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Old   July 4, 2013, 11:40
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Martin Novák
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The crash is caused by the big time step. It shoudn't be greater than 0.1 DEG. Therefore you might lower it to 0.05 to be safe. I think that this error is caused by turbulence::correct. When you look at the velocity magnitude, it is seen that the calculation is unstable (too high velocity magnitude).

I am not familiarized with pointMotionUz but it might be similar to MotionU, therefore I recommend to try using the componentMixed like in the Jasak's simpleCase in order to force the piston to move.

Did you tried slip for valveStem?

-M

PS: Try to have at least five layers of mesh between valve poppet and valve seat. This is the area of interest in ICEs.
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Old   July 4, 2013, 12:35
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Quote:
Originally Posted by sasanghomi View Post
Hi Dear Marco,

I have some questions about using fvmotion solver . Please guide me.
1) you said to me that I should set the pointMotionUz for piston uniform 0 . But by doing this action the piston doesn't move .Any idea ?? I think I should set a time varying boundary condition for piston (an equation between velocity of piston and Time ). I want to know that is it possible to define a time varying boundary condition in pointMotionUz file ??
[...]
I appreciate any help from you.
Thanks and best regards,
Sasan.
Are you using fvMotionSolver from dynamicMeshDict or fvMotionSolverEngineMesh from engineMesh? The first one does not move the piston automatically based on engineGeometry, but the second one does.
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Old   July 4, 2013, 12:43
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@martin : thanks for your reply dear martin. I think slip is a good choice for valveStem .

@marco :thanks for your reply dear marco . the dynamicmeshDict and engineGeometry are as below :

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM Extend Project: Open Source CFD        |
|  \\    /   O peration     | Version:  1.6-ext                               |
|   \\  /    A nd           | Web:      www.extend-project.de                 |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant";
    object      engineGeometry;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

 engineMesh        fvMotionSolver;
 motionSolver        z ;
conRodLength    conRodLength [0 1 0 0 0 0 0] 132.56459;

bore            bore [0 1 0 0 0 0 0] 100;

stroke          stroke [0 1 0 0 0 0 0] 92;

clearance       clearance [0 1 0 0 0 0 0] 10;

rpm             rpm [0 0 -1 0 0 0 0] 1500;


// ************************************************************************* //
Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  1.5                                   |
|   \\  /    A nd           | Web:      http://www.OpenFOAM.org               |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      motionProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

solver velocityLaplacian;

diffusivity  uniform;

// ************************************************************************* //
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Old   July 4, 2013, 14:23
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I don't know about boundary condition for piston in pointMotionUz file !!
Please guide me ....
by using uniform 0 the piston doesn't move .

best regards
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Old   July 4, 2013, 14:58
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Martin Novák
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This should be in meters.
Quote:
conRodLength conRodLength [0 1 0 0 0 0 0] 132.56459;

bore bore [0 1 0 0 0 0 0] 100;

stroke stroke [0 1 0 0 0 0 0] 92;

clearance clearance [0 1 0 0 0 0 0] 10;

rpm rpm [0 0 -1 0 0 0 0] 1500;
Please check, if it corresponds to the mesh.

Again, I am not familiarized with pointMotionUz but I think, that the boundary condition describes the velocity of the motion of the patch. If you have uniform (constant) 0 then the displacement of piston, which is velocity * time step is also 0, therefore the piston is not moving.

Try to check the mesh and try to set the velocity to 5. With this velocity, the displacement of the piston in 1DEG shall be 0.5 mm.
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Old   June 17, 2014, 23:45
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I am using foam-extend-3.0 and want to simulate 3D engine. I choose verticalValves in engineTopoChangerMesh for mesh topo change. but there are many cellzones and pointzones such as
valveTopPointsV1
valveBottomPointsV1
movingCellsTopV1
movingCellsBotV1
I don't know how to define. can anyone give me a hand?
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