CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Programming & Development

Particle transport

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   September 3, 2012, 11:34
Default Particle transport
  #1
Senior Member
 
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 9
nandiganavishal is on a distinguished road
Dear Foamers,

I would like to solve the following Newton's law of motion:

dp/dt = F(x), where p is the position of the particle, and x corresponds to the current p value. I have the distribution of F with respect to x.

In other words, in algebraic sense,

p_new = p_old + (delta_t)*F(p_old).

My query is how to calculate F(p_old) at every time step. Please let me know.

Regards
Vishal
nandiganavishal is offline   Reply With Quote

Old   September 4, 2012, 05:12
Default
  #2
Senior Member
 
Julien
Join Date: Jun 2012
Location: France
Posts: 153
Rep Power: 5
Djub is on a distinguished road
Hi vishal
your question is quite strange here, in an OpenFOAM forum.
OpenFOAM is a computing tool which works on FIELDS.
A field is a concept of "something" which can vary respect to time and 3D space. Let say function f(x,y,z,t). This "something" can be a lot of different things: pressure, velocity, temperature, density, strain, stress, phase,...
Mathematically, these "things" are described in terms of scalars, vectors, tensors.

The power of OpenFOAM relies on a formal language which is able to solve for partial derivative equations.

You can download here some documentation:
www.openfoam.org/docs/

Mathematically, your problem seems to be "simply" a problem of integration. GNU Octave should be better tool for you.

Physically, I think you are mysunderstanding: in this equation, p is not the position but the momentum, saying a product of a mass m and a velocity v. Velocity is the derivative of the position x.
Djub is offline   Reply With Quote

Old   September 4, 2012, 10:25
Default
  #3
Senior Member
 
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 9
nandiganavishal is on a distinguished road
Hi Julien,

Thanks for the reply.

Well, the equation I wanted to solve is the Langevin/Brownian dynamics with White noise, and neglecting the acceleration term in it. I wanted to couple this equation into Poisson - Nernst Planck equation which I have developed in OpenFOAM. However, before incorporating the noise and complicating it I wanted to know, if it is possible to calculate the variable f at a particular position, in the following equation.

dp/dt = A*f(x=p_old)

You are right, it is a momentum equation, however, I neglect the acceleration and consider a position dependent force. Please let me know, how to incorporate this equation in OF or in general how to solve for a Langevin equation.

Thanks

Regards
Vishal
nandiganavishal is offline   Reply With Quote

Old   September 4, 2012, 15:10
Default
  #4
Super Moderator
 
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 8,511
Blog Entries: 34
Rep Power: 86
wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Greetings to all!

@Vishal: If I understand you correctly, I think you can look into the Lagrangian capabilities that OpenFOAM has: http://www.openfoam.com/features/lagrangian.php

Another possibility would be to look into the tutorial "mesh/moveDynamicMesh/simpleHarmonicMotion", which I think it solves a weight box hanging on elastics or cables...

Best regards,
Bruno

edit: I've moved this thread to the programming section, which is where this fits the best...

Last edited by wyldckat; September 4, 2012 at 15:12. Reason: see "edit:"
wyldckat is offline   Reply With Quote

Old   September 4, 2012, 15:52
Default
  #5
Senior Member
 
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 9
nandiganavishal is on a distinguished road
Thanks Bruno. I would read it and would contact you.

Regards

Vishal
nandiganavishal is offline   Reply With Quote

Old   January 26, 2013, 23:02
Default
  #6
Senior Member
 
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 9
nandiganavishal is on a distinguished road
Hi Bruno,

I want to simulate a chain of particles, whose interaction potential is known (say a nonlinear spring potential + Lennard-Jones potential). I want to study the dynamics of this chain using Lagrangian approach. However, I would like to know if it is possible to add a noise force with a Gaussian distribution in the Newton's equation. Also, is it possible to implement Lennard-Jones type potential in OF while solving the dynamics.

Kindly let me know where I could find some tutorials for such cases.

Thanks a lot for the help

Regards

Vishal
nandiganavishal is offline   Reply With Quote

Old   January 27, 2013, 07:04
Default
  #7
Super Moderator
 
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 8,511
Blog Entries: 34
Rep Power: 86
wyldckat is just really nicewyldckat is just really nicewyldckat is just really nicewyldckat is just really nice
Hi Vishal,

I don't know of any tutorials that have all of those characteristics, but here's a list of links that can help you start to track down this kind of information:
Good luck!
Bruno
wyldckat is offline   Reply With Quote

Old   February 6, 2013, 11:16
Default
  #8
Senior Member
 
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 9
nandiganavishal is on a distinguished road
Hi Bruno,

I would like to solve the following equation

fvm::laplacian(eps_r,Phi) == -alpha * Z1*C1-alpha*Z2*C2

where eps_r is spatially varying. I wrote the code to solve this problem when eps_r(x) at time t=0 is specified. However I would like to know if it is possible to define a function in OpenFOAM where eps_r is a function of time and space. Once this is defined, I want to read this variable at every time instant and solve the above governing equation.

Please let me know.

Thanks

Regards
Vishal
nandiganavishal is offline   Reply With Quote

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Particle Transport & Termination Control with User FORTRAN Julian K. CFX 3 January 12, 2012 10:48
DPM UDF particle position using the macro P_POS(p)[i] dm2747 FLUENT 0 April 17, 2009 01:29
particle transport model Fabiana CFX 0 January 10, 2006 16:00
Particle transport model! Danney CFX 2 April 15, 2003 02:24
convergence in particle transport model Jose Tinoco CFX 0 March 3, 2003 04:10


All times are GMT -4. The time now is 19:31.