
[Sponsors] 
September 3, 2012, 11:34 
Particle transport

#1 
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
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 

September 4, 2012, 05:12 

#2 
Senior Member
Julien
Join Date: Jun 2012
Location: France
Posts: 152
Rep Power: 7 
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. 

September 4, 2012, 10:25 

#3 
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
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 

September 4, 2012, 15:10 

#4 
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,021
Blog Entries: 39
Rep Power: 109 
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:" 

September 4, 2012, 15:52 

#5 
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
Thanks Bruno. I would read it and would contact you.
Regards Vishal 

January 26, 2013, 23:02 

#6 
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
Hi Bruno,
I want to simulate a chain of particles, whose interaction potential is known (say a nonlinear spring potential + LennardJones 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 LennardJones 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 

January 27, 2013, 07:04 

#7 
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,021
Blog Entries: 39
Rep Power: 109 
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:
Bruno
__________________


February 6, 2013, 11:16 

#8 
Senior Member
Vishal Nandigana
Join Date: Mar 2009
Location: Champaign, Illinois, U.S.A
Posts: 208
Rep Power: 11 
Hi Bruno,
I would like to solve the following equation fvm::laplacian(eps_r,Phi) == alpha * Z1*C1alpha*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 

Thread Tools  
Display Modes  


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 