Pipeline water hammer pressure calculation method in valve closing process

Abstract

The invention discloses a pipeline water hammer pressure calculation method in a valve closing process. The method comprises the following steps: constructing a three-dimensional geometric model of a butterfly check valve; adding a front pipeline and a rear pipeline according to the geometric model of the butterfly check valve, extracting a fluid model, and performing mixed structure grid division on the fluid model; performing numerical simulation on the water hammer generated when the valve is closed under different working conditions by adding different heavy hammer torques and damping torques; setting boundary conditions of a fluid domain in Fluent; solving a fluid domain and outputting a curve of valve opening changing along with time and pressure data; a water hammer simulation model is established in COMSOL, and the valve opening change curve along with time is converted and then imported into the water hammer model; setting a water hammer model and boundary conditions; and performing numerical simulation by using the water hammer model, and solving and outputting the water hammer pressure when the valve is closed and a corresponding pipeline pressure cloud picture. Compared with a traditional theoretical calculation method, the method is more in line with engineering practice.

Description

Technical Field

[0001] The invention relates to a pipeline water hammer pressure calculation technology, and in particular to a pipeline water hammer pressure calculation method during a valve closing process. Background Art

[0002] As a crucial component in media delivery systems, butterfly check valves are widely used in chemical, drainage, and oil and gas pipelines. Their unique valve structure effectively prevents backflow and suppresses destructive water hammer, ensuring safe pipeline operation. A butterfly check valve primarily consists of a valve body, stem, valve disc, weight, seal, and pressure plate. When the pump begins operating, flow through the valve inlet gradually increases. The disc, driven by the combined forces of fluid pressure, the weight of the weight, and its own weight, rotates counterclockwise around the stem to open. When the pump stops, flow through the inlet decreases, and the fluid force on the disc is unable to overcome its own weight and the weight of the weight. The disc rotates clockwise, re-engaging with the valve body and fulfilling its check function. This structure effectively reduces water hammer and mitigates the impact and collision of the disc against the valve seat during valve closing. Due to the complexity of the check valve structure and fluid flow, obtaining specific data on water hammer during valve closing is difficult. Consequently, a lack of data supports the evaluation of its water hammer performance, hindering appropriate adjustments for optimal installation and commissioning in real-world applications.

[0003] Compared with experiments, numerical simulation can significantly shorten the R&D cycle and reduce costs for the medium flow and valve movement characteristics within the butterfly check valve. However, the pipeline water hammer pressure generated during the closing process of the butterfly check valve is relatively complex. It is difficult to accurately calculate the water hammer pressure under different working conditions using only a single numerical simulation tool. In addition, most existing research focuses on the numerical simulation of water hammer pressure in long-distance transportation pipelines, and there is little research on the calculation of water hammer pressure caused by different valve structures and closing speeds.

[0004] Traditional methods for calculating water hammer pressure when a valve is closed include one-dimensional numerical simulation using the characteristic line method and experimental measurement. Traditional one-dimensional numerical simulations are overly simplistic in simulating the actual conditions when a valve is closed, ignoring the effects of the valve structure and closing speed on water hammer waves. They are not well suited for simulating the water hammer pressure generated by different valves and lack accuracy and precision. Experimental measurement methods often require high costs and are difficult to implement due to equipment and site limitations. Furthermore, the stability of the test objects and operating conditions, as well as the accuracy of the measurement results, are limited. While some papers have conducted numerical simulations based on experiments, most focus on water pipeline systems, particularly long-distance water transmission systems. These studies consider water hammer caused by elevation differences in terrain and pump stoppages due to accidents, but have not examined water hammer pressure caused by different valve structures. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for calculating the water hammer pressure in the pipeline during the valve closing process. Based on basic theories such as fluid mechanics and dynamics, combined with numerical simulations such as Fluent and the Comsol water hammer model, a butterfly check valve is numerically simulated.

[0006] The technical solution adopted in the present invention is:

[0007] A method for calculating water hammer pressure in a pipeline during a valve closing process comprises the following steps:

[0008] Step 1, constructing a three-dimensional geometric model of the butterfly check valve;

[0009] Furthermore, in step 1, based on the two-dimensional drawing of the butterfly check valve, the geometric modeling of the butterfly check valve is performed in the three-dimensional modeling software SOLIDWORKS; and the geometric model is imported into SpaceClaim to simplify the geometric model in order to remove structural factors that affect the simulation results.

[0010] Step 2: Add front and rear pipes according to the geometric model of the butterfly check valve, extract the fluid model, and perform hybrid structure meshing on the fluid model;

[0011] Step 3, by adding different weight torques and damping torques, numerical simulation is performed on the water hammer generated when the valve is closed under different working conditions;

[0012] Furthermore, in step 3, the torque generated by the weight torque at the initial position on the valve shaft is calculated by SpaceClaim, and the damping coefficient is calculated based on the cylinder model parameters in the three-dimensional geometric model of the butterfly check valve.

[0013] Specifically, the damping force calculation formula is:

[0014]

[0015] Where, k is the viscosity coefficient, which is 8.663 Pa·s; l is the length of the piston rod hole, which is 10 mm; D is the inner diameter of the cylinder, which is 80 mm; d is the diameter of the piston rod, which is 35 mm; m is the flow index, which is 1; s is the number of holes with different diameters; n is the number of holes; d i is the diameter of the small hole; c is the damping coefficient.

[0016] Then the damping coefficient is:

[0017]

[0018] Step 4: Set the boundary conditions of the fluid domain in Fluent. Set the outer surface medium of the fluid domain to water, the outer surface of the fluid domain to a wall, select the Ke realizable model for the turbulence model, and set the inlet to a pressure inlet with a pressure of 0.2 MPa; the outlet to a pressure outlet with a pressure of 0.1 MPa.

[0019] Specifically, the outer surface of the fluid domain was set as a wall to prevent fluid from flowing out through the wall and affecting the accuracy of the simulation results. The Ke realizable model was selected as the turbulence model, which is well suited for simulating valve rotation. The inlet was set to a pressure inlet with a pressure of 0.2 MPa, and the outlet was set to a pressure outlet with a pressure of 0.1 MPa. The solution method selected was the Piso algorithm + skewness correction. This algorithm can prevent the generation of highly distorted meshes during mesh movement, further improving the accuracy of the simulation results. This algorithm also has advantages for transient simulation calculations and small time steps.

[0020] Step 5: Solve the fluid domain and output the valve opening change curve over time and pressure data.

[0021] Specifically, the numerical simulation adopts a calculation method of steady-state simulation first and then transient simulation, so as to be more in line with the actual situation when the valve moves. At the same time, the pressure field data obtained by the steady-state simulation is output so that it can be subsequently input into the water hammer model for water hammer pressure research. At the same time, the opening curve of the valve during the closing process under this working condition is output.

[0022] Step 6: Establish a water hammer simulation model in COMSOL, and transform the valve opening versus time curve and import it into the water hammer model;

[0023] Furthermore, in step 6, the mass average pressure is used as the initial pressure of the water hammer simulation model, and the volume flow rate data is used as the initial flow rate of the water hammer simulation model;

[0024] Specifically, the mass average pressure and volume flow rate data are the initial pressure and initial flow rate of the water hammer model, respectively. The valve opening time curve is transformed and imported using the Comsol interpolation function as the boundary condition at the outlet of the water hammer model.

[0025] Step 7: Set the water hammer model and boundary conditions: transform the curve of valve opening over time as the boundary condition of the water hammer model outlet position;

[0026] Set the outer surface medium of the fluid domain to water, the outer surface of the fluid domain to a wall, select the transient solver in the solver settings, and set the inlet and outlet pressures of the water hammer model.

[0027] Specifically, the pipe length of the water hammer pipe model is 20m, the coordinate origin is the inlet position, and a monitoring point is set at 11.15m from the origin to measure the pressure and flow rate changes in the pipe. The Young's modulus of the pipe is 2.1E11 Pa, the pipe wall thickness is 19.5mm, and the initial pressure and initial flow rate in the entire pipe are set to 1.2672E5 Pa and 10.772m / s, respectively.

[0028] When the valve is closed, due to the compressibility of water and the elasticity of the pipe, a sharp pressure pulse is generated upstream of the valve. c Given by the following expression

[0029]

[0030] Among them, v s is the isentropic speed of sound in the bulk fluid (1481 m / s for water), while the second term is due to the elasticity of the tube wall. The water density is ρ, β A is the pipe cross-sectional compression coefficient, resulting in an effective wave velocity of 1037 m / s. The instantaneous closure of the valve will generate a water hammer pulse with an amplitude of P, which is given by the Joukowsky basic equation:

[0031] P=ρv c u0 (1.5)

[0032] Where u0 is the average fluid velocity before the valve closes.

[0033] The maximum element size of the mesh for the water hammer model is set to L / N, the minimum element is set to 1 mm, the maximum element growth rate is 1.5, the curvature factor is 0.6, and the narrow area resolution is 0.5.

[0034] The water hammer boundary conditions are set, the inlet is set to the pressure inlet, the pressure magnitude is p0, the outlet is set to the velocity outlet, and the velocity magnitude is the interpolation function imported in step 6.

[0035] In the solver setup, select the transient solver, set the output time step to range (0, 1e-3, 0.3), and set the solver time step to parameter dt. In order to make the transient solver better express the water hammer phenomenon, the pressure change during the time step dt cannot completely cross the grid unit. Here, the maximum change during dt is set to 10% of the moving grid length dx. In other words, the distance traveled by the pressure signal during dt, i.e., v c dt, must be smaller than the typical grid size dx. This can be achieved by imposing the following CFL number condition:

[0036]

[0037] Step 8: Use the water hammer model to perform numerical simulation to solve and output the water hammer pressure when the valve is closed and the corresponding pipeline pressure cloud map.

[0038] The present invention adopts the above technical solution and performs transient simulation of the closing process of the butterfly check valve under different conditions based on the Fluent numerical simulation software to obtain the flow field characteristics and closing characteristic curve of the closing process. At the same time, the output flow field pressure data and valve closing characteristic curve are imported into the Comsol water hammer model to perform numerical simulation calculation of water hammer pressure. This can more realistically calculate the water hammer pressure generated by the check valve closing process and provide an accurate method for calculating and simulating pipeline water hammer pressure during valve closing. The pipeline water hammer pressure calculation method proposed by the present invention can not only be used to calculate the pipeline water hammer pressure changes caused by the application of different external torque conditions or different structural parameters to the valve, but also has good applicability for calculating pipeline water hammer pressure changes of other types of valves. At the same time, this method can more intuitively display the changes in pipeline water hammer pressure by outputting the water hammer pressure and flow velocity cloud map in the pipeline at any time period of the entire pipeline.

[0039] The present invention provides an accurate and simple method for calculating the water hammer pressure in the pipeline during the closing process of a butterfly check valve, and provides a numerical simulation tool for calculating the water hammer pressure generated in the pipeline during the closing process of a butterfly check valve based on fluid simulation software. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0041] Figure 1 This is a flow chart of a method for calculating water hammer pressure in a pipeline during a valve closing process according to the present invention;

[0042] Figure 2 This is a schematic diagram of the three-dimensional model structure of a butterfly check valve;

[0043] Figure 3 Schematic diagram of fluid domain model and mesh division;

[0044] Figure 4 Schematic diagram of valve opening changing with time under set working conditions;

[0045] Figure 5 This is a schematic diagram of the water hammer pipeline model structure of the present invention;

[0046] Figure 6 Schematic diagram of mesh division of the water hammer pipeline model of the present invention;

[0047] Figure 7 This is the pipeline pressure cloud diagram of the present invention;

[0048] Figure 8 This is a schematic diagram of a curve showing changes in pressure versus pipeline distance according to the present invention;

[0049] Figure 9 This is the pipeline flow velocity cloud map of the present invention;

[0050] Figure 10 Schematic diagram of the curve of flow velocity changing with pipeline distance in the present invention;

[0051] Figure 11 It is a schematic diagram of the pressure change curve at a specified measuring point over time;

[0052] Figure 12 Schematic diagram of the pressure change curve at the valve over time. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0054] On the one hand, the present invention can solve the problems of long cycle and high cost of experimental measurement methods. On the other hand, by using Fluent to perform three-dimensional numerical simulation, the closing conditions of the valve under different working conditions are studied, and the result data obtained by the simulation is imported into the Comsol water hammer model. The water hammer wave and pressure conditions generated by the valve under different closing conditions can be obtained more accurately, laying the foundation for subsequent numerical simulation research and providing reference indicators for enterprises to evaluate the performance of valves.

[0055] like Figures 1 to 12 As shown in FIG1 , the present invention discloses a method for calculating the water hammer pressure in a pipeline during a valve closing process, which comprises the following steps:

[0056] Step 1, constructing a three-dimensional geometric model of the butterfly check valve;

[0057] Furthermore, in step 1, based on the two-dimensional drawing of the butterfly check valve, the geometric modeling of the butterfly check valve is performed in the three-dimensional modeling software SOLIDWORKS; and the geometric model is imported into SpaceClaim to simplify the geometric model in order to remove structural factors that affect the simulation results.

[0058] Specifically, after saving the geometric modeling in step format, the geometric model is imported into SpaceClaim to process the model, including some pores, chamfers and sharp points, to prevent them from affecting the subsequent simulation process and causing inaccurate results.

[0059] Step 2: Add front and rear pipes according to the geometric model of the butterfly check valve, extract the fluid model, and perform hybrid structure meshing on the fluid model;

[0060] Specifically, hybrid structured grids can reduce computational costs, shorten computational time, and improve numerical simulation efficiency. Figure 3 shown.

[0061] Step 3, by adding different weight torques and damping torques, numerical simulation is performed on the water hammer generated when the valve is closed under different working conditions;

[0062] The present invention can perform numerical simulation on the water hammer generated when the valve is closed under different working conditions. Considering adding different weight torque and damping torque, the present invention sets one of the schemes as an example. The specific parameters of the weight torque and damping coefficient of this working condition are shown in Table 1. The torque generated by the weight torque in the initial position on the valve shaft shown in Table 1 is calculated by SpaceClaim. The damping coefficient is based on Figure 1 The parameters of the three-dimensional cylinder model shown are calculated according to the formula.

[0063] Table 1

[0064] plan Weight torque (N·m) Damping (Ns / m) a 25.41 14107.61

[0065] According to the damping force calculation formula:

[0066]

[0067] Where, k is the viscosity coefficient, which is 8.663 Pa·s; l is the length of the piston rod hole, which is 10 mm; D is the inner diameter of the cylinder, which is 80 mm; d is the diameter of the piston rod, which is 35 mm; m is the flow index, which is 1; s is the number of holes with different diameters; n is the number of holes; d i is the diameter of the small hole.

[0068] If the damping force is expressed as

[0069] F=c·v m (1.2)

[0070] Then the damping coefficient is:

[0071]

[0072] The calculated result is c=14107.61057Ns / m

[0073] Step 4: Set the boundary conditions of the fluid domain in Fluent. Set the outer surface medium of the fluid domain to water, the outer surface of the fluid domain to a wall, select the Ke realizable model for the turbulence model, and set the inlet and outlet pressures.

[0074] In Fluent, set the fluid domain medium to water. The specific parameters are shown in Table 2.

[0075] Table 2 Specific parameters of water medium in fluid domain

[0076] Temperature (K) Density (kg / m^3) Viscosity (kg / m·s) Specific heat (J / kg·K) Thermal conductivity (W / m·K) Molecular weight 293.15 998.2 1.003×10^-3 4182 0.599 18.02

[0077] At the same time, the outer surface of the fluid domain is set as wall to prevent the fluid from flowing out through the wall and affecting the accuracy of the simulation results. The turbulence model selects the Ke realizable model, which has good applicability for simulating the rotation of the valve. At the same time, the inlet is set as the pressure inlet with a pressure of 0.2MPa, and the outlet is set as the pressure outlet with a pressure of 0.1MPa. The solution method selects the Piso algorithm + skewness correction. This algorithm can prevent the generation of highly distorted grids during grid movement, further improving the accuracy of the simulation results. At the same time, this algorithm has good advantages for transient simulation calculations and small time steps. Specific boundary condition settings are shown in Table 3

[0078] Table 3 Specific boundary conditions of the fluid domain

[0079]

[0080]

[0081] Step 5: Solve the fluid domain and output the valve opening change curve over time and pressure data.

[0082] Specifically, the numerical simulation adopts a calculation method of steady-state simulation first and then transient simulation, in order to better conform to the actual situation when the valve moves. At the same time, the pressure field data obtained by the steady-state simulation is output so that it can be subsequently input into the water hammer model for water hammer pressure research. The pressure data is shown in Table 4. At the same time, the opening curve of the valve closing process under this working condition is output, as shown in Figure 4. Figure 4 shown.

[0083] Table 4 Pressure data and volume flow rate

[0084] name Mass average pressure fff-fluid 126717.13Pa name Volume flow rate outlet 1.3536m / s

[0085] Step 6: Establish a water hammer simulation model in COMSOL, and transform the valve opening versus time curve and import it into the water hammer model;

[0086] Furthermore, in step 6, the mass average pressure is used as the initial pressure of the water hammer simulation model, and the volume flow rate data is used as the initial flow rate of the water hammer simulation model;

[0087] Specifically, the input parameters are shown in Table 5. At the same time, the mass average pressure and volume flow rate data shown in Table 4 are filled in the corresponding positions in Table 5, which correspond to the initial pressure and initial flow rate of the water hammer model respectively. Figure 4 The valve opening variation curve shown is transformed and imported through the Comsol interpolation function as the boundary condition of the water hammer model outlet position.

[0088] Table 5 Input parameters of water hammer simulation model

[0089]

[0090]

[0091] Step 7: Set the water hammer model and boundary conditions: transform the curve of valve opening over time as the boundary condition of the water hammer model outlet position;

[0092] Set the outer surface medium of the fluid domain to water, the outer surface of the fluid domain to a wall, select the transient solver in the solver settings, and set the inlet and outlet pressures of the water hammer model.

[0093] like Figure 5 The figure shows a water hammer pipe model. The pipe is 20 m long, the coordinate origin is the inlet position, and a monitoring point is set at 11.15 m from the origin to measure the pressure and flow rate changes in the pipe. The Young's modulus of the pipe is 2.1E11 Pa, the pipe wall thickness is 19.5 mm, and the initial pressure and initial flow rate in the entire pipe are set to 1.2672E5 Pa and 10.772 m / s, respectively.

[0094] When the valve is closed, due to the compressibility of water and the elasticity of the pipe, a sharp pressure pulse is generated upstream of the valve. c Given by the following expression

[0095]

[0096] Where v s is the isentropic speed of sound in the bulk fluid (1481 m / s for water), while the second term is due to the elasticity of the tube wall. The water density is ρ, β A is the pipe cross-sectional compression coefficient, resulting in an effective wave velocity of 1037 m / s. The instantaneous closure of the valve will generate a water hammer pulse with an amplitude of P, which is given by the Joukowsky basic equation

[0097] P=ρv c u0 (1.5)

[0098] Where u0 is the average fluid velocity before the valve closes.

[0099] Figure 6 Shown is the meshing of the water hammer model, with the maximum element size set to L / N, the minimum element set to 1 mm, the maximum element growth rate to 1.5, the curvature factor to 0.6, and the narrow area resolution to 0.5.

[0100] Water hammer boundary condition setting, Figure 5 Point 1 is set as the pressure inlet with a pressure value of p0, and point 3 is set as the velocity outlet with a velocity value of the interpolation function imported in step 6.

[0101] In the solver setup, select the transient solver, set the output time step to range (0, 1e-3, 0.3), and set the solver time step to parameter dt. In order to make the transient solver better express the water hammer phenomenon, the pressure change during the time step dt cannot completely cross the grid unit. Here, the maximum change during dt is set to 10% of the moving grid length dx. In other words, the distance traveled by the pressure signal during dt, i.e., v c dt, must be smaller than the typical grid size dx. This can be achieved by imposing the following CFL number condition:

[0102]

[0103] Step 8: Use the water hammer model to perform numerical simulation to solve and output the water hammer pressure when the valve is closed and the corresponding pipeline pressure cloud map.

[0104] Specifically, here are the results of the numerical simulation of the water hammer model: the pressure cloud map, flow velocity cloud map and related curves of scheme a in Table 1 are selected for illustration. Figure 7 The pipeline pressure cloud diagram at the simulation time of 0.098s is selected. The maximum pressure at this time appears at the valve position, which is 6.8859MPa. This pressure is the maximum water hammer pressure generated in the pipeline during the valve closing process of scheme C. The specific pressure data is distributed along the pipeline as shown in the following figure. Figure 8 As shown in the figure.

[0105] Figure 9 and Figure 10 As shown in the figure, it is the pipeline velocity cloud at 0.098s. The velocity in the pipeline at this time is relatively low near the valve, mainly due to the obstruction after the valve is closed. At this time, the dynamic energy of the fluid is converted into pressure energy, causing the pressure near the valve to rise, resulting in water hammer phenomenon, causing a sudden increase in pressure. At the same time, Figure 7 The pressure cloud map corresponds exactly to its corresponding phenomenon.

[0106] Figure 11 and Figure 12 The following curve shows the pressure variation over time at different monitoring points during valve closure for Scheme A in Table 1. The water hammer pressure generated in the pipeline during the butterfly check valve closing process is 6.886 MPa. This curve clearly demonstrates the water hammer phenomenon in the pipeline during valve closing, providing a reference for evaluating valve water hammer resistance.

[0107] Currently, most research focuses on water hammer caused by terrain or accidents in long-distance pipelines. However, little attention has been paid to the water hammer pressure caused by different check valve operating conditions or due to different structures. On the one hand, compared to traditional experimental measurements, this method can provide far more detailed flow field characteristics than traditional experiments. On the other hand, compared to traditional numerical simulation methods, by outputting data such as the pipeline flow field pressure and closing characteristic curve during valve closing and importing it into the water hammer model to study pipeline water hammer pressure, it can more realistically and accurately demonstrate the changes in pipeline water hammer pressure during the check valve closing process. Its calculation accuracy is high, and the results are closer to actual operating conditions. This method is accurate, simple, and has certain versatility.

[0108] The present invention adopts the above technical solution and performs transient simulation of the closing process of the butterfly check valve under different conditions based on the Fluent numerical simulation software to obtain the flow field characteristics and closing characteristic curve of the closing process. At the same time, the output flow field pressure data and valve closing characteristic curve are imported into the Comsol water hammer model to perform numerical simulation calculation of water hammer pressure. This can more realistically calculate the water hammer pressure generated by the check valve closing process and provide an accurate method for calculating and simulating pipeline water hammer pressure during valve closing. The pipeline water hammer pressure calculation method proposed by the present invention can not only be used to calculate the pipeline water hammer pressure changes caused by the application of different external torque conditions or different structural parameters to the valve, but also has good applicability for calculating pipeline water hammer pressure changes of other types of valves. At the same time, this method can more intuitively display the changes in pipeline water hammer pressure by outputting the water hammer pressure and flow velocity cloud map in the pipeline at any time period of the entire pipeline.

[0109] The present invention calculates the water hammer pressure generated when the valve is closed based on the Fluent numerical simulation software combined with the Comsol water hammer model. This method is more in line with engineering practice than traditional theoretical calculation methods. At the same time, the methods and theories used have certain versatility for simulating water hammer of other types of valves and have good applicability for promotion in the engineering field.

[0110] Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of the present application is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

Claims

1. A method for calculating water hammer pressure in a pipeline during valve closing, characterized by: It includes the following steps: Step 1, constructing a three-dimensional geometric model of the butterfly check valve; Step 2: Add front and rear pipes according to the geometric model of the butterfly check valve, extract the fluid model, and perform hybrid structure meshing on the fluid model; Step 3, by adding different weight torques and damping torques, numerical simulation is performed on the water hammer generated when the valve is closed under different working conditions; Step 4: Set the boundary conditions of the fluid domain in Fluent; Step 5, solve the fluid domain and output the valve opening change curve over time and pressure data; Step 6: Establish a water hammer simulation model in COMSOL, and transform the valve opening versus time curve and import it into the water hammer model; Step 7: Set the water hammer model and boundary conditions; Step 8: Use the water hammer model to perform numerical simulation to solve and output the water hammer pressure when the valve is closed and the corresponding pipeline pressure cloud map.

2. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In step 1, based on the two-dimensional drawing of the butterfly check valve, the geometric modeling of the butterfly check valve is performed in the three-dimensional modeling software SOLIDWORKS; The geometric model is then imported into SpaceClaim to simplify the model in order to remove structural factors that affect the simulation results.

3. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In step 3, SpaceClaim is used to calculate the torque generated by the weight torque at the initial position on the valve shaft, and the damping coefficient is calculated based on the cylinder model parameters in the three-dimensional geometric model of the butterfly check valve.

4. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 3, characterized in that: The damping coefficient calculation formula is: Where, k is the viscosity coefficient; l is the length of the piston rod hole; D is the inner diameter of the cylinder; d is the diameter of the piston rod; m is the flow index; s is the number of groups of holes with different apertures; n is the number of holes; d i is the diameter of the small hole; c is the damping coefficient.

5. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In step 4, the outer surface medium of the fluid domain is set to water, the outer surface of the fluid domain is set to the wall, the turbulence model is selected as the K-erealizable model, and the inlet is set as the pressure inlet with a pressure of 0.2 MPa; the outlet is set as the pressure outlet with a pressure of 0.1 MPa; the solution method is selected as the Piso algorithm and skewness correction.

6. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In step 7, the mass average pressure is used as the initial pressure of the water hammer simulation model, and the volume flow rate data is used as the initial flow rate of the water hammer simulation model; the transient solver is selected in the water hammer model solver, and the inlet of the water hammer model is set as the pressure inlet, and the pressure magnitude is set as the initial pressure; the outlet of the water hammer model is set as the velocity outlet, and the valve opening change curve over time is transformed as the boundary condition of the velocity magnitude at the outlet position of the water hammer model.

7. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In the water hammer model solver of step 7, select the transient solver and set the solver time step to parameter dt. The pressure change during the time step dt cannot completely cross the grid unit. Here, the maximum change during dt is set to 10% of the moving grid length dx, that is, the distance traveled by the pressure signal during dt, that is, v c dt, which must be smaller than the typical grid size dx; this is obtained by imposing the following CFL number condition: Among them, v c Indicates the water hammer wave speed when the valve is closed in the water hammer model.

8. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 7, characterized in that: In the water hammer model, the water hammer wave velocity v is when the valve is closed. c is given by the following expression: Among them, v s is the isentropic sound speed in the bulk fluid, ρ is the water density, β A is the pipe cross-section compression coefficient.

9. The method for calculating water hammer pressure in a pipeline during valve closing according to claim 1, characterized in that: In the water hammer model in step 8, when the valve is closed, the instantaneous closing of the valve will generate a water hammer pulse with an amplitude P. The amplitude P is given by the Joukowsky basic equation: P=ρv c u0 (1.5) Where ρ is the water density; v c is the water hammer wave speed when the valve is closed; u0 is the average fluid velocity before the valve is closed.

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