Regarding solver in diffusion.h

[Shyam Sunder Yadav]

Dear All

I was solving the energy equation in terms of temperature using the diffusion routine in diffusion.h.

During the implicit solution of heat conduction step, if I use theta=rho * Cp and D = thermal conductivity, the solver do not converge.

While if I use theta=1 and D = thermal diffusivity, the solver converges.

Why this difference? Is something wrong with my implementation or is it related to the solution process of multigrids?

Please let me know.

Thank you. Regards

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Dr. Shyam Sunder Yadav
Associate Professor
Mechanical Engineering
BITS Pilani
09902346342
http://www.bits-pilani.ac.in/pilani/ssyadav/Profile

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[Wojciech (Voitek) Aniszewski]

Dear SSY,

we've done a hefty dose of such simulations using diffusion.h. Now, what usually makes it stiff (not divergent, stiffness was a better description of our case) was: 1. often, parameters ended up not well chosen, i.e. in parameter studies we had inputs orders of magnitude off the physical ones, diffusion.h was very sensitive to that; 2. certain grid resolutions. This means that e.g. you can have a stiff solver with octree at maxlevel N, but at N-1 or N+1 (if you can afford it) it's not stiff.

I know this is very empirical, but usually, after making sure all params are physical, convergence was in reach.

kindly

Voitek A.

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 /^..^\      
( (••) )    Wojciech (vôitek) ANISZEWSKI
(|)_._(|)~  Researcher@ U. Paris-Saclay (EM2C)
OrcId   : https://orcid.org/0000-0002-4248-1194
Scholar : https://tinyurl.com/y28b8gfp

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