[pille]

Hello everyone,

I've got a problem probably caused by the mesh displacement in OpenFOAM 4.1.
It only occurs when the displacement is relatively high and I really don't understand why it moves the points in this way.

The case:
- 2D
- rectangular box with walls on all sides
- a piston in the middle which moves horizontally with a given frequency and amplitude
- the mesh was made by blockMesh
- the solver is "compressibleInterDyMFoam" because there are two phases (water, air)
and compressibility may have an influence at high frequencies
- a simplyfied mesh is shown in the attached picture


Description of the problem:

For small amplitudes everything works fine. But if the amplitude goes above a certain level the simulations aborts.
I tried some variations in the dynamicMeshDict such as changing from displacementLaplacian to displacementSBRStress or changing the diffusivity parameters
but the problem only changed the place place or time of occurrence.
In the attached pictures the problem is shown by a exemplarily case.
2 of the last four time steps are shown.
piston on the left, wall on the right side. colored by pressure

dynamicMeshDict:

dynamicFvMesh dynamicMotionSolverFvMesh;
motionSolverLibs ( "libfvMotionSolvers.so" );
solver displacementLaplacian;
displacementLaplacianCoeffs
{
      diffusivity quadratic inverseDistance (cylinder walls);
}

The test case is attached too, for anybody who may wants to give it a try.
(you have to execute blockMesh first)


Any help will be appreciated.
Best regards,
Henry

[dduque]

Originally Posted by pille

displacementLaplacianCoeffs {
      diffusivity quadratic inverseDistance (cylinder walls);
}

I think you have to specify you have two patches. I am currently moving two patches at the same time, and the "2" seems to do the trick:

displacementLaplacianCoeffs {
      diffusivity quadratic inverseDistance 2 (cylinder walls);
}