Water hammer prevention method and design method of bidirectional pressure regulating tower with different water inlet and outlet channels

Abstract

The application relates to a water hammer prevention method and design method of a bidirectional pressure regulating tower with different flow channels for water inlet and outlet, which comprises a tower body, a connecting pipe and a water delivery pipe. The connecting pipe is composed of two short pipes with different diameters. The short pipe with a large diameter is a one-way flow channel, and a one-way valve is arranged in the one-way flow channel. The one-way valve is only opened to the water delivery pipe. The short pipe with a small diameter is a two-way flow channel. When the demand for increasing the minimum pressure in the water delivery pipe is higher than that for reducing the maximum pressure, the one-way valve is opened to the water delivery pipe side, so that the rate and extreme value of pressure drop are reduced. When the demand for reducing the maximum pressure in the water delivery pipe is higher than that for increasing the minimum pressure, the one-way valve is closed, water in the water delivery pipe slowly enters the tower body, the rate and extreme value of pressure rise are reduced, and the maximum pressure is reduced. The application can adapt to the water hammer prevention demand of different water delivery systems and topological structures by different configuration of the one-way flow channel and the two-way flow channel, effectively reduces the overall size of the bidirectional pressure regulating tower, and greatly saves the engineering cost.

Description

Technical Field

[0001] This invention relates to a method and design method for preventing water hammer in a bidirectional surge tank with different inlet and outlet water channels, a disaster prevention method and design method for hydraulic facilities, and a safe operation guarantee method and design method for large-scale long-distance water conveyance projects. Background Technology

[0002] When large-scale, long-distance water transmission systems (transporting water at rates ranging from several to tens of cubic meters per second, over distances of tens to hundreds of kilometers) experience power outages or require flow regulation or valve operation, the flow velocity in the pipeline changes, causing pressure increases or decreases and resulting in water hammer. To address this, bidirectional surge tanks are typically used to limit pressure fluctuations within the limits allowed by regulations and equipment, thus resolving the water hammer problem. However, the requirements for reducing maximum pressure and increasing minimum pressure are not entirely the same when using bidirectional surge tanks for water hammer protection in water transmission systems. Generally, increasing the minimum pressure is more important than reducing the maximum pressure. Most existing surge tanks use the same flow path for both inlet and outlet water, which makes it difficult to meet these differentiated needs and thus fails to maximize the protective effect. Given the enormous costs of large-scale water transmission projects, and the massive size of bidirectional surge tanks (reaching several meters or even tens of meters in height), with project costs often reaching hundreds of millions of yuan, failure to fully utilize their effectiveness would be a significant waste. Therefore, improving the efficiency of surge tanks while effectively protecting against water hammer and reducing construction costs is a problem that needs to be solved. Summary of the Invention

[0003] To overcome the problems of existing technologies, this invention proposes a method and design for preventing water hammer in a bidirectional surge tank with different inlet and outlet water flow channels. The method improves the water hammer prevention efficiency of the surge tank by controlling the different flow rates between the surge tank and the water pipeline, thereby creating a difference in the water flow entering and leaving the surge tank. This also allows for a smaller overall size of the surge tank and reduces its construction cost.

[0004] The objective of this invention is achieved as follows: a method for preventing water hammer in a bidirectional pressure regulating tower with different inlet and outlet water flow channels. The pressure regulating tower used in this method comprises: a tower body open to the atmosphere at its upper end; the tower body is connected to a water supply pipe via a connecting pipe, which consists of two short pipes of different diameters. The shorter pipe with the larger diameter is a unidirectional flow channel and contains at least one one-way valve, which opens only in the direction of the water supply pipe. The shorter pipe with the smaller diameter is a bidirectional flow channel. The steps of the method are as follows:

[0005] Step 101: When the demand for increasing the minimum pressure in the water supply pipeline is higher than the demand for decreasing the maximum pressure, the one-way valve opens to the water supply pipeline side, allowing water in the tower body to quickly enter the water supply pipeline, reducing the rate and extreme value of pressure drop, and playing the role of increasing the minimum pressure. The flow area of ​​the connecting pipe at the water outlet is the area of ​​the one-way flow channel + the area of ​​the two-way flow channel.

[0006] Step 102: When the demand to reduce the maximum pressure in the water supply pipeline is higher than the demand to increase the minimum pressure, the one-way valve closes, and the water in the water supply pipeline slowly enters the tower body, reducing the rate and extreme value of pressure rise, thereby reducing the maximum pressure. The flow area of ​​the connecting pipe during water inlet is the bidirectional flow channel area.

[0007] The flow rates at the inlet and outlet of the bidirectional pressure regulating tower are:

[0008]

[0009] In the formula: ; ; ; ; ; ; ; Let be the piezometric head of the left-hand calculation node, in meters (m). For coefficients, ; The water hammer wave velocity is in m / s; It is the acceleration due to gravity. ; For the pipe area, , ; The diameter of the water pipeline is in meters (m). The flow of the left-hand node is calculated. ; ; For coefficients, ; Darcy-Weisbach coefficient of friction; Let m be the spatial step size. ; Let be the piezometric head of the right-hand calculation node, in meters (m). The flow of the right-hand compute node is calculated. ; ; To detect the water level at the start time; For time step; To detect the flow rate at the start time; To detect the water head in the pressure gauge at the connection point of the pipeline at the initial moment; For the area of ​​the voltage regulating tower, ; The local head loss coefficient for the inlet and outlet of the bidirectional surge tank; The area of ​​the flow channel; The diameter is the diameter of the cylindrical voltage regulating tower.

[0010] A design method for the above-mentioned bidirectional voltage regulating tower, the steps of which are as follows:

[0011] Step 1, set the diameter of the bidirectional flow channel , The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. ;

[0012] Step 2, settings ( The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. ;

[0013] i represents the detection point number and quantity along the research object; The maximum pressure at a certain detection point i;

[0014] Step 3, compare the results of each detection point. ( ),Pick ; There are two conditions that need to be met: ① The maximum pressure is less than the larger of 0.9 times the design bearing pressure and the design bearing pressure minus 10m, that is, ② Among the data that satisfy condition ①, the smallest ;

[0015] Step 4, Setting ( The water hammer process of the entire water conveyance system is calculated, and the minimum pressure along the pipeline is recorded. and the minimum piezometric head of the surge tank ;

[0016] Step 5, Compare , ( ),Pick . There are two conditions that must be met: ① The minimum pressure must be greater than the minimum allowable pressure, and the minimum piezometric head must be greater than the minimum piezometric head. , ② Among the data that satisfy condition ①, the largest ;

[0017] Step 6: Reduce the height of the voltage regulating tower. ,diameter The water hammer process of the water conveyance system was calculated, and the maximum pressure along the pipeline was recorded. Minimum pressure along the pipeline and the minimum piezometric head of the surge tank ;

[0018] Step 7, if satisfied , , Then return to step 6 and continue to reduce the height of the voltage regulating tower. ,diameter This continues until the above formula is no longer satisfied. The pressure regulating tower from the previous cycle step... ,diameter This allows for the final size of the pressure regulating tower;

[0019] Step 8, Substitute into the pressure regulating tower ,diameter unidirectional flow channel bidirectional flow channel The water hammer process of the entire water conveyance system is calculated, and the calculation results are verified.

[0020] The advantages and beneficial effects of this invention are as follows: This invention utilizes differentiated configurations of unidirectional and bidirectional flow channels to adapt to the water hammer protection requirements of different water conveyance systems and topologies. Based on multi-point detection data of water conveyance pipelines, the overall structure of the pressure regulating tower is optimized to maximize the water hammer protection effect of the bidirectional pressure regulating tower, effectively reduce the overall size of the bidirectional pressure regulating tower, and significantly save engineering costs. Attached Figure Description

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

[0022] Figure 1 This is a schematic diagram of the voltage regulating tower described in Embodiment 1 of the present invention;

[0023] Figure 2 This is a flow diagram of water being conveyed from the pressure regulating tower to the water delivery pipe according to Embodiment 1 of the present invention;

[0024] Figure 3 This is a flow diagram of water being transported from the water pipeline to the surge tank according to Embodiment 1 of the present invention;

[0025] Figure 4 This is a schematic diagram of the various symbols of the pressure regulating tower described in Embodiment 1 of the present invention (inlet flow state);

[0026] Figure 5 This is a schematic diagram of the various symbols of the pressure regulating tower described in Embodiment 1 of the present invention (outflow state). Detailed Implementation

[0027] Example 1:

[0028] This embodiment describes a method for preventing water hammer in a bidirectional pressure regulating tower with different inlet and outlet water flow channels. The pressure regulating tower used in this method includes: a tower body 1 with its upper end open to the atmosphere; the tower body is connected to a water supply pipe 3 via a connecting pipe 2; the connecting pipe consists of two short pipes with different diameters. The shorter pipe with the larger diameter is a unidirectional flow channel 201, containing at least one one-way valve 4. The one-way valve only opens in the direction of the water supply pipe, allowing water to flow only from the tower body to the water supply pipe in the unidirectional flow channel. The shorter pipe with the smaller diameter is a bidirectional flow channel 202, allowing water to flow both from the tower body to the water supply pipe and vice versa. Figure 1 As shown.

[0029] The surge tank described in this embodiment is equivalent to a water storage tank, and can be cylindrical, rectangular, or other polygonal or cubic shapes. For large-scale water conveyance projects, traditional surge tanks typically have diameters and heights of several meters, or even tens of meters, or lengths, widths, and heights of tens of meters, with capacities of tens of cubic meters, or even hundreds of cubic meters. After the modification in this embodiment, the overall size of the surge tank can be reduced, which can save hundreds of millions of yuan in construction costs for large surge tanks.

[0030] The water pipelines mentioned are those used in large-scale water transmission projects, typically with a diameter of 500 mm or more. Surge towers are positioned at local high points along the water pipeline to fully utilize the effect of gravity.

[0031] The connecting pipes are typically two straight, circular pipes installed vertically at the bottom of the tower, perpendicular or nearly perpendicular to the water supply pipe. It must be clear that, since the surge tank is a water flow control facility, the positions of the surge tank, connecting pipe, and water supply pipe are precisely defined: the surge tank is at the top, the connecting pipe is in the middle, and the water supply pipe is at the bottom. This arrangement is designed to utilize gravity to create different flow patterns in the forward and reverse directions as water enters and exits the surge tank, thus mitigating the impact of water hammer. This embodiment modifies the traditional connecting pipe by dividing it into two pipes of different diameters and adding a one-way valve to the larger diameter pipe. This further enhances this effect and improves the efficiency in preventing water hammer.

[0032] The water hammer protection process of a two-way pressure regulating tower can be divided into two parts: ① When the pressure of the water pipeline increases, the water in the pipeline enters the pressure regulating tower, reducing the rate and extreme value of pressure rise, thus reducing the maximum pressure; ② When the pressure of the water pipeline decreases, the water in the pressure regulating tower enters the pipeline, reducing the rate and extreme value of pressure drop, thus increasing the minimum pressure.

[0033] The method for preventing water hammer in the pressure regulating tower shown in this embodiment is as follows: when the demand for increasing the minimum pressure in the water supply pipeline is higher than the demand for decreasing the maximum pressure, the one-way valve opens to the water supply pipeline side, such as... Figure 2As shown, increasing the flow channel in process ② allows water inside the tower to quickly enter the water supply pipe. Its flow area is the sum of the outlet flow channel area and the bidirectional flow channel area, while the flow area in process ① is only the bidirectional flow channel area. When the demand to reduce the maximum pressure exceeds the demand to increase the minimum pressure, the one-way valve closes, and water can only enter the tower through the bidirectional flow channel. At this time, the one-way flow channel is closed, reducing the flow channel in process ①, whose flow area is equal to the bidirectional flow channel area, as shown... Figure 3 As shown.

[0034] By differentiating between unidirectional and bidirectional flow channels, the water hammer protection requirements of different water conveyance systems and topologies can be adapted to maximize the water hammer protection effect of the bidirectional surge tank, effectively reducing the overall size of the bidirectional surge tank and saving engineering costs.

[0035] To enable water to flow quickly from the tower into the water supply pipe, multiple check valves can be installed to increase the opening speed of the check valves.

[0036] There are several ways to arrange two connecting pipes. They can be arranged sequentially according to the direction of water flow, or side by side. The two pipes can be installed separately or intermittently, or they can be integrated into one unit, among other installation methods.

[0037] The diameters of the two connecting pipes can be different or equal.

[0038] The steps of the method are as follows:

[0039] Step 101: When the demand for increasing the minimum pressure in the water supply pipeline is higher than the demand for decreasing the maximum pressure, the one-way valve opens to the water supply pipeline side, allowing water in the tower body to quickly enter the water supply pipeline, reducing the rate and extreme value of pressure drop, and playing the role of increasing the minimum pressure. The flow area of ​​the connecting pipe at the water outlet is the area of ​​the one-way flow channel + the area of ​​the two-way flow channel.

[0040] Step 102: When the demand for reducing the maximum pressure in the water supply pipeline is higher than the demand for increasing the minimum pressure, the one-way valve closes, and the water in the water supply pipeline slowly enters the tower body, reducing the rate and extreme value of pressure rise, thereby reducing the maximum pressure. When water enters, the flow area of ​​the connecting pipe is the bidirectional flow channel area.

[0041] Traffic analysis is as follows:

[0042] The flow rates in and out of the bidirectional surge tank, the flow rates in the upstream and downstream pipes of the surge tank, satisfy the continuity equation, i.e.

[0043] (1)

[0044] In the formula: For the flow rate on the upstream side of the surge tank, ; For the flow rate entering and exiting the bidirectional pressure regulating tower, ; For the flow rate downstream of the pressure regulating tower, , see symbol Figure 4 , 5 As shown.

[0045] When water enters and flows out of the surge tank, the water head in the surge tank's pressure measuring pipe and the pipeline satisfy the energy conservation equation.

[0046] (2)

[0047] In the formula: The pressure head at the connection pipe of the two-way surge tank is in meters (m). The pressure head of the two-way surge tank is in meters (m). The local head loss coefficient for the inlet and outlet of the bidirectional surge tank; It is the acceleration due to gravity. ; The area of ​​the flow channel, Because the inlet and outlet water channels are different, , They are also different; the calculation formula is:

[0048] (3)

[0049] (4)

[0050] In the formula: The local head loss coefficient for water entering the bidirectional surge tank; The local head loss coefficient for the outflow from the bidirectional surge tank; The diameter of the unidirectional flow channel is in meters (m). denoted as the diameter of the bidirectional flow channel, in meters (m).

[0051] The characteristic line equations satisfied by the upstream and downstream sides of the surge tank are:

[0052] (5)

[0053] (6)

[0054] In the formula: The pressure head (m) of the pressure measuring pipe connected to the surge tank is given.

[0055] The water depth in the surge tank and the flow rate entering the surge tank satisfy the following conditions:

[0056] (7)

[0057] In the formula: The value is the water depth in the surge tank, expressed in meters (m). The subscript 0 indicates the value at the previous time step. Let be the time step, in seconds; For the area of ​​the voltage regulating tower, , ; The diameter of the voltage regulating tower is in meters (m).

[0058] The flow rates at the inlet and outlet of the bidirectional pressure regulating tower are:

[0059] (8)

[0060] In the formula: Transition symbol; ; ; ; ; ; ; ; Let be the piezometric head of the left-hand calculation node, in meters (m). For coefficients, ; The water hammer wave velocity is in m / s; It is the acceleration due to gravity. ; For the pipe area, , ; The diameter of the water pipeline is in meters (m). The flow of the left-hand node is calculated. ; ; For coefficients, ; Darcy-Weisbach coefficient of friction; Let m be the spatial step size. ; Let be the piezometric head of the right-hand calculation node, in meters (m). The flow of the right-hand compute node is calculated. ; ;

[0061] To detect the water level at the start time; For time step; To detect the flow rate at the start time; To detect the water head in the pressure gauge at the connection point of the pipeline at the initial moment; For the area of ​​the voltage regulating tower, ; The local head loss coefficient for the inlet and outlet of the bidirectional surge tank; The area of ​​the flow channel; The diameter is the diameter of the cylindrical voltage regulating tower.

[0062] Example 2:

[0063] This embodiment describes a design method for a bidirectional surge tank with different inlet and outlet water flow channels. The method calculates the pressure at each monitoring point in the water supply pipe to identify weak points in the water hammer protection pressure. Based on this, the protective effect of the bidirectional surge tank with different inlet and outlet water flow channels is analyzed.

[0064] The steps of the method are as follows:

[0065] Step 1, set the diameter of the bidirectional flow channel , The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. .

[0066] The diameter of the first flow channel is a unidirectional flow channel, which is a flow channel with a large diameter and a unidirectional valve. The diameter of the water supply pipeline; The diameter of the second flow channel is a bidirectional flow channel with a smaller diameter.

[0067] Along the route of a high-flow, long-distance water pipeline, a surge tank is typically installed at intervals (e.g., tens of kilometers). Therefore, this embodiment focuses on this section of the water pipeline. All data here are derived from this section of the pipeline under study.

[0068] Step 2, settings ( The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. .

[0069] i represents the detection point number and quantity along the research object; The maximum pressure at a certain detection point i;

[0070] Step 3, compare the results of each detection point. ( ),Pick . There are two conditions that need to be met: ① The maximum pressure is less than the larger of 0.9 times the design bearing pressure and the design bearing pressure minus 10m, that is, ② Among the data that satisfy condition ①, the smallest .

[0071] Step 4, Setting ( The water hammer process of the entire water conveyance system is calculated, and the minimum pressure along the pipeline is recorded. and the minimum piezometric head of the surge tank .

[0072] Step 5, Compare , ( ),Pick . There are two conditions that must be met: ① The minimum pressure must be greater than the minimum allowable pressure, and the minimum piezometric head must be greater than the minimum piezometric head. , ② Among the data that satisfy condition ①, the largest .

[0073] Step 6: Reduce the height of the voltage regulating tower. ,diameter The water hammer process of the water conveyance system was calculated, and the maximum pressure along the pipeline was recorded. Minimum pressure along the pipeline and the minimum piezometric head of the surge tank .

[0074] Step 7, if satisfied , , Then return to step 6 and continue to reduce the height of the voltage regulating tower. ,diameter This continues until the above formula is no longer satisfied. The pressure regulating tower from the previous cycle step... ,diameter This gives the final size of the pressure regulating tower.

[0075] Step 8, Substitute into the pressure regulating tower ,diameter unidirectional flow channel bidirectional flow channel The water hammer process of the entire water conveyance system is calculated, and the calculation results are verified.

[0076] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention (such as the form of the pressure regulating tower, the inlet and outlet water flow of the pressure regulating tower, the application of various formulas, the order of steps, etc.) without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preventing water hammer in a bidirectional surge tank with different inlet and outlet water channels, wherein the surge tank used in the method comprises: The tower body, open to the atmosphere at its upper end, is connected to a water supply pipe via a connecting pipe consisting of two short pipes of different diameters. The larger diameter pipe is a unidirectional flow channel containing at least one one-way valve, which opens only in the direction of the water supply pipe. The smaller diameter pipe is a bidirectional flow channel. The method is characterized by the following steps: Step 101: When the demand for increasing the minimum pressure in the water supply pipeline is higher than the demand for decreasing the maximum pressure, the one-way valve opens to the water supply pipeline side, allowing water in the tower body to quickly enter the water supply pipeline, reducing the rate and extreme value of pressure drop, and playing the role of increasing the minimum pressure. The flow area of ​​the connecting pipe at the water outlet is the area of ​​the one-way flow channel + the area of ​​the two-way flow channel. Step 102: When the demand to reduce the maximum pressure in the water supply pipeline is higher than the demand to increase the minimum pressure, the one-way valve closes, and the water in the water supply pipeline slowly enters the tower body, reducing the rate and extreme value of pressure rise, thereby reducing the maximum pressure. The flow area of ​​the connecting pipe during water inlet is the bidirectional flow channel area. The flow rates at the inlet and outlet of the bidirectional pressure regulating tower are: In the formula: ; ; ; ; ; ; ; Let be the piezometric head of the left-hand calculation node, in meters (m). For coefficients, ; The water hammer wave velocity is in m / s; It is the acceleration due to gravity. ; For the pipe area, , ; The diameter of the water pipeline is in meters (m). The flow of the left-hand node is calculated. ; ; For coefficients, ; Darcy-Weisbach coefficient of friction; Let m be the spatial step size. ; Let be the piezometric head of the right-hand calculation node, in meters (m). The flow of the right-hand compute node is calculated. ; ; To detect the water level at the start time; For time step; To detect the flow rate at the start time; To detect the water head in the pressure gauge at the connection point of the pipeline at the initial moment; For the area of ​​the voltage regulating tower, ; The local head loss coefficient for the inlet and outlet of the bidirectional surge tank; The area of ​​the flow channel; The diameter is the diameter of the cylindrical voltage regulating tower.

2. A design method for the bidirectional voltage regulating tower as described in claim 1, characterized in that, The steps of the method are as follows: Step 1, set the diameter of the bidirectional flow channel , The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. ; Step 2, settings ( The water hammer process of the entire water conveyance system is calculated, and the maximum pressure along the pipeline is recorded. ; i represents the detection point number and quantity along the research object; The maximum pressure at a certain detection point i; Step 3: Compare the various detection points ( ),Pick ; There are two conditions that must be met: ① The maximum pressure is less than the larger of 0.9 times the design bearing pressure and the design bearing pressure minus 10m, that is, ② Among the data that satisfy condition ①, the smallest ; Step 4, Setting ( The water hammer process of the entire water conveyance system is calculated, and the minimum pressure along the pipeline is recorded. and the minimum piezometric head of the surge tank ; Step 5, Compare , ( ),Pick . There are two conditions that must be met: ① The minimum pressure must be greater than the minimum allowable pressure, and the minimum piezometric head must be greater than the minimum piezometric head. , ② Among the data that satisfy condition ①, the largest ; Step 6: Reduce the height of the voltage regulating tower. ,diameter The water hammer process of the water conveyance system was calculated, and the maximum pressure along the pipeline was recorded. Minimum pressure along the pipeline and the minimum piezometric head of the surge tank ; Step 7, if satisfied , , Then return to step 6 and continue to reduce the height of the voltage regulating tower. ,diameter This continues until the above formula is no longer satisfied. The pressure regulating tower from the previous cycle step... ,diameter This allows for the final size of the pressure regulating tower; Step 8, Substitute into the pressure regulating tower ,diameter unidirectional flow channel bidirectional flow channel The water hammer process of the entire water conveyance system is calculated, and the calculation results are verified.

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