A method for measuring the velocity of bedload particles based on Doppler velocity profiler acoustic scattering correction

Abstract

This invention discloses a method for measuring bedload particle velocity based on Doppler current profiler acoustic scattering correction, comprising: selecting a measurement section of a river; sampling sediment from the riverbed surface in the uninundated floodplain; sieving the sampled sediment; calculating the median particle size of the bed sediment in the river section based on the sieving results; selecting a measurement area; using an ADCP and a matching unmanned surface vessel equipped with DGPS for constant-speed cruise current measurement to obtain current measurement data; calculating the riverbed velocity based on the vessel speed data; filtering the riverbed velocity data and calculating the characteristic values ​​of the filtered riverbed velocity data; calculating the bedload vertical projection area ratio and the bedload scattering correction coefficient based on the characteristic values ​​of the filtered riverbed velocity data; and calculating the bedload velocity based on the bedload vertical projection area ratio and the bedload scattering correction coefficient. This invention overcomes the current difficulty of directly measuring accurate bedload velocity using a Doppler current profiler.

Description

Technical Field

[0001] This invention relates to a method for measuring the velocity of bedload particles based on acoustic scattering correction using a Doppler current profiler, belonging to the fields of hydraulics and river dynamics. Background Technology

[0002] According to different states of motion, sediment in rivers can be divided into bed sediment, suspended sediment and bedload. Among them, bedload movement has always been a very important and extremely complex scientific problem in river dynamics. It is an important foundation for studying numerical simulation of water and sediment and prevention and control of sediment disasters. It is of great significance to the stability of river morphology, the safety of river-related structures, and river restoration. Theoretical research on bedload movement began at the end of the 19th century. Based on the shear stress of water flow, the French Du Boys pioneered the theory of bedload transport and established a formula for predicting the sediment transport rate. Subsequently, many scholars have carried out in-depth research on the laws of bedload movement, including law analysis based on experimental methods and theoretical research based on physical derivation. Among them, the most important are: (1) studying the laws of bedload movement through flume test methods. The most representative is the formula for bedload transport rate established by Meyer-Peter and Muller based on a large amount of flume test data and multi-factor dimensional analysis, with the shear stress of water flow as the index of water flow intensity; (2) (3) Through theoretical analysis, physical equations are used to study the conditions for sediment initiation. The most representative example is Einstein's use of the jump initiation model, which takes the instantaneous upward force as greater than the underwater gravity as the criterion. It assumes that the probability of sediment settling at different points on the bed surface is the same, and derives the bed sediment transport rate when the exchange between the moving sediment and the bed sediment reaches equilibrium. (4) The sediment movement process is analyzed with the help of computer algorithms. The most representative example is Ancey's study of the probability distribution of particle dwell time using image recognition algorithms. It was found that the bed sediment transport rate exhibits significant non-Gaussian fluctuations.

[0003] Bedload measurement technology has received attention from various countries since the beginning of the 20th century. The International Union of Hydrological Sciences held a conference on bedload measurement technology in Italy, and the International Symposium on River Sedimentation also had a dedicated topic on indoor and outdoor bedload measurement techniques. Bedload measurement methods can be divided into direct measurement methods and indirect measurement methods. Direct bedload measurement involves obtaining riverbed sediment samples through sampling. Typical samplers include the Helley-Smith sampler designed by the U.S. Geological Survey and the Y781 sampler designed by the Yangtze River Water Resources Commission. Indirect bedload measurement uses sensors placed in the riverbed to record the signals generated by the natural movement of bedload sediment. Typical sensors include Swiss vibrating plates, Japanese acoustic tubes, and hydrophones. By analyzing the acoustic or vibration signals generated by bedload sediment through physical principles, the relationship between bedload movement parameters and measurement signals can be established. However, the above-mentioned bedload measurement method has the following drawbacks: (1) The manual operation of the measurement equipment is difficult and the sampling efficiency is low; (2) The deployment and maintenance costs of the measurement equipment are high, and the measurement data needs to be checked in advance when used at different sites, which is difficult; (3) The measurement equipment is difficult to provide bedload motion data with high spatiotemporal resolution.

[0004] The bottom-tracking function of the Acoustic Doppler Current Profiler (ADCP) emits bottom-penetrating acoustic waves and measures the riverbed velocity based on the Doppler frequency shift of the acoustic signal reflected from the riverbed. This velocity has a strong correlation with bedload velocity and has been proven in recent years to have the potential for high spatiotemporal resolution bedload measurement, representing a cutting-edge direction in bedload measurement technology. However, because the acoustic waves reflected from the fixed bed surface introduce errors into the riverbed velocity measured by the Acoustic Doppler Current Profiler, it is impossible to directly use ADCP to measure the accurate bedload particle velocity. Currently, there is no accurate ADCP-based method for measuring bedload velocity, which severely restricts the development of ADCP bedload measurement technology. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a method for measuring the velocity of bedload particles based on Doppler velocity profiler acoustic scattering correction.

[0006] The technical solution provided by this invention to solve the above-mentioned technical problems is: a method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction, comprising the following steps:

[0007] Select a river section for measurement, sample the sediment on the riverbed surface in the floodplain of the uninundated area, and measure the sediment gradation to obtain the median particle size of the bed sand;

[0008] Select a measurement area, use ADCP and a matching unmanned boat equipped with DGPS to conduct constant speed cruise flow measurement, obtain flow measurement data, and extract boat speed data from the flow measurement data;

[0009] Calculate the riverbed movement speed based on the ship speed data;

[0010] Filter the riverbed velocity data and calculate the characteristic values ​​of the filtered riverbed velocity data;

[0011] Calculate the vertical projection area ratio of bedload and the bedload scattering correction coefficient based on the characteristic values ​​of the filtered riverbed velocity data.

[0012] The velocity of the bedload is calculated based on the ratio of the vertical projected area of ​​the bedload and the bedload scattering correction factor.

[0013] A further technical solution is that the water depth in the measurement area is greater than the minimum detection threshold of the bottom tracking function, which is 30cm.

[0014] A further technical solution is to disable the ADCP intelligent pulse function in the constant speed cruise flow measurement, use a 3MHz fixed frequency sound wave for measurement, and enable the integrated track function to simultaneously perform bottom tracking ship speed measurement and GPS ship speed measurement, with a measurement time of more than 3 minutes.

[0015] A further technical solution is that the ship speed data includes bottom-tracking ship speed and GPS ship speed.

[0016] A further technical solution is that the formula for calculating the riverbed movement velocity is:

[0017] v a =v DGPS -v BT

[0018] In the formula: v a v is the velocity of the riverbed movement, in m / s. DGPS The speed of the boat is determined by GPS, in m / s; v BT The bottom tracking speed is m / s;

[0019] A further technical solution is that the filtered riverbed movement velocity data includes:

[0020] Remove all negative riverbed velocity data;

[0021] Calculate the standard deviation of the remaining riverbed velocity data;

[0022] Remove riverbed movement velocity data that are more than three times the standard deviation;

[0023] Remove riverbed velocity data that are less than the ADCP bottom tracking measurement threshold of 0.001.

[0024] A further technical solution is that the feature values ​​include the average value, standard deviation, and percentage of noise data of the riverbed movement velocity data.

[0025] A further technical solution is that the formula for calculating the vertical projected area ratio of the transported mass is:

[0026]

[0027] In the formula: c p The vertical projected area ratio of the transported mass, %; The average value of the riverbed velocity data is in m / s; v astd P represents the standard deviation of the riverbed velocity data, in m / s; f The percentage of noise in the riverbed velocity data, expressed as %.

[0028] A further technical solution is that the formula for calculating the transport mass scattering correction coefficient is:

[0029]

[0030] In the formula: D is the correction factor for transport mass scattering; 50 The median particle size of the bed sand is in meters (m); v astd The standard deviation of the riverbed velocity data is given in m / s; v a This represents the average velocity data of the riverbed movement, in m / s.

[0031] A further technical solution is that the formula for calculating the velocity of the transported mass is:

[0032]

[0033] In the formula: v p The velocity of the bedload particles is expressed in m / s. v is the correction factor for transport mass scattering; a c is the average value of the riverbed velocity data, in m / s; p The vertical projected area ratio of the transported mass is %.

[0034] The present invention has the following beneficial effects:

[0035] 1. This invention can continuously measure the velocity of bedload movement over a long period of time, with high measurement efficiency and spatiotemporal resolution, realizing an effective and continuous measurement of bedload movement velocity in a convenient and simple way;

[0036] 2. This invention, when combined with an unmanned vessel, can achieve remote surveying of large water areas without disturbing the river's flow field, and can accurately measure the distribution of bedload velocity within the river channel.

[0037] 3. This invention is simple to operate, has low measurement and verification costs, and can achieve the measurement of the velocity of transported mass without requiring a large amount of manpower. Attached Figure Description

[0038] Figure 1 This is a flowchart of the method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction according to the present invention.

[0039] Figure 2 A comparison chart of the vertical projected area ratio of the bedload in a simulation experiment for measuring the velocity of the bedload;

[0040] Figure 3 A comparison chart of the velocity of bedload in a simulation experiment. Detailed Implementation

[0041] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0042] like Figure 1 As shown, the present invention provides a method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction, comprising the following steps:

[0043] Step 1: Select a suitable river section for measurement, ensuring it represents the riverbed characteristics. In the uninundated area of ​​the measurement section, i.e., the floodplain, select three sampling areas. These areas should be evenly distributed to ensure the representativeness of the measurement data. Use a standard bed sediment sampler (such as an HS-type differential pressure sampler) to sample the bed sediment in each sampling area. Each sampling area should be sampled at least three times to ensure sample reliability. Dry the collected bed sediment samples to remove moisture, then perform sieving analysis. Use sieves of different particle sizes to sieve the samples, calculate the gradation by weighing, and calculate the median particle size of the bed sediment in each sampling area based on the sieving results. Calculate the average value of the three areas as the median particle size D of the bed sediment in the measurement section. 50 ;

[0044] Step 2: Select an area with a water depth of not less than 30cm in the river section as the measurement range; then install ADCP on the unmanned vessel and connect it to the unmanned vessel via cable to ensure that the ADCP installation position is stable and not subject to external interference. Use the PCM communication module to wirelessly connect the ADCP to the computer. The PCM communication module is connected to the DGPS device through a dedicated GPS connection cable to ensure real-time positioning accuracy. Keep the unmanned vessel hovering at a constant speed within the measurement range to perform constant speed cruise flow measurement, ensuring that the unmanned vessel does not make any sharp turns or tilts during the measurement process to ensure the accuracy of the measurement data.

[0045] Turn on the ADCP device and use a 3MHz fixed frequency sound wave for measurement. Simultaneously measure the bottom tracking speed and GPS speed. Turn off the ADCP smart pulse function and turn on the integrated track function. Set the measurement time to 10 minutes to obtain sufficient data. Save the current measurement data as a ".rivr" file, ensuring that the data is complete and in the correct format.

[0046] Step 3: Open the ".rivr" file saved in Step 2 using the "River Survey" software. Ensure that the software version is compatible with the equipment and that the data can be read normally. Select the "Matlab File Output" option in the data processing toolbox to export the current measurement data. Select "Bottom Tracking Reference" for the vessel track reference to ensure the accuracy of the data. Export the measurement time, water depth, and bottom tracking vessel speed data as a custom ".mat" file and save it in the specified directory. Ensure that the data file naming is standardized for easy subsequent processing.

[0047] Step 4: Read the ".mat" file generated in Step 3, ensuring the data file is complete and undamaged. Open the "bottom track" array in the Matlab workspace, find the "BT Vel" field, and obtain the bottom tracking ship velocity components in different directions measured by ADCP;

[0048] Step 5: Read the “.mat” file generated in Step 3, open the “Boat Vel” field in the “summary” array in the workspace, and obtain the GPS boat speed components in different directions measured by ADCP.

[0049] Step 6: Calculate the riverbed movement speed based on the bottom tracking boat speed data extracted in Step 4 and the GPS boat speed data extracted in Step 5.

[0050] v a =v DGPS -v BT

[0051] In the formula: v a v is the velocity of the riverbed movement, in m / s. DGPSThe speed of the boat is determined by GPS, in m / s; v BT The bottom tracking speed is m / s;

[0052] Step 7: Filter the riverbed movement velocity obtained in Step 6 to remove unreasonable noise data;

[0053] Specifically, the steps include: 1) removing all negative riverbed velocity data; 2) calculating the standard deviation of the remaining riverbed velocity data; 3) removing riverbed velocity data that are more than three times the standard deviation; 4) removing riverbed velocity data that are less than the ADCP bottom tracking measurement threshold of 0.001 m / s.

[0054] Step 8: Calculate the average value, standard deviation, and percentage of noise data of the filtered riverbed motion velocity data obtained in Step 7, and use them as the feature values ​​of the riverbed motion velocity data.

[0055] Step 9: Calculate the vertical projected area ratio c of bedload using the characteristic values ​​of riverbed velocity data. p ;

[0056]

[0057] In the formula: c p The vertical projected area ratio of the transported mass, %; The average value of the riverbed velocity data is in m / s; v astd P represents the standard deviation of the riverbed velocity data, in m / s; f The percentage of noise in the riverbed velocity data, expressed as %.

[0058] Step 10: Use the median particle size D of the bed sand obtained in Steps 1 and 8. 50 Calculate the bedload scattering correction factor using the characteristic values ​​of riverbed motion velocity data

[0059]

[0060] In the formula: D is the correction factor for transport mass scattering; 50 The median particle size of the bed sand is in meters (m); v astd The standard deviation of the riverbed velocity data is given in m / s; v a The average value of the riverbed velocity data is in m / s;

[0061] Step 11: Calculate the velocity of the bedload particles using the ratio of the vertical projected area of ​​the bedload obtained in steps 9 and 10 and the bedload scattering correction coefficient.

[0062]

[0063] In the formula: v pThe velocity of the bedload particles is expressed in m / s. v is the correction factor for transport mass scattering; a c is the average value of the riverbed velocity data, in m / s; p The vertical projected area ratio of the transported mass is %.

[0064] Example

[0065] This invention uses steps 3-11 to calculate the vertical projected area ratio of the bedload, the bedload scattering correction coefficient, and the bedload particle velocity. The results are compared in the appendix. Figure 2 , 3 It can be seen that the vertical projection area ratio and velocity of the bedload calculated by this invention are basically consistent with the actual values. The scattered points are distributed near the 1:1 line, and the error of most data points is within one order of magnitude. Therefore, it shows that the bedload particle velocity measurement method based on Doppler current profiler acoustic scattering correction meets the actual needs and has high feasibility. It can provide a new approach for existing bedload measurement.

[0066] The above description is not intended to limit the present invention in any way. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction, characterized in that, Includes the following steps: Select a river section for measurement, sample the sediment on the riverbed surface in the floodplain of the uninundated area, and measure the sediment gradation to obtain the median particle size of the bed sand; Select a measurement area, use ADCP and a matching unmanned boat equipped with DGPS to conduct constant speed cruise flow measurement, obtain flow measurement data, and extract boat speed data from the flow measurement data; Calculate the riverbed movement speed based on the ship speed data; Filter the riverbed velocity data and calculate the characteristic values ​​of the filtered riverbed velocity data; The feature values ​​include the average value, standard deviation, and percentage of noise data for riverbed movement velocity. Calculate the vertical projection area ratio of bedload and the bedload scattering correction coefficient based on the characteristic values ​​of the filtered riverbed velocity data. The formula for calculating the vertical projected area ratio of the transported mass is: In the formula: c p The vertical projected area ratio of the transported mass is % The average value of the riverbed velocity data is in m / s; v astd The standard deviation of the riverbed velocity data is given in m / s. P f The percentage of noise in the riverbed velocity data, % The formula for calculating the transport mass scattering correction coefficient is as follows: In the formula: This is the correction factor for transport mass scattering; D 50 The median particle size of the bed sand is in meters. v astd The standard deviation of the riverbed velocity data is given in m / s. The average value of the riverbed velocity data is in m / s; The velocity of the transport mass is calculated based on the ratio of the vertical projected area of ​​the transport mass and the transport mass scattering correction factor. In the formula: v p The velocity of the bedload particles is expressed in m / s. This is the correction factor for transport mass scattering; The average value of the riverbed velocity data is in m / s; c p The ratio of the vertical projected area of ​​the transported mass is %.

2. The method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction as described in claim 1, characterized in that, The water depth in the measurement area is greater than the minimum detection threshold of the bottom tracking function, which is 30cm.

3. The method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction according to claim 2, characterized in that, In the constant-speed cruise flow measurement, the ADCP intelligent pulse function is turned off, a 3MHz fixed frequency sound wave is used for measurement, and the integrated track function is turned on. At the same time, bottom tracking ship speed measurement and GPS ship speed measurement are performed, and the measurement time is more than 3 minutes.

4. The method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction according to claim 1, characterized in that, The ship speed data includes bottom-tracking ship speed and GPS ship speed.

5. The method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction according to claim 4, characterized in that, The formula for calculating the riverbed movement velocity is: In the formula: v a The velocity of the riverbed is in m / s; v DGPS The speed of the boat is the GPS speed, in m / s; v BT The base tracking speed is in m / s.

6. The method for measuring the velocity of bedload particles based on Doppler current profiler acoustic scattering correction according to claim 1, characterized in that, The filtered riverbed movement velocity data includes: Remove all negative riverbed velocity data; Calculate the standard deviation of the remaining riverbed velocity data; Remove riverbed movement velocity data that are more than three times the standard deviation; Remove riverbed velocity data that are less than the ADCP bottom tracking measurement threshold of 0.001.

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