A steady-state detection method based on two-fluid six-equation transient calculation

Abstract

The application discloses a steady-state detection method based on two-fluid six-equation transient calculation, which comprises the following steps: before a detection time point, data required for local convergence judgment and TASS judgment are calculated and arranged; time local convergence of a system is judged according to enthalpy change of the system; after the convergence judgment is completed, TASS judgment is started on a historical state of the system, so that the system is ensured to completely enter a final stable state. The application improves the reliability under a low-energy and small-step working condition through a mixed relative convergence-time average judgment method, and meanwhile, the original steady-state detection efficiency is maintained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steady state detection, and particularly relates to a steady state detection method based on two-fluid six-equation transient calculation. BACKGROUND

[0002] The basic concept of steady state is that the basic state of the system does not change with time. In the process of fluid dynamics solving, the time-varying condition of the basic state of the system can be evaluated by monitoring three items of density, specific internal energy and pressure. The three items can be combined into one item, i.e. enthalpy. Therefore, in the related solving process of fluid dynamics, for the steady state calculation of one-dimensional two-fluid six-equation, whether the system has reached a steady state can be judged by monitoring the change of enthalpy with time, i.e. whether the system has reached a steady state is judged by detecting the energy of the system.

[0003] In other commercial software, the processing of the convergence judgment is to perform curve fitting on the square root of the spatial average enthalpy mean square, and then perform time derivation to judge the convergence, i.e. the traditional convergence-time average judgment, which has certain instability problem:

[0004] 1) When the system enthalpy is small, it is likely to be misjudged;

[0005] 2) The second order derivative of the system enthalpy with respect to time only measures the speed of the time-varying of the system energy, and cannot directly reflect the size of the time-varying of the system energy. In the early heating stage with small time step, due to the small time step and small heat energy input, the change of the system energy with respect to time is approximately linear. Obviously, the second order derivative is approximately 0 at this time, but the system has not reached a stable state.

[0006] In summary, the traditional convergence-time average judgment is prone to misjudgment under the condition of small step and low energy, and a large amount of model test is often required to determine the standard to overcome the problem. Therefore, a detection method which can accurately perform convergence judgment in the steady state calculation module and improve the stability of the system solving is needed. SUMMARY

[0007] In view of this, the present application provides a steady state detection method based on two-fluid six-equation transient calculation, which improves the reliability under the condition of low energy and small step by using the mixed relative convergence-time average judgment method, while maintaining the original steady state detection efficiency.

[0008] The present application discloses a steady state detection method based on two-fluid six-equation transient calculation, comprising the following steps:

[0009] Step 1: Before the detection time point, the data required for local convergence judgment and TASS judgment are calculated and arranged;

[0010] Step 2: Convergence judgment of time local convergence of the system according to the system enthalpy change;

[0011] Step 3: After the convergence judgment is completed, start TASS judgment on the historical state of the system to ensure that the system completely enters the final stable state.

[0012] Further, the step 1 comprises:

[0013] Before the detection time point, initialize the calculation of related variables and calculate the control body set related variables in the system:

[0014]

[0015]

[0016] In the formula, V total is the total volume of the control body, NVols is the total number of control bodies, V i is the volume of the i-th control body, V rms is the volume square sum, and i is the control body number.

[0017] Further, the step 2 comprises:

[0018] The total internal energy in the volume v is:

[0019] ρ mix U mix V=(α g ρ g U g +α f ρ f U f )V (3)

[0020] Wherein, ρ mix =α g ρ g +α f ρ f ;

[0021]

[0022] Wherein, α g is the gas volume fraction, α f is the liquid volume fraction, U g is the gas specific internal energy, U f is the liquid specific internal energy, ρ g is the gas density, ρ f is the liquid density, ρ mix is the mixed density, U mix is the mixed energy;

[0023] Then the enthalpy in a single control body is recorded as:

[0024] ph = p mix h mix = p mix U mix + P (4)

[0025] where h is the system enthalpy, h mix is the mixing enthalpy, and P is the control volume pressure;

[0026] The single control volume enthalpy change rate is:

[0027]

[0028] where the superscript n indicates the quantity is calculated at the nth time step;

[0029] The system spatial average enthalpy change rate mean square sum is:

[0030]

[0031] The system spatial average enthalpy is:

[0032]

[0033] In the problem solving process, formula (7) can be used to monitor the system to tend to be stable, and formula (6) can be used to detect whether the system is converging to a steady state, that is, convergence judgment;

[0034] The curve fitting function of the system spatial average enthalpy change rate mean square sum is:

[0035]

[0036] The coefficients a, b, g and f are calculated by the least square method in any reasonable time interval greater than four time steps; if it is the first calculation, the coefficients a, b, g and f are calculated by the least square method in any reasonable time interval greater than ten time steps.

[0037] Further, in order to facilitate the fitting of formula (8), it is converted into a polynomial form:

[0038] Ln[y(t n )] = a + b t n + g(t n ) 2 + f(t n ) 3 , t o ≤ t n ≤ t (9)

[0039] According to the basic principle of the least square method, the following fitting coefficient calculation formula can be obtained:

[0040] Ac X c = b c (10)

[0041] wherein,

[0042]

[0043] X c = [a b g f] T

[0044] By solving formula (10), a fitting function in the form of formula (8) is obtained; the relative derivative and the direct first derivative are introduced to process the fitting function in the form of formula (8), and the following formula (11) is obtained:

[0045]

[0046] In the formula, t now is the time corresponding to the first step calculation of the steady state judgment monitoring time point; std_con is the convergence judgment standard, which is adjusted according to the actual working condition.

[0047] Further, if stedyy is true, a first convergence judgment is further performed: if it is not the first convergence, a TASS judgment calculation of the next stage is performed; if it is the first convergence, the steady state detection time point t check is changed according to formula (13) to continue the transient calculation and perform the convergence judgment again:

[0048]

[0049] In the formula, N con is the maximum detection step number of convergence, which prevents the interval of two t check time points from being too long, and the specific value is adjusted according to the actual working condition; k con is the convergence time control rate, and the specific value is adjusted according to the actual working condition.

[0050] If stedyy is false, divergence processing is performed, and the TASS calculation related container must be reset, and the divergence time interval At c is calculated.

[0051] Further, the process of calculating the divergence time interval At c is as follows:

[0052] Let the convergence judgment detection starting time point be t start , and the initial value of At c is:

[0053] At c = 0.5*(t check -tstart ) (14) The following judgment is made:

[0054] y(t now +Δt c )≤y(t now ) (15)

[0055] If formula (15) is true, t check =t now +Δt c ; otherwise, Δt c is doubled, and the judgment is made again by formula (15) until Δt c becomes four times the initial value; at this time, even if formula (15) is false, t check =t now +Δt c is set, and the transient calculation is performed; before entering the transient calculation, t line_A_left =t now is set, and the previous TASS accumulation needs to be cleared, that is, A TASS =0, b TASS =0, and the convergence-related accumulations do not need to be cleared.

[0056] Further, the step 3 comprises:

[0057] Step 3-1: based on the calculation formula of the system space average enthalpy, draw TASS three lines; wherein the TASS three lines comprise line_A, line_B and line_C;

[0058] Step 3-2: use the three-line relationship criterion tree to make TASS relationship judgments on line_A, line_B and line_C;

[0059] Step 3-3: based on the TASS relationship judgment, detect whether the system as a whole reaches a steady state.

[0060] Further, the step 3-1 specifically comprises:

[0061] The steady-state module uses the least square method to fit the straight line formula based on the calculation of the system space average enthalpy to judge whether the system reaches the final convergence state;

[0062] The system space average enthalpy curve fitting function is fitted and converted into a polynomial form, and the fitting coefficient calculation formula is obtained according to the basic principle of the least square method;

[0063] In the steady-state module, first draw the C line, then set the C line as the A line, set the first line drawing control symbol as 0, and then immediately return to the transient calculation;

[0064] When entering the TASS module again, a new line B is drawn based on the data in the new time period and the old data, and a final line C is drawn based on the data in the new time period; and whether the system as a whole reaches a final steady state is judged based on the convergence of the slopes of A, B and C.

[0065] Further, the straight line formula is:

[0066]

[0067] Both a and b are linear coefficients;

[0068] Next steady state detection time point t check The calculation formula is as follows:

[0069] t check = t now + min(N TASS · dt, k TASS (t line_A_right -t line_A_left )) (20)

[0070] Where N TASS is the maximum detection step number, to prevent the time interval between two t check from being too long, and the specific value is adjusted according to the actual working condition; k TASS is the convergence time control rate, and the specific value is adjusted according to the actual working condition;

[0071] The criterion for the TASS three-line to reach a steady state is:

[0072] stedy = |b| < conv (27)

[0073]

[0074] Where sdrhsq is the cumulative influence of the absolute error of the density of the control body on the system enthalpy in the TASS detection time period, sumstd is the cumulative influence of the accuracy of the property library on the system enthalpy in the TASS detection time period, conv is the convergence standard of the TASS line, and stedyy is the convergence criterion.

[0075] Further, in the step 3-2:

[0076] After the TASS three-line relationship is judged, the steady state module has two types of results: the first type is that the TASS line diverges, and the divergence restart module is called; the second type is that the B line or the C line is set as the A line, which can make the integrator TWC increase by 1.

[0077] When the line B or the line C is set as the line A, the transient calculation is entered, and the calculation of the next steady state detection time point t check is performed.

[0078] The step 3-3 specifically comprises:

[0079] If the TASS judgment TWC is 1 for two times in succession, then the three-line steady state final integral knets is automatically added by 1, and if the TWC fails once, then the knets is reset to 0;

[0080] When the knets is greater than 2, then it indicates that the system has reached the final steady state, and the transient calculation is terminated; otherwise, the transient calculation is continued.

[0081] Due to the adoption of the above technical solutions, the present application has the following advantages:

[0082] (1) By introducing the relative derivative of the system enthalpy with respect to time, the adaptability under the condition that the time step is extremely likely to be misjudged as convergence when the system enthalpy is small is improved.

[0083] (2) The mixed relative derivative of the system enthalpy with respect to time and the direct first-order derivative eliminate the problem that the traditional second-order absolute derivative of the system enthalpy with respect to time cannot directly reflect the size of the system energy time variation.

[0084] (3) The mixed convergence-time average judgment improves the reliability of the six-equation transient calculation steady state detection method (i.e., the convergence-time average judgment method) of two-phase fluid under the condition of low energy and small step length.

[0085] (4) In combination with the two major functional modules of the convergence judgment and the TASS judgment, the time history state of the system is judged after the local convergence judgment is completed, so as to ensure that the system completely enters the final stable state. BRIEF DESCRIPTION OF DRAWINGS

[0086] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art according to these drawings.

[0087] Figure 1 is a general planning technical route schematic diagram of the embodiments of the present application;

[0088] Figure 2 is a general detailed technical route schematic diagram of the embodiments of the present application;

[0089] Figure 3 is a TASS three-line relationship judgment schematic diagram of the embodiments of the present application;

[0090] Figure 4 is a convergence detection criterion explanation schematic diagram of the embodiments of the present application. DETAILED DESCRIPTION

[0091] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application are described. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application, that is, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0092] Referring to Figure 1 and Figure 2 , the present application provides an embodiment of a steady state detection method based on two-fluid six-equation transient calculation, which is specifically divided into three stages:

[0093] 1. Preparation stage: Before the detection time point, the module calculates and arranges the data required for convergence judgment and TASS judgment (mainly the data taken by curve fitting);

[0094] Initialize the related variables and calculate the related variables of the control body set in the system (only superimpose the control body in the pipe, ignore the boundary):

[0095]

[0096]

[0097] In the formula, V total is the total volume of the control body, NVols is the total number of control bodies, V i is the volume of the i-th control body, V rms is the volume square sum, and i is the control body number.

[0098] Initialization preparation is only called when entering the steady state detection module for the first time, and after that, when entering the steady state monitoring again, it is no longer repeated and automatically skipped.

[0099] 2. Convergence judgment: judging the time-local convergence of the system according to the enthalpy change of the system;

[0100] 2.1 Convergence related data calculation

[0101] The basic concept of steady state is that the basic state of the system does not change with time. In the process of fluid dynamics solution, the time variation of the basic state of the system can be evaluated by monitoring the density ρ, specific internal energy U and pressure P. Further, these three items can be combined into an item, that is, enthalpy ρh=ρU+P. Therefore, in NUMAP, the enthalpy change with time is monitored to judge whether the system has reached a steady state.

[0102] The total internal energy in the volume V is:

[0103] ρmix U mix V=(α g ρ g U g +α f ρ f U f )V (3)

[0104] where, ρ mix =α g ρ g +α f ρ f ;

[0105]

[0106] where, α g is the gas volume fraction, α f is the liquid volume fraction, U g is the gas specific internal energy, U f is the liquid specific internal energy, ρ g is the gas density, ρ f is the liquid density, ρ mix is the mixture density, U mix is the mixture energy;

[0107] The enthalpy (density) in a single control volume can be written as:

[0108] ρh=ρ min h mix =ρ mix U mix +P (4)

[0109] The enthalpy change rate of a single control volume:

[0110]

[0111] where the superscript n indicates the quantity calculated at the nth time step;

[0112] The system space average enthalpy change rate mean square sum:

[0113]

[0114] The system space average enthalpy:

[0115]

[0116] In the problem solving process, equation (7) can be used to monitor the system's tendency to reach steady state, since as each volume element tends to steady state, its overall rate of change will also tend to zero. Thus, equation (6) can be used to detect whether the system is converging to steady state, i.e., a convergence criterion. However, equation (7) has another property that it will fluctuate wildly within an amplitude. As the calculation progresses toward steady state, the amplitude of these fluctuations decreases. Thus, equation (7) is not a well-behaved function and it is difficult to monitor its behavior. However, a well-behaved function can be curve fitted to the results of equation (7) at a reasonable time interval. Exponential functions are of this type. The reasonable time interval here depends on the trend of the working condition change and the calculation efficiency consideration: in principle, it is only meaningful to fit the original data when a certain trend appears, but this judgment needs to be based on a global understanding of the working condition. Since this method is a general method, it is not possible to give a specific time interval.

[0117] The system space average enthalpy curve fitting function is shown below:

[0118]

[0119] The coefficients a, β, γ, and φ can be calculated by the least square method at any reasonable time interval greater than four time steps. Equation (8) has the property that it can increase from a small value to a large value, and then decrease to a small value as time increases and the system approaches steady state.

[0120] For the convenience of fitting equation (8), it is converted to a polynomial form:

[0121] Ln[y(t n )]=α+βt n +γ(t n ) 2 +φ(t n ) 3 , t o ≤t n ≤t (9)

[0122] According to the basic principle of the least square method, the following fitting coefficient calculation formula can be obtained:

[0123] A c X c =b c (10)

[0124] where,

[0125]

[0126] X c =[α β γ φ]T

[0127] 2.2 Convergence judgment and divergence restart processing

[0128] By solving formula (10), we get the fitting function in the form of formula (8). The traditional judgment method uses the derivative of formula (8) for judgment, and the specific judgment method is shown in formula (11):

[0129]

[0130] Where, t now is the time corresponding to the first step calculation of the time point exceeding the steady state judgment monitoring time; std_con is the convergence judgment standard, which is adjusted according to the actual working condition.

[0131] However, using formula (11) to judge convergence has the following problems:

[0132] 1) Formula (11) is an absolute standard, so it is very likely to misjudge as convergence when the system enthalpy is small;

[0133] 2) Formula (11) is the second derivative of system enthalpy with respect to time, which only measures the speed of system energy time variation, and cannot directly reflect the size of system energy time variation. In the early heating stage with small time step, the system energy changes approximately linearly with respect to time due to small time step and small heat energy input. Obviously, the second derivative is approximately 0 at this time, but the system has not reached a stable state.

[0134] To solve the above problems, the relative derivative and the direct first derivative are introduced to improve the adaptability of the convergence criterion to the above problems, and the specific form is as follows:

[0135]

[0136] If stedyy is true, further first convergence judgment is performed: if it is not the first convergence, Time Average Steady Stage (TASS) calculation of the next stage is performed; if it is the first convergence, the steady state detection time point t check is changed as follows to continue the transient calculation and perform convergence judgment again:

[0137]

[0138] Where, N con is the maximum detection step number for convergence, which prevents the interval between two t check time points from being too long, and the specific value is adjusted according to the actual working condition; k con is the convergence time control rate, and the specific value is adjusted according to the actual working condition.

[0139] If stedyy is false, then divergence processing is performed. The relevant containers for TASS calculation must be reset, and the divergence time interval Δt must be calculated according to the following rules. c ;

[0140] Let the convergence detection start time point be t. start Then Δt c The initial value is:

[0141] Δt c =0.5*(t) check -t start (14)

[0142] Make the following judgment:

[0143] y(t now +Δt c )≤y(t now (15)

[0144] If formula (15) is true, then t check =t now +Δt c Conversely, let Δt c Double the result and repeat the judgment described in formula (15) until Δt. c It becomes four times the initial value. Even if formula (15) is false at this point, let t... check =t now +Δt c Then, perform transient calculations. Before proceeding with the transient calculations, let t... line_A_left =t now And it is necessary to clear the previously accumulated TASS amount (i.e., A). TASS =0, b TASS =0), while the convergence-related accumulated amount does not need to be cleared.

[0145] 3. TASS Check: Time Average Steady State Check, also known as TASS. See also... Figure 4 After the local convergence judgment is completed, the system begins to judge the system's time history state to ensure that the system fully enters the final stable state.

[0146] 3.1 TASS Three-Line Calculation

[0147] After passing the convergence test, the steady-state module uses the least squares method to fit the linear formula shown in formula (16) based on the spatial average enthalpy of formula (7) to determine whether the system has reached the final convergence state:

[0148]

[0149] The spatial average enthalpy of the system is calculated at the completion of each successful time step And the linear coefficients a and b are solved using the least square method at a reasonable time interval.

[0150] In order to suppress numerical oscillation, the system spatial average enthalpy curve fitting function is as follows:

[0151]

[0152] In order to facilitate the fitting of formula (17), it is converted into a polynomial form:

[0153] Ln[y(t n )]=α+βt n , t o ≤t n ≤t (18)

[0154] According to the basic principle of the least square method, the following fitting coefficient calculation formula can be obtained:

[0155] A TASS X TASS =b TASS (19)

[0156] Where,

[0157]

[0158] In the steady state module, first draw line_A (first draw C line, and then set C line as A line), and set the first line drawing control symbol to 0, and then immediately return to enter the transient calculation. The next steady state detection time point t check The calculation formula is as follows:

[0159] t check =t now +min(N TASS ·dt,k TASS (t line_A_right -t line_A_left )) (20)

[0160] Where, N TASS is the maximum detection step number, to prevent the time interval between two t check time points from being too long, the specific value is adjusted according to the actual working condition; k TASS is the convergence time control rate, the specific value is adjusted according to the actual working condition.

[0161] When entering the TASS module again, the combined line C is drawn based on the data in the new time period and the old data, and finally the new line B is drawn. Based on the slope convergence of A, B and C, it is judged whether the system as a whole reaches the final steady state.

[0162] The convergence of TASS line is considered in the actual calculation in the following way: first, the effect of the absolute error of mass on the system enthalpy production is considered. For a certain control volume, the absolute error of density is:

[0163]

[0164] where, is the density obtained from the property library, is the density obtained based on the Taylor expansion.

[0165] The cumulative effect of the above on the system enthalpy production in the TASS detection period can be expressed as:

[0166]

[0167] Let the lower limit of the relative accuracy of the property library be η, that is, the maximum error caused by the property table is:

[0168]

[0169] The cumulative effect of the above on the system enthalpy production in the TASS detection period can be expressed as:

[0170]

[0171] The convergence criterion of the TASS line can be expressed as:

[0172]

[0173] The error criterion of the slope of the TASS line is:

[0174]

[0175] The time-averaged steady-state criterion reached by the TASS line is:

[0176] stedy = |β| < conv (27)

[0177] After the above quantities of line_A, line_B and line_C are calculated, then the TASS three-line relationship criterion tree can be entered for relevant judgment to determine whether the system has entered the final steady-state stage.

[0178] 3.2 Three-line TASS relationship judgment

[0179] Referring to Figure 3 After the TASS three-line relationship judgment, the steady-state module will have two types of results: the first type: the TASS line diverges, then the divergence restart module is called; the second type: the TASS line does not diverge, then the B line or the C line is set as the A line, which can make the integrator TWC increase by 1.

[0180] When line B or line C is set to line A, the transient calculation will be entered, and the next steady state detection time point t check The calculation method is the same as described in 3.1.

[0181] 3.3 Three-line steady-state integral calculation and time history steady-state judgment

[0182] If the TWC is 1 for two consecutive times, the three-line steady-state final integral knets is automatically added by 1, and if the TWC fails once, the knets is reset to 0.

[0183] When knets is greater than 2, it indicates that the system has reached the final steady state, and the transient calculation is terminated. Otherwise, the transient calculation is continued.

[0184] As shown in Table 1, the proposed new two-fluid six-equation transient calculation steady-state state detection method has a steady-state detection time comparable to other commercial software lines, and is superior to other commercial software lines in the single-phase non-heating condition, and meets the requirements of engineering applications.

[0185] Table 1 Comparison of steady-state detection time of the application with other commercial software lines

[0186]

[0187] The above description is only the preferred embodiment of the present application, and it should be understood that the present application is not limited to the form disclosed herein, and should not be considered as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein by the above-mentioned teaching or related art or knowledge. Any modification and change made by those skilled in the art without departing from the spirit and scope of the present application shall be within the protection scope of the appended claims of the present application.

Claims

1. A steady state detection method based on two-fluid six-equation transient calculation, characterized in that, The method comprises the following steps: Step 1: before the detection time point, data required for local convergence judgment and TASS judgment are calculated and arranged; Step 2: Convergence judgment is made on the time local convergence of the system according to the system enthalpy change; (12) In the formula, is the convergence criterion, is the system space average enthalpy, is the system space average enthalpy change rate mean square sum, is the first step calculation corresponding time of the monitoring time point exceeding the steady state judgment; is the convergence criterion, which is adjusted according to the actual working condition. If stedyy is true, the first convergence judgment is made: if not the first convergence, the next stage of TASS judgment calculation is made; if the first convergence, the steady state detection time point is changed according to formula (13) to continue the transient calculation and make the convergence judgment again: (13) In the formula, is a single control body enthalpy, is the maximum number of detection steps for convergence, to prevent two The time interval is too long, and the specific value is adjusted according to the actual working condition; is the convergence time control rate, and the specific value is adjusted according to the actual working condition; If stedyy is false, then the divergence process is performed, and the TASS calculation related containers must be reset, while the divergence time interval is calculated ; Step 3: after the convergence judgment is completed, the TASS judgment on the historical state of the system is started to ensure that the system completely enters the final stable state; The step 3 comprises: Step 3-1: based on the calculation formula of the system space average enthalpy, TASS three lines are drawn; wherein the TASS three lines comprise A line, B line and C line; Step 3-2: the TASS relationship judgment is performed on the A line, B line and C line by using a three-line relationship criterion tree; Step 3-3: based on the TASS relationship judgment, whether the system as a whole reaches the steady state is detected; The step 3-1 specifically comprises: The system space average enthalpy curve fitting function is fitted to be converted into a polynomial form, and the fitting coefficient calculation formula is obtained according to the basic principle of the least square method; In the steady state module, the C line is first drawn, then the C line is set as the A line, the first line drawing control symbol is set as 0, and then the transient calculation is immediately returned; When the TASS module is entered again, the C line is drawn based on the data in the new time period and the old data, and finally the new B line is drawn; and whether the system as a whole reaches the final steady state is judged based on the slopes of the A, B and C lines; In the step 3-2: After the TASS three-line relationship judgment, the steady state module has two types of results: the first type is that the TASS line diverges, and the divergence restart module is called; the second type is that the B line or the C line is set as the A line, which can make the integrator TWC increase by 1; When the B line or the C line is set to the A line, a transient calculation is entered, and the next steady-state detection time point is performed calculation: The step 3-3 specifically comprises: If TASS judges TWC as 1 for two times in succession, then three-line steady-state final integration knets Automatically add 1, if one TWC fails knets Reset to 0; When knets If greater than 2, then the system has reached final steady state and the transient calculation is terminated; otherwise, the transient calculation is continued.

2. The method of claim 1, wherein, The step 1 comprises: Before the detection time point, the related variables are initialized and the related variables of the control body set in the system are calculated: (1) (2) In the formula, V is the total volume of the control bodies, N is the total number of the control bodies, Vi is the volume of the i-th control body, V2 is the sum of the volumes, and i is the control body number.

3. The method of claim 1, wherein, The step 2 comprises: Volume The total amount of internal energy within the volume (3) wherein ; wherein, is the gas volume fraction, is the liquid volume fraction, is the gas specific internal energy, is the liquid specific internal energy, is the gas density, is the liquid density, is the mixture density, is the mixture energy; Then the enthalpy in a single control body is recorded as: (4) wherein, is the mixing enthalpy, is the control body pressure; The enthalpy change rate of a single control body is: (5) Wherein, the superscript n represents the calculation amount at the nth time step; The system space average enthalpy change rate mean square sum is: (6) wherein, is the total number of control volumes, is the volume of the i-th control volume; The system space average enthalpy is: (7) In the problem solving process, formula (7) is used to monitor the system to tend to be stable, and formula (6) is used to detect whether the system converges to the steady state, that is, convergence judgment; The curve fitting function of the system space average enthalpy change rate mean square sum is: (8) coefficient , , and are calculated by least squares over any reasonable time interval greater than four time steps; if initial, coefficient , , and are calculated by least squares over any reasonable time interval greater than ten time steps.

4. The method of claim 3, wherein, In order to facilitate the fitting of formula (8), it is converted into a polynomial form: (9) According to the basic principle of the least square method, the following fitting coefficient calculation formula is obtained: (10) wherein ; By solving formula (10), the fitting function like formula (8) is obtained; the relative derivative and the direct first-order derivative are introduced to process the fitting function like formula (8), and the following formula is obtained: (12) In the formula, is the convergence criterion, is the system space average enthalpy, is the system space average enthalpy, is the first step calculation corresponding to the time of the monitoring time point exceeding the steady state judgment; is the convergence criterion, which is adjusted according to the actual working condition.

5. The method of claim 1, wherein, The calculated divergence time interval The process is: Let the convergence judgment detection starting time point be Then The initial value is: (14) The following judgment is performed: (15) If formula (15) is true, then ; otherwise, let double and re-pass formula (15) to determine, until becomes four times the initial value; at this time, even if formula (15) is false, still let , and proceed to the transient calculation; before entering the transient calculation, let , and the previous TASS accumulation needs to be cleared, , , and the convergence-related accumulations do not need to be cleared.

6. The method of claim 1, wherein, The straight line formula is: and are straight line coefficients, is the system space averaged enthalpy; Next steady state detection time point The calculation formula is as follows: (20) Wherein, is the maximum detection step number, preventing two times The time interval is too long, and the specific value is adjusted according to the actual working condition; is the convergence time control rate, and the specific value is adjusted according to the actual working condition; The criterion for the TASS three lines to reach the steady state is: wherein, is the cumulative impact of the absolute error in the density of the control volume on the system enthalpy over the TASS detection time period, is the cumulative impact of the accuracy of the property library on the system enthalpy over the TASS detection time period, is the convergence criteria for the TASS line, is the convergence criterion.

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