"Failed to find consistent initial values" error from time dependent study

Posted Dec 11, 2023, 7:12 p.m. EST General, Studies & Solvers, Modeling Workflow 3 Replies

Duanhui Li

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Hi guys,

I am new to Comsol so I am guessing this is a newbie bug. What I am trying to do is a time dependent study, so I can simulate the thermomechnical stress in temperature cycling using the fatigue module next. I am basically following the example from comsol "Thermal fatigue of a surface mount resistor", but apply the procedure in my own 3D model. https://www.comsol.com/model/thermal-fatigue-of-a-surface-mount-resistor-16083

So when I tried to calculate the time dependent study, I get the error message like this: "Failed to find consistent initial values. Failed to compute local equation variables. Geometry: geom1, Domain: 13 Failed to evaluate variable. Variable: comp1.solid.eiel11, Defined as: comp1.solid.lemm1.te1.eth11+comp1.solid.lemm1.cmm1.ecl11 Failed to evaluate variable. Variable: comp1.solid.eel11, Defined as: comp1.solid.el11-comp1.solid.eiel11 Failed to evaluate variable. Variable: comp1.solid.sel11, Defined as: ((comp1.solid.D11comp1.solid.eel11)+(comp1.solid.D12comp1.solid.eel22))+(comp1.solid.D13comp1.solid.eel33) Failed to evaluate variable. Variable: comp1.solid.Sel11, Defined as: comp1.solid.sel11 Failed to evaluate variable. Variable: comp1.solid.Sl11, Defined as: comp1.solid.Sel11 Failed to evaluate variable. Variable: comp1.solid.sl11, Defined as: comp1.solid.Sl11 Failed to evaluate variable. Variable: comp1.solid.Wcdr, Defined as: (((((comp1.solid.sl11comp1.solid.lemm1.cmm1.ecRate11)+((2comp1.solid.sl12)comp1.solid.lemm1.cmm1.ecRate12))+((2comp1.solid.sl13)comp1.solid.lemm1.cmm1.ecRate13))+(comp1.solid.sl22comp1.solid.lemm1.cmm1.ecRate22))+((2comp1.solid.sl23)comp1.solid.lemm1.cmm1.ecRate23))+(comp1.solid.sl33comp1.solid.lemm1.cmm1.ecRate33) Failed to evaluate expression. Expression: nojac(comp1.solid.Wcdr) Failed to evaluate expression. Expression: dvol(d(comp1.solid.Wc,TIME)-nojac(comp1.solid.Wcdr)) Failed to evaluate Jacobian of expression. Expression: ((d(comp1.solid.Wc,TIME)-nojac(comp1.solid.Wcdr))test(comp1.solid.Wc))*(dvol) Last time step is not converged."

I am wondering what could lead to this error and what will be a reasonable debug approach. Thank you for your kind assistance!

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3 Replies Last Post Jan 4, 2024, 6:31 p.m. EST

Laksmi Sampath Reddy Pulagam

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Posted: 5 months ago

hello Duanhui, please check the mesh quality and initial values before computing.As in the uploaded mph file the mesh quality is not good enough.In the uploaded images you can see information 1, information 2 ........ please check those and for your reference i have attached the image where it says "Failed to find consistent initial values". I hope it helps.

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Duanhui Li

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Posted: 4 months ago

Updated: 4 months ago

hello Duanhui, please check the mesh quality and initial values before computing.As in the uploaded mph file the mesh quality is not good enough.In the uploaded images you can see information 1, information 2 ........ please check those and for your reference i have attached the image where it says "Failed to find consistent initial values". I hope it helps.

Hi Laksmi,

Thank you very much for your help. I tried a few different things and debugging and now I can narrow down the bug lies at the Creep 1 under the Linear Elastic Material 1. So it feels like that this is a setting issue, as you pointed out.

What I don't get is that I am following the Comsol example to set up the creep and the materials property, but still get this kind of error. :P I will try to further debug and get a narrower scope of the issue. Probabaly I will have a new post more focusing on the Creep settings after that.

BTW, may I know how you get the ref.png in the comsol software? This summary of the input error is very cool and helpful.

Thank you!

Duanhui Li

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Posted: 4 months ago

Updated: 4 months ago

It turns out that I need to use a step function to smooth the initial temperature profile to make it work. It's surprising to me that using the stationary study results as the initial values does not work but this works.

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