Method for determining a critical condition for resuspending drifting fish eggs

Abstract

The present application relates to a kind of determination method of drift fish egg resuspension critical condition, comprising: preparation model egg;Carry out the flume experiment of fish egg transport process;Energy characterization of fish egg transport state;Identify the key factor that influences fish egg resuspension;Resuspension characteristic flow rate formula is constructed;Resuspension critical threshold determination.The present application simultaneously introduces fish egg resuspension characteristic flow rate formula with hydraulic factor and fish egg physical characteristic factor, breaks through the technical bottleneck that traditional method directly ignores fish egg resuspension process or simplifies it as probability or random problem to handle;Based on energy conservation principle, the energy threshold mechanism of fish egg resuspension is revealed, provides theoretical basis for the selection and combination of flow rate, vorticity, drag force and other key factors in resuspension characteristic flow rate, establishes the internal link between fish egg energy state and movement state.Construction resuspension characteristic flow rate E c , and found that resuspension rate Q with E c Monotone increasing rule, provide scientific basis for protecting fish egg safety hatching.

Description

Technical Field

[0001] This invention relates to a method for determining the critical conditions for the resuspension of drifting fish eggs. It is a method for quantitatively judging and assessing the impact of hydropower projects on the spawning and hatching environment of fish, providing a scientific basis and quantitative tool for the ecological impact assessment of hydropower projects. Background Technology

[0002] Hydropower development has led to a decrease in reservoir flow velocity, a change that drastically alters the spawning habitat and hatching environment of drifting-egg-laying fish, threatening the reproduction of this species. Drifting-egg-laying fish, due to their unique hatching strategy, are particularly sensitive to changes in hydrodynamic conditions, and early resource changes can effectively reflect the environmental impact of hydropower development. These fish eggs are slightly heavier than water and, after being laid, need to be suspended in the water column by a certain flow velocity to be transported and complete embryonic development. Therefore, whether the fish eggs can remain suspended during drifting and avoid sinking to the riverbed and dying is a crucial factor in their successful hatching. Currently, there is no consensus in the academic community regarding the main factors and mechanisms determining fish egg drifting. One view holds that the safe drifting of fish eggs depends on the water flow velocity, specifically the safe drifting velocity range of 0.2–0.7 m / s; another view suggests that fish egg drifting is influenced by gravity, buoyancy, resistance, and drag. Currently, a mainstream view in research on the impact of hydropower development on drift-egg-laying fish is that after reservoir construction, the reduced flow velocity in the reservoir area means that the kinetic energy of the water is insufficient to maintain the suspension of fish eggs, causing a large number of eggs to sink to the riverbed and die, thus leading to a sharp decline in early fish populations. Based on this understanding, many studies equate "low flow velocity" with "fish egg sinking" and "hatching failure," believing that hydropower projects have a significant impact on the replenishment of drift-egg-laying fish populations. However, field surveys and experimental observations show that fish eggs do not necessarily die after sinking to the riverbed. Under suitable hydrodynamic conditions, deposited fish eggs may be affected by water flow, detach from the riverbed, resuspend in the water, continue to be transported with the current, and complete embryonic development. This "re-suspension" mechanism indicates that fish eggs can regain vitality under the influence of water flow after settling. Therefore, the impact of hydropower projects on fish resources may require a more careful assessment. A scientific understanding of the re-suspension mechanism of fish eggs and an objective assessment of the actual impact of hydropower projects on fish that lay drifting eggs are of great theoretical and practical significance for accurately judging the spawning ground pattern of fish after dam construction and formulating reasonable ecological scheduling strategies.

[0003] Currently, relevant studies either fail to consider the resuspension process or simplify it to a random event, lacking a systematic understanding of the resuspension mechanism. Key scientific questions remain unanswered: what are the hydrodynamic conditions and key controlling factors that enable fish eggs to resuspension, and how can these resuspension conditions be quantitatively described? Solving these problems is directly related to the accurate prediction of fish egg transport paths, effective drift duration, and hatching success rates after hydropower development, and also to the scientific identification of new spawning grounds that may form after dam construction. Summary of the Invention

[0004] To overcome the problems of existing technologies, this invention proposes a method for determining the critical conditions for the resuspension of drifting fish eggs. The method constructs a resuspension characteristic flow velocity E based on hydrodynamic parameters (flow velocity, eddy current) and physiological characteristics of fish eggs (egg density, egg diameter, mass). c This addresses the problems of insufficient understanding of the resuspension mechanism of floating fish eggs after settling and the inability to quantitatively determine the resuspension conditions in existing technologies.

[0005] The objective of this invention is achieved as follows: a method for determining the critical conditions for the resuspension of drifting fish eggs, the steps of which are as follows:

[0006] Step 1: Preparation of model eggs: Prepare model eggs with physical characteristics consistent with real fish eggs, and obtain the physical characteristic parameters of the target fish species' eggs, including density. Egg diameter d, still water settling velocity Agar model eggs with physical properties consistent with real fish eggs were prepared, and model eggs with sedimentation velocities similar to real eggs were screened through static water sedimentation experiments.

[0007] Step 2: Conduct flume experiments on fish egg transport process: Construct a variable slope flume with varying terrain at the bottom to simulate the complex hydraulic conditions of a natural river. Induce a characteristic flow field similar to a natural river by laying characteristic sand waves at the bottom of the flume. The shape of the sand waves is determined based on the sand wave equation, which describes the combined effects of water flow and sediment transport.

[0008]

[0009] In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. denoted as , where is the horizontal coordinate along the channel direction (m); A is the wave height (m); L is the wavelength (m); and F is the parameter affecting the ratio of the water-facing to the back-facing side of the sand wave. , These are the waveform control parameters. By adjusting these parameters, the flow field structure induced by sand waves can be altered.

[0010] Fish egg transport experiments were conducted under different hydraulic conditions, and the horizontal velocity of the flow field in the tank was measured. Vertical flow velocity Distribution, calculation of resultant velocity U, vorticity The distributions and formulas are as follows:

[0011]

[0012] In the formula: For the resultant velocity, ; The horizontal flow velocity, ; Vertical flow velocity, .

[0013]

[0014] In the formula: The horizontal flow velocity, ; Vertical flow velocity, ; The vertical coordinate is m;

[0015] The movement trajectory of fish eggs in the water tank was photographed, and the entire process of "sinking-retention-re-suspension" of fish eggs was observed. The synchronous fish egg trajectory and flow field data of each group of working conditions were summarized as the data basis for subsequent analysis.

[0016] Step 3: Energy characterization of fish egg transport state: Coupled analysis of fish egg movement trajectory and synchronous flow field data is performed. The transport state of fish eggs is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish eggs themselves, the kinetic and potential energy changes of fish eggs in the flow field are analyzed based on the principle of energy conservation.

[0017] The energy of a fish egg at any given moment in the flow field includes its gravitational potential energy and its kinetic energy while moving within the flow field. The transport state of the fish egg is correlated with its energy state (kinetic and potential energy) within the flow field. Coupled analysis of the fish egg's trajectory and synchronous flow field data reveals that the transport state of the fish egg (e.g., settling, resuspension) is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish egg itself, the transport state of the fish egg is analyzed based on energy conservation. The calculation formula is as follows:

[0018]

[0019] in: This is the sum of the changes in kinetic and potential energy of the fish eggs, hereinafter referred to as "energy change"; Fish egg density, ; For water density, ; Let be the height of the fish egg at time t, in meters. For fish eggs in Position and altitude at any given time, in meters (m); Let be the velocity of the fish egg at the current time step t. ; For fish eggs in the previous time step The speed of time m represents the mass of the fish eggs, in kg. g is the acceleration due to gravity. Take g = 9.81 m / s² 2 .when The total energy of the fish eggs is insufficient to overcome the resistance of the bed surface, resulting in a "stagnant" state. The energy changes of the fish eggs are mainly affected by small fluctuations in potential energy, while the kinetic energy is almost zero. Fish eggs are affected by changes in the hydrodynamic environment, and their kinetic energy increases. When the energy change of the fish eggs is greater than 0, the fish eggs overcome gravity and bed resistance, and are resuspended from the bottom and enter the water body to continue to be transported.

[0020] Step 4: Identifying Key Factors Affecting Fish Egg Resuspension: Based on multiple sets of synchronous flow field and fish egg motion data obtained from variable slope flume experiments under different hydraulic conditions, Pearson correlation analysis was used to analyze the correlation between fish egg energy changes and various hydrodynamic factors, environmental factors, and the characteristics of the fish eggs themselves, in order to screen key factors that have a significant impact on fish egg resuspension, including: energy changes. Resultant velocity U, vorticity ω, Reynolds number Re, relative velocity ΔV, drag force Using fish egg diameter d, experimental tank slope J, sand wave height A, and sand wave wavelength L, a Pearson correlation heatmap was constructed; the correlation coefficient r and its significance level p-value were used to evaluate the relationship between each variable and the experimental tank. The relationship between them;

[0021] Step 5: Constructing the resuspension characteristic velocity formula: Taking into account the key factors selected in Step 4 and the physical characteristics of fish eggs, and based on the principle of dimensional homogeneity, the resuspension characteristic velocity is constructed. The expression structure.

[0022] Select the resultant velocity U and vorticity Water flow drag force Sinking speed Using fish egg mass m as a feature quantity, construct Its expression is:

[0023]

[0024] Substitute the dimensions of each physical quantity ( The equation must have consistent dimensions on both sides. The dimensions are Solving the system of equations simultaneously, we get a=1, b=1, c=-1, d=-1, e=-1, which means... The expression is:

[0025]

[0026] In the formula, U is the resultant velocity, m / s; vorticity, Water flow drag force N; sinking velocity , m / s; fish egg mass m, kg.

[0027] The formula is rearranged as follows:

[0028]

[0029] In the formula, U is the characteristic velocity of resuspension, in m / s; U is the resultant velocity, in m / s. The drag force of the water flow is N; ω is the settling velocity of the fish eggs, in m / s; ω is the vorticity. m represents the mass of fish eggs, in kg.

[0030] in:

[0031]

[0032]

[0033] In the formula: The velocity is relative, in m / s; Let be the cross-sectional area of ​​the fish eggs and the water flow. , C D Drag force coefficient, dimensionless;

[0034] Fish eggs are generalized as spheres, based on the Reynolds number of water flow. Calculate C D The formula is as follows:

[0035] Stokes district :

[0036]

[0037] transition zone :

[0038]

[0039] Newton District :

[0040] ;

[0041] Step 6: Determination of the critical resuspension threshold: Calculate and analyze the relationship between the energy change of fish eggs and the characteristic resuspension velocity, and use the generalized additive model (GAM) to establish the relationship between the fish egg resuspension rate Q and the characteristic resuspension velocity. The nonlinear relationship, fitting The relationship is used to output multi-level critical thresholds under different suspension rates;

[0042] When fish eggs Value greater than or equal to When the critical threshold is reached, the fish eggs can be resuspended, thus enabling the determination of the critical conditions for fish egg resuscitation.

[0043] Furthermore, the static water settling experiment described in step 1 includes the following sub-steps:

[0044] Sub-step 1.1, prepare experimental facilities: use a transparent, graduated tall container, fill the container with clean water, and set up a high-speed camera on one side of the tall container; prepare model eggs with the same density and diameter as the fish eggs being studied;

[0045] Sub-step 1.2, Model egg release: Place the model egg inside the glass column at a depth of 0.02m below the water surface and release it with no initial velocity, one egg at a time;

[0046] Sub-step 1.3, Image acquisition: Adjust the relative position between the high-speed camera and the sedimentation column, and use particle tracking velocimetry technology to continuously capture the sedimentation process of the model egg at a frame rate of 50 frames / s to obtain high-resolution time-series images;

[0047] Sub-step 1.4, velocity calculation: Based on the centroid position (x, z) of the model egg and the time interval between images, calculate the instantaneous falling velocity of the model egg at different depths; the experiment only considers the vertical displacement of the model egg and ignores the lateral displacement. When the velocity is stable, the measured value is the final vertical settling velocity.

[0048] Sub-step 1.5, repeat the experiment: For model eggs with two diameters of 5mm and 6mm, which are consistent with the diameter of real fish eggs, repeat the above steps 50 times respectively, and use the final settling velocity of the stable stage to fit the formula of the settling velocity of a single model egg.

[0049] Sub-step 1.6, Sedimentation Process Analysis: The sedimentation process of the model egg in still water can be divided into two stages:

[0050] The first stage is the accelerated settling stage. The model egg begins to fall from rest, and the initial settling fluctuations are relatively large. The distance traveled in this stage is approximately 0.3m.

[0051] The second stage is the uniform settling stage. As the settling velocity gradually increases, the resistance experienced by the model egg continuously increases until a state of force equilibrium is reached. Afterward, the model egg undergoes uniform settling motion at a free settling velocity. When the velocity tends to stabilize, this velocity value is taken as the final settling velocity of the model egg.

[0052] After data analysis and regression fitting, the egg settling velocity V was obtained. g The formula is:

[0053]

[0054] In the formula, d is the settling velocity of fish eggs in still water; d is the diameter of the egg. and ρ represents the density of the model egg and water, respectively; g is the acceleration due to gravity.

[0055] Furthermore, in the water tank experiment of the fish egg transfer process described in step 2, the apparatus used in the water tank experiment includes:

[0056] A long, rectangular water tank is constructed, with at least one section jacked up to create an inclined surface. The angle of inclination is adjustable using the jacks. Uneven obstacles are placed at the bottom of the tank to simulate realistic underwater terrain. The tank is equipped with a water circulation system, including a water pump, a reservoir, and a flow meter, to create a continuously flowing water effect for experimental purposes. Lasers and high-speed photography / videography equipment are installed above and on the sides of the tank to collect data on the movement and trajectory of the fish eggs.

[0057] Flow field construction method: By laying characteristic sand waves at the bottom of the flume, a characteristic flow field similar to that of a natural river is induced. The shape of the sand waves is determined based on the sand wave equation, which relates to the combined effects of water flow and sediment transport.

[0058]

[0059] In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. , where A is the horizontal coordinate along the channel direction, in meters; L is the wave height; F is the wavelength; and F is the parameter affecting the ratio of the water-facing and back-facing sides of the sand wave. , These are waveform control parameters;

[0060] The water tank experiment includes the following sub-steps:

[0061] Sub-step 2.1 Experimental preparation: Adjust the height of the support rod of the water tank and set the slope of the water tank to the target value; fix the model sand wave of the corresponding shape to the bottom wall of the water tank; prepare model eggs with the target egg diameter and density and place them in a beaker for later use;

[0062] Sub-step 2.2, initial conditions and working conditions of the water tank: adjust the water level control plate of the water supply tank to the low water level, so that the water tank flows through at a low flow rate. After the water flow stabilizes, release 100 model eggs at the trough of the model sand wave without initial velocity.

[0063] Experimental setup: To systematically study the hydrodynamic response mechanism of fish egg resuspension, three variable parameters were selected: hydraulic gradient, sand wave morphology, and fish egg diameter. Specifically, for hydraulic gradient, considering the adjustable slope of the experimental tank bottom, five hydraulic gradients were set, namely... , , , , The sand dune morphology was set in two ways: large sand waves (wavelength 18cm, wave height 3.6cm) and small sand waves (wavelength 9cm, wave height 1.8cm); fish egg diameters were 5mm and 6mm. A total of 20 experimental conditions were formed using these parameter combinations.

[0064] Sub-step 2.3, Flow Regulation and Resuspension Observation: Gradually adjust the height of the sliding plate in the water supply tank, control the flow rate of the water tank through the triangular weir, and simultaneously observe the movement of fish eggs in the model sand waves. Three consecutive sand waves are used as the observation objects: when all fish eggs in the upstream sand wave are transferred to the downstream sand wave, and resuspension occurs in the sand wave, but no transfer is observed in the downstream sand wave, the flow rate is stopped. Through multiple preliminary experiments, the resuspension of fish eggs is determined as follows: With continuous sand waves laid at the bottom of the water tank, in the observation section of the large sand wave: 70% of the fish eggs are transferred to the next sand wave within 20 seconds; in the observation section of the small sand wave: 70% of the fish eggs are transferred to the next sand wave within 10 seconds.

[0065] Sub-step 2.4, Data Acquisition: After the fish eggs meet the resuspension criteria, record the following hydrodynamic parameters. The data collected for each operating condition includes flow field and fish egg trajectory data. Flow field data: The instantaneous velocity field is obtained through the PIV system to obtain the resultant velocity U and horizontal velocity of the flow field in the tank. Vertical flow velocity vorticity Hydrodynamic parameters; Fish egg trajectory data: Fish egg movement videos are acquired synchronously using a high-speed camera, and the fish egg movement trajectory is extracted using background subtraction and particle tracking technology; Synchronous fish egg trajectories are obtained for each working condition;

[0066] Each working condition was repeated twice, and the average value was used for subsequent analysis. Using the above data, the resuspension of fish eggs and their movement trajectory characteristics under different hydraulic conditions were analyzed, providing basic data for the analysis of resuspension mechanisms.

[0067] The advantages and beneficial effects of this invention are as follows: This invention establishes for the first time a characteristic flow velocity formula for fish egg resuspension, and introduces hydraulic factors such as flow velocity and vorticity, as well as physiological characteristic factors of fish eggs, as key factors into the characteristic flow velocity formula for fish egg resuspension, revealing the hydrodynamic mechanism of drifting fish egg resuspension, and breaking through the technical bottleneck of traditional methods that directly ignore the fish egg resuspension process or simplify it into a probability or random problem; Based on the principle of energy conservation, it reveals the energy threshold mechanism of fish egg resuspension (the transition of fish eggs from settling and retention to resuspension depends on whether the energy input from external hydrodynamic forces (flow velocity, vorticity, drag force) is sufficient to overcome gravity and bed resistance). The point at which the value changes from negative to positive, known as "zero," is the critical energy threshold for resuspension—this threshold is the characteristic resuspension velocity E. c This provides a physical basis for the construction of the resuspension characteristic flow velocity, and provides a theoretical basis for the selection and combination of key factors such as velocity, vorticity, and drag force in the resuspension characteristic flow velocity, establishing the intrinsic relationship between fish egg energy changes and resuspension state. The resuspension characteristic flow velocity was constructed. Furthermore, it was found that there is a certain relationship between the energy changes of fish eggs and the resuspension characteristic flow velocity. When the value is small, ΔE is negative (in a stagnant state); as the value increases... Increase Gradually changing from negative to positive, and the positive value continues to increase; when When the speed exceeds a certain critical threshold (e.g., 0.00244 m / s), all data points... All are greater than 0; further, the generalized additive model GAM is used for fitting. The relationship is defined by using the fish egg resuspension rate Q as the response variable and the resuspension characteristic flow velocity. As a predictor variable, a GAM model was constructed using a binomial distribution family and a logit link function, revealing that the resuspension rate Q varies with... The invention employs a monotonically increasing pattern to output multi-level critical thresholds for different suspension rates, providing flexible options for engineering applications with varying risk appetites. It is widely used in ecological impact assessments of hydropower projects, fish resource protection, and reservoir ecological management, providing a scientific basis for ensuring the safe hatching of fish eggs. Attached Figure Description

[0068] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0069] Figure 1 This is a flowchart of the method for determining the critical conditions for resuspension of drifting fish eggs as described in Embodiment 1 of the present invention;

[0070] Figure 2 This is a schematic diagram of the large sand wave morphology in a water tank experiment of the method for determining the critical condition for resuspension of drifting fish eggs according to Embodiment 1 of the present invention:

[0071] Figure 3This is a schematic diagram of the small sand wave morphology in a water tank experiment of the method for determining the critical condition for resuspension of drifting fish eggs according to Embodiment 1 of the present invention:

[0072] Figure 4 This is an application example of the method for determining the critical conditions for resuspension of drifting fish eggs as described in Embodiment 1 of the present invention, showing the relationship between energy change and resuspension characteristic flow velocity.

[0073] Figure 5 This is an application example of the method for determining the critical conditions for resuspension of drifting fish eggs described in Embodiment 1 of the present invention, showing the relationship between the resuspension characteristic flow velocity and the resuspension rate.

[0074] Figure 6 This is a schematic diagram of the still water settling velocity experimental device described in Embodiment 2 of the present invention;

[0075] Figure 7 This is a schematic diagram of the variable slope water tank structure used in the water tank experiment method described in Embodiment 3 of the present invention;

[0076] Figure 8 This is a schematic diagram of the particle image velocimetry (PIV) system structure of the water tank experimental method described in Embodiment 3 of the present invention. Detailed Implementation

[0077] Example 1:

[0078] This embodiment describes a method for determining the critical conditions for the resuspension of drifting fish eggs. The steps of the method are as follows, and the process is as follows: Figure 1 As shown:

[0079] Step 1: Preparation of model eggs: Prepare model eggs with physical characteristics consistent with real fish eggs, and obtain the physical characteristic parameters of the target fish species' eggs, including density. Egg diameter d, still water settling velocity Agar model eggs with physical characteristics (egg diameter, density, and settling velocity) consistent with those of real fish eggs were prepared, and model eggs with settling velocities similar to those of real eggs were screened through static water settling experiments.

[0080] Alternatively, real fish eggs can be used directly; if so, this step can be omitted. The density, diameter, and still-water settling velocity of real fish eggs can be obtained by consulting literature or experts, or through measurement, salt selection, and still-water settling velocity experiments.

[0081] The physical properties of the prepared model eggs were compared with those of real eggs, and the model eggs with the same physical properties as the real eggs were selected for subsequent steps. Because the spawning period of fish is limited and the hatching window is short, real fish eggs may not be sufficient for conducting experiments; therefore, it is generally more practical to use model eggs instead of real eggs. Hereinafter, both model eggs and real fish eggs will be referred to as fish eggs.

[0082] Step 2: Conduct a flume experiment on fish egg transport: Construct a variable-slope flume (i.e., the flume has a certain slope, which can be adjusted according to experimental needs). Create undulating terrain at the bottom of the flume to simulate the complex hydraulic conditions of a natural river. Induce a characteristic flow field similar to that of a natural river by laying characteristic sand waves at the bottom of the flume. The shape of the sand waves is determined based on the sand wave equation, which describes the combined effects of water flow and sediment transport.

[0083]

[0084] In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. Let be the horizontal coordinate along the direction of the water tank, in meters (m). A represents wave height (m); L represents wavelength (m); F represents the parameter affecting the ratio of the water-facing to the back-facing side of the sand wave. , These are the waveform control parameters. By adjusting these parameters, the flow field structure induced by sand waves can be altered.

[0085] The water tank experiment shown can select various sand wave patterns, for example, using two sand wave patterns, the parameters of which are shown in Table 1, and the patterns are as follows. Figure 2 , 3 As shown, Figure 2 A big sand wave, Figure 3 Small sand waves. Both types of sand waves can induce recirculation zones and vortex structures, but their flow field characteristics differ: large sand waves ( =0.18m, The eddy current induced by the sand wave (=0.036m) is relatively small, and the small sand wave ( The vorticity induced by the vorticity (A=0.09m, A=0.018m) is relatively large.

[0086] Table 1. Parameters of two types of sand wave morphology

[0087]

[0088] Fish egg transport experiments were conducted under different hydraulic conditions, and the horizontal velocity of the flow field in the tank was measured using a flow velocity measurement system. Vertical flow velocity Distribution, calculation of vorticity Distribution, the formula is as follows:

[0089] Formula for resultant velocity U

[0090]

[0091] In the formula: The horizontal flow velocity is expressed in m / s. The vertical flow velocity is in m / s; Let m be the vertical coordinate.

[0092] The movement trajectory of fish eggs in the water tank was captured by a high-frequency camera to observe the entire process of "sinking-retention-resuspending" of the fish eggs; the data from the above experiments were summarized, and the synchronous trajectory of the fish eggs (including position, such as height) was obtained for each working condition. ,speed ,time ) and flow field data (resultant velocity U, vorticity) (etc.), serving as the data foundation for subsequent analysis.

[0093] Step 3, Energy characterization of fish egg transport state: Coupled analysis of fish egg movement trajectory and synchronous flow field data is performed. The transport state of fish eggs is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish eggs themselves, the kinetic and potential energy changes of fish eggs in the flow field are analyzed based on the principle of energy conservation.

[0094] The energy of a fish egg at any given moment in the flow field includes its gravitational potential energy and its kinetic energy while moving within the flow field. The transport state of the fish egg is correlated with its energy state (kinetic and potential energy) within the flow field. Coupled analysis of the fish egg's trajectory and synchronous flow field data reveals that the transport state of the fish egg (e.g., settling, resuspension) is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish egg itself, the transport state of the fish egg is analyzed based on energy conservation. The calculation formula is as follows:

[0095]

[0096] in: This is the sum of the changes in kinetic and potential energy of the fish eggs, hereinafter referred to as "energy change"; Fish egg density, ; For water density, ; Let m be the height of the fish egg at time t. For fish eggs in Position and altitude at any given time, in meters (m); Let be the velocity of the fish egg at the current time step t, in m / s; For fish eggs in the previous time step The velocity at a given moment, in m / s; The mass of fish eggs, in kg. g is the acceleration due to gravity, in m / s². 2 Take g = 9.81 m / s² 2 .when The total energy of the fish eggs is insufficient to overcome the resistance of the bed surface, resulting in a "stagnant" state. The energy changes of the fish eggs are mainly affected by small fluctuations in potential energy, while the kinetic energy is almost zero. Fish eggs are affected by changes in the hydrodynamic environment, and their kinetic energy increases. When the energy change of the fish eggs is greater than 0, the fish eggs overcome gravity and bed resistance, and are resuspended from the bottom and enter the water body to continue to be transported.

[0097] Step 4: Identify key factors affecting fish egg resuspension: Based on multiple sets (e.g., 20 sets) of synchronous flow field and fish egg motion data under different hydraulic conditions obtained from variable slope flume experiments, Pearson correlation analysis was used to analyze the correlation between fish egg energy changes and various hydrodynamic factors, environmental factors, and fish egg characteristics, in order to screen key factors that have a significant impact on fish egg resuspension.

[0098] To comprehensively examine the relationship between energy changes in fish eggs and hydrodynamics, topography, and the characteristics of the fish eggs themselves, energy changes were selected as a factor. Resultant velocity U, vorticity Reynolds number of water flow Relative velocity Drag force A Pearson correlation heatmap was constructed using variables such as fish egg diameter (d), experimental tank slope (J), sand wave height (A), and sand wave wavelength (L). The relationship between each variable and ΔE was evaluated using the correlation coefficient (r) and its significance level (p-value).

[0099] Analysis results show that the resultant velocity U is related to energy change. Significantly correlated, flow velocity directly affects drag force. and vorticity Eddy power is significantly negatively correlated with energy change, reflecting the influence of fluid rotation intensity on energy dissipation or conversion, and has physical significance for the hydrodynamic mechanism of fish egg resuspension. Relative velocity and drag force are significantly positively correlated with energy change, and drag force is highly correlated with relative velocity, exhibiting collinearity. Drag force is the hydrodynamic load directly acting on the fish eggs, and in characteristic flow velocities, it can represent the pushing effect of water flow on particles. Egg diameter d is significantly correlated with energy change and is an important parameter reflecting the physical characteristics of the fish eggs themselves. Topographic factors (slope, wave height, wavelength) and water flow Reynolds number have extremely weak or statistically insignificant correlations with ΔE, and have no substantial impact on energy change.

[0100] In summary, the key factors that have a direct controlling effect on fish egg resuspension were screened out: (1) Hydrodynamic parameters: flow velocity vorticity and water flow drag force (2) Biophysical characteristics of fish eggs: sinking velocity of fish eggs and the mass of fish eggs m (both are derived from the density of fish eggs) 卵 Egg diameter (Extracted) to construct a characterization formula for resuspended characteristic flow velocities.

[0101] Step 5, Constructing the resuspension characteristic flow velocity formula: Taking into account the key factors selected in Step 4 and the physical characteristics of fish eggs, based on the principle of dimensional homogeneity, the resuspension characteristic flow velocity is constructed. The expression structure;

[0102] set up The general expression is:

[0103]

[0104] Substitute the dimensions of each physical quantity ( The equation requires that the dimensions on both sides be consistent. The dimensions are Solving the system of equations simultaneously, we get... , , , , ,Right now The calculation formula is:

[0105]

[0106] In the formula, U is the characteristic velocity of resuspension, in m / s; U is the resultant velocity, in m / s. The drag force of the water flow is N; The settling velocity of the fish eggs is m / s; vorticity, m represents the mass of the fish eggs, in kg.

[0107] in: Both m and m are basic factors The extension of d.

[0108]

[0109]

[0110]

[0111] In the formula: The density of water is kg / m³. 3 ; The velocity is relative, in m / s; Let be the cross-sectional area of ​​the fish eggs and the water flow. m 2 C D The drag force coefficient is dimensionless.

[0112] Fish eggs are generalized as spheres, based on the Reynolds number of water flow. Calculate C D The formula is as follows:

[0113] Stokes district ):

[0114]

[0115] Transition zone ( ):

[0116]

[0117] Newton District ( ):

[0118] ;

[0119] Among them: Reynolds number of water flow The formula is:

[0120]

[0121] In the formula: For water density, U is the resultant velocity, i.e., the current velocity at the location of the fish eggs, in m / s; R is the hydraulic radius. ,in The cross-sectional area of ​​the water passage. For wetted perimeter, m; Let be the dynamic viscosity of water, Pa·s, and take . .

[0122] Step 6: Determination of the critical resuspension threshold: The relationship between the energy change of fish eggs and the characteristic resuspension velocity was calculated and analyzed. Studies have shown that... and There is a good positive correlation between them: as The increase, The overall trend is increasing. When smaller, Negative; Increase, The values ​​are distributed on both positive and negative sides, and some characteristic flow velocities correspond to <0 indicates that the fish eggs are in a state of energy dissipation (sinking or stagnation). When When a certain critical threshold is exceeded, all data points All are greater than 0, and as Further increase The positive value continues to increase. This means that when the resuspension characteristic flow rate of the fish eggs is greater than this threshold, the fish eggs can obtain enough energy input to overcome the bed surface constraint and achieve resuspension.

[0123] It is worth noting that the same The value may correspond to multiple The value indicates that energy changes are also influenced by other local factors. However, the overall pattern is: The larger, The higher the percentage of >0, the greater the possibility of fish eggs being resuspended.

[0124] Based on this relationship, a generalized additive model (GAM) is used to establish the relationship between the fish egg resuspension rate Q and the resuspension characteristic velocity. The nonlinear relationship between the resuspension rate Q and the characteristic flow velocity is shown in the study. There is a clear monotonically increasing relationship between them. Based on this, the fitting... The relationship is established, and multi-level critical thresholds at different resuspension rates are output, such as critical thresholds at 70%, 80%, and 100% resuspension rates, to determine the critical thresholds at different resuspension rates. value.

[0125] When fish eggs Value greater than or equal to When the critical threshold is reached, the fish eggs can be 100% resuspended, thus determining the critical condition for fish egg resuspension.

[0126] Application examples:

[0127] Taking the round-mouthed copper fish (Coreius guichenoti) as an example, the critical conditions for egg resuspension were determined. Using the round-mouthed copper fish (Coreius guichenoti), which lays drifting eggs in the lower reaches of the Jinsha River, as the target species, indoor flume experiments and data analysis were conducted to determine the key factors and characteristic resuspension velocities for its eggs. The critical threshold.

[0128] Step 1, Prepare model eggs: Prepare model eggs with physical characteristics consistent with real fish eggs.

[0129] Based on the measured physical characteristics of the eggs of the round-mouthed copper fish: the egg diameter is concentrated between 0.00484 and 0.00623 μm, and the density is... The average settlement velocity is 0.0119 m / s.

[0130] Model eggs were prepared using agar material: 100 mL of distilled water was added, along with 0.4 g of agar and 0.4 g of sodium alginate. The mixture was heated in a water bath until completely melted. While still hot, the solution was poured into spherical molds with diameters of 5 mm and 6 mm. After cooling, the molds were removed.

[0131] Density screening uses the salt selection method: a density gradient of... NaCl solution (interval) The model eggs were placed in separate 50 mL beakers. The eggs were then added to the target solution and stirred at 30 rpm for 3 minutes, maintaining the water temperature at [temperature missing]. After settling, determine the density based on whether the eggs sink or float: Sinking eggs density > solution density, suspended eggs density ≈ solution density (error) The density of floating eggs is less than the density of the solution. Screening process: First, in... Collect suspended eggs in the solution, and then... The sedimented eggs were removed from the solution to obtain the final density range. The model eggs were washed three times with deionized water to remove residual salts before use.

[0132] The settling velocity of eggs in still water was measured using an acrylic settling column (0.2m long, 0.1m wide, and 0.8m high), with a ruler attached to one side. The experimental procedure is as follows:

[0133] (1) Release of model eggs: The model eggs were placed 0.02m below the water surface inside the glass column and released without initial velocity, one egg at a time. In order to reduce the influence of water turbulence caused by the release of model eggs on the experiment, after each egg settled, we waited for 5 minutes until the water flow inside the glass column stabilized before releasing the next model egg.

[0134] (2) Image acquisition: Adjust the relative position between the high-speed camera and the sedimentation column, and use particle tracking velocimetry technology to continuously capture the sedimentation process of the model egg at a frame rate of 50 frames / s to obtain high-resolution time-series images.

[0135] (3) Velocity calculation: Based on the centroid position (x, z) of the model egg and the time interval between images, the instantaneous falling velocity of the model egg at different depths is calculated. Only the vertical (z-direction) displacement of the model egg is considered, and the lateral displacement is ignored. When the velocity is stable, the measured value is the final vertical settling velocity.

[0136] (4) Repeated experiment: For model eggs with two diameters of 5 mm and 6 mm, the above steps were repeated 50 times respectively, and the final settling velocity in the stable stage was statistically analyzed.

[0137] Analysis of the settling velocity process showed that the settling of the model eggs in still water consisted of two stages: an accelerated settling stage (traveling a distance of approximately 0.3 m) and a uniform settling stage. During the uniform settling stage, the model eggs moved at a constant free settling velocity. Measured settling velocities were 0.010 m / s at 0.005 m and 0.012 m / s at 0.006 m.

[0138] After data analysis and regression fitting, the egg settling velocity was obtained. The formula is:

[0139] The settlement velocity comparison and verification uses the settlement velocity formula fitted in this embodiment:

[0140]

[0141] In the formula, d represents the settling velocity of the fish eggs in still water, in m / s; d represents the diameter of the fish eggs, in m. and This indicates the density of fish eggs and water. g is the acceleration due to gravity. ,Pick Real eggs of the round-mouthed copper fish can also be used directly, but real eggs are greatly affected by the environment (developmental stage, water temperature, etc.), so it is recommended to use the model eggs mentioned above to ensure the reproducibility of the experiment.

[0142] Step 2: Conduct a water tank experiment on the fish egg transfer process:

[0143] A variable-slope flume system was constructed: the flume was 2m long, 0.15m wide, and 0.75m high, with an adjustable slope (0~16%). An undulating sand wave topography was laid at the bottom of the flume to simulate the complex hydraulic conditions of a natural river. Two types of sand waves were set up: large sand waves (wavelength 0.18m, wave height 0.036m) and small sand waves (wavelength 0.09m, wave height 0.018m). Five hydraulic slopes were set up in the experiment (…). , , , , ), 2 types of sand wave morphology, 2 types of egg diameter (5mm, 6mm), a total of 20 working conditions.

[0144] (1) Experimental preparation: Adjust the height of the pole of the water tank support and set the slope of the water tank to the target value; fix the model sand wave of the corresponding shape to the bottom wall of the water tank; prepare model eggs with target egg diameter and density and place them in a beaker for later use.

[0145] (2) Initial conditions of the water tank: Adjust the water level control plate of the water supply tank to the low water level so that the water tank flows through at a low flow rate. After the water flow stabilizes, release 100 fish eggs at the trough of the model sand wave without initial velocity.

[0146] (3) Flow regulation and resuspension observation: The height of the sliding plate of the water supply tank was gradually adjusted, and the flow rate of the water tank was controlled by the triangular weir. The movement of fish eggs in the model sand waves was observed simultaneously. Three consecutive sand waves were used as the observation objects: when all the fish eggs in the upstream sand wave were transferred to the downstream sand wave and the fish eggs in the sand wave showed resuspension, but no fish eggs were transferred in the downstream sand wave, the flow rate was stopped. Through multiple preliminary experiments, the resuspension of fish eggs was judged as follows: when continuous sand waves were laid at the bottom of the water tank, the large sand wave in the observation section showed that 70% of the fish eggs were transferred to the next sand wave within 20 seconds; the small sand wave in the observation section showed that 70% of the fish eggs were transferred to the next sand wave within 10 seconds.

[0147] (4) Data acquisition: After the fish eggs meet the resuspension criteria, the following data are recorded: water level in the water supply tank; flow rate displayed by the electromagnetic flowmeter (i.e., resuspension flow rate); flow field images are acquired through the PIV system to obtain hydrodynamic parameters such as resultant velocity and vorticity; and fish egg movement videos are acquired simultaneously through a high-speed camera to obtain the fish egg trajectory.

[0148] After the above experiments are completed, turn off the water pump, remove the baffle, drain the water from the tank, and end the current experimental condition. Change the sand wave pattern, adjust the tank slope, or replace the model egg to begin subsequent experiments.

[0149] Flow velocity measurement system:

[0150] A particle image velocimetry (PIV) system was used to measure the near-bottom flow field near the sand ripple. The PIV system consisted of a laser source, a high-speed camera, and image processing software. The laser source was a continuous-wave laser (LWPIV-H, 10W, 532nm wavelength), mounted above the flume and movable along the flume direction via a hanging ring, forming a sheet light source approximately 1mm thick to illuminate the observation section. A high-speed motion camera (IDTos10, 1280×1024 pixels resolution) was placed on one side of the flume, with its lens axis perpendicular to the laser sheet plane, and the frame rate set to 200Hz. To prevent refraction of the laser by water ripples, an acrylic wave plate was connected to the outer frame via a hanging rope, ensuring it was parallel and just touching the water surface inside the flume, eliminating ripples and preventing laser refraction that could cause dark bands in the observation section. The entire measurement area was covered with a light-shielding cloth to eliminate interference from ambient light. The PIV observed the flow field at the location of the sand ripple, close to the riverbed bottom, with the imaging range being [missing information]. m.

[0151] The experiment used hollow glass beads as tracer particles, with a density of The median particle size is 50µm, and the particles can move with the water flow. Images of the tracer particles' motion were continuously captured using a high-speed camera. After image preprocessing (image denoising, grayscale conversion, binarization), correlation calculations, and velocity field reconstruction using JFmeter post-processing software, a two-dimensional instantaneous velocity field of the water tank facade based on the time series was obtained. Furthermore, the vorticity field was calculated using the following formula:

[0152]

[0153] In the formula: The horizontal flow velocity is expressed in m / s. The vertical flow velocity is in m / s. Let m be the vertical coordinate.

[0154] Fish egg trajectory acquisition system:

[0155] The fish egg trajectory acquisition system is used to obtain the movement trajectory data of fish eggs under different hydraulic conditions, providing a basis for subsequent analysis and model verification.

[0156] The fish egg trajectory acquisition system was independently developed using Python and ImageJ image processing software to extract fish egg movement trajectories from recorded video sequences. The core algorithm is as follows: First, the original video is preprocessed using background subtraction and morphological processing. Background subtraction is applied to separate the moving fish eggs from the static or slowly changing background water flow and experimental setup images. Second, using a built-in particle analysis and tracking plugin, the centroid coordinates (x, z) of each fish egg in each frame are automatically identified. Finally, based on continuous frame sequences, nearest neighbor association and other methods are used to connect the positions of the same fish egg at different time points, constructing a complete time-egg position trajectory dataset. Each trajectory includes the fish egg ID, time t, and the corresponding two-dimensional spatial coordinate sequence.

[0157] The fish egg trajectory acquisition system described above has the following characteristics:

[0158] (1) Spatial matching: The observation area of ​​fish egg movement video tracking is completely consistent with the PIV flow field measurement. Spatial matching of fish egg movement trajectory and flow field structure provides a data basis for revealing the coupling relationship between fish egg resuspension and vortex structure.

[0159] (2) Spatiotemporal resolution: The system uses a sampling frequency of 20Hz / s and a temporal resolution of 0.05s, which can record the entire process of fish egg movement. Based on the fish egg re-suspension start-up speed (about 0.05m / s), the spatial resolution is estimated to be about 2.5mm, which is about half the diameter of the fish egg, and can effectively capture the movement trajectory and position changes of the fish egg.

[0160] (3) Non-contact observation: No need to deploy sensors or markers in the flow field, and no disturbance to the water flow.

[0161] Step 3: Energy characterization of fish egg transport status:

[0162] Based on the principle of energy conservation, the changes in kinetic and potential energy of fish eggs in a flow field are analyzed. Ignoring egg deformation, the calculation formula is:

[0163]

[0164] Where: ΔE is the sum of the changes in kinetic and potential energy of the fish eggs; Hereinafter referred to as "energy change"; Fish egg density, ; For water density, ; Let be the height of the fish egg at time t, in meters. For fish eggs in Position and altitude at any given time, in meters (m); Let be the velocity of the fish egg at the current time step t, in m / s; For fish eggs in the previous time step The velocity at a given time is m / s; m is the mass of the fish eggs, kg. g is the acceleration due to gravity, in m / s². 2 Take g = 9.81 m / s² 2 .when The total energy of the fish eggs is insufficient to overcome the resistance of the bed surface, resulting in a "stagnant" state. The energy changes of the fish eggs are mainly affected by small fluctuations in potential energy, while the kinetic energy is almost zero. Fish eggs are affected by changes in the hydrodynamic environment, and their kinetic energy increases. When the energy change of the fish eggs is greater than 0, the fish eggs overcome gravity and bed resistance, and are resuspended from the bottom and enter the water body to continue to be transported.

[0165] Step 4: Identify key factors affecting fish egg resuspension:

[0166] Based on 20 sets of synchronous flow field and fish egg movement data under different hydraulic conditions obtained from variable slope flume experiments, Pearson correlation analysis was used to analyze the correlation between fish egg energy changes and various hydrodynamic factors, environmental factors and fish egg characteristics, in order to screen key factors that have a significant impact on fish egg resuspension.

[0167] To comprehensively examine the relationship between energy changes in fish eggs and hydrodynamics, topography, and the characteristics of the fish eggs themselves, energy changes were selected as a factor. Resultant velocity U, vorticity Reynolds number Re and relative velocity Drag force Fish egg diameter , slope of the experimental water tank Pearson correlation heatmaps were constructed using variables such as sand wave height A and sand wave wavelength L.

[0168] Analysis results show that the resultant velocity U is related to energy change. Significantly correlated, flow velocity (resultant velocity) can directly affect drag force. and vorticity Eddy volume is significantly negatively correlated with energy change, reflecting the influence of fluid rotation intensity on energy dissipation or conversion, and has physical significance for the hydrodynamic mechanism of fish egg resuspension. Relative velocity and drag force are significantly positively correlated with energy change, and drag force is highly correlated with relative velocity, exhibiting collinearity. Drag force is the hydrodynamic load directly acting on the fish eggs, and in characteristic flow velocities, it can represent the pushing effect of water flow on the fish eggs. Egg diameter d is significantly correlated with energy change and is an important parameter reflecting the physical characteristics of the fish eggs themselves. Topographic factors (slope, wave height, wavelength) and water flow Reynolds number have extremely weak or statistically insignificant correlations with ΔE, and have no substantial impact on energy change.

[0169] In summary, the key factors that have a direct controlling effect on fish egg resuspension were screened out: (1) Hydrodynamic parameters: resultant velocity vorticity and water flow drag force (2) Biophysical characteristics of fish eggs: sinking velocity of fish eggs and the mass of fish eggs m (both are derived from the density of fish eggs) 卵 Egg diameter (Extracted) to construct a characterization formula for resuspended characteristic flow velocities.

[0170] Step 5: Construct the resuspension characteristic velocity formula:

[0171] Taking into account the key factors screened in step 4 and the physical characteristics of fish eggs, and based on the principle of dimensional homogeneity, a resuspension characteristic flow velocity E is constructed. c Its formula is:

[0172]

[0173] In the formula, E c The characteristic velocity for resuspension is U, m / s; the resultant velocity is U, m / s; F d For the drag force of the water flow, N; V g V is the settling velocity of the fish eggs, m / s; ω is the vorticity, s⁻¹; m is the mass of the fish eggs, with the egg shape generalized as a sphere, kg. Where: V g Both m and ρ are basic factors. 卵 The extension of d.

[0174]

[0175]

[0176]

[0177] In the formula: Fluid density, kg / m³ 3 ; A is the relative velocity, in m / s;e Let be the cross-sectional area of ​​the fish eggs and the water flow. m 2 C D The drag force coefficient is dimensionless.

[0178] Fish eggs are generalized as spheres, based on the Reynolds number of water flow. Calculate C D The formula is as follows:

[0179] Stokes district ):

[0180] Transition zone ( ):

[0181] Newton District ( ):

[0182] ;

[0183] Among them: Reynolds number of water flow The formula is:

[0184]

[0185] In the formula: ρ 水 The density of water is kg / m³. 3 U is the resultant velocity, i.e., the current velocity at the location of the fish eggs, in m / s; R is the hydraulic radius, R=A w / χ, where A w χ is the cross-sectional area of ​​the water passage, m is the wetted perimeter; μ is the dynamic viscosity of water, Pa·s, taken as 1.003 × 10⁻⁶. − 3 Pa·s.

[0186] Step 6: Determining the resuspension critical threshold:

[0187] Calculate the E of fish eggs under various working conditions c And the corresponding energy change ΔE. Analysis shows that ΔE is related to E... c There is a certain positive correlation: E c When E is small, ΔE is mostly negative; as E increases... c As E increases, ΔE gradually becomes positive; when E c Once a certain critical value is exceeded, all ΔE>0, and the fish eggs can be resuspended.

[0188] A generalized additive model (GAM) is used to establish the relationship between resuspension rate Q and E. c The nonlinear relationship between Q and E is shown in the fitting results. c Monotonically increasing. The critical E value for different resuspension rates is determined based on the model.c Value, such as Figure 4 , 5 As shown:

[0189] when At that time, E c _0.7=0.00144 m / s;

[0190] when At that time, E c _0.8=0.00177 m / s;

[0191] when At that time, E c _1.0=0.00244m / s.

[0192] Therefore, if the location of the fish eggs is E c Greater than or equal to E c If the threshold is 1.0 (1.0 guarantee rate threshold), then all fish eggs can be resuspended.

[0193] The determined critical value for resuspension of round-mouthed copper fish eggs is: characteristic flow velocity E c The recommended resuscitation speeds are 0.00144 m / s (70% of the fish eggs can be resuspended), 0.00177 m / s (80% of the fish eggs can be resuspended), and 0.00244 m / s (100% of the fish eggs can be resuspended). In practical engineering applications, the appropriate resuscitation rate threshold can be selected based on risk preference.

[0194] Example 2:

[0195] This embodiment is an improvement upon Embodiment 1, detailing the still water settling experiment. The still water settling experiment includes the following sub-steps:

[0196] Sub-step 1.1, Prepare experimental facilities: Use a transparent, graduated tall container, fill it with clean water, and place a high-speed camera on one side of the container, such as... Figure 6 As shown. Model eggs with the same density and diameter as the eggs of the fish being studied were prepared;

[0197] The density, diameter, and still-water settling velocity of real fish eggs can be obtained by consulting literature or experts, or through measurement, salt selection, and still-water settling velocity experiments. In this embodiment, artificial preparation was used, therefore still-water settling velocity experiments were employed to obtain the various parameters of the model eggs.

[0198] Taking the preparation of eggs from the round-mouthed copper fish as an example: Agar model eggs with the same physical characteristics as the target fish species, the round-mouthed copper fish, were prepared. The diameters of the prepared model eggs were 0.005 μm and 0.006 μm, respectively, and the densities ranged from 1.007 to 1.009 × 10⁻⁶. 3 kg / m3 .

[0199] A transparent plexiglass column, 0.2m long, 0.1m wide, and 0.8m high, was used for measurement. A ruler was attached to one side of the column to record the egg's settling displacement. Clean water was placed in a container, and the descent speed of the model eggs was observed to obtain model eggs that approximate the still-water settling speed of real fish eggs. The physical properties of the prepared model eggs were compared with those of real eggs, and the model eggs with the same physical properties as real eggs were selected for subsequent steps.

[0200] Sub-step 1.2, Egg Release: Place the egg model inside the glass column at a depth of 0.02m below the water surface and release it with no initial velocity, one egg at a time. To reduce the impact of water turbulence caused by egg release on the experiment, after each egg settles, wait for a period of time, such as 5 minutes, until the water flow inside the glass column stabilizes before releasing the next egg model.

[0201] Sub-step 1.3, Image acquisition: Adjust the relative position between the high-speed camera and the sedimentation column, and use particle tracking velocimetry technology to continuously capture the sedimentation process of the model egg at a frame rate of 50 frames / s to obtain high-resolution time-series images;

[0202] Sub-step 1.4, velocity calculation: Based on the centroid position (x, z) of the model egg and the time interval between images, calculate the instantaneous falling velocity of the model egg at different depths; the experiment only considers the vertical displacement of the model egg and ignores the lateral displacement. When the velocity is stable, the measured value is the final vertical settling velocity.

[0203] Sub-step 1.5, repeat the experiment: For model eggs with two diameters of 5mm and 6mm, which are consistent with the diameter of real fish eggs, repeat the above steps 50 times respectively, and use the final settling velocity of the stable stage to fit the formula of the settling velocity of a single model egg.

[0204] Sub-step 1.6, Sedimentation Process Analysis: The sedimentation process of the model egg in still water can be divided into two stages:

[0205] The first stage is the accelerated settling stage. The model egg begins to fall from rest, and the initial settling fluctuations are relatively large. The distance traveled in this stage is approximately 0.3m.

[0206] The second stage is the uniform settling stage. As the settling velocity gradually increases, the resistance experienced by the model egg continuously increases until a state of force equilibrium is reached. Afterward, the model egg undergoes uniform settling motion at a free settling velocity. When the velocity tends to stabilize, this velocity value is taken as the final settling velocity of the model egg.

[0207] After data analysis and regression fitting, the egg settling velocity V was obtained. g The formula is:

[0208]

[0209] In the formula: V g ρ is the settling velocity of fish eggs in still water, m / s; d is the egg diameter, m; 卵 and ρ 水 These represent the densities of the model eggs (or fish eggs) and water, respectively, in kg / m³. 3 g is the acceleration due to gravity, in m / s². 2 Take 9.81 m / s 2 .

[0210] If real eggs of the target fish are used, only the physical parameters of the real eggs need to be measured. However, because the hatching of real fish eggs is affected by the environment, the window for conducting experiments is short, making it difficult to guarantee the acquisition of effective data. Therefore, it is recommended to use model eggs.

[0211] The density calculated using the above formula is 1.007~1.009×10⁻⁶. 3 kg / m 3 The settling velocities of eggs with diameters of 0.005 m and 0.006 m were: 0.012 m / s for the larger egg and 0.010 mm / s for the smaller egg. The egg diameter of the round-mouthed copperfish eggs was concentrated between 0.005 and 0.006 m, with a density of 1.007 to 1.009 × 10⁻⁶ m. 3 The model eggs prepared in this example have a density and average settling velocity of 0.012 m / s, and their volume is approximately 100 kg / m³. The model eggs prepared in this example closely match the egg diameter, density, and settling velocity of the round-mouthed copper fish eggs. Using the model eggs prepared in this case to replace real eggs can effectively reflect the various physical properties of the round-mouthed copper fish eggs. The model eggs will be referred to as fish eggs below.

[0212] Example 3:

[0213] This embodiment is an improvement upon the above embodiment, and is a refinement of step 2 of the above embodiment regarding the variable slope flume experiment. The variable slope flume experiment described in this embodiment includes the following sub-steps:

[0214] Sub-step 1, Constructing a variable-slope flume: To systematically study the resuspension process of drifting fish eggs under complex hydraulic conditions, this embodiment designs a variable-slope flume experimental system. The variable-slope flume experimental system integrates functions such as adjustable hydraulic slope, interchangeable bottom topography, high-precision flow field measurement, and fish egg trajectory tracking. It can simulate the complex flow field structure in natural rivers to a certain extent, simultaneously obtaining fish egg movement and flow field information. The experimental device consists of four parts: a flume, a water circulation facility, a flow velocity measurement device, and a fish egg trajectory acquisition device.

[0215] Variable slope water channel Figure 7As shown, a long, rectangular water tank is set up, with at least one section jacked up to form an inclined tank. The angle of inclination is adjusted using the jacks. Uneven obstacles are placed at the bottom of the tank to simulate realistic underwater terrain. The tank is equipped with a water circulation system, including a water pump, a reservoir, and a flow meter, to create a continuously flowing water effect for experimental purposes. Lasers and high-speed photography / videography equipment are installed above and on the sides of the tank to collect data on the movement and trajectory of the fish eggs.

[0216] Variable slope flume system, such as Figure 3 As shown, it mainly includes the main body of the water tank, the water supply tank, the water storage tank, the slope adjustment device, and the flow control device.

[0217] (1) Water tank and slope adjustment device:

[0218] The water tank is made of plexiglass and measures 2×0.15×0.75m. The water inlet is connected to the water supply tank via a pivot, with a bellows-style water-passing connector between them. The outlet is mounted on a steel support frame. Several adjustment holes are installed along the vertical rods of the support frame, allowing adjustment of the tank's tilt angle by changing the rod height. The slope adjustment range is 0~16° to meet the needs of experiments with different hydraulic gradients.

[0219] (2) Water supply tank and flow control:

[0220] The water supply tank is made of stainless steel and measures 0.5×0.5×0.5m. It is mounted above the water inlet of the water tank via a support bracket and provides a maximum flow rate of 3.5L / s. A vertically installed water level control plate divides the tank into two independent chambers: an inlet chamber and an outlet chamber. The inlet chamber is located near the water connection, with the end of the inlet pipe positioned above it. The outlet chamber has an outlet pipe connected to its inner bottom wall, with the other end of the outlet pipe connected to the storage tank. The water level in the tank can be precisely controlled by adjusting the height of a sliding plate, thereby regulating the inlet flow rate of the water tank. A triangular weir is located on the side of the water supply tank near the water tank; water flows through the weir and the water connection before entering the water tank.

[0221] (3) Downstream outflow and water circulation:

[0222] A vertically sliding baffle is installed downstream of the water tank, forming a tailwater collection area between the baffle and the side wall of the water tank's outlet. One end of the tailwater collection pipe is connected to the bottom wall of the water tank in this area, and the other end is connected to a storage tank. An electromagnetic flow meter is installed on the pipe to monitor the flow rate in real time. The storage tank is located below the water tank and contains a submersible pump. Water is pumped to the water supply tank through the inlet pipe to achieve water circulation.

[0223] Flow field construction method: By laying characteristic sand waves at the bottom of the flume, a characteristic flow field similar to that of a natural river is induced. The shape of the sand waves is determined based on the sand wave equation, which relates to the combined effects of water flow and sediment transport.

[0224]

[0225] In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. denoted as , where is the horizontal coordinate along the channel direction (m); A is the wave height (m); L is the wavelength (m); and F is the parameter affecting the ratio of the water-facing to the back-facing side of the sand wave. , These are the waveform control parameters. By adjusting these parameters, the flow field structure induced by sand waves can be changed.

[0226] This experiment selected two sand wave morphologies, the parameters of which are shown in Table 1, and the morphologies are as follows: Figure 2 , 3 As shown. Both types of sand waves can induce recirculation zones and vortex structures, but the flow field characteristics differ: large sand waves ( =0.18m, The eddy current induced by the sand wave (=0.036m) is relatively small, and the small sand wave ( The vorticity induced by the vorticity (A=0.09m, A=0.018m) is relatively large.

[0227] Flow velocity measurement device: A particle image velocimetry (PIV) system is used to measure the near-bottom flow field near the sandbar. For example... Figure 8 As shown, the PIV system consists of a laser source, a high-speed camera, and image processing software. The laser source is a continuous-wave laser (LWPIV-H, 10W power, 532nm wavelength), mounted above the water tank. It can be moved along the water tank direction via a hanging ring, forming a sheet light source approximately 1mm thick to illuminate the observation section. The high-speed camera (IDTos10, 1280×1024 pixels resolution) is placed on one side of the water tank, with its lens axis perpendicular to the laser sheet, and the shooting frame rate set to 200Hz. To prevent water ripples from refracting the laser, an acrylic wave plate is connected to the outer frame via a hanging rope, ensuring it is parallel and just touching the water surface inside the tank, eliminating water ripples and preventing laser refraction that could cause dark bands on the observation section. The entire measurement area is covered with a light-shielding cloth to eliminate interference from ambient light. The PIV observes the flow field at the location of the sand ripples, close to the riverbed bottom, with a shooting range of [missing information]. m.

[0228] Hollow glass beads with a density of 0.9–1.0 g / cm³ were used as tracer particles in the experiment. 3The median particle size is 50µm, and the particles can move with the water flow. Images of the tracer particles' motion were continuously captured using a high-speed camera. The images were then preprocessed using JFmeter post-processing software (image denoising, grayscale conversion, binarization), correlation calculations were performed, and the velocity field was reconstructed to obtain a two-dimensional instantaneous velocity field of the water tank facade based on the time series, and the vorticity field was calculated.

[0229] Fish egg trajectory acquisition system: The fish egg trajectory acquisition system is used to acquire the movement trajectory data of fish eggs under different hydraulic conditions, providing a basis for subsequent analysis and model verification.

[0230] The fish egg trajectory acquisition system was independently developed using Python and ImageJ image processing software to extract fish egg movement trajectories from recorded video sequences. The core algorithm is as follows: First, the original video is preprocessed using background subtraction and morphological processing. Background subtraction is applied to separate the moving fish eggs from the static or slowly changing background water flow and experimental setup images. Second, using a built-in particle analysis and tracking plugin, the centroid coordinates (x, z) of each fish egg in each frame are automatically identified. Finally, based on continuous frame sequences, nearest neighbor association and other methods are used to connect the positions of the same fish egg at different time points, constructing a complete time-egg position trajectory dataset. Each trajectory includes the fish egg ID, time (t), and the corresponding two-dimensional spatial coordinate sequence.

[0231] This system has the following characteristics:

[0232] (1) Spatial matching: The observation area of ​​fish egg movement video tracking is completely consistent with the PIV flow field measurement. Spatial matching of fish egg movement trajectory and flow field structure provides a data basis for revealing the coupling relationship between fish egg resuspension and vortex structure.

[0233] (2) Spatiotemporal resolution: The system uses a sampling frequency of 20Hz / s and a temporal resolution of 0.05s, which can record the entire process of fish egg movement. Based on the fish egg re-suspension start-up speed (about 0.05m / s), the spatial resolution is estimated to be about 2.5mm, which is about half the diameter of the fish egg, and can effectively capture the movement trajectory and position changes of the fish egg.

[0234] (3) Non-contact observation: No need to deploy sensors or markers in the flow field, and no disturbance to the water flow.

[0235] Experimental Procedure: Different combinations of operating conditions were designed, covering varying hydraulic gradients, sand wave morphologies, and fish egg diameters. Each operating condition was conducted according to the following steps:

[0236] (1) Experimental preparation: Adjust the height of the pole of the water tank support and set the slope of the water tank to the target value; fix the model sand wave of the corresponding shape to the bottom wall of the water tank; prepare model eggs with target egg diameter and density and place them in a beaker for later use.

[0237] (2) Initial conditions for the water tank:

[0238] Adjust the water level control plate of the water supply tank to the low water level so that the water tank flows through at a low flow rate. After the water flow stabilizes, release 100 fish eggs at the trough of the model sand wave without initial velocity.

[0239] (3) Flow regulation and observation of resuspension:

[0240] The height of the sliding plate in the water supply tank was gradually adjusted, and the flow rate in the water tank was controlled by a triangular weir. The movement of fish eggs in the model sand waves was observed simultaneously. Three consecutive sand waves were used as the observation targets: when all fish eggs in the upstream sand wave were transferred to the downstream sand wave, and resuspension of the fish eggs was observed, but no transfer of fish eggs was observed in the downstream sand wave, the flow rate was stopped. Through multiple preliminary experiments, the following criteria were established for determining fish egg resuspension: With continuous sand waves laid at the bottom of the water tank, in the observation section of the large sand wave: 70% of the fish eggs were transferred to the next sand wave within 20 seconds; in the observation section of the small sand wave: 70% of the fish eggs were transferred to the next sand wave within 10 seconds.

[0241] (4) Data collection:

[0242] Once the fish eggs meet the resuspension criteria, the following data are recorded: electromagnetic flowmeter reading; flow field images are acquired through the PIV system to obtain hydrodynamic parameters such as flow velocity and vortex; and fish egg movement videos are simultaneously acquired through a high-speed camera to obtain the fish egg trajectory.

[0243] After the above experiments are completed, turn off the water pump, remove the baffle, empty the water tank, and end the current experimental condition. Replace the sand, adjust the water tank slope, or replace the model eggs to begin subsequent experiments;

[0244] Experimental setup: To systematically study the hydrodynamic response mechanism of fish egg resuspension, three variable parameters were selected: hydraulic gradient, sand wave morphology, and fish egg diameter. Specifically: For hydraulic gradient, considering the adjustable slope of the experimental tank bottom, five hydraulic gradients were set: 3.47°, 4.69°, 6.79°, 7.99°, and 9.5°; for sand wave morphology, two types were set: large sand wave (wavelength 18cm, wave height 3.6cm) and small sand wave (wavelength 9cm, wave height 1.8cm); for fish egg diameter, two types were set: 5mm and 6mm. A total of 20 experimental setups were formed by combining these parameters, as shown in Table 2.

[0245] Table 2 Experimental Operating Conditions Setting Table

[0246]

[0247] Experimental data acquisition and processing:

[0248] The data collected for each operating condition includes flow field and fish egg trajectory data. The flow field data is obtained by acquiring the instantaneous velocity field through the PIV system, which yields the resultant velocity U and the horizontal velocity within the tank. Vertical flow velocity vorticity Isohydrodynamic parameters;

[0249] Fish egg trajectory data: Fish egg movement videos were acquired synchronously using a high-speed camera, and the fish egg trajectories were extracted using background subtraction and particle tracking techniques. Synchronous fish egg trajectories (including position, such as height h, velocity V, and time t) were obtained for each working condition.

[0250] Each operating condition was repeated twice, and the average value was used for subsequent analysis. Using the above data, the resuspension of fish eggs and their movement trajectory characteristics under different hydraulic conditions can be analyzed, providing fundamental data for the analysis of resuspension mechanisms.

[0251] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention (such as the type of fish, the application of various formulas, the order of steps, etc.) without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for determining the critical conditions for resuspension of drifting fish eggs, characterized in that, The steps of the method are as follows: Step 1: Preparation of model eggs: Prepare model eggs with physical characteristics consistent with real fish eggs, and obtain the physical characteristic parameters of the target fish species' eggs, including density ρ. 卵 Egg diameter d, still water settling velocity V g Agar model eggs with physical properties consistent with real fish eggs were prepared, and model eggs with sedimentation velocities similar to real eggs were screened through static water sedimentation experiments. Step 2: Conduct flume experiments on fish egg transport process: Construct a variable slope flume with varying terrain at the bottom to simulate the complex hydraulic conditions of a natural river. Induce a characteristic flow field similar to a natural river by laying characteristic sand waves at the bottom of the flume. The shape of the sand waves is determined based on the sand wave equation, which describes the combined effects of water flow and sediment transport. In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. denoted as , where is the horizontal coordinate along the channel direction (m); A is the wave height (m); L is the wavelength (m); and F is the parameter affecting the ratio of the water-facing to the back-facing side of the sand wave. , These are waveform control parameters. By adjusting these parameters, the flow field structure induced by sand waves can be changed. Fish egg transport experiments were conducted under different hydraulic conditions, and the horizontal velocity of the flow field in the tank was measured. Vertical flow velocity Distribution, calculation of resultant velocity U, vorticity Distribution, the formula is as follows: In the formula: The horizontal flow velocity is expressed in m / s. The vertical flow velocity is in m / s; Let m be the vertical coordinate. The movement trajectory of fish eggs in the tank was photographed, and the entire process of "sinking-retention-re-suspension" of fish eggs was observed. The synchronous fish egg trajectory and flow field data of each group of working conditions were summarized as the data basis for subsequent analysis. Step 3: Energy characterization of fish egg transport state: Coupled analysis of fish egg movement trajectory and synchronous flow field data is performed. The transport state of fish eggs is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish eggs themselves, the kinetic and potential energy change laws of fish eggs in the flow field are analyzed based on the principle of energy conservation. Coupled analysis of fish egg movement trajectory and synchronous flow field data reveals that the transport state of fish eggs is closely related to a specific hydrodynamic threshold. Ignoring the deformation of the fish eggs themselves, the transport state is analyzed based on energy conservation, and the calculation formula is as follows: Where: ΔE is the sum of the changes in kinetic and potential energy of the fish egg, hereinafter referred to as "energy change"; ρ 卵 Fish egg density, kg / m³ 3 ;ρ 水 The density of water is kg / m³. 3 h t Let h be the height of the fish egg at time t, in meters (m); t-Δt V represents the height of the fish egg at time t-Δt, in meters. t V is the velocity of the fish egg at the current time step t, in m / s; t-Δt The velocity of the fish egg at the previous time step t-Δt is m / s; m is the mass of the fish egg, kg. g is the acceleration due to gravity, in m / s². 2 When ΔE < 0, the total energy of the fish eggs is insufficient to overcome the resistance of the bed surface, and they are in a "stagnant" state. The energy change of the fish eggs is mainly affected by small fluctuations in potential energy, and the kinetic energy is almost zero. When ΔE > 0, the fish eggs are affected by changes in the hydrodynamic environment, and the kinetic energy increases significantly. When the energy change of the fish eggs is greater than 0, the fish eggs overcome gravity and bed surface resistance, and are resuspended from the bottom and enter the water body to continue transport. Step 4: Identifying Key Factors Affecting Fish Egg Resuspension: Based on multiple sets of synchronous flow field and fish egg motion data obtained from variable slope flume experiments under different hydraulic conditions, Pearson correlation analysis was used to analyze the correlation between fish egg energy changes and various hydrodynamic factors, environmental factors, and the characteristics of the fish eggs themselves, in order to screen key factors that have a significant impact on fish egg resuspension, including: energy change ΔE, resultant velocity U, vorticity ω, flow Reynolds number Re, relative velocity ΔV, and drag force F. d The Pearson correlation heatmap was constructed using the egg diameter d, the slope J of the experimental tank, the wave height A, and the wave wavelength L. The relationship between each variable and ΔE was evaluated using the correlation coefficient r and its significance level p. Step 5: Constructing the resuspension characteristic velocity formula: Taking into account the key factors selected in Step 4 and the physical characteristics of fish eggs, based on the principle of dimensional homogeneity, the resuspension characteristic velocity E is constructed. c The formula is: In the formula, E c U is the characteristic velocity of resuspension; F is the resultant velocity; d The drag force of the water flow; V g ω is the settling velocity of the fish eggs; ω is the vorticity; m is the mass of the fish eggs; in: In the formula: A represents relative velocity; e Let be the cross-sectional area of ​​the fish eggs and the water flow. C D Drag force coefficient, dimensionless; Fish eggs are generalized as spheres, based on the Reynolds number of water flow. Calculate C D The formula is as follows: Stokes District, : Transition zone : Newton District : ； Step 6: Determination of the critical resuspension threshold: Calculate and analyze the relationship between the energy change of fish eggs and the characteristic resuspension velocity. Use the generalized additive model (GAM) to establish the relationship between the fish egg resuspension rate Q and the characteristic resuspension velocity E. c The nonlinear relationship, fitting QE c The relationship is used to output multi-level critical thresholds under different suspension rates; When fish eggs E c Value greater than or equal to E c When the critical threshold is 1.0, the fish eggs can be resuspended, thus determining the critical condition for fish egg resuspension.

2. The method according to claim 1, characterized in that, The static water settling experiment described in step 1 includes the following sub-steps: Sub-step 1.1, prepare experimental facilities: use a transparent, graduated tall container, fill the container with clean water, and set up a high-speed camera on one side of the tall container; prepare model eggs with the same density and diameter as the fish eggs being studied; Sub-step 1.2, Model egg release: Place the model egg inside the glass column at a depth of 0.02m below the water surface and release it with no initial velocity, one egg at a time; Sub-step 1.3, Image acquisition: Adjust the relative position between the high-speed camera and the sedimentation column, and use particle tracking velocimetry technology to continuously capture the sedimentation process of the model egg at a frame rate of 50 frames / s to obtain high-resolution time-series images; Sub-step 1.4, velocity calculation: Based on the centroid position (x, z) of the model egg and the time interval between images, calculate the instantaneous falling velocity of the model egg at different depths; the experiment only considers the vertical displacement of the model egg and ignores the lateral displacement. When the velocity is stable, the measured value is the final vertical settling velocity. Sub-step 1.5, repeat the experiment: For model eggs with two diameters of 5mm and 6mm, which are consistent with the diameter of real fish eggs, repeat the above steps 50 times respectively, and use the final settling velocity of the stable stage to fit the formula of the settling velocity of a single model egg. Sub-step 1.6, Sedimentation Process Analysis: The sedimentation process of the model egg in still water can be divided into two stages: The first stage, the accelerated settling stage: the model egg begins to fall from rest. In the initial stage, the settling fluctuations are large, and the movement distance in this stage is about 0.3m. The second stage, uniform settling stage: As the settling speed gradually increases, the resistance on the model egg increases continuously until it reaches a state of force equilibrium. After that, the model egg undergoes uniform settling motion at a free settling speed. When the speed tends to stabilize, this speed value is taken as the final settling speed of the model egg. After data analysis and regression fitting, the egg settling velocity V was obtained. g The formula is: In the formula, V g ρ is the settling velocity of fish eggs in still water; d is the diameter of the egg; 卵 and ρ 水 ρ represents the density of the model egg and water, respectively; g is the acceleration due to gravity.

3. The method according to claim 2, characterized in that, The water tank experiment for the fish egg transfer process described in step 2, wherein the apparatus used in the water tank experiment includes: A long, rectangular water tank is constructed, with at least one section jacked up to form an inclined tank. The angle of inclination is adjusted by the jacks. Uneven obstacles are placed at the bottom of the tank to simulate real underwater terrain. The tank is equipped with a water circulation system, including a water pump, a reservoir, and a flow meter, to create a continuously flowing water effect for experimental purposes. Lasers and high-speed photography / videography equipment are installed above and on the sides of the tank to collect fish egg trajectory data for observing the movement of fish eggs. Flow field construction method: By laying characteristic sand waves at the bottom of the flume, a characteristic flow field similar to that of a natural river is induced; the shape of the sand waves is determined based on the sand wave equations that represent the combined effects of water flow and sediment transport. In the formula: Let x be the vertical height of the sand wave at the horizontal position x, in meters. denoted as , where is the horizontal coordinate along the channel direction (m); A is the wave height (m); L is the wavelength (m); and F is the parameter affecting the ratio of the water-facing to the back-facing side of the sand wave. , These are waveform control parameters; The water tank experiment includes the following sub-steps: Sub-step 2.1 Experimental preparation: Adjust the height of the support rod of the water tank and set the slope of the water tank to the target value; fix the model sand wave of the corresponding shape to the bottom wall of the water tank; prepare model eggs with the target egg diameter and density and place them in a beaker for later use; Sub-step 2.2, initial conditions and working conditions of the water tank: adjust the water level control plate of the water supply tank to the low water level, so that the water tank flows through at a low flow rate. After the water flow stabilizes, release 100 fish eggs at the trough of the model sand wave without initial velocity. Experimental setup: To systematically study the hydrodynamic response mechanism of fish egg resuspension, three variable parameters were selected for the experiment: hydraulic gradient, sand wave morphology, and fish egg diameter. Specifically: For hydraulic gradient, considering the adjustable slope of the experimental tank bottom, five hydraulic gradients were set: 3.47°, 4.69°, 6.79°, 7.99°, and 9.5°; for sand wave morphology, two types were set: large sand wave (wavelength 18cm, wave height 3.6cm) and small sand wave (wavelength 9cm, wave height 1.8cm); for fish egg diameter, two types were set: 5mm and 6mm. A total of 20 experimental setups were formed by combining these parameters. Sub-step 2.3, Flow Regulation and Resuspension Observation: Gradually adjust the height of the sliding plate of the water supply tank, control the flow rate of the water tank through the triangular weir, and simultaneously observe the movement of fish eggs in the model sand waves. Take three consecutive sand waves as the observation objects: when all the fish eggs in the upstream sand wave are transferred to the downstream sand wave, the fish eggs in the sand wave show resuspension, while no transfer of fish eggs is observed in the downstream sand wave, then stop increasing the flow rate; through multiple preliminary experiments, the resuspension of fish eggs is judged as follows: with continuous sand waves laid at the bottom of the water tank, the observation section of the large sand wave: 70% of the fish eggs are transferred to the next sand wave within 20 seconds; the observation section of the small sand wave: 70% of the fish eggs are transferred to the next sand wave within 10 seconds; Sub-step 2.4, Data Acquisition: After the fish eggs meet the resuspension criteria, record the following hydrodynamic parameters. The data collected for each operating condition includes flow field and fish egg trajectory data. Flow field data: The instantaneous velocity field is obtained through the PIV system to obtain the resultant velocity U and horizontal velocity of the flow field in the tank. Vertical flow velocity vorticity Hydrodynamic parameters; Fish egg trajectory data: Fish egg movement videos are acquired synchronously using a high-speed camera, and the fish egg movement trajectory is extracted using background subtraction and particle tracking technology; Synchronous fish egg trajectories are obtained for each working condition; Each working condition was repeated twice, and the average value was used for subsequent analysis. Using the above data, the resuspension of fish eggs and their movement trajectory characteristics under different hydraulic conditions were analyzed, providing basic data for the analysis of resuspension mechanisms.

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