A water tank experimental apparatus and method for transporting microplastics by turbidity.

Abstract

This invention relates to the field of fluid dynamics experimental measurement technology, and discloses a water tank experimental apparatus and method for transporting microplastics in turbid flow. The apparatus includes a water tank main body, an optical measurement subsystem, and an ultrasonic Doppler flow velocity measurement system. The ultrasonic emission path and the optical measurement window overlap spatially to form a cross-view window. The method includes: applying a first fluorescent label and a second fluorescent label to microplastic particles and sediment particles; simultaneously acquiring optical and acoustic data within the cross-view window; establishing a concentration correction function and a flow velocity correction function within the cross-view window using acoustic backscattering intensity data and flow velocity data as references; applying the correction functions to the entire optical window to obtain a globally corrected concentration field and a globally corrected flow velocity field; and distinguishing and quantifying microplastics and sediments based on the corrected data. By employing the cross-correction principle, the problem of signal distortion in optical measurements in highly turbid fluids is solved.

Description

Technical Field

[0001] This invention relates to the field of fluid dynamics experimental measurement technology, specifically to a water tank experimental apparatus and method for transporting microplastics in turbid flow. Background Technology

[0002] Microplastics, as a novel pollutant, have become a research hotspot due to their migration and fate in aquatic environments such as rivers, lakes, and oceans. Turbidity currents (also known as turbidity or density currents) are density flows in water bodies carrying high concentrations of sediments and are the main driving force for the underwater transport of sediments and related pollutants (including microplastics). Therefore, simulating the physical processes of microplastic transport in turbidity currents in laboratory tanks and accurately measuring the concentration distribution of microplastics and sediment particles, as well as the velocity field of the fluid during this process, is crucial for revealing the transport mechanism of microplastics.

[0003] Currently, in fluid dynamics experiments, particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are commonly used optical measurement techniques for obtaining high-resolution velocity and concentration fields. PIV acquires the instantaneous flow field by tracking tracer particles, while PLIF uses the fluorescence intensity emitted by fluorescently labeled particles under laser excitation to invert the concentration field. However, turbid flows contain high concentrations of background sediment particles, which poses a significant challenge to optical measurements. High concentrations of particles strongly absorb and scatter the laser light, causing severe attenuation of the optical signal during transmission. This reduces the signal-to-noise ratio of the PIV image, making it difficult to identify particles. Furthermore, the linear calibration relationship between the fluorescence intensity measured by PLIF and the actual particle concentration fails, resulting in severely distorted measurement data.

[0004] To perform measurements in turbid fluids, researchers also employ ultrasonic Doppler velocity measurement systems (UVP). This technique utilizes the acoustic Doppler effect, emitting ultrasonic waves and receiving the echo signals from particles to calculate the velocity profile. Its acoustic backscattering intensity (ABS) can also be used to invert concentration under certain conditions. The main advantage of acoustic methods is their ability to penetrate highly turbid fluids and their relative insensitivity to optical transparency. However, their limitation lies in the fact that UVP typically only provides profile data along a one-dimensional acoustic path, resulting in relatively low spatial resolution and making it difficult to capture the fine two-dimensional or three-dimensional flow field structure and concentration distribution characteristics in turbid flows. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a water tank experimental apparatus and method for transporting microplastics in turbid flow, which solves the problem that existing technologies struggle to simultaneously obtain high-resolution and high-accuracy flow velocity and concentration fields in highly turbid flow.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a water tank experimental apparatus for transporting microplastics by turbidity, comprising;

[0007] Main body of the water tank device; used for conducting microplastic experiments involving turbidity transport.

[0008] The main body of the water tank device includes a water storage tank and a ramp. A ramp is installed on one side of the water storage tank, and the inner bottom of the ramp away from the water storage tank is higher than the side close to the water storage tank.

[0009] An optical measurement subsystem, which is fixed to the outer wall of the water storage tank and the inclined trough by a bracket, is used to acquire the original image sequence of the turbid mixture;

[0010] The optical measurement subsystem includes;

[0011] A particle image velocimetry device, wherein the outer wall of the particle image velocimetry device is fixedly connected to the inside of the fixed frame, and is used to capture the movement of PIV tracer particles in water.

[0012] A planar laser-induced fluorescence device, wherein the outer wall of the planar laser-induced fluorescence device is fixedly connected to the inside of the fixture, and is used to capture the fluorescence signal emitted by fluorescently labeled microplastics and deposits;

[0013] A dual-wavelength laser is fixedly connected to the outer wall of the water storage tank and the inclined trough, and is used to emit a laser sheet light source;

[0014] An image acquisition device, electrically connected to a particle image velocimetry device and a planar laser-induced fluorescence device, is used to collect image information;

[0015] The optical measurement subsystem is used to define an optical measurement window and acquire the original image sequence within the window;

[0016] An ultrasonic Doppler flow velocity measurement system is installed at the inner bottom of a water storage tank away from the inclined channel or on the side of the inclined channel close to the water storage tank. It includes a UVP flow meter, which is used to define an ultrasonic emission path and acquire flow velocity data and acoustic backscattering intensity data along the path.

[0017] An inflow control system, installed at the end of the ramp away from the storage tank, is used to transport turbidity and microplastics;

[0018] The inflow control system includes a storage tank, one end of which is connected to a delivery pump via a pipe. The output end of the delivery pump is fixedly connected to a delivery pipe, and the outer wall of the delivery pipe is fixedly connected to the outer wall of the inclined trough.

[0019] Preferably, the water storage tank is 8m long, 3.0m wide, and 1.0m high, the inclined trough is 2.2m long and 1.0m high, and both the water storage section and the inclined section are made of plexiglass.

[0020] Furthermore, to meet the scale requirements of physical simulations and provide good optical observation conditions.

[0021] Preferably, the planar laser-induced fluorescence device and the particle image velocimetry device share a portion of the optical path, and the dual-wavelength laser is a shared excitation source for both the particle image velocimetry device and the planar laser-induced fluorescence device.

[0022] Preferably, the ultrasonic emission path and the optical measurement window overlap in space to form a cross window.

[0023] A method for a water tank experiment to transport microplastics by turbidity includes the following steps;

[0024] S1. Experimental preparation steps: First, prepare turbidity mud containing microplastic particles, label the microplastic particles with a first fluorescent label, label the sediment particles with a second fluorescent label, add PIV tracer particles to the turbidity mixture, and saturate each pipe of the turbidity flow control system.

[0025] S2. Data Acquisition Steps: The turbid mixture is delivered to the main body of the water tank device through the inflow control system. The optical window forming the cross-view window and the ultrasonic emission path are synchronously acquired through the composite visualization measurement system, which includes a UVP flow meter, a particle image velocimeter, and a planar laser-induced fluorescence device; to obtain the flow velocity data, acoustic backscattering intensity data, and original image sequence.

[0026] S3. Data preprocessing steps: Perform quality control and spur removal on the flow velocity data and acoustic backscatter intensity data, and batch process the original image sequence to obtain the original flow velocity field data and the original fluorescence intensity field data respectively.

[0027] S4. Concentration field correction steps: In the cross window, the concentration reference value is inverted using the acoustic backscattering intensity data, a concentration correction function is established between the concentration reference value and the original fluorescence intensity field data, and the concentration correction function is applied to the optical window to obtain the globally corrected concentration field.

[0028] S5. Velocity field correction steps: Within the cross window, using the velocity data as the correction reference, establish a velocity correction function between the correction reference and the original velocity field data, and apply the velocity correction function to the optical window to obtain the globally corrected velocity field.

[0029] S6. Data application and analysis steps: Based on the globally corrected velocity field and the globally corrected concentration field, calculate the turbulence parameters of the turbidity flow, and distinguish and quantify the microplastic particles and the sediment particles.

[0030] Furthermore, in the concentration field correction step:

[0031] In the cross window Internally, using preprocessed acoustic backscattering intensity data By pre-setting calibration relationships Inversely derived concentration benchmark value :

[0032] ;

[0033] In the formula;

[0034] This represents the volumetric concentration reference value within the area overlapping the acoustic path and the optical measurement window.

[0035] This represents acoustic backscattering intensity data obtained using a UVP (Ultrasonic Velocity Profiler).

[0036] This represents the mapping function between intensity and concentration obtained through calibration experiments;

[0037] This indicates the area of ​​overlapping views (i.e., the spatial overlap between the acoustic measurement path and the optical measurement window).

[0038] A spatial position vector, which can usually be represented as , used to determine the location of the measurement point;

[0039] It is a time variable.

[0040] Establish the concentration benchmark value Compared with the original fluorescence intensity field data The mapping relationship within the cross-window yields the concentration correction function. .

[0041] The concentration correction function Applied to the entire optical window Raw fluorescence intensity field data The globally corrected concentration field is calculated. ;

[0042] ;

[0043] In the formula;

[0044] This represents the concentration field after global correction.

[0045] This represents the raw fluorescence intensity data;

[0046] This represents the concentration correction function used to adjust the original fluorescence intensity data. Convert to concentration value;

[0047] Indicates the entire optical viewing window area;

[0048] A spatial position vector, typically a three-dimensional coordinate. , used to determine the measurement location;

[0049] It is a time variable.

[0050] Preferably, in step S1, during experimental preparation:

[0051] The first fluorescent label used was Rhodamine 6G;

[0052] The second fluorescent label uses sodium fluorescein;

[0053] The PIV tracer particles are hollow glass microspheres.

[0054] Preferably, in step S2 data acquisition, the composite visualization measurement system is time-synchronized by a hardware trigger so that the original image sequence, the flow velocity data and the acoustic backscatter intensity data have a unified time reference.

[0055] Preferably, step S3, data preprocessing, includes:

[0056] The flow velocity data and the acoustic backscatter intensity data are filtered and burr points are removed based on the signal-to-noise ratio.

[0057] Preferably, step S5, flow field correction, includes:

[0058] Within the cross-view window, the original velocity field data is spatially interpolated to extract the velocity component that coincides with the ultrasonic emission path;

[0059] A flow velocity correction function is established by performing statistical regression analysis on the calibration benchmark and the flow velocity component.

[0060] Furthermore, in the velocity field correction step;

[0061] In the cross window The flow rate data obtained using the UVP flow meter is then used. This serves as a calibration benchmark. The calibration benchmark is established. With the original flow field data The mapping relationship within the cross-window yields the flow rate correction function. ;

[0062] ;

[0063] In the formula;

[0064] Indicates spatial location and time The calibration reference flow rate is measured by the UVP flow meter.

[0065] Indicates the same spatial location and time The raw flow field data obtained by the particle image velocimetry device;

[0066] For flow rate correction function;

[0067] is a spatial position vector, representing the three-dimensional coordinate position in the flow field;

[0068] It is a time variable;

[0069] Indicates the cross-window area.

[0070] The flow rate correction function Applied to the entire optical window Raw velocity field data within The globally corrected flow field was calculated. ;

[0071] ;

[0072] In the formula;

[0073] This represents the velocity field after global correction, i.e., in spatial location. and time Above, via the flow rate correction function Corrected flow rate results;

[0074] This represents the original PIV velocity field data;

[0075] For flow rate correction function;

[0076] It is a spatial position vector, representing the coordinate position of any point in the flow field;

[0077] For time variables, the time points of measurement or calculation are used to describe the time evolution characteristics of the flow field;

[0078] The optical viewing window area encompasses the entire flow field being observed; it is a cross-viewing window. The extended region.

[0079] Preferably, in step S6, the step of distinguishing and quantifying microplastic particles and sediment particles in the data application analysis includes:

[0080] The total volume concentration is obtained based on the globally corrected concentration field;

[0081] The concentration ratio of the microplastic particles to the sediment particles was obtained based on the original fluorescence intensity field data and the preset calibration relationship.

[0082] By combining the total volume concentration and the concentration ratio, the concentrations of microplastic particles and sediment particles can be obtained.

[0083] This invention provides a water tank experimental apparatus and method for transporting microplastics by turbidity current. It has the following beneficial effects:

[0084] 1. This invention establishes a correction function for flow velocity and concentration by setting up a cross window that overlaps the optical measurement window and the ultrasonic emission path, and using the flow velocity data and acoustic backscattering intensity data obtained by the UVP flowmeter as a correction benchmark. The correction function can be applied to the entire optical window to correct the measurement deviation caused by signal attenuation and distortion of the particle image velocimetry device and the planar laser-induced fluorescence device in highly turbid fluids. It combines the anti-interference characteristics of acoustic measurement with the high resolution characteristics of optical measurement, and solves the technical problem of simultaneously obtaining high-resolution and high-accuracy flow field and concentration field under highly turbid conditions.

[0085] 2. The present invention extends the established flow rate correction function and concentration correction function to the entire two-dimensional high-resolution optical window covered by the particle image velocimetry device and the planar laser-induced fluorescence device, so that the final data field has both the high spatial resolution of optical measurement and the accuracy of acoustic measurement in a highly turbid environment.

[0086] 3. This invention enables the differentiation and quantification of microplastic particles and sediment particles by applying first and second fluorescent labels respectively, combined with subsequent data application and analysis. This method allows for the independent analysis of the concentration distribution, transport flux, and interaction with hydrodynamic structures of microplastics and sediments during mixed transport, thereby revealing the unique transport patterns of microplastics in turbidity current environments. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the device of the present invention;

[0088] Figure 2 This is a schematic diagram of the method flow of the present invention;

[0089] Figure 3 This is a flowchart of the data preprocessing sub-steps of the present invention.

[0090] Among them, 1. Water storage tank; 2. Inclined trough; 3. Fixing frame; 4. Particle image velocimetry device; 5. Planar laser-induced fluorescence device; 6. Dual-wavelength laser; 7. UVP flow meter; 8. Storage tank; 9. Transfer pump; 10. Transfer pipe. Detailed Implementation

[0091] The technical solutions in 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.

[0092] Please see the appendix Figure 1 This invention provides a water tank experimental apparatus for transporting microplastics by turbidity, comprising:

[0093] The main body of the water tank device serves as a load-bearing structure for conducting physical simulation experiments on microplastics transported in turbid flow.

[0094] The main body of the water tank device includes a water storage tank 1 and a ramp trough 2. The ramp trough 2 is installed and connected to one side of the water storage tank 1. The ramp trough 2 is designed such that the inner bottom of the side away from the water storage tank 1 is higher than the inner bottom of the side close to the water storage tank 1, thereby forming a ramp with a preset slope for initial acceleration of turbidity flow.

[0095] To simulate a vast sedimentation area, the water storage section can be designed to be 8m long, 3.0m wide, and 1.0m high. To simulate the acceleration process of turbidity currents, the slope section can be designed to be 2.2m long and 1.0m high. For ease of subsequent optical measurements, both the water storage section and the slope section are preferably made of highly transparent materials, such as plexiglass.

[0096] An inflow control system is installed at the end of the inclined trough 2 away from the water storage tank 1. It is used to transport turbidity and microplastics. The inflow control system includes a storage tank 8. One end of the storage tank 8 is connected to a delivery pump 9 through a pipe. The output end of the delivery pump 9 is fixedly connected to a delivery pipe 10. The outer wall of the delivery pipe 10 is fixedly connected to the outer wall of the inclined trough 2. It is used to stably and continuously transport the pre-prepared turbidity mixture containing microplastic particles and sediments to the top of the inclined trough 2 of the main body of the water tank device through the delivery pump 9 and the delivery pipe 10 according to the flow rate and concentration set by the experimental conditions.

[0097] An optical measurement subsystem, which is fixed to the outer wall of the water storage tank 1 and the inclined trough 2 by a fixing frame 3, is used to acquire the original image sequence of the turbid mixture.

[0098] The optical measurement subsystem includes a particle image velocimetry device 4, a planar laser-induced fluorescence device 5, a dual-wavelength laser 6, and an image acquisition device;

[0099] The particle image velocimetry device 4 is fixedly connected to the inside of the fixing frame 3 on its outer wall. It is used to capture the motion of PIV tracer particles in the water body in order to solve the fluid velocity field.

[0100] The planar laser-induced fluorescence device 5 has its outer wall fixedly connected to the inside of the fixture 3. It shares part of the optical path with the particle image velocimetry device 4, forming a cross window. This window is used to capture the fluorescence signals emitted by fluorescently labeled microplastics and deposits in order to calculate their concentration distribution.

[0101] The dual-wavelength laser 6 serves as the shared excitation source for the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5. The dual-wavelength laser 6 is fixedly connected to the outer wall of the water storage tank 1 and the inclined tank 2, and is used to emit laser sheet light source to illuminate the measurement area inside the water tank.

[0102] The image acquisition device is electrically connected to the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5. The image acquisition device is used to capture the light signals excited by PIV tracer particles and the light signals excited by PLIF fluorescent dye at high speed, and transmit the optical image information to the subsequent data processing unit.

[0103] The ultrasonic Doppler flow velocity measurement system includes a UVP flow meter 7, which is installed at the inner bottom of the water tank 1 away from the ramp trough 2 or on the side of the ramp trough 2 closer to the water tank 1. These probes are used to emit ultrasonic beams along their acoustic path and receive echo signals from particulate matter, including silt and microplastics, to calculate the velocity profile of particulate matter in the fluid and the intensity of acoustic backscattering.

[0104] This allows one or more ultrasonic emission paths of the ultrasonic Doppler velocity measurement system to partially or completely overlap in space with the optical measurement windows of the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5, i.e., the areas illuminated by the laser and captured by the image acquisition device.

[0105] The experimental method for transporting microplastics in a turbid flow tank described below can be referred to in conjunction with the experimental apparatus for transporting microplastics in a turbid flow tank described above.

[0106] Please see the appendix Figure 2 -Appendix Figure 3 The present invention also provides a water tank experimental method for transporting microplastics by turbidity; including the following steps;

[0107] S1. Experimental preparation steps: First, prepare turbidity mud containing microplastic particles, label the microplastic particles with a first fluorescent label, label the sediment particles with a second fluorescent label, add PIV tracer particles to the turbidity mixture, and saturate each pipe of the turbidity flow control system.

[0108] Specifically, in step S1 of this embodiment, preset experimental conditions are provided for subsequent synchronous measurement and data acquisition.

[0109] The microplastic particles to be tested were labeled using a first fluorescent dye solution, specifically Rhodamine 6G dye, which binds to the microplastic particles through adsorption or permeation. After labeling, the particles were washed to remove excess dye from the surface and then dried for later use.

[0110] The sediment particles used in the experiment (e.g., kaolin or silt) are labeled in a second fluorescent dye solution, for example, using sodium fluorescein.

[0111] Prepare the turbidity mixture. Microplastic particles labeled with a first fluorescent marker, sediment particles labeled with a second fluorescent marker, and (if necessary) unlabeled background sediment are thoroughly mixed with water in a stirred vessel according to the concentration gradient required by the experimental design to form a homogeneous turbidity mixture. PIV tracer particles are then added to this mixture. The physical properties of the PIV tracer particles, such as density close to that of the water, are crucial to ensure they can effectively follow fluid movement, while also possessing good light scattering properties. For example, neutral hollow glass microspheres can be used as PIV tracer particles.

[0112] The prepared turbidity mixture is pumped into the reservoir and all delivery pipes of the inflow control system until it is completely filled. This operation aims to purge all air from the piping system and establish a stable hydraulic gradient. The purpose is to ensure that, when the inflow control system is officially started, a stable flow rate and concentration of turbidity mixture, consistent with the set values, is instantaneously provided at the inlet at the top of ramp trough 2, thus avoiding interference with data acquisition in the initial stage due to system startup delays or unstable fluid conditions within the pipes.

[0113] S2. Data Acquisition Steps: The turbid mixture is delivered to the main body of the water tank device through the inflow control system. The composite visualization measurement system is synchronized with the time through a hardware trigger. The composite visualization measurement system includes a UVP flow meter 7, a particle image velocimeter and a planar laser-induced fluorescence device 5; to acquire flow velocity data, acoustic backscattering intensity data and raw image sequences.

[0114] Specifically, in step S2 of this embodiment, the instantaneous information of particulate motion and fluid dynamics in the turbid flow is captured by synchronously running a composite visualization measurement system.

[0115] The inflow control system is activated, allowing the turbid mixture to enter the main body of the water tank from the top of the inclined trough 2 at a stable flow rate and concentration set experimentally. Under the influence of gravity, the turbid mixture accelerates along the inclined trough 2 and forms an evolving turbid flow within the storage tank 1.

[0116] Once the turbidity flow has stabilized within the main body of the water tank device, an external hardware trigger synchronizes the composite visual measurement system and initiates data acquisition. The hardware trigger sends a synchronization trigger signal to all core components of the composite visual measurement system, including the UVP flowmeter 7, the particle image velocimeter 4, the planar laser-induced fluorescence device 5, and the dual-wavelength laser. This synchronization signal ensures that all subsequently acquired data streams have a unified time reference, providing a prerequisite for data fusion and cross-calibration.

[0117] The ultrasonic transducer of the UVP flowmeter 7 emits ultrasonic pulses along its acoustic path and receives echo signals generated by particulate matter (including microplastic particles, sediment particles, and PIV tracer particles) in the turbid mixture. By analyzing the Doppler frequency shift of the echo signals, the flow velocity profile along the acoustic path is calculated, and the flow velocity data is obtained. Simultaneously, the intensity of the echo signal is recorded to obtain acoustic backscattering intensity data. .

[0118] At the same time, the dual-wavelength laser 6 emits laser sheet light of a preset wavelength to illuminate the measurement area located within the optical window.

[0119] The image acquisition unit of the particle image velocimetry device 4 selectively captures the laser signals scattered by PIV tracer particles through its configured bandpass filter, and performs this capture at extremely short time intervals. A series of image pairs are captured. The image acquisition unit of the planar laser-induced fluorescence device 5 captures the fluorescence signals emitted by the first and second fluorescent labels after excitation through its configured high-pass or band-pass filters. All the images acquired by these two devices together constitute the original image sequence.

[0120] S3. Data preprocessing steps: Perform quality control and spur removal on the flow velocity data and acoustic backscatter intensity data, and batch process the original image sequence to obtain the original flow velocity field data and the original fluorescence intensity field data respectively.

[0121] Specifically, in this embodiment, step S3 improves the quality and converts the format of the original data to provide reliable input for subsequent cross-correction and physical analysis.

[0122] Step S3 may include the following sub-steps;

[0123] Flow rate data acquired by UVP flow meter 7 Acoustic backscattering intensity data Conduct quality control.

[0124] Data points are filtered based on signal-to-noise ratio (SNR). A SNR threshold is set, and data points below the threshold are considered invalid and discarded.

[0125] Spike removal is performed on the filtered data. Isolated data points that are physically unreasonable or exhibit abrupt changes from their neighbors are identified and removed using predefined physical thresholds or statistical methods (such as the three-standard-deviation criterion or median filtering). Data gaps left by removed spikes can be filled using surrounding valid data points through spatial or temporal linear or higher-order interpolation methods to ensure the integrity of the data profile.

[0126] The raw image sequences acquired by the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5 are batch-processed to generate raw flow velocity field data respectively. and raw fluorescence intensity field data .

[0127] The image sequence acquired by the particle image velocimetry device 4 is processed using a particle image velocimetry algorithm. This process typically includes pre-enhancement operations such as image denoising, followed by dividing the image into multiple query windows. By performing cross-correlation calculations on corresponding query windows in two consecutive frames, the PIV tracer particles' activity in extremely short time intervals is obtained. The displacement vectors within the query window. The set of displacement vectors from all query windows constitutes the original two-dimensional or three-dimensional velocity field data at that moment. .

[0128] For the image sequence acquired by the planar laser-induced fluorescence device 5, the processing mainly involves intensity extraction. After optional image denoising, the grayscale value or color channel value of each image pixel is directly extracted. These intensity values ​​constitute the two-dimensional raw fluorescence intensity field data at that moment. The value of each data point represents the fluorescence signal intensity at its corresponding spatial location.

[0129] S4. Concentration field correction steps: In the cross window, the concentration reference value is inverted using the acoustic backscattering intensity data, a concentration correction function is established between the concentration reference value and the original fluorescence intensity field data, and the concentration correction function is applied to the optical window to obtain the globally corrected concentration field.

[0130] Specifically, step S4 in this embodiment involves using acoustic measurement data to correct the optical fluorescence signal that is distorted by high turbidity, thereby obtaining an accurate global concentration distribution.

[0131] Step S4 may include the following sub-steps:

[0132] Invert the concentration baseline value. This step is performed within the cross-view window (i.e., the area where the acoustic path of the UVP flowmeter 7 and the optical measurement window spatially overlap). Preprocessed acoustic backscattering intensity data is used. Through a pre-established calibration relationship Inversely, the volume concentration reference value along the acoustic path is obtained. ;

[0133] ;

[0134] In the formula;

[0135] This represents the volumetric concentration reference value within the area overlapping the acoustic path and the optical measurement window.

[0136] This represents acoustic backscattering intensity data obtained using a UVP (Ultrasonic Velocity Profiler).

[0137] This represents the mapping function between intensity and concentration obtained through calibration experiments;

[0138] This indicates the area of ​​overlapping views (i.e., the spatial overlap between the acoustic measurement path and the optical measurement window).

[0139] A spatial position vector, which can usually be represented as , used to determine the location of the measurement point;

[0140] It is a time variable.

[0141] The calibration relationship The establishment of the method can be obtained by acoustic measurement of a turbid mixture sample of known concentration before the main experiment, a process that is a routine experimental skill for those skilled in the art.

[0142] Establish a concentration correction function. In the cross-view tube... Within, there exists a concentration benchmark value with a one-to-one spatial location. and raw fluorescence intensity field data By performing statistical regression analysis on these two sets of data, a concentration correction function that can describe the mapping relationship between them is established. The concentration correction function essentially quantifies the optical fluorescence signal under high turbidity conditions. The attenuation effect caused by light absorption and scattering. In practical implementation, the concentration correction function... It can be in the form of a polynomial function, exponential function, or other nonlinear function, the specific form and coefficients of which are minimized within the cross-window. and The residuals between them are determined by a method.

[0143] Calculate the globally corrected concentration field. Use the concentration correction function established in the previous step. As a universal correction model, it is applied to the entire optical window. Raw fluorescence intensity field data within the range Thus, the globally corrected concentration field can be calculated. .

[0144] ;

[0145] In the formula;

[0146] This represents the concentration field after global correction.

[0147] This represents the raw fluorescence intensity data;

[0148] This represents the concentration correction function used to adjust the original fluorescence intensity data. Convert to concentration value;

[0149] Indicates the entire optical viewing window area;

[0150] A spatial position vector, typically a three-dimensional coordinate. , used to determine the measurement location;

[0151] It is a time variable.

[0152] The high concentration measurement accuracy of the UVP flowmeter 7 in a one-dimensional profile was extended to a two-dimensional high-resolution field of view covered by the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5, ultimately obtaining data... .

[0153] S5. Velocity field correction steps: Within the cross window, using the velocity data as the correction reference, establish a velocity correction function between the correction reference and the original velocity field data, and apply the velocity correction function to the optical window to obtain the globally corrected velocity field.

[0154] Specifically, in this embodiment, step S5 utilizes the reliability of the UVP flowmeter 7 in measuring flow velocity in highly turbid fluids to correct for measurement deviations that may occur in the particle image velocimetry device 4 under high particle concentrations.

[0155] Step S5 may include the following sub-steps;

[0156] Determine the calibration reference. This step is performed in the cross view. Internal execution. The flow rate data obtained in data preprocessing step S3, after quality control and burr removal, is processed. This serves as a high-precision calibration benchmark. The flow velocity data... It is a one-dimensional profile data along the acoustic path of the UVP flowmeter 7.

[0157] Establish the flow rate correction function. In the cross window... Within, there are two sets of flow velocity measurement data that correspond to spatial location and time synchronization: a calibration reference from the UVP flowmeter 7. and raw velocity field data from particle image velocimetry device 4 .

[0158] To establish the mapping relationship between the two, it is first necessary to convert the original two-dimensional velocity field data into a single data set. The velocity component that completely overlaps with the one-dimensional acoustic path of the UVP flowmeter 7 was extracted using spatial interpolation.

[0159] For the correction reference Original velocity field data at the corresponding interpolated location Statistical regression analysis was performed to establish a flow rate correction function describing the systematic deviation between the two. .

[0160] ;

[0161] In the formula;

[0162] Indicates spatial location and time The calibration reference flow rate is measured by UVP flow meter 7;

[0163] Indicates the same spatial location and time The original flow velocity field data obtained by particle image velocimetry device 4;

[0164] For flow rate correction function;

[0165] is a spatial position vector, representing the three-dimensional coordinate position in the flow field;

[0166] It is a time variable;

[0167] Indicates the cross-window area.

[0168] Calculate the globally corrected velocity field. Use the velocity correction function established in the cross-window in the previous step. Promote its application throughout the entire optical window Raw velocity field data within the region The globally corrected flow field was calculated. .

[0169] ;

[0170] In the formula;

[0171] This represents the velocity field after global correction, i.e., in spatial location. and time Above, via the flow rate correction function Corrected flow rate results;

[0172] This represents the original PIV velocity field data;

[0173] For flow rate correction function;

[0174] It is a spatial position vector, representing the coordinate position of any point in the flow field;

[0175] For time variables, the time points of measurement or calculation are used to describe the time evolution characteristics of the flow field;

[0176] The optical viewing window area encompasses the entire flow field being observed; it is a cross-viewing window. The extended region.

[0177] The PIV measurement bias characteristics caused by high turbidity within the cross-viewing window also apply to the entire optical window with similar flow patterns and concentration ranges. This extends the flow velocity measurement accuracy of the UVP velocimeter 7 in a one-dimensional profile to the two-dimensional high-resolution field of view covered by the particle image velocimeter 4, ultimately obtaining… It provides high-resolution and high-accuracy flow field data.

[0178] S6. Data application and analysis steps: Based on the globally corrected velocity field and the globally corrected concentration field, calculate the turbulence parameters of the turbidity flow, and distinguish and quantify the microplastic particles and the sediment particles.

[0179] Specifically, in this embodiment, step S6 is based on the globally corrected velocity field with high spatiotemporal resolution and high accuracy obtained in the preceding steps. and the globally corrected concentration field Then, the final physical parameters are extracted and the mechanism is analyzed.

[0180] ;

[0181] In the formula;

[0182] Indicates average speed over time;

[0183] This represents the instantaneous velocity field after global correction, i.e., at position and time At that point, through the flow rate correction function Corrected PIV measurement flow rate data;

[0184] Time scale;

[0185] It is a spatial position vector;

[0186] It is a time variable;

[0187] This is a time integration operator.

[0188] Pulsation velocity The result is obtained by subtracting the time-averaged velocity from the instantaneous velocity:

[0189] ;

[0190] In the formula, Indicates the pulsation velocity, that is, in spatial position. and time At a given location, the deviation of the instantaneous flow velocity from the time-averaged flow velocity. This represents the instantaneous flow velocity after global correction. Indicates the average speed over time. It is a spatial position vector. It is a time variable.

[0191] Based on the fluctuating velocity, a series of key turbulence parameters can be calculated. For example, the turbulent kinetic energy (TGI) can be calculated. );

[0192] ;

[0193] In the formula, Represents turbulent kinetic energy;

[0194] Indicates the pulsation velocity in the x-direction;

[0195] Represents the pulsation velocity in the z-direction;

[0196] It is a spatial position vector;

[0197] It is a time variable.

[0198] The microplastic particles and the sediment particles are distinguished and quantified by utilizing the signal difference between the first and second fluorescent labels introduced in S1, combined with the globally corrected concentration field obtained in S4. To achieve this.

[0199] Globally corrected concentration field This represents the total volume concentration of microplastic particles and sediment particles:

[0200] ;

[0201] In the formula, This indicates the concentration of microplastic particles. The concentration of microplastic particles. The concentration of sediment particles, This indicates the concentration of microplastic particles. This indicates the concentration of sediment particles.

[0202] Meanwhile, the raw fluorescence intensity field data obtained from data preprocessing step S3 In the process, the raw signal intensities corresponding to the first fluorescent label (microplastic) are extracted by spectral separation (e.g., using specific optical filters matched to the labeling dye). and the original signal intensity corresponding to the second fluorescent label (deposit). ,

[0203] Under ideal conditions where fluorescence attenuation is not considered, the ratio of their concentrations has a calibration relationship with the ratio of their original signal intensities. ;

[0204] ;

[0205] In the formula, This indicates the concentration of microplastic particles. Indicates the concentration of sediment particles. This indicates the intensity of the original fluorescence signal corresponding to the microplastic particles. This indicates the intensity of the original fluorescence signal corresponding to the sediment particles. The calibration coefficient is used to characterize the proportional relationship between fluorescence response intensity and concentration for different particulate components.

[0206] By analyzing the transport and deposition patterns of particles, and based on the obtained turbulent field and concentration-discriminating field, in-depth physical mechanism analysis can be conducted, and the transport flux of microplastic particles can be calculated. and transport flux of sediment particles Comparing the two under different turbulence intensities The differences in transport efficiency under different conditions reveal the unique transport characteristics of microplastic particles in turbidity streams.

Claims

1. A turbidity current transporting microplastics flume experimental apparatus, characterized in that, Include; Water tank device body for carrying out turbidity current transportation microplastic experiment; The water tank device body includes a water storage tank (1) and a slope tank (2), one side of the water storage tank (1) is provided with a slope tank, and the inner bottom of the slope tank away from the water storage tank (1) side is higher than the side close to the water storage tank (1); An optical measurement subsystem is fixed on the outer wall of the water storage tank (1) and the slope tank (2) through a fixing frame (3), which is used to obtain the original image sequence of the turbidity current mixed solution; The optical measurement subsystem includes; A particle image velocimetry device (4) is fixedly connected to the inside of the fixing frame (3), which is used to capture the movement of PIV tracer particles in the water body; A planar laser-induced fluorescence device (5) is fixedly connected to the inside of the fixing frame (3), which is used to capture the fluorescence signal emitted by the fluorescently labeled microplastics and sediments; A dual-wavelength laser (6) is fixedly connected to the outer wall of the water storage tank (1) and the slope tank (2), which is used to emit laser sheet light source; An image collector is electrically connected with the particle image velocimetry device (4) and the planar laser-induced fluorescence device (5), which is used to collect image information; The optical measurement subsystem is used to define an optical measurement window and obtain the original image sequence in the window; An ultrasonic Doppler flow velocity measurement system is installed on the inner bottom of the water storage tank (1) away from the slope tank (2) or on the side of the slope tank (2) close to the water storage tank (1), which includes a UVP flowmeter (7), and the UVP flowmeter (7) is used to define an ultrasonic emission path and obtain flow velocity data and acoustic backscatter intensity data on the path; An inflow control system is installed at one end of the slope tank (2) away from the water storage tank (1), which is used to transport turbidity current and microplastics; The inflow control system includes a storage tank (8), one end of the storage tank (8) is connected with a delivery pump (9) through a pipeline, the output end of the delivery pump (9) is fixedly connected with a delivery pipe (10), and the outer wall of the delivery pipe (10) is fixedly connected with the outer wall of the slope tank (2); The ultrasonic emission path and the optical measurement window overlap in space to form a cross window.

2. The experimental apparatus for turbidity current transporting microplastics in a flume according to claim 1, wherein, The length of the water storage tank (1) is 8m, the width is 3.0m, and the height is 1.0m, the length of the slope tank is 2.2m, and the height is 1.0m, and the water storage tank and the slope tank are both organic glass.

3. The experimental apparatus for turbidity current transporting microplastics in a flume according to claim 1, wherein, The planar laser-induced fluorescence device (5) and the particle image velocimetry device share part of the optical path, and the dual-wavelength laser (6) is a shared excitation light source of the particle image velocimetry device (4) and the planar laser-induced fluorescence device (5).

4. A method for turbidity current transporting microplastics in a flume experiment, applied to the turbidity current transporting microplastics in a flume experiment device according to any one of claims 1-3, characterized in that, The method includes the following steps: S1, experimental preparation step: first prepare turbidity current mud containing microplastic particles, first fluorescently label microplastic particles, second fluorescently label sediment particles, add PIV tracer particles in the turbidity current mixed solution, and let the turbidity current saturate the pipelines of the inflow control system; S2, data acquisition step: the turbid flow mixture is transported into the water tank device main body through the inflow control system, and the optical window and the ultrasonic wave transmission path forming the cross window are synchronously data-acquired by the composite visual measurement system, the composite visual measurement system comprising a UVP flowmeter (7), a particle image velocimetry device (4) and a planar laser-induced fluorescence device (5); so as to obtain the flow rate data, the acoustic backscatter intensity data and the original image sequence; S3, data preprocessing step: the flow rate data and the acoustic backscatter intensity data are subjected to quality control and burr point elimination, and the original image sequence is subjected to batch processing, so as to obtain the original flow rate field data and the original fluorescence intensity field data respectively; S4, concentration field correction step: in the cross window, the concentration reference value is inversed by using the acoustic backscatter intensity data, the concentration correction function between the concentration reference value and the original fluorescence intensity field data is established, and the concentration correction function is applied to the optical window, so as to obtain the globally corrected concentration field; S5, flow rate field correction step: in the cross window, the flow rate correction function between the correction reference and the original flow rate field data is established by using the flow rate data as the correction reference, and the flow rate correction function is applied to the optical window, so as to obtain the globally corrected flow rate field; S6, data application and analysis step: based on the globally corrected flow rate field and the globally corrected concentration field, the turbulent flow parameters of the turbid flow are calculated, and the microplastic particles and the sediment particles are distinguished and quantified.

5. The experimental method of turbidity current transporting microplastics in a flume according to claim 4, wherein, In the step S1 experimental preparation: The first fluorescent label uses rhodamine 6G; The second fluorescent label uses fluorescein sodium; The PIV tracer particle is a hollow glass microbead.

6. The experimental method of turbidity current transporting microplastics in a flume according to claim 4, wherein, In the step S2 data acquisition, the composite visual measurement system is time-synchronized by a hardware trigger, so that the original image sequence, the flow rate data and the acoustic backscatter intensity data have a unified time reference.

7. The experimental method of turbidity current transporting microplastics in a flume according to claim 4, wherein, The step S3 data preprocessing includes: The flow rate data and the acoustic backscatter intensity data are subjected to signal-to-noise ratio-based screening and burr point elimination.

8. The experimental method of turbidity current transporting microplastics in a flume according to claim 4, wherein, The step S5 flow rate field correction includes: In the cross window, the flow rate component coinciding with the ultrasonic wave transmission path is extracted from the original flow rate field data through spatial interpolation; The flow rate correction function is established by statistical regression analysis on the correction reference and the flow rate component.

9. The experimental method of turbidity current transporting microplastics in a flume according to claim 4, wherein, In the step S6 data application and analysis, the step of distinguishing and quantifying the microplastic particles and the sediment particles includes: The total volume concentration is obtained based on the globally corrected concentration field; The concentration ratio of the microplastic particles to the sediment particles is obtained based on the original fluorescence intensity field data and a preset calibration relationship; The concentration of the microplastic particles and the concentration of the sediment particles are solved based on the total volume concentration and the concentration ratio.

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