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lt.quibbler January 13, 2012 09:28

Breaking of constraint conditions
Hi, foamers!

I've faced a very strange problem while trying to calculate the 2DoF movement of a cuboid in a canal with interDyMFoam. Cuboid is half submerged in water and the inflow velocity in longitudinal direction ( X ) is 0.5 m/s. I use the constraint fixedLine in the vertical ( Z ) direction ( not to let the cuboid move downstream the canal ) and fixedAxis around Y-axis ( to let only the trim change ).

For some time the constraint condition is satisfied, but after 2-3 seconds of model time, the object starts shifting downstream the canal ( along the X-axis ), and the shifting velocity is quite large. I see this movement in Paraview, but when I look at the log it reports that the body is moving not in the X-direction but in Z direction ( ! ).

So, there are two questions:

1. Why the constraint condition is not satisfied after some time?
2. Why the log and the actual mesh movement ( in Paraview ) do not coincide.

I use OpenFOAM 2.1.x, but this behavior can be seen in earlier versions too.
I tried to make the same simulation in OF 1.6 ext , but it gave the similar result.
I also tried using different constraint combinations, varying the relaxation factor and tolerance - still no effect.

The only way I've found to reduce this movement is to increase the inertia moments ( ! ) ( But I can not understand, how they are connected. )

Has anybody faced such problems?

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