Iskanje po katalogu digitalne knjižnice

Opis: The present work focuses on the comparison of the capabilities of Blade Element Momentum Theory, with and without the high induction factor value model and Computational Fluid Dynamics modelling in relation to experimental measurements of the power coefficient for a model-sized horizontal axial wind turbine. Initially, an analytical investigation was performed to obtain the power coefficient curve. Furthermore, three-dimensional numerical simulations were performed, where a lot of effort was devoted to the preparation of a low y+ structured mesh. Analytical and numerical results of the power coefficient were compared with experimental results, which were obtained with our own conducted experiments in the wind tunnel. The most significant conclusions are that the classic BEM method deviates from measured data in the entire range of tip speed ratios, the BEM method with Spera correction predicts a significantly better agreement with experimental measurements compared to the classic BEM method, especially the part where the power coefficient decreases and finally that CFD computations can accurately predict the performance of wind turbines and compute the flow around an aerofoil of the blade.
Ključne besede: BEM method, CFD, measurements, wind turbine
Objavljeno v DKUM: 06.11.2025; Ogledov: 0; Prenosov: 1
Celotno besedilo (1,49 MB)
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Opis: Gallium nitride (GaN) technology has emerged as a transformative solution in the semiconductor industry due to its exceptional performance in highpower and high-frequency applications. With its inherent radiation resilience, GaN is particularly suited for environments such as space electronics and nuclear instrumentation. While static parameter testing under radiation has been extensively studied, dynamic parameter degradation—including propagation delays, rise/fall times, and efficiency losses—remains underexplored. These dynamic characteristics are useful for applications requiring precise timing, signal integrity, and rapid response, such as satellite communication and nuclear systems. This study evaluates the radiation resilience of three commercially available GaN transistors during a 100-krad (Si) Co-60 gamma irradiation campaign, with a focus on both static and dynamic parameters. Static parameters, such as threshold voltage and ON-state resistance, exhibited minimal degradation, while a larger change was observed in gate current. In contrast, dynamic parameters revealed smaller changes, including faster propagation delays and reduced efficiency, with variability observed across device types. The findings support a device-specific co-design of transistors and driver electronics for radiation-tolerant power stages
Ključne besede: Co-60 gamma, drain current, gallium nitride, GaN, gamma irradiation, gate current, in situ measurements, propagation delay, rise and fall times, voltage threshold
Objavljeno v DKUM: 17.10.2025; Ogledov: 0; Prenosov: 1
Celotno besedilo (1,97 MB)

Opis: In railway infrastructure, particularly where concrete sleepers are employed, certain critical zones exhibit pronounced degradation of the ballast layer. Previous studies have identified several contributing factors, including the presence of welds, heterogeneity in the substructure beneath the sleepers, and variations in the track’s geometric parameters. Of these factors, the presence of welds seems to have the most significant influence. This article aims to determine whether differences in the ballast railway track’s response to traffic loads at weld locations can be identified in the initial phase, before obvious damage appears. Vibration responses in terms of displacement, velocity, and acceleration were measured on upgraded concrete sleepers equipped with rubber under-sleeper pads. The results indicate that velocities and accelerations at rail weld locations differ significantly from those in adjacent track sections, when the railway track is in an intact, undamaged condition. These results suggest a high likelihood of damage formation in these critical locations, indicating the necessity of preventive measures to mitigate damage. Possible mitigation measures that could help reduce the formation of damage are proposed.
Ključne besede: ballast railway track, degradation, critical areas, welds, vibration parameters, measurements, mitigation measures
Objavljeno v DKUM: 06.08.2025; Ogledov: 0; Prenosov: 7
Celotno besedilo (5,08 MB)
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Opis: This article aims to provide an accurate mathematical model with the minimum number of degrees of freedom for describing the floating sleeper phenomenon. This was accomplished using mathematical modeling supported by extensive field measurements of the railway track. Although the observed phenomenon is very complex, the simplified single degree of freedom (SDOF) mathematical model proved accurate enough for its characterization. The progression of the deterioration of the railway track was successfully correlated to changes in the maximal dynamic factor for different types of pulse loading. The results of the presented study might enable the enhanced construction and maintenance of railroads, particularly in karst areas.
Ključne besede: floating sleepers, dynamic factor, pulse loading, field measurements, SDOF mathematical model
Objavljeno v DKUM: 28.11.2024; Ogledov: 0; Prenosov: 23
Celotno besedilo (6,27 MB)
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Opis: The manuscript presents the optical properties of directly deposited films of gold nanoparticles (AuNPs) prepared by the Ultrasonic Spray Pyrolysis (USP) technology. Four samples were produced, with AuNP deposition times on the glass substrate of 15 min, 30 min, 1 h and 4 h. The morphological characterisation of the deposited films showed that the size of the first deposited AuNPs was between 10 and 30 nm, while, with a longer duration of the deposition process, larger clusters of AuNPs grew by coalescence and aggregation. The prepared layers were characterised optically with Ultraviolet–visible spectroscopy (UV–vis) and ellipsometry. The ellipsometric measurements showed an increasingly denser and thicker effective thickness of the AuNP layers. The extinction spectra displayed a clear local surface plasmonic resonance (LSPR) signature (peak 520–540 nm), indicating the presence of isolated particles in all the samples. For all AuNP layers, the imaginary part of the parallel and perpendicular components of the anisotropic dielectric function was dominated by a central peak at around 2.2 eV, corresponding to the LSPR of isolated particles, and a high-energy shoulder due to Au interband transitions. It was shown that, as the density of particles increased, the extinction cross-section grew over the whole spectral range where measurements are taken. Thus, the response can be explained with an enhanced electromagnetic response between the AuNPs that can be connected to the increase in particle density, but also by the formation of clusters and irregular structures.
Ključne besede: optical characteristics, gold nanoparticles’ films, UV–vis, ellipsometry measurements
Objavljeno v DKUM: 28.05.2024; Ogledov: 124; Prenosov: 0