Bed load particle movement velocity measurement method based on Doppler flow velocity profiler sound wave scattering correction

Abstract

The invention discloses a bed load particle movement velocity measurement method based on Doppler flow velocity profiler sound wave scattering correction. The method comprises the following steps: selecting a measurement river reach, sampling silt on the surface of a riverbed on a floodplain of an unsubmerged area, screening the sampled silt, and calculating the median particle size of the bed sand of the river reach according to the screening result; a measurement area is selected, an ADCP and a matched unmanned ship carrying DGPS are used for constant-speed cruise type flow measurement, and flow measurement data are obtained; calculating a riverbed movement speed according to the ship speed data; filtering the riverbed movement speed data, and calculating a characteristic value of the filtered riverbed movement speed data; respectively calculating a bed load vertical projection area ratio and a bed load scattering correction coefficient according to the filtered riverbed movement speed data characteristic value; and calculating the movement speed of the bed load according to the vertical projection area ratio of the bed load and the scattering correction coefficient of the bed load. According to the invention, the difficulty that the Doppler flow velocity profiler cannot be directly used to measure the accurate movement velocity of the bed load at present is overcome.

Description

Technical Field

[0001] The invention relates to a method for measuring the movement velocity of bed load particles based on Doppler flow profiler sound wave scattering correction, and belongs to the technical field of hydraulics and river dynamics. Background Art

[0002] Sediment in rivers can be divided into bed sediment, suspended sediment and bed load according to their different movement states. Among them, bed load movement has always been a very important and extremely complex scientific issue in river dynamics. It is an important basis for studying issues such as 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 buildings, and river restoration. Theoretical research on bed load movement began in the late 19th century. Based on the shear stress of water flow, Du boys in France pioneered the bed load transport theory and established a sediment transport rate prediction formula. Subsequently, many scholars conducted in-depth research on the laws of bed load movement, including law analysis based on experimental methods and theoretical research based on physical deduction. The most important ones are: (1) Studying the laws of bed load movement through flume test methods. The most representative one is the bed load transport rate formula using water flow shear stress as the water flow intensity index established by Meyer-Peter and Muller through multi-factor dimensional analysis based on a large amount of flume experimental data; (2 ) Through theoretical analysis, physical equations are used to study the conditions for sediment movement. The most representative one is Einstein, who used the jump start model and took the instantaneous lifting force greater than the underwater gravity as the judgment condition. Assuming that the probability of sediment settling at all locations on the bed is the same, the bedload transport rate is derived when the exchange between the moving sediment and the bed sediment reaches equilibrium. (3) Computer algorithms are used to assist in the analysis of the sediment movement process. The most representative one is Ancey, who used image recognition algorithms to study the probability distribution of particle stop time and found that the bedload transport rate exhibits significant non-Gaussian fluctuations.

[0003] Bed load measurement technology has been valued by various countries since the beginning of the 20th century. The International Association of Hydrological Sciences held a conference on bed load measurement technology in Italy, and the International Symposium on River Sediment also had a special topic to discuss indoor and outdoor bed load measurement technology. Bed load measurement methods can be divided into direct measurement methods and indirect measurement methods. Direct measurement of bed load is to obtain riverbed sediment samples through sampling. Typical samplers include the Helley-Smith sampler designed by the United States Geological Survey and the Y781 sampler designed by the Yangtze River Commission; indirect measurement of bed load uses sensors arranged in the riverbed to record the signals generated by the natural movement of bed load sediment. Typical sensors include Swiss vibration plates, Japanese sound tubes and hydrophones. The acoustic or vibration signals generated by bed load sediment are analyzed through physical principles to establish the relationship between bed load motion parameters and measurement signals. However, the above bed load measurement method has the following defects: (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 need to be calibrated in advance when used at different sites, which is difficult; (3) The measurement equipment is difficult to provide bed load movement data with high temporal and spatial resolution.

[0004] The bottom tracking function of the Acoustic Doppler Current Profiler (ADCP) can emit bottom sound waves and measure the velocity of the riverbed according to the Doppler frequency shift of the sound signal reflected by the riverbed. It has a strong correlation with the velocity of bedload and has been proven to have the potential for high temporal and spatial resolution bedload measurement in recent years. It is the frontier direction of bedload measurement technology. However, since the sound waves reflected by the fixed bed surface will cause errors in the riverbed velocity measured by the Acoustic Doppler Current Profiler, it is impossible to directly use ADCP to measure the accurate bedload particle velocity. At present, there is no accurate ADCP-based bedload velocity measurement method, which seriously restricts the development of ADCP bedload measurement technology. Summary of the invention

[0005] In order to overcome the defects in the prior art, the present invention aims to provide a method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction.

[0006] The present invention provides a technical solution to solve the above technical problems: a method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction, comprising the following steps:

[0007] Select a measuring river section, sample the sediment on the riverbed surface in the floodplain of the unflooded area, measure the sediment gradation, and 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 perform constant speed cruise flow measurement, obtain flow measurement data, and extract ship speed data from the flow measurement data;

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

[0010] Filtering the riverbed movement speed data, and calculating the characteristic value of the filtered riverbed movement speed data;

[0011] According to the characteristic values ​​of the bed movement velocity data after filtering, the vertical projection area ratio of bed load and the bed load scattering correction coefficient are calculated respectively;

[0012] The bed load velocity is calculated based on the bed load vertical projection area ratio and bed load scattering correction coefficient.

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

[0014] A further technical solution is to turn off the ADCP intelligent pulse function in the cruise-type current measurement, use 3MHz fixed frequency sound waves for measurement, and turn on the comprehensive track function, while performing bottom tracking ship speed measurement and GPS ship speed measurement, with the measurement time being 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 calculation formula for the riverbed movement speed is:

[0017] v a =v DGPS -v BT

[0018] Where: v a is the velocity of the riverbed, m / s; v DGPS is GPS ship speed, m / s; v BT is the bottom tracking ship speed, m / s;

[0019] A further technical solution is that the filtering of riverbed movement speed data includes:

[0020] Remove all negative riverbed velocity data;

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

[0022] The riverbed movement velocity data with a value higher than three times the standard deviation were removed;

[0023] The riverbed movement velocity data with a value less than the ADCP bottom tracking measurement threshold of 0.001 were removed.

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

[0025] A further technical solution is that the calculation formula of the vertical projection area ratio of the bed load is:

[0026]

[0027] Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %.

[0028] A further technical solution is that the calculation formula of the bed load scattering correction coefficient is:

[0029]

[0030] Where: is the bed load scattering correction factor; D 50 is the median particle size of bed sand, m; v astd is the standard deviation of riverbed velocity data, m / s; v a is the average value of riverbed movement velocity data, m / s.

[0031] A further technical solution is that the calculation formula for the bed load movement velocity is:

[0032]

[0033] Where: v p is the moving speed of bed load particles, m / s; is the bed load scattering correction factor; v a is the average value of riverbed movement velocity data, m / s; c p is the vertical projection area ratio of bed load, %.

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

[0035] 1. The present invention can continuously measure the movement velocity of bed load for a long time, has high measurement efficiency and time-space resolution, and realizes effective and continuous measurement of the movement velocity of bed load in a convenient and simple way;

[0036] 2. The present invention can be used with unmanned boats to realize remote inspections of large areas of water without interfering with the flow field of the river, and can accurately measure the distribution of the movement speed of bed load in the river;

[0037] 3. The present invention is easy to operate, has low measurement and calibration costs, and can measure the movement velocity of bed load without requiring a large amount of manpower. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of the method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction of the present invention;

[0039] Figure 2 This is a comparison chart of the vertical projection area ratio of bed load in the simulation test of bed load movement velocity measurement;

[0040] Figure 3 This is a comparison chart of the bed load movement velocity from a simulation test of bed load movement velocity measurement. DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] like Figure 1 As shown, a method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction of the present invention comprises the following steps:

[0043] Step 1. Select a suitable measuring river section to ensure that it has representative riverbed characteristics. In the unflooded area of ​​the measuring river section, i.e., on the floodplain, select three sampling areas. The selected sampling areas should be evenly distributed to ensure the representativeness of the measured data. Use a standard bed load sampler (such as an HS-type differential pressure sampler) to sample the bed sand in each sampling area. Repeat the sampling in each sampling area at least three times to ensure the reliability of the sample. Dry the collected bed sand samples, remove the moisture, and then sieve and analyze them. Use sieves of different particle sizes to sieve the samples, calculate the gradation by weighing, and calculate the median particle size of the bed sand 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 sand in the measuring river section. 50 ;

[0044] Step 2. Select an area with a water depth of not less than 30 cm in the measured river section as the measurement range; then install the ADCP on the unmanned boat and connect it to the unmanned boat through cables 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 GPS dedicated connection line to ensure real-time positioning accuracy. Keep the unmanned boat in a hovering and uniform speed state within the measurement range, and perform constant speed cruise flow measurement to ensure that the unmanned boat does not make sharp turns or tilts during the measurement process to ensure the accuracy of the measurement data;

[0045] Turn on the ADCP device, use 3MHz fixed frequency sound waves for measurement, measure the bottom tracking ship speed and GPS ship speed at the same time, turn off the ADCP intelligent pulse function, turn on the comprehensive track function, set the measurement time to 10 minutes to obtain enough data, save the current measurement data as a ".rivr" file, and ensure that the data is complete and in the correct format;

[0046] Step 3. Use the "River Survey" software to open the ".rivr" file saved in step 2, ensure that the software version matches the device and the data can be read normally, select the "Matlab file output" option in the data processing toolbox, export the current measurement data, and select "bottom tracking reference" as the ship track reference to ensure the accuracy of the data; export the measurement time, water depth, and bottom tracking ship speed data as a custom ".mat" file and save it in the specified directory, ensuring that the data file is named in a standardized manner for subsequent processing.

[0047] Step 4. Read the ".mat" file generated in step 3 to ensure that the data file is complete and undamaged. Open the "bottom track" array in the Matlab workspace, search for 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 ship speed components in different directions measured by ADCP;

[0049] Step 6, calculating the riverbed movement speed based on the bottom tracking ship speed data extracted in step 4 and the GPS ship speed data extracted in step 5;

[0050] v a =v DGPS -v BT

[0051] Where: v a is the velocity of the riverbed, m / s; v DGPSis GPS ship speed, m / s; v BT is the bottom tracking ship speed, m / s;

[0052] Step 7, filtering the riverbed movement speed calculated in step 6 to remove unreasonable noise data;

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

[0054] Step 8, calculating the average value, standard deviation, and noise data percentage of the filtered riverbed movement speed data obtained in step 7, and using them as characteristic values ​​of the riverbed movement speed data;

[0055] Step 9: Use the characteristic value of the riverbed velocity data to calculate the vertical projection area ratio c of the bedload p ;

[0056]

[0057] Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %;

[0058] Step 10: Use the median particle size D of the bed sand obtained in steps 1 and 8 50 Calculation of bed load scattering correction coefficients using characteristic values ​​of riverbed velocity data

[0059]

[0060] Where: is the bed load scattering correction factor; D 50 is the median particle size of bed sand, m; v astd is the standard deviation of riverbed velocity data, m / s; v a is the average value of riverbed movement velocity data, m / s;

[0061] Step 11, using the bed load vertical projection area ratio obtained in steps 9 and 10 and the bed load scattering correction coefficient to calculate the bed load particle movement velocity;

[0062]

[0063] Where: v pis the moving speed of bed load particles, m / s; is the bed load scattering correction factor; v a is the average value of riverbed movement velocity data, m / s; c p is the vertical projection area ratio of bed load, %.

[0064] Example

[0065] The present invention uses steps 3 to 11 to calculate the vertical projection area ratio of the bed load, the bed load scattering correction coefficient and the bed load particle movement speed. The results are compared in the attached figure. Figure 2 , 3 It can be seen that the vertical projection area ratio of the bed load and the bed load movement velocity calculated by the present invention are basically consistent with the actual values, the scatter points are distributed near the 1:1 line, and the errors of most data points are also within one order of magnitude. Therefore, it is explained that the bed load particle movement velocity measurement method based on the Doppler flow profiler acoustic wave scattering correction meets the actual needs, has high feasibility, and can provide a new idea for the existing bed load measurement.

[0066] The above description is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, 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 technical solution of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction, characterized in that: The following steps are involved: Select a measuring river section, sample the sediment on the riverbed surface in the floodplain of the unflooded area, measure the sediment gradation, and obtain the median particle size of the bed sand; Select a measurement area, use ADCP and a matching unmanned boat equipped with DGPS to perform constant speed cruise flow measurement, obtain flow measurement data, and extract ship speed data from the flow measurement data; Calculate the riverbed movement speed based on the ship speed data; Filtering the riverbed movement speed data, and calculating the characteristic value of the filtered riverbed movement speed data; According to the characteristic values ​​of the bed movement velocity data after filtering, the vertical projection area ratio of bed load and the bed load scattering correction coefficient are calculated respectively; The bed load velocity is calculated based on the bed load vertical projection area ratio and bed load scattering correction coefficient.

2. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 1 is characterized in that: The water depth in the measurement area is greater than the minimum detection threshold of the bottom tracking function of 30 cm.

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

4. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 1 is characterized in that: The ship speed data includes bottom tracking ship speed and GPS ship speed.

5. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 4 is characterized in that: The calculation formula of the riverbed movement speed is: v a =v DGPS -v BT Where: v a is the velocity of the riverbed, m / s; v DGPS is GPS ship speed, m / s; v BT is the bottom tracking ship speed, m / s.

6. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 1, characterized in that: The filtered riverbed movement speed data includes: Remove all negative riverbed velocity data; Calculate the standard deviation of the remaining riverbed movement velocity data; The riverbed movement velocity data with a value higher than three times the standard deviation were removed; The riverbed movement velocity data with a value less than the ADCP bottom tracking measurement threshold of 0.001 were removed.

7. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 1, characterized in that: The characteristic values ​​include the mean value, standard deviation and noise data percentage of the riverbed movement speed data.

8. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 7, characterized in that: The calculation formula of the vertical projection area ratio of the bed load is: Where: c p is the vertical projection area ratio of bed load, %; is the average value of riverbed movement velocity data, m / s; v astd is the standard deviation of riverbed velocity data, m / s; P f is the noise data percentage of riverbed movement velocity data, %.

9. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 7, characterized in that: The calculation formula of the bed load scattering correction coefficient is: Where: is the bed load scattering correction factor; D 50 is the median particle size of bed sand, m; v astd is the standard deviation of riverbed movement velocity data, m / s; is the average value of riverbed movement velocity data, m / s.

10. The method for measuring the movement velocity of bed load particles based on Doppler flow profiler acoustic wave scattering correction according to claim 1, characterized in that: The calculation formula for the bed load velocity is: Where: v p is the moving speed of bed load particles, m / s; is the bed load scattering correction factor; is the average value of riverbed movement velocity data, m / s; c p is the vertical projection area ratio of bed load, %.

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