A method for calculating the water entrainment rate of culvert water in a power plant based on closed open boundary method

Abstract

The present invention relates to a method for calculating the water intake entrainment rate of a power plant culvert based on a closed open boundary method, including: establishing a two-dimensional hydrodynamic mathematical model; setting a closed open boundary of a culvert water intake in a calculation domain; giving boundary conditions that characterize the closed open boundary of the water intake culvert; establishing a two-dimensional particle tracking mathematical model; simulating and calculating the particle migration trajectory; and calculating the water intake entrainment rate of the power plant culvert. The present invention takes the power plant of the culvert water intake type as the research object, establishes a two-dimensional hydrodynamic mathematical model, sets the culvert water intake as a closed open boundary and gives boundary conditions according to the water intake flow rate of the power plant operation, and on this basis, uses a tracer particle method to simulate and calculate the migration trajectory of floating objects, counts the number of particles sucked into the culvert water intake under the water intake suction action, and calculates the water intake entrainment rate of the power plant culvert. The present invention proposes an engineering feasible, relatively fast and effective method for calculating the water intake entrainment rate of a power plant culvert. It provides a scientific basis for the planning and design of water intake safety warning and emergency measures for nuclear power plants.

Description

Technical Field

[0001] The present invention relates to a method for calculating the water intake rate of a power plant culvert based on a closed open boundary mode, an environmental hydraulic calculation method, and a method for calculating the water intake rate of a power plant culvert suitable for coastal power plants with culvert water intake types. Background Art

[0002] During the operation of coastal nuclear power plants, water needs to be taken from seawater through the water intake system to cool the units. When the water intake system is blocked, the units will be forced to reduce power or shut down, and in serious cases, even cause nuclear safety accidents. The suction of blockages at the water intake has become a major risk that affects the safety of the cold source of nuclear power plants, and the safety of cold sources has received increasing attention. The water intake types commonly used in nuclear power plants include open channel water intake and culvert water intake. Most of the power plants that have been built in my country use open channel water intake, but with the increasing prosperity of domestic nuclear power plant construction, culvert water intake is becoming more and more widely used in newly built power plants. For the open channel water intake type, due to the existence of the diversion dike of the water intake open channel, the calculation method of the water intake suction rate of the power plant is relatively mature. Usually, the number of particles entering the water intake open channel is directly counted, and the ratio of the number of particles entering the water intake open channel to the total number of particles put in is obtained, that is, the water intake suction rate. However, for the culvert water intake type, the water intake is located in the open water area, and there is no water intake engineering structure around it. The conventional water intake entrainment rate calculation method similar to the open channel water intake type is no longer applicable. At present, there is a lack of relatively convenient and feasible methods for calculating the water intake entrainment rate of the culvert water intake of power plants. At present, some scholars use full three-dimensional computational fluid dynamics (CFD) software to perform detailed simulations of the power plant water intake culvert to calculate the water intake entrainment rate of the culvert. However, due to the large amount of calculation and long time required for full three-dimensional CFD simulation, there are certain difficulties in practical engineering applications, especially in the water intake scheme comparison stage, which cannot meet the requirements of multiple scheme simulation comparison within a limited time. Therefore, how to relatively quickly and effectively calculate the water intake entrainment rate of the culvert water intake method of the power plant is a problem that needs to be solved. Summary of the invention

[0003] In order to overcome the problems of the prior art, the present invention proposes a method for calculating the entrainment rate of culvert water intake in a power plant based on a closed open boundary method. The method is aimed at nuclear power plants with culvert water intake, and uses a two-dimensional hydrodynamic mathematical model and a tracer particle method to propose a method for calculating the entrainment rate of culvert water intake in a power plant based on a closed open boundary processing method. It provides a scientific basis for the planning and design of nuclear power plant water intake safety warnings and emergency measures.

[0004] The present invention is a method for calculating the water entrainment rate of a power plant culvert based on a closed open boundary method, and the steps of the method are as follows:

[0005] Step 1: Establish a two-dimensional hydrodynamic mathematical model: The control equation of the calculation model in the Cartesian coordinate system is as follows:

[0006] Continuity equation:

[0007] Equations of motion:

[0008] x-direction:

[0009]

[0010] y direction:

[0011]

[0012] In the above formula: t is time, x, y are Cartesian coordinates; η is water level, h = d + η is total water depth, d is still water depth; is the average velocity of water depth in the x direction, is the average velocity of water depth in the y direction: z is the Cartesian coordinate; f is the Coriolis force parameter, f = 2Ωsinφ, where: Ω is the angular velocity of rotation, φ is the geographic latitude; g is the gravitational acceleration; ρ is the density of water, ρ0 is the reference water density; p a is the atmospheric pressure; A is the eddy viscosity coefficient; τ b =(τ bx ,τ by ) is the bottom stress, τ bx is τ b The x-component of by is τ b The y-direction component of c f is the drag coefficient, Flow velocity above the bed bottom; τ s =(τ sx ,τ sy ) is the surface wind stress, τ sx is τ s The x-component of sy is τ s The y-direction component of ρ a is the air density, c d is the air resistance coefficient, Wind speed 10m above the water surface; S is the source and sink term.

[0013] Step 2, setting the closed open boundary of the culvert water intake in the computational domain: In the computational domain including the culvert water intake of the power plant, according to the design plan of the culvert water intake type of the power plant (position, shape, size, etc.), the culvert water intake is set as a closed open boundary (the boundary is a non-computational domain), and the grid file required for the mathematical model is generated based on this.

[0014] Step 3, giving boundary conditions for the closed and open boundaries representing the culvert water intake: according to the water intake flow conditions of the power plant operation, the boundary conditions for the closed and open boundaries representing the culvert water intake are given.

[0015] Step 4, establish a two-dimensional particle tracking mathematical model: Based on the hydrodynamic model, the particle tracking mathematical model for simulating the migration trajectory of floating objects is established by using the tracer particle method; the simulation calculation mainly considers the carrying effect of the water flow, and does not consider the influence of the shape of the floating objects; the particle motion trajectory simulation control equation is as follows:

[0016] dX t =a(t,X t )dt+b(t,X t )ξ t dtWhere: X t is the particle position at time t, a(t, X t ) is the drift movement term caused by the flow and wind, b(t, X t ) is the diffusion term caused by molecular motion and turbulence, ξ t is a random number;

[0017] Step 5, simulation of particle migration trajectory: simulate the migration trajectory of tracer particles in the calculation domain and analyze the distribution of particles near the culvert water intake.

[0018] Step 6, calculation of the water entrainment rate of the power plant culvert: count the number of particles that flow out of the closed open boundary representing the culvert water intake (i.e., the culvert water intake) under the action of water intake suction, and calculate the change of the water entrainment rate of the power plant culvert over time. The culvert water entrainment rate ψ is the ratio of the number of particles m that flow out of the closed open boundary to the total number of particles M currently placed:

[0019]

[0020] The beneficial effects of the present invention are as follows: the present invention takes the power plant with culvert water intake as the research object, establishes a two-dimensional hydrodynamic mathematical model, sets the culvert water intake as a closed open boundary in the model and gives boundary conditions according to the water intake flow rate of the power plant operation, and on this basis, uses the tracer particle method to simulate and calculate the migration trajectory of floating objects, counts the number of particles sucked into the culvert water intake under the water intake suction, and calculates the culvert water intake entrainment rate of the power plant. The present invention proposes an engineering feasible, relatively fast and effective method for calculating the culvert water intake entrainment rate of the power plant. It provides a scientific basis for the planning and design of water intake safety warning and emergency measures for nuclear power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0022] Figure 1is a schematic flow chart of the method described in an embodiment of the present invention;

[0023] FIG. 2 is a diagram showing the calculation domain and the location of the culvert water intake in the example of use of the embodiment of the present invention ( Figure 2-a : Full computational domain; Figure 2-b : Schematic diagram of the area near the culvert water intake;

[0024] Figure 3 It is a schematic diagram of the grid distribution in the vicinity of the culvert water intake in the use example described in the embodiment of the present invention;

[0025] Figure 4 It is a schematic diagram of the position of the particle delivery section in the use example described in the embodiment of the present invention;

[0026] Figure 5 It is a schematic diagram of the short-term migration trajectory of tracer particles in the vicinity of the culvert water intake at a certain moment in the use example described in the embodiment of the present invention;

[0027] Figure 6 is a process line showing the change of the number of particles sucked into the culvert water intake over time in the use example described in the embodiment of the present invention;

[0028] Figure 7 It is a process line of the culvert water intake rate changing with time in the use example described in the embodiment of the present invention. DETAILED DESCRIPTION

[0029] Example:

[0030] This embodiment is a method for calculating the water entrainment rate of a power plant culvert based on a closed open boundary method. The process is as follows: Figure 1 The method described in this embodiment includes the following steps:

[0031] Step 1: Establish a two-dimensional hydrodynamic mathematical model:

[0032] The control equation of the calculation model in the Cartesian coordinate system is as follows:

[0033] Continuity equation:

[0034] Equations of motion:

[0035] x-direction:

[0036]

[0037] y direction:

[0038]

[0039] In the above formula: t is time, x, y are Cartesian coordinates; η is water level, h = d + η is total water depth, d is still water depth; is the average velocity of water depth in the x direction, is the average velocity of water depth in the y direction: z is the Cartesian coordinate; f is the Coriolis force parameter, f = 2Ωsinφ, where: Ω is the angular velocity of rotation, φ is the geographic latitude; g is the gravitational acceleration; ρ is the density of water, ρ0 is the reference water density; p a is the atmospheric pressure; A is the eddy viscosity coefficient; τ b =(τ bx ,τ by ) is the bottom stress, τ bx is τ b The x-component of by is τ b The y-direction component of c f is the drag coefficient, Flow velocity above the bed bottom; τ s =(τ sx ,τ sy ) is the surface wind stress, τ sx is τ s The x-component of sy is τ s The y-direction component of ρ a is the air density, c d is the air resistance coefficient, Wind speed 10m above the water surface; S is the source and sink term.

[0040] Application example: A water tank with a length of 2000m (500000±1000m), a width of 400m (0±200m), and a water depth of 10m, an ambient flow rate of 0.5m / s, and a flow direction from west (upstream) to east (downstream) (from Figure 2-a The left side of the paper flows to the right side. Figure 2-b , 3 , 4, and 5 are all in this direction). A hidden culvert water intake is arranged in the water tank, located in the middle of the water tank ( Figure 2-a Coordinates (500000, 0), the size of the water intake is 4m long and 4m wide, located in the center of the tank, the full calculation domain is as follows Figure 2-a The schematic diagram of the area near the water intake is shown in Figure 2-b The horizontal cross-section shown is a 4×4m rectangle. The upstream and downstream boundary conditions in the model give the flow velocity, and the bottom roughness is selected as the Manning number M = 50m 1 / 3 / s.

[0041] Step 2, setting the closed open boundary of the culvert water intake in the computational domain: In the computational domain including the culvert water intake of the power plant, according to the design plan of the culvert water intake type of the power plant (position, shape, size, etc.), the culvert water intake is set as a closed open boundary (the boundary is a non-computational domain), and the grid file required for the mathematical model is generated based on this.

[0042] In the application example, when the grid file is generated, the location of the water intake located in the center of the water tank with a length of 4m and a width of 4m is set as a closed open boundary. The closed area within the boundary is a non-computational domain (no computational grid). The grid distribution of the computational domain near the water intake is as follows: Figure 3 As shown. Usually, the traditional method of setting up a water intake is to set the water intake as a "sink" within the calculation water area in the hydrodynamic model, and to achieve water "sinking" into the water intake (water flowing out of the water intake) through the source-sink term "S" in the hydrodynamic control equation. When calculating the particle migration trajectory simulation based on the hydrodynamic conditions obtained by applying this method, since the water intake is within the calculation domain, although the water flow can flow out in the form of a "sink", the particles will not disappear in the calculation domain. Therefore, the traditional method of calculating the water intake entrainment rate is based on counting the number of particles in a certain range of waters near the water intake (for example, the open channel water intake type directly counts the number of particles entering the water intake open channel). However, for the culvert water intake type, the water intake is located in open waters, and there is no cover of water intake engineering structures around it. How to select a reasonable water area range to count the number of particles is a major problem. The present invention abandons this traditional method and sets the water intake as a closed open boundary. The closed area within the boundary (non-computational domain) can be regarded as a "funnel". When water flows out of the computational domain from the "funnel", when simulating the particle migration trajectory, the particles can also pass through the open boundary with the water flow into the "funnel" and flow out of the computational domain.

[0043] Step 3, give the boundary conditions of the closed open boundary representing the culvert water intake: according to the water intake flow conditions of the power plant operation, the boundary conditions of the closed open boundary representing the culvert water intake are given. In the application example, the water intake flow is Q in =10m 3 / s. The closed open boundary directly gives the discharge boundary condition. At the water intake, the water flow is sucked into the culvert water intake, that is, the water flows into the "funnel" and flows out of the calculation domain. Therefore, the given discharge boundary condition is a negative value, that is, the boundary flow Q of the closed open boundary BC =-10m 3 / s.

[0044] Step 4, establish a two-dimensional particle tracking mathematical model: Based on the hydrodynamic model, the particle tracking mathematical model for simulating the migration trajectory of floating objects is established by using the tracer particle method; the simulation calculation mainly considers the carrying effect of the water flow, and does not consider the influence of the shape of the floating objects; the particle motion trajectory simulation control equation is as follows:

[0045] dX t =a(t,X t )dt+b(t,X t )ξ t dtWhere: X t is the particle position at time t, a(t, X t ) is the drift movement term caused by the flow and wind, b(t, X t ) is the diffusion term caused by molecular motion and turbulence, ξ t is a random number;

[0046] The particle delivery method in the application example is as follows: particles are delivered at a section 10m away from the upstream boundary in the water area. Delivery points are arranged every 0.1m within the range of y=±20m in the y direction, with a total of 400 points. The delivery section is located upstream of the culvert water intake, with the horizontal coordinate position x=499010m. Figure 4 As shown; 10 particles are released synchronously at each point each time, once every 10 seconds, for a continuous period of 20 minutes, with a total of 480,000 particles released.

[0047] Step 5, simulation calculation of particle migration trajectory: simulate the migration trajectory of tracer particles in the calculation domain, and analyze the distribution of particles in the vicinity of the culvert water intake. In the application example, the total duration of the simulation calculation is 9 hours. 6 hours after the start of the calculation, the flow field basically reaches stability, and particles are released at this time. All released particles flow out of the closed open boundary of the culvert water intake or the downstream boundary of the calculation domain within 3 hours. The short-term migration trajectory of tracer particles in the vicinity of the culvert water intake at a certain moment in the simulation process is as follows Figure 5 shown. Figure 5 It can be seen that at the front edge of the water intake (left side), the trajectory of the particles is interrupted, indicating that the particles have flowed out of the closed open boundary (i.e., they are sucked in by the culvert water intake).

[0048] Step 6, calculation of the water entrainment rate of the power plant culvert: count the number of particles that flow out of the closed open boundary representing the culvert water intake (i.e., are sucked into the culvert water intake) under the action of water intake suction, and calculate the change of the water entrainment rate of the power plant culvert over time. The culvert water entrainment rate ψ is the ratio of the number of particles m that flow out of the closed open boundary to the total number of particles M currently placed:

[0049]

[0050] In the application example, the process line of the number of particles flowing out of the closed open boundary changing with time is as follows: Figure 6 As shown in the figure, it can be seen that before 6:34, the particles have not reached the water intake. After this moment, particles are sucked into the culvert water intake and flow out of the closed open boundary. At 6:52, the number of particles flowing out of the closed open boundary reaches a maximum value of 20,950. After this moment, no new particles are sucked into the water intake, indicating that other particles that are not sucked into the water intake bypass the water intake and move downstream. Based on the above definition of the culvert water intake entrainment rate, the process line of the culvert water intake entrainment rate changing with time is calculated as follows Figure 7 As shown. When particles began to be sucked into the water intake at 6:34, the particle release source had stopped releasing particles (release time was 6:00-6:20) and the total number of released particles was 480,000. The maximum value of the culvert water intake entrainment rate during the entire simulation process of the application example was 4.36%.

[0051] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention (such as the selection of models, the application of formulas, etc.) can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the water entrainment rate of a power plant culvert based on a closed open boundary method, characterized in that: The steps of the method are as follows: Step 1: Establish a two-dimensional hydrodynamic mathematical model: The control equation of the calculation model in the Cartesian coordinate system is as follows: Continuity equation: Equations of motion: x-direction: y direction: In the above formula: t is time, x, y are Cartesian coordinates; η is water level, h = d + η is total water depth, d is still water depth; is the average velocity of water depth in the x direction, is the average velocity of water depth in the y direction: z is the Cartesian coordinate; f is the Coriolis force parameter, f = 2Ωsinφ, where: Ω is the angular velocity of rotation, φ is the geographic latitude; g is the gravitational acceleration; ρ is the density of water, ρ0 is the reference water density; p a is the atmospheric pressure; A is the eddy viscosity coefficient; τ b =(τ bx ,τ by ) is the bottom stress, τ bx is τ b The x-component of by is τ b The y-direction component of c f is the drag coefficient, Flow velocity above the bed bottom; τ s =(τ sx ,τ sy ) is the surface wind stress, τ sx is τ s The x-component of sy is τ s y-direction component; ρ a is the air density, c d is the air resistance coefficient, Wind speed 10m above the water surface; S is the source and sink term; Step 2, setting the closed open boundary of the culvert water intake in the computational domain: in the computational domain including the culvert water intake of the power plant, according to the design scheme of the culvert water intake type of the power plant, the culvert water intake is set as a closed open boundary, and the boundary is a non-computational domain, based on which the grid file required for the mathematical model is generated; Step 3, giving boundary conditions for the closed and open boundaries representing the culvert water intake: according to the water intake flow conditions of the power plant operation, the boundary conditions for the closed and open boundaries representing the culvert water intake are given; Step 4, establish a two-dimensional particle tracking mathematical model: Based on the hydrodynamic model, the particle tracking mathematical model for simulating the migration trajectory of floating objects is established by using the tracer particle method; the simulation calculation mainly considers the carrying effect of the water flow, and does not consider the influence of the shape of the floating objects; the particle motion trajectory simulation control equation is as follows: dX t =a(t,X t )dt+b(t,X)ξ t dt Where: X t is the particle position at time t, a(t, X t ) is the drift movement term caused by the flow and wind, b(t, X t ) is the diffusion term generated by molecular motion and turbulence, ξt is a random number; Step 5, simulation of particle migration trajectory: simulate the migration trajectory of tracer particles in the calculation domain and analyze the distribution of particles near the culvert water intake; Step 6, calculation of the water entrainment rate of the culvert of the power plant: count the number of particles that flow out of the closed open boundary representing the culvert water intake under the action of water intake suction, that is, the number of particles sucked into the culvert water intake, and calculate the change of the water entrainment rate of the culvert of the power plant over time. The culvert water entrainment rate ψ is the ratio of the number of particles m flowing out of the closed open boundary to the total number of particles M currently put in:

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