A self-calibration method for a river flow measurement system using a two-layer velocity measurement method and time difference method

Abstract

A self-calibration method for a two-layer velocity measurement method using a time-difference method for river flow measurement includes the following steps: installing two layers of ultrasonic transducers in a river section to synchronously measure the actual flow velocity of the two layers; using a logarithmic velocity distribution model to convert horizontal layer velocity to cross-sectional velocity and calculate the velocity coefficients of the upper and lower horizontal layers; calculating the real-time flow rate from the cross-sectional average velocity and cross-sectional area; statistically obtaining the average relationship between the water level and the water surface velocity coefficient, establishing the relationship between the water level and the water surface velocity coefficient and the water level and the layer velocity coefficient, obtaining a curve relationship based on the distribution of the point group, calculating the comprehensive value of the layer velocity coefficient based on the water level, and inferring the cross-sectional average velocity and cross-sectional flow rate. The present invention can make the ultrasonic time-difference method a flow measurement method independent of other conventional flow measurement methods, eliminating the need to separately deploy a set of conventional testing facilities such as a rotor flowmeter for comparative measurement and calibration, thereby enabling the ultrasonic time-difference method flow monitoring system to be put into operation and applied immediately after completion.

Description

Technical Field

[0001] The invention belongs to the technical field of water flow measurement, and in particular relates to a self-calibration method for a river flow measurement system using a time difference method with a two-layer speed measurement mode. Background Art

[0002] Ultrasonic waves are directional and can propagate in straight lines like light waves. They can propagate through gases, liquids, and solids. The ultrasonic transit time method uses the principle that the time difference between the downstream and upstream propagation of ultrasound waves is proportional to the flow rate of the fluid. By measuring the time difference between the downstream and upstream propagation of ultrasound waves, the flow rate of the river can be determined.

[0003] Since its pilot study in Hunan Province in 1970, the ultrasonic transit time method has undergone nearly 50 years of research and development in my country, achieving initial application, particularly in flow monitoring in some artificial canals. However, due to the irregular cross-sections of natural rivers and the complex influencing factors, the success of the construction and implementation of transit time flow measurement systems is directly determined by the reliability of the velocity of one or more horizontal layers measured by the ultrasonic transit time method, as well as the ability to establish a relationship between the measured horizontal layer velocity and the actual flow velocity at the cross section. Therefore, the initial development of ultrasonic transit time method monitoring systems in natural rivers requires in-depth technical demonstration and a lengthy system calibration process, which, to a certain extent, has limited the widespread application of the ultrasonic transit time method in river flow monitoring.

[0004] The multi-layer flow measurement method is to install multiple pairs of transducers in parallel at different water depths along the two banks of the river channel, measure the average flow velocity of the horizontal layers at different water depths on the cross section, and obtain the cross-sectional flow velocity distribution changes. Based on this, the flow rate of each horizontal layer is calculated and the cross-sectional flow rate is deduced. The fixed installation arrangement of the multi-channel transducers of the multi-layer flow measurement method is as follows: Figure 1 shown.

[0005] The cross-sectional flow calculation of the multi-layer flow measurement method is similar to the conventional flow meter method, which uses the accumulation of layered partial flow. Its finite difference formula is:

[0006]

[0007] Where: v μ is the horizontal layer velocity of the μth velocity measuring layer. When μ=n, it is the boundary velocity of the river bottom blind zone. A μ is the cross-sectional area of ​​the μth part; k 表 is the surface velocity coefficient; k 底 is the bottom layer velocity coefficient; the other symbols have the same meanings as above.

[0008] The single-layer flow measurement method is to select a suitable fixed position along both sides of the river channel, install a pair of transducers horizontally, and use the horizontal average flow velocity of the horizontal layer measured by the transducer to represent the average flow velocity of the entire section, based on which the cross-sectional flow rate is calculated. The transducer arrangement of the single-layer flow measurement method is as follows: Figure 2 shown.

[0009] The calculation formula of cross-sectional flow rate of single-layer flow measurement method can be expressed as:

[0010]

[0011] Where: is the average flow velocity of the section; A is the cross-sectional area; v θ is the laminar flow velocity at a fixed velocity measurement layer; k θ It is the conversion coefficient between horizontal layer velocity and cross-sectional average velocity, generally called horizontal layer velocity coefficient; the other symbols have the same meaning as above.

[0012] From the above, it can be seen that when using the ultrasonic transit time method to measure river flow, whether it is a multi-layer flow measurement method or a single-layer flow measurement method, it is difficult to obtain a complete cross-sectional flow velocity distribution through measurement. Therefore, when using the ultrasonic transit time method, the system must be calibrated after the instrument is installed to establish the relationship between the measured flow velocity and the actual average flow velocity of the cross section, that is, to calculate k in formula (1). 表 、k 底 Or k in formula (2) θ .

[0013] Therefore, whether using multi-layer or single-layer flow measurement, the transit-time flow measurement system must be calibrated. Therefore, when deploying ultrasonic transit-time flow measurement system facilities, a rotor velocimeters or underway acoustic Doppler current profilers (ADCPs) must be deployed in accordance with the "River Flow Measurement Specification" (GB50179). Precision measurements of the full-section flow rate must be performed simultaneously with the transit-time flow measurement method to analyze the relationship between transit-time flow velocity and the full-section flow velocity. Due to the complex water conditions in natural rivers, calibration can be a lengthy process, which is not only time-consuming and labor-intensive, but also hinders the timely commissioning and effectiveness of transit-time flow measurement, significantly hindering its application in newly established hydrological stations. Summary of the Invention

[0014] The purpose of the present invention is to provide a self-calibration method for a river flow measurement system using a two-layer velocity measurement method using a time difference method. Based on a laminar velocity and cross-sectional velocity conversion model of a logarithmic vertical velocity distribution, the laminar velocity and cross-sectional average velocity are converted and calculated using the velocity measurement information of the ultrasonic time difference method itself. This allows the ultrasonic time difference method to become a flow measurement method independent of other conventional flow measurement methods, without the need to separately deploy a set of conventional testing facilities such as a rotor flowmeter for comparative measurement and calibration. This allows the ultrasonic time difference method flow monitoring system to be put into operation and applied as soon as it is built.

[0015] To achieve the above object, the technical solution adopted by the present invention is:

[0016] A self-calibration method for a river flow measurement system using a time difference method with a two-layer velocity measurement method comprises the following steps:

[0017] (1) Install upper and lower layers of ultrasonic transducers in the river section;

[0018] (2) Use the ultrasonic transducer to synchronously measure the actual flow rate of the upper and lower layers and follow the "Water Level Observation Standard"

[0019] (GB / T50138) Observe the water level Z when measuring the river section;

[0020] (3) Using the velocity coefficient conversion model based on logarithmic velocity distribution, the measured velocity v of the upper and lower layers is θ1 、v θ2 The water surface velocity coefficient K0 is deduced from the river section measurement data, and then the upper layer velocity coefficient k corresponding to this flow measurement is deduced from the water surface velocity coefficient K0 and the river section measurement data. θ1 and the lower layer velocity coefficient k θ2 ;

[0021] (4) According to the measured water level Z, the cross-sectional area A of the river corresponding to the measured water level Z is obtained from the actual measured value of the section;

[0022] (5) The measured flow velocity v in the upper layer θ1 and the upper layer velocity coefficient k θ1 The product of (or the measured velocity v of the lower layer θ2 and the upper layer velocity coefficient k θ2 The product of the cross-sectional average velocity

[0023] (6) Average flow velocity of the cross section and the cross-sectional area A, calculate the real-time flow rate Q by the velocity-area method;

[0024] (7) Repeat steps (2) to (6) for several times, and draw the correlation diagram between the water level Z and the water surface velocity coefficient K0 at each flow measurement. Draw the relationship line between the water level Z and the water surface velocity coefficient K0 (i.e., the Z-K0 relationship line) according to the distribution center of the point group. Then, the corresponding K0 and cross-sectional measurement data of each water level are obtained by tracing the Z-K0 relationship line, and the upper and lower layer velocity coefficients k corresponding to each water level are calculated. θ1 、k θ2 And establish the relationship line between water level and upper and lower layer velocity coefficient (i.e. Z~k θ1 、Z~k θ2 Relationship line), by the Z~k θ1 、Z~k θ2The relationship line is calculated based on the water level to calculate the velocity coefficient k of the upper and lower layers. θ1 、k θ2 Then, go to steps (5) to (6) to calculate the average flow velocity and flow rate of the cross section, which can further improve the flow measurement accuracy.

[0025] As a preferred embodiment of the above method, in step (3), the water surface velocity coefficient calculation formula is:

[0026]

[0027] in,

[0028]

[0029] Where: K0 is the water surface velocity coefficient; B1 is the width of the upper horizontal layer; B2 is the width of the lower horizontal layer; v θ1 is the measured velocity of the upper layer; v θ2 is the measured flow velocity of the lower layer; h μ is the average water depth of the μth part (μ = 1, 2, ..., n); b μ is the water surface width of the μth part of the area; j1 represents the starting perpendicular number below the upper layer; j2 represents the starting perpendicular number below the lower layer; m1 represents the final perpendicular number below the upper layer; m2 represents the final perpendicular number below the lower layer; θ is the relative water depth calculated from the river bottom, and its value is between 0 and 1.

[0030] As a preferred embodiment of the above method, in step (3),

[0031] The upper layer velocity coefficient calculation formula is:

[0032]

[0033] The calculation formula of the lower layer velocity coefficient is:

[0034]

[0035] in,

[0036] Where: k θ1 is the upper layer velocity coefficient; k θ2 is the velocity coefficient of the lower layer; the other symbols have the same meanings as above.

[0037] As a preferred embodiment of the above method, in step (6), the real-time flow rate Q is calculated as follows:

[0038]

[0039] Where: Q is the flow rate; A is the cross-sectional area of ​​the river; is the average flow velocity of the section; the other symbols have the same meanings as above.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The flow rate calculation accuracy of the laminar flow velocity and cross-sectional average flow velocity conversion model constructed by the present invention basically meets the accuracy requirements of normal hydrological measurements. After collecting a certain number of two-layer velocity measurements to determine the relationship between the water level (or other hydraulic factors) and the laminar flow velocity coefficient, the flow rate measurement accuracy meets the accuracy requirements of Class I stations in the "River Flow Measurement Specifications". Using a single two-layer velocity measurement information to instantly calculate the laminar flow velocity and cross-sectional flow velocity conversion coefficient to directly calculate the flow rate, the flow rate measurement accuracy is reduced, but it can basically meet the accuracy requirements of Class II stations in the "River Flow Measurement Specifications".

[0042] (2) The laminar velocity and cross-sectional velocity conversion model based on the vertical velocity distribution completely utilizes the velocity measurement information of the ultrasonic time difference method itself to convert the laminar velocity and the cross-sectional average velocity. This makes the ultrasonic time difference method a flow measurement method independent of other conventional flow measurement methods. Therefore, there is no need to set up a set of conventional test facilities such as rotor flowmeters for comparison and calibration, so that the ultrasonic time difference method flow monitoring system can be put into production and applied as soon as it is built.

[0043] (3) From the perspective of the calculation parameters of the laminar velocity and cross-sectional velocity conversion model based on the vertical velocity distribution, the laminar velocity coefficient mainly depends on the structural characteristics of the water flow (represented by K0 in the formula) and the cross-sectional morphology of the river. Therefore, on the one hand, the layout of the ultrasonic time difference velocity measurement layer should be able to reflect the information of the vertical distribution of the river cross-sectional velocity, so as to achieve the complementarity of the velocity distribution information between the velocity measurement layers. Regarding the optimal layout of the measurement layer spacing, the present invention proposes a corresponding algorithm. On the other hand, when the river cross-section undergoes a major change or the control conditions of the measuring station undergo a major change, resulting in a change in the vertical distribution law of the velocity, the present invention proposes technical requirements for the calibration and inspection of the laminar velocity coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a diagram of the fixed installation of the multi-channel transducer.

[0045] Figure 2 This is a schematic diagram of the installation of a single-layer flow measurement transducer.

[0046] Figure 3 This is a schematic diagram of the installation of the two-layer flow measurement transducer.

[0047] Figure 4 This is the relationship diagram between water level and water surface velocity coefficient, and water level and laminar velocity coefficient. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is described in detail below in conjunction with embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0049] Example 1:

[0050] The vertical velocity distribution of a river, or the variation in velocity distribution along vertical lines at different locations on a cross-section, is highly complex and is primarily influenced by factors such as water depth, riverbed roughness, sediment content, and upstream and downstream cross-section variations. Therefore, in-depth research is needed to determine cross-sectional flow rate calculation methods for velocity distributions with varying distribution patterns. In our long-term ultrasonic transit-time flow measurement experiments, we have discovered that velocity information from different horizontal layers consistently exhibits a degree of complementarity. The velocity of each horizontal layer reflects the cross-sectional velocity distribution pattern. By mining and adapting velocity information from two or more complementary layers, we can derive the morphological distribution of velocity across the river channel. Combined with cross-sectional area measurement information, we can then obtain cross-sectional flow rate information.

[0051] The specific implementation steps are as follows:

[0052] (1) Install upper and lower layers of ultrasonic transducers in the river section;

[0053] (2) Use the ultrasonic transducer to synchronously measure the actual flow rate of the upper and lower layers and follow the "Water Level Observation Standard"

[0054] (GB / T50138) Observe the water level Z when measuring the river section;

[0055] (3) Using the velocity coefficient conversion model based on logarithmic velocity distribution, the measured velocity v of the upper and lower layers is θ1 、v θ2 The water surface velocity coefficient K0 is deduced from the river section measurement data, and then the upper layer velocity coefficient k corresponding to this flow measurement is deduced from the water surface velocity coefficient K0 and the river section measurement data. θ1 and the lower layer velocity coefficient k θ2 ;

[0056] (4) According to the measured water level Z, the cross-sectional area A of the river corresponding to the measured water level Z is obtained from the actual measured value of the section;

[0057] (5) The measured flow velocity v in the upper layer θ1 and the upper layer velocity coefficient k θ1 The product of (or the measured velocity v of the lower layer θ2 and the upper layer velocity coefficient k θ2 The product of the cross-sectional average velocity

[0058] (6) Average flow velocity of the cross section and the cross-sectional area A, calculate the real-time flow rate Q by the velocity-area method;

[0059] (7) Repeat steps (2) to (6) for several times, and draw the correlation diagram between the water level Z and the water surface velocity coefficient K0 at each flow measurement. Draw the relationship line between the water level Z and the water surface velocity coefficient K0 (i.e., the Z-K0 relationship line) according to the distribution center of the point group. Then, the corresponding K0 and cross-sectional measurement data of each water level are obtained by tracing the Z-K0 relationship line, and the upper and lower layer velocity coefficients k corresponding to each water level are calculated. θ1 、k θ2 And establish the relationship line between water level and upper and lower layer velocity coefficient (i.e. Z~k θ1 、Z~k θ2 Relationship line), by the Z~k θ1 、Z~k θ2 The relationship line is calculated based on the water level to calculate the velocity coefficient k of the upper and lower layers. θ1 、k θ2 Then, go to step (5)

[0060] (6) The flow measurement accuracy can be further improved by estimating the average flow velocity and flow rate of the cross section.

[0061] The conversion between horizontal layer velocity and cross-sectional velocity is deduced using the logarithmic velocity distribution:

[0062] The logarithmic distribution formula of vertical flow velocity in natural rivers and canals is:

[0063]

[0064] In the above two formulas: v θ is the flow velocity at the relative water depth θ on the vertical line of the channel section; θ is the relative water depth value from the river bottom, and its value is between 0 and 1; v * is the dynamic velocity; C is the coefficient of gravity; g is the acceleration of gravity, generally g = 9.81m / s 2 ; K1 is the Karman constant; h is the vertical water depth; s is the water surface slope.

[0065] According to formula (5) and formula (6), the formula for the vertical average flow velocity can be deduced as:

[0066]

[0067] Therefore, the average flow velocity on the flow measurement section can be calculated as follows:

[0068]

[0069] Where: h μ is the average water depth of the μth part (μ = 1, 2, ..., n); b μ is the water surface width of the μth part; the other symbols have the same meanings as above.

[0070] For example, if two fixed horizontal layer transducers 1-1 and 2-2 are installed on the cross section to measure the flow velocity, Figure 3 shown.

[0071] For the 1-1 horizontal plane, the average flow velocity of the cross section can be obtained by integrating after appropriate transformation, that is:

[0072]

[0073] Where: B1 is the width of the river surface at the upper horizontal layer; j1 represents the number of the starting vertical line below the upper horizontal layer; m1 represents the number of the final vertical line below the upper horizontal layer; is the average flow velocity of the 1-1 horizontal layer; B1 is the river width of the 1-1 horizontal layer; the other symbols have the same meanings as above.

[0074] in:

[0075] Then the average velocity formula of the 1-1 horizontal layer, that is, formula (7), can be simplified as:

[0076]

[0077] According to the relationship between the Karman constant K1 and the water surface velocity coefficient K0:

[0078]

[0079] Substituting (11) into (10) we obtain:

[0080]

[0081] From formula (12), the upper layer velocity coefficient can be expressed as:

[0082]

[0083] in,

[0084] From formula (13), we can know that the horizontal layer velocity coefficient of the canal section is mainly related to the shape of the canal section and the water surface velocity coefficient K0 of the test section. The canal section shape can be obtained through cross-section measurement data. At this point, the problem of calculating the horizontal layer velocity coefficient is transformed into the problem of calculating the water surface velocity coefficient.

[0085] exist Figure 3 Then, we calculate the average velocity of the 2-2 horizontal layer, and use j2 to represent the starting vertical line number below the 2-2 horizontal layer, and m2 to represent the final vertical line number below the 2-2 horizontal layer. Similarly, we can get:

[0086]

[0087] In the above two formulas: is the average flow velocity of the 2-2 horizontal layer; B2 is the river width of the 2-2 horizontal layer; is the 2-2 horizontal layer velocity coefficient;

[0088] Then, we can use formula (4) to calculate the cross-sectional flow rate for the upper and lower horizontal layers respectively, and we have:

[0089]

[0090] Substituting equations (11) and (13) into equation (14), we have:

[0091]

[0092] It can be seen from the above formula that the water surface velocity coefficient is only related to the cross-sectional shape and the horizontal flow velocity of the two horizontal layers.

[0093] Therefore, when using the ultrasonic time difference method to measure flow, the velocity of two horizontal layers can be measured each time before the application is put into production. Combined with the cross-section measurement data, the water surface velocity coefficient K0 can be calculated by formula (17); then according to formulas (13) and (15), the laminar velocity coefficient k of the two fixed horizontal layers can be successfully solved. θ1 、k θ2 , and then the river cross-section flow can be calculated by formula (4).

[0094] The experimental data are as follows:

[0095] The ultrasonic transit time method test data from Xiangtan Hydrological Station were used to verify the laminar velocity and cross-sectional velocity conversion model based on logarithmic vertical velocity distribution and the self-calibration method of the ultrasonic transit time method flow monitoring system.

[0096] Xiangtan Station is the central control station for the Xiangjiang River entering Dongting Lake, with a controlled catchment area of ​​81,638 km 2 The highest water level in history is 41.95m, and the maximum flow in history is 26200m 3 The station's test section is straight, with a riverbed composed of fine sand and pebbles, resulting in a generally stable cross-section. At high water levels, the water surface can reach 750 meters wide. Backwater from floods in the Yangtze River and Dongting Lake can reach the test section. Therefore, the station is affected by the combined effects of flood rise and fall rates and the support of backwater from the Yangtze River and Dongting Lake. The water level-discharge relationship is complex, and flow data are compiled using methods such as loop curves, continuous time series, and drop methods. To explore the feasibility of applying ultrasonic transit time measurement in wide river channels, the station has conducted ultrasonic dual-machine transit time flow measurement experiments for over ten years, generating a wealth of experimental data.

[0097] (1) Verification of the conversion between laminar velocity and cross-sectional velocity

[0098] The data of 92 ultrasonic transit time method two-layer velocity measurement tests at Xiangtan Station were collected. The transit time method velocity measurement layer settings are as follows:

[0099] (1) When the water level is higher than 38.50 m, the velocity measurement layers of the time difference method are the fixed elevation layers of 30.0 m and 37.5 m (the frozen base elevation of the hydrological station, the same below);

[0100] (2) When the water level is between 34.50m and 37.50m, the time difference velocity measurement layers are the fixed elevation layers of 30.0m and 34.2m.

[0101] The logarithmic water surface velocity coefficient K0 is calculated using 92 ultrasonic time difference method velocity measurement data using formula (1). Then, the relationship line between water level and water surface velocity coefficient is drawn. Then, the water surface velocity coefficient K0 at different water levels is calculated based on the water level and water surface velocity coefficient. Combined with the river section measurement data, the relationship between the upper and lower water levels and the layer velocity coefficient of the logarithmic velocity distribution is solved using formulas (2) and (3).

[0102] The above 92 time difference speed measurement tests were conducted simultaneously with the rotor velocity meter carried by the survey ship. The flow amplitude of the 92 flow measurements was 493m 3 / s~19200m 3 / s. Take the velocity value of any layer in the two-layer velocity measurement test, and solve the flow value of the time difference method from the corresponding layer velocity coefficient according to formula (4). Taking the measurement results of the rotor flowmeter as the standard value, calculate the single flow error, systematic error, standard deviation and random uncertainty respectively.

[0103] (1) Single flow error:

[0104]

[0105] Where: R i is the relative error of the i-th flow rate, %; Q ms，i The flow value calculated by the time difference method for the i-th measurement, m 3 / s;Q mc，i is the flow rate value measured by the multi-line and multi-point method of the i-th rotor flowmeter, m 3 / s.

[0106] (2) Systematic error:

[0107]

[0108] Where: m Q is the flow system error, %; n is the total number of flow measurements.

[0109] (3) Standard deviation:

[0110]

[0111] Where: σ Q is the flow standard deviation, %; the other symbols have the same meanings as before.

[0112] (4) Random uncertainty:

[0113] X' Q =2σ Q (twenty one)

[0114] Where: X' Q is the random uncertainty with a confidence level of 95%; the other symbols have the same meanings as before.

[0115] The error results of the 92 flow measurements calculated above are listed in Table 1. It can be seen that the measurement accuracy is relatively high. Compared with the "River Flow Measurement Specification", its error can reach the flow measurement accuracy requirements of Class I hydrological stations.

[0116] Table 1 shows the flow error statistics of the time difference method calculated from the single layer velocity coefficient.

[0117] Single flow error range (%) -5.0～4.9 System error (%) -0.1 Standard deviation of measurements (%) 2.5 Random uncertainty of measurement times (%) 5.0

[0118] (2) Layer 2 single speed test instant conversion traffic verification

[0119] The previous verification calculation calculates flow by collecting data from multiple velocity measurements and establishing an average relationship between water level and the surface velocity coefficient. This method, when applied to a newly established station using the time-difference method, still requires some initial data collection time. Velocity distribution parameters (such as the surface velocity coefficient and laminar velocity coefficient) are obtained by measuring the velocity of two water layers. Only after establishing a relationship between the velocity coefficient and the water level or other factors at the test section can the laminar velocity and cross-sectional velocity be converted.

[0120] From formula (1), we can see that each single two-layer horizontal velocity measurement can instantly calculate the water surface velocity K0 corresponding to the logarithmic distribution. Substituting K0 into formulas (2) and (3) can obtain the laminar velocity coefficient corresponding to the logarithmic distribution of the two horizontal layers. Therefore, the conversion coefficient between laminar velocity and cross-sectional average velocity can be directly obtained through a single ultrasonic time-difference method two-layer velocity measurement. The laminar velocity coefficient was independently solved for 92 ultrasonic time-difference method two-layer velocity measurement data and the flow rate was calculated accordingly. The results of the rotor flow meter synchronous flow measurement were also used as the standard value, and the error statistics were performed. The results are listed in Table 2.

[0121] Table 2 is the flow error statistics of the two-layer method single speed measurement self-rate timing difference method

[0122] Single flow error range (%) -7.0～7.5 System error (%) -0.5 Standard deviation of measurements (%) 4.0 Random uncertainty of measurement times (%) 8.0

[0123] As can be seen from the table above, due to the influence of flow velocity pulsation and other accidental factors, the flow error when converting laminar flow velocity directly from a single two-layer velocity measurement to cross-sectional flow velocity is larger than the flow error calculated by establishing a laminar flow coefficient conversion relationship using multiple two-layer velocity measurements. Compared with the "River Flow Measurement Specification," the errors shown in Table 2 essentially meet the Class II accuracy requirements for flow measurement at hydrological stations.

[0124] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0125] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention.

[0126] The above is only a preferred embodiment of the present invention. It should be pointed out that due to the limitations of textual expression, there are objectively infinite specific structures. For ordinary technicians in this technical field, without departing from the principles of the present invention, they can make several improvements, modifications or changes, and can also combine the above technical features in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the inventive concept and technical solution to other occasions without improvement, should be regarded as the scope of protection of the present invention.

Claims

1. A self-calibration method for a river flow measurement system using a two-layer velocity measurement method and a time difference method, characterized in that: The steps include: (1) Install upper and lower layers of ultrasonic transducers in the river section; (2) using the ultrasonic transducer to synchronously measure the actual flow velocity of the upper and lower layers, and observing the water level Z of the river section according to the water level observation standard; (3) Using the velocity coefficient conversion model based on logarithmic velocity distribution, the measured velocity v of the upper and lower layers is θ1 、v θ2 The water surface velocity coefficient K0 is deduced from the river section measurement data, and then the upper layer velocity coefficient k corresponding to this flow measurement is deduced from the water surface velocity coefficient K0 and the river section measurement data. θ1 and the lower layer velocity coefficient k θ2 ; (4) According to the measured water level Z, the cross-sectional area A of the river corresponding to the measured water level Z is obtained from the actual measured value of the section; (5) The measured flow velocity v in the upper layer θ1 and the upper layer velocity coefficient k θ1 The product of the velocity v of the lower layer θ2 and the upper layer velocity coefficient k θ2 The average flow velocity of the cross section is calculated by the product of (6) Average flow velocity of the cross section and the cross-sectional area A, calculate the real-time flow rate Q by the velocity-area method; (7) Repeat steps (2) to (6) for several times, and draw the correlation diagram between the water level Z and the water surface velocity coefficient K0 at each flow measurement. Draw the relationship line between the water level Z and the water surface velocity coefficient K0 according to the distribution center of the point group, that is, the Z~K0 relationship line. Then, the corresponding K0 and cross-sectional measurement data of each water level are obtained by tracing the Z~K0 relationship line, and the upper and lower layer velocity coefficients k corresponding to each water level are calculated. θ1 、k θ2 And establish the relationship line between water level and upper and lower layer velocity coefficient, namely Z~k θ1 、Z~k θ2 Relationship line, by the Z~k θ1 、Z~k θ2 The relationship line is calculated based on the water level to calculate the velocity coefficient k of the upper and lower layers. θ1 、k θ2 Then, go to steps (5) to (6) to calculate the average flow velocity and flow rate of the cross section to improve the flow measurement accuracy.

2. The self-calibration method of a two-layer velocity measurement mode time difference method river flow measurement system according to claim 1 is characterized in that: In step (3), The water surface velocity coefficient calculation formula is: in, Where: K0 is the water surface velocity coefficient; B1 is the width of the upper horizontal layer; B2 is the width of the lower horizontal layer; v θ1 is the measured velocity of the upper layer; v θ2 is the measured flow velocity of the lower layer; h μ is the average water depth of the μth part, μ = 1, 2, ..., n; b μ is the water surface width of the μth part of the area; j1 represents the starting perpendicular number below the upper layer; j2 represents the starting perpendicular number below the lower layer; m1 represents the final perpendicular number below the upper layer; m2 represents the final perpendicular number below the lower layer; θ is the relative water depth calculated from the river bottom, and its value is between 0 and 1.

3. The self-calibration method of a two-layer velocity measurement method time difference method river flow measurement system according to claim 1 is characterized in that: In step (3), The upper layer velocity coefficient calculation formula is: The calculation formula of the lower layer velocity coefficient is: in, Where: k θ1 is the upper layer velocity coefficient; k θ2 is the velocity coefficient of the lower layer; the other symbols have the same meanings as above.

4. The self-calibration method of a two-layer velocity measurement method time difference method river flow measurement system according to claim 1 is characterized in that: In step (6), the real-time flow Q is calculated as: Where: Q is the flow rate; A is the cross-sectional area of ​​the river; is the average flow velocity of the section; the other symbols have the same meanings as above.

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