[weicent]

Hi Foamers,

I am doing a simulation related to 3 incompressible fluids (ethanol, water and air), two of them are misible, from the Openfoam User Guide, I used interMixingFoam, my concentration is on the mixing process of water and ethanol. The physical process is firstly put the ethanol and water in a cup that have a inlet hole in the bottom, and then pump air into the cup from the bottom to help the mixing process (the geometry of the cup is shown in attatched pictures, the second picture shows that the ethanol is initially at the center of the water), the air is pumped into the cup within a specified time interval (which means the pressure at inlet is a time-dependent variable, and the inlet velocity should be calculated via this inlet pressure).

At the first time, I create the cup geometry by blockMeshDict and setup the varying pressure by uniformTotalPressure (I'm not familiar about this boundary condition, before this I have attempt timeVaryingTotalPressure, timeVaryingUniformFixedValue, timeVaryingMappedFixedValue and uniformFixedValue but all failed, the Openfoam returns an error indicate that there is no such a BC for the former two, I used Openfoam 2.3.1, for the latter two, I don't know how to use them since I didn't found a clear tutorial), after I start the simulation, it diverges at the begining and I don't know how to fix this problem.

After that, I tried to change the time-dependent boundary condition since I dont't familiar about it, I modified the inlet pressure to a fixed value and restart the simulation, but the diverge problem still exist. I have tried refine the mesh, decrease (or increase) the Courant number, decrease the deltaT value but all failed.

Then I have changed the geometry of the cup to a simple cylinder, and the simulation converges in the first 0.06s but diverges after that (under the fixed inlet pressure BC).

I have attatched the zip files of my simulation code (include varying pressure and fixed pressure) , could anyone help me to check my case file? I don't where is the problem, and if possible, could you help me to check if my time-dependent pressure BC is correct? Any suggestion will be appreaciated!

Best,

weicent

[weicent]

the below is the message come from terminal window, as you can see, the courant number is extremly large, which is not normal.

Courant Number mean: 3250.96 max: 2.49028e+08
Interface Courant Number mean: 0 max: 0
deltaT = 2.2309e-12
--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 6 to 7 to distinguish between timeNames at time 0.00111111
Time = 0.001111111

--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 7 to 8 to distinguish between timeNames at time 0.00111111
diagonal: Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver: Solving for alpha.other, Initial residual = 1.05882e-06, Final residual = 8.58729e-18, No Iterations 1
Air phase volume fraction = 0.60692 Min(alpha1) = 0 Max(alpha1) = 1.1154
Liquid phase volume fraction = 0.605912 Min(alpha2) = 0 Max(alpha2) = 1.1154

[weicent]

the below is the message come from terminal window, as you can see, the courant number is extremly large, which is not normal.

Courant Number mean: 3250.96 max: 2.49028e+08
Interface Courant Number mean: 0 max: 0
deltaT = 2.2309e-12
--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 6 to 7 to distinguish between timeNames at time 0.00111111
Time = 0.001111111

--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 7 to 8 to distinguish between timeNames at time 0.00111111
diagonal: Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver: Solving for alpha.other, Initial residual = 1.05882e-06, Final residual = 8.58729e-18, No Iterations 1
Air phase volume fraction = 0.60692 Min(alpha1) = 0 Max(alpha1) = 1.1154
Liquid phase volume fraction = 0.605912 Min(alpha2) = 0 Max(alpha2) = 1.1154

[dzordz]

Try this.

For /U BC:
walls
{
type fixedValue;
value uniform (0 0 0);
}
outlet
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
inlet
{
type fixedValue;
value uniform (0 0 1);
}

For /p BC:
walls
{
type fixedFluxPressure;
}
inlet
{
type zeroGradient;
}
outlet
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;
}

Other is good. Hope it works with this combination

[weicent]

Hi dzordz;

Thank you very much for you reply!

I have tried your code, but the problem still exist, I put it below, its actually still diverges:

Courant Number mean: 0.000236288 max: 7.53633
Interface Courant Number mean: 0 max: 0
deltaT = 1.68055e-12
--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 7 to 8 to distinguish between timeNames at time 4.56634e-05
Time = 4.5663439e-05

diagonal: Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver: Solving for alpha.other, Initial residual = 4.12149e-10, Final residual = 4.12149e-10, No Iterations 0
Air phase volume fraction = 0.392911 Min(alpha1) = 0 Max(alpha1) = 1
Liquid phase volume fraction = 0.60608 Min(alpha2) = -5.37996e-73 Max(alpha2) = 1.00064
--> FOAM Warning :
From function Time:perator++()
in file db/Time/Time.C at line 1055
Increased the timePrecision from 8 to 9 to distinguish between timeNames at time 4.56634e-05
diagonal: Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver: Solving for alpha.other, Initial residual = 4.12149e-10, Final residual = 4.12149e-10, No Iterations 0
Air phase volume fraction = 0.392911 Min(alpha1) = 0 Max(alpha1) = 1
Liquid phase volume fraction = 0.60608 Min(alpha2) = -5.37996e-73 Max(alpha2) = 1.00064
DICPCG: Solving for p_rgh, Initial residual = 0.00332591, Final residual = 0.00015166, No Iterations 9
DICPCG: Solving for p_rgh, Initial residual = 0.00450806, Final residual = 0.000213074, No Iterations 7
DICPCG: Solving for p_rgh, Initial residual = 0.00645848, Final residual = 0.000316934, No Iterations 7
time step continuity errors : sum local = 4.90275e-07, global = 4.19724e-14, cumulative = -4.96021e-05
DICPCG: Solving for p_rgh, Initial residual = 0.00844886, Final residual = 0.000409655, No Iterations 7
DICPCG: Solving for p_rgh, Initial residual = 0.0127241, Final residual = 0.000561724, No Iterations 8
DICPCG: Solving for p_rgh, Initial residual = 0.0162193, Final residual = 0.000758191, No Iterations 9
time step continuity errors : sum local = 1.17456e-06, global = -5.09239e-15, cumulative = -4.96021e-05
DICPCG: Solving for p_rgh, Initial residual = 0.0242594, Final residual = 0.00102831, No Iterations 11
DICPCG: Solving for p_rgh, Initial residual = 0.0363386, Final residual = 0.00165169, No Iterations 11
DICPCG: Solving for p_rgh, Initial residual = 0.0423467, Final residual = 9.83501e-08, No Iterations 166
time step continuity errors : sum local = 1.48924e-10, global = 1.54726e-11, cumulative = -4.96021e-05
time step continuity errors : sum local = 1.48924e-10, global = 1.54726e-11, cumulative = -4.96021e-05
ExecutionTime = 17.87 s ClockTime = 17 s

thanks for your kind help again;

weicent

[weicent]

I actually found some problems in setFieldsDict, before using the interMixingFoam, I have been working with interFoam, which is a two phase solver, so this is the first time I tried to manage three fluids in setFieldsDict by VOF method, I misunderstand something when modify this dictionary, now I have changed it, but the diverge problem still exist, I put the new setFieldsDict here so that someone can check my case to see where is the diverge problem.

[dzordz]

Originally Posted by weicent

Increased the timePrecision from 8 to 9 to distinguish between timeNames

weicent

Since this happens I would try raising time and write precision in ControlDict to 8 for example.

[weicent]

Originally Posted by dzordz

Since this happens I would try raising time and write precision in ControlDict to 8 for example.

Hi dzordz;

thanks for your help, I have made some modify in alpha.air, alpha.water and alpha.other, and also in geometry. I have delete the arc edges in blockMeshDict now, since the curved geometry make the mesh quality is not good, I'm planning to establish this curved geometry later on, but before that, I need to check if the modified case can running well, actually, it seems converges untill 0.43, and the simulation still running I'm waiting to see if it can finally yield a stable result.

below is the new alpha.xx documents I used:

PHP Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      alpha.air;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            inletOutlet;
        inletValue      uniform 1;
        value           uniform 1;
    }
    outlet
    {
        type            zeroGradient;
    }
    walls
    {
        type            zeroGradient;
    }
}

// ************************************************************************* // 


PHP Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      alpha.water;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;

boundaryField
{
    inlet
    {
        type            zeroGradient;
    }
    outlet
    {
        type            zeroGradient;
    }
    walls
    {
        type            zeroGradient;
    }
}

// ************************************************************************* // 


PHP Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.1                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0";
    object      alpha.other;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField   uniform 0;


boundaryField
{
    inlet
    {
        type            inletOutlet;
        inletValue      uniform 0;
        value           uniform 0;
    }
    outlet
    {
        type            zeroGradient;
    }
    walls
    {
        type            zeroGradient;
    }
}

// ************************************************************************* // 


[weicent]

the cylinder geometry and mesh should be created like the first and second picture, while my geometry is shown in the third picture, which i think probably a mistake which lead to simulation divergence.

I will try to modify the new blockMeshDict later and update the outcomes.

[weicent]

Originally Posted by weicent

the cylinder geometry and mesh should be created like the first and second picture, while my geometry is shown in the third picture, which i think probably a mistake which lead to simulation divergence.

I will try to modify the new blockMeshDict later and update the outcomes.

sorry, i just forget put my mistake mesh screenshot, here is it:

[dzordz]

What output do you get with checkMesh? There might be some skew faces or big non-orthogonal cells that are messing up your simulation.

[weicent]

Originally Posted by dzordz

What output do you get with checkMesh? There might be some skew faces or big non-orthogonal cells that are messing up your simulation.

Hi dzorzd:

below is my checkMesh output, thanks for help:

PHP Code:

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:           19481
    faces:            51300
    internal faces:   44700
    cells:            16000
    faces per cell:   6
    boundary patches: 3
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     16000
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     0

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
    Patch               Faces    Points   Surface topology                  
    inlet               100      121      ok (non-closed singly connected)  
    outlet              100      121      ok (non-closed singly connected)  
    walls               6400     6440     ok (non-closed singly connected)  

Checking geometry...
    Overall domain bounding box (-0.00636396 0 -0.00636396) (0.00636396 0.077 0.00636396)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-4.83852e-18 3.40064e-16 8.22549e-18) OK.
    Max cell openness = 2.50633e-16 OK.
    Max aspect ratio = 4.71405 OK.
    Minimum face area = 1.125e-08. Maximum face area = 1.62e-06.  Face area magnitudes OK.
    Min volume = 4.27603e-12. Max volume = 8.91e-10.  Total volume = 6.91938e-06.  Cell volumes OK.
    Mesh non-orthogonality Max: 43.7185 average: 7.73539
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.21537 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End 


[weicent]

Originally Posted by dzordz

Try this.

For /U BC:
walls
{
type fixedValue;
value uniform (0 0 0);
}
outlet
{
type pressureInletOutletVelocity;
value uniform (0 0 0);
}
inlet
{
type fixedValue;
value uniform (0 0 1);
}

For /p BC:
walls
{
type fixedFluxPressure;
}
inlet
{
type zeroGradient;
}
outlet
{
type totalPressure;
p0 uniform 0;
U U;
phi phi;
rho rho;
psi none;
gamma 1;
value uniform 0;
}

Other is good. Hope it works with this combination

Hi dzordz:

After last time I modify the alpha.xxx and blockMesh, the simulation seems converges, while after 0.82s, it still diverge.

Then I made some modify again and combined your P/U code and finally it worked, the simulation now looks very good and paraview shows a satisfied result, thank you my friend!

For summary, below is what I modified from last time:

1. I have changed the inletValue and value for alpha.air and alhpa.other

for alpha.air, the updated code is:

inlet
{
type inletOutlet;
inletValue uniform 0.5;
value uniform 0.5;
}


for alpha.other, the updated code is:

inlet
{
type inletOutlet;
inletValue uniform 0.5;
value uniform 0;
}


2. I have replace the P/U boundary condition with your code.

3. I have disable the arc edges

4. I set the inlet velocity as 'uniform (0 0.5 0)', which is 0.5m/s



But I actually don't understand what does 'value' specified? In my opinion, in alpha.xxx file, the 'inletValue' command specify the volume phase fraction at inlet, 1 represents inlet is full of that phase, 0 means there is no that phase at inlet (I'm not sure if I am right), so what on earth the 'value'command specify?


Best;

weicent

[weicent]

Originally Posted by weicent

Hi dzordz:

After last time I modify the alpha.xxx and blockMesh, the simulation seems converges, while after 0.82s, it still diverge.

Then I made some modify again and combined your P/U code and finally it worked, the simulation now looks very good and paraview shows a satisfied result, thank you my friend!

For summary, below is what I modified from last time:

1. I have changed the inletValue and value for alpha.air and alhpa.other

for alpha.air, the updated code is:

inlet
{
type inletOutlet;
inletValue uniform 0.5;
value uniform 0.5;
}


for alpha.other, the updated code is:

inlet
{
type inletOutlet;
inletValue uniform 0.5;
value uniform 0;
}


2. I have replace the P/U boundary condition with your code.

3. I have disable the arc edges

4. I set the inlet velocity as 'uniform (0 0.5 0)', which is 0.5m/s



But I actually don't understand what does 'value' specified? In my opinion, in alpha.xxx file, the 'inletValue' command specify the volume phase fraction at inlet, 1 represents inlet is full of that phase, 0 means there is no that phase at inlet (I'm not sure if I am right), so what on earth the 'value'command specify?


Best;

weicent

The updated code works good, but still diverges after 1.75s, I open the paraview and it shows a good result before 1.75s.

After the simulation diverges, I open the controlDict and change the start time from 0s to 1.75s (also change the 'startFrom' from 'latestTime' to 'startTime') and then restart the simulation, it seems the simulation running again.

I will update if there is any other problem occurs.

Below is some of the diverge messege in terminal window at 1.75s, does anyone know what lead to the below error?

PHP Code:

--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 184 to 185 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 2.3696e-08, Final residual = 2.3696e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25589e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 185 to 186 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 2.48385e-08, Final residual = 2.48385e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25589e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 186 to 187 to distinguish between timeNames at time 1.75539
DICPCG:  Solving for p_rgh, Initial residual = 1, Final residual = 0.0498738, No Iterations 7
DICPCG:  Solving for p_rgh, Initial residual = 0.406991, Final residual = 0.0133185, No Iterations 7
DICPCG:  Solving for p_rgh, Initial residual = 0.215131, Final residual = 0.00506178, No Iterations 9
time step continuity errors : sum local = 1.17047e-07, global = 2.02128e-16, cumulative = 0.000179792
DICPCG:  Solving for p_rgh, Initial residual = 0.297671, Final residual = 0.0142627, No Iterations 6
DICPCG:  Solving for p_rgh, Initial residual = 0.189953, Final residual = 0.00501451, No Iterations 6
DICPCG:  Solving for p_rgh, Initial residual = 0.104014, Final residual = 0.00271376, No Iterations 7
time step continuity errors : sum local = 6.37272e-08, global = 1.14816e-16, cumulative = 0.000179792
DICPCG:  Solving for p_rgh, Initial residual = 0.0767467, Final residual = 0.00226053, No Iterations 7
DICPCG:  Solving for p_rgh, Initial residual = 0.0474809, Final residual = 0.00236649, No Iterations 5
DICPCG:  Solving for p_rgh, Initial residual = 0.027869, Final residual = 5.98415e-08, No Iterations 162
time step continuity errors : sum local = 1.58523e-12, global = 4.33374e-14, cumulative = 0.000179792
time step continuity errors : sum local = 1.58523e-12, global = 4.33374e-14, cumulative = 0.000179792
ExecutionTime = 3137.39 s  ClockTime = 3152 s

Courant Number mean: 1.94382e-06 max: 0.0831665
Interface Courant Number mean: 4.44921e-07 max: 0.0235118
deltaT = 1.51092e-98
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 187 to 188 to distinguish between timeNames at time 1.75539
Time = 1.75538779576766668100162860355339944362640380859375

--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 188 to 189 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 1.74632e-08, Final residual = 1.74632e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25588e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 189 to 190 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 1.77111e-08, Final residual = 1.77111e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25588e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 190 to 191 to distinguish between timeNames at time 1.75539
DICPCG:  Solving for p_rgh, Initial residual = 0.0402945, Final residual = 0.0017694, No Iterations 13
DICPCG:  Solving for p_rgh, Initial residual = 0.0373714, Final residual = 0.0014712, No Iterations 13
DICPCG:  Solving for p_rgh, Initial residual = 0.0242536, Final residual = 0.000964903, No Iterations 13
time step continuity errors : sum local = 2.23938e-07, global = -1.23237e-15, cumulative = 0.000179792
DICPCG:  Solving for p_rgh, Initial residual = 0.0156767, Final residual = 0.000338695, No Iterations 14
DICPCG:  Solving for p_rgh, Initial residual = 0.0309064, Final residual = 0.000904599, No Iterations 14
DICPCG:  Solving for p_rgh, Initial residual = 0.0423388, Final residual = 0.00153878, No Iterations 13
time step continuity errors : sum local = 2.39132e-07, global = -1.06414e-15, cumulative = 0.000179792
DICPCG:  Solving for p_rgh, Initial residual = 0.0430841, Final residual = 0.00124343, No Iterations 14
DICPCG:  Solving for p_rgh, Initial residual = 0.040241, Final residual = 0.00181448, No Iterations 16
DICPCG:  Solving for p_rgh, Initial residual = 0.0282049, Final residual = 8.08715e-08, No Iterations 188
time step continuity errors : sum local = 2.21815e-11, global = -1.40556e-12, cumulative = 0.000179792
time step continuity errors : sum local = 2.21815e-11, global = -1.40556e-12, cumulative = 0.000179792
ExecutionTime = 3137.71 s  ClockTime = 3152 s

Courant Number mean: 0.000108574 max: 6.09365
Interface Courant Number mean: 1.63388e-05 max: 0.91143
deltaT = 1.23975e-99
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 191 to 192 to distinguish between timeNames at time 1.75539
Time = 1.75538779576766668100162860355339944362640380859375

--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 192 to 193 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 3.89654e-08, Final residual = 3.89654e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25582e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 193 to 194 to distinguish between timeNames at time 1.75539
diagonal:  Solving for alpha.air, Initial residual = 0, Final residual = 0, No Iterations 0
smoothSolver:  Solving for alpha.other, Initial residual = 4.01786e-08, Final residual = 4.01786e-08, No Iterations 0
Air phase volume fraction = 0.324605  Min(alpha1) = -4.25576e-08  Max(alpha1) = 1.00001
Liquid phase volume fraction = 0.669053  Min(alpha2) = 8.56707e-08  Max(alpha2) = 0.994056
--> FOAM Warning : 
    From function Time::operator++()
    in file db/Time/Time.C at line 1055
    Increased the timePrecision from 194 to 195 to distinguish between timeNames at time 1.75539
DICPCG:  Solving for p_rgh, Initial residual = 0.811475, Final residual = 0.0353421, No Iterations 23
DICPCG:  Solving for p_rgh, Initial residual = 0.501662, Final residual = 0.0248784, No Iterations 54
DICPCG:  Solving for p_rgh, Initial residual = 0.213015, Final residual = 0.00977048, No Iterations 56
time step continuity errors : sum local = 0.000131555, global = -2.43499e-07, cumulative = 0.000179549
DICPCG:  Solving for p_rgh, Initial residual = 0.233642, Final residual = 0.0090329, No Iterations 120
DICPCG:  Solving for p_rgh, Initial residual = 0.0983941, Final residual = 0.00459639, No Iterations 56
DICPCG:  Solving for p_rgh, Initial residual = 0.238709, Final residual = 0.01156, No Iterations 56
time step continuity errors : sum local = 7.26265, global = -0.0134776, cumulative = -0.013298
DICPCG:  Solving for p_rgh, Initial residual = 0.235003, Final residual = 0.0102599, No Iterations 120
#0  Foam::error::printStack(Foam::Ostream&) at ??:?
#1  Foam::sigFpe::sigHandler(int) at ??:?
#2   in "/lib/x86_64-linux-gnu/libc.so.6"
#3  double Foam::sumProd<double>(Foam::UList<double> const&, Foam::UList<double> const&) at ??:?
#4  Foam::PCG::solve(Foam::Field<double>&, Foam::Field<double> const&, unsigned char) const at ??:?
#5  Foam::fvMatrix<double>::solveSegregated(Foam::dictionary const&) at ??:?
#6  Foam::fvMatrix<double>::solve(Foam::dictionary const&) at ??:?
#7  
 at ??:?
#8  __libc_start_main in "/lib/x86_64-linux-gnu/libc.so.6"
#9  
 at ??:?
Floating point exception (core dumped) 


Best;

Weicent

[weicent]

The simulation finished, I set the endTime equal to 2.5s, the diverge message did not appear again, and the result seems fine, while I still don't know why the diverge problem appears at 1.75s.

[dzordz]

I'm glad that you have been able to solve it. For why divergence happens I also have no clue

[weicent]

Originally Posted by dzordz

I'm glad that you have been able to solve it. For why divergence happens I also have no clue

thanks dzordz, thanks you very much for your help. :

[wavefunction]

Originally Posted by weicent

But I actually don't understand what does 'value' specified? In my opinion, in alpha.xxx file, the 'inletValue' command specify the volume phase fraction at inlet, 1 represents inlet is full of that phase, 0 means there is no that phase at inlet (I'm not sure if I am right), so what on earth the 'value'command specify?

I remember reading somewhere that the keyword 'value' refers to the value used for initialisation. The keyword 'inletValue' refers to the fixedValue that is assigned if inlet flow occurs.