A device and method for measuring the underwater angle of repose of sand bodies under dynamic water conditions with controllable background turbulence intensity.

Abstract

This invention discloses an underwater angle of repose measurement device and method for sand bodies under controllable background turbulence intensity in dynamic water conditions. The device includes a support frame, a base plate, a cylindrical platform, a hollow cylindrical baffle, sidewalls, an upstream baffle, a downstream baffle, a turbulence grid, an image acquisition module, and a supplementary lighting module. The hollow cylindrical baffle is fitted around the cylindrical platform to laterally confine the sand sample and form an initial cylindrical sand body. After extraction, the sand body naturally collapses underwater to form a cone. The upstream and downstream baffles form a local still water measurement zone. The turbulence grid can be inserted into different slots on the upstream side of the cylindrical platform, and different background turbulence intensity conditions can be created by changing the grid parameters. The image acquisition module is used to acquire a side view image of the sand cone and calculate the underwater angle of repose. This invention can achieve angle of repose measurement under still water, incoming current, and controllable background turbulence intensity in dynamic water conditions within the same device, and has the advantages of convenient operation and good measurement repeatability.

Description

Technical Field

[0001] This invention relates to the field of experimental equipment technology for sediment dynamics, specifically to a device and method for measuring the underwater angle of repose of a sand body under dynamic water conditions with controllable background turbulence intensity. Background Technology

[0002] The underwater angle of repose is an important parameter characterizing the stable state of sediment particles in water, directly related to the initiation, transport, deposition, and local topographic evolution of substrate materials. In river, estuary, coastal, and nearshore engineering, the underwater angle of repose is often used as a fundamental parameter for analyzing the stability of scour pit slopes, sediment deposition morphology, and the extent of substrate evolution.

[0003] Most underwater angle of repose parameters used in existing research and engineering models are derived from laboratory test results under still water or constant uniform flow conditions. While this type of measurement can obtain relatively stable geometric slope angles in ideal environments, there are still significant differences between the test conditions and actual hydrodynamic environments. The bottom boundary layer in natural water bodies is usually in a complex turbulent state. During sedimentation, rolling, and redistribution, sediment particles are affected by instantaneous pulsating velocities, eddy structures, and local shear changes. Therefore, the angle of repose results obtained under still water conditions cannot directly reflect the true stable slope of the sand body under complex hydrodynamic effects.

[0004] Currently, common methods for measuring underwater angles of repose mainly include the disc method, funnel method, and natural sedimentation method. Most of these methods are based on still water environments and focus on obtaining the final slope angle after the sediment pile collapses naturally. They have the following shortcomings: First, it is difficult to achieve comparative measurements under still water, incoming flow, and different turbulence intensities in the same device. Second, the devices usually lack local flow isolation structures, making it difficult to establish a stable and repeatable local still water measurement area in the mainstream environment of the flume. Third, in the measurement or simulation process under existing dynamic water conditions, the turbulence intensity often changes synchronously with the mainstream flow velocity, flow rate, or water depth, making it difficult to adjust and characterize the background turbulence intensity as an independent variable while maintaining relatively consistent incoming flow conditions. Fourth, some measurement methods rely on manual reading or contact measurement, which are easily affected by water disturbance, line-of-sight obstruction, and reading errors, thus limiting the repeatability and accuracy of the measurement.

[0005] Therefore, there is an urgent need for an experimental device with a relatively simple structure that can be installed inside a water tank, can achieve static water comparison, inflow effect and dynamic water background turbulence intensity adjustment in the same measurement unit, and can be easily combined with image acquisition methods to measure the underwater angle of repose of sand bodies, so as to meet the needs of sediment dynamics research and related engineering tests. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a device and method for measuring the underwater angle of repose of sand bodies under dynamic water conditions with controllable background turbulence intensity, so as to overcome the problems in the prior art that it is difficult to switch between still water and dynamic water conditions in the same device, it is difficult to independently adjust the turbulence intensity under dynamic water conditions, it is difficult to construct a local still water environment, and the accuracy and repeatability of the angle of repose measurement are insufficient.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] An underwater repose angle measuring device for sand bodies with controllable background turbulence intensity under dynamic water conditions, as disclosed in this invention, comprises:

[0009] A support frame, used for installation inside the experimental water tank;

[0010] A support platform, mounted on the support frame, is used to support the sand body to be tested;

[0011] The confinement component is detachably installed on the periphery of the bearing platform to laterally confine the sand sample on the bearing platform to form a columnar sand body, and after removal, the columnar sand body will naturally collapse underwater to form a cone.

[0012] Multiple mounting positions are spaced apart on the support frame along the direction of incoming flow;

[0013] The enclosure is selectively installed in the mounting position to form a local measurement area on the front and rear sides of the area where the bearing platform is located, and to selectively isolate the local measurement area from the main flow area of ​​the water tank;

[0014] Turbulence generators are selectively installed at different mounting positions on the upstream side of the support platform. They are used to adjust the background turbulence intensity in the local measurement area by changing the relative distance to the support platform and / or replacing turbulence generators with different parameters, while keeping the incoming flow conditions relatively consistent.

[0015] An image acquisition module is located downstream of the local measurement area and is used to acquire a side view image of the cone.

[0016] A supplementary lighting module is positioned above or around the local measurement area to improve underwater imaging conditions.

[0017] The present invention provides a method for measuring the underwater angle of repose of sand bodies under dynamic water conditions with controllable background turbulence intensity, comprising the following steps:

[0018] The measuring device is installed in the experimental water tank. The measuring device includes a support frame, a bearing platform set on the support frame, a confinement component detachably set around the bearing platform, multiple sets of mounting positions spaced apart on the support frame along the direction of the incoming flow, and an image acquisition module set on the downstream side of the bearing platform.

[0019] Depending on the target measurement conditions, selectively install enclosure components and / or turbulence generators in the installation position to form a local measurement zone in the area where the support platform is located, and isolate or connect the local measurement zone with the main flow zone of the water tank, and / or adjust the background turbulence intensity in the local measurement zone by changing the relative distance between the turbulence generator and the support platform and / or replacing the turbulence generator with different parameters while keeping the incoming flow conditions relatively consistent;

[0020] Sand samples are filled into the bearing platform and laterally confined using the confinement components to form a columnar sand body;

[0021] Remove the confining elements to allow the columnar sand body to collapse underwater or adjust to form a cone shape under the action of the incoming current;

[0022] The image acquisition module is used to obtain a side view image of the cone, and the underwater angle of repose is calculated based on the side view image.

[0023] The present invention has the following beneficial effects:

[0024] 1) This invention avoids direct modification of the experimental water tank body by setting an independent support frame inside the water tank, which facilitates the installation, disassembly and reuse of the device.

[0025] 2) By setting multiple sets of slots on both sides of the support frame, the present invention enables the upstream baffle, downstream baffle and turbulence grid to be quickly replaced and adjusted in position according to the test requirements, thereby realizing the switching between still water conditions, incoming flow conditions and conditions with different background turbulence intensities in the same device.

[0026] 3) By setting multiple sets of slots on the upstream side and replacing turbulence grids, the present invention can change the relative distance between the grid and the cylindrical platform while keeping the incoming flow conditions relatively consistent, thereby adjusting the background turbulence intensity when the grid wake develops to the measurement area, providing a device basis for conducting underwater angle of repose tests with turbulence intensity as a relatively independent variable.

[0027] 4) This invention uses a cylindrical platform and a detachable hollow cylindrical baffle to form an initial cylindrical sand body, which allows the sand body to naturally collapse underwater to form a stable cone. The measurement process is clear and has good repeatability.

[0028] 5) By arranging an image acquisition module on the downstream side of the measurement area and combining it with a supplementary lighting module to image the cone, this invention can reduce manual reading errors and improve the accuracy and efficiency of underwater repose angle measurement.

[0029] 6) This invention can provide a controllable, stable and repeatable experimental platform for studying the influence of background turbulence on the underwater angle of repose of sand bodies, and is suitable for sediment dynamics and related engineering model tests. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall structure of an underwater repose angle measuring device for sand bodies with controllable background turbulence intensity under dynamic water conditions, according to the present invention.

[0031] Figure 2 This is a schematic diagram of the main structure of the measuring device of the present invention.

[0032] Figure 3 This is a schematic diagram of the installation state of the hollow cylindrical baffle in this invention.

[0033] Figure 4 This is a schematic diagram of the local static water measurement zone formed after the upstream and downstream baffles are installed in this invention.

[0034] Figure 5 This is a schematic diagram showing the turbulence grid installed at different slot positions upstream to change the relative distance between the grid and the cylindrical platform in this invention.

[0035] Figure 6 This is a schematic diagram of the present invention measuring dynamic water conditions under the action of incoming flow.

[0036] Figure 7 This is a schematic diagram of the arrangement of the underwater camera and supplementary lighting in this invention.

[0037] Figure 8 This is an example of extracting the angle of repose of sediment under static water reference conditions. Detailed Implementation

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be used to limit the scope of protection of the present invention.

[0039] This application provides a sand body underwater angle of repose measurement device with controllable background turbulence intensity under dynamic water conditions, including a support frame, a base plate disposed at the bottom of the support frame, a cylindrical platform fixed on the base plate, a hollow cylindrical baffle detachably disposed around the cylindrical platform, and multiple sets of slots disposed on the inner sides of both sides of the support frame.

[0040] The support frame is used to be installed inside the experimental water tank and to provide an installation base for the baffles and grids;

[0041] The cylindrical platform is used to support the sand body to be tested;

[0042] The hollow cylindrical baffle is sleeved around the cylindrical platform to laterally confine the sand sample on the cylindrical platform to form an initial cylindrical sand body; after the hollow cylindrical baffle is removed, the initial cylindrical sand body naturally collapses underwater to form a cone.

[0043] The multiple sets of slots are used to selectively insert upstream baffles, downstream baffles, or turbulence grids to create different measurement conditions.

[0044] Furthermore, the support frame includes two opposing side panels and a frame structure connecting the two side panels. The multiple sets of slots are spaced apart on the inner surfaces of the two side panels along the incoming flow direction, and each slot extends vertically so that the baffle or grille can be inserted and installed from top to bottom. The upstream side is provided with 3 to 8 sets of slots, and the downstream side is provided with at least 1 set of slots. Adjacent upstream slots are spaced apart along the incoming flow direction so that the turbulence grille can form multiple different installation positions relative to the cylindrical platform.

[0045] Furthermore, the support frame also includes an installation beam connected to the upper support structure of the experimental water tank, used to suspend or fix the device inside the experimental water tank and adjust the installation height of the base plate relative to the bottom of the water tank.

[0046] Furthermore, the upstream baffle and the downstream baffle can be inserted into the slot to form a relatively closed local measurement area before and after the cylindrical platform; when both the upstream baffle and the downstream baffle are inserted, the local measurement area is relatively isolated from the main flow area of ​​the water tank, and is used to measure the underwater angle of repose under still water conditions.

[0047] Furthermore, the turbulence grid can be selectively inserted into different slot positions located upstream of the cylindrical platform to change the relative distance between the grid and the cylindrical platform; while keeping the incoming flow velocity or flow rate conditions relatively consistent, by changing the insertion position of the turbulence grid and / or replacing the turbulence grid with different grid parameters, the background turbulence intensity when the grid wake develops to the measurement area can be adjusted, which is used to measure the underwater angle of repose of the sand body under different background turbulence intensity conditions.

[0048] Furthermore, the turbulence grid is a square-hole mesh plate structure, with its plate surface perpendicular to the incoming flow direction; the grid parameters include aperture, grid bar width and / or opening ratio, and the aperture of the turbulence grid is 2cm to 6cm, and the grid bar width is 0.5cm to 2cm.

[0049] Furthermore, the inner diameter of the hollow cylindrical baffle is larger than the outer diameter of the cylindrical platform. After the hollow cylindrical baffle is fitted around the cylindrical platform, it forms a circumferential enclosure for the sand sample on the cylindrical platform. After the sand is loaded, the hollow cylindrical baffle is pulled out vertically, allowing the initial cylindrical sand body to collapse naturally in the water and form the cone to be tested.

[0050] Furthermore, the device also includes an image acquisition module located downstream of the measurement area. The image acquisition module is used to acquire a side view image of the sand cone and extract the cone's contour coordinates through image processing, thereby calculating the angle between the cone's slope and the baseline horizontal line.

[0051] Furthermore, the device also includes a supplementary lighting module disposed above or around the measurement area to improve underwater imaging conditions and enhance the clarity and stability of sand body contour recognition.

[0052] Furthermore, the baffle located downstream of the measurement area can be made of a light-transmitting material so that the image acquisition module can capture images of the cone through the baffle; the baffle located upstream of the measurement area can be made of a transparent material or a low-reflective material to improve the contrast between the cone outline and the background.

[0053] This application provides a method for measuring the underwater angle of repose of a sand body, comprising the following steps:

[0054] S1. A hollow cylindrical baffle is fitted around the cylindrical platform, and sand samples are filled into the cylindrical platform to form an initial cylindrical sand body;

[0055] S2. Selectively insert an upstream baffle, a downstream baffle, or a turbulence grid into the slot according to the working condition to be tested;

[0056] S3. Inject water into the measurement area, or create an inflow condition in the experimental water tank;

[0057] S4. The hollow cylindrical baffle is removed vertically, so that the initial cylindrical sand body collapses or is adjusted to form a sand cone under the conditions of still water, incoming flow or background turbulence intensity that can be controlled.

[0058] S5. Obtain a side view image of the sand cone and calculate the underwater angle of repose of the sand body based on the side view image.

[0059] Furthermore, when upstream and downstream baffles are installed simultaneously, the measurement area is relatively isolated from the main flow area of ​​the experimental water tank to perform underwater angle of repose measurement under still water conditions.

[0060] Furthermore, when the upstream and downstream baffles are not installed, the measurement area is connected to the main water body of the experimental tank to measure the underwater angle of repose under incoming flow conditions.

[0061] Furthermore, when turbulence grids are installed at different slot positions on the upstream side, different background turbulence intensity conditions are formed by changing the relative distance between the turbulence grid and the cylindrical platform, and / or by replacing turbulence grids with different grid parameters, so as to measure the underwater angle of repose under dynamic water conditions with controllable background turbulence intensity.

[0062] Further, step S5 includes: extracting the contour coordinates of the left and right sides of the sand cone, performing least squares fitting on the slope lines of the left and right sides respectively, calculating the angle between the fitted straight line and the reference horizontal line of the cylindrical platform surface, and taking the average value of the angle between the left and right sides as the underwater angle of repose under the corresponding working condition, wherein the reference horizontal line is the projection line of the cylindrical platform surface in the side view image.

[0063] Example:

[0064] like Figure 1 and Figure 2 As shown, an underwater repose angle measuring device for sand bodies with controllable background turbulence intensity under dynamic water conditions includes a support frame 1, a base plate 2, a cylindrical platform 3, a hollow cylindrical baffle 4, a side wall plate 5, a slot 6, an upstream baffle 7, a downstream baffle 8, a turbulence grid 9, an underwater camera 10, a supplementary light 11, a sand body cone 12, and an installation beam 14.

[0065] In this embodiment, the device is installed inside an experimental water tank. The experimental water tank is 16m long, 0.5m wide, and 0.5m high, with a maximum test water depth of 0.4m, a maximum flow rate of 120L / s, and a flow generation accuracy of no more than ±0.02m / s. The device is preferably located in the stable inflow zone in the middle section of the water tank, near the centerline. In this embodiment, the center of the device is preferably located approximately 8m from the water tank inlet to reduce the impact of inlet disturbances on the measurement area 13.

[0066] The support frame 1 is used to form an independent device installation unit inside the experimental water tank. It includes a base plate 2, side wall plates 5 disposed on both sides of the base plate 2, and an installation beam 14 disposed on the upper part. By setting the support frame 1, it is not necessary to directly groove or install on the glass side wall of the experimental water tank, thereby facilitating the disassembly, assembly, and reuse of the device.

[0067] In this embodiment, the base plate 2, side wall panels 5, and cylindrical platform 3 are all made of acrylic material. The base plate 2, side wall panels 5, and cylindrical platform 3 can be formed by integral processing, or they can be processed separately and then fixedly connected by adhesive bonding; in this embodiment, the structure of integral processing and fixed installation is preferred to improve the overall rigidity and installation stability.

[0068] The base plate 2 is 0.5m long, 0.4m wide, and preferably 5mm to 10mm thick, with 8mm being preferred in this embodiment. There are two sidewall panels 5, respectively disposed on the left and right sides of the base plate 2, arranged along the flow direction; each sidewall panel 5 is 0.4m long, 0.3m high, and preferably 5mm to 10mm thick, with 8mm being preferred in this embodiment. The two sidewall panels 5 are recessed inwards relative to the edge of the base plate 2 to reserve installation and flow-around space between the outer edge of the base plate 2 and the sidewall panels 5.

[0069] The mounting beam 14 is positioned above the support frame 1 and is used to suspend or fix the device to the upper support structure of the experimental water tank, and to adjust the installation height of the base plate 2 relative to the bottom of the water tank. Preferably, the mounting beam 14 can be made of aluminum profile or other lightweight materials with sufficient rigidity. In this embodiment, the support frame 1 is fixed to the support frame above the experimental water tank by the mounting beam 14, so that the height of the base plate 2 from the bottom of the water tank is 15cm.

[0070] The cylindrical platform 3 is fixedly mounted on the base plate 2, serving to support the sand sample to be tested and as a reference support surface for forming the sand cone 12. In this embodiment, the cylindrical platform 3 has an outer diameter of 15cm, a height of 5cm, and its center is located on the central axis of the base plate 2; along the flow direction, the center of the cylindrical platform 3 is 30cm from the upstream edge of the base plate 2 and 20cm from the downstream edge of the base plate 2.

[0071] The hollow cylindrical baffle 4 is fitted around the cylindrical platform 3 to laterally confine the sand sample located on the cylindrical platform 3, thereby forming an initial cylindrical sand body. The hollow cylindrical baffle 4 is made of acrylic material, with an inner diameter of 15.2 cm, an outer diameter of 16.2 cm, a wall thickness of 5 mm, and a height of 12.5 cm. Because the inner diameter of the hollow cylindrical baffle 4 is slightly larger than the outer diameter of the cylindrical platform 3, it can be fitted around the cylindrical platform 3 and provide circumferential constraint on the sand sample during the sand loading process. Figure 3 .

[0072] In this embodiment, the bottom surface of the hollow cylindrical baffle 4 is a planar structure. Instead of being positioned by a special groove, it is directly fitted onto the outer periphery of the cylindrical platform 3. The hollow cylindrical baffle 4 is provided with a handle at the top. During the test, it is slowly lifted vertically by hand, causing the initial cylindrical sand body to collapse naturally underwater to form a sand cone 12.

[0073] The inner surface of the sidewall panel 5 is provided with multiple sets of slots 6 extending vertically for selectively inserting the upstream baffle 7, downstream baffle 8, and turbulence grid 9. The slots 6 can be formed by directly milling grooves into the acrylic sheet, or by adding a guide groove structure to the inner surface of the sidewall panel 5. In this embodiment, the slots 6 are directly formed on the inner surface of the sidewall panel 5 through machining.

[0074] In this embodiment, five sets of slots 6 are provided on the upstream side and one set of slots 6 is provided on the downstream side. Each set of slots 6 is 8mm wide, 4mm deep, and 30cm long vertically, matching the height of the side wall panel 5. The center-to-center distance between two adjacent sets of slots 6 on the upstream side is 2cm. The center-to-center distance of the upstream slot 6 closest to the center of the cylindrical platform 3 is 15cm, and the center-to-center distances of the other four sets of upstream slots 6 are 17cm, 19cm, 21cm, and 23cm, respectively. The downstream slots 6 are symmetrically arranged with respect to the center of the cylindrical platform 3, as are the nearest upstream slots 6.

[0075] The upstream baffle 7 and downstream baffle 8 are used to form local enclosure spaces before and after the measurement area 13, respectively. Both are identical in size, 30cm × 30cm × 8mm, and can be inserted vertically into their corresponding slots 6. After insertion, the bottom edge of the baffle fits against the base plate 2 to minimize the exchange between the measurement area 13 and the external mainstream water body.

[0076] Preferably, the downstream baffle 8 is made of transparent acrylic material to allow the underwater camera 10 to obtain a side view image of the sand cone 12 through it; the upstream baffle 7 can be made of transparent material or low-reflectivity dark material to improve the contrast between the cone outline and the background. In this embodiment, the upstream baffle 7 is made of matte black acrylic sheet, and the downstream baffle 8 is made of transparent acrylic sheet.

[0077] When the upstream baffle 7 and downstream baffle 8 are respectively inserted into their innermost corresponding slots 6, a partial enclosure space is formed in front of and behind the cylindrical platform 3. This area is the measurement area 13. In this embodiment, without considering the thickness of the baffles and the space occupied by the slots, the planar dimensions of the measurement area 13 are approximately 30cm × 30cm, and the height is approximately 30cm. The actual effective water depth is related to the installation height of the device and the test water level, see [reference needed]. Figure 4 .

[0078] The turbulence grid 9 is disposed on the upstream side of the measurement area 13 to create different background turbulence conditions before the incoming flow enters the measurement area 13. The overall dimensions of the turbulence grid 9 are the same as the upstream baffle 7, both being 30cm × 30cm × 8mm, and it can be vertically inserted into slots 6 at different positions on the upstream side. The turbulence grid 9 has a square-hole mesh plate structure; in this embodiment, its aperture is 4cm, and the grid strip width is 1cm, extending throughout the entire local water depth. Figure 5 .

[0079] By changing the position of the turbulence grid 9 installed in different upstream slots 6, the relative distance between the turbulence grid 9 and the cylindrical platform 3 can be altered, thereby changing the turbulence characteristics when the grid wake develops to the measurement area 13. In this embodiment, the center distance of the turbulence grid 9 from the center of the cylindrical platform 3 can be 15cm, 17cm, 19cm, 21cm, and 23cm, respectively. For implementations requiring more operating conditions, the number of upstream slots 6 can be increased, or replaceable grids with different apertures and rib widths can be used to create more background turbulence conditions.

[0080] To clearly illustrate the different optional installation positions of the turbulence grid 9, the accompanying drawings may use a combination of solid and dashed lines to show the state of the turbulence grid 9 inserted into different upstream slots 6. In actual testing, the turbulence grid 9 is installed in one of the slot positions according to the target background turbulence intensity, or by replacing it with a turbulence grid 9 with different apertures, open areas, or grid bar widths to obtain different grid turbulence conditions. See [link / reference]. Figure 6 .

[0081] The underwater camera 10 is located downstream of the measurement area 13 and in the water of the experimental tank. The underwater camera 10 can be fixed by a support in the water or by a support connected to the mounting beam 14 or the upper support structure of the experimental tank, extending into the water for fixation. The optical axis of the underwater camera 10 is aligned with the cylindrical platform 3 and flush with its center, used to capture a side view image of the sand cone 12. In this embodiment, the underwater camera 10 has a resolution of 8K and a lens equivalent focal length of 40mm. Figure 7 .

[0082] The supplementary light 11 is positioned directly above the measurement area 13 and fixed to the mounting beam 14 or its connecting components to enhance underwater imaging brightness and improve the clarity of the boundary identification of the sand cone 12. In this embodiment, there is one supplementary light 11 with a maximum power of 40W, located approximately 35cm from the bottom plate 2 and approximately 30cm from the top of the cylindrical platform 3.

[0083] To improve the clarity and stability of the side view contour recognition of the sand cone 12, in this embodiment, the image acquisition module, the supplementary lighting module, and the baffle material form a collaborative imaging structure. Specifically, the downstream baffle 8 is made of transparent acrylic material to ensure that the underwater camera 10 can acquire the side view image of the sand cone 12 through the downstream baffle 8; the upstream baffle 7 is made of matte black acrylic sheet or other low-reflection dark material to reduce background reflection and enhance the grayscale difference between the sand cone 12 and the background; the supplementary lighting 11 is set directly above the measurement area 13 to improve the underwater imaging brightness and reduce local shadows; the optical axis of the underwater camera 10 is aligned with the center line of the cylindrical platform 3 so that the acquired image can reflect the lateral slope morphology of the sand cone 12. Preferably, before image acquisition, the underwater camera 10 can be calibrated using a 3cm×3cm checkerboard grid to correct lens distortion and improve the accuracy of subsequent contour extraction and angle calculation.

[0084] In this embodiment, the total water depth is set to 30cm. Since the height of the base plate 2 from the bottom of the tank is 15cm, the effective water depth above the base plate 2 is approximately 15cm; considering that the height of the cylindrical platform 3 is 5cm, the water depth above the top of the cylindrical platform 3 is approximately 10cm. This water depth condition can meet the image acquisition requirements for the initial formation of the cylindrical sand body, natural collapse, and after the cone stabilizes.

[0085] The sand sample to be tested is quartz sand, which is a uniform, non-cohesive granular material with a median particle size d50 of 0.15 mm. The amount of sand loaded each time preferably corresponds to an initial cylindrical sand body with a height of approximately 7.5 cm and a diameter of approximately 15 cm. During loading, a hollow cylindrical baffle 4 is first placed around the cylindrical platform 3, and then quartz sand is filled within the confinement area of ​​the baffle, shaping it into an initial cylindrical sand body with an approximately horizontal top.

[0086] The first operating condition is the static water measurement condition. For example... Figure 4 As shown, the upstream baffle 7 and the downstream baffle 8 are respectively inserted into the corresponding slots 6 to form a local enclosure space in front of and behind the measurement area 13; then water is injected into the measurement area 13 so that the effective water depth above the bottom plate 2 reaches 15cm and the water depth above the top of the cylindrical platform 3 reaches about 10cm; after the local water body stabilizes, the hollow cylindrical baffle 4 is slowly lifted vertically so that the initial cylindrical sand body naturally collapses in the local still water environment to form a sand cone 12; after the outline of the sand cone 12 no longer changes significantly within a certain period of time, the underwater camera 10 is used to collect images to obtain the underwater angle of repose under still water conditions.

[0087] The second operating condition is the incoming flow measurement condition. For example... Figure 6As shown, the upstream baffle 7 and downstream baffle 8 are not installed, so that the measurement area 13 is connected to the main water body of the experimental tank. After a stable inflow is established in the experimental tank, the sand cone 12 is adjusted under the action of the inflow and eventually reaches a stable shape. In this embodiment, three sets of flow conditions are selected for the inflow conditions, namely 12L / s, 16L / s and 20L / s. After the cone profile is stable, the underwater camera 10 is used to collect images to obtain the underwater angle of repose under the inflow conditions.

[0088] The third operating condition is the dynamic water measurement condition where the background turbulence intensity is controllable. For example... Figure 5 As shown, the turbulence grid 9 is inserted into a set of slots 6 on the upstream side. The inflow rate is kept constant in the experimental water tank. By changing the installation position of the turbulence grid 9 and / or replacing the turbulence grid 9 with different grid parameters, the background turbulence intensity in the measurement area 13 is changed. After the water flows through the turbulence grid 9, a wake disturbance zone is formed downstream. When this disturbance zone develops to the measurement area 13 where the cylindrical platform 3 is located, the sand cone 12 can reach a new stable shape under different background turbulence intensity conditions. In this embodiment, the turbulence grid 9 is installed at positions 15cm, 17cm, 19cm, 21cm and 23cm away from the center of the cylindrical platform 3, respectively, to form different turbulence conditions.

[0089] In the specific experimental process, to establish the correspondence between the installation position of the turbulent grid 9 and the background turbulence intensity of the measurement area 13, the downstream flow field of the grid can be pre-calibrated under sand-free conditions. As one implementation method, an acoustic Doppler velocimeter can be used to measure the flow velocity and turbulence parameters at different distances downstream of the grid. The acoustic Doppler velocimeter can be a Nortek Vectrino ADV. During calibration, the turbulent grid 9 is installed in an empty water tank, and multiple measuring points are arranged along the downstream direction of the grid. The height of the measuring points can be set to approximately 5 cm from the bottom plate 2, corresponding to the height position of the upstream edge of the cylindrical platform 3 or the entrance of the measurement area in subsequent sand-containing experiments. Each measuring point can collect three-dimensional instantaneous velocity signals at a sampling frequency of 25 Hz and a sampling duration of 120 s. Each measuring point is repeatedly sampled three times, and the phase space method is used to remove spike noise from the ADV velocity data.

[0090] Time-averaged decomposition of the denoised triaxial velocity signal yields flow parameters such as average velocity, fluctuating velocity, turbulent kinetic energy, and Reynolds stress. The turbulent kinetic energy k can be calculated using the following formula:

[0091]

[0092] In the formula, , , These represent the pulsating velocity components in three directions. Through the above pre-calibration process, a correspondence between the distance from the grid plane to the measuring point and the background turbulence intensity can be established, and this correspondence will serve as the basis for selecting the insertion position of the turbulence grid 9 in subsequent sand-induced angle of repose tests. The above flow field calibration process is used for operating condition characterization and test condition determination, and does not constitute a necessary structural limitation of the device of this invention.

[0093] In a representative calibration embodiment, the distance x from the plane where the grid is located to the measuring point is used as the independent variable, and the turbulent kinetic energy k at the measuring point is used as the characterization quantity of the background turbulence intensity.

[0094] For the regularly decaying region downstream of the grid, the turbulent kinetic energy can be fitted using the following power-law relationship:

[0095]

[0096] In the formula, , , n and The parameters are for fitting. As an example, under inflow conditions of 12 L / s, 16 L / s, and 20 L / s, the following representative fitting relationship can be obtained:

[0097]

[0098] The above fitting results show that, under relatively consistent inflow conditions, the turbulent kinetic energy downstream of the grid decreases systematically with increasing distance from the grid to the measuring point. Therefore, different background turbulence intensity conditions can be created in the measurement area 13 by changing the relative distance between the turbulent grid 9 and the upstream edge of the cylindrical platform 3, or by replacing the turbulent grid 9 with one of different grid parameters.

[0099] After the sand cone 12 is formed and stabilized, the underwater camera 10 acquires its side view image. In this embodiment, an image processing program written in Matlab can be used to process the side view image. Specifically, firstly, the image is distorted according to the camera calibration results, then the image is converted into a grayscale image or a brightness image, and the region containing the sand cone 12 and the cylindrical platform 3 is cropped; subsequently, the initial binary image of the sand cone 12 is obtained through background correction and threshold segmentation, and the largest connected component is extracted as the main region of the sand cone 12; further, the coordinates of the boundary points of the main region are extracted, and the projection line of the surface of the cylindrical platform 3 in the side view image is automatically identified, using the projection line as the reference horizontal line.

[0100] For the obtained boundary point coordinates, the contour points of the left and right slopes of sand cone 12 can be selected respectively, and fitted into straight lines using the least squares method:

[0101]

[0102] In the formula, , These represent the slope and intercept of the fitted straight line for the left slope, respectively. , These represent the slope and intercept of the fitted straight line on the right side slope, respectively.

[0103] The left slope angle and the right slope angle can be expressed as follows:

[0104]

[0105] underwater angle of repose under corresponding working conditions The average value of the slope angles on the left and right sides can be taken:

[0106]

[0107] The above image processing procedure reduces human reading errors and improves the repeatability of repose angle measurement results under different working conditions. In this embodiment, the image processing result is as follows: Figure 8 As shown in the figure, the left angle of repose is 32.24°, the right angle of repose is 32.50°, and the final underwater angle of repose is 32.37°.

[0108] In this embodiment, five images are captured under each operating condition, and each experiment is repeated five times. The criterion for determining whether the cone has reached a stable state is that the cone's profile no longer changes significantly within a certain time period. Repeated measurements can improve the reliability and statistical stability of the results.

[0109] To verify the repeatability of the device under still water reference conditions, five sets of repeated still water measurements were performed using the same sand sample and imaging conditions. Five stable images were taken from each set for angle recognition, resulting in 25 repose angle recognition results. The results are shown in the table below. The results show that the average underwater repose angle under still water conditions was 32.589°, the sample standard deviation was 0.225°, and the coefficient of variation was 0.690%; the coefficient of variation within each group did not exceed 0.116%. These results demonstrate that the device and image recognition process described in this invention have good measurement repeatability under still water reference conditions.

[0110] Table 1. Angle of repose of sediment in still water conditions in the examples.

[0111]

[0112] In summary, this invention integrates a cylindrical platform, a hollow cylindrical baffle, multiple slots, an upstream baffle, a downstream baffle, and a turbulence grid into a single supporting frame, enabling the same device to quickly switch between still water, incoming flow, and different background turbulence intensities. Simultaneously, combined with a downstream underwater camera and an overhead supplemental light, it achieves non-contact image acquisition and angle recognition of sand cones. The device has a simple structure, convenient operating condition switching, and can adjust the background turbulence intensity by adjusting the grid position and / or grid parameters while maintaining relatively consistent incoming flow conditions. The measurement results show good repeatability and are suitable for sediment dynamics experiments and related engineering model studies.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements should also fall within the protection scope of the present invention.

Claims

1. A device for measuring the underwater repose angle of sand under the condition of dynamic water, wherein the background turbulence intensity is controllable, characterized in that, include: A support frame, used for installation inside the experimental water tank; A support platform, mounted on the support frame, is used to support the sand body to be tested; The confinement component is detachably installed on the periphery of the bearing platform to laterally confine the sand sample on the bearing platform to form a columnar sand body, and after removal, the columnar sand body will naturally collapse underwater to form a cone. Multiple mounting positions are spaced apart on the support frame along the direction of incoming flow; The enclosure is selectively installed in the mounting position to form a local measurement area on the front and rear sides of the area where the bearing platform is located, and to selectively isolate the local measurement area from the main flow area of ​​the water tank; Turbulence generators are selectively installed at different mounting positions on the upstream side of the support platform. They are used to adjust the background turbulence intensity in the local measurement area by changing the relative distance to the support platform and / or replacing turbulence generators with different parameters, while keeping the incoming flow conditions relatively consistent. An image acquisition module is located downstream of the local measurement area and is used to acquire a side view image of the cone. A supplementary lighting module is positioned above or around the local measurement area to improve underwater imaging conditions.

2. The underwater repose angle measuring device for sand body under dynamic water condition with controllable background turbulence intensity according to claim 1, characterized in that, The support frame includes a base plate, side wall plates disposed opposite to both sides of the base plate, and an installation beam disposed on the upper part. The installation beam is used to connect with the upper support structure of the experimental water tank to suspend or fix the device inside the water tank and adjust the installation height of the base plate relative to the bottom of the water tank.

3. The underwater repose angle measuring device of sand body under dynamic water condition with controllable background turbulence intensity according to claim 1 or 2, characterized in that, The supporting platform is a cylindrical platform, fixed on the central axis of the base plate; the confinement component is a hollow cylindrical baffle, which can be sleeved on the periphery of the cylindrical platform. The inner diameter of the hollow cylindrical baffle is larger than the outer diameter of the cylindrical platform, so as to form a circumferential confinement for the sand sample on the cylindrical platform.

4. The underwater repose angle measuring device of claim 1, wherein the underwater repose angle measuring device is characterized by, The mounting position is a slot extending in the vertical direction, and the slots are spaced apart on the inner sides of both sides of the support frame along the flow direction.

5. The underwater repose angle measuring device of claim 1, wherein the background turbulence intensity is controlled. The enclosure includes an upstream baffle and a downstream baffle. The upstream baffle and the downstream baffle can be inserted vertically into the slots on the upstream and downstream sides of the bearing platform, respectively, and their bottom edges fit against the base plate after insertion.

6. The underwater repose angle measuring device of sand body under dynamic water condition with controllable background turbulence intensity according to claim 4 or 5, characterized in that, The turbulence generator is a turbulence grid with a square hole mesh plate structure. The aperture, opening ratio, or grid bar width of the turbulence grid can be changed according to the target background turbulence intensity.

7. The underwater repose angle measuring device of claim 1, wherein the background turbulence intensity is controlled. The image acquisition module, the supplementary lighting module, and the upstream and downstream baffles form a collaborative imaging structure: the downstream baffle uses a light-transmitting material so that the image acquisition module can obtain a side view image of the cone through it; the upstream baffle uses a low-reflective material to enhance the contrast between the cone outline and the background; the supplementary lighting module is positioned directly above the local measurement area to improve underwater imaging brightness; and the optical axis of the image acquisition module is aligned with the centerline of the support platform.

8. A method for measuring the underwater repose angle of sand under the condition of dynamic water and controllable background turbulence intensity, using the device of any one of claims 1 to 7, characterized in that Includes the following steps: The measuring device is installed in the experimental water tank. The measuring device includes a support frame, a bearing platform set on the support frame, a confinement component detachably set around the bearing platform, multiple sets of mounting positions spaced apart on the support frame along the direction of the incoming flow, and an image acquisition module set on the downstream side of the bearing platform. Depending on the target measurement conditions, selectively install enclosure components and / or turbulence generators in the installation position to form a local measurement zone in the area where the support platform is located, and isolate or connect the local measurement zone with the main flow zone of the water tank, and / or adjust the background turbulence intensity in the local measurement zone by changing the relative distance between the turbulence generator and the support platform and / or replacing the turbulence generator with different parameters while keeping the incoming flow conditions relatively consistent; Sand samples are filled into the bearing platform and laterally confined using the confinement components to form a columnar sand body; Remove the confining elements to allow the columnar sand body to collapse underwater or adjust to form a cone shape under the action of the incoming current; The image acquisition module is used to obtain a side view image of the cone, and the underwater angle of repose is calculated based on the side view image.

9. The method according to claim 8, wherein the underwater repose angle of the sand body is measured under the condition that the background turbulence intensity is controllable. The selective installation of enclosure components and / or turbulence generators based on the target measurement conditions includes: When performing static water measurements, the upstream and downstream baffles are installed in the mounting positions on the upstream and downstream sides of the bearing platform, respectively, to isolate the local measurement area from the main flow area of ​​the water tank. When measuring the incoming flow, the upstream and downstream baffles are not installed, so that the local measurement area is connected to the main flow area of ​​the water tank; When performing dynamic water measurements with controllable background turbulence intensity, the turbulence grid is installed in the mounting position on the upstream side of the bearing platform, while keeping the incoming flow rate constant.

10. A method for measuring the underwater angle of repose of a sand body under controllable background turbulence intensity under dynamic water conditions, as described in claim 8 or 9, characterized in that... The calculation of the underwater angle of repose based on the side view image includes: The side view image is distorted and converted into a grayscale image. The coordinates of the boundary points of the main body region of the cone are extracted through background correction and threshold segmentation. The projection line of the surface of the bearing platform in the side view image is identified as the reference horizontal line; Select the contour points of the left and right slopes of the cone respectively, fit them into a straight line using the least squares method and calculate the left and right slope angles; The average value of the slope angles on the left and right sides is taken as the underwater angle of repose.

Images