Discussion Forum

Maciej,

there may be different ways to achieve that, depending on what the parameter is actually doing. If it controls a boundary condition, you may try the following: - Duplicate the respective BC node - Use the start parameter in the first node - Use the calculated variable in the second node - Set up two successive stationary steps - Modify the physics tree: disable the second BC version in the first study and the first BC version in the second study.

This should work for any kind of physics subnode, not only BCs. If the parameter is doing something that affects geometry or mesh, things get more difficult.

Cheers Edgar

Dear Edgar, thank you for your reply!

One thing I don't understand - "Use the calculated variable in the second node" - how can I refer to an integral calculated in the previous study? If I would just replace parameter "p0" with "p0/intop1(w)" in the second BC, the integral would keep being evaluated and updated during the calculation of the second study. I would like to save its value from the first study and use that in the second one.

Best regards Maciej

Hi Maciej,

you are right, it doesn't work this way. Actually, my suggestion didn't come out of the blue, but my case was indeed different. One other way, that comes to my mind is to duplicate the whole physics node and add a global equation to the first physics. Check here: https://www.comsol.de/blogs/using-the-previous-solution-operator-in-transient-modeling/ to see an example how to take advantage of global equations. It is again different from what you need, but it may trigger an idea.

Good luck Edgar

Dear Edgar,

Thank you for your suggestion, I used global equations instead and they work great!

Best regards
Maciej

Hi,

Edgar's first suggestion should work if you wrap 'w' in the withsol() operator so that you can explicitly point to the intended solution.

Regards,

Henrik

Hi Henrik,

interesting! But is withsol() useable in the solver sequence in such a case? So far I assumed (and experienced) that it only works reliably in post processing? Well, it seems to work during solving in specific cases which are not documented as far as I know.

Cheers Edgar

Hi Edgar,

You are probably thinking of the 'with()' operator, which is only available in postprocessing.

The 'withsol()' operator (which was added in version 5.1) can be used anywhere; in expressions, variables, etc. The only restriction is that the solution you are pointing to must have been computed when the expression is evaluated.

Some examples from previous forum discussions:

https://www.comsol.com/forum/thread/90501/is-it-possible-toselect-a-particular-solution-of-a-certain-data-set-using-withsol

https://www.comsol.com/forum/thread/101611/previous-solution-as-constant

https://www.comsol.com/forum/thread/86181/reusing-solution-displacements-should-be-easy-help-please

Regards,

Henrik

Henrik,

yes in this case the solution is finished and it is possible to point to it with withsol(). I failed with withsol() in cases when I would have had to reference a parametric solution while the auxiliary sweep is still running.

Cheers Edgar