Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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.

Nonuniform initial temperature distribution in the heat transfer module

Please login with a confirmed email address before reporting spam

I seem to remember that at some point, Comsol allowed a nonuniform initial temperature distribution in the heat transfer module. In Comsol 4.4, it appears that only one initial temperature can be used for an entire domain. Is there a way to add an initial temperature point-by-point in a domain? Thanks

5 Replies Last Post 1 ago 2014, 10:17 GMT-4
Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 18 lug 2014, 15:16 GMT-4
Hi Greg,
Just like before, you can enter for your Initial Value an expression that is spatially dependent and/or you can also have several Initial Value nodes for different domains.
Do I misunderstand your question?
Best,
Jeff
Hi Greg, Just like before, you can enter for your Initial Value an expression that is spatially dependent and/or you can also have several Initial Value nodes for different domains. Do I misunderstand your question? Best, Jeff

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 31 lug 2014, 13:53 GMT-4
Hi Jeff,
Actually, I need to be able input discrete initial values (i.e., I have no spatially dependent expression) within a domain. The reason is that I am approximating the heating of a food being rotated on a turntable in a microwave oven by discrete rotation steps. One step involves rotating the food a small angle, recalculating the microwave field, then allow heating to occur for a small time interval. The "initial" temperature for one step is the final temperature distribution of the previous step.

I was going to implement this using Livelink for Matlab, so that Matlab will handle the data manipulation between steps and set up the new step (new food position, initial values) in Comsol.

This has been done with other FEM packages, but it seems always with two different packages, one handling the actual FEM heat transfer modeling and the other handling the electromagnetic field setup. I'd like to be able to do this with Comsol alone, but I am stuck at how to transfer the output from the previous step (discrete temperatures within the food domain at one position) to the input of the next step (discrete initial values within the food domain at a slightly rotated position).

I thought of another way of doing this, but not sure if it would work. Instead of rotating the food within the oven, I thought it would be easier rotating the oven around the food. This would fix the food in space and eliminate the need to remap temperatures from the food's previous position onto the new position for the next heating step. But again, I'd have to make Comsol understand to retain the temperatures from the previous step for the next one.
Greg
Hi Jeff, Actually, I need to be able input discrete initial values (i.e., I have no spatially dependent expression) within a domain. The reason is that I am approximating the heating of a food being rotated on a turntable in a microwave oven by discrete rotation steps. One step involves rotating the food a small angle, recalculating the microwave field, then allow heating to occur for a small time interval. The "initial" temperature for one step is the final temperature distribution of the previous step. I was going to implement this using Livelink for Matlab, so that Matlab will handle the data manipulation between steps and set up the new step (new food position, initial values) in Comsol. This has been done with other FEM packages, but it seems always with two different packages, one handling the actual FEM heat transfer modeling and the other handling the electromagnetic field setup. I'd like to be able to do this with Comsol alone, but I am stuck at how to transfer the output from the previous step (discrete temperatures within the food domain at one position) to the input of the next step (discrete initial values within the food domain at a slightly rotated position). I thought of another way of doing this, but not sure if it would work. Instead of rotating the food within the oven, I thought it would be easier rotating the oven around the food. This would fix the food in space and eliminate the need to remap temperatures from the food's previous position onto the new position for the next heating step. But again, I'd have to make Comsol understand to retain the temperatures from the previous step for the next one. Greg

Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 1 ago 2014, 08:28 GMT-4
I am no EM expert so there may be some fundamental reason not to do this that I don't know about, but my first instinct would be to perform a single time-dependent analysis with a moving geometry. Then the temperature distribution at the end of a particular time interval would automatically be the initial temperature distribution for the next time interval.
Jeff
I am no EM expert so there may be some fundamental reason not to do this that I don't know about, but my first instinct would be to perform a single time-dependent analysis with a moving geometry. Then the temperature distribution at the end of a particular time interval would automatically be the initial temperature distribution for the next time interval. Jeff

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 1 ago 2014, 10:12 GMT-4
I think I made this more complicated than it needed to be. At the very basic level, independent of any physics involved, if I have a table of coordinates within a domain and the associated temperatures at each of those coordinates, is there a way to input those to Comsol as an initial condition?
I think I made this more complicated than it needed to be. At the very basic level, independent of any physics involved, if I have a table of coordinates within a domain and the associated temperatures at each of those coordinates, is there a way to input those to Comsol as an initial condition?

Jeff Hiller COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 1 ago 2014, 10:17 GMT-4
Yes, by using an interpolation function. See Reference Manual, version 4.4, page 245 for the details.
Jeff
Yes, by using an interpolation function. See Reference Manual, version 4.4, page 245 for the details. Jeff

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.