Flow velocity measurement system, flow velocity measurement method, and flow velocity measurement program

Abstract

To accurately measure a flow velocity on a water surface whose inclination changes over time.SOLUTION: A flow velocity measurement system 1 comprises: a camera 2 that images a water surface S; a light irradiation device 3 that irradiates the water surface S with a plurality of light beams L1-L3; and a flow velocity computation device 4 that computes the flow velocity on the water surface S on the basis of the images captured by the camera 2. The flow velocity computation device 4 comprises: an arrival position specifying unit 42 that specifies, in the image, coordinates of positions P1-P3 at which the plurality of light beams L1-L3 reach the water surface S; an inclination computation unit 43 that computes an inclination of a region R surrounded by the positions P1-P3 on the basis of the coordinates; a temporary flow velocity computation unit 44 that computes an apparent temporary flow velocity in the region R by analyzing the image; and an actual flow velocity computation unit 45 that computes an actual flow velocity in the region R by correcting the temporary flow velocity using the inclination.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for measuring flow velocity on a water surface. [Background technology]

[0002] A technique for measuring water surface flow velocity by photographing the water surface with a camera and analyzing the obtained image using PIV (Particle Image Velocimetry) has been known (for example, Patent Document 1). Patent Document 1 discloses a technique in which the surface water flow of a river is photographed with a video camera, the water level of the river is detected with a water level gauge installed in the river, the image signal of the surface water flow of the river and water level data are input into an analyzer installed on land, and the oblique image of the surface water flow of the river is geometrically corrected to a vertical plane image using preset orientation condition parameters and water level data in the analyzer, and PIV analysis is performed on the vertical plane image after the geometric correction to determine the surface flow velocity distribution of each section on a virtual cross-section of the river. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-117119 Summary of the Invention [Problem to be solved by the invention]

[0004] The conventional technology described in Patent Document 1 can accurately measure flow velocity if the slope of the water surface is always constant. However, in actual rivers, especially small and medium-sized rivers, the slope of the water surface often changes over time, so the conventional technology is prone to errors between the measured flow velocity and the actual flow velocity.

[0005] The present invention has been made in consideration of the above problems, and an object of the present invention is to accurately measure the flow velocity on a water surface whose slope changes over time. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention includes the following aspects. Section 1. A camera that photographs the water surface, a light irradiation device that irradiates a plurality of lights onto the water surface; a flow velocity calculation device that calculates a flow velocity on the water surface based on the image captured by the camera; Equipped with The flow velocity calculation device is an arrival position specifying unit that specifies coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation unit that calculates a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation unit that calculates an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation unit that calculates an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity measurement system equipped with Section 2. Item 2. The flow velocity measurement system according to item 1, wherein the light irradiation device irradiates three lights. Section 3. the tentative flow velocity calculation unit calculates a tentative flow velocity in an area surrounded by three positions where the three lights reach the water surface; Item 3. The flow velocity measurement system according to item 2, wherein the actual flow velocity calculation unit calculates the actual flow velocity in the region. Section 4. 4. The flow velocity measurement system according to any one of items 1 to 3, wherein the light irradiation device irradiates the light from a direction different from the shooting direction of the camera. Section 5. 5. The flow velocity measurement system according to any one of items 1 to 4, wherein the light is laser light. Section 6. Item 6. The flow velocity measurement system according to Item 5, wherein the wavelength of the light is 490 to 690 nm. Section 7. a photographing step of photographing the water surface with a camera; an irradiation step of irradiating the water surface with a plurality of lights; a flow velocity calculation step of calculating a flow velocity on the water surface based on the image captured by the camera; Equipped with The flow velocity calculation step an arrival position specifying step of specifying coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation step of calculating a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation step of calculating an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation step of calculating an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity measurement method comprising: Section 8. A flow velocity calculation program for calculating a flow velocity on a water surface based on an image of the water surface illuminated with a plurality of lights, an arrival position specifying step of specifying coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation step of calculating a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation step of calculating an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation step of calculating an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity calculation program that causes a computer to execute the above. Section 9. Item 9. A computer-readable recording medium having the flow velocity calculation program according to Item 8 recorded thereon. [Effects of the Invention]

[0007] According to the present invention, it is possible to accurately measure the flow velocity on a water surface whose slope changes over time. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the configuration of a flow velocity measurement system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the configuration of a flow velocity calculation device. [Figure 3] 3 is a flowchart showing a processing procedure of a flow velocity measurement method according to an embodiment of the present invention. [Figure 4] 1 is an example of an image of a water surface. [Figure 5] 10 is an example of reference point coordinate data. [Figure 6] FIG. 10 is a diagram for explaining a method for calculating the inclination of the water surface. [Figure 7] 10 is an example of reference point coordinate data. [Figure 8] FIG. 10 is a diagram showing the trajectory of the position where light reaches the water surface. [Figure 9] 10 is a heat map showing the distribution of the x-component of the flow velocity vector. [Figure 10] 10 is a heat map showing the distribution of the y component of the flow velocity vector. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0010] (System Configuration) FIG. 1 is a schematic diagram showing the configuration of a flow velocity measurement system 1 according to one embodiment of the present invention. The flow velocity measurement system 1 is a system that measures the flow velocity of a water surface S in a place where a water current occurs, such as a river or the ocean. In this embodiment, the place where a water current occurs is a river. The flow velocity measurement system 1 includes a camera 2, a light irradiation device 3, and a flow velocity calculation device 4.

[0011] The camera 2 photographs an area of ​​the water surface S where the flow velocity is to be measured. The installation location of the camera 2 is not particularly limited as long as the camera 2 can be stably attached, and may be, for example, on the porch of a bridge or the underside of a bridge girder. The photographing direction D of the camera 2 is also not particularly limited; in this embodiment, it is oblique to the water surface S, but it may also be vertical.

[0012] The light irradiation device 3 irradiates a plurality of lights onto an area of ​​the water surface S to be measured for the water current from a direction different from the shooting direction D of the camera 2. In this embodiment, the light irradiation device 3 includes three light sources 31, 32, and 33, which irradiate three lights L1, L2, and L3, respectively.

[0013] The light L1 to L3 are laser beams, but are not particularly limited as long as they are light with a certain degree of directionality. Furthermore, at night or in a relatively dark place, the light sources 31 to 33 may be beam light sources such as LEDs. The wavelengths of the light L1, L2, and L3 are not particularly limited as long as they are wavelengths that can be detected by the camera 2, but a wavelength that is easily reflected by the water surface S (for example, 490 to 690 nm, particularly 532 nm) is preferable. Furthermore, the traveling direction of the light L1 to L3 is all vertical, but may also be oblique to the water surface S. The traveling directions of the light L1 to L3 do not need to be parallel to each other, but are preferably all different from the shooting direction D of the camera 2.

[0014] The camera 2 captures an image of an area including positions P1, P2, and P3 where the three lights L1, L2, and L3 reach the water surface S, and transmits the obtained images in real time to the flow velocity calculation device 4. The transmission method is not particularly limited, and may be either wireless or wired.

[0015] 2 is a block diagram showing the configuration of the flow velocity calculation device 4. The flow velocity calculation device 4 can be configured as a general-purpose computer, and is installed, for example, in a river management facility. The flow velocity calculation device 4 includes, as its hardware configuration, a processor such as a CPU or GPU (not shown), a main memory device such as a DRAM or SRAM (not shown), and an auxiliary memory device 40 such as an HDD or SSD. The auxiliary memory device 40 stores a flow velocity calculation program P, reference point coordinate data C, etc.

[0016] The flow velocity calculation device 4 includes, as functional blocks, an image acquisition unit 41, an arrival position identification unit 42, a gradient calculation unit 43, a tentative flow velocity calculation unit 44, an actual flow velocity calculation unit 45, and a vorticity / divergence calculation unit 46. These functional blocks may be realized in hardware using logic circuits formed on an integrated circuit, or in software by a processor in the flow velocity calculation device 4 reading a flow velocity calculation program P into a main memory device and executing it. The flow velocity calculation program P may be downloaded to the flow velocity calculation device 4 via a communication network such as the Internet, or may be recorded on a computer-readable non-transitory recording medium such as a CD-ROM or an SD card and installed in the flow velocity calculation device 4 via the recording medium. The specific functions of each functional block will be described later.

[0017] (Processing procedure for flow velocity measurement method) 3 is a flowchart showing the processing steps of the flow velocity measurement method according to this embodiment. The flow velocity measurement method includes steps S1 to S8, of which steps S3 to S8 are executed by the above-mentioned functional blocks of the flow velocity calculation device 4. That is, the flow velocity calculation program P causes the flow velocity calculation device 4 to execute steps S3 to S8.

[0018] In step S1, the water surface S is photographed by the camera 2.

[0019] In step S2, the light irradiation device 3 irradiates the water surface S with three light beams L1 to L3. The light beams L1 to L3 have equal optical axis intervals, and the area enclosed by the arrival positions P1 to P3 forms an equilateral triangle, but the optical axes of the light beams L1 to L3 are not particularly limited as long as they are positioned on a single straight line. Furthermore, the area enclosed by the arrival positions P1 to P3 may be large enough so that the water surface S within that area can approximate a plane.

[0020] Note that step S1 may be executed after step S2, or step S1 and step S2 may be executed simultaneously.

[0021] Steps S3 to S8 correspond to the flow velocity calculation step recited in the claims.

[0022] In step S3, the image acquisition unit 41 of the flow velocity calculation device 4 acquires the image captured by the camera 2. If the camera 2 has the function of the flow velocity calculation device 4, step S3 can be omitted.

[0023] In step S4 (arrival position specifying step), the arrival position specifying unit 42 of the flow velocity calculation device 4 specifies the coordinates in the image of the positions P1 to P3 at which the light L1 to L3 arrive at the water surface S.

[0024] Fig. 4 is an example of an image of the water surface S. In Fig. 4, the x direction is the horizontal direction along the upstream and downstream of the river, and the y direction is the horizontal direction along the width of the river. The position identification unit 42 identifies the coordinates of pixels corresponding to positions P1 to P3. The coordinates of positions P1 to P3 are assumed to be P1 (x1, y1), P2 (x2, y2), and P3 (x2, y2), respectively.

[0025] In step S5 (gradient calculation step), the gradient calculation unit 43 of the flow velocity calculation device 4 calculates the gradient of the region R surrounded by the positions P1 to P3 based on the coordinates of the positions P1 to P3. The gradient calculation unit 43 refers to the reference point coordinate data C to calculate the three-dimensional coordinates of the positions P1 to P3, and calculates the gradient of the region R from the three-dimensional coordinates.

[0026] The reference point coordinate data C indicates the relationship between the water level of the water surface S obtained by prior measurement and the coordinates of the reference points PR1 to PR3, which are the arrival positions of the lights L1 to L3 on the water surface S. An example of the reference point coordinate data C is shown in FIG.

[0027] For example, if the coordinates of position P1 identified by the arrival position identifying unit 42 are (x1, y1), as described above, the water level (i.e., z-coordinate) of position P1 is calculated by fitting the coordinates of position P1 to an approximation curve derived from the relationship between the water level in the reference point coordinate data C and the coordinate of reference point PR1. The z-coordinates of other positions P2 and P3 are calculated in a similar manner, thereby calculating the three-dimensional coordinates of positions P1 to P3, and further, the normal vector of the plane including positions P1 to P3. This allows the slope of region R to be calculated.

[0028] Although FIG. 5 shows the coordinates of the reference points PR1 to PR3 corresponding to three water levels, it is also possible to show only the coordinates of the reference points PR1 to PR3 corresponding to two water levels.

[0029] In step S6 (provisional flow velocity calculation step), the provisional flow velocity calculation unit 44 of the flow velocity calculation device 4 calculates an apparent provisional flow velocity in the region R by analyzing the image. As shown in FIG. 4, in this embodiment, a number of tracers T flowing on the water surface S are analyzed using PIV (Particle Image Velocimetry) to calculate a provisional flow velocity V(u, w). Here, u is the x-component of the provisional flow velocity V, and w is the y-component of the provisional flow velocity V. The tracers T are fine particles such as air bubbles or dust, but are not particularly limited as long as they move on the water surface S at the same speed as the water current. Furthermore, the method for calculating the provisional flow velocity V is not limited to PIV analysis.

[0030] Note that step S6 may be executed before step S4 or S5 or in parallel with step S4 or S5.

[0031] In step S7 (actual flow velocity calculation step), the actual flow velocity calculation unit 45 of the flow velocity calculation device 4 calculates the actual flow velocity V'(u', w') in the region R by correcting the tentative flow velocity V using the gradient. For example, as shown in FIG. 6, if the normal vector A of the water surface S is (a, b) and the angle between the shooting plane B of the camera 2 (plane perpendicular to the shooting direction D) and the normal vector A is θ, then u'=u / sinθ The angle θ can be measured from the normal vector A by, for example, the beam reflection method, so the actual flow velocity calculation unit 45 can calculate u', which is the x-component of the actual flow velocity V', based on the angle θ and u, which is the x-component of the tentative flow velocity V. Similarly, w', which is the y-component of the actual flow velocity V', can be calculated based on the y-component (w) of the tentative flow velocity V and the normal vector A.

[0032] In step S8, the vorticity / divergence calculation unit 46 of the flow velocity calculation device 4 calculates the instantaneous vorticity and instantaneous divergence on the water surface S based on the distribution of the effective flow velocity V' within the region R. The instantaneous vorticity is calculated by the following equation (1), and the instantaneous divergence is calculated by the following equation (2).

number

number

[0033] It should be noted that by repeating steps S1 to S7 while moving the camera 2 in the width direction of the river, it is possible to obtain an accurate flow velocity distribution in the width direction of the river, thereby enabling the flow rate of the river to be obtained accurately.

[0034] (Summary) As described above, in this embodiment, the coordinates in the image of positions P1 to P3 where multiple light beams L1 to L3 irradiated onto the water surface S reach the water surface S are identified, and the slope of the region R surrounded by positions P1 to P3 is calculated based on these coordinates. In addition, the image is analyzed to calculate an apparent tentative flow velocity V in the region R, and further, the tentative flow velocity V is corrected using the slope to calculate an actual flow velocity V' in the region R. In this way, it is possible to calculate the actual flow velocity at the water surface S taking the slope of the region R into consideration. Therefore, it is possible to accurately measure the flow velocity at a water surface whose slope changes over time.

[0035] (Additional notes) Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0036] In the above embodiment, the light irradiation device 3 is equipped with three light sources 31 to 33, but the number of light sources may be four or more, or only two. When there are two light sources, the slope calculation unit 43 calculates the slope between two positions where the light irradiated from the light source reaches the water surface S, the provisional flow velocity calculation unit 44 calculates the apparent provisional flow velocity between the positions, and the actual flow velocity calculation unit 45 calculates the actual flow velocity between the positions.

[0037] In addition, in the above embodiment, the light irradiation device 3 is provided in the space above the water surface S, but the light irradiation device 3 may be provided underwater. In this case, the light irradiation device 3 irradiates light from underwater toward the water surface S.

[0038] Furthermore, in the above embodiment, the light sources 31 to 33 of the light irradiation device 3 irradiate the lights L1 to L3 from a direction different from the shooting direction D of the camera 2, but the lights L1 to L3 may be irradiated from the same direction as the shooting direction D of the camera 2. In this case, the directivity of the lights L1 to L3 may be adjusted so that the size of the area on the water surface S reached by the lights L1 to L3 varies depending on the distance between each light source 31 to 33 and the water surface S. [Example]

[0039] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0040] In this example, we verified whether the flow velocity measurement system 1 shown in Figure 1 can measure the flow velocity of a water surface whose slope changes over time in an indoor wave-making flume (width 0.40 m). As shown in Figure 1, a camera 2 was placed diagonally downstream relative to the water surface S. A high-speed camera was used as the camera 2. Three light sources 31-33 of the light irradiation device 3 were positioned so that light L1-L3 was emitted vertically. Laser pointers emitting green laser light were used as the light sources L1-L3. Black paint was mixed into the water at a concentration of 0.11%, and white lime powder was used as the tracer T.

[0041] First, to obtain reference point coordinate data C, light sources 31-33 irradiated the water with lights L1-L3, and camera 2 captured still images while changing the water level (depth) while the water was not flowing. By analyzing these images, the coordinates of the positions where lights L1-L3 reached the water surface S when the water level was 8.2 cm, 6.0 cm, and 2.3 cm were recorded as reference points Pf1(x1, y1), Pf2(x2, y2), and Pf3(x3, y3). The obtained reference point coordinate data C is shown in Figure 7.

[0042] Next, a water current was generated in the waterway, and while the water surface S was photographed with camera 2, lights L1 to L3 were emitted from light projection device 3, and multiple images were acquired. At this time, the water depth was 6 cm, the flow rate was 12.75 L / s, the cross-sectional average flow velocity was 0.53 m / s, and the Froude number was 0.69. Furthermore, for each image, Python was used to capture the contours of positions P1 to P3 where lights L1 to L3 reached the water surface S, and their coordinates (unit pixel) were extracted.

[0043] The trajectories of positions P1 to P3 extracted from multiple images are shown in Figure 8. The tracer T and the reflection point of the laser pointer on the water surface S were clearly distinguishable, and positions P1 to P3 were properly extracted. The time fluctuations of positions P1 to P3 were also captured.

[0044] Furthermore, the three-dimensional coordinates of positions P1 to P3 were calculated by referring to the reference point coordinate data C, and the plane equation of the region R surrounded by positions P1 to P3 was found from the three-dimensional coordinates, and the slope (normal vector) of region R was calculated.

[0045] In addition, the apparent instantaneous flow velocity in region R was calculated from the spatiotemporal changes in the distribution of tracer T in the image (PIV analysis). Furthermore, the effective flow velocity vector (u', w') in region R was calculated by correcting the apparent instantaneous flow velocity using the normal vector.

[0046] Figure 9 is a heat map showing the distribution of the x-component (u') of the flow velocity vector, and Figure 10 is a heat map showing the distribution of the z-component (w') of the flow velocity vector. In both cases, the water surface flow velocity within the triangular region R was measured. Note that the flow velocity outside region R is set to 0. [Explanation of symbols]

[0047] 1. Flow velocity measurement system 2 Cameras 3 Light irradiation device 31 Light source 32 light source 33 Light source 4 Flow velocity calculation device 40 Auxiliary storage 41 Image acquisition unit 42 Location identification part 42 Arrival position identification part 43 Slope calculation section 44 Virtual flow velocity calculation unit 45 Actual flow velocity calculation unit 46 Vorticity and divergence calculation section A normal vector B Shooting surface C Reference point coordinate data D Shooting direction L1 light source L2 light source L3 light source P Flow velocity calculation program P1 position P2 position P3 position PR1 reference point PR2 reference point PR3 reference point R area S water surface T tracer V virtual flow velocity V’ actual flow velocity

Claims

1. A camera that photographs the water surface, a light irradiation device that irradiates a plurality of lights onto the water surface; a flow velocity calculation device that calculates a flow velocity on the water surface based on the image captured by the camera; Equipped with The flow velocity calculation device is an arrival position specifying unit that specifies coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation unit that calculates a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation unit that calculates an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation unit that calculates an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity measurement system equipped with

2. The flow velocity measurement system according to claim 1 , wherein the light irradiation device irradiates three lights.

3. the tentative flow velocity calculation unit calculates a tentative flow velocity in an area surrounded by three positions where the three lights reach the water surface; The flow velocity measurement system according to claim 2 , wherein the actual flow velocity calculation unit calculates the actual flow velocity in the region.

4. The flow velocity measurement system according to claim 1 , wherein the light irradiation device irradiates the light from a direction different from a photographing direction of the camera.

5. The flow velocity measurement system according to claim 1 , wherein the light is a laser light.

6. 6. The flow velocity measurement system according to claim 5, wherein the wavelength of the light is 490 to 690 nm.

7. a photographing step of photographing the water surface with a camera; an irradiation step of irradiating the water surface with a plurality of lights; a flow velocity calculation step of calculating a flow velocity on the water surface based on the image captured by the camera; Equipped with The flow velocity calculation step an arrival position specifying step of specifying coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation step of calculating a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation step of calculating an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation step of calculating an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity measurement method comprising:

8. A flow velocity calculation program for calculating a flow velocity on a water surface based on an image of the water surface illuminated with a plurality of lights, an arrival position specifying step of specifying coordinates in the image of positions where the plurality of lights reach the water surface; a gradient calculation step of calculating a gradient of an area surrounded by the positions or a gradient between the positions based on the coordinates; a tentative flow velocity calculation step of calculating an apparent tentative flow velocity in the region or between the positions by analyzing the image; an actual flow velocity calculation step of calculating an actual flow velocity in the region or between the positions by correcting the tentative flow velocity using the gradient; A flow velocity calculation program that causes a computer to execute the above.

9. A computer-readable recording medium on which the flow velocity calculation program according to claim 8 is recorded.

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