Open channel flow velocity monitoring method based on data analysis

Abstract

The invention discloses an open channel flow velocity monitoring method based on data analysis, and belongs to the technical field of open channel measurement, and the method specifically comprises the steps: setting a measurement point at each of the upstream and downstream of an open channel, measuring the water surface elevation of the measurement points through a millimeter-wave radar, carrying out the sliding window and normalization processing of the water surface elevation data of each position, and obtaining the flow velocity of the open channel. The method comprises the following steps: determining node elevations when fluctuations are the same through dispersion analysis, recording corresponding node time, comparing upstream and downstream node time differences and distances to calculate the water body flow velocity, setting an initial measurement period t and period duration, and measuring the flow velocity once every t time, calculating a mean value, a data proportion m exceeding an interval and a slope k obtained by performing piecewise linear fitting on the broken line graph, calculating an adjustment coefficient alpha based on an index in the previous period after each complete period T, and then adjusting a measurement interval in the next period by using alpha; according to the invention, accurate measurement of the flow velocity of the open channel and dynamic adjustment of the measurement period are realized.

Description

Technical Field

[0001] The invention relates to the technical field of open channel measurement, and in particular to an open channel flow velocity monitoring method based on data analysis. Background Art

[0002] Open channel velocity measurement occupies a core position in hydrological research and has far-reaching significance for water resources management, flood prevention and disaster reduction, environmental protection and water conservancy project design. It is not only related to the accurate determination of water flow velocity, but also involves multiple aspects such as flow estimation, water quality monitoring and ecosystem health assessment. Through scientific velocity measurement technology, such as ultrasonic Doppler method, radar velocity measurement and other non-contact methods, combined with traditional flow meters and water level meters, it is possible to accurately monitor the flow state of water bodies such as rivers, channels and drainage systems. These data provide a solid foundation for the rational allocation of water resources, early warning of flood risks, and protection of the ecological environment, and are an indispensable technical support for modern water management.

[0003] In traditional open channel flow velocity measurement, the average velocity of the water flow in the liquid level meter installation interval is calculated by measuring the time difference when the upstream liquid level change value is the same as the downstream liquid level change value, and combining it with the spacing between the upstream and downstream liquid level meters. However, in actual applications, due to the different hydrological conditions at the upstream and downstream locations, the liquid level changes caused by the same water flow at the upstream and downstream locations are also different. Therefore, by measuring the same liquid level change value, it is not possible to accurately calculate the flow time and flow velocity of the same water flow between the upstream and downstream. The existing technology also lacks dynamic adjustment of the flow rate measurement cycle. It often uses a fixed period for measurement and cannot monitor the change of water flow rate in time. When the water flow rate is too slow, it will cause sediment and other suspended matter to settle at the bottom of the channel, thereby reducing the effective water-passing section and affecting the water conveyance capacity of the channel. It will also increase the time that the water body is in contact with the air, resulting in more water evaporation loss. When the water flow rate is too fast, it will cause greater impact and wear on the channel wall, shorten the service life of the channel, and may cause damage to the channel structure and the soil base of the farmland. Therefore, it is necessary to make the flow rate measurement cycle dynamic according to the flow rate, so as to promptly detect the situation where the open channel flow rate is too fast or too slow. Summary of the invention

[0004] The purpose of the present invention is to provide a method for monitoring open channel flow rate based on data analysis to solve the following technical problems: Due to the different hydrological conditions at upstream and downstream locations, the flow time and velocity of the same water flow between upstream and downstream cannot be accurately calculated simply by measuring the same liquid level change value. The existing technology also lacks dynamic adjustment of the flow velocity measurement cycle and cannot monitor changes in water flow velocity in a timely manner.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A method for monitoring open channel flow velocity based on data analysis comprises the following steps: A measuring point is set at each upstream and downstream position of the open channel, and the distance between the two measuring points is set to D. The measuring points measure the water surface elevation of the liquid surface in the open channel based on the millimeter wave radar, and the water surface elevation is the height of the liquid surface in the open channel relative to the bottom of the slope of the open channel; For any position, obtain the water surface elevation sequence at that position, perform sliding window processing on the water surface elevation sequence, and normalize the water surface elevation data in the window. Analyze the water surface elevation data when the upstream and downstream water surface fluctuations are the same based on the discreteness, mark them as node elevations, mark the specific measurement time of the node elevation as node time, obtain the node times corresponding to the upstream and downstream positions respectively, and measure the water flow velocity v of the open channel to be measured according to the node time difference and the distance D between them; Set the initial measurement cycle t and the cycle duration T, measure the water flow velocity v in the open channel every measurement cycle t, and obtain the water flow velocity sequence v1, v2, ..., v n , and draw the corresponding line graph, where n=T / t, n is a positive integer, and calculate the mean value v of the water velocity series a , the proportion m of the number of values ​​exceeding the set interval [A, B] in the water velocity sequence accounts for the total number n, and the line graph is piecewise linearly fitted to calculate the slope k of each piecewise linear equation; Every cycle lasts T, the measurement adjustment coefficient α is calculated based on the indicators obtained in the previous cycle lasting T, the indicators include the mean value v a , ratio m and slope k, the calculation formula of the adjustment coefficient α is: ; Among them, k i represents the slope of the i-th segment in the line graph, i∈[1,n-1], k min Indicates the minimum value of all segment slope values ​​of the line graph, k max It represents the maximum value of all segment slope values ​​of the line graph. A and B represent the two endpoint values ​​of the set interval [A, B]. According to the obtained adjustment coefficient α, the measurement period t' within the duration T of the next period is adjusted and calculated, t'=t / α.

[0006] As a further solution of the present invention: the number of flow velocity measurements n'=T / t' within the adjusted single cycle duration T is calculated. When the calculation result n' is not an integer, the value of n' is rounded up to obtain N, and the optimized measurement cycle t'=T / N.

[0007] As a further solution of the present invention: the specific process of obtaining the node elevation is: The water surface elevations are sorted in chronological order to obtain a water surface elevation sequence H1, H2, ..., H M , M is a positive integer, and the water surface elevation values ​​in the water surface elevation sequence are sequentially placed into the window, and the number of values ​​accommodated in the window is set to X, and W1, W2, ..., W are obtained. X , when the number of values ​​in the window reaches X, X is a positive integer, and X<M, then the earliest water surface elevation value measured in the current window is deleted. Each time a new water surface elevation value is added, the earliest water surface elevation value is deleted, and the sequence number is reallocated. The normalized data sequence is marked as w1, w2, ..., w X , each time it is put in, all the data w1, w2, ..., w in the current window are calculated X When the difference between the two variances of the upstream and downstream of five consecutive windows is less than the preset threshold, the water surface elevation data with the earliest measurement time in the five windows is marked as the node elevation.

[0008] As a further solution of the present invention: the number of numerical values ​​X that the window can accommodate is set according to the open channel water discharge flow rate. When the water flow rate increases, the number of numerical values ​​that the window can accommodate is increased in proportion to the increase in the water flow rate.

[0009] As a further solution of the present invention: the formula for the normalization process is: ; where w j represents the jth normalized value in the window, j∈[1,X], W j represents the jth value in the window, W min Indicates the minimum value in the window, W max Indicates the maximum value in the window.

[0010] As a further solution of the present invention: in the window, each time a new water surface elevation value is placed, and each time the earliest water surface elevation value in the current window is deleted, the serial number of the data sequence is reallocated, and the serial number of the earliest water surface elevation value in the window is updated to 1.

[0011] As a further solution of the present invention: it also includes calculating the average value of the water surface flow velocities upstream and downstream based on the water surface flow velocity at the measuring point measured by the millimeter wave radar, and calculating the absolute value of the difference between the average value and the water flow velocity v, and the ratio of the absolute value of the difference to the water flow velocity v, and proportionally increasing the number of water flow velocity measurements within the cycle duration T according to the ratio.

[0012] Beneficial effects of the present invention: (1) The present invention collects data in the water surface elevation sequence in real time through a sliding window. Due to hydrological conditions, even when the same water flow passes through upstream and downstream locations, the absolute values ​​of the water surface fluctuations at the two locations are not the same, but the trend and relative change of the water surface fluctuations caused by the water flow are similar. Therefore, the present invention sets a sliding window of fixed length and normalizes the values ​​in the window to eliminate the influence of the data magnitude on the calculation, thereby better reflecting the waveform trend of the up and down fluctuations of the water flow, thereby more accurately obtaining the node time when the same water flow passes through the upstream and downstream locations, and thus calculating the flow rate of the open channel water body in the interval; (2) The present invention sets an initial measurement period t and a period duration T, and uses the mean value of the water flow velocity to represent the flow velocity of the water flow. The fluctuation of the water body is represented by the ratio of the values ​​exceeding the set interval within the period duration. The slope of the water flow velocity line graph is used to represent the fast or slow change trend of the water flow velocity. The initial measurement period is essentially used to represent the measurement period of the water body under absolutely stable conditions. Based on this, corresponding measurement periods are set for open channel water bodies under different conditions according to the flow velocity, fluctuation conditions and change trends. As the degree of abnormality of the water body increases, the measurement frequency is gradually increased. Compared with a measurement period of a fixed length, the abnormality of the water body can be discovered in a timely manner. When the water body is stable, the measurement frequency will also be reduced, thereby achieving the effect of energy saving and efficiency improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be further described below in conjunction with the accompanying drawings.

[0014] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 It is a measurement schematic diagram of the millimeter wave radar of the present invention. DETAILED DESCRIPTION

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] See also Figure 1-Figure 2 As shown, the present invention is a method for monitoring open channel flow rate based on data analysis, comprising the following steps: 1. Setting of measuring points: Select two suitable locations and set up a measurement point upstream and downstream of the open channel. The two points should be separated by a certain distance D, which can be determined according to the specific size of the open channel and the measurement requirements. Make sure that the locations of the two measurement points can represent the water flow conditions of the entire open channel to avoid local disturbances affecting the overall measurement results.

[0017] 2. Measurement and processing of water surface elevation: Millimeter wave radar technology is used to measure the water surface elevation of the open channel liquid level at each measuring point. First, the distance S between the millimeter wave radar and the water surface is calculated by analyzing the echo signal of the millimeter wave radar, and then the distance S is subtracted from the installation height of the millimeter wave radar relative to the bottom of the open channel to obtain the water surface elevation relative to the bottom of the open channel. This technology can provide high-precision water level measurement and is suitable for monitoring water level changes.

[0018] The acquired water surface elevation sequence is processed by sliding window to smooth the data and reduce the influence of noise. The size of the window can be adjusted according to actual needs.

[0019] Due to hydrological conditions, even when the same water flow passes through upstream and downstream locations, the absolute values ​​of the water surface fluctuations at the two locations are not the same, but the trends and relative changes of the water surface fluctuations caused by the water flow are similar. Therefore, the present invention sets a sliding window of fixed length and normalizes the values ​​in the window to eliminate the influence of data magnitude on the calculation, thereby better reflecting the waveform trend of the up and down fluctuations of the water flow, thereby more accurately obtaining the node time when the same water flow passes through the upstream and downstream locations, and thus calculating the flow rate of the open channel water body in the interval.

[0020] 3. Determination of node elevation and marking of node time: The water surface elevation data when the upstream and downstream water surface fluctuations are the same are found through the discrete degree analysis method, and these data are marked as node elevations. At the same time, the specific measurement time of these node elevations is recorded, that is, the node time.

[0021] 4. Calculation of water flow rate: According to the node time corresponding to the upstream and downstream positions and the distance D between them, the water flow velocity v of the open channel to be tested is calculated.

[0022] 5. Set the initial measurement cycle: Set the initial measurement cycle t and the cycle duration T, measure the water flow velocity v in the open channel every measurement cycle t, and obtain the water flow velocity sequence v1, v2, ..., v n , and draw the corresponding line graph, where n=T / t, n is a positive integer.

[0023] 6: Data Analysis: Calculate the mean v of the water velocity series a. Indicates the flow velocity of water in the interval.

[0024] The ratio m of the number of values ​​exceeding the set interval [A, B] to the total number n is counted. It indicates the fluctuation of the water body.

[0025] Perform piecewise linear fitting on the line graph and calculate the slope k of each piecewise linear equation, which indicates the fast or slow change trend of the water flow rate.

[0026] 7. Calculation and application of adjustment coefficient: Every cycle lasts T, the measurement adjustment coefficient α is calculated based on the indicators obtained in the previous cycle lasting T, the indicators include the mean value v a , ratio m and slope k, the calculation formula of the adjustment coefficient α is: ; Among them, k i represents the slope of the i-th segment in the line graph, that is, the slope between each pair of adjacent flow velocity coordinate points in the coordinate system where the line graph is located, i∈[1,n-1], k min Indicates the minimum value of all segment slope values ​​of the line graph, k max It represents the maximum value of all segmented slope values ​​of the line graph. A and B represent the two endpoint values ​​of the set interval [A, B] respectively. The measurement period t' within the duration T of the next period is adjusted and calculated according to the obtained adjustment coefficient α, t'=t / α. The initial measurement period t is essentially used to represent the measurement period of the water body under absolutely stable conditions. Based on this, the corresponding measurement period is set for the open channel water body under different conditions according to the flow rate, fluctuation and change trend, and the measurement frequency is gradually increased as the degree of abnormality of the water body increases.

[0027] In a preferred embodiment of the present invention, the number of flow velocity measurements within a single cycle duration T after adjustment is calculated as n'=T / t'. When the calculation result n' is not an integer, since it is necessary to ensure the validity and simplicity of the water flow velocity measurement data within each cycle duration T, as well as to facilitate calculation, the value of n' is rounded up to obtain N, and the optimized measurement cycle t'=T / N.

[0028] In another preferred embodiment of the present invention, the specific process of obtaining the node elevation is: The water surface elevations are sorted in chronological order to obtain a water surface elevation sequence H1, H2, ..., H M , M is a positive integer, and the water surface elevation values ​​in the water surface elevation sequence are sequentially placed into the window, and the number of values ​​accommodated in the window is set to X, and W1, W2, ..., W are obtained. X, X is a positive integer, and X<M. When the number of values ​​in the window reaches X, the earliest water surface elevation value measured in the current window is deleted. Each time a new water surface elevation value is added, the earliest water surface elevation value is deleted and the sequence number is reallocated. The normalized data sequence is marked as w1, w2, ..., w X , each time it is put in, all the data w1, w2, ..., w in the current window are calculated X The variance of the data in the continuous window is calculated, and a threshold is set to judge the consistency of the upstream and downstream water surface fluctuations. When the difference between the two variances of the upstream and downstream of 5 consecutive windows is less than the preset threshold, the water surface elevation data with the earliest measurement time in the 5 windows is marked as the node elevation, that is, the initial water surface elevation points with similar time periods of upstream and downstream position fluctuations. Such node elevations can more accurately reflect the true state of water flow in the open channel and provide a reliable basis for subsequent water velocity calculations.

[0029] In a preferred case of this embodiment, the number of numerical values ​​X that the window can accommodate is set according to the open channel water discharge flow rate. When the water flow rate increases, the fluctuation time caused by the same water flow will be prolonged. Therefore, it is necessary to increase the number of numerical values ​​that the window can accommodate in proportion to the increase in the water flow rate.

[0030] In another preferred embodiment of the present invention, the formula for the normalization process is: ; where w j represents the jth normalized value in the window, j∈[1,X], W j Indicates the first j values, W min Indicates the minimum value in the window, W max It represents the maximum value in the window. The values ​​in the window are normalized to eliminate the influence of data magnitude on the calculation, so as to better reflect the waveform trend of the ups and downs of the water flow.

[0031] It is worth noting that, in the window, each time a new water surface elevation value is placed, and each time the earliest water surface elevation value in the current window is deleted, the serial number of the data sequence is reallocated, and the serial number of the earliest water surface elevation value in the window is updated to 1. By dynamically updating the water surface elevation value in the sliding window and reallocating the serial number of the data sequence, the timeliness and continuity of the data are effectively maintained, which is beneficial to the subsequent normalization processing and variance calculation.

[0032] Please refer to the attached Figure 2As shown, in another preferred embodiment of the present invention, the millimeter wave radar technology is used to not only measure the water surface elevation, but also to directly or indirectly measure the water surface velocity at the measuring point. This can be achieved by analyzing the Doppler frequency shift in the radar echo signal. In the figure, L represents the distance from the farthest end of the irradiation area of ​​the radar velocity measurement beam on the water surface to the radar directly below. After the distance S is obtained by the radar ranging wave velocity measurement, the beam angle of the radar velocity measurement beam is adjusted so that the ratio of L to S is close to L=1.643S. This ensures that the length of the irradiation area can cover the representative water flow part to obtain the accurate movement speed of the water surface.

[0033] First, the surface velocity of the two measuring points upstream and downstream is averaged to obtain a comprehensive average value of the surface velocity of the upstream and downstream water bodies. This average value can be used as an important indicator to reflect the water flow state in the entire measurement area.

[0034] Then, the absolute value of the difference between the average upstream and downstream water surface velocity obtained above and the water body velocity v calculated previously by the change in water surface elevation is calculated. In addition, the ratio of the absolute value of this difference to the water body velocity v, that is, the size of the relative error, is further calculated.

[0035] Finally, the number of water velocity measurements within the cycle duration T is dynamically adjusted according to the calculated ratio. If a large difference is found between the average upstream and downstream surface velocity and the velocity calculated based on elevation changes (i.e., a high ratio), it indicates that the current measurement method may be biased or the water flow conditions are more complex. In this case, the measurement frequency should be increased to improve the reliability of the data; otherwise, the number of measurements can be appropriately reduced to save resources and improve efficiency.

[0036] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for monitoring open channel flow rate based on data analysis, characterized in that: The following steps are involved: A measuring point is set at each upstream and downstream position of the open channel, and the distance between the two measuring points is set to D. The measuring points measure the water surface elevation of the liquid surface in the open channel based on the millimeter wave radar, and the water surface elevation is the height of the liquid surface in the open channel relative to the bottom of the slope of the open channel; For any position, obtain the water surface elevation sequence at that position, perform sliding window processing on the water surface elevation sequence, and normalize the water surface elevation data in the window. Analyze the water surface elevation data when the upstream and downstream water surface fluctuations are the same based on the discreteness, mark them as node elevations, mark the specific measurement time of the node elevation as node time, obtain the node times corresponding to the upstream and downstream positions respectively, and measure the water flow velocity v of the open channel to be measured according to the node time difference and the distance D between them; Set the initial measurement cycle t and the cycle duration T, measure the water flow velocity v in the open channel every measurement cycle t, and obtain the water flow velocity sequence v1, v2, ..., v n , and draw the corresponding line graph, where n=T / t, n is a positive integer, and calculate the mean value v of the water velocity series a , the proportion m of the number of values ​​exceeding the set interval [A, B] in the water velocity sequence accounts for the total number n, and the line graph is piecewise linearly fitted to calculate the slope k of each piecewise linear equation; Every cycle lasts T, and the adjustment coefficient α is calculated based on the indicators obtained in the previous cycle lasting T. The indicators include the mean value v a , ratio m and slope k, the calculation formula of the adjustment coefficient α is: ； Among them, k i represents the slope of the i-th segment in the line graph, i∈[1,n-1], k min Indicates the minimum value of all segment slope values ​​of the line graph, k max It represents the maximum value of all segment slope values ​​of the line graph. A and B represent the two endpoint values ​​of the set interval [A, B]. According to the obtained adjustment coefficient α, the measurement period t' within the duration T of the next period is adjusted and calculated, t'=t / α.

2. The open channel flow rate monitoring method based on data analysis according to claim 1 is characterized in that: The number of flow velocity measurements within the adjusted single cycle duration T is calculated as n'=T / t'. When the calculated result n' is not an integer, the value of n' is rounded up to get N, and the optimized measurement cycle t'=T / N.

3. The open channel flow rate monitoring method based on data analysis according to claim 1 is characterized in that: The specific process of obtaining the node elevation is as follows: The water surface elevations are sorted in chronological order to obtain a water surface elevation sequence H1, H2, ..., H M , M is a positive integer, and the water surface elevation values ​​in the water surface elevation sequence are sequentially placed into the window, and the number of values ​​accommodated in the window is set to X, and W1, W2, ..., W are obtained. X , when the number of values ​​in the window reaches X, X is a positive integer, and X<M, then the earliest water surface elevation value measured in the current window is deleted. Each time a new water surface elevation value is added, the earliest water surface elevation value is deleted, and the sequence number is reallocated. The normalized data sequence is marked as w1, w2, ..., w X , each time it is put in, all the data w1, w2, ..., w in the current window are calculated X When the difference between the two variances of the upstream and downstream of five consecutive windows is less than the preset threshold, the water surface elevation data with the earliest measurement time in the five windows is marked as the node elevation.

4. The open channel flow rate monitoring method based on data analysis according to claim 3 is characterized in that: The number of numerical values ​​X that the window can accommodate is set according to the open channel water discharge flow rate. When the water flow rate increases, the number of numerical values ​​that the window can accommodate is increased in proportion to the increase in the water flow rate.

5. The open channel flow rate monitoring method based on data analysis according to claim 3 is characterized in that: The formula for the normalization process is: ； where w j represents the jth normalized value in the window, j∈[1,X], W j represents the jth value in the window, W min Indicates the minimum value in the window, W max Indicates the maximum value in the window.

6. The open channel flow rate monitoring method based on data analysis according to claim 3 is characterized in that: In the window, each time a new water surface elevation value is placed, and each time the earliest water surface elevation value in the current window is deleted, the sequence number of the data sequence is reallocated, and the sequence number of the earliest water surface elevation value in the window is updated to 1.

7. The open channel flow rate monitoring method based on data analysis according to claim 1 is characterized in that: It also includes calculating the average value of the water surface flow velocities upstream and downstream based on the water surface flow velocity at the measuring point measured by the millimeter wave radar, and calculating the absolute value of the difference between the average value and the water flow velocity v, as well as the ratio of the absolute value of the difference to the water flow velocity v, and proportionally increasing the number of water flow velocity measurements within the cycle duration T according to the ratio.

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