JPH0663906B2 - Visualization method of flow by image processing - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of visualizing a flow by image processing.

[Conventional technology]

There have been many attempts to grasp the flow by the visualization method of the flow field, and the wall tracing method, the tuft method, the direct injection method, etc. are well known.

The wall surface tracing method is a method in which oil or the like is applied to the surface of an object and the flow state, direction, and velocity are obtained from the streak pattern that appears due to the flow.

The tuft method is a method in which a large number of threads are stretched on the surface of an object and the flow is measured from the degree of fluttering.

The direct injection method involves putting a dye in the stream and visualizing the stream by the trace of the dye.

In recent years, there has been remarkably strong interest in visualizing the entire flow region at one time and calculating physical quantities such as a flow velocity and a flow function, and calculating temporal changes in the physical quantity of the entire flow region.
There is a strong interest in visualizing arbitrary cross sections in the flow region, for example, not only the velocity of water but also the velocity of bubbles in water, and as an attempt to enable this visualization, the paper `` Japan The Japan Society of Mechanical Engineers (Part B) "No. 5
Volume 5, No. 509 (1989-1), pages 107 to 114 have been proposed. In this method, tracer particles are mixed in the flow field, and the tracer particles are irradiated with continuous light or strobe light to image-process the trajectory thereof. In image processing, for example, an image is input from a television camera, its frame information is converted into field information, and the field information for four consecutive times is subjected to image processing to trace the trajectory of each particle. Then, the flow field is visualized from the traces of the individual tracer particles to obtain various physical quantities.

Explaining the method shown in the above paper in brief, first, field information for four consecutive times is extracted from a signal input from a television camera, and image processing is performed at each time to obtain tracer particles. Find the center of gravity of. The image processing executed at this time is noise processing,
It is a binarization process and a gravity center position calculation process. That is, after removing the background image from the obtained image information, binarization is performed at a predetermined threshold value, and noise processing for removing particles smaller than tracer particles is performed, and then labeling processing is performed. The position of the center of gravity of each particle is calculated from the constituent pixels (x _i , y _i ) of each particle obtained by the processing.

Next, the particles are associated with each other. First, the search range is designated by an appropriate radius from the position of the center of gravity of the particles to be tracked at the first time. Then, the barycentric positions of all the particles existing within this search range in the image at the second time are extracted as the barycentric positions of the destination candidates. Next, the velocity vector of the particle of each destination candidate is calculated from the position of the center of gravity of the particle at the first time and the position of the center of gravity of each destination candidate extracted at the second time. And based on those velocity vectors,
Each search center point at the third time is determined, and the search range is set around each search center point with a relatively small radius. Then, the position of the center of gravity of the particles existing in each search range is extracted as the destination candidate at the third time. Further, the destination candidates at the fourth time are extracted by the same procedure. In this way, the route in which the destination candidate exists at all of the second to fourth times is extracted as the virtual route of the particle. And
If there is one extracted virtual path, it is recognized as the movement path of the particle. On the other hand, when there are a plurality of extracted virtual routes, the most appropriate route is selected from them based on a predetermined determination condition.

The above tracking process is performed for all particles, and if there is a path that shares the same coordinates at the same time, they are deleted as defective data. In addition, the data of particles that could not be associated at all times due to reasons such as flowing out of the measurement area within the measurement time is not adopted.
A predetermined physical quantity, such as a flow velocity or a stream function, is obtained from the movement path of each tracer particle thus obtained.

[Problems to be Solved by the Invention]

However, the wall tracing method has a problem that it is difficult to visualize a flow in a space away from the surface of the object, and the tuft method has a problem that it is difficult to visualize a flow in an arbitrary cross section. Further, the direct injection method has a problem that the velocity of the dye on the flow track can be grasped, but the entire flow region cannot be visualized at one time.

Further, the method described in the above paper is an excellent method that solves all the above problems, but in this method, a predetermined physical quantity from the moving path of each tracer particle, for example, the flow velocity and the stream function, There was a problem that it was difficult to grasp the flow field concretely unless the flow field was visualized using physical quantities. That is, it is difficult to grasp the flow field concretely or intuitively with an image in which only the barycentric position of each tracer particle is obtained.

Therefore, an object of the present invention is to solve the problem that it is not possible to visualize the flow region at a time, which is a drawback of the conventional wall tracing method, tuft method and direct injection method, while performing a relatively simple process. , It is to provide a flow visualization method that makes it easy to grasp the flow field concretely or intuitively.

[Means for Solving the Problems]

In order to solve the above problems, in the flow visualization method by image processing of the present invention, a laser light is spread in a light sheet to irradiate a fluid mixed with particles having a predetermined particle diameter,
The scattered light or fluorescence of the particles due to the irradiation is imaged with a television camera, and at that time, one laser light pulse is irradiated to one of the front field and the rear field of each frame, and the other has two to six lasers. The information obtained by irradiating light pulses intermittently and combining the information of the front field and the rear field of the previous frame in the two consecutive frames obtained by this is first
Information recorded in the recording medium as the second image information is recorded on the recording medium as the second image information and is recorded on the recording medium as the second image information. 1st and 2nd
Image information of the particles is subjected to image processing to form respective barycentric images of the particles.

[Action]

In the present invention, visualization of an arbitrary cross section in the flow region is performed by the sheet-shaped laser light.

In the irradiation of the laser light, for example, as shown in FIG. 1, once in the latter half of the previous field of each frame,
Intermittent irradiation of 2 degrees or more and 6 degrees or less is performed in the first half of the rear field of the frame. The irradiation of the laser light may be reversed between the front field and the rear field. Then, the scattered light or fluorescence of the particles in this sheet-shaped irradiation light is recorded on a recording medium through a television camera.
For example, the light of the front field and the rear field of the two consecutive frames is integrated to obtain the image information of the front field of the front frame in the recording signal, and the light information of the rear field and the front field of the rear field of the previous frame is integrated. The light is integrated to form image information of the rear field of the previous frame in the recording signal.

Next, two pieces of field information on the same frame are extracted from the recorded image information, and the barycentric positions of the particles are calculated by image processing, and the barycentric positions of the particles are imaged to form a barycentric image of the particles. To do.

The images of the center of gravity of the particles formed in this manner are as shown in FIGS. 3 and 4, for example, and the flow state can be intuitively and relatively easily grasped. Then, it is possible to directly calculate the flow velocity and the flow direction from these images.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

2 (A) and 2 (B) are a perspective view and a block configuration diagram showing an example of the configuration of an apparatus for carrying out the method of the present invention. As shown in FIG. 1A, this device includes an argon laser source 1, a laser controller 2, an optical fiber 3, a pinhole 4, an optical lens 5, an acrylic container 6 having a thickness of 10 mm, and a CCD camera 7 conforming to the NTSC standard. The recording / reproducing apparatus 8 and the monitor 9 connected to the recording / reproducing apparatus 8 are provided. Further, as shown in FIG. 1B, a computer 10 is connected to the recording / playback device 8, and the computer 10 has a frame memory 11, an external storage device 12 and a monitor 1.
3 are connected respectively.

In this apparatus, the laser light emitted from the argon laser source 1 is once entered into the laser controller 2, and is incident on the optical fiber 3 at arbitrary intervals by the acousto-optic cell in the controller 2, and is attached to the tip of the optical fiber 3. A laser sheet 1A having a thickness of 2 mm or less is made with the lens 5 and irradiated into the fluid in the acrylic container 6. The fluid used in this example is water.

When the laser beam is incident on the optical fiber 3 from the argon laser source 1, the larger the core diameter of the optical fiber 3 is, the less the light loss in the optical fiber 3 is. However, when the core diameter is increased, the argon laser sheet 1A is formed. Since the thickness increases, it is preferable to provide the pinhole 4 and the like between the optical fiber 3 and the lens 5 to thin the argon laser sheet 1A.

In this embodiment, the core diameter of the optical fiber 3 is 100.
μm to reduce the loss of light in the optical fiber 3,
Between the lens 5 at the tip and the optical fiber 3, a pinhole 4 having an inner diameter of 1 mm is located at a position 30 mm from the tip of the optical fiber 3.
Was provided to adjust the thickness of the laser sheet.

In FIG. 2 (A), the acrylic container 6 is filled with water, and the front surface of the acrylic container 6 in the drawing is open to the atmosphere. Water is continuously supplied to the acrylic container 6 from the upper surface in the figure, and water is continuously drained from the lower surface in the figure.

In order to visualize the flow field of water in the acrylic container 6, particles that follow the flow of water are continuously introduced from the upper surface of the acrylic container, and an argon laser beam is emitted from the optical lens 5 to the section to be visualized in the container. Is irradiated in a sheet form. Then, the CCD is mounted in the direction orthogonal to the surface of the laser sheet 1A.
By placing the camera 7 and photographing the light scattered or fluorescent when the particles pass through the surface of the laser sheet from a direction orthogonal to the sheet surface and continuously recording the same on the recording / reproducing device 8, the inside of the laser sheet 1A can be recorded. Record the video. During this recording, the monitor 9 connected to the recording / playback device 8
Check the recording status with.

As the particles to be mixed, it is preferable to use acrylic spherical particles or particles whose surface has been surface-modified with a dye such as methylene blue to increase scattering or fluorescence intensity.
In this example, particles having a surface diameter of 30 μm and a density of 1 g / cm ³ were used without surface modification.

Next, the recorded information is reproduced by the recording / reproducing device 8 and
Frame information in units of / 30 seconds is stored in the external storage device 12 through the frame memory 11 connected to the computer 10. Then, this frame information is further calculated by the computer 1.
After being divided into 1/60 second field information by the software inside 0, it is stored again in the external storage device 12.

The information of each time stored in the external storage device 12 is temporarily
It is copied to the frame memory 11, image processing is performed for each field information, and the barycentric position of particles is calculated. The image processing used here is noise processing, binarization, and particle centroid calculation processing. The calculated center-of-gravity position data is temporarily stored in the external storage device 12 of the computer 10.

Next, a specific visualization method of the flow of an arbitrary cross section in the flow region according to the present embodiment will be described.

First, a sheet-like argon laser beam having a thickness of 3 mm or less is irradiated into the flow region. In this laser light irradiation, as shown in laser light pulse of FIG. 1, as shown in (1) in the latter half of the front field of the previous frame and in the first half of the rear field of the previous frame, 2 ° to 6 ° (3 in FIG. Irradiate intermittently. When measuring a single-phase flow of liquids, gases, etc., the diameter of particles that can be fluorescent or scattered is 2 mm or less 10
Particles with a size of μm or more (30 μm in the example) are put in.

Next, the scattered light or fluorescence of the particles within the irradiation light of the laser sheet 1A is recorded on the recording medium through the CCD camera 7. In this recording, first, the camera outputs a, b, c, d of each field are recorded. From the output a of the front field of the previous frame and the output b of the output of the rear field to form an integration a of the light, which is used as image information of the front field of the previous frame in the recording signal. The light from the output b of the field and the light from the output c of the front field of the rear frame are integrated into a light integration b, which is recorded on the recording medium as image information of the rear field of the front frame in the recording signal.

From the image information recorded as described above, two pieces of field information before and after the same frame in the recording signal are extracted, and the barycentric position of the particle is calculated by image processing.
Then, a barycentric image of the particle is formed from the data.

FIG. 3 shows a center-of-gravity image as a result of image processing of the output a of the recording / reproducing apparatus 8 in the previous field of the previous frame shown in FIG. Further, FIG. 4 shows a center-of-gravity image as a result of image-processing the output b of the recording / reproducing device 8 in the rear field of the previous frame shown in FIG. The black circles in the figure show the positions of the centers of gravity of the particles imaged by the laser light emitted intermittently. In FIG. 3, the particles imaged by the pulse of the laser light are shown in FIG. Each particle imaged by a pulse of laser light is shown.

FIG. 5 shows the correspondence of particles by superposing FIGS. 3 and 4, and the correspondence of particles is obtained by the characteristic laser beam irradiation method and signal processing method of the present embodiment. It turns out that is very easy. As a result, the flow direction and the flow velocity (since the irradiation interval of the laser light pulse is known) can be directly obtained from these images. The arrows in the figure represent the obtained flow direction and flow velocity in vector display.

As a particle tracking method, it is possible to make the computer perform a method similar to the method described in the above-mentioned paper. In that case, especially in a flow field with a high flow velocity, when the moving distance of the particles is large, it is usually difficult to associate the particles, but the features of the particle image obtained by the method of the present embodiment are incorporated into the algorithm. This allows for fairly accurate tracking. Further, in an attempt to follow a trace of a complicated flow, according to the method of the above-mentioned paper, it is premised that the fluid does not behave in a complicated manner for continuous 3/60 seconds, but the method of this embodiment is applied. Then, even in that case, fairly accurate tracking is possible.

〔The invention's effect〕

As is clear from the above description, according to the flow visualization method of the present invention, it is possible to visualize the flow of an arbitrary cross section and at the same time, intuitively and relatively easily grasp the flow state. You can get images of various flow fields.

It is also possible to quantitatively analyze the flow field using the image.

[Brief description of drawings]

FIG. 1 is a timing chart showing the relationship between pulse laser emission, camera output, and light integration according to an embodiment of the present invention, and FIGS. 2 (A) and 2 (B) are structural examples of an apparatus for carrying out the present invention. FIG. 3 is a schematic perspective view and a block configuration diagram showing FIG. 3, FIG. 3 is a conceptual diagram showing a center of gravity image of a particle obtained by image-processing the front field information of FIG. 1, and FIG. FIG. 5 is a conceptual diagram showing a centroid image, and FIG. 5 is a conceptual diagram showing a state in which particles are associated with each other by superposing FIGS. 3 and 4. In the reference numerals used in the drawings, 1 ... Argon laser source 1A ... Laser sheet 2 ... Laser controller 6 ... Acrylic container 7 ... TV camera 8 ... Recording / playback device 9, 13 ... Monitor 10 ... ... Computer 11 ... Frame memory 12 ... External storage device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Matsumoto 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Stock Co., Ltd.

Claims (1)

[Claims] 1. A laser light is spread on a fluid mixed with particles having a predetermined particle diameter in a light sheet shape and irradiated, and the scattered light or fluorescence of the particles caused by the irradiation is imaged by a television camera. One laser light pulse is irradiated to one of the front field and the rear field of each frame, and the other is intermittently irradiated with two or more and six or less laser light pulses,
The output of the television camera thus obtained is recorded as the first image information on the recording medium as information obtained by combining the information of the front field and the information of the rear field of the previous frame in two consecutive frames, and Information obtained by combining the information of the rear field and the information of the previous field of the rear frame is recorded as the second image information on the recording medium, and the first and second image information read from the recording medium are subjected to image processing to perform the image processing. A method of visualizing a flow by image processing, which comprises forming respective centroid images of particles.