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June 14, 2012, 17:03 
Coupled Brownian Dynamics with OpenFoam

#1 
New Member
A Sharma
Join Date: Mar 2012
Location: Germany
Posts: 14
Rep Power: 7 
Hello OpenFoam Users,
I am working on solutions to Poisson Nernst Planck Equation (Diffusion Equation with drift of charged particles due to external electric field) to study dynamics of charged particles. The geometry consists of microfluidic channels over microelectrode assembly. I want to take into account fluid motion by coupling Navier Stokes Equation with PNP equation, as an example case : to see the dynamics of charged particles inside the droplets which are created from a TJunction. This means fluid flow should be included and particles are constraint by dynamics of droplets. Is it possible to resolve the droplet shape at each time step and to couple velocity profile from OpenFoam solutions to dynamics of particles dynamically, assuming there is no significant change in droplet behavior due to external electric fields ? Regards, A. Sharma 

September 3, 2012, 11:43 

#2 
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Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
Hi Sharma,
I am working to simulate similar dynamics !! Were you able to incorporate the Brownian dynamics in the PNP solver. Please let me know. Regards Vishal 

August 17, 2013, 17:27 
Hi nandiganavishal,

#3 
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J.B.
Join Date: Aug 2010
Posts: 2
Rep Power: 0 
I'm simulating the nanoparticle size motion and one of the important mechanism in this size is Brownian motion respect to the particles high diffusion, could you help me please, how can I add it in OpenFoam?
thanks best regards 

August 17, 2013, 21:28 

#4  
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
Quote:
Hi, I do not fully understand the objective of your problem. Do you want to couple the Brownian dynamics of the particle with the continuum equation or do you want to incorporate only Brownian dynamics? Vishal 

August 18, 2013, 03:28 
Hi

#5  
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J.B.
Join Date: Aug 2010
Posts: 2
Rep Power: 0 
Quote:
I am using one way interaction (fluidparticle) with solidParticleFoam solver based on Lagrangian approach. I incorporated the gravity and Stoks drag forces in particle equation of motion but I can't add the Brownian force in equation. I've seen code file for brownian motion in directory : /opt/openfoam210/src/lagrangian/intermediate/submodels/Thermodynamic/ParticleForces /BrownianMotion but I don't know how can I link this library to particle equation and what additional parameters and changing must be added in the before solidParticleFoam solver I'll be very thankful Javadu 

June 1, 2016, 14:37 
Brownian force

#6  
Member
Evangelos
Join Date: Sep 2011
Posts: 85
Rep Power: 8 
do you solve the problem ?
can you help me ? I am interested to add brownian force to icouncoupledkinematicparcelFoam Quote:


June 2, 2016, 00:34 

#7 
Member
Bijan Darbari
Join Date: Nov 2015
Posts: 45
Rep Power: 4 
Dear Danath
Brownian force only works when the solver, solve heat transfer in continuous phase, because for calculating this force, temperature of continuous phase must be known. I think your solver didn't solve heat transfer equation. and so you can't add Brownian force to this solver. you must use "reactingparcelfoam" or same solver that have brownian force. 

June 2, 2016, 05:33 

#8  
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Evangelos
Join Date: Sep 2011
Posts: 85
Rep Power: 8 
Hello Bijan and thanks for the reply .
Tc = absolute temperature of the fluid If i set a constant temperature of the fluid ( 20 C ) Is it right or wrong ? I set a new force under the name BrownForce and i compile the lagrangian. Now my solver can see the brownian force Quote:


June 2, 2016, 07:05 

#9 
Member
Bijan Darbari
Join Date: Nov 2015
Posts: 45
Rep Power: 4 
Dear Danath
I thing it's true. the temperature of fluid can be uniform. read this pdf: http://web2.clarkson.edu/projects/cr...2_Brownian.pdf at the end of that file, the author simulate brownian motion of particles in uniform temperature and velocity filed of fluid. If pissible please send me your new brownian force files!!(.C & .H ) or at least tell me some information about it. because when I use openfoam standard brownian force, my particles extremely accelerate ( their speed become 10000 times of fluid speed ) and I think some thing is wrong in openfoam standard brownian force. ( my prticles diameter is 60 nanometer). Did you got a reasonable reasult ( speed and positions of particles ) when use your new brownian force?? Last edited by bijan darbari; June 2, 2016 at 13:27. 

June 3, 2016, 10:36 

#10  
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Evangelos
Join Date: Sep 2011
Posts: 85
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Something is going wrong !!!
the force is multiplied with the mass but the velocity is very high !!! Quote:


June 3, 2016, 15:10 

#11 
Member
Bijan Darbari
Join Date: Nov 2015
Posts: 45
Rep Power: 4 
Dear Danath
So my guess is true and openfoam standard brownian force does not work well. because brownian force is a very complex and sensible force and need very attention when the programmer write it in the software or code. (also fluent has a wrong brownian force.) I need to correct this force for my thesis simulation. So I will working on it and I hope solve this problem next two month. If you solve this problem in the future, please inform in this forum. 

June 3, 2016, 19:05 

#12  
Member
Evangelos
Join Date: Sep 2011
Posts: 85
Rep Power: 8 
I think the problem is located in the unit variance independent Gaussian random numbers
Quote:


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