Monte Carlo simulation of air resistance on an ellipsoid in motionVeronika Bukina
, 2021, magistrsko delo
Opis: The main goal of the master's thesis was the analysis of air resistance on the body in motion in a model that does not require solving the Navier-Stokes equations, but works on the basis of mechanics and statistical physics. The model was a Monte Carlo (MC) simulation of the motion of ideal gas molecules in a closed container in which a body was placed, moving along one of the axes. For the most part of calculations, the approach was used when the body was fixed in the middle of the simulation cell, and one of the components of the molecular velocity had an additional term that simulated the flow, as if the body was moving at this speed in the opposite direction. First of all, a linear dependence of the drag force on speed was found for low flow speed for a flat plate, which was predicted by linear drag law. For high molecular flow rates, the quadratic dependence predicted by the Bernoulli equation was clearly observed. The results of calculating the corresponding resistivity coefficients for the flat plate were in agreement with the analytical values for both regimes of speeds. By analogy, a simulation was made for a spherical body, which also demonstrated a strong quadratic dependence at high speeds and the drag coefficient value is approximately equal to the analytical one. In the following, we studied systematically ellipsoids with circular cross-section, where we varied the ratio between semiaxes in the direction of motion and perpendicular direction, respectively. The results for the ellipsoid showed that the drag coefficient value is maximum for a flat plate (a limiting case of an ellipsoid, when the semiaxis in the direction of motion tends to 0) and decreases with stretching of the body along the flow axis. When the Maxwell distribution of molecular speeds that was mainly used was replaced with uniform Root-Mean-Square (RMS) speed the results for drag coefficient were slightly different.
Ključne besede: Air resistance, drag force, quadratic drag law, drag coefficient, Monte Carlo (MC) simulation, Maxwell distribution.
Objavljeno v DKUM: 13.10.2021; Ogledov: 258; Prenosov: 25
Celotno besedilo (1,64 MB)
Selective distribution restrictions in the EU competition lawDaria Kostecka-Jurczyk
, 2020, izvirni znanstveni članek
Opis: The dynamic development of digital technologies favours the rapid increase the popularity of electronic commerce, but at the same time causes an ever-stronger competitive pressure, prompting manufacturers and wholesalers to use various tools for controlling the sales system, especially prices. They often impose various restrictions on commercial partners (e.g. distributors) by preventing them from using certain sales channels. However, it is difficult to delimit the legality of such sales restrictions. It is very difficult to find an answer to the question of where the appropriate demarcation line should be drawn that determines the violation of competition rules, especially in online sales. Regulation 330/2010 seems not to be tailored to the assessment of restrictions in online distribution channels. The aim of the article is to point out the lack of appropriate tools to assess the restrictions of internet sales. The article shows that there is currently no uniform approach by antitrust authorities, which in turn results in legal uncertainty. It seems that the amendment of Regulation 330/2010 should be considered and the market share threshold set out in it should be lowered, while at the same time ensuring that it will be an actual safe harbour for companies, including online distributors.
Ključne besede: anticompetitive agreements, block exemption regulation, competition law, online sales, selective distribution, vertical agreements
Objavljeno v DKUM: 15.01.2021; Ogledov: 431; Prenosov: 0
Transport and Localization in Classical and Quantum BilliardsČrt Lozej
, 2020, doktorska disertacija
Opis: In this thesis the classical and quantum dynamics in billiard systems are considered. Extensive numerical studies of the classical transport properties in several examples of billiard families including the ergodic Bunimovich stadium and cut-circle billiards and the mixed-type Robnik and lemon billiards are performed. The analysis of the transport is based on the random model of diffusion which assumes that due the strongly chaotic dynamics the motion of the orbit on the discretized phase space is temporally uncorrelated. The cause of the deviations from the random model dynamics is traced to dynamical trapping due to stickiness. A novel approach to locally quantifying stickiness based on the statistics of the recurrence times is presented and applied to distinguish between exponential decays of recurrence times and other types of decays. This enables the identification of sticky areas in the chaotic components. Detailed maps of their structure for a wide range of parameter values, mapping the evolution of the mixed-phase spaces and revealing some particularly interesting special examples are presented. The recurrence time distributions in sticky areas are found to be well described by a mixture of exponential decays. The transport of particle ensembles in the momentum space of classical billiards is described by using an inhomogeneous diffusion model and the classical transport times are determined. The classical transport times are vital for the analysis of the localization of chaotic eigenstates in quantum billiards. The control parameter that describes the the degree of localization of the chaotic quantum eigenstates is the ratio between the Heisenberg time (Planck's constant divided by the mean level spacing) and the classical transport time. Extensive numerical calculations of the high-lying spectra and eigenstates of the stadium, Robnik and lemon quantum billiards are performed. The spectral statistics are analysed in terms of the standard methods of quantum chaos. The level repulsion exponent of localized eigenstates is found to be a rational function of the control parameter. The degree of localization is determined with respect to localization measures based on the Poincaré-Husimi representation of the eigenstates. The mean localization measure is found to be a rational function of the control parameter and linearly related to the level repulsion exponent. The distributions of the localization measures are analysed and found to be of a universal shape well described by a two parameter empirical distribution in billiards with no apparent stickiness. The nonuniversal system specific features of localization measure distributions are related to the presence of sticky areas in the phase spaces of classical billiards with specific examples shown.
Ključne besede: Transport, localization, chaos, quantum chaos, Hamiltonian systems, level spacing distribution, mixed phase space, billiard, quantum billiard, Husimi functions, stickiness, cantorus, chaotic eigenstates, level repulsion.
Objavljeno v DKUM: 13.01.2021; Ogledov: 728; Prenosov: 111
Celotno besedilo (24,93 MB)
Optimization of the distribution network operation by integration of distributed energy resources and participation of active elements : doctoral thesisNevena Srećković
, 2020, doktorska disertacija
Opis: Distribution Networks (DNs) are evolving from a once passive to an active part of the electricity network. This evolution is driven by the current political and environmental decisions, Directives and Incentives, as well as the technological development, observed in the everincreasing integration of renewable energy resources, advanced network control and measurement devices, the upcoming energy exibility market, etc. This Doctoral Thesis deals with the problem of optimization of the technical aspects of a DN operation, enabled by the proliferated integration of the photovoltaic systems (PV) and other active devices. The main objective of the Thesis is the optimization of a DN operation in terms of minimization of electrical energy losses while ensuring the proper voltage profiles and preventing thermal overloadingof lines. Therefore, three Differential Evolution-based optimization procedures were developed and tested on real medium and low voltage DNs. The first methodology determines the optimal rooftop surfaces for the installation of PV systems, yielding minimum annual energy losses. It is based on the simultaneous consideration of high-resolution spatio-temporal solar and PV potential data, as well as long-term measured profiles of consumption and generation of electrical energy within the network of a given configuration. The second algorithm minimizes network losses in a time-discrete operation point, by determining the optimal operation of the following active elements: PV systems capable of cooperation in reactive power provision, On-Load Tap Changer equipped transformer substations and remotely controlled switches for network reconfiguration. The final algorithm was developed by a proper consolidation of the first two approaches, yielding the synergistic effects expressed as the increase of loss reduction and network exibility. The results of the performed case studies show that the locations of the highest suitability for PV installation with respect to the solar energy availability, are not necessarily the best choice from the network operation standpoint. Therefore, both standpoints should be considered simultaneously when choosing the rooftop surfaces for PV installation. Furthermore, by determining optimal hourly operation of the considered active elements, not only the additional reduction of annual network losses was achieved, but also increased accommodation of the PV systems that doesn't violate operation constraints.
Ključne besede: distribution network, optimization of operation, active network elements, PV system placement, minimization of losses
Objavljeno v DKUM: 11.06.2020; Ogledov: 1081; Prenosov: 241
Celotno besedilo (44,58 MB)
A new European market in insurance distributionMaría Rocío Quintás Eiras
, 2017, izvirni znanstveni članek
Opis: The present work provides an approach to the main changes brought to the insurance market by the introduction of the Directive (EU) 2016/1997 of the European Parliament and of the Council of 20 January 2016, which comprises the recast of Directive 2002/92 on insurance mediation. The new Directive implements relevant changes with the paramount aim of reaching a harmonization of the different national provisions concerning insurance and reinsurance distribution of the EU, both on the application scope and on the insurance consumer protection.
Ključne besede: insurance and reinsurance distribution, distribution channels, insured protection
Objavljeno v DKUM: 02.08.2018; Ogledov: 462; Prenosov: 56
Celotno besedilo (712,64 KB)
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Interactional approach of cantilever pile walls analysisStanislav Škrabl
, 2006, izvirni znanstveni članek
Opis: This paper proposes a new method for the geomechanical analysis and design of cantilever retaining structures. It is based on the limit equilibrium method, but it uses some additional conditions for interaction between the retaining structure and the ground, when referring to the distribution of the mobilized earth pressures on the structure. The greatest benefit of the proposed method is shown in the analysis of structures of layered ground (heterogeneous above the dredge level and homogeneous below it), embedded in frictional and cohesive materials, and in the possibility of considering the influence of surcharge loadings on the active or passive side of the retaining structure. When analyzing such cases in practice, the proposed method gives results which are in better agreement with the results of FEM based elasto-plastic interaction analyses than with the results of currently used methods. At the same time, its results are in accordance with those published for homogeneaus cohesionless ground. Since in practice almost all retaining structures are erected in layered ground (heterogeneaus above the dredge level and homogeneous below it), the proposed method is very convenient and applicable for the analyses and design of cantilever structures under arbitrary geomechanical conditions.
Ključne besede: geomechanics, soil-structure interaction, retaining walls, embedment, cantilevers, earth pressure, pressure distribution, friction soil - wall, limit analysis, shear forces
Objavljeno v DKUM: 17.05.2018; Ogledov: 815; Prenosov: 56
Celotno besedilo (411,22 KB)
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The function of Zagreb as a factor of the transformation of the greater Zagreb girdle : with a separate commentary on daily migrationPetar Feletar
, 2009, pregledni znanstveni članek
Opis: With an almost monocentric development, the most powerful central functions in Croatia are concentrated in Zagreb. These functions have a powerful influence on the transformation of the area towards which they gravitate. This influence is greatest on the geographic area of the Greater Zagreb girdle area, i.e. Zagreb County. The processes of the transformation of the Greater Zagreb girdle relate above all to the urbanisation and suburbanisation of the area. These processes extend to rural areas in a very spatially differentiated way, depending primarily on the level of development and the spatial distribution of the transport network. Spatial differentiation and the level of urbanisation and suburbanisation in the Zagreb environs are illustrated through an analysis of the intensity and distribution of daily migration in Zagreb and through expressed changes in the spatial distribution of inhabitation. These processes were considered to be in parallel in the period from 1948 to 2001, the period of the most intensive change.
Ključne besede: greater Zagreb girdle, spatial distribution of inhabitation, daily migration, suburbanisation, spatial differentiation
Objavljeno v DKUM: 20.03.2018; Ogledov: 744; Prenosov: 79
Celotno besedilo (135,87 KB)
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Spatial mobility of the employed population and occupational structure of the labour force in industry of the Tuzla ValleyRahman Nurković
, 2007, izvirni znanstveni članek
Opis: The objective of this paper is to show, to a certain extent, daily migrations of labour force in industry of the Tuzla valley. In addition to Tuzla, the three centres are distinguished according to importance of their function of work: Lukavac, Živinice and Banovići. On one hand, we have a strong concentration of industrial jobs, and on the other, almost unindustrialised remaining territory.
Ključne besede: daily migrations, distribution of industry, the Tuzla valley, skilled labour
Objavljeno v DKUM: 13.03.2018; Ogledov: 629; Prenosov: 96
Celotno besedilo (429,22 KB)
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