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

Fri May 27 16:45:28 EDT 2016

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 <mailto:rjfarmer at asu.edu>>
>> *Sent:* Thursday, May 26, 2016 11:32:20 PM
>> *To:* Ryan Mckinven
>> *Cc:* mesa-users at lists.sourceforge.net 
>> <mailto: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 <mailto: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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