A 3D3C-PIV-based underwater three-dimensional space flow field measurement system and method

Abstract

The application provides an underwater three-dimensional space flow field measuring system and method based on 3D3C-PIV, mainly comprising a guide sword rod, a main thunder body, a secondary thunder body, a laser system and an aluminum profile fixing frame; the system can be freely fixed on the lifting mechanism of an environment such as a towing tank or a circulating water tank through the aluminum profile fixing frame, and the main thunder body and the secondary thunder body are lowered to the depth to be measured under the water surface during work; the laser generated by the laser system is transmitted to the center of the main thunder body through the built-in light guide arm of the sword rod, and is converted into a volume light source by a lens group to illuminate the position to be measured; four high-speed cameras built-in on both sides of the main thunder body and the secondary thunder body acquire the particle images of the illuminated position, and the data is transmitted to the system control host located on the trailer through the camera cable guide arm built-in the sword rod for subsequent analysis. The application makes the 3D3C-PIV system suitable for the working environment of large water areas such as towing tanks and circulating water tanks, and meets the measurement test requirements of various underwater three-dimensional space flow field information.

Description

Technical Field

[0001] This invention belongs to the field of underwater testing, specifically relating to an underwater three-dimensional spatial flow field measurement system and method based on 3D3C-PIV. Background Technology

[0002] 3D3C-PIV (3 Dimension 3 Component Particle Image Velocimetry) can measure the three-directional velocity vectors of fluid particles in a three-dimensional flow field. It mainly consists of four high-speed cameras (no fewer than three) and a dual-pulse laser. The laser illuminates the tracer particles in the flow field, and the four high-speed cameras at a certain angle record the changing images of the tracer particles to analyze the velocity information of the flow field. It is a powerful scientific research tool for conducting experimental research on flow mechanisms.

[0003] In the field of marine engineering, model tests of ships in towed water tanks or circulating water tanks are the most common test methods for judging the quality of ship types. The velocity distribution and turbulence characteristics in the flow field around a ship have strong three-dimensional spatial characteristics. However, there is still a lack of test methods to obtain the three-dimensional flow field of a ship model in a water tank. This requires the improvement of existing test systems so that they can be applied to the experimental environment of towed water tanks or circulating water tanks.

[0004] Existing underwater flow field testing systems still have many technical defects and shortcomings:

[0005] 1. At present, the most common underwater flow field testing system is the underwater SPIV (Stereoscopic Particle Image Velocimetry) testing system, but it can only obtain the three-dimensional velocity vector information of fluid particles in a two-dimensional plane, and cannot be applied to the measurement of flow fields with strong three-dimensional spatial characteristics.

[0006] 2. The existing 3D3C-PIV system is mainly used in air environment and can be applied to small water tank test environment with transparent walls. The cross-media tilt shooting near the wall will cause obvious image distortion, and the subject needs to be close to the wall. Therefore, it is not suitable for large-scale pool environment.

[0007] 3. The only existing underwater Tomo-PIV measurement system is located at the Institute for Water Science and Engineering at the University of Iowa (IIHR). Its laser guide arm and three high-speed cameras are each inserted into the water through independent cylindrical structures, which lacks structural reliability. At high speeds, relative shaking will occur, affecting the measurement results. It occupies a large space and has limited application scenarios. During operation, the waves generated by the multi-cylinder structure will pose a great challenge to the structural strength of the system. Summary of the Invention

[0008] The objective of this invention is achieved through the following technical solution:

[0009] An underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV includes a flow guide spar, a main mine body, a secondary mine body, a laser system, and an aluminum profile mounting frame. The laser system is located at the uppermost end of the flow guide spar and includes a laser body. Both the flow guide spar and the laser system are fixed to the aluminum profile mounting frame. The flow guide spar has a hollow structure, i.e., a hollow chamber. The hollow chamber contains a laser guide arm and a camera cable guide arm. The lower end is sequentially fixed with the main mine body and the secondary mine body. The main mine body includes two mine body flow guide caps, two camera reflector chambers, two camera chambers, and a laser adjustment chamber. The laser adjustment chamber is located in the middle of the main mine body. The laser adjustment chamber includes a laser guide arm extending from the hollow chamber, a laser reflector, a lens group located in the middle, and a laser outlet located on the wall of the mine body. On both sides of the laser adjustment chamber are, in sequence, a camera chamber, a camera reflector chamber, and a mine body guide cap. Each camera chamber and camera reflector chamber contains a set of high-speed camera groups. The high-speed camera group includes a high-speed camera mounted on a rotating platform, a fixed camera lens, a camera reflector, and a camera shooting window located on the wall of the mine body. The secondary mine body contains the same camera chamber, camera reflector chamber, and two sets of high-speed camera groups as the main mine body.

[0010] Furthermore, the flow guide scimitar includes a fixed frame, a hollow chamber, and flow guide plates. The fixed frame is connected to the hollow chamber, providing an external outlet for the laser guide arm and camera cable. The hollow chamber contains a laser guide arm and a camera cable guide arm. The laser guide arm extends from the laser system above the fixed frame to the center of the main mine body. The camera cable guide arm branches into two cables at the main mine body to control two sets of high-speed camera groups at both ends of the main mine body, and extends downward to the secondary mine body to control two sets of high-speed camera groups in the secondary mine body. The front and rear streamlined flow guide plates are connected to the hollow chamber to ensure the stability of the flow guide scimitar when operating in water.

[0011] Furthermore, the high-speed camera is separated from the camera lens and can be angularly offset by a rotating platform, thus forming an angle with the camera lens.

[0012] Furthermore, the camera reflector chamber is connected to the outside world and is filled with water when in operation.

[0013] Furthermore, the camera compartment and laser adjustment compartment must be kept watertight.

[0014] Furthermore, the mirrors in the camera reflector compartment and the laser adjustment compartment can rotate in multiple stages around the central axis of the laser body.

[0015] The present invention may also include:

[0016] A method for measuring underwater three-dimensional spatial flow field based on 3D3C-PIV, the specific steps of which are as follows:

[0017] Step 1: The entire measurement system is connected to the three-dimensional moving mechanism on the trailer or shore base through an aluminum profile fixing frame. Then, the laser body is connected to the laser controller, and the camera optical cable extending from the upper end of the guide spar is connected to the system control host.

[0018] Step 2: After completing Step 1, adjust the angles of the camera reflector cabins and laser adjustment cabins of the main and secondary laser bodies according to the shooting position requirements, so that the shooting areas of the four cameras are consistent and within the laser irradiation range of the body.

[0019] Step 3: After the reflector angle adjustment in Step 2 is completed, the main and secondary torpedo bodies are placed underwater using the three-dimensional moving mechanism, and the Tomo-PIV system is calibrated. During the calibration, the Scheimpflug angle and lens focal length of the four cameras can be adjusted by controlling the main unit of the system.

[0020] Step 4: After the Tomo-PIV system calibration in Step 3 is completed, the main and auxiliary mine bodies are moved to the underwater measurement position through the three-dimensional moving mechanism. The operating parameters of the Tomo-PIV system are set through the system control host. At the same time, tracer particles of appropriate concentration and uniform distribution are spread in the entire flow field range within the measurement pool, and the ambient light of the water pool test environment is kept at a dark level.

[0021] Step 5: Begin the test measurement. In the towed water tank environment: the main and auxiliary torpedo bodies are driven by a trailer at the target speed, and the main and auxiliary torpedo bodies remain relatively stationary with respect to the model ship under test. After the trailer speed stabilizes, particle image data is recorded and recording stops before the trailer decelerates. At this time, particle images from four high-speed cameras are obtained. The velocity vector information of the flow field in the three-dimensional space range can be calculated through post-processing. In the circulating water tank environment: the water is made to flow at the target speed. After the flow velocity is uniform, the flow information in the area to be tested is recorded.

[0022] Step 6: The experiment is over. Extend the mine out of the water.

[0023] The beneficial effects of this invention are as follows:

[0024] The streamlined design of the flow guide spar and flow guide plate device of the present invention will minimize wave-making interference and structural load.

[0025] The mirrors in the main and secondary mine camera reflector compartments and the laser adjustment compartment of this invention can rotate around the central axis of the mine in multiple stages to change the relative position of the measurement area and the mine, providing a wider range of application scenarios.

[0026] In this invention, the high-speed camera body in the main and secondary radar bodies is mounted on a rotating platform, which can achieve a small-amplitude rotation. The camera lens is separated from the camera and fixed. The rotating platform can be remotely controlled to rotate so that the camera and lens are at a certain angle, satisfying Scheimpflug's law, and obtaining a clear full-frame image when shooting at an angle.

[0027] The camera reflector of the present invention has a separate compartment that is connected to the outside world, so that the compartment is filled with water during operation, thereby avoiding image distortion caused by the camera tilting across the medium.

[0028] The camera cable of the present invention includes a control cable for the camera lens, which can remotely focus the camera lens through the system control host. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV of the present invention.

[0030] Figure 2 This is a structural diagram of the flow guide spar of the present invention;

[0031] Figure 3 These are front views of the main and secondary mine bodies of the present invention;

[0032] Figure 4 These are side views of the main and secondary mine bodies of the present invention;

[0033] Figure 5 This is a detailed internal view of the main body of the present invention;

[0034] Figure 6 This is a detailed view of the interior of the secondary mine body of the present invention;

[0035] Figure 7 This is a detailed view of the laser system and aluminum profile mounting bracket of the present invention. Detailed Implementation

[0036] The present invention will now be further described with reference to the accompanying drawings.

[0037] according to Figure 1 The present invention provides an underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV, which mainly includes a flow guide spar 1, a main mine body 2, a secondary mine body 3, a laser system 4, and an aluminum profile fixing frame 5.

[0038] according to Figure 2 , 3The flow guide 1 consists of a fixed frame 1a, a hollow chamber 1b, and flow guide plates 1c. The fixed frame 1a is connected to the hollow chamber 1b, providing an external outlet for the laser guide arm 18 and the camera cable, and also serves to fix the overall frame. The hollow chamber 1b has a built-in steel frame beam to ensure the overall structural strength, and includes a laser guide arm 18 and a camera cable guide arm 21. The laser guide arm 18 extends from the laser system 4 above the fixed frame 1a to the center of the main mine body 2. The camera cable guide arm 21 branches off into two bundles of cables at the main mine body 2 to control the two sets of camera groups at both ends of the main mine body 2, and extends downward to the secondary mine body 3 to control the two sets of camera groups in the secondary mine body 3. The two streamlined flow guide plates 1c are connected to the hollow chamber 1b by rivets to ensure the stability of the flow guide 1 when working in water.

[0039] according to Figures 3 to 7 The main laser body 2 is connected to the flow guide scimitar 1 and is mainly divided into five compartments and front and rear flow guide caps. The middle compartment is the laser adjustment compartment 12, which mainly contains the laser guide arm 18, lens group 19, laser reflector 20, and laser outlet 7, which extend from the hollow compartment 1b. The line laser emitted by the laser body 23 is transmitted to the laser adjustment compartment 12 via the laser guide arm 1, and then converted into a volume laser 9 by the lens group. The volume laser 9 is then emitted perpendicularly to the laser body through the laser outlet 7 by the laser reflector 20, illuminating the space to be measured in the flow field. Secondly, two camera compartments 13 and two camera mirror compartments 11 are symmetrically distributed on both sides of the laser adjustment compartment 12. Each camera compartment 13 primarily houses a high-speed camera 16 fixed to the rotating platform 22 and a fixed camera lens 15. Three cables extend from the camera compartment 13 via camera cable guides 21 to the system control unit on the trailer, controlling the rotating platform 22, the high-speed camera 16, and the camera lens 15 respectively. The high-speed camera 16 is separate from the camera lens 15 and can be slightly offset by the rotating platform 22 to form a certain angle with the lens, satisfying Scheimpflug's law. This allows for clear full-frame images during tilted shooting. The camera lens 15 can be remotely focused via cables. The camera mirror compartment 11 houses a camera mirror 14, allowing the camera to capture particle images of the measurement area through the camera shooting window 6. To avoid image distortion caused by tilted shooting across the medium, the camera mirror compartment 11 must be connected to the outside and filled with water during operation. Except for the camera mirror compartment 11, the other three compartments must be kept watertight to prevent water damage to the instrument. The mirrors in the camera reflector compartment 11 and the laser adjustment compartment 12 can rotate in multiple stages around the central axis of the mine body to change the relative position of the measurement area and the mine body, providing a wider range of application scenarios. Except for the absence of the laser adjustment compartment 12, the auxiliary mine body 3 is structurally identical to the main mine body 2.

[0040] according to Figure 7The laser system 4 includes a laser body 23 mounted on a laser mounting bracket 27 above the guide beam 1 mounting frame 1a. The laser beam is transmitted from the laser outlet at the front end of the laser system 4 to the laser guide arm 18 via a multi-stage adapter 24. The rear end of the laser system 4 needs to be connected to the control power supply and circulating water cooling system via a laser controller and power interface 25 and a laser water cooling interface 26 to ensure normal operation. The laser system 4 must always maintain a safe distance from the water surface to avoid the risk of water ingress. The laser system 4 needs to be synchronized with four high-speed cameras 16 via a synchronization controller. Both the guide beam 1 mounting frame 1a and the laser system 4 are fixed using standard aluminum profile mounting frames 5, allowing for free installation on towed pool trailers or other mechanisms or lifting platforms on the shoreline of the circulating water tank.

[0041] The specific measurement method of the underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV of the present invention is as follows:

[0042] First, the equipment is installed: the entire set of equipment can be connected to the three-dimensional moving mechanism on the trailer or shore base through the national standard aluminum profile fixing frame. Then, the laser body is connected to the laser controller, and the camera optical cable extending from the upper end of the guide sword is connected to the system control host.

[0043] After installation, adjust the angles of the reflectors in the main and secondary mine camera cabins and the laser adjustment cabin according to the shooting location requirements to ensure that the shooting areas of the four cameras are consistent and within 10° of the volumetric laser illumination range. After the angle adjustment, lower the mine into the water using a three-dimensional moving mechanism and calibrate the Tomo-PIV system. During calibration, the Scheimpflug angle and lens focal length of the four cameras can be adjusted via the system control host. After calibration, move the mine to the underwater measurement position using the three-dimensional moving mechanism, and set the operating parameters of the Tomo-PIV system via the system control host, including laser energy, shooting frequency, and frame interval. Simultaneously, distribute tracer particles of appropriate concentration and uniform distribution throughout the entire flow field range within the measurement area in the water tank, while maintaining a relatively dim ambient light level in the water tank test environment.

[0044] After all preparations for the experiment were completed, the measurements began. In the towed water tank environment, the torpedo body was propelled by a trailer at the target speed, maintaining relative stillness with the model ship under test. Once the trailer speed stabilized, particle image data was recorded, and recording ceased before the trailer decelerated. Particle images from four high-speed cameras were then obtained. Post-processing allowed for the calculation of velocity vector information of the flow field within the captured three-dimensional space. In the circulating water tank environment, water was allowed to flow at the target speed, and once the flow rate was uniform, flow information within the test area was recorded. After the experiment, the torpedo body was extended above the water surface and stored in a dry environment.

[0045] It is important to note that before each test, a standard test without a ship model of a single torpedo body must be conducted, and the accuracy of the flow field test of the 3D3C-PIV system must be verified by using the towing speed and flow velocity as a uniform standard flow field.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV, characterized in that: The system includes a flow guide spar (1), a main mine body (2), a secondary mine body (3), a laser system (4), and an aluminum profile mounting bracket (5). The laser system (4) is located at the top of the flow guide spar (1) and includes a laser body (23). Both the flow guide spar (1) and the laser system (4) are fixed on the aluminum profile mounting bracket (5). The flow guide spar (1) is a hollow structure, i.e., a hollow cabin (1b). The hollow cabin (1b) contains a laser guide arm (18) and a camera cable guide arm (21). The lower end is fixed with the main mine body (2) and the secondary mine body (3). The main mine body (2) includes two mine body flow guide caps (8), two camera reflector cabins (11), two camera cabins (13), and a laser adjustment cabin (12). The laser adjustment cabin ( 12) Located in the middle of the main mine body (2), the laser adjustment chamber (12) includes a laser guide arm (18) extending from the hollow chamber body (1b), a laser reflector (20), a lens group (19) located in the middle, and a laser outlet (7) located on the wall of the mine body; the two sides of the laser adjustment chamber (12) are, in order, a camera chamber (13), a camera reflector chamber (11), and a mine body flow guide cap (8). Each side of the camera chamber (13) and the camera reflector chamber (11) contains a set of high-speed camera groups. The high-speed camera group includes a high-speed camera (16) mounted on the rotating platform (22), a fixed camera lens (15), a camera reflector (14), and a camera shooting window located on the wall of the mine body. The main mine body (2) includes a camera compartment (13), a camera reflector compartment (11), and two sets of high-speed cameras, which are the same as those in the main mine body (2). The guide scimitar (1) consists of a fixed frame (1a), a hollow chamber (1b), and a guide plate (1c). The guide scimitar (1) includes a fixed frame (1a), a hollow chamber (1b), and a guide plate (1c). The fixed frame (1a) is connected to the hollow chamber (1b) to provide an external outlet for the laser guide arm (18) and the camera cable. The hollow chamber (1b) includes a laser guide arm (18) and a camera cable guide arm (21). The laser guide arm (18) starts from the laser system (4) above the fixed frame (1a) and goes to the main mine body (2). Up to the center, the camera cable guide arm (21) branches off two bundles of cables from the main mine body (2) to control the two sets of high-speed camera groups at both ends of the main mine body (2), and extends downward to the secondary mine body to control the two sets of high-speed camera groups of the secondary mine body (3); the front and rear streamlined guide vanes (1c) are connected to the hollow cabin (1b) to ensure the stability of the guide sword rod (1) when working in the water; the camera cable guide arm (21) branches off two bundles of cables from the main mine body (2) to control the two sets of camera groups at both ends of the main mine body (2), and extends downward to the secondary mine body (3) to control the two sets of camera groups of the secondary mine body (3); the reflectors in the camera reflector cabin (11) and the laser adjustment cabin (12) can rotate around the central axis of the mine body in multiple stages.

2. The underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV according to claim 1, characterized in that: The high-speed camera (16) is separated from the camera lens (15) and can be driven by the rotating platform (22) to make an angular offset, thereby forming an angle with the camera lens (15).

3. The underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV according to claim 1, characterized in that: The camera reflector compartment (11) is connected to the outside world and is filled with water when in operation.

4. The underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV according to claim 1, characterized in that: The camera compartment (13) and the laser adjustment compartment (12) must be kept watertight.

5. The measurement method of the underwater three-dimensional spatial flow field measurement system based on 3D3C-PIV according to any one of claims 1 to 4, characterized in that: Step 1: The entire measurement system is connected to the three-dimensional moving mechanism on the trailer or shore base through an aluminum profile fixing frame. Then, the laser body is connected to the laser controller, and the camera optical cable extending from the upper end of the guide spar is connected to the system control host. Step 2: After completing Step 1, adjust the angles of the camera reflector cabins and laser adjustment cabins of the main and secondary laser bodies according to the shooting position requirements, so that the shooting areas of the four cameras are consistent and within the laser irradiation range of the body. Step 3: After the reflector angle adjustment in Step 2 is completed, the main and secondary torpedo bodies are placed underwater using the three-dimensional moving mechanism, and the Tomo-PIV system is calibrated. During the calibration, the Scheimpflug angle and lens focal length of the four cameras can be adjusted by controlling the main unit of the system. Step 4: After the Tomo-PIV system calibration in Step 3 is completed, the main and auxiliary mine bodies are moved to the underwater measurement position through the three-dimensional moving mechanism. The operating parameters of the Tomo-PIV system are set through the system control host. At the same time, tracer particles of appropriate concentration and uniform distribution are spread in the entire flow field range within the measurement pool, and the ambient light of the water pool test environment is kept at a dark level. Step 5: Begin the test measurement. In the towed water tank environment: the main and auxiliary torpedo bodies are driven by a trailer at the target speed, and the main and auxiliary torpedo bodies remain relatively stationary with respect to the model ship under test. After the trailer speed stabilizes, particle image data is recorded and recording stops before the trailer decelerates. At this time, particle images from four high-speed cameras are obtained. The velocity vector information of the flow field in the three-dimensional space range can be calculated through post-processing. In the circulating water tank environment: the water is made to flow at the target speed. After the flow velocity is uniform, the flow information in the area to be tested is recorded. Step 6: The experiment is over. Extend the mine out of the water.

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