Method and System for Constructing Simulation Model of Air Valve in Transient Flow Process of Water Transmission Pipeline

Abstract

This invention provides a method and system for constructing a simulation model of an air valve in a water pipeline during transient flow processes, belonging to the field of fluid mechanics. The method includes: first, determining the volume of the pipe sections on both sides of the air valve, defining the pipe section connection as a node, and acquiring the water volume of each pipe section in real time after air intake; then, determining the water column height of the boundary pipe section based on the ratio of water volume to volume, and calculating the pressure at the boundary node accordingly; further determining the flow rate at the boundary node, and then calculating the relationship between the air bladder volume and pressure; calculating the inlet and outlet mass flow rates of the air valve based on the air bladder pressure, and determining the air bladder mass through the relationship between the inlet volume and mass flow rate; finally, using the gas laws and the relationship between air bladder pressure, volume, and mass, solving for the real-time air bladder pressure using an iterative method, thereby determining the air bladder volume change and constructing a dynamic simulation model. This method proposes a new air valve model that synchronizes air bladder volume changes with boundary motion, more closely resembling the actual flow process.

Description

Technical Field

[0001] This invention relates to the field of fluid mechanics, specifically to a method and system for constructing a simulation model of an air valve during transient flow in a water pipeline. Background Technology

[0002] The installation of air valves is crucial in long-distance water transmission and urban water supply and drainage pipeline systems. They effectively expel air accumulated during operation, preventing flow drops and pressure fluctuations caused by air resistance. Simultaneously, they automatically draw in air when the pipeline is emptied or during sudden pump shutdowns, preventing pipeline collapse or equipment damage caused by negative pressure. Air valves are indispensable safety protection devices in pressure pipeline engineering. The accuracy of the air valve calculation model directly determines the reliability of hydraulic transient analysis and profoundly affects the effectiveness of predictive control schemes for pressure pipeline systems. An accurate mathematical model can precisely characterize the multiphase flow evolution during the opening and closing of the air valve, providing key parameter support for cavitation volume prediction, water hammer protection design, and system dynamic response simulation. Model errors can lead to distortion in gas-liquid two-phase flow simulation, causing water hammer protection failure, inaccurate pressure oscillation prediction, and consequently, excessive pipeline vibration or structural damage. Therefore, constructing a refined air valve calculation model is not only the technical foundation for intelligent control of pipeline systems but also a core element in ensuring the hydraulic stability of the pipeline network and preventing major operational accidents.

[0003] Air valves are indispensable water hammer protection devices in long-distance pressurized water transmission projects, mainly used for pipeline venting and negative pressure control. Under various pipeline operating conditions, such as pipeline filling, emergency maintenance, valve opening and closing (whether normal or abnormal), and pump start-up and shutdown (normal or emergency), properly installed air valves can not only expel harmful gases from the pipeline but also replenish air in time when negative pressure occurs, preventing liquid column separation and effectively avoiding water hammer accidents. Compared with pressure tanks and pressure regulating towers, air valves have the advantages of simple structure, low cost, and convenient installation, and are therefore widely used in long-distance water transmission projects. The air intake and exhaust characteristics of air valves are crucial for ensuring the safe operation of long-distance water transmission projects. Domestic and foreign scholars have conducted analysis and research on the mathematical model of air valves and achieved some research results. Wylie and Streeter proposed a mathematical model for the hydraulic calculation of air valves based on ideal gases; the four basic assumptions of subsonic inflow / outflow and sonic inflow / outflow are still in use today. Lee believed that the air entering the pipeline follows a polyhedral process, and based on this, he introduced a polyhedral exponent n, which is related to the heat exchange of the system and more accurately expresses the heat conduction characteristics of the compression and expansion of the gas entering the pipeline. Yang Xiaodong et al., combined with the situation that multiple air valves are often required for joint protection on long-distance pipelines in the application of air valves, used the equivalent pipeline method and the adjusted wave velocity method to complete the automatic segmentation in water hammer calculation, and combined it with the intake and exhaust mathematical model.

[0004] Traditional air valve models mostly adopt the following assumptions: (1) the gas entering the pipeline through the air intake and exhaust valve (hereinafter referred to as the air valve) always accumulates near the air valve and can be fully discharged when the water pressure increases; (2) the volume of gas in the pipeline is very small relative to that in the water body, and there is no slippage in the flow between the gas and water phases, etc. The traditional air valve model fixes the cavity on the grid node where the air valve is located, so even if the air intake exceeds the pipe section volume, it will not spread to the adjacent nodes. This results in the water level of the nodes without the air valve remaining unchanged, that is, the pressure does not change with the air intake of the air valve. For the case where the air intake does not exceed the unit pipe step volume, the impact is not significant. However, for the case where the continuous air intake is very large, or even when multiple pipe section nodes are emptied continuously, the cavity fixed model will produce a large error in calculating the pipeline pressure, and may even lead to an incorrect protection scheme. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method and system for constructing a simulation model of an air valve during transient flow in a water pipeline. This method proposes a novel air valve model that synchronizes the movement of the air valve boundary with the volume change of the air bladder, thus more closely reflecting the actual situation.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] A method for constructing a simulation model of an air valve during transient flow in a water pipeline, wherein the pipeline on both sides of the air valve is divided into multiple pipe segments, and the connection points of the pipe segments are defined as nodes; when air enters the air valve, the air column in the cavities on both sides is pressurized to generate an air bladder, and the pipe segment partially occupied by the air bladder is defined as a boundary pipe segment, and the node at the full water end of the boundary pipe segment is the boundary node of the air bladder. The method includes the following steps:

[0008] Determine the pipe volume of each pipe section on both sides of the air valve, and obtain the water volume of each pipe section in real time after the air valve is inlet;

[0009] Based on the ratio of water volume to pipe volume in the boundary pipe section, the water column height in the boundary pipe section is determined. Based on the airbag pressure and water column height, the boundary node pressures on both sides of the air valve are determined. The boundary node flow rate is determined based on the boundary node pressure. The airbag volume is determined based on the boundary node flow rate, thus obtaining the relationship between airbag pressure and airbag volume.

[0010] The mass flow rate of the air valve intake and exhaust is determined based on the air pressure. The mass of the airbag is determined based on the air intake volume of the left and right pipe sections after the air valve intake and the mass flow rate of the air valve intake and exhaust. The relationship between the airbag pressure and the airbag mass is obtained.

[0011] Based on the real-time water volume of each pipe section after the air valve is inlet, and based on the gas law equation and the relationship between airbag pressure, airbag volume and airbag mass, the real-time airbag pressure is determined by iterative method; based on the real-time airbag pressure, the real-time change of airbag volume is determined, and a dynamic simulation model of the air valve for simulating the movement of the airbag boundary is constructed.

[0012] Preferably, determining the water column height of the boundary pipe section based on the ratio of water volume to pipe volume includes the following steps:

[0013] Δ in each simulation period t At the end of the time, the water volume of all pipe sections is recorded. The boundaries on both sides of the airbag are determined by the ratio of the water volume of the pipe sections on both sides to the volume of the pipe sections. For pipe sections that are completely occupied by the airbag, the node position inside the airbag is recorded. The pipe sections that are partially occupied by the airbag are the boundary pipe sections. The node on the full water side of the boundary pipe section is the boundary node of the airbag.

[0014] In each Δ t At the end of the time interval, the water volume of all pipe segments is recorded. When the water volume of a pipe segment is zero, the left boundary pipe segment number expands outward from the airbag, and the cumulative airbag volume is... ;

[0015] If time Left airbag The volume lies between the sum of the volumes of all pipe segments from the air valve node to the nearest full water pipe segment on the left and the sum of the volumes of all pipe segments from the air valve node to the farthest empty pipe segment on the left, that is:

[0016] ;

[0017] In the formula, L This is the number of the left boundary pipe section. The pipe segment number indicating the location of the air valve;

[0018] Then in each At the end of the time interval, record the water volume of all pipe sections and the position of the boundary pipe sections on both sides of the airbag. The formula for determining the water column height of the boundary pipe sections is as follows:

[0019] ;

[0020] In the formula: This refers to the volume of the pipe section; This refers to the volume of the left airbag; The elevation difference between the two nodes of the left boundary pipe section;

[0021] The process for determining the water column height in the right boundary pipe section is the same as that in the left boundary pipe section.

[0022] Preferably, obtaining the relationship between airbag pressure and airbag volume includes the following steps:

[0023] After air is introduced through the air valve, the air intake volume to the left and right pipe sections is obtained respectively. Considering the water-air coupling effect, the flow rate equation and gas state equation at the air-water boundary nodes on both sides of the airbag are combined to obtain the volume of the airbag on both sides:

[0024] ;

[0025] In the formula: for The volume of the airbag at any given time; for The volume of the left airbag at any given time; for The volume of the right-side airbag at any given time; for Boundary flow rate at the left boundary node of the airbag at any given time; for Boundary flow rate at the right boundary node of the airbag at any given time; for Boundary flow rate at the left boundary node of the airbag at any given time; for Boundary flow rate at the right boundary node of the airbag at any given time;

[0026] For the boundary nodes on both sides of the airbag, the compatibility equation according to the method of characteristics is:

[0027] ;

[0028] ;

[0029] The flow equations for the boundary nodes are as follows:

[0030] ;

[0031] ;

[0032] ;

[0033] ;

[0034] ;

[0035] ;

[0036] ;

[0037] ;

[0038] In the formula: for t +Δ tThe pressure of the air bladder in the pipeline at all times; for t +Δt time: water column height in the left boundary tube section of the airbag; for t +Δ t The height of the water column in the right boundary tube section of the airbag at any given moment; for t +Δ t Hydraulic gradient at the left boundary node of the airbag at any given time; for t +Δ t Hydraulic gradient at the right boundary node of the airbag at any given moment; The elevation of the left boundary node of the airbag; The elevation of the right boundary node of the airbag; a The water hammer wave velocity; D This refers to the inner diameter of the pipe. A This refers to the cross-sectional area of ​​the pipeline through which water flows. f The coefficient of friction; Airbag pressure;

[0039] The equation for the airbag volume is obtained by solving the simultaneous equations:

[0040] .

[0041] Preferably, obtaining the relationship between airbag pressure and airbag mass includes the following steps:

[0042] According to the isentropic intake and exhaust principle of air valves, the expression for the mass flow rate of air flowing in and out is:

[0043] Air inflow:

[0044] when :

[0045] ;

[0046] when :

[0047] ;

[0048] Air outflow:

[0049] when :

[0050] ;

[0051] when :

[0052] ;

[0053] In the formula: for t The quality of the air at all times; for t +Δ t The quality of the air at all times; for t Quality flow rate at any given moment; for t +Δ t Quality flow rate at any given moment;

[0054] Then the airbag mass for:

[0055] .

[0056] Preferably, the gas law equation is:

[0057] ;

[0058] In the formula: for t +Δ t The pressure of the air bladder in the pipeline at all times; for t +Δ t The volume of the air bladder in the pipeline at any given time; for t +Δ t The mass of the airbag in the pipeline at all times; R is the gas constant of air; T is the absolute temperature.

[0059] This application also proposes a simulation model construction system for air valves during transient flow processes in water pipelines, the system comprising:

[0060] The data acquisition module is used to determine the volume of each pipe section on both sides of the air valve and to acquire the water volume of each pipe section in real time after the air valve is inlet.

[0061] The data analysis module is used to determine the water column height of the boundary pipe section based on the ratio of water volume to pipe volume, serving as the dynamic boundary equation for the airbag; determine the boundary node pressure based on the airbag pressure and water column height; determine the boundary node flow rate based on the boundary node pressure; determine the airbag volume based on the boundary node flow rate, obtaining the relationship between airbag pressure and airbag volume; determine the air valve inlet and outlet mass flow rate based on the airbag pressure; and determine the airbag mass based on the air intake volume of the pipe sections on both sides after the air valve intake and the air valve inlet and outlet mass flow rate, obtaining the relationship between airbag pressure and airbag mass.

[0062] The simulation module is used to determine the real-time airbag pressure by using the gas law equation and the relationship between airbag pressure, airbag volume and airbag mass, based on the real-time water volume of each pipe section after the air valve is inlet, and by using an iterative method. Based on the real-time airbag pressure, the module determines the real-time changes in airbag volume and constructs a dynamic simulation model of the air valve to simulate the movement of the airbag boundary.

[0063] This application also proposes a computer-readable storage medium storing a data processing program, which, when executed by a processor, implements the method for constructing a simulation model of an air valve during transient flow in a water pipeline.

[0064] This application also proposes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the method for constructing a simulation model of an air valve during transient flow in a water pipeline.

[0065] The beneficial effects of this invention are:

[0066] This invention proposes a method for constructing a simulation model of an air valve during transient flow in a water pipeline. The air valve model comprises three parts: impacting water, trapped air mass, and a water-air interface. It is solved using three equations: the air mass volume equation, the air mass dynamic boundary equation, and the air mass equation. This invention improves and designs a new air valve calculation model based on the aforementioned new calculation mode. The new model can determine the position and shape of the water-air interface by analyzing the movement of the air mass boundary based on the volume change of the air mass. The generated model can accurately simulate the changes in air mass volume and water-air interface position during the transient process of the air valve cavity. The simulated flow rate and pressure at the cavity boundary of each pipe section are also more reasonable than those of traditional air valve models. This makes the water hammer pressure calculated by the new model closer to the measured values ​​than those of traditional air valve models. The generated model can more reasonably and accurately simulate the pressure changes during the hydraulic transition process, correctly guiding the formulation of water hammer protection schemes. The generated model can more accurately simulate the changes in cavity position and volume over time, and can simulate the pipeline venting process and its venting time, providing guidance for pipeline system maintenance and drainage. Attached Figure Description

[0067] Figure 1 This is a flowchart of a method according to an embodiment of the present invention.

[0068] Figure 2 This is a diagram showing the arrangement of air valves according to an embodiment of the present invention.

[0069] Figure 3 This is a flowchart illustrating the calculation process of an embodiment of the present invention.

[0070] Figure 4This is a comparison diagram of pressure verification during the hydraulic transition process of a pipeline system in engineering practice, according to an embodiment of the present invention. Figure 4 (a) is the maximum hydraulic gradient line of the fixed air valve model. Figure 4 (b) Maximum hydraulic gradient line of the propagation air valve model, Figure 4 (c) Instantaneous hydraulic gradient at 1600s.

[0071] Figure 5 This is a comparison diagram of the air bladder volume at the air valve during the hydraulic transition process of a pipeline system according to an embodiment of the present invention. Figure 5 (a) The volume of the air bladder for air valve model 1 is fixed. Figure 5 (b) is the volume of the air bladder for air valve model 1. Figure 5 (c) The volume of the air bladder for air valve model #2 is fixed. Figure 5 (d) Propagation air valve model 2# air valve airbag volume.

[0072] Figure 6 This is a comparison diagram of flow rate and pressure at the pipeline end during the hydraulic transition process of the pipeline system according to an embodiment of the present invention. Figure 6 (a) is the terminal flow process line. Figure 6 (b) is the end pressure process line. Detailed Implementation

[0073] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0074] Example 1

[0075] This invention proposes a method for constructing a simulation model of an air valve during transient flow in a water pipeline. The method divides the pipeline on both sides of the air valve into multiple pipe segments, with the connection points of these segments defined as nodes. When air enters the air valve, the air column in the cavities on both sides pressurizes to generate an air bladder. The pipe segment partially occupied by the air bladder is defined as a boundary pipe segment, and the node at the full water end of the boundary pipe segment is designated as the boundary node of the air bladder. Specific steps are as follows: Figure 1 As shown, it includes:

[0076] S1: Determine the pipe volume of each pipe section on both sides of the air valve, and obtain the water volume of each pipe section after the air valve enters in real time.

[0077] S2: Determine the water column height of the boundary pipe section based on the ratio of water volume to pipe volume, which serves as the dynamic boundary equation for the airbag; determine the boundary node pressures on both sides of the air valve based on the airbag pressure and water column height; determine the boundary node flow rate based on the boundary node pressure; determine the airbag volume based on the boundary node flow rate, thus obtaining the relationship between airbag pressure and airbag volume.

[0078] S3: Determine the air valve intake and exhaust mass flow rate based on the airbag pressure. Determine the airbag mass based on the intake volume of the left and right pipe sections after the air valve intakes and the air valve intake and exhaust mass flow rate, and obtain the relationship between airbag pressure and airbag mass.

[0079] S4: Based on the real-time water volume of each pipe section after the air valve is inlet, and based on the gas law equation and the relationship between airbag pressure, airbag volume and airbag mass, the real-time airbag pressure is determined by the iterative method; based on the real-time airbag pressure, the real-time change of airbag volume is determined, and a dynamic simulation model of the air valve for simulating the movement of the airbag boundary is constructed.

[0080] The air valve model of this invention comprises three parts: impacting water, trapped air mass, and water-air interface. Node recording parameters include pressure and flow rate; pipe segment recording parameters include water volume, water level, pipe segment volume, and pipe segment number. The calculation parameters involved include airbag pressure, airbag volume, airbag mass, water column height in the boundary pipe segment, and boundary node pressure. The air valve is divided into left-side and right-side airbag volumes, with the node where the air valve is located as the boundary. The airbag volume is calculated based on the flow rates at the left and right boundary nodes, respectively. The boundary node flow rate is determined by the boundary node pressure, which is the airbag pressure plus the water column height in the boundary pipe segment, and is subsequently affected by the airbag pressure. The airbag mass is determined by the air valve's inlet and outlet mass equations, and the inlet and outlet mass flow rates are affected by the airbag pressure. Therefore, during the inlet and outlet processes, the airbag pressure constantly affects the airbag volume, airbag mass, and the pressures at both boundary nodes. To accurately solve these coupled calculation parameters, an air valve calculation model needs to be established based on different airbag pressures, satisfying the mass conservation equation, continuity equation, momentum equation, and gas state equation. The full-water pipe section was calculated using the traditional method of characteristics (MOC), and the calculation model of the air valve and the dynamic equations of the airbag boundary were solved simultaneously. Figure 2 Provide explanations and descriptions of the model.

[0081] Figure 2An air valve is located at node 4. After a sustained negative pressure occurs at node 4, the air valve begins to introduce air, and the air bladder spreads to both sides of the downcomer pipe sections. Pipe sections P3, P4, and P5 are completely occupied by air, forming a continuous, large-volume air bladder. Pipe sections P2 and P6 are partially occupied by the air bladder. The node at the water-filled end of the boundary pipe section is designated as the boundary node of the air bladder; that is, the left boundary of the air bladder is node 2, and the right boundary is node 7. The hydraulic gradient of node 2 is calculated as: air bladder pressure + vertical height difference between the water column in the pipe section and node 2 + elevation of node 2. Similarly, the hydraulic gradient of node 7 is... .

[0082] Among them, superscript characters L , R Indicates left and right, subscript i Indicates time t , i+ 1 represents the next moment, i.e. ; The absolute pressure of the airbag. The vertical height of the water column. This represents the location elevation.

[0083] The air inside the pipe obeys the gas law:

[0084] (1);

[0085] In the formula: for Pressure (Pa) in the air bladder in the pipeline at any given time; for The volume (m³) of the air bladder in the pipeline at any given time; for Mass of the airbag in the pipeline at any given time (kg); is the gas constant for air, with a value of 287 (J / (kg·K)); The absolute temperature is 293.5 K, and the water temperature in the model pipe is 20 °C.

[0086] See the calculation process. Figure 3 .

[0087] Node recording parameters include pressure and flow rate; pipe segment recording parameters include water volume, water level, pipe segment volume, and pipe segment number. The model consists of three parts: airbag volume equation, airbag dynamic boundary equation, and airbag mass equation.

[0088] Airbag volume equation:

[0089] After air is introduced through the air valve, the air volume introduced into the left and right pipe sections is recorded respectively. Considering the water-air coupling effect, the flow rate equation and gas state equation are established simultaneously at the air-water boundary nodes on both sides of the airbag to obtain the volume of the airbag on both sides. The airbag volume at the current moment is expressed as... The calculation equation is as follows:

[0090] (2);

[0091] In the formula: for The volume of the airbag at any given time (m³); for The volume (m³) of the left airbag at any given time.

[0092] for Volume of the right airbag at any given time (m³); for Boundary flow rate (m³ / s) at the left boundary node of the airbag at any given time. for Boundary flow rate (m³ / s) at the right boundary node of the airbag at any given time. for Boundary flow rate (m³ / s) at the left boundary node of the airbag at any given time. for Boundary flow rate (m³ / s) at the right boundary node of the airbag at any given time.

[0093] For the boundary nodes on both sides of the airbag, according to the compatibility equation of the method of characteristics:

[0094] (3);

[0095] (4);

[0096] The flow equations for the boundary nodes can be obtained as follows:

[0097] (5);

[0098] (6);

[0099] (7);

[0100] (8);

[0101] (9);

[0102] (10);

[0103] (11);

[0104] (12);

[0105] In the formula: The pressure (m) of the air bladder in the pipeline at time t+Δt; The height of the water column (m) in the left boundary tube section of the airbag at time t+Δt. The height of the water column (m) in the right boundary tube section of the airbag at time t+Δt. Let t+Δt be the hydraulic gradient (m) of the left boundary node of the airbag at time t+Δt. Let t+Δt be the hydraulic gradient (m) of the right boundary node of the airbag at time t+Δt. The elevation (m) of the left boundary node of the airbag; The elevation (m) of the right boundary node of the airbag; a The water hammer wave velocity (m / s); D Pipe inner diameter (m) 2 A is the cross-sectional area of ​​the pipe (m²). 2 f is the friction coefficient (N·s / m²).

[0106] Solving equations (2) to (12) simultaneously, we obtain the airbag volume equation:

[0107] (13);

[0108] The airbag volume equation (13) only contains airbag pressure. Unknown.

[0109] Airbag dynamic boundary equations;

[0110] At the end of each Δt time, the water volume of all pipe segments is recorded. The boundaries on both sides of the airbag are determined by the ratio of the water volume of the pipe segments on both sides to the volume of the pipe segments. For pipe segments completely occupied by the airbag, the node positions inside the airbag are recorded. The pipe segments partially occupied by the airbag are identified as boundary pipe segments. The nodes on the full water side of the boundary pipe segment are the boundary nodes of the airbag.

[0111] The airbag boundary always satisfies the continuity equation and the pressure balance equation. For the boundary segment, its location is determined by… and Sure, Combination Figure 2 The method for determining the numbering of the left boundary pipe segment is as follows:

[0112] At the end of each Δt time step, the water volume of all pipe segments is recorded. When the water volume of a pipe segment is zero, the boundary pipe segment numbering expands outward from the airbag, and the cumulative airbag volume is... Where L is the number of the left boundary pipe segment, This is the pipe segment number where the air valve is located. If at time... Left airbag The volume lies between the sum of the volumes of all pipe segments from the air valve node to the nearest full water pipe segment on the left and the sum of the volumes of all pipe segments from the air valve node to the farthest completely empty pipe segment on the left, where the specific location of the water-air boundary node on the left is.

[0113] (14);

[0114] Each At the end of each time step, record the water volume of all pipe sections and the positions of the boundary pipe sections on both sides of the airbag. The formula for determining the water column height of the boundary pipe sections is as follows:

[0115] (15);

[0116] In the formula: The volume of the pipe section is (m³). The volume of the left airbag is (m³). The elevation difference (m) between the two nodes of the left boundary pipe segment is given by equation (14) and equation (15) are the dynamic boundary equations of the airbag.

[0117] Airbag mass equation

[0118] Based on the isentropic intake and exhaust principle of air valves, the expression for the mass flow rate of air flowing in and out is shown below.

[0119] Air inflow:

[0120] when :

[0121] (16);

[0122] when :

[0123] (17);

[0124] Air outflow:

[0125] when :

[0126] (18);

[0127] when :

[0128] (19);

[0129] In the formula: Let t be the mass of air at time t (kg). Let t be the mass of air (kg) at time t+Δt. Let t be the mass flow rate (kg / s) at time t. Let be the mass flow rate (kg / s) at time t+Δt.

[0130] At this time, the airbag mass for:

[0131] (20);

[0132] Substituting (16) to (19) into the airbag mass equation (20), only the airbag pressure... The parameter is unknown.

[0133] Solving the simultaneous equations of the gas law (1), the gas volume equation (13), the airbag dynamic boundary equation (14) and (15), and the airbag mass equation (20), only the airbag pressure is considered. The parameters are unknown. The airbag pressure is obtained by solving the problem using an iterative method. The relevant parameters with airbag pressure as the variable are also readily solved.

[0134] In this embodiment:

[0135] Taking a pressure water pipeline project as an example, the established air valve model is validated. The total length of the pipeline is 4144.36m, with the initial water tank level at 113.5m and the final water tank level at 95m. Two high points are located along the route: High Point 1 is located at chainage K1+005, elevation 149.52m; High Point 2 is located at chainage K2+215, elevation 151.266m. The pipeline uses DN500 steel pipe with a wall thickness of 10mm. The water pump has a rated flow rate of 0.3m³ / s, a rated head of 52m, a rated speed of 1480r / min, a power of 180kW, and an efficiency of 87%. The simulated operating condition is a power outage and pump shutdown, with a slow-closing hydraulically controlled butterfly valve installed at the pump outlet. The valve uses a two-stage closing mechanism: the first stage is a rapid closure to 78% (i.e., valve plate angle 70°), and the second stage is a slow closure to complete closure. This invention selects two steady-state flow rates (0.3 m³ / s and 0.2 m³ / s) and two valve closing time schemes (5s rapid closing to 78% opening, 30s full closing, and 30s rapid closing to 78% opening, 120s full closing) for combined calculations, resulting in four operating conditions. The calculation results are shown below. Wherein, 0.2Q represents a steady-state flow rate of 0.2 m³ / s, 0.3Q represents a steady-state flow rate of 0.3 m³ / s, 30s represents the "5s rapid closing, 30s full closing" valve closing scheme, and 120s represents the "30s rapid closing, 120s full closing" valve closing scheme. The simulation results of the fixed air valve model are obtained from calculations using a certain internationally recognized software.

[0136] (1) Envelope results of the hydraulic transient process during pump shutdown

[0137] A comparison of calculations of the hydraulic transient process using different air valve models after pump shutdown, such as... Figure 4 As shown. Figure 4 As shown in (a), the hydraulic transition process after pump shutdown was calculated using a fixed air valve model. In all operating conditions, air valve #1 (K1+005) experienced water column closure, with the maximum pressure exceeding 1.5 times the normal operating pressure at the pump outlet (52.02m), which does not meet the specifications. Figure 4 (c) As shown in the hydraulic gradient line 1600 seconds after the pump stops, with the valve at the end of the pipeline open, water continuously flows out of the pipeline from the higher point due to gravity, causing the air valve to continuously intake air. However, the water level in the pipeline on both sides of the air valve does not drop. Clearly, this result does not match the actual situation. Figure 4 As shown in (b), using the propagation air valve model, during the hydraulic transition, air valve #1 only showed slight closing at 0.2Q30s, with a maximum pressure of 75.028m, which did not exceed 1.5 times the normal operating pressure (52.02m). Under other operating conditions, the maximum pipeline pressure was the steady-state pressure, i.e., 52.02m. Because the valve at the end of the pipeline was not closed, the pipeline emptied approximately 1600s after the pump was stopped. Figure 4 As shown in (c), the hydraulic gradient line of the venting section decreases to the pipeline elevation.

[0138] The fundamental reason for the inaccuracy of the fixed air valve model lies in the simplification assumptions that lead to incorrect simulation of the air bladder boundary. Because the water level in the fixed air valve model remains constant and does not decrease with air intake, the water flowing back upstream always accelerates at the pressure corresponding to this fixed high water level, ultimately resulting in a huge pressure surge. Furthermore, due to its fixed water level, it cannot simulate the phenomenon of pipe cavitation. The improved propagation air valve model, on the other hand, can accurately and dynamically track water level changes, thus avoiding unrealistic pressure peaks. It can also accurately simulate the phenomenon of pipe cavitation.

[0139] (2) Changes in the volume of the air bladder at the air valve during the hydraulic transition process

[0140] like Figure 5 As shown in (a), in the fixed air valve model, the volume of the air bladder at air valve #1 increases with the increase of steady-state flow rate and valve closing time. However, under all operating conditions, regardless of the intake air volume, water column closure will eventually occur. This is also the reason why the transient pressure increases under various operating conditions. Figure 5As shown in (b), the volume of the air bladder at air valve #1 in the propagating air valve model increases with the steady-state flow rate and valve closing time. However, except for the 0.2Q30s condition, the air bladder is not completely emptied, meaning no water column closure occurs. This is because the air bladder boundary in the improved propagating air valve model can move freely, and the water level changes dynamically. As air enters at the second high point, the water level gradually decreases, and the flow rate of water flowing back to the first high point gradually decreases, ultimately preventing closure at the first high point. While water column closure occurs in the 0.2Q30s condition, the pressure fluctuation amplitude is significantly lower than in the fixed air valve model due to the dynamic boundary and water level changes. This avoids the situation in the fixed air valve model where, due to the fixed water level, the water at the second high point always maintains a high flow rate, resulting in multiple unrealistic and violent water column closures.

[0141] like Figure 5 (c) The air bladder volume change curve at air valve #2 shows that the air bladder volume in the fixed air valve model increases infinitely, exceeding the pipe's volume, which is clearly inconsistent with reality. This is because the air bladder boundary and water level in the fixed air valve model remain constant and cannot dynamically change with end-point drainage and air valve intake. Figure 5 (d) The propagating air valve model, as the downstream water level drops, gradually stops air intake after all the water in the downstream pipeline has been drained, realistically simulating the coordinated process of air valve intake and water level drop during gravity-driven drainage. Furthermore, since air valve #2 is located at the highest point of the entire pipeline, its intake blocks most pressure fluctuations; therefore, changes in steady-state flow velocity and valve closing time have almost no impact on the downstream pipeline. This phenomenon is reflected in the simulation results of both the propagating air valve model and the fixed air valve model.

[0142] (3) Comparison of terminal flow rate and pressure

[0143] like Figure 6 (a) It can be seen that after the pump stops, the end valve is not closed. As the pipeline empties, the water level in the fixed air valve model cannot change dynamically, resulting in a constant flow rate and pressure at the end of the pipeline. This is inconsistent with reality, and the fixed air valve model cannot simulate the drainage process. Figure 6 (b) As can be seen, using the propagating air valve model, as water is released from the end of the pipeline, the air intake of the air valve gradually increases, and the water level gradually decreases. Simultaneously, the pressure and flow rate at the end of the pipeline also gradually decrease with the dynamic changes in water level. When the pressure drops to 0, it indicates that the pipeline has emptied. The pressure and flow rate changes at the end of the pipeline are not linear but are affected by the pipeline slope, and the rate of change of water level also changes dynamically. The propagating air valve model can accurately simulate this process. It can also accurately predict the time it takes for the water to empty from the pipeline; in this case, the time for the water to empty from the end of the pipeline is approximately 1600 seconds under all operating conditions.

[0144] The engineering example shows that during the hydraulic transition process after a simulated pump shutdown, the maximum water hammer pressure calculated using the fixed air valve model exhibited a significant pressure increase under different operating conditions, exceeding 1.5 times the normal operating pressure at the pump outlet. This does not meet the specifications and requires additional water hammer protection equipment. However, when using the propagating air valve model, only a small pressure increase occurred under certain operating conditions (such as 0.2Q30s), and the maximum pressure remained below the specification limit. The maximum pressure under all other operating conditions was a steady-state pressure, meeting the specifications and requiring no additional water hammer protection equipment. Furthermore, there were no requirements regarding the switching pressure between the large and small exhaust ports of the air valve.

[0145] The fixed air valve model, due to its simplified assumptions that result in a fixed air bladder boundary and water level, exhibits significant errors in several aspects, including the envelope, pressure and flow rate, and air valve inlet and outlet volumes, when simulating the hydraulic transition process after a pump shutdown and the venting conditions. This could mislead engineering protection designs. The propagating air valve model, by dynamically tracking changes in the air bladder boundary and water level, more realistically simulates the entire process of gas propagation, water column movement, and venting. Its calculation results have higher reliability and engineering application value.

[0146] By comparing and verifying the calculation results of the two air valve models under different steady-state flow rates and different valve closing times, it can be seen that the propagation air valve model exhibits good stability and applicability under various operating conditions, and the variation law of the calculation results is consistent with the physical process.

[0147] The above is an embodiment of the method for constructing a simulation model of an air valve during transient flow in a water pipeline. Based on the same idea, this embodiment also provides a corresponding system for constructing a simulation model of an air valve during transient flow in a water pipeline. Specific limitations of the system for constructing a simulation model of an air valve during transient flow in a water pipeline can be found in the limitations of the method for constructing a simulation model of an air valve during transient flow in a water pipeline described above, and will not be repeated here. Each module in the above-described system for constructing a simulation model of an air valve during transient flow in a water pipeline can be implemented entirely or partially through software, hardware, or a combination thereof. Each module can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0148] This embodiment also provides a computer-readable storage medium storing a computer program that can be used to execute the above-described... Figure 1 A method for constructing a simulation model of an air valve during transient flow in a water pipeline is provided.

[0149] Those skilled in the art will understand that implementing all or part of the processes in the above embodiments can be accomplished by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical storage, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0150] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing an air valve simulation model in transient flow of a water delivery pipeline, wherein a pipeline on both sides of an air valve is divided into multiple pipe sections, and a connection of the pipe sections is defined as a node; when the air valve is filled with air, an air column in a cavity on both sides of the air valve is pressurized to form an air bag, a pipe section occupied by the air bag is defined as a boundary pipe section, and a node at a full water end of the boundary pipe section is defined as a boundary node of the air bag, characterized in that, The method includes the following steps: Determine the pipe volume of each pipe section on both sides of the air valve, and obtain the water volume of each pipe section in real time after the air valve is inlet; The water column height of the boundary pipe section is determined based on the ratio of water volume to pipe volume, serving as the dynamic boundary equation for the airbag. The boundary node pressure is determined based on the airbag pressure and water column height. The boundary node flow rate is determined based on the boundary node pressure. The airbag volume is determined based on the boundary node flow rate, thus obtaining the relationship between airbag pressure and airbag volume. The mass flow rate of the air valve intake and exhaust is determined based on the air pressure. The mass of the airbag is determined based on the air intake volume of the left and right pipe sections after the air valve intake and the mass flow rate of the air valve intake and exhaust. The relationship between the airbag pressure and the airbag mass is obtained. Based on the real-time water volume of each pipe section after the air valve is inlet, and based on the gas law equation and the relationship between airbag pressure, airbag volume and airbag mass, the real-time airbag pressure is determined by iterative method; based on the real-time airbag pressure, the real-time change of airbag volume is determined, and a dynamic simulation model of the air valve for simulating the movement of the airbag boundary is constructed.

2. The method for constructing a simulation model of an air valve during transient flow in a water pipeline according to claim 1, characterized in that, Determining the water column height of the boundary pipe section based on the ratio of water volume to pipe volume includes the following steps: Δ in each simulation period t At the end of the time, the water volume of all pipe sections is recorded. The boundaries on both sides of the airbag are determined by the ratio of the water volume of the pipe sections on both sides to the volume of the pipe sections. For pipe sections that are completely occupied by the airbag, the node position inside the airbag is recorded. The pipe sections that are partially occupied by the airbag are the boundary pipe sections. The node on the full water side of the boundary pipe section is the boundary node of the airbag. In each Δ t At the end of the time interval, the water volume of all pipe segments is recorded. When the water volume of a pipe segment is zero, the left boundary pipe segment number expands outward from the airbag, and the cumulative airbag volume is... ; If time Left airbag The volume lies between the sum of the volumes of all pipe segments from the air valve node to the nearest full water pipe segment on the left and the sum of the volumes of all pipe segments from the air valve node to the farthest empty pipe segment on the left, that is: ； In the formula, L This is the number of the left boundary pipe section. The pipe segment number indicating the location of the air valve; Then in each At the end of the time interval, record the water volume of all pipe sections and the position of the boundary pipe sections on both sides of the airbag. The formula for determining the water column height of the boundary pipe sections is as follows: ； In the formula: This refers to the volume of the pipe section; This refers to the volume of the left airbag; The elevation difference between the two nodes of the left boundary pipe section; The process for determining the water column height in the right boundary pipe section is the same as that in the left boundary pipe section.

3. The method for constructing a simulation model of an air valve during transient flow in a water pipeline according to claim 1, characterized in that, Obtaining the relationship between airbag pressure and airbag volume includes the following steps: After air is introduced through the air valve, the air intake volume to the left and right pipe sections is obtained respectively. Considering the water-air coupling effect, the flow rate equation and gas state equation at the air-water boundary nodes on both sides of the airbag are combined to obtain the volume of the airbag on both sides: ； In the formula: for The volume of the airbag at any given time; for The volume of the left airbag at any given time; for The volume of the right-side airbag at any given time; for Boundary flow rate at the left boundary node of the airbag at any given time; for Boundary flow rate at the right boundary node of the airbag at any given time; for Boundary flow rate at the left boundary node of the airbag at any given time; for Boundary flow rate at the right boundary node of the airbag at any given time; For the boundary nodes on both sides of the airbag, the compatibility equation according to the method of characteristics is: ； ； The flow equations for the boundary nodes are as follows: ； ； ； ； ； ； ； ； In the formula: for t +Δ t The pressure of the air bladder in the pipeline at all times; for t +Δt time: water column height in the left boundary tube section of the airbag; for t +Δ t The height of the water column in the right boundary tube section of the airbag at any given moment; for t +Δ t Hydraulic gradient at the left boundary node of the airbag at any given time; for t +Δ t Hydraulic gradient at the right boundary node of the airbag at any given moment; The elevation of the left boundary node of the airbag; The elevation of the right boundary node of the airbag; a The water hammer wave velocity; D This refers to the inner diameter of the pipe. A This refers to the cross-sectional area of ​​the pipeline through which water flows. f The coefficient of friction; Airbag pressure; The equation for the airbag volume is obtained by solving the simultaneous equations: 。 4. The method for constructing a simulation model of an air valve during transient flow in a water pipeline according to claim 1, characterized in that, Obtaining the relationship between airbag pressure and airbag mass includes the following steps: According to the isentropic intake and exhaust principle of air valves, the expression for the mass flow rate of air flowing in and out is: Air inflow: when : ； when : ； Air outflow: when : ； when : ； In the formula: for t The quality of the air at all times; for t +Δ t The quality of the air at all times; for t Quality flow rate at any given moment; for t +Δ t Quality flow rate at any given moment; Then the airbag mass for: 。 5. The method for constructing a simulation model of an air valve during transient flow in a water pipeline according to claim 1, characterized in that, The gas law equation is: ； In the formula: for t +Δ t The pressure of the air bladder in the pipeline at all times; for t +Δ t The volume of the air bladder in the pipeline at any given time; for t +Δ t The mass of the airbag in the pipeline at all times; is the gas constant of air; T is the absolute temperature.

6. A system for constructing a simulation model of an air valve during transient flow in a water pipeline, characterized in that the system... include: The data acquisition module is used to determine the volume of each pipe section on both sides of the air valve and to acquire the water volume of each pipe section in real time after the air valve is inlet. The data analysis module is used to determine the water column height of the boundary pipe section based on the ratio of water volume to pipe volume, serving as the dynamic boundary equation for the airbag; determine the boundary node pressure based on the airbag pressure and water column height; determine the boundary node flow rate based on the boundary node pressure; determine the airbag volume based on the boundary node flow rate, obtaining the relationship between airbag pressure and airbag volume; determine the air valve inlet and outlet mass flow rate based on the airbag pressure; and determine the airbag mass based on the air intake volume of the pipe sections on both sides after the air valve intake and the air valve inlet and outlet mass flow rate, obtaining the relationship between airbag pressure and airbag mass. The simulation module is used to determine the real-time airbag pressure by using the gas law equation and the relationship between airbag pressure, airbag volume and airbag mass, based on the real-time water volume of each pipe section after the air valve is inlet, and by using an iterative method. Based on the real-time airbag pressure, the module determines the real-time changes in airbag volume and constructs a dynamic simulation model of the air valve to simulate the movement of the airbag boundary.

7. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a data processing program, which, when executed by a processor, implements the method for constructing a simulation model of an air valve during transient flow in a water pipeline as described in any one of claims 1 to 5.

8. A computer device, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the method for constructing a simulation model of an air valve during transient flow in a water pipeline as described in any one of claims 1 to 5.

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