A particle true value data acquisition method suitable for particle image velocimetry

Abstract

The application discloses a kind of particle true value data acquisition methods suitable for particle image velocimetry technology, first, three identical specifications calibration plate are made, then three-dimensional calibration system is built under Cartesian coordinate system, and N measured tracer particles are suspended downwards from top calibration plate using wire;Second, fix a tracer particle as anchor particle, and the relative displacement of the remaining N-1 tracer particles relative to anchor particle is calculated according to its projection position on the coordinate system;Then, a group of light field image tracer particle true three-dimensional coordinates is obtained according to coordinate system transformation;Finally, keep the anchor particle position unchanged, move the remaining tracer particles to obtain the next group of particle coordinates by coordinate system transformation, and repeat the above method to form a tracer particle dataset from multiple groups of particle coordinates.The tracer particle information obtained by the method of the application is real and accurate, and can not only be used for flow field measurement calculation, but also quantitatively verify and evaluate the accuracy of flow field measurement results.

Description

Technical Field

[0001] This invention belongs to the field of computer vision technology, specifically relating to a method for acquiring particle truth data. Background Technology

[0002] Particle image velocimetry (PEV) is a flow field measurement technique. Before measuring the flow field, tracer particles with a particle size and specific gravity matching the test flow field and good reflectivity are uniformly dispersed in the flow field. At a certain time t1, the location of the tracer particles in the flow field is photographed, and then at time t2, the location of the tracer particles at the same imaging position is photographed again. By calculating the displacement of the tracer particles within the time interval, the velocity field information of the tracer particles can be determined. Accurate acquisition of t... i Constantly tracking the three-dimensional position information of particles is crucial for ensuring fluid velocity field measurement.

[0003] Traditional methods for obtaining the true three-dimensional position of tracer particles mainly include optical calculation and computer simulation generation. Optical calculation involves scattering tracer particles within a measurement container, then acquiring images of the tracer particles using optical devices such as lasers or light field cameras, and finally obtaining the t value through numerical calculation. i While the three-dimensional position information of tracer particles at different times can be obtained, the small size, large number, and dynamic nature of these particles lead to significant errors in the calculated position information, making it impossible to quantitatively verify and evaluate the accuracy of the flow field measurement results. Computer simulation to generate tracer particles uses commercial software to generate particle images at different times; however, these simulations often differ significantly from real particle images, and the software-generated particle datasets are limited in number and cannot simulate sufficient flow field morphologies, making it difficult to meet the needs of flow field measurement tasks in real-world scenarios.

[0004] In summary, existing particle information acquisition methods cannot meet the requirements for flow field measurement and quantitative evaluation of measurement results in real-world scenarios. It is necessary to establish a three-dimensional information acquisition system for tracer particles to obtain the true value of particle spatial information and meet the needs of flow field calculation. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for acquiring true particle data suitable for particle image velocimetry. First, three identical calibration plates are fabricated. Then, a three-dimensional calibration system is built in a Cartesian coordinate system, and N tracer particles to be measured are suspended downwards from the top calibration plate by a string. Next, one tracer particle is fixed as the anchor particle, and the relative displacements of the remaining N-1 tracer particles relative to the anchor particle are calculated based on their projection positions in the coordinate system. Then, a set of true three-dimensional coordinates of the tracer particles in the light field image is obtained through coordinate system transformation. Finally, keeping the anchor particle's position unchanged, the remaining tracer particles are moved to obtain and, through coordinate system transformation, the next set of particle coordinates is obtained. This process is repeated to form a tracer particle dataset from multiple sets of particle coordinates. The tracer particle information obtained by this method is true and accurate, and can not only be used for flow field measurement calculations but also to quantitatively verify and evaluate the accuracy of flow field measurement results.

[0006] The technical solution adopted by this invention to solve its technical problem includes the following steps:

[0007] Step 1: First, make a calibration plate with a*a millimeter as the smallest unit. In the Cartesian coordinate system, place the three planes XOY, XOZ and YOZ on the horizontal plane, coronal plane and sagittal plane respectively, with the horizontal plane calibration plate at the top, to construct the O-XYZ three-dimensional calibration system.

[0008] Step 2: After fixing N tracer particles to be tested with a line, suspend them downward through the horizontal calibration plate, and fix any one of the tracer particles to be tested as the other N-1 tracer particles.

[0009] Step 3: Denote P0 as the origin of the coordinate system (0,0,0). Obtain the three-dimensional coordinates of the tracer particles relative to the origin based on the projection positions of the other N-1 tracer particles on the three orthogonal planes. Then, obtain the set of true three-dimensional coordinates of the other N-1 tracer particles through coordinate system transformation, denoted as S. t1 ;

[0010] Step 4: Keeping the position of the anchor particle P0 unchanged, move the remaining tracer particles and obtain the set of three-dimensional coordinates of the tracer particles at different times using the same method as in Step 3. t1 ,S t2 ,…,S tk}

[0011] Further, the specific method of step 2 is as follows: after fixing N tracer particles to be tested with a line, they are suspended downward through the horizontal calibration plate. The length of the suspension line is adjusted to determine the position of the tracer particles to be tested on the OZ coordinate axis. The position of the tracer particles to be tested on the XOY plane is changed by using the position of the suspension line through the horizontal plane. Any one of the tracer particles to be tested is used as the anchor particle P0. When the position of the other tracer particles to be tested is changed by the suspension line, the position of the anchor particle P0 remains constant.

[0012] Furthermore, the specific method of step 3 is as follows: Let the anchor point P0 be the origin (0,0,0) of the calibration coordinate system, and read the values ​​of the remaining tracer particles P0 respectively. i The perpendicular projection of point P0 onto the XOZ plane and the distance Δx and P from point P0 in the P0X direction. i The perpendicular projection of point P0 onto the YOZ plane and the distance Δy from point P0 in the P0Y direction, P i The perpendicular projection of point P0 onto the XOY plane and the distance Δz between point P0 and point P0 in the P0Z direction give us P. i The three-dimensional coordinates P of the tracer particle i (Δx, Δy, Δz), i = 1, 2, ..., N-1; the two-dimensional spatial information (x1, z1) of all tracer particles in the pixel coordinate system is read out through the mapping relationship from the world coordinate system to the pixel coordinate system. The true depth information y1 of the particles is obtained from the distance from the optical center of the light field camera to the tracer particles, and denoted as set S. t1 ;

[0013] Furthermore, the specific method of step 4 is as follows: keeping the position of the anchor particle P0 unchanged and moving the remaining N-1 tracer particles, the three-dimensional coordinate set S of the tracer particles is obtained using the method in step 3. t2 Then, keeping the position of the anchor particle P0 unchanged, the remaining particles are moved to obtain the three-dimensional coordinate set of the tracer particles at different times. The total tracer particle data set is denoted as {St1,St2,…,Stk}.

[0014] Furthermore, a = 1.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention can obtain accurate three-dimensional position information of all tracer particles at any time through a three-dimensional calibration plate. By moving the position of the tracer particles, the motion pattern of the fluid velocity field at continuous time can be simulated. The obtained tracer particle information is real and accurate, which can not only be used for flow field measurement and calculation, but also quantitatively verify and evaluate the accuracy of flow field measurement results. Attached Figure Description

[0017] Figure 1This is a calibration plate manufactured according to an embodiment of the present invention, with 1*1mm as the smallest unit.

[0018] Figure 2 This is a three-dimensional calibration system constructed using three calibration plates in an embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the anchored particle P0 position in the calibration system of this invention.

[0020] Figure 4 This is a schematic diagram of the calibration system of the present invention with P0 as the origin of the coordinate system.

[0021] Figure 5 This is a schematic diagram of the projection positions of the other N-1 tracer particles on three orthogonal planes in an embodiment of the present invention.

[0022] Figure 6 It is the set of relative coordinate positions of the tracer particle image and the read-out particles in the embodiments of the present invention.

[0023] Figure 7 This is a three-dimensional position diagram of the tracer particles after the computer coordinate system transformation in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The purpose of this invention is to provide a method for acquiring true particle data suitable for particle image velocimetry technology, so as to solve the problems of poor reliability of flow field measurement results and inability to quantitatively verify and evaluate the accuracy of flow field measurement results caused by inaccurate three-dimensional position information of tracer particles.

[0026] This invention provides a method for acquiring three-dimensional true value data of tracer particles suitable for particle image velocimetry technology, such as... Figure 1 As shown, a calibration plate with a minimum unit of 1*1mm was fabricated; as shown Figure 2 As shown, in the Cartesian coordinate system, the three planes XOY, XOZ, and YOZ are placed in the horizontal, coronal, and sagittal planes, respectively, with the horizontal plane calibration plate at the top; as... Figure 3 As shown, the position of the suspending line across the horizontal plane is used to determine the position of the tracer particle in the XOY plane, and any one of the tracer particles is used as the anchor particle P0; as... Figure 4 As shown, let the anchor point P0 be the origin (0,0,0) of the calibration coordinate system; as Figure 5 , Figure 6 As shown, anchor point P0 is the origin (0,0,0) of the calibration coordinate system. The values ​​of the remaining tracer particles P are then read. i The perpendicular projection of point P0 onto the XOZ plane and the distance Δx and P from point P0 in the P0X direction. iThe perpendicular projection of point P0 onto the YOZ plane and the distance Δy from point P0 in the P0Y direction, P i The perpendicular projection of point P0 onto the XOY plane and the distance Δz between point P0 and point P0 in the P0Z direction give us P. i The three-dimensional coordinates P of the tracer particle i (Δx, Δy, Δz); such as Figure 7 As shown, the required three-dimensional position map of the tracer particles is obtained through computer coordinate system transformation.

[0027] Step 1, as follows Figure 1 As shown, firstly, a calibration plate with a minimum unit of 1*1mm is fabricated, as follows: Figure 2 As shown, an O-XYZ three-dimensional calibration system is constructed using three calibration plates in the Cartesian coordinate system;

[0028] Step 2, as follows Figure 3 As shown, N tracer particles to be tested are fixed with a wire and then suspended downward through the top calibration plate, with one of the tracer particles fixed as the anchor particle P0.

[0029] Step 3, as follows Figure 4 As shown, P0 is first denoted as the origin of the coordinate system (0,0,0), as follows: Figure 5 As shown, the projected positions of the other N-1 tracer particles on three orthogonal planes are obtained, as follows: Figure 6 As shown, the three-dimensional coordinates of the other N-1 tracer particles relative to the origin are obtained, as follows: Figure 7 The true three-dimensional coordinate set of the tracer particles in the light field image obtained by coordinate system transformation is denoted as S. t1 ;

[0030] Step 4: Keeping the position of the anchor particle P0 unchanged, move the remaining tracer particles and obtain the set of three-dimensional coordinates of the tracer particles at different times using the same method as in Step 3. t1 ,S t2 ,…,S tk}

[0031] In the specific operation process of this invention, firstly, three calibration plates of the same specifications are made. Then, a three-dimensional calibration system is built in the Cartesian coordinate system, and N tracer particles to be tested are fixed by lines and suspended from the top calibration plate downwards. Next, one tracer particle is fixed as the anchor particle, and the relative displacement of the remaining N-1 tracer particles relative to the anchor particle is calculated based on their projection position in the coordinate system. Then, a set of light field images of the tracer particles' true three-dimensional coordinates is obtained by coordinate system transformation. Finally, keeping the anchor particle's position unchanged, the remaining tracer particles are moved to obtain and the next set of particle coordinates is obtained through coordinate system transformation. The above method is repeated to form a tracer particle dataset from multiple sets of particle coordinates.

[0032] This implementation example first produces a calibration plate with a minimum unit of 1*1mm, as shown below. Figure 1 As shown, in the Cartesian coordinate system, the XOY, XOZ, and YOZ planes are placed on the horizontal, coronal, and sagittal planes, respectively. The horizontal calibration plate is located at the top. N tracer particles to be measured are fixed with a string and suspended downwards through the top calibration plate. The length of the suspension string is adjusted to determine the position of the tracer particles on the OZ coordinate axis. The position of the tracer particles in the XOY plane is determined by the position of the suspension string passing through the horizontal plane. Figure 2 As shown, any one of the tracer particles is used as the anchor particle P0. Figure 3 As shown, when the positions of the other tracer particles are changed by the suspension line, the position of the anchor particle P0 remains constant; let the anchor point P0 be the origin (0,0,0) of the calibration coordinate system, as follows. Figure 4 As shown, the remaining tracer particles P were read respectively. i The perpendicular projection of point P0 onto the XOZ plane and the distance Δx and P from point P0 in the P0X direction. i The perpendicular projection of point P0 onto the YOZ plane and the distance Δy from point P0 in the P0Y direction, P i The perpendicular projection of point P0 onto the XOY plane and the distance Δz between point P0 and point P0 in the P0Z direction give us P. i The three-dimensional coordinates P of the tracer particle i (Δx, Δy, Δz) are as follows Figure 5 , Figure 6 As shown, the two-dimensional spatial information (x, y) of all tracer particles in the pixel coordinate system is read out through the mapping relationship from the world coordinate system to the pixel coordinate system. i ,z i The true depth information of the particle is obtained by measuring the distance from the optical center of the light field camera to the tracer particle. i This coordinate system transformation method can be used to obtain the three-dimensional coordinate data set of the tracer particles in the light field image, denoted as S. ti like Figure 7 As shown; then, keeping the position of the anchor particle P0 unchanged, the remaining particles are moved to obtain the three-dimensional coordinate set of the tracer particles at different times. The total tracer particle data set is denoted as {S}. t1 ,S t2 ,…,S tk}

Claims

1. A method for acquiring true particle data suitable for particle image velocimetry, characterized in that, Includes the following steps: Step 1: First, make a calibration plate with a*a millimeter as the smallest unit. In the Cartesian coordinate system, place the three planes XOY, XOZ and YOZ on the horizontal plane, coronal plane and sagittal plane respectively, with the horizontal plane calibration plate at the top, to construct the O-XYZ three-dimensional calibration system. Step 2: After fixing N tracer particles to be tested with a line, suspend them downward through the horizontal calibration plate, and fix one of the tracer particles as the anchor particle P0. Step 3: Denote P0 as the origin of the coordinate system (0,0,0). Obtain the three-dimensional coordinates of the tracer particles relative to the origin based on the projection positions of the other N-1 tracer particles on the three orthogonal planes. Then, obtain the set of true three-dimensional coordinates of the other N-1 tracer particles through coordinate system transformation, denoted as S. t1 ; Step 4: Keeping the position of the anchor particle P0 unchanged, move the remaining tracer particles and obtain the set of three-dimensional coordinates of the tracer particles at different times using the same method as in Step 3. t1 , S t2 , … , S tk } 2. The method for acquiring particle truth data suitable for particle image velocimetry technology according to claim 1, characterized in that, The specific method of step 2 is as follows: after fixing N tracer particles to be tested with a line, they are suspended downward through the horizontal calibration plate. The length of the suspension line is adjusted to determine the position of the tracer particles to be tested on the OZ coordinate axis. The position of the tracer particles to be tested on the XOY plane is changed by using the position of the suspension line through the horizontal plane. Any one of the tracer particles to be tested is used as the anchor particle P0. When the position of the other tracer particles to be tested is changed by the suspension line, the position of the anchor particle P0 remains constant.

3. The method for acquiring particle truth data suitable for particle image velocimetry technology according to claim 1, characterized in that, The specific method of step 3 is as follows: Let the anchor point P0 be the origin (0,0,0) of the calibration coordinate system, and read the values ​​of the remaining tracer particles P0 respectively. i The perpendicular projection of point P0 onto the XOZ plane and the distance Δx and P from point P0 in the P0X direction. i The perpendicular projection of point P0 onto the YOZ plane and the distance Δy from point P0 in the P0Y direction, P i The perpendicular projection of point P0 onto the XOY plane and the distance Δz between point P0 and point P0 in the P0Z direction give us P. i The three-dimensional coordinates P of the tracer particle i (Δx, Δy, Δz), i=1,2,…,N-1; the two-dimensional spatial information (x1, z1) of all tracer particles in the pixel coordinate system is read out through the mapping relationship from the world coordinate system to the pixel coordinate system. The true depth information y1 of the particles is obtained from the distance from the optical center of the light field camera to the tracer particles, and denoted as set S. t1 .

4. The method for acquiring particle truth data suitable for particle image velocimetry technology according to claim 1, characterized in that, The specific method of step 4 is as follows: keep the position of the anchor particle P0 unchanged and move the remaining N-1 tracer particles, and obtain the three-dimensional coordinate set S of the tracer particles using the method in step 3. t2 Then, keeping the position of the anchor particle P0 unchanged, the remaining particles are moved to obtain the three-dimensional coordinate set of the tracer particles at different times. The total tracer particle data set is denoted as {S}. t1 , S t2 , … , S tk } 5. The method for acquiring particle truth data suitable for particle image velocimetry technology according to claim 1, characterized in that, The a=1.

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