailgate is adjusted to gradually lower the water level while maintaining a constant inlet flow.

[0016] Step 5: Synchronous Measurement and Data Acquisition: Under stable water levels at each level, observe the sediment initiation status. When the standard is met, simultaneously carry out PIV flow field measurement, automatic water level monitoring, and record the initiation position.

[0017] Step 6: Multi-parameter flow field data analysis: Import the acquired image sequence into the integrated data processing unit to process the relevant data;

[0018] Step 7: Critical Condition Correlation Analysis: Correlate the critical starting state with the corresponding hydrodynamic parameters, and use measured starting flow velocity and water depth data to verify or calibrate the formulas for the starting flow velocity and shear stress of sediment on the bank slope of the deposited body.

[0019] Preferably, in step two, the preset geometric parameters include the radius and slope of the accumulation body.

[0020] Preferably, in step four, the water level drops by 1 cm at a time, and the next drop is carried out after the water flow stabilizes, until different levels of sediment are induced to move.

[0021] Preferably, in step five, the PIV flow field measurement unit is activated, and a high-speed camera continuously acquires a sequence of flow field images; an automatic water level meter is used to measure and record the water depth along the current test section; and the current flow rate and the observed sediment initiation location are recorded.

[0022] Preferably, in step six, the data processing procedure of the integrated data processing unit is as follows:

[0023] The instantaneous and average two-dimensional velocity fields of the flow field near the accumulation body were obtained by processing the images using PIV analysis software.

[0024] Based on the velocity field, the data analysis module automatically calculates and plots the distribution of the following key hydrodynamic parameters under different flow layers and different influencing factors: vertical average velocity distribution curve; shear strain rate distribution cloud map and friction distribution curve; vertical vorticity distribution cloud map and friction distribution curve.

[0025] An apparatus for measuring the critical condition PIV flow field of sediment initiation in an accumulation body, used to implement a method for measuring the critical condition PIV flow field of sediment initiation in an accumulation body, comprising:

[0026] The water tank used to simulate the water flow environment has sand for testing laid at the bottom, and water pumps with adjustable flow rates and regulating tailgates for controlling the water level in the tank are installed at both ends. A first slide rail is fixedly installed on the water tank.

[0027] The screening and dyeing equipment includes a first sliding frame that is slidably installed on a water tank, a screening plate and a stirring rod set on the first sliding frame, for screening fixed bed sand and sedimentary sand of target particle size from natural river sand and dyeing them;

[0028] The measuring component mounting unit includes a mounting bracket that is slidably mounted on a first sliding frame, a synchronous controller that is fixedly mounted on the mounting bracket, a high-speed camera and a continuous laser, and the spatial position of the above components relative to the water tank can be adjusted by the mounting bracket.

[0029] The integrated data processing unit connects to and controls a high-speed camera, and has built-in PIV analysis software and a data analysis module. The PIV analysis software is used to calculate the two-dimensional velocity field from the image sequence. The data analysis module is further used to automatically calculate and output the vertical average velocity distribution, shear strain rate distribution, and vertical vorticity distribution cloud map and curve within the flow field cross section based on the velocity field data.

[0030] Preferably, the first sliding frame is slidably mounted on the first slide rail via the first slider, and the second slider is slidably connected to the first sliding frame. The screening chamber is detachably connected to the second slider via bolts. The upper surface of the screening chamber is provided with a feed inlet, and a drive motor is provided above the feed inlet. The drive motor is fixedly mounted on the motor mounting plate, and the motor mounting plate is fixedly connected to the screening chamber via the first connecting rod. A screening plate is coaxially fixedly installed inside the screening chamber, and a waste bin is provided on the side of the screening plate. The waste bin is fixedly connected to the lower end of the screening chamber. The cross-section of the waste bin is annular, and a waste storage area is provided on it. The waste storage area is connected to the side of the screening plate.

[0031] The output shaft of the drive motor is fixedly connected to the upper end of the drive rod, the lower end of the drive rod passes through the axis of the screen plate, and a stirring rod is fixedly installed on the part of the drive rod that passes through the screen plate. The stirring rod is located inside the stirring chamber, and the stirring chamber is fixedly connected to the lower surface of the waste bin. A resistance wire for heating and drying is fixedly installed on the surface of the stirring chamber.

[0032] A discharge port is fixedly installed at the axial position on the lower surface of the mixing chamber. A rotating ring is coaxially mounted on the discharge port. An inclined discharge port is detachably connected to the rotating ring and is connected to the discharge port. A baffle is detachably connected to the rotating ring.

[0033] Preferably, a mounting bracket is detachably mounted on the second slider, and a high-speed camera is fixedly mounted on the mounting bracket. The high-speed camera is set perpendicular to the side wall of the water tank. An L-shaped rod is fixedly mounted on the side of the mounting bracket and fixedly connected to one end of the L-shaped rod. The other end of the L-shaped rod is fixedly connected to a continuous laser. A synchronization controller is set above the high-speed camera, and the synchronization controller is connected to the high-speed camera and the continuous laser.

[0034] Preferably, the high-speed camera has a resolution of not less than 1024×1024 pixels and an adjustable shooting frequency to adapt to different flow rate conditions; the continuous laser has a power of not less than 15W, a wavelength of preferably 532nm, and the thickness of the resulting sheet laser is less than 5mm.

[0035] Preferably, the dye added to the mixing chamber is a water-based dye, which deepens the color of the treated mud and sand.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1. This invention involves screening and dyeing natural sand before the experiment, using water-based dyes to deepen the color of the sand, significantly reducing its specular reflection under laser irradiation, and greatly improving the signal-to-noise ratio of tracer particles in the PIV image. This treatment does not affect the physical properties of the sand, but effectively solves the key obstacle to the application of PIV in natural sand moving bed experiments, improves image recognition accuracy, and lays the foundation for subsequent high-precision flow field measurements.

[0038] 2. Based on the two-dimensional instantaneous velocity field obtained by PIV, this invention further derives the distribution cloud map and friction curves of shear strain rate and vertical vorticity. These parameters can intuitively reflect the shear intensity and vortex structure of water flow near the slope of the deposit, revealing the intrinsic relationship between sediment initiation and scour pit morphology, and providing multi-dimensional data support for mechanism research.

[0039] 3. This invention is specifically designed for permeable sedimentary models, using dyed sand to construct permeable banks, realistically simulating the infiltration and flow coupling effects of water within the sedimentary body. By vertically illuminating key sections of the slope with laser beams and simultaneously acquiring data using a high-speed camera, it achieves precise capture of complex flow field structures, overcoming the limitation of existing technologies that are only suitable for flat surfaces. Attached Figure Description

[0040] Figure 1 This is a flowchart of a method for measuring the PIV flow field of sediment initiation critical conditions in an accumulation body, according to the present invention.

[0041] Figure 2 This is a schematic diagram of the water tank circulation system structure of the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0042] Figure 3 This is a schematic diagram of the location of the screening and dyeing unit in the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0043] Figure 4 This is a schematic diagram of the main structure of the screening and dyeing unit of the PIV flow field measurement device for the critical conditions of sediment initiation in an accumulation body according to the present invention.

[0044] Figure 5 This is a schematic diagram showing the positional structure of the drive motor, screening plate, and stirring rod of the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0045] Figure 6 This is a schematic diagram of the baffle of the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0046] Figure 7 This is a schematic diagram of the structure of a sediment accumulation near the side wall of a water tank, which is part of the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0047] Figure 8 This is a schematic diagram of the mounting frame, high-speed camera, continuous laser, and synchronous controller of the PIV flow field measurement device for the critical conditions of sediment initiation in an accumulation body according to the present invention.

[0048] Figure 9This is a schematic diagram of the adjustable tailgate structure of the PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to the present invention.

[0049] In the diagram: 1. Water tank; 101. First slide rail; 201. First sliding frame; 202. First slider; 203. Second slider; 204. Screening bin; 2041. Feed inlet; 205. First connecting rod; 206. Motor mounting plate; 207. Drive motor; 208. Drive rod; 209. Screening plate; 210. Waste bin; 211. Waste storage area; 212. Stirring rod; 213. Stirring bin; 214. Resistance wire; 215. Discharge port. 216. Rotating ring; 217. Inclined discharge port; 218. Baffle; 301. Mounting bracket; 302. Synchronous controller; 303. High-speed camera; 304. L-shaped rod; 305. Continuous laser; 4. Water inlet; 5. Water pump; 501. Water storage tank; 6. Adjustable tailgate; 601. Through-hole plate; 602. Through hole; 603. Rotating rod; 604. Baffle plate; 605. Water outlet tank; 606. Driven gear; 607. Transmission gear; 609. Rocker arm. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Please see Figure 1 This invention proposes a method for measuring the critical condition PIV flow field of sediment initiation in an accumulation body. This method is implemented using the PIV velocity measuring device for sediment initiation in an accumulation body constructed below, which includes:

[0052] Step 1: Pretreatment of experimental sediment: Using a screening and dyeing device, fixed-bed sand and sediment of target particle size are screened from natural river sand and dyed. After completion, the sediment is dried for later use.

[0053] Step 2, Model Preparation and Initial Flow Field Establishment: Lay a fixed bed of sand and level it in the test section of the flume; using dyed sand, build a permeable accumulation model on the bank of the flume according to the preset geometric parameters (radius, slope); slowly inject water into the flume until the accumulation is completely submerged, and soak it for a preset time (e.g., 6 hours).

[0054] Step 3: PIV System Calibration and Debugging: Install and adjust the positions of the high-speed camera and laser to ensure that the laser sheet light accurately illuminates the vertical cross-section containing key areas of the accumulation slope (such as the bank slope); uniformly release tracer particles into the water; use a calibration board to spatially calibrate the shooting area and establish the mapping relationship between image pixel coordinates and actual physical coordinates.

[0055] Step 4: Unsteady Flow Simulation: The stepped drop-off method is used to simulate the unsteady flow (i.e., unsteady water level) conditions during flood discharge. Starting from a high water level, the water level is gradually lowered by adjusting the tailgate while maintaining a constant inlet flow rate.

[0056] The water level drops in increments of 1 cm, and the next drop is carried out only after the water flow stabilizes, until different levels of sediment are triggered.

[0057] Step 5, Synchronous Measurement and Data Acquisition: At each stable water level, when the sediment movement on the slope of the accumulation body reaches the preset standard (e.g., individual movement (i.e., sporadic sediment movement), small-scale movement (i.e., sediment movement in 10%–50% of the bed surface area), large-scale movement (i.e., sediment movement in more than 50% of the bed surface area)), immediately perform the following synchronous operations:

[0058] a) Start the PIV flow field measurement unit and continuously acquire a sequence of flow field images using a high-speed camera;

[0059] b) Use an automatic water level gauge to measure and record the water depth along the current test section;

[0060] c) Record the current flow rate and the observed location of sediment initiation.

[0061] Step 6: Multi-parameter flow field data analysis: Import the acquired image sequence into the integrated data processing unit;

[0062] a) The instantaneous and average two-dimensional velocity fields of the flow field near the accumulation body were obtained by processing the images using PIV analysis software;

[0063] The PIV cross-correlation algorithm was used to process the image sequence to obtain the two-dimensional instantaneous velocity field near the pile. ,in For flow velocity, The vertical velocity is obtained by averaging the time series. The grid spacing is denoted as... .

[0064] b) Based on the velocity field, the data analysis module automatically calculates and plots the distribution of the following key hydrodynamic parameters under different flow layers (near bottom, middle layer, and upper layer) and different influencing factors (start-up state, flow rate, sediment particle size):

[0065] 1) Vertical average velocity distribution curve (i.e., velocity profile along the water depth direction);

[0066] For each flow direction location Extract the flow velocity of all grid points along the vertical line. and corresponding vertical coordinates The distribution is obtained. To analyze the hydrodynamic characteristics of different flow layers ( They represent a certain cross-section and a certain flow layer, respectively. Representing the vertical coordinate (water depth), defined as:

[0067] Near the bottom layer: ( (for water depth)

[0068] Middle layer:

[0069] upper layer:

[0070] Calculate the average flow velocity for each layer separately. Plot the velocity variation curve along the flow direction. It can also output the velocity value at any specified vertical position (e.g., 1 mm above the bed surface) for subsequent startup analysis.

[0071] Starting flow rate Extraction: Defined as the instantaneous directional velocity at a height of 1 mm directly above the original position of a target-size sediment particle (near the bottom layer) when the particle is just induced to move. Specifically, based on the "sediment initiation position" recorded in step five and the two-dimensional velocity field data obtained in step six, the coordinate point is located in the PIV post-processing software, and the instantaneous directional velocity value corresponding to the image of the grid cell containing that point at the "initiation" moment is extracted. For the three states of "individual initiation," "few initiations," and "numerous initiations," the corresponding initiation velocities are recorded respectively. , , .

[0072] 2) Shear strain rate distribution contour map and friction curve;

[0073] Shear strain rate is defined as: (In the formula, For flow velocity, (Vertical velocity)

[0074] The internal grid points are calculated using a second-order central difference scheme. Partial derivatives of )

[0075] , In step six, the flow field is divided into several grid points, each grid point being indexed ( The only certainty is that... The position number indicates the direction of flow. Indicates the vertical position number. It calculates the flow velocity. For vertical coordinates partial derivatives A portion representing the difference in directional velocity between two points above and below the same location in the same flow direction, its specific meaning is as follows: This represents the velocity of the water flow above, i.e., at the location in the same flow direction. One grid vertically upwards The flow velocity, This represents the flow velocity of the water below, i.e., at the location in the same flow direction. , down to the next grid The flow velocity is calculated by dividing the difference between the two points by [the value of the flow velocity]. Then you can get the center point ( Approximate value of the vertical gradient at point ().

[0076] Similarly, It calculates the vertical velocity. Flow direction coordinates partial derivatives A portion representing the vertical velocity difference between two points on the left and right of the same vertical position, its specific meaning is as follows: Represents the vertical velocity on the right, that is, at the same vertical position. Flow to the next grid vertical velocity, Represents the vertical velocity on the left, that is, at the same vertical position. Flow forward one grid The vertical velocity is calculated by dividing the difference between the two points by the flow distance between them. Then we get the center point ( The approximate value of the flow gradient at point ().

[0077] Through calculation The measured “flow velocity” is converted into “flow velocity change per unit height”, which directly corresponds to the shear stress acting on the particle surface.

[0078] The boundary points are subjected to first-order forward / backward differences to obtain a two-dimensional scalar field. To draw cloud maps.

[0079] Distribution curves along the path: Extract the near-bottom layer (e.g., z=1 mm or the lowest mesh). Value follows The changes, or extracting the vertical maximum value at each flow direction position. The changes along the course.

[0080] 3) Vertical vorticity distribution cloud map and distribution curve along the path.

[0081] Vertical vorticity (pointing to) Direction, vertical A plane is defined as:

[0082] (In the formula, For flow velocity, (Vertical velocity)

[0083] Similarly, the partial derivatives are calculated using the central difference method to obtain the two-dimensional vorticity field ( ), and plot the cloud map. Flow distribution curve: extract the vertical extreme values ​​(maximum positive value or minimum negative value) near the bottom layer or at each flow direction location along the flow path.

[0084] Shear strain rate This represents the intensity of the drag force (shear force) exerted by the water flow on the particles in the bed. One of the direct driving forces for particle initiation is the frictional effect of the water flow on its surface. The larger the gradient, the greater the near-bottom velocity gradient, and the greater the flow-directed thrust on the particles.

[0085] Vertical vorticity This represents the turbulent pulsation and vortex intensity of the water flow. Strong vorticity (especially near the bottom) generates a large instantaneous vertical pressure difference (i.e., uplift force), which is a key factor that causes particles to jump off the bed surface (start-up).

[0086] Therefore, by obtaining the shear strain rate Vertical vorticity Only when the water flow reaches a certain critical velocity can sufficiently large shear be generated in the near-bottom region. and a sufficiently strong vortex This overcomes the gravity and friction of the particles, enabling them to start.

[0087] Step 7: Critical Condition Correlation Analysis: A correlation analysis is performed between the critical starting states recorded in Step 5 (individual starting, few starting, large starting) and the corresponding hydrodynamic parameters obtained in Step 6 (such as the starting flow velocity at a specific location). Using measured starting flow velocity, water depth, and other data, the sediment starting flow velocity formula and starting shear stress formula applicable to the bank slope of the sedimentary body are verified or calibrated. The specific analysis process is as follows:

[0088] 1) A nonlinear multiple regression method was used to establish a mathematical model relating the critical initiation parameters to the hydrodynamic parameters, sediment geometric parameters, and sediment physical parameters. (This mathematical model is the premise for the sediment grading initiation formula proposed below; the mathematical model is a dimensionless analysis, while the sediment grading initiation formula is a dimensional empirical formula.) The model expression is as follows: (In the formula, It is the dimensionless critical Shields number (characterizing the critical shear stress). Let θ be the Reynolds number of the water flow, and θ be the slope of the sedimentary bank. (This refers to the dimensionless particle size of sediment.)

[0089] Establishing a mathematical model can verify whether the experimental results conform to physical laws (compared with the Shields curve) and establish the basic combination form between the variables (i.e., the one proposed below). Why this item must exist.

[0090] Given water depth Sediment particle size Under the premise of this, the starting flow velocity empirical formula is constructed by fitting all the valid data extracted in step six using statistical software with the nonlinear least squares method:

[0091]

[0092] (in, To measure the starting flow rate, Because of the water depth, For sediment particle size, It is the acceleration due to gravity. The empirical coefficients to be fitted are... This refers to the error term (the measurement error value). The density of sediment and water (the density of sediment was obtained using the gas displacement method, and the density of water was obtained using a liquid density meter)).

[0093] 3) Based on the above process, this method, under the staged initiation state, for working conditions with particle size of 1-5mm and slope of 15°-30°, yields the following complete sediment staged initiation velocity formula model:

[0094] Individual startup:

[0095] Small-scale startup:

[0096] Massive startup:

[0097] 4) Regularity Analysis: As can be seen from the above formula, the empirical coefficient gradually increases as the scale of startups increases from "individual" to "large-scale". The slope impact index increased from 1.62 to 2.21, and the slope impact index ( The slope also gradually increases. This quantitatively reveals that triggering large-scale startup requires stronger hydrodynamic force, and the steeper the slope, the more significant the amplification effect on large-scale startup.

[0098] Please see Figure 2-7This embodiment proposes a PIV flow field measurement device for the critical condition of sediment initiation in a sedimentary mass, to realize the PIV velocity measurement method for the critical condition of sediment initiation in a sedimentary mass proposed above. It includes a water tank 1 for simulating a water flow environment. The water tank 1 is a hollow cuboid made of transparent tempered glass, allowing observation of the sediment flow within the tank. The sidewalls are smooth and transparent. The inner surface and bottom of the water tank 1 are flat for laying the sediment to be tested. A water inlet 4 is fixedly installed on one side of the water tank 1. The water inlet 4 is fixedly connected to the output end of a water pump 5 via an inlet pipe. The water inlet 4 of the water pump 5 is connected to a water storage tank 501. The water pump 5 is a conventional model water pump. The water pump 5 allows water from the water storage tank 501 to be injected into the water tank 1 through the water inlet 4. A regulating tailgate 6 is fixedly installed on the other side of the water tank 1, communicating with the water storage tank 501. The regulating tailgate 6 includes a through-hole plate 601 (shown in…). Figure 9 middle).

[0099] To adjust the water level in tank 1 in step four and regulate the water flow out of tank 1, the side of tank 1 opposite the inlet is fixedly connected to the outlet tank 605. A through-hole plate 601 is detachably installed on this side by bolts.

[0100] The perforated plate 601 has three rows of through holes 602 arranged vertically at equal intervals on its surface, with four through holes 602 in each row, totaling twelve through holes 602, forming four longitudinal channels, each containing three through holes 602. Corresponding to the four rows of through holes 602, four rotating rods 603 are rotatably mounted on the inner side of the perforated plate 601, each rotating rod 603 being positioned along the longitudinal centerline of a row of through holes 602. Each rotating rod 603 is fixedly mounted with three disc-shaped baffles 604, the positions of which correspond one-to-one with the three through holes 602 in its row, and the rotating rods 603 and baffles 604 are concentrically fixed. In the initial state, each baffle 604 completely blocks the corresponding through hole 602, preventing water flow.

[0101] After the upper end of the rotating rod 603 extends out of the through-hole plate 601, it is fixed to four driven gears 606 respectively. Each driven gear 606 meshes with a transmission gear 607 rotatably mounted on the through-hole plate 601. Adjacent driven gears 606 are linked through a transmission gear 607, thus forming a gear transmission system that enables the four rotating rods 603 to rotate synchronously and in the same direction.

[0102] A rocker arm 609 is provided on the outer side of the through-hole plate 601, which is coaxially fixed with the driven gear 606 located on the side. By rotating the rocker arm 609, the driven gear 606 can be driven to rotate, which in turn drives the other driven gears 606 to rotate synchronously through the transmission gear 607, ultimately causing all rotating rods 603 and their baffles 604 to rotate uniformly. When the baffle 604 rotates a certain angle from its initial fully blocked position, the through holes 602 in the corresponding row gradually open, allowing water to flow into the water tank 605 through the through holes 602. The maximum rotation angle of the baffle 604 is 90 degrees. At this position, the baffle 604 is parallel to the water flow direction, the flow area is the largest, and the drainage volume reaches its peak. As the rotation angle of the baffle 604 decreases, its blocking area on the through holes 602 increases, and the drainage volume decreases accordingly. When the water inlet flow rate is large, the rotation angle of the baffle 604 is increased to increase the water outflow rate; when the water inlet flow rate is small, the rotation angle of the baffle 604 is decreased to decrease the water outflow rate.

[0103] This structure, through the corresponding arrangement of four rotating rods 603 and four rows of through holes 602, combined with a linkage gear system, achieves unified control of all drainage channels. The total water output can be flexibly adjusted by simply operating the rocker arm 609, thus enabling the adjustment of the water level in tank 1 as described in step four.

[0104] An electromagnetic flow meter is fixedly connected to the output end of the water pump 5. The electromagnetic flow meter is an existing technology component. By setting this technology component, the water output of the water pump 5 can be statistically analyzed. The water pump 5 adopts an existing variable frequency water pump with adjustable water output. The variable frequency water pump can control the amount of water injected into the water tank 1 and the water injection speed.

[0105] To achieve the screening and dyeing of fixed-bed sand and target-size sedimentary sand from natural river sand in step one, a screening and dyeing device is proposed. The screening and dyeing device includes a screening plate 209 and a stirring rod 212. Two first slide rails 101 are fixedly installed above the water tank 1 along its long side. A first slider 202 is slidably installed on the first slide rail 101. A first sliding frame 201 is fixedly installed above the first slider 202. The installation direction of the first sliding frame 201 is perpendicular to that of the first slide rail 101. The first sliding frame 201 can slide along the extension direction of the first slide rail 101 through the first slider 202. A second slider 203 is slidably connected to the first sliding frame 201. The second slider 203 can slide along the extension direction of the first sliding frame 201.

[0106] The second slider 203 is detachably connected to the screening chamber 204 by bolts. The screening chamber 204 is a hollow cylinder. The upper surface of the screening chamber 204 is provided with a feed inlet 2041, through which material can be fed into the screening chamber 204. The screening plate 209 is coaxially fixed inside the screening chamber 204. The screening plate 209 is in the shape of a boss, that is, the axial position is gradually higher than the side position. The surface of the screening plate 209 is provided with screen holes. The side of the screening plate 209 is provided with a waste bin 210. The waste bin 210 is fixedly connected to the lower end of the screening chamber 204. The cross-section of the waste bin 210 is annular, and a waste storage area 211 is provided on it. The waste storage area 211 is connected to the side of the screening plate 209.

[0107] When mud and sand are manually fed into the screening bin 204 through the feed inlet 2041, mud and sand with particle size that meets the requirements of the stock test fall through the sieve holes on the screening plate 209 and into the mixing bin 213 mentioned below. Mud and sand that does not meet the test requirements fall into the waste storage area 211 in the waste bin 210 under the action of gravity and subsequent mud and sand impact.

[0108] A drive motor 207 is installed above the feed inlet 2041. The drive motor 207 uses existing technology components and is fixedly mounted on a motor mounting plate 206. The motor mounting plate 206 is fixedly connected to the screening chamber 204 via a first connecting rod 205. The upper and lower ends of the first connecting rod 205 are fixedly connected to the motor mounting plate 206 and the screening chamber 204, respectively. The output shaft of the drive motor 207 is fixedly connected to the upper end of a drive rod 208. The lower end of the drive rod 208 passes through the axis of the screening plate 209, but... During the rotation operation of 208, the screening plate 209 does not move at all. Two sets of stirring rods 212 are fixedly installed on the surface of the drive rod 208 located below the screening plate 209. The two sets of stirring rods 212 are arranged longitudinally, and the installation direction of the stirring rods 212 is the same as the radial direction of the drive rod 208. The stirring rods 212 are located inside the stirring chamber 213. The stirring chamber 213 is fixedly connected to the lower surface of the waste bin 210. A resistance wire 214 for heating and drying is fixedly installed on the surface of the stirring chamber 213. The resistance wire 214 adopts existing technology components.

[0109] The dye added to the mixing chamber 213 is a water-based dye. By using water-based fuel, the color of the treated mud and sand can be deepened without affecting its basic physical properties.

[0110] After the silt with a particle size that meets the requirements of the packing test falls into the mixing chamber 213, the drive motor 207 is started. The drive motor 207 drives the drive rod 208 to rotate. When the drive rod 208 rotates, it drives the stirring rod 212, which is fixedly connected to its surface, to rotate synchronously. When the stirring rod 212 rotates, it stirs the silt material in the mixing chamber 213 with the water-based dye, thus completing the silt dyeing function. The dyed silt can significantly reduce its reflectivity under the irradiation of the continuous laser 305 mentioned below, ensuring the effective distinction between tracer particles and background bed sand in the PIV image.

[0111] After the mud and sand are dyed, the resistance wire 214 is energized. The energized resistance wire 214 heats the wall of the mixing chamber 213 and dries the dyed mud and sand material in the mixing chamber 213 for subsequent mud and sand loading and stacking.

[0112] To allow the mud and sand material in the mixing chamber 213 to be deposited and accumulated close to the side wall of the water tank 1, a discharge port 215 is fixedly provided at the axial position of the lower surface of the mixing chamber 213. The material in the mixing chamber 213 can flow out through the discharge port 215. A rotating ring 216 is coaxially mounted on the discharge port 215. A baffle 218 that can close the discharge port 215 is inserted and detachably mounted on the rotating ring 216. An inclined discharge port 217 is detachably connected to the lower end of the rotating ring 216 by bolts. The inclined discharge port 217 is connected to the discharge port 215 and can change the falling direction of the mud and sand flowing out of the discharge port 215.

[0113] When the material in the mixing chamber 213 needs to be put into the water tank 1, the baffle 218 on the rotating ring 216 is pulled outward, and the discharge port 215 on the mixing chamber 213 is in the open state. The mud and sand can fall vertically into the water tank 1 through the discharge port 215. When it is necessary to pile the mud and sand close to the side wall of the water tank 1, the rotating ring 216 is rotated so that the discharge end of the inclined discharge port 217 is close to the side wall of the water tank 1. At this time, the mud and sand flowing out through the discharge port 215 falls to the position close to the side wall of the water tank 1 under the guidance of the inclined discharge port 217.

[0114] To acquire experimental data inside the water tank 1, a measurement component mounting unit is proposed, including a mounting frame 301, a synchronization controller 302, a high-speed camera 303, and a continuous laser 305. The mounting frame 301 is detachably mounted on the second slider 203 via bolts. Both the mounting frame 301 and the screening chamber 204 mentioned above can be mounted on the second slider 203 via bolts. The high-speed camera 303 is fixedly mounted on the mounting frame 301. The high-speed camera 303 uses existing technology components, has a resolution of no less than 1024×1024 pixels, and an adjustable shooting frequency to adapt to different flow rate conditions. The high-speed camera 303 is set perpendicular to the side wall of the water tank 1, with its camera facing the upper surface of the sediment layer inside the water tank 1, enabling it to detect changes in sediment movement. For image acquisition, an L-shaped rod 304 is fixedly installed on the side of the mounting bracket 301 and fixedly connected to one end of the L-shaped rod 304. The other end of the L-shaped rod 304 is fixedly connected to a continuous laser 305. The continuous laser 305 can illuminate the flow field cross-section that the high-speed camera 303 is aimed at, which facilitates image acquisition by the high-speed camera 303. The continuous laser 305 adopts existing technical components, and the power of the continuous laser 305 is not less than 15W, the wavelength is preferably 532nm, and the thickness of the formed sheet light is less than 5mm. A synchronization controller 302 is fixedly installed above the high-speed camera 303. The synchronization controller 302 is connected to the high-speed camera 303 and the continuous laser 305 by signal connection. The synchronization controller 302 can control the start and stop of the high-speed camera 303 and the continuous laser 305.

[0115] After the screening, dyeing, drying and feeding of the silt are completed, the screening chamber 204 is removed from the second slider 203, and the mounting frame 301 is installed on the second slider 203 with bolts. The position of the mounting frame 301 relative to the water tank 1 is adjusted by sliding the first sliding frame 201 and the second slider 203, thereby adjusting the working position of the high-speed camera 303 and the continuous laser 305.

[0116] To achieve the aggregated processing of experimental data, a comprehensive data processing unit is proposed. The comprehensive data processing unit is connected to the signal of the high-speed camera 303. The comprehensive data processing unit has built-in PIV analysis software and data analysis module. The PIV analysis software is used to calculate the two-dimensional velocity field from the image sequence. The data analysis module is further used to automatically calculate and output the vertical average velocity distribution, shear strain rate distribution, and vertical vorticity distribution cloud map and curve within the flow field cross section based on the velocity field data.

[0117] The data processing procedure of the integrated data processing unit is as follows:

[0118] a) The instantaneous and average two-dimensional velocity fields of the flow field near the accumulation body are obtained by processing the images acquired by the high-speed camera 303 using PIV analysis software;

[0119] b) Based on the velocity field, the data analysis module automatically calculates and plots the distribution of the following key hydrodynamic parameters under different flow layers (near bottom, middle layer, and upper layer) and different influencing factors (start-up state, flow rate, sediment particle size):

[0120] 1) Vertical average velocity distribution curve;

[0121] 2) Shear strain rate distribution contour map and friction curve;

[0122] 3) Vertical vorticity distribution cloud map and distribution curve along the path.

[0123] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for measuring the critical condition of sediment initiation in a sedimentary mass using a PIV flow field, characterized in that... include: Step 1: Pretreatment of test sediment: Sand that meets the test particle size is screened from natural river sand using a screening and dyeing device, dyed and dried for later use. Step 2, Model Preparation and Initial Flow Field Establishment: Lay a fixed bed of sand and level it in the test section of the water tank. Use dyed sand to build a permeable pile model according to the preset geometric parameters. Pour water into the water tank until the pile is completely submerged and soak for a preset time to stabilize. Step 3: PIV System Calibration and Debugging: Install and adjust the measurement component mounting unit so that the laser sheet on it illuminates the vertical cross-section of the accumulation slope, release tracer particles, complete the spatial calibration of the high-speed camera's shooting area through the calibration plate, and establish the mapping relationship between pixel coordinates and physical coordinates; Step 4: Unsteady Flow Simulation: The stepped drop water level method is used to simulate the unsteady flow during flood season. Starting from the high water level, the tailgate is adjusted to gradually lower the water level while maintaining a constant inlet flow. In step four, the water level drops by 1 cm at a time, and the next drop is carried out after the water flow stabilizes, until different levels of sediment are induced to move. Step 5: Synchronous Measurement and Data Acquisition: Under stable water levels at each level, observe the sediment initiation status. When the standard is met, simultaneously carry out PIV flow field measurement, automatic water level monitoring, and record the initiation position. Step 6: Multi-parameter flow field data analysis: Import the acquired image sequence into the integrated data processing unit to process the relevant data; In step six, the data processing procedure of the integrated data processing unit is as follows: The instantaneous and average two-dimensional velocity fields of the flow field near the accumulation body were obtained by processing the images using PIV analysis software. Based on the velocity field, the data analysis module automatically calculates and plots the distribution of the following key hydrodynamic parameters under different flow layers and different influencing factors: vertical average velocity distribution curve; shear strain rate distribution cloud map and friction distribution curve; vertical vorticity distribution cloud map and friction distribution curve. Step 7: Critical condition correlation analysis: Correlate the critical start-up state with the corresponding hydrodynamic parameters, and use measured start-up velocity and water depth data to verify or calibrate the start-up velocity and shear stress formulas for sediment on the bank slope of the deposited body. The specific process is as follows: A mathematical model is established using a nonlinear multiple regression method to connect the critical initiation parameters with hydrodynamic parameters, sediment geometric parameters, and sediment physical parameters; the model expression is as follows: , The dimensionless critical Shields number characterizes the critical shear stress. Let θ be the Reynolds number of the water flow, and θ be the slope of the sedimentary bank. The particle size of the sediment is dimensionless. Given water depth Sediment particle size Under the premise of this, the starting flow velocity empirical formula is constructed by fitting all the valid data extracted in step six using statistical software with the nonlinear least squares method: ,in, To measure the starting flow rate, Because of the water depth, For sediment particle size, It is the acceleration due to gravity. The empirical coefficients to be fitted are... This is the error term.

2. The method for measuring the PIV flow field of sediment initiation critical conditions in an accumulation body according to claim 1, characterized in that: In step two, the preset geometric parameters include the radius and slope of the accumulation body.

3. The method for measuring the PIV flow field of sediment initiation critical conditions in an accumulation body according to claim 1, characterized in that: In step five, the PIV flow field measurement unit is activated, and a high-speed camera continuously acquires a sequence of flow field images; an automatic water level meter is used to measure and record the water depth along the current test section; the current flow rate and the observed sediment initiation location are recorded.

4. A device for measuring the PIV flow field of sediment initiation critical conditions in a sedimentary accumulation body, used to implement the PIV flow field measurement method for sediment initiation critical conditions in a sedimentary accumulation body as described in any one of claims 1-3, characterized in that... include: The water tank (1) used to simulate the water flow environment has sand for testing laid at the bottom. It has a water pump (5) with adjustable flow rate and an adjustable tailgate (6) for controlling the water level in the water tank (1) respectively. The first slide rail (101) is fixedly installed on the water tank (1). The screening and dyeing equipment includes a first sliding frame (201) that is slidably installed on a water tank (1), a screening plate (209) and a stirring rod (212) set on the first sliding frame (201), for screening fixed bed sand and target particle size sedimentary sand from natural river sand and dyeing them; The measuring component mounting unit includes a mounting bracket (301) slidably mounted on a first sliding frame (201), a synchronous controller (302) fixedly mounted on the mounting bracket (301), a high-speed camera (303) and a continuous laser (305), and the spatial position of the above components relative to the water tank (1) can be adjusted by the mounting bracket (301); The integrated data processing unit connects to and controls the high-speed camera (303), and has built-in PIV analysis software and data analysis module. The PIV analysis software is used to calculate the two-dimensional velocity field from the image sequence. The data analysis module is further used to automatically calculate and output the vertical average velocity distribution, shear strain rate distribution, and vertical vorticity distribution cloud map and curve within the flow field cross section based on the velocity field data.

5. The PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to claim 4, characterized in that: The first sliding frame (201) is slidably mounted on the first slide rail (101) via the first slider (202). A second slider (203) is slidably connected to the first sliding frame (201). The screening chamber (204) is detachably connected to the second slider (203) via bolts. An inlet (2041) is provided on the upper surface of the screening chamber (204). A drive motor (207) is provided above the inlet (2041). The drive motor (207) is fixedly mounted on the motor mounting plate (206). The motor mounting plate (206) is fixedly connected to the screening chamber (204) via the first connecting rod (205). The screening chamber (204) is coaxially fixedly installed with a screening plate (209). A waste bin (210) is provided on the side of the screening plate (209). The waste bin (210) is fixedly connected to the lower end of the screening chamber (204). The cross-section of the waste bin (210) is circular, and a waste storage area (211) is provided on it. The waste storage area (211) is connected to the side of the screening plate (209). The output shaft of the drive motor (207) is fixedly connected to the upper end of the drive rod (208). The lower end of the drive rod (208) passes through the shaft of the screen plate (209). A stirring rod (212) is fixedly installed on the part of the drive rod (208) that passes through the screen plate (209). The stirring rod (212) is located inside the stirring chamber (213). The stirring chamber (213) is fixedly connected to the lower surface of the waste bin (210). A resistance wire (214) for heating and drying is fixedly installed on the surface of the stirring chamber (213). A discharge port (215) is fixedly provided at the axial position of the lower surface of the mixing chamber (213). A rotating ring (216) is coaxially mounted on the discharge port (215). An inclined discharge port (217) is detachably connected to the rotating ring (216). The inclined discharge port (217) is connected to the discharge port (215). A baffle (218) is detachably connected to the rotating ring (216).

6. The PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to claim 5, characterized in that: A mounting bracket (301) is detachably mounted on the second slider (203). A high-speed camera (303) is fixedly mounted on the mounting bracket (301). The high-speed camera (303) is set perpendicular to the side wall of the water tank (1). An L-shaped rod (304) is fixedly mounted on the side of the mounting bracket (301) and fixedly connected to one end of the L-shaped rod (304). The other end of the L-shaped rod (304) is fixedly connected to a continuous laser (305). A synchronization controller (302) is set above the high-speed camera (303). The synchronization controller (302) is connected to the high-speed camera (303) and the continuous laser (305) via signal connection.

7. The PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to claim 6, characterized in that: The high-speed camera (303) has a resolution of no less than 1024×1024 pixels and an adjustable shooting frequency to adapt to different flow rate conditions; the continuous laser (305) has a power of no less than 15W, a wavelength of 532nm, and forms a sheet of light with a thickness of less than 5mm.

8. The PIV flow field measurement device for the critical condition of sediment initiation in an accumulation body according to claim 5, characterized in that: The dye added to the mixing chamber (213) is a water-based dye, which deepens the color of the treated mud and sand.

Images