A numerical simulation method for extracting discharge gates under siltation conditions

Abstract

The invention relates to a numerical simulation method for extracting a discharge gate under silting conditions, and belongs to the technical field of computer numerical simulation in water conservancy projects. The method comprises the following steps: step 1, drawing a geometric model according to actual project conditions, outputting the drawn geometric model in the form of an electronic file, and the output format is specifically *.STEP, importing the geometric model file into a fluid simulation software and dividing a calculation grid, the fluid simulation software is specifically FLUENT, and the geometric model and the grid include a gate solid area, a water-sand-air fluid area, and a fluid-solid interface area; step 2, giving initial conditions and boundary conditions for each area, the invention fully considers the type of sediment, the accumulation morphology and the characteristic parameters of the sediment, and the influence of the bedload transport process, and provides an effective method for finely simulating the extraction process of the discharge gate under silting conditions.

Description

Technical Field

[0001] The invention relates to a numerical simulation method for extracting a discharge gate under silting conditions, and belongs to the technical field of computer numerical simulation in water conservancy projects. Background Art

[0002] In modern water conservancy projects, sluice gates are widely used in hydraulic structures such as reservoirs, rivers, and hydropower stations, and play an important role in the safe operation and dispatching control of water conservancy hub projects. However, during long-term operation, the silt and suspended matter carried in the water flow will be deposited in the gate area, forming siltation. This siltation will not only affect the normal opening and closing function of the gate, but may also cause the gate to become stuck, aggravated by wear, or even damaged, thus threatening the safe operation of hydraulic structures. Therefore, it is of great significance to study and simulate the operating status of sluice gates under siltation conditions.

[0003] In the prior art, the numerical simulation analysis methods for gate extraction under siltation conditions mainly consider the effects of sediment pressure and shear force. In actual engineering, due to the different types of sediment, accumulation forms and sediment characteristic parameters, gate extraction belongs to the dynamic change process of water-air-sand three phases, accompanied by bedload transport process. The existing numerical simulation methods generally ignore the effects of these factors, making the numerical simulation of gate extraction relatively rough and difficult to accurately predict the impact of sediment on gate extraction, resulting in difficulty in formulating effective operation and maintenance plans in actual engineering applications.

[0004] In order to solve the above problems, it is urgent to propose a numerical simulation analysis method for extracting the discharge gate under siltation conditions based on the characteristic information of the discharge gate sediment, fully considering the influence of the sediment characteristics and the bedload transport process. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in order to overcome the shortcomings of the existing technology, a numerical analysis method for gate extraction under siltation conditions that takes into account the influence of silt characteristics is provided, which can consider the dynamic changes of the three phases of water, air and sand and the bedload transport process, and realize the refined numerical simulation of gate extraction under the influence of silt in front of the gate.

[0006] The technical solution adopted by the present invention to solve the above problem is: a numerical simulation method for extracting a discharge gate under siltation conditions, comprising the following steps:

[0007] Step 1: Draw a geometric model according to the actual engineering situation. The drawn geometric model is output in the form of an electronic file. The output format is *.STEP. The geometric model file is imported into the fluid simulation software and the calculation grid is divided. The fluid simulation software is FLUENT. The geometric model and grid include the gate solid area, the water-sand-air fluid area, and the fluid and solid interface area.

[0008] Step 2: Given the initial conditions and boundary conditions of each region, define the parameters and grid regions of the three-phase fluids of water, gas, and sand, and initialize them.

[0009] Step 3: Select the dynamic mesh update method, define the UDF (User-Defined Function) of the gate movement, and simulate the gradual opening process of the gate.

[0010] Specifically: set the gate opening speed, compile the defined UDF through the Compiled UDFs panel provided by FLUENT software, and dynamically connect it to the FLUENT solver;

[0011] Step 4, solve the VOF (Volume of Fluid) two-phase flow model, calculate the flow field and pressure field variables, and extract the coordinates, velocity, and shear force parameters of the water-sand two-phase contact surface.

[0012] Step 5, compile a UDF function, calculate the sediment Shields number, solve the bed load transport equation, and adjust the maximum slope of the sediment according to the maximum angle of repose, and calculate the adjusted sediment elevation accordingly.

[0013] Step 6: Use the adjusted water-sand interface elevation and dynamic mesh technology to control the movement of interface nodes and readjust the mesh inside the calculation area.

[0014] Step 7, repeat the above steps 4 to 6 until the specified calculation time is completed, and output the calculation results of fluid distribution, vertical dynamic water pressure, sediment shear force, and suction force at each time step.

[0015] Furthermore, in step 1, the influence of the silt accumulation morphology is considered when establishing the geometric model, and the silt in front of the gate is divided into three types: horizontal accumulation, positive slope accumulation, and funnel-shaped accumulation. Among them, the horizontal distribution of the silt surface in front of the gate is called horizontal accumulation; the silt surface is inclined toward the gate side, which is called positive slope accumulation; the discharge water flow scours the silt to form a funnel-shaped depression in front of the gate, which is called funnel-shaped accumulation.

[0016] Furthermore, in step 2, the fluid domain inlet and outlet are set as pressure boundary conditions, the wall is set as a solid wall no-slip boundary condition, and the wall function is used to process the flow near the wall. When the flow field is initialized, the gate panel is used as the dividing line, the upstream is filled with water and silt, and the downstream is filled with air. The calculation termination principle of the gate at a certain opening is that the flow field is stable under the calculation conditions.

[0017] Furthermore, in step 2, the initial condition takes into account the influence of the fine particle content, and the friction coefficient between the coarse particles and the gate is calculated as follows:

[0018]

[0019] Among them, γ s ' is the dry bulk density of sediment, in kN / m 3 ; γ s is the bulk density of sediment, in kN / m 3 .

[0020] Fine particles and gate shear stress, the shear stress equation of Bingham body mud is:

[0021]

[0022] Where, τ is the shear stress, in kPa; τ b is the limiting shear stress, in kPa; η is the viscosity, in kPa·s; dv / dn is the velocity gradient, in s -1 .

[0023] Furthermore, in step 4, the k-ε turbulence model is used for turbulence calculation, and the free liquid surface of the water-air two-phase flow and the water-sand two-phase flow is tracked by the VOF model; its turbulent kinetic energy transport equation and dissipation rate equation are in the following form:

[0024]

[0025] Where k is the turbulent kinetic energy, in m 2 / s 2 ; ε is the turbulent kinetic energy dissipation rate, unit is W / kg; G k It represents the turbulent kinetic energy generated by the average velocity gradient of the water flow, in m 2 / s 2 ; G b It represents the turbulent kinetic energy generated by buoyancy and lift, in m 2 / s 2 ; Y M is the effect of compressible turbulent pulsation expansion on the entire dissipation rate; μ t is the turbulent viscosity coefficient, in Pa·s;

[0026] The calculation formula of turbulent viscosity coefficient is: μ t =ρC μ k 2 / ε;

[0027] σ k , σ ε , C μ、 C 1ε , C 2ε , C 3ε is a constant coefficient.

[0028] Furthermore, in step 5, the bed load transport equation is as follows:

[0029]

[0030] Among them, τ i , τ is the shear force on the surface of the sediment, in kPa, calculated by the hydraulic model; h is the sedimentation elevation, in m; q 0 is the volume sediment transport rate of a single width of the plane, and the calculation formula is as follows:

[0031]

[0032] Where s is the specific gravity of sediment; θ is the Shields number on the sediment surface; d s is the median particle size of sediment, in m; θ cr is the critical Shields number for sediment, where the slope effect is taken into account; the calculation formula for the critical Shields number for sediment on a horizontal bed is as follows:

[0033]

[0034] Among them, D * is the dimensionless sediment particle size:

[0035]

[0036] The calculation formula of critical starting Shields number of sediment on a sloped bed is:

[0037]

[0038] Among them, α is the slope foot of the bed surface and the horizontal plane, in degrees; is the angle of repose of sediment, in degrees.

[0039] Furthermore, in step 5, the sediment height adjustment method is as follows: Use programming software such as C language to write a custom UDF function "Adjust_sediment.c" to implement the following functions:

[0040] 1) Obtain the water-sand interface velocity and shear force after the VOF model calculation is completed at each time step, and solve the Shields number to obtain the sediment starting conditions;

[0041] 2) Solve the current sediment transport rate according to the sediment transport rate formula and adjust the sediment height according to the sediment transport rate;

[0042] 3) Calculate the maximum slope of each unit. If the slope exceeds the underwater angle of repose, adjust the height of the sediment so that the slope does not exceed the maximum angle of repose.

[0043] Furthermore, in step 3 and step 6, the adjusted water-sand interface is simulated using a dynamic mesh technology, and the dynamic mesh update method uses a local redrawing model.

[0044] Compared with the prior art, the advantages of the present invention are:

[0045] The present invention provides a numerical simulation method for extracting a sluice gate under siltation conditions. Considering that the existing methods can only consider the effects of sediment pressure and shear force, it is difficult to take into account the characteristics of silt and the influence of the bedload transport process, and the numerical simulation results are relatively rough, the present invention fully considers the type of silt, accumulation morphology and characteristic parameters of silt, as well as the influence of the bedload transport process, and provides an effective method for finely simulating the extraction process of the sluice gate under siltation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of a numerical simulation analysis method for extracting a sluice gate under siltation conditions according to the present invention;

[0047] Figure 2 This is the geometric model diagram of the gate;

[0048] Figure 3 Calculate the meshing diagram for the gate;

[0049] Figure 4 Initialize the mesh for the fluid;

[0050] Figure 5 It is the cloud map of fluid elevation change;

[0051] Figure 6 It is a cloud map of sediment elevation change;

[0052] Figure 7 It is the pressure cloud diagram of the gate panel;

[0053] Figure 8 It is the pressure cloud diagram of the gate longitudinal section;

[0054] Fig. 9 It is the process line diagram of the maximum negative pressure at the bottom of the gate changing with the opening;

[0055] Fig.10It is the process diagram of the vertical shear force of sediment under different sediment thickness;

[0056] Fig.11 It is the process diagram of vertical dynamic water pressure change under different sediment thickness;

[0057] Fig.12 It is the process diagram of shear force variation of sediment under different fine particle contents;

[0058] Fig.13 It is the line diagram of the negative pressure change process of the gate bottom edge under different fine particle contents;

[0059] Fig.14 This is a process line diagram of the calculated and measured values ​​of the gate extraction force as the gate opening changes. DETAILED DESCRIPTION

[0060] Example 1. The preferred embodiment of the present invention selects the numerical simulation of the extraction process of the working gate at the inlet of a reservoir spillway. The selected engineering gate is a flat steel gate. The gate adopts downstream side water stop. The orifice size is 2m×2m (width×height). The gate is 2.56m wide, 2.20m high, and has a maximum thickness of 0.55m. The inlet bottom plate elevation is 1480.00m and the normal water storage level is 1510.00m.

[0061] Figure 1 The flowchart of the method of the present invention is shown in the figure. As shown in the figure, the method of the present invention includes 7 steps:

[0062] Step 1: Use the pre-processing software Solidworks to draw the three-dimensional geometric model of the gate and fluid. The drawn geometric model is output in the form of an electronic file. The output format is *.STEP. The geometric model file is imported into the fluid simulation software and the calculation grid is divided. The fluid simulation software is FLUENT. The geometric model and grid include the gate solid area, the water-sand-air fluid area, and the fluid and solid interface area. See the geometric model for details. Figure 2 , computational mesh generation see Figure 3 and Figure 4 The total number of gate units is 58458, and the total number of nodes is 187649; the total number of fluid area units is 31234, and the total number of nodes is 73625.

[0063] Step 2, define the boundary type:

[0064] (1) The left side and top of the upstream fluid domain are pressure boundaries;

[0065] (2) The outlet on the right side of the fluid domain is the pressure outlet. The initial unit area of ​​water, air and sediment is defined: under the initial conditions, the upstream side of the gate is sediment and water, the downstream side is air, and the wall surface adopts the default no-slip boundary condition.

[0066] Step 3, define the gate motion UDF function, set the gate opening speed to 0.3m / s, and compile the defined UDF through the Compiled UDFs panel provided by the FLUENT software to dynamically connect to the FLUENT solver.

[0067] Step 4: The standard k-ε turbulence model and VOF model are selected for the turbulence and two-phase flow models respectively, the flow field and pressure field variables are calculated, and the coordinates, velocity, and shear force parameters of the water-sand two-phase contact surface are extracted.

[0068] Step 5: Prepare a custom UDF function "Adjust_sediment.c" to read fluid parameters, calculate the Shields number and adjust the sediment height. By binding the UDF to the ADJUST macro, the sediment height is adjusted after each iteration step to achieve the coupled calculation of three-phase flow and bedload transport. The cloud map of fluid and sediment elevation changes is shown in Figure 5 and Figure 6 .

[0069] Step 6. Set up dynamic mesh updates: Enter the "Dynamic Mesh" window, select the area near the water-sand interface, set the update method to "Remeshing", and configure relevant parameters in "Dynamic Mesh Parameters" to ensure that the mesh is updated as the silt height changes.

[0070] Step 7: Select SIMPLEC as the solution method for the algebraic equations, set the time step to 0.02s, and use the FLUENT solver to iteratively solve the calculation area until the set iteration accuracy (10 -3 ) and output the calculation results of fluid distribution, vertical dynamic water pressure, sediment shear force and suction force at each time step.

[0071] Calculation results:

[0072] Gate panel and longitudinal section pressure cloud diagram Figure 7 and Figure 8 As can be seen from the figure, the sediment and water flow form a large negative pressure area at the bottom of the gate, mainly between the two middle longitudinal beams. This part of the negative pressure forms a downward suction at the bottom of the gate. Although the pressure in the area below the bottom main beam on both sides of the negative pressure area is positive, it is significantly lower than the area above the lower main beam. The two act together on the bottom main beam, forming a "pressure difference" locally, forming a vertical downward dynamic water pressure component on the gate body.

[0073] Figures 9 to 11 They respectively represent the variation patterns of the maximum negative pressure at the bottom of the gate, the vertical shear force of the sediment, and the dynamic water pressure with the opening under different siltation thickness conditions.

[0074] Depend on Fig. 9 It can be seen that as the gate opening gradually increases, the maximum negative pressure at the bottom of the gate increases first and then decreases. When the gate is located in the silt, the negative pressure is relatively large, and the greater the thickness of the silt, the longer the high negative pressure lasts.

[0075] Depend on Fig.10 It can be seen that as the gate opening gradually increases, the shear force of the sediment gradually decreases. When the gate opening height reaches the sediment thickness, the shear force becomes zero. Under the same sediment type and fine particle content conditions, as the sediment thickness increases, the sediment shear force gradually increases.

[0076] Depend on Fig.11 It can be seen that the dynamic water pressure gradually increases with the increase of the opening, mainly because the flow velocity gradually increases with the increase of the opening, resulting in an increase in the pressure difference between the upper and lower surfaces of the bottom main beam.

[0077] Fig.12 It shows the influence of different fine particle contents on the vertical shear force of sediment under the same sedimentation type and sedimentation thickness conditions, corresponding to fine particle contents of 30%, 20% and 10% respectively. It can be seen from the figure that with the increase of fine particle content, the shear force of sediment that needs to be overcome when the gate is opened gradually increases. Since the increase of fine particles will increase the fluidity of sediment and make it easier to meet the hydraulic scouring and silting conditions, the sediment thickness decreases faster under the action of plastic flow and scouring and silting, and the shear force duration is shortened at the same gate opening speed.

[0078] Fig.13 It shows the variation law of negative pressure at the bottom edge of the gate under different fine particle contents of sediment. It can be seen from the figure that when a large negative pressure area is formed, the gate is basically located in the sediment, and with the increase of fine particle content, the maximum negative pressure gradually increases.

[0079] The thickness and fine particle content of the sediment in front of the gate are the same. The maximum shear force of the sediment under the three working conditions of positive sedimentation, funnel-shaped sedimentation and horizontal sedimentation are 43.658kN, 45.827kN and 47.119kN respectively. Under the same sediment thickness in front of the gate, the maximum shear force of the sediment is horizontal > positive > funnel, and the maximum vertical dynamic water pressure and downward suction are similar. Therefore, maintaining positive or funnel-shaped sedimentation in front of the gate and opening the gate for adjustment regularly will help open the gate.

[0080] Example 2. In order to verify the effectiveness of the model, Example 2 of the present invention selects the actual engineering parameters and measured data of the working gate of a flood discharge tunnel of a hydropower station project for calculation and comparative analysis. The gate type is a flat steel gate, and the specific parameters are as follows: gate size 7.5m×6.5m-24m (width×height-working water head); the measured silt thickness in front of the gate is 4.3m. The vertical dynamic water pressure, the negative pressure at the bottom edge of the gate, and the shear force of the silt are calculated using the numerical simulation method of the present invention. The calculation steps are the same as those in Example 1. The friction force of the water stop and walking support, the gravity of the gate and the silt, etc. are calculated using the empirical formula method. The calculated values ​​and measured values ​​of the gate extraction force changing with the opening are shown in Table 1, and the process line is shown in Table 1. Fig.14 .

[0081] Table 1: Comparison table of calculated and measured values ​​of gate extraction force as the gate opening changes

[0082]

[0083]

[0084] According to Table 1 and Fig.14 It can be seen that the change trends of the calculated values ​​and the measured values ​​are in good agreement, which proves that the numerical analysis method is correct.

[0085] The present invention is not limited to the specific scheme described in the above embodiment. For ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principle of the invention. These improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A numerical simulation method for extracting a sluice gate under siltation conditions, characterized in that: The steps include: Step 1: Draw a geometric model according to the actual engineering situation, output the drawn geometric model in the form of an electronic file, import the geometric model file into the fluid simulation software and divide the calculation grid. The geometric model and grid include the gate solid area, the water-sand-air fluid area, and the fluid and solid interface area; Step 2: Given the initial conditions and boundary conditions of each region, define the parameters and grid regions of the three-phase fluids of water, gas and sand, and initialize them; Step 3, select the dynamic grid update mode, define the UDF function of the gate movement, and simulate the gradual opening process of the gate; Specifically: set the gate opening speed, compile the defined UDF through the Compiled UDFs panel provided by FLUENT software, and dynamically connect it to the FLUENT solver; Step 4, solve the VOF two-phase flow model, calculate the flow field and pressure field variables, and extract the coordinates, velocity, and shear force parameters of the water-sand two-phase contact surface; Step 5, compile a UDF function, calculate the sediment Shields number, solve the bedload transport equation, and adjust the maximum slope of the sediment according to the maximum angle of repose, and calculate the adjusted sediment elevation accordingly; Step 6, using the adjusted water-sand interface elevation and dynamic mesh technology, control the movement of interface nodes and readjust the mesh inside the calculation area; Step 7, repeat the above steps 4 to 6 until the specified calculation time is completed, and output the calculation results of fluid distribution, vertical dynamic water pressure, sediment shear force, and suction force at each time step.

2. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In the step 1, the influence of the silt accumulation morphology is taken into consideration when establishing the geometric model, and the silt in front of the gate is divided into three types: horizontal accumulation, slope accumulation, and funnel-shaped accumulation; among them, the silt surface is horizontally distributed in front of the gate, which is called horizontal accumulation; the silt surface is sloped toward one side of the gate, which is called slope accumulation; the discharge water flow scours the silt to form a funnel-shaped depression in front of the gate, which is called funnel-shaped accumulation.

3. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 2, the inlet and outlet of the fluid domain are set as pressure boundary conditions, the wall is set as a solid wall no-slip boundary condition, and the wall function is used to process the flow near the wall. When the flow field is initialized, the gate panel is used as the dividing line, the upstream is filled with water and silt, and the downstream is filled with air; the calculation termination principle of the gate at a certain opening is that the flow field is stable under the calculation conditions.

4. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 2, the initial condition takes into account the influence of fine particle content, and the friction coefficient between coarse particles and the gate is calculated by: Among them, γ′ s is the dry bulk density of sediment, in kN / m 3 ; γ s is the bulk density of sediment, in kN / m 3 ; Fine particles and gate shear stress, the shear stress equation of Bingham body mud is: Where, τ is the shear stress, in kPa; τ b is the limiting shear stress, in kPa; η is the viscosity, in kPa·s; dv / dn is the velocity gradient, in s -1 .

5. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 4, the k-ε turbulence model is used for turbulence calculation, and the free liquid surface of the water-air two-phase flow and the water-sand two-phase flow is tracked by the VOF model; Its turbulent kinetic energy transport equation and dissipation rate equation are as follows: Where k is the turbulent kinetic energy, in m 2 / s 2 ; ε is the turbulent kinetic energy dissipation rate, unit is W / kg; G k It represents the turbulent kinetic energy generated by the average velocity gradient of the water flow, in m 2 / s 2 ; G b It represents the turbulent kinetic energy generated by buoyancy and lift, in m 2 / s 2 ; Y M is the effect of compressible turbulent pulsation expansion on the entire dissipation rate; μ t is the turbulent viscosity coefficient, in Pa·s; The calculation formula of turbulent viscosity coefficient is: μ t =ρC μ k 2 / ε; σ k , σ ε , C μ , C 1ε , C 2ε , C 3ε is a constant coefficient.

6. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 5, the bed load transport equation is as follows: Among them, τ i , τ is the shear force on the surface of the sediment, in kPa, calculated by the hydraulic model; h is the sedimentation elevation, in m; q0 is the volumetric sediment transport rate per plane width, calculated as follows: Where s is the specific gravity of sediment; θ is the Shields number on the sediment surface; d s is the median particle size of sediment, in m; θ cr is the critical Shields number for sediment to start. The slope effect is taken into account here. The calculation formula for the critical Shields number for sediment on a horizontal bed is as follows: Where D* is the dimensionless sediment particle size: The calculation formula of critical starting Shields number of sediment on a sloped bed is: Among them, α is the slope foot of the bed surface and the horizontal plane, in degrees; is the angle of repose of sediment, in degrees.

7. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 5, the sediment height adjustment method is as follows: Use programming software to write a custom UDF function "Adjust_sediment.c" to implement the following functions: 1) Obtain the water-sand interface velocity and shear force after the VOF model calculation is completed at each time step, and solve the Shields number to obtain the sediment starting conditions; 2) Solve the current sediment transport rate according to the sediment transport rate formula and adjust the sediment height according to the sediment transport rate; 3) Calculate the maximum slope of each unit. If the slope exceeds the underwater angle of repose, adjust the height of the sediment so that the slope does not exceed the maximum angle of repose.

8. A numerical simulation method for extracting a sluice gate under siltation conditions as claimed in claim 1, characterized in that: In step 3 and step 6, the adjusted water-sand interface is simulated using a dynamic mesh technology, and the dynamic mesh update method uses a local redrawing model.

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