Survivability of planetary systems in young and dense star clusters

GalaxiesComputational astrophysic

The Oceanographic Multipurpose Software Environment

Computational astrophysic

HyMUSE: a multi-model framework for Hydrology

Computational astrophysic

Steady-state Reynolds-stress simulations of a stirred tank

This report describes steady-state predictions of the turbulent flow generated by a disc turbine inside a baffled tank. The impeller has been modeled by prescribing experimental flow profiles in the outflow of the impeller. The effects of these boundary conditions and of the grid size and turbulence model have been investigated. The turbulence models also have been investigated in a simpler channel-flow situation to asses the effect of different modeling parameters. No grid independent solutions could be found. Still, one grid has been chosen on which accurate and efficient simulations could be made. On this grid, simulations as to. the effect of the impeller boundary conditions showed that using the correct mean velocity profiles is important. Using appropriate dissipation rate and kinetic energy profiles is important to model the turbulence correctly. The effect of errors in the Reynolds stress cross terms was found to be small. Simulations as to the channel flow showed that the k-e and Reynolds stress models can predict the mean velocity and kinetic energy correctly. The error found in the predicted anisotropy tensor was found to be significant. This error was related to the boundary conditions. In the stirred tank, the k-e model was found to provide better predictions inside the impeller outflow, while the Reynolds stress model predicts the flow inside the bulk region more accurately.Kramers Laboratorium voor Fysische TechnologieApplied Science

Multi-scale high-performance computing in astrophysics: simulating clusters with stars, binaries and planets

Computational astrophysic

The signatures of the parental cluster on field planetary systems

Due to the high stellar densities in young clusters, planetary systems formed in these environments are likely to have experienced perturbations from encounters with other stars. We carry out direct N-body simulations of multiplanet systems in star clusters to study the combined effects of stellar encounters and internal planetary dynamics. These planetary systems eventually become part of the Galactic field population as the parental cluster dissolves, which is where most presently known exoplanets are observed. We show that perturbations induced by stellar encounters lead to distinct signatures in the field planetary systems, most prominently, the excited orbital inclinations and eccentricities. Planetary systems that form within the cluster's half-mass radius are more prone to such perturbations. The orbital elements are most strongly excited in the outermost orbit, but the effect propagates to the entire planetary system through secular evolution. Planet ejections may occur long after a stellar encounter. The surviving planets in these reduced systems tend to have, on average, higher inclinations and larger eccentricities compared to systems that were perturbed less strongly. As soon as the parental star cluster dissolves, external perturbations stop affecting the escaped planetary systems, and further evolution proceeds on a relaxation time-scale. The outer regions of these ejected planetary systems tend to relax so slowly that their state carries the memory of their last strong encounter in the star cluster. Regardless of the stellar density, we observe a robust anticorrelation between multiplicity and mean inclination/eccentricity. We speculate that the ‘Kepler dichotomy’ observed in field planetary systems is a natural consequence of their early evolution in the parental cluster.Computational astrophysicsStars and planetary system

The Oceanographic Multipurpose Software Environment

Computational astrophysic