Team GRAAL

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Section: Application Domains

Cosmological Simulations

Ramses (http://www.projet-horizon.fr/ )is a typical computational intensive application used by astrophysicists to study the formation of galaxies. Ramses is used, among other things, to simulate the evolution of a collisionless, self-gravitating fluid called “dark matter” through cosmic time. Individual trajectories of macro-particles are integrated using a state-of-the-art “N body solver”, coupled to a finite volume Euler solver, based on the Adaptive Mesh Refinement technique. The computational space is decomposed among the available processors using a mesh partitioning strategy based on the Peano-Hilbert cell ordering.

Cosmological simulations are usually divided into two main categories. Large scale periodic boxes requiring massively parallel computers are performed on a very long elapsed time (usually several months). The second category stands for much faster small scale “zoom simulations”. One of the particularity of the HORIZON project is that it allows the re-simulation of some areas of interest for astronomers.

We designed a Grid version of Ramses through the Diet middleware. From Grid'5000 experiments we proved Diet is capable of handling long cosmological parallel simulations: mapping them on parallel resources of a Grid, executing and processing communication transfers. The overhead induced by the use of Diet is negligible compared to the execution time of the services. Thus Diet permits to explore new research axes in cosmological simulations (on various low resolutions initial conditions), with transparent access to the services and the data.


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