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Old   August 30, 2007, 05:51
Default Negative Volume
  #1
saurav pathak
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can anyone kindly explain me what is meant by "negative volume" in a mesh?
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Old   August 30, 2007, 06:43
Default Re: Negative Volume
  #2
rt
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degenerated elements, reverse or inconsistence node ordering
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Old   August 30, 2007, 08:23
Default Re: Negative Volume
  #3
Ahmed
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How volumes are calculated?

the scalar triple product of vectores formed from the sides of a cell, the formula is found in any linear algebra book, play a bit with the numbers and see by yourself how could you get a negative volume. Some times the cell you are calculating its volume is not deformed at all, but its vertices are numbered clock wise, in this case remeshing is the only solution to this nasty problem
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Old   August 30, 2007, 11:01
Default Re: Negative Volume
  #4
Anantha
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It depends.. If you are using commercial tool like ICEM, you have the option of 'invert block' to get rid of this problem.. though the mesh will look perfect for eyes, we will get negative volume error because of the reason as said by Ahmed and some times you can fix it up by this block inversion method.
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Old   August 31, 2007, 07:34
Default Re: Negative Volume
  #5
Charles
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All of the above comments are true, but sometimes, when dealing with nasty geometry, hexahedral meshes can simply get folded, which will also show up as a negative volume. Imagine taking a rectangle, and twisting one edge through 180 degrees. So negative volumes can't always be solved by re-ordering. You may need to look a it to see if the cells make physical sense.
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Old   August 31, 2007, 13:18
Default Re: Negative Volume
  #6
Joe
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I'm assuming this is a structured or hex mesh. If all the volumes are negative, then your system is left handed. Reordering the indicies will fix that - easy. If just a few of the volumes are negative, then you have crossing grid lines - much harder. You need to find the location and source of the problem to fix this. Sometimes smoothing the mesh will an elliptic solver will work. But most of the time there is an underlying problem with your database or grid structure.
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Old   September 1, 2007, 11:26
Default Re: Negative Volume come back
  #7
jorge
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I have ansys turbogrid 10 in workbench environment, but this send a error when i want to do a mesh.(negative volume). I read many post about this(These advice move the master control points)but the problem is not solved. Help me.Please. Jorge
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