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Numerical simulations of the flow and aerosol dispersion in a violent expiratory event : Outcomes of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events
Jordi Pallares, Alexandre Fabregat Tomas, Akim Lavrinenko, Hadifathul Akmal bin Norshamsudin, Gabor Janiga, David Frederick Fletcher, Kiao Inthavong, Marina Zasimova, Vladimir Ris, Nikolay Ivanov, Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush, Hadrien Calmet, Daniel Mira, Jana Wedel, Mitja Štrakl, Jure Ravnik, Douglas Hector Fontes, Francisco José De Souza, Cristian Marchioli, Salvatore Cito, 2023, izvirni znanstveni članek

Opis: This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.
Ključne besede: numerical simulations, computational fluid dynamics
Objavljeno v DKUM: 28.03.2024; Ogledov: 55; Prenosov: 3
.pdf Celotno besedilo (8,63 MB)
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Robotic bin-picking : benchmarking robotics grippers with modified YCB object and model set
Tone Lerher, Primož Bencak, Luka Bizjak, Darko Hercog, Boris Jerman, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Robotic bin-picking is increasingly important in the order-picking process in intralogistics. However, many aspects of the robotic bin-picking process (object detection, grasping, manipulation) still require the research community's attention. Established methods are used to test robotic grippers, enabling comparability of the research community's results. This study presents a modified YCB Robotic Gripper Assessment Protocol that was used to evaluate the performance of four robotic grippers (twofingered, vacuum, gecko, and soft gripper). During the testing, 45 objects from the modified YCB Object and Model Set from the packaging categories, tools, small objects, spherical objects, and deformable objects were grasped and manipulated. The results of the robotic gripper evaluation show that while some robotic grippers performed substantially well, there is an expressive grasp success variation over diverse objects. The results indicate that selecting the object grasp point next to selecting the most suitable robotic gripper is critical in successful object grasping. Therefore, we propose grasp point determination using mechanical software simulation with a model of a two-fingered gripper in an ADAMS/MATLAB cosimulation. Performing software simulations for this task can save time and give comparable results to real-world experiments.
Ključne besede: intralogistics, robotic bin-picking, YCB protocol, robotic gripper evaluation, mechanical software simulations, performance analysis
Objavljeno v DKUM: 21.03.2024; Ogledov: 79; Prenosov: 7
.pdf Celotno besedilo (773,38 KB)
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Introduction to the Computer Simulations : Script
Nejc Novak, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2024

Opis: The script entitled „Introduction to the computer simulations“ in the field of Engineering Computer Simulations is intended as a study aid in the lectures of the courses Engineering Computer Simulations for foreign students at the University of Maribor and for students at Kumamoto University, Japan. It explains all the material that students must master in these subjects, and is consistent with the subject curriculum. The basics of computational simulations, based on the Finite Element Method, are given from the theoretical basics to step-by-step preparation of simple computational models and their analysis in PrePoMax software.
Ključne besede: computational simulations, solid mechanics, Finite Element Method, designing, numerical methods
Objavljeno v DKUM: 12.03.2024; Ogledov: 124; Prenosov: 5
.pdf Celotno besedilo (7,73 MB)
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Vibration fatigue analysis of two different variants of oil suction pipes
Marko Zadravec, Srečko Glodež, Christian Buzzi, Peter Brunnhofer, Martin Leitner, Janez Kramberger, 2024, izvirni znanstveni članek

Opis: In order to reduce the overall mass of the product, an improved variant of the engine oil suction pipe in hybrid design is developed and analysed as part of this paper. The vibration fatigue analysis of a simple all-metal suction pipe and the new hybrid suction pipe variant is derived using computer FEA simulations and vibration measurements on the shaker. The hybrid design of the technical components makes it possible to combine different types of materials in order to achieve the best possible properties and behaviours for the components under the influence of external loads. In our case, we combine a suction pipe made of S235JR mild steel with a 3D-printed polyamide intake funnel featuring a grid designed to prevent particles from entering the engine’s lubrication circuit. This design reduces the mass and shifts the centre of gravity closer to the attachment point of the pipe, as well as to the engine crankcase, which has a positive effect on the values of natural frequencies and vibration amplitudes. The main objective of such a hybrid suction pipe is precisely to reduce vibrations, and thus extend the service life of the components.
Ključne besede: oil suction pipe, vibration fatigue, failure analyses, experimental testing, numerical simulations
Objavljeno v DKUM: 26.02.2024; Ogledov: 118; Prenosov: 5
.pdf Celotno besedilo (6,90 MB)
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Exploring the possibilities of adjusting gensets to NATO requirements
Dejan Barešić, Željko Hederić, Miralem Hadžiselimović, 2019, izvirni znanstveni članek

Opis: Stationary and mobile gensets are used in the Armed Forces of the Republic of Croatia. In this research, priority was given to mobile gensets which have a variety of uses. In addition to being used in the Republic of Croatia, the mobile gensets are also used in international military operations in various modes of operation. Therefore, it is necessary to be very familiar with their characteristics and the possibility of adjusting them to NATO requirements. For the purpose of the adjustment, a test was performed on a P-B40.R1 genset. A model that simulates the genset behaviour with different tested fuels was developed. The investigated genset, together with some others, was introduced into the Armed Forces pursuant to the Product Quality Protocol that was in force during the 1990s. The Protocol did not cover all requirements and recommendations for the genset operation in an international military environment. Therefore, research was conducted, which has resulted in the adjustment of the equipment and in the harmonisation of the Product Quality Protocol with the ISO standard and NATO requirements. When adjusting the materiel, special emphasis is given to defining certain genset types that are able to use the modified F-34 kerosene-type fuel instead of diesel fuel. The F-34 fuel is obtained from kerosene used in aviation; this fuel can be easily obtained in international military operations where the tendency is to use the same type of fuel for airplanes, vehicles, and diesel engine equipment. When F-34 is used as the genset fuel, the quality of the generated electrical energy might be reduced. For the purpose of bringing the output characteristics of the generator within prescribed limits, simulations were performed both with and without the tuning of the regulation parameters.
Ključne besede: genset, F-34 fuel, regulator adjustment, simulations
Objavljeno v DKUM: 22.02.2024; Ogledov: 85; Prenosov: 8
.pdf Celotno besedilo (1,24 MB)
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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: 144; Prenosov: 3
.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: 128; Prenosov: 12
.pdf Celotno besedilo (7,73 MB)
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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: 262; Prenosov: 10
.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: 269; Prenosov: 36
.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: 903; Prenosov: 130
.pdf Celotno besedilo (3,96 MB)

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