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error of 'Failed to find consistent initial values'

Posted 01.12.2011, 11:51 GMT-5 Modeling Tools & Definitions Version 4.3a 2 Replies

Patel Chiragkumar
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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 26.03.2013, 00:16 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 02.12.2011, 03:47 GMT-5
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
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Posted: 1 decade ago 26.03.2013, 00:16 GMT-4
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

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