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Velocity in some elements imediately goto infinity

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Old   July 16, 2006, 04:31
Default Velocity in some elements imediately goto infinity
  #1
Shane
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Hi all,

I'm having a problem with my final year uni project...

I have created a geometry in gambit of a 2d beach, of which a tsunami wave will break over. In FLUENT I'm using VOF, NITA, Fractional Step, PRESTO as some of my controls...For my geometry, in GAMBIT I have broken the complete model into small sections, mainly of rectangles and some triangles. Upon running the model, it seems to successfully run for about 100 timesteps with good error residuals, and then all of a sudden, without warning the continuity error shoots to infinity. Upon close inspection, i found that at points within my mesh where rectangles intersect, (similar to shown below) the velocity magnitude in a few elements, which should be small increases slowly over time, until suddenly approaching infinity.

.......................... |...........................

................ Rec 1 | Rec 2.......................

.......................... |...........................

-------------------------------------------------------

.......................... |...........................

.................Rec 3 | Rectangle 4.................

.......................... |...........................

Does anybody know why this is happening, and how to avoid it???

Many thanks

Shane
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Old   July 17, 2006, 08:00
Default Re: Velocity in some elements imediately goto infi
  #2
Vidya
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Hi,

I'm having a similar problem in my simulation too.
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Old   July 18, 2006, 14:52
Default Re: Velocity in some elements imediately goto infi
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Geoff Moss
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This sounds like a meshing problem. You can try one of two things. 1) In the solution-controls window, try lowering the under relaxation factors. This may or may not solve the problem... 2) Use the refine mesh command within fluent. Gambit (as I'm sure you've experienced) is not always great at creating dense meshes in areas where you have a sudden change. Without looking at your specific mesh I cant' tell you exatly how to do it, but Fluent has a fairly good mesh adaption tool built into it. ~Geoff
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Old   July 20, 2006, 05:20
Default Re: Velocity in some elements imediately goto infi
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MKP
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Try to use Structured Meshing all over the domain and see...!

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