Method for accurately determining the structure size of a water hammer protection device

Abstract

The application provides a method for accurately determining the structural size of a water hammer protection device, comprising the following steps: 1, initially determining the size parameters of the water hammer elimination tank; 2, simplifying the water flow in the water hammer elimination tank into one-dimensional flow to form a two-node mathematical model of the water hammer elimination tank; 3, performing initial value calculation of the water hammer elimination tank; 4, performing transient process solution of the water hammer elimination tank; 5, if the minimum pressure H min of the water supply system along the pipeline does not satisfy 0<H c , then the volume of the water hammer elimination tank is modified, and steps 2-4 are repeated until 0<H min . c < threshold value, then the volume of the water hammer elimination tank is modified, and steps 2-4 are repeated until 0<H min . c

Description

Technical Field

[0001] This invention relates to a method for accurately determining the structural dimensions of a water hammer protection device, and more particularly to a method for accurately determining the structural dimensions of a water hammer protection device based on the concept of virtual water level. The water hammer protection device includes a water hammer elimination box and other gas-liquid two-phase water hammer protection devices with air valves. Background Technology

[0002] With the acceleration of urbanization in my country, solving urban water supply issues through inter-regional and inter-basin water transfer projects is an inevitable development trend. Water transfer projects involve long pipelines that are susceptible to various factors, exhibiting significant fluctuations and complex variations. This makes them prone to water hammer accidents, resulting in phenomena such as air intake, water column separation, and water hammer caused by flow interruption, seriously threatening the safe operation of the entire system. In practical engineering, water hammer protection equipment is typically used to ensure the safety of the water transfer system.

[0003] As a water hammer protection device, the water hammer suppression box replenishes water to the supply pipeline through a connecting pipe during negative water hammer, while an air valve simultaneously injects air into the suppression box to form an air cushion, effectively preventing water column separation. During positive water hammer, water in the supply pipeline flows back to the suppression box, and the air valve vents air, protecting against positive water hammer. This device does not rely on mechanical parts, ensuring reliable performance. Furthermore, the water inside the box is automatically replenished, effectively preventing freezing. In addition, the water hammer suppression box offers a significant price advantage and is suitable for water hammer protection in large-scale water conveyance projects.

[0004] When using a water hammer suppression box for water hammer protection, it is necessary to determine the appropriate structural dimensions. If the suppression box is too small, it will not be effective in protecting against water hammer, while a large size will increase costs. Generally, numerical calculation methods are used to determine the structural dimensional parameters.

[0005] The flow within the water hammer elimination box involves the conversion between single-phase flow and gas-liquid two-phase flow. Furthermore, the air valve, elimination box, connecting pipe, and water supply pipe interact with each other, making the mathematical model complex and the program difficult to develop. Currently, there is no calculation method specifically for this problem, so the structural parameters of the water hammer elimination box are difficult to determine. Summary of the Invention

[0006] The purpose of this invention is to provide a method for accurately determining the structural dimensions of a water hammer protection device, reducing the volume of the elimination tank while ensuring its water hammer protection function. To this end, this invention adopts the following technical solution:

[0007] A method for accurately determining the structural dimensions of a water hammer protection device, characterized by comprising the following steps:

[0008] Step 1: Initially determine the various dimensional parameters of the water hammer elimination box, including the length, cross-sectional area, and height of the water hammer elimination box. Also determine the flow characteristic parameters of the water hammer elimination box, including the axial flow loss coefficient, the loss coefficient of the front connecting pipe, the loss coefficient of the rear connecting pipe, the opening area and flow coefficient of the inflow air valve, the opening area and flow coefficient of the outflow air valve, the loss coefficient of the water supply pipe between the front and rear connecting pipes, and the length and loss coefficient of the water supply pipe between the two connecting pipes. The front and rear connecting pipes are both connected between the water hammer elimination box and the water supply pipe, and the front connecting pipe is located upstream of the rear connecting pipe.

[0009] Step 2: Simplify the water flow in the water hammer elimination box into a one-dimensional flow to form a two-node mathematical model of the water hammer elimination box. The two nodes of the water hammer elimination box are the intersection of the two connecting pipes of the water hammer elimination box and the water supply pipe.

[0010] Step 3: Calculate the initial values ​​for the water hammer elimination box;

[0011] Step 4: Solve the transient process of the water hammer elimination box;

[0012] Step 5, if the lowest pressure H along the water supply system... min With system pressure control value H c Not satisfied with 0 <H min -H c If the threshold is exceeded, modify the water hammer elimination tank volume and repeat steps 2-4 until the threshold is reached. <H min -H c <threshold.

[0013] Furthermore, the method also includes step 6: applying the obtained parameters to the water hammer elimination tank volume setting.

[0014] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions:

[0015] Step 2, which describes the specific steps for establishing the mathematical model of the water hammer elimination box, includes:

[0016] Step 2.1, introduce the concept of virtual water level, the virtual water level corresponding to section A1 where the connecting pipe before the water hammer elimination box is located: H L1 =H n1 +k w1 Q w1 |Q w1 |+H atm -H a The virtual water level corresponding to section A2, where the connecting pipe after the water hammer elimination box is located: H L2 =H n2 +k w2 Q w2 |Qw2 |+H atm -H a ;

[0017] In the formula, k w1 and k w2 H represents the loss coefficients of the front and rear connecting pipes, respectively. n1 H represents the pressure at the junction of the connecting pipe and the water supply pipe. n2 H is the pressure at the junction of the downstream connecting pipe and the water supply pipe. a H represents the air cushion pressure. atm For atmospheric pressure, Q w1 and Q w2 These are the flow rates of the front and rear connecting pipes, respectively.

[0018] Step 2.2, according to the continuity equation, the flow rates of the upstream and downstream connecting pipes satisfy...

[0019]

[0020] In the formula, V a This refers to the volume of the air cushion.

[0021] Step 2.3: Based on the energy equation required for water flow to eliminate water hammer in the tank, the relationship between the virtual water level and the flow rate in the connecting pipe is obtained.

[0022]

[0023] In the formula, A w1 and A w2 The cross-sectional areas of water passages at sections A1 and A2 are respectively, H w For head loss, H m For inertial head;

[0024] Step 2.4: Based on the energy equation, obtain the relationship between the flow rate and the node pressure in the water supply pipe between the upstream and downstream connecting pipes.

[0025]

[0026] In the formula, k p Let L be the loss coefficient of the water supply pipe between the front and rear connecting pipes, L be the length of the water supply pipe between the front and rear connecting pipes, A be the cross-sectional area of ​​the water supply pipe, and Q be the flow rate of the water supply pipe between the front and rear connecting pipes.

[0027] The specific steps for calculating the initial value of the water hammer elimination tank in step 3 are as follows:

[0028] Initially, the flow inside the water hammer elimination tank is a single-phase flow, satisfying the following relationship:

[0029] Air cushion volume Va =0

[0030] Air cushion pressure H a =H atm

[0031] Water hammer elimination tank head loss H w =k w Q w2 |Q w2 |,k w The coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber;

[0032] Water hammer elimination box inertial head H m =0

[0033] Water supply pipeline flow rate change rate

[0034] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method.

[0035] The specific steps for solving the transient process described in step 4 are as follows:

[0036] Step 4.1: Introduce a virtual water level to solve for the intermediate variable H. L1 0 H L2 0 Both are equal to the virtual water level H at the previous moment. L1 (N-1) H L2 (N-1) ;

[0037] Step 4.2, if H is satisfied L1 0 ≥Z T And H L2 0 ≥Z T In the formula Z T If the current value is the height of the container, then it is assumed that the current flow is single-phase and proceed to step 4.3; otherwise, it is a two-phase flow and proceed to step 4.4.

[0038] Step 4.3, under single-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship:

[0039] Air cushion volume V a =0

[0040] Air cushion pressure H a =H atm

[0041] Water hammer elimination tank head loss H w =k w Q w2 |Qw2 |,k w The coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber;

[0042] Water hammer elimination box inertial head L w For the water hammer elimination tank length, A w Eliminate the cross-sectional area of ​​the tank to prevent water hammer;

[0043] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method;

[0044] Step 4.4, under two-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship:

[0045] Air cushion volume V a =V-∑A wi Δx

[0046] Divide the water hammer elimination box into several equal segments along the axial direction, where A in the above formula... wi Δx is the cross-sectional area of ​​each section where water flows through, V is the segment interval, and V is the volume of the water hammer elimination box.

[0047] Water hammer elimination tank head loss H w =∑k wi Q wi |Q wi |

[0048] In the formula, Q wi To determine the water flow rate at each cross-section of the water hammer elimination box, k wi The coefficient of water flow loss at each cross section under open flow conditions;

[0049] Water hammer elimination box inertial head

[0050] The mass flow rate of the air valve and the air cushion pressure satisfy the following relationship:

[0051]

[0052] In the formula, The air valve mass flow rate is positive when air is flowing inwards; C i A is the flow coefficient of the air inflow valve. i C represents the opening area of ​​the air inlet valve. o A is the flow coefficient of the outflow air valve. o ρ is the opening area of ​​the air outlet valve. w ρ is the density of water, ρ0 is the density of air at normal temperature and pressure, R is the gas constant, and T is the temperature.

[0053] The pressure and volume of the air cushion inside the water hammer elimination chamber satisfy the following relationship:

[0054]

[0055] In the formula, a and b are van der Waals constants, and M is the molar mass of air;

[0056] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method;

[0057] Step 4.5, if the obtained virtual water level H L1 H L2 Satisfy (H) L1 0 -Z T (H) L1 -Z T )≥0 and (H L2 0 -Z T (H) L2 -Z T If H ≥ 0, the calculation ends; otherwise, let H L1 0 =H L1 H L2 0 =H L2 Repeat steps 4.2 to 4.5;

[0058] Step 4.6, calculate the water pressure at the bottom of any cross-section inside the tank:

[0059]

[0060] In the formula, l is the distance from the cross section to the front wall of the elimination box; L1 and L2 are the distances from cross section A1 and cross section A2 to the front wall of the elimination box, respectively.

[0061] If the current virtual water level H L1 H L2 Satisfying H L1 <Z T or H L2 <Z T Determine the water depth at any cross-section inside the box:

[0062]

[0063] Step 4.7: If the current time is greater than or equal to the calculation time of the transient process, the calculation ends; otherwise, repeat steps 4.1 to 4.6.

[0064] The threshold value in step 5 is preferably 1m.

[0065] This invention proposes a method for accurately determining the structural dimensions of a water hammer elimination box.

[0066] This invention proposes the concept of a "virtual water level," assuming that the top of the water hammer elimination tank contains a narrow groove with a cross-sectional area much smaller than the tank's cross-sectional area and an infinitely upward-extending height. The groove wall is smooth and lossless, and the top of the groove acts as an air valve. Thus, the pressure at the two nodes of the water hammer elimination tank under single-phase flow conditions is equivalent to the water level in the narrow groove. Based on the construction of the virtual water levels at sections A1 and A2, the mathematical models for single-phase and two-phase flow are unified. Furthermore, by introducing the virtual water level, the conversion conditions between single-phase and two-phase flow are proposed.

[0067] This invention proposes a method for accurately determining the structural dimensions of a water hammer suppression tank. The structural dimensions are determined by numerical calculations of the fluid movement within the tank. When using a water hammer suppression tank for water hammer protection in a water conveyance system, an effective protection scheme can be formulated based on the calculation results of this invention.

[0068] This invention proposes a virtual water level, which unifies the mathematical models of single-phase and two-phase flow, reducing the difficulty of programming calculations and improving code execution efficiency. Furthermore, the conversion conditions between single-phase and two-phase flow can be directly expressed in the form of a virtual water level, avoiding cumbersome condition judgments and improving the efficiency of model programming development. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of a water hammer elimination box according to an embodiment of the present invention. In the diagram, 1 is an air valve, 2 is the water hammer elimination box, 3 is the front connecting pipe, 4 is the rear connecting pipe, 5 is the water supply pipe, 6 is the front wall of the water hammer elimination box, 7 is section A1, which is the cross-section where the front connecting pipe 3 of the water hammer elimination box is located, and 8 is section A2, which is the cross-section where the rear connecting pipe 4 of the water hammer elimination box is located. The front connecting pipe 3 and the rear connecting pipe 4 are respectively connected between the water supply pipe 5 and the lower part of the water hammer elimination box 2, wherein the front connecting pipe 3 is located upstream of the rear connecting pipe 4.

[0070] Figure 2 This is a flowchart illustrating the process of accurately determining the structural dimensions of the water hammer elimination box in an embodiment of the present invention.

[0071] Figure 3 This is a flowchart illustrating the calculation process of the water hammer elimination box transient process in an embodiment of the present invention.

[0072] Figure 4 This is a schematic diagram of a virtual water level according to an embodiment of the present invention, wherein 9 is a narrow channel with infinite length and infinitely small cross-sectional area, and 10 is a virtual water level.

[0073] Figure 5 This is a graph showing the change in water level / water pressure in the water hammer elimination tank over time, according to an embodiment of the present invention.

[0074] Figure 6 This is a graph showing the change in gas pressure over time inside the water hammer elimination chamber according to an embodiment of the present invention.

[0075] Figure 7 A graph showing the change in gas mass flow rate over time in the water hammer elimination chamber.

[0076] Figure 8 The relationship curve between the volume of the water hammer elimination tank and the minimum pressure along the water supply system. Detailed Implementation

[0077] Referring to the accompanying drawings, the invention will be described in detail below with reference to a specific engineering example. A water supply project draws water from a water source, pressurizes it using a pump, and then transports it to the forebay. The total length of the water transmission line is approximately 8.9 km, and the design flow rate is 10 m³ / s. 3 / s. To prevent water hammer caused by sudden power outages at the power station, a water hammer suppression box is installed in the pipeline after the pump as a protective measure.

[0078] This method is used to accurately determine the structural dimensions of the water hammer elimination box under power failure and shutdown conditions. The process includes the following steps:

[0079] Step 1: Initially determine the parameters of the water hammer elimination chamber as follows: Water hammer elimination chamber 2, height 4m, volume 200m³. 3 The cross-sectional area of ​​both the front connecting pipe 3 and the rear connecting pipe 4 is 3m³. 2 Air valve 1 is located on top of water hammer elimination box 2, with an air inlet area of ​​314 cm². 2 The flow coefficient is 0.975, and the exhaust port area is 15.7 cm². 2 The flow coefficient is 0.65.

[0080] Step 2: Simplify the water flow within the water hammer elimination box 2 into a one-dimensional flow, forming a two-node mathematical model of the water hammer elimination box. The two nodes of the water hammer elimination box are the intersections of the two connecting pipes 3 and 4 with the water supply pipe 5. The specific steps are as follows:

[0081] Step 2.1: Introduce the concept of virtual water level, the virtual water level corresponding to section A1.

[0082] H L1 =H n1 +k w1 Q w1 |Q w1 |+H atm -H a

[0083] Virtual water level corresponding to section A2

[0084] H L2 =H n2 +k w2 Q w2 |Q w2 |+H atm -H a

[0085] In the formula, k w1 and k w2 The loss coefficients H for the front connecting pipe 3 and the rear connecting pipe 4 are respectively. n1 H is the pressure at the junction of the connecting pipe 3 and the water supply pipe 5. n2 For the pressure at the junction of the downstream connecting pipe 4 and the water supply pipe 5, H a H represents the air cushion pressure. atm For atmospheric pressure, Q w1 and Q w2 The flow rates of the front connecting pipe 3 and the rear connecting pipe 4 are shown in the attached figure. Figure 1 As shown.

[0086] Step 2.2, according to the continuity equation, the flow rates of the front connecting pipe 3 and the rear connecting pipe 4 satisfy...

[0087]

[0088] In the formula, V a This represents the volume of the air cushion.

[0089] Step 2.3: Based on the energy equation required for water flow to eliminate water hammer in the tank, the relationship between the virtual water level and the flow rate in the connecting pipe is obtained.

[0090]

[0091] In the formula, A w1 and A w2 The cross-sectional areas of water passages at sections A1 and A2 are respectively, H w For head loss, H m It is the inertial head.

[0092] Step 2.4: Based on the energy equation, obtain the relationship between the flow rate and the node pressure in the water supply pipe 5 between the upstream connecting pipe 3 and the downstream connecting pipe 4.

[0093]

[0094] In the formula, k p Let L be the loss coefficient of the water supply pipe 5 between the connecting pipe 3 and the rear connecting pipe 4, L be the length of the water supply pipe 5 between the front connecting pipe 3 and the rear connecting pipe 4, A be the cross-sectional area of ​​the water supply pipe, and Q be the flow rate of the water supply pipe between the two connecting pipes.

[0095] Step 3: Calculate the initial values ​​for the water hammer suppression tank. Initially, the flow inside water hammer suppression tank 2 is a single-phase flow, satisfying the following relationship:

[0096] Air cushion volume V a =0

[0097] Air cushion pressure H a =Hatm

[0098] Water hammer elimination box 2 head loss H w =k w Q w2 |Q w2 |,k w The coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber.

[0099] Water hammer elimination box 2 inertial head H m =0

[0100] Water supply pipeline flow rate change rate

[0101] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method.

[0102] Step 4: Solve the transient process of water hammer elimination chamber 2. The specific steps are as follows:

[0103] Step 4.1: Introduce a virtual water level to solve for the intermediate variable H. L1 0 H L2 0 Both are equal to the virtual water level H at the previous moment. L1 (N-1) H L2 (N-1) .

[0104] Step 4.2, if H is satisfied L1 0 ≥Z T And H L2 0 ≥Z T In the formula Z T To determine the height of the water hammer elimination box 2, assume that the current flow is single-phase and proceed to step 4.3; otherwise, assume that the flow is two-phase and proceed to step 4.4.

[0105] Step 4.3, under single-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship:

[0106] Air cushion volume V a =0

[0107] Air cushion pressure H a =H atm

[0108] Water hammer elimination tank head loss H w =k w Q w2 |Q w2 |,k wThe coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber.

[0109] Water hammer elimination box inertial head L w For the water hammer elimination tank length, A w Eliminate the cross-sectional area of ​​the box to prevent water hammer.

[0110] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method.

[0111] Step 4.4, under two-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship:

[0112] Air cushion volume V a =V-∑A wi Δx

[0113] Divide the water hammer elimination box into several equal segments along the axial direction, where A in the above formula... wi Let be the cross-sectional area of ​​each section where water flows through, Δx be the segment interval, and V be the volume of the water hammer elimination box.

[0114] Water hammer elimination tank head loss H w =∑k wi Q wi |Q wi |

[0115] In the formula, Q wi To determine the water flow rate at each cross-section of the water hammer elimination box, k wi This represents the flow loss coefficient of water body at each cross section under open flow conditions.

[0116] Water hammer elimination box inertial head

[0117] The mass flow rate of the air valve and the air cushion pressure satisfy the following relationship:

[0118]

[0119] In the formula, The air valve mass flow rate is positive when air is flowing inwards; C i A is the flow coefficient of the air inflow valve. i C represents the opening area of ​​the air inlet valve. o A is the flow coefficient of the outflow air valve. o ρ is the opening area of ​​the air outlet valve. w Let ρ be the density of water, ρ0 be the density of air at normal temperature and pressure, R be the gas constant, and T be the temperature.

[0120] The pressure and volume of the air cushion inside the water hammer elimination chamber satisfy the following relationship:

[0121]

[0122] In the formula, a and b are van der Waals constants, and M is the molar mass of air.

[0123] Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method.

[0124] Step 4.5, if the obtained virtual water level H L1 H L2 Satisfy (H) L1 0 -Z T (H) L1 -Z T )≥0 and (H L2 0 -Z T (H) L2 -Z T If H ≥ 0, the calculation ends; otherwise, let H L1 0 =H L1 H L2 0 =H L2 Repeat steps 4.2 to 4.5.

[0125] Step 4.6, calculate the water pressure at the bottom of any cross-section inside the tank:

[0126]

[0127] In the formula, l is the distance from the cross section to the front wall of the elimination box; L1 and L2 are the distances from cross section A1 and cross section A2 to the front wall of the elimination box, respectively.

[0128] If the current virtual water level H L1 H L2 Satisfying H L1 <Z T or H L2 <Z T Determine the water depth at any cross-section inside the box:

[0129]

[0130] Step 4.7: If the current time is greater than or equal to the calculation time of the transient process, the calculation ends; otherwise, repeat steps 4.1 to 4.6.

[0131] Step 5, if the lowest pressure H along the water supply system... min With system pressure control value H c Not satisfied with 0 <H min -H c If the volume is less than 1m, modify the water hammer elimination tank volume and repeat steps 2-4 until 0m. <H min -Hc <1m.

[0132] Step 6: Apply the obtained parameters to the water hammer elimination tank volume setting.

[0133] The water level (water pressure), air pressure, and air flow rate of the water hammer elimination tank were calculated, as shown in the appendix. Figures 5-7 Analysis and calculations show that, under steady-state conditions, the water hammer elimination tank is filled with water, and the water pressure is 8.64 m³. At 10 seconds, the water pump suddenly loses power, and the pressure in the downstream water supply pipeline drops rapidly. The water pressure inside the elimination tank drops to 4 m³ at 15.90 seconds, at which point the air valve opens, allowing air to enter the tank. As the water supply pipeline pressure decreases, the water level in the elimination tank further decreases, increasing the negative pressure inside the tank, and a large amount of air rushes in. After 153.1 seconds, the water pressure in the elimination tank begins to rise again. As the water level rises, the gas volume decreases, and the pressure gradually increases. After 165.3 seconds, the gas pressure exceeds atmospheric pressure, and the elimination tank begins to expel air. Expelling air ends at 281.1 seconds, at which point a large amount of air remains inside the tank. The elimination tank then enters a second air intake process, but due to the attenuation of system energy and the presence of an air cushion, the peak value and duration of the second intake are much smaller than the first. Afterward, the water level in the elimination tank fluctuates periodically, and the air valve slowly expels air.

[0134] Appendix Figure 8 This is a curve showing the relationship between the structural dimensions of the water hammer suppression tank and the minimum pressure along the water supply system. It can be seen that the initial volume of the water hammer suppression tank is 200 m³. 3 Unable to meet protection requirements, the volume was increased to 400m. 3 Afterwards, the lowest pressure along the system is 0.56m, which meets the control requirement of pressure greater than 0m and less than 1m.

[0135] Therefore, the method proposed in this invention can obtain the structural dimensional parameters of the water hammer elimination tank, and can reflect the effect of the water hammer elimination tank in eliminating positive and negative water hammer during the power outage of the water pump. The method proposed in this invention can be used in the design of water supply systems to determine the parameters of the water hammer elimination tank.

Claims

1. A method for accurately determining the structural dimensions of a water hammer protection device, characterized in that, Includes the following steps: Step 1: Initially determine the various dimensional parameters of the water hammer elimination box, including the length, cross-sectional area, and height of the water hammer elimination box. Also determine the flow characteristic parameters of the water hammer elimination box, including the axial flow loss coefficient, the loss coefficient of the front connecting pipe, the loss coefficient of the rear connecting pipe, the opening area and flow coefficient of the inflow air valve, the opening area and flow coefficient of the outflow air valve, the loss coefficient of the water supply pipe between the front and rear connecting pipes, and the length and loss coefficient of the water supply pipe between the two connecting pipes. The front and rear connecting pipes are both connected between the water hammer elimination box and the water supply pipe, and the front connecting pipe is located upstream of the rear connecting pipe. Step 2: Simplify the water flow in the water hammer elimination box into a one-dimensional flow to form a two-node mathematical model of the water hammer elimination box. The two nodes of the water hammer elimination box are the intersection of the two connecting pipes of the water hammer elimination box and the water supply pipe. Step 3: Calculate the initial values ​​for the water hammer elimination box; Step 4: Solve the transient process of the water hammer elimination box; Step 5, if the water supply system has the lowest pressure along the path With system pressure control value Not satisfied If the water hammer elimination tank volume is changed, steps 2-4 are repeated until... ; Step 2, establishing the two-node mathematical model of the water hammer elimination box, includes the following steps: Step 2.1, introduce the concept of virtual water level, the virtual water level corresponding to section A1 where the connecting pipe before the water hammer elimination box is located: The virtual water level corresponding to section A2 where the connecting pipe after the water hammer elimination box is located: ; In the formula, and These are the loss coefficients for the front and rear connecting pipes, respectively. The pressure at the junction of the connecting pipe and the water supply pipe. The pressure at the junction of the connecting pipe and the water supply pipe. For air cushion pressure, Atmospheric pressure, and These are the flow rates of the front and rear connecting pipes, respectively. The virtual water level refers to the following: There is a narrow groove at the top of the water hammer elimination box with a cross-sectional area much smaller than the cross-sectional area of ​​the box body and an infinitely upward height. The wall of the narrow groove is smooth and without loss. The top of the narrow groove is an air valve. The pressure of the two nodes of the water hammer elimination box under single-phase flow is equivalent to the water level of the narrow groove. Step 2.2, according to the continuity equation, the flow rates of the upstream and downstream connecting pipes satisfy... In the formula, This refers to the volume of the air cushion. Step 2.3: Based on the energy equation required for water flow to eliminate water hammer in the tank, the relationship between the virtual water level and the flow rate in the connecting pipe is obtained. In the formula, and These are the cross-sectional areas of the water passage at sections A1 and A2, respectively. For head loss, For inertial head; Step 2.4: Based on the energy equation, obtain the relationship between the flow rate and the node pressure in the water supply pipe between the upstream and downstream connecting pipes. In the formula, This represents the loss coefficient of the water supply pipeline between the upstream and downstream connecting pipes. This refers to the length of the water supply pipe between the front and rear connecting pipes. The cross-sectional area of ​​the water supply pipe. This refers to the flow rate of the water supply pipe between the front and rear connecting pipes.

2. The method for accurately determining the structural dimensions of a water hammer protection device as described in claim 1, characterized in that, The specific steps for calculating the initial value of the water hammer elimination tank in step 3 are as follows: Initially, the flow inside the water hammer elimination tank is a single-phase flow, satisfying the following relationship: air cushion volume air cushion pressure Water hammer elimination tank head loss , The coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber; Water hammer elimination box inertial head Water supply pipeline flow rate change rate Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method.

3. The method for accurately determining the structural dimensions of a water hammer protection device as described in claim 1, characterized in that, The specific steps for solving the transient process described in step 4 are as follows: Step 4.1: Introduce virtual water level to solve for intermediate variables. , Both are equal to the virtual water level at the previous moment. , ; Step 4.2, if the following conditions are met and In the formula If the current value is the height of the container, then it is assumed that the current flow is single-phase and proceed to step 4.3; otherwise, it is a two-phase flow and proceed to step 4.

4. Step 4.3, under single-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship: air cushion volume air cushion pressure Water hammer elimination tank head loss , The coefficient for axial flow loss of water under full-flow conditions in the water hammer elimination chamber; Water hammer elimination box inertial head , To eliminate water hammer, the length of the tank. Eliminate the cross-sectional area of ​​the tank to prevent water hammer; Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method; Step 4.4, under two-phase flow conditions, the air cushion volume, water hammer elimination tank head loss, and inertial head satisfy the following relationship: air cushion volume Divide the water hammer elimination box into several equal segments along the axial direction, as shown in the above formula. The cross-sectional area of ​​the water passage at each section, For segmented intervals, Eliminate tank volume to reduce water hammer; Water hammer elimination tank head loss In the formula, To eliminate water hammer, the water flow rate at each cross-section of the tank is... The coefficient of water flow loss at each cross section under open flow conditions; Water hammer elimination box inertial head The mass flow rate of the air valve and the air cushion pressure satisfy the following relationship: In the formula, The mass flow rate of the air valve is positive when air is introduced into the air. The flow coefficient of the air inflow valve. The opening area of ​​the air inlet valve; The flow coefficient of the outflow air valve. The opening area of ​​the air outlet valve; The density of water, The density of air at normal temperature and pressure. The gas constant is... For temperature; The pressure and volume of the air cushion inside the water hammer elimination chamber satisfy the following relationship: In the formula, and These are van der Waals constants. The molar mass of air; Substitute the above relationships into the mathematical model in step 2 and solve using Newton's iteration method; Step 4.5, if the obtained virtual water level , satisfy and If the result is positive, the calculation ends; otherwise, let... , Repeat steps 4.2 to 4.5; Step 4.6, calculate the water pressure at the bottom of any cross-section inside the tank: In the formula, The distance between the cross-section and the front wall of the box is eliminated; , These are the distances from section A1 and section A2 to the front wall of the elimination box, respectively. If the current virtual water level , satisfy or Determine the water depth at any cross-section inside the box: Step 4.7: If the current time is greater than or equal to the calculation time of the transient process, the calculation ends; otherwise, repeat steps 4.1 to 4.

6.

4. The method for accurately determining the structural dimensions of a water hammer protection device as described in claim 1, characterized in that, The threshold is 1m.

5. The method for accurately determining the structural dimensions of a water hammer protection device as described in claim 1, characterized in that, It also includes step 6: applying the obtained parameters to the water hammer elimination tank volume setting.

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