JPH07120279A - Measuring method for flow rate of open channel - Google Patents

Abstract

PURPOSE:To obtain a measuring method wherein a fluctuation in measured flow velocity due to a fluctuation in the water level of an open channel is avoided, a precise flow rate can be obtained, the structure can be simplified, installation cost is reduced and troublesome work is omitted. CONSTITUTION:A float-type water level meter 2 in which a float part 2A to be held always at a constant water depth is arranged and installed in an open channel 1 having a specified water-passage cross-sectional shape, an ultrasonic flow velocity meter 3 is attached to the float part 2A, a water level WL1 and a flow velocity V1 are measured, and measured values are input to an operation means 4. On the other hand, a water-passage cross-sectional area A which is found from a relationship between an actual water level WL and a water- passage cross-sectional shape and an average flow velocity V which is found by the measured flow velocity V1 are input in advance as data to the operation means 4, the water-passage cross-sectional area A and the average flow velocity V are computed on the basis of the data, the input measured water level WL1 and the measured water velocity V1, and a flow rate Q is operated (Q=A.V).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an open channel flow rate measuring method for measuring the flow rate in an open channel.

[0002]

2. Description of the Related Art Conventionally, as a flow rate measuring method of this kind, as shown in FIGS. 3 and 4, an upper portion of an open water channel 1 having a predetermined water passage sectional shape, for example, an open water channel 1 having a uniform width W. An ultrasonic water level meter 2 is arranged at the position to measure the water level H, an ultrasonic velocity meter 3 is arranged at one side of the open water channel 1 to measure the flow velocity V, and the width W of the open water channel, the water level H and the flow velocity V are measured. Is known by applying the flow rate calculation formula Q = WHHV.

By the way, the flow velocity distribution in the open channel 1 is shown in FIG.
As shown in the chart, the flow velocity near the bottom surface 1A is slower due to the frictional resistance between the bottom face 1A and water, and the flow velocity near the water surface WL is slightly slower due to the frictional resistance with the air. It has the fastest flow velocity. That is, the velocity of the water flow shows different characteristics at each point of the cross section. However, in the conventional flow rate measuring method, since the flow velocity V is measured by the ultrasonic velocity meter 3 fixed at a predetermined position, when the water level H changes, the ultrasonic velocity is not changed even though the actual flow velocity does not change. The flow velocity V measured by the flow velocity meter 3 fluctuates, and an error occurs between the actual flow velocity and the measured flow velocity V, which makes it impossible to perform accurate flow rate measurement. Also, due to the decrease in the water level H, the ultrasonic velocity meter 3 moves to the water surface W
If exposed above L, there is a concern that measurement becomes impossible.

Such a problem can be solved to some extent by disposing a plurality of ultrasonic velocity meters 3 at appropriate intervals in the depth direction of the open water channel 1. However, it has a drawback that the measurement structure becomes complicated and the equipment cost becomes high.

On the other hand, the partial flume method, that is, a narrowed portion in the width direction is formed in the open water channel 1, the water levels of this narrowed portion and other portions are measured, and the flow rate is determined from experimentally obtained water level data. Such a flow rate measuring method is also known. However, this measuring method requires a troublesome civil engineering work to form a narrowed portion in the width direction in the open water channel 1, and the construction is difficult in the large open water channel 1, so there is a problem that the applicable range is restricted. There is.

[0006]

The problem to be solved is that when the water level in the open channel fluctuates, the flow velocity measured by the anemometer also fluctuates even though the actual flow velocity does not fluctuate. , There is an error between the actual flow velocity and the measured flow velocity, and it is not possible to perform accurate flow rate measurement, and there is a concern that measurement may not be possible if the velocity meter is exposed above the water surface due to the drop in water level. However, to solve such a problem would complicate the measurement structure and increase the cost of equipment, and the measurement method of forming a narrowed part in the width direction in the open channel requires complicated civil engineering work. There is also a point that the applicable range is restricted.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, a float type water level gauge provided with a float portion which is always kept at a constant water depth is provided in an open water channel having a predetermined water passage cross section, and the float portion is provided with the float portion. A flowmeter is attached to measure the water level and flow velocity in the open water channel and take them into the calculating means. The area is calculated based on the data entered in advance, and the average flow velocity determined by the flow velocity of the constant water depth obtained by the anemometer is calculated based on the data entered in advance, and the calculated water flow cross-sectional area is calculated. It is characterized by calculating the flow rate based on the average flow velocity and the average flow velocity, avoiding the fluctuation of the measured flow velocity due to the fluctuation of the water level in the open channel, enabling accurate flow measurement, simplification of the structure and equipment. Aims to reduce the, yet to achieve the omitted purpose cumbersome civil engineering construction.

[0008]

[Operation] The cross-sectional area of water flow can be obtained from the relationship between the cross-sectional shape of the open channel and the actual water level. The actual water level is the water level measured by the float type water level meter plus the water depth at which the float type water level gauge is held. Can be determined by Further, since the anemometer is attached to the float part of the float type water level meter and is constantly maintained at a constant water depth, the distance from the water surface to the measuring point varies even if the velocity distribution changes due to fluctuations in the water level. Instead, the flow velocity is always measured at a measured water level where the flow velocity distribution is constant, and the average flow velocity can be obtained based on the measured flow velocity. Therefore, the water flow cross-sectional area obtained by the relationship between the cross-sectional shape of the open channel and the actual water level,
By inputting the average flow velocity obtained based on the measured flow velocity into the calculation means in advance, the water flow cross-sectional area can be calculated by inputting the measured water level measured by the float type water level gauge to the calculation means, Since the average flow velocity can be calculated by inputting the measured flow velocity measured by the anemometer to the calculating means, the flow amount can be calculated by the calculated water flow cross-sectional area and the average flow velocity.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. In addition, in the same or corresponding portion as the conventional example,
The description will be given with the same reference numerals. FIG. 1 is a cross-sectional front view of an open water channel applied to the practice of the present invention. In this figure, the open water channel 1 has a rectangular water passage cross-section with a uniform width W and a bottom surface 1A horizontal. A float type water level meter 2 provided with a float portion 2A which is always kept at a constant water depth D from the water surface is provided on one side of the open water channel 1, and an ultrasonic velocity meter 3 is attached to the float type water level meter 2. It is installed.

Reference numeral 4 is a calculation means, and the calculation water level WL1 measured by the float type water level gauge 2 and the measurement flow velocity V1 measured by the ultrasonic velocity meter 3 are input to the calculation means 4, and the rectangular cross section of the open water channel 1 is inputted. Shape and actual water level WL
Cross-sectional area A of water flow obtained by the relationship with the measured flow velocity V1
The average flow velocity V obtained based on the above is input as data in advance.

In the above structure, the height H1 (measured water level WL1) from the position of the float 2 to the bottom surface 1A of the open water channel 1 is measured by the float type water level gauge 2, and this value is taken into the calculating means 4. Since the water flow cross-sectional area A obtained from the relationship between the rectangular cross-sectional shape of the open water channel 1 and the actual water level WL is input as data in advance to the calculation means 4, a constant water depth D is obtained by taking in the measured water level WL1. The water flow cross-sectional area A is calculated from the relationship between the added actual water level and the width W. On the other hand, water depth D
The flow velocity V1 at the position, that is, the flow velocity V1 of the measured water level WL1 is measured, and this value is taken into the calculation means 4. Since the average flow velocity V calculated based on the measured flow velocity V1 is previously input as data to the calculation means 4, the measured flow velocity V
The average flow velocity V is calculated by taking in 1.
Therefore, the flow rate Q can be calculated (Q = A · V) by the calculated water flow cross-sectional area A and the average flow velocity V.

According to the present invention, for example, as shown in FIG. 2, even if the water flow rate WL is changed to the position shown by the solid line or the position shown by the phantom line, the flow velocity distribution is displaced. It is possible to measure the flow velocity V1 at the measured water level WL1 where the flow velocity distribution is constant and the average flow velocity V is obtained based on the measured flow velocity V1. That is, even if the flow velocity distribution is displaced due to fluctuations in the water level, the ultrasonic velocity meter 3 can be displaced along with the displacement of the float portion 2A of the float type water level meter 2 to measure the flow velocity V1. Since the average flow velocity is calculated based on the flow velocity V1, the flow rate Q can always be measured accurately regardless of the water level H, and the measurement cannot be impossible. Further, since the float type water level meter 2 and the ultrasonic velocity meter 3 do not have to be separately provided and a plurality of velocity meters are not required, the structure can be simplified and the facility cost can be reduced, and it is troublesome. Civil engineering work can be omitted.

In the above embodiment, an ultrasonic type is used as the velocity meter, but an electromagnetic type or Doppler type velocity meter 3 is attached to the float type water level gauge 2. May be. Further, although the flow rate measurement of the open water channel 1 having a rectangular water flow cross-sectional shape with a uniform width W and a horizontal bottom surface 1A is described, the water flow cross-sectional shape of the open water channel 1 is limited to the above-mentioned embodiment. However, it can be applied to the flow rate measurement of the open water channel 1 having various cross-sectional shapes of water passage.

[0014]

As described above, the present invention is designed to measure the flow velocity at the measured water level where the flow velocity distribution is always constant, by the flow velocity meter attached to the float type water level meter and constantly maintained at a constant water depth. Therefore, the distance from the water surface to the measurement point does not change even if the velocity distribution changes due to changes in the water level. In other words, even if the flow velocity distribution is displaced due to fluctuations in the water level, the anemometer is also displaced following this displacement, and it is possible to always measure the flow velocity at a fixed position in the flow velocity distribution. Is calculated,
It is possible to measure the flow rate accurately regardless of the water level, and there is no possibility of measurement failure. In addition, because the float type water level gauge is equipped with a velocity meter and multiple velocity meters are not required, the structure can be simplified and equipment costs can be reduced, and troublesome civil engineering work can be omitted. You can also do it.

[Brief description of drawings]

FIG. 1 is a cross-sectional front view showing an example of an open water channel applied to the implementation of the present invention.

FIG. 2 is a diagram showing a relationship between a flow velocity distribution displaced along with a water level change and a flow velocity measurement point.

FIG. 3 is a cross-sectional front view of a conventional example.

FIG. 4 is a plan view of FIG.

FIG. 5 is a diagram showing a flow velocity distribution in an open water channel.

[Explanation of symbols]

 1 Open channel 2 Float type water level meter 2A Float type of float type water level meter 3 Ultrasonic velocity meter (velocity meter) 4 Calculation means A Water cross section D Water depth WL Actual water level of open channel WL1 Water level measured by float type water level meter Q Flow rate V Average velocity V1 Velocity measured by velocity meter

Claims (1)

[Claims] 1. A float-type water level gauge provided with a float part which is always kept at a constant water depth is provided in an open channel having a predetermined water flow cross-sectional shape, and a velocity meter is attached to the float part, Data in which the water level and the flow velocity in the open channel are measured and taken into the calculating means, and the water cross section at the time of measuring the water level determined by the measured water level and the cross sectional shape of the water in the open channel is input in advance. And the average flow velocity determined by the flow velocity at a constant water depth obtained by the anemometer is calculated on the basis of previously input data, and the flow amount is calculated by the calculated water flow cross-sectional area and the average flow velocity. A method for measuring the flow rate of an open water channel, which is characterized in that