[GAMBIT] Mesh refinement for melting during welding

vekh · February 17, 2015, 15:30

Hello, I have problem with mesh creation for laser welding simulation. I'm working with 2D rectangular samples and I want to create model with VOF for conduction mode welding (so I need to exploit volumetric (w/m3) heat source). I wrote suitable UDF which taking into account both laser power and laser penetration depth (with respect to extinction coefficient and refractive index).
The obstacle is a shallow depth of laser penetration. It is the order of ~900 nm - that is approximate depth at which laser power extinguish. So I need to create mesh at certain area with cell size 100 nm size. Considering that whole sample have 4x4 mm output mesh will be enormous big. I tried to use grading, manualy dividing etc. but there is always high aspect ratio during mesh chceck in Fluent or mesh is "too big" to grab the heat source...
Do you know how to create 2D mesh with certain area mesh refinement which will be the "base" for mesh generation for outer regions?

-mAx- · February 18, 2015, 01:19

you may use size function.
Can you post a picture of your geometry?

vekh · February 18, 2015, 09:46

This is my best - at the moment - mesh with my geometry. It's rectangle with symmetry at X-axis. Red dotted line is border between air and steel. 1 is air 2 is steel (steel is patched after initialization). Blue arrow is laser spot center and gravitational acceleration works in X+ direction.
At the moment 2D model with 2x3 mm dimmension is meshed with ~125k elements. I don't have huge experience with such kind of simulations but It's seems to that there is too many element like for that element size... Beside that I have weird pressure jumps from ~3e-5 to 6e8 and problem with courant number - I think that it's mesh fault.
-mAx- I do not want to being pushy but can You give me some advice where to find similar example or something of which I could learn size functions? Thanks in advance.

-mAx- · February 18, 2015, 10:19

If your problem is mesh ratio, then I would refine in y-direction, untill aspect ratio is ok
125k elements isn't a big mesh.
You may have problem, with mesh over several millions of elements.
Let me know

vekh · February 18, 2015, 19:05

OK. I'm training with size functions... It's weird a bit but maybe will help ;-)

Quote:

125k elements isn't a big mesh.
You may have problem, with mesh over several millions of elements.

Agree but it's 2x3 mm testing case for VoF preparation. Target is to create 3D model with moving heat source. Approx. model size will be ~50x50x3 mm like on the picture (sorry I'm bad at paint

)

The red area is the "refined" mesh for heat source path... That could be kinda huge mesh. I wonder if there will be a need to use moving/dynamic mesh to limit cells amount or other trick...

-mAx- · February 19, 2015, 01:00

in worst case, you will work with tri elements and size function.
If your final work will handle moving mesh, you should think about a strategy to treat moving domain (remeshing, smoothing or layering), because you won't prepare a geometry with moving mesh (remeshing) like a geometry with moving mesh (layering)
Can you provide your dbs file?

February 17, 2015, 15:30	Mesh refinement for melting during welding	#1
vekh Member Rafal Join Date: Aug 2013 Location: CK Posts: 36 Rep Power: 12	Hello, I have problem with mesh creation for laser welding simulation. I'm working with 2D rectangular samples and I want to create model with VOF for conduction mode welding (so I need to exploit volumetric (w/m3) heat source). I wrote suitable UDF which taking into account both laser power and laser penetration depth (with respect to extinction coefficient and refractive index). The obstacle is a shallow depth of laser penetration. It is the order of ~900 nm - that is approximate depth at which laser power extinguish. So I need to create mesh at certain area with cell size 100 nm size. Considering that whole sample have 4x4 mm output mesh will be enormous big. I tried to use grading, manualy dividing etc. but there is always high aspect ratio during mesh chceck in Fluent or mesh is "too big" to grab the heat source... Do you know how to create 2D mesh with certain area mesh refinement which will be the "base" for mesh generation for outer regions?

February 18, 2015, 01:19		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	you may use size function. Can you post a picture of your geometry? __________________ In memory of my friend Hervé: CFD engineer & freerider

February 18, 2015, 10:19		#4
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	If your problem is mesh ratio, then I would refine in y-direction, untill aspect ratio is ok 125k elements isn't a big mesh. You may have problem, with mesh over several millions of elements. Let me know __________________ In memory of my friend Hervé: CFD engineer & freerider

February 19, 2015, 01:00		#6
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	in worst case, you will work with tri elements and size function. If your final work will handle moving mesh, you should think about a strategy to treat moving domain (remeshing, smoothing or layering), because you won't prepare a geometry with moving mesh (remeshing) like a geometry with moving mesh (layering) Can you provide your dbs file? __________________ In memory of my friend Hervé: CFD engineer & freerider

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February 18, 2015, 09:46		#3
vekh Member Rafal Join Date: Aug 2013 Location: CK Posts: 36 Rep Power: 12	This is my best - at the moment - mesh with my geometry. It's rectangle with symmetry at X-axis. Red dotted line is border between air and steel. 1 is air 2 is steel (steel is patched after initialization). Blue arrow is laser spot center and gravitational acceleration works in X+ direction. At the moment 2D model with 2x3 mm dimmension is meshed with ~125k elements. I don't have huge experience with such kind of simulations but It's seems to that there is too many element like for that element size... Beside that I have weird pressure jumps from ~3e-5 to 6e8 and problem with courant number - I think that it's mesh fault. -mAx- I do not want to being pushy but can You give me some advice where to find similar example or something of which I could learn size functions? Thanks in advance.