having limits on partice velocities

Submitted by Mac-grad on Wed, 07/04/2012 - 04:33

Hi, is there a way to impose limits on particle velocities? although my time steps are well in the range on 0.1 rayleigh number (using fix check/timestep gives no warnings), I still get overlap of two particles and as a results elimination of one particle in contact with the other. it is the same with the walls. I was wondering to impose a limit to particle velocities? can you please help me how to do so?
(particles have radius of 3e-3, density of 1.8, and young modulus of 1e6, cells are 0.015 cm, time step is 1e-8 s, all in cgs system)
Thanks,
Vajiheh

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Philippe | Wed, 07/04/2012 - 08:37

Hi,

fix nve/limit is probably what you are looking for. However, if your particles overlap too much, your time step may still be too high...

best
Philippe

Mac-grad | Thu, 07/05/2012 - 03:43

Thanks, so is one cell size a good limit? besides, my particles have a maximum diameter of 1/3 of a cell size. is that too big?
Vajiheh

moritzhoefert | Wed, 07/04/2012 - 08:55

Hi Vajiheh,

have you got a moving geometry? If so that influences the maximum allowable time step. I always assert that in one time step no part of the moving geometry moves further than 10% of the smallest particle diameter.

Best,
Moritz