Open channel flow velocity measurement method based on liquid level gradient

Abstract

The invention discloses an open channel flow velocity measurement method based on liquid level gradient, and belongs to the technical field of open channel measurement, and the method specifically comprises the steps: arranging two water surface measurement devices at the upstream and downstream positions of a to-be-measured open channel, and continuously and repeatedly measuring the water surface elevation of the position through the water surface measurement devices; for any position, acquiring a water surface height program sequence of the position, sequentially putting numerical values in the sequence into a preset set, and when a numerical value contained in the set reaches n, rejecting a water surface elevation numerical value with the earliest measurement time in the set at the moment; continuously calculating the variance of all the water surface elevation values in the set, when the variance is smaller than a preset threshold value, acquiring the water surface elevation measurement time with the earliest measurement time in the current set, marking the water surface elevation measurement time as node time, respectively acquiring node time corresponding to upstream and downstream positions, and measuring the water body flow velocity of the open channel to be measured according to the node time difference and the distance; according to the invention, accurate measurement of the open channel flow velocity in a stable state is 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 measurement method based on liquid surface gradient. Background Art

[0002] The measurement of open channel flow velocity is of great significance for water resource management, water conservancy project design and environmental protection. Traditional methods for measuring open channel flow velocity mainly include mechanical velocimeters, electromagnetic flowmeters, ultrasonic flowmeters, etc. These methods can measure open channel flow velocity to a certain extent, but there are still some shortcomings. For example, mechanical velocimeters are easily affected by water flow fluctuations and have low accuracy; although electromagnetic flowmeters and ultrasonic flowmeters have high accuracy, the equipment cost is high and the environmental conditions are more stringent. Therefore, a simple, accurate and low-cost method for measuring open channel flow velocity is needed.

[0003] The liquid level gradient method is a flow velocity measurement method based on the continuity equation and energy equation of open channel flow. By measuring the water surface elevation difference between the upstream and downstream sections of the open channel, combined with the geometric dimensions and hydraulic conditions of the open channel, the average flow velocity of the open channel can be calculated.

[0004] The invention patent with the publication number CN112067841A discloses a device and method for measuring the flow velocity in an open channel by using the time difference of the liquid level. 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 gauges, the average flow velocity of the water flow in the liquid level gauge installation interval can be calculated; however, this method still has certain limitations in practical applications. Since the water surface fluctuates violently when the water is initially released in the open channel, measuring the time difference when the upstream and downstream liquid level change values ​​are the same does not mean that the change in the liquid level is caused by the same reason, which leads to misjudgment of the measurement. Summary of the invention

[0005] The purpose of the present invention is to provide an open channel flow velocity measurement method based on liquid level gradient to solve the following technical problems:

[0006] Since the water surface fluctuates violently when water is initially released into the open channel, measuring the time difference when the upstream and downstream liquid level changes are the same does not mean that the liquid level changes are caused by the same reason, which can lead to misjudgment of the measurement.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for measuring flow velocity in an open channel based on liquid level gradient comprises the following steps:

[0009] Two water surface measuring devices are set at the upstream and downstream positions of the open channel to be measured, and the distance between the upstream and downstream positions is set to D. The water surface measuring device is fixed at the bottom of the open channel slope, and the water surface elevation at the position is continuously and reciprocally measured by the water surface measuring device. The water surface elevation is the height of the open channel liquid level relative to the bottom of the open channel slope;

[0010] For any position, obtain the water surface elevation sequence of the position, and put the values ​​in the sequence into a preset set in sequence. The number of values ​​contained in the set is set to n. When the number of values ​​contained in the set reaches n, the water surface elevation value with the earliest measurement time in the set is removed;

[0011] Continuously calculate the variance of all water surface elevation values ​​in the set. When the variance is less than the preset threshold, obtain the water surface elevation with the earliest measurement time in the current set and mark it as the node elevation. Mark the specific measurement time of the node elevation as the node time, and obtain the node time t1 corresponding to the upstream position and the node time t2 corresponding to the downstream position respectively. Measure the water flow velocity of the open channel to be measured based on the node time difference and the distance between them.

[0012] As a further solution of the present invention: the water surface measuring device drives the measuring needle to move toward the water surface through a stepper motor, and adjusts the step angle and pulse number of the stepper motor to control the movement speed and accuracy of the measuring needle. When the measuring needle touches the water surface, the current extension length of the measuring needle is obtained, and the water surface elevation at this time is calculated according to the extension length, and then the measuring needle is driven upward to leave the water surface. When the measuring needle moves upward to the initial position, the measuring needle is driven downward again to move toward the water surface.

[0013] As a further solution of the present invention: recording the extended length of the measuring needle and the corresponding measuring time by an encoder;

[0014] A timer is set to control the movement cycle of the measuring needle. In each cycle, the measuring needle is controlled to move upward for a certain distance, then move downward for a certain distance, and repeat this cycle. The movement frequency and cycle of the measuring needle can be changed by adjusting the parameters of the timer.

[0015] As a further solution of the present invention: the recorded data of the encoder is transmitted wirelessly to a remote monitoring center in real time, and a curve chart showing the change of water surface elevation over time is drawn in real time.

[0016] As a further solution of the present invention: the specific process of obtaining the node elevation is:

[0017] The water surface elevations are sorted in chronological order to obtain a water surface elevation sequence H1, H2, ..., H m, m>n, the water surface elevation values ​​in the water surface elevation sequence are placed into the preset set in order. When the number of values ​​in the set reaches n, the water surface elevation value with the highest measurement time in the current set is deleted. Each time a new water surface elevation value is placed, the earliest water surface elevation value is deleted. Each time a new water surface elevation value is placed, all water surface elevation data H in the current set are calculated. i , H i+1 , ..., H i+n-1 When the variance is lower than the preset threshold for three consecutive times, the water surface elevation with the earliest measurement time in the set when the first variance is lower than the preset threshold is marked as the node elevation.

[0018] As a further solution of the present invention: the water surface elevation collected each time the measuring needle touches the water surface when it moves downward is marked as Ha, and the water surface elevation collected when the measuring needle moves upward and leaves the water surface is marked as Hb, and the difference between Ha and Hb is calculated, and the water surface elevation whose difference is less than the preset error is not counted in the valid water surface elevation value.

[0019] As a further solution of the present invention: the number of values ​​n that the set can accommodate is set according to the water flow and the open channel slope. When the water flow and the open channel slope increase, the number of values ​​n that the set can accommodate is increased.

[0020] Beneficial effects of the present invention:

[0021] The present invention sets a water surface measuring device at the upstream and downstream positions of the open channel, continuously measures the water surface elevation, and obtains the node elevation and node time by calculating the variance in the set, thereby calculating the water flow rate. This method uses a stepper motor to drive the measuring needle to accurately control the movement speed and accuracy of the measuring needle, combines an encoder to record the extension length of the measuring needle and the corresponding measurement time, and a timer to control the measurement cycle, thereby realizing real-time monitoring of water surface elevation changes and data transmission. By setting a suitable set size and a preset threshold, the water flow rate when the water level is in a stable state is measured, ensuring the validity and accuracy of the data. In addition, the influence of water flow and open channel slope on the set size is taken into account, which improves the adaptability and flexibility of the measurement. Overall, this measurement method provides an efficient, accurate and automated way to monitor and calculate the water flow rate in the open channel, which is helpful for water resource management and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings.

[0023] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] See also Figure 1 As shown, the present invention is a method for measuring open channel flow velocity based on liquid level gradient, comprising the following steps:

[0026] First, a water level measuring device is placed upstream and downstream of the open channel. The two devices are separated by a certain distance D and firmly fixed to the bottom of the slope or the bank of the open channel. These devices can continuously perform reciprocating measurements to capture the changes in the water surface elevation at their location. The water surface elevation here refers to the height of the liquid level in the open channel relative to the bottom of the slope.

[0027] For each measurement point, the system collects a series of water surface elevation data and stores them in a preset collection in chronological order. The design capacity of this collection is n data points. Once the data in the collection reaches the maximum capacity, the system will automatically remove the earliest water surface elevation value to ensure that the collection is always up to date.

[0028] Next, the system will continue to calculate the variance of all water surface elevation values ​​in the set. Variance is an important statistic to measure the degree of data dispersion. When its value is less than a preset threshold, it indicates that the current open channel liquid surface elevation fluctuation is small and the fluctuation is relatively stable. Different preset thresholds are appropriately set according to the hydrological conditions of different open channels to determine the process of the water surface changing from violent fluctuations to stable fluctuations. At this time, the system will extract the water surface elevation value with the earliest measurement time in the set and mark it as "node elevation", and record the corresponding measurement time, namely "node time". By comparing the node times of the upstream and downstream positions (represented as t1 and t2 respectively), combined with the distance D between the two measurement points, the flow velocity of the open channel water body can be calculated. The distance D is set according to the actual situation. The water surface flow velocity can be measured by a simple method, so that the distance between the two measurement points is set to an appropriate distance to ensure that there is enough node difference time for measurement.

[0029] The present invention sets a water surface measurement device at the upstream and downstream positions of the open channel, continuously measures the water surface elevation, and obtains the node elevation and node time by calculating the variance of the set, thereby calculating the water flow rate. This method uses a stepper motor to drive the measuring needle to accurately control the movement speed and accuracy of the measuring needle, combines an encoder to record the extension length of the measuring needle and the corresponding measurement time, and a timer to control the measurement cycle, thereby realizing real-time monitoring of water surface elevation changes and data transmission. By setting a suitable set size and a preset threshold, the water flow rate when the water level is in a stable state is measured, ensuring the validity and accuracy of the data.

[0030] In another preferred embodiment of the present invention, the water surface measuring device drives the measuring needle to move toward the water surface through a stepper motor. Specifically, the step angle and pulse number of the stepper motor are adjusted to accurately control the movement speed and accuracy of the measuring needle. When the measuring needle contacts the water surface, the system obtains the current extension length of the measuring needle and converts the water surface elevation at this time based on the length. Then, the measuring needle is driven upward to leave the water surface, and when the measuring needle moves upward to the initial position, the measuring needle is driven downward again to move toward the water surface to achieve continuous reciprocating measurement. This design ensures the accuracy and continuity of the measurement, and provides reliable data support for the accurate measurement of open channel flow rate.

[0031] In this embodiment, the use of a stepper motor is key. The stepper motor can accurately control the movement of the measuring needle, including speed, direction and distance. By adjusting the step angle and pulse number of the stepper motor, the movement speed and accuracy of the measuring needle can be accurately controlled, thereby ensuring the accuracy of the measurement results.

[0032] When the measuring needle touches the water surface, the system will immediately obtain the current extended length of the measuring needle. This length is an important parameter because it is directly related to the calculation of the water surface elevation. The system will calculate the current water surface elevation based on this length and other related parameters.

[0033] Then, the system will drive the measuring needle upward to leave the water surface. Since the measuring needle has a small diameter and does not penetrate the water surface, it will not be impacted by the water flow and affect the measurement stability. When the measuring needle moves upward to the initial position, the system will drive the measuring needle downward again to move toward the water surface to start the next round of measurement, and generate a sequence of the water surface elevation data obtained from each measurement.

[0034] In another preferred embodiment of the present invention, the extended length of the measuring needle and the corresponding measuring time are recorded by an encoder. The encoder is a high-precision sensor device that can accurately record the extended length of the measuring needle and the corresponding measuring time in real time. These data are crucial for subsequent flow velocity calculations.

[0035] Set a timer to control the movement cycle of the measuring needle. In each cycle, the measuring needle is controlled to move up a certain distance, then move down a certain distance, and repeat this cycle. By adjusting the parameters of the timer, the movement frequency and cycle of the measuring needle can be changed. This design enables the system to flexibly adjust the movement state of the measuring needle according to actual needs to adapt to different water flow conditions and measurement requirements.

[0036] An encoder is a sensor device that can convert rotational or linear displacement into an electrical signal output. It can accurately measure information such as the position, velocity, and acceleration of an object. By using an encoder to record the extension length of the measuring needle and the corresponding measurement time, the accuracy and reliability of the measurement data can be ensured. At the same time, the system also sets a timer to control the movement cycle of the measuring needle. A timer is an electronic device that can trigger an event at a set time interval. It can set different time intervals as needed to control the movement frequency and cycle of the measuring needle. By adjusting the parameters of the timer, the movement frequency and cycle of the measuring needle can be changed to adapt to different water flow conditions and measurement requirements.

[0037] In another preferred embodiment of the present invention, the recorded data of the encoder is transmitted to a remote monitoring center in real time by wireless means. This wireless transmission method is not only convenient and fast, but also can ensure the real-time and accuracy of the data. The monitoring center can receive the data from the scene in real time and conduct further analysis and processing.

[0038] In the remote monitoring center, the received data is used to draw a real-time curve graph of the water surface elevation over time. By observing the trend and change pattern of the curve graph, the change of open channel flow rate can be more intuitively understood. At the same time, the curve graph can also be saved and analyzed as historical data, providing strong support for future water resources management and decision-making.

[0039] In another preferred embodiment of the present invention, the specific process of obtaining the node elevation is:

[0040] 1. Construction of water surface elevation series

[0041] Data collection and sorting: First, the system collects the water surface elevation data of each measuring point in the canal in real time or regularly. These data are arranged in chronological order to form an orderly water surface elevation sequence H1, H2, ..., H m , where m represents the number of data points, and m is greater than n (n is the preset set size).

[0042] Sliding window set: In order to capture the short-term change trend of water surface elevation and reduce the impact of noise, a sliding window set of size n is used. This set is continuously updated as new data is added, and always contains the latest n water surface elevation values.

[0043] 2. Dynamic adjustment and variance calculation

[0044] Set update strategy: Whenever a new water surface elevation value Hi+1 enters the set, the oldest value Hi in the set (i.e. the value that entered the set earliest) will be deleted. This "first in, first out" strategy ensures that the set always contains the most recent n measured values, reflecting the latest water surface elevation status.

[0045] Variance calculation: After each collection is updated, all water surface elevation data in the current collection are calculated immediately Hi ,H i+1 ,...,H i+n-1 Variance. Variance is an important statistic to measure the dispersion of values ​​in a data set. Low variance means that the difference between data points is small, that is, the water surface elevation is relatively stable.

[0046] 3. Node elevation determination

[0047] Stability judgment: In order to ensure the accuracy and reliability of node elevation, the system not only focuses on the calculation results of single variance, but also introduces a mechanism for multiple consecutive variance comparisons. Specifically, if the variance calculated three times in a row is lower than the preset threshold, it is considered that the current water surface elevation data has achieved sufficient stability.

[0048] Node elevation marking: When the above stability conditions are met, the system marks the earliest water surface elevation value in the set when the first variance is lower than the preset threshold as the node elevation. This value is considered to be the most representative and stable water surface elevation point in the time period and can be used as the basis for subsequent analysis, comparison or control.

[0049] Through this method of dynamic adjustment, continuous monitoring and variance comparison, the present invention can accurately extract stable node elevations from a series of changing water surface elevation data. This not only improves the accuracy and reliability of measurement, but also provides important data support for the management and optimization of the canal system.

[0050] In another preferred embodiment of the present invention, in order to ensure the accuracy and reliability of the measured data and eliminate the influence of sewage data with low surface tension, a differential analysis of the measured data is introduced. Specifically, the water surface elevation collected each time the measuring needle touches the water surface is marked as Ha, and the water surface elevation collected when the measuring needle leaves the water surface is marked as Hb. By calculating the difference in water surface elevations under these two states (Ha-Hb), the errors that may occur during the measurement process can be evaluated.

[0051] In another preferred embodiment of the present invention, the number of values ​​n that can be accommodated in the set is set according to the water flow rate and the open channel slope. Specifically, when the water flow rate and the open channel slope increase, the number of values ​​n that can be accommodated in the set will increase. This design takes into account the data requirements under different hydrological conditions and ensures the accuracy and reliability of the measurement results.

[0052] In practical applications, water flow and open channel slope are important factors that affect the change of water surface elevation. When the water flow is large or the open channel slope is steep, the change of water surface elevation will be more frequent and drastic. Therefore, in order to capture these changes more accurately and calculate the variance, it is necessary to increase the number of values ​​n that can be accommodated in the set. In this way, the variance can be calculated in a larger sample space, thereby reducing the impact of accidental errors and improving the stability and reliability of the measurement results.

[0053] 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 measuring open channel flow velocity based on liquid level slope, characterized in that: The following steps are involved: Two water surface measuring devices are set at the upstream and downstream positions of the open channel to be measured, and the distance between the upstream and downstream positions is set to D. The water surface measuring device is fixed at the bottom of the open channel slope, and the water surface elevation at the position is continuously and reciprocally measured by the water surface measuring device. The water surface elevation is the height of the open channel liquid level relative to the bottom of the open channel slope; For any position, obtain the water surface elevation sequence of the position, and put the values ​​in the sequence into a preset set in sequence. The number of values ​​contained in the set is set to n. When the number of values ​​contained in the set reaches n, the water surface elevation value with the earliest measurement time in the set is removed; Continuously calculate the variance of all water surface elevation values ​​in the set. When the variance is less than the preset threshold, obtain the water surface elevation with the earliest measurement time in the current set and mark it as the node elevation. Mark the specific measurement time of the node elevation as the node time, and obtain the node time t1 corresponding to the upstream position and the node time t2 corresponding to the downstream position respectively. Measure the water flow velocity of the open channel to be measured based on the node time difference and the distance between them.

2. The method for measuring open channel flow velocity based on liquid level gradient according to claim 1, characterized in that: The water surface measuring device drives the measuring needle to move toward the water surface through a stepper motor, and adjusts the step angle and pulse number of the stepper motor to control the movement speed and accuracy of the measuring needle. When the measuring needle touches the water surface, the current extension length of the measuring needle is obtained, and the water surface elevation at this time is calculated according to the extension length, and then the measuring needle is driven upward to leave the water surface. When the measuring needle moves upward to the initial position, the measuring needle is driven downward again to move toward the water surface.

3. The method for measuring open channel flow velocity based on liquid level gradient according to claim 2, characterized in that: The extended length of the measuring needle and the corresponding measuring time are recorded by an encoder; A timer is set to control the movement cycle of the measuring needle. In each cycle, the measuring needle is controlled to move upward for a certain distance, then move downward for a certain distance, and repeat this cycle. The movement frequency and cycle of the measuring needle can be changed by adjusting the parameters of the timer.

4. The method for measuring open channel flow velocity based on liquid level gradient according to claim 3, characterized in that: The recorded data of the encoder is transmitted wirelessly to the remote monitoring center in real time, and a curve chart showing the change of water surface elevation over time is drawn in real time.

5. The method for measuring open channel flow velocity based on liquid level gradient according to claim 1, 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>n, the water surface elevation values ​​in the water surface elevation sequence are placed into the preset set in order. When the number of values ​​in the set reaches n, the water surface elevation value with the highest measurement time in the current set is deleted. Each time a new water surface elevation value is placed, the earliest water surface elevation value is deleted. Each time a new water surface elevation value is placed, all water surface elevation data H in the current set are calculated. i , H i+1 , ..., H i+n-1 When the variance is lower than the preset threshold for three consecutive times, the water surface elevation with the earliest measurement time in the set when the first variance is lower than the preset threshold is marked as the node elevation.

6. The method for measuring open channel flow velocity based on liquid level gradient according to claim 2, characterized in that: The water surface elevation collected each time the measuring needle touches the water surface is marked as Ha, and the water surface elevation collected when the measuring needle leaves the water surface as Hb. The difference between Ha and Hb is calculated, and the water surface elevation for which the difference is less than the preset error is not included in the valid water surface elevation value.

7. The method for measuring open channel flow velocity based on liquid level gradient according to claim 1, characterized in that: The number of values ​​n that the set can accommodate is set according to the water flow and the slope of the open channel. When the water flow and the slope of the open channel increase, the number of values ​​n that the set can accommodate is increased.

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