Menu

Discussion Forum

New Discussion
Filtrer

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 The information provided may be out of date.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.

Why dont Lagrange Multipliers have units

Posted 25 févr. 2012, 11:11 UTC−5 Parameters, Variables, & Functions Version 4.2a 3 Replies

John
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Comsol dutifully assigns units to things like pressure ("p"), dervied units like velocity "dl.u", etc.

But it doesn't assign units to Lagrange multiplers (like p_lm).

Why?

I have a more subtle reason for asking, I'm in the middle of working out if p_lm includes already contains an area term (i.e. is it flux * area) or not... I find the documentation confusing on this, but can work this out by running a quick case. But if the units were there already, then I would know immediately.

Thanks, John
3 Replies Last Post 26 févr. 2012, 03:05 UTC−5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 25 févr. 2012, 12:42 UTC−5
Hi

excellent question, I have already asked COMSOL some time ago, about this, they told me they were preparing this for one of the future releases.

In the mean time the units of the LM's (fluxes) have always been in the doc, so, it's easy to add a *1[W/m^2] in HT or whatever is appropriate for you ;)

see doc Comsol User Guide 4.2a p460 table 7-2 "PHYSICS INTERFACE INTERPRETATION OF LAGRANGE MULTIPLIERS"

--
Good luck
Ivar
Hi excellent question, I have already asked COMSOL some time ago, about this, they told me they were preparing this for one of the future releases. In the mean time the units of the LM's (fluxes) have always been in the doc, so, it's easy to add a *1[W/m^2] in HT or whatever is appropriate for you ;) see doc Comsol User Guide 4.2a p460 table 7-2 "PHYSICS INTERFACE INTERPRETATION OF LAGRANGE MULTIPLIERS" -- Good luck Ivar
John
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 25 févr. 2012, 12:58 UTC−5
Yeh, what caught me out was my equation being solved is div (rho*kappa/mu grad p), so that p_lm has units of density*perm/viscosity*pressure/length.

I had missed the density term being inside the div, so I was expecting p_lm to have units of perm/viscosity*pressure/length

Regards, John
Yeh, what caught me out was my equation being solved is div (rho*kappa/mu grad p), so that p_lm has units of density*perm/viscosity*pressure/length. I had missed the density term being inside the div, so I was expecting p_lm to have units of perm/viscosity*pressure/length Regards, John
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago 26 févr. 2012, 03:05 UTC−5
Hi

yes indeed its very easy to overlook such things, that is why I love the unit feature, would just appreciate that they arrive EVERYWHERE including material parameters, LMs, all plot scales, also time, and in the graphics window for the units of the graphics scale ;)

--
Good luck
Ivar
Hi yes indeed its very easy to overlook such things, that is why I love the unit feature, would just appreciate that they arrive EVERYWHERE including material parameters, LMs, all plot scales, also time, and in the graphics window for the units of the graphics scale ;) -- Good luck Ivar

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