
[Sponsors] 
September 14, 2013, 10:43 
OF meshless

#1 
Member
Join Date: Jun 2011
Posts: 51
Rep Power: 7 
Dear all,
Considering how time consuming is the mesh process in any of our simulations, is there anybody aware of the implementation of "meshless methodoly" in OF? I am expecting with this approach reduce significantly the hours spent in mesh debug and improve the solution performance by reducing the nonconvergence solutions. There are any validation tests together with the code ready to run? It would be quite interesting try out some performance tests of OF with this mesh methodology. Regards, 

September 15, 2013, 06:26 

#2 
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 9,651
Blog Entries: 39
Rep Power: 99 
Greetings cfdivan,
It took me a while to remember about this... but I remembered just now. There is a nonofficial implementation (aka it's not in the official and public OpenFOAM version) of the "Immersed Boundary Method" developed by Wikki: http://wikki.gridcore.se/application...BoundaryMethod AFAIK, always keep in mind that there is no such thing as a silver bullet in CFD. One meshing strategy might be excellent for one thing, but terrible for another. And the "Immersed Boundary Method" and/or meshless are always implied meshing strategies, namely that even though you do not have to bother to generate a mesh, a mesh does still exist, since the geometry is still analysed in a discrete way, not in a continuous way! Best regards, Bruno
__________________


September 16, 2013, 07:24 

#3 
Senior Member

Hello,
just my 2 cent you can dig into Immersed Boundary Meth. (IBM) =>Z. Tuković (source code 4 OFextend) by studing OFworkshop material (OFW7_2012_Darmstadt) http://sourceforge.net/projects/open...darySlides.tgz http://sourceforge.net/projects/open...lmMaterial.tgz I remember two guys that implemented Smoothed Particle Hydrodynamics (SPH)method with OpenFOAM one presentation at OFW6 @ Penn State http://sourceforge.net/projects/open...mar_slides.pdf the second guy Basti Werdelmann was giving a presentation at OFStammtisch @ Karlsruhe http://www.rz.unikarlsruhe.de/~hj16...Stammtisch.pdf. You should contact Hendrik Rusche (Wikki) or Ivana BunticOgor (on the OFStammtisch List) if you want the Stammtischpresentation they might have it But I am not aware of any SPHcode for OF out in the wilderness to the public. But these examples show it can be done with enough OFexpertise, s.th I do not have :( 

September 17, 2013, 17:28 

#4 
Member
Join Date: Jun 2011
Posts: 51
Rep Power: 7 
Hi all,
Thank you very much for both posts...they are quite usefull. Bruno, Yes, even for "meshless" approach the domain/flow is solved in discrete way but, I meant the immersed BL approach . It is tipically quite easy do a pretty decent surface meshes. Even with the decent surface mesh, problems in "BL zone" (the prism layer extrusion process) are quite often. Those areas are usually the origin for some solution divergence. I knew that wikki already tried that approach. I guess that karalit also implemented that approach. I was just wondering if this approach was already implemented by someone in the forum who can share the code/expereciences. "AFAIK, always keep in mind that there is no such thing as a silver bullet in CFD. One meshing strategy might be excellent for one thing, but terrible for another". Do you know what kind of applications that immersed BL approach could be terrible? Elvis, Thank you very much for all the links. I'll try to dig in a bit more and share the findings/ideas here. Regards, 

September 17, 2013, 18:07 

#5  
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 9,651
Blog Entries: 39
Rep Power: 99 
Hi cfdivan,
Quote:
Which is why I ended writing about what has been found several times in CFD for many other situations: no matter how many new methods we find for simulating or meshing, they always have some flaw that leads us to go back to the good old standard procedures/methods/models. Best regards, Bruno
__________________


September 30, 2013, 03:13 

#6 
Senior Member

Hi,
I saw http://www.wire.tubs.de/workshops/nofun13/d_nofun.html =>"LBM mesh generation in OpenFoam" a presentation by Andrea Pasquali (TU Braunschweig) so some kind of Lattice Bolzmann Method might be possible to be handled with as well 

October 2, 2013, 17:25 

#7 
Member
Join Date: Jun 2011
Posts: 51
Rep Power: 7 
Hi Elvis,
Thk u very much for your link. "LBM mesh generation", means a meshless process? What is the main difference between "LBM mesh generation" and "Immersed Boundary Method"? I checked on the website but I did not find any additional information about the topic. Do you know where I can find more documentation about the topic LBM mesh generation in OpenFoam and/or comparision with classic methods or Immersed Boundary Method? Many thank 

October 5, 2013, 01:51 

#8 
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 9,651
Blog Entries: 39
Rep Power: 99 
Greetings to all!
@cfdivan: Nope. LBM is this: http://en.wikipedia.org/wiki/Lattice_Boltzmann_methods In a nutshell, based on what I studied a few years ago:
Best regards, Bruno
__________________


October 5, 2013, 05:43 

#9 
Senior Member

Hi,
basicly I wanted to say that OF is a Computational Continuum Mechanics (CCM) toolkit which can be used for different methods like FVM and FEM which are already implemented. But other people used it for different methods like SPH 

October 5, 2013, 07:12 

#10 
Member
Join Date: Jun 2011
Posts: 51
Rep Power: 7 
Hi wyldckat,
Thk u very much for your link. Pretty usefull for a brief review. Regarding FVM  I already tried to investigate this point some time ago and I found that they likely use FD...is it true? I never was able to confirm that With FD we have several advantages when we are working with structured meshes....it is very simple and effective and quite easy to obtain higherorder schemes (HighMach numbers applications for example). "The data is passed between the cells as if using a particle based mechanism"  This really sounds a restriction for high machnumber flows where you need higherorder schemes . Considering that you have different sizes of the cells in your domain and the equations are solved in "Lattice world", in one time step you can have one particle go to the neighbor cell while in the other zone of your domain the particle can travel 2 or more cells. Based on this assumption, we will not be able to track the particle distribution. They need to work around with field update, is it right? The paralelization is in fact an significant advantage of this code. The algorithm is quite simple and only the stream step needs exchange of information with neighbors which does not happen in FVM. It looks that the efficieny of this code comes from the implementation of simple algorithms where non higherorder schemes are needed. Though, when it comes to highmach numbers and coupling of density to temperature variations, higherorder schemes are nedded and the simplycity/efficiency of the code decreases. There is also a point regarding the full unsteadiness of this approach. When compared with DESSA of NS for example, it might be more fast/easy to obtain a unsteady converged solution. Nevertheless there are an wide range of engineering applications where the RANS/steady state provide us enough accuracy for very low prices in terms of CPh which migh not be possible with LBM. It looks like LBM fits better for applications where the unsteadiness is the king. In any case, what looks really interesting for me is the "meshless concept" that is very painfull process on my simulations that I am expecting that we do not have neither in IBM nor LBM. From time to time I spend a lot of hours to check why there is no convergence on simulation, ending up play around with disc schemes and mesh. Regards, 

October 5, 2013, 07:22 

#11 
Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 9,651
Blog Entries: 39
Rep Power: 99 
Hi cfdivan,
As far as I can remember, LBM works in a similar way to the Courant number restriction that we're taught in the very first tutorial OpenFOAM User Guide: http://www.openfoam.org/docs/user/cavity.php In essence, the size of each cube must respect the flow speed limit, otherwise it simply cannot present properly your problem. In addition, the cube sizes also had to take into account the properties of the fluid, mainly the viscosity. In other words, LBM is almost a "Similitude" modelling strategy: http://en.wikipedia.org/wiki/Similitude_%28model%29 Therefore, with any luck, for supersonic flow, you only need several billion LBM cells, working on a cluster with 8 GPUs per node... As for "FD": which "FD" are you talking about? Best regards, Bruno
__________________


October 9, 2013, 20:10 

#12 
Member
Join Date: Jun 2011
Posts: 51
Rep Power: 7 
Hi Bruno,
Sorry for the delay on reply FD, I meant Finite diffrences. I also agree that the LBM might works in similiar way of Courant number. To me it sounds that the scalling of the flow properties (like velocity for example) to the "Lattice world" take in consideration the cell size and the speed of the sound, is it right? The "Courant number" in LBM is ajusted at each cell in order to keep the tracking of the particles at each timestep. Regards, 

October 9, 2013, 21:47 

#13 
Senior Member

Hi cfdivan/Bruno,
Great discussion. The openFoam solvers (simpleFoam, etc) are based on FVM discretisation of the NS equations. Wouldn't it be great to have access to various methods (FVM, IBM, LBM, SPH) using a unique and compatible set of input data rather than juggling between solvers, preprocessors, etc.... This would make it easier to use the right tool for the right job.
__________________
 Julien de Charentenay 

November 9, 2014, 07:49 
"Basti Werdelmann" presentation at OFStammtisch

#14  
Member
Alireza Atrian
Join Date: May 2014
Posts: 39
Rep Power: 4 
Quote:
could you please give me a more accurate address of "Basti Werdelmann"? I'm going to know how to implement SPH in openFoam so I googled the name for hours but noo cunclusion! is the presentation on 6th openfoam workshop (1316 June 2011)? or ...? the link you have inserted does not work any more! do you know any other presentation, work, coding, tutorials on the issue? Best Regards 

November 10, 2014, 03:33 

#15 
Senior Member

Hi Alireza,
the implementation of the SPH presented at Karlsruhe OFStammtisch is a different one to that presented at Penn State OFworkshop, but both are closed source to my knowledge. You should find his address in https://wiki.manchester.ac.uk/spheri..._Abstracts.pdf Hope you are not a headhunter ;) 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Xflow Meshless aproach ??  leo_NM  Main CFD Forum  1  June 23, 2013 19:38 
meshless  Hamou SADAT  Main CFD Forum  4  January 3, 2008 17:48 
Looking for two Papers on Meshless  Gerrit Groot  Main CFD Forum  4  September 20, 2007 09:21 
Meshless FD method over FEM?  Shyam  Main CFD Forum  2  May 5, 2004 02:35 
Meshless CFD  Des Aubery  Main CFD Forum  1  August 17, 2003 08:42 