Prediction method for hydraulic transient characteristics of water supply systems with diverse flow regimes

Abstract

The present invention relates to a method for predicting the hydraulic transition characteristics of a water supply system with diverse flow patterns, characterized by: S1, determining the pressurized flow section, open channel flow section, and open-filled flow alternating flow section in the water supply system; S2, determining the calculation time step length of each calculation time step during the hydraulic transition process; S3, approximating the open channel flow section and open-filled flow alternating flow section in the water supply system to pressurized flow sections using a virtual pressurized flow pattern, thereby converting the entire water supply system into a fully pressurized water diversion system and solving the initial state of the water supply system; S4, temporally stratifying the open channel flow section and open-filled flow alternating flow section according to the determined calculation time step length, and determining the number of time layers required for calculation; S5, calculating the instantaneous state of the water supply system at each calculation time step length until the entire pressurized water diversion system reaches a stable state, thereby obtaining the hydraulic characteristics of typical locations during the entire hydraulic transition process. The present invention is applicable to water supply systems with diverse layouts.

Description

Technical Field

[0001] The present invention relates to a method for predicting hydraulic transient characteristics of a water supply system with various flow patterns, and is applicable to water supply systems with various layout types. Background Art

[0002] Currently, some water supply projects utilize pressurized systems. Due to the simplicity and low cost of open channels, open channels are often used in water supply projects where they are feasible. However, due to fluctuations in the pressure of the water supply intake reservoir or system, some systems may experience alternating operating conditions between pressurized and unpressurized. This can lead to alternating open-fill flow patterns in some pipelines, particularly during the hydraulic transition process, where the alternating open-fill flow becomes more dramatic. For pressurized systems, the characteristic line method is typically used for hydraulic transition analysis; for open channel flow patterns, the implicit difference method, which solves the Saint-Venant equations, is typically used for hydraulic transition prediction analysis; and for open-fill flow, the slit method is typically used for hydraulic transition prediction analysis.

[0003] After a large number of actual engineering tests, corresponding prediction and analysis calculation methods are available for the hydraulic transition process prediction and analysis of simple pressurized flow, open channel flow, and open-channel alternating flow. Moreover, the relevant prediction methods have been verified to have high calculation accuracy and can meet the needs of the project. However, for water supply systems containing two or three flow patterns of pressurized flow, open channel flow, and open-channel alternating flow, since the propagation speed of water hammer waves in pressurized pipes and open channels differs by several orders of magnitude, and the boundary types of arbitrarily connected water supply systems are diverse, there is currently no solution to the prediction of the hydraulic transition process characteristics of the entire system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in response to the above-mentioned problems, a method for predicting the hydraulic transient process characteristics of a water supply system with diverse flow patterns is provided.

[0005] The technical solution adopted by the present invention is: a method for predicting the hydraulic transient characteristics of a water supply system with diverse flow patterns, characterized by:

[0006] S1. Identify the pressurized flow section, open channel flow section, and open-channel flow alternating section in the water supply system;

[0007] S2. Determine the calculation time step of each calculation time step during the hydraulic transition process;

[0008] S3. Approximate the open channel flow section and the open-full flow alternating flow section in the water supply system as pressurized flow sections using a virtual pressurized flow state, thereby transforming the entire water supply system into a fully pressurized water diversion system and solving the initial state of the water supply system;

[0009] S4, time-stratifying the open channel flow section and the open full flow alternating flow section according to the determined calculation time step, and determining the number of time layers required for calculation;

[0010] S5. Calculate the instantaneous state of the water supply system at each calculation time step until all pressurized water diversion systems reach a stable state, and obtain the hydraulic characteristics of typical locations during the entire hydraulic transition process.

[0011] The step S3 comprises:

[0012] S31, dividing the corresponding open channel flow section or open-full flow alternating flow section into m segments, and marking the segment nodes as 1, 2, ···, m+1;

[0013] S32. Assume the water level corresponding to the section where the m+1th node is located as the design water level, and the corresponding flow rate as the system water supply flow rate;

[0014] S33. Take the section where the m+1th node of the open channel flow section or the alternating open and full flow section is located as the calculation starting point. Using the energy conservation equation, with the hydraulic elements of the section where the m+1th node is located as the known quantities, extrapolate to the section where the mth node is located. Then extrapolate from the section where the mth node is located to the m-1th node, and so on until the section where the first node is located.

[0015] S34. Take the average cross-section of all sections of the open channel flow section or the open-channel alternating full-flow section as the equivalent cross-section of the corresponding pressurized flow section, and make the total head losses of the two equal. Using these two conditions as constraints, all open channel flow sections or open-channel alternating full-flow sections are equivalent to their corresponding pressurized flow sections.

[0016] The step S3 further includes:

[0017] S35. Establish a structural matrix equation for the water supply system under a pressurized water diversion system and solve the hydraulic elements at the beginning and end of the pressurized flow section in the system;

[0018] S36. Convert the hydraulic element at the end of the pressure flow section into the hydraulic element at the section where the m+1th node of the corresponding open channel flow section or the open-full alternating flow section is located;

[0019] S37. Compare the hydraulic element of the terminal section obtained in the k+1th iteration with the hydraulic element of the terminal section obtained in the kth iteration. If the accuracy requirement is met, proceed to the next step; if not, return to S33.

[0020] S38. For open channel flow sections or open-channel and open-full alternating flow sections in the water supply system, the hydraulic elements of the section where the iteratively obtained m+1th node is located are recursively extrapolated to the section where the 1st node is located, and serve as the initial state of each section of the open channel flow section or open-channel and open-full alternating flow section; for pressurized flow sections in the water supply system, the values obtained by iterative iteration are used as the initial state of each hydraulic node.

[0021] Step S33 includes:

[0022]

[0023] Where: Z i (k) is the water level of the section where the i-th node is located at the k-th iteration; B i is the average cross-sectional width of the section where the i-th node is located; Z i，d is the bottom elevation of the section where the i-th node is located; ζ i is the head loss coefficient of the section where the i-th node is located.

[0024] Step S34 includes:

[0025]

[0026]

[0027] Where: λ is the head loss coefficient along the way; using this formula, the open channel flow section or the open and full alternating flow section is quantified into a cross-sectional area of A eq (k), length L eq (k) The pressurized flow section.

[0028] In solving the initial steady state conditions and hydraulic transition process, the calculation time step of the open channel flow section, the open-full alternating flow section, and the pressurized flow section is the same, and the selection of the calculation time step satisfies the Courant condition.

[0029] The number m of segments into which the length of the open channel flow section or the open-full flow alternating flow section is evenly divided is determined based on the length of the corresponding open channel flow section or the open-full flow alternating flow section and the distance corresponding to the calculation time step.

[0030] Step S5 includes:

[0031] S51, based on the hydraulic elements of the current n-th time layer of the section where the i-node is located, calculate the virtual water level and virtual flow rate of the section where the i-node is located at the n+1-th time layer;

[0032] S52, calculating the actual water level and actual flow rate at the n+1 time layer of the section where the i node is located based on the virtual water level and virtual flow rate at the n+1 time layer of the section where the i node is located;

[0033] S53, calculating the error between the actual water level of the section where the i node is located at the kth iteration in the n+1th time layer and the virtual water level of the kth iteration in the n+1th time layer. If the calculation requirement is not met, return to step S52; if the calculation requirement is met, proceed to the next step;

[0034] S54, calculate the error between the actual flow of the section where the i node is located in the kth iteration in the n+1th time layer and the kth virtual flow in the n+1th time layer. If the calculation requirement is not met, return to step S52; if the calculation requirement is met, proceed to the next step;

[0035] S55. Using the water level and flow obtained in the previous step of the iteration of the section where the second node and the mth node are located, perform a one-sided difference quotient to estimate the water level and flow in the section where the first node and the m+1th node are located in the n+1th time layer.

[0036] S56. Substitute the structural matrix equation of the entire water supply system into the equation and solve the hydraulic elements of each node;

[0037] S57. Determine whether the current time layer number n meets the requirement of the total simulation time N. If not, enter the next time layer and return to step S51; if it meets the requirement of the total simulation time, end the calculation.

[0038] Step S51 includes:

[0039]

[0040]

[0041] Where: is the k-th iterative water level result in the n+1th layer of the section where the i-node is located; is the k-th iteration flow result of the section where node i is located in the n+1th layer; is the final iterative flow result of the section where the i+1 node is located in the nth time layer; S f is the hydraulic gradient of the open flow section; α is the iteration coefficient, which is 0.5≤α≤1; B is the water surface width of the calculation section; A is the average water-passing cross-sectional area of the calculation section;

[0042] The step S52 includes:

[0043]

[0044]

[0045] Where: are the actual water level and actual flow of the section where node i is located at the kth iteration in the n+1th time layer; are the k-th virtual water level and flow rate of the section where the i+1 node is located in the n+1th time layer, and their values are equal to the k-1th iterative water level and flow rate of the n+1th time layer in step S51; is the average width of the water surface at the kth iteration in the nth time layer at the section where the i node is located; S0 is the bottom slope of the channel.

[0046] The step S55 includes:

[0047]

[0048]

[0049]

[0050]

[0051] The beneficial effects of the present invention are: 1) The present invention virtually equates the open channel flow section or the open-channel alternating flow with a pressurized flow section, cleverly avoiding the mathematical difficulties of directly solving the initial stable state of the open channel flow section or the open-channel alternating flow, which can greatly simplify the complexity of the hydraulic characteristics of the initial stable state of the water supply system, and enable the prediction of the hydraulic transition process characteristics of the water supply system with diverse flow states to be realized.

[0052] 2) The present invention proposes to virtually quantize the open channel flow section or the open-and-filled alternating flow section as a pressurized flow section during the initial state solution process, which is the most difficult part of numerical simulation, and then use the matrix structure method to solve it. This prediction and analysis method has good stability and high calculation accuracy, which can greatly improve the applicability of numerical simulation of complex water supply systems.

[0053] 3) The half-step timeline difference method proposed in the present invention reduces the difference time step from the previous 2Δt to Δt, improves the iterative stability of the calculation, and improves the simulation accuracy of the overall water supply system.

[0054] 4) The method proposed in the present invention for solving the virtual flow and virtual water level of the next time layer in advance avoids directly solving the implicit difference equation of the Saint-Venant equation for open channel flow. This method can replace the unknown quantity to be solved on the right side of the equal sign of the original implicit difference equation with the virtual flow and virtual water level of the next time layer obtained in the previous iterative cycle, and convert the implicit equation into a quasi-implicit equation. This prediction method avoids solving all sections of the open flow section at the same time, reducing the difficulty of the prediction calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Schematic diagram of the layout of a typical water supply system with diverse flow patterns in an embodiment.

[0056] Figure 2 Schematic diagram of the principle of virtually quantifying an open channel flow section or an open-full alternating flow section as a pressurized flow section in the embodiments.

[0057] Figure 3 Schematic diagram of the principle of half-step timeline calculation in the embodiment.

[0058] Figure 4This is a schematic diagram showing the principle of solving the hydraulic transient characteristics prediction method for a typical water supply system with diverse flow patterns in the embodiment.

[0059] Figures 5-7 1 is a typical part process line diagram of the embodiment. DETAILED DESCRIPTION

[0060] This embodiment provides a method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns, specifically comprising the following steps:

[0061] S1. Determine the pressurized flow section, open channel flow section, and open-channel-full-flow alternating flow section in the water supply system. The water supply system is divided into pressurized flow section, open channel flow section, and open-channel-full-flow alternating flow section according to the flow pattern. The criteria for distinguishing open channel flow section, open-channel-full-flow alternating flow section, and pressurized flow section are as follows: the part of the fluid that is in direct contact with the atmosphere during movement is the open channel flow section and open-channel-full-flow alternating flow section, and the part of the fluid that is not in direct contact with the atmosphere during movement is the pressurized flow section.

[0062] S2. Determine the calculation time step Δt of each calculation step during the hydraulic transition process. The calculation time step of the open channel flow section, the open-full alternating flow section, and the pressurized flow section should be the same when solving the initial stable state conditions and the hydraulic transition process. At the same time, the selection of the calculation time step should meet the Courant condition to obtain better convergence and use the characteristic line method for calculation.

[0063] S3. Approximate the open-channel alternating flow section and the open channel flow section as pressurized flow sections using virtual pressurized flow states, transform the entire water supply system into a fully pressurized system, and find the initial state of the entire water supply system.

[0064] This embodiment bypasses the complex solution process of the open flow implicit function by treating the open flow structure as a full flow structure, and achieves rapid iterative convergence of the initial conditions of the open flow structure. The solution method for treating the open flow section (open and full alternating flow section, open channel flow section) as a full flow structure can be completed according to the following points:

[0065] S31, divide the open flow section into m segments, and the segment nodes can be marked as 1, 2, ···, m+1;

[0066] The length segmentation of open channel flow section or open-full alternating flow section refers to dividing the length of open flow structure into segments according to Δx corresponding to the time step Δt;

[0067] in,

[0068] Where V is the average water velocity in the open channel flow section or the open-channel alternating flow section; A is the average cross-sectional area of the open channel flow section or the open-channel alternating flow section; B is the water surface width of the open channel flow section or the open-channel alternating flow section;

[0069] m=L / Δx

[0070] Where m is the number of segments divided by the open flow section length; L is the total length of the corresponding open flow section;

[0071] S32. Assume the water level corresponding to the section where the m+1th node of the open flow section is located as the design water level, and the corresponding flow rate as the design flow rate. The formula is as follows:

[0072] Z m+1 (k) = Z m+1，P

[0073] Q i (k) = Q m+1,p i=1,2,3,···,m+1

[0074] Where: k is the number of iterations; Z m+1，P is the design water level corresponding to the section where the m+1th node is located; Z m+1 (k) is the water level of the section where the m+1th node is located at the kth iteration; Q m+1，P is the design flow rate corresponding to the section where the m+1th node is located; Q i (k) is the flow rate of the section where the i-th node is located at the k-th iteration; since it is under the initial steady-state conditions, the flow rate of each section of the open flow section is equal everywhere.

[0075] S33. Starting from the section where the m+1th node of the open flow section is located, using the energy conservation equation and the hydraulic elements of the section where the m+1th node is located as known quantities, extrapolate to the section where the mth node is located, then extrapolate from the section where the mth node is located to the m-1th node, and so on, you can continue to extrapolate to the section where the open flow section is inlet, that is, the section where the first node is located. The recursive formula is as follows:

[0076]

[0077] Where: Z i (k) is the water level of the section where the i-th node is located at the k-th iteration; B i is the average cross-sectional width of the section where the i-th node is located; Z i，d is the bottom elevation of the section where the i-th node is located; ζ i is the head loss coefficient of the section where the i-th node is located. The recursive equation contains the unknown number Z on the right side of the equation. i (k), its numerical solution can be obtained through iterative calculation.

[0078] S34. Take the average cross-section of all sections in the open flow section as the equivalent cross-section of the corresponding full flow structure, and make the total head loss of the two equal. Using these two conditions as constraints, all open flow structures are quantified as their corresponding full flow structures. The calculation formula is as follows:

[0079]

[0080]

[0081] Where: λ is the head loss coefficient along the flow. Using this formula, the open flow section can be quantified into area A in the kth iteration. eq (k), length L eq (k) The pressurized flow section.

[0082] S35. Establish a structural matrix equation for the water supply system under a pressurized water diversion system and solve the hydraulic elements at the beginning and end of the pressure section. The matrix equation is as follows:

[0083]

[0084] Where: [A] is the total structural matrix of the entire water supply system; is the pressure head vector of the entire water supply system; is the flow vector of the entire water supply system. It is worth noting that when the matrix structure method is used to solve the problem, an iterative calculation of the pressurized flow section after quantization has been completed.

[0085] S36. Convert the hydraulic elements at the end of the pressure section to the hydraulic elements at the section of the open flow section where the m+1th node is located. The conversion formula is as follows:

[0086] Z m+1 (k+1)=h m+1 (k+1)+Z m+1，d

[0087] Q m+1 (k+1)=q m+1 (k+1)

[0088] S37, comparing the hydraulic element of the end section obtained in the k+1th iteration with the hydraulic element of the end section obtained in the kth iteration. If the accuracy requirement is met, proceed to the next step; if not, return to step S33;

[0089] S38. For open channel flow sections or open-channel and open-full alternating flow sections in the water supply system, the hydraulic elements of the section where the iteratively obtained m+1th node is located are recursively extrapolated to the section where the 1st node is located, and serve as the initial state of each section of the open channel flow section or open-channel and open-full alternating flow section; for pressurized flow sections in the water supply system, the values obtained by iterative iteration are used as the initial state of each hydraulic node.

[0090] S4. Divide the open channel flow section or the open-channel and full-channel alternating flow section into layers according to time, and determine the number of time layers required for calculation.

[0091] Time stratification refers to the uniform segmentation of the total simulation time according to the determined calculation time step Δt.

[0092] n=N / Δt

[0093] Where n is the number of time layers evenly divided by the open channel flow section or the alternating open and full flow; N is the total simulation time.

[0094] The initial states of each section of the open flow section and other hydraulic nodes obtained by iteration in step S3 are taken as the zero-time layer, that is, the hydraulic elements when n=0.

[0095] S5, calculates the instantaneous state of the water supply system at each time step until the entire water supply system reaches a new stable state. The whole process ends, thereby obtaining the hydraulic characteristics of typical parts during the entire hydraulic transition process to ensure the safety of the water supply system.

[0096] Calculate the instantaneous state of the water supply system at each time step. Specifically, use the half-step timeline to split the single time layer and reduce the time step of the difference quotient from the original 2Δt to Δt, which can improve the calculation iteration accuracy. The implementation steps are as follows:

[0097] S51. Based on the hydraulic elements of the current n-th time layer of the section where the i-node is located, the virtual water level and virtual flow rate of the section where the i-node is located at the n+1-th time layer are calculated. The calculation formula is as follows:

[0098]

[0099]

[0100] Where: is the k-th iterative water level result in the n+1th layer of the section where the i-node is located; is the k-th iteration flow result of the section where node i is located in the n+1th layer; is the final iterative flow result of the section where the i+1 node is located in the nth time layer; S f is the hydraulic gradient of the open flow section; α is the iteration coefficient (in this example, the recommended value is 0.5 ≤ α ≤ 1); B is the water surface width of the calculation section; and A is the average cross-sectional area of the calculation section. It is important to note that one iteration has already been completed when the virtual water level and virtual flow rate at the section where node i is located are calculated at the time layer (n+1).

[0101] S52. Calculate the actual water level and actual flow rate at the n+1 time layer of the section where the i node is located based on the virtual water level and virtual flow rate at the n+1 time layer of the section where the i node is located. The calculation formula is as follows:

[0102]

[0103]

[0104] Where: are the actual water level and actual flow of the section where node i is located at the kth iteration in the n+1th time layer; are the k-th virtual water level and flow rate of the section where the i+1 node is located in the n+1th time layer, and their values are equal to the k-1th iterative water level and flow rate of the n+1th time layer in step S51; is the average width of the water surface at the kth iteration in the nth time layer at the section where the i node is located; S0 is the bottom slope of the channel.

[0105] S53, calculate the actual water level of the section where the i node is located in the kth iteration in the n+1th time layer and the virtual water level of the kth iteration in the n+1th layer If the error does not meet the calculation requirements, return to S52; if the calculation requirements are met, go to the next step;

[0106] S54. Calculate the actual flow of the section where node i is located in the kth iteration in the n+1th time layer. and the kth virtual flow in the n+1th layer If the error does not meet the calculation requirements, return to S52; if the calculation requirements are met, go to the next step;

[0107] S55. Using the water level and flow obtained in the previous step iteratively at the sections where the second node and the mth node are located, perform a one-sided difference quotient to estimate the water level and flow at the sections where the first node and the m+1th node are located in the n+1th time layer. The estimation formula is as follows:

[0108]

[0109]

[0110]

[0111]

[0112] S56. Substitute the structural matrix equation of the entire water supply system into the equation and solve for the hydraulic elements of each node. The matrix equation is as follows:

[0113]

[0114] S57. Determine whether the current time layer number meets the requirement of the total simulation time N (n=N / Δt). If not, enter the next time layer and return to S51; if it meets the requirement of the total simulation time, end the calculation.

Claims

1. A method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns, characterized by: S1. Identify the pressurized flow section, open channel flow section, and open-channel flow alternating section in the water supply system; S2. Determine the calculation time step of each calculation time step during the hydraulic transition process; S3. Approximate the open channel flow section and the open-full flow alternating flow section in the water supply system as pressurized flow sections using a virtual pressurized flow state, thereby transforming the entire water supply system into a fully pressurized water diversion system and solving the initial state of the water supply system; S4, time-stratifying the open channel flow section and the open full flow alternating flow section according to the determined calculation time step, and determining the number of time layers required for calculation; S5. Calculate the instantaneous state of the water supply system at each calculation time step until all pressurized water diversion systems reach a stable state, and obtain the hydraulic characteristics of typical locations during the entire hydraulic transition process; The step S3 comprises: S31, dividing the corresponding open channel flow section or open-full flow alternating flow section into m segments, and marking the segment nodes as 1, 2, ···, m+1; S32. Assume the water level corresponding to the section where the m+1th node is located as the design water level, and the corresponding flow rate as the system water supply flow rate; S33. Take the section where the m+1th node of the open channel flow section or the alternating open and full flow section is the starting point for calculation. Using the energy conservation equation and the hydraulic elements of the section where the m+1th node is located as known quantities, extrapolate to the section where the mth node is located. Then extrapolate from the section where the mth node is located to the m-1th node, and so on until the section where the first node is located. S34. The average cross-section of all cross-sections in the open channel flow section or the alternating open and full flow section is taken as the equivalent cross-section of the corresponding pressurized flow section, and the total head losses of the two sections are made equal. These two conditions are used as constraints to make all open channel flow sections or alternating open and full flow sections equivalent to their corresponding pressurized flow sections. The step S3 further comprises: S35. Establish a structural matrix equation for the water supply system under a pressurized water diversion system and solve the hydraulic elements at the beginning and end of the pressurized flow section in the system; S36. Convert the hydraulic element at the end of the pressure flow section into the hydraulic element at the section where the m+1th node of the corresponding open channel flow section or the open-full alternating flow section is located; S37. Compare the hydraulic element of the terminal section obtained in the k+1th iteration with the hydraulic element of the terminal section obtained in the kth iteration. If the accuracy requirement is met, proceed to the next step; if not, return to S33. S38. For open channel flow sections or open-channel and open-full alternating flow sections in the water supply system, the hydraulic elements of the section where the iteratively obtained m+1th node is located are recursively extrapolated to the section where the 1st node is located, and serve as the initial state of each section of the open channel flow section or open-channel and open-full alternating flow section; for pressurized flow sections in the water supply system, the values obtained by iterative iteration are used as the initial state of each hydraulic node.

2. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 1, characterized in that: Step S33 includes: ； Where: is the water level of the section where the i-th node is located at the k-th iteration; is the average cross-sectional width of the section where the i-th node is located; is the bottom elevation of the section where the i-th node is located; is the head loss coefficient of the section where the i-th node is located.

3. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 2, characterized in that: Step S34 includes: ； ； Where: is the head loss coefficient along the way; using this formula, the open channel flow section or the open and full alternating flow section is quantified into a cross-sectional area of , the length is The pressurized flow section.

4. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 1, characterized in that: In solving the initial steady state conditions and hydraulic transition process, the calculation time step of the open channel flow section, the open-full alternating flow section, and the pressurized flow section is the same, and the selection of the calculation time step satisfies the Courant condition.

5. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 1, characterized in that: The number m of segments into which the length of the open channel flow section or the open-full flow alternating flow section is evenly divided is determined based on the length of the corresponding open channel flow section or the open-full flow alternating flow section and the distance corresponding to the calculation time step.

6. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 1, characterized in that: Step S5 includes: S51, based on the hydraulic elements of the current n-th time layer of the section where the i-node is located, calculate the virtual water level and virtual flow rate of the section where the i-node is located at the n+1-th time layer; S52, calculating the actual water level and actual flow rate at the n+1 time layer of the section where the i node is located based on the virtual water level and virtual flow rate at the n+1 time layer of the section where the i node is located; S53, calculating the error between the actual water level of the section where the i node is located at the kth iteration in the n+1th time layer and the virtual water level of the kth iteration in the n+1th time layer. If the calculation requirement is not met, return to step S52; if the calculation requirement is met, proceed to the next step; S54, calculate the error between the actual flow of the section where the i node is located in the kth iteration in the n+1th time layer and the kth virtual flow in the n+1th time layer. If the calculation requirement is not met, return to step S52; if the calculation requirement is met, proceed to the next step; S55. Using the water level and flow obtained in the previous step of the iteration of the section where the second node and the mth node are located, perform a one-sided difference quotient to estimate the water level and flow in the section where the first node and the m+1th node are located in the n+1th time layer. S56. Substitute the structural matrix equation of the entire water supply system into the equation and solve the hydraulic elements of each node; S57. Determine whether the current time layer number n meets the requirement of the total simulation time N. If not, enter the next time layer and return to step S51; if it meets the requirement of the total simulation time, end the calculation.

7. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 6, characterized in that: Step S51 includes: ； ； Where: is the k-th iterative water level result in the n+1th layer of the section where the i-node is located; is the k-th iteration flow result of the section where node i is located in the n+1th layer; is the final iterative flow result of the section where the i+1 node is located in the nth time layer; It is the hydraulic gradient of the open flow section; is the iteration coefficient, which takes ; B is the water surface width of the calculation section; A is the average water-passing cross-sectional area of the calculation section; The step S52 includes: ； ； Where: 、 are the actual water level and actual flow of the section where node i is located at the kth iteration in the n+1th time layer; 、 are the k-th virtual water level and flow rate of the section where the i+1 node is located in the n+1th time layer, and their values are equal to the k-1th iterative water level and flow rate of the n+1th time layer in step S51; is the average width of the water surface at the kth iteration in the nth time layer at the section where the i node is located; The bottom slope of the channel.

8. The method for predicting hydraulic transient characteristics of a water supply system with diverse flow patterns according to claim 6, characterized in that: The step S55 includes: ； ； ； 。

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