Measurements of material heat transfer properties : master study programmeMiha Donša
, 2022, magistrsko delo
Opis: An experimental setup was created to observe temperature change at two points inside the experimental body. Such an experimental setup created data that was used as an anchor point of optimization that was coupled with numerical models to find unknown variables of heat conductivity and specific heat of the materials. Two numerical models were created. A 1D numerical model was created for possibilities of fast optimization ignoring the insulation and heat transfer through it. Such a model did not manage to describe the experimental setup accurately. Therefore, a 3D numerical model was created simulating the whole experimental setup and yielded much more promising results. Problems with the model were soon seen when experimental data was compared to the numerical solution where variables that were initially not taken into the account showed a much greater effect than first anticipated. Therefore, the 3D numerical model was adjusted to describe the experimental setup as accurately as possible. The experiment was done with two different materials. The materials were picked based on their heat conductivity (high and low). High heat conductivity material was easy to understand and to find a solution to it. With low conductivity material, some problems were quickly observed and as such created a lot of questions as to why and how to find the unknown variables of the material. It was then shown that the masses of the materials in the experiment and the length of the experiment played the most important role in the experiment and quickly explained why and how the experimental setup should be modified to obtain better results.
Ključne besede: heat transfer, material heat transfer properties, specific heat, heat conductivity, optimization, numerical simulation of heat transfer
Objavljeno v DKUM: 07.07.2022; Ogledov: 159; Prenosov: 20
Celotno besedilo (6,54 MB)
Pressurized Water Nuclear Reactor Downcomer Flow Simulation : diplomsko deloAljaž Kekec
, 2021, diplomsko delo
Opis: In the diploma thesis the flow pattern and conditions in the downcomer of a pressurized water nuclear reactor were simulated, to study coolant mixing inside the primary circuit. This was done using computational dynamics software Ansys CFX. The nuclear reactor in Krško (Slovenia) was used as a basis for the model. The downcomer geometry was simplied for a more feasible study. Three separate simulations were done: one with normal conditions, one with loss of coolant accident conditions and one with a modified geometry. The flow was then studied at different condition at the same levels using velocity contours. The results showed that the axial velocity profiles at the downcomer outlet are not completely uniform.
Ključne besede: Nuclear Power Plant, Pressurized Water Reactor, Downcomer, Flow simulation, Ansys CFX
Objavljeno v DKUM: 13.10.2021; Ogledov: 421; Prenosov: 38
Celotno besedilo (2,49 MB)
Monte Carlo simulation of air resistance on an ellipsoid in motionVeronika 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: 355; Prenosov: 28
Celotno besedilo (1,64 MB)
Measurement and modelling of power SiC MOSFET transistors : master's thesisDarjan Molnar
, 2021, magistrsko delo
Opis: The increasing demand for smaller, faster, and more efficient switch mode power supplies (SMPS) and energy converters has led to the development of new power MOSFET technologies, such as SiC (silicon carbide) power MOSFET transistors. Switching parameters, output voltages and currents and power consumption need to be measured accurately to assess different types of power electronics components more efficiently in today’s rapid implementation of new energy transfer and modulation technology. The need for improving switching circuits in power electronics and trying to use simple simulation circuits for designing PCBs to measure output values of said power electronics transistors is the basis of this thesis. Even though manufacturers of power electronics transistors provide data on drain-source voltages and currents, these are mostly measured for specific conditions regarding pulse duration, gate-source voltage, case temperature of the transistor etc., and as such do not provide information as to where the limits of the drain source voltages and currents for different measurement parameter values are. The goal of the thesis is to find a way to measure the limits of drain-source voltages and currents of power electronics transistors (in this case a SiC MOSFET transistor), and to see if a simple SPICE-model could be built for other power electronic transistors as well, based on the results of this thesis.
Ključne besede: SiC, MOSFET, transistor, simulation, PCB
Objavljeno v DKUM: 02.06.2021; Ogledov: 471; Prenosov: 44
Celotno besedilo (4,35 MB)
Ergonomsko oblikovanje delovnega mesta na montažni liniji žarometov : diplomsko deloAljaž Majcen
, 2020, diplomsko delo
Opis: V diplomski nalogi ergonomsko oblikovanje delovnega mesta na montažni liniji žarometov je predstavljena ergonomska analiza delovnega mesta na montažni liniji žarometov. V uvodu je predstavljeno podjetje, znanstvena veda ergonomija, ter njena načela. Opisani sta tudi ergonomski metodi OWAS in RULA, ter programski paket Tecnomatix Jack. Osrednji del diplomske naloge predstavlja predstavitev delovnega mesta, ki je predmet analize, ocena kontrole z vidika ergonomskih načel in opravljene ergonomske analize. Analize so opravljene ročno in računalniško z uporabo paketa Human simulation Jack. V zaključnem delu diplome so predstavljeni rezultati vseh analiz in predlogi izboljšav.
Ključne besede: ergonomija, Human simulation Jack, OWAS, RULA, ergonomske metode, ergonomska analiza
Objavljeno v DKUM: 22.09.2020; Ogledov: 675; Prenosov: 111
Celotno besedilo (2,56 MB)
Electrified powertrain configurator : magistrsko deloJernej Kosi
, 2019, magistrsko delo
Opis: This master’s thesis describes the development, use and simulation results of the Excel based electrified powertrain configurator tool. First, different electrified powertrains are introduced and divided based on the powertrain type. Within the scope of this master’s thesis, we focused on battery electric vehicles. A mathematical vehicle model was developed to describe different battery electric vehicle powertrain architectures. The mathematical vehicle model was implemented in Excel. The performance of the Excel tool was demonstrated by simulating various driving cycles. To evaluate the accuracy and usability of the tool, simulation results from Excel tool were compared with those from AVL Cruise.
Ključne besede: electrified powertrain, vehicle longitudinal dynamic, driving simulation, Excel, tool development
Objavljeno v DKUM: 23.12.2019; Ogledov: 888; Prenosov: 5
Celotno besedilo (3,03 MB)
Technological valley of death as an emergent evolutionary phenomenonPetra Fic
, 2019, magistrsko delo
Opis: Perceptual researchers often argue that natural selection supports veridical perceptions, respectively those that accurately reflect the environment. They also claim that beings whose perceptions are truer are also more fit. This assumption was tested using standard tools of evolutionary game theory in a simple environment. The result was that more veridical perceptions are not necessarily more successful. In the majority of the parameter space, veridical perceptions are extinct in competition with simplified perceptions, based on adaptive behavior in a given environment. In the thesis, we build upon mentioned territorial games introduced by Mark, Marion, and Hoffman in 2010, and extend four of their territory perception and selection strategies with two novel ones that together constitute a model of technological readiness valley of death. Whenever utility of a resource is not monotonous in the amount of that resource, the technological valley of death emerges. While the development of the science behind these models is in its infancy, modeling and understanding the phenomenon may shed light on progress and related phenomena in society.
Ključne besede: evolution, perception, utility, Monte Carlo simulation, game theory
Objavljeno v DKUM: 22.11.2019; Ogledov: 1072; Prenosov: 135
Celotno besedilo (1,56 MB)
Use of a simulation environment and metaheuristic algorithm for human resource management in a cyber-physical systemHankun Zhang
, Borut Buchmeister
, S. Liu
, Robert Ojsteršek
, 2019, samostojni znanstveni sestavek ali poglavje v monografski publikaciji
Ključne besede: simulation modelling, evolutionary computation, cyber-physical system, heuristic kalman algorithm, human resource management
Objavljeno v DKUM: 06.06.2019; Ogledov: 986; Prenosov: 309
Celotno besedilo (1,41 MB)