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Posted:
1 decade ago
06.11.2010, 03:18 GMT-4
well I will suggest that before using comsol [ or any other code for that matters...[l you check a book on elasticity theory...
poisson ratio CANNOT be 0.5 as part of its definition in the context of linear elasticity theory..
comsol has nothing to do with that...
jf
well I will suggest that before using comsol [ or any other code for that matters...[l you check a book on elasticity theory...
poisson ratio CANNOT be 0.5 as part of its definition in the context of linear elasticity theory..
comsol has nothing to do with that...
jf
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Posted:
1 decade ago
06.11.2010, 03:25 GMT-4
Thanks for your advice jf.
However, the poison ratio I direct get from PDMS substance which I consider constant in my case.
I now just place the poisson ratio as 0.49, I know it sound stupid but I cant find any solution for that.
Any advice?
Many thanks.
Regards,
PS
Thanks for your advice jf.
However, the poison ratio I direct get from PDMS substance which I consider constant in my case.
I now just place the poisson ratio as 0.49, I know it sound stupid but I cant find any solution for that.
Any advice?
Many thanks.
Regards,
PS
Ivar KJELBERG
COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted:
1 decade ago
07.11.2010, 05:08 GMT-5
Hi
if you works with Poisson nu close to 0.5, it could be worth trying with the "Nearly incompressible material" check on, this will add the pressure field and mostly the solver will converge better, but as François said, check the structural doc carefully to really understand what you are asking for
--
Good luck
Ivar
Hi
if you works with Poisson nu close to 0.5, it could be worth trying with the "Nearly incompressible material" check on, this will add the pressure field and mostly the solver will converge better, but as François said, check the structural doc carefully to really understand what you are asking for
--
Good luck
Ivar
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Posted:
9 years ago
21.01.2016, 10:48 GMT-5
PLEASE try 0.49, it works.
PLEASE try 0.49, it works.
Jeff Hiller
COMSOL Employee
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Posted:
9 years ago
21.01.2016, 11:50 GMT-5
Even if you are able to get a solution at nu=.49, you should still consider using the Nearly Incompressible Formulation whenever nu is close to .5, because for a given mesh you will get a much more accurate solution (especially noticeable in stress plots). Like others have already mentioned, there is abundant literature on this topic. Pick up just about any textbook on the finite element method; what we're talking about here is called the "locking" phenomenon for incompressible or near-incompressible materials and the remedy is to use a "u-p" (or "mixed") formulation (which is what is triggered by checking the "Nearly Incompressible Formulation" checkbox in COMSOL). For instance, the topic is covered in Bathe, Finite Element Procedures, 2nd edition, 1992, page 276 and following.
Jeff
Even if you are able to get a solution at nu=.49, you should still consider using the Nearly Incompressible Formulation whenever nu is close to .5, because for a given mesh you will get a much more accurate solution (especially noticeable in stress plots). Like others have already mentioned, there is abundant literature on this topic. Pick up just about any textbook on the finite element method; what we're talking about here is called the "locking" phenomenon for incompressible or near-incompressible materials and the remedy is to use a "u-p" (or "mixed") formulation (which is what is triggered by checking the "Nearly Incompressible Formulation" checkbox in COMSOL). For instance, the topic is covered in Bathe, Finite Element Procedures, 2nd edition, 1992, page 276 and following.
Jeff
