JP2012168065A - Free interface simulation apparatus and free interface simulation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simulate a position of a free interface with excellent accuracy in the case where an inflow port and an outflow port for fluids are located in a calculation area.SOLUTION: A free interface simulation apparatus is provided which analyzes positions of interfaces of two or more fluids in a vessel having an inflow port and an outflow port using numerical fluid calculation according to a continuum model (Eulerian-Euleria approach). The apparatus includes means which inputs an analysis model, means which sets an analysis condition, and analysis execution means. The analysis model includes a model for a body of the vessel and a model for a connection channel which connects the inflow port and the outflow port of the vessel. The analysis condition includes a setting value for a flow velocity of a fluid flowing in the connection channel. The analysis execution means executes the analysis under a such condition that the flow velocity of each fluid element on a cross section at a predetermined position in the connection channel becomes the setting value.

Description

  The present disclosure relates to a free interface simulation apparatus and a free interface simulation method using numerical fluid calculation based on a continuum model (Eulerian-Euleria method).

  As a free interface simulation apparatus, a method of calculating a fluid velocity distribution and interface shape by combining a Navier-Stokes equation, a method of dividing a space into a calculation grid, and a pressure Poisson equation is generally known.

  Various interface calculation methods have been developed (see, for example, Patent Document 1). The calculation method described in Patent Document 1 relates to microscopic modeling of the interface shape.

JP 2001-99749 A

  However, the conventional method as disclosed in the above-mentioned patent document 1 mainly has the purpose of analyzing the fluctuation of the liquid level due to the vibration of the entire container and the ripples when the droplet reaches the liquid level. If there are inlets and outlets in the calculation area, etc., there is a problem with numerical stability, and even if it can be calculated, the result of the liquid level varies depending on the calculation conditions, and obviously the result is not realistic There were drawbacks such as. For example, in agitation tank analysis, the amount of liquid (liquid level) during operation is often fixed and calculated, and it is difficult to calculate that includes fluctuations in the liquid level due to outlet pressure loss due to changes in liquid viscosity or flow rate. In estimating the liquid level in such a situation, internal observation with an actual machine was indispensable.

  Therefore, the present disclosure aims to provide a free interface simulation apparatus and a free interface simulation method capable of simulating the position of a free interface with good accuracy when there are a fluid inlet and outlet in a calculation region. .

In order to achieve the above object, according to one aspect of the present disclosure, an interface between two or more fluids in a container having an inlet and an outlet using a numerical fluid calculation by a continuum model (Eulerian-Euleria method) A free interface simulation device for analyzing the position of
Means for inputting the analysis model;
Means for setting analysis conditions for performing the analysis;
Analysis execution means for performing the numerical fluid calculation,
The analysis model includes a model of the main body of the container, and a model of a connection channel that connects an inlet and an outlet of the container,
The analysis condition includes a set value of a flow velocity of the fluid flowing through the connection channel,
Provided is a free interface simulation device characterized in that the analysis execution means executes the analysis under a condition that the flow velocity of each fluid element in a cross section at a predetermined position of the connection flow path becomes the set value. .

  According to the present disclosure, it is possible to obtain a free interface simulation apparatus and a free interface simulation method capable of simulating the position of a free interface with good accuracy when there are a fluid inlet and outlet in a calculation region.

It is a figure showing an example of important section composition of free interface simulation device 1 concerning this indication. 2A is a top view of an apparatus (container) to which the free interface simulation according to the present disclosure is applied, and FIG. 2B is a cross-sectional view taken along line PP in FIG. 2A. It is. FIG. 3 is a diagram illustrating an example of an analysis model 300 that may be used in a free interface simulation according to the present disclosure. It is a flowchart which shows the flow of an example of the principal part of the free interface simulation method which concerns on this indication. It is a figure which shows the steady calculation result by Example 1. FIG. It is a figure which shows typically the part of the setting cross section (part of a setting flow velocity) in the connection flow path model 305 with a steady calculation result. It is a figure which shows the transient calculation result by Example 2. FIG. It is a figure which shows the change aspect of the flow volume set by the transient calculation by Example 2. FIG. It is a figure which shows the example of a result which shows the transient calculation initial stage (example in case the lower ceiling height is substantially the same as the initial liquid level height). It is a figure which shows the example of a result which shows the transient calculation initial stage (example whose gas layer initial stage thickness under the lower ceiling is about 15 mm). It is a figure which shows the example of steady calculation by the comparative example 1. 10 is a diagram illustrating an example of steady calculation according to Comparative Example 2. FIG.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  Here, first, the basic concept (principle) of the present disclosure will be described.

  The present disclosure relates to a free interface simulation apparatus and method for obtaining interface positions of two or more fluids (incompressible fluids) using a numerical calculation technique. According to the present disclosure, the inlet and the outlet are connected, and the inflow and outflow conditions are set by providing a region for fixing the flow rate in a part of the calculation region. By directly connecting the fluid inlet / outlet, the amount (volume, volume fraction) of each fluid included in the calculation area is fixed during the calculation, so it is much more stable than the method that does not directly connect the fluid outlet / inlet. Calculation is possible.

  Here, in order to realize the present disclosure, it is necessary to fix the flow rate of a part of the calculation region. However, the flow rate is set to a constant value and direction in a specified region in the calculation grid (calculation cell). This is realized by fixing, and will be specifically described below.

(1) is the Navier-Stokes equation that gives the time variation of the velocity in the computational grid,

[Outside 1]
Is a velocity vector, p is pressure, ρ is density, t is time μ is viscosity, and ∇ is a differential operator (nabla). In the normal region, the velocity field after a minute time is calculated from the velocity vector of the initial condition and other conditions in each lattice, and the calculation is performed up to the designated time. The speed corresponding to the inflow condition of the fluid in the conventional method is a partial area of the pipe cross section corresponding to the flow path connecting the outlet and the inlet.

[Outside 2]
This is realized by replacing the numerical value of the predetermined direction component (especially the component in the reference flow direction of the pipe) of the (speed vector) with a value corresponding to the inflow amount every calculation step.

  In order to realize the present disclosure, the initial calculation value is preferably set so that the area of the fluid interface does not change suddenly due to a change in the liquid level. This is because the volume of gas and liquid is fixed, and a very large velocity component is generated in the horizontal direction due to a sudden change in the interface area, making the calculation of the liquid level unstable. (Refer to Example 3 described later).

  FIG. 1 is a diagram illustrating an example of a main configuration of a free interface simulation apparatus 1 according to the present disclosure.

  As shown in FIG. 2, the free interface simulation device 1 according to the present disclosure includes an input parameter generation unit 10, a model input unit 12, a numerical analysis unit 14, and a flow velocity correction unit 16. Note that these units 10, 12, 14, and 16 may be realized by a combination of software and hardware. At this time, these units 10, 12, 14, and 16 may be realized by common software, or may be realized in cooperation with a plurality of software. Similarly, these units 10, 12, 14, and 16 may be realized by common hardware or may be realized by cooperation of a plurality of hardware. For example, the function (described later) of the flow velocity correction unit 16 may be incorporated in the numerical analysis unit 14.

  The input parameter generation unit 10 generates (sets) input parameters (analysis conditions) necessary for analysis in the numerical analysis unit 14 based on external input data (typically input data from a user). The input parameter may include a calculation initial value (for example, an initial liquid level height), a set value (described later) of a flow velocity with respect to a fluid flowing through a flow path (connection flow path) connecting the outlet and the inlet, and the like.

  The model input unit 12 inputs an analysis model (mesh model) to the numerical analysis unit 14. As the analysis model, an analysis model created by an external model creation device may be imported and stored in the free interface simulation device 1, or a model creation function that can be included in the free interface simulation device 1. What is generated / corrected by (software) and stored in the free interface simulation apparatus 1 may be read out.

  The numerical analysis unit 14 uses the input parameters generated by the input parameter generation unit 10, the analysis model input from the model input unit 12, and set values (described later) supplied from the flow velocity correction unit 16 described later. Then, the interface position of two or more fluids is obtained by numerical fluid calculation based on the continuum model. The details of the fluid analysis method in the numerical analysis unit 14 are arbitrary if a continuum model is used. For example, the numerical analysis unit 14 may be realized by general-purpose fluid calculation software called a fluid solver and hardware such as a CPU. As such general-purpose fluid calculation software, ANSYS general-purpose fluid calculation software CFX is known. The numerical analysis unit 14 may be realized in cooperation with a hardware resource (for example, a supercomputer) located at a remote location.

  The flow velocity correction unit 16 corrects the calculation result of the flow velocity used in the next calculation step (the calculation result obtained in the current calculation step) for each calculation step of the numerical analysis unit 14. For each calculation step of the numerical analysis unit 14, the flow velocity correction unit 16 calculates the calculation result of the flow velocity (the calculation result obtained in this calculation step) for the fluid flowing through the flow path (tube) connecting the fluid outlet and inlet. , Correct (replace) to the set value. Details of this processing will be described later.

  FIG. 2 shows an example of an apparatus to which the free interface simulation according to the present disclosure is applied. The apparatus shown in FIG. 2 is a container having an inlet and an outlet. 2A is a top view of the container, and FIG. 2B is a cross-sectional view taken along line PP in FIG. 2A. The container shown in FIG. 2 is a simplified reaction stirring tank (container), and includes a container main body 201 that contains two or more fluids (liquid and gas in this example), and a fluid in the container main body 201. (In this example, an inflow port 202 through which liquid flows in) and an outflow port (outflow path) 204 through which the fluid flows out of the container body 201 are included. The outlet 204 may be set at a position (height) at which two or more fluids can flow out from the container body 201. That is, the outlet 204 may be set near the liquid level of the lower layer fluid (in this example, liquid) in the container main body 201. The inflow port 202 may be set in an arbitrary manner. For example, in the illustrated example, the inflow port 202 is arranged so that the fluid is introduced into the container main body 201 from the upper surface side, but may be set, for example, on the side surface side or the lower surface side.

  Note that the overall shape, volume, cross-sectional shape, and the like of the container body 201 may be arbitrary. Similarly, the cross-sectional shape, cross-sectional change mode (including a mode in which the cross-section is constant), length, and the like of the outlet 204 may be arbitrary.

  The free interface simulation according to the present disclosure is suitable for analyzing the positions (heights and shapes) of two or more fluid interfaces in the container 200. For example, the calculation of the interface position (liquid level height and shape) is indirect, for example, in the reaction agitation tank, when the viscosity of the liquid changes greatly due to the reaction, and the progress of the reaction is indirectly determined by observing the liquid level in the outlet pipe. You can use it if you want to know. In particular, in the conventional agitation tank analysis, the amount of liquid during operation (liquid level) is often calculated temporarily, and calculations involving liquid level fluctuations caused by outlet pressure loss due to changes in liquid viscosity or flow rate are In the estimation of the liquid level in such a situation, internal observation with an actual machine was indispensable, but according to the free interface simulation according to the present disclosure, the liquid level in such a situation Can be accurately estimated.

  FIG. 3 is a diagram illustrating an example of an analysis model 300 that may be used in the free interface simulation according to the present disclosure. The illustrated analysis model 300 is an analysis model for the apparatus (container 200) shown in FIG.

  The analysis model 300 includes a container body model unit 301 that models the container body 201, an outlet model unit 304 that models an outlet (outflow pipe) 204, and a connection channel that models a virtual connection channel. A model 305 and a fluid reservoir model 306 that models a virtual fluid reservoir that stores fluid are included.

  On the analysis model 300, the container body model portion 301 and the outlet model portion 304 are in fluid communication with each other via a connection channel model 305. The connection channel model 305 corresponds to a model of a pipe connecting the outlet and the inlet of the container 200. The container main body model portion 301 and the outlet model portion 304 preferably communicate with each other via a fluid reservoir container model 306 and a connection channel model 305, as shown in FIG. Specifically, on the analysis model 300, the fluid flowing out from the container main body model part 301 through the outlet model part 304 once flows into the fluid reservoir container model 306, and from the fluid reservoir container model 306 to the connection channel. It flows into the container body model part 301 via the model 305. Further, on the analysis model 300, the outlet model part 304 is configured so that two or more fluids in the container main body model part 301 can flow out at the same time, as in the actual flow manner in the outlet 204. Similarly, the outlet model part 304 is connected to the fluid reservoir model 306 in such a manner that two or more fluids can flow into the fluid reservoir model 306 simultaneously. On the analysis model 300, the connection channel model 305 is such that only the lower layer fluid (lower than the interface) in the fluid reservoir container model 306 (in this example, only the liquid) flows into the container body model unit 301. Configured as follows. An end (inlet) on the container body model portion 301 side in the connection channel model 305 may be set at an arbitrary position. Further, the connection channel model 305 may include a straight line portion and a curved portion, and the cross section does not necessarily have an equal cross section. Further, the connection channel model 305 may be arranged along a path including a height difference. In the example shown in the figure, the connection channel model 305 extends along a straight path (with no difference in height) having an equal cross section.

  FIG. 4 is a flowchart showing a flow of an example of a main part of the free interface simulation method according to the present disclosure.

  In step 400, the model input unit 12 inputs data of the analysis model 300 (see FIG. 3).

  In step 402, initial condition setting is executed by the input parameter generation unit. As initial conditions, in addition to characteristics such as the density of the fluid (in this example, gas and liquid), the flow velocity in the connection channel modeled by the connection channel model 305 is set. This flow velocity may be a flow velocity in a cross section (hereinafter referred to as a set cross section) at a predetermined position in the connection channel model 305, and is commonly applied to each fluid element passing through the set cross section. That is, this flow velocity allows each fluid element that passes through the set cross section (corresponding to the individual calculation cell that defines the set cross section) to pass through the set cross section at a common flow rate (set flow rate). It is a set value. That is, the fluid has the same flow velocity at any location on the set cross section, and the same flow velocity is determined by the installation value. The set value of the flow velocity may be set with respect to the flow direction in the connection channel model 305 (in this example, the component perpendicular to the set cross section, see the arrow R in FIG. 3), and the flow velocity of other direction components is arbitrary. There may be (that is, no settings are made). Alternatively, the flow velocity of the other direction component in the set cross section may be a set value zero (fixed value). The set cross section may be set at an arbitrary position in the connection channel model 305. For example, the set cross section may be set near the center of the connection channel model 305. Further, the set flow rate may be any desired value, and may be set based on the flow rate in the actual apparatus (see FIG. 2).

  In the present disclosure, since the closed analysis model 300 in which no fluid enters and leaves the outside is used, it is not necessary to set conditions related to fluid input and output (exit conditions such as outlet pressure).

  In Step 404 and Step 406, the numerical analysis unit 14 (fluid solver) performs time step calculation of a minute time based on the analysis model 300 input in Step 402 in accordance with the setting conditions set in Step 400. .

  In step 404, first, using the known pressure and momentum equation in each calculation cell obtained in the previous calculation step, a predicted value of the flow velocity after a minute time advance is calculated for each calculation cell, and this calculation is performed. It is given as the initial flow rate used in the step (initial flow rate not satisfying the mass conservation equation). At this time, in this step 404, the calculation result of the previous calculation step is obtained by the flow velocity correction unit 16 for each fluid element (individual calculation cells that define the set section) in the set section in the connection channel model 305. The flow velocity (set value) set in step 402 is replaced (replaced), and a predicted flow velocity value is given for each calculation cell. That is, only for each fluid element on the set cross section in the connection channel model 305, the flow velocity analysis result of the previous calculation step is not used, and a predicted flow velocity value is given based on the set value. In the first calculation step, the flow velocity (set value) set in step 402 may be used.

  In step 406, the numerical analysis unit 14 (fluid solver) initializes the calculation result (velocity field) calculated in step 404 based on the setting condition set in step 400 and the analysis model 300 input in step 402. The values are used to calculate the final flow velocity and pressure field that simultaneously satisfy mass conservation and momentum equations. This calculation may follow the Navier-Stokes equation (see Equation 1) or the pressure Poisson equation. In step 406, the calculation result may be corrected based on the influence of gravity (density difference) or the like. However, the free interface simulation method according to the present disclosure does not use an exit and does not require correction of mass balance (for example, correction of mass balance at an entrance / exit).

  In step 408, the numerical analysis unit 14 determines the calculation end condition. If the calculation end condition is satisfied, the process ends. If the calculation end condition is not satisfied, the process returns to step 404 to satisfy the calculation end condition. Steps 404 and 406 are repeated for each time step.

  In step 410, the analysis result is output. The output of the analysis result may be displayed on a display device (not shown). For example, a calculation result as shown in FIG. The analysis result may include an indication of two or more fluid interfaces (in this example, a liquid-expectation interface). In the case of this example, this interface (interface between the liquid and air) may be displayed by an isosurface with a volume fraction of 0.5.

  In addition, although the calculation method by the above-mentioned numerical analysis part 14 uses the separation solution methods (separate speed and pressure, for example) like SIMPLE method (Semi-Implicit Pressure Linked Equations), for example, other calculation methods ( For example, a coupled solution method may be used.

  Next, various examples will be described. The following various examples are examples of simulating the water surface height and shape when water flows through a flow path open to the upper atmosphere.

  Example 1 is an example of steady-state calculation, FIG. 5 is a diagram illustrating a calculation result, and FIG. 6 is a set cross-section portion X (set flow velocity is applied) in the connection channel model 305 in Example 1. It is a figure which shows part X) typically with a calculation result.

  In this example, steady calculation was performed with the liquid flow rate (flow velocity) at the set cross section in the connection flow channel model 305 being 10 times the reference flow rate (actual assumed flow rate). Further, as an initial condition for the calculation, the liquid level was set to the height of the lower end surface of the cylindrical portion (outlet model part 304). As a result, as shown in FIG. 5, the calculation did not diverge and the liquid level could be calculated.

  Example 2 is an example of transient calculation, FIG. 7 is a diagram showing calculation results, and FIG. 8 is a flow rate change mode set in this calculation, that is, in a set cross section in the connection channel model 305. The change mode of the set flow rate (change mode with respect to the simulation time on the horizontal axis) is shown. FIG. 7 shows calculation results (simulation results) for a simulation time of 0 to 450 ms every 50 ms. In the second embodiment, the set flow velocity in the set cross section in the connection channel model 305 is set in such a manner that it changes from 0 to 1/10 times the reference flow rate as shown in FIG.

  In Example 2, the same analysis model as in Example 1 was used. FIG. 7 shows an example of transient calculation when the flow rate changes as shown in FIG. Also in this case, as shown in FIG. 7, the height of the liquid level could be calculated as the flow rate changed with time.

  9 and 10 show an example of the result showing the initial transient calculation, and the flow rate (the set flow velocity at the set section in the connection channel model 305) is 0 to 1/10 times the reference flow rate as shown in FIG. It was set in a manner that changes to

  In Example 3, an analysis model having a ceiling shape of the fluid reservoir container model 306 different from the analysis model used in Examples 1 and 2 was used. In other words, the ceiling shape of the fluid reservoir container model 306 of the analysis model used in Examples 1 and 2 has the highest ceiling height on the connection side with the outlet model part 304, and the connection side with the outlet model part 304. In contrast to the shape in which the ceiling height gradually decreases as the distance from the center increases, the fluid reservoir container model 306 of the analysis model used in the third embodiment has two different constant ceiling height portions 306a and 306b. Become. The part 306a is a part connected to the outlet model part 304, and has the same ceiling height as the highest ceiling height of the fluid reservoir container model 306 of the analysis model used in the first and second embodiments. Part 306b has a lower ceiling height than part 306a.

  FIG. 9 and FIG. 10 show the calculation results under the same conditions except that the lower one of the two ceiling heights (the ceiling height of the part 306b) is different. In FIG. 9, the lower ceiling height (the ceiling height of the portion 306b) is substantially the same as the initial liquid level height, and the lower ceiling is in the initial state where it is immersed in the liquid. On the other hand, in FIG. 10, the initial thickness of the gas layer under the lower ceiling is about 15 mm, and the lower ceiling is in contact with the gas. As can be seen by comparing the two, the calculation of FIG. 10 is stable, but the calculation of FIG. 9 is unstable. The reason for this is that in the calculation of FIG. 9, as the liquid level decreases with time, the area of the interface between the gas and the liquid increases rapidly, and the gas rapidly enters the gap between the lower ceiling and the fluid interface. For this reason, a very large velocity of the horizontal component is generated compared with the velocity in the direction of the height (gravity) of the liquid surface, and the calculation becomes unstable. Therefore, it is important that the area of the fluid interface does not change suddenly during the calculation. Therefore, for example, the ceiling height may be gradually reduced as in the analysis models used in Examples 1 and 2, and a gas layer may be formed under the ceiling as shown in FIG. An initial value or an analysis model may be configured. For example, the thickness of the gas layer under the ceiling may have a thickness corresponding to 5 meshes of calculation cells (mesh elements).

Comparative example

  FIG. 11 is a diagram illustrating an example of steady calculation according to Comparative Example 1, and FIG. 12 is a diagram illustrating an example of steady calculation according to Comparative Example 2.

  Comparative Examples 1 and 2 are calculation examples for simulating the water surface height and shape in the case where water flows through a flow path open to the upper atmosphere, as in Example 1. This comparative example is the same as the example of steady calculation in the same shape model as FIGS. 5 and 6 except for the set cross section (set flow velocity) in the connection channel model 305. The liquid flow rate at the inlet is the same condition as in FIG. 5 (10 times the reference flow rate), and the outlet is the same as the pressure boundary in Comparative Example 1, and the same as the inlet in Comparative Example 2. The mass flow boundary of the quantity. Two calculation examples with different outlet positions are shown. In either case, the liquid filled the upstream calculation area, and a reasonable calculation result could not be obtained. In addition, the transient calculation according to the same flow rate change (refer FIG. 8) as the above-mentioned Example 2 was tried by the same setting as the comparative examples 1 and 2, but all became an error at the beginning of calculation, and a calculation result is obtained. I couldn't.

  As described above, according to the present embodiment, the amount (volume) of each fluid included in the calculation area is fixed during the calculation by directly connecting the fluid inlet / outlet, so the fluid outlet and the inlet are not directly connected. Compared to the comparative example, a much more stable calculation is possible. This is not the main cause of instability during the calculation, but the microscopic calculation model as in the past, but the configuration of the entire calculation model, especially the calculation routine for conservation of mass. As a result, it is an realized technique. In general, in a model with a long residence time, it takes time to converge the calculation of the mass of the entire calculation region. In particular, in the calculation of a stirring tank or the like, the mass balance becomes a vibration state when the liquid surface shape is undulated, and the vibration of the mass balance becomes a vibration of the liquid surface shape. Therefore, in the calculation of the stirring tank, etc., by applying the present disclosure, the mass conservation calculation routine for the entire calculation area that becomes an instability factor becomes unnecessary, and the vibration of the liquid level and the vibration of the mass balance increase with each other. Since it does not cause problems, stable calculation is possible.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above, for the purpose of explaining the principle of the present disclosure, reaction in a fluid (liquid in the above example) is not considered, but according to the present disclosure, for example, in a reaction stirring tank, by reaction It can be used when the progress of the reaction is indirectly known from the observation of the liquid level in the outlet pipe when the viscosity of the liquid changes greatly. In this case, for example, the viscosity of the fluid may be given a temporally changing viscosity in consideration of the reaction without setting the viscosity of the fluid to a fixed value. Similarly, it is possible to consider the reaction between two fluids (in the above example, water and gas).

  In the above description, the set cross section is set to be perpendicular to the reference flow direction in the connection channel model 305, but is set obliquely with respect to the reference flow direction (the longitudinal direction of the channel) in the connection channel model 305. May be.

  In the above description, a closed model (a model in which the balance of each fluid is fixed) in which no fluid enters and exits from the outside is used, but a reaction between two fluids (in the above example, water and gas). It is also possible to consider the flow of fluids to and from the outside.

DESCRIPTION OF SYMBOLS 1 Free interface simulation apparatus 10 Input parameter production | generation part 12 Model input part 14 Numerical analysis part 16 Flow velocity correction | amendment part 200 Container 201 Container main body 202 Inlet 204 Outlet 300 Analysis model 301 Container main body model part 304 Outlet model part 305 Connection flow path Model 306 Fluid reservoir model

Claims (8)

A free interface simulation device that analyzes the position of the interface of two or more fluids in a container having an inlet and an outlet using numerical fluid calculation by a continuum model (Eulerian-Euleria method),
Means for inputting the analysis model;
Means for setting analysis conditions for performing the analysis;
Analysis execution means for performing the numerical fluid calculation,
The analysis model includes a model of the main body of the container, and a model of a connection channel that connects an inlet and an outlet of the container,
The analysis condition includes a set value of a flow velocity of the fluid flowing through the connection channel,
The free interface simulation device, wherein the analysis executing means executes the analysis under a condition that a flow velocity of each fluid element in a cross section at a predetermined position of the connection flow path becomes the set value.   The analysis execution unit executes the next calculation step by replacing the calculation result of the flow velocity of each fluid element in the cross section by the current calculation step with the set value for the cross section at a predetermined position of the connection flow path. The free interface simulation apparatus according to claim 1.   3. The free interface simulation device according to claim 1, wherein the analysis execution unit executes the analysis under a condition in which a volume fraction of the two or more fluids is maintained.   The free interface simulation device according to any one of claims 1 to 3, wherein the set value is a fixed value or a variable value that changes as the simulation time elapses.   The analysis model further includes a model of a fluid reservoir that stores fluid, and an inlet and an outlet in the model of the container body are connected via the model of the fluid reservoir and the model of the connection channel. The free interface simulation apparatus according to any one of claims 1 to 4.   6. The free interface simulation device according to claim 1, wherein the analysis model is a model that forms a closed space in which a fluid does not enter and exit from the outside. The analysis condition includes an initial value of calculation,
The initial value of the calculation is set so that the area of the fluid interface does not change suddenly during the change of the fluid interface height assumed during the calculation by the analysis execution unit. The free interface simulation apparatus according to any one of the preceding claims. A free interface simulation method for analyzing the position of the interface of two or more fluids in a vessel having an inlet and an outlet using a numerical fluid calculation by a continuum model (Eulerian-Euleria method),
Inputting an analysis model, the step of inputting an analysis model including a model of the main body of the container and a model of a connecting flow path connecting an inlet and an outlet of the container;
Setting analysis conditions including a set value of the flow velocity of the fluid flowing through the connection flow path;
And executing the analysis under a condition that the flow velocity of each fluid element in a cross section at a predetermined position of the connection flow path becomes the set value.