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From: | Martin Kaiser |
Subject: | Re: system time step appropriate values |
Date: | Tue, 29 Jun 2021 11:21:05 +0200 |
Hey Benyamin, in my humble experience, it is extremely difficult to set-up the system exactly how you described it. From what I understand, you are trying to simulate a nanometer sized object in some sort of channel that is in the centimetre range that has a flow inside. Therefore, the characteristic lengths (size of your particle and size of the channel) are separated by several orders of magnitude, which is also true for the time scales of those systems. This poses a huge issue on its own and usually requires special techniques to achieve, depending also on the effects you want to capture in your system. The fact that you want to simulate several seconds, paired with the fact that typical time-scales in simulation on that particle scale are, as you already found out, picoseconds or even smaller, means that you would need insanely long simulations. Apart from the time-scale, if you want to stick to the correct ratio between your particle and channel size, you will get technically unmanageable system sizes. In my opinion it would be worth to reconsider what the effects are that you want to measure and to rescale the system to a more manageable size. Regarding the simulation parameters, I remember a sentence about the parameters in the tutorials saying something along the lines of “we use those parameters for no other reason than them being stable”. I have not looked at the tutorials in a while, so I don’t know if this is still true, but keep that in mind. It is always advised to triple check and calculate your parameters, which can be troublesome when using LB. The guys from reference [1] did a great job with LB and it helped us a lot when setting up our own systems. There is only a limited range of parameters for with LB is stable, so you not being able to increase your tilmestep beyond your given value does not surprise me. I can also recommend book [2], especially sections about stability, to get an overview over the possibilities within LB. I hope that helps. Best, Martin [1] Kreissl, Patrick, Christian Holm, and Rudolf Weeber. "Frequency-dependent magnetic susceptibility of magnetic nanoparticles in a polymer solution: a simulation study." arXiv preprint arXiv:2010.00299 (2020). https://arxiv.org/abs/2010.00299 [2] Krüger, Timm, et al. "The lattice Boltzmann method." Springer International Publishing 10.978-3 (2017): 4-15.
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Martin Kaiser, M.Sc. Computational and Soft Matter Physics Dipolar Soft Matter Group Faculty of Physics, University of Vienna Kolingasse 14-16, 1090, Vienna, Austria
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