[FloB]

Hi,

These last days, I studied floating object modeling on openFoam particularly thanks to floating object tutorial of interDyMFoam (https://github.com/OpenFOAM/OpenFOAM...floatingObject).

In this tutorial, the solid is constrained by a fixed line and a fixed axis, which prevent vertical motions.
I suppressed these constraints and chose an initial submerged volume and a mass so that buoyancy force is equal to weight force. With these parameters, normally, the solid should stay at the equilibrium (no velocity is applied at the inlet : water is still).

However, I observed the solid directly sinks and reaches huge velocities (vertical but also... horizontal !!) after 0.1 s. Then, logically, it crashes.


I deduced buoyancy force is not taken into account by the model.

Am I right ? If yes, how to use it ? I don't want a constant force pointing upward : I would like a real buoyancy force which change every time in function of the submerged volume at time t.


Thanks in advance,

Florian

[FloB]

In fact, I think buoyancy is taken into account because pressure is increasing with depth, which create automatically an upward force applied on the floater.

My cases crash because of a bug that I do not know how to solve.
When I change the geometry of my floater (particularly when it is much more long than large) or when I suppress the original constraints (fixed line and fixed axis) applied in the tutorial, pressure explodes which provokes huge velocities and so a crash after a certain time.

When I visualize the results in paraFoam (the first 0.1 s, with a time step of 1e-3s), I observe an oscillation of pressure in time and space with positive and negative values which increase in absolute value until it explodes... You'll find attached some screenshots from paraFoam.


I do not know where this bug is coming from. Changing the schemes seem to help but it is not sufficient, I've tried many other things without success..

If someone has already got this kind of problem, I would appreciate some help, thanks.

[zweihuehner]

I am not sure if it is related to the problem. But I also had similar results with the floating Object tutorial after I changed the position of the object. I however did not change the density.


The pressure exploded after a while and simulation blew up.

I realized the center of mass was not set correctly in dynamicMeshDict and it worked afterwards.

[Ranj]

Hi Florian, did you manage to solve this problem??