CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

small question about the functionalities of topological changes in OpenFoam

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 28, 2013, 06:42
Default small question about the functionalities of topological changes in OpenFoam
  #1
ngj
Senior Member
 
Niels Gjoel Jacobsen
Join Date: Mar 2009
Location: Deltares, Delft, The Netherlands
Posts: 1,619
Rep Power: 25
ngj will become famous soon enoughngj will become famous soon enough
Dear All,

I have a small question about the functionalities of topological changes in OpenFoam. These questions are more out of curiosity than based on actually problems, since my underlying source code would have to undergo a substantial modification to allow for topological changes, hence before undertaking this work, I would like to know a bit about the options.

My question can be nicely based on this small animation of scour under an elevated wall in front of a partial standing, free surface wave:

http://www.student.dtu.dk/~ngja/elevatedWallScour.mpg

The attention should be given to the poor mesh quality just below the vertical wall. In this case it could easily be resolved by changing the diffusivity of the mesh motion, though a great number of test cases would require some sort of topological change/re-meshing, e.g. a pipeline place with a minute gap to the bed of e.g. 0.2 mm from the bed and an expected final scour depth of say 100 mm.

My question is as follows:

Are there any methods available, which allows for the mesh lines attached to the vertical wall to slide off and fill the gap under the wall and creating new cells along the way, thus keeping a certain mesh quality? The vertical wall would potentially be replaced by a cylinder, where the mesh lines flow from above the cylinder to below in a constant attaching-detaching of lines to the cylinder surface.

In case of a positive answer, would this method also allow for the reverse operation, i.e. pushing the mesh lines onto the patch again in case the hole starts infilling for some reason.

Thank you for your attention

Niels

P.S. For those of you who are not familiar with the term, then scour is the response of a sediment bed due to the presence of a structure. Therefore, the modelling consists of a sediment transport simulation and the evaluation of the change in bed level based on the divergence of the transport field.
ngj is offline   Reply With Quote

Old   February 28, 2013, 09:43
Default
  #2
Senior Member
 
Sandeep Menon
Join Date: Mar 2009
Location: Amherst, MA
Posts: 386
Rep Power: 15
deepsterblue will become famous soon enough
Niels,

Impressive animation! I can see how there's a potential for topological changes in your simulation.

In your case, if you prefer a hex mesh, I suppose layering would be an ideal candidate. Since you have a boundary layer next to the bottom surface, you may have to split cells based on some ratio using distance to the wall (rather than a simple 0.5) if you're looking to maintain that during the simulation.

If you're looking for a tet / tri-prism based solution, you can use dynamicTopoFvMesh (which includes some limited layering support too). The only concern to me is that mapping discontinuous volume-fraction fields is sometimes not so obvious. I'm also usually wary of VOF simulations on anything other than a hex mesh, but I may be wrong.
__________________
Sandeep Menon
University of Massachusetts Amherst
https://github.com/smenon
deepsterblue is offline   Reply With Quote

Old   February 28, 2013, 11:02
Default
  #3
ngj
Senior Member
 
Niels Gjoel Jacobsen
Join Date: Mar 2009
Location: Deltares, Delft, The Netherlands
Posts: 1,619
Rep Power: 25
ngj will become famous soon enoughngj will become famous soon enough
Hi Sandeep,

Thanks for your thoughts on the possibilities. Just to recapitulate for my own sake:

dynamicTopoFvMesh only works with tetrahedra or prism if I understand you correctly, and there I should rather use it for remeshing/refinements than actual layering techniques. Correct?

I concur with respect to VOF-methods. I have hardly ever seen any methods, which gave good results on anything but hex-cells, and in my experience MULES is definitely only suited for hex-cells. I see your point on the mapping of the void fraction and in particular how to do it such that mass and momentum is preserved.

With respect to the layering, I suppose that you are referring to those methods included in the engineTopoChangerMesh? This is a good place to gain knowledge, at least to gain the needed inspiration into developing my own tailored method.

=== Conclusion ===
It is as I suspected: Many, many weeks of development ahead, if the code should be compatible with these topics - especially considering that I also have to synchronise everything between three different meshes: region0 (fvMesh), a subsetMesh of region0 (fvMesh), where the location of the interface should be fixed irrespectively of topological changes and a faMesh.

Thanks for your time,

Niels
ngj 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
Memory protection in OpenFOAM / combinig with FORTRAN botp OpenFOAM Programming & Development 1 February 6, 2013 05:26
Summer School on Numerical Modelling and OpenFOAM hjasak OpenFOAM 5 October 12, 2008 13:14
Question on specify gcc compiler for OpenFOAM 15 peterlai OpenFOAM Installation 2 October 2, 2008 07:20
small question faiz rauf FLUENT 3 September 9, 2004 11:22
small question regarding mesh export faiz rauf FLUENT 7 August 9, 2004 12:14


All times are GMT -4. The time now is 20:47.