CN112036043A

CN112036043A - Method for calculating fracture model of long-distance gravity flow large-pipe-diameter water supply pipeline

Info

Publication number: CN112036043A
Application number: CN202010912356.8A
Authority: CN
Inventors: 向小华; 吴晓玲; 张焱; 王船海
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2020-09-02
Filing date: 2020-09-02
Publication date: 2020-12-04
Anticipated expiration: 2040-09-02
Also published as: CN112036043B

Abstract

The invention discloses a method for calculating a fracture model of a long-distance gravity flow large-pipe-diameter water supply pipeline, which comprises the following steps of: s1: after a pipeline breakage accident occurs, calculating a model that a water head of an upstream water inlet is constant when a gate of an upstream water inlet is closed and a break is leaked under the constant water head; s2: calculating a model that the residual water in the pipeline continuously leaks until the water is exhausted after the gate is closed; the problem of seamless integration of the GIS and a professional model is solved, and the problem of expansion of GIS objects and analysis functions as required is solved.

Description

Method for calculating fracture model of long-distance gravity flow large-pipe-diameter water supply pipeline

Technical Field

The invention relates to the field of fracture model calculation of a large-diameter water supply pipeline, in particular to a method for calculating a fracture model of a long-distance gravity flow large-diameter water supply pipeline.

Background

Although the burst accident submergence simulation calculation modes are various, the simulation calculation of any breaking point model is realized on the cold long-distance gravity flow large-pipe-diameter water supply pipeline; the double-object sharing structure framework for realizing the sharing of the GIS object and the model object provides GIS core functions of spatial analysis, spatial information management and the like for the model object, provides core functions of professional model simulation analysis of physical mechanism, space-time process and the like for the GIS object, and realizes the management and analysis of the space-time attribute information of the GIS object. A GIS framework of a double-object sharing structure is constructed, the problem of seamless integration of a GIS and a professional model is solved, the problem of expansion of GIS objects and analysis functions as required is solved, and model calculation for creating a GIS of a multi-dimensional space-time structure to solve any breaking point is the first time.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a method for calculating a fracture model of a long-distance gravity flow large-pipe-diameter water supply pipeline, which solves the problem of seamless integration of a GIS and a professional model and simultaneously solves the problem of expansion of GIS objects and analysis functions as required.

The invention adopts the technical scheme that the method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline comprises the following steps:

s1: after a pipeline breakage accident occurs, calculating a model that a water head of an upstream water inlet is constant when a gate of an upstream water inlet is closed and a break is leaked under the constant water head;

s2: calculating a model that the residual water in the pipeline continuously leaks until the water is exhausted after the gate is closed;

s3: the starting point of the long-distance water transmission pipeline of the stone mill mountain is arranged on the right side of a stone mill mountain reservoir, the distance from the dam is 50.0m, the elevation of the center point of the inlet of the pipeline is 292.54m, the designed water intake level is 298.0m, the normal water storage level of the reservoir is 318.0m, the check flood level of the reservoir is 323.26m, and the water heads at the inlet of the pipeline obtained under the three water levels are 5.46m, 25.46m and 30.72m respectively;

s4: on the basis of S3, a pipeline fracture model is established by taking a crevasse point as a center, and a water seepage flooding model is established by comprehensively considering river channels, roads and civil house infrastructure;

s5: calculating and analyzing the break flow of the one-storey house area and the Wuchang city;

s6: a GIS framework of a double-object sharing structure for realizing the sharing of a GIS object and a model object;

s7: a GIS object and a model are used for providing spatial analysis and spatial information management;

s8: a GIS object and a model provide a core function of a physical mechanism and space-time process professional model simulation analysis;

s8: the GIS objects and the model provide space-time attribute information management and analysis, a GIS framework with a double-object sharing structure is constructed, and the problem of seamless integration of the GIS and a professional model is solved;

s9: the problem of expanding GIS objects and analysis functions as required is solved by the GIS objects and models, and a GIS with a multi-dimensional space-time structure is created.

The method for calculating the fracture model of the long-distance gravity flow large-pipe-diameter water supply pipeline has the following beneficial effects:

1. in order to effectively deal with serious consequences such as farmland inundation, casualties, traffic interruption, property loss and the like possibly caused by the burst of the long-distance water transmission pipeline of the millstone mountain, a burst model, namely a pipe burst model of the long-distance water transmission pipeline of the millstone mountain is established by combining the engineering construction practice of the long-distance water transmission pipeline of the millstone mountain, around the risk assessment and the normal-abnormal management target and by utilizing the two-dimensional shallow water flow principle. The model comprises two parts of simulation of overflow of water flow caused by pipeline fracture and simulation of overflow flooding, a simulation system which takes single-point bursting and multi-source influence as the core is constructed by taking the digital elevation of the DEM along a long-distance water conveying pipeline of nearly 177km as the support, and the simulation system is used for predicting and evaluating the flooding influence range and the disaster degree caused by pipeline fracture.

2. The pipeline bursting overflow simulation is divided into a flow process before closing the gate and a flow process after closing the gate, the water flow overflow situation of a break point in the flow process is simulated in actual production, flooding simulation is carried out on crossing points such as a pressure amplitude severe point, an overpressure point, a safety concern city, a river channel, a road and the like of the most explosive point pipe, such as a five-normal city and a single-storey house area, and detailed calculation is carried out on the flooding area and the flooding depth generated after pipe bursting to form a pipe bursting simulation result library, so that a better effect is obtained, and simulation analysis results can provide important reference basis for the starting decision of an emergency plan.

Drawings

FIG. 1 is a flow chart for modeling a line break model according to the present invention.

FIG. 2 is a schematic diagram of a discrete grid of surface computing units in accordance with the present invention.

FIG. 3 is a model calculation flow of the present invention.

FIG. 4 is a GIS processing feature information according to the present invention.

FIG. 5 is a GIS processing feature information according to the present invention.

FIG. 6 is a schematic diagram of a two-dimensional differential grid according to the present invention.

FIG. 7 is a flow chart of the calculation of the outflow before the flow regulating valve is closed.

FIG. 8 is a flow chart of the calculation of the outflow after the flow regulating valve is closed according to the present invention.

Fig. 9 is a schematic of the present invention along the line total head and free head.

FIG. 10 is a schematic view of the break point and simulation range of the single-storey house area of the present invention.

FIG. 11 is a plot of the calculated area building distribution for the single-story zone of the present invention.

Fig. 12 is a plot of the calculated area building distribution for the one-storey house area of the present invention.

FIG. 13 is a plot of the present invention flat-bed break leakage flow rate.

FIG. 14 is a simulation of the present invention for the breach flooding in the bungalow area (condition 1).

FIG. 15 is a line graph showing the change of each process of the present invention in the single-story building area (condition 1).

FIG. 16 is the present invention bungalow area breach leak flow process (condition 2).

FIG. 17 is a simulation of the present invention for the breach flooding in the bungalow area (condition 2).

FIG. 18 is a line graph showing the change of each process of the present invention in the single-story building area (condition 2).

FIG. 19 is the present invention bungalow area breach leak flow process (condition 3).

FIG. 20 is a simulation of the present invention for bungalow area breach submergence (condition 3).

FIG. 21 is a line graph showing the change of each process of the present invention in the single-story building area (condition 3).

FIG. 22 is a schematic diagram of the breach point and simulation range of Wuchang City according to the present invention.

FIG. 23 is a calculated regional building distribution diagram for Wuchang city according to the present invention.

FIG. 24 is a topographical view of the periphery of a breach point in Wuchang City of the present invention.

FIG. 25 is a topographical view of the periphery of a breach point in Wuchang City of the present invention.

FIG. 26 is a simulation of breach submergence in Wuchang City of the present invention (condition 1).

FIG. 27 is a graph showing the line change of the process of the present invention (working condition 1).

FIG. 28 is a crevasse leak flow process in Wuchan City of the invention (condition 2).

FIG. 29 is a simulation of breach submergence in Wuchang City (condition 2) of the present invention.

FIG. 30 is a graph showing the line change of the process of the present invention (condition 2).

FIG. 31 shows the crevasse leakage flow process of Wuchangshi (condition 3) of the present invention.

FIG. 32 is a simulated breach flooding diagram (condition 3) in Wuchang City of the present invention.

FIG. 33 is a graph showing the line change of the process of the present invention (condition 3).

Fig. 34 is a schematic view of a weak section breaking point 1 and a simulation range according to the present invention.

Fig. 35 is a calculated area building map of weak section 1 of the present invention.

Figure 36 is a topographical view around the point of weakness breach 1 in accordance with the present invention.

Figure 37 is a graph of the weak section break point 1 leak flow rate process of the present invention.

Fig. 38 is a simulated flooding pattern for a weak section breach 1 leak in accordance with the present invention.

Fig. 39 is a schematic view of a weak section breaking point 2 and a simulation range according to the present invention.

Fig. 40 is a calculated area building map of the weak section 2 of the present invention.

Figure 41 is a topographical view of the present invention around the point of weakness breach 2.

Figure 42 is a graph illustrating the weak section breach point 2 leakage flow process of the present invention.

Fig. 43 is a simulated flooding pattern for a weak section breach 2 leak in accordance with the present invention.

FIG. 44 is a comparison of average submergence depths at three roughness levels of the present invention.

FIG. 45 is a plot of the area of submersion at three roughness levels of the present invention.

Detailed Description

The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.

The pipeline explosion is the most serious accident for the long-distance water transmission pipeline of the millstone mountain. From the risk impact analysis, it is known that a pipe burst, once it occurs, can lead to a water supply interruption and a certain extent of flooding downstream. And the interruption of water supply can cause large-scale water cut-off in urban areas, which seriously affects the normal life of people, and if the water cut-off time is too long, the water cut-off device can cause people dissatisfaction and panic, which causes extremely bad influence on social stability. Meanwhile, the surrounding area is submerged by the pipe explosion pipe, and the surrounding ecological environment can be damaged. In order to scientifically predict and evaluate the influence and the consequence caused by the pipeline rupture, the pipeline rupture submerging model is used for simulating the change process of the submerging range, the submerging water depth and other elements, and an important decision basis is provided for the starting of an emergency plan, so that a series of problems caused by the pipeline rupture can be effectively solved.

1. General working idea

The primary total length of the water supply engineering water transmission pipeline of the millstone mountain reservoir is 175.33km, the secondary total length is 176.93km, the starting point is the millstone mountain reservoir in Harbin Wuchang City, the whole course respectively passes through the single-storey houses of Wuchang city, Alcity, double city and Harbin city, and the ending point is the millstone mountain water purification plant in the single-storey houses. The pipeline passing area is large, the landform is complex, and the shape is long and narrow.

The modeling is mainly considered from the following two points:

(1) is the selection of the rupture point: theoretically, the long-distance pipeline is influenced by various factors such as natural environment, water supply flow change, pipeline corrosion, non-resistance, management measure effectiveness, a third party and the like, and the pipeline can be broken at any point along the pipeline, so that leakage or overflow accidents can occur. Thus, any point of the pipeline can be chosen in the modeling process taking into account the point of rupture.

(2) Is the selection of relevant simulation parameters after rupture: the actual overflow process caused by the broken pipeline is quite complex and is difficult to simulate by a physical-mathematical formula under general conditions, so that the modeling of the time is suitable for simplifying some conditions and setting the following conditions:

1) after a pipeline breakage accident occurs, the water head of the upstream water inlet is constant when the upstream water inlet gate is closed, and a broken opening leaks under the constant water head;

2) the remaining amount of water in the pipe continues to leak until exhausted after the gate is closed.

The starting point of the millstone mountain long-distance water transmission pipeline is arranged on the right side of the millstone mountain reservoir, the distance from the starting point to the dam is about 50.0m, the elevation of the central point at the inlet of the pipeline is about 292.54m, the designed water intake level is 298.0m, the normal water storage level of the reservoir is 318.0m, and the check flood level of the reservoir is 323.26 m. The water heads at the inlet of the pipeline obtained under the three water level conditions are respectively 5.46m, 25.46m and 30.72 m. On the basis of the conditions, the establishment of the pipeline fracture model takes the break point as the center, comprehensively considers the infrastructures such as the river channel, the highway, the civil house and the like, and establishes the seepage flooding model. The basic idea is as follows:

1.1 basic data processing: extracting terrain information of the submerged area, generating a terrain DEM, and establishing a computational model triangular mesh; treating buildings such as houses and the like as non-water units; and extracting information such as road elevation and the like, and setting the elevation in the calculation grid to simulate the water blocking effect of the road.

1.2 model calculation parameter settings: the method comprises the steps of setting pipeline parameters, setting a water level of a pipeline inlet reservoir, a position of a breaking point and time for closing a gate after a pipeline is broken, and closing the gate, namely the time for closing the flow regulating pressure regulating valve after the pipeline is broken, wherein once the pipeline is broken, an upstream flow regulating pressure regulating valve closest to the breaking point is closed firstly.

1.3 break point outlet flow process simulation: the method comprises an outflow process before closing the gate and an outflow process after closing the gate.

1.4 building a flooding simulation model: and establishing a submerging model of regional water flow, and simulating a submerging process of the water flow with the break flow process as an input condition.

1.5 inundation range and impact analysis: and analyzing the change process of the submerging depth and the submerging range along with time to make influence assessment.

2. The specific process is shown in the following figure and figure 1.

3. Theoretical basis of model building

(1) Contents of model construction

1) Three-dimensional topography

In Arc info 9.0 or 10.0, a digital elevation model (DEM, scale 1:10000) is purchased, a millstone mountain long-distance water transmission pipeline is used as a center, the pipeline extends 10km-15km towards two sides respectively, and the digital elevation model of the pipeline and the surrounding region is established. And through the superposition of other related information, a complete three-dimensional terrain is obtained, and basic support is provided for model simulation calculation and simple result display.

2) Development and application of pipeline bursting and submerging simulation model

The model development comprises four stages, wherein the first stage is submerged model principle analysis and comprises mathematical and physical model establishment, and the second stage is program development (code writing) of the model; the third stage comprises model debugging and parameter calibration; the fourth stage includes model application.

Simulation of water overflow

And establishing a water quantity overflow model according to the position of a fracture point, the flow speed in the pipeline and the pipeline fracture mode by combining a pipeline correlation theory, a two-dimensional dynamic wave model and the like, wherein the water quantity overflow model is used for simulating the water quantity overflowing along with the change of time, and the support is provided for the submergence analysis. Pipeline rupture is generally modeled in two modes:

a sudden rupture: causing a large gush of water (instantaneous point source), but as the incident progresses, until the water in the pipe (upstream of the break point to the butterfly valve closure) gushes out

b, slow cracking: the water flow in the pipe is relatively slow to gush out (can be regarded as constant flow), but as the accident treatment progresses, until the water in the pipe (upstream of the breaking point to the butterfly valve closing point) gushes out

(ii) flood routing calculations

a surface confluence

The continuous equation:

in areas where buildings are distributed, the following formula can be shown:

the momentum equation:

in the X direction

Y direction

Neglecting the inertia term to obtain (the diffusion wave equation):

wherein u and v are flow velocities in x and y directions respectively; h is the depth of water (m); h is the water surface elevation (m); h + z, z being ground elevation; n is a Manning coefficient; and q is a source-sink item (m/s) and reflects rainfall and overflow processes and the like.

Reflecting the influence of the building on the water flow, linear ratio of building area with water blocking on the unit, no water blocking buildingTake 0, A_bThe area is the area of the building land, and A is the unit area; s_fx，S_fyFriction gradient in x, y direction respectively:

a schematic diagram of a discrete grid of surface elements is shown in fig. 2

Solving the diffusion wave equation by applying an explicit difference format:

according to the (5) and the friction gradient (. +), the flow velocities u and v along the x and y directions can be calculated, and the flow Q entering and exiting the unit along the x and y directions is obtained by multiplying the water depth h and the side length d of the unit grid₁，Q₂，Q₃，Q₄: then calculating according to a water balance equation (1) to obtain the water depth h:

wherein:

Q₁to Q₄: flow into and out of the cell (positive in and negative out)

q_ij: the source and sink items of the unit (source is positive and sink is negative) mainly include rainfall, water exchange with a rainwater port, water exchange with a river network and the like.

b river course confluence

And solving the unsteady flow of the natural river channel and the channel confluence according to a continuous equation and a momentum equation of the one-dimensional unsteady flow, namely a one-dimensional Saint-Vietnam equation set.

The continuous equation:

the momentum equation:

substituting the continuity equation into the momentum equation then is:

wherein: q-flow through river, m³S; v-river water flow speed, m/s; a-area of flow area, m²(ii) a H-water head, river bottom elevation and water depth, m; a. the_s-nodal water surface area, m²；S_f-friction gradient, solved by the manning equation:

wherein K is gn²N is Mannich roughness, R is hydraulic radius, m.

Solving the river (pipe) network flow problem expressed by the basic equation by applying an explicit difference format: for (8), the following differential format is employed:

finishing to obtain:

for (6), in order to make the node water level solution convenient, the continuous equation is rewritten as:

the differential format is therefore:

wherein:

A_S: calculating the water surface area of the control body for water balance;

∑Q_t: the water quantity balance calculates the algebraic sum of the inlet flow and the outlet flow of the control body.

The fundamental variables Q and H are solved using flow equation (11) and continuous equation (13).

Simulation and analysis of inundation calculation

Considering that the factors causing flooding due to pipeline bursting have multiplicity, the models are divided into a single-source model and a multi-source model during modeling. The single-source model means that the flooding is only caused by the burst of the pipeline, and no other water source factors exist; the multisource model mainly combines local river channels, and other water sources such as pipe explosion sources and river water flows are considered comprehensively. The flooding simulation analysis based on GIS and RS involves two key problems: simulation of the submerging surface and calculation of the submerging range.

A single-source model: and establishing a three-dimensional terrain in combination, taking a pipeline fracture point as a center, taking the overflow water amount caused by pipeline fracture as the total water amount, taking time dynamic evolution as a parameter, simulating and analyzing the submerging range and the submerging area caused by analysis, and providing decision support for taking targeted measures.

Multi-source model: if the pipe burst water flow is converged to enter the river channel or burst at the river channel crossing position, the pipe burst water flow and the river channel water flow are considered together, and the analysis and calculation of the submerging range and the area of the multi-water source are carried out, such as the rupture of the river channel nearby or at the river channel crossing position.

The inundation simulation calculation method comprises the following steps: by using the advanced technology in the current river confluence and flooding theory, referring to a distributed hydrological model, calculating the flooding area (taking evolution time as reference) according to the current related technology for judging flooding, and calculating different types and corresponding areas of the flooded ground objects by using tools such as arc info and the like, thereby providing data support for flooding analysis and post-disaster evaluation.

The model calculation flow is shown in FIG. 3 below;

3) model development

The Fortran is combined with VB to develop a model, a main program is compiled by the Fortran, the method has the advantages of being fast in calculation, simple and fast in programming of program codes and the like, but the interface friendliness is poor, and a good input and output interface can be compiled by the VB to be dynamically linked with the GIS (secondary development) so that the interface is friendly (part of the content of informatization work).

4) Model debugging and parameter calibration

On the basis of the completion of the development of the main program, the collected existing data is utilized to debug and calculate the model, and the parameters are calibrated to ensure the good effect of the model application.

5) Model application

(ii) analog computation

The method has the advantages that the flooding area and the flooding range caused by pipeline rupture at a plurality of places can be simulated through the calibration of model parameters, and the flooding area and the flooding range can be simulated by taking the position and the rupture mode of the pipeline rupture point and the environment around the rupture point as input conditions.

② dynamic display and simulation of submerging range

According to the established pipeline bursting flooding simulation model, flooding ranges, flooding areas and the like in different time after the pipeline is broken are dynamically displayed by a time axis, and corresponding flooding things (villages, roads, railways, farmlands and the like) are analyzed and evaluated.

(2) Work is emphasized

The position of the pipeline accident: the occurrence of the risk accident has uncertainty, and according to the initial result of the risk assessment (pipeline high risk point), the model can assume any point of the pipeline as the position where the accident may occur according to the actual distribution position of the pipeline, and the position is used as a model input alternative condition.

And (3) overflow simulation calculation: and performing overflow calculation by adopting a single-source and multi-source mode and considering a pipeline fracture mode and a fracture position.

Determining the simulation range: according to the primary analysis of the crossing position of the water pipeline, the position where an accident is likely to occur and the regional topographic map, the simulation range is determined in a key mode, and decision support is provided for pipeline operation scheduling, accident emergency plan processing and the like in the future.

Selecting a model discrete method: and (4) taking the actual requirements of the model into consideration, and performing the discretization of the model equation by adopting a finite difference method and the like.

(3) Technical route and working scheme

The work is carried out on the principle of taking the whole body into consideration and highlighting the key points;

on the basis of widely collecting data and field investigation, a project develops a method section combining theory and practice, takes practical application as a starting point, combines advanced GIS, RS and other technologies, develops a pipeline bursting and submerging simulation model research on the basis of flood evolution equations such as Saint-Venn's equation and two-dimensional diffusion wave equation, and provides decision support for guaranteeing safe operation and fault emergency treatment of a water pipeline.

4. Terrain data preprocessing

The simulation relates to a large range, wherein the data related to the submerging simulation comprises terrain elevation points, water systems, water supply pipelines, roads, buildings and other terrain features, and the ArcGIS 9.0 software is adopted to extract the features of the terrain features. In the modeling process, a house is assumed to be impervious, the house is treated as a watertight boundary, and the ground elevation is set in a grid to reflect the water blocking effect of buildings such as roads. The topographic data processed by the GIS software is shown in FIG. 4, and the local topography behind the house is shown in FIG. 5.

5. Breach flow process simulation

The simulation of the break outflow needs to consider the actual conditions when the accident occurs, such as the opening and closing state of the gate, the current flow in the pipe and other factors. Referring to actual operation conditions, the outlet flow of the pipeline after the opening is broken can be divided into an outlet flow before the gate is closed (outlet flow before the gate is closed for short) and an outlet flow after the gate is closed (outlet flow after the gate is closed). Since the principles of these two parts of the simulated outflow are different, they will be discussed separately below.

(1) Flow process before gate closing

The total design flow of the millstone mountain reservoir water supply project is 95.481 ten thousand meters³D, single pipe design flow of 47.741 km³D, i.e. single tube inflow of 5.53m³And s. From the hydraulic analysis, the single pipe network leakage point can be regarded as free outflow or submerged outflow of a small orifice, and is calculated by an orifice outflow equation:

in the formula: q-amount of leakage water, m³/s；

A-area of the leakage opening, m²；

H-free water pressure of the pipeline, m;

the mu-orifice flow coefficient is generally between 0.60 and 0.62.

A series of tests carried out by researchers in countries such as the united kingdom, japan, etc. have shown that the following empirical relationship exists between the amount of water leakage and the free water pressure at the node:

Q＝λH^1.18 (0-2)

in the formula: lambda-loss coefficient, m^1.9/s。

The flow rate of the broken pipe proposed by Zhou Jianhua, etc. of Harbin Industrial university should be composed of two parts: the flow generated by the first part due to the fact that the area of the rigid material leakage opening does not change along with the pressure, the flow generated by the second part due to the fact that the area of the flexible pipe leakage opening increases along with the pressure, and the sum of the two flow is leakage flow and is expressed as follows:

Q＝Q₁+Q₂ (0-5)

in the formula: a. the₁First partial leakage area, not variable with pressure, m²；

A₂Second partial leakage area, varying with pressure, m²；

The characteristic coefficient of the k-leakage opening area expanding and contracting along with the pressure.

The experimental research of Zhoujianhua and the like shows that the water leakage quantity and H of the crack or the hole of the pipeline caused by pipe explosion and the like^0.5In a direct proportion to the total weight of the composition,the leak area will not change with pressure changes and the orifice flow equation can be applied to leaks caused by pipe breaks such as pipe bursts. Consider that the pipeline that adopts in this project is mostly rigid pipe, and the simulation is the process of effluenting after the booster, so adopt the drill way to effluent the simulation process of effluenting, promptly:

the key to flow process simulation is to determine the free water pressure H, which can be calculated using the following formula:

H＝H₀-c₁×L×Q₀ (0-7)

c₁＝10.667L/(c^1.852d^4.87) (0-8)

in the formula: h₀-head of water at the inlet of the pipe, m;

Q₀flow at the inlet of the pipe, m³/s；

L-the distance, m, from the point of disruption to the entrance of the pipeline;

c-Hazen-Williams coefficient, determined by the pipe material;

d-pipe diameter, m.

(2) Flow process after closing the gate

After the gate is closed, the remaining water flow in the pipe gradually decreases with leakage until it is totally discharged. The leak outflow process is also calculated according to the orifice outflow pattern, i.e. the following equation:

in the formula: the mu-orifice flow coefficient is generally between 0.60 and 0.62;

h_fthe head of water from the free water surface to the leak point in the pipe at present, unit: m, can be calculated from the following formula:

in the formula: v-flow velocity in the pipe, m/s;

r-hydraulic radius, m;

j-head gradient;

c-metabolic capacity coefficient;

n-roughness of the pipeline, which is 0.013 according to the material of the pipeline simulated at this time;

l-the distance from the position of the free water surface in the pipe to the break point, m;

d-pipe diameter, m.

Because the diameter of the water supply pipeline in the project is more than 2.0m, y in the theory coefficient C formula is calculated by adopting a Pavlofsky formula.

The complete flow process of the leakage point can be obtained by the simulation of the two stages and is used as an input condition of the flooding model.

5.1 submerged model calculation principle

After water leakage leaks from the pipeline, water flow is propelled to the periphery on the dry ground, the simulation at the moment is equivalent to the water flow simulation of a flooding area, and the simulation can be described by adopting two-dimensional shallow water flow. The equation is in the form:

in the formula: z is water level, u and v are flow velocity in x and y directions respectively; u, V single width flows in the x and y directions, respectively;

is a vector of the single-wide traffic,

is a mold for the same, and is,

q is a source item considering rain fall and other factors; g is the gravity acceleration, c is the allelochemical coefficient, and f is the Coriolis force coefficient; tau is_wx、τ_wyThe components of the wind stress in the x and y directions, respectively, can be calculated using the following formula:

wherein: rho_a-the density of the air;

c_D-a drag coefficient;

-wind velocity vector at 10m height from the water surface.

For the two-dimensional shallow water wave equation, splitting the equation into the following two steps by adopting a breaking operator method; and then solving them separately by a suitable method.

A first step:

the second substep:

and (4) solving the numerical value of the above bipartite step equation set by adopting a volume control method of a non-uniform rectangular grid under a rectangular coordinate system. The urban area is normally the waterless ground, and there is water exchange between the break and the general area under the condition of burst of the pipeline, and the following description takes a second step equation set as an example, as shown in fig. 6:

first, for the discretization of the x-direction momentum equation in (0-14), the interface between cells I and J is taken as an example as follows:

in the formula: the subscript "0" indicates the known value at the beginning of the time.

The finishing is simplified to obtain:

U＝₀(Z_I-Z_J)+β₀ (0-16)

multiplying Δ y by the above equation gives the flow from unit I into unit J as:

Q_X＝_X(Z_I-Z_J)+β_X (0-17)

similarly, the flow rate of the unit K to the unit J obtained by dispersing the y-direction momentum equation in the pairs (0-14) is as follows:

Q_Y＝_Y(Z_K-Z_J)+β_Y (0-18)

discretizing the continuous equation in (5.3-14) to obtain:

simplifying to obtain:

in the formula: a is the area of unit J, ∑ Q_iRepresenting the algebraic sum of the amount of water flowing into unit J per unit time, including rainfall.

6. Breach flow analysis

Taking the bungalow area and the crevasses in Wuchang city as examples, after the crevasses occur, the outflow process is respectively considered according to the two states before and after the flow regulating pressure regulating valve is closed. The calculation flow before closing the flow control pressure regulating valve is shown in fig. 7, and the calculation flow after closing the flow control pressure regulating valve is shown in fig. 8.

According to the calculation process, the outlet flow and the head loss of the bungalow area and the breach of Wuchang city before the flow regulating and pressure regulating valve is closed are obtained and are shown in table 1.

According to calculation, when the reservoir water level is the check flood level, the first pressure stabilizing well and the second pressure stabilizing well both play a role in pressure regulation, and the water head at the corresponding position is regulated to the overflow water level. At the moment, the water head at the first pressure stabilizing well is 278.00m, the water head at the second pressure stabilizing well is 239.00m, and the on-way total water head and the free water head before and after pressure regulation are shown in fig. 9.

TABLE 1 calculation table for single-tube crevasse outflow of one-storey house district and Wuchang city

Before the upstream flow regulating pressure regulating valve is closed, the upstream water level is constant, and the water purifying head at the break point is correspondingly constant, so that the break flow is relatively constant, and after one hour, the break flow is reduced due to the pressure reduction of the break point after the valve is closed until the water purifying head at the break point is close to zero, and the break point does not outflow any more. The simulation assumes that the gate is closed instantaneously, wherein water does not seep from the crevasses 2 hours after the valve is closed in the bungalow area, and water does not seep 1 hour and 20 minutes after the valve is closed in Wuchangshi, and the specific simulation process is shown in the following section.

7. Flooding simulation and result analysis

The simulation mainly considers the selection of a typical case of pipeline rupture flooding simulation from two aspects:

in areas with dense population and developed economy, the flooding easily causes great loss and needs to pay attention;

the weak section (point) of the long-distance pipeline is relatively easy to explode, and also needs to pay attention.

By combining the two conditions, the simulation selects a 'Wuchang city area' and a 'Harbin bunk area' as typical areas with dense population, and simultaneously selects two areas with relatively weak pipelines (connected with the research result of pipeline water hammer protection) as explosive pipe areas to carry out submergence simulation respectively so as to reflect the influence degree and range of the explosive pipes and provide a basis for emergency decision.

7.1 Haerban City flat-room area

The Halbin city bungalow area is positioned at the tail end of a long-distance pipeline, buildings and other buildings are concentrated, the population density is high, and the Halbin city bungalow area is one of areas needing important precaution. The simulated crevasses and the simulation range of the model are shown in fig. 10, the building distribution is shown in fig. 11, the simulation area terrain is shown in fig. 12, the upper right corner of the area is a river channel, the whole area terrain is high in the middle and at the bottoms of two sides in the north-south direction, the crevasses are located on the central high ground, and the periphery of the area is a dense population area, so that the large loss is caused by inundation. The pipeline distance between the break point and the water taking point of the millstone landscape reservoir is 173.2 km. The following three working conditions are set for respectively simulating, wherein the most unfavorable water level state is taken by the upstream millstone mountain reservoir, namely the water level of the millstone mountain reservoir is the check flood level 323.26 m:

(1) the water level of the millstone landscape reservoir is 323.26m, and the normal water delivery flow of the single pipe is 5.53m³The single pipe is broken, and the upstream nearest flow regulating pressure regulating valve is closed 1 hour after the pipeline is broken;

(2) the water level of the millstone landscape reservoir is 323.26m, and the normal water delivery flow of the double-pipe is 11.06m³(s) breaking the double pipes, and closing the upstream nearest flow regulating pressure regulating valve 1 hour after the pipeline is broken;

(3) the third working condition is the most unfavorable condition, the water level of the grinding disc mountain reservoir is 323.26m, and the normal water delivery flow of the double-pipe is 11.06m³And/s, the last time (2 hours) after the double tube rupture did not close the upstream most recent flow regulating pressure regulating valve.

The probability of double-pipe rupture in actual operation is low, so the first working condition (working condition 1) is a general condition, the second working condition (working condition 2) is an rare condition, the third working condition (working condition 3) is the most unfavorable condition, and rupture submergence simulation is respectively carried out on the three working conditions.

Working condition 1:

the leakage flow at the break in the first condition is shown in figure 13. Before the gate is closed, the water head of the water inlet of the water supply pipe is constant, and leakage flows out at a constant flow rate; when the gate is closed, the pressure of water flow in the pipe is reduced, the outflow flow of the leakage port is reduced, and the maximum flow in the whole leakage process is 11.6m³S for a total time of 2 hours.

The breach leak flow was greatest within 1 hour after the pipeline was breached to close the gate, resulting in the greatest extent of flooding, simulating flooding within 2 hours after the breach occurred, as shown in fig. 14. Calculation shows that after the pipeline at the selected position is broken, the water flow submerging range extends along the northeast direction of the broken point and finally converges into the northeast corner river channel, buildings in a submerging area are few, water flow quickly passes through the area and converges into the river channel, and the detention time is short.

The average submerging depth of the submerging area, the total water volume of the submerging area and the change rule of the submerging area along with time under the working condition are shown in figure 15, and the average submerging depth is 0.22m after 2 hours of breach; the maximum submerged depth is 0.51m when the initial breach appears; the submerged area increases with the amount of water in the breach and is about 0.27km²。

Working condition 2:

the leakage flow process of the crevasses under the second working condition is shown in figure 16, and the maximum flow in the whole leakage process is 23.3m³And/s, before the gate is closed.

The simulation process of submerging within 2 hours after the break occurs is shown in fig. 17, the submerging direction of water flow is similar to that of the working condition 1, the water flow finally flows into the northeast corner river channel, and the submerging range at the moment is obviously larger than that of the working condition 1.

The average submerging depth of the submerging area, the total water volume of the submerging area and the change rule of the submerging area along with time under the working condition are shown in figure 18, and the average submerging depth is 0.34m after 2 hours of breach; the maximum submerged depth is 0.65m when the initial breach appears; the submerged area increases with the increase of the amount of water at the breach, and is about 0.36km²。

Working condition 3:

the leakage flow process of the third working condition is shown in FIG. 19, and the maximum flow in the whole leakage process is 23.3m³And/s, the gate is not closed. Since the whole process is constant flow, only 2 hours are intercepted in time in order to keep the same with the former two working conditions.

Because the simulation of the former two working conditions shows that after the selected point is broken, the water flow flows to the northeast corner, and the influence on the left area is very small, so that the calculation area is concentrated in the right area under the working condition.

The submergence process within 2 hours after the simulated break occurs is shown in fig. 20, the submergence direction of water flow is similar to that of the working condition 1, the water flow finally flows into the northeast corner river channel, and the submergence speed and the submergence range at the moment are obviously larger than those of the first two working conditions. The average submerged water depth of the submerged area, the total water volume of the submerged area and the change rule of the submerged area along with time under the working condition are shown inFIG. 21. As can be seen from the figure, after 2 hours of breaching, the average depth of the flood was 0.39 m; the maximum submergence depth is 0.65m when the initial breach appears; the submerged area increases with the increase of the water flow at the break, and is about 0.43km²。

And 3 working condition comparisons:

the simulation is carried out on 3 conditions that the single pipe breaks for 1 hour and closes the gate, the double pipe breaks for 1 hour and closes the gate and the double pipe breaks for a longer time and does not close the gate, the flooding trends of 3 working conditions are approximately the same in the selected flooding area, the directions of the flooding ranges are approximately consistent, the flooding conditions are only different in the flooding degree, and the flooding conditions after 2 hours of breakage of the 3 working conditions are shown in a table 2. The submerged area caused by 3 working conditions is large, the average submerged depth exceeds 0.20m, and if the duration is long, certain loss is caused.

TABLE 2 comparison table for flooding conditions under three working conditions in single-storey house area

7.2 Wuchang city

The positions of the crevasses in the Wuchang city area and the simulation range of the model are shown in figure 22, the building distribution is shown in figure 23, the terrain of the simulation area is shown in figure 24, the right side of the area is a mountain area highland, the left side of the area is a low-lying area, and the crevasses are located on a central high slope. The pipeline distance between the break point and the water taking point of the millstone mountain of the water pipeline is 73.7km and is 101.8km away from a water purification plant. The set working condition of the simulation is the same as that of the bungalow area:

(3) the third working condition is the most unfavorable condition, the water level of the grinding disc mountain reservoir is 323.26m, and the normal water delivery flow of the double-pipe is 11.06m³S, long after rupture of the double tubeThe most upstream flow regulating pressure regulating valve is not closed in the time (2 hours).

Working condition 1:

the process of leakage flow rate from the break under the first condition is shown in fig. 25, before the gate is closed, the water head at the inlet of the water supply pipe is constant, the leakage flows out at a constant flow rate, after the gate is closed, the pressure of the water flow in the pipe is reduced, the outflow flow rate from the leak is reduced, and the maximum flow rate in the whole leakage process is 18.5m³And s. The maximum leakage flow from the breach to the time before the gate is closed, and the maximum flooding range, as shown in fig. 26, simulates the flooding process within 1 hour and 20 minutes after the breach. Calculation shows that after the pipeline at the selected position is broken, the water flow submerging range extends towards the west and the south along the broken point respectively, and buildings in a submerging area are fewer.

The average submergence depth of the submerging area, the total water volume of the submerging area and the change process of the submerging area with time under the working condition are shown in figure 27. As can be seen from the figure, after the breach is carried out for 1 hour and 20 minutes, the water depth of the flooding water tends to be stable, and the average water depth of the flooding water is 0.22 m; the maximum submerged depth is 0.78m when the initial breach occurs; the submerged area increases along with the increase of the water amount of the crevasse, and after 1 hour and 20 minutes of crevasse opening, the submerged area is about 0.46km²。

Working condition 2:

the leakage flow process of the crevasses under the second working condition is shown in figure 28, and the maximum flow in the whole leakage process is 37.1m³And/s, before closing the gate. The submergence process within 1 hour and 20 minutes after the simulated break occurred is shown in FIG. 29, and the water flow submergence direction is similar to that of condition 1. The submerging range is obviously larger than that of the working condition 1, and most of the submerging area has no buildings.

The average submerging depth of the submerging area, the total water volume of the submerging area and the change process of the submerging area along with time under the working condition are shown in a figure 30. As can be seen from the figure, after the breach is carried out for 1 hour and 20 minutes, the submergence depth tends to be stable, and the average submergence depth is 0.26 m; the maximum submerged depth is 0.80m when the initial breach appears; the submerged area increases along with the increase of the amount of water at the breach, and after 1 hour and 20 minutes of the breach, the submerged area is about 0.91km²。

Working condition 3:

the leakage flow process of the third working condition is shown in fig. 31, and the maximum flow in the whole leakage process is 37.1m³And/s, the gate is not closed for a long time. Since the whole process is constant flow, only 1 hour and 20 minutes are intercepted in time in order to keep the consistency with the former two working conditions.

The simulation of the former two working conditions shows that after the selected point is broken, the influence of water flow on the north is small, so that the calculation area is concentrated in the south area under the working condition.

The submergence process within 4 hours after the simulated break occurs is shown in fig. 32, the submergence direction of the water flow is similar to that of the working

conditions

1 and 2, the water flow finally flows to the south and the west, and the submergence speed and the submergence range at the moment are obviously larger than those of the former two working conditions. The average submerged water depth of the submerged area, the total water volume of the submerged area and the change process of the submerged area along with time under the working condition are shown in a figure 33, and the average submerged water depth is 0.25m after 4 hours of breaking; the maximum submergence depth is 0.82m when the initial breach appears; the submerged area increases with the increase of the water flow of the breach, and after 4 hours of the breach, the submerged area is about 3.05km²。

And 3 working condition comparisons:

the above simulation was performed for 3 cases, such as 1 hour gate closing by single-tube rupture, 1 hour gate closing by double-tube rupture, and no longer gate closing by double-tube rupture, and the comparative cases of the three conditions at 1 hour and 20 minutes are shown in table 3 in order to maintain the consistency in time. The submerging area is larger in 3 working conditions, and the average submerging depth is smaller due to the fact that the terrain of the submerging area is wider. When the flooding time lasts longer, certain loss is caused.

TABLE 3 comparison table of flooding conditions under 3 working conditions in Wuchang City

7.2.1 weak segment breach 1 simulation

Analysis of pipeline hydraulic transitionThe calculation result shows that the position of the weak section break 1 and the model simulation range are shown in fig. 34, the weak point is located between the No. 1 surge shaft and Wuchangshi, and the pile number is 5+ 900. The building distribution is as shown in figure 35. The terrain of a simulation area set by the model is shown in figure 36, the northeast part of the area is a mountain area, a slope with the height between 190-200 m is arranged below the mountain area, and a break point is positioned on a central slope. Because this section is the weak area, the pipeline is cracked relatively easily, and this area is located the mountain area, and the population is less, and this simulation adopts double-barrelled broken as the simulation condition altogether, and the settlement parameter is: the water level of the millstone landscape reservoir is 323.26m, and the normal water delivery flow of the double-pipe is 11.06m³And/s, the double pipe is broken, and the upstream flow regulating pressure regulating valve is closed 1 hour after the pipeline is broken.

Under the set adverse conditions, the breach leak flow process is shown in FIG. 37. Before the gate is closed, the water head at the inlet of the water supply pipe is constant, the leakage flows out at a constant flow rate, after the gate is closed, the pressure of water flow in the pipe is reduced, the outflow flow rate of the leakage opening is reduced, and the maximum flow rate in the whole leakage process is 41.0m³And/s, because the break point is close to the upstream entry point, residual water flow in the pipeline after the gate is closed can flow through the break point in a short time, and the leakage time is relatively short. The maximum leak flow to the breach, and thus the maximum extent of flooding, occurred within a few hours before the breach reached the closed gate, and the simulated flooding process within 1 hour and 20 minutes after the breach occurred is shown in fig. 38. Calculation shows that after the pipeline at the selected position is broken, the water flow submerging range extends towards the west and south directions along the breaking point respectively, part of the building area can be submerged after 1 hour and 20 minutes of breaking, the average submerging water depth is 0.21m, and the submerging area is 0.71km²。

7.2.2 weak segment breach 2 simulation

The position of the weak section break 2 and the simulation range of the model are shown in fig. 39, the weak point is positioned between a No. 2 surge well and Harbin city, and the pile number is 143+ 700. The distribution of buildings in the area is shown in figure 40. The model is provided with a simulated region terrain as shown in figure 41, the region is a groove terrain, and a break point is positioned in a low-lying groove. The weak area also adopts the most unfavorable condition as a simulation condition, and the set parameters are as follows: the water level of the millstone landscape reservoir is 323.26m, and the double pipes are normalThe water delivery flow is 11.05m³And/s, the double pipe is broken, and the upstream flow regulating pressure regulating valve is closed 1 hour after the pipeline is broken.

Under the set adverse conditions, the breach leak flow process is shown in FIG. 42. Before the gate is closed, the water head at the inlet of the water supply pipe is constant, the leakage flows out at a constant flow, after the gate is closed, the pressure of water flow in the pipe is reduced, the outflow flow of the leakage opening is reduced, and the maximum flow in the whole leakage process is 30.4m³And s. The submergence process within 1 hour and 20 minutes after the simulated opening occurs is shown in figure 43, and the calculation shows that after the pipeline at the selected position is cracked, the water flow submergence range advances along the grooves of the terrain, the average submerged water depth is 0.46m, and the submerged area is 0.36km². The building is located on the high ground beside the groove and is not influenced by flooding.

8. Reliability analysis of calculation results

The numerical model is adopted to simulate the flow of the actual nature, and certain errors are inevitable. In terms of error, it mainly comes from three parts: the error of the measured data, the error of the real reflection degree of the mathematical theory to the nature and the error of the numerical calculation model. For error analysis, there are two methods, i.e., a theoretical analysis method and a comparison with an actual measurement value. The model adopted by the project has second-order precision theoretically, and the simulation error mainly comes from the topographic survey error. In addition, no actually measured data of engineering accidents are compared and analyzed, so that a parameter sensitivity analysis method is mainly adopted for reliability analysis of the model.

The main parameter of the model is roughness, and the roughness influences the advancing speed of water flow on the ground. The degree of influence of the roughness parameter variation on the model simulation results was considered by adjusting the roughness to 0.015, 0.020 and 0.030. If the adjustment of the parameters has little influence on the calculation result, the parameters are not sensitive to the simulation result. The submergence degree is controlled by the terrain and the outflow rate, and the outflow process determines the submergence condition, so that the model can obtain similar results under various parameters, and the result is reliable. The parameter adjustment scheme is simulated by taking the 1-hour closing of the single pipe break in the single-storey house area as a reference.

(1) Influence of roughness on average submergence depth

The submergence depth is the final factor in the submergence assessment, and the water depth directly determines the submergence loss, so the submergence area under the three roughness parameters is considered to be compared, the reaction of the test model to the working condition is tested, and the average submergence depth in a submergence area is shown in figure 44.

The general trend is the same for the three roughness values in fig. 44, but the roughness values decrease, which leads to an increase in the water velocity and tends to form a rapid water-blocking effect in a local area. In general, the average water depth in the three cases is within 5cm, which shows that the submerging water depths in the three cases have consistent trend, the submerging depths are approximately the same, and the model calculation has higher precision.

(2) Influence of roughness on the submerged area

The inundation area directly affects the inundation loss, and fig. 45 is the inundation area comparison at three roughness levels.

As can be seen from FIG. 45, the tendency of the flooding area under the three roughness rates is approximately the same, and the flooding range is greatly different only in a local area, and is not more than 0.05km at most of the time²It shows that the model is less sensitive to roughness in this solution.

The main factors influencing flooding are terrain factors and breach flow factors. When the approximate flooding condition is determined after the breach flow is determined, the model adopts a plurality of roughness rates to verify the conclusion, and the model is high in reliability. The simulation result can be used as a reference basis for actual decision.

9. Small knot

Through the simulation of the above 4 typical examples, the following conclusions can be preliminarily drawn:

(1) after the flat-roofed area is broken, the water flows to the sparsely populated area, the water flows rapidly pass through the slope and finally converge into the river channel, under the conditions that a single pipe is broken, double pipes are broken simultaneously and the gates are not closed, the average submerged water depth is 0.22m, 0.34m and 0.39m respectively, and the submerged area is 0.27km respectively²、0.36km²、0.43km². The submerged water depth is larger, and larger loss is easily caused.

(2) After the pipeline in Wuchang city area is broken, the water flows in the direction far away from Wuchang city areaThere are fewer buildings passing through the area. Under the first two working conditions, the average submerged water depth is 0.22m and 0.26m respectively, and the submerged area is 0.46km respectively²And 0.91km². Under the most unfavorable working condition, the average submerged water depth 4 hours after the breach is 0.25m, and the submerged area is 3.05km²Although the submerged depth is smaller than that of a single-storey house area, the submerged area is larger, and the loss caused by the submerged depth cannot be ignored.

(3) For the weak area break 1, the slope form where the break point is located is divergent, the water flow submerging flowing range is large, part of buildings are affected, the submerging water depth is relatively small due to the large water flow coverage area, the average submerging water depth is about 0.21m, the area is mostly a mountain area, the population is small, and the economic loss caused by the small area is correspondingly small.

(4) For the weak area breach 2, due to the groove topography, the submerging flow direction of the water flow is more concentrated, the water flow advances along the groove, and the average submerging depth is 0.46 m. Although the depth of the flooding is larger, the flooding area is positioned in the bottom of one groove valley, no buildings are arranged, and the flooding loss is easier to control.

The problem of the break outflow is only considered in the break inundation simulation, if the break meets adverse weather factors such as rainstorm and the like, the loss to the bungalow district and the five-normal city district is larger, corresponding engineering measures are adopted to dredge the break outflow, and the loss is reduced to the minimum.

Claims

1. The method for calculating the fracture model of the long-distance gravity flow large-pipe-diameter water supply pipeline is characterized by comprising the following steps of:

s8: a GIS object and a model provide a core function of physical mechanism and space-time process professional model simulation analysis;

2. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 1, wherein the upstream water inlet gate closing the front water inlet head is constant at S1, and the model of the seepage at the fracture under the constant water head is as follows:

in the formula: q-water loss; a-the area of the leak; h-free water pressure of the pipeline; mu-orifice flow coefficient, generally between 0.60 and 0.62, g-acceleration of gravity;

H＝H₀-c₁×L×Q₀

c₁＝10.667L/(c^1.852d^4.87)

in the formula: h₀-head of water at the inlet of the conduit; q₀-flow at the inlet of the conduit; l-the distance from the point of disruption to the entrance of the pipeline; c-Hazen-Williams coefficient, determined by the pipe material; d-diameter of pipeline, mu-orifice flow coefficient and A-leak area.

3. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 1, wherein the model that the residual water amount in the pipeline continues to leak until the water is exhausted after the S2 gate is closed is as follows:

in the formula: the flow coefficient of a mu-orifice is generally between 0.60 and 0.62, the area of an A-leakage opening and g-gravity acceleration;

h_fthe current head from the free water surface to the leak point in the pipe can be calculated by the following formula:

in the formula: v-flow velocity in the pipe; r-hydraulic radius; j-head gradient; c-metabolic capacity coefficient;

l is the distance from the position of the free water surface in the pipe to the break point;

d-the diameter of the pipeline, because the diameter of the water supply pipeline in the project is more than 2.0m, y in the talent-rejection coefficient C formula is calculated by adopting a Pavlofsky formula.

4. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 1, wherein the S4 comprises the following sub-steps:

s41: establishing a two-dimensional shallow water wave equation of the flooding model;

s42: for the two-dimensional shallow water wave equation, splitting the equation into the following two steps by adopting a breaking operator method; and then solving them respectively by adopting a proper method.

5. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 4, wherein the water submergence model of S41 is:

after water leaks from the pipeline, water flow is propelled to the periphery on dry ground, the simulation at the moment is equivalent to the water flow simulation of a flooding area, and can be described by adopting two-dimensional shallow water flow, and the equation form is as follows:

is a vector of the single-wide traffic,

is a mold for the same, and is,

q is a source item considering rainfall and other factors; g is the gravity acceleration, c is the allelochemical coefficient, and f is the Coriolis force coefficient; tau is_wx、τ_wyThe components of the wind stress in the x and y directions, respectively, can be calculated using the following formula:

wherein: rho_a-air density; c. C_D-a drag coefficient;

wind velocity vector 10m high from the water surface.

6. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 4, wherein the breaking operator method adopted in the S42 splits the equation into the following two steps;

a first step:

the second substep:

wherein Z is water level, u and v are flow velocity in x and y directions respectively; u, V single width flows in the x and y directions, respectively;

is a vector of the single-wide traffic,

is a mold for the same, and is,

q is a source item considering rainfall and other factors; g is the gravity acceleration, c is the allelochemical coefficient, and f is the Coriolis force coefficient; tau is_wx、τ_wyThe components of the wind stress in the x and y directions, respectively.

7. The method for calculating the fracture model of the long-distance gravity flow large-pipe-diameter water supply pipeline according to claim 1, wherein the S5 is used for calculating and analyzing the flow rate of the break between the bungalow area and the Wuchangshi, and the calculation is divided into two states, namely before closing the flow regulating pressure regulating valve and before and after closing the flow regulating pressure regulating valve.

8. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 7, wherein the calculation flow before the flow regulating and pressure regulating valve is closed is as follows:

s51: setting a water level reservoir and breaking;

s52: whether the break is at the downstream of the pressure stabilizing well or not; if yes, whether the water head of the second pressure stabilizing well exceeds 239 meters or not is judged, and whether the water head of the first pressure stabilizing well exceeds 278 meters or not is judged;

s53: if so, calculating the water level at the upstream end of the break point according to 239 meters, and setting the action position as a No. 2 pressure stabilizing well; if not, whether the water head of the first pressure stabilizing well exceeds 278 meters or not is judged,

s54: if so, calculating the water level of the upstream end of the break point according to 278 meters, and setting the action position as a No. 1 pressure stabilizing well, otherwise, calculating the water level of the upstream end of the break point according to the water level of a reservoir, and setting the action position at the pipeline inlet;

s55: calculating the head loss from the action position to the break edge;

s56: calculating a water purifying head;

s57: the breach outflow is calculated according to the formula.

9. The method for calculating the fracture model of the long-distance gravity flow large-pipe water supply pipeline according to claim 7, wherein the calculation process after the flow regulating and pressure regulating valve is closed is as follows:

s511: a breach occurs;

s512: the upstream regulating flow and pressure regulating valve at the break point is nearest;

s513: closing the nearest upstream flow regulating and pressure regulating valve;

s514: searching an elevation peak between a current water flow upstream point and a break point, and taking the elevation peak as a water head acting position;

s515: the total water amount TQ between the upstream point of the water flow and the break point;

s51: 6: the remaining water after one hour step is:

TQ-Q τ; if the dQ is larger than 0, calculating the loss of the water head along the city from the action position to the break point; if dQ is less than 0, stopping calculation;

s516: calculating the average flow of the pipeline according to the Manning formula according to the result of the S514;

s517: calculating a water purifying head; and if the water purification head is larger than 0, calculating the break outflow according to the formula, and if the water purification head is not larger than 0, stopping the calculation.