Menu

Discussion Forum

New Discussion
Filtern

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.

initialize timestep and Temperature to use prev()

Posted 02.04.2019, 07:10 GMT-4 General Version 5.3a 5 Replies

Christian Berwanger
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hello, to calculate the current cooling rate I use the formula (T-prev(T,1))/(t-prev(t,1)). However. In the first step I cannot use the prev() command, as there are no values before the first step. Can I somehow initialize these values? Or can I even calculate the cooling rate more elegant? Kind regards, Christian

5 Replies Last Post 05.04.2019, 02:57 GMT-4
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 6 years ago 02.04.2019, 07:37 GMT-4

Hi,

More elegant is to use the built in time derivative of the temperature, 'Tt'.

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi, More elegant is to use the built in time derivative of the temperature, 'Tt'. Regards, Henrik
Christian Berwanger
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 6 years ago 03.04.2019, 08:30 GMT-4

Hi,

thank you for your answer. But I still have a similar problem: Variable Tt cannot be evaluated. The problem is in the first step I think. I do have the starting temperature T at t=0 for all points in x,y,z. The problem was with the older method using prev() that I could not evaluate dT/dt at the first point as I do not have enough Data. I think this time I have a similar problem. If necessarily could even provide an initial value for Tt, if I would know where to assign the initial value of Tt.

Currently I do have an analytic function defined in the components and I just used Tt for the cooling rate.

Kind regards, Christian

Hi, thank you for your answer. But I still have a similar problem: Variable Tt cannot be evaluated. The problem is in the first step I think. I do have the starting temperature T at t=0 for all points in x,y,z. The problem was with the older method using prev() that I could not evaluate dT/dt at the first point as I do not have enough Data. I think this time I have a similar problem. If necessarily could even provide an initial value for Tt, if I would know where to assign the initial value of Tt. Currently I do have an analytic function defined in the components and I just used Tt for the cooling rate. Kind regards, Christian
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 6 years ago 03.04.2019, 10:53 GMT-4

Hi Christian,

What study type (and settings) are you using?

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi Christian, What study type (and settings) are you using? Regards, Henrik
Christian Berwanger
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 6 years ago 03.04.2019, 11:05 GMT-4

Hi Henrik,

My Study looks like this: I am using an optimization and as Step 1 I use a Time Dependent Study Step. In the Solver Configurations the optimization solver is also time dependent. The error appears in the optimization solver (as I use my function as an Objective for my optimization). Kind regards, Christian

Hi Henrik, My Study looks like this: I am using an optimization and as Step 1 I use a Time Dependent Study Step. In the Solver Configurations the optimization solver is also time dependent. The error appears in the optimization solver (as I use my function as an Objective for my optimization). Kind regards, Christian
Henrik Sönnerlind COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 6 years ago 05.04.2019, 02:57 GMT-4

Hi Christian,

I think you should either contact support, or upload a simplified version of your model here.

Regards,
Henrik

-------------------
Henrik Sönnerlind
COMSOL
Hi Christian, I think you should either contact support, or upload a simplified version of your model here. Regards, Henrik

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.

Suggested Content