1. Use of active elements for providing suitable voltage profiles and prevent overloads in radial distribution networksMarko Vodenik, Matej Pintarič, Gorazd Štumberger, 2022, izvirni znanstveni članek Opis: The article deals with the issue of providing suitable voltage profiles and preventing congestion of network elements in distribution networks. Active network elements and network users’ energy flexibility services are used to provide a suitable voltage profile and prevent congestion in distribution networks. The discussed active network elements include a transformer with on-load tap changer, reactive power compensation devices, energy storage systems, distributed energy resources, and network users’ energy flexibility services, where the active consumers adjust their consumption, production and storage of energy. Based on the Backward Forward Sweep load flow computation method, the case studies are performed for the discussed low voltage distribution network, where the measurement results were available. The case studies for preventing overload of the distribution transformer are performed using a battery energy storage system and network users’ energy flexibility services. The case studies for providing suitable voltage profiles are performed using all listed active elements and a combination of different active elements. In addition, to provide suitable voltage profiles, the existing conductors are replaced with conductors of a larger cross-section. Technically acceptable solutions that can provide a suitable voltage profile and prevent the overloading of network elements in the most demanding operating conditions are presented in this article.
Ključne besede: voltage profile, radial distribution network, load flow calculations, active network elements, energy flexibility
Objavljeno v DKUM: 30.10.2023; Ogledov: 115; Prenosov: 3
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2. Fractal geometry as an effective heat sinkMatjaž Ramšak, 2022, izvirni znanstveni članek Opis: "How long is the coast of Britain?" was the question stated by Mandelbrot. Using smaller and smaller rulers the coast length limits to infinity. If this logic is applied to the fractal heat sink geometry, infinite cooling capacity should be obtained using fractals with mathematically infinite surface area. The aim of this article is to check this idea using Richardson extrapolation of numerical simulation results varying the fractal element length from one to zero. As expected, the extrapolated heat flux has a noninfinite limit. The presented fractal heat sink geometry is non-competitive to the straight fins.
Ključne besede: fractal heat sink, LED cooling, CPU cooling, conjugate heat transfer, laminar flow, boundary element method, Koch snowflake
Objavljeno v DKUM: 14.07.2023; Ogledov: 429; Prenosov: 10
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3. 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: 741; Prenosov: 54
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5. Primerjava in migracija aplikacij iz ogrodja Vaadin v platformo Vaadin Flow : diplomsko deloNejc Zagrušovcem, 2019, diplomsko delo Opis: Svet razvoja spletnih aplikacij se razvija in nadgrajuje iz dneva v dan, zato se proces učenja nikoli ne konča. Z nadgradnjami je potrebno novo znanje ter tudi osveževanje kode starih aplikacij. V diplomskem delu bomo razvili aplikacijo v ogrodju Vaadin ter aplikacijo migrirali v platformo Vaadin Flow, nato bomo naredili primerjavo obeh aplikacij ter izluščili prednosti, slabosti in razlike med razvojem aplikacij v ogrodju Vaadin in platformi Vaadin Flow.
Ključne besede: Vaadin, Vaadin Flow, spletne aplikacije, migracija spletne aplikacije, programski jezik Java.
Objavljeno v DKUM: 13.11.2019; Ogledov: 794; Prenosov: 77
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6. Numerical analysis of fluid flow in a vial : [master thesis]Žiga Časar, 2019, magistrsko delo Opis: Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.
Ključne besede: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition
Objavljeno v DKUM: 09.07.2019; Ogledov: 1262; Prenosov: 182
Celotno besedilo (2,66 MB) |
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8. Orodje node-red in alternativeDomen Mori, 2018, magistrsko delo Opis: Node-RED je orodje za vizualno programiranje na podlagi opisa podatkovnih tokov, namenjeno povezovanju različnih spletnih protokolov in aplikacijskih programskih vmesnikov. Uporablja se predvsem na področju interneta stvari. V tem delu opišemo njegove ključne lastnosti, nato pa izdelamo preprosto aplikacijo in opišemo nekaj praktičnih primerov uporabe. Sledi opis alternativnih orodij, povezanih z vsaj enim izmed naštetih področij, in njihova primerjava z Node-RED. Dodamo še kratek preizkus zmogljivosti delovanja. Ugotovimo, da je Node-RED primerno orodje za povezovanje naprav in protokolov ter preprosto obdelavo njihovih podatkov. Izdelava kompleksnejših programov je možna, a orodje za takšno uporabo ni priročno.
Ključne besede: Node-RED, Flow, Apache Nifi, internet stvari, programiranje na podlagi opisa podatkovnih tokov
Objavljeno v DKUM: 01.03.2019; Ogledov: 1243; Prenosov: 157
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9. Impacts of different factors on seepage and land uplift due to compressed-air injectionZang Yongge, Sun Dongmei, Feng Ping, Stephan Semprich, 2017, izvirni znanstveni članek Opis: In this study, using an in-situ, air-flow test in Essen, the impacts of different factors on multiphase flow and land uplift during and after compressed-air injection were investigated using numerical simulations. A loosely coupled, two-phase flow and geo-mechanical modeling approach, linking two numerical codes (TOUGH2/EOS3 and FLAC3D) was employed to simulate the in-situ, air-flow test for comparing the simulated and measured results. As the compressed air is injected, it flows upwards and laterally, and the vertical effective stress near and above the injection zones decreases owing to the pore pressure increasing here, causing an expansion of the soil skeleton in the corresponding zones. The land uplift, induced mainly by support actions from lower deformed soils, is relevant to the distribution of the porosity increments in the soil interior, and it increases rapidly during air injection. After the compressed-air injection stops, the land uplift decreases gradually to zero due to the overpressure dissipation. With a combination of intensive rainfall, the land uplift is slightly greater near the borehole, but it is significantly greater at a distance from the borehole than the land uplift with no or low rainfall, but the air-injection rate remains almost unchanged due to the unchangeable pore pressure near the injection region. As the intrinsic permeability increases or the air entry pressure decreases in the injected strata, both the land uplift and the air injection rate increase, but the time required for the land uplift to become zero is slightly advanced with either a small permeability or a high air entry pressure.
Ključne besede: loosely coupled two-phase flow and geo-mechanical model, in-situ, air-flow test, compressed-air injection, multiphase flow, land uplift, air loss
Objavljeno v DKUM: 18.06.2018; Ogledov: 974; Prenosov: 89
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10. Rheological properties of marine sediments from the port of KoperJasna Smolar, Matej Maček, Ana Petkovšek, 2016, izvirni znanstveni članek Opis: Subaqueous, fine-grained, cohesive sediments are continuously fluidized by waves and other disturbances that cause their movement, which can be described with numerical models incorporating rheological parameters. The rheological behaviour depends on the soil (solid) type, the volume concentration, the salinity and the testing methods.
In this study, rheological investigations of marine sediments from the Port of Koper were carried out by using two coaxial cylinder rheometers (DV3T HB, Brookfield and ConTec Viscometer 5). The influence of the specimen volume, the size of the gap and the type of measuring spindles were analysed and compared.
The measured data were evaluated using the Bingham model. For each data set, the boundary between the sheared (“fluid”) and the un-sheared (“solid”) material was calculated and then the calculated boundary was used instead of the outer radius of the cylinder for the evaluation of the rheological parameters, where necessary.
A good comparison of the results was found when using this approach. The results are also in agreement with the literature data. The ConTec Viscometer 5, primarily designed for mortars and concrete, was shown to be also suitable for the investigation of sediments.
Ključne besede: marine sediments, Bingham model, yield stress, plastic viscosity, coaxial cylinder rheometer, plug flow, Bay of Koper
Objavljeno v DKUM: 18.06.2018; Ogledov: 946; Prenosov: 73
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