Method and system for calculating flow near river bottom of river channel by using acoustic time difference method

Abstract

The invention relates to a method and a system for calculating the near-river-bottom flow of a river channel by using an acoustic time difference method. The method comprises the steps of 1, determining riverway conversion bottom elevation; and 2, calculating the average flow velocity of each flow layer by using a formula, calculating the partial flow qi of each flow layer by using a flow velocity area method, and accumulating the partial flow qi of each flow layer to finally obtain the overflowing flow q of the flow measurement section. And calculating the total instantaneous flow q = q0 + q1 + q2 +... qi... + qT.

Description

Technical Field

[0001] The invention relates to a method and system for calculating flow near the riverbed of a river channel by using an acoustic time difference method, and belongs to the technical field of water conservancy metering. Background Art

[0002] The current standard followed by national river hydrological testing is the "River Flow Testing Specification" GB 50179-2015, among which the velocity meter method is recognized as the basic hydrological flow testing method. However, the velocity meter method has many disadvantages. For example, due to the working principle and structural design of the mechanical velocity meter, its measurement error is relatively large. Especially when the flow velocity changes rapidly or the water flow conditions are complex, the velocity meter may not be able to accurately capture the change in flow velocity, resulting in deviations in the measurement results. For example, when measuring flow in natural rivers, using the velocity meter method for flow measurement may indeed face the problem of complex operation. In addition, the velocity meter cannot complete online monitoring.

[0003] The existing technology of flow meter method for measuring flow is to select the point method to measure the vertical average flow velocity, which can be selected from 6 options: one point method, two point method, three point method, five point method, six point method, and eleven point method. However, this method may be subject to various restrictions in actual operation, and it is necessary to ensure that the selected points are representative in advance, resulting in large errors in the results.

[0004] The acoustic time-difference flow measurement technology has achieved good results in pipeline and channel flow measurement applications. However, there are still many difficulties in its application in natural river flow measurement. For example, the cross-section of natural river channels is complex. During the promotion and application process, it was found that the layout of acoustic channels for flow measurement in natural rivers is much more difficult than that of artificial channels. Calculating cross-sectional flow from the actual flow velocity measured in the acoustic channel is also much more complicated than pipeline and channel flow measurement.

[0005] At present, the commonly used river flow calculation models are mainly the velocity logarithmic formula and the velocity exponential formula. The velocity logarithmic formula is based on the mixing length theory, which is a turbulent gradient transport theory proposed by German fluid mechanic Prandtl in the 1930s. It is used to analyze the behavior of the turbulent exchange coefficient and establish its relationship with other turbulent parameters. Although the logarithmic velocity distribution has a relatively rigorous theoretical basis, simple structure, easy to use, and is more consistent with the actual velocity distribution in the river, it is recommended and used by most people. However, it has three insurmountable shortcomings: (1) In the deduction of the formula, it is assumed that the mixing length L is linearly related to the water depth, which is inconsistent with the experimental data; (2) The velocity at the bottom of the river is negative infinity, which is inconsistent with the actual situation.

[0006] The velocity exponential formula was a pure empirical formula in the early days, and was later explained by the incomplete similarity theory of Brandt et al., which proved that the exponential formula and the logarithmic formula are essentially the same, and also have the above-mentioned insurmountable shortcomings. The exponential formula only makes up for the shortcomings of the logarithmic formula on the river bottom. The fact that the velocity vertical distribution exponential formula and the logarithmic formula have the same limitations is determined by their theoretical basis. Summary of the invention

[0007] The technical problem to be solved by the present invention is generally to provide a calculation method and system using the acoustic time difference method, which is particularly suitable for flow calculation near the riverbed of a river, can solve the above-mentioned technical problems, and lay a solid foundation for the application of time difference flow measurement technology in natural rivers.

[0008] To solve the above problems, the technical solution adopted by the present invention is: A method for calculating flow near the riverbed of a river channel using an acoustic time difference method comprises the following steps: Step 1, determine the converted bottom elevation of the river channel; Step 2: Use the formula to calculate the average velocity of each flow layer, and use the velocity area method to calculate the partial flow q of each flow layer. i , sum up the partial flow q of each flow layer i Finally, the flow rate q of the measuring section is obtained.

[0009] Calculate the total instantaneous flow q = q0 + q1 + q2 +…q iT …+q T ; ; q i= partial flow rate of each flow layer; q T= flow in the surface flow layer; T represents the surface flow layer; A i , unit m 2 , is the cross-sectional area between the elevation of the ith channel and the elevation of the i-1th channel in the river section, called the flow layer area, i.e., the partial area; where, when i=1, A1 is the area between the elevation of the first channel and the elevation of the converted bottom of the river; A0 is the area below the converted bottom elevation of the river, i.e., the bottom area of ​​the river; V i , in units of m / s, is the average velocity of the flow layer between the elevation of the ith channel and the elevation of the i-1th channel, i.e., the partial area velocity; wherein, when i=1, V1 is the average velocity of the flow layer between the elevation of the first channel and the elevation of the converted bottom of the river channel; V0 is the average velocity of the water flow below the elevation of the converted bottom of the river channel; further, in step 2, perform the following steps; S2.1, set parameters; S2.2, get the average flow velocity of adjacent channel flow layers ; S2.3, obtain the average flow velocity of the bottom flow layer near the river ; S2.4, obtain the average flow velocity V0 of the bottom flow layer; In step S2.1, Z * , unit: m, converted bottom elevation of the river channel; Z0, unit: m, starting elevation of water depth; H0, unit: m, calculated water depth, the difference between the current water level and the starting elevation of the water depth; Z i , unit: m, the ith channel and channel elevation; Z1, Z2, Z3, and Z4 are, respectively, the near-river bottom channel, the section control channel, the medium-normal water channel, and the large flood channel; V m,i , in m / s, is the average velocity of the horizontal line measured in the ith ultrasonic channel; when i=0, V m,0 The average flow velocity of the horizontal line corresponding to the bottom elevation of the river channel; y, dimensionless, relative water depth, the water depth at the elevation above the water depth divided by the calculated water depth.

[0010] Further, in step S2.2, the average velocity of the flow layer between two adjacent channels is calculated by the horizontal velocity of the two channels, and the calculation formula is: ; In step S2.3, the near-river bottom flow layer is the first channel elevation Z1 of the near-river bottom channel and the channel converted bottom elevation Z * the water flow between; The calculation process of the average flow velocity V1 of the bottom flow layer near the river considers the following working conditions; S2.3A When the working state is in low water level state, Only the Z1 channel works, and the process of solving the average velocity of the near-water surface flow layer is as follows: S2.3.1A, Calculate the water surface velocity V 0.0 , assuming that the hydraulic slope is equal to the riverbed gradient of the station section, ; Among them, V m，1 is the measured value of channel Z1, ; Where, g=9.8, j=river gradient, H=H0; S2.3.2A, based on the water surface velocity V 0.0, calculate the horizontal velocity of the converted bottom elevation of the river channel ; ; S2.3.3A, calculate the average velocity of the bottom flow layer near the river ; Average flow velocity near the bottom layer of the river It is obtained by the following formula: ; S2.3B, when the working state is in the low water level state, there are two or more sound channels working, and the equipment is in the normal flow measurement state; the specific calculation steps are as follows; S2.3.1B, obtain the average flow velocity V2 of the flow layer between the first channel and the second channel; ; S2.3.2B, obtain the average velocity V of the flow layer between the two channels below the water surface i The integral formula of ; S2.3.3B, V is derived from the integral formula of S2.3.2B * The expression of / K is as follows: ; S2.3.4B, change V of S2.3.2B * / K is substituted into the following formula to obtain the horizontal velocity of the river channel converted bottom elevation ; ; S2.3.5B, Average flow velocity in the bottom layer near the river It is obtained by the following formula: ; S2.3.6B, calculate the flow rate of the flow section near the river bottom, ; In the formula, It is the flow area of ​​the cross section of the river bottom flow layer.

[0011] Further, S2.4, obtaining the average flow velocity V0 of the bottom flow layer; The bottom flow layer is the river channel converted bottom elevation Z * The water flow corresponding to the cross-sectional area A0 of the following river channel, the average flow velocity V0 of the bottom flow layer depends on the converted bottom elevation Z of the river channel * The horizontal velocity V m,0 and bottom section shape coefficient; The calculation steps of the average flow velocity V0 of the bottom flow layer are as follows; S2.4.1, Bottom Section Shape Factor Formula; If the cross-sectional area of ​​the river below the water depth elevation is calculated , then the bottom section shape coefficient formula is defined as: ; S2.4.2, calculate the average velocity V0 of the bottom flow layer; The average velocity of the bottom flow layer V0 is the converted bottom elevation Z of the river channel. * Horizontal velocity V m,0 The linear function of the bottom flow layer average velocity V0 is calculated as: ; In the formula, is the shape coefficient of the riverbed section, which is obtained from the riverbed boundary conditions; S2.4.3, calculation of cross-sectional flow at the bottom flow layer, .

[0012] Further, in step S2.4.3, the bottom section shape coefficient is obtained through data accumulation, which includes continuous accumulation of calculated data and measured data, and the calculation parameters under different water flow states are obtained, and the big data AI model is used for optimization. The AI ​​model adopts a deep learning model with a lifelong learning mechanism. The data accumulation steps are as follows; S2.4.3.1, collect riverbed data related to riverbed shape coefficients, including riverbed elevation data, cross-sectional measurement data, flow data, and flow velocity data; S2.4.3.2, clean the data, remove outliers, erroneous data and incomplete data according to the distribution of collected riverbed data; standardize or normalize the riverbed data; formula: ; The data is linearly mapped to the specified range by the formula, where X is the original data, X min and X max They are the minimum and maximum values ​​in the data set respectively; then the feature data that meets the requirements is extracted from the original data, and the feature data is used as the input of the AI ​​model; S2.4.3.3, use neural network model learning. Use training set data to train the AI ​​model and optimize the model's performance by adjusting the model's parameters and structure.

[0013] S2.4.3.4, deploy the trained AI model to actual application scenarios to predict new riverbed shape coefficients.

[0014] Furthermore, the premise is that the characteristics of the water flow at the bottom of the river channel are viscosity and friction, and the vertical flow velocity obeys a linear distribution.

[0015] Furthermore, the water flow in the section above the converted bottom elevation of the river channel follows a logarithmic distribution.

[0016] Furthermore, the river channel is a natural river channel.

[0017] A system for calculating flow near the riverbed in a river channel using an acoustic time difference method, the system comprising an ultrasonic transducer arranged in the river channel; Used to execute the above calculation method; along the vertical direction of flow velocity, the converted bottom elevation of the river channel is divided into a linear distribution area and a logarithmic distribution area.

[0018] This patent introduces the concept of river channel conversion bottom elevation. The bottom of the river channel section is a range, which is a narrow space close to the uneven river bottom. The characteristics of the water flow at the bottom of the river channel are mainly viscosity and friction, and the vertical flow velocity obeys a linear distribution; the water flow in the section above the river channel conversion bottom elevation obeys a logarithmic distribution. For the convenience of calculation, the river channel conversion bottom elevation is used to divide the vertical distribution of flow velocity into two areas, namely: a linear distribution area and a logarithmic distribution area. Among them, the linear distribution area close to the bottom of the river channel is calculated using a linear formula, and the logarithmic distribution area above the river channel conversion bottom elevation is calculated using a logarithmic formula. In this way, the limitation of the logarithmic formula to negative infinity when the water depth is zero is avoided, and the characteristics of the bottom water flow are better understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the layout elements of the sound channel of the river flow measurement section of the present invention.

[0020] Figure 2 It is a schematic diagram of river flow calculation of the present invention.

[0021] Figure 3 It is a schematic diagram of flow calculation of the near-water-surface portion of the present invention. DETAILED DESCRIPTION

[0022] like Figure 1-Figure 3 , the present application considers that the characteristics of the water flow at the bottom of the river channel are mainly viscosity and friction, and the vertical flow velocity follows a linear distribution; the water flow in the section above the converted bottom elevation of the river channel follows a logarithmic distribution. For the convenience of calculation, the present invention uses the converted bottom elevation of the river channel to divide the vertical distribution of the flow velocity into two zones, namely: a linear distribution zone and a logarithmic distribution zone.

[0023] Step 1: Determination of the bottom elevation of the river channel First, determine the converted bottom elevation of the river channel; Elevation refers to the distance from a point along the plumb line to the absolute base surface, which is called absolute elevation, or elevation for short. The distance from a point along the plumb line to a hypothetical leveling base surface is called hypothetical elevation.

[0024] The present invention determines the river channel conversion bottom elevation based on multiple determination methods such as empirical judgment, equipment installation conditions, standard water level, characteristic water level, etc., which has little impact on the flow measurement calculation results. In addition, the river channel conversion bottom elevation is not continuous and can be changed according to changes in conditions. The specific determination method is as follows: (1) Determined by experience; A characteristic point near the river bottom on the river section is artificially selected by hydrological survey personnel who have experience in flow measurement and are familiar with the conditions of the measuring station, and the elevation of the characteristic point is defined as the converted bottom elevation of the river.

[0025] (2) Determined according to the installation conditions of the flow measuring equipment; The river topography determines the installation conditions of the flow measuring equipment. The first channel should be installed as close to the river bottom as possible. The average river bottom elevation corresponding to the installation elevation of the first channel can be defined as the converted river bottom elevation.

[0026] (3) Determined by standard water level; In rivers where changes in river channel siltation are more serious, especially in the lower reaches of the Yellow River, a standard water level is often determined when analyzing changes in river channel scouring and siltation. The average river channel elevation corresponding to this standard water level can be defined as the converted bottom elevation of the river channel.

[0027] (4) Determined by a certain characteristic water level; It is determined by referring to a certain characteristic water level of a hydrological station, such as the historical lowest water level, the dry-off water level, etc. The average riverbed elevation corresponding to this characteristic water level can be defined as the converted bottom elevation of the river channel.

[0028] exist Figure 1 The symbols and their meanings are explained as follows: Z * , unit: m, converted bottom elevation of the river channel; Z0, unit: m, starting elevation of water depth; H0, unit: m, calculated water depth, the difference between the current water level and the starting elevation of the water depth; Z i , unit: m, the ith channel and its elevation.

[0029] Z1, Z2, Z3, and Z4 are, respectively, the near-river bottom channel, the section control channel, the medium-normal water channel, and the large flood channel; A i , unit m 2 , is the cross-sectional area between the elevation of the i-th channel and the i-1-th channel of the river section, called the flow layer area, also known as the partial area. Among them, when i=1, A1 is the area between the elevation of the first channel and the elevation of the converted bottom of the river; A0 is the area below the converted bottom elevation of the river, that is, the bottom area of ​​the river; V i , unit m / s, the average velocity of the flow layer between the elevation of the ith channel and the elevation of the i-1th channel, that is, the partial area velocity. Among them, when i=1, V1 is the average velocity of the flow layer between the elevation of the first channel and the elevation of the converted bottom of the river channel; V0 is the average velocity of the water flow below the converted bottom elevation of the river channel.

[0030] V m,i , in m / s, is the average velocity of the horizontal line measured in the ith ultrasonic channel. When i=0, V m,0 The average flow velocity of the horizontal line corresponding to the converted bottom elevation of the river channel.

[0031] y, dimensionless, relative water depth, the water depth at the elevation above the water depth divided by the calculated water depth, defined as relative water depth.

[0032] The flow measurement calculation uses the formula to calculate the average flow velocity of each flow layer, and the velocity area method is used to calculate the partial flow of each flow layer. The partial flow of each flow layer is accumulated to finally get the flow rate of the flow measurement section.

[0033] Calculate the total instantaneous flow q = q0 + q1 + q2 +…q iT …+q T ; ; q i= partial flow rate of each flow layer; q T= flow in the surface flow layer; T represents the surface flow layer; A i , unit m 2 , is the cross-sectional area between the elevation of the ith channel and the elevation of the i-1th channel in the river section, called the flow layer area, i.e., the partial area; where, when i=1, A1 is the area between the elevation of the first channel and the elevation of the converted bottom of the river; A0 is the area below the converted bottom elevation of the river, i.e., the bottom area of ​​the river; V i , unit is m / s, which is the average velocity of the flow layer between the elevation of the ith channel and the elevation of the i-1th channel, that is, the partial area velocity; where, when i=1, V1 is the average velocity of the flow layer between the elevation of the first channel and the elevation of the converted bottom of the river channel; V0 is the average velocity of the water flow below the converted bottom elevation of the river channel; the average velocity of the flow layer of adjacent channels is obtained, and the average velocity of the flow layer between two adjacent channels can be calculated by the horizontal velocity of the two channels, and the calculation formula is: ; Get the average flow velocity of the bottom flow layer near the river. The bottom flow layer near the river refers to the elevation Z1 of the bottom channel near the river (the first channel) and the bottom elevation Z of the river channel. * The calculation process of the average flow velocity V1 of the bottom flow layer near the river needs to consider the following two different working conditions; (1) When the water level is low; If only the Z1 channel is working, it can be considered that the river is in a low water state, and the solution process of the average flow velocity of the near-surface flow layer is as follows: The first step is to calculate the water surface velocity V 0.0 Assuming that the hydraulic slope is equal to the riverbed gradient of the measuring station section, the logarithmic formula of the vertical velocity distribution is used to obtain ; Among them, V m，1 is the measured value of channel Z1, ; Where, g=9.8, j=river gradient, H=H0; The second step is to use the water surface velocity V 0.0 , calculate the horizontal velocity of the converted bottom elevation of the river channel ; ; The third step is to calculate the average flow velocity of the bottom flow layer near the river. ; Average flow velocity near the bottom layer of the river It can be obtained by the following formula: ; (2) Normal flow measurement; If two or more channels are working and the device is in normal flow measurement state.

[0034] The specific calculation steps are as follows: The first step is to obtain the average flow velocity V between the first channel and the second channel. 2； ; The second step is to obtain the average velocity V of the flow layer between the two channels near the water surface. i The integral formula of ; The third step is to derive V from the above integral formula. * The expression of / K is as follows: ; The fourth step is to convert V * / K is substituted into the following formula to obtain the horizontal velocity of the converted bottom elevation of the river channel ; ; Step 5: Average flow velocity of the bottom layer near the river It can be obtained by the following formula: ; Step 6: Calculate the flow rate of the section near the riverbed. ; In the formula, It is the flow area of ​​the cross section of the river bottom flow layer.

[0035] Get the average flow velocity V0 of the bottom flow layer, The bottom flow layer refers to the river channel converted bottom elevation Z * The water flow corresponding to the cross-sectional area A0 of the following river channel, the average flow velocity V0 of the bottom flow layer depends on the converted bottom elevation Z of the river channel * The horizontal velocity V m,0 and bottom section shape coefficient.

[0036] The calculation process of the average flow velocity V0 of the bottom flow layer is as follows: Step 1: Bottom section shape coefficient formula; If the cross-sectional area of ​​the river below the water depth elevation is calculated The formula for defining the bottom section shape coefficient is: ; The second step is to calculate the average velocity V of the bottom flow layer. 0， The average velocity of the bottom flow layer V0 is the converted bottom elevation Z of the river channel. * Horizontal flow velocity V m,0 The linear function of the bottom flow layer average velocity V0 is calculated as: ; In the formula, is the shape coefficient of the riverbed section, which is obtained from the riverbed boundary conditions.

[0037] The third step is to calculate the flow rate of the bottom flow layer section. ; Since the average flow velocity of the bottom flow layer is the river channel converted bottom elevation Z * The horizontal velocity V m,0 The linear function of the bottom section shape coefficient is obtained through data accumulation. It also needs to continuously accumulate measured data to obtain the calculation parameters under different water flow states, and continuously optimize it using the big data AI model. The technology to be adopted is the deep learning model of the lifelong learning mechanism.

[0038] Step 1: Collect various data related to the riverbed shape coefficient, including riverbed elevation data, cross-sectional measurement data, flow data, flow velocity data, etc. Make sure the data covers different rivers, different river sections, and different water flow conditions so that the AI ​​model can learn a wide range of patterns.

[0039] Step 2: Clean the data, remove outliers, erroneous data, and incomplete data. Standardize or normalize the data; formula: ; Description: This formula linearly maps the data to a specified range (usually [0,1]), where X is the original data, X min and X max They are the minimum and maximum values ​​in the data set, respectively, so that the AI ​​model can better process data of different dimensions. Feature extraction may be required to extract meaningful features from the raw data, which will serve as the input of the AI ​​model.

[0040] Step 3: Use neural network model learning. Use training set data to train the AI ​​model and optimize the model's performance by adjusting the model's parameters and structure.

[0041] Step 4: Deploy the trained model to the actual application scenario to predict the new riverbed shape coefficient. Monitor the performance of the model and regularly update and optimize the model based on new measured data.

[0042] The steps for optimizing the training of the neural network model are as follows; First, the parameters are initialized, including weight u and bias parameter v, which can be initialized randomly; then, forward propagation is performed by inputting the training data into the neural network model and obtaining each layer of the output until the final prediction result value is obtained; secondly, loss calculation is performed, the prediction result of the neural network is compared with the actual data obtained, and the loss function is used to represent the gap between the calculated prediction result and the actual data obtained; thirdly, reverse propagation is performed, and the gradient of the loss function for each parameter is calculated through the back-propagation algorithm. The propagation process propagates the gradient from the output layer to the input layer, thereby adjusting the parameters of each layer; after that, , update the parameters, and use the optimized gradient descent algorithm to update the parameters in the neural network according to the calculated gradient information to reduce the loss function; then, repeat the iterations and repeat the steps from forward propagation to parameter update until the set stop condition is reached; the stop condition can be such as reaching the maximum number of iterations or the loss function convergence; the next step is to execute the evaluation model, and the validation set or test set can be used to evaluate the performance of the trained neural network model, so as to adjust the parameters or improve the model structure; then, execute the model application, and when the training model is completed and the performance meets the set requirements, the model can be used for prediction or classification tasks.

[0043] The present invention first selects a natural river channel, and arranges channels at different heights according to the different roles played by the arrangement positions of ultrasonic channels in flow measurement using the time difference method. The ultrasonic channels are used to monitor the horizontal average flow velocity at the elevation of the channels in the water-passing section, and the flow velocity at the bottom of the river channel is calculated according to the calculation steps in the above-mentioned key points of the invention.

[0044] The present invention is fully described for a clearer disclosure, and the prior art is not listed one by one.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents; it is obvious for those skilled in the art to combine multiple technical solutions of the present invention. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention. The technical contents not described in detail in the present invention are all known technologies.

Claims

1. A method for calculating flow near the riverbed using the acoustic time difference method, characterized in that: The steps include: Step 1, determine the converted bottom elevation of the river channel; Step 2: Use the formula to calculate the average velocity of each flow layer, and use the velocity area method to calculate the partial flow q of each flow layer. i , sum up the partial flow q of each flow layer i Finally, the flow rate q of the flow measurement section is obtained; Calculate the total instantaneous flow q = q0 + q1 + q2 +…q iT …+q T ; ； q i= partial flow rate of each flow layer; q T= flow in the surface flow layer; T represents the surface flow layer; A i , unit m 2 , is the cross-sectional area between the elevation of the ith channel and the elevation of the i-1th channel in the river section, called the flow layer area, i.e., the partial area; where, when i=1, A1 is the area between the elevation of the first channel and the elevation of the converted bottom of the river; A0 is the area below the converted bottom elevation of the river, i.e., the bottom area of ​​the river; V i , unit is m / s, which is the average flow velocity of the flow layer between the elevation of the ith channel and the elevation of the i-1th channel, that is, the partial area flow velocity; among them, when i=1, V1 is the average flow velocity of the flow layer between the elevation of the first channel and the converted bottom elevation of the river channel; V0 is the average flow velocity of the water flow below the converted bottom elevation of the river channel.

2. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 1, characterized in that: In step 2, perform the following steps: S2.1, set parameters; S2.2, get the average flow velocity of adjacent channel flow layers ; S2.3, obtain the average flow velocity of the bottom flow layer near the river ; S2.4, obtain the average flow velocity V0 of the bottom flow layer; In step S2.1, Z * , unit: m, converted bottom elevation of the river channel; Z0, unit: m, starting elevation of water depth; H0, unit: m, calculated water depth, the difference between the current water level and the starting elevation of the water depth; Z i , unit: m, the ith channel and channel elevation; Z1, Z2, Z3, and Z4 are, respectively, the near-river bottom channel, the section control channel, the medium-normal water channel, and the large flood channel; V m,i , in m / s, is the average velocity of the horizontal line measured in the ith ultrasonic channel; when i=0, V m,0 The average flow velocity of the horizontal line corresponding to the bottom elevation of the river channel; y, dimensionless, relative water depth, the water depth at the elevation above the water depth divided by the calculated water depth.

3. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 2 is characterized in that: In step S2.2, the average velocity of the flow layer between two adjacent channels is calculated by the horizontal velocity of the two channels, and the calculation formula is: ； In step S2.3, the near-river bottom flow layer is the first channel elevation Z1 of the near-river bottom channel and the channel converted bottom elevation Z * the water flow between; The calculation process of the average flow velocity V1 of the bottom flow layer near the river considers the following working conditions; S2.3A When the working state is in low water level state, Only the Z1 channel works, and the process of solving the average velocity of the near-water surface flow layer is as follows: S2.3.1A, Calculate the water surface velocity V 0.0 , assuming that the hydraulic slope is equal to the riverbed gradient of the station section, ； Among them, V m，1 is the measured value of channel Z1, ; Among them, g=9.8, j=river gradient, H=H0; S2.3.2A, based on the water surface velocity V 0.0 , calculate the horizontal velocity of the converted bottom elevation of the river channel ; ； S2.3.3A, calculate the average velocity of the bottom flow layer near the river ; Average flow velocity near the bottom layer of the river It is obtained by the following formula: ； S2.3B, when the working state is in the low water level state, there are two or more sound channels working, and the equipment is in the normal flow measurement state; the specific calculation steps are as follows; S2.3.1B, obtain the average flow velocity V2 of the flow layer between the first channel and the second channel; ； S2.3.2B, obtain the average velocity V of the flow layer between the two channels below the water surface i The integral formula of ； S2.3.3B, V is derived from the integral formula of S2.3.2B * The expression of / K is as follows: ； S2.3.4B, change V of S2.3.2B * / K is substituted into the following formula to obtain the horizontal velocity of the river channel converted bottom elevation ; ； S2.3.5B, Average flow velocity in the bottom layer near the river It is obtained by the following formula: ； S2.3.6B, calculate the flow rate of the flow section near the river bottom, ； In the formula, It is the flow area of ​​the cross section of the river bottom flow layer.

4. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 3 is characterized in that: S2.4, obtain the average flow velocity V0 of the bottom flow layer; The bottom flow layer is the river channel converted bottom elevation Z * The water flow corresponding to the cross-sectional area A0 of the following river channel, the average flow velocity V0 of the bottom flow layer depends on the converted bottom elevation Z of the river channel * The horizontal velocity V m,0 and the bottom section shape coefficient; The calculation steps of the average flow velocity V0 of the bottom flow layer are as follows; S2.4.1, Bottom Section Shape Factor Formula; If the cross-sectional area of ​​the river below the water depth elevation is calculated , then the bottom section shape coefficient formula is defined as: ； S2.4.2, calculate the average velocity V0 of the bottom flow layer; The average velocity of the bottom flow layer V0 is the converted bottom elevation Z of the river channel. * Horizontal velocity V m,0 The linear function of the bottom flow layer average velocity V0 is calculated as: ； In the formula, is the shape coefficient of the riverbed section, which is obtained from the riverbed boundary conditions; S2.4.3, calculation of cross-sectional flow at the bottom flow layer, 。 5. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 4, characterized in that: In step S2.4.3, the bottom cross-section shape coefficient is obtained through data accumulation, which includes the continuous accumulation of calculated data and measured data, and the calculation parameters under different water flow states are obtained. The big data AI model is used for optimization. The AI ​​model adopts a deep learning model with a lifelong learning mechanism. The data accumulation steps are as follows; S2.4.3.1, collect riverbed data related to riverbed shape coefficients, including riverbed elevation data, cross-sectional measurement data, flow data, and flow velocity data; S2.4.3.2, clean the data, remove outliers, erroneous data and incomplete data according to the distribution of collected riverbed data; standardize or normalize the riverbed data; official: ; The data is linearly mapped to the specified range by the formula, where X is the original data, X min and X max They are the minimum and maximum values ​​in the data set respectively; then the feature data that meets the requirements is extracted from the original data, and the feature data is used as the input of the AI ​​model; S2.4.3.3, adopt neural network model learning; use training set data to train AI model, and optimize model performance by adjusting model parameters and structure; S2.4.3.4, deploy the trained AI model to actual application scenarios to predict new riverbed shape coefficients.

6. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 1, characterized in that: The premise is that the characteristics of the water flow at the bottom of the river channel are viscosity and friction, and the vertical flow velocity obeys a linear distribution.

7. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 1, characterized in that: The water flow in the section above the converted bottom elevation of the river channel follows a logarithmic distribution.

8. The method for calculating flow near the riverbed using the acoustic time difference method according to claim 1 is characterized in that: The river channel is a natural river channel.

9. A system for calculating flow near the riverbed using the acoustic time difference method, characterized in that: The system includes an ultrasonic transducer arranged in a river channel; Used to execute the calculation method described in claim 1; along the vertical direction of flow velocity, the converted bottom elevation of the river channel is divided into a linear distribution area and a logarithmic distribution area.

Images