Method and system for calculating flow rate near the river bottom in a river channel using the acoustic time difference method

Abstract

The present invention relates to a method and system for calculating the flow rate near the river bottom in a river channel by using the acoustic time difference method, which includes the following steps: Step 1, determining the converted bottom elevation of the river channel; Step 2, calculating the average velocity of each flow layer by using a formula, and calculating the partial flow rate q of each flow layer by using the velocity-area method i , and accumulating the partial flow rate q of each flow layer i Finally, the flow rate q passing through the measuring section is obtained. Calculate the total instantaneous flow rate q = q0 + q1 + q2 + … q i … + q T .

Description

Technical Field

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

[0002] The current national standard for river channel hydrological measurement is the "Code for Measurement of River Discharge" GB 50179-2015. Among them, the current meter method is recognized as the basic hydrological discharge measurement method. However, the current meter method has many disadvantages. For example, due to the working principle and structural design of the mechanical current meter, its measurement error is relatively large. Especially in the case of rapid flow velocity changes or complex water flow conditions, the current meter may not be able to accurately capture the changes in flow velocity, resulting in measurement result deviations. Another example is that when measuring the flow velocity in a natural river channel using the current meter method, it may indeed face the problem of complex operation. Additionally, the current meter cannot complete online monitoring.

[0003] For the current meter method for measuring flow in the prior art, when measuring the average velocity of a vertical line, there are 6 options in total, namely the one-point method, two-point method, three-point method, five-point method, six-point method, and eleven-point method. However, this method may be restricted in actual operation and requires ensuring in advance that the selected points are representative, resulting in relatively large errors in the results.

[0004] The acoustic time difference method for flow measurement has achieved good results in the application of pipeline flow measurement and channel flow measurement. However, there are still many difficulties in the application of natural river channel flow measurement. For example, the cross-section of a natural river channel is complex. During the popularization and application process, it is found that the layout of the flow measurement sound channel in a natural river channel is much more difficult than that in an artificial channel. Calculating the cross-section flow rate from the actually measured flow velocity of the sound channel is also much more complex than pipeline flow measurement and channel flow measurement.

[0005] Currently, the commonly used river channel flow calculation models are mainly the velocity logarithmic formula and the velocity exponential formula. The velocity logarithmic formula is established on the basis of the mixing length theory, which is a turbulent gradient transport theory proposed by the German fluid dynamicist Prandtl in the 1930s of the last century, used to analyze the behavior of the turbulent exchange coefficient and establish its relationship with other turbulent parameters. The logarithmic form of the velocity distribution, although having a relatively rigorous theoretical basis, is simple in structure, convenient to use, and relatively consistent with the actual velocity distribution in the river, and is recommended and used by most people. However, it has three insurmountable disadvantages: (1) In the formula derivation, it is assumed that the mixing length L is linearly related to the water depth, which does not conform to the experimental data; (2) The flow velocity at the river bottom in the formula is negative infinity, which does not conform to the actual situation.

[0006] The velocity index formula was initially a purely empirical formula and was later theoretically explained by the incomplete similarity theory of Brandt et al. This proved that the exponential formula and the logarithmic formula are essentially the same and also have the above-mentioned insurmountable drawbacks. The exponential formula only compensates for the deficiencies of the logarithmic formula at 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] Generally speaking, the technical problem to be solved by the present invention is to provide a method and system for calculating flow using the acoustic time difference method, which is particularly suitable for calculating the flow near the river bottom of a river channel, can solve the above technical problems, and lay a solid foundation for the application of the time difference method for flow measurement in natural river channels.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] A method for calculating the flow near the river bottom of a river channel using the acoustic time difference method, comprising the following steps;

[0010] Step 1, determine the converted bottom elevation of the river channel;

[0011] Step 2, calculate the average velocity of each flow layer using the formula, and calculate the partial flow rate q of each flow layer using the velocity-area method i , and accumulate the partial flow rates q of each flow layer i Finally, obtain the flow rate q passing through the flow measurement section.

[0012] Calculate the total instantaneous flow rate q = q0 + q1 + q2 +…q iT …+ q T ;

[0013] ;

[0014] q i= The partial flow rate of each flow layer;

[0015] q T= The flow rate of the surface flow layer;

[0016] T represents the surface flow layer;

[0017] A i , in units of m 2 , is the cross-sectional area between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound channel of the river channel cross-section, called the flow layer area, that is, the partial area; among them, when i = 1, A1 is the area between the elevation of the first sound channel and the converted bottom elevation of the river channel; A0 is the area below the converted bottom elevation of the river channel, that is, the river bottom area;

[0018] V i, in m / s, is the average velocity of the flow layer between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound channel, i.e., the partial area velocity; where when i = 1, V1 is the average velocity of the flow layer between the elevation of the first sound channel and the converted bottom elevation of the river channel; V0 is the average velocity of the water flow below the converted bottom elevation of the river channel; further, in step two, the following steps are executed;

[0019] S2.1, Set parameters;

[0020] S2.2, Obtain the average velocity of the flow layer between adjacent sound channels ;

[0021] S2.3, Obtain the average velocity of the flow layer near the river bottom ;

[0022] S2.4, Obtain the average velocity V0 of the bottom flow layer;

[0023] In step S2.1,

[0024] Z * , in m, is the converted bottom elevation of the river channel;

[0025] Z0, in m, is the starting elevation of water depth;

[0026] H0, in m, is the calculated water depth, the difference between the current water level and the starting elevation of water depth;

[0027] Z i , in m, is the i-th sound channel and its elevation;

[0028] Z1, Z2, Z3, Z4 are, in sequence, the sound channel near the river bottom, the cross-section control sound channel, and the medium-flow sound channel, the large-flood sound channel;

[0029] V m,i , in m / s, is the measured horizontal average velocity of the i-th ultrasonic sound channel; where when i = 0, V m,0 is the horizontal average velocity corresponding to the converted bottom elevation of the river channel;

[0030] y, dimensionless, is the relative water depth, the water depth measured from the starting elevation of water depth divided by the calculated water depth.

[0031] Further, in step S2.2, the average velocity of the flow layer between two adjacent sound channels is obtained from the horizontal velocities of the two sound channels, and the calculation formula:

[0032] ;

[0033] In step S2.3, the flow layer near the river bottom is the water flow between the first channel elevation Z1 of the sound channel near the river bottom and the converted bottom elevation Z of the river channel * ;

[0034] The calculation process of the average velocity V1 of the near-bottom flow layer considers the following working conditions;

[0035] S2.3A When the working condition is in the low water level state,

[0036] Only the Z1 channel works, and the solution process of the average velocity of the near-surface flow layer is as follows:

[0037] S2.3.1A, calculate the water surface velocity V 0.0 , assuming that the hydraulic gradient is equal to the river bottom slope of the gauging station section,

[0038] ;

[0039] where V m，1 is the measured value of channel Z1, ; where g = 9.8, j = river slope, H = H0;

[0040] S2.3.2A, from the water surface velocity V 0.0 , calculate the horizontal velocity of the converted bottom elevation of the river channel ;

[0041] ;

[0042] S2.3.3A, calculate the average velocity of the near-bottom flow layer ;

[0043] The average velocity of the near-bottom flow layer is obtained from the following formula:

[0044] ;

[0045] S2.3B, when the working condition is in the low water level state, two or more channels work, and the equipment is in the normal flow measurement state; the specific calculation steps are as follows;

[0046] S2.3.1B, obtain the average velocity V2 of the flow layer between the first channel and the second channel;

[0047] ;

[0048] S2.3.2B, obtain the integral formula of the average velocity V i of the flow layer between the two channels below the near water surface;

[0049] ;

[0050] S2.3.3B, the expression of V * / K derived from the integral formula in S2.3.2B is as follows:

[0051] ;

[0052] S2.3.4B, Substitute the V * / K in the following formula to obtain the cross-sectional velocity of the converted bottom elevation of the river channel ;

[0053] ;

[0054] S2.3.5B, Average velocity of the near-bottom flow layer Obtained from the following formula:

[0055] ;

[0056] S2.3.6B, Calculate the flow rate of the near-bottom flow cross-section,

[0057] ;

[0058] In the formula, is the cross-sectional flow area of the near-bottom flow layer.

[0059] Furthermore, S2.4, Obtain the average velocity V0 of the bottom flow layer;

[0060] The bottom flow layer is the water flow corresponding to the cross-sectional area A0 of the river channel below the converted bottom elevation Z * of the river channel. The average velocity V0 of the bottom flow layer depends on the cross-sectional velocity V * of the converted bottom elevation Z m,0 and the bottom cross-sectional shape coefficient;

[0061] The calculation steps of the average velocity V0 of the bottom flow layer are as follows;

[0062] S2.4.1, Bottom cross-sectional shape coefficient formula;

[0063] If the cross-sectional area of the river channel below the starting water depth elevation , then the bottom cross-sectional shape coefficient formula is defined as:

[0064] ;

[0065] S2.4.2, Calculate the average velocity V0 of the bottom flow layer;

[0066] The average velocity V0 of the bottom flow layer is a linear function of the cross-sectional velocity V * of the converted bottom elevation Z m,0 of the river channel. Then the calculation formula for the average velocity V0 of the bottom flow layer is:

[0067] ;

[0068] In the formula, is the shape coefficient of the river bottom section, which is obtained from the river bottom boundary conditions;

[0069] S2.4.3, Calculation of the cross-sectional flow rate of the bottom flow layer,

[0070] .

[0071] Furthermore, in step S2.4.3, the bottom section shape coefficient is obtained through data accumulation. The data accumulation includes continuous accumulation of calculation data and measured data, obtaining calculation parameters under different water flow regimes, and optimizing using a big data AI model. The AI model adopts a deep learning model with a lifelong learning mechanism. The data accumulation steps are as follows;

[0072] S2.4.3.1, Collect river bottom data related to the river bottom shape coefficient. The river bottom data includes riverbed elevation data, cross-sectional measurement data, flow rate data, and flow velocity data;

[0073] S2.4.3.2, Clean the data. According to the distribution of the collected river bottom data, remove outliers, incorrect data, and incomplete data; perform standardization or normalization processing on the river bottom data;

[0074] Formula: ;

[0075] Linearly map the data to a specified range through the above formula, where X is the original data, X min and X max are the minimum and maximum values in the dataset respectively; then extract the feature data that meets the requirements from the original data, and the feature data is used as the input of the AI model;

[0076] S2.4.3.3, Adopt a neural network model for learning. Use the training set data to train the AI model, and optimize the performance of the model by adjusting the parameters and structure of the model.

[0077] S2.4.3.4, Deploy the trained AI model to the actual application scenario for predicting the new river bottom shape coefficient.

[0078] Furthermore, on the premise that the characteristics of the water flow at the bottom of the river channel have viscosity and friction, the vertical flow velocity follows a linear distribution.

[0079] Furthermore, the water flow in the cross-section above the converted bottom elevation of the river channel follows a logarithmic distribution.

[0080] Furthermore, the river channel is a natural river channel.

[0081] A system for calculating the flow rate near the river bottom in a river channel using the acoustic time difference method. The system includes ultrasonic transducers arranged in the river channel;

[0082] For implementing the above calculation method; along the vertical direction of the flow velocity, the converted bottom elevation of the river channel is divided into a linear distribution area and a logarithmic distribution area.

[0083] In this patent, by introducing the concept of the converted bottom elevation of the river channel, 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 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 vertical distribution of the flow velocity is divided into two zones by using the converted bottom elevation of the river channel, namely: the linear distribution zone and the logarithmic distribution zone. Among them, for the linear distribution zone close to the bottom of the river channel, it is calculated by a linear formula, and for the logarithmic distribution zone above the converted bottom elevation of the river channel, it is calculated by a logarithmic formula. In this way, it not only avoids the limitation of the logarithmic formula being negative infinity when the water depth is zero but also better reflects the characteristics of the bottom water flow. Description of the Drawings

[0084] Figure 1 It is a schematic diagram of the layout elements of the sound channel of the river channel flow measurement section of the present invention.

[0085] Figure 2 It is a schematic diagram of the river channel flow calculation of the present invention.

[0086] Figure 3 It is a schematic diagram of the flow calculation of the near-water surface part of the present invention. Detailed Embodiment

[0087] As Figures 1 - 3 , this application believes 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 divides the vertical distribution of the flow velocity into two zones by using the converted bottom elevation of the river channel, namely: the linear distribution zone and the logarithmic distribution zone.

[0088] Step 1, determination of the converted bottom elevation of the river channel

[0089] First, determine the converted bottom elevation of the river channel;

[0090] Elevation refers to the distance from a certain point along the plumb line direction to the absolute base surface, called absolute elevation, or simply elevation. The distance from a certain point along the plumb line direction to a certain assumed level base surface is called assumed elevation.

[0091] Based on various determination methods such as empirical discrimination, equipment installation conditions, standard water level, and characteristic water level, the present invention determines the converted bottom elevation of the river channel, which has little influence on the flow measurement calculation results. Moreover, the converted bottom elevation of the river channel is not continuous and can be changed according to the change of conditions. The specific determination method is as follows:

[0092] (1) Determined by empirical discrimination;

[0093] A certain characteristic point near the river bottom on the river cross-section is artificially selected by hydrological survey personnel with experience in flow measurement and familiar with the situation of the gauging station, and the elevation of this characteristic point is defined as the converted bottom elevation of the river channel.

[0094] (2) Determined according to the installation conditions of the flow measurement equipment;

[0095] The river channel topography determines the installation conditions of the flow measurement equipment. The first sound channel should be installed as close to the river bottom as possible, and the average river bottom elevation corresponding to the installation elevation of the first sound channel can be defined as the converted bottom elevation of the river channel.

[0096] (3) Determined by the standard water level;

[0097] In rivers with relatively severe changes in river channel sedimentation, especially in the lower reaches of the Yellow River, a standard water level is often determined when analyzing the erosion and deposition changes of the river channel. The average river channel elevation corresponding to this standard water level elevation can be defined as the converted bottom elevation of the river channel.

[0098] (4) Determined by a certain characteristic water level;

[0099] Determined by referring to a certain characteristic water level of the hydrological station, such as the historical lowest water level, the cut-off water level, etc. The average river bottom elevation corresponding to this characteristic water level can be defined as the converted bottom elevation of the river channel.

[0100] In Figure 1 The symbols and their meanings are explained as follows:

[0101] Z * , unit m, the converted bottom elevation of the river channel;

[0102] Z0, unit m, the elevation from which the water depth is calculated;

[0103] H0, unit m, the calculated water depth, the difference between the current water level and the elevation from which the water depth is calculated;

[0104] Z i , unit m, the i-th sound channel and the sound channel elevation.

[0105] Z1, Z2, Z3, Z4 are, in sequence, the near-river-bottom sound channel, the cross-section control sound channel, the medium-flow sound channel, and the flood sound channel;

[0106] A i , unit m 2 , is the cross-sectional area between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound channel of the river cross-section, called the flow layer area, also called the partial area. Among them, when i = 1, A1 is the area between the elevation of the first sound channel and the converted bottom elevation of the river channel; A0 is the area below the converted bottom elevation of the river channel, that is, the river bottom area;

[0107] V i , in m / s, is the average velocity of the flow layer between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound 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 sound channel and the converted bottom elevation of the river channel; V0 is the average velocity of the water flow below the converted bottom elevation of the river channel.

[0108] V m,i , in m / s, is the measured horizontal average velocity of the i-th ultrasonic sound channel. Among them, when i = 0, V m,0 is the horizontal average velocity corresponding to the converted bottom elevation of the river channel.

[0109] y, dimensionless, is the relative water depth, which is the water depth measured upward from the elevation of the water depth divided by the calculated water depth, defined as the relative water depth.

[0110] For flow measurement calculation, the average velocity of each flow layer is calculated using the formula, and the partial flow of each flow layer is calculated using the velocity-area method. By accumulating the partial flows of each flow layer, the flow rate passing through the flow measurement section can be obtained finally.

[0111] Calculate the total instantaneous flow rate q = q0 + q1 + q2 +…q iT …+ q T ;

[0112] ;

[0113] q i= The partial flow of each flow layer;

[0114] q T= The flow rate of the surface flow layer;

[0115] T represents the surface flow layer;

[0116] A i , in m 2 , is the cross-sectional area between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound channel of the river channel cross-section, called the flow layer area, that is, the partial area; among them, when i = 1, A1 is the area between the elevation of the first sound channel and the converted bottom elevation of the river channel; A0 is the area below the converted bottom elevation of the river channel, that is, the river bottom area;

[0117] V i, in m / s, is the average velocity of the flow layer between the elevation of the i-th channel and the elevation of the (i - 1)-th 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 converted bottom elevation of the river channel; V0 is the average velocity of the water flow below the converted bottom elevation of the river channel; Obtain the average velocity of the flow layer between adjacent channels. The average velocity of the flow layer between two adjacent channels can be obtained by calculating the horizontal velocities of the two channels. The calculation formula:

[0118] ;

[0119] Obtain the average velocity of the flow layer near the river bottom. The flow layer near the river bottom refers to the water flow between the elevation Z1 of the channel near the river bottom (the first channel) and the converted bottom elevation Z of the river channel * between them. The calculation process of the average velocity V1 of the flow layer near the river bottom needs to consider the following two different working states;

[0120] (1) When in the low water level state;

[0121] If only the Z1 channel is working, it can be considered that the river is in the low water level state. The solution process of the average velocity of the near-surface flow layer is as follows:

[0122] The first step is to calculate the water surface velocity V 0.0 Assume that the hydraulic gradient is equal to the river bottom slope of the gauging station section at this time, and obtain it through the logarithmic formula of the vertical velocity distribution

[0123] ;

[0124] Among them, V m，1 is the measured value of the channel Z1, ; where, g = 9.8, j = river channel slope, H = H0;

[0125] The second step is to calculate the horizontal velocity of the converted bottom elevation of the river channel from the water surface velocity V 0.0 ;

[0126] ;

[0127] The third step is to calculate the average velocity of the flow layer near the river bottom ;

[0128] The average velocity of the flow layer near the river bottom can be obtained by the following formula:

[0129] ;

[0130] (2) Normal flow measurement;

[0131] If two or more channels are working and the device is in the normal flow measurement state.

[0132] The specific calculation steps are as follows:

[0133] First, obtain the average flow velocity V of the flow layer between the first channel and the second channel 2；

[0134] ;

[0135] Second, obtain the integral formula for the average flow velocity V of the flow layer between the two channels below the water surface i ;

[0136] ;

[0137] Third, the expression of V * / K can be derived from the above integral formula as follows:

[0138] ;

[0139] Fourth, substitute V * / K in the above formula into the following formula to obtain the horizontal flow velocity of the river channel conversion bottom elevation ;

[0140] ;

[0141] Fifth, the average flow velocity of the near-bottom flow layer can be obtained from the following formula:

[0142] ;

[0143] Sixth, calculate the flow rate of the near-bottom flow cross-section,

[0144] ;

[0145] In the formula, is the cross-sectional flow area of the near-bottom flow layer.

[0146] Obtain the average flow velocity V0 of the bottom flow layer,

[0147] The bottom flow layer refers to the water flow corresponding to the cross-sectional area A0 of the river channel conversion bottom elevation Z * below. The average flow velocity V0 of the bottom flow layer depends on the horizontal flow velocity V * of the river channel conversion bottom elevation Z m,0 and the bottom cross-sectional shape coefficient.

[0148] The calculation process of the average flow velocity V0 of the bottom flow layer is as follows:

[0149] Step 1: Formula for the bottom cross-section shape coefficient;

[0150] If the cross-sectional area of the river channel below the starting water depth elevation The formula for defining the bottom cross-section shape coefficient is:

[0151] ;

[0152] Step 2: Calculate the average velocity V of the bottom flow layer 0，

[0153] The average velocity V0 of the bottom flow layer is a linear function of the converted bottom elevation Z of the river channel * The cross-stream velocity V m,0 The calculation formula for the average velocity V0 of the bottom flow layer is:

[0154] ;

[0155] In the formula, is the bottom cross-section shape coefficient, which is obtained from the bottom boundary conditions of the river.

[0156] Step 3: Calculate the cross-sectional flow rate of the bottom flow layer,

[0157] ;

[0158] Since the average velocity of the bottom flow layer is a linear function of the cross-stream velocity V of the converted bottom elevation Z of the river channel * The bottom cross-section shape coefficient needs to be obtained through continuous accumulation of measured data. To obtain calculation parameters under different flow regimes, a deep learning model with a lifelong learning mechanism is proposed to continuously optimize using big data AI models. m,0 Step 1: Collect various data related to the bottom shape coefficient, including riverbed elevation data, cross-sectional measurement data, flow rate data, velocity data, etc. Ensure that the data covers different rivers, different river reaches, and different flow conditions so that the AI model can learn a wide range of patterns.

[0159] Step 2: Clean the data, removing outliers, incorrect data, and incomplete data. Standardize or normalize the data;

[0160] Formula:

[0161] ; ;

[0162] Explanation: This formula linearly maps the data to a specified range (usually [0,1]), where X is the original data, X min and X maxThey are the minimum and maximum values in the dataset respectively, so that the AI model can better process data with different dimensions. Feature extraction may be required to extract meaningful features from the original data, and these features will be used as the input of the AI model.

[0163] Step 3: Adopt a neural network model for learning. Use the training set data to train the AI model, and optimize the performance of the model by adjusting the parameters and structure of the model.

[0164] Step 4: Deploy the trained model to the actual application scenario for predicting the new river bottom shape coefficient. Monitor the performance of the model and regularly update and optimize the model according to the new measured data.

[0165] The preferred training steps of the neural network model are as follows;

[0166] First, perform parameter initialization. The parameters include the weight u and the bias parameter v, which can be randomly initialized; then, perform forward propagation by inputting the training data into the neural network model and obtaining the output of each layer until the final predicted result value is obtained; secondly, perform loss calculation by comparing the predicted result of the neural network with the actual data obtained, and use the loss function to represent the gap between the predicted result and the actual data obtained; thirdly, perform backpropagation. Through the backpropagation algorithm, calculate the gradient of the loss function for each parameter, and the propagation process propagates the gradient from the output layer to the input layer to adjust the parameters of each layer; after that, update the parameters. According to the calculated gradient information, use the optimized gradient descent algorithm to update the parameters in the neural network and reduce the loss function; then, perform iterative repetition, repeating the steps from forward propagation to parameter update until the set stop condition is reached; the stop condition can be, for example, reaching the maximum number of iterations or the convergence of the loss function; next, perform model evaluation. 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; immediately afterwards, perform model application. When the training model is completed and the performance reaches the set requirements, the model can be used for tasks such as prediction or classification.

[0167] The present invention first selects a natural river channel. According to the different roles played by the layout positions of the ultrasonic channels in the flow measurement by the time difference method, channels with different heights are arranged. The ultrasonic channels are used to monitor the horizontal average velocity of the water cross-section at the elevation where the channels are located, and the river bottom velocity is calculated according to the calculation steps in the above invention points.

[0168] The present invention is fully described for a clearer disclosure, and the prior arts will not be listed one by one.

[0169] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; as is obvious to those skilled in the art, multiple technical solutions of the present invention can be combined. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. The technical content not described in detail in the present invention is well-known technology.

Claims

1. A method for calculating the flow rate near the river bottom in a river channel using the acoustic time difference method, characterized in that: Including the following steps; Step 1, determine the converted bottom elevation of the river channel; Step 2: Calculate the average velocity of each flow layer using the formula, and calculate the partial flow rate q of each flow layer by the velocity-area method i , and accumulate the partial flow rate q of each flow layer i Finally, obtain the flow rate q passing through the measuring cross-section; Calculate the total instantaneous flow rate q = q0 + q1 + q2 +…q iT …+ q T ; ； ； ； ； q i= Partial flow rate of each flow layer; q T= Flow rate of the surface flow layer; T represents the surface flow layer; A i , in m 2 , which is the cross-sectional area between the elevation of the i-th sound channel and the elevation of the (i - 1)-th sound channel of the river channel cross-section, and is called the flow layer area, that is, the partial area; among them, when i = 1, A1 is the area between the elevation of the first sound channel and the converted bottom elevation of the river channel; A0 is the area below the converted bottom elevation of the river channel, that is, the river channel bottom area; V i , in m / s, is the average flow velocity of the flow layer between the elevation of the i-th channel and the elevation of the (i - 1)-th channel, that is, the partial area flow velocity; where 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; In Step 2, perform the following steps; S2.1, set parameters; S2.2, Obtain the average flow velocity of adjacent channel stream layers ; S2.3, obtain the average velocity of the near-bottom flow layer ; S2.4, obtain the average velocity V0 of the bottom flow layer; In Step S2.1, Z * , in m, is the converted bottom elevation of the river channel; Z0, in units of m, is the elevation from which the water depth is measured; H0, in units of m, is the calculated water depth, which is the difference between the current water level and the elevation from which the water depth is measured; Z i , in meters, the i-th sound channel and the sound channel elevation; Z1, Z2, Z3, Z4 are the near-bottom channel, the cross-section control channel, the normal water channel, and the flood channel in sequence; V m,i , in m / s, is the measured horizontal average velocity of the i-th ultrasonic sound channel; where, when i = 0, V m,0 is the horizontal average velocity corresponding to the converted bottom elevation of the river channel; y, dimensionless, is the relative water depth, which is the water depth measured upward from the elevation from which the water depth is measured divided by the calculated water depth; In Step S2.2, the average velocity of the flow layer between two adjacent channels is obtained from the horizontal velocities of the two channels, and the calculation formula is: ； In step S2.3, the near-bottom flow layer is the water flow between the first channel elevation Z1 of the near-bottom channel and the converted bottom elevation Z of the river channel * of the river channel; The calculation process of the average velocity V1 of the near-bottom flow layer considers the following working conditions; S2.3A When the working condition is in the low water level state, Only the Z1 channel is working, and the solution process of the average velocity of the near-surface flow layer is as follows: S2.3.1A, calculate the water surface velocity V 0.0 , assuming that the hydraulic gradient is equal to the bottom slope of the cross-section at the gauging station at this time ； Among them, V m，1 is the measured value of sound channel Z1, where g = 9.8, j = river bed slope, H = H0; S2.3.2A, from the water surface velocity V 0.0 , calculate the converted bottom elevation cross-sectional velocity of the river channel ; ； S2.3.3A, Calculate the average velocity of the near-bottom flow layer ; Average velocity of near-bottom flow layer It is obtained by the following formula: ； S2.3B, when the working condition is in the low water level state, two or more channels are working, and the device is in the normal flow measurement state; the specific calculation steps are as follows; S2.3.1B, obtain the average velocity V2 of the flow layer between the first channel and the second channel; ； S2.3.2B, Obtain the average flow velocity V of the flow layer between the two channels below the near water surface i The integral formula of; ； S2.3.3B, the expression of V * / K is derived from the integral formula of S2.3.2B as follows: ； S2.3.4B, substitute V in S2.3.2B * / K into the following formula to obtain the horizontal velocity of the converted bottom elevation of the river channel ; ； S2.3.5B, average velocity of the near-bottom flow layer Obtained by the following formula: ； S2.3.6B, calculate the flow rate of the near-bottom process cross-section, ； In the formula, is the cross-sectional flow area of the near-bottom flow layer; S2.4, obtain the average velocity V0 of the bottom flow layer; The bottom flow layer is the converted bottom elevation Z of the river channel * For the water flow corresponding to the cross-sectional area A0 of the river channel below, the average 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 cross-sectional shape factor; The calculation steps of the average velocity V0 of the bottom flow layer are as follows; S2.4.1, the formula for the bottom cross-section shape coefficient; If the cross-sectional area of the river channel is below the starting water depth elevation , then the formula for defining the bottom cross-sectional shape coefficient is as follows: ; S2.4.2, calculate the average velocity V0 of the bottom flow layer; The average velocity V0 of the bottom flow layer is the cross-sectional velocity V * of the channel conversion bottom elevation Z m,0 which is a linear function. Then the calculation formula for the average velocity V0 of the bottom flow layer is as follows: ； In the formula, is the shape coefficient of the river bottom section, which is obtained from the river bottom boundary conditions; S2.4.3, calculate the flow rate of the bottom flow layer cross-section, ； In Step S2.4.3, the bottom cross-section shape coefficient is obtained through data accumulation. The data accumulation includes continuous accumulation of calculation data and measured data to obtain calculation parameters under different water flow regimes, and is optimized using a big data AI model. The AI model uses a deep learning model with a lifelong learning mechanism. The data accumulation steps are as follows; S2.4.3.1, collect river bottom data related to the river bottom shape coefficient. The river bottom data includes river bed elevation data, cross-section measurement data, flow rate data, and velocity data; S2.4.3.2, clean the data. According to the distribution of the collected river bottom data, remove outliers, incorrect data, and incomplete data; perform standardization or normalization processing on the river bottom data; Formula: ; Linearly map the data to a specified range through the said formula, where X is the original data, X min and X max are respectively the minimum value and the maximum value in the dataset; then extract the feature data that meets the requirements from the original data, and the feature data is used as the input of the AI model; S2.4.3.3, use a neural network model for learning; use the training set data to train the AI model, and optimize the performance of the model by adjusting the parameters and structure of the model; S2.4.3.4, deploy the trained AI model to the actual application scenario to predict the new river bottom shape coefficient; Along the vertical direction of the velocity, the converted bottom elevation of the river channel is divided into a linear distribution area and a logarithmic distribution area; The water flow above the converted bottom elevation of the river channel follows a logarithmic distribution; The river channel is a natural river channel; Provided that the characteristics of the water flow at the bottom of the river channel have viscosity and friction, and the vertical velocity follows a linear distribution.

2. A flow calculation system near the river bottom in a river channel using the acoustic time difference method, characterized in that: The system includes ultrasonic transducers arranged in the river channel; For performing the calculation method described in Claim 1.

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