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Deformed geometry model converges until I try to use the lagrange multiplier

Posted Jun 18, 2014, 5:59 p.m. EDT Heat Transfer & Phase Change, Geometry, Mesh, Studies & Solvers Version 4.3b 2 Replies

Aaron Curtis
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Hi all,

I'm trying to model the growth of a cavity in a block of ice in response to a flow of hot air. I have a model that works fairly well, with conjugate heat transfer and a deformed geometry to track the air / ice interface as melting progresses. At least, it works fine as long as I prescribe the melting rate at a fixed value of 0.001 m/s. In order to simulate melting I followed the approach of the Tin Melting Front example "Stefan problem" model: set the boundary temperature as a weak constraint, and use the lagrange multiplier as input to a prescribed normal deformation on that boundary.

The problem is that whenever I switch from the fixed value to the "Stefan problem" expression for the Prescribed Normal Mesh Velocity, my model no longer converges -- it says:

Nonlinear solver did not converge.
Time: 0
Attempt to evaluate real square root of negative number.

The model is attached. Thanks in advance for any advice!

Aaron

Attachments:

2 Replies Last Post Nov 25, 2014, 11:22 a.m. EST
COMSOL Moderator

Hello Aaron Curtis

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Leonard Rossmann
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Posted: 1 decade ago Nov 25, 2014, 9:20 a.m. EST
Hej Aaron,

I am having roughly the same problem. Did you find a solution for yours, I would be keen to know.

best regards
leonard
Hej Aaron, I am having roughly the same problem. Did you find a solution for yours, I would be keen to know. best regards leonard
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Nov 25, 2014, 11:22 a.m. EST
There are a couple of things to try when Time 0 in a time dependent analysis does not converge. One is to apply all loads gradually so that there are no discontinuities at Time 0. Another is to use more “stringent” solver settings helps, usually at the cost of a slower solver. I tried this second approach on your model by changing the Jacobian update in your Fully Coupled solver to “On every iteration”. That worked for a few time steps and then fails again. I hope this helps.

Nagi Elabbasi
Veryst Engineering
There are a couple of things to try when Time 0 in a time dependent analysis does not converge. One is to apply all loads gradually so that there are no discontinuities at Time 0. Another is to use more “stringent” solver settings helps, usually at the cost of a slower solver. I tried this second approach on your model by changing the Jacobian update in your Fully Coupled solver to “On every iteration”. That worked for a few time steps and then fails again. I hope this helps. Nagi Elabbasi Veryst Engineering

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