Parallel multithreading algorithms forself-gravity computation inESyS-Particle

This thesis describes the design, implementation, and evaluation of efficient algorithms for self-gravity simulations in astronomical agglomerates. Due to the intrinsic complexity of modeling interactions between particles, agglomerate are studied using computational simulations. Self-gravity affects every particle in agglomerates, which can be composed of millions of particles. So, to perform a realistic simulation is computationally expensive. This thesis presents three parallel multithreading algorithms for self-gravity calculation, including a method that updates the occupied cells on an underlying grid and a variation of the Barnes & Hut method that partitions and arranges the simulation space in both an octal and a binary tree to speed up long range forces calculation. The goal of the algorithms is to make efficient use of the underlying grid that maps the simulated environment. The three methods were evaluated and compared over two scenarios: two agglomerates orbiting each other and a collapsing cube. The experimental evaluation comprises the performance analysis of the two scenarios using the two methods, including a comparison of the results obtained and the analysis of the numerical accuracy by the study of the conservation of the center of mass and angular momentum. Both scenarios were evaluated scaling the number of computational resources to simulate instances with different number of particles. Results show that the proposed octal tree Barnes & Hut method allows improving the performance of the self-gravity calculation up to 100 with respect to the occupied cell method. This way, efficient simulations are performed for the largest problem instance including 2,097,152 particles. The proposed algorithms are efficient and accurate methods for self-gravity simulations in astronomical agglomerates

Small Solar System Bodies as granular media

Asteroids and other Small Solar System Bodies (SSSBs) are of high general and scientific interest in many aspects. The origin, formation, and evolution of our Solar System (and other planetary systems) can be better understood by analysing the constitution and physical properties of small bodies in the Solar System. Currently, two space missions (Hayabusa2, OSIRIS-REx) have recently arrived at their respective targets and will bring a sample of the asteroids back to Earth. Other small body missions have also been selected by, or proposed to, space agencies. The threat posed to our planet by near-Earth objects (NEOs) is also considered at the international level, and this has prompted dedicated research on possible mitigation techniques. The DART mission, for example, will test the kinetic impact technique. Even ideas for industrial exploitation have risen during the last years. Lastly, the origin of water and life on Earth appears to be connected to asteroids. Hence, future space mission projects will undoubtedly target some asteroids or other SSSBs. In all these cases and research topics, specific knowledge of the structure and mechanical behaviour of the surface as well as the bulk of those celestial bodies is crucial. In contrast to large telluric planets and dwarf planets, a large proportion of such small bodies is believed to consist of gravitational aggregates (‘rubble piles’) with no—or low—internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges). Bodies with such structure can sustain some plastic deformation without being disrupted in contrast to the classical visco-elastic models that are generally valid for planets, dwarf planets, and large satellites. These SSSBs are hence better described through granular mechanics theories, which have been a subject of intense theoretical, experimental, and numerical research over the last four decades. This being the case, it has been necessary to use the theoretical, numerical and experimental tools developed within soil mechanics, granular dynamics, celestial mechanics, chemistry, condensed matter physics, planetary and computer sciences, to name the main ones, in order to understand the data collected and analysed by observational astronomy (visible, thermal, and radio), and different space missions. In this paper, we present a review of the multi-disciplinary research carried out by these different scientific communities in an effort to study SSSBs.Made possible by the International Space Science Institute (ISSI, Bern) support to the international team “Asteroids and Self-Gravitating Bodies as Granular Systems”