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Comsol Particle tracing + Brownian Force taking too long.

Posted Apr 2, 2015, 9:09 a.m. EDT Charged Particle Tracing, Computational Fluid Dynamics (CFD), Particle Tracing for Fluid Flow Version 5.0 2 Replies

George Pamfilis
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I wish to add brownian motion to a single particle in a simple geometry (50X25mm).

What works so far is:

1. solved Laminar flow (STATIC).
2. Solved Particle tracing (time dependent with drag force) everything ok so far.
the previus two worked and were solved.

the third step for me is to add a brownian force and re-solve step 2. it takes super long!!!! (i dont let it complete due to overheating of the laptop).

is this normal?

ill be happy to send the model to someone to check it. (maybe i screwd up some parameter)


2 Replies Last Post Nov 14, 2016, 2:32 p.m. EST
Daniel Smith COMSOL Employee

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Posted: 10 years ago Apr 2, 2015, 2:05 p.m. EDT
Hi John, you can relax the solver tolerances when including the Brownian force, which will let the model solve faster. This means changing the relative tolerance to say, 1e-3 in the Time Dependent study settings. You could also change the absolute tolerance which is present in the Study 1>Solver Configurations>Solution 1>Time-Dependent Solver 1 node. There is a section called Absolute Tolerance, which you could also change to 1e-3.

Dan
Hi John, you can relax the solver tolerances when including the Brownian force, which will let the model solve faster. This means changing the relative tolerance to say, 1e-3 in the Time Dependent study settings. You could also change the absolute tolerance which is present in the Study 1>Solver Configurations>Solution 1>Time-Dependent Solver 1 node. There is a section called Absolute Tolerance, which you could also change to 1e-3. Dan
Bill
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Posted: 8 years ago Nov 14, 2016, 2:32 p.m. EST

Hi John, you can relax the solver tolerances when including the Brownian force, which will let the model solve faster. This means changing the relative tolerance to say, 1e-3 in the Time Dependent study settings. You could also change the absolute tolerance which is present in the Study 1>Solver Configurations>Solution 1>Time-Dependent Solver 1 node. There is a section called Absolute Tolerance, which you could also change to 1e-3.

Dan


Hi Dan,
I have met the same problem. However, if I change the tolerance according to your suggestions, it seems that the particles will not be injected in to the fluid domain and will stay at the initial locations.
Thank you in advance for any possible help.
Regards,
Bill
[QUOTE] Hi John, you can relax the solver tolerances when including the Brownian force, which will let the model solve faster. This means changing the relative tolerance to say, 1e-3 in the Time Dependent study settings. You could also change the absolute tolerance which is present in the Study 1>Solver Configurations>Solution 1>Time-Dependent Solver 1 node. There is a section called Absolute Tolerance, which you could also change to 1e-3. Dan [/QUOTE] Hi Dan, I have met the same problem. However, if I change the tolerance according to your suggestions, it seems that the particles will not be injected in to the fluid domain and will stay at the initial locations. Thank you in advance for any possible help. Regards, Bill

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