Experimental correction method and system for density interface optical deformation in density stratified fluid

Abstract

The invention discloses an experimental correction method and system for optical deformation of a density interface in density stratified fluid, and the method comprises the steps: S1, obtaining a continuous original image of spherical particles passing through the interface, controlling the displacement of particles in adjacent images not to exceed the average pixel radius, and setting the falling direction of the particles as the y-axis positive direction; s2, selecting an image i before particles enter an interface, extracting a contour to obtain a y coordinate, and establishing a mapping array of a corrected y'and an original y; s3, selecting an (i + n) th image (n is greater than or equal to 1 and represents the processed n images), extracting a contour to obtain a y coordinate and a particle center, determining a particle center correction position according to the mapping array, obtaining a corrected y'of a specific line through a formula, and adding the corrected y 'into the mapping array; s4, repeating S3 to obtain a complete mapping array; and S5, correcting a subsequent image according to the complete mapping array. According to the method, the mapping array is constructed in stages to realize accurate correction, and the reliability of related experimental image measurement data can be improved.

Description

Technical Field

[0001] This invention relates to the field of density-stratified fluids, and more specifically, to an experimental method and system for correcting optical deformation of density interfaces in density-stratified fluids. Background Technology

[0002] Density stratification of fluids is a common phenomenon in nature, such as atmospheric stratification and the halocline and thermocline in the ocean. Density stratification alters the settling characteristics of immersed particulate matter, primarily by increasing particle drag, slowing settling velocity, and intensifying aggregation. Many large-scale environmental problems are closely related to fluid density stratification, such as the spread of smog, the accumulation of marine snow, the propagation and diffusion of marine microplastics, and sediment deposition at river estuaries. Developing stratified fluids in an experimental environment and conducting relevant measurements is crucial for understanding and mastering the settling and aggregation patterns of particles in stratified fluids.

[0003] In experiments, solutions with different medium concentrations are generally used to prepare density-stratified fluids, such as sodium chloride solution (saline), glycerol and water, or a mixture of water and alcohol. Changes in solution density also lead to differences in optical refractive index, causing optical distortion in the image of the density interface and severely reducing the accuracy of particle position and velocity measurements.

[0004] Particles exhibit severe optical distortion when crossing density interfaces, making it difficult to directly measure their position from images. Existing literature and patents lack methods for correcting this optical distortion. Two main approaches exist: one uses a graduated ruler placed on the vertical plane through which the particles settle before the experiment, takes an image of the ruler, and then extracts the pixel coordinates corresponding to the scale markings for calibrating the actual spatial position of the particles. This method increases flow field disturbance, accelerating mixing and diffusion at the density interface, and can only calibrate the true coordinates of the scale positions, achieving only millimeter-level calibration accuracy, with limited measurement precision. The other approach does not directly address optical distortion but instead uses the optical refractive indices of three or more solutes to achieve density changes while maintaining a consistent refractive index. This method increases experimental costs, and the refractive index matching limits the range of density choices for the fluid particles, narrowing the parameter space for experimental particle measurements, and can easily introduce significant viscosity changes, affecting experimental control. This invention provides an optical correction method based on particle images, which can achieve pixel-level calibration accuracy without introducing additional disturbances to the flow field, and can be effectively applied to planar PIV and PTV measurements of stratified fluids. Summary of the Invention

[0005] This invention addresses the image distortion problem caused by changes in optical refractive index in density-stratified flow by providing a method and system for position correction using the particle's own size characteristics. This method can effectively correct distorted particle images without adding additional disturbances, thereby improving the accuracy of particle position and velocity calculations.

[0006] The present invention is achieved by the following technical solution: An experimental method for correcting optical deformation at the density interface in a density-stratified fluid includes the following steps: S1. Acquire several consecutive original images of the spherical particles passing through the density interface process. The displacement of the spherical particles between adjacent original images does not exceed the average pixel radius of the spherical particles. The falling direction of the spherical particles is taken as the positive direction of the y-axis. S2. From the continuous original images, take image i before the spherical particle enters the density interface, extract the outline of the spherical particle, obtain the y-coordinates of all rows of the spherical particle and the center of the spherical particle in image i, and construct the y-axis pixel coordinates y' of the corrected spherical particle. The mapping array; S3. Take the (i+n)th image, where n≥1, indicating that n images have been processed. Extract the outline of the spherical particles to obtain the y-coordinates of all rows of the spherical particles and the center of the spherical particles in image i+n. Obtain the corrected center position of the spherical particles in image i+n according to the mapping array in S2. For the rows in image i+n where the y-coordinate is greater than the center coordinate of the spherical particles but less than the bottom position coordinate of the spherical particles, obtain the corrected y-axis coordinate y' of the corresponding row through the correction formula. Add the y' obtained in S3 and its corresponding y to the mapping array. S4. Repeat S3 to process the remaining images in sequence, and obtain the complete mapping array of the original image y-axis pixel positions and the corrected positions y'. S5. Based on the mapping array obtained in S4, the subsequent images in the density-stratified fluid are corrected.

[0007] Furthermore, in S1, the average pixel radius of the spherical particles is obtained from the original image of the undeformed spherical particles.

[0008] Furthermore, in S2, the y-axis pixel coordinate y' of the constructed corrected spherical particle is compared with... The mapping array is specifically as follows: The spherical particles in image i and previous images did not undergo deformation, and the mapping relationship was y'= .

[0009] Furthermore, in S3, the method for obtaining the center of the spherical particle is as follows: Obtain the pixel width of the spherical particle in all rows of image i+n. The point with the maximum pixel width is the center of the spherical particle. If the maximum value is not unique, take the average of the pixel coordinates on the y-axis as the center of the spherical particle.

[0010] Furthermore, in S3, the corrected y-axis coordinate y' for the corresponding row is obtained through the correction formula as follows: y'= ; in, Let r be the center correction position of the spherical particle in image i+n, and r be the average pixel radius of the spherical particle. Let y be the pixel width corresponding to row y in image i+n.

[0011] An experimental correction system for optical deformation of density interfaces in density-stratified fluids, used to implement any of the methods described above.

[0012] Furthermore, including: The image acquisition module acquires several consecutive images of the spherical particles passing through the density interface. The data processing and storage module processes the image and stores a mapping array, which is used to correct subsequent images in the density-stratified fluid.

[0013] Furthermore, the image acquisition module uses a high-speed camera, and the data processing and storage module uses a computer.

[0014] Beneficial effects: This invention utilizes the shape characteristics of spherical particles and a correction formula to correct the optical deformation of particles after they enter the density interface, thereby obtaining accurate particle position information. The operation is simple. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments; Figure 1 This is a correction principle diagram of one embodiment of the present invention, wherein the black solid line outline represents the deformed particle outline obtained by actual shooting, and the blue dashed line represents the corrected particle outline. Based on this diagram, a mapping relationship between the original position and the corrected position can be established.

[0016] Figure 2 This is an original particle image acquired in one embodiment of the present invention, showing obvious deformation of particles near the density interface.

[0017] Figure 3 This is a particle outline extracted from the original image in one embodiment of the present invention, used for particle pixel position and width statistics.

[0018] Figure 4This is an embodiment of the present invention with a particle horizontal pixel width. A graph showing the variation of pixel position y in the vertical direction.

[0019] Figure 5 This is a mapping diagram of the original pixel coordinates y and the corrected pixel coordinates y' of a particle obtained in one embodiment of the present invention.

[0020] Figure 6 This is a corrected particle image established based on a mapping relationship according to an embodiment of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all process steps, structures, and experimental results.

[0022] One specific embodiment of an experimental correction method for optical deformation of density interfaces in density-stratified fluids includes the following steps: S1. Acquire several consecutive original images of the spherical particles passing through the density interface process. The displacement of the spherical particles between adjacent original images does not exceed the average pixel radius of the spherical particles. The falling direction of the spherical particles is taken as the positive direction of the y-axis. S2. From the continuous original images, take image i before the spherical particle enters the density interface, extract the contour of the spherical particle, obtain the y-coordinates of all rows of the spherical particle, and construct the y-axis pixel coordinates y' of the corrected spherical particle. The mapping array; S3. Take the (i+n)th image, where n≥1, indicating that n images have been processed. Extract the outline of the spherical particles to obtain the y-coordinates of all rows of the spherical particles and the center of the spherical particles in image i+n. Obtain the corrected center position of the spherical particles in image i+n according to the mapping array in S2. For the rows in image i+n where the y-coordinate is greater than the center coordinate of the spherical particles but less than the bottom position coordinate of the spherical particles, obtain the corrected y-axis coordinate y' of the corresponding row through the correction formula. Add the y' obtained in S3 and its corresponding y to the mapping array. S4. Repeat S3 to process the remaining images in sequence, and obtain the complete mapping array of the original image y-axis pixel positions and the corrected positions y'. S5. Based on the mapping array obtained in S4, the subsequent images in the density-stratified fluid are corrected.

[0023] Example 1: Step 1: Capture the process of spherical particles passing through the density interface, obtaining a series of continuous particle images, such as... Figure 2As shown. Ensure that the particle displacement between adjacent images does not exceed the particle radius. Due to the change in optical refractive index, there is obvious optical distortion in the particle images within the density interface. The image resolution acquired in this example is 2560*1600 pixels, and the vertical pixel coordinate y ranges from [1, 2560], increasing from top to bottom.

[0024] Step 2: Calculate the average pixel radius of the undeformed region of the particle image, denoted as r. In this example, r = 63, meaning the particle radius occupies 63 pixels in width.

[0025] Step 3: Begin processing from any image before the particles enter the density interface, let's call this image i. In this example, we start processing from the first image, taking i=1. First, extract the particle outline, such as... Figure 3 As shown. Record the y-value of the particle image location and the corresponding pixel width for each row. In this example, As y changes as Figure 4 As shown. The widest point is the center of the particle. If the maximum value is not unique, then the average y-value is taken. In this example, Let y' represent the corrected vertical pixel coordinates. Since the particles in this image have not yet been deformed, y' = can be directly constructed. The mapping array, where the pixel coordinates corresponding to the bottom position of the particle at this time are . Expand the mapping relationship to The mapping relationship above the density interface, within the range, follows y'= .

[0026] Step 4: Process the (i+n)th image, where n≥1, indicating that n images have been processed. Here, i=1, n=1. First, extract the y-values ​​of the particle outline and the corresponding pixel width of each row. The center coordinates of the spherical particle are determined based on its maximum width. Since the particle displacement in adjacent images is less than the particle radius, therefore... ,exist Within the range. Therefore, the corrected position of the sphere's center can be obtained based on the mapping relationship established in the previous step. For y> in the particle image All rows, based on the row width Calculate its corrected position y'= Let the pixel coordinates corresponding to the bottom position of the particle at this moment be . Adding the newly calculated y' and its corresponding y to the mapping array can expand the mapping range to... .

[0027] Step 5: Repeat Step 4 to process the remaining images sequentially, thus obtaining the complete mapping relationship between the original image pixel positions and the corrected positions. In this example, the mapping relationship between y and y' is as follows: Figure 5 As shown.

[0028] Step Six: Using the obtained mapping relationship, calculate the correction position of each pixel in the original image and perform image correction. The corrected image obtained in this example is as follows: Figure 6 As shown, Figure 1 In the correction formula, δy is... .

[0029] Example 2: An experimental correction system for optical deformation of density interfaces in density-stratified fluids, used to implement the method described in Example 1.

[0030] It includes: an image acquisition module, which acquires several consecutive images of spherical particles passing through a density interface; and a data processing and storage module, which processes the images and stores a mapping array for use in correcting subsequent images in the density-stratified fluid. The image acquisition module uses a high-speed camera, and the data processing and storage module uses a computer.

[0031] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. An experimental method for correcting optical deformation at the density interface in a density-stratified fluid, characterized in that, Includes the following steps: S1. Acquire several consecutive original images of the spherical particles passing through the density interface process. The displacement of the spherical particles between adjacent original images does not exceed the average pixel radius of the spherical particles. The falling direction of the spherical particles is taken as the positive direction of the y-axis. S2. From the continuous original images, take image i before the spherical particle enters the density interface, extract the contour of the spherical particle, obtain the y-coordinates of all rows of the spherical particle, and construct the y-axis pixel coordinates y' of the corrected spherical particle. The mapping array; S3. Take the (i+n)th image, where n≥1, indicating that n images have been processed. Extract the outline of the spherical particles to obtain the y-coordinates of all rows of the spherical particles and the center of the spherical particles in image i+n. Obtain the corrected center position of the spherical particles in image i+n according to the mapping array in S2. For the rows in image i+n where the y-coordinate is greater than the center coordinate of the spherical particles but less than the bottom position coordinate of the spherical particles, obtain the corrected y-axis coordinate y' of the corresponding row through the correction formula. Add the y' obtained in S3 and its corresponding y to the mapping array. S4. Repeat S3 to process the remaining images in sequence, and obtain the complete mapping array of the original image y-axis pixel positions and the corrected positions y'. S5. Based on the mapping array obtained in S4, the subsequent images in the density-stratified fluid are corrected.

2. The method according to claim 1, characterized in that, In S1, the average pixel radius of the spherical particles is obtained from the original image of the undeformed spherical particles.

3. The method according to claim 1, characterized in that, In S2, the y-axis pixel coordinate y' of the constructed corrected spherical particle is... The mapping array is specifically as follows: The spherical particles in image i and previous images did not undergo deformation, and the mapping relationship was y'= .

4. The method according to claim 1, characterized in that, In S3, the method for obtaining the center of the spherical particle is as follows: Obtain the pixel width of the spherical particle in all rows of image i+n. The point with the maximum pixel width is the center of the spherical particle. If the maximum value is not unique, take the average of the pixel coordinates on the y-axis as the center of the spherical particle.

5. The method according to claim 4, characterized in that, In S3, the corrected y-axis coordinate y' of the corresponding row is obtained through the correction formula as follows: y'= ； in, Let r be the center correction position of the spherical particle in image i+n, and r be the average pixel radius of the spherical particle. Let y be the pixel width corresponding to row y in image i+n.

6. An experimental correction system for optical deformation of density interfaces in density-stratified fluids, characterized in that, Used to implement the method as described in any one of claims 1-5.

7. The system according to claim 6, characterized in that, include: The image acquisition module acquires several consecutive images of the spherical particles passing through the density interface. The data processing and storage module processes the image and stores a mapping array, which is used to correct subsequent images in the density-stratified fluid.

8. The system according to claim 7, characterized in that, The image acquisition module uses a high-speed camera, and the data processing and storage module uses a computer.

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