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Cavitation erosion modelling : comparison of different driving pressure approaches
Luka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, izvirni znanstveni članek

Opis: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Ključne besede: cavitation, erosion potentional, driving pressure, numerical simulations
Objavljeno v DKUM: 21.02.2024; Ogledov: 27; Prenosov: 0
.pdf Celotno besedilo (796,29 KB)
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Dynamic characterisation of novel three-dimensional axisymmetric chiral auxetic structure
Anja Mauko, Yunus Emre Yilmaz, Nejc Novak, Tomáš Doktor, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.
Ključne besede: axisymmetric chiral structure, auxetic, chiral unit cell, impact testing, dynamic characterisation, finite element simulations
Objavljeno v DKUM: 15.02.2024; Ogledov: 36; Prenosov: 4
.htm Celotno besedilo (164,25 KB)
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The effect of the Ala16Val mutation on the secondary structure of the manganese superoxide dismutase mitochondrial targeting sequence
Matic Broz, Veronika Furlan, Samo Lešnik, Marko Jukič, Urban Bren, 2022, izvirni znanstveni članek

Opis: Manganese Superoxide Dismutase (MnSOD) represents a mitochondrial protein that scavenges reactive oxygen species (ROS) responsible for oxidative stress. A known single nucleotide polymorphism (SNP) rs4880 on the SOD2 gene, causing a mutation from alanine to valine (Ala16Val) in the primary structure of immature MnSOD, has been associated with several types of cancer and other autoimmune diseases. However, no conclusive correlation has been established yet. This study aims to determine the effect of the alanine to valine mutation on the secondary structure of the MnSOD mitochondrial targeting sequence (MTS). A model for each variant of the MTS was prepared and extensively simulated with molecular dynamics simulations using the CHARMM36m force field. The results indicate that the alanine variant of the MTS preserves a uniform α-helical secondary structure favorable for the protein transport into mitochondria, whereas the valine variant quickly breaks down its α-helix. Thus, the alanine MTS represents the more active MnSOD variant, the benefits of which have yet to be determined experimentally.
Ključne besede: manganese superoxide dismutase, polymorphism rs4880, mutation Ala16Val, molecular dynamics simulations, oxidative stress
Objavljeno v DKUM: 21.08.2023; Ogledov: 225; Prenosov: 9
.pdf Celotno besedilo (5,14 MB)
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Development, fabrication and mechanical characterisation of auxetic bicycle handlebar grip
Nejc Novak, Vasja Plesec, Gregor Harih, Andrej Cupar, Jasmin Kaljun, Matej Vesenjak, 2023, izvirni znanstveni članek

Opis: The auxetic cellular structures are one of the most promising metamaterials for vibration damping and crash absorption applications. Therefore, their use in the bicycle handlebar grip was studied in this work. A preliminary computational design study was performed using various auxetic and non-auxetic geometries under four load cases, which can typically appear. The most representative geometries were then selected and fabricated using additive manufacturing. These geometries were then experimentally tested to validate the discrete and homogenised computational models. The homogenised computational model was then used to analyse the biomechanical behaviour of the handlebar grip. It was observed that handle grip made from auxetic cellular metamaterials reduce the high contact pressures, provide similar stability and hereby improve the handlebar ergonomics.
Ključne besede: auxetic cellular structures, computational simulations, experimental testing
Objavljeno v DKUM: 23.05.2023; Ogledov: 230; Prenosov: 33
.pdf Celotno besedilo (2,63 MB)

Analysis and implementation of different modulation strategies for one-phase inverter based on TMS320F28335 microcontroller : magistrsko delo
Tomislav Sinković, 2019, magistrsko delo

Opis: This master’s thesis is about researching different modulation strategies used on one-phase inverters. Given results and quality of the particular modulation strategy will be measured on output terminals of the whole system or load, which will be, for this purpose, a classical pure resistive load. Signal response will be measured with oscilloscope and the obtained signal will be saved in CSV form for further computer analysis using MATLAB/Simulink. Stored results will be passed through Fast Fourier Transformation method, which can estimate the magnitude of higher harmonics component in the output signal and thus quality of the signal. Whole algorithm and low-level signal generation is performed with TMS320F28335 microcontroller which supports MATLAB/Simulink to be compiled in C language. Real »Power board« is done with the milling machine with prior designing in Altium Designer PCB software package.
Ključne besede: one-phase inverter, different modulation strategies, TMS320F28335, power board, simulations
Objavljeno v DKUM: 22.11.2019; Ogledov: 876; Prenosov: 128
.pdf Celotno besedilo (3,96 MB)

Simulation of automotive air-conditioning system in 1D simulation software : diplomsko delo
Marko Copot, 2019, diplomsko delo

Opis: The development of state-of-the-art vehicles requires advanced simulations tools in heating, ventilation and air-conditioning (HVAC). The focus of this thesis is the construction of an automotive HVAC model, its calibration and the simulation of the behaviour of the HVAC model in various ambient conditions. The theoretical background of refrigeration system as part of the HVAC system is presented. The model is constructed with following components: compressor, condenser, throttling device, evaporator and battery chiller, which is a heat exchanger between coolant and refrigerant. The description and role of each component in the HVAC model is presented. All heat exchangers are calibrated, which is done with multiple simulations that have defined input data. The results are compared to experimental data. With addition of vehicle cabin with air recirculation, HVAC control logic is implemented. The behaviour of the system is simulated in defined environmental conditions. The results of the simulations are presented in graphs and tables.
Ključne besede: 1D simulations, air-conditioning, HVAC, calibration, thermodynamics, cooling
Objavljeno v DKUM: 23.09.2019; Ogledov: 1255; Prenosov: 95
.pdf Celotno besedilo (1,54 MB)

Peter Fajs, 2019, magistrsko delo

Opis: The objective of the master thesis is to determine the filling properties of injection moulding process for newly created material, and to understand how the variation of processing parameters affects the flow possibilities. In thesis two materials were analysed, i.e. neat PLA material, which was used as a benchmark material and newly created composite CitrusPLA that is based on biodegradable PLA matrix and reinforced with citrus fibres. To fulfil the aim, the virtual and experimental design of experiment with the Taguchi methodology was conducted with use of spiral flow test, where the flow length of material through mould cavity was observed. The experimental results were the basis for the accuracy validation of numerical results and also to determine the optimum process parameters for injection moulding products with best flow conditions through statistical evaluation. It has been concluded that the newly created composite has lower viscosity compared to benchmark virgin PLA which results in better flow conditions in spiral flow test analysis. Both materials have the same optimal conditions in terms of flow conditions. The contribution of mould temperature is in both cases negligible. However, other two variated parameters i.e. melt temperature and injection speed have higher influence on filling characteristics for both materials.
Ključne besede: injection moulding optimization, material characterization, Moldflow, injection moulding simulations, Taguchi DOE, bio-composites, citrus waste fibres, PLA
Objavljeno v DKUM: 07.06.2019; Ogledov: 1430; Prenosov: 27
.pdf Celotno besedilo (3,19 MB)

Perspectives on the introduction of computer-supported real laboratory exercises into biology teaching in secondary schools : teachers as part of the problem
Andreja Špernjak, Andrej Šorgo, 2009, izvirni znanstveni članek

Opis: Computer supported virtual and real laboratories are recognized as tools that can help in raising the quality of biology instruction, and raising development competences in students. Yet biology teachers have been treating the computer as typewriter, as a source of information and as a tool for communication, all of which usages are common to all subjects. The uses of ICT that can significantly help in developing scientific literacy and that are primary tools in science teaching - such as the use of data loggers - are only rarely on the syllabus. The lack of equipment is not the most important reason for failure to use such applications; instead, this is probably due to teachers' attitudes, opinions and knowledge. Students cannot be recognized as an obstacle in working with ICT. Lawer secondary school students aged between 10 and 14 performed three laboratory exercises (Activity of yeast, Gas exchange in breathing, Heart rate) using three different methods: classic, computer-supported and virtual laboratory. As a result of testing, we know that all three methods are suitable even for younger students. When students were asked which method they liked the most, their first choice was computer-supported laboratory, followed by classic laboratory, with virtual laboratory in the third place.
Ključne besede: education, biology, secondary education, computer-supported laboratory, laboratory work, ICT, simulations
Objavljeno v DKUM: 15.12.2017; Ogledov: 1589; Prenosov: 114
.pdf Celotno besedilo (783,64 KB)
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How close to reality is the „as-is” business process simulation model?
Bartlomiej Gawin, Bartosz Marcinkowski, 2015, izvirni znanstveni članek

Opis: Background and Purpose: Business process simulation (BPS) model is based on real-life data form sources like databases, observations and interviews. It acts as “as-is” business scenario can used for reengineering. The main challenge is to gather relevant data and to develop simulation model. Research aims to elaborate BPS model and to systematically assess how close to reality it is. Design/Methodology/Approach: The research has been performed in Polish telecommunications company. Authors investigate technical process of expanding cellular network. After elaborating “as-is” model, authors use ADONIS simulation tool to run a series simulations and confront simulation results with actual historical events. After this, assessment whether computer simulation model can precisely map real-life business process - and consequently act as credible basis for process improvement - is made. Results: The simulation model has been constructed with data from the WfMS database, observations, staff knowledge and their experience. Fully equipped simulation model is found to allow reconstructing the historical execution of business activity with low margin for error. Some limitation were identified and discussed. Conclusion: BPS is not a popular approach for process reengineering and improvement yet. Data collection issues for BPS that require adopting process mining techniques and additional information sources are among the reasons for that. In our study, computer simulation outputs are compatible with historical events. Hence the model reflects the business reality and can be taken as a reference model while redesigning the process.
Ključne besede: business process, business process simulations, data acquisition, workflow systems
Objavljeno v DKUM: 30.11.2017; Ogledov: 1167; Prenosov: 425
.pdf Celotno besedilo (827,45 KB)
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Numerical analysis of temperature field during hardfacing process and comparison with experimental results
Vukić Lazić, Ivana Ivanović, Aleksandar Sedmak, Rebeka Rudolf, Mirjana Lazić, Zoran Radaković, 2014, izvirni znanstveni članek

Opis: The three-dimensional transient nonlinear thermal analysis of the hard facing process is performed by using the finite element method. The simulations were executed on the open source Salome platform using the open source finite element solver Code Aster. The Gaussian double ellipsoid was selected in order to enable greater possibilities for the calculation of the moving heat source. The numerical results were compared with available experimental results.
Ključne besede: welding simulations, numerical analysis, thermal analysis, simulations, transient heat conduction, moving heat source
Objavljeno v DKUM: 07.07.2017; Ogledov: 1302; Prenosov: 382
.pdf Celotno besedilo (975,43 KB)
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