ORCA
Online Research @ Cardiff

# Adaptive smoothing lengths in SPH

 Attwood, Rhianne Elizabeth, Goodwin, S. P. and Whitworth, Anthony Peter 2007. Adaptive smoothing lengths in SPH. Astronomy & Astrophysics 464 (2) , pp. 447-450. 10.1051/0004-6361:20066606

 Preview
PDF - Published Version

## Abstract

Context.There is a need to improve the fidelity of SPH simulations of self-gravitating gas dynamics. Aims.We remind users of SPH that, if smoothing lengths are adjusted so as to keep the number of neighbours, ${\cal N}$, in the range ${\cal N}_{{\rm NEIB}}\pm\Delta{\cal N}_{{\rm NEIB}}$, the tolerance, $\Delta{\cal N}_{{\rm NEIB}}$, should be set to zero, as first noted by Nelson & Papaloizou. We point out that this is a very straightforward and computationally inexpensive constraint to implement. Methods.We demonstrate this by simulating acoustic oscillations of a self-gravitating isentropic monatomic gas-sphere (cf. Lucy), using ${\cal N}_{{\rm TOT}}\sim6000$ particles and ${\cal N}_{{\rm NEIB}}=50$. Results.We show that there is a marked reduction in the rates of numerical dissipation and diffusion as $\Delta{\cal N}_{{\rm NEIB}}$ is reduced from 10 to zero. Moreover this reduction incurs a very small computational overhead. Conclusions.We propose that this should become a standard test for codes used in simulating star formation. It is a highly relevant test, because pressure waves generated by the switch from approximate isothermality to approximate adiabaticity play a critical role in the fragmentation of collapsing prestellar cores. Since many SPH simulations in the literature use ${\cal N}_{{\rm NEIB}}=50$ and $\Delta{\cal N}_{{\rm NEIB}}\geq10$, their results must be viewed with caution.

Item Type: Article Publication Published Physics and Astronomy Q Science > QB Astronomy hydrodynamics -- methods ; numerical -- stars ; oscillations Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 16/04/2014) EDP Sciences 0004-6361 30 March 2016 04 Jun 2017 04:55 http://orca-mwe.cf.ac.uk/id/eprint/46418