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meaning of "crazy" inverted mesh warning
Posted Jan 22, 2010, 4:28 a.m. EST 1 Reply
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Hi all
while running a moving mesh time dependant simulation, I have in the middle of the simulation ONE [ and only One ] inverted mesh warning at a coordinate point which is apparently crazy [ something like -1.xxxe7 while my simulation useonly positive coordinate and the size of the computational space is meters ]
The simulation appears to be fine otherwise
any idea on why this warning could appear and whether or not it can be indicator of other problems in the simulation?
Thanks
JF
while running a moving mesh time dependant simulation, I have in the middle of the simulation ONE [ and only One ] inverted mesh warning at a coordinate point which is apparently crazy [ something like -1.xxxe7 while my simulation useonly positive coordinate and the size of the computational space is meters ]
The simulation appears to be fine otherwise
any idea on why this warning could appear and whether or not it can be indicator of other problems in the simulation?
Thanks
JF
1 Reply Last Post Jan 23, 2010, 3:50 a.m. EST
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Posted:
1 decade ago
Hi
there are a already few discussions explanations about ALE and inverted elements on the forum, do a search for more.
Basically when you deform your mesh some elements might invert (nodes passing through the plane defined by the others = topology change hence always a "danger") specially if you use higher orders polynomials, therefore COMSOL tries out first to hcange to linear elements for local elements with this warning. This is "bad" as the results might be affected (but must-not be globally "wrong" so its a warning).
If you say its small and "single", it could indicate that you have some "small" details that are locally meshed very fine and that do not support your global deformation field. Or that you have locally fixed a "point" boundary that cannot follow the deformation so that the elements linked to this "point" node have little freedom to adapt their shape to follow the global mesh deformation.
This can also happen specially at the end points of a border that is fixed.
It somewhat similar to the effect of getting infinite stress concentration that you find on all sharpes edges in static structural analysis.
THe mathematics of FEM does not like singularities ;) but who does ?
Good luck
Ivar
there are a already few discussions explanations about ALE and inverted elements on the forum, do a search for more.
Basically when you deform your mesh some elements might invert (nodes passing through the plane defined by the others = topology change hence always a "danger") specially if you use higher orders polynomials, therefore COMSOL tries out first to hcange to linear elements for local elements with this warning. This is "bad" as the results might be affected (but must-not be globally "wrong" so its a warning).
If you say its small and "single", it could indicate that you have some "small" details that are locally meshed very fine and that do not support your global deformation field. Or that you have locally fixed a "point" boundary that cannot follow the deformation so that the elements linked to this "point" node have little freedom to adapt their shape to follow the global mesh deformation.
This can also happen specially at the end points of a border that is fixed.
It somewhat similar to the effect of getting infinite stress concentration that you find on all sharpes edges in static structural analysis.
THe mathematics of FEM does not like singularities ;) but who does ?
Good luck
Ivar