[mesa-users] Removing Mass Convergence Issue ("fix v_center to hit piston_Rmin exactly")

Fri May 27 17:03:54 EDT 2016

So a idea that might do what you want, with regards to removing the ashes.
If you only want the composition gone (but don't mind keeping the mass)
would be to use from:
http://mesa.sourceforge.net/star_job_defaults.html#modifications_to_model

replace_element = .false.
replace_initial_element = .false.
chem_name1 = 'he3'
chem_name2 = 'he4'
replace_element_nzlo = -1
replace_element_nzhi = -1

To replace the ashes with an inert isotope (add an extra isotope to your
network that is much heavier than anything else, such that there are no
nuclear reactions possible between it and the next heaviest isotope).

Which gives me an idea for craig's question which would be to accrete an
amount of an inert isotope to the required total mass, set up a custom
mixing routine to mix that isotope downwards to a prescribed location then
use the replace_element to turn it into whatever the companion is made off.
Whether it would work i don't know...

Rob

On Fri, May 27, 2016 at 1:45 PM, Craig Wheeler <wheel at astro.as.utexas.edu>
wrote:

> As a variation on this theme, is it possible to add mass
> in the middle of a model? I'm thinking of mocking up
> a stellar merger where the swallowed companion might
> not come apart until deep in the envelope of the primary.
>
> Craig
>
>
>
>
> On 5/27/16 2:39 PM, Bill Paxton wrote:
>
> Hi Ryan,
>
> You'll to be sneaky on this one.  the trick with mesa/star is that you
> must always be dealing with a model that is "acceptable" to the newton
> solver.  and that excludes one with its guts ripped out.  we can remove
> cells at surface or at center, but not from the middle.
>
> to make use of results from running previous cases, try to find a way to
> save intermediate models for later use.
> or just learn to put up with the cost of rerunning the accretion each time.
>
> b
>
>
>
> On May 27, 2016, at 12:28 PM, Ryan Mckinven wrote:
>
> Hi,
>
>
> Sorry about that typo. I would like to remove mass from the bottom of the
> modelled *envelope*, though I'm not aware of any direct means of doing
> this. I don't want the inner boundary to shift and I was told to use the
> "remove_center..." controls to achieve this. From my understanding the
> "remove_center..." control tells mesa to remove a certain amount of mass
> from the core and transfers the missing mass from bottom of the envelope to
> the core in order to maintain the boundary condition. Is this correct?
>
>
> My project involves running through a grid of models under different
> accretion conditions (e.g. accretion rate, base heating, etc.). The
> methodology I'm using has me incrementally changing one of these
> conditions after a fixed amount of mass has been accreted. Since each new
> model is evolved from the preceding model I would like to find a way to
> remove some of the thermonuclear ashes of the old model from the bottom of
> the envelope.
>
>
> I've attached the most pertinent inlist to look over. Let me know if you
> have any other questions and I'll try to be more prompt in responding.
>
>
> Thanks in advance!
>
>
> -Ryan
> ------------------------------
> *From:* Robert Farmer < <rjfarmer at asu.edu>rjfarmer at asu.edu>
> *Sent:* Thursday, May 26, 2016 11:32:20 PM
> *To:* Ryan Mckinven
> *Cc:* mesa-users at lists.sourceforge.net
> *Subject:* Re: [mesa-users] Removing Mass Convergence Issue ("fix
> v_center to hit piston_Rmin exactly")
>
> Hi
>
> To clarify when you say remove remove mass from the "bottom of the modeled
> outer", do you mean envelope or core? Remember that MESA models a NS by
> setting an inner boundary condition (at some M,R and L and the for the test
> case will be 1.4Msun, 10km and some L) and puts material on top as the
> envelope of the NS and only evolves that. So are you trying to change the
> inner boundary condition or do something to the envelope?
>
> Inlists are also helpful when trying to describe a problem.
>
> Regards
> Rob
>
>
>
> On Thu, May 26, 2016 at 7:38 PM, Ryan Mckinven <
> ryan.mckinven at mail.mcgill.ca> wrote:
>
>>
>> Hi mesa-users,
>>
>>
>> Operating system: Mac OS X El Capitan
>>
>> Mesa version Number: 8118
>>
>>
>> I'm studying unstable carbon burning on an accreting neutron star using a
>> modified version of the 'ns_c' test suite. I would like to modify mesa to
>> remove mass from the bottom of the modelled outer. To this end, I've tried
>> using the star_job control 'remove_initial_center_at_cell_k' to establish a
>> threshold beyond which mass will be removed but I'm getting a convergence
>> error,
>>
>>
>> "fix v_center to hit piston_Rmin exactly
>>
>>
>>
>> stopping because of convergence problems dt < min_timestep_limit"
>>
>>
>> I've tried increasing 'min_timestep_limit' but get the same error. I was
>> wondering if you have any advice on how to tackle this issue.
>>
>>
>> P.s. I should note that I have used alternative methods of removing mass
>> from the bottom of the modelled envelope using controls like
>> 'removing_center_by_mass_Msun' to no avail.
>>
>>
>> Best Regards,
>>
>> Ryan Mckinven
>>
>>
>>
>>
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> --
> J. Craig Wheeler
> Samuel T. and Fern Yanagisawa Regents Professor of Astronomy
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> 2515 Speedway, Stop C1400
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