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Name of variables in a two PDE problem (works for u and u2 but not for u and theta)
Posted 29 juil. 2017, 08:15 UTC−4 Modeling Tools & Definitions, Parameters, Variables, & Functions 2 Replies
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Dear friends from COMSOL,
I am trying to solve a coupled system of PDEs in COMSOL using the "Coefficient Form PDE". I have seen in a paper and in forum discussions that this is doable. This is a very simple 1D problem.
I create the model defining two coefficient form PDEs, such that the first PDE has as variable a scalar quantity u (and a source term that depends on a variable theta) while the second PDE has a variable theta (and a source term that depends on ut, derivative of u with respect to time).
However, the model does not solve, as it says that theta is an unknown variable. If I change theta for u2 in all places, then it solves.
I like using u and theta rather than u and u2 as my two variables are completely independent, and I like to use u and u2 when I am in 2D problems and they refer to both components of the vector solution (here we have 2 solutions). And in the paper they report doing it like this. Why do I get an error? Can one operate with different names?
Thank you
I am trying to solve a coupled system of PDEs in COMSOL using the "Coefficient Form PDE". I have seen in a paper and in forum discussions that this is doable. This is a very simple 1D problem.
I create the model defining two coefficient form PDEs, such that the first PDE has as variable a scalar quantity u (and a source term that depends on a variable theta) while the second PDE has a variable theta (and a source term that depends on ut, derivative of u with respect to time).
However, the model does not solve, as it says that theta is an unknown variable. If I change theta for u2 in all places, then it solves.
I like using u and theta rather than u and u2 as my two variables are completely independent, and I like to use u and u2 when I am in 2D problems and they refer to both components of the vector solution (here we have 2 solutions). And in the paper they report doing it like this. Why do I get an error? Can one operate with different names?
Thank you
2 Replies Last Post 1 août 2017, 05:08 UTC−4
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Posted:
7 years ago
Did you change "field name" AND "Dependent Variables" in the top level of "Coeffiicient Form PDE"?
See pic for an example.
Regards
Jens
See pic for an example.
Regards
Jens
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Posted:
7 years ago
Thank you, Jens, I had not changed the "Dependent variables" part (I thought that it was not editable). Now it works flawlessly.