1. Numerical analysis of temperature field during hardfacing process and comparison with experimental resultsVukić Lazić, Ivana Ivanović, Aleksandar Sedmak, Rebeka Rudolf, Mirjana Lazić, Zoran Radaković, 2014, izvirni znanstveni članek Opis: The threedimensional 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: 816; Prenosov: 336 Celotno besedilo (975,43 KB) Gradivo ima več datotek! Več...

2. Simulations of transformer inrush current by using BDFbased numerical methodsAmir Tokić, Ivo Uglešić, Gorazd Štumberger, izvirni znanstveni članek Opis: This paper describes three different ways of transformer modeling for inrush current simulations. The developed transformer models are not dependent on an integration step, thus they can be incorporated in a statespace form of stiff differential equation systems. The eigenvalue propagations during simulation time cause very stiff equation systems. The statespace equation systems are solved by using A and Lstable numerical differentiation formulas (NDF2) method. This method suppresses spurious numerical oscillations in the transient simulations. The comparisons between measured and simulated inrush and steadystate transformer currents are done for all three of the proposed models. The realized nonlinear inductor, nonlinear resistor, and hysteresis model can be incorporated in the EMTPtype programs by using a combination of existing trapezoidal and proposed NDF2 methods. Ključne besede: simulations, transformers, numerical methods Objavljeno v DKUM: 15.06.2017; Ogledov: 1178; Prenosov: 327 Celotno besedilo (3,24 MB) Gradivo ima več datotek! Več...

3. ERROR PROBABILITY MODEL FOR IEEE 802.15.4 WIRELESS TRANSMISSION WITH COCHANNEL INTERFERENCE AND BACKGROUND NOISEUroš Pešović, 2016, doktorska disertacija Opis: Data transmission sent through wireless channel is usually affected by background noise, multipath fading and interference which cause data errors. Influence of such disturbances is the most commonly expressed in a form of error probability statistics. Effects of these disturbances on IEEE 802.15.4 wireless transmissions are previously studied, except influence of cochannel interference (CCI) which originates from collision between IEEE 802.15.4 devices which perform simultaneous radio transmission. Our thesis puts forward the assumption that it is possible to derive more accurate analytical error probability model for higher data level error probability parameters without the idealization of PN spreading sequences. Additionally, thesis is that is possible to derive an accurate analytical error probability model in the case of CCI influenced by background noise by consideration of constellation diagram. IEEE 802.15.4 standard uses CSMA/CA (Carrier Sense Multiple Access with Collision Detection) channel access mechanism to prevent collisions between devices, but this mechanism doesn't provide protection from hidden node problem which is primary source of cochannel interference. Using Monte Carlo simulations we determined frequency of hidden node collisions, which shown that cochannel interference frequently occur in parts of the network with high traffic load. Some prior works in this field tend to idealize these nonideal spreading sequences in order to simplify calculations for error probability parameters. Our doctor thesis presents analytical model of data level error probability parameters (symbol, bit and packet) for IEEE 802.15.4, which uses original nonideal spreading sequences without their idealization. Proposed error probability model consists of mutually dependent chip, symbol, bit and packet error probability models. Derived error probability models are linked together, so each of error probability parameters can be determined using error probability parameter from the previous stage. Error probability model for IEEE 802.15.4 wireless communication could be used in network simulation tools in order to accurately simulate energy efficient medium access protocols in realistic scenarios. Presented theoretical results are tested by independent numerical simulation of IEEE 802.15.4 transmission according to Monte Carlo method. Simulation results shows that derived models for error probability parameters were matched by two simulation scenarios in background noise, for multipath fading and cochannel interface, respectively Furthermore, the accuracy of derived mathematical models was tested in realworld experiment using IEEE 802.15.4 compliant wireless transceivers for creating cochannel interference. Packets were received by software defined radio platform, which enabled realization of coherent receiver in which all error probability statistics could be collected. The results of the experiment show consistency with proposed analytical error probability models, but some deviations are caused by poor preamble synchronization under low SNR (Signal to Noise Ratio) value. The thesis was proved with Monte Carlo simulations of the physical level of the IEEE 802.15.4 communication and experimental measurements on a real physical communication system. Ključne besede: IEEE 802.15.4 standard; error probability model; cochannel interference; Rician fading channel; additive white Gaussian noise; wireless transmission, wireless sensor networks, numerical simulations, software defined radio Objavljeno v DKUM: 14.10.2016; Ogledov: 1710; Prenosov: 91 Celotno besedilo (8,20 MB) 
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5. Computational model for the analysis of bending fatigue in gearsJanez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek Opis: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strainlife method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from throughhardened steel 42CrMo4. Ključne besede: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics Objavljeno v DKUM: 01.06.2012; Ogledov: 2697; Prenosov: 82 Povezava na celotno besedilo 
6. Diesel and biodiesel fuel spray simulationsPrimož Pogorevc, Breda Kegl, Leopold Škerget, 2008, izvirni znanstveni članek Opis: This paper deals with the investigation of the influential parameters of a mathematical spray breakup model using different fuels. Beside injection system measurements, fuel physical properties and injection process characteristics were measured, because they are necessary for the spray simulation input. For validation purposes, spray was injected into motionless air at atmospheric pressure and room temperature and filmed with a highspeed camera. Spray macrocharacteristics have been determined on the recorded images. Using the simulation program, the injection processes for diesel, biodiesel, and their 50% blend B50 have been simulated. Spray mathematical model parameters were tuned based on the experimentally gained results. Primary breakup model parameters showed the biggest impact on the spray characteristics and were therefore expressed using the fuel physical properties, the injection process characteristics, and the working regime parameters. Spray simulations into the combustion chamber were made in the end. All of these results are presented and discussed in this paper. Ključne besede: fuel spray, spray breakup, biodiesel fuel, fuels, numerical simulations, mathematical model Objavljeno v DKUM: 31.05.2012; Ogledov: 1397; Prenosov: 74 Povezava na celotno besedilo 
7. Optimization of a fuel injection system for diesel and biodiesel usageBreda Kegl, Marko Kegl, Stanislav Pehan, 2008, izvirni znanstveni članek Opis: This paper presents an optimization procedure of a fuel injection system of a bus diesel engine. Attention is focused on the differences resulting from using two different types of fuel: diesel and biodiesel. The proposed design procedure relies on the assumption that the atomization of fuel spray influences the diesel engine performance, fuel consumption, and harmful emission significantly. As a measure of spray atomization, the Sauter mean diameter is employed and introduced into the objective function. The design problem is formulated in the form of a multiobjective optimization problem, taking into account the ESC 13 mode test for diesel engines of commercial vehicles. The design variables of the injection system are related to the shape of the cam profile, to the nozzle geometry, and to the control parameters influencing the injection quantity and timing. The geometrical properties of the cam profile and the injection parameters are kept within acceptable limits by the imposed constraints. The results of optimization using diesel and biodiesel are compared to each other to show the influence offuel type on final design and performance of the system. Ključne besede: fuel injection system, diesel engine, biodiesel fuel, engine performance, numerical simulations Objavljeno v DKUM: 31.05.2012; Ogledov: 1859; Prenosov: 71 Povezava na celotno besedilo 