Re: gas smoothing length options

From: Nathan Goldbaum <goldbaum_at_ucolick.org>
Date: Tue, 27 Mar 2012 16:27:39 -0700

Hi Dave,

In that case your smoothing lengths will be overwritten when the gas smoothing lengths are recalculated in density.c. If you want to calculate the gas density using the smoothing lengths you're writing out to the initial conditions file, you'll need to modify density.c so they are not immediately overwritten.

Apologies if you already know this, but In general it's a bad idea to impose a non-adaptive smoothing length in SPH calculations. See Price 2012 Section 2.4.

-Nathan

On Mar 27, 2012, at 4:10 PM, David Riethmiller wrote:

> Hi Nathan -
>
> I think I asked the question incorrectly. I want to specify the SPH smoothing length for every particle myself, and not have Gadget compute it. I'm not referring to the gravitational softening length, but rather to the kernel size. According to the Gadget manual (section 6.4), "gas densities, SPH smoothing lengths, and all further blocks need not be provided." What I'm asking is, what if I DO want to specify further blocks, namely the densities and SPH smoothing lengths?
>
> Dave
>
>
>
> On Mar 27, 2012, at 6:19 PM, Nathan Goldbaum wrote:
>
>> Hi David,
>>
>> As far as I know the gas smoothing lengths are already adaptive in Gadget-2. The smoothing lengths are calculated at runtime based on the DesNumNgb parameter so it's not necessary to read them in from an input file. The minimum smoothing length is set by the parameter MinGasHsmlFractional which can be equal to zero if you want to allow the SPH smoothing length to go to zero for dense particle groupings.
>>
>> The gravitational smoothing lengths for SPH particles can be set equal to their SPH smoothing lengths by turning on ADAPTIVE_GRAVSOFT_FORGAS in the makefile.
>>
>> Nathan Goldbaum
>> Graduate Student
>> Astronomy & Astrophysics, UCSC
>> goldbaum_at_ucolick.org
>> http://www.ucolick.org/~goldbaum
>>
>> On Mar 27, 2012, at 3:09 PM, David Riethmiller wrote:
>>
>>> Hi Gadget users -
>>>
>>> Has anyone enabled a variable smoothing length option for gas particles? I'd like to relax the requirement that all type 0 particles have the same smoothing length as set in the control file, and instead include HSML in the list of attributes read in from the initial conditions. I'm about to start editing read_ic.c; am I on the right path?
>>>
>>> Thanks,
>>> Dave
>>>
>>> -------------------------------------------------
>>> David A. Riethmiller
>>> Ph.D. Candidate, Astrophysical Institute
>>> Ohio University
>>>
>>> Clippinger Labs 338
>>> http://www.phy.ohiou.edu/~rieth/
>>>
>>>
>>>
>>>
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>
> -------------------------------------------------
> David A. Riethmiller
> Ph.D. Candidate, Astrophysical Institute
> Ohio University
>
> Clippinger Labs 338
> http://www.phy.ohiou.edu/~rieth/
>
>
>
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Received on 2012-03-28 01:27:43

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