
[Sponsors] 
January 9, 2020, 04:34 
Particles Forces on Wall

#1 
New Member
Antonio Sereno
Join Date: Dec 2019
Posts: 7
Rep Power: 2 
Hi everyone !
Does anyone have experience with the solver icoUncoupledKinematicParcelFoam? I'd like to know if there's a way to compute forces exerted by particles on a wall. I'm trying to do it using the functionObject 'force' but apparently this method only works with fluid fields. Let's say I have a rotating cylinder with rigid particles in it; since the cylinder is rotating, the particles will start moving, colliding and sliding on the internal surface leading to contact forces that (considering the particlewall friction) generate a torque around the axis of rotation of the cylinder. I'm interested in this torque value in order to compute the power draw. Does anyone have any idea of how this should be achieved? thank you! 

January 9, 2020, 06:07 

#2 
Senior Member
Join Date: Aug 2014
Location: UK
Posts: 208
Rep Power: 8 
Not sure if it would be rigorous enough but one of the ways could be to postprocess particle velocity data (using paraview or similar software). One could postprocess the timedependent velocity arrays to get average acceleration and hence force vectors (using known particle mass), crossproduct of which with position vector could yield torque. Summation over all particles would then be your total particulate torque.


January 9, 2020, 06:12 
Thanks for your help!

#3 
New Member
Antonio Sereno
Join Date: Dec 2019
Posts: 7
Rep Power: 2 
I'll think about this method! At a first glance, I'm just not sure if it works considering more layers of particles since the force is basically transmitted through contact, isn't it? Thanks a lot !!


January 9, 2020, 07:14 

#4 
Senior Member
Join Date: Aug 2014
Location: UK
Posts: 208
Rep Power: 8 
Yes, firstly apologies, I callously assumed that you're not solving interparticle collisions in icoUncoupledKinematicParcelFoam i.e. all particles are in contact with cylinder wall and will contribute.
However, given interparticle collisions, I would think that under elastic collision assumption the force vectors of all particles in contact (cylinder wall or other particles) would ordinarily sum up. On a slightly different note, a long shot probably, if you could compute the integrated centre of mass position vector of the particle cloud then the very weight of it and perpendicular distance will provide you the average torque. Tracking this, as the particle cloud takes different shapes (due to particleparticle and particlewall interactions), would provide the changes over time/rotation, which can then be averaged. Does this seem useful? Needless to say that this would be an overall effect of the particle cloud and not particlelevel details; although, may suffice given your objective variable (Power) is also a derived one/ cumulative. 

January 14, 2020, 11:42 
That's a good hint

#5 
New Member
Antonio Sereno
Join Date: Dec 2019
Posts: 7
Rep Power: 2 
Your first approach is actually a good idea. I am doing some check on Liggghts, that makes it easier to verify if the assumption is correct (indeed, they provide a command that prints out the forces on the wall when it solves the particlewall contact).
Basically what I am looking at, is a system of particles on which 2 external forces are applied: gravitational force and force transmitted by the cylinder; the linear momentum can be used recalling that internal forces doesn't affect the change of linear momentum (I would say that it works even considering friction between particleparticle collision since the reciprocal force is on the same direction). Thus, by computing the velocity of every single particle, multipling each value with the respective mass of the particle and summing up all the values, what I get is the Linear Momentum of the system of particles; I've computed it for each step of my simulation and that allowed me to determine its rate of change (L1  L0)/dt that is equal to the force applied on the mesh for each timestep (there's just some small percentage of difference with the results provided by Liggghts ). I'm now working on the momentum to double check if it works, I'll write a reply as soon as I work it out. Thanks Fresty!! Now I've a second question for you! Are you comfortable with paraview? What do you think it would be the best way to achieve this procedure? Would you suggest me to print out a .csv data file and rearrange my data outside of paraview? Thank you! 

January 15, 2020, 06:54 

#6 
Senior Member
Join Date: Aug 2014
Location: UK
Posts: 208
Rep Power: 8 
Thanks, good to hear that the approach is coherent, at least to some extent.
I normally use either ParaView Python API OR a combination of ParaView and Python separately; the latter as you suggested is simply extracting required arrays and manipulating it outside, which in my opinion can be especially handy/quick when establishing a procedure. To extract Momentum from ParaView, you could conveniently export the individual particle velocity (U) array .csv from Lagrangian Arrays Dataset. However, to extract mass, not knowing the details of your 'InjectionModels', I would think out loud a potential way to acquire it. One could extract the dParticle array to compute (spherical) volumes and multiply by rho_Particle (rho0 in kinematicCloudPropeties) to calculate mass of respective particles. This array can then help form the integrand [m_particle_i * U_i], in order to integrate and get total momentum, ultimately divided by 'dt' to get force applied for each time step. Does this seem reasonable and doable? 

January 15, 2020, 08:44 

#7 
Senior Member
Join Date: Aug 2014
Location: UK
Posts: 208
Rep Power: 8 
Alternatively, and much conveniently, I just realized that icoUncoupledKinematicParcelFoam would output the Linear momentum (components and magnitude) at every time step while solving the case. So, all that I said in my previous email may fall into the category of reinventing the wheel...


January 17, 2020, 09:43 
Not Really!

#8 
New Member
Antonio Sereno
Join Date: Dec 2019
Posts: 7
Rep Power: 2 
What you say is right, I didn't notice it as well in a first moment; however, angular momentum calculation is necessary and it is not printed in the log at runtime, thus, your procedure is essential
If angular momentum and center of mass data was printed out in the log as well, it would be handy! Otherwise, I' think I'll have to run the simulation and write results every step; will my PC be able to cope with all these folder? If you don't see any reply for a while, you'll now the answer 

Tags 
forces, lagrangian, particle 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Centripetal forces on particles in incompressible fluid  sam1984_b  OpenFOAM Running, Solving & CFD  4  December 14, 2018 07:16 
forces on particles  netmaster  STARCCM+  6  March 16, 2017 05:27 
Wrong flow in ratating domain problem  Sanyo  CFX  17  August 15, 2015 07:20 
Water subcooled boiling  Attesz  CFX  7  January 5, 2013 04:32 
UDF for wall slipping  HFLUENT  Fluent UDF and Scheme Programming  0  April 27, 2011 13:03 