<p> Despite numerous efforts to better understand binary star evolution, some aspects of it remain poorly constrained. In particular, the evolution of eccentric binaries has remained elusive mainly because the Roche lobe formalism derived for circular binaries does not apply, and other approximations must be used. Here, we report the results of our Smoothed Particle Hydrodynamics simulations of eccentric binaries using a novel way of modeling only the outermost layers of the stars with appropriate boundary conditions. We find that our boundary treatment conserves energy well and that it is well suited for the modeling of interacting binary stars. Using this new technique, along with properly relaxed model stars, we find clear trends in the mass transfer episodes. In particular, we show that these episodes can be described by Gaussians with a FWMH of ~ 0.12 P orb and that the peak rates occur after periastron, around an orbital phase of ~ 0.55, independent of the eccentricity and masses of the stars. The accreted material, on the other hand, is observed to form a rather sparse envelope around either or both stars. Although the fate of this envelope is not modeled in our simulations, we show that a constant fraction (~5%) of the material transferred is ejected from the systems. We discuss this result in terms of the poorly constrained non-conservative mass transfer scenario and argue that it can help calibrate it. Finally, we discuss the limitations of our technique and conditions under which it performs best. The results presented in this thesis represent an improvement upon previous hydrodynamical work and could be used in analytical and binary population synthesis studies to better constrain the evolution of eccentric binaries and the formation of exotic stellar populations. </p> / Thesis / Doctor of Philosophy (PhD)

Two of the methods common in video game fluid simulation are SmoothedParticle Hydrodynamics (SPH), and Position Based Dynamics (PBD). They are both Lagrangian methods of fluid simulation. SPH has been used for many years in offline simulations and has truthful visuals, but is not as stable as the newer method PBD when using larger timesteps. SPH also tends to become unstable during compression. In this report both methods have been tested on different scenarios as the methods’ performance and visual depend on the scenario used. Additionally, the size of the particle radius was varied when comparing Compressible SPH (CSPH), Weak Compressible SPH (WCSPH), and PBD. From these tests, the conclusion could be drawn that CSPH performed slightly better than PBD regarding frames per second (FPS) in all cases except one. However, WCSPH and sometimes CSPH had stability issues. The stability of PBD and its possibility for larger timesteps with only minor FPS difference lead to the conclusion that PBD is overall the more suitable method for fluid simulation in video games. / Två av metoderna som är vanliga vid vätskesimulering i videospel är SmoothedParticle Hydrodynamics (SPH) och Position Based Dynamics (PBD). De är båda Lagrangiska metoder för vätskesimulering. SPH har använts i många år i offline-simuleringar och har realistiskt utseende, men är inte lika stabil som den nyare metoden PBD vid användning av större tidssteg. SPH tenderar också att bli instabil under kompression. Båda metoderna blev testade i olika scenarion eftersom deras prestanda och utseende beror på det använda scenariot. Storleken av partikelradien har också varierat när Compressible SPH (CSPH), Weak Compressible SPH (WCSPH) och PBD jämfördes. Från dessa tester kunde man se att CSPH presterade lite bättre än PBD gällande bilder per sekund (FPS) i alla fall utom ett. Däremot hade WCSPH och ibland CSPH stabilitetsproblem. Stabiliteten av PBD och dess möjlighet att ta större tidssteg med endast minimala FPS skillnader ledde till slutsatsen att PBD är överlag den mer lämpliga metoden för vätskesimulering i videospel.