Break-Through Opportunities in Modeling Star and Planet Formation with DISPATCH
By Åke Nordlund (Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen)
Tuesday 19 Sep
Place: Room 507 (Pere Pascual), 5th floor
The new DISPATCH code framework promises great new opportunities in the modeling of star and planet formation – contexts that require extreme ranges of scales to be covered, in order to avoid having to impose arbitrary initial and boundary conditions. Starting out from the observationally well-constrained conditions at scales of tens of parsecs (~1020 cm), there are about 5 orders of magnitude down to outer scales of protoplanetary disks, about 9 orders of magnitude down to the outer scales of planet formation (Hill spheres), and about 14 orders of magnitude down to the scale heights of rocky planet atmospheres.
Simulations covering the whole range of scales are now within reach, using the new high-performance simulation framework DISPATCH. DISPATCH uses a hybrid MPI/OpenMP execution model, where tasks are controlled by a rank-local `dispatcher'. The definition of a task can vary, for example, with some solving the equations of ideal magnetohydrodynamics (MHD), others non-ideal MHD, radiative transfer, or the motions of and accretion onto sink particles, representing newly formed stars. A feature of decisive importance for the overall performance of the framework is that time steps are determined and applied locally; this allows large reductions in computing time when the allowed time step varies greatly across the computational domain.
The framework generally relies on already existing solvers, whose performance is augmented when run under the framework, due to more efficient cache usage, vectorization, local time stepping, plus near linear and in principle, unlimited OpenMP and MPI scaling.