Three-dimensional flow field measurement system with adaptive adjustment function

Abstract

The invention discloses a three-dimensional flow field measurement system with a self-adaptive adjustment function, and relates to the field of three-dimensional flow field measurement. In each image acquisition process of the three-dimensional flow field measurement system, a laser sheet light source is used for generating sheet laser to enable tracer particles to scatter light; each camera shoots a measurement domain to obtain a particle speckle image and transmits the particle speckle image to the control host, the control host firstly performs image quality analysis on each particle speckle image obtained in the current image acquisition process, and when it is determined that the image quality does not reach the standard, the control host sends the particle speckle image to the camera; according to the method, the focusing adjusting mechanism is used for adjusting the focal length of the cameras to improve the quality of the particle speckle images, and the particle speckle images with the image quality reaching the standard are used for three-dimensional flow field reconstruction until the image quality of the particle speckle images obtained by all the cameras reaches the standard, so that the accuracy of a three-dimensional flow field reconstruction result is improved.

Description

Technical Field

[0001] The present application relates to the field of three-dimensional flow field measurement, and in particular to a three-dimensional flow field measurement system with an adaptive adjustment function. Background Art

[0002] Flow field testing technology is a very important experimental technology for exploring flow field characteristics, especially the wake field of underwater vehicles and the wake field of thrusters, which has an important impact on the speed, maneuverability and propulsion characteristics of vehicles. Optical measurement, especially three-dimensional optical measurement, has the characteristics of non-contact, will not interfere with the flow field, and can carry out flow field measurement of an area or a volume. It is a flow field measurement technology with broad application space.

[0003] The 3D measurement system is complex and requires two cameras to simultaneously obtain particle speckle images of comparable quality in order to reconstruct the 3D velocity field. However, particle speckle images are affected by many factors and can cause interference, resulting in low accuracy of the currently reconstructed 3D velocity field. Summary of the invention

[0004] In view of the above problems and technical requirements, this application proposes a three-dimensional flow field measurement system with adaptive adjustment function. The technical solution of this application is as follows:

[0005] A three-dimensional flow field measurement system with an adaptive adjustment function, the three-dimensional flow field measurement system comprises a control host, a laser sheet light source, multiple cameras and a focus adjustment mechanism, the multiple cameras are arranged on one side of a water pool test section and face a measurement domain in the water pool test section, and a predetermined angle is formed between the optical axes of any two cameras; tracer particles are sown in the water pool test section, and the irradiation area of ​​the laser sheet light source covers the measurement domain of the water pool test section;

[0006] In each image acquisition process, the laser sheet light source is used to generate a sheet laser to illuminate the measurement domain of the water pool test section so that the tracer particles scatter light. Each camera is used to photograph the measurement domain to obtain a particle speckle image and transmit it to the control host.

[0007] The control host performs image quality analysis on each particle speckle image acquired during the current image acquisition process;

[0008] When the control host detects that the image quality of the particle speckle image collected by any camera does not meet the standard, the control host controls the focus adjustment mechanism to adjust the focus parameters of the corresponding camera, and then re-executes the image acquisition process and performs image quality analysis; until the control host detects that the image quality of the particle speckle images collected by all cameras meets the standard, the three-dimensional velocity field is reconstructed based on the particle speckle images collected by all cameras.

[0009] A further technical solution is that the host computer is controlled to perform image quality analysis on each particle speckle image acquired during the current image acquisition process, including:

[0010] The particle speckle image is subjected to image cross-correlation analysis to obtain the corresponding two-dimensional velocity field;

[0011] When it is determined that the effective vectors in the two-dimensional velocity field corresponding to the particle speckle image reach the quantity threshold, it is determined that the image quality of the particle speckle image meets the standard, otherwise it is determined that the image quality of the particle speckle image does not meet the standard.

[0012] A further technical solution is that the control host performs image quality analysis on each particle speckle image acquired during the current image acquisition process, and further includes:

[0013] Calculate the average gray value of the particle speckle image;

[0014] When the average gray value of the particle speckle image reaches the gray threshold, performing image cross-correlation analysis on the particle speckle image to obtain a corresponding two-dimensional velocity field;

[0015] When the average gray value of the particle speckle image does not reach the gray threshold, it is determined that the image quality of the particle speckle image does not meet the standard.

[0016] A further technical solution is that each set of focus parameters of each camera includes an object distance and a focal length that have a corresponding relationship, and controlling the focus adjustment mechanism to adjust the focus parameters of the corresponding camera includes:

[0017] A focus parameter scatter plot of the camera is constructed with the object distance of the camera as the horizontal coordinate and the focal length of the camera as the vertical coordinate, wherein each discrete point in the focus parameter scatter plot represents a set of focus parameters of the camera and includes the corresponding object distance and focal length;

[0018] Based on the focus parameter scatter plot, the focus parameters of the camera are adjusted in a surrounding radiation manner with the first focus parameter of the camera in the current image acquisition process as the center.

[0019] A further technical solution is to adjust the focus parameters of the camera in a surrounding radiation manner with the first focus parameter of the camera in the current image acquisition process as the center, including:

[0020] Arrange the focus parameter groups of the camera in order of the distances from the discrete points of the focus parameter scatter plot to the first focus parameter from near to far to obtain a focus parameter sequence;

[0021] The first group of focus parameters in the focus parameter sequence is used as the second focus parameter; the focus adjustment mechanism is controlled to adjust the camera to the second focus parameter, and the image acquisition process is re-executed and image quality analysis is performed;

[0022] When the image quality of the particle speckle image acquired by the camera under the second focus parameter still does not meet the standard, and the image quality is worse than that of the particle speckle image acquired by the camera under the first focus parameter, reselecting the next set of focus parameters in the focus parameter sequence as the second focus parameters, and performing the step of controlling the focus adjustment mechanism to adjust the camera to the second focus parameters again;

[0023] When the image quality of the particle speckle image acquired by the camera under the second focus parameter still does not meet the standard, but the image quality is better than the particle speckle image acquired by the camera under the first focus parameter, the focus parameter of the camera is adjusted in a surrounding radiation manner with the second focus parameter of the camera as the center.

[0024] A further technical solution is that when there are multiple sets of focus parameters with equal discrete point distances to the first focus parameter on the focus parameter scatter plot, the focus parameters in the multiple sets of focus parameters with equal object distances or equal focal lengths to the first focus parameter are sorted higher in the focus parameter sequence.

[0025] Its further technical solution is that the three-dimensional flow field measurement system also includes a synchronization trigger, which is respectively connected to the control host, the laser sheet light source and each camera; in each image acquisition process, the control host controls the synchronization trigger to synchronously trigger the laser sheet light source and each camera, and the laser sheet light source generates a sheet laser when triggered by the synchronization trigger to illuminate the measurement domain of the water pool test section so that the tracer particles scatter light, and each camera simultaneously exposes and shoots the measurement domain when triggered by the synchronization trigger to obtain the particle speckle image at the same time.

[0026] The beneficial technical effects of this application are:

[0027] The present application discloses a three-dimensional flow field measurement system with an adaptive adjustment function. After obtaining a particle speckle image of a flow field through non-contact optical measurement, the three-dimensional flow field measurement system does not directly perform three-dimensional flow field reconstruction, but first performs image quality analysis, and when it is determined that the image quality does not meet the standard, uses a focus adjustment mechanism to adjust the camera focal length to improve the quality of the particle speckle image, until the image quality of the particle speckle images acquired by all cameras meets the standard, and then uses the particle speckle images with the image quality meeting the standard to perform three-dimensional flow field reconstruction, thereby facilitating improving the accuracy of the three-dimensional flow field reconstruction result. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the system structure of a three-dimensional flow field measurement system according to an embodiment of the present application.

[0029] Figure 2 It is a schematic diagram of the three-dimensional flow field measurement process of an embodiment of the present application.

[0030] Figure 3It is a schematic diagram of a process for detecting whether the image quality of a particle speckle image meets the standard in one embodiment of the present application.

[0031] Figure 4 It is a schematic diagram of a particle speckle image obtained in an example and the corresponding two-dimensional velocity field obtained by image cross-correlation analysis.

[0032] Figure 5 is a schematic diagram of a focus parameter scatter plot in an example. DETAILED DESCRIPTION

[0033] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0034] This application discloses a three-dimensional flow field measurement system with adaptive adjustment function, please refer to Figure 1 As shown in the system structure diagram, the three-dimensional flow field measurement system includes a control host 1, a laser sheet light source 2, multiple cameras 3 and a focus adjustment mechanism 4.

[0035] The three-dimensional flow field measurement system is used to perform three-dimensional non-contact measurement of the flow field in the test pool, and tracer particles are spread in the test section of the pool. Multiple cameras 3 are arranged on one side of the test section of the pool and face the measurement area 5 in the test section of the pool, such as Figure 1 Take two cameras 3 as an example. A predetermined angle θ is formed between the optical axes of any two cameras. The predetermined angle θ is determined according to the overlap degree of the required field of view. In practical applications, the predetermined angle is 12° to 15°. Each camera uses a high-resolution test camera with an adjustable frame rate.

[0036] The irradiation area of ​​the laser sheet light source 2 covers the measurement domain 5 of the water pool test section, and is used to illuminate the measurement domain 5 of the water pool test section so that the tracer particles scatter light.

[0037] The control host 1 is connected to multiple cameras 3, and the control host 1 is also connected to control the focus adjustment mechanism 4 to adjust the focus parameters of each camera 3. The focus adjustment mechanism 4 of the present application is an electric control mechanism with the function of adjusting the object distance and focal length of the camera, and can be implemented by various existing mechanisms with this function.

[0038] The method for performing three-dimensional flow field measurement by the three-dimensional flow field measurement system includes the following steps, please refer to Figure 2 The flowchart shown:

[0039] In each image acquisition process, the laser sheet light source 2 is used to generate a sheet laser to illuminate the measurement domain of the pool test section so that the tracer particles scatter light, and each camera 3 is used to photograph the measurement domain to obtain a particle speckle image and transmit it to the control host 1. In one embodiment, in order to ensure that the camera can collect the particle speckle image when the sheet laser illuminates the measurement domain, as shown in FIG. Figure 1As shown, the three-dimensional flow field measurement system also includes a synchronization trigger 6, which is respectively connected to the control host 1, the laser sheet light source 2 and each camera 3. In each image acquisition process, the control host 1 controls the synchronization trigger 6 to synchronously trigger the laser sheet light source 2 and each camera 3. The laser sheet light source 1 generates a sheet of laser light under the triggering of the synchronization trigger 6 to illuminate the measurement domain of the pool test section so that the tracer particles scatter light. Under the triggering of the synchronization trigger 6, each camera 3 simultaneously exposes and shoots the measurement domain 5 to obtain the particle speckle image at the same time.

[0040] The traditional approach is to directly reconstruct each particle speckle image acquired during the current image acquisition process, but the interference in the particle speckle image often leads to a low accuracy of the reconstructed three-dimensional velocity field. Therefore, the present application does not directly reconstruct, but the control host 1 first performs image quality analysis on each particle speckle image acquired during the current image acquisition process. When the control host 1 detects that the image quality of the particle speckle image acquired by any camera is not up to standard, the control host 1 controls the focus adjustment mechanism 4 to adjust the focus parameters of the corresponding camera, re-executes the image acquisition process and performs image quality analysis, and repeats the above process. Until the control host 1 detects that the image quality of the particle speckle images acquired by all cameras is up to standard, the three-dimensional velocity field is reconstructed based on the particle speckle images acquired by all cameras. The specific reconstruction method can refer to the existing method, and this embodiment will not be pursued. It includes carrying out time series speckle image acquisition, and after processing and analysis, obtaining the characteristics of the velocity field changing with time, thereby providing high-quality flow field input parameters for the design of navigation bodies, thrusters, etc.

[0041] In the above process, when the control host 1 performs image quality analysis on the particle speckle images respectively, the image quality considered includes the effective vector of the velocity field contained in the particle speckle images. The image quality analysis of each particle speckle image includes the following steps, please refer to Figure 3 The flowchart shown:

[0042] The particle speckle image is subjected to image cross-correlation analysis to obtain the corresponding two-dimensional velocity field. The obtained two-dimensional velocity field includes several valid vectors and invalid vectors. For example, in one example, the particle speckle image collected by the camera is as follows: Figure 4 As shown in (a) in the figure, image cross-correlation analysis is performed to obtain the corresponding two-dimensional velocity field as shown in Figure 4 As shown in (b), Figure 4In (b), "√" indicates a valid vector, and "cross" indicates an invalid vector. When it is determined that the valid vectors in the two-dimensional velocity field corresponding to the particle speckle image reach the quantity threshold, it is determined that the image quality of the particle speckle image meets the standard, otherwise it is determined that the image quality of the particle speckle image does not meet the standard. The quantity threshold is customized according to actual needs. Through this image quality analysis process, it can be ensured that the valid vectors of the two-dimensional velocity field contained in the particle speckle image reach the quantity threshold, thereby ensuring the quality of subsequent three-dimensional flow field reconstruction.

[0043] In another embodiment, before analyzing the effective vectors of the velocity field contained in the particle speckle image, the pixel quality of the particle speckle image is first analyzed and screened, and the image quality considered also includes the pixel quality of the particle speckle image. Figure 3 As shown in the figure, the average gray value of the particle speckle image is first calculated. When the average gray value of the particle speckle image reaches the gray threshold, the step of performing image cross-correlation analysis on the particle speckle image to obtain the corresponding two-dimensional velocity field is performed. When the average gray value of the particle speckle image does not reach the gray threshold, it means that the pixel quality of the particle speckle image is poor at this time, and the difficulty and effect of the subsequent image cross-correlation analysis will not be very good. It is directly determined that the image quality of the particle speckle image does not meet the standard, and there is no need to perform subsequent image cross-correlation analysis. The gray threshold here can be set by default.

[0044] When the image quality of the particle speckle image collected by any camera does not meet the standard, if the particle speckle image collected by the camera is directly used to reconstruct the three-dimensional flow field, the reconstruction accuracy is low. Therefore, it is necessary to adjust until the image quality of the particle speckle image collected by the camera meets the standard. The adaptability of the camera focal length and object distance is a very important factor affecting the image quality of the acquired particle speckle image. Therefore, the control host 1 uses the focus adjustment mechanism to automatically adjust the camera focal length and object distance to improve the quality of the image collected.

[0045] The size and clarity of the acquired camera particle speckle image can be adjusted by changing the object distance and focal length of the camera. The object distance and focal length also affect each other. It is very important to efficiently adjust the focal length and object distance of the camera. In one embodiment, multiple object distances are first determined according to the object distance adjustment step within the object distance range of the camera, and multiple focal lengths are determined according to the focal length adjustment step within the focal length range of the camera. Then, the multiple object distances and multiple focal lengths of the camera are fully arranged and combined to obtain multiple sets of focus parameters, and each set of focus parameters includes object distances and focal lengths that have a corresponding relationship. Then, a focus parameter scatter plot of the camera is constructed with the object distance of the camera as the horizontal coordinate and the focal length of the camera as the vertical coordinate. The horizontal and vertical axes of the focus parameter scatter plot use the same graduation values. Each discrete point in the focus parameter scatter plot represents a set of focus parameters of the camera and includes the corresponding object distance and focal length. Please refer to Figure 5The schematic diagram of the focus parameter scatter diagram shown includes 20 groups of discrete points corresponding to the focus parameters. Figure 5 For illustration purposes only, the specific values ​​of the object distance and focal length are not shown.

[0046] Then, based on the focus parameter scatter plot of the camera, the focus parameter of the camera is adjusted in a surrounding radiation manner with the first focus parameter of the camera in the current image acquisition process as the center. This is because when setting up the system and setting up the camera, the initial focus parameter of the camera is generally set based on human experience. The particle speckle image collected by the camera under the initial focus parameter often has a good image quality observed by the human eye, so it is usually only necessary to fine-tune around the focus parameter. Therefore, each adjustment is made with the current first focus parameter as the center and fine-tuned in all directions to improve the adjustment efficiency.

[0047] Specifically, the method of adjusting the focus parameters of the camera using the surrounding radiation method includes:

[0048] (1) Arrange the focus parameter groups of the camera in order of the distance from the discrete points on the focus parameter scatter plot to the first focus parameter from near to far to obtain a focus parameter sequence. When there are multiple focus parameter groups with the same discrete point distance from the first focus parameter on the focus parameter scatter plot, the focus parameters with the same object distance or focal length as the first focus parameter in the multiple focus parameter groups are ranked higher in the focus parameter sequence, and the specific arrangement order of the focus parameters with the same object distance or focal length as the first focus parameter can be random, thereby ensuring that when adjusting, the focus parameters that can keep the object distance or focal length unchanged can be selected first, thereby improving the adjustment efficiency. For example, in Figure 5 In the example of , the first focus parameter corresponds to discrete point 50, then Figure 5 The discrete points corresponding to the other 19 groups of focus parameters are arranged in sequence from 51 to 519 to obtain a focus parameter sequence.

[0049] (2) Using the first set of focus parameters in the focus parameter sequence as the second focus parameters, then controlling the focus adjustment mechanism to adjust the camera to the second focus parameters, re-execute the image acquisition process and perform image quality analysis. Figure 5 In the example, the focus parameter 51 is first used as the second focus parameter, and the camera is used to reacquire the particle speckle image under the focus parameter 51.

[0050] (3) When the image quality of the particle speckle image collected by the camera under the second focus parameter still does not meet the standard, and the image quality is worse than the particle speckle image collected by the camera under the first focus parameter, it means that the adjustment direction of the second focus parameter selected at this time is incorrect, and a new second focus parameter is selected again by a surrounding radiation method with the first focus parameter as the center, so the next set of focus parameters in the focus parameter sequence is reselected as the second focus parameter, and the step of controlling the focus adjustment mechanism to adjust the camera to the second focus parameter is performed again. Among them, the more the number of effective vectors in the two-dimensional velocity field corresponding to the particle speckle image, the better the image quality of the particle speckle image.

[0051] (4) When the image quality of the particle speckle image acquired by the camera under the second focus parameter still does not meet the standard, but the image quality is better than that of the particle speckle image acquired by the camera under the first focus parameter, it means that the adjustment direction of the second focus parameter selected at this time is correct. At this time, the focus parameter of the camera is adjusted in a surrounding radiation manner with the second focus parameter of the camera as the center, which is similar to the process of adjusting the focus parameter of the camera in a surrounding radiation manner with the first focus parameter as the center, and the focus parameter that has been selected is no longer selected. The adjustment is continued until the image quality of the particle speckle image meets the standard.

[0052] For example, Figure 5 In the example, focus parameter 50 is used as the first focus parameter. For the first time, focus parameter 51 is used as the second focus parameter. It is assumed that the image quality of the particle speckle image acquired by the camera under the focus parameter 51 is detected to be worse than the image quality of the particle speckle image acquired under the focus parameter 50. Then focus parameter 52 is reselected as the second focus parameter, and it is detected that the image quality of the particle speckle image acquired by the camera under the focus parameter 52 is better than the image quality of the particle speckle image acquired under the focus parameter 50. At this time, the focus parameter of the camera is adjusted in a surrounding radiation manner with the focus parameter 52 as the center. Then, the focus parameter groups of the camera are rearranged in the order of the distance from the discrete point to the focus parameter 52 on the focus parameter scatter plot from near to far to obtain a focus parameter sequence. In the rearranged focus parameter sequence, the closest distance to the focus parameter 52 is Figure 5 The focus parameter in is 59. At this time, the camera is adjusted to the focus parameter 59, and the iteration continues until the image quality of the particle speckle image meets the standard.

[0053] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A three-dimensional flow field measurement system with adaptive adjustment function, characterized in that: The three-dimensional flow field measurement system includes a control host, a laser sheet light source, multiple cameras and a focus adjustment mechanism, wherein the multiple cameras are arranged on one side of a water pool test section and face a measurement domain in the water pool test section, and a predetermined angle is formed between the optical axes of any two cameras; tracer particles are sown in the water pool test section, and the irradiation area of ​​the laser sheet light source covers the measurement domain of the water pool test section; During each image acquisition process, the laser sheet light source is used to generate a sheet laser to illuminate the measurement domain of the water pool test section so that the tracer particles scatter light, and each camera is used to photograph the measurement domain to obtain a particle speckle image and transmit it to the control host; The control host performs image quality analysis on each particle speckle image acquired during the current image acquisition process; When the control host detects that the image quality of the particle speckle image collected by any camera does not meet the standard, the control host controls the focus adjustment mechanism to adjust the focus parameters of the corresponding camera, and then re-executes the image acquisition process and performs image quality analysis; until the control host detects that the image quality of the particle speckle images collected by all cameras meets the standard, the three-dimensional velocity field is reconstructed based on the particle speckle images collected by all cameras.

2. The three-dimensional flow field measurement system according to claim 1, characterized in that: The control host performs image quality analysis on each particle speckle image acquired during the current image acquisition process, including: Performing image cross-correlation analysis on the particle speckle image to obtain a corresponding two-dimensional velocity field; When it is determined that the effective vectors in the two-dimensional velocity field corresponding to the particle speckle image reach the quantity threshold, it is determined that the image quality of the particle speckle image meets the standard; otherwise, it is determined that the image quality of the particle speckle image does not meet the standard.

3. The three-dimensional flow field measurement system according to claim 1, characterized in that: The control host performs image quality analysis on each particle speckle image acquired during the current image acquisition process, and further comprises: Calculating an average gray value of the particle speckle image; When the average gray value of the particle speckle image reaches a gray threshold, executing the step of performing image cross-correlation analysis on the particle speckle image to obtain a corresponding two-dimensional velocity field; When the average gray value of the particle speckle image does not reach the gray threshold, it is determined that the image quality of the particle speckle image does not meet the standard.

4. The three-dimensional flow field measurement system according to claim 1, characterized in that: Each set of focus parameters of each camera includes an object distance and a focal length that have a corresponding relationship, and the control of the focus adjustment mechanism to adjust the focus parameters of the corresponding camera includes: A focus parameter scatter plot of the camera is constructed with the object distance of the camera as the abscissa and the focal length of the camera as the ordinate, wherein each discrete point in the focus parameter scatter plot represents a set of focus parameters of the camera and includes a corresponding object distance and focal length; Based on the focus parameter scatter plot, the focus parameters of the camera are adjusted in a surrounding radiation manner with the first focus parameter of the camera in the current image acquisition process as the center.

5. The three-dimensional flow field measurement system according to claim 4, characterized in that: The adjusting the focus parameter of the camera in a surrounding radiation manner with the first focus parameter of the camera in the current image acquisition process as the center includes: Arranging the focus parameter groups of the camera in order of the distances of the discrete points from the first focus parameter on the focus parameter scatter plot from near to far to obtain a focus parameter sequence; Using the first group of focus parameters in the focus parameter sequence as the second focus parameters; controlling the focus adjustment mechanism to adjust the camera to the second focus parameters, re-executing the image acquisition process and performing image quality analysis; When the image quality of the particle speckle image acquired by the camera under the second focus parameter still does not meet the standard, and the image quality is worse than that of the particle speckle image acquired by the camera under the first focus parameter, reselecting the next set of focus parameters in the focus parameter sequence as the second focus parameters, and performing the step of controlling the focus adjustment mechanism to adjust the camera to the second focus parameters again; When the image quality of the particle speckle image acquired by the camera under the second focusing parameter still does not meet the standard, but the image quality is better than the particle speckle image acquired by the camera under the first focusing parameter, the focusing parameter of the camera is adjusted in a surrounding radiation manner with the second focusing parameter of the camera as the center.

6. The three-dimensional flow field measurement system according to claim 5, characterized in that: When there are multiple groups of focus parameters with the same discrete point distance as the first focus parameter on the focus parameter scatter plot, the focus parameters in the multiple groups of focus parameters with the same object distance or focal length as the first focus parameter are sorted higher in the focus parameter sequence.

7. The three-dimensional flow field measurement system according to claim 1, characterized in that: The three-dimensional flow field measurement system also includes a synchronization trigger, which is respectively connected to the control host, the laser sheet light source and each camera; in each image acquisition process, the control host controls the synchronization trigger to synchronously trigger the laser sheet light source and each camera, and the laser sheet light source generates a sheet laser under the triggering of the synchronization trigger to illuminate the measurement domain of the water pool test section so that the tracer particles scatter light, and each camera is triggered by the synchronization trigger to simultaneously expose and shoot the measurement domain to obtain the particle speckle image at the same time.

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