Tank gas-liquid two-phase modeling and breathing behavior processing method based on finite element method

Abstract

The application discloses a finite element method-based gas-liquid two-phase modeling and breathing behavior processing method for a storage tank, and relates to the technical field of storage tank monitoring. A geometric model of the storage tank is established to obtain a fluid model inside the storage tank; a gas-liquid two-phase model of the storage tank is obtained, the geometric model is meshed, the actual state of the storage tank is simulated, and state data of a breathing accessory are obtained; a fluid-structure coupling model of the breathing accessory is established, the opening behavior of the breathing accessory is calculated, and the fluid-structure coupling model is verified; and the opening behavior of the breathing accessory is predicted according to the rated opening pressure of the breathing accessory and the pressure change of the gas space of the storage tank. The gas-liquid two-phase and fluid-structure coupling models are established, the gas-liquid two-phase flow in the storage tank can be accurately simulated, the behavior of a breathing system composed of a breathing valve, a pressure relief manhole and other structures can be dynamically predicted, real-time data are used to adaptively correct model parameters, the prediction accuracy is improved, and the safe operation of the storage tank is ensured.

Description

Technical Field

[0001] This invention relates to the field of storage tank monitoring technology, and in particular to a method for modeling gas-liquid two-phase systems and processing breathing behavior in storage tanks based on the finite element method. Background Technology

[0002] As a critical piece of equipment for storing liquid media, the performance of the breathing system, such as the breather valve and pressure relief manhole, directly affects the safe operation of the storage tank. When the volume of the medium inside the tank changes due to temperature variations, filling / unloading, etc., the breathing system needs to adjust the pressure inside the tank in a timely manner to prevent overpressure or vacuum damage. However, the design and monitoring of existing storage tank breathing systems have the following shortcomings: First, insufficient accuracy in gas-liquid two-phase modeling: Traditional storage tank models mostly adopt the assumption of single-phase flow, ignoring the dynamic changes at the gas-liquid interface (such as liquid level fluctuations and bubble generation), resulting in the model failing to accurately reflect the actual flow state inside the storage tank; Second, lagging prediction of breathing system behavior: Existing methods mostly predict breathing system behavior based on empirical formulas or static experimental data, failing to dynamically capture the real-time response of the breather valve opening / closing (such as opening pressure fluctuations and leakage changes); Third, lack of specificity in correction methods: When the operating conditions of the storage tank change (such as medium temperature fluctuations or breather valve aging), existing models cannot correct parameters in a timely manner, resulting in a large deviation between the predicted results and the actual behavior. Summary of the Invention

[0003] To address the shortcomings of existing models, such as their inability to accurately and dynamically reflect the flow state of the medium inside the storage tank and their inability to predict and correct the respiratory system behavior in a timely manner, this invention provides a method for modeling the gas-liquid two-phase flow in storage tanks and processing respiratory behavior based on the finite element method.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The method for modeling and processing the breathing behavior of a gas-liquid two-phase storage tank based on the finite element method includes the following steps: S1, establishing a geometric model of the storage tank and obtaining the internal fluid model of the storage tank through volume extraction; S2, obtaining a gas-liquid two-phase model of the storage tank through gas-liquid two-phase partitioning, and performing mesh generation on the geometric model to simulate the actual storage tank state and obtain the state data of the breathing attachment; S3, establishing a fluid-structure interaction model of the breathing attachment, calculating the opening behavior of the breathing attachment through the state data of the breathing attachment, and verifying the fluid-structure interaction model through actual monitoring data of the breathing attachment; S4, predicting the opening behavior of the breathing attachment based on the rated opening pressure of the breathing attachment and the pressure change in the gas phase space of the storage tank.

[0005] Furthermore, in S1, a structural model of the gas phase space, liquid phase space, breather valve inlet, pressure relief manhole inlet, and inlet and outlet pipelines of the storage tank is established, and the liquid level, pressure, and temperature parameters of the actual storage tank in its current state are used as the initial conditions of the geometric model.

[0006] Furthermore, in S2, the lumped parameter method is used to divide the storage tank into a gas phase space, a liquid phase space, and a gas-liquid interface. The calculation formulas for the liquid level and pressure field distribution are derived through the mass conservation equation, the volatilization model, and the equation of state, which are used to establish the gas-liquid two-phase model of the storage tank. The expression for the liquid phase mass conservation equation is as follows: ; In the formula, It is time, measured in seconds (s). This is the volume of the liquid, measured in m³. It is the density of the liquid, which varies with temperature, and is expressed in kg / m³. It is the inlet liquid volume flow rate, in m³ / s; It is the volatile mass flow rate in kg / s; The expression for the gas phase mass conservation equation is: ; In the formula, This is the molar mass of gasoline, expressed in kg / mol. It is the total number of moles; The expression for the gas-phase equation of state is: ; In the formula, It is the real-time gas pressure; This is the real-time gas temperature, used as input, in Kelvin (K). It is the universal gas constant, with units of J / mol·K; It is the volume of gas, and the unit is m³. The expression for the volatile model is: ; In the formula, It is the volatile mass transfer coefficient, with units of kg / m²∙s∙Pa; This represents the gas-liquid interface area, in square meters (m²). This is the radius of the storage tank, in meters (m). It is the partial pressure of gasoline vapor in the gas phase, and the unit is Pa; This is the saturated vapor pressure of gasoline, measured in Pa, where the Antoine equation is: ; In the formula, , , These are all constants corresponding to the properties of gasoline; The expression for the liquid level equation is: ; In the formula, This is the liquid level height, in meters (m). It is the number of moles of gasoline; The expression for the pressure field equation is: ; In the formula, It is the pressure diffusion coefficient, with units of m² / s.

[0007] Furthermore, in S2, the geometric model is divided using an unstructured mesh, with the mesh density at and near the inlet and outlet pipes of the storage tank ranging from 0.001 m to 0.01 m.

[0008] Furthermore, in S3, the breathing accessories include a breathing valve and a pressure relief manhole. The state data obtained from the gas-liquid two-phase model of the storage tank is used as the input of the fluid-structure interaction model to predict the real-time state of the breathing valve and the pressure relief manhole. The iterative coupling method is used to solve the governing equations for the fluid and solid separately, and to transfer the forces and displacements at the coupling interface through iteration. The specific steps include: S31. Apply fluid force to a solid and solve the solid equations to obtain a new displacement; S32. Based on the solid displacement, resolve the fluid equations to obtain the fluid force; S33. Repeat the iteration until convergence.

[0009] Furthermore, the isentropic flow equation for the compressible fluid model is expressed as follows: when hour: ; When the critical pressure ratio is reached: ; In the formula, It is mass flow rate; It is the flow coefficient; It is the flow area between the valve seat and the valve disc; It is the gas inlet side pressure; It is the specific heat capacity ratio; It is the gas inlet side temperature; The motion control equation of the valve disc is: ; In the formula, It is the quality of the valve disc; It is the instantaneous opening height of the valve disc, and ; It is a fluid force; , representing downward gravity; This indicates the valve seat contact force, and only when... It exists at that time; The expression for fluid force is: ; Simplified to: ; In the formula, Where D is the projected area of ​​the valve disc, and D is the diameter of the valve disc. It is the reaction force generated by the change in fluid momentum; The expression for the fluid pressure field is: ; In the formula, It is the fluid-structure interaction interface, that is, the boundary between the valve disc surface and the fluid. It is a position vector on the interface.

[0010] Furthermore, in S4, based on the rated opening pressure of the breather valve and the pressure relief manhole and the pressure change trend of the gas phase space in the storage tank, the opening behavior of the breather valve and the pressure relief manhole is predicted in real time: The positive pressure opening pressure of the pressure relief manhole is higher than the positive pressure opening pressure of the breather valve, and the negative pressure opening pressure of the pressure relief manhole is lower than the negative pressure opening pressure of the breather valve. When the gas pressure inside the storage tank is lower than the positive pressure opening pressure of the breather valve and higher than the negative pressure opening pressure of the breather valve, a simulation of the tank-gas-liquid two-phase model is performed. When the gas phase space pressure of the storage tank is higher than the opening pressure of the breather valve and the pressure relief manhole, the gas pressure at the connection between the breather valve, the pressure relief manhole and the storage tank is used as the input condition to perform fluid-structure interaction model simulation of the breather valve and the pressure relief manhole, and the ventilation volume is predicted. Then the ventilation volume data is transmitted to the gas-liquid two-phase model of the storage tank and the gas-liquid two-phase model of the storage tank is updated. The updated gas phase space pressure of the storage tank is fed back to the inlet of the breather valve and the pressure relief manhole.

[0011] The beneficial effects of this invention are: by establishing a gas-liquid two-phase and fluid-structure interaction model for storage tanks, this invention can accurately simulate the gas-liquid two-phase flow in storage tanks, and can dynamically predict the behavior of the breathing system composed of structures such as breather valves and pressure relief manholes, such as the opening or closing time of the breather valves and leakage data. Moreover, it can use real-time data to adaptively correct model parameters, improve prediction accuracy, and ensure the safe operation of storage tanks. Attached Figure Description

[0012] Figure 1 The diagram shown is a flowchart of one embodiment of the present invention.

[0013] Figure 2 The diagram shows a grid division diagram of the gas-liquid two-phase flow field model inside the storage tank.

[0014] Figure 3 The image shown is a schematic diagram of the three-dimensional model of the breathing valve.

[0015] Figure 4 The diagram shows a three-dimensional model of the flow field inside the breather valve.

[0016] Figure 5 The figure shown is a data curve of the ventilation volume of the breathing valve. Detailed Implementation

[0017] The method for modeling and processing the breathing behavior of a gas-liquid two-phase storage tank based on the finite element method includes the following steps: S1, establishing a geometric model of the storage tank and obtaining the internal fluid model of the storage tank through volume extraction; S2, obtaining a gas-liquid two-phase model of the storage tank through gas-liquid two-phase partitioning, and performing mesh generation on the geometric model to simulate the actual storage tank state and obtain the state data of the breathing attachment; S3, establishing a fluid-structure interaction model of the breathing attachment, calculating the opening behavior of the breathing attachment through the state data of the breathing attachment, and verifying the fluid-structure interaction model through actual monitoring data of the breathing attachment; S4, predicting the opening behavior of the breathing attachment based on the rated opening pressure of the breathing attachment and the pressure change in the gas phase space of the storage tank.

[0018] Furthermore, in S1, a structural model of the gas phase space, liquid phase space, breather valve inlet, pressure relief manhole inlet, and inlet and outlet pipelines of the storage tank is established, and the liquid level, pressure, and temperature parameters of the actual storage tank in its current state are used as the initial conditions of the geometric model.

[0019] Furthermore, in S2, the lumped parameter method is used to divide the storage tank into a gas phase space, a liquid phase space, and a gas-liquid interface. The calculation formulas for the liquid level and pressure field distribution are derived through the mass conservation equation, the volatilization model, and the equation of state, which are used to establish the gas-liquid two-phase model of the storage tank. The expression for the liquid phase mass conservation equation is as follows: ; In the formula, It is time, measured in seconds (s). This is the volume of the liquid, measured in m³. It is the density of the liquid, which varies with temperature, and is expressed in kg / m³. It is the inlet liquid volume flow rate, in m³ / s; It is the volatile mass flow rate in kg / s; The expression for the gas phase mass conservation equation is: ; In the formula, This is the molar mass of gasoline, expressed in kg / mol. It is the total number of moles; The expression for the gas-phase equation of state is: ; In the formula, It is the real-time gas pressure; This is the real-time gas temperature, used as input, in Kelvin (K). It is the universal gas constant, with units of J / mol·K; It is the volume of gas, and the unit is m³. The expression for the volatile model is: ; In the formula, It is the volatile mass transfer coefficient, with units of kg / m²∙s∙Pa; This represents the gas-liquid interface area, in square meters (m²). This is the radius of the storage tank, in meters (m). It is the partial pressure of gasoline vapor in the gas phase, and the unit is Pa; This is the saturated vapor pressure of gasoline, measured in Pa, where the Antoine equation is: ; In the formula, , , These are all constants corresponding to the properties of gasoline; The expression for the liquid level equation is: ; In the formula, This is the liquid level height, in meters (m). It is the number of moles of gasoline; The expression for the pressure field equation is: ; In the formula, It is the pressure diffusion coefficient, with units of m² / s.

[0020] Furthermore, in S2, the geometric model is divided using an unstructured mesh, with the mesh density at and near the inlet and outlet pipes of the storage tank ranging from 0.001 m to 0.01 m.

[0021] Furthermore, in S3, the breathing accessories include a breathing valve and a pressure relief manhole. The state data obtained from the gas-liquid two-phase model of the storage tank is used as the input of the fluid-structure interaction model to predict the real-time state of the breathing valve and the pressure relief manhole. The iterative coupling method is used to solve the governing equations for the fluid and solid separately, and to transfer the forces and displacements at the coupling interface through iteration. The specific steps include: S31. Apply fluid force to a solid and solve the solid equations to obtain a new displacement; S32. Based on the solid displacement, resolve the fluid equations to obtain the fluid force; S33. Repeat the iteration until convergence.

[0022] Furthermore, the isentropic flow equation for the compressible fluid model is expressed as follows: when hour: ; When the critical pressure ratio is reached: ; In the formula, It is mass flow rate; It is the flow coefficient; It is the flow area between the valve seat and the valve disc; It is the gas inlet side pressure; It is the specific heat capacity ratio; It is the gas inlet side temperature; The motion control equation of the valve disc is: ; In the formula, It is the quality of the valve disc; It is the instantaneous opening height of the valve disc, and ; It is a fluid force; , representing downward gravity; This indicates the valve seat contact force, and only when... It exists at that time; The expression for fluid force is: ; Simplified to: ; In the formula, Where D is the projected area of ​​the valve disc, and D is the diameter of the valve disc. It is the reaction force generated by the change in fluid momentum; The expression for the fluid pressure field is: ; In the formula, It is the fluid-structure interaction interface, that is, the boundary between the valve disc surface and the fluid. It is a position vector on the interface.

[0023] Furthermore, in S4, based on the rated opening pressure of the breather valve and the pressure relief manhole and the pressure change trend of the gas phase space in the storage tank, the opening behavior of the breather valve and the pressure relief manhole is predicted in real time: The positive pressure opening pressure of the pressure relief manhole is higher than the positive pressure opening pressure of the breather valve, and the negative pressure opening pressure of the pressure relief manhole is lower than the negative pressure opening pressure of the breather valve. When the gas pressure inside the storage tank is lower than the positive pressure opening pressure of the breather valve and higher than the negative pressure opening pressure of the breather valve, a simulation of the tank-gas-liquid two-phase model is performed. When the gas phase space pressure of the storage tank is higher than the opening pressure of the breather valve and the pressure relief manhole, the gas pressure at the connection between the breather valve, the pressure relief manhole and the storage tank is used as the input condition to perform fluid-structure interaction model simulation of the breather valve and the pressure relief manhole, and the ventilation volume is predicted. Then the ventilation volume data is transmitted to the gas-liquid two-phase model of the storage tank and the gas-liquid two-phase model of the storage tank is updated. The updated gas phase space pressure of the storage tank is fed back to the inlet of the breather valve and the pressure relief manhole.

[0024] This invention discloses a method for modeling gas-liquid two-phase systems in storage tanks and processing their breathing behavior based on the finite element method, such as... Figure 1 As shown, it includes the following steps: The first step is to (1) use CAD software to establish structural models of the storage tank, including the gas phase space, liquid phase space, breather valve inlet, pressure relief manhole inlet, and inlet and outlet pipelines. (2) use the parameters of the existing state of the storage tank, such as liquid level, pressure, and temperature, as the initial conditions of the geometric model to ensure that the geometric model is consistent with the actual state of the storage tank. (3) obtain the internal fluid model of the storage tank by volume extraction.

[0025] The second step is to establish a gas-liquid two-phase model of the storage tank and simulate the actual tank conditions. Using the lumped parameter method, the tank is divided into a gas phase space, a liquid phase space, and a gas-liquid interface. The gas phase space contains compressible fluids such as gases or vapors, while the liquid phase space contains incompressible fluids such as liquids. The gas-liquid interface represents a dynamic phase transition, involving evaporation or condensation. Then, using the mass conservation equation, the volatilization model, and the equation of state, formulas for calculating the liquid level and pressure field distribution are derived to establish the gas-liquid two-phase model of the storage tank.

[0026] The expression for the liquid phase mass conservation equation (considering influent and evaporation) is as follows: ; In the formula, It is time, measured in seconds (s). This is the volume of the liquid, measured in m³. It is the density of the liquid, which varies with temperature, and is expressed in kg / m³. It is the inlet liquid volume flow rate, in m³ / s; It is the volatile mass flow rate in kg / s; In the gas phase mass conservation equation (assuming the gas phase is an ideal gas mixture, such as air and gasoline vapor), the expression for the change in total moles is: ; In the formula, This is the molar mass of gasoline, expressed in kg / mol. It is the total number of moles; The expression for the gas-phase equation of state is: ; In the formula, It is the real-time gas pressure; This is the real-time gas temperature, used as input, in Kelvin (K). It is the universal gas constant, with units of J / mol·K; It is the volume of gas, and the unit is m³. The expression for the evaporation model is as follows (evaporation rate is temperature-dependent): ; In the formula, It is the volatile mass transfer coefficient, with units of kg / m²∙s∙Pa; This represents the gas-liquid interface area, in square meters (m²). This is the radius of the storage tank, in meters (m). It is the partial pressure of gasoline vapor in the gas phase, and the unit is Pa; This is the saturated vapor pressure of gasoline, measured in Pa, where the Antoine equation is: ; In the formula, , , These are all constants corresponding to the properties of gasoline.

[0027] Based on the above equations, the expression for the liquid level equation can be derived as follows: ; In the formula, This is the liquid level height, in meters (m). It is the number of moles of gasoline; And the expression for the pressure field equation is: ; In the formula, It is the pressure diffusion coefficient, with units of m² / s.

[0028] When observing the gas-liquid two-phase model of the storage tank, if a pressure dynamic response lag occurs, it may be necessary to adjust the volatile mass transfer coefficient. When abnormal liquid level issues occur, it may be necessary to optimize the gasoline characteristic constants. , , .

[0029] The geometric model was divided using an unstructured mesh, and the mesh size was adjusted according to the importance of the area. The mesh density at and near the inlet and outlet pipes of the storage tank ranged from 0.001 m to 0.01 m.

[0030] The third step is to establish a fluid-structure interaction model of the breathing accessories and calculate their opening behavior using the state data of the breathing accessories, which include the breathing valve and the pressure relief manhole. The state data obtained from the gas-liquid two-phase model of the storage tank is used as the input of the fluid-structure interaction model to predict the real-time state of the breathing valve and the pressure relief manhole. The fluid-structure interaction model is then verified and corrected using the monitoring data of the breathing accessories in practice.

[0031] An iterative coupling method is used to solve the governing equations of the fluid and the solid separately, and the forces and displacements at the coupling interface are transmitted iteratively.

[0032] First, the fluid force is applied to the solid, and the solid equations are solved to obtain the new displacement: The isentropic flow equation for a compressible fluid model is expressed as follows: when hour: ; When the critical pressure ratio is reached: ; In the formula, It is mass flow rate; It is the flow coefficient; It is the flow area between the valve seat and the valve disc; It is the gas inlet side pressure; It is the specific heat capacity ratio; It is the gas inlet side temperature; The motion control equation of the valve disc is: ; In the formula, It is the quality of the valve disc; It is the instantaneous opening height of the valve disc, and ; It is a fluid force; , representing downward gravity; This indicates the valve seat contact force, and only when... It exists at that time.

[0033] Then, based on the solid displacement, the fluid equations are solved again to obtain the fluid force: The expression for fluid force is: ; Simplified to: ; In the formula, Where D is the projected area of ​​the valve disc, and D is the diameter of the valve disc. It is the reaction force generated by the change in fluid momentum.

[0034] Finally, the iterations are repeated until convergence is achieved, resulting in the fluid-structure interaction model: The expression for the fluid pressure field is: ; In the formula, It is the fluid-structure interaction interface, that is, the boundary between the valve disc surface and the fluid. It is a position vector on the interface.

[0035] The fourth step involves predicting the opening behavior of the breathing accessories based on their rated opening pressure and the pressure changes in the tank's gas phase space. The positive pressure opening pressure of the pressure relief manhole is higher than that of the breathing valve, while the negative pressure opening pressure is lower. When the gas pressure inside the tank is lower than the positive pressure opening pressure of the breathing valve but higher than its negative pressure opening pressure, a tank-gas-liquid two-phase model simulation is performed. When the pressure in the tank's gas phase space is higher than the opening pressures of the breathing valve and the pressure relief manhole, the gas pressure at the connection between the breathing valve, the pressure relief manhole, and the tank is used as input to perform a fluid-structure interaction model simulation of the breathing valve and the pressure relief manhole, predicting the ventilation rate. The ventilation rate data is then transmitted to the tank's gas-liquid two-phase model, updating the model. The updated tank gas phase space pressure is then fed back to the inlet of the breathing valve and the pressure relief manhole.

[0036] The present invention will be described below: (1) Establish a geometric model of the storage tank, using the existing liquid level, pressure, and temperature parameters of the actual storage tank as the initial conditions for the geometric model, ensuring that the liquid level, pressure, and temperature parameters in the geometric model are the same as those in the actual storage tank. Then, obtain the internal fluid model of the storage tank through volume extraction, and obtain the internal gas-liquid two-phase model of the storage tank through gas-liquid two-phase partitioning. Mesh the geometric model, and refine the mesh of the inlet and outlet of the storage tank and the surrounding area to a range of 0.001m to 0.01m. The liquid phase space mesh is denser than the gas phase space mesh, with a total of 63,000 meshes. Figure 2 As shown.

[0037] (2) Real-time simulation and model update. When the external temperature changes or liquid enters or leaves the tank, the change is used as the input condition to perform real-time simulation and update the gas-liquid two-phase model of the tank.

[0038] (3) Verification and correction of the gas-liquid two-phase model of the storage tank. Parameters such as the liquid level and pressure of the storage tank are collected in real time and compared with the actual storage tank data. When the difference between the simulation parameters and the actual parameters exceeds a certain range (e.g., 1%), the adaptive Kalman filter method is used to correct the gas-liquid two-phase model of the storage tank.

[0039] (4) Pressure monitoring and safety accessory activation. Based on the pressure change trend of the gas phase space of the storage tank, the opening behavior of the breather valve and the pressure relief manhole can be predicted and an alarm can be issued; when the monitored or simulated pressure exceeds the opening pressure of the breather valve and the pressure relief manhole, the gas phase space pressure of the storage tank is transmitted to the breather valve model in real time for simulation analysis of the breather valve fluid-structure interaction model.

[0040] (5) Construction of the 3D model of the breathing valve. A detailed 3D digital model of the breathing valve was created using 3D modeling technology. The 3D digital model is shown below. Figure 3 As shown.

[0041] (6) Establishing the flow field inside the breather valve. Import the three-dimensional digital model into the simulation software, and use the volume extraction function of the simulation software to obtain the flow field model inside the breather valve, such as... Figure 4 As shown. When processing the flow field model, non-critical structures such as chamfers were simplified. Subsequently, positive pressure valve discs and negative pressure valve discs were sequentially established within the flow field. The specific operational steps are as follows: when constructing the positive pressure valve disc, the negative pressure valve seat needs to be sealed; similarly, when constructing the negative pressure valve disc, the positive pressure valve seat should also be sealed.

[0042] (7) Fluid-structure Interaction Simulation Analysis and Structural Optimization. A two-way fluid-structure interaction simulation analysis model was established, using the force in the flow field as input to the valve disc and the displacement of the valve disc in the flow field as input to the fluid. After multiple simulations, the simulation parameters were determined as follows: k-ε turbulence model, moderate turbulence intensity, 500,000 mesh elements, and a time step of 0.005 s. After determining these basic parameters, a two-way fluid-structure interaction simulation analysis and model optimization were performed in the simulation software, obtaining the breathing valve ventilation data as follows: Figure 5 As shown.

[0043] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for modeling gas-liquid two-phase gas in storage tanks and processing breathing behavior based on the finite element method, characterized in that, Includes the following steps: S1. Establish the geometric model of the storage tank and obtain the fluid model inside the storage tank through volume extraction; S2. Obtain the gas-liquid two-phase model of the storage tank by dividing the gas-liquid two-phase model, and perform meshing on the geometric model to simulate the actual storage tank state and obtain the state data of the breathing accessories. S3. Establish a fluid-structure interaction model of the respiratory accessories, calculate the opening behavior of the respiratory accessories using the state data of the respiratory accessories, and verify the fluid-structure interaction model using the monitoring data of the respiratory accessories in actual practice. S4. Based on the rated opening pressure of the breathing accessory and the pressure change in the gas phase space of the storage tank, the opening behavior of the breathing accessory is predicted.

2. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 1, characterized in that, In S1, a structural model of the gas phase space, liquid phase space, breather valve inlet, pressure relief manhole inlet, and inlet and outlet pipelines of the storage tank is established, and the liquid level, pressure, and temperature parameters of the actual storage tank in its current state are used as the initial conditions of the geometric model.

3. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 2, characterized in that, In S2, the lumped parameter method is used to divide the storage tank into gas phase space, liquid phase space and gas-liquid interface. The calculation formulas for liquid level and pressure field distribution are derived through mass conservation equation, volatilization model and state equation, which are used to establish the gas-liquid two-phase model of the storage tank. The expression for the liquid phase mass conservation equation is as follows: ； In the formula, It is time, measured in seconds (s). This is the volume of the liquid, measured in m³. It is the density of the liquid, which varies with temperature, and is expressed in kg / m³. It is the inlet liquid volume flow rate, in m³ / s; It is the volatile mass flow rate (kg / s); The expression for the gas phase mass conservation equation is: ； In the formula, This is the molar mass of gasoline, expressed in kg / mol. It is the total number of moles; The expression for the gas-phase equation of state is: ； In the formula, It is the real-time gas pressure; This is the real-time gas temperature, used as input, in Kelvin (K). It is the universal gas constant, with units of J / mol·K; It is the volume of gas, and the unit is m³. The expression for the volatile model is: ； In the formula, It is the volatile mass transfer coefficient, with units of kg / m²∙s∙Pa; This represents the gas-liquid interface area, in square meters (m²). This is the radius of the storage tank, in meters (m). It is the partial pressure of gasoline vapor in the gas phase, and the unit is Pa; This is the saturated vapor pressure of gasoline, measured in Pa, where the Antoine equation is: ； In the formula, , , These are all constants corresponding to the properties of gasoline; The expression for the liquid level equation is: ； In the formula, This is the liquid level height, in meters (m). It is the number of moles of gasoline; The expression for the pressure field equation is: ； In the formula, It is the pressure diffusion coefficient, with units of m² / s.

4. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 3, characterized in that, In S2, the geometric model is divided using an unstructured mesh, with the mesh density at and near the inlet and outlet pipes of the storage tank ranging from 0.001 m to 0.01 m.

5. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 4, characterized in that, In S3, the breathing accessories include a breathing valve and a pressure relief manhole. The state data obtained from the gas-liquid two-phase model of the storage tank is used as the input of the fluid-structure interaction model to predict the real-time state of the breathing valve and the pressure relief manhole. The iterative coupling method is used to solve the governing equations for the fluid and solid separately, and to transfer the forces and displacements at the coupling interface through iteration. The specific steps include: S31. Apply fluid force to a solid and solve the solid equations to obtain a new displacement; S32. Based on the solid displacement, resolve the fluid equations to obtain the fluid force; S33. Repeat the iteration until convergence.

6. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 5, characterized in that, in, The isentropic flow equation for a compressible fluid model is expressed as follows: when hour: ； When the critical pressure ratio is reached: ； In the formula, It is mass flow rate; It is the flow coefficient; It is the flow area between the valve seat and the valve disc; It is the gas inlet side pressure; It is the specific heat capacity ratio; It is the gas inlet side temperature; The motion control equation of the valve disc is: ； In the formula, It is the quality of the valve disc; It is the instantaneous opening height of the valve disc, and ; It is a fluid force; , representing downward gravity; This indicates the valve seat contact force, and only when... It exists at that time; The expression for fluid force is: ； Simplified to: ； In the formula, Where D is the projected area of ​​the valve disc, and D is the diameter of the valve disc. It is the reaction force generated by the change in fluid momentum; The expression for the fluid pressure field is: ； In the formula, It is the fluid-structure interaction interface, that is, the boundary between the valve disc surface and the fluid. It is a position vector on the interface.

7. The method for modeling gas-liquid two-phase gas in a storage tank and processing its breathing behavior based on the finite element method according to claim 6, characterized in that, In S4, the opening behavior of the breather valve and pressure relief manhole is predicted in real time based on the rated opening pressure of the breather valve and pressure relief manhole and the pressure change trend of the gas phase space in the storage tank. The positive pressure opening pressure of the pressure relief manhole is higher than the positive pressure opening pressure of the breather valve, and the negative pressure opening pressure of the pressure relief manhole is lower than the negative pressure opening pressure of the breather valve. When the gas pressure inside the storage tank is lower than the positive pressure opening pressure of the breather valve and higher than the negative pressure opening pressure of the breather valve, a simulation of the tank-gas-liquid two-phase model is performed. When the gas phase space pressure of the storage tank is higher than the opening pressure of the breather valve and the pressure relief manhole, the gas pressure at the connection between the breather valve, the pressure relief manhole and the storage tank is used as the input condition to perform fluid-structure interaction model simulation of the breather valve and the pressure relief manhole, and the ventilation volume is predicted. Then the ventilation volume data is transmitted to the gas-liquid two-phase model of the storage tank and the gas-liquid two-phase model of the storage tank is updated. The updated gas phase space pressure of the storage tank is fed back to the inlet of the breather valve and the pressure relief manhole.

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