CN108197070A - Natural gas not exclusively blocks pipeline method for numerical simulation - Google Patents
Natural gas not exclusively blocks pipeline method for numerical simulation Download PDFInfo
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Abstract
The present invention provides a kind of natural gases not exclusively to block pipeline method for numerical simulation, based on continuity equation, the equation of momentum and state equation that the present invention is flowed according to gas in pipelines, establishes gas propagation of disturbance mathematical model in natural gas line；For gas Shock propagation model in the natural gas line established, based on Matlab mathematical computation tools, the method of characteristic curves is selected to solve Gas Caused By Pipeline Accidents Disturbance Model, and pass through finite difference calculus, Newton iteration method and boundary condition and determine, numerical computations go out the continuous flow field in pipeline and continuous pressure field.The present invention relies on the natural gas line transient flow model established, explore the propagation law of transient pressure fluctuation in Long-distance Transmission Pipeline, can accurate simulation not exclusively block gas in pipelines mobility status, provide not exclusively to block pipeline and theoretical foundation and put into practice method.
Description
Technical field
The present invention relates to a kind of natural gases not exclusively to block pipeline numerical simulation technology, and specially a kind of natural gas is incomplete
Pipeline method for numerical simulation is blocked, i.e., is calculated by establishing not exclusively blocking gas in pipelines Shock propagation model.
Background technology
Long-distance Transmission Pipeline construction is the important component of China's oil and gas industry, since natural gas length is defeated
Pipe-line construction and the time gone into operation it is long, across area is more, weather conditions are complicated, go into operation run during be likely occurred one
A little accidents influence the operation of pipelines, so to the maintenance of Long-distance Transmission Pipeline with regard to increasingly important.Wherein line clogging is not
But it can influence normally to produce, the unimpeded work in later stage can also consume a large amount of human and material resources.
In order to solve the blockage problem of pipeline appearance, some effective methods are explored both at home and abroad at present, have probably been divided into：
Pipeline strain method, oiling pressure testing method, gamma-rays method, instrument probe method, transient analysis method.Pipeline strain method needs are laid with along pipeline
Optical fiber is not applied to for being completed without being laid with the pipeline of optical fiber, and optical fiber, early investment and later maintenance are laid with to newly-built pipeline
Expense it is all higher, it is difficult to promote and apply；Oiling pressure testing method is suitable for pipeline, and there is a situation where completely plugged, it is impossible to which solution is never
Completely plugged situation；Gamma-rays method detecting instrument is expensive, and accurate visit for being only applicable to local pipeline section is blocked up；Utilize transient analysis
Method, which to pipeline visit, stifled has many advantages, such as achievable remote detection, using equipment is few, detection efficiency is high.Now with transition point
Analysis method also mainly concentrates fluid pipeline to the research that line clogging is detected, and grows defeated pipe to gas pipeline, particularly natural gas
The research in road is also fewer.And in the prior art based on the transition method detecting system completely plugged to pipeline and detection method compared with
More, to pipeline, incomplete clogging detecting system and detection method are less.
If the position not exclusively blocked can be found at line clogging initial stage, estimate and not exclusively block harmfulness etc., can be
Manager provides the reference information for formulating unimpeded plan, and completely plugged possibility occurs so as to evade pipeline.Occur in pipeline stifled
Plug initial stage takes related unimpeded measure, can effectively avoid by pipeline further occur it is completely plugged caused by stopping transportation, halt production institute
Caused by huge human and material resources loss, ensure the stable operation of pipeline.
At present, natural gas line is not exclusively blocked both at home and abroad and is still in the research and probe stage, wherein based on transient analysis
Method proposes thinking to explore not exclusively blocking pipeline.It is as shown in Figure 2 it is incomplete block pipeline, pipeline section starting point is point A, terminal
It is starting point of point B, the P point not exclusively to block section, Q points are the incomplete terminal for blocking section.A quality is injected in pipeline section starting point A
Pulse, the quality pulse are propagated in pipeline along the direction of arrow.Quality pulse arrives at stifled not exclusively blocking section front end P points
Afterwards, on the one hand constricted flow, kinetic energy decrease the quality pulse due to blocking, and potential energy increases, and cause not exclusively stifled
The unexpected lift-rising of forefront pressure for filling in section is high, and is propagated in the form of barotropic wave to A points；Another aspect quality pulse continues along pipeline
It is propagated through forward after the not exclusively non-blocking section of blocking section arrival since area of passage increases, gas can expand suddenly, lead to this
Point pressure reduces form negative pressure suddenly, and negative pressure can be in the form of suction wave to propagation at A points at entrance.Theoretically it is based on wink
Become analytic approach by time difference of two pressure response signals for being monitored in starting point A points, combination pressure wave is in the duct
Spread speed, you can obtain the distance of the pressure-wave emission in the time interval of pressure response signal twice, and the two of the distance
/ mono- is the distance between pressure monitoring point and plugging point.
Thinking is proposed to explore not exclusively blocking pipeline based on transient analysis method, however currently based on transient analysis method pair
The endless piping study that blocks of natural gas is more in the experimental study stage, is difficult profit based on current achievement in research and experiment condition
The above-mentioned incomplete continuous flow field distribution blocked in gas in pipelines and continuous pressure field distribution are carried out with existing equipment real
When measure, so as to which pressure response signal data at entrance A points can not be obtained in real time.Experiment can only collect specific simultaneously
The pressure change data of point, it is impossible to obtain the pressure value of entire pipeline each point, and experiment can not also apply the quality of all size
Pulse, therefore limited by various factors that experiment cannot fully operation of the researching natural gas pipeline in incomplete block be special in detail
Point, incomplete blocking feature and mechanism, and then influence the method that research and probe goes out to detect the incomplete blocking position of natural gas line.
It is therefore desirable to invent a kind of natural gas not exclusively to block pipeline method for numerical simulation, so that researching natural gas pipeline is incomplete
Operation characteristic, incomplete blocking feature and mechanism during blocking.Numerical simulation can apply the condition that experimental method is not achieved and
And method for numerical simulation can carry out stress analysis to each region, each measuring point, carry out providing theories integration for experiment.
Invention content
For the defects in the prior art, the present invention provides a kind of natural gas and not exclusively blocks pipeline method for numerical simulation,
It has directive significance to experimental study and theory analysis, largely pushes and not exclusively blocks piping study to natural gas
Progress.
Technical solution of the present invention is as follows：
A kind of natural gas not exclusively blocks pipeline method for numerical simulation, which is characterized in that includes the following steps：
Step S1, flowing progress gas Shock propagation model modeling in pipeline is not exclusively being blocked to natural gas；
Step S2, according to not exclusively blocking, the input of pipeline geometric parameter is incomplete to block pipeline geometrical model；
Step S3, mesh generation is carried out to the incomplete blocking pipeline using mathematical computation tool Matlab；
Step S4, numerical computations are carried out on the basis of gridding flow field, carrying out finite element grid using the method for characteristic curves asks
Solution is calculated and not exclusively blocks continuous flow field and continuous pressure field in pipeline.
Preferably, it is base according to continuity equation, the equation of momentum and the state equation that gas in pipelines flows in step S1
Plinth establishes gas in pipelines Shock propagation model, ignores inertia force, and the incomplete of foundation blocks gas in pipelines propagation of disturbance mould
Type is：
In formula:P --- gas absolute pressure, Pa；T --- time variable, s；A --- gas velocity of wave, m/s；A --- pipeline
Actual internal area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density,
kg/m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；
λ --- pipe friction factor；D --- internal diameter of the pipeline, m；
Preferably, the incomplete blocking gas in pipelines Shock propagation model detailed process established in step S1 is as follows：
The continuity equation that S11, gas flow in the duct is
In formula：ρ --- gas density, kg/m3；The flow velocity of v --- gas, m/s；T --- time variable；s；X --- edge
Pipe range variable, m；
The equation of motion that S12, gas flow in the duct is：
In formula：G --- acceleration of gravity, m/s；The inclination angle of θ --- pipeline and horizontal plane, rad；
λ --- hydraulic simulation experiment；D --- internal diameter of the pipeline, m；P --- air in pipeline pressure, Pa；
S13, continuity equation are：
P=z ρ RT (3)
In formula：P --- gas pressure, Pa；Z --- the compressed coefficient；R --- gas constant, J/ (kg.K)；ρ --- gas
Density, kg/m3；T --- absolute temperature, K；
Under the assumed condition of isothermal Flow of Single, T is constant, and gas velocity of wave is：
S14, compressibility factor calculate：Compressibility factor is calculated using California, USA natural gas association formula：
In formula：P --- gas pressure (exhausted), MPa；T --- gas temperature, K；The relative density of Δ --- gas；
S15, Shock propagation model are established：Mass flow in gas pipeline is expressed as M=ρ vA, is then substituted into respectively
Continuity equation formula (1) and equation of motion (2) are replaced the gas flow rate in equation, can be obtained by variation following
Mathematical differentiation equation containing mass flow：
Ignore Inertia, then formula (7) can be converted to：
In formula：A --- pipeline flow sectional area, m2；M --- gas mass flow, kg/s；P --- gas absolute pressure,
Pa；ρ --- gas density, kg/m3；G --- local gravitational acceleration, m/s2；λ --- pipe friction factor；θ --- computer tube
The angle of inclination formed between road and horizontal plane, rad；D --- internal diameter of the pipeline, m；The differential variable of x --- duct length, m；
T --- time variable, s；
Obtaining gas thermal insulation propagation velocity of sound by thermodynamics is：
For isothermal Flow of Single：
Then formula (5), formula (7) become
In formula:P --- gas absolute pressure, Pa；T --- time variable, s；A --- gas velocity of wave, m/s；A --- pipeline
Actual internal area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density,
kg/m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；
λ --- pipe friction factor；D --- internal diameter of the pipeline, m.
Preferably, it is calculated in step S4 using the method for characteristic curves and not exclusively blocks continuous flow field and continuous pressure field in pipeline
Further comprise following steps：
S41, formula (11) is multiplied by after a undetermined coefficient η be added again with formula (12) construct two total differential equations and with
C+And C-To mark：
In formula:A --- gas velocity of wave, m/s；P --- gas absolute pressure, Pa；T --- time variable, s；A --- pipeline
Actual internal area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density,
kg/m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；
λ --- pipe friction factor；D --- internal diameter of the pipeline, m；
S42, respectively to above-mentioned two total differential equation in its corresponding characteristic curve upper integral, obtain being convenient at numerical value
The finite difference equations of reason：
S43, formula (26) (27) are nonlinear equation, are solved using Newton iteration method：
The iterative formula of Newton method：
S44, boundary condition is determined, the continuous flow not exclusively blocked in pipeline is calculated in two characteristic strips equations of simultaneous
Measure field and continuous pressure field.
The present invention has the advantages that compared with prior art：
The present invention establishes natural gas tube using the incomplete blockage problem of Long-distance Transmission Pipeline physical presence as research object
Gas Shock propagation model in road carries out mesh generation using mathematical computation tool Matlab to the incomplete blocking pipeline；
Numerical computations are carried out on the basis of gridding flow field, using the method for characteristic curves the gas propagation of disturbance in the natural gas line of foundation
The partial differential equation of model are converted into being convenient for the total differential equation of numerical solution, then to complete micro- on corresponding characteristic curve
Equation is divided to be integrated the finite difference equations so as to obtain being convenient for numerical value processing.Propose single pipeline endpoint and not
Boundary condition of the completely plugged section of endpoint in Unsteady flow computation.It is changed using Newton iteration method to Nonlinear System of Equations
In generation, solves, and the basic program for calculating natural gas line UNSTEADY FLOW is write with Matlab mathematical softwares.It is calculated not
Transient pressure wave in the defeated incomplete blocking pipeline of natural gas length is explored in continuous flow field and continuous pressure field in completely plugged pipeline
Dynamic propagation law, so gas in pipelines operation characteristic when further not exclusively being blocked to natural gas, not exclusively block it is special
Mechanism of seeking peace is analyzed.So that the present invention is provided not exclusively to be blocked the research of pipeline to natural gas based on transition method
It is a kind of effectively to assist Supplementary Study method.It is long to can be used for natural gas for gas Shock propagation model in the natural gas line of foundation
Defeated Transient Flow in Pipeline analysis, is the incomplete jam detection technical research based theoretical of following researching natural gas pipeline.
Experiment can only collect the pressure change data of specified point simultaneously, it is impossible to obtain the pressure value of entire material each point, and numerical value
Analogy method can carry out stress analysis to each region, each measuring point, and theories integration is provided for experiment.
Description of the drawings
It, below will be to specific in order to illustrate more clearly of the specific embodiment of the invention or technical solution of the prior art
Embodiment or attached drawing needed to be used in the description of the prior art are briefly described.In all the appended drawings, similar element
Or part is generally identified by similar reference numeral.In attached drawing, each element or part might not be drawn according to practical ratio.
Fig. 1 is flow diagram of the present invention；
Fig. 2 is not exclusively blocks pipeline physical model；
Fig. 3 is the characteristic curve schematic diagram that the present invention solves pipeline gas Shock propagation model；
Fig. 4 is Fig. 3 characteristic curve xt grid charts；
Fig. 5 is borderline characteristic curve；
Fig. 6 is not exclusively blocks pipeline endpoint feature line schematic diagram；
Fig. 7 is simulated program block diagram；
Pressure change along when Fig. 8 is not exclusively blocks pipeline stabilization operation；
Changes in flow rate along when Fig. 9 is not exclusively blocks pipeline stabilization operation；
Figure 10 adds in the whole line pressure wave propagation figure of quality pulse numerical simulation not exclusively to block pipeline
Figure 11 adds in the whole pipeline flow waves propagation figure of quality pulse numerical simulation not exclusively to block pipeline
Figure 12 is the curve of cyclical fluctuations at any time of pressure at entrance.
Specific embodiment
Below by way of particular specific embodiment and embodiments of the present invention are described with reference to the drawings.
The specific embodiment of the invention as shown in Figure 1 is using following technical scheme, a kind of pipeline based on Transient Analysis
The localization method of incomplete blocking position, including step：
Step S1, flowing progress gas Shock propagation model modeling in pipeline is not exclusively being blocked to natural gas；
Step S2, according to not exclusively blocking, the input of pipeline geometric parameter is incomplete to block pipeline geometrical model；
Step S3, mesh generation is carried out to the incomplete blocking pipeline using mathematical computation tool Matlab；
Step S4, numerical computations are carried out on the basis of gridding flow field, carrying out finite element grid using the method for characteristic curves asks
Solution is calculated and not exclusively blocks continuous flow field and continuous pressure field in pipeline；
Specifically：
(1) gas in pipelines Shock propagation model is established
In gas transient flowing, inertia force is inessential for pressure and frictional force.Therefore, the present invention is establishing
Ignore the influence of inertia force during natural gas line transient flow model.
In the theory for establishing natural gas line transient flow, following hypothesis is done：
1. the flowing of natural gas is isothermal；
2. the expansion of tube wall can be ignored；
3. in any given pipeline section, the slope of pipeline remains unchanged；
4. state equation is selected tests formula through P=z ρ RT, wherein z is compressibility coefficient, and any given transition is asked
Topic, the average value of commonly used z, this process are Single-issue range, and z is considered as constant；
5. flow relational expression using unitary；
6. friction coefficient is the function of wall roughness and Reynolds number, empirically steady motion is used in transition calculating
Friction coefficient；
7. the variation influence along the kinetic energy of pipeline is smaller, ignore during modeling.
(1.1) governing equation
(1.1.1) continuity equation
For gas pipeline since gas compressibility is strong, can be first with the applying gas due to pressure during tube contacts
It is spread to both ends, so can not consider the changes of section of pipeline when calculating.With according to mass conservation law, gas flows in the duct
The common form of dynamic continuity equation can be rewritten as following reduced form by transformation：
In formula：ρ --- gas density, kg/m3；The flow velocity of v --- gas, m/s；T --- time variable；s；X --- edge
Pipe range variable, m；
(1.1.2) equation of motion
According to Newton's second law, the equation of motion form flowed in the duct by the gas that hydrodynamics is established is writeable
For：
In formula：G --- acceleration of gravity, m/s2The inclination angle of θ --- pipeline and horizontal plane, rad；
λ --- hydraulic simulation experiment；D --- internal diameter of the pipeline, m；P --- air in pipeline pressure, Pa；
(1.1.3) continuity equation
For real gas, the state equation of gas adds in correction factor to represent with The Ideal-Gas Equation.
It is of the invention to be for the state equation of natural gas：
P=z ρ RT (3)
In formula：P --- gas pressure, Pa；Z --- the compressed coefficient；R --- gas constant, J/ (kg.K)；ρ --- gas
Density, kg/m3；T --- absolute temperature, K；
Under the assumed condition of isothermal Flow of Single, T is constant, and gas velocity of wave is：
(1.1.4) compressibility factor calculates
Compressibility factor uses California, USA natural gas association formula：
In formula：P --- gas pressure (exhausted), MPa；T --- gas temperature, K；The relative density of Δ --- gas；
(1.2) Shock propagation model is established
The flow regime of gas in the duct is described with continuity equation and the equation of motion, so as to obtain pipeline
Pressure, the changes in flow rate situation of upper difference.Mass flow in gas pipeline is expressed as M=ρ vA, then substitution connects respectively
Continuous property equation (1) and equation of motion (2) are replaced the gas flow rate in equation, and following contain can be obtained by variation
There is the mathematical differentiation equation of mass flow：
The computational methods of Inertia are very cumbersome in formula (7), can influence computational efficiency when calculating.And due in pipeline
Inertia influence in gas motion equation is very small, in order to improve computational efficiency, usually ignores Inertia, then formula (7)
It can be converted to：
In formula：A --- pipeline flow sectional area, m2；M --- gas mass flow, kg/s；P --- gas absolute pressure,
Pa；ρ --- gas density, kg/m3；G --- local gravitational acceleration, m/s2；λ --- pipe friction factor；θ --- computer tube
The angle of inclination formed between road and horizontal plane, rad；D --- internal diameter of the pipeline, m；The differential variable of x --- duct length, m；
T --- time variable, s；
Obtaining gas thermal insulation propagation velocity of sound by thermodynamics is：
For isothermal Flow of Single：
Then formula (5), formula (7) become
In formula:P --- gas absolute pressure, Pa；T --- time variable, s；A --- gas velocity of wave, m/s；A --- pipeline
Actual internal area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density,
kg/m3；G --- local gravitational acceleration, m/s m/s2；θ --- the angle of inclination formed between pipeline and horizontal plane is calculated,
rad；λ --- pipe friction factor；D --- internal diameter of the pipeline, m.
The UNSTEADY FLOW in natural gas line can be described in formula (11) and formula (12).Pressure and flow be all in formula
It is position and the function of time, the pressure at any time of any position on pipeline and stream can be obtained by two equations of simultaneous
Amount.Pressure and flow are dependent variable in formula (11), formula (12), and position and time are independent variable.Pressure, flow are disturbed in order to obtain
Dynamic situation of change needs to carry out simultaneous solution to two dependent variables.
(2) it is as shown in Figure 2 not exclusively to block natural gas line physical model for input
(3) mesh generation is carried out to the incomplete blocking pipeline using mathematical computation tool Matlab
(4) numerical computations are carried out on the basis of gridding flow field, finite element grid solution, meter are carried out using the method for characteristic curves
Calculation obtains not exclusively blocking continuous mass flow field and continuous pressure field in pipeline
The present invention selects the method for characteristic curves to solve natural gas line transient flow model, with solving precision it is high,
Fireballing feature.And pass through finite difference calculus, Newton iteration method and boundary condition and determine that simultaneous solves known variables.
(4.1) feature based collimation method model solution
Two partial differential equation are obtained in above-mentioned modeling, the method for characteristic curves is exactly that two obtained partial differential equation are distinguished
It is added after being multiplied by a undetermined coefficient, so as to construct two total differential equations, then respectively to two total differential equations at it
Corresponding characteristic curve upper integral, so as to obtain being convenient for the finite difference equations of numerical value processing.
(4.1.1) characteristic strips equation
Formula (10) is multiplied by after a undetermined coefficient η and is added to obtain with formula (11) again：
It is arbitrary to select two real number η not waited that retrieve two equations using P and M as dependent variable, and the two
Equation is equivalent with formula (10) and formula (11).If suitably two particular values of selection η, it is possible to which formula (13) obtains letter
Change.
Because have：
If it enables：
Then formula (13) reforms into ODE：
Solution formula (16), two particular values for obtaining η are：
It is by the relationship of formula (16) x and t：
Show that the change in location of wave and time change are connected with the spread speed a of wave by formula (19) and formula (20)
's.When η takes positive value in equation (16), the η in equation (17) must also take positive value；When η takes negative value in equation (16), equation
(17) η in also takes negative value.Two values of η are brought into equation (17), two equations is obtained, is grouped and with C+And C-
To mark.
In this way, using two real number η, two original partial differential equation two ODEs (21) have been transformed into just
(22).But there are one constraintss for each equation, i.e., only when corresponding constraints is set up, ODE is
It sets up.
Equation (21) and (22) can be illustrated with Fig. 3.
Isothermal gas is flowed, velocity of wave can be approximately considered as constant, therefore, two constraintss (19) and (20) are in xt
Two straight lines are expressed as in plane.We term it characteristic curves.On this two characteristic curves, two partial differential equation are set up, I
Be referred to as compatible equations.Each compatible equations are only just set up on characteristic curve.
(4.1.2) finite difference equations
The pipeline given is divided into N deciles, each decile length is dx, at that time step-length degree dt=dxa, as shown in Figure 4
X-t planes.Obviously, in C+Meet equation (21) on characteristic curve AD, since pressure and the flow of initial time A points are it is known that therefore,
(21) are integrated along AD, an equation of the pressure and flow about D points can be obtained.Equally, in C-Satisfaction side on characteristic curve BD
Journey (22), pressure and the flow of B points are it is known that available about another of D point pressures and flow along the line integral equation (22)
Equation.The two equation solutions of simultaneous can obtain the pressure and uninterrupted of D points.
Equation (21) is multiplied by adt, and consider dt=dx/a, can be obtained along C+Integrated form：
The relationship of p, M and x are not known in advance under left side third, the 4th two sign of integration in above formula, therefore, draw in the calculation
With following approximate relation.
P under the Section 3 sign of integration of the left side is replaced with the average pressure of A and D points, i.e.,
Formula under the Section 4 sign of integration of the left side, obtains
Integration type (23) can obtain
It is similar, along C-Characteristic curve integrates between B and D
Formula (26) and formula (27) are two nonlinear equations, and iteration usually can be used and solved.Non-stationary flow is carried out to ask
Topic analysis when, usually since the time be zero stationary flow.Therefore, after the p and M on △ t moment mesh points are calculated, Ran Houjie
And calculated on t=2 △ t, and using p the and M values of △ t moments as initial value, and so on, calculate always to it is required when
Between until.
The Newton iteration method of (4.1.3) Nonlinear System of Equations
The solution of finite difference calculus obtains two nonlinear equations, since Newton method is to solve for the classics of Nonlinear System of Equations
Algorithm, therefore solved using Newton iteration method.
For nonlinear equation：
It is unfolded at x (k) by Taylor's formula, and linear term is taken to obtain：
The iterative formula of Newton method is just obtained in this way：
(4.1.4) boundary condition determines
It can be seen from figure 4 that on the boundary of pipe ends, due to can only respectively there is a characteristic curve, it is impossible to calculate
P the and M values of endpoint, and after the first time step, start the calculating of each grid node inside gradually influence.This is because do not have
There is the reason of considering boundary condition.So in order to make any instantaneous solution complete, need to introduce corresponding boundary condition.
For any one end of single tube, only there are one the compatibility conditions of two variables can be used.As shown in figure 5, upstream end side
Journey (27) is along C-Characteristic curve is set up；And to downstream boundary, equation (26) is along C+Characteristic curve is set up.This is two about MDAnd PDIt is non-
Linear equation.Each case is required for a subsidiary equation to carry out regulation MDAnd PDOr provide certain relationship between them.It is and right
May also there are boundary, such as reducer pipe, branch pipe tie point, valve or compressor among pipeline.Here is that several natural gases are discussed
The commonly used boundary condition of long distance pipeline.
1. known pipeline endpoint stream amount is a fixed value or the function of time
If known pipeline upstream end flow is the function of time, such as
MD1=fM(t) (32)
Due to MD1It is instantaneously both known about any, the pressure P of each time step upstream end can directly be obtained with equation (29)D1。
If similary known pipeline downstream flow is the function of time, each time step downstream can also be acquired by equation (26)
End pressure PND+1。
2. known pipeline endpoint pressure is a fixed value or the function of time
If known pipeline upstream end pressure is the function of time, such as
pD1=fp(t) (33)
Due to PD1It is instantaneously both known about any, can each time step upstream end flow M directly be obtained with (27)D1。
Equally, it if the function of known pipeline downstream pressure type time, can also be acquired under each time step by equation (26)
Swim end flow MDN+1。
3. not exclusively block section endpoint
As shown in fig. 6, tie point is the downstream endpoint of pipeline section 1, the C1 of the pipeline section+Equation is applicable in it, meanwhile, it is again
The upstream endpoint of pipeline section 2, the C2 of the pipeline section-Equation is applicable in it.
Contain known variables P in two equations1, N+1,M1,N+1,P2,1And M2,1.Meanwhile on tie point, upstream and downstream flow
It is equal, i.e.,
M1,N+1=M2,1 (34)
If ignoring the difference of local resistance, upstream and downstream pressure is equal, i.e.,
P1,N+1=P2,1 (35)
Two characteristic strips equations of simultaneous can acquire four known variables to be asked and continuous flow in pipeline is obtained by calculation
Measure field and continuous pressure field.
The specific steps are：Numerical value is carried out to natural gas line transient flow using method of characteristic curves combination Matlab mathematical softwares
Simulation calculates, and the calculating program frame chart that natural gas line transient flow simulation calculation is carried out using the method for characteristic curves is as shown in Figure 7.
(5) verify that natural gas of the present invention not exclusively blocks pipeline method for numerical simulation
As shown in Fig. 2, the Long-distance Transmission Pipeline of pipeline long 5km, internal diameter 600mm occur not exclusively to block, it is not exclusively stifled
Section is filled in away from the distance L at entrance0=1km not exclusively blocks segment length L1=100m blocks intensity B=20%.Stablize fortune
Pressure is 6MPa at entrance during row, and flow is 8,000,000 m3/d.Air in pipeline flowing is isothermal, and temperature is set as
293.15K, velocity of sound is 353.6m/s under isothermal.The relative density of natural gas is 0.573, and pipeline hydraulic friction resistance coefficient is
0.01.Line pressure and mass flow distribution be as shown in Figure 8, Figure 9 during stable operation.
Add quality pulse to entrance as shown in Figure 2, work as t>Allow flow at entrance linearly increasing suddenly during 0s, t
Reach 16,000,000 m3/d of peak value during=0.5s, then start linear decrease, when t=1s is decremented to 8,000,000 m3/ d, later flow protect
It holds constant.
The flow instabilities of pipeline are analyzed using the method for characteristic curves, pipeline is subjected to mesh generation, is averagely divided into
1000 grids, i.e.,：1001 nodes, pipeline section step-length take 5m, time step to take 0.0139s.
Figure 10,11 clearly show pressure wave and quality compressional wave being propagated through along whole pipeline of numerical simulation respectively
Journey.It is worth noting that the propagation of pressure wave and quality compressional wave can be accurate with the method for this numerical simulation discretization parameter
True captures.Interval time between adjacent pressure wave and quality compressional wave is 18s, and entire simulated time is 72s.Pressure wave
It is determined with the communication form of quality compressional wave by the gentle bulk wave speed of compressibility factor of gas.Velocity of sound wave is traveled to from entrance
Pipe end needs 215s.
It obtains not exclusively blocking real-time continuous flow field and continuous pressure field in pipeline, and then calculate by numerical simulation
And it records pressure at entrance and changes with time as shown in figure 12.In t>Pressure linearly increases suddenly at entrance during 0s
Add, when t=0.5s reaches peak value 6.08MPa, then starts linear decrease, and when t=1s is decremented to 6MPa；Then in t=1 to t
=5.7s period internal pressure power is maintained at 6MPa；Pressure starts linearly increasing again during t=5.7s, and pressure reaches another during t=6.20s
Start linear decrease after one peak value 6.015MPa, when t=6.7s is decremented to a valley value 5.99MPa；Pressure starts later
It is incremented by, reaches 6MPa in t=7.11s.Later since pressure wave can be reflected in pipe at inlet and incomplete blocking
In propagate repeatedly, pressure at entrance can recurrent fluctuations.But pressure wave is during propagation due to damping action, pressure
The increase and decrease amplitude of wave will gradually weaken, and final pipeline can be restored to the stable state of beginning.
The pressure oscillation that numerical simulation obtains entrance is as shown in figure 12, at entrance add in flow pulse it
Afterwards, the pressure of inlet is changed, and two pressure peaks and a pressure valley value occurs.First pressure peak be
Directly caused by the flow pulse applied, second pressure peak is that the barotropic wave generated by not exclusively blocking section front end causes
, caused by pressure valley value is the suction wave generated as not exclusively blocking section rear end.Occur pressure rise and drop in Figure 12
Low situation illustrates that incomplete blocking has occurred in pipeline.
Inlet flow increase causes the corresponding time t0 of first peak value that pressure at inlet changes for 0.5s, return
For the corresponding time t1 of second peak value that pressure at inlet caused by barotropic wave changes for 6.2s, blocking position can be with by formula (36)
Calculate distance L of the plugging point at entrance0For：
The blocking position L gone out based on transition method by numerical simulation calculation0With the error of experimental channel actual blockage position
It is 0.776%.
By to Long-distance Transmission Pipeline, there is a situation where a variety of not exclusively block carries out numerical simulation and pass through transition point
Analysis method calculates the incomplete blocking position of pipeline, it is found that the detection error of incomplete blocking position and reality are relatively small.Explanation
Method for numerical simulation of the present invention is accurate to not exclusively blocking flow field in pipeline, pressure field stimulation.
Finally it should be noted that：The above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although
The present invention is described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that；It still may be used
Either which part or all technical features are equal with modifying to the technical solution recorded in previous embodiment
It replaces；And these modifications or replacement, the model for technical solution of the embodiment of the present invention that it does not separate the essence of the corresponding technical solution
It encloses, should all cover in the claim of the present invention and the range of specification.
Claims (4)
1. a kind of natural gas not exclusively blocks pipeline method for numerical simulation, which is characterized in that includes the following steps：
Step S1, flowing progress gas Shock propagation model modeling in pipeline is not exclusively being blocked to natural gas；
Step S2, according to not exclusively blocking, the input of pipeline geometric parameter is incomplete to block pipeline geometrical model；
Step S3, mesh generation is carried out to the incomplete blocking pipeline using mathematical computation tool Matlab；
Step S4, numerical computations are carried out on the basis of gridding flow field, finite element grid solution, meter are carried out using the method for characteristic curves
Calculation obtains not exclusively blocking continuous flow field and continuous pressure field in pipeline.
2. natural gas according to claim 1 not exclusively blocks pipeline method for numerical simulation, it is characterised in that：In step S1
The gas in pipelines propagation of disturbance is established based on the continuity equation, the equation of momentum and the state equation that are flowed according to gas in pipelines
Model, ignores inertia force, and the incomplete gas in pipelines Shock propagation model that blocks of foundation is：
In formula:P --- gas absolute pressure, Pa；T --- time variable, s；A --- gas velocity of wave, m/s；A --- pipeline flow
Sectional area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density, kg/
m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；λ——
Pipe friction factor；D --- internal diameter of the pipeline, m.
3. natural gas according to claim 2 not exclusively blocks pipeline method for numerical simulation, which is characterized in that foundation is not
Completely plugged gas in pipelines Shock propagation model detailed process is as follows：
The continuity equation that S11, gas flow in the duct is
In formula：ρ --- gas density, kg/m3；The flow velocity of v --- gas, m/s；T --- time variable；s；X --- become along pipe range
Amount, m；
The equation of motion that S12, gas flow in the duct is：
In formula：G --- acceleration of gravity, m/s2；The inclination angle of θ --- pipeline and horizontal plane, rad；
λ --- hydraulic simulation experiment；D --- internal diameter of the pipeline, m；P --- air in pipeline pressure, Pa；
S13, continuity equation are：
P=z ρ RT (3)
In formula：P --- gas pressure, Pa；Z --- the compressed coefficient；R --- gas constant, J/ (kg.K)；ρ --- gas density,
kg/m3；T --- absolute temperature, K；
Under the assumed condition of isothermal Flow of Single, T is constant, and gas velocity of wave is：
S14, compressibility factor calculate：Compressibility factor is calculated using California, USA natural gas association formula：
In formula：P --- gas pressure (exhausted), MPa；T --- gas temperature, K；The relative density of Δ --- gas；
S15, Shock propagation model are established：Mass flow in gas pipeline is expressed as M=ρ vA, is then substituted into respectively continuous
Property equation (1) and equation of motion (2) gas flow rate in equation is replaced, by variation can obtain it is following containing
The mathematical differentiation equation of mass flow：
Ignore Inertia, then formula (7) can be converted to：
In formula：A --- pipeline flow sectional area, m2；M --- gas mass flow, kg/s；P --- gas absolute pressure, Pa；
ρ --- gas density, kg/m3；G --- local gravitational acceleration, m/s2；λ --- pipe friction factor；θ --- calculate pipeline with
The angle of inclination formed between horizontal plane, rad；D --- internal diameter of the pipeline, m；The differential variable of x --- duct length, m；t——
Time variable, s；
Obtaining gas thermal insulation propagation velocity of sound by thermodynamics is：
For isothermal Flow of Single：
Then formula (5), formula (7) become
In formula:P --- gas absolute pressure, Pa；T --- time variable, s；A --- gas velocity of wave, m/s；A --- pipeline flow
Sectional area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density, kg/
m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；λ——
Pipe friction factor；D --- internal diameter of the pipeline, m.
4. natural gas according to claim 3 not exclusively blocks pipeline method for numerical simulation, which is characterized in that in step S4
Continuous flow field and continuous pressure field in not exclusively blocking pipeline, which are calculated, using the method for characteristic curves further comprises following steps：
S41, it formula (11) is multiplied by after a undetermined coefficient η to be added with formula (12) again constructs two total differential equations and with C+With
C-Label：
In formula:A --- gas velocity of wave, m/s；P --- gas absolute pressure, Pa；T --- time variable, s；A --- pipeline flow
Sectional area, m2；M --- gas mass flow, kg/s；The differential variable of x --- duct length, m；ρ --- gas density, kg/
m3；G --- local gravitational acceleration, m/s2；θ --- calculate the angle of inclination formed between pipeline and horizontal plane, rad；λ——
Pipe friction factor；D --- internal diameter of the pipeline, m；
S42, respectively to above-mentioned two total differential equation in its corresponding characteristic curve upper integral, obtain being convenient for numerical value processing
Finite difference equations：
S43, formula (26) (27) are nonlinear equation, are solved using Newton iteration method：
The iterative formula of Newton method is：
S44, boundary condition is determined, the continuous flow field not exclusively blocked in pipeline is calculated in two characteristic strips equations of simultaneous
With continuous pressure field.
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