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Method for measuring start flow velocity of silt

A flow velocity and sediment technology, applied in the measurement device, fluid velocity measurement, velocity/acceleration/impact measurement, etc., can solve the problems of water turbidity, inability to determine the starting state of sediment, backwardness, etc., and achieve the effect of strong adaptability

Inactive Publication Date: 2012-12-19
WUHAN UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, the existing method for measuring the start-up flow velocity of sediment is still relatively backward, mainly relying on the method of manual observation, that is, manually adjusting the flow velocity in the test tank, and manually visually observing the start-up of the sediment on the test tank bed surface, and then judging Whether it reaches the start-up velocity of the sediment
This method has the following problems: 1. It is greatly affected by human factors, and different personnel, different habits, and different lighting conditions may obtain different critical start-up flow rates; 2. There is no reasonable, quantitative, objective and consistent basis for discrimination. very random
3. It is greatly affected by the transparency of water flow
There are often many tiny dust particles in sandy water, which are suspended in the water for a long time, especially in the flowing water, making the water turbid, and the experimenters cannot see the movement of the sediment on the bed surface clearly, so they cannot judge the sediment. start state

Method used

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  • Method for measuring start flow velocity of silt
  • Method for measuring start flow velocity of silt
  • Method for measuring start flow velocity of silt

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0032] Example 1, Imaging the plastic sand in still water by B-ultrasound

[0033] Experiments have confirmed that according to the particle size of the measured particles, using a medical B-ultrasound instrument, selecting an appropriate ultrasonic frequency (2.5~7.5MHZ) and an appropriate signal gain, the reflection image of sand particles in the water can be obtained.

[0034] figure 1 ,2,3 are the actual collected images of suspended particles at different particle sizes. It can be seen that the B-ultrasound can obtain clear images of sand particles with a particle size as small as 0.1 mm.

[0035]

Embodiment 2

[0036] Example 2 Imaging of sediment in water before and after starting by B-mode ultrasound

[0037] According to the particle size of the measured particles, a medical B-ultrasound instrument is used to select an appropriate ultrasonic frequency (2.5~7.5MHZ) and an appropriate signal gain to obtain the image signals of underwater suspended particles near the riverbed interface before and after the start of the flow velocity of sand particles in the water. Such as Figure 4 , As shown in 5. The bright line in the figure is the boundary of the river bed, and the bright spot above the river bed is the image of suspended sand particles. It can be seen from the figure that the number of suspended particles above the river bed boundary changes significantly before and after the start.

[0038]

Embodiment 3

[0039] Example 3 Take the model test plastic sand as an example, Image 6 It is the relationship curve between the concentration of suspended particles and the flow velocity measured by this method.

[0040] It can be seen that when the flow velocity is less than 3.11cm / s, the concentration of suspended particles near the bed surface is very low, the curve is flat, and the particle concentration changes little, about 8~11 particles per frame, and the average concentration is 10 particles / each Frame (hereinafter referred to as basic concentration, which is caused by some other light suspended matter, not real suspended sand). At this time, there is no obvious start-up movement of sand particles at the river bed interface; when the flow velocity increases to 3.21cm / s, the suspended particle concentration increases from 10 per frame to 27 per frame. The particle concentration is relative to the flow velocity. The rate of change (that is, the slope of the curve) is: 170 particles / c...

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Abstract

The invention relates to a method for measuring start flow velocity of silt, which comprises the following steps: starting from the flow velocity of zero, the concentration of suspended particles above a riverbed boundary is measured and recorded by a B-ultrasound instrument, and the concentration of the particles is the number of suspended particles contained in each frame of image, and is shown with N; the water velocity is gradually increased, the concentration and the concentration rate of change of the suspended particles are measured and recorded, the water velocity is shown in V with the unit of cm / s, and the concentration rate of change is delta N / delta V; and when the concentration of the suspended particles exceeds the concentration of suspended particles in still water by 3-6 times, N is larger than 30, and at the same time the concentration rate of change of the suspended particles achieves 100-200 particles / (cm / s), the water velocity at this time is the start velocity of the silt, and the start velocity is measured. According to the method disclosed by the invention, the suspended particles in water flow can be quantitatively analyzed, so that a quantitative, objective and consistent judgment standard is established.

Description

[0001] technical field [0002] The invention belongs to the technical field of river engineering measurement and relates to a method for measuring the start-up velocity of sediment. Background technique [0003] In the river engineering model test, the measurement of the initial flow velocity of sediment is of great significance for the study of sediment transport law. Sediment activation refers to the phenomenon that the sediment turns from stillness to movement under certain water flow conditions. However, the existing method for measuring the start-up flow velocity of sediment is still relatively backward, mainly relying on the method of manual observation, that is, manually adjusting the flow velocity in the test tank, and manually visually observing the start-up of the sediment on the test tank bed surface, and then judging Whether to reach the starting velocity of the sediment. This method has the following problems: 1. It is greatly affected by human factors, and d...

Claims

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Application Information

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IPC IPC(8): G01P5/24G01M10/00
Inventor 马志敏赵小红胡向阳许明邹先坚
Owner WUHAN UNIV