Hi Zhengyang,
Let me try to answer your questions:
1. The number of particles of each type is essentially given by your
initial condition file. If you don't have such a file at hand and
want to create initial conditions for cosmological simulations you
can use NGENIC to do so. NGENIC, by default also uses an initial
condition file, however, so if you want to really create initial
conditions from scratch you will need to compile with the
option**CREATE_GRID. In that case the parameter "GridSize"
determines the number of DM particles to be (GridSize)³. NGENIC also
allows you to create gas particles by splitting up the DM particles
giving you 1 DM and 1 gas particle for each DM particle, so 2
x**(GridSize)³ particles in total. In order to enable this, compile
with the option GENERATE_GAS_IN_ICS*.*
2. In principle all you need to know about the particle types is, that
type 0 (i.e. gas) is an SPH particle, i.e. besides gravity also
participates in hydrodynamics, and all other particle types are
collisionless, i.e. only participate in the gravitational
interaction. Of course if you implement your own subgrid model you
can give the other particle types special meaning, and add some
extra physics for them. There are more than two types, so one can
make use of mass tables more efficiently for the different types.
3. As described above "Bndry" is simply a name given to one of the
collisionless particle types. In zoom-in simulations this type is
typically reserved for the DM particles of the low resolution region.
4. This really depends on your implementation of star formation. Some
models transform gas particles directly into star particles, in this
case the total number of particles and also the particles mass is
unchanged. Other models spawn stars from gas particles without
actually disposing of the gas. In that case the spawned star
particles split up some fraction of the total mass of the gas among
themselves. In that case both the number of particles and the mass
of the particles changes.
I hope I could answer your questions!
Best regards,
Leonard
On 01.06.21 18:59, 张正阳 wrote:
>
> Hi,all,
>
> I am now an undergraduate student,and I have read the manual
> carefully,but there are still a few important questions that I don't
> understand.
>
> 1.What is the number of each particle in the simulation.For
> example,we choose Nsample=128,So how many gas particles are there, and
> how many other particles are there.
>
> 2.I now understand that the gas particle is the kind of SPH
> particle, but the other particles, such as disk, are it a
> collision-free gravitational particle or SPH plus collision-free
> particle.
>
> 3.What kind of particle is "Bndry", and does it have any practical
> effect.
>
> 4.In the simulation, will gas particles be transformed into stars
> particles, and if so, will the number or mass of particles be changed.
>
>
> I would be most grateful if you could answer my questions.
>
> Best wishes,
>
> Zhengyang Zhang
>
>
--
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Leonard Romano, B.Sc.（レオナルド・ロマノ）
Physics Department
Technical University of Munich (TUM), Germany
Theoretical Astrophysics Group
Department of Earth and Space Science
Graduate School of Science, Osaka University, Japan
he / him / his
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Received on 2021-06-01 22:07:01