Pipeline leakage point positioning method considering gas-liquid two-phase flow

Abstract

The invention discloses a pipeline leakage point positioning method considering gas-liquid two-phase flow, and belongs to the technical field of pipeline leakage point positioning. In order to solve the problem that an existing pipeline system leakage detection method is single in monitoring form and inaccurate, the method comprises the steps that a horizontal pipeline gas-liquid two-phase stratified flow motion model is established; judging the relation between the gas phase and the liquid phase in the pipeline and the pressure of the gas phase and the liquid phase relative to the pipeline; expressing and calculating the leakage rate of the pipeline system; establishing a two-phase flow model for leakage point positioning; and finally positioning a leakage point. The method is suitable for leakage point positioning of a single-phase flow pipeline system and is also suitable for leakage point positioning of a gas-liquid two-phase flow pipeline system. Necessary data are provided for leakage point positioning through a model simulation method, excessive dependence on pipeline system data monitoring is reduced, the leakage point positioning efficiency is greatly improved, and the leakage point positioning cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline leakage point positioning, and in particular relates to a pipeline leakage point positioning method taking gas-liquid two-phase flow into consideration. Background Art

[0002] Pipeline systems are used in many practical projects such as agricultural irrigation, oil and gas transportation, and urban water supply. Leakage losses in pipeline systems are a problem that China needs to face in any practical project. Leakage will lead to waste of resources themselves. What is more serious is that leakage in the pipeline system causes open contact between resources and the outside world, which may cause more widespread pollution. Therefore, for practical projects, once there is a leak point, it is very important to locate the leak point as soon as possible.

[0003] Most of the current leak detection methods are based on the assumption that there is only one fluid in the pipeline. However, in actual projects, when there is a coexistence of gas and liquid in the pipeline, both gas and liquid can leak from the leak point on the pipeline. Therefore, the leak point location method applicable to single-phase flow pipelines is no longer applicable to this type of pipeline system. Another point that cannot be ignored is that many pipeline systems are often buried deep below the ground, and the status monitoring of the pipeline system may not be complete. Summary of the invention

[0004] In view of the problem that the current pipeline system leakage detection method has a single monitoring form and is inaccurate, the present invention provides a pipeline leakage point positioning method considering gas-liquid two-phase flow, by which the position of the leakage point on the pipeline can be quickly determined.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A pipeline leakage point locating method considering gas-liquid two-phase flow comprises the following steps:

[0007] Step 1, establishing a gas-liquid two-phase stratified flow motion model in a horizontal pipeline;

[0008] Step 2, determining the connection between the gas and liquid phases in the pipeline and the pressure of the gas and liquid phases on the pipeline;

[0009] Step 3, expression and calculation of pipeline system leakage;

[0010] Step 4, establishing a two-phase flow model for leak point location;

[0011] Step 5: Locate the leak.

[0012] Furthermore, the step 1 is to establish a horizontal pipeline gas-liquid two-phase stratified flow motion model, specifically:

[0013] According to the motion equations of gas and liquid in the pipeline, a gas-liquid two-phase stratified flow motion model of the horizontal pipeline is established, which is expressed as follows:

[0014]

[0015] Where t is the time coordinate (s); x is the space coordinate (m); ρ a is the density of the gas in the pipeline (kg / m 3 );A a is the cross-sectional area of ​​gas flow in the pipeline (m 2 );u a is the flow rate of gas in the pipeline (m / s); ρ L is the density of the gas in the pipeline (kg / m 3 );A L is the cross-sectional area of ​​the liquid in the pipe (m 2 );u L is the flow rate of the liquid in the pipeline (m / s); x (x l ) indicates the location of the leak on the pipeline; Indicates the amount of gas leakage at the leak point. Indicates the amount of liquid leaking at the leak point, (kg / (m·s)); P is the pressure of the liquid in the pipe (Pa); g is the acceleration due to gravity (m / s 2 ); n is the Manning roughness coefficient of the liquid (s / m 1 / 3 );M L is the mass flow rate of liquid through any section (m 3 / s), M L =ρ L A L u L ; r is the hydraulic radius (m).

[0016] Further, the step 2, determining the connection between the gas and liquid phases in the pipeline and the pressure of the gas and liquid phases on the pipeline, is specifically:

[0017] For any pipeline flow cross section, the sum of the cross-sectional proportions of gas and liquid at the cross section is the pipeline flow cross section, expressed as:

[0018] A a +A w =A (5)

[0019] Where A represents the cross-sectional area of ​​the pipe (m 2 );A w Indicates the cross-sectional area of ​​the liquid in the pipe (m 2 );A a Indicates the cross-sectional area of ​​gas flow in the pipeline (m 2 );

[0020] The pressure of the gas in the pipeline is expressed as:

[0021] P a =Zρ a RT (6)

[0022] Among them, P a Indicates the pressure of the gas in the pipeline (Pa), Z is the gas compressibility coefficient, ranging from 1.0 to 1.08; ρ a is the density of the gas in the pipeline (kg / m 3 );R is the gas constant;T is the Kelvin temperature of the gas in the pipeline, which is K=273.15+Celsius temperature;

[0023] The pressure of the liquid in the pipe is expressed as:

[0024] P L =ρ L gh (7)

[0025] Among them, P L represents the pressure of the liquid in the pipe (Pa), and h is the depth of the liquid at the corresponding position in the pipe (m);

[0026] For any position in the pipeline, the magnitude of the liquid pressure in the pipeline is P, which is determined by the pressure that can be generated by the gas and liquid phases at this position; the pressure value in the pipeline at any position in the pipeline is obtained by adding the pressure of the gas and liquid, which is divided into the following three situations:

[0027] When only the liquid moves in the full pipe, the pressure in the pipe is generated by the liquid movement. At this time:

[0028] P=P L (8)

[0029] When there is no liquid passing through the pipeline, only gas flows in the pipeline, and the pipeline pressure is generated by the movement of gas. At this time:

[0030] P=P a (9)

[0031] When the pipeline is partially full of liquid, the pressure there is formed by liquid and gas. At this time:

[0032] P=P L +P a (10).

[0033] Furthermore, the step 3, the expression and calculation of the leakage of the pipeline system, is specifically:

[0034] When a leak occurs somewhere in the pipeline system, the fluid in the pipe passing through the leak will be discharged from the pipeline from the leak point;

[0035]

[0036] When there is a circular leak point with an inner diameter of d on the pipeline, the constant leakage volume is expressed as follows:

[0037]

[0038] Among them, A h Leakage area of ​​the leak point (m 2 ), when the inner diameter of the leak point is d, A h =πd 2 / 4;c a Indicates the gas flow coefficient; C L represents the liquid flow coefficient; P(x) represents the pressure at the leakage point, which is determined by formulas (8)-(10) according to the actual conditions of the gas-liquid two-phase at that location; P 0 Indicates atmospheric pressure.

[0039] Further, in step 4, a two-phase flow model for leak point location is established, specifically:

[0040] When the fluid in the pipeline is in a steady flow state, the motion elements of the fluid do not change with time, and equations (1)-(4) can be rewritten as the following nonlinear ordinary differential equations:

[0041]

[0042] Definition C a =ρ a A a u a and C L =ρ L α L u L , as shown in formulas (14) and (15), for a pipeline that has reached a stable flow state, both are constants at any cross section along the pipeline; formulas (14)-(17) are transformed as follows:

[0043]

[0044]

[0045] Based on the derived formulas (18)-(21) and the aforementioned formulas (1)-(4), a two-phase flow model for leak point location is established.

[0046] Further, the step 5, locating the leakage point, is specifically:

[0047] Step 5.1, unify formulas (1)-(4) into the following vector form:

[0048]

[0049] Based on the vector form uniformly expressed by formulas (1)-(4), spatial discretization is performed. The spatial discretization form of formula (22) is expressed as follows:

[0050]

[0051] Among them, dt and dx are the time and space steps of numerical calculation respectively; i is a spatial discrete node; i+1 / 2 is the midpoint between spatial discrete nodes i and i+1; i-1 / 2 is the midpoint between spatial discrete nodes i and i-1;

[0052] For the second term on the left side of formula (25),

[0053]

[0054] (uU) i+1 / 2 、(uU) i-1 / 2 are the fluxes at the cell interface i+1 / 2 and i-1 / 2 respectively, and the discrete value is:

[0055] (uU) i+1 / 2 -(uU) i-1 / 2 =α i U i-1 +β i U i +γ i U i+1 (27)

[0056] in:

[0057]

[0058] For the first term on the right side of formula (25), the spatial discretization is expressed as:

[0059]

[0060] For the second term on the right side of formula (25), the spatial discretization is expressed as:

[0061]

[0062] For the second term on the right side of formula (25), the spatial discretization is expressed as:

[0063]

[0064] After spatial discretization, formula (25) is expressed as:

[0065]

[0066] Continue to discretize equation (34) in time, and get the time-space discretization as follows:

[0067]

[0068] The dual time step method is used to process the space-time discretization formula (35):

[0069]

[0070] Wherein, the superscript p in formula (36) represents the virtual time iteration step; Δτ is the virtual time step (s); if the virtual time step converges, the first term on the left side of formula (36) tends to zero, and this virtual time term enables formula (36) to achieve the purpose of unconditional stable simulation in the form of absolute convergence;

[0071] To clarify this point, by combining similar terms in equation (36), we obtain the following equation to be solved:

[0072]

[0073] Where λ = Δt / Δx i is the ratio of the real space-time step; ω = Δt / Δτ is the ratio of the real time step to the virtual time step;

[0074] Substituting the specific quantities in the vectors in formulas (23) and (24) into the general form of the discrete solution of the formula (37), the entire motion state of the gas and liquid in the tube can be obtained;

[0075] Step 5.2, solve formulas (18) to (21):

[0076] Formulas (18)-(21) are expressed in the following form:

[0077]

[0078] W=[PA L u a u L ] T (39)

[0079]

[0080] Step 5.3, numerical algorithm and leakage point location;

[0081] For a pipe with a length of l, solve the equations (14) to (17) under the premise of determining the initial conditions; the initial conditions required to solve the equations include four variables, pressure P, liquid proportion AL , gas velocity u a and liquid velocity u L Initial data of

[0082] Initial conditions consisting of the above four variables are specified at the pipeline inlet x=0 and the pipeline outlet x=l;

[0083] At a certain moment t = t (k) , the pipeline system with the leak point is already in a stable motion state. At this time, the initial conditions required to solve equations (14) to (17) are written as follows:

[0084]

[0085] First, using equation (44) as the initial condition, we calculate (40) to (43) from the pipeline inlet to the pipeline outlet to obtain a set of pipeline pressure distribution curves, which are recorded as Then, using equation (45) as the initial condition, we calculate (40) to (43) from the outlet of the pipeline to the inlet of the pipeline, and obtain a set of pipeline pressure distribution curves, which are recorded as The two sets of pressure distribution curves obtained through the two calculations provide the two sets of pressure distributions required for leak location. According to the difference in pressure distributions calculated under the two calculation schemes, pipeline leak location can be achieved. For this purpose, the following formula is defined:

[0086]

[0087] if It can be determined that the location of the pipeline leakage point is at point l; at this point, the location of the pipeline system leakage point is completed.

[0088] Compared with the prior art, the present invention has the following advantages:

[0089] (1) The method of the present invention is applicable to the leakage point location of a single-phase flow pipeline system, and is also applicable to the leakage point location of a gas-liquid two-phase flow pipeline system.

[0090] (2) The model simulation method provides the necessary data for leak point location, reducing the excessive reliance on pipeline system data monitoring, greatly improving the efficiency of leak point location, and reducing the cost of leak point location. DETAILED DESCRIPTION

[0091] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0092] A pipeline leakage point locating method considering gas-liquid two-phase flow comprises the following steps:

[0093] Step 1, establishing a gas-liquid two-phase stratified flow motion model in a horizontal pipeline;

[0094] According to the motion equations of gas and liquid in the pipeline, a gas-liquid two-phase stratified flow motion model of the horizontal pipeline is established, which is expressed as follows:

[0095]

[0096] Where t is the time coordinate (s); x is the space coordinate (m); ρ a is the density of the gas in the pipeline (kg / m 3 );A a is the cross-sectional area of ​​gas flow in the pipeline (m 2 );u a is the flow rate of gas in the pipeline (m / s); ρ L is the density of the gas in the pipeline (kg / m 3 );A L is the cross-sectional area of ​​the liquid in the pipe (m 2 );u L is the flow rate of the liquid in the pipeline (m / s); x (x l ) indicates the location of the leak on the pipeline; Indicates the amount of gas leakage at the leak point. Indicates the amount of liquid leaking at the leak point, (kg / (m·s)); P is the pressure of the liquid in the pipe (Pa); g is the acceleration due to gravity (m / s 2 ); n is the Manning roughness coefficient of the liquid (s / m 1 / 3 );M L is the mass flow rate of liquid through any section (m 3 / s), M L =ρ L A L u L ; r is the hydraulic radius (m).

[0097] Step 2, determining the connection between the gas and liquid phases in the pipeline and the pressure of the gas and liquid phases on the pipeline;

[0098] For any pipeline flow cross section, the sum of the cross-sectional proportions of gas and liquid at the cross section is the pipeline flow cross section, expressed as:

[0099] A a +A w =A (5)

[0100] Where A represents the cross-sectional area of ​​the pipe (m 2 );Aw Indicates the cross-sectional area of ​​the liquid in the pipe (m 2 );A a Indicates the cross-sectional area of ​​gas flow in the pipeline (m 2 );

[0101] The pressure of the gas in the pipeline is expressed as:

[0102] P a =Zρ a RT (6)

[0103] Among them, P a Indicates the pressure of the gas in the pipeline (Pa), Z is the gas compressibility coefficient, ranging from 1.0 to 1.08; ρ a is the density of the gas in the pipeline (kg / m 3 );R is the gas constant;T is the Kelvin temperature of the gas in the pipeline, which is K=273.15+Celsius temperature;

[0104] The pressure of the liquid in the pipe is expressed as:

[0105] P L =ρ L gh (7)

[0106] Among them, P L represents the pressure of the liquid in the pipe (Pa), and h is the depth of the liquid at the corresponding position in the pipe (m);

[0107] For any position in the pipeline, the magnitude of the liquid pressure in the pipeline is P, which is determined by the pressure that can be generated by the gas and liquid phases at this position; the pressure value in the pipeline at any position in the pipeline is obtained by adding the pressure of the gas and liquid, which is divided into the following three situations:

[0108] When only the liquid moves in the full pipe, the pressure in the pipe is generated by the liquid movement. At this time:

[0109] P=P L (8)

[0110] When there is no liquid passing through the pipeline, only gas flows in the pipeline, and the pipeline pressure is generated by the movement of gas. At this time:

[0111] P=P a (9)

[0112] When the pipeline is partially full of liquid, the pressure there is formed by liquid and gas. At this time:

[0113] P=P L +P a (10).

[0114] Step 3: Expression and calculation of pipeline system leakage, specifically:

[0115] When a leak occurs somewhere in the pipeline system, the fluid in the pipe passing through the leak will be discharged from the pipeline from the leak point;

[0116]

[0117] When there is a circular leak point with an inner diameter of d on the pipeline, the constant leakage volume is expressed as follows:

[0118]

[0119]

[0120] Among them, A h Leakage area of ​​the leak point (m 2 ), when the inner diameter of the leak point is d, A h =πd 2 / 4;c a Indicates the gas flow coefficient; c L represents the liquid flow coefficient; P(x) represents the pressure at the leakage point, which is determined by formulas (8) to (10) according to the actual conditions of the gas-liquid two-phase at that location; P 0 Indicates atmospheric pressure.

[0121] Step 4: Establish a two-phase flow model for leak point location, specifically:

[0122] When the fluid in the pipeline is in a steady flow state, the motion elements of the fluid do not change with time, and equations (1)-(4) can be rewritten as the following nonlinear ordinary differential equations:

[0123]

[0124] Definition C a =ρ a A a u a and C L =ρ L α L u L , as shown in formulas (14) and (15), for a pipeline that has reached a stable flow state, both are constants at any cross section along the pipeline; formulas (14)-(17) are transformed as follows:

[0125]

[0126] Based on the derived formulas (18) to (21) and the aforementioned formulas (1) to (4), a two-phase flow model for leak point location is established.

[0127] Step 5: Locate the leak point, specifically:

[0128] Step 5.1, express formulas (1) to (4) in the following vector form:

[0129]

[0130] Based on the vector form uniformly expressed by formulas (1)-(4), spatial discretization is performed. The spatial discretization form of formula (22) is expressed as follows:

[0131]

[0132] Among them, dt and dx are the time and space steps of the numerical calculation respectively; i is a spatial discrete node; i+1 / 2 is the midpoint between spatial discrete nodes i and i+1; i-1 / 2 is the midpoint between spatial discrete nodes i and i-1;

[0133] For the second term on the left side of formula (25),

[0134]

[0135] (uU) i+1 / 2 、(uU) i-1 / 2 are the fluxes at the cell interface i+1 / 2 and i-1 / 2 respectively, and the discrete value is:

[0136] (uU) i+1 / 2 -(uU) i-1 / 2 =α i U i-1 +β i U i +γ i U i+1 (27)

[0137] in:

[0138]

[0139] For the first term on the right side of formula (25), the spatial discretization is expressed as:

[0140]

[0141] For the second term on the right side of formula (25), the spatial discretization is expressed as:

[0142]

[0143] For the second term on the right side of formula (25), the spatial discretization is expressed as:

[0144]

[0145] After spatial discretization, formula (25) is expressed as:

[0146]

[0147] Continue to discretize equation (28) in time, and get the time-space discretization as follows:

[0148]

[0149] The dual time step method is used to process the space-time discretization formula (29):

[0150]

[0151] Wherein, the superscript p in formula (36) represents the virtual time iteration step; Δτ is the virtual time step (s);

[0152] If the virtual time step converges, the first term on the left side of equation (36) tends to zero, and this virtual time term enables equation (36) to achieve the purpose of unconditionally stable simulation in the form of absolute convergence;

[0153] To clarify this point, by combining similar terms in equation (36), we obtain the following equation to be solved:

[0154]

[0155] Where λ = Δt / Δx i is the ratio of the real space-time step; ω = Δt / Δτ is the ratio of the real time step to the virtual time step;

[0156] Substituting the specific quantities in the vectors in formulas (23) and (24) into the general form of the discrete solution of the formula (37), the entire motion state of the gas and liquid in the tube can be obtained;

[0157] Step 5.2, solve formulas (18) to (21):

[0158] Formulas (18) to (21) are expressed in the following form:

[0159]

[0160] W=[PA L u a u L ] (39)

[0161]

[0162] Step 5.3, numerical algorithm and leakage point location;

[0163] For a pipe with a length of l, solve the equations (14) to (17) under the premise of determining the initial conditions. The initial conditions required to solve the equations include four variables, P is the pressure of the liquid in the pipe; A L is the cross-sectional area of ​​the liquid in the pipe; u a is the flow rate of gas in the pipeline; u L is the flow rate of the liquid in the pipe;

[0164] Initial conditions consisting of the above four variables are specified at the pipeline inlet x=0 and the pipeline outlet x=l;

[0165] At a certain moment t = t (k) , the pipeline system with the leak point is already in a stable motion state. At this time, the initial conditions required to solve equations (14) to (17) are written as follows:

[0166]

[0167]

[0168] First, using equation (44) as the initial condition, we calculate (40) to (43) from the pipeline inlet to the pipeline outlet to obtain a set of pipeline pressure distribution curves, which are recorded as Then, using equation (45) as the initial condition, we calculate (40) to (43) from the outlet of the pipeline to the inlet of the pipeline, and obtain a set of pipeline pressure distribution curves, which are recorded as The two sets of pressure distribution curves obtained through the two calculations provide the two sets of pressure distributions required for leak location. According to the difference in pressure distributions calculated under the two calculation schemes, pipeline leak location can be achieved. For this purpose, the following formula is defined:

[0169]

[0170] if It can be determined that the location of the pipeline leakage point is at point l; at this point, the location of the pipeline system leakage point is completed.

[0171] Example 1

[0172] In a horizontal pipeline with a length of 45 km, there is a stratified flow of gas and liquid in the pipeline. The specific attributes of the pipeline and the physical properties of the gas and liquid flowing in the pipeline are shown in Table 1.

[0173] Table 1. Pipeline properties and fluid properties

[0174]

[0175] 1. Initial conditions and boundary conditions

[0176] First, the boundary conditions required to solve equations (1) to (4) are defined, as shown in Table 2. In addition to the pressure at the pipeline outlet, the gas-liquid velocity and liquid area ratio at the pipeline inlet are also specified. a 、u L , A L The values ​​of and P are specified across the domain at t = 0 as initial conditions for the initial transient simulation before the leak is opened. Once a steady state is achieved, the leak is opened and the simulation continues until a new steady state is reached with the leak present. As described above, the initial conditions are provided for the solution of equations (14)-(17).

[0177] Table 2. Boundary conditions of the gas-liquid two-phase flow calculation model

[0178]

[0179] Table 3 defines the initial conditions for solving the leak location model. The pressure, liquid holdup, and gas-liquid velocity at the pipe outlet are required for specifying the solution starting from the pipe inlet and the solution starting from the pipe outlet.

[0180] Table 3. Initial conditions of pipeline leak location model

[0181]

[0182] 2. Results Analysis

[0183] In this example verification, the way in which the pipeline generates leakage is specified according to the following specific circumstances: the leakage is 5% of the flow rate at the pipeline inlet. The leakage occurs through a circular leakage point on the pipeline. The diameter of the circular leakage point is 0.0138 meters, the flow coefficient is about 0.47, and the leakage occurs at 12.5km and 32.5km from the pipeline inlet. Based on the aforementioned leakage location strategy and the calculation method of the leakage point, the error between the leakage point location calculated by the method and the actual leakage location can be used to evaluate the calculation accuracy and practicality of the invention method. The corresponding results are given in Table 4, which show that for leakage point 1, the error between the actual position and the calculated position is 0.78%, and for leakage point 2, the error between the calculated position and the actual position is 1.52%. It can be shown that the method established in the present invention has good calculation accuracy in locating pipeline leakage points.

[0184] Table 5: Pipeline leak locations

[0185]

[0186]

[0187] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A pipeline leakage point location method considering gas-liquid two-phase flow, characterized in that: The following steps are involved: Step 1, establishing a gas-liquid two-phase stratified flow motion model in a horizontal pipeline; Step 2, determining the connection between the gas and liquid phases in the pipeline and the pressure of the gas and liquid phases on the pipeline; Step 3, expression and calculation of pipeline system leakage; Step 4, establishing a two-phase flow model for leak point location; Step 5: Locate the leak.

2. A pipeline leakage point location method considering gas-liquid two-phase flow according to claim 1, characterized in that: The step 1 is to establish a horizontal pipeline gas-liquid two-phase stratified flow motion model, specifically: According to the motion equations of gas and liquid in the pipeline, a gas-liquid two-phase stratified flow motion model of the horizontal pipeline is established, which is expressed as follows: Among them, t is the time coordinate; x is the space coordinate; ρ a is the density of the gas in the pipeline; A a is the flow cross-sectional area of ​​the gas in the pipeline; u a is the flow rate of the gas in the pipeline; ρ L is the density of the gas in the pipeline; A L is the cross-sectional area of ​​the liquid in the pipe; u L is the flow rate of the liquid in the pipe; x (x l ) indicates the location of the leak on the pipeline; Indicates the amount of gas leakage at the leak point. Indicates the amount of liquid leaking at the leaking point; P is the pressure of the liquid in the pipeline; g is the acceleration of gravity; n is the Manning roughness coefficient of the liquid; M L is the mass flow rate of liquid through any section, M L =ρ L A L u L ; r is the hydraulic radius.

3. The pipeline leakage point location method considering gas-liquid two-phase flow according to claim 1 is characterized by: The step 2, determining the connection between the gas and liquid phases in the pipeline and the pressure of the gas and liquid phases on the pipeline, is specifically: For any pipeline flow cross section, the sum of the cross-sectional proportions of gas and liquid at the cross section is the pipeline flow cross section, expressed as: A a +A w =A (5) Where A represents the cross-sectional area of ​​the pipe; A w Indicates the cross-sectional area of ​​the liquid in the pipe; A a Indicates the cross-sectional area of ​​gas flow in the pipeline; The pressure of the gas in the pipeline is expressed as: P a =Zρ a RT (6) Among them, P a Indicates the pressure of the gas in the pipeline, Z is the gas compression coefficient, ranging from 1.0 to 1.08; ρ a is the density of the gas in the pipeline; R is the gas coefficient; T is the Kelvin temperature of the gas in the pipeline, which is K = 273.15 + Celsius temperature; The pressure of the liquid in the pipe is expressed as: P L =ρ L gh (7) Among them, P L It represents the pressure of the liquid in the pipe, and h is the depth of the liquid at the corresponding position in the pipe; For any position in the pipeline, the magnitude of the liquid pressure in the pipeline is determined by the pressure that can be generated by the gas and liquid phases at that position; the pressure value in the pipeline at any position in the pipeline is obtained by adding the pressure of the gas and liquid, which is divided into the following three situations: When only the liquid moves in the full pipe, the pressure in the pipe is generated by the liquid movement. At this time: P=P L (8) When there is no liquid passing through the pipeline, only gas flows in the pipeline, and the pipeline pressure is generated by the movement of gas. At this time: P=P a (9) When the pipeline is partially full of liquid, the pressure there is formed by liquid and gas. At this time: P=P L +P a (10)。 4. The pipeline leakage point location method considering gas-liquid two-phase flow according to claim 1 is characterized by: The step 3, the expression and calculation of the leakage of the pipeline system, is specifically: When a leak occurs somewhere in the pipeline system, the fluid in the pipe passing through the leak will be discharged from the pipeline from the leak point; When there is a circular leak point with an inner diameter of d on the pipeline, the constant leakage volume is expressed as follows: Among them, A h The leakage area of ​​the leakage point. When the inner diameter of the leakage point is d, A h =πd 2 / 4;c a Indicates the gas flow coefficient; c L represents the liquid flow coefficient; P(x) represents the pressure at the leakage point; P0 represents the atmospheric pressure.

5. The pipeline leakage point location method considering gas-liquid two-phase flow according to claim 1 is characterized by: The step 4 is to establish a two-phase flow model for leak point location, specifically: When the fluid in the pipeline is in a steady flow state, the motion elements of the fluid do not change with time, and equations (1)-(4) can be rewritten as the following nonlinear ordinary differential equations: Definition C a =ρ a A a u a and C L =ρ L α L u L , as shown in formulas (14) and (15), for a pipeline that has reached a stable flow state, both are constants at any cross section along the pipeline; formulas (14) to (17) are transformed as follows: Based on the derived formulas (18) to (21) and the aforementioned formulas (1) to (4), a two-phase flow model for leak point location is established.

6. The pipeline leakage point location method considering gas-liquid two-phase flow according to claim 1 is characterized by: Step 5: Locate the leak point, specifically: Step 5.1, express formulas (1) to (4) in the following vector form: Based on the vector form uniformly expressed by formulas (1) to (4), spatial discretization is performed. The spatial discretization form of formula (22) is expressed as follows: Among them, dt and dx are the time and space steps of numerical calculation respectively; i is a spatial discrete node; i+1 / 2 is the midpoint between spatial discrete nodes i and i+1; i-1 / 2 is the midpoint between spatial discrete nodes i and i-1; For the second term on the left side of formula (25), (uU) i+1 / 2 、(uU) i-1 / 2 are the fluxes at the cell interface i+1 / 2 and i-1 / 2 respectively, and the discrete value is: (and) i+1 / 2 -(uU) i-1 / 2 =α i And i-1 +β i And i +γ i And i+1 (27) in: For the first term on the right side of formula (25) The spatial discretization of is: For the second term on the right side of formula (25), The spatial discretization of is: For the third term on the right side of the equal sign in formula (25), The spatial discretization of is: After spatial discretization, formula (25) is expressed as: Continue to discretize equation (34) in time, and get the time-space discretization as follows: The dual time step method is used to process the space-time discretization formula (35): Wherein, the superscript p in formula (36) represents the virtual time iteration step; Δτ is the virtual time step (s); If the virtual time step converges, the first term on the left side of equation (36) tends to zero, and this virtual time term enables equation (36) to achieve the purpose of unconditionally stable simulation in the form of absolute convergence; To clarify this point, by combining similar terms in equation (36), we obtain the following equation to be solved: Where λ = Δt / Δx i is the ratio of the real space-time step; ω = Δt / Δτ is the ratio of the real time step to the virtual time step; Substituting the specific quantities in the vectors in formulas (23) and (24) into the general form of the discrete solution of the formula (37), the entire motion state of the gas and liquid in the tube can be obtained; Step 5.2, solve formulas (18) to (21): Formulas (18) to (21) are expressed in the following form: W=[PA L u a u L ] T (39) Step 5.3, numerical algorithm and leakage point location; For a pipe with a length of l, solve the equations (14) to (17) under the premise of determining the initial conditions. The initial conditions required to solve the equations include four variables, P is the pressure in the pipe; A L is the cross-sectional area of ​​the liquid in the pipe; u a is the flow rate of gas in the pipeline; u L is the flow rate of the liquid in the pipe; Initial conditions consisting of the above four variables are specified at the pipeline inlet x=0 and the pipeline outlet x=l; At a certain moment t = t (k) , the pipeline system with the leak point is already in a stable motion state. At this time, the initial conditions required to solve equations (14) to (17) are expressed as follows: First, using equation (44) as the initial condition, we calculate (40) to (43) from the pipeline inlet to the pipeline outlet to obtain a set of pipeline pressure distribution curves, which are recorded as Then, using equation (45) as the initial condition, we calculate (40) to (43) from the outlet of the pipeline to the inlet of the pipeline, and obtain a set of pipeline pressure distribution curves, which are recorded as The two sets of pressure distribution curves obtained through two calculations provide the two sets of pressure distributions required for leak location. According to the difference in pressure distributions calculated under the two calculation schemes, pipeline leak location is achieved. To this end, the following formula is defined: if The position of the pipeline leakage point is determined to be at l; at this point, the location of the pipeline system leakage point is completed.

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