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different results-same conditions...
Posted Feb 8, 2010, 9:58 a.m. EST 2 Replies
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Hi all,
I've noticed COMSOL gives differens answers under the same conditions..
For simlicity I took a cube and a cilinder that are not connected.
Then I fixed [xy] bottom boundary planes of both solids and load -5 N/m^2 in Z-direction on [xy] upper boundary planes.
Comsol gave solution #1
Than I moved cylinder to -70 in x direction and solve again.
Comsol gave very strange result in this case... it completly differs from solution #1
can anybody tell me what is the problem?
Am I allowed to move elements or this movements just occurs mistakes in calculdtions?
regards,
Alex
I've noticed COMSOL gives differens answers under the same conditions..
For simlicity I took a cube and a cilinder that are not connected.
Then I fixed [xy] bottom boundary planes of both solids and load -5 N/m^2 in Z-direction on [xy] upper boundary planes.
Comsol gave solution #1
Than I moved cylinder to -70 in x direction and solve again.
Comsol gave very strange result in this case... it completly differs from solution #1
can anybody tell me what is the problem?
Am I allowed to move elements or this movements just occurs mistakes in calculdtions?
regards,
Alex
2 Replies Last Post Feb 9, 2010, 6:00 a.m. EST
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Posted:
1 decade ago
Hi
certainly you should get the same results, if the initial conditions are the same,
but:
by moving a part you go back from analysed (=indexed boundaries and geometry) to the "raw geometry" mode, meshing and solutions are cleaned out, then you move a part and their relative positions have changed = a "topology change". When you re-enter BC mode, you do a new "geomanalyse" as parts have moved you might get a different index order for your boundaries and volumes, in result material data and fixed boundaries indexes might have changed and COMSOL cannot fully know what you wanted to do, hence a possible change in the overall BC's, with thereafter different results,
This is in my view the most plausible cause, but there are other traps too, pls ALWAYS carefully check ALL your BC when you rearrange your geometry, also when you delete or add a simple line. Mostly, everything is OK, but sometimes, when you expect it least (was it Murphy again) you get surprises.
And do not mix solve and resolve/restart without having tought about it, first
Good luc
Ivar
certainly you should get the same results, if the initial conditions are the same,
but:
by moving a part you go back from analysed (=indexed boundaries and geometry) to the "raw geometry" mode, meshing and solutions are cleaned out, then you move a part and their relative positions have changed = a "topology change". When you re-enter BC mode, you do a new "geomanalyse" as parts have moved you might get a different index order for your boundaries and volumes, in result material data and fixed boundaries indexes might have changed and COMSOL cannot fully know what you wanted to do, hence a possible change in the overall BC's, with thereafter different results,
This is in my view the most plausible cause, but there are other traps too, pls ALWAYS carefully check ALL your BC when you rearrange your geometry, also when you delete or add a simple line. Mostly, everything is OK, but sometimes, when you expect it least (was it Murphy again) you get surprises.
And do not mix solve and resolve/restart without having tought about it, first
Good luc
Ivar
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Posted:
1 decade ago
Hi Ivar,
I've tried it by another way:
I've created a box and a cylinder.. then I moved cylinder to 50 in y direction and only after that I set boundary conditions of both bodies.
Result is unreal... I set deformed shape in plot parameters and these shapes are unreal.. they are turned inside out!!
What I'm doing wrong?
thx,
Alex
I've tried it by another way:
I've created a box and a cylinder.. then I moved cylinder to 50 in y direction and only after that I set boundary conditions of both bodies.
Result is unreal... I set deformed shape in plot parameters and these shapes are unreal.. they are turned inside out!!
What I'm doing wrong?
thx,
Alex