[mesa-users] mass loss, rotation, binaries, and a hydrodynamic surface boundary conditions

[David Arnett]

Nice response Tomasz, and worthy of further discussion. I believe we agree.
Mother Nature has more cores and time steps that we will ever afford. We
must do what we can, keep an open mind, and think very hard.
Dave

On Wed, Jun 17, 2015 at 2:59 PM, Tomasz Plewa <tomekplewa at gmail.com> wrote:

>  If your physics model is wrong, it makes no difference how many cores
> you use.
>
> Someone told me a couple of years ago, "Oh but they are running their code
> on 100,000 cores now!" implying they will know very soon now how the thing
> works. My answer was that mother nature does not need petaflops.
> Statement "we need more computing power" is a construct expressing our
> fundamental inability to explain realities within the adopted (physics,
> computational) model. To escpae that we blame the big iron. Duh.
>
> Or else, we do believe our models are right. Uh-huh.
>
> Tomek
> --
>
> On 06/17/15 14:30, Pablo Marchant wrote:
>
> I would also ask you to elaborate Tomasz. My impression is that the main
> limitation is computing power. Despite some uncertainties, given enough
> computing power we would get very useful insight at least in a qualitative
> level. Probably the biggest issue is that to get a complete enough picture
> it would be necessary to model a system in a timescale comparable to that
> at which accretion is happening, i.e. the thermal timescale of the donor in
> most cases of interest.
>
>  But it would be interesting to see the reaction on shorter timescales of
> the accretion disk when the accreting object reaches critical rotation.
> Would not care about believing it in detail, just the broad picture coming
> from it.
>
> On Wed, Jun 17, 2015 at 8:06 PM, David Arnett <wdarnett at gmail.com> wrote:
>
>>  OK Tomasz, maybe we should be explicit. It would be useful for people
>> who are using approximate methods to know the cause of errors.
>>
>> First, what worries you about the equations? We can write them out
>> generally in an inertial frame in 3D; conservation of mass, momentum and
>> energy, with radiative transfer and MHD. We just can't solve them
>> accurately. Are you thinking of something else?
>>
>> Second, what is wrong with the methods? My favorite worry is that a grid
>> code will have errors because the fluid sweeps through the mesh rapidly,
>> and an SPH code, which can move with the matter, will have resolution too
>> low to represent turbulence. I suppose the issue is a general one with
>> zoning for high Reynolds number and optically thick-thin plasmas.
>>
>>  What are your favorites?
>>
>>  Dave
>>
>> On Wed, Jun 17, 2015 at 11:39 AM, Tomasz Plewa <tomekplewa at gmail.com>
>> wrote:
>>
>>>  No. There is no code in existence that could solve this problem in 3D,
>>> regardless computational resources. The problem is with equations, then
>>> with methods, and perhaps only then with the available computing power.
>>>
>>> Tomek
>>> --
>>>
>>> On 06/17/15 10:44, David Arnett wrote:
>>>
>>>   Hmmm.  It sounds like a problem that can be done, but probably not
>>> with sufficient resolution to be believed in detail, unfortunately. Maybe
>>> when Moore's law has more time to help us.
>>>  Dave
>>>
>>> On Tue, Jun 16, 2015 at 11:55 PM, Pablo Marchant <pamarca at gmail.com>
>>> wrote:
>>>
>>>> There is a big uncertainty in accretion when you reach critical
>>>> rotation. Whether or not the material gets ejected, and how much angular
>>>> momentum it would carry with it has a very large impact on the final fates
>>>> of several binary systems. 3D simulations would certainly be enlightening
>>>> here, but my experience on 3D hydro is definitely insufficient to attempt
>>>> this on my own.
>>>>
>>>> On Mon, Jun 15, 2015 at 9:19 PM, David Arnett <wdarnett at gmail.com>
>>>> wrote:
>>>>
>>>>> This sounds interesting. It seems that you are exploring a region of
>>>>> parameter space in which some of our approximations need to be merged into
>>>>> a more wholistic formulation. We encounter the same sort of issue when we
>>>>> simulate turbulent convection near a boundary in a star. When the flow is
>>>>> no longer radial, interesting new things may happen. We should look for
>>>>> instances in which the purely 1D representation needs more careful thought,
>>>>> and maybe 3D simulation "spot checks" for guidance.
>>>>>
>>>>> --
>>>>> David Arnett
>>>>> Regents Professor
>>>>> Steward Observatory
>>>>> University of Arizona
>>>>>
>>>>> Facts are stubborn, but statistics are more pliable.  Mark Twain
>>>>> Facts do not cease to exist because they are ignored.  Aldous Huxley
>>>>>
>>>>
>>>>
>>>>
>>>>   --
>>>> Pablo Marchant Campos
>>>> M.Sc on Astrophysics, Universidad Católica de Chile
>>>> PhD student, Argelander-Institut für Astronomie
>>>>
>>>
>>>
>>>
>>> --
>>> David Arnett
>>> Regents Professor
>>> Steward Observatory
>>> University of Arizona
>>>
>>> Facts are stubborn, but statistics are more pliable.  Mark Twain
>>> Facts do not cease to exist because they are ignored.  Aldous Huxley
>>>
>>>
>>>  ------------------------------------------------------------------------------
>>>
>>>
>>>
>>> _______________________________________________
>>> mesa-users mailing listmesa-users at lists.sourceforge.nethttps://lists.sourceforge.net/lists/listinfo/mesa-users
>>>
>>>
>>>
>>
>>
>> --
>> David Arnett
>> Regents Professor
>> Steward Observatory
>> University of Arizona
>>
>> Facts are stubborn, but statistics are more pliable.  Mark Twain
>> Facts do not cease to exist because they are ignored.  Aldous Huxley
>>
>
>
>
>  --
> Pablo Marchant Campos
> M.Sc on Astrophysics, Universidad Católica de Chile
> PhD student, Argelander-Institut für Astronomie
>
>
>


-- 
David Arnett
Regents Professor
Steward Observatory
University of Arizona

Facts are stubborn, but statistics are more pliable.  Mark Twain
Facts do not cease to exist because they are ignored.  Aldous Huxley
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