The discussion revolves around the search for publicly available collision simulators for planets that utilize Smoothed Particle Hydrodynamics (SPH). Participants explore existing software options, their capabilities, and limitations regarding planetary collision simulations.
Participants express differing views on the capabilities of GADGET 2 regarding planetary collisions, with some asserting it cannot perform such simulations while others believe it could be adapted with the right setup. The discussion remains unresolved regarding the availability of a suitable SPH simulator for planetary collisions.
Participants highlight limitations in existing software, particularly regarding the generation of initial conditions and the interpretation of output data. There are also mentions of specific formats and requirements for using GADGET 2 effectively.
Sadly that doesn't do planetary collisions.|Glitch| said:GADGET 2 - "GADGET computes gravitational forces with a hierarchical tree algorithm (optionally in combination with a particle-mesh scheme for long-range gravitational forces) and represents fluids by means of smoothed particle hydrodynamics (SPH)." - Free software, released in May 2005
MrQuack said:Bump, don't know when i can bump but I haven't found a rule book thing
Ah sorry. I didn't see thatDrakkith said:The link to PF Terms and Rules can be found at the bottom right of every page on the site and under the "Info" tab at the top.
Per the rules:
Bumping
Do not "bump" one of your threads to the top of a forum's thread list by posting a basically empty message to it, until at least 24 hours have passed since the latest post in the thread; and then do it only once per thread.
MrQuack said:Sadly that doesn't do planetary collisions.
afaik I don't know any way to create new conditions for it. The .param file is just for the loading and not the objects. a.k.a It doesn't say where the particles and motion it just says stuff like when the simulation should end & write the files for loading.phyzguy said:Why do you say it doesn't do planetary collisions? If you have gravity and fluid mechanics, what in your mind is missing? Why isn't it just a matter of setting up the initial conditions properly?
Oh also it is for gas and dark matter simulations.MrQuack said:afaik I don't know any way to create new conditions for it. The .param file is just for the loading and not the objects. a.k.a It doesn't say where the particles and motion it just says stuff like when the simulation should end & write the files for loading.
MrQuack said:afaik I don't know any way to create new conditions for it. The .param file is just for the loading and not the objects. a.k.a It doesn't say where the particles and motion it just says stuff like when the simulation should end & write the files for loading.
I mean, the data is .dat files and it's binary littleendian and bigendian so it's very very hard to interpret it!phyzguy said:You will need to write code to generate the particle initial conditions. If you don't know how to do this, then you won't know how to interpret the simulator output either, because it is just files with lists of particle positions and velocities. I think Gadget could do the job, but I won't argue the point. I know that Rosswog's group uses the SPH code MAGMA to simulate neutron star collisions, but as far as I know it is not publicly available.
#!/usr/bin/env python
from pylab import *
import arraydef ReadGadgetICFile(filename):# Reads an initial conditions file
class ICfile:
pass
icfile = ICfile()
file = open(filename,"rb")
icfile.header = ReadGadgetHeader(file) # Header data
icfile.data = ReadGadgetData(file, icfile.header,1)
file.close()
return icfile
def ReadGadgetHeader(file): # Reads the header of the snapshot or IC file
class HeadData:
pass
header=HeadData()
header.blocksize = array.array("i")
header.Npart = array.array("I")
header.Massarr = array.array("d")
header.Time = array.array("d")
header.Redshift = array.array("d")
header.FlagSfr = array.array("i")
header.FlagFeedback = array.array("i")
header.Nall = array.array("i")
header.FlagCooling = array.array("i")
header.NumFiles = array.array("i")
header.BoxSize = array.array("d")
header.Omega0 = array.array("d")
header.OmegaLambda = array.array("d")
header.HubbleParam = array.array("d")
header.FlagAge = array.array("i")
header.FlagMetals = array.array("i")
header.NallHW = array.array("i")
header.flag_entr_ics = array.array("i")
header.unused = array.array("i")
header.blocksize.fromfile(file,1)
header.Npart.fromfile(file,6)
header.Massarr.fromfile(file,6)
header.Time.fromfile(file,1)
header.Redshift.fromfile(file,1)
header.FlagSfr.fromfile(file,1)
header.FlagFeedback.fromfile(file,1)
header.Nall.fromfile(file,6)
header.FlagCooling.fromfile(file,1)
header.NumFiles.fromfile(file,1)
header.BoxSize.fromfile(file,1)
header.Omega0.fromfile(file,1)
header.OmegaLambda.fromfile(file,1)
header.HubbleParam.fromfile(file,1)
header.FlagAge.fromfile(file,1)
header.FlagMetals.fromfile(file,1)
header.NallHW.fromfile(file,6)
header.flag_entr_ics.fromfile(file,1)
header.unused.fromfile(file,15)
header.blocksize.fromfile(file,1)
return header
def ReadGadgetData(file,header,filetype):
# Reads the data (position, velocity, mass, ...)
# filetype=0->snapshot file, filetype=1->IC file
class Data:
pass
data=Data()
Npart=header.Npart
Massarr=header.Massarr
Ngas=header.Npart[0]
N=0
for i in range(6):
N = N+Npart[i]
Nm=0
for i in range(6):
if Massarr[i]==0:
Nm = Nm+Npart[i]
data.blocksize = array.array("i")
data.pos = array.array("f")
data.vel = array.array("f")
data.id = array.array("i")
data.masses = array.array("f")
data.u = array.array("f")
data.rho = array.array("f")
if header.FlagCooling[0]==1:
data.ne = array.array("f")
data.np = array.array("f")
data.hsml = array.array("f")
data.blocksize.fromfile(file,1)
data.pos.fromfile(file,3*N)
data.blocksize.fromfile(file,1)
data.blocksize.fromfile(file,1)
data.vel.fromfile(file,3*N)
data.blocksize.fromfile(file,1)
data.blocksize.fromfile(file,1)
data.id.fromfile(file,N)
data.blocksize.fromfile(file,1)
if Nm!=0:
data.blocksize.fromfile(file,1)
data.masses.fromfile(file,Nm)
data.blocksize.fromfile(file,1)
if Ngas!=0:
data.blocksize.fromfile(file,1)
data.u.fromfile(file,Ngas)
data.blocksize.fromfile(file,1)
if filetype==0:
data.blocksize.fromfile(file,1)
data.rho.fromfile(file,Ngas)
data.blocksize.fromfile(file,1)
if header.FlagCooling[0]==1:
data.blocksize.fromfile(file,1)
data.ne.fromfile(file,Ngas)
data.blocksize.fromfile(file,1)
data.blocksize.fromfile(file,1)
data.np.fromfile(file,Ngas)
data.blocksize.fromfile(file,1)
data.blocksize.fromfile(file,1)
data.hsml.fromfile(file,Ngas)
data.blocksize.fromfile(file,1)
return data
icfile = ReadGadgetICFile('bullet.dat')
id = 17
print "Particle # %d has mass %f, position (%f,%f,%f), and velocity (%f,%f,%f)"%(icfile.data.id[id], icfile.data.masses[id], icfile.data.pos[id], icfile.data.pos[id+1], icfile.data.pos[id+2], icfile.data.vel[id], icfile.data.vel[id+1], icfile.data.vel[id+2])