
[Sponsors] 
January 10, 2008, 06:16 
Hi OFFolks,
working on a s

#1 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
Hi OFFolks,
working on a simulation of a sinking (rigid) particle in a water cylinder with a modified icoDyMFoam(OF1.4.1) I run in trouble with the mesh quality. I tried several diffusivity algorithms: directional: bad results after a relative short time quadratic: good results for mesh quality, even if the particle goes through half of the cylinder exponential: bad and confusing mesh moving after a short time It was more or less trial and error because I dont really know what the different diffusivity algorithms do and stand for. And I dont know what the values after the keyword stand for, like: exponential 2000 Does anyone know and has experience with the different diffusivity options and the influence of the values???Is there a documentation of this? For solvers I use: dynamicFvMesh dynamicMotionSolverFvMesh motionSolverLibs libfvMotionSolvers.so solver velocityComponentLaplacian I know from several "moving mesh" threads from the forum that there exits other solvers in OF, but does anyone know in which case it is better to use which solver? I know, alot of question to a often discussed topic. But I really appreciate any help and hints! Thanks & Kindest Regards, Flo 

January 10, 2008, 17:02 
Hi Florian,
Generally quad

#2 
Senior Member
Frank Bos
Join Date: Mar 2009
Location: The Netherlands
Posts: 340
Rep Power: 10 
Hi Florian,
Generally quadratic inverseDistance diffusivity gives pretty good (if not the best) results for plunging bodies. For that kind of simulations I use the fvMotionSolver, velocityLaplacian. When you are encountering large rotations, the laplacian is not the right equation to use, a good alternative would be the displacementSBRStress motion solver. For really large rotation, subsets of meshes or user defined diffusivity could provide solutions......This is what I am dealing with now :S The following paper describes some theory about the laplacian motion solver: http://powerlab.fsb.hr/ped/kturbo/Op...Manuscript.pdf Regards, Frank
__________________
Frank Bos 

January 10, 2008, 17:15 
How large is you body translat

#3 
Senior Member
Frank Bos
Join Date: Mar 2009
Location: The Netherlands
Posts: 340
Rep Power: 10 
How large is you body translation / rotation ???
Frank
__________________
Frank Bos 

January 10, 2008, 17:41 
Hi Frank,
by now I have no

#4 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
Hi Frank,
by now I have no (or very less) rotation of my particle, but I think large deformation. The paper from Jasak and Tukovic is definitly what I was searching for  its a good discription of the background of the solver and the diffusivity terms I will send you a two pictures  one of the deformed mesh and one of the undeformed mesh  to your eMail adress ok?! Regards, Florian 

January 10, 2008, 18:11 
ok.. I try to post them here

#5 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
ok.. I try to post them here
I use quadratic diffusivity in this case, and at this time I only have some nonorthogonal faces Regards, Florian 

January 10, 2008, 18:52 
In fact the screeshot of the d

#6 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
In fact the screeshot of the deformed mesh is not really representative and only gives an idea of the mesh deformation... My 3D Mesh only consists of hexa cells, but making a cut in paraView the visualization of the cut cells is very strange  something like RTrias...
But this is another, not soo important issue ;) Regards, Florian 

January 11, 2008, 04:04 
If the sphere is moving down a

#7 
Senior Member
Frank Bos
Join Date: Mar 2009
Location: The Netherlands
Posts: 340
Rep Power: 10 
If the sphere is moving down all the way, you really need some cell layering.
Visualization of moving 3D meshes is really a pain, I use ensight to visualize complete cells instead of a cutting plane..... Frank
__________________
Frank Bos 

January 11, 2008, 05:33 
Frank,
I agree with you reg

#8 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
Frank,
I agree with you regarding the use of additional/removal layer because my cell layers faces are parallel. But what happens when I have a unstructured Tet mesh? The structued Hex Mesh was only possible because I have only one sphere and buliding the more or less good hex mesh around the cylinder was not the easiest thing. For the add/rem cell layer I think I need something like: dynamicFvMeshLibs ("libtopoChangerFvMesh.so"); dynamicFvMesh topoChangerFvMesh; solver velocityLaplacian ; How can I define the max and min layer thickness in the dynamicMeshDict? Regards, Florian 

January 11, 2008, 05:44 
I haven't use cell layering be

#9 
Senior Member
Frank Bos
Join Date: Mar 2009
Location: The Netherlands
Posts: 340
Rep Power: 10 
I haven't use cell layering before, so I don't know ....Try to look inside the code to find out how you define the dictionary....it's quit easy.
Frank
__________________
Frank Bos 

January 11, 2008, 05:54 
I found a topo Change movingCo

#10 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
I found a topo Change movingCone example from the OF 1.4.1 dev source, I will check on it what is necassary for add/rem cell layers
Regards, Florian 

January 11, 2008, 07:10 
Florian, for the sphere are yo

#11 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
Florian, for the sphere are you also solving for the conservation of angular momentum?


January 11, 2008, 21:35 
Hi pUI,
when I simulate the

#12 
Senior Member
Florian Krause
Join Date: Mar 2009
Location: Munich
Posts: 103
Rep Power: 9 
Hi pUI,
when I simulate the sinking process, I start with a (0 0 0) velcoity vector for the sphere. For the next iteration I calculate the new velocity for n+1 iteration with the resulting gravity force, the pressure/viscous force and the velocity from iteration n. Further, I calculate the moments on the sphere BUT I dont use the results for the moments to update the the velocity and dont take into account the possible influence of the moments on the rotation of the sphere. So, I dont think that I solve the conservation of angular momentum, but its a good hint for the future... ;) Is this what you mean? Regards, Florian 

January 11, 2008, 22:33 
yup, thanks

#13 
Senior Member
Srinath Madhavan (a.k.a pUl)
Join Date: Mar 2009
Location: Edmonton, AB, Canada
Posts: 703
Rep Power: 13 
yup, thanks


Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Turbulent compressible solver rhoTurbFoam with dynamic moving mesh  eno  OpenFOAM Running, Solving & CFD  4  December 12, 2011 04:38 
value for dynamic diffusivity  soup  CFX  0  December 29, 2008 15:14 
Bug in turbulent dynamic Mesh Solver  thomas  OpenFOAM Running, Solving & CFD  0  October 29, 2008 04:48 
Problems using dynamic mesh and 6dof solver  Brett  FLUENT  0  March 3, 2006 18:45 
coupled solver and dynamic mesh  steph  FLUENT  0  June 11, 2004 08:28 