Menu

Discussion Forum

New Discussion
Filter

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 The information provided may be out of date.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.

error of 'Failed to find consistent initial values'

Posted Dec 1, 2011, 11:51 a.m. EST Modeling Tools & Definitions Version 4.3a 2 Replies

Patel Chiragkumar
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam



Dear all,


I have been trying to develop heat transfer (laser pulse model), but After building model when I run the program, COMSOL showing me error ....
-----------------------------------------------------------------------------------------------------------------------------------------------------
Failed to find consistent initial values.
Failed to evaluate variable.
Variable: T, Geometry: 1, Boundary: 3
Failed to evaluate variable.
Variable: R, Defined as: ((0.58999999999999997*(T<Ttrans))+(0.65000000000000002*(T>=Ttrans)))
Failed to evaluate variable.
Variable: Gt1, Defined as: ((((1-R)*Pin)*exp((y/da)))/da)
Failed to evaluate variable.
Variable: Gt, Defined as: (((Gt1>=Gt2)*(Gt1-Gt2))*(y<=0))
Failed to evaluate variable.
Variable: mod1.ht.q0 hf1, Defined as: Gt
Failed to evaluate expression.
Expression: d((mod1.ht.q0 hf1*test(mod1.T))*(dvol),{test@0})
Last time step is not converged.
-------------------------------------------------------------------------------------------------------------------------------------------------------
I think it is not identifying Temperature 'T' !!!! al other errors are due to that only..

Please kindly help me in this matter.

I have attached .mph file of my model

Thanks in advance & Regards,
Chirag

Attachments:

2 Replies Last Post Mar 26, 2013, 12:16 a.m. EDT
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 Dec 2, 2011, 3:47 a.m. EST
Hi

the error is because T is not defined on the boundary at start-up (t=0), only in the domain. You can get around by defining a Parameter T = 293.15[K] that will be updated by COMSOL once the solver runs, at least you get rid of your error message

But that is not enough, you have not really done fully your homework: check the diffusivity alpha=k/rho/Cp of Si, you will see that it is of the order of 1E-4[m^2/s] or a diffusivity time constant of about 10 nsec per micron, and your mesh size is about 1 [um] but your pulse length, hence time sampling is in the nsec. You are not resolving your heat flux at all, you need a mesh size I would say 10 times finer, at least in the direct vicinity of the input heat deposit, then further away the heat capacity time constant will slow down the effect and you can use a coarser mesh

You could try with a 16 times boundary layer on the top region, and probably you need to tweak the time solver

--
Good luck
Ivar
Hi the error is because T is not defined on the boundary at start-up (t=0), only in the domain. You can get around by defining a Parameter T = 293.15[K] that will be updated by COMSOL once the solver runs, at least you get rid of your error message But that is not enough, you have not really done fully your homework: check the diffusivity alpha=k/rho/Cp of Si, you will see that it is of the order of 1E-4[m^2/s] or a diffusivity time constant of about 10 nsec per micron, and your mesh size is about 1 [um] but your pulse length, hence time sampling is in the nsec. You are not resolving your heat flux at all, you need a mesh size I would say 10 times finer, at least in the direct vicinity of the input heat deposit, then further away the heat capacity time constant will slow down the effect and you can use a coarser mesh You could try with a 16 times boundary layer on the top region, and probably you need to tweak the time solver -- Good luck Ivar
me
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Mar 26, 2013, 12:16 a.m. EDT
I have been having the same error. I am implementing a cahn hilliard equation which is a time dependent fourth order PDE in space. I have one of my dependent variable having no time derivative.So I set it to zero. But I have been getting that error. What do you thin is the problem.

See attached COMSOL file
I have been having the same error. I am implementing a cahn hilliard equation which is a time dependent fourth order PDE in space. I have one of my dependent variable having no time derivative.So I set it to zero. But I have been getting that error. What do you thin is the problem. See attached COMSOL file

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