GRADSPH: A parallel smoothed particle hydrodynamics code for self-gravitating astrophysical fluid dynamics

We describe the algorithms implemented in the first version of GRADSPH, a parallel, tree-based, smoothed particle hydrodynamics code for simulating self-gravitating astrophysical systems written in FORTRAN 90. The paper presents details on the implementation of the Smoothed Particle Hydro (SPH) description, where a gridless approach is used to model compressible gas dynamics. This is done in the conventional SPH way by means of ‘particles’ which sample fluid properties, exploiting interpolating kernels. The equations of self-gravitating hydrodynamics in the SPH framework are derived self-consistently from a Lagrangian and account for variable smoothing lengths (‘GRAD-h’) terms in both the hydrodynamic and gravitational acceleration equations. A Barnes–Hut tree is used for treating self-gravity and updating the neighbour list of the particles. In addition, the code updates particle properties on their own individual timesteps and uses a basic parallelisation strategy to speed up calculations on a parallel computer system with distributed memory architecture. Extensive tests of the code in one and three dimensions are presented. Finally, we describe the program organisation of the publicly available 3D version of the code, as well as details concerning the structure of the input and output files and the execution of the program.Program summaryProgram title: GRADSPH 1.0Catalogue identifier: AECX_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECX_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 11 123No. of bytes in distributed program, including test data, etc.: 1 561 909Distribution format: tar.gzProgramming language: Fortran 90/MPIComputer: HPC clusterOperating system: UnixHas the code been vectorised or parallelised?: YesRAM: 56 Mwords with 1.2 million particles on 1 CPUWord size: 32 bitsClassification: 12Nature of problem: Evolution of a self-gravitating fluid.Solution method: Hydrodynamics is described using SPH, self-gravity using the Barnes–Hut tree method.Running time: The test case provided with the distribution takes less than 10 minutes for 500 time steps on 10 processors.