[Mesa-users] taking very small steps during accretion

Tue Aug 17 17:20:07 UTC 2021

Hi Harish, "relax" is a namelist setting that refers to the act of changing
the model by only adjusting one quantity while turning the rest of
evolution off. So this would not strictly be a realistic astrophysical
scenario, but more of a "stellar engineering" step. With the stellar
modelling, there are often limitations between what we believe happens in
real life vs what we can model, and we have to apply numerical fixes to get
as close as we can. This is one such scenario.

Bill, when last I tried to do high accretion rates, I found that for WD
masses, I couldn't get higher than 1d-4 and still have a stable model. I
did find that the highest tolerable rate would increase with the starting
model mass. Has this situation improved since then? Thanks.
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On Tue, Aug 17, 2021 at 1:47 AM harish sorrout via Mesa-users <
mesa-users at lists.mesastar.org> wrote:

> Thankyou sir,
>
> I have some query regarding the relax mass_ change .
>
> 1. When I will do relax mass_change over 100 yrs. Does white dwarf cool
> during this years?
> 2. Does physical values of WD change or not?
> 3. What is the purpose of relax mass_change.
>
>
>
>  I request you  Please clarify.
>
> With regards
>
> Harish Kumar
>
>
> On Tue, 17 Aug, 2021, 07:56 Wolf, William M, <WOLFWM at uwec.edu> wrote:
>
>> You can still do that. You just need to relax the value of mass_change
>> over many time steps (which can be short) rather than turning it on
>> instantaneously. Once the new value of mass_change is achieved, it can
>> remain at the high value indefinitely. It’s the process of getting from one
>> value of mass_change to another that requires the relaxation process.
>>
>> For instance, you might relax the value of mass_change slowly over 100
>> years of evolution, and then leave it on at the new constant high rate for
>> 100,000 more years of evolution.
>>
>> Regards,
>>
>> Bill Wolf
>> ------------------------------
>> *From:* harish sorrout <harishsorrout at gmail.com>
>> *Sent:* Monday, August 16, 2021 8:11:01 PM
>> *To:* Wolf, William M <WOLFWM at uwec.edu>
>> *Cc:* Mesa-users <mesa-users at lists.mesastar.org>
>> *Subject:* Re: [Mesa-users] taking very small steps during accretion
>>
>> Thanks for the tip!
>> But sir I wanted to study long term evolution of steady buring of helium
>> during accretion on to WD i.e accretion with fixed rate. Also some people
>> have done this with such high accretion rates.
>>
>>
>> On Tue, 17 Aug, 2021, 02:37 Wolf, William M, <WOLFWM at uwec.edu> wrote:
>>
>> Hi Harish,
>>
>>
>>
>> It looks like in your inlist, you have mass_change = 1.5d6. I advise that
>> instead of just turning on the mass change full blast, you ramp it over
>> time. In particular, I’d look at the relax_mass_change controls, which let
>> you change the value of mass_change over time.
>>
>>
>>
>> However, with such a high accretion rate, you might have to do this in
>> steps, as this control increases the accretion rate linearly. That is, if
>> you ramp things up from 0 to 1.5d-6 over 100 timesteps, the very first
>> timestep will abruptly turn on accretion at 1.5d-8 Msun/yr, which may also
>> be too fast. Perhaps first adjust it to 1d-8, save a model, and then adjust
>> it again to your final accretion rate. If the model you are loading was
>> already accreting matter, you may be able to be more aggressive and do this
>> in one relaxation.
>>
>>
>>
>> Good luck!
>>
>>
>>
>> Regards,
>>
>>
>>
>> Bill Wolf
>>
>>
>>
>> *From: *Mesa-users <mesa-users-bounces at lists.mesastar.org> on behalf of
>> harish sorrout via Mesa-users <mesa-users at lists.mesastar.org>
>> *Date: *Monday, August 16, 2021 at 6:09 AM
>> *To: *Mesa-users <mesa-users at lists.mesastar.org>
>> *Subject: *[Mesa-users] taking very small steps during accretion
>>
>> Respected sir,
>>
>>
>>
>> I am performing a simulation of long term evolution of WD accreting
>> matter with accretion rate 1d-6 on my laptop with 4 threads and 16 GB ram.
>> It is taking very small time steps and to increase time steps I have done
>> many things like change mesh_coeff, var_control but I have failed to
>> increase the time steps and I have run it more than 3-4 days. I wanted to
>> achieve the Chandrasekhar limit of WD but it looks very different with this
>> time step . because it will take 20 to 25 days to achieve ch mass limit.
>> Here I am sharing an inlist file and TRHO plot.
>>
>>
>>
>> kindly help me where am i wrong. and how can i achieve the target.
>>
>>
>>
>> Thanking you
>>
>>
>>
>> with regards
>>
>> Harish kumar
>>
>> research scholar
>>
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