Water tank experiment device and method for transporting micro-plastics through turbidity current

Abstract

The invention relates to the technical field of fluid dynamics experimental measurement, and discloses a water tank experimental device and method for muddy current transportation of micro-plastics, the device comprises a water tank device main body, an optical measurement subsystem and an ultrasonic Doppler flow velocity measurement system, an ultrasonic emission path and an optical measurement window are overlapped in space, and the optical measurement subsystem and the ultrasonic Doppler flow velocity measurement system are arranged in the water tank device main body. The method comprises the following steps: performing first fluorescence labeling and second fluorescence labeling on the micro-plastic particles and the sediment particles; synchronously acquiring optical data and acoustic data in the cross window; respectively establishing a concentration correction function and a flow velocity correction function by taking acoustic backscattering intensity data and flow velocity data as references in the cross window; applying the correction function to the whole optical window to obtain a globally corrected concentration field and a globally corrected flow velocity field; and distinguishing and quantifying the micro-plastics and the sediments based on the corrected data. Through the cross correction principle, the problem of signal distortion of optical measurement in high-turbidity fluid is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fluid dynamics experimental measurement, in particular to a flume experimental device and method for turbidity current transporting microplastics. BACKGROUND

[0002] As a new type of pollutant, the migration and fate of microplastics in water environment such as rivers, lakes and oceans have become a research hotspot. Turbidity current (also known as muddy current or density current) is a density current carrying high concentration of sediments in water, which is the main driving process of sediment and related pollutants (including microplastics) transport under water. Therefore, it is crucial to simulate the physical process of turbidity current transporting microplastics in the laboratory flume, and accurately measure the concentration distribution of microplastics and sediment particles and the velocity field of fluid in this process, in order to reveal the transport mechanism of microplastics.

[0003] Currently, in fluid mechanics experiments, particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) are common optical measurement methods for obtaining high-resolution flow velocity field and concentration field. PIV obtains instantaneous flow field by tracking tracer particles, and PLIF uses the fluorescence intensity emitted by fluorescent dye-labeled particles under laser excitation to inverse the concentration field. However, turbidity current contains high concentration of background sediment particles, which poses a serious challenge to optical measurement. High concentration of particles will cause strong absorption and scattering of laser sheet, resulting in serious attenuation of optical signal during penetration, which reduces the signal-to-noise ratio of PIV image and even makes it impossible to identify particles. At the same time, the linear calibration relationship between the fluorescence intensity measured by PLIF and the actual concentration of particles is invalid, causing serious distortion of measurement data.

[0004] In order to measure in turbid fluid, researchers also use ultrasonic Doppler velocity measurement system (UVP). This technology uses acoustic Doppler effect to calculate flow velocity profile by emitting ultrasonic waves and receiving particle echo signals, and the acoustic backscattering intensity (ABS) can also be used to inverse the concentration under certain conditions. The main advantage of acoustic method is that it can penetrate high turbidity fluid and is not easily affected by optical transparency. However, its limitation is that UVP can usually only provide one-dimensional profile data along the acoustic path, and its spatial resolution is relatively low, making it difficult to capture the fine two-dimensional or three-dimensional flow field structure and concentration distribution characteristics in turbidity current. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a flume experimental device and method for turbidity current transporting microplastics, which solves the problem that the prior art cannot simultaneously obtain high-resolution and high-accuracy flow velocity field and concentration field in high-turbidity turbidity current.

[0006] To achieve the above object, the present application is implemented by the following technical solutions: a turbidity current microplastic transport water tank experimental device, comprising: a water tank device main body; for carrying out turbidity current microplastic experiment; The water tank device main body comprises a water storage tank and a slope tank, one side of the water storage tank is provided with a slope tank, and the inner bottom of the slope tank away from the water storage tank side is higher than the side close to the water storage tank; An optical measurement subsystem is fixed on the outer wall of the water storage tank and the slope tank through a fixing frame, and is used to obtain the original image sequence of the turbidity current mixed solution; The optical measurement subsystem comprises: A particle image velocimetry device is fixedly connected to the inner part of the fixing frame, and is used to capture the movement of PIV tracer particles in the water body; A planar laser-induced fluorescence device is fixedly connected to the inner part of the fixing frame, and is used to capture the fluorescence signal emitted by the fluorescently labeled microplastics and sediments; A dual-wavelength laser is fixedly connected to the outer wall of the water storage tank and the slope tank, and is used to emit laser sheet light source; An image collector is electrically connected with the particle image velocimetry device and the planar laser-induced fluorescence device, and 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 away from the slope tank or on the side of the slope tank close to the water storage tank, and comprises a UVP flowmeter, which is used to define an ultrasonic wave emission path and obtain flow velocity data and acoustic backscattering intensity data on the path; An inflow control system is installed at one end of the slope tank away from the water storage tank, and is used to transport turbidity current and microplastics; The inflow control system comprises a storage tank, one end of the storage tank is connected with a conveying pump through a pipeline, the output end of the conveying pump is fixedly connected with a conveying pipe, and the outer wall of the conveying pipe is fixedly connected with the outer wall of the slope tank.

[0007] Preferably, the length of the water storage tank 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 section and the slope section are both organic glass.

[0008] Further, to meet the scale requirements of physical simulation and provide good optical observation conditions.

[0009] Preferably, the planar laser induced fluorescence device shares part of the optical path with the particle image velocimetry device, and the dual-wavelength laser is a shared excitation light source of the particle image velocimetry device and the planar laser induced fluorescence device.

[0010] Preferably, the ultrasonic wave transmission path and the optical measurement window are spatially overlapped to form a cross window.

[0011] A turbidity current transporting microplastics in a flume experiment method, comprising the following steps: S1, experimental preparation step: first prepare turbidity current mud containing microplastic particles, first fluorescently label the microplastic particles, second fluorescently label the sediment particles, add PIV tracer particles to the turbidity current mixture, and saturate the inflow control system pipes with the turbidity current; S2, data acquisition step: transport the turbidity current mixture to the flume device main body through the inflow control system, and synchronously collect data of the optical window and the ultrasonic wave transmission path forming a cross window through the composite visual measurement system, the composite visual measurement system comprising a UVP flowmeter, a particle image velocimetry device and a planar laser induced fluorescence device; to obtain the flow velocity data, the acoustic backscatter intensity data and the original image sequence; S3, data preprocessing step: quality control and burr point rejection are performed on the flow velocity data and the acoustic backscatter intensity data, and batch processing is performed on the original image sequence to obtain the original flow velocity field data and the original fluorescence intensity field data, respectively; S4, concentration field correction step: in the cross window, the concentration reference value is inverted using the acoustic backscatter intensity data, a 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 to obtain the globally corrected concentration field; S5, flow velocity field correction step: in the cross window, a flow velocity correction function between the correction reference and the original flow velocity field data is established using the flow velocity data as the correction reference, and the flow velocity correction function is applied to the optical window to obtain the globally corrected flow velocity field; S6, data application and analysis step: based on the globally corrected flow velocity field and the globally corrected concentration field, the turbulent flow parameters of the turbidity current are calculated, and the microplastic particles and the sediment particles are distinguished and quantified.

[0012] Further, in the concentration field correction step: in the cross window , the preprocessed acoustic backscatter intensity data is used to invert the concentration reference value through a preset calibration relationship : ; wherein represents the volume concentration reference value within the region of overlap between the acoustic path and the optical measurement window; represents the acoustic backscatter intensity data obtained by an ultrasonic velocity profiler (UVP); represents the mapping function between intensity and concentration obtained through the calibration experiment; represents the cross- window region (i.e. the region of spatial overlap between the acoustic measurement path and the optical measurement window); is a spatial position vector, typically represented as , used to determine the position of the measurement point; is a time variable.

[0013] establishes the mapping relationship between the concentration reference value and the raw fluorescence intensity field data within the cross- window, resulting in a concentration correction function .

[0014] applies the concentration correction function to the raw fluorescence intensity field data within the entire optical window , resulting in a globally corrected concentration field ; ; wherein represents the globally corrected concentration field; represents the raw fluorescence intensity data; represents the concentration correction function used to convert the raw fluorescence intensity data into concentration values; represents the entire optical window region; is a spatial position vector, typically a three-dimensional coordinate used to determine the measurement position; is a time variable.

[0015] Preferably, in the step S1 experimental preparation: the first fluorescent marker uses Rhodamine 6G; the second fluorescent marker uses fluorescein sodium; The PIV tracer particles are hollow glass microspheres.

[0016] 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.

[0017] Preferably, step S3, data preprocessing, includes: The flow velocity data and the acoustic backscatter intensity data are filtered and burr points are removed based on the signal-to-noise ratio.

[0018] Preferably, step S5, flow field correction, includes: 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; A flow velocity correction function is established by performing statistical regression analysis on the calibration benchmark and the flow velocity component.

[0019] Furthermore, in the velocity field correction step; 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. ; ; In the formula; Indicates spatial location and time The calibration reference flow rate is measured by the UVP flow meter. Indicates the same spatial location and time The raw flow field data obtained by the particle image velocimetry device; For flow rate correction function; is a spatial position vector, representing the three-dimensional coordinate position in the flow field; It is a time variable; This indicates the area of ​​the cross viewport.

[0020] The flow rate correction function Applied to the entire optical window Raw velocity field data within , the global corrected flow velocity field is calculated ; ; wherein represents the global corrected flow velocity field, i.e. the flow velocity result corrected via the flow velocity correction function and time ; represents the original PIV flow velocity field data; is the flow velocity correction function; is the spatial position vector, representing the coordinate position of any point in the flow field; is the time variable, the measured or calculated time point, used to describe the time evolution characteristics of the flow field; is the optical window area, the entire flow field range observed, which is the extended area of the cross window .

[0021] Preferably, the step of distinguishing and quantifying the microplastic particles and the sediment particles in the step S6 data application analysis comprises: obtaining the total volume concentration based on the global corrected concentration field; obtaining the concentration ratio of the microplastic particles to the sediment particles based on the original fluorescence intensity field data and the preset calibration relationship; simultaneously considering the total volume concentration and the concentration ratio, and solving to obtain the concentration of the microplastic particles and the concentration of the sediment particles.

[0022] The present application provides a turbidity current transporting microplastic water tank experimental device and method. Has the following beneficial effects: 1、The present application sets up the cross window of the overlapping of the optical measurement window and the ultrasonic wave emission path, uses the flow velocity data and the acoustic backscattering intensity data obtained by the UVP flowmeter as the correction reference, establishes the correction function of the flow velocity and the concentration, the correction function can be applied to the whole optical window, to correct the measurement deviation of the particle image velocimetry device and the planar laser induced fluorescence device in the high turbidity fluid due to signal attenuation and distortion, combines the anti-interference of acoustic measurement and the high resolution characteristics of optical measurement, solves the technical problem that it is difficult to obtain high resolution and high accuracy flow field and concentration field at the same time under high turbidity condition.

[0023] ​2、The application extends to the entire two-dimensional high-resolution optical window covered by the particle image velocimetry device and the planar laser-induced fluorescence device through the established flow rate correction function and concentration correction function, so that the finally obtained data field has both the high spatial resolution of optical measurement and the accuracy of acoustic measurement in a highly turbid environment.

[0024] 3、The application can realize the differentiation and quantification of the two kinds of particles by respectively performing first fluorescence labeling and second fluorescence labeling on the microplastic particles and the sediment particles, and combining with subsequent data application analysis steps. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of the device of the application; Figure 2 It is a schematic diagram of the method flow of the application; Figure 3 It is a data preprocessing sub-step flowchart of the application.

[0026] 1, water storage tank; 2, inclined chute; 3, fixed frame; 4, particle image velocimetry device; 5, planar laser-induced fluorescence device; 6, dual-wavelength laser; 7, UVP flowmeter; 8, storage tank; 9, delivery pump; 10, delivery pipe. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the specification of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0028] Please refer to the drawings in the specification of the application Figure 1 The embodiment of the application provides a water tank experimental device for turbidity current transportation of microplastics, which comprises: The water tank device main body is used for carrying out turbidity current transportation of microplastics physical simulation experiment bearing structure. The water tank device main body comprises a water storage tank 1 and an inclined chute 2, and the inclined chute 2 is connected to one side of the water storage tank 1. The inclined chute 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 an inclined slope with a preset slope for initial acceleration of turbidity current.

[0029] To simulate a wide sedimentation area, the size of the water storage section can be designed as 8m long, 3.0m wide and 1.0m high. To simulate the acceleration process of turbidity current, the size of the slope section can be designed as 2.2m long and 1.0m high. To facilitate subsequent optical measurement, the water storage section and the slope section are preferably made of high-transparency materials, such as organic glass.

[0030] An inflow control system is installed at the end of the slope tank 2 away from the water storage tank 1 for transporting turbidity current and microplastics, which includes a storage tank 8, one end of which is connected with a delivery pump 9 through a pipeline, and the output end of the delivery pump 9 is fixedly connected with a delivery pipe 10, the outer wall of which is fixedly connected to the outer wall of the slope tank 2, for stably and continuously delivering the pre-configured turbidity current mixture containing microplastic particles and sediments to the top end of the slope tank 2 of the water tank device main body according to the flow rate and concentration set by the experimental working condition through the delivery pump 9 and the delivery pipe 10.

[0031] An optical measurement subsystem is fixed to the outer wall of the water storage tank 1 and the slope tank 2 through a fixed frame 3 for obtaining the original image sequence of the turbidity current mixture.

[0032] 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 collector. The particle image velocimetry device 4 is fixedly connected to the inside of the fixed frame 3, which is used to capture the movement of PIV tracer particles in the water body, and to calculate the fluid velocity field. The planar laser-induced fluorescence device 5 is fixedly connected to the inside of the fixed frame 3, which shares part of the optical path with the particle image velocimetry device 4, forms an intersection window, and is used to capture the fluorescence signals emitted by the fluorescently labeled microplastics and sediments to calculate their concentration distribution.

[0033] The dual-wavelength laser 6 serves as a shared excitation light source for the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5, and is fixedly connected to the outer wall of the water storage tank 1 and the slope tank 2 for emitting laser sheet light source to illuminate the measurement area inside the water tank.

[0034] The image collector is electrically connected to the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5, and is used to capture the light signals excited by the PIV tracer particles and the light signals excited by the PLIF fluorescent dye at high speed, and transmit the optical image information to the subsequent data processing unit.

[0035] The ultrasonic Doppler velocity measurement system includes UVP current meters 7 installed on the inner bottom of the reservoir tank 1 away from the slope tank 2 or installed on the side of the slope tank 2 close to the reservoir tank 1. These probes are used to emit ultrasonic beams along their acoustic paths and receive echo signals of particulate matter including sediment and microplastics to calculate the velocity profile and acoustic backscatter intensity of the particulate matter in the fluid.

[0036] The ultrasonic Doppler velocity measurement system is made to partially or completely overlap in space with one or more ultrasonic emission paths of the particle image velocimetry device 4 and the optical measurement window of the planar laser-induced fluorescence device 5, i.e., the area illuminated by the laser and captured by the image collector.

[0037] A turbidity current microplastics transportation water tank experimental method described below can be correspondingly referred to the turbidity current microplastics transportation water tank experimental device described above.

[0038] Please refer to the accompanying Figure 2 - the accompanying Figure 3 The present application also provides a turbidity current microplastics transportation water tank experimental method; comprising the following steps: S1, experimental preparation step: first prepare turbidity current slurry containing microplastic particles, first fluorescently label microplastic particles, second fluorescently label sediment particles, and add PIV tracer particles to the turbidity mixture, and saturate the turbidity inflow control system pipes; Specifically, the embodiment step S1 provides preset experimental conditions for subsequent synchronous measurement and data collection.

[0039] The microplastic particles to be tested are labeled in the first fluorescent dye solution, and rhodamine 6G dye is used to combine with the microplastic particles by adsorption or penetration. After labeling, the particles are washed to remove excess dye on the surface, and then dried for use.

[0040] The sediment particles (such as kaolin or silt) used in the experiment are labeled in the second fluorescent dye solution, for example, using fluorescein sodium for labeling.

[0041] Prepare the turbidity mixture. Mix the first fluorescently labeled microplastic particles, the second fluorescently labeled sediment particles, and (as needed) unlabeled background sediment with the water body in a stirring container according to the concentration gradient requirements of the experimental design to form a uniform turbidity mixture. In this mixture, further add PIV tracer particles. The physical properties of the PIV tracer particles, such as density, need to be close to the water body density to ensure that they can follow the fluid movement well, and at the same time, their surface has good light scattering properties. For example, neutral hollow glass microbeads can be selected as PIV tracer particles.

[0042] The prepared turbidity current mixture is pumped into the storage tank and all the delivery pipelines of the inflow control system until the liquid completely fills them. This operation aims to expel all the air in the pipeline system and establish a stable hydraulic gradient. The purpose is to provide a consistent and stable flow rate and concentration of the turbidity current mixture at the entrance of the top end of the chute 2 consistent with the set value when the inflow control system is officially started, so as to avoid interference with the data acquisition in the initial stage due to system start-up delay or unstable fluid state in the pipe.

[0043] S2, data acquisition step: deliver the turbidity current mixture to the tank device main body through the inflow control system, time synchronize the composite visualization measurement system through a hardware trigger, the composite visualization measurement system including the UVP flowmeter 7, the particle image velocimetry device and the planar laser induced fluorescence device 5; to obtain flow rate data, acoustic backscatter intensity data and raw image sequences; Specifically, the step S2 of the embodiment captures the instantaneous information of the particle movement and fluid dynamics in the turbidity current by synchronously operating the composite visualization measurement system.

[0044] Start the inflow control system to make the turbidity current mixture enter the tank device main body from the top end of the chute 2 at a stable flow rate and concentration set by the experiment. The turbidity current mixture accelerates along the chute 2 under the action of gravity and forms an evolving turbidity current in the water storage tank 1.

[0045] When the turbidity current develops stably in the tank device main body, time synchronize and start the acquisition of the composite visualization measurement system through an external hardware trigger. The hardware trigger sends a synchronous trigger signal to all core components of the composite visualization measurement system, including the UVP flowmeter 7, the particle image velocimetry device 4, the planar laser induced fluorescence device 5 and the dual-wavelength laser. This synchronous signal ensures that all subsequent data streams have a unified time reference, providing a prerequisite for data fusion and cross-correction.

[0046] The ultrasonic transducer of the UVP flowmeter 7 emits ultrasonic pulses along its acoustic path and receives echo signals generated by particles (including microplastic particles, sediment particles and PIV tracer particles) in the turbidity current mixture. By analyzing the Doppler shift of the echo signal, the flow rate profile along the acoustic path is calculated to obtain flow rate data . At the same time, the intensity of the echo signal is recorded to obtain acoustic backscatter intensity data .

[0047] At the same time, the dual-wavelength laser 6 emits laser sheet light of a preset wavelength to illuminate the measurement area located in the optical window.

[0048] The image acquirer of the particle image velocimetry device 4 selectively captures the laser signal scattered by the PIV tracer particles through the band-pass filter configured therewith, and at extremely short time intervals The image acquirer of the planar laser induced fluorescence device 5 captures the fluorescence signal emitted by the first and second fluorescent markers after being excited through the high-pass or band-pass filter configured therewith. All the images acquired by the two devices together constitute the raw image sequence.

[0049] S3, data preprocessing step: quality control and spike removal are performed on the flow velocity data and acoustic backscatter intensity data, and batch processing is performed on the raw image sequence to obtain raw flow velocity field data and raw fluorescence intensity field data, respectively; Specifically, the step S3 of the embodiment performs quality improvement and format conversion on the raw data to provide reliable input for subsequent cross-correction and physical analysis.

[0050] The step S3 can include the following sub-steps: The flow velocity data acquired by the UVP flowmeter 7 and the acoustic backscatter intensity data are subjected to quality control.

[0051] The data points are screened based on signal-to-noise ratio (SNR). A signal-to-noise ratio threshold is set, and data points below the threshold are considered invalid data and are removed.

[0052] Spike removal is performed on the screened data. Through a set physical threshold or statistical method (such as the three-sigma criterion or median filtering method), isolated data points that are physically unreasonable or have a sharp jump with neighboring points are identified and removed. The data gap left by the removed spike points can be filled with the surrounding valid data points through linear or high-order interpolation method in space or time to ensure the integrity of the data profile.

[0053] The raw image sequence acquired by the particle image velocimetry device 4 and the planar laser induced fluorescence device 5 is batch-processed to generate raw flow velocity field data and raw fluorescence intensity field data , respectively.

[0054] For the image sequence acquired by the particle image velocimetry device 4, a particle image velocimetry algorithm is used for processing. This process usually includes pre-enhancement operations such as denoising the image, and then dividing the image into multiple query windows. By performing cross-correlation calculation on the corresponding query windows in two consecutive images, the displacement vector of the PIV tracer particles within an extremely short time interval is obtained. The set of displacement vectors of all query windows constitutes the two-dimensional or three-dimensional raw flow velocity field data at that time .

[0055] For the image sequence acquired by the planar laser-induced fluorescence device 5, the processing procedure is mainly intensity extraction. After optional image denoising, the gray 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 this moment , where the value of each data point represents the fluorescence signal intensity of its corresponding spatial position.

[0056] S4, concentration field correction step: in the cross window, the concentration reference value is inverted using the acoustic backscatter intensity data, the concentration correction function between the concentration reference value and the raw fluorescence intensity field data is established, and the concentration correction function is applied to the optical window to obtain the globally corrected concentration field; Specifically, the step S4 of the embodiment is to correct the optical fluorescence signal distorted by high turbidity using acoustic measurement data, so as to obtain an accurate global concentration distribution.

[0057] The step S4 can include the following sub-steps: Invert the concentration reference value. This step is performed in the cross window (i.e. the region where the acoustic path of the UVP flowmeter 7 and the optical measurement window overlap in space). Using the pre-processed acoustic backscatter intensity data , a pre-established calibration relationship is used to invert the volume concentration reference value along the acoustic path; ; In the formula; represents the volume concentration reference value in the region where the acoustic path and the optical measurement window overlap; represents the acoustic backscatter intensity data obtained by the ultrasonic velocity profiler (UVP); represents the mapping function between intensity and concentration obtained by calibration experiment; represents the cross window region (i.e. the region where the acoustic measurement path and the optical measurement window overlap in space); is a spatial position vector, which can be generally represented as , used to determine the position of the measurement point; is a time variable.

[0058] The calibration relationship The establishment of the concentration correction function can be obtained by acoustic measurement of a sample of the turbid flow mixture of known concentration before the main experiment. This is within the routine experimental skills of a person skilled in the art.

[0059] The concentration correction function is established. In the cross-viewing window , there is a spatial position-to-corresponding concentration reference value and original fluorescence intensity field data . By statistical regression analysis of the two sets of data, a concentration correction function is established which can describe the mapping relationship between the two . The concentration correction function essentially quantifies the attenuation effect of the optical fluorescence signal caused by light absorption and scattering in a highly turbid environment. In a specific implementation, the concentration correction function may be a polynomial function, an exponential function or other non-linear function form, and its specific form and coefficients are determined by minimizing the residual error between and .

[0060] The global corrected concentration field is calculated. The concentration correction function established in the previous step is applied to the original fluorescence intensity field data in the entire optical viewing window range as a universal correction model, thereby calculating the global corrected concentration field .

[0061] ; wherein represents the global corrected concentration field; represents the original fluorescence intensity data; represents the concentration correction function for converting the original fluorescence intensity data into a concentration value; represents the entire optical viewing window area; is a spatial position vector, usually a three-dimensional coordinate , used to determine the measurement position; is a time variable.

[0062] The high concentration measurement accuracy of the UVP flowmeter 7 in one-dimensional profile is extended to the two-dimensional high-resolution field of view covered by the particle image velocimetry device 4 and the planar laser-induced fluorescence device 5, and the final data obtained.

[0063] S5, a flow velocity field correction step: in the intersection window, using the flow velocity data as a correction reference, establishing a flow velocity correction function between the correction reference and the original flow velocity field data, and applying the flow velocity correction function to the optical window to obtain a globally corrected flow velocity field; Specifically, the step S5 utilizes the reliability of the UVP flow meter 7 in measuring the flow velocity in the high-turbidity fluid to correct the measurement deviation that may be generated by the particle image velocimetry device 4 under high particle concentration.

[0064] The step S5 can include the following sub-steps: Determine the correction reference. This step is performed in the intersection window. The flow velocity data obtained in the data preprocessing step S3, which has passed the quality control and the burr point rejection, is used as a high-precision correction reference. The flow velocity data is one-dimensional profile data along the acoustic path of the UVP flow meter 7.

[0065] Establish the flow velocity correction function. In the intersection window , there are two sets of flow velocity measurement data corresponding to the spatial position and the time synchronization: the correction reference from the UVP flow meter 7 and the original flow velocity field data from the particle image velocimetry device 4 .

[0066] To establish the mapping relationship between the two, the two-dimensional original flow velocity field data is first extracted by spatial interpolation to obtain the flow velocity component completely coinciding with the one-dimensional acoustic path of the UVP flow meter 7.

[0067] Statistical regression analysis is performed on the correction reference and the original flow velocity field data at the corresponding position after interpolation, thereby establishing a flow velocity correction function describing the systematic deviation between the two.

[0068] ; In the formula, represents the correction reference flow velocity measured by the UVP flow meter 7 at the spatial position and the time ; represents the original flow velocity field data obtained by the particle image velocimetry device 4 at the same spatial position and the time ; is the flow velocity correction function; ​​ is a spatial position vector, representing the coordinate position of any point in the flow field; is a time variable; represents the cross- window region.

[0069] The globally corrected flow velocity field is calculated. The flow velocity correction function established in the cross- window region in the previous step is applied to the original flow velocity field data in the entire optical window region to calculate the globally corrected flow velocity field .

[0070] ; wherein, represents the globally corrected flow velocity field, i.e. the flow velocity result corrected via the flow velocity correction function in the spatial position and the time ; represents the original PIV flow velocity field data; is a flow velocity correction function; is a spatial position vector, representing the coordinate position of any point in the flow field; is a time variable, a time point measured or calculated, used to describe the time evolution characteristics of the flow field; is an optical window region, the entire flow field range observed, which is the extension region of the cross- window .

[0071] The PIV measurement deviation characteristics caused by high turbidity in the cross- window region are also applicable to the entire optical window with similar flow state and concentration range. The flow velocity measurement accuracy of the UVP flowmeter 7 in the one-dimensional profile is extended to the two-dimensional high-resolution field covered by the particle image velocimetry device 4, and the finally obtained is the high-resolution and high-accuracy flow velocity field data.

[0072] S6, data application analysis step: based on the globally corrected flow velocity field and the globally corrected concentration field, calculating the turbulent flow parameters of the turbidity current, and distinguishing and quantifying the micro-plastic particles and the sediment particles.

[0073] Specifically, the embodiment step S6 is based on the high-spatiotemporal resolution and high-accuracy globally corrected flow velocity field and the globally corrected concentration field obtained in the previous steps​ , the final physical parameter extraction and mechanism analysis are performed.

[0074] ; wherein denotes the time-averaged velocity; denotes the globally corrected instantaneous velocity field, i.e. the PIV measured velocity data corrected by the velocity correction function at position and time ; is the time scale; is the spatial position vector; is the time variable; is the time integration operator.

[0075] The fluctuating velocity is obtained by subtracting the time-averaged velocity from the instantaneous velocity: ; wherein denotes the fluctuating velocity, i.e. the deviation of the instantaneous velocity from the time-averaged velocity at spatial position and time , denotes the globally corrected instantaneous velocity, denotes the time-averaged velocity, is the spatial position vector, is the time variable.

[0076] Based on the fluctuating velocity, a series of key turbulent parameters can be calculated. For example, the turbulent kinetic energy is calculated; ; wherein denotes the turbulent kinetic energy; denotes the fluctuating velocity in x-direction; denotes the fluctuating velocity in z-direction; is the spatial position vector; is the time variable.

[0077] The differentiation and quantification of the microplastic particles and the sediment particles is performed using the signal difference of the first and second fluorescent labels introduced in S1 and in combination with the globally corrected concentration field To achieve this, the following steps are taken:

[0078] Global corrected concentration field represents the total volume concentration of microplastic particles and sediment particles: ; wherein, denotes the concentration of microplastic particles, is the concentration of microplastic particles, is the concentration of sediment particles, denotes the concentration of microplastic particles, denotes the concentration of sediment particles.

[0079] At the same time, the raw fluorescence intensity field data obtained from the data preprocessing step S3 Among them, the raw signal intensity corresponding to the first fluorescent label (microplastic) and the raw signal intensity corresponding to the second fluorescent label (sediment) are extracted by spectral separation (for example, using specific optical filters matched with the labeled dye) and , In the ideal case without considering fluorescence decay, the concentration ratio of the two has a calibrated relationship with the raw signal intensity ratio ; ; wherein, denotes the concentration of microplastic particles, denotes the concentration of sediment particles, denotes the raw fluorescence signal intensity corresponding to the microplastic particles, denotes the raw fluorescence signal intensity corresponding to the sediment particles, is a calibration coefficient, which is used to characterize the proportional relationship between the fluorescence response intensity and the concentration of different particle components.

[0080] The transport and deposition law of the particles is analyzed, based on the obtained turbulent flow field and the distinguished concentration field, in-depth physical mechanism analysis can be carried out, by calculating the transport flux of microplastic particles and the transport flux of sediment particles , the transport efficiency difference of the two under different turbulent intensity is compared, so as to reveal the unique migration characteristics of microplastic particles in turbidity current.

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, the inner bottom of the slope tank far away from the water storage tank (1) side is higher than the side close to the water storage tank (1); Optical measurement subsystem, which is fixed on the outer wall of the water storage tank (1) and the slope tank (2) through the fixing frame (3), is used to obtain the original image sequence of turbidity current mixed solution; The optical measurement subsystem includes; Particle image velocimetry device (4), the outer wall of the 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 water; Planar laser induced fluorescence device (5), the outer wall of the 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; Dual-wavelength laser (6), fixedly connected to the outer wall of the water storage tank (1) and the slope tank (2), is used to emit laser sheet light source; Image collector, which is electrically connected with the particle image velocimetry device (4) and the planar laser induced fluorescence device (5), 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; Ultrasonic Doppler flow velocity measurement system, installed on the inner bottom of the water storage tank (1) far away from the slope tank (2) or on the side of the slope tank (2) close to the water storage tank (1), includes UVP flowmeter (7), which is used to define an ultrasonic emission path and obtain flow velocity data and acoustic backscatter intensity data on the path; Inflow control system, installed at one end of the slope tank (2) far away from the water storage tank (1), 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 to the outer wall of the slope tank (2).

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, the water storage tank (1) and the slope tank (2) are both made of 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. The turbidity current transporting microplastics flume experimental device according to claim 1, wherein, The ultrasonic emission path and the optical measurement window overlap in space to form an intersection window.

5. 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 1-4, 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 turbidity current mixed solution, and let turbidity current saturate each pipeline 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.

6. The experimental method of turbidity current transporting microplastics in a flume according to claim 5, 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.

7. The experimental method of turbidity current transporting microplastics in a flume according to claim 5, 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.

8. The experimental method of turbidity current transporting microplastics in a flume according to claim 5, 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.

9. The experimental method of turbidity current transporting microplastics in a flume according to claim 5, 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.

10. The experimental method of transporting microplastics by turbidity current in a flume according to claim 5, 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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