Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Coupling heat transfer with an ODE
Posted Aug 17, 2015, 8:52 p.m. EDT Heat Transfer & Phase Change Version 5.0 6 Replies
Please login with a confirmed email address before reporting spam
I am working on a problem that involves solving temperature (T)- and a new dimensionless variable called conversion (alpha). These variables need to be solved simultaneously, since T=f(alpha) and alpha=f(T). Here is the ODE for alpha:
dalpha/dt=C*exp(B/T)(1-alpha)
where A,B are constants and T is the Temperature; alpha on the other hand is dimensionless. I used the heat transfer module and I inserted alpha using the global ODE module. My problem is that when I define the new variable alpha as a function of T, COMSOL does not recognize T, and I get the following error:
Undefined variable.
- Variable: comp1.T
- Global scope:
Failed to evaluate expression.
- Expression: comp1.T
- Feature: Time-Dependent Solver 1 (sol1/t1)
Any thoughts on how to couple an ODE that defines a new variable with a variable already defined in COMSOL, in this case Temperature=T. I have attached a simplified version of my problem.
Thank you
Attachments:
Please login with a confirmed email address before reporting spam
The temperature T is a field variable, defined in the 2D domain as a field T(x,y,t). In order to use a temperature in the ODE, you need to use a scalar value such as the average temperature or the temperature in a point in the 2D geometry. For example, to use the average temperature, define an Average coupling operator aveop1 in all domains and then replace T with aveop1(T) in the ODE.
Best regards,
Magnus Ringh, COMSOL
Please login with a confirmed email address before reporting spam
I work with John. We need alpha to change through our thickness based on the changing temperature T produced by the heat transfer, but so far, it's not coupling correctly.
Preferably, we want to come as close as we can to including a scalar value of T in our alpha equation. Which scalar coupling technique (maximum, minimum, integration, average) would best suit this purpose? Which boundaries/domains/points would we use when we implement this feature? So far, we have tried a few variations with the features and boundaries/domains/points that they utilize, but we could use some guidance.
Thank you
Please login with a confirmed email address before reporting spam
It's hard to tell what scalar temperature that is applicable in your case. I suggest that you contact us at support@comsol.com for full technical support.
Best regards,
Magnus Ringh, COMSOL
Please login with a confirmed email address before reporting spam
Thanks
Please login with a confirmed email address before reporting spam
I am also encountering the same problem.
In my case, the Global ODEs equation doesn't have any dependence in T. Even then the error of comp1.T not recognised is coming.
Please help.
Please login with a confirmed email address before reporting spam
It seems that there may be a misunderstanding here. "T" is a field variable that varies spatially over the domains in which you are solving heat transfer. A "Global ODE" is only meant if there is a single global scalar value that you want to track.
Based upon the descriptions in this thread, it is more likely that what you are really wanting to use here is the "Domain ODE" interface, as exemplified here:
www.comsol.com/blogs/modeling-the-thermal-curing-process/