A device and method for simulating the influence of micro-topography on the initiation of drifting fish eggs

Abstract

The present invention discloses a device and method for simulating the influence of micro-topography on the start-up of drifting fish eggs, including a PIV image velocity measurement system and an inclined water tank, wherein the inner bottom wall of the water tank is provided with a model sand wave; the experimental device of the present invention can be used to observe the critical start-up problem of fish eggs on the bed surface, and the PIV system can not only record the movement process of the fish eggs, but also reflect the flow field state during the movement of the fish eggs, and explore the connection between the movement mechanism of the fish eggs and the flow field. The experimental device of the present invention can carry out experiments under different micro-topography conditions and collect flow field data, and the hydrodynamic conditions can be reflected by the flow field data. In the present method, the hydraulic gradient, sand wave morphology, and fish egg size / specific gravity are all adjustable, and the start-up state of different floating fish eggs under a variety of micro-topography and water flow combination conditions can be simulated to obtain rich experimental data.

Description

Technical Field

[0001] The invention relates to the field of ecohydraulics, and in particular to a device and method for simulating the influence of micro-topography on the initiation of drifting fish eggs. Background Art

[0002] With the accelerated pace of construction of cascade hydropower stations, river habitats have undergone major changes, with the drifting area of ​​fish eggs changing from natural rivers to slow-flowing reservoirs, which has had a significant impact on the suspension and sedimentation of drifting fish eggs. Since the turbulence intensity of the reservoir water flow is much smaller than that of natural rivers, drifting fish eggs are prone to sinking, and may even be covered by sediment and die due to lack of oxygen.

[0003] Existing research mainly focuses on the hydrodynamic conditions for the safe drifting of fish eggs. Existing technical document 1: Application number 201611225478.X discloses a test device and method for studying the movement mechanism of fish eggs. By simulating the release of fish eggs in the natural spawning process and adjusting the flow rate and turbulence intensity of the water body, the movement law of fish eggs under laminar and turbulent hydraulic conditions can be tested. However, Existing Technical Document 1 only focuses on the impact of water flow turbulence on the movement law of fish eggs, and does not consider the impact of micro-topography on the movement law of fish eggs; only focuses on the process of fish eggs gradually falling after release, and does not consider the possibility of fish eggs restarting after falling; the camera device only records the movement process of fish eggs, but does not reflect the flow field state when the fish eggs move, and cannot observe the connection between the movement mechanism of fish eggs and the flow field.

[0004] Prior art document 2: Hu Peng et al. Experimental study on critical hydrodynamic conditions for safe drifting of drifting fish eggs, Journal of Hydraulic Engineering, 2021, 52(12), which introduces the effects of different flow rates, water depths, water surface widths and water flow Reynolds numbers on the drifting of fish eggs in an outdoor large open channel experiment. The experiment was carried out with a water flow Reynolds number of 7.9×10 4 When the above, the fish egg collection rate exceeds 90%, which is used as the threshold for achieving safe drifting. However, the prior art document 2 only focuses on the impact of hydrodynamic conditions on the safe drifting of fish eggs, and does not consider the effect of micro-topography on the fish eggs sinking vertically to the bed surface and then starting to drift; the sodium alginate used to prepare the model fish eggs needs to react with calcium lactate to form a film, which is difficult to prepare directly. Summary of the invention

[0005] The purpose of the present invention is firstly to consider the influence of micro-topography on the starting of drifting fish eggs, and propose a starting threshold of drifting fish eggs after settlement. Secondly, experiments are carried out by changing flow rate, hydraulic gradient, sand wave morphology and fish eggs to explore the influence of the above conditions on the starting threshold of fish eggs.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A device for simulating the influence of micro-topography on the start of drifting fish eggs, comprising a PIV image velocity measurement system and an inclined water tank, wherein the higher end of the water tank is a water inlet end, and the lower end is a water outlet end; a water supply tank is arranged at the water inlet end of the water tank through a water supply tank bracket, and a triangular weir is provided on the side wall of the water supply tank close to the water tank; a flow stabilizing grid is vertically arranged on the bottom wall of the water tank, and a plurality of water permeable holes are provided on the flow stabilizing grid, and water in the water supply tank flows into the water tank through the triangular weir and the flow stabilizing grid;

[0008] The inner bottom wall of the water tank is equipped with a model sand wave, which is made of 25k foam board and the surface of the sand wave is covered with D 50 The sand is 0.9 mm thick and coated with matte black pigment to prevent the laser from hitting the surface of the sand waves and causing overexposure of the captured image;

[0009] A water reservoir is provided below the water tank, a water pump and a water inlet pipe are provided in the water reservoir, one end of the water inlet pipe is connected to the water reservoir, and the other end is connected to the water supply tank; a partition is provided downstream of the water tank, a gap is provided between the partition and the side wall of the water outlet end of the water tank, the partition slides vertically and is sealed and connected to the inner wall of the water tank, one end of the tailwater collecting pipe is connected to the inner bottom wall of the water tank between the partition and the side wall of the water outlet end of the water tank, the other end of the tailwater collecting pipe is connected to the water reservoir, and an electromagnetic flowmeter is connected to the tailwater collecting pipe;

[0010] The PIV image speed measurement system includes an image acquisition system and an image processing system. The image acquisition system includes a high-speed camera arranged on one side of the water tank, a laser light source arranged above the water tank, a blackout cloth and an outer frame. The water tank is located in the outer frame, the blackout cloth covers the outer frame, and the laser light source is arranged on the outer frame above the water tank.

[0011] By setting up model sand waves at the bottom of the water tank and setting different slopes, the influence of micro-topography on the movement of fish eggs is simulated; the movement process of fish eggs is recorded by the PIV image velocimetry system, and the flow field state during the movement of fish eggs can be automatically reflected, which facilitates the observation of the connection between the movement mechanism of fish eggs and the flow field.

[0012] Furthermore, in order to adjust the inclination angle of the water tank and change the hydraulic slope, the water inlet end of the water tank is connected to the water supply tank by a rotating shaft, and a water passing connector is connected between the water supply tank and the water tank. The water passing connector is an accordion structure and is made of flexible material. The water passing connector is sealed to the inner wall of the water tank, and the connection is sealed and waterproof; a triangular weir is provided on the side wall where the water supply tank is connected to the water passing connector, and the flow stabilizer is located at the water outlet of the water passing connector.

[0013] The tilt angle of the water tank can be adjusted by adjusting the height of the water outlet end of the water tank. The water connection piece can not only ensure the water flow between the water supply tank and the water tank, but also ensure that the rotation of the water tank relative to the water supply tank is not restricted.

[0014] Furthermore, the structure for adjusting the height of the water outlet of the sink is a door-shaped sink bracket, and a plurality of adjustment holes are arranged on the vertical rod of the sink bracket along the height direction. The insertion rod is inserted between the vertical rods of the sink bracket through the corresponding adjustment holes, and the water outlet of the sink is placed on the insertion rod.

[0015] Furthermore, in order to control and stabilize the water level in the water supply tank, a water level control panel is vertically arranged in the water supply tank. The water level control panel divides the water supply tank into two independent chambers, namely an inlet chamber and an outlet chamber. The inlet chamber is close to the water connection piece. One end of the inlet pipe is placed above the inlet chamber. The bottom wall of the outlet chamber is connected to an outlet pipe, and the other end of the outlet pipe is connected to the water reservoir.

[0016] Furthermore, the structure for controlling the adjustable water level height in the water supply tank is as follows: the water level control plate includes two relatively sliding plates, namely plate one and plate two, plate one is located on the side close to the water inlet chamber, and plate two is located on the side away from the water inlet chamber, plate one is fixedly connected to the inner wall of the water supply tank, the connection is sealed and waterproof, the height of plate one is relatively low, plate two is slidably connected to plate one, and there is a dynamic seal between plate two and the inner wall of the water supply tank.

[0017] Furthermore, in order to prevent the water surface ripples from refracting the laser of the PIV image velocity measurement system, a wave suppression plate is connected to the outer frame through a hanging rope. The wave suppression plate is made of organic glass and is parallel to the water surface in the water tank and just in contact with the water surface. The function of the wave suppression plate is to remove the water surface ripples and prevent the dark bands from appearing in the observation section due to laser refraction.

[0018] Furthermore, the floating fish eggs in the present invention are prepared by heating distilled water and agar in a water bath and pouring them into spherical molds with different diameters.

[0019] Compared with the traditional method of preparing fish eggs using sodium alginate solution, the model fish eggs prepared by this method using agar can directly determine the diameter and density of the fish eggs, while sodium alginate needs to react with calcium lactate to form a film, which makes it difficult to prepare it directly.

[0020] An experimental method for simulating the effect of micro-topography on the initiation of drifting fish eggs comprises the following steps:

[0021] Different combinations of working conditions were designed, including different hydraulic gradients, sand wave shapes, and drifting fish eggs. Each working condition was tested according to the following steps:

[0022] Step 1, adjusting the height of the water level control plate in the water supply tank to keep the water level in the water supply tank at a low water level, allowing the water in the water tank to flow at a low flow rate, and after the water in the water tank overflows over the baffle and the water flow stabilizes, releasing the drifting fish eggs without an initial velocity at the sand wave trough of the lower and middle section of the water tank model, and releasing 100 drifting fish eggs in each experiment;

[0023] Step 2, only by adjusting the height of the second plate of the water level control plate in the water supply tank, adjusting the flow entering the water tank, and observing whether the drifting fish eggs in the model sand wave meet the critical start;

[0024] Step 3: gradually increase the flow rate and find the critical starting time, record the water depth in the water supply tank and the flow value of the electromagnetic flowmeter in the tailwater collection pipe at this time. The flow value of the electromagnetic flowmeter is the starting threshold flow rate, and use the PIV image acquisition device to record the flow field parameters at this time;

[0025] Step 4: Turn off the water pump, remove the baffle, drain the water in the sink, and end this set of experiments.

[0026] In the present application, under the sand wave 1 condition, 70% of the drifting fish eggs can jump out of this model sand wave within 20 seconds, which is regarded as critical start; under the sand wave 2 condition, 70% of the drifting fish eggs can jump out of this model sand wave within 10 seconds, which is regarded as critical start, and the flow value corresponding to the critical start moment is the starting threshold flow.

[0027] In order to describe the state of the critical starting moment of drifting fish eggs using mathematical expression, a parameter of starting threshold is set. The relationship between the starting threshold and the sand wave morphology parameters, the near-bed surface flow velocity and the fish egg parameters in the present invention is as follows:

[0028]

[0029] Where: ξ is the starting threshold of drifting fish eggs, which is a dimensionless parameter formed by coupling micro-topography parameters, fish egg parameters and flow field parameters, α is the coefficient to be determined, U b is the velocity near the bed surface, D is the egg diameter, R e Reynolds number, r s is the specific gravity of the egg, r is the specific gravity of water, g is the acceleration of gravity, λ is the wavelength of the sand wave, h s is the height of sand waves. Hydraulic slope, as another micro-topographic parameter besides sand wave related parameters, is not directly reflected in the formula, but its change will be reflected in the change of near-bed velocity. The larger the hydraulic slope, the greater the near-bed velocity.

[0030] Compared with the prior art, the present invention is beneficial in that:

[0031] 1. The experimental device of the present invention can be used to observe the critical start-up problem of fish eggs on the bed surface, which solves the problem that the prior art does not consider the influence of micro-topography on the movement law of fish eggs, only focuses on the suspension process after the fish eggs are released, and does not consider the possibility of restarting after the fish eggs settle; the present invention can not only record the movement process of fish eggs through the PIV system, but also reflect the flow field state during the movement of fish eggs, and observe the connection between the movement mechanism of fish eggs and the flow field. The experimental device of the present invention can carry out experiments under different micro-topography conditions and collect flow field data, and the hydrodynamic conditions can be reflected through the flow field data.

[0032] 2. In this method, the hydraulic gradient, sand wave shape, and fish egg size / specific gravity are all adjustable, which can simulate the starting state of different floating fish eggs under a variety of micro-topography and water flow combination conditions, and obtain rich experimental data for subsequent research.

[0033] 3. Through the experimental device and experimental method described in the present invention, the changes in the movement of different types of floating fish eggs under the influence of micro-topography can be explored, the micro-topography parameters, fish egg parameters and flow field parameters that affect the movement of fish eggs can be coupled into a dimensionless parameter, and the dimensionless parameter value when 70%-100% of the fish eggs are started during the sand wave coverage time can be used as a threshold for reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The sink device structure of the present invention is shown with the front side wall of the sink removed to show the interior details.

[0035] Figure 2 The overall structure of the experimental device of the present invention is shown, and the front side wall of the tank is removed to show the internal details.

[0036] Figure 3 The three-dimensional structure of the water connection piece and the water supply tank of the present invention is shown.

[0037] Figure 4 The top view of the water tank and water supply box of the present invention is shown.

[0038] Figure 5 Schematic diagram of two sand wave forms in an embodiment of the present invention.

[0039] Figure 6 The following is a flow chart of an example of the experimental method.

[0040] Figure 7 Shown is the flow field as the fish eggs are caught in the sand waves.

[0041] The meanings of the symbols in the accompanying drawings are as follows:

[0042] Water tank 1, flow stabilizing fence 11, wave pressure plate 12, hanging rope 121, drifting fish eggs 13, model sand wave 14, partition 15, water supply tank 2, water level control board 21, triangular weir 22, water connection piece 23, rotating shaft 24, water outlet pipe 25, water supply tank bracket 26, water pump 3, water tank bracket 4, plug rod 41, tailwater collecting pipe 5, electromagnetic flowmeter 51, water reservoir 6, water inlet pipe 7, high-speed camera 811, laser light source 812, blackout cloth, outer frame 814 and hanging ring 8141. DETAILED DESCRIPTION

[0043] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments, and are an explanation of the present invention, rather than a limitation of the present invention. Any solution that is simply modified from the present invention belongs to the protection scope of the present invention.

[0044] Embodiment 1:

[0045] like Figure 1 The present embodiment provides an experimental device for simulating the influence of micro-topography on the initiation of drifting fish eggs, including a water tank 1, a water supply tank 2, a water pump 3, a tailwater collection pipe 5, a water reservoir 6, a water inlet pipe 7, a flow stabilizer 11, a model sand wave 14, a baffle 15, a triangular weir 22, a water connection 23 and a water supply tank bracket 26.

[0046] The water tank 1 is a rectangular box structure with an open top, and is tilted by a bracket 4. Figure 1 As shown, the right end of the water tank 1 is high, and the left end is low. The high end of the water tank 1 is the water inlet end, and the low end is the water outlet end, and the water inlet end is an open design.

[0047] The water reservoir 6 is arranged below the water tank 1, the water pump 3 is located in the water reservoir 6, one end of the water inlet pipe 7 is connected to the water reservoir 6, and the other end is connected to the water supply tank 2. The water pump 3 pumps the water in the water reservoir 6 into the water inlet pipe 7 and sends it into the water supply tank 2. The optional model of the water pump 3 is WQD15-15-1.5. The water supply tank 2 is arranged at the water inlet end of the water tank through the water supply tank bracket 26. The water connection piece 23 is connected between the water supply tank 2 and the water tank 1. The side wall of the water supply tank 2 connected to the water connection piece 23 is provided with a triangular weir 22. The flow stabilizing fence 11 is vertically arranged on the bottom wall of the water tank 1 and is located at the water outlet of the water connection piece 23. The flow stabilizing fence 11 has a plurality of water permeable holes. The water in the water supply tank 2 flows into the water tank 1 through the triangular weir 22, the water connection piece 23 and the flow stabilizing fence 11.

[0048] A partition 15 is arranged downstream of the water tank 1, and there is a gap between the partition 15 and the side wall of the water tank outlet end. The partition 15 is slidably and sealedly connected to the inner wall of the water tank. One end of the tailwater collecting pipe 5 is connected to the inner bottom wall of the water tank between the partition 15 and the side wall of the water tank outlet end. The other end of the tailwater collecting pipe 5 is connected to the water reservoir 6. The tailwater collecting pipe is connected to an electromagnetic flowmeter 51. The partition 15 plays the role of water blocking and water discharge. After the water in the water tank overflows the partition 15, it flows into the water reservoir 6 through the tailwater collecting pipe 5.

[0049] like Figure 4As shown, in this embodiment, the water tank 1 is made of plexiglass, with a length of 2m, a width of 0.35m, a height of 0.6m, and a rectangular cross-section; the water supply tank 2 is made of stainless steel, with dimensions of 0.5×0.5×0.5m; the water reservoir 6 is made of stainless steel, with dimensions of 0.5×0.5×1m; the tail water collecting pipe 5 and the water inlet pipe 7 are made of plastic, both with a diameter of 6.5cm.

[0050] In this embodiment, the model sand wave 14 is made of 25k foam board, and the surface of the sand wave is covered with D 50 The sand is 0.9 mm thick and painted with matte black paint. An iron block is attached to the bottom and fixed to the inner bottom wall of the water tank 1. The shape of the model sand wave 14 can be formulated according to the sand wave equation:

[0051]

[0052] Wherein, A (Amplitude): parameter affecting wave height, wave height is the distance from the top of the sand dune to the riverbed surface (m); L (Wavelength): parameter affecting wavelength, wavelength is the distance between adjacent wave crests or troughs (m); F (Frequency): parameter affecting the ratio of the water-facing surface to the water-back surface; a: relative horizontal position between the moving wave crest and the wave trough, a>0; b: two inflection points of the moving sand wave profile, b>0.

[0053] The parameters of the two sand wave forms prepared in this experiment are shown in Table 1 below. Figure 5 :

[0054] Table 1 Parameters of two types of sand wave morphology

[0055] Shabo F L A a b 1 0.2 18 1.8 0.782 0.2 2 0.2 9 0.9 0.782 0.2

[0056] Embodiment 2:

[0057] like Figure 3 As shown, in this embodiment, based on embodiment 1, a water level control panel 21 is vertically arranged in the water supply tank 2, and the water level control panel divides the water supply tank 2 into two independent chambers, namely a water inlet chamber and a water outlet chamber. The water inlet chamber is close to the water connection piece 23, one end of the water inlet pipe 7 is placed above the water inlet chamber, and the bottom wall of the water outlet chamber is connected to a water outlet pipe 25, and the other end of the water outlet pipe 25 is connected to the water reservoir 6.

[0058] The water pump 3 pumps the water in the water reservoir 6 into the water inlet chamber through the water inlet pipe 7, controls the water level in the water supply tank 2 through the water level control board 21, and the excess water flows over the water level control board 21 into the water outlet chamber and flows back to the water reservoir 6 through the water outlet pipe 25.

[0059] In this embodiment, the water level control plate 21 includes two relatively sliding plates, namely plate one and plate two. Plate one is located on the side close to the water inlet chamber, and plate two is located on the side away from the water inlet chamber. Plate one is fixedly connected to the inner wall of the water supply tank, and the connection is sealed and waterproof. The height of plate one is relatively low to meet the low flow required at the beginning of the experiment. Plate two is slidably connected to plate one, and there is a dynamic seal between plate two and the inner wall of the water supply tank. The water level in the water supply tank is raised by sliding plate two.

[0060] The water pump 3 pumps the water in the water reservoir 6 into the water inlet chamber through the water inlet pipe 7, and controls the water level in the water supply tank 2 by the sliding plate 2. The excess water overflows through the plates 1 and 2 and enters the water outlet chamber, and flows back to the water reservoir 6 through the water outlet pipe 25.

[0061] Embodiment 3:

[0062] like Figure 1-Figure 2 As shown, based on Example 1, this embodiment adds a slope adjustment function to the water tank 1 in order to change the hydraulic slope, so as to ensure that the water flow is leak-free while achieving the adjustment of the water tank slope.

[0063] The water inlet of the water tank is connected to the water supply box 2 via a rotating shaft 24. The water connection piece 23 is an accordion structure made of a flexible material. The water connection piece 23 is sealed and connected to the inner wall of the water tank, and the connection is sealed and watertight.

[0064] It also includes a door-shaped sink bracket 4, on which a plurality of adjustment holes are arranged along the height direction of the vertical rod. An insertion rod 41 is inserted between the vertical rods of the sink bracket 4 through the corresponding adjustment holes, and the water outlet of the sink is placed on the insertion rod 41.

[0065] When adjusting the slope of the water tank 1, the slope can be adjusted by adjusting the installation height of the plug rod on the water tank bracket 4, and the adjustment range is 0-15°.

[0066] Embodiment 4:

[0067] like Figure 2 As shown, based on Example 1, this embodiment is further provided with a PIV image velocity measurement system, including an image acquisition system and an image processing system. The image acquisition system includes a high-speed camera 811, a laser light source 812, a shading cloth and an outer frame 814, and the outer frame 814 is slidably connected with a plurality of hanging rings 8141; the image processing system is JFmeter post-processing software.

[0068] The high-speed camera 811 is placed in the middle and rear observation section 30 cm outside the water tank 1 (40-140 cm from the downstream) to achieve accurate observation of the start of the model fish eggs 13. The blackout cloth is covered on the outside of the outer frame 814. The laser light source 812 is connected to the hanging ring 8141, and the hanging ring 8141 can carry the laser light source 812 to slide left and right along the top railing of the outer frame 814.

[0069] High-speed camera 811 can use IDTos10 high-speed motion camera.

[0070] Embodiment 5:

[0071] like Figure 2 In this embodiment, based on the fourth embodiment, four hanging ropes 121 are arranged on the outer frame 814, and the bottom of the hanging ropes is fixedly connected to the wave compression plate 12, and the wave compression plate 12 is made of organic glass. The height of the wave compression plate 12 can be adjusted by the hanging ropes 121 so that the wave compression plate 12 is parallel to the water surface of the water tank 1 and just touches the water surface.

[0072] By installing a turbulence generator in the water tank of the present application, the laminar / turbulent flow conditions in the traditional experimental device can be simulated, and the water flow and topographic conditions required for the suspension of floating fish eggs can be studied.

[0073] Embodiment 6:

[0074] The drifting fish eggs 13 of this embodiment are prepared by heating distilled water and agar (analytical grade) in a water bath and pouring them into spherical molds of different diameters. The diameter of the drifting fish eggs 13 can range from 3 to 7 mm, the specific gravity ranges from 1.001 to 1.05, and the color is white.

[0075] In this embodiment, three model fish eggs of different sizes and densities are prepared, A (diameter 4.2mm, specific gravity 1.002), B (diameter 5mm, specific gravity 1.002), and C (diameter 4.5mm, specific gravity 1.003), which correspond to the model fish eggs of grass carp, black carp, and silver carp, respectively.

[0076] like Figure 4 As shown, in this embodiment, the trough of the sand wave 14 in the middle and lower section of the water tank 1 (40-140 cm from the downstream) is the fish egg placement site and the observation section.

[0077] Embodiment 7:

[0078] like Figure 6 This embodiment provides an experimental method for simulating the effect of micro-topography on the initiation of drifting fish eggs, comprising the following steps:

[0079] (1) Preparation before the experiment: including adjusting the height of the water tank bracket 4 according to the pre-set hydraulic slope and sand wave shape of the water tank 1, placing the model sand wave 14, preparing the drifting fish eggs 13 used in the experiment, placing the partition 15 at the water outlet of the water tank 1, etc.

[0080] (2) Experimental preparation: Turn on the water pump 3, and water flows into the water supply tank 2 through the water inlet pipe 7. Adjust the height of the water level control plate 21 in the water supply tank 2 to control the flow rate into the water tank 1. The water level in the water tank 1 gradually rises until it passes over the partition 15 and begins to drain water to the tail gate of the water tank 1. Adjust the height of the hanging rope 121 so that the wave pressure plate 12 is flush with the water surface in the rear section of the water tank 1. Wait until the water flow state is stable before starting the experiment. The electromagnetic flowmeter 51 measures the flow rate of the tailwater collection pipe 5 in real time.

[0081] (3) Formal experimental process:

[0082] Step 1, adjusting the height of the water level control plate 21 in the water supply tank 2 to keep the water level in the water supply tank at a low water level, allowing the water in the water tank to flow at a low flow rate, and after the water in the water tank 1 overflows the baffle 15 and the water flow is stable, the floating fish eggs 13 are released without initial velocity at the bottom of the water tank 1 at the middle and lower section (40-140 cm from the downstream outlet) of the model sand wave 14 trough, and 100 floating fish eggs 13 are released in each group of experiments;

[0083] Step 2, only by adjusting the height of the water level control plate 21 in the water supply tank 2, the flow rate entering the water tank 1 is adjusted to observe whether the drifting fish eggs 13 in the model sand wave 14 meet the critical start. The present application stipulates that: under the sand wave 1 working condition, 70% of the drifting fish eggs 13 can jump out of the model sand wave within 20 seconds, which is regarded as critical start; under the sand wave 2 working condition, 70% of the drifting fish eggs 13 can jump out of the model sand wave within 10 seconds, which is regarded as critical start; the flow rate when reaching the critical start is the start threshold flow rate.

[0084] In reality, sand waves will move with the flow of water, if more than 70% of the fish eggs 13 can jump out of the sand waves before being covered by the sand waves (the covering time of sand wave 1 and sand wave 2 is approximately 20 seconds / 10 seconds, respectively), it is considered that the starting condition is met; if 100% of the fish eggs jump out before 20 / 10 seconds, it is considered that the threshold is exceeded and the flow rate needs to be reduced.

[0085] According to previous studies (Tang Mingying et al., Experiments on the hydrodynamic characteristics of grass, green, seam and fin fish eggs and preliminary predictions of their hatching conditions in the Three Gorges Reservoir area, Fishery Resources, 1989, 26-30), it is known that the lower limit of the vertical average velocity for the safe drifting of drifting fish eggs is 0.25m / s, that is, this velocity can ensure the safe drifting of drifting fish eggs without sinking.

[0086] Considering that drifting fish eggs may not necessarily die after sinking, they may restart on the bottom of the water and move in a similar manner to bedload due to the influence of micro-topography and hydraulic conditions. This application is to study the threshold value of drifting fish eggs restarting and moving after sinking.

[0087] Step 3: After gradually increasing the flow rate and finding the starting threshold flow rate, record the water depth in the water supply tank at this time, the flow value of the electromagnetic flowmeter in the tailwater collection pipe (i.e., the starting threshold flow rate), and use the PIV image acquisition device to record the flow field parameters at this time. First, cover the outer frame 814 with a shade cloth, then turn on the laser light source 812, and use the high-speed camera 811 to record the water flow picture of the entire process of fish egg migration under the threshold;

[0088] Step 4, turn off the water pump 3, take out the partition 15, drain the water in the water tank 1, and end this group of experiments.

[0089] Design different combined working conditions (different hydraulic gradients, sand wave shapes and drifting fish eggs 13) and repeat the above steps 1-4 of pre-experimental preparation (1), experimental preparation (2) and experimental process (3). Repeat the experiment 3 times for each group of working conditions. The specific experimental working conditions are shown in Table 2 below:

[0090] Table 2 Experimental conditions

[0091]

[0092]

[0093] (4) Experimental data processing: The water flow images captured by the high-speed camera 811 are processed by JFmeter post-processing software to obtain the flow field information corresponding to the critical starting time of the drifting fish eggs 13 under each working condition, and obtain the near-bed surface flow velocity. Taking working condition 7 as an example, the flow field at the sand wave is as follows: Figure 7 As shown, the water flow formed a vortex at the trough, causing the fish eggs to be captured by the sand waves. After the flow velocity near the bed increased, the fish eggs started to move. The average flow velocity of the vertical line 1 cm above the crest of the sand wave was taken as the flow velocity near the bed.

[0094] Through dimensional analysis, this application obtains the relationship between the starting threshold of different model fish eggs and micro-geomorphological parameters (sand wave morphology parameters), PIV parameters (near-bed velocity, etc.) and fish egg parameters (diameter, density), and the results are as follows:

[0095]

[0096] Where: ξ is the threshold for drifting eggs to start, α is the coefficient to be determined, U b is the velocity near the bed surface, D is the egg diameter, R e Reynolds number, r s is the specific gravity of the egg, r is the specific gravity of water, g is the acceleration of gravity, λ is the wavelength of the sand wave, h s is the height of sand waves. Hydraulic slope, as another micro-topographic parameter besides sand wave related parameters, is not directly reflected in the formula, but its change will be reflected in the change of near-bed velocity. The larger the hydraulic slope, the greater the near-bed velocity.

[0097] The Reynolds number can be obtained by the value of the electromagnetic flowmeter 51 and the experimental water depth.

[0098] The PIV flow field information obtained from the various working condition experiments in Example 7 is processed, and the various parameters obtained from the experiments are substituted into the above-mentioned starting threshold formula for calculation, the applicability of the formula in the various working conditions of this experiment is verified, and the value of the unknown coefficient α is obtained, and further parameter sensitivity analysis can be performed on each parameter.

Claims

1. A device for simulating the effect of micro-topography on the initiation of drifting fish eggs, characterized in that: The invention comprises a PIV image velocity measurement system and an inclined water tank (1), wherein the higher end of the water tank (1) is a water inlet end and the lower end is a water outlet end; a water supply tank (2) is arranged at the water inlet end of the water tank (1) through a water supply tank bracket (26), and a triangular weir (22) is provided on the side wall of the water supply tank (2) close to the water tank (1); a flow stabilizing fence (11) is vertically arranged on the bottom wall of the water tank (1), and the flow stabilizing fence (11) has a plurality of water permeable holes, and water in the water supply tank (2) flows into the water tank (1) through the triangular weir (22) and the flow stabilizing fence (11); The inner bottom wall of the water tank (1) is provided with a model sand wave (14), the model sand wave (14) is made of a 25k foam board, and the surface of the model sand wave (14) is covered with D 50 0.9mm sand and coated with matte black pigment; A water reservoir (6) is arranged below the water tank (1), a water pump (3) and a water inlet pipe (7) are arranged in the water tank (6), one end of the water inlet pipe (7) is connected to the water reservoir (6), and the other end is connected to the water supply tank (2); a partition (15) is arranged downstream of the water tank (1), a gap is provided between the partition (15) and the side wall of the water outlet end of the water tank (1), the partition (15) slides vertically and is sealedly connected to the inner wall of the water tank (1), one end of the tailwater collecting pipe (5) is connected to the inner bottom wall of the water tank (1) between the partition (15) and the side wall of the water outlet end of the water tank (1), the other end of the tailwater collecting pipe (5) is connected to the water reservoir (6), and an electromagnetic flowmeter (51) is connected to the tailwater collecting pipe (5); The PIV image speed measurement system comprises an image acquisition system and an image processing system. The image acquisition system comprises a high-speed camera (811) arranged at one side of a water tank, a laser light source (812) arranged above the water tank, a shading cloth and an outer frame (814). The water tank (1) is located in the outer frame (814), the shading cloth covers the outer frame (814), and the laser light source (812) is arranged on the outer frame (814) above the water tank (1). The water inlet end of the water tank (1) is connected to the water supply box (2) via a rotating shaft (24); a water-passing connector (23) is connected between the water supply box (2) and the water tank (1); the water-passing connector (23) is an accordion-type structure and is made of a flexible material; the water-passing connector (23) is sealed to the inner wall of the water tank (1); the connection is sealed and watertight; a triangular weir (22) is provided on the side wall of the water supply box (2) connected to the water-passing connector (23); and a flow-stabilizing grid (11) is located at the water outlet of the water-passing connector (23); A water level control panel (21) is vertically arranged in the water supply tank (2), and the water level control panel divides the water supply tank (2) into two independent chambers, namely a water inlet chamber and a water outlet chamber. The water inlet chamber is close to the water connection piece (23), one end of the water inlet pipe (7) is placed above the water inlet chamber, and the bottom wall of the water outlet chamber is connected to a water outlet pipe (25), and the other end of the water outlet pipe (25) is connected to the water reservoir (6).

2. The device for simulating the effect of micro-topography on the initiation of drifting fish eggs according to claim 1, characterized in that: It also comprises a door-shaped water tank bracket (4), wherein a plurality of adjustment holes are arranged on the vertical rods of the water tank bracket (4) in the height direction, and the insertion rod (41) is inserted between the vertical rods of the water tank bracket (4) through the corresponding adjustment holes, and the water outlet of the water tank is mounted on the insertion rod (41).

3. The device for simulating the effect of micro-topography on the initiation of drifting fish eggs according to claim 1, characterized in that: The water level control plate (21) comprises two plates that slide relative to each other, namely plate one and plate two. Plate one is located on a side close to the water inlet chamber, and plate two is located on a side away from the water inlet chamber. Plate one is fixedly connected to the inner wall of the water supply tank (2), and the connection is sealed and watertight. Plate one is relatively low in height. Plate two is slidably connected to plate one, and a dynamic seal is formed between plate two and the inner wall of the water supply tank (2).

4. The device for simulating the effect of micro-topography on the initiation of drifting fish eggs according to claim 1, characterized in that: The outer frame is connected to a wave compression plate (12) via a hanging rope (121); the wave compression plate (12) is made of organic glass; the wave compression plate (12) is parallel to the water surface in the water tank (1) and just contacts the water surface.

5. The device for simulating the effect of micro-topography on the initiation of drifting fish eggs according to claim 1, characterized in that: Drifting fish eggs (13) are prepared by heating distilled water and agar in a water bath and pouring them into spherical molds of different diameters.

6. A method for simulating the effect of microtopography on the initiation of drifting fish eggs, based on the device according to any one of claims 1 to 5, characterized in that: The following steps are involved: Different combinations of working conditions were designed, including different hydraulic gradients, sand wave shapes, and drifting fish eggs. Each working condition was tested according to the following steps: Step 1, adjusting the height of the water level control plate (21) in the water supply tank (2) to keep the water level in the water supply tank (2) at a low water level, allowing water to flow into the water tank (1) at a low flow rate, and after the water in the water tank (1) overflows the baffle (15) and the water flow stabilizes, releasing the drifting fish eggs (13) without an initial velocity at the trough of the model sand wave (14) in the middle and lower section of the water tank (1), and releasing 100 drifting fish eggs (13) in each experiment; Step 2, adjusting the flow rate entering the water tank (1) by adjusting the height of the second plate of the water level control plate (21) in the water supply tank (2), and observing whether the drifting fish eggs (13) in the model sand wave (14) meet the critical start-up; Step 3, gradually increase the flow rate and after finding the critical starting time, record the water depth in the water supply tank (2) and the flow value of the electromagnetic flow meter (51) in the tailwater collection pipe (5) at this time, the flow value of the electromagnetic flow meter (51) is the starting threshold flow rate, and use a PIV image acquisition device to record the flow field parameters at this time; Step 4: Turn off the water pump (3), remove the partition (15), drain the water in the water tank (1), and end this set of experiments.

7. The method for simulating the effect of microtopography on the initiation of drifting fish eggs according to claim 6, characterized in that: The relationship between the starting threshold and sand wave morphology parameters, near-bed velocity and fish egg parameters is as follows: Where: is the starting threshold of drifting fish eggs, is the coefficient to be determined, U b is the velocity near the bed surface, D is the egg diameter, R e Reynolds number, r s is the egg specific gravity, r is the specific gravity of water, g is the acceleration due to gravity, is the wavelength of the sand wave, h s It is the height of sand waves.

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