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Gas in Thermal Stress

Posted 6 févr. 2013, 05:29 UTC−5 Heat Transfer & Phase Change, Structural Mechanics Version 4.3a 2 Replies

Louis-Daniel Théroux
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I am trying to characterize a flaw in a structure (a hole filled with air) for a thermal stress simulation. From a structural point of view, the gas has a Young molulus of zero which cause the computation to crash during the calculation of the inverse matrix. So to solve this problem, I've decided to replace the air by a teflon disc. For the geometry, I've used the ''Form Assembly'' option (instead of form union) and excluded the teflon so it's not attached to the rest of the structure (since its supposed to be a gas, there must be no structural contribution from the teflon). The problem is, from a thermal point of view, the teflon is insulated and I cannot add any thermal boundary condition such has a thin thermally resistive layer (say its not applicable) because, as mentionned before, in the geometry, the teflon is not attached to the structure.

What can I do to represent a gas, something that influence the thermal transfer but not the structural resistance?
2 Replies Last Post 6 févr. 2013, 07:03 UTC−5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 6 févr. 2013, 05:36 UTC−5
Hi

do not include the gas in the structural analysis (remove the domain), but keep it in the HT model

or set a reasonable bulk modulus (remembering that the speed of sound v states v^2=Ebulk/rho and E approx 1/3 Ebulk, use 1 kg/m^3 for the density and 0.495 for Poisson (this is almost a "simple air" model as nu=0.5 fails

--
Good luck
Ivar
Hi do not include the gas in the structural analysis (remove the domain), but keep it in the HT model or set a reasonable bulk modulus (remembering that the speed of sound v states v^2=Ebulk/rho and E approx 1/3 Ebulk, use 1 kg/m^3 for the density and 0.495 for Poisson (this is almost a "simple air" model as nu=0.5 fails -- Good luck Ivar
Louis-Daniel Théroux
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Posted: 1 decade ago 6 févr. 2013, 07:03 UTC−5
Thank you for answering so quickly, I was using the thermal stress module but I switched to the strucure and the thermal transfer modules so I could remove the gas from the structural domain like you said. It wroks fine now, thanks again.
Thank you for answering so quickly, I was using the thermal stress module but I switched to the strucure and the thermal transfer modules so I could remove the gas from the structural domain like you said. It wroks fine now, thanks again.

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