Research output: Contribution to journal › Article

Original language | English |
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Pages (from-to) | 619-648 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 319 |

State | Published - 1 Dec 2000 |

We analyse the performance of 12 different implementations of Smoothed
Particle Hydrodynamics (SPH) using seven tests designed to isolate key
hydrodynamic elements of cosmological simulations which are known to
cause the SPH algorithm problems. In order, we consider a shock tube,
spherical adiabatic collapse, cooling flow model, drag, a cosmological
simulation, rotating cloud-collapse and angular momentum transport. In
the implementations special attention is given to the way in which force
symmetry is enforced in the equations of motion. We study in detail how
the hydrodynamics are affected by different implementations of the
artificial viscosity including those with a shear-correction
modification. We present an improved first-order smoothing-length update
algorithm that is designed to remove instabilities that are present in
simple forward prediction algorithms. Gravity is calculated using the
adaptive particle-particle, particle-mesh algorithm. For all tests we
find that the artificial viscosity is the single most important factor
distinguishing the results from the various implementations. The shock
tube and adiabatic collapse problems show that the artificial viscosity
used in the hydra code prior to version 4.0 performs relatively poorly
for simulations involving strong shocks when compared to a more standard
artificial viscosity. The shear-correction term is shown to reduce the
shock-capturing ability of the algorithm and to lead to a spurious
increase in angular momentum in the rotating cloud-collapse problem. For
the disc stability test, the shear-corrected and previous hydra
artificial viscosities are shown to reduce outward angular momentum
transport. The cosmological simulations produce comparatively similar
results, with the fraction of gas in the hot and cold phases varying by
less than 10 per cent amongst the versions. Similarly, the drag test
shows little systematic variation amongst versions. The cooling flow
tests show that implementations using the force symmetrization of Thomas
& Couchman are more prone to accelerate the overcooling instability
of SPH, although the problem is generic to SPH. The second most
important factor in code performance is the way force symmetry is
achieved in the equation of motion. Most results favour a kernel
symmetrization approach. The exact method by which SPH pressure forces
are included in the equation of motion appears to have comparatively
little effect on the results. Combining the equation of motion presented
by Thomas & Couchman with a modification of the Monaghan &
Gingold artificial viscosity leads to an SPH scheme that is both fast
and reliable.

- HYDRODYNAMICS, METHODS: NUMERICAL, GALAXIES: FORMATION, COSMOLOGY: THEORY

ID: 21663561