Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Sink Particles and Applications for FLASH
Christoph Federrath (Monash University)Paul Clark (University of Heidelberg)Thomas Peters (Zurich University)Philipp Girichidis (University of Hamburg)Daniel Seifried (University of Hamburg)...
Robi BanerjeeHamburger Sternwarte
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Why Sink Particles?
• modeling of dense regions in collapse simulations, e.g. star formation (M.Bate et al. 1995)• ‘controlled’ violation of the Truelove criterion (Truelove et al. 1997): preventing artificial fragmentation by resolving the Jeans length• allows long term runs of star forming regions: binaries, stellar clusters, outflows also: feedback, drag forces, ... • BUT: ‘arithmetic’ part of the system, i.e. ⇒ physical interpretation?
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
ImplementationBased Paul Ricker’s particle module in FLASH• handles boundaries• moves particles across CPUs/blocks• mapping of grid variables onto particles and vice versa• advances particles
Extensions / modifications:• creation of particles on the ‘fly’• gravity: use 1/r2 force for particle contribution• time dependent particle masses: accretion / loss• momentum transfer onto the particles• back-reaction onto the grid (feedback)• MPI communication of global particle list
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Implementation• Gravity
originally:1. mapping of particle density onto grid (CIC, NGP, TSC)2. solve Poisson’s equation with gas-density + particle-density3. map acceleration to particle4. advance particle (Euler, Leapfrog)
Sink Particle Module:• use direct acceleration from particles ⇒ more accurate (e.g. binary system)
⇒ faster for small particle numbers
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Implementation• Gravity
with 1/r2 → f(r,rsoft) : gravitational softening
particles
grid
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Implementation
• Gravitational softening
Linear
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Sub-Cycling
• close “binary” interaction can limit time step:
⇒ sub-cycle on particle-particle interaction till:
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Sub-Cycling
• after 10 orbits
Federrath et al. 2010
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Sub-Cycling
• after 1000 orbits (two particles around the common center)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Particle creation
Implementation
Conditions by gravitational collapse:
0. Density criterion (within accretion radius raccr):
ρgas > ρcrit (ρcrit parameter)
⇒ choose ρcrit so that Truelove criterion is not violated:
λJ > NJ Δxmin
Jeans refinement condition available (λJ = (πc2/Gρ)1/2)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Particle creation
Implementation
Federrath, RB, Clark, Klessen, ApJ 2010
Conditions by gravitational collapse:
0. Density criterion: ρgas > ρcrit (ρcrit parameter)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Particle creation
Implementation
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Mass accretion / momentum transfer
Implementation
• Mass accretion from excess gas density within ri < raccr :
Mi = Mi + Σj ΔVolj (ρj − ρcrit)
• Check for convergent flow, i.e. vrad < 0• Mass conservation ensured
• linear momentum conservation:
Pi = Pi + Σj Δmj vj
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• angular momentum
Implementation
no unique solution for angular momentum conservation:
⇒ internal spin:
use for sub-grid modelling, e.g. outflows from young stars
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Particle merging (optional)
Implementation
dynamicalmerging
• merged particle at center of mass • ensures conservation of mass, momentum and spin
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Inter CPU communication
Implementation
Communicate global particle list (Module GetInfoAllParticle)
CPU1 CPU2
raccr
Sink
Use global list• to find particles• for gas-sink interaction• sink-sink interaction• “integrate” quantities (e.g. mass within sink-radius)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Tests
• sinks in an external potential (SIS density profile)• sink refinement
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Tests
• sinks in an external potential (SIS density profile)• sink refinement• sub-cycling necessary
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
• Star cluster formation (Philipp Girichidis)• Self-consistent jet-launching (Daniel Seifried)
+ Feedback (sub-grid models):• radiation feedback (Thomas Peters, Mikhail Klassen)• Jets/Outflows (Martin Schrön)• Supernovae• gas drag ....
Applications
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Comparison to SPH implementation
• collapse of turbulent cloud cores (see also Philipp Girichids’ talk)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Comparison to SPH implementation
• collapse of turbulent cloud cores (see also Philipp Girichids’ talk)
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Comparison to SPH implementation
• good agreement• differences due to hydro ⇒ SPH slightly more dissipative
⇒ cluster more centrally condensed
Federrath et al. 2010
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Applications
feedback from ionizing radiation by Thomas Peters
disc formation and jet launching by Daniel Seifried
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Outflows form YSOs
Sub-grid modelling
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Outflows form YSOs
Sub-grid modelling
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
SN Feedback
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Particle-Gas drag
• “easy” implementations of gas-particle interaction• e.g. particle-gas drag via elastic scattering
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Particle-Gas drag
• “easy” implementations of gas-particle interaction• e.g. particle-gas drag via elastic scattering
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Particle-Gas drag
• “easy” implementations of gas-particle interaction• e.g. particle-gas drag via elastic scattering
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Particle-Gas drag
• “easy” implementations of gas-particle interaction• e.g. particle-gas drag via elastic scattering
Robi Banerjee, FLASH Workshop, Hamburger Sternwarte, Feb 15th 2012
Outlook• prospect for many more applications: e.g. planets in viscous disks, ...• further intrinsic properties
• chemical properties for chemical networks• sticking properties: build up of planetesimals• non rigid body for angular momentum exchange• ...
• more flexible interfaces to use for sub-grid modelling (so far: only one big module)• combine with Tree-Gravity Code (Richard Wünsch) ⇒ faster gravity
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