A system and method for simulating and monitoring sand shape evolution and near bottom water dynamic characteristics under reciprocating flow conditions in a laboratory

Abstract

The application discloses a system and method for simulating and monitoring sand wave form evolution and near-bottom water dynamic characteristics under reciprocating flow conditions in a laboratory, and relates to the technical field of sand wave form evolution and near-bottom water dynamic characteristics. The system comprises a water tank assembly, a power assembly for generating reciprocating flow in the water tank assembly, and the water tank assembly comprises a U-shaped water tank with two open top ends and an internal communication. An opening for removing air bubbles and a sealing top cover matched with the opening are arranged at the upper end of the middle part of the water tank. A sediment tank for laying a sand bed is arranged below the opening. The power assembly comprises a wave pushing plate arranged on one side of the sediment tank. The wave pushing plate is pushed by a transmission rod to reciprocate in the water tank to generate reciprocating flow, so as to drive the sand bed to change forms. The method comprises the following steps: constructing an environment for simulating a coastal bed surface; generating reciprocating flow; collecting images of water flow and sand bed changes, and analyzing sand wave form evolution and near-bottom water dynamic characteristics. The application solves the problem that it is difficult to accurately obtain sand wave form evolution and near-bottom water dynamic characteristics in the prior art.

Description

Technical Field

[0001] This invention relates to the field of coastal geomorphology research technology, and in particular to a laboratory system and method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions. Background Technology

[0002] Sand ripples are the smallest geomorphic units shaped by hydrodynamics in estuarine and coastal areas. Sediment particles undergo initiation, transport, and deposition under wave action, forming rhythmic patterns. Water particles move in a reciprocating motion under wave action, making the study of sand ripples under reciprocating flow conditions a classic topic in coastal dynamics. The undulating morphology of sand ripples alters the roughness of the seabed, disturbs near-bottom flow, and generates vortex structures that significantly enhance water turbulence and sediment resuspension, contributing up to twice the sediment flux under flat-bed conditions. A deeper understanding of the laws and mechanisms governing sand ripple morphology evolution is crucial for more accurately predicting near-bottom hydrodynamic processes, sediment transport, and even large-scale, long-term geomorphic evolution in estuarine and coastal areas. Therefore, the simulation and monitoring of sand ripple morphology evolution and near-bottom dynamic characteristics are of great significance for constructing empirical predictive formulas for sand ripple morphology evolution and understanding its mechanisms.

[0003] Currently, simulation devices for sand ripple morphology evolution under reciprocating flow conditions are rare, and no suitable system for morphology evolution simulation and near-bottom hydrodynamic monitoring in laboratory studies has been found. Most laboratory studies on sand ripple morphology evolution are conducted in long, straight wave flumes. These flumes require stabilization, experimental, and wave-dissipating sections, with the stabilization and wave-dissipating sections requiring considerable distances, resulting in significant space requirements and a relatively short usable experimental section. Furthermore, the bottom of long, straight wave flumes is rough, with high and uneven bottom friction, resulting in significant wave dissipation and wave instability in the experimental section, necessitating rigorous and complex calibration. Additionally, the use of single-point velocity instruments to measure near-bottom velocity in long, straight wave flumes makes it difficult to capture the complex water turbulence near the bottom of the sand ripple bed. Therefore, the development of a system for simulating and monitoring sand ripple morphology evolution and near-bottom hydrodynamics under reciprocating flow conditions is essential. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a system and method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions in the laboratory. By creating reciprocating flow, the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics can be obtained more accurately.

[0005] Technical Solution: To achieve the above objectives, the present invention provides a laboratory system for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions. The system includes a water tank assembly simulating a coastal bed environment and a power component that generates reciprocating flow within the water tank assembly. The water tank assembly includes a U-shaped water tank with openings at both ends and internal connections. An opening for venting air bubbles and a matching sealed top cover are provided at the upper middle part of the water tank. Below the opening is a settling trough for laying a sand bed. The power component includes a wave-pushing plate located on one side of the settling trough. The wave-pushing plate is driven by a transmission rod to reciprocate within the water tank, generating a reciprocating flow that causes changes in the sand bed morphology.

[0006] The sealing top cover includes a large top cover, which also has an opening and a small top cover that matches the opening and has a sealing function.

[0007] Its characteristic is that the water tank, the large top cover, the small top cover, and the wave-pushing plate are all made of transparent materials.

[0008] The water tank is equipped with guide rails, and the wave-pushing plate moves back and forth along the guide rails inside the water tank.

[0009] A recessed sand filter opening is provided between the settling tank and the wave-pushing plate.

[0010] The settling tank is equipped with a sand plate whose height can be adjusted by a sealing plug, and a sand bed is laid on the sand plate.

[0011] The sand in the sand bed is cohesive sand, silt, or fine sand.

[0012] The power assembly also includes an electric cylinder connected to the other end of the transmission rod, which is driven by a servo motor controlled by the controller.

[0013] The system also includes a monitoring component for collecting changes in the internal environment of the water tank assembly. The monitoring component includes a laser emitter that emits a line laser to the cross-section of the sand bed located on the sealed top cover, a first high-speed camera that collects images of the area containing the line laser, and a second camera that collects changes on the surface of the sand bed.

[0014] The present invention discloses a laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, comprising the following steps:

[0015] S1: Construct a simulated coastal bed environment;

[0016] A sand bed is laid in the settling tank, with the surface of the sand bed flush with the top of the settling tank. Water is added through the top opening at the left end of the tank until the water level is level with the bottom of the opening. After scraping out the air bubbles formed on the inner wall of the upper side of the tank, water is added until the water level is level with the top of the opening. The sealing cap is then placed on the tank, creating a closed space below the opening without obvious air bubbles. Water is added until the water level at both ends of the tank is higher than the sealing cap. The added water contains multiple sets of tracer particles that move with the water flow.

[0017] S2: Use the controller to set the operating parameters of the power component, so that the wave pusher plate moves back and forth along the guide rail to create a reciprocating flow;

[0018] S3: Acquire images of cross-sectional and sandbed changes;

[0019] The laser emitter generates a line laser that shines vertically downward onto the cross-section of the test area. A first high-speed camera continuously acquires images containing the cross-section. By analyzing the motion patterns of tracer particles in the images, the near-bottom hydrodynamic characteristics are monitored.

[0020] A second camera was used to acquire lateral images of the sand bed at a frequency of N seconds. The evolution of the sand ripples was monitored by analyzing the state of the sand ripples in the images. The experiment was stopped when the sand bed accumulated and formed rhythmic sand ripple morphology.

[0021] Beneficial effects: The present invention has the following advantages: 1. The top of the water tank test area of ​​the present invention adopts a detachable structure design. During the water intake process, it can efficiently drive the air bubbles in the water tank to the double circular top cover area and finally close the top cover to achieve a seal, thereby reducing the influence of the top air bubbles on the experimental observation and improving the accuracy of the simulation of sand ripple morphology evolution under reciprocating flow conditions.

[0022] 2. This invention features a simple structure, small footprint, ease of observation, and strong applicability. Compared to large, long, straight wave flumes, the U-shaped flume of this invention, through its closed U-shaped design and the movement of the wave-pushing plate, can effectively generate the same reciprocating motion of water flow as waves. Its effect on the sand bed is consistent with wave conditions. Commonly used wave flumes require approximately 80m in length, with the practically usable area being the middle 10-20m section. Each test requires 400-500kg of sediment and 20-40m of [unclear - possibly referring to a specific type of material]. 3 The duration of wave generation also needs to be strictly controlled. Excessive time will intensify wave reflection and affect the sand ripple morphology in the experimental area. Compared to the reciprocating flow under a large, straight wave tank, this invention only requires approximately 100 kg of sediment and 3 m³ of water during the experiment. 3 Water is used, and it takes up little space, which improves the operability of the experiment;

[0023] 3. Laying sand in the settling channel to form a coastal bed surface, so that the surface of the sand bed is flush with the bottom of the channel (the upper end of the settling channel), which helps to control the hydrodynamic forces acting on the surface of the sand bed.

[0024] 4. This invention enables laboratory research on the morphological evolution of sand ripples and near-bottom hydrodynamic characteristics under different particle sizes of sediment, thereby verifying existing empirical prediction formulas for sand ripple equilibrium morphology and providing a scientific basis for further quantifying the variation law of sand ripple morphological characteristics (such as sand ripple wavelength and wave height) under different particle sizes and dynamic conditions. Subsoil roughness is an important parameter in large-scale numerical simulation and is linearly related to sand ripple height. This invention can provide important support for the accurate simulation of future large-scale geomorphological evolution. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the system structure;

[0026] Figure 2 A schematic diagram of the internal structure of the water tank assembly and the power assembly;

[0027] Figure 3 This is a cross-sectional schematic diagram of the water tank assembly;

[0028] Figure 4 This is a schematic diagram of the smooth mesh structure;

[0029] Figure 5 A schematic diagram illustrating the process of extracting sand wave height variations from photographs taken by a second camera;

[0030] Figure 6 A schematic diagram illustrating the process of extracting flow velocities at different points on the sand ripple peak from images taken by the first high-speed camera.

[0031] 1. Water tank, 1.1. Opening, 1.2. Settling tank, 2. Smooth mesh, 3. Large top cover, 3.1. Opening, 4. Small top cover, 5. Sand plate, 6. Rubber plug, 7. Sand filter section, 8. Guide rail, 9. Wave pusher plate, 10. Transmission rod, 11. Sealing kit, 12. Electric cylinder, 13. Servo motor, 14. Controller, 15. Laser emitter, 16. First high-speed camera, 17. Second camera. Detailed Implementation

[0032] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0033] like Figure 1As shown, this invention discloses a laboratory system for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions. The system includes a water tank assembly, a power assembly, a control assembly, and a monitoring assembly. The water tank assembly, by laying sand and water, constructs an environment simulating a coastal bed. This environment can simulate wave action on a real coastline, thereby achieving the goal of studying the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under laboratory conditions. In this environment, different hydrodynamic conditions can be simulated by changing the amplitude (A) and period (T) of the wave-pushing plate, thereby studying the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics. Furthermore, the sand ripple morphology characteristics formed under different bottom sand conditions can be studied by changing the particle size of the laid sand.

[0034] like Figure 2 and 3 As shown, the water tank assembly includes a U-shaped water tank 1 mounted on a support. The water tank 1 has openings at both ends on the left and right sides, and the internal channels are connected. A rectangular opening 1.1 is provided in the middle area. This structural design allows water to flow freely in the U-shaped channel, providing a basis for simulating the reciprocating flow conditions of the coastal surface.

[0035] A large top cover 3 is provided at the rectangular opening 1.1, and a circular opening 3.1 is provided in the middle of the large top cover 3. A small top cover 4 is provided at the circular opening 3.1. Sealing gaskets are provided between the rectangular opening 1.1 and the large top cover 3, and between the circular opening 3.1 and the small top cover 4. The shapes of the opening 1.1 and the opening 3.1 in this system are not limited to rectangular or circular shapes.

[0036] The test area is located directly below the rectangular opening 1.1. A square sinkhole 1.2 is provided at the bottom of the water tank 1 within the test area. This sinkhole 1.2 is used to lay sand to form a coastline. This method ensures that the surface of the sand is flush with the bottom of the water tank 1 (the upper end of the sinkhole 1.2), which helps to control the hydrodynamic forces acting on the sand surface.

[0037] Sand is laid on the sand plate 5 inside the settling tank 1.2. A rubber plug 6 is installed under the sand plate 5 to adjust its height. The bottom end of the rubber plug 6 is located outside the bottom of the settling tank 1.2 and passes through the through hole set at the bottom of the settling tank 1.2. It is also marked with graduations. This structure can not only adjust the height of the sand plate 5 by adjusting the height of the rubber plug 6, but also prevent water leakage at the bottom of the settling tank 1.2.

[0038] like Figure 4 As shown, a smoothing net 2 is provided on the left side of the settling tank 1.1 in the water tank. The smoothing net is a honeycomb structure made of hollow plastic tubes stacked in space, which is used to smooth the water flow.

[0039] A V-shaped sand filter section 7 is provided on the right side of the settling tank 1.2 inside the water tank 1. The design of the sand filter section 7 prevents the sand from affecting the operation of the power component on the right side as it flows with the water.

[0040] The power assembly includes a guide rail 8 installed inside the water tank 1 and a wave-pushing plate 9 that reciprocates on the guide rail 8. A transmission rod 10 is fixed to the wave-pushing plate 9. A servo motor 13 controls an electric cylinder 12 to drive the transmission rod 10, thereby causing the wave-pushing plate 9 to reciprocate. The edges of the wave-pushing plate 9 are as close as possible to the inner wall of the water tank 1 to facilitate the reciprocating motion of the wave-pushing plate 9 and to push more water flow.

[0041] To facilitate observation of the interior of the water tank 1, the water tank 1, the large top cover 3, the small top cover 4, and the wave-pushing plate 9 in this system are made of transparent plexiglass.

[0042] The servo motor 13 and the electric cylinder 12 are located on the outside of the water tank 1. The transmission rod 10 passes through the through hole provided on the right side of the water tank 1, and the through hole is provided with a sealing kit 11 that does not affect the reciprocating motion of the transmission rod 10.

[0043] This system controls the rotational speed, direction, and duration of the servo motor 13 by setting parameters of the control component (controller 14), thereby driving the wave pusher 9 to reciprocate left and right. When the wave pusher 9 moves to the left, it pushes the water in the test area to flow to the left; when the wave pusher 9 moves to the right, the water in the test area flows to the right due to the higher water level on the left. By setting the parameters of the control component, the water flow velocity in the test area can be made to change in a sinusoidal curve.

[0044] The monitoring components include a non-contact laser emitter 15, a first high-speed camera 16, and a second camera 17. The first high-speed camera 16 is a high-speed imaging camera, and the second camera 17 is a standard high-definition camera. The laser emitter 15 is located directly above the test area, emitting a line laser perpendicularly into the test area. The first high-speed camera 16 and the second camera 17 are located to the side of the test area, with the first high-speed camera 16 capturing high-speed images of the line laser area and the second camera 17 capturing high-definition images of the sand bed surface.

[0045] The laser emitter uses a wavelength of 532nm. The laser emission of laser 15 is synchronized with the acquisition of data by the first high-speed camera 16. By analyzing adjacent images acquired by the first high-speed camera 16 within a very short time, the flow velocity distribution characteristics of the test area can be obtained. The second camera is set to acquire one image every 10 seconds to record the evolution of sand ripple morphology from the side. The sand ripple morphology is extracted through algorithms, and the sand ripple morphology characteristics, including the changes in wave height and wavelength over time, are quantified. This enables the integrated simulation and measurement of sand ripple morphology evolution and bed dynamics under reciprocating flow.

[0046] The present invention discloses a laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, which specifically includes the following steps:

[0047] I. Constructing a simulated coastal surface environment

[0048] Adjust the height of sand plate 5 so that it is 10cm away from the top of the settling trough 1.2, and lay 10cm thick sand, with the sand surface flush with the bottom of the U-shaped water tank 1 (top of the settling trough 1.2).

[0049] First, seal the large top cover 3 at the rectangular opening 1.1. Then, add water through the top opening at the left end of the water tank 1 until the water level is flush with the bottom of the removable large top cover 3. Use a glass cleaning scraper to scrape the air bubbles formed on the inner wall of the water tank 1 (including the lower surface of the large top cover 3) to the area of ​​the removable double small top covers 4.

[0050] Continue to add a small amount of water to the water tank 1, ensuring the water level is slightly below the top of the large top cover 3 without overflowing. Seal the small top cover 4 to create a closed space without obvious air bubbles in the test area. Continue adding water until the water level at both ends of the water tank 1 is 30cm above the top of the large top cover 3, ensuring sufficient water pressure when creating the reciprocating flow.

[0051] The added water contains tracer particles that move with the water flow in the body of water.

[0052] II. Setting the motion parameters of the power components

[0053] The reciprocating flow amplitude (A), period (T), and running time are set in the controller 14. After the settings are completed, the servo motor 13 rotates, driving the electric cylinder 12 and the transmission rod 10 to move. The transmission rod 10 drives the wave pusher 9 to reciprocate left and right along the guide rail 8. When the wave pusher 9 moves to the left, a water flow to the left is generated on the sand surface of the test area. When the wave pusher 9 moves to the right, a water flow to the right is generated under the action of the water pressure on the left side of the U-shaped water tank 1, thus generating a reciprocating flow.

[0054] Under the influence of water flow, the sand in the test area moves back and forth, and then accumulates to form rhythmic sand ripples.

[0055] III. Acquiring images of water tracer particles and sand bed changes.

[0056] The laser emitter 15 is activated to generate a line laser, which illuminates the cross-section of the test area vertically downwards. The first high-speed camera 16 and the laser emitter 15 are synchronized to continuously acquire images of the cross-section at extremely short time intervals.

[0057] The open-source software PIVLab was used to analyze and process the images. By analyzing the motion patterns of tracer particles in the images, the two-dimensional (cross-sectional) vertical flow field distribution of the test area was obtained. Furthermore, the flow velocity at the crests of the sand ripples and the flow velocity processes at the free surface were extracted. Figure 5 As shown, two points were selected in the near-bottom region of the sand ripples (PR-2) and the higher region (PR-1) to analyze the flow velocity process. The flow velocity at PR-1 was similar to the sinusoidal flow velocity process generated by the wave pusher, with less turbulence, indicating that the device effectively generated a reciprocating flow on the sand surface. The results at PR-2 clearly demonstrated the strong water turbulence caused by the generation of sand ripples in the near-bottom region, which is consistent with previous research.

[0058] The second camera 17 was activated, and a lateral photograph of the test area was captured every 10 seconds. Because the sand ripples exhibit a significant grayscale difference between the sand and the upper water, a threshold was set to extract the sand ripple profile development process from the photographs. Figure 6 As shown, the extracted sand ripple wave height variation process can be used to further explore the correlation between the sand ripple development and evolution process and the near-bottom surface dynamic process, and reveal the dynamic mechanism of sand ripple morphological evolution.

Claims

1. A method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions in a laboratory setting, and a system for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, characterized in that... The system for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions includes a water tank component that simulates the coastal bed environment and a power component that generates reciprocating flow within the water tank component. The water tank component includes a U-shaped water tank (1) with openings at the top left and right ends and internal connections. The upper middle part of the water tank (1) is provided with an opening (1.1) for excluding air bubbles and a sealed top cover that matches the opening (1.1). Below the opening (1.1) is a settling trough (1.2) for laying sand beds. The power component includes a wave pusher (9) located on one side of the settling trough (1.2). The wave pusher (9) is driven by a transmission rod (10) to reciprocate within the water tank (1) to generate reciprocating flow, thereby causing changes in the sand bed morphology. A smooth mesh is provided on the other side of the settling tank (1.2). The smooth mesh is a honeycomb structure made of hollow plastic tubes stacked in space. The sealing top cover includes a large top cover (3), which also has an opening (3.1) and a small top cover (4) that matches the opening (3.1) and has sealing properties. The water tank (1) is provided with a guide rail (8), and the wave pusher (9) moves back and forth in the water tank (1) along the guide rail (8); It also includes a monitoring component for collecting changes in the internal environment of the water tank assembly. The monitoring component includes a laser emitter (15) that emits a line laser to the cross section of the sand bed located on the sealed top cover, a first high-speed camera (16) that collects images of the area containing the line laser, and a second camera (17) that collects changes on the surface of the sand bed. The method includes the following procedures: S1: Construct a simulated coastal bed environment; A sand bed is laid in the settling tank (1.2), with the surface of the sand bed flush with the top of the settling tank (1.2). The large top cover (3) is sealed at the rectangular opening (1.1). Water is added through the top opening at the left end of the water tank (1) until the water level is flush with the bottom of the removable large top cover (3). A glass cleaning scraper is inserted into the water to scrape the air bubbles formed on the inner wall of the water tank (1) to the area of ​​the removable small top cover (4). A small amount of water is added to the water tank (1) until the water level is slightly lower than the top of the large top cover (3) and does not overflow the water tank. The small top cover (4) is sealed to form a closed space without obvious air bubbles in the test area. Water is added until the water level at both ends of the water tank (1) is 30cm higher than the top of the large top cover (3) to ensure sufficient water pressure when creating the reciprocating flow. The added water contains multiple sets of tracer particles that move in the water body with the water flow. S2: Use the controller (14) to set the working parameters of the power component so that the wave pusher (9) moves back and forth along the guide rail (8) to create a reciprocating flow; S3: Acquire images of cross-sectional and sandbed changes; The laser emitter (15) generates a line laser that illuminates the cross section of the test area vertically downwards. The first high-speed camera (16) continuously acquires images containing the cross section. By analyzing the motion patterns of the tracer particles in the images, the near-bottom hydrodynamic characteristics are monitored. The second camera (17) is used to acquire lateral images of the sand bed at a preset frequency. By analyzing the state of the sand ripples in the images, the evolution process of the sand ripple morphology is monitored. The experiment was stopped when the sand bed accumulated and formed rhythmic sand ripples.

2. The laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, as described in claim 1, is characterized in that... The water tank (1), the large top cover (3), the small top cover (4), and the wave-pushing plate (9) are all made of transparent material.

3. The laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, as described in claim 1, is characterized in that... A recessed sand filter port (7) is provided between the settling tank (1.2) and the wave-pushing plate (9).

4. The laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, as described in claim 1, is characterized in that... The settling tank (1.2) is equipped with a sand plate (5) whose height can be adjusted by a sealing plug (6), and the sand bed is laid on the sand plate (5).

5. The laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, as described in claim 1, is characterized in that... The sand in the sand bed is cohesive sand, silt, or fine sand.

6. The laboratory method for simulating and monitoring the evolution of sand ripple morphology and near-bottom hydrodynamic characteristics under reciprocating flow conditions, as described in claim 1, is characterized in that... The power assembly also includes an electric cylinder (12) connected to the other end of the transmission rod (10), which is driven by a servo motor (13) controlled by the controller (14).

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