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time derivatives in weak forms (COMSOL 4.3)
Posted 30 ott 2015, 06:52 GMT-4 0 Replies
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I want to enter some equations in weak form. I have been reading the Reference Guide (ch7 "The Finite Element Method") but it ignores time derivatives. I do not understand if COMSOL assumes something by default. I have tried to enter the with "d" operator (as "test(u)*d(u,t)") but I get errors when COMSOL tries to evaluate some "temporary symbolic derivative variable". Is there a good reference about this subject (Chien Liu's tutorial is very good but it does not treat time derivatives)?
Another question is about geometric factors in axisymmetric cylindrical coordinates. The geometric factor 2*pi*r must be explicitly included? According to this thread
www.comsol.com/community/forums/general/thread/18950/
it must be included in any mathematics interface. However, I have checked that if you enter the equation as a "weak contribution" it includes the 2*pi*r factor.
Thank you
Hello Carlos Soria-Hoyo
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