[mesa-users] Problems with 'newton iters' determined timesteps

[Bill Paxton]

Hi,

Please send inlists, saved models, and whatever else is needed for others to reproduce the problem.

Thanks,
Bill



On Jan 9, 2014, at 5:28 PM, Wonseok Chun wrote:

> I am currently running He Zams evolution with semiconvection. However, as calculation progress on, I have issues with small timestep, about 0.01yr. 
> 
> First issue appears near the start of calculation, and timestep is reduced from 'newton iters'.
> I was able to raise timestep by rasing newton_iteration_limit.
> 
> However, timestep is again reduced at age around log_age~5.29. Timestep is again forcibly reduced from failure of convergence from newton_hydro check, and I presume this is due to steep gradiant of c12 reaching surface, while there is still large enough mass loss from wind.
> (Mass loss reduces convective core size, which in turn makes c12 abundance gradient.)
> 
> Similar problems occurs in 10M model too, but without apparent reason.
> 
> Initial model used is 20M, he4=0.98, Z=0.02 with dxdt_nuc_factor=0 relaxtion.
> ZAMS model was constructed by following steps.
> 
> - make pre_ms with y=0,z=0, 20m
> - relax y to y=1
> - calculate until central he4=0.98, with dxdt_nuc_factor=0.01
> - set uniform initial abundance - h1,h2,he3=0, he4=0.98
> 
> And additional parameters are 
> 
> - Wind : dutch
> - semiconvection : Ledoux, a=0.01
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