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Derivatives in COMSOL
Posted Jan 1, 2012, 9:17 p.m. EST Version 4.0 1 Reply
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Hi! Is there any way to define in COMSOL 4.0 a derivative with respect to a variable which isn't an environment variable (like x,y,z, or time?)
Basically, I defined radius r = sqrt(x^2+y^2+z^2), and I want to define a radial derivative, but I believe COMSOL 4.0 doesn't allow me to use coordinates other than cartesian. How can I get around this problem?
Also, is it correct that I can denote the time derivative of variable "U" by "Ut"? My model gives me an error, I don't know why, and I want to know if this "Ut" notation is what is causing the error, or if it is something else.
Basically, I defined radius r = sqrt(x^2+y^2+z^2), and I want to define a radial derivative, but I believe COMSOL 4.0 doesn't allow me to use coordinates other than cartesian. How can I get around this problem?
Also, is it correct that I can denote the time derivative of variable "U" by "Ut"? My model gives me an error, I don't know why, and I want to know if this "Ut" notation is what is causing the error, or if it is something else.
1 Reply Last Post Jan 2, 2012, 4:14 a.m. EST
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Posted:
1 decade ago
Hi
check the doc or the help (better upgrade to a newer version) you have spatial and time derivatives, mostly predefined for your dependent variables up to 2nd order if you use "2nd order shape function" with your solver (the default)
else you must create your derivatives via an specific ODE, chekc the KB on the main site
--
Good luck
Ivar
check the doc or the help (better upgrade to a newer version) you have spatial and time derivatives, mostly predefined for your dependent variables up to 2nd order if you use "2nd order shape function" with your solver (the default)
else you must create your derivatives via an specific ODE, chekc the KB on the main site
--
Good luck
Ivar