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1.
Pantograph driven with a linear induction motor with adaptive fuzzy control
Costica Nituca, Gabriel Chiriac, 2019, original scientific article

Abstract: This article presents an adaptive fuzzy control for a linear induction motor, which is used to control the vertical movement of a pantograph, which supplies an electric locomotive from a contact line. The system has the goal of eliminating all the discontinuity on the route, the resonance phenomenon, the separation of the pantograph head from the contact wire, and electric arches. The simulations demonstrate functional control of the pantograph driven with a linear induction motor system using fuzzy control techniques.
Keywords: linear induction motor, fuzzy control, locomotive pantograph, simulation
Published in DKUM: 05.12.2023; Views: 106; Downloads: 3
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2.
Designing an electromechanical generator for energy harvesting
Franjo Pranjić, Nejc Smolar, Peter Virtič, 2021, original scientific article

Abstract: Five different designs of tubular electromechanical generator for low frequency energy harvesting have been investigated in this paper. In order to design a simple and robust generator, models were constructed out of permanent magnets, steel and windings. In all five generator models, round movers were used in spherical and cylindrical form- for four models solely permanent magnets were used, and in one model, there was steel present in the mover. The movers are slid or rolled through a tube, and induce voltage in the stator winding. All windings were constructed with the same cross- -section dimensions and number of turns. To compare different models, 3D analysis with the Finite Element Method was performed, in order to determine the magnetic flux through the windings. The induced voltage was calculated using the results of the analysis. As a result of the different winding geometries, the average turn length varied for the different designs, subsequently altering resistance and inductance, which affected the generator`s power output and losses. To simulate the generator`s dynamics, an equivalent circuit model was constructed using the Simulink software and data obtained previously from a 3D electromagnetic analysis. With the Simulink model, we coupled the mechanical and electrical systems together to acquire the harvester yields.
Keywords: energy harvest, linear generator, permanent magnets, Finite Element Method
Published in DKUM: 13.11.2023; Views: 129; Downloads: 4
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3.
Experimental verification of the numerically determined parameters for the non-linear two-axis model of a synchronous motor with interior permanent magnets
Željko Hederić, Venco Ćorluka, Toni Varga, 2021, original scientific article

Abstract: Synchronous machines belong to the family of electrical machines characterised by a synchronous magnetic rotating field in the air gap of the machine, the speed of which depends on the frequency of the currents in the armature winding. The paper presents procedures and methods for the numerical determination and experimental verification of the parameters for a nonlinear two-axis model of a synchronous motor with permanent magnets in the rotor (IPMSM) and a concentrated stator winding. To calculate the distribution of electro-magnetic fields in the motor accurately, models with distributed parameters are used in motor design, for which the Finite Element Method (FEM) is usually employed. The improvement by using the model with concentrated parameters considerably simplifies the physical model, by describing it with a system of (non)linear differential equations, the so‐called partial differential equations, which is presented in this paper.
Keywords: synchronous motor, flux linkage, interior permanent magnets, non-linear
Published in DKUM: 13.11.2023; Views: 114; Downloads: 3
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4.
Generalised fuzzy linear programming
Janez Usenik, Maja Žulj, 2023, original scientific article

Abstract: Linear programming is one of the widely used methods for optimising business systems, which includes organisational, financial, logistic and control subsystems of energy systems in general. It is possible to express numerous real-world problems in a form of linear program and then solve by simplex method [1]. In the development of linear programming, we are facing a number of upgrades and generalisations, as well as replenishment. Particularly interesting in recent years is an option that decision variables and coefficients are fuzzy numbers. In this case we are dealing with fuzzy linear programming. If we also include in a fuzzy linear program a generalisation with respect to Wolfe’s modified simplex method [1], we obtain a generalised fuzzy linear program (GFLP). Usenik and Žulj introduced methods for solving those programs and proved the existence of the optimal solution in [2]. In the article, the simplex algorithm which enables the determining of an optimal solution for GFLP is described. There is a numerical example at the end of the article that illustrates the algorithm.
Keywords: linear programming, fuzzy linear programming, generalised linear programming, generalised fuzzy linear programmin
Published in DKUM: 11.10.2023; Views: 147; Downloads: 4
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5.
A note on star partial order preservers on the set of all variance-covariance matrices
Gregor Dolinar, Bojan Kuzma, Janko Marovt, Dijana Mosić, 2023, original scientific article

Abstract: Let ▫$H_n^+(\mathbb{R})$▫ be the cone of all positive semidefinite ▫$n \times n$▫ real matrices. We describe the form of all surjective maps on ▫$H_n^+(\mathbb{R})$▫, ▫$n=3$▫, that preserve the star partial order in both directions.
Keywords: preserver, star partial order, linear model, variance-covariance matrix
Published in DKUM: 10.07.2023; Views: 387; Downloads: 12
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6.
A comparison of linear and nonlinear seismic tunnel-ground interaction analyses
Elefterija Zlatanović, Marina Trajković-Milenković, Dragan Lukić, Stanko Brčić, Vlatko Šešov, 2016, original scientific article

Abstract: In order to study the effects of a seismically induced tunnel–ground interaction, two-dimensional numerical analyses are performed using the sofware ANSYS. The study employs a coupled beam–spring model subjected to earthquake loading that is simulated under pure shear conditions and determined by a free-field ground-response analysis using the code EERA. The properties of the soil material are considered as both linear and nonlinear. The results obtained by linear dynamic analyses are compared with state-of-practice analytical elastic solutions. A comparison of the results of both linear and nonlinear analyses is also performed, and significant differences, as well as important factors influencing the tunnel–ground interaction for both cases, are evaluated.
Keywords: circular tunnel, linear/nonlinear soil behaviour, beam–spring model, plane-strain conditions, simplified dynamic FE analysis, soil–structure interaction
Published in DKUM: 18.06.2018; Views: 1162; Downloads: 69
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7.
Non-linear finite-element modelling of room and pillar mine workings including the strain-softening behaviour of the rock mass
Salim Bensehamdi, Abdelbaki Seriani, 2008, original scientific article

Abstract: A two-dimensional model adopting post-failure criteria was used to simulate the behaviour of the rock mass and the development of yield zones around room and pillar mine workings. The model conformed to the strain-softening behaviour of the rock mass and accounted for its post-failure residual strength. The structural-stability-analysis approach accounted for the main features of the mine structures’ yield produced during loading through changes in the rock material’s stiffness and the subsequent evolution of the stresses. A comprehensive parametric analysis was performed and the inevitable effect of the interaction of the roof, pillar and floor on the overall stability limit of the mine was investigated. The numerical results clearly showed that the finite-element linear models could not realistically represent the true behaviour of the mine structure. However, they clearly demonstrated the limitations of the finite-element linear solutions in representing the true behaviour of the mine structure, particularly when the rock-mass structure is relatively weak, and that a non-linear approach was justified.
Keywords: non-linear FE analysis, yielding, plastic zones, room and pillar mining, residual strength, stability assessment
Published in DKUM: 05.06.2018; Views: 1039; Downloads: 143
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8.
Neuroscience, world wide web and reading curriculum
Metka Kordigel Aberšek, 2012, original scientific article

Abstract: Neuroscience has proved a malleable nature of our brain. The way of thinking is changing lifelong and not only in early childhood. New media as television, video games, and the Internet change students' cognitive skills. New visual-spatial skills, such as iconic representation and spatial visualization are developed. But parallel to these changes new weaknesses occur. Those are in higher-order cognitive processes, as abstract vocabulary, mindfulness, reflection, inductive problem solving, critical thinking, and imagination (Greefield, 2009). Those are the reasons why reading curriculum in contemporary educational system should focus on two groups of aims: deep online reading and linear literature reading. By deep reading is meant the sophisticated processes that propel comprehension and that include inferential and deductive reasoning, analogical skills, critical analysis, reflection, and insight. By linear literature reading is meant primarily reading of fiction, which develops the imagination, inductive analysis, critical and abstract thinking.
Keywords: cognitive skills, linear resding, neuroscience, reading curriculum
Published in DKUM: 15.12.2017; Views: 1350; Downloads: 124
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9.
Nonlinear spillovers between euro area sovereign bond markets
Silvo Dajčman, 2015, original scientific article

Abstract: This paper examines nonlinear spillover effects between sovereign bond markets of six euro area countries (France, Ireland, Italy, Germany, Portugal, and Spain), four of which were among the hardest hit by the sovereign debt crisis, by applying a nonlinear Granger causality test of Diks and Panchenko (2006). The test is applied on the sovereign bond yield dynamics (i.e. yield changes) time series for the time period from 3 January 2000 - 31 August 2011. We also test for ˝pure˝ spillovers between sovereign bond yield dynamics, i.e. the spillovers after controlling for common and regional factors that impact the sovereign bond yield changes of all countries simultaneously. To verify if the nature of spillovers has changed after the start of the euro are sovereign debt crisis, we test for the nonlinear spillovers for the whole observed period and separately for the period be fore and after the start of the euro area sovereign debt crisis (period from the start of April 2010 until the end of our sample, i.e. 31 August 2011). The results of our study show that strong bi-directional Granger causality exists between the investigated sovereign bond markets. Very similar results are obtained whether the regional and world factors are or are not controlled for. We find strong bi-directional non-linear Granger causality for the investigated euro area countries prior the euro area sovereign debt crisis. After the start of the euro area sovereign debt crisis the interdependence be- tween the markets has reduced. We can no longer detect non-linear spillovers running from Germany and France to the ˝periphery˝ euro area countries. The findings of this study have important implications for the policymakers as they show that shocks spill-over quickly across the sovereign bond markets and the intensity and nature of spillovers can change throughout time. The sovereign bond markets of the ˝core˝ euro area decoupled from the ˝periphery˝ euro area sovereign bond markets after the start of euro are debt crisis. The findings are also of relevance for individual investors in the sovereign bond markets for the purpose of portfolio diversification.
Keywords: stock exchanges, bonds, financial crisis, econometric models, EU, sovereign bond markets, spillovers, non-linear Granger causality
Published in DKUM: 07.08.2017; Views: 1139; Downloads: 335
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10.
Computing the weighted Wiener and Szeged number on weighted cactus graphs in linear time
Blaž Zmazek, Janez Žerovnik, 2003, original scientific article

Abstract: Cactus is a graph in which every edge lies on at most one cycle. Linear algorithms for computing the weighted Wiener and Szeged numbers on weighted cactus graphs are given. Graphs with weighted vertices and edges correspond to molecular graphs with heteroatoms.
Keywords: mathematics, graph theory, Wiener number, Szeged number, weighted cactus, linear algorithm
Published in DKUM: 05.07.2017; Views: 771; Downloads: 96
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