1. Simulation cases of advanced driver-assistance systemsOliver Angelov, 2023, diplomsko delo Opis: In the bachelor’s thesis, advanced driver-assistance systems are discussed and explained. The focus of the explanation is placed on two specific systems, the anti-lock braking system and the automatic transmission system. To provide a deeper understanding of these systems, simulations were created using the computer program. Computer simulation is explained and the types of computer simulation are discussed. Programs used for computer simulation are presented and explained. The program used for computer simulation in this bachelor’s thesis is Scicos, and the visual and interactive representation of the anti-lock braking system and the automatic transmission system is made. For the anti-lock braking system, the simulation scheme is divided into models representing various components of the system, such as the vehicle, wheel, slip, friction, and control. Each of these models interacts with one another to replicate the functioning of the anti-lock braking system. Similarly, for the automatic transmission system, the simulation scheme is divided into models representing the driver and environment, engine, transmission, vehicle, and controller. These models interact to simulate the operation of the automatic transmission system. The thesis presents the results from the simulation of these two systems to analyze the difference in using the systems in different driving scenarios. The effect of the advanced driver-assistance systems in the vehicles is also showcased.
Ključne besede: Advanced driver-assistance systems, computer simulation, Scicos, anti-lock braking system, automatic transmission system.
Objavljeno v RUNG: 03.10.2023; Ogledov: 836; Prenosov: 9
 Celotno besedilo (3,04 MB) |
2. RELATIVISTIC TIDAL DISRUPTIONS OF REALISTIC STARS BY SUPERMASSIVE BLACK HOLESTaj Jankovič, 2023, doktorska disertacija Opis: Stellar tidal disruption events (TDEs), where a star gets disrupted by strong tidal forces of a supermassive black hole (SMBH), offer a unique opportunity for studies of SMBHs and stellar dynamics in galactic nuclei and provide insights into accretion physics. Currently, there are ≈ 100 observed TDEs, however, this number is expected to increase significantly with the start of new wide-field optical surveys, e.g. with the Vera Rubin Observatory.
We focus on hydrodynamic simulations of TDEs with the smoothed particle hydrodynamics code Phantom. To begin with, we simulate TDEs in a general relativistic and Newtonian description of an SMBH’s gravity. Stars, which are placed on parabolic orbits with different parameters β (to be defined here), are constructed with the stellar evolution code MESA and therefore have realistic stellar density profiles. We study the mass fallback rate of the debris Ṁ, a quantity often assumed to determine the TDE light curves, and its dependence on the β, stellar mass and age as well as the black hole’s spin and the choice of the gravity’s description. We find that relativistic disruptions at the same pericenter distance are stronger than disruptions in a Newtonian description of the SMBH’s gravity. We also determine the differences between Ṁ of realistic stars with various ages and masses. In addition, we characterize the effect of SMBH’s rotation on the Ṁ and find that it depends on the orientation of SMBH’s spin vector relative to the stellar orbital angular momentum. Encounters on prograde orbits result in narrower Ṁ curves with higher peak values, while the opposite occurs for retrograde orbits.
Stellar disruption results in an elongated stream of gas that partly falls back to the pericenter. Due to apsidal precession, the returning stream may collide with itself, leading to a self-crossing shock that launches an outflow. If the black hole spins, this collision may additionally be affected by Lense-Thirring precession which can cause an offset between the two stream components. We study the impact of this effect on the outflow properties by carrying out local simulations of collisions between offset streams. As the offset increases, we find that the geometry of the outflow becomes less spherical and more collimated along the directions of the incoming streams, with less gas getting unbound by the interaction. However, even the most grazing collisions we consider significantly affect the trajectories of the colliding gas, likely promoting subsequent strong interactions near the black hole and rapid disc formation. We analytically compute the offset to stream width ratio, finding that even slowly spinning black holes can cause both strong and grazing collisions. We propose that the deviation from outflow sphericity may enhance the self-crossing shock luminosity due to a reduction of adiabatic losses, and cause significant variations of the efficiency at which X-ray radiation from the disc is reprocessed to the optical band depending on the viewing angle. These potentially observable features hold the promise of constraining the black hole spin from tidal disruption events.
Ključne besede: Computer modelling and simulation, hydrodynamics, black holes, infall
Objavljeno v RUNG: 29.08.2023; Ogledov: 710; Prenosov: 9
Celotno besedilo (16,29 MB) |
3. A study of stellar debris dynamics during a tidal disruption eventAurora Clerici, 2020, doktorska disertacija Opis: The number of observed tidal disruption events is increasing rapidly with the advent of new surveys. Thus, it is becoming increasingly important to improve TDE models using different stellar and orbital parameters.
We study the dynamical behaviour of tidal disruption events produced by a massive black hole like Sgr A* by changing different initial orbital parameters, taking into account the observed orbits of S stars. Investigating different types of orbits and penetration factors is important since their variations lead to different timescales of the tidal disruption event debris dynamics, making mechanisms such as self-crossing and pancaking act strongly or weakly, thus affecting the circularisation and accretion disk formation.
We have performed smoothed particle hydrodynamics simulations. Each simulation consists in modelling the star with $10^5$ particles, and the density profile is described by a polytrope with $\gamma$ = 5/3. The massive black hole is modelled with a generalised post-Newtonian potential, which takes into account relativistic effects of the Schwarzschild space-time.
Our analyses find that mass return rate distributions of solar-like stars and S-like stars with same eccentricity have similar durations, but S-like stars have higher mass return rate, as expected due to their larger mass. Regarding debris circularisation, we identify four types of evolution, related to the mechanisms and processes involved during circularisation: in type 1 the debris does not circularise efficiently, hence a disk is not formed or is formed after relatively long time; in type 2 the debris slowly circularises and eventually forms a disk with no debris falling back; in type 3 the debris relatively quickly circularises and forms a disk while there is still debris falling back; finally, in type 4 the debris quickly and efficiently circularises, mainly through self-crossings and shocks, and forms a disk with no debris falling back. Finally, we find that the standard relation of circularisation radius $r_{\rm circ} = 2r_{\rm t}$ holds only for $\beta = 1$ and eccentricities close to parabolic.
Ključne besede: 07.05.Tp Computer modeling and simulation, 95.30.Lz Hydrodynamics, 98.35.Jk Galactic center, bar, circumnuclear matter, and bulge, 98.62.Js Galactic nuclei (including black holes), circumnuclear matter, and bulges, 98.62.Mw Infall, accretion, and accretion disks
Objavljeno v RUNG: 29.09.2020; Ogledov: 3616; Prenosov: 77
Celotno besedilo (37,55 MB) |
