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1.
Monte Carlo simulation of air resistance on an ellipsoid in motion
Veronika Bukina, 2021, magistrsko delo

Opis: The main goal of the master's thesis was the analysis of air resistance on the body in motion in a model that does not require solving the Navier-Stokes equations, but works on the basis of mechanics and statistical physics. The model was a Monte Carlo (MC) simulation of the motion of ideal gas molecules in a closed container in which a body was placed, moving along one of the axes. For the most part of calculations, the approach was used when the body was fixed in the middle of the simulation cell, and one of the components of the molecular velocity had an additional term that simulated the flow, as if the body was moving at this speed in the opposite direction. First of all, a linear dependence of the drag force on speed was found for low flow speed for a flat plate, which was predicted by linear drag law. For high molecular flow rates, the quadratic dependence predicted by the Bernoulli equation was clearly observed. The results of calculating the corresponding resistivity coefficients for the flat plate were in agreement with the analytical values for both regimes of speeds. By analogy, a simulation was made for a spherical body, which also demonstrated a strong quadratic dependence at high speeds and the drag coefficient value is approximately equal to the analytical one. In the following, we studied systematically ellipsoids with circular cross-section, where we varied the ratio between semiaxes in the direction of motion and perpendicular direction, respectively. The results for the ellipsoid showed that the drag coefficient value is maximum for a flat plate (a limiting case of an ellipsoid, when the semiaxis in the direction of motion tends to 0) and decreases with stretching of the body along the flow axis. When the Maxwell distribution of molecular speeds that was mainly used was replaced with uniform Root-Mean-Square (RMS) speed the results for drag coefficient were slightly different.
Ključne besede: Air resistance, drag force, quadratic drag law, drag coefficient, Monte Carlo (MC) simulation, Maxwell distribution.
Objavljeno v DKUM: 13.10.2021; Ogledov: 1038; Prenosov: 64
.pdf Celotno besedilo (1,64 MB)

2.
Numerical modeling of the negative skin friction on single vertical and batter pile
Mohammad Mahdi Hajitaheri Ha, Mahmoud Hassanlourad, 2015, izvirni znanstveni članek

Opis: In this paper the negative skin friction on single vertical and batter piles is investigated. First, a finite-element model (using ABAQUS software) based on the studies Lee et al. and Comodromos and Bareka was developed. After that, the results of the model were compared and validated. Then a single vertical end bearing and a single skin friction pile under different earth-surface loadings were analyzed and the down-drag force as well as the neutral plane location were studied. Subsequently, the performances of the single end bearing and the friction pile, with different inclination angles between 0 and 30º, were analyzed. Moreover, the sensitivity analysis was implemented using 2-D models. This showed a satisfactory compatibility with the results of the study of Lee et al. and Comodromos and Bareka. Finally, it was concluded that the drag load of the pile and the neutral plane position depend on the condition of the soil surrounding the pile, the 2D or 3D model type , the earth-surface loading intensity, the type of end-bearing pile or friction pile and the pile’s inclination angle. The simulation results agree well with the experimental findings.
Ključne besede: negative skin friction, batter pile, down-drag force, neutral plane
Objavljeno v DKUM: 15.06.2018; Ogledov: 1554; Prenosov: 119
.pdf Celotno besedilo (341,89 KB)
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