A kind of water temperature coupling simulation method for layered water intake reservoir of stoplog gate

Abstract

A kind of method for simulating water temperature coupling of layered intake reservoir with stoplog gate, establishes module for stoplog gate operation process, and couples into vertical two-dimensional reservoir water temperature mathematical model, to establish water temperature coupling mathematical model of layered intake reservoir with stoplog gate, to realize water temperature simulation of layered intake reservoir with stoplog gate through iteration inside the model, to automatically determine the relationship between stoplog gate top water depth and minimum submerged water depth according to reservoir water level change, to dynamically adjust stoplog gate quantity and gate top elevation, to realize stoplog gate operation change with reservoir water level change, to avoid the shortcoming of needing to constantly manually update boundary conditions by using segmented calculation, to greatly improve simulation efficiency.The technical idea is simple and clear, and the model data pre-processing and post-processing are more simple and convenient, suitable for various large and medium-sized water conservancy and hydropower projects.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower engineering technology, and relates to the study of stratified water intake to mitigate the release of low-temperature water from reservoirs. In particular, it relates to a method for coupled simulation of water temperature in a reservoir with stratified water intake through a stacked beam gate, specifically a method for coupled simulation of water temperature in a reservoir with stratified water intake through a stacked beam gate based on a two-dimensional mathematical model of water temperature in a vertical reservoir. Background Technology

[0002] Hydropower, as a renewable and clean energy source, is one of the important ways to achieve carbon neutrality. Since the 21st century, my country has planned and constructed a large number of hydropower projects in various river basins. After the impoundment of water in large hydropower projects, the reservoirs form a stratified water temperature structure with large temperature differences in the water depth direction. Using deeper inlets to draw water for power generation will result in the discharged water temperature being lower than the natural water temperature in spring and summer, and higher than the natural water temperature in autumn and winter. This changes the original water temperature change pattern of the natural river channel, and thus has a significant impact on the aquatic ecosystem downstream of the reservoir, especially the spawning and reproduction of important fish. The impact of the discharged low-temperature water has received widespread attention from the industry.

[0003] Stacked-beam gates are one of the most common engineering measures for stratified water intake in reservoirs. They involve installing several stacked steel gates upstream of the intake to block water flow. A mobile hoist at the top of the intake tower automatically increases or decreases the number of stacked gates, preventing the entry of low-temperature water from the lower layers of the reservoir into the intake, thus controlling the temperature of the water released from the reservoir. Stacked-beam gates offer relatively flexible temperature control and stable flow patterns, effectively mitigating the impact of hydropower development on the aquatic ecosystem. They are widely used in large and medium-sized water conservancy and hydropower projects in my country.

[0004] In actual engineering operations, stacked girder gates are generally used during the peak spawning and breeding season for fish, such as late spring and early summer, to mitigate the impact of the released low-temperature water on fish spawning and reproduction. The operation mode of the stacked girder gates is mainly based on changes in the reservoir water level and the minimum submersion depth requirements, by increasing or decreasing the number of stacked girder gates to adjust the elevation of the released water body. Current research on water temperature in stratified water intake reservoirs mostly employs mathematical models, which can be categorized into one-dimensional, two-dimensional, and three-dimensional models based on their spatial dimensions. In current numerical simulations of water temperature in stratified water intake reservoirs with stacked beam gates, the stacked beam gate is typically generalized as a fixed structure. During simulation, the entire research period is subdivided into multiple simulation periods based on the changes in the stacked beam gate. After the simulation of the previous period is completed, the elevation of the fixed structure is modified manually or through external programming. The water temperature field and flow field at the end of the previous period are then used as initial conditions for the simulation of the next period. For example, Chinese Patent No. CN112580230A discloses a method for analyzing the water temperature structure of a reservoir. Based on the CE-QUAL-W2 model, the method continuously modifies the boundary conditions outside the model to simulate the changes in the water-resistant curtain wall, thereby simulating the changes in the reservoir water temperature when the water-resistant curtain wall is constantly changing. However, this method requires frequent interruptions of model calculations to modify boundary conditions, resulting in discontinuous calculations. Although the above operations can be achieved through external programming, it still suffers from drawbacks such as low computational efficiency and cumbersome pre- and post-processing of the model. In their paper "Simulation and Analysis of Dynamic Process of Water Temperature-Hydrodynamics in Layered Water Intake of Stacked Beam Gate", Zheng Tiegang et al. established a three-dimensional model and used dynamic mesh simulation technology to realize the operation and scheduling process of stacked beam gate. However, the three-dimensional model has a huge computational load, and the use of dynamic mesh further limits the computational efficiency of the model. The model described in this paper has only been used for verification in physical model experiments, and there have been no reports on the application of this method in prototype simulation.

[0005] Currently, the mainstream model for reservoir water temperature simulation in China is the vertical two-dimensional reservoir water temperature mathematical model, such as the CE-QUAL-W2 model developed by the U.S. Army Corps of Engineers and the WWL model developed by the State Key Laboratory of Hydraulics and Mountain River Development and Protection at Sichuan University. The vertical two-dimensional reservoir water temperature mathematical model has high computational efficiency and simulation accuracy, and has been widely used in the prediction of reservoir water temperature in large and medium-sized water conservancy and hydropower projects in China in recent years. However, this model has not yet established the dynamic change process of the stacked beam gate operation and the reservoir water level, and cannot realize the continuous simulation of reservoir water temperature for layered water intake by the stacked beam gate. Therefore, it is urgent to establish a coupled simulation method for reservoir water temperature based on the vertical two-dimensional reservoir water temperature mathematical model for layered water intake by the stacked beam gate. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for coupled simulation of water temperature in a stratified intake reservoir with a stacked beam gate. The stacked beam gate is generalized as a water-retaining overflow weir that can move freely along the water depth direction. Based on the control requirements for the minimum submerged water depth of the stacked beam gate, a dynamic relationship between the reservoir water level and the elevation of the top of the stacked beam gate is established and coupled into a two-dimensional mathematical model of the reservoir water temperature. This establishes a coupled mathematical model of water temperature in a stratified intake reservoir with a stacked beam gate, realizing the real-time dynamic water-retaining process of the stacked beam gate as the reservoir water level changes. This allows for continuous prediction of the hydrodynamic and water temperature changes in the reservoir during the operation of the stacked beam gate, thereby improving the efficiency of water temperature simulation in a stratified intake reservoir with a stacked beam gate.

[0007] To achieve the above objectives, the present invention employs the following technical solutions.

[0008] The present invention provides a method for coupled simulation of water temperature in reservoirs with layered intake via stacked beam gates. Taking reservoirs employing layered intake via stacked beam gates as the research object, it establishes a coupled mathematical model of water temperature in reservoirs with layered intake via stacked beam gates based on a two-dimensional mathematical model of water temperature in the vertical plane, nested within a stacked beam gate module. The reservoir is divided into several rectangular grids along the flow direction and water depth direction. The water temperature of each grid represents the water temperature at its location. The outflow temperature is the flow-weighted average temperature of all rectangular grids corresponding to the inlet elevation. Based on a given simulation period and the grid division of the simulated reservoir, the method for coupled simulation of water temperature in reservoirs with layered intake via stacked beam gates specifically includes the following steps: S1. Given the reservoir boundary conditions, initial conditions, and related parameters required for reservoir water temperature simulation, the given reservoir boundary conditions include: inflow rate, outflow rate, inflow water temperature, and daily data of meteorological elements; the given initial conditions include: reservoir water level, longitudinal and vertical flow fields in the reservoir area, and water temperature field distribution; the given related parameters include the elevation range of the inlet and its corresponding vertical grid number, the height of a single-section stacked beam gate, the minimum submerged water depth, the operating period of the stacked beam gate for stratified water intake, the longitudinal grid number of the stacked beam gate and the vertical grid number at the start of operation, hydrodynamic parameters, and water-air-heat exchange parameters; S2. The hydrodynamic module and water temperature module in the layered water intake reservoir water temperature coupling mathematical model of stacked beam gate are used to obtain the reservoir water level, flow field and water temperature field distribution at the current moment, and the calculation grid is updated according to the reservoir water level. S3. Enter the stacked beam gate module and determine whether the current time is within the set stacked beam gate layered water intake operation period. If it is within the stacked beam gate layered water intake operation period, proceed to step S4; if it is outside the stacked beam gate layered water intake period, proceed to step S6. S4. Obtain the current reservoir water level and the top elevation of the stacked beam gate. Take the difference between the reservoir water level and the top elevation of the stacked beam gate, and adjust the top elevation of the stacked beam gate according to the difference. If the difference between the reservoir water level and the top elevation of the stacked beam gate is less than the minimum submerged water depth at the top of the gate, the water depth at the top of the stacked beam gate does not meet the minimum submerged water depth control requirements. Then, reduce the number of stacked beam gate sections, i.e., lower the top elevation. If the difference meets the minimum submerged water depth control requirements, i.e., greater than or equal to the minimum submerged water depth and less than or equal to the sum of the minimum submerged water depth and the height of a single stacked beam gate section, then the number of stacked beam gates remains unchanged, i.e., the top elevation remains unchanged. If the difference between the reservoir water level and the top elevation of the stacked beam gate is greater than the sum of the minimum submerged water depth at the top of the gate and the height of a single stacked beam gate section, then the water depth at the top of the stacked beam gate increases, and the effect of slowing down the water temperature of the stratified water intake weakens. Then, increase the number of stacked beam gate sections, i.e., raise the top elevation. S5. Update the vertical grid number where the stacked beam gate is located, and set the vertical grid where the stacked beam gate is located to the non-water-passing state, and set all other vertical grids to the water-passing state; S6. Based on the current time, increase the time step; if the increased time is within the set simulation period, return to step S2; otherwise, end the current program and obtain the reservoir water level, vertical flow field, vertical water temperature field distribution, and reservoir discharge water temperature changes at different times.

[0009] In the above-mentioned method for coupled simulation of reservoir water temperature in a layered intake reservoir with a stacked beam gate, step S1 involves providing the reservoir boundary conditions and initial conditions according to conventional reservoir water temperature simulation methods in this field. Initial conditions such as the longitudinal and vertical flow fields and water temperature field distributions of the reservoir area at the initial moment within a given time period can be directly given as constants. The influence of initial values ​​is eliminated by extending the model calculation time, resulting in initial field parameters that more closely approximate the actual situation. The stacked beam gate is generalized as a water-retaining overflow weir, located upstream of the intake. The minimum submerged water depth is determined based on the principle that no penetrating vortex is generated at the top of the stacked beam gate, specifically provided by hydraulic engineering calculations.

[0010] Set the required hydrodynamic and water-air heat exchange parameters for simulation in accordance with conventional methods in this field. The hydrodynamic parameters mainly include the longitudinal eddy viscosity coefficient and the longitudinal diffusion coefficient, which can be the values ​​recommended by the model. The water-air heat exchange coefficients include the surface solar radiation absorption coefficient, the solar radiation attenuation coefficient in pure water, the wind shading coefficient, and the dynamic light shading coefficient. These can be the values ​​recommended by the model or obtained by verification and calibration through measured water temperature data from the reservoir.

[0011] The aforementioned method for simulating water temperature coupling in reservoirs with layered water intake via stacked beam gates comprises a hydrodynamic module, a water temperature module, and a stacked beam gate module. The water temperature includes the spatiotemporal distribution of water temperature in the reservoir area during layered water intake via stacked beam gates, and the change in released water temperature over time after layered water intake.

[0012] The hydrodynamic module is used to simulate the flow field and water level changes in the layered intake reservoir area with stacked beam gates. Specifically, it is a two-dimensional hydrodynamic model of the elevation, mainly including the continuity equation. x Directional momentum equation, hydrostatic pressure assumption, and free surface equation.

[0013] The continuity equation is: (1) The x The equation for directional momentum is: (2) The hydrostatic pressure is assumed to be: (3) The equation for the free water surface is: (4) in: U For vertical ( x (Directional) Flow velocity, m / s; W For vertical ( z (Directional) Flow velocity, m / s; q The lateral unit volume net inflow rate per unit width is m. 3 / s; B The width of the river is in meters (m). α Riverbed slope, in rad; τ For turbulent shear stress, N / m 2 ; η The elevation is the water surface, in meters (m). U x For the tributary flow velocity x Directional component, m / s; g is gravitational acceleration, m / s² 2 ; ρ The density of water is kg / m³. 3 ; p Atmospheric pressure, N / m 2 , η Water level, in meters (m); B η The width of the water surface is in meters (m).

[0014] The water temperature module is used to simulate the water temperature field distribution and discharge water temperature of the reservoir's layered water intake through the stacked beam gate. It takes into account the heat exchange between water vapor and the riverbed, and the main equation is the heat conservation equation.

[0015] The heat conservation equation is: (5) in: T w Water temperature, °C; D x Where m is the longitudinal diffusion coefficient. 2 / s; D z Where m is the vertical diffusion coefficient. 2 / s; The rate of lateral heat flux inflow and outflow in the unit control volume, in J / m. 3 / s; S Source and sink terms, including surface heat exchange and riverbed heat exchange, J / m 3 / s.

[0016] The discharge water temperature is the flow-weighted average water temperature of the rectangular grid cells corresponding to the inlet elevation, specifically: (6) in: Q i The first corresponding to the elevation of the inlet i The flow rate of each grid cell, m 3 / s; T i For the first i Water temperature of each grid cell, °C; T o The temperature of the discharged water is ℃.

[0017] The stacked beam door module is as follows: Assuming the height of a single-section stacked beam door is x The reservoir water level is H The elevation of the top of the stacked beam door is Z The water depth at the top of the stacked beam gate is h The minimum submerged water depth is Δ h All units above are in meters (m).

[0018] The water depth at the top of the stacked beam door h It is expressed as follows: h = H - Z (7) When the stacked beam gate is in operation, the water depth at the top of the stacked beam gate shall be used as the reference. h Not less than the minimum flood depth Δ h And not higher than the minimum flood depth Δ h Height of a single-section stacked beam door x The principle is to ensure the stability of the water flow at the top of the gate and the mitigation effect of low-temperature water.

[0019] The operating and scheduling principles of the stacked beam gate in accordance with changes in reservoir water level are as follows: (1) When h <Δ h At that time, the water depth above the stacked beam gate was... h If the minimum submersion depth condition is not met, a section of the stacked beam gate must be raised to increase the water depth at the top of the gate and increase the flow area. (2) When Δh ≤ h ≤Δ h + x If the water depth at the top of the stacked beam gate meets the minimum submersion water depth control requirement, then the number of stacked beam gates and the elevation of the gate top remain unchanged. (3) When h >Δ h + x If the water depth at the top of the gate is too great, the effect of blocking the lower low-temperature water will be weakened. In this case, a section of the stacked beam gate must be lowered to block the lower low-temperature water and release the higher-temperature water near the surface.

[0020] Based on the above-mentioned operation and scheduling principles of the stacked beam gate, when the reservoir water level changes, the stacked beam gate module automatically determines the water depth at the top of the gate. h With minimum flood depth Δ h Single-section stacked beam door height x Based on the relationship, the number of stacked beam doors is dynamically adjusted in real time. Specifically, the adjustment method is to adjust the top elevation of the stacked beam doors. Z All vertical grids along the water depth direction are considered as overflow weirs, meaning the vertical grid where the stacked beam gate is located is set to a non-water-passing state.

[0021] The principles for setting the water flow status of the stacked beam gate are as follows: (8) In the formula DL ( i , j () indicates the grid position of the stacked beam door.

[0022] Preferably, a mathematical model coupling water temperature of a reservoir with stacked beam gates is established. To adapt to the needs of rectangular grid simulation, the vertical grid spacing is determined based on the height of a single stacked beam gate. That is, the height of the vertical grid unit should be a value that can be divided by the height of a single stacked beam gate, so as to accommodate the increase or decrease of the number of stacked beam gates.

[0023] Preferably, the vertical grid number at the start of operation of the stacked beam gate is set. The specific method is as follows: subtract the minimum submerged water depth from the reservoir water level at the start of operation of the stacked beam gate to obtain the top elevation of the stacked beam gate at the start of operation. The grid corresponding to the bottom elevation of the inlet below the top elevation of the stacked beam gate is the vertical grid number at the start of operation of the stacked beam gate. It is set to a non-water-passing state to simulate the water-blocking effect of the stacked beam gate in the vertical water flow direction.

[0024] Preferably, in order to better protect fish spawning and reproduction and reduce the frequency of gate operation, the gate can be operated only during the fish spawning and reproduction period. The gate setting requirements are as follows: during the fish spawning and reproduction period, the gate is operated and scheduled according to the principle of changing the reservoir water level. Outside of the fish spawning and reproduction period, the vertical grid where the gate is located is set to water flow state, so as to realize the simulation of the whole reservoir water temperature and downstream water temperature for stratified water intake during specific fish spawning and reproduction periods.

[0025] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) This invention establishes a module for the scheduling and operation of the stacked beam gate and couples it into a two-dimensional mathematical model of reservoir water temperature on the facade. This establishes a coupled mathematical model of reservoir water temperature for layered water intake through stacked beam gates. Through iteration within the model, the water temperature simulation of the layered water intake reservoir is achieved. Based on changes in reservoir water level, the relationship between the water depth at the top of the stacked beam gate and the minimum submerged water depth can be automatically determined, and the number of stacked beam gates and the elevation at the top of the gates can be dynamically adjusted. This allows the scheduling and operation of the stacked beam gates to change with the reservoir water level, avoiding the drawback of needing to manually update boundary conditions continuously using segmented calculations, and greatly improving simulation efficiency. The technical concept of this invention is simple and clear, and the pre- and post-processing of model data is simpler and more convenient, making it suitable for various large and medium-sized water conservancy and hydropower projects.

[0026] (2) The present invention generalizes the stacked beam gate as a water-blocking overflow weir that can move freely in the direction of water depth. Compared with the stacked beam gate being generalized as a fixed water-blocking structure, the method provided by the present invention can update the flow field and water temperature field in real time according to the changes of the stacked beam gate, which is more in line with the actual scheduling process of the stacked beam gate, and the simulation results are more accurate and precise.

[0027] (3) This invention can simulate the water temperature of the entire reservoir and the downstream water temperature for specific time periods (such as the spawning and reproduction period of fish) by limiting the water intake time of the reservoir's stacked beam gate. Attached Figure Description

[0028] Figure 1 A schematic diagram of layered water intake at a stacked beam gate; Figure 2 A simulation flowchart for water temperature simulation in a reservoir with a stacked beam gate and stratified water intake. Figure 3 A framework diagram of a water temperature coupling model for a layered water intake reservoir with stacked beam gates; Figure 4 Comparison of water temperature and flow fields in front of the single-layer water intake and the layered water intake with stacked beam gate at the R hydropower station; Figure 5 This is a comparison chart of the water temperature during discharge from a single-layer water intake and a layered water intake with a stacked beam gate at the R hydropower station. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0030] The embodiment of the invention method relies on the L-River-R Hydropower Station on the Qinghai-Tibet Plateau, which is the leading reservoir in the upper reaches of the L-River. It has annual regulation capabilities, a normal water level of 2895m, and a corresponding storage capacity of 3.754 billion cubic meters. 3 The dam has a maximum height of 315m, and the bottom elevation of the water intake for the hydropower system is 2794m. After the reservoir is filled, significant temperature stratification occurs, with the maximum annual temperature difference between the reservoir surface and bottom reaching 15.1℃. This results in the discharged water temperature in April (spring and summer) being up to 3.0℃ lower than the natural water temperature, with a maximum temperature delay of up to 30 days, which will adversely affect the spawning and reproduction of fish downstream of the dam site. To mitigate the impact of the low-temperature discharged water on fish, it is proposed to install a sluice gate upstream of the power station intake to increase the discharged water temperature. Figure 1 As shown, in order to evaluate the effect of the stacked beam gate on the temperature of the discharged water, based on the water temperature simulation of the single-layer water intake (i.e. the original design intake), it is necessary to conduct numerical simulation analysis on the reservoir water temperature and the discharged water temperature after the hydropower station adopts the stacked beam gate layered water intake measure.

[0031] Before simulation, the reservoir needs to be divided into grids using unequal-spacing rectangular grids based on the measured cross-section of the reservoir area. The size of the rectangular grids is set according to the characteristics of the reservoir. The longitudinal grid in the area in front of the dam is appropriately densified, and the vertical grid spacing is determined based on the elevation and height of the stacked beam gates. The grid near the intake is also appropriately densified. In this embodiment, the reservoir area of ​​the R hydropower station is discretized into 215×145 rectangular grids. The longitudinal grid (in the direction of water flow) size is 50-500m, the vertical grid size (in the direction of water depth) is 1-2m, and the elevation range of the stacked beam gates is densified to 1m. Each grid is a control unit, and the water temperature of each control unit represents the water temperature at its location.

[0032] Based on the above work, this embodiment follows the steps (such as...). Figure 2 (As shown) A simulation of the reservoir water temperature and outflow temperature under the reservoir operation conditions of the R hydropower station during a normal water year, using a stacked beam gate for stratified water intake: S1. Given the reservoir boundary conditions, initial conditions, and related parameters required for reservoir water temperature simulation, the given reservoir boundary conditions include: inflow rate, outflow rate, inflow water temperature, and daily data of meteorological elements; the given initial conditions include: reservoir water level, longitudinal and vertical flow fields in the reservoir area, and water temperature field distribution; the given related parameters include the elevation range of the inlet and the corresponding vertical grid number, the height of a single-section stacked beam gate, the minimum submerged water depth, the operating period of the stacked beam gate for stratified water intake, the longitudinal grid number of the stacked beam gate and the vertical grid number at the start of operation, hydrodynamic parameters, and water-air-heat exchange parameters.

[0033] In this step, the reservoir boundary conditions and initial conditions for the given time period (January 1st to December 31st of a normal water year) involved in the reservoir temperature simulation of the layered water intake reservoir with stacked beam gate in Example R hydropower station are as follows: (1) Reservoir boundary conditions The boundary conditions of the layered water intake reservoir involving stacked beam gates include hydrodynamic boundary conditions, inflow water temperature boundary conditions, and meteorological boundary conditions.

[0034] The hydrodynamic boundary conditions are given by the daily inflow and outflow in a typical normal water year. The inflow water temperature boundary condition is given by the multi-year average daily water temperature process at the reservoir tail section, which is derived by collecting historical water temperature data from hydrological stations in the basin and supplementing monitoring water temperatures. The meteorological boundary conditions mainly include humidity, cloud cover, air temperature, wind speed, and solar radiation. The data source is meteorological stations near the reservoir, and the air temperature needs to be converted to the elevation of the average water level of the reservoir based on the air temperature lapse rate.

[0035] (2) Initial conditions The initial reservoir water level was given as the water level at 00:00 on January 1st, the first day of a normal water year. The longitudinal and vertical flow velocities and water temperatures in the entire reservoir were given as constant values. In this embodiment, the initial flow velocity was 0, and the initial water temperature in the reservoir was given as the multi-year average water temperature at the inlet section, which was 8.8℃. By cyclically calculating for 2 years, the flow field and water temperature field at the end of the second year were taken as the actual initial field for simulation to eliminate the influence of the initial flow field and water temperature field on the simulation results.

[0036] (3) Relevant parameters Based on the intake design data, the elevation range and corresponding vertical grid number of the intake are given. In this embodiment, the height of a single-section stacked beam gate is 3m, and the minimum submerged water depth is calculated to be 21m according to hydraulic engineering. The longitudinal grid number of the stacked beam gate is given according to the intake layout. The vertical grid number at the start of the stacked beam gate's operation is determined based on the height of the single-section stacked beam gate and the minimum submerged water depth. The operation time of the stacked beam gate is set; in this embodiment, the operation time is from 00:00 on April 1st to 24:00 on September 30th. During other periods, single-layer water intake (i.e., water intake from the original design intake) is used. It is worth noting that since the number and location of the stacked beam gates only change in the water depth direction, the longitudinal grid number will not change during the simulation after being given, while the vertical grid number will change as the stacked beam gates operate. The hydrodynamic and water-air-heat exchange parameters required in the model all use the model's recommended values.

[0037] S2. The water level, flow field, and water temperature field distribution of the reservoir at the current moment are obtained by using the hydrodynamic module and water temperature module in the layered water intake mathematical model of the stacked beam gate reservoir.

[0038] In this step, the overall framework of the coupled mathematical model of layered water intake reservoir with stacked beam gate is as follows: Figure 3 As shown, the system includes a hydrodynamic module, a water temperature module, and a stacked beam gate module. The core idea of ​​the stacked beam gate layered water intake reservoir water temperature coupling simulation method provided in this embodiment is to establish a dynamic relationship between the reservoir water level and the scheduling and operation of the stacked beam gate based on the reservoir hydrodynamic and water temperature model. Since the stacked beam gate only changes in the water depth direction and remains unchanged in the downstream direction, the corresponding vertical grid where the stacked beam gate is located is set to either no-water or water-passing state according to the change of the top elevation of the stacked beam gate. Further calculations of reservoir hydrodynamics and water temperature are carried out. This process is repeated to achieve the coupled calculation of water temperature in the stacked beam gate layered water intake reservoir.

[0039] The hydrodynamic module is used to simulate the reservoir flow field and water level changes in a stratified water intake system with stacked beam gates. Specifically, it is a two-dimensional hydrodynamic model of the elevation, mainly including continuity equations. x Directional momentum equation, hydrostatic pressure assumption, and free surface equation.

[0040] The continuity equation is: (1) The x The equation for directional momentum is: (2) The hydrostatic pressure is assumed to be: (3) The equation for the free water surface is: (4) in:U For vertical ( x (Directional) Flow velocity, m / s; W For vertical ( z (Directional) Flow velocity, m / s; q The lateral unit volume net inflow rate per unit width is m. 3 / s; B The width of the river is in meters (m). α Riverbed slope, in rad; τ For turbulent shear stress, N / m 2 ; η The elevation is the water surface, in meters (m). U x For the tributary flow velocity x Directional component, m / s; g is gravitational acceleration, m / s² 2 ; ρ The density of water is kg / m³. 3 ; p Atmospheric pressure, N / m 2 , η Water level, in meters (m); B η The width of the water surface is in meters (m).

[0041] The water temperature module is mainly used to simulate the water temperature field distribution and downstream water temperature of a reservoir with layered water intake at the stacked beam gate. It takes into account the heat exchange between water vapor and riverbed, and the main equation is the heat conservation equation.

[0042] The heat conservation equation is: (5) in: T w Water temperature, °C; D x Where m is the longitudinal diffusion coefficient. 2 / s; D z Where m is the vertical diffusion coefficient. 2 / s; The rate of lateral heat flux inflow and outflow in the unit control volume, in J / m. 3 / s; S Source and sink terms, including surface heat exchange and riverbed heat exchange, J / m 3 / s.

[0043] The discharge water temperature is the flow-weighted average water temperature of the rectangular grid cells corresponding to the inlet elevation, specifically: (6) in: Q i The first corresponding to the elevation of the inlet i The flow rate of each grid cell, m 3 / s;T i For the first i Water temperature of each grid cell, °C; T o The temperature of the discharged water is ℃.

[0044] In this step, the differential equations are discretized using the finite difference method to obtain the discrete equations of each model. The difference equations are solved using the ULTIMATE algorithm. In the calculation, the free water surface discrete equations are solved first to obtain the free water surface elevation. Then, the equations of each hydrodynamic model and the heat conservation equation are coupled and solved to obtain the flow field and water temperature field distribution. The calculation grid is updated according to the water surface elevation (i.e., the reservoir water level).

[0045] S3. Enter the stacked beam gate module and determine whether the current time is within the set stacked beam gate layered water intake operation period. If it is within the stacked beam gate layered water intake operation period, proceed to step S4; if it is outside the stacked beam gate layered water intake period, proceed to step S6.

[0046] In this step, the operating period of the stacked beam gate is set from 00:00 on April 1st to 24:00 on September 30th. It is determined whether the current time is within the period from 00:00 on April 1st to 24:00 on September 30th. If the condition is met, proceed to step S4; otherwise, proceed to step S6.

[0047] S4. Obtain the current reservoir water level and the elevation of the top of the stacked beam gate. Take the difference between the reservoir water level and the elevation of the top of the stacked beam gate. If the difference is less than the minimum submerged water depth at the top of the gate, the water depth at the top of the stacked beam gate does not meet the minimum submerged water depth control requirement. In this case, the stacked beam gate is reduced by one section, i.e., the elevation of the top of the gate is lowered. If the difference meets the minimum submerged water depth control requirement, i.e., it is greater than or equal to the minimum submerged water depth and less than or equal to the sum of the minimum submerged water depth and the height of a single stacked beam gate section, the number of stacked beam gates remains unchanged, i.e., the elevation of the top of the gate remains unchanged. If the difference is greater than the sum of the minimum submerged water depth at the top of the gate and the height of a single stacked beam gate section, the water depth at the top of the stacked beam gate increases, and the effect of slowing down the water temperature of the stratified water intake weakens. In this case, the stacked beam gate is increased by one section, i.e., the elevation of the top of the gate is raised.

[0048] The stacked beam door module is as follows: Assuming the height of a single-section stacked beam door is x The reservoir water level is H The elevation of the top of the stacked beam door is Z The water depth at the top of the stacked beam gate is h The minimum submerged water depth is Δ h All units are in meters (m). The elevation corresponding to the top vertical grid where the stacked beam door is located is the elevation of the top of the stacked beam door.

[0049] The water depth at the top of the stacked beam door h It is expressed as follows: h = H - Z (7) When the stacked beam gate is in operation, the water depth at the top of the stacked beam gate shall be used as the reference. h Not less than the minimum flood depth Δ h And not higher than the minimum flood depth Δ h Height of a single-section stacked beam door x The principle is to ensure the stability of the water flow at the top of the gate and the mitigation effect of low-temperature water.

[0050] The operating and scheduling principles of the stacked beam gate in accordance with changes in reservoir water level are as follows: (1) When h <Δ h At that time, the water depth above the stacked beam gate was... h If the minimum submersion depth condition is not met, a section of the stacked beam gate must be raised to increase the water depth at the top of the gate and increase the flow area. (2) When Δ h ≤ h ≤Δ h + x If the water depth at the top of the stacked beam gate meets the minimum submersion water depth control requirement, then the number of stacked beam gates and the elevation of the gate top remain unchanged. (3) When h >Δ h + x If the water depth at the top of the gate is too great, the effect of blocking the lower low-temperature water will be weakened. In this case, a section of the stacked beam gate must be lowered to block the lower low-temperature water and release the higher-temperature water near the surface.

[0051] Based on the aforementioned stacked beam gate operation and scheduling principle, when the reservoir water level changes, the stacked beam gate module automatically determines the water depth at the top of the gate. h With minimum flood depth Δ h Single-section stacked beam door height x Based on the relationship, the number of stacked beam doors is dynamically adjusted in real time. Specifically, the adjustment method is to adjust the top elevation of the stacked beam doors. Z All grids along the water depth direction are considered as overflow weirs, meaning the vertical grid where the stacked beam gate is located is set to a non-water-passing state.

[0052] The principles for setting the water flow status of the stacked beam gate in this step are as follows: (8) In the formula DL ( i , j () indicates the grid position of the stacked beam door.

[0053] S5. Update the vertical grid number where the stacked beam gate is located, and set the vertical grid where the stacked beam gate is located to a non-water-passing state, while setting all other grids to a water-passing state.

[0054] In this step, based on the elevation change of the top of the stacked beam gate, the vertical grid number range where the stacked beam gate is located is determined and reassigned, setting it to a non-water-contaminated state. DL ( i , j When )=0, this portion of the vertical mesh will no longer participate in the flow field and water temperature field calculations, and the remaining vertical meshes will be reset to the water-passing state, i.e. DL ( i , j )=1, the grid participates in the calculation of flow field and water temperature field.

[0055] S6 increases the time step based on the current time; if the increased time is within the set simulation period, it returns to S2; otherwise, it ends the current program and obtains the reservoir water level, the longitudinal and vertical flow field of the reservoir area, the longitudinal and vertical water temperature field distribution, and the changes in the reservoir discharge water temperature at different times.

[0056] In this step, a time step Δ is added based on the current time. t And determine whether the increased time reaches the set time limit. t end If the set time period limit is not reached. t end Returning to step S2, the parameters of reservoir water level, flow field, and water temperature obtained at the current moment are used to assign values ​​to each variable, which are then used as the initial values ​​for the reservoir water level, flow field, and water temperature parameters at the next moment. Steps S2 to S6 are repeated. If the set time limit is exceeded, the program ends. By summarizing and statistically analyzing the calculated data of reservoir water level, flow velocity, reservoir water temperature, and outflow water temperature at different times, the simulation results of the reservoir water temperature and its outflow temperature at the layered intake of the stacked beam gate can be obtained.

[0057] For any given moment, adding the obtained water temperature and flow velocity data to the reservoir flow displacement (distance from the reservoir inlet) - elevation coordinate system will yield a two-dimensional elevation distribution map of the reservoir area's water temperature and flow field. Figure 4 Two-dimensional elevation views of water temperature and flow field distribution in the 1km upstream area of ​​the R hydropower station reservoir in April, obtained using the stacked beam gate stratified water intake method provided by this invention, are presented. It can be seen that after implementing the stacked beam gate stratified water intake measure, the elevation range of the flow layer upstream of the dam in the direction of water flow was significantly increased, and this had a significant impact on the water temperature and flow field of the entire reservoir area. In April, the reservoir water temperature stratification was obvious, with the main temperature difference concentrated in the surface layer. After adopting the stacked beam gate stratified water intake measure, the flow layer upstream of the dam moved upwards into the reservoir, increasing in elevation by approximately 25m.

[0058] By statistically analyzing the daily average discharge water temperature data of power stations with single-layer water intake and layered water intake using stacked beam gates within a given time period, and comparing it with the multi-year average natural water temperature at the dam site and its variation range, the improvement effect of water temperature reduction through layered water intake using stacked beam gates can be obtained. Table 1 shows the ten-day average improvement effect of water temperature reduction using layered water intake with stacked beam gates.

[0059] Table 1. Analysis of the ten-day average water temperature improvement effect of using stacked beam gate for layered water intake and discharge.

[0060] Figure 5 This paper presents a comparison of the effects of the stacked-beam gate stratified intake reservoir water temperature coupling simulation method provided by this invention on the improvement of the discharge water temperature of the R hydropower station. Overall, the stacked-beam gate stratified intake method mitigated the impact of low-temperature water to a certain extent, with the most significant improvement in April. The average water temperature rise was largest in the first and middle ten days of April, both at 1.2℃. The maximum daily average temperature rise was 1.5℃ (April 26th). After the power station adopted the stacked-beam gate stratified intake measure, the discharge water temperature gradually approached the lowest natural daily water temperature at the dam site, and the low-temperature discharge was mitigated to a certain extent. These results indicate that the stacked-beam gate stratified intake reservoir water temperature coupling simulation method established by this invention can effectively simulate the water temperature in the stratified intake reservoir area and the discharge water temperature, and can quantitatively evaluate its effect on mitigating low-temperature water.

[0061] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for coupled simulation of water temperature in a reservoir with stacked beam gates and layered water intake, characterized in that, Includes the following steps: S1. Based on the measured cross-section of the reservoir area, the reservoir is divided into grids using unequal-spacing rectangular grids. Given the reservoir boundary conditions, initial conditions, and relevant parameters required for reservoir water temperature simulation; The given reservoir boundary conditions include: daily data on inflow, outflow, inflow water temperature, and meteorological elements; the given initial conditions include: reservoir water level, longitudinal and vertical flow fields in the reservoir area, and water temperature field distribution; the given relevant parameters include the elevation range of the inlet and its corresponding vertical grid number, the height of a single-section stacked beam gate, the minimum submerged water depth, the operating period of the stacked beam gate for stratified water intake, the longitudinal grid number of the stacked beam gate and the vertical grid number at the start of operation, hydrodynamic parameters, and water-air-heat exchange parameters; S2. The hydrodynamic module and water temperature module in the layered water intake reservoir water temperature coupling mathematical model of stacked beam gate are used to obtain the reservoir water level, flow field and water temperature field distribution at the current moment, and the calculation grid is updated according to the reservoir water level. S3. Enter the stacked beam gate module and determine whether the current time is within the set stacked beam gate layered water intake operation period. If it is within the stacked beam gate layered water intake operation period, proceed to step S4; if it is outside the stacked beam gate layered water intake period, proceed to step S6. S4. Obtain the current reservoir water level and the elevation of the top of the stacked beam gate. Take the difference between the reservoir water level and the elevation of the top of the stacked beam gate, and adjust the elevation of the top of the stacked beam gate according to the difference. The stacked beam gate module is as follows: the height of a single stacked beam gate section is... x The reservoir water level is H The elevation of the top of the stacked beam door is Z The water depth at the top of the stacked beam gate is h The minimum submerged water depth is Δ h All units are in meters (m); water depth at the top of the stacked beam door. h It is expressed as follows: h = H - Z （7） In step S4, the operation and scheduling principle of the stacked beam gate according to the reservoir water level changes is as follows: when h <Δ h At that time, the water depth above the stacked beam gate was... h If the minimum submersion depth condition is not met, a section of the stacked beam gate must be raised to increase the water depth at the top of the gate and increase the flow area. When Δ h ≤ h ≤Δ h + x If the water depth at the top of the stacked beam gate meets the minimum submersion water depth control requirement, then the number of stacked beam gates and the elevation of the gate top remain unchanged. when h >Δ h + x If the water depth at the top of the gate is too great, the effect of blocking the low-temperature water in the lower layer will be weakened. In this case, a section of the stacked beam gate must be lowered to block the low-temperature water in the lower layer and release the water with a higher temperature near the surface. The principles for setting the water flow status of the stacked beam gate are as follows: ； S5. Update the vertical grid number where the stacked beam gate is located, and set the vertical grid where the stacked beam gate is located to the non-water-passing state, and set all other vertical grids to the water-passing state; S6. Increase the time step based on the current time. If the increased time is within the set simulation period, return to step S2; otherwise, end the current program.

2. The method for coupled simulation of water temperature in a layered water intake reservoir with stacked beam gates as described in claim 1, characterized in that: The hydrodynamic module is used to simulate the flow field and water level changes in the layered intake reservoir area with stacked beam gates. Specifically, it is a two-dimensional hydrodynamic model of the elevation, including continuity equations. x Directional momentum equation, hydrostatic pressure assumption, and free surface equation; The continuity equation is: （1） The x The equation for directional momentum is: （2） The hydrostatic pressure is assumed to be: （3） The equation for the free water surface is: （4） in: U For vertical ( x (Directional) Flow velocity, m / s; W For vertical ( z (Directional) Flow velocity, m / s; q The lateral unit volume net inflow rate per unit width is m. 3 / s; B The width of the river is in meters (m). α Riverbed slope, in rad; τ For turbulent shear stress, N / m 2 ; U x For the tributary flow velocity x Directional component, m / s; g is gravitational acceleration, m / s² 2 ; ρ The density of water is kg / m³. 3 ; p Atmospheric pressure, N / m 2 , η Water level, in meters (m); B η The width of the water surface is in meters (m).

3. The method for coupled simulation of water temperature in a layered water intake reservoir with stacked beam gates as described in claim 2, characterized in that: The water temperature module is used to simulate the water temperature field distribution and downstream water temperature of a reservoir with stratified water intake through a stacked beam gate. The equation used is a heat conservation equation. The heat conservation equation is: （5） in: T w Water temperature, °C; D x Where m is the longitudinal diffusion coefficient. 2 / s; D z Where m is the vertical diffusion coefficient. 2 / s; The rate of lateral heat flux inflow and outflow in the unit control volume, in J / m. 3 / s; S Source and sink terms, including surface heat exchange and riverbed heat exchange, J / m 3 / s; The discharge water temperature is the flow-weighted average water temperature of the rectangular grid cells corresponding to the inlet elevation, specifically: （6） in: Q i The first corresponding to the elevation of the inlet i The flow rate of each grid cell, m 3 / s; T i For the first i Water temperature of each grid cell, °C; T o The temperature of the discharged water is ℃.

4. The method for coupled simulation of water temperature in a reservoir with stacked beam gates as described in claim 1, characterized in that, In step S2, a mathematical model of water temperature coupling in a reservoir with stacked beam gates is established. To adapt to the needs of rectangular grid simulation, the vertical grid spacing is determined based on the height of a single stacked beam gate. That is, the height of the vertical grid unit should be a value that can be divided by the height of a single stacked beam gate, so as to accommodate the increase or decrease in the number of stacked beam gates.

5. The method for coupled simulation of water temperature in a reservoir with stacked beam gates as described in claim 1, characterized in that, The vertical grid number at the start of operation of the stacked beam gate is set as follows: the minimum submerged water depth is submerged from the reservoir water level at the start of operation of the stacked beam gate to obtain the top elevation of the stacked beam gate at the start of operation. The grid corresponding to the bottom elevation of the inlet below the top elevation of the stacked beam gate is the vertical grid number at the start of operation of the stacked beam gate. It is set to a non-water-passing state to simulate the water-blocking effect of the stacked beam gate in the vertical direction of water flow.

6. The method for coupled simulation of water temperature in a reservoir with stacked beam gates as described in claim 1, characterized in that, The requirements for setting up the stacked beam gate are as follows: During the fish spawning and breeding season, the operation and scheduling of the stacked beam gate shall be carried out in accordance with the principle of operation and scheduling of the stacked beam gate according to the changes in the reservoir water level; outside the fish spawning and breeding season, all vertical grids where the stacked beam gate is located shall be set to the water passage state.

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