JPS607204B2 - Average fluid velocity or flow rate measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the average flow velocity or flow rate in a waterway having a free surface, and in particular to a method for measuring the average flow velocity or flow rate in a waterway having a free surface, particularly in a waterway with a floor or an opening in a sewage treatment plant, etc., using two pairs of partial flow velocity detectors. The present invention relates to a measurement method suitable for flow rate measurement.

In the conventional method of measuring the average flow velocity or flow rate of a waterway using two pairs of partial flow velocity detectors, measurement at low water levels is only possible when the water level reaches the upper flow velocity detection position or higher and detects the upper and lower flow velocity. However, there was a drawback that even a trial run was impossible unless the water level was above the upper flow velocity detection position at the start of measurement.

An object of the present invention is to eliminate the drawbacks of the prior art described above, to provide a flow velocity or flow rate that can be measured even when the water level at the start of measurement is below the upper or lower flow velocity detection position, and that can be measured with higher accuracy as the water level rises. To provide a measurement method.
For this reason, the present invention divides a waterway into a region 1 including a lower current meter from the bottom of the waterway, a region 0 above this region 1 and including a higher order current meter, and a region m above this. When the water level of the fluid is in region 1, the average flow velocity of the fluid is determined by a preset formula, and when the water level of the fluid is in region B, the average flow velocity of the fluid is determined based on the flow velocity value of the lower current meter. , when the water level of the fluid is in area m, calculate the average flow velocity of the fluid based on the flow velocity values of the lower and upper current meters, and after the water level of the fluid reaches area m, calculate the average flow velocity of the fluid when the water level reaches area m. The average flow velocity in the region 1 or region D is determined based on the flow velocity values obtained by the lower and upper flow velocity meters.

The preset formula is a formula that includes the water gradient 1, such as Manning's formula. Hereinafter, one embodiment of the present invention will be described based on the drawings. In Fig. 1, an ultrasonic flow velocity detector 2 for measuring the flow velocity between A and B is installed on the side wall of an open channel 1 at a position y from the bottom surface, and an ultrasonic flow velocity detector 2 for measuring the flow velocity between A and B is further provided at a position y2 above this between C and D. An ultrasonic flow velocity detector 3 for measuring the flow velocity is provided, and a water level gauge 4 for measuring the water level is provided above the water surface.

Generally, there are many equations that express the average flow velocity in an open channel, but recently Manning's equation shown in equation {1} has been widely used.

UaV=1R%・%. ．． ．． m where "Uav; average flow velocity n; roughness coefficient of the channel wall surface 1; hydraulic gradient (gradient of the water surface in the flow direction), which is the same as the channel bottom gradient in the case of uniform flow; Wh in the case of a rectangular channel with diameter depth /W+h In this equation, n and 1 are waterway constants, but since their numerical accuracy is low, it is desirable to eliminate these constants by other methods.

First, equation (2) is derived based on Prandtl and Karman's theory of fluid flow.

Then, from the formula [1] and the formula [2-, the formula {3- is unrelated to 1]. UaV = U - Autumn 1 (An length)...■Here, LU; Average flow velocity g between A, B or C, D; Gravity acceleration pond: The mounting position of the flow velocity detector y (y, , &), is a function of water depth h and W in the channel, and is determined experimentally in a model channel.

k: Kalman's constant = 0.4 y: installation position of the flow velocity detector y, The geothermal equation is a formula that allows you to obtain the average flow velocity if n is determined. It is effective in many cases, and has higher accuracy and accuracy than water level measurement using only the m-type.

Furthermore, when the flow velocity is detected at two positions between A and B and between C and 0 as shown in Figure 1, the '2} formula becomes '4' and {5), respectively.
The average flow velocity Uav is expressed by the formula '6}.

UaV = U' Misaki 1 (An. 10 things n old days)... (41 UaV:
U2-Noran (Ayama Jutakushi...'5) Here, U1, U
2; Average flow velocity Am, between A and B or C and D, An2:
Correction coefficient for y or mede Since this equation does not include either n or 1, it can be said to be the most accurate average flow velocity equation.

Therefore, if the water level is always above the position of flow velocity detectors 2 and 3 and the flow velocity between A and B and between C and D can be detected, use these flow velocity values and the water level value at that time, {6} By configuring a computing unit according to the formula, it becomes possible to measure the average flow velocity or flow rate with higher accuracy. However, the water level is not necessarily limited to such cases, and the water level at the time of startup may be below the flow rate detector, or even be in between.

Therefore, the waterway is divided into the following three areas in the water depth direction.

Ryōyanagi: a・Region 1: From the bottom of the waterway to the position where the flow velocity detector 2 can detect the average flow velocity between A and B in a sufficiently stable manner (0 to L,).

Region B: From the upper limit of region 1 to the position where the flow velocity detector 3 can stably detect the average flow velocity between C and ○ (~, ~~2)
.

Region m: Region 0, above the upper limit (~2~) Then, the calculations shown in FIG. 2 are performed using the output signals Vu, V, of each flow velocity detector and the output signal Vh of the water level gauge.

This calculation has the following calculation functions for each water level area. Area 1; a-U fence = R%・Hiiragi--(,')b-
UaV = (vine) % U fence (7) Here, the '7} formula of formula b in regions 1 and 0 is the average flow velocity Uavo measured and calculated by formula (6') at a certain diameter depth Ro2 in region m. [11 or (
1′) can be obtained by applying Eq.

That is, the average flow velocity at Ro2 is UaV when converted to the Manning equation.

:Yo's %〆-- side, and the Manning formula in R is the formula [1}, so the formula '7) can be obtained from the formula '8} and the formula [1}.

In the above, a is the calculation form for areas 1 and 0 at the time when the water level has not reached area m, and b is the calculation form for areas 1 and 0 after the water level has reached area 3 at least once.

This will be detailed below. In an example using the microcomputer shown in FIG. 2, the first output of each detector Vu, ,
Vboard and Vh are input to each calculation unit 12 to 16 in the form of U, , U2, h or R, respectively.

On the other hand, each of the water level regions 1 to m is determined based on the water level signal h input to the water level input section 5, and is outputted as an average flow velocity and flow rate through a calculation mode according to each region.

That is, when the water level determination units 6 and 7 determine that hZ~2, the calculation unit 12 performs calculation and outputs the average flow velocity Uav.

Then, at the time h=L2, the current water level ~2 or the diameter depth R and the average flow velocity Uavo are held in the diameter depth hold circuit 8 and the average flow velocity hold circuit 9, respectively. Then, when the water level determination unit 6 determines that h<ho, the Uav
The o determination unit 10 determines whether Uavo=0 or sheep 0,
When Uavo=0, the calculation unit 15 outputs the average flow velocity Uav.

This shows that the water level has never reached ho2, and means the measurement of a in region 1. Further, in the case of Uavoki0, the water level has already reached L2 at least once, which means that Uavo and Ro2 are held in the circuit, so the calculation result of the calculation unit 13 is output. This means the measurement of b in region 1, and the measurement of region 1 is automatically made more precise. Further, when the water level determining section 6 determines that hZho, the process moves to the water level determining section 7, and when it determines that ho, mih<ho2, Ua
The process moves to the determination unit 11 of vo.

Here, if it is determined that Uavo=0, the calculation unit 14 outputs the average flow velocity Uav. This means that the water level is L
, but has not yet reached ho2, which is the measurement of a in area B. Also Uavo
In the case of 0, it indicates that the water level has already reached h at least once and is held in the circuit by Uavo and Ro2, which are not 0 at that time. Uav is output. This is the measurement result of b in region 0, and it means that the measurement result in region 0 has been automatically improved in precision. Next, the water level determination section 7 determines hZh.
When it is determined that it is a female, the calculation unit 12 performs the calculation as described above, and the resulting average flow velocity Uav is output.At the same time, at h=~2, the diameter depth 2 and the average flow velocity Uavo at that time are calculated.
They are held in the diameter depth hold circuit 8 and the average flow velocity hold circuit 9, respectively.

Further, the calculating unit 16 calculates the average flow velocity Uav and the waterway cross-sectional area S determined by the water depth, and outputs the flow rate Q.

According to one embodiment of the present invention, measurement is possible even if the water level does not reach the flow rate detector at the start of measurement, and moreover, if the water level rises during the measurement and exceeds the flow rate detector, all water levels can be automatically measured. Therefore, it is possible to maintain measurement precision and accuracy that are not affected by hydraulic motion, slope 1, and roughness coefficient n.

In addition, even if the water level does not reach the flow velocity detector 3 or higher, it is possible to obtain a high measurement accuracy that is not affected by the measured value of equation (3), that is, the uncertain value of the water flow gradient 1. I can do it. Furthermore, since the determination of areas 1, ro, and m is made based on the water level, Uavo and Ro2 are placed at appropriate positions that can hold Uavo and Ro2 stably against ripples on the water surface and instantaneous and transient changes in water level. There are effects that can be set.

On the other hand, in a waterway where the water level changes slowly and the water surface is slightly rippled, it is easy to imagine that it would be possible to determine areas 1, 0, and blood using the output signals of each flow velocity detector. can. The above is a detailed description of a rectangular cross-section waterway as an example, but each relational expression is based on the diameter depth R, the cross-sectional area S, and the correction term A.
Since it is a general formula that does not depend on the shape of the waterway cross section except for n,, Ah2, if An,, A- are experimentally determined for each cross-sectional shape and the respective diameter depth R and cross-sectional depth S are used, It can also be applied to various waterways such as circular and trapezoidal.

Further, in the embodiment, the average flow velocity between AB is used as the partial flow velocity, but the correction term An may be thinned even when the flow velocity is at a point between AB. According to the present invention, a waterway is divided into three regions determined by the position of the flow velocity detector, and an appropriate average flow velocity formula is introduced for each region to obtain the average flow velocity at each water level, and The calculation mode is automatically switched at the boundary of each region, and the roughness coefficient n' is adjusted for when the region is not reached and after the region is reached, and once region m is reached, the roughness coefficient n' Since this is also localized in an unrelated measurement state, there are practical effects as described below.

1 The water level at the start of measurement was insufficient ~, measurement can be performed even below.

2. Measurement is possible even when the water level at the start of measurement is between ~ and ~h, and high accuracy independent of the hydraulic gradient 1 can be obtained.

3. When the water level reaches ho2 or higher, high precision measurement that does not depend on region 1, co-moving water gradient 1 or roughness coefficient n becomes possible, and this precision is maintained for any subsequent changes in water level.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between each detector and a waterway according to an embodiment of the present invention, and FIG. 2 is a flowchart showing the operation of FIG. 1. 1... Waterway 2, 3... Flow velocity detector, 4...
...Water level gauge, 5...Water level input section, 6,7...
・Water level determination section, 8...Diameter depth hold circuit, 9.
...Average flow velocity hold circuit, 10, 11...
Uavo determination unit, 12 to 16... Calculation unit, 17...
...Reset circuit. Multi/Multiple 2 drawings

Claims (1)

[Claims] 1. Measure the partial flow velocity of the fluid in the waterway with lower and upper current meters installed at different water depths in the waterway, and measure the water level of the fluid with a water level gauge, and calculate the waterway from the partial flow velocity and water level of the fluid. In the method of measuring the average flow velocity or flow rate of a fluid in the waterway, the waterway is divided into a region I including the lower current meter from the bottom of the waterway, a region II above this region I including the upper current meter; Area III above area II
When the water level of the fluid is in region I, the average flow velocity of the fluid is determined using a preset formula, and when the water level of the fluid is in region II, the average flow velocity of the fluid is determined based on the flow velocity value of the lower current meter. The average flow velocity of the fluid is determined, and the water level of the fluid is determined in area I.
In the case of II, the average flow velocity of the fluid is determined based on the flow velocity values of the lower and upper current meters, and the water level of the fluid is in the region III.
After reaching region III, the average flow velocity of the fluid in region I or region II is determined based on the flow velocity values obtained by the lower and upper current meters when region III is reached. or flow measurement method.