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Imposing Dirichlet domain condition

Guillaume Maîtrejean

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Hello all,
I wonder if there is a way to impose a Dirichlet condition not on a boundary but on a domain. Let's say, for instance, that at a time tn of my calculation I want to impose null velocity in my fluid depending on local temperature/concentration/etc. Weak constraints (Lagrange multipliers) are not well suited as the velocity condition is not initially set nor permanent...
So, how can I achieve that ?

Thanks in advance for your help !
Guillaume

2 Replies Last Post 07.03.2014, 04:12 GMT-5
Luke Gritter Certified Consultant

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Posted: 1 decade ago 06.03.2014, 16:04 GMT-5
Guillaume,

If you have "Advanced Physics Options" activated in the Show menu, you can right-click on any physics interface and see sub-menus entitled "More" in the domain, boundary, etc. sections. These sub-menus contain options for adding pointwise or weak constraints on the various geometric entity levels. If you multiply the constraint expression by a conditional expression [e.g. u*(t>1)*(t<2)], you can turn the constraints on and off as a function of time.

This type of technique can be successfully implemented on a domain, but if you use it to specify something non-physical, strange results may ensue...

--
Luke Gritter
AltaSim Technologies
Guillaume, If you have "Advanced Physics Options" activated in the Show menu, you can right-click on any physics interface and see sub-menus entitled "More" in the domain, boundary, etc. sections. These sub-menus contain options for adding pointwise or weak constraints on the various geometric entity levels. If you multiply the constraint expression by a conditional expression [e.g. u*(t>1)*(t

Guillaume Maîtrejean

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Posted: 1 decade ago 07.03.2014, 04:12 GMT-5
Hi Luke
I already tried with weak constraint but it lead to a singular matrix at the first step (even with a conditionally stated constraint ). However I did not try with pointwise constraints (I had not noticed this option ) which seems to work. Unfortunately I experience strong convergence problem with this condition enabled: as soon as the constraint is active, the calculation does not converge !

Well, thanks anyway for the tip !

Guillaume


Hi Luke I already tried with weak constraint but it lead to a singular matrix at the first step (even with a conditionally stated constraint ). However I did not try with pointwise constraints (I had not noticed this option ) which seems to work. Unfortunately I experience strong convergence problem with this condition enabled: as soon as the constraint is active, the calculation does not converge ! Well, thanks anyway for the tip ! Guillaume

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