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Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Macháček, Michael ; Hračov, Stanislav
Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, critical onset wind speeds, and global dynamic response of a very low-tensioned line with simulated icing observed on similar real conductors. Due to the highly nonlinear mechanical behavior of such a flexible cable, we employed the Newmark integration method combined with the iterative Newton-Raphson method. We analyzed two numerical models of the overhead line loaded by the wind: one assuming nonlinearity only in the wind load, while retaining the linearity of the mechanical system itself, and the other representing a fully nonlinear system including geometrical nonlinearity. Our analysis revealed that the determined critical wind speeds for the onset of galloping are in relatively close ranges for both models. However, numerical simulations with the fully nonlinear system indicated significantly lower amplitudes of limit cycle oscillations, especially at higher wind speeds, compared to the linear model of the line. This underscores the necessity of using fully nonlinear models during the design stage of such low-tensioned aerial conductors.
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LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka ; Hračov, Stanislav ; Macháček, Michael
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method.
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Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav ; Macháček, Michael
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis.
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Interviews with Graphic Designers
Šafářová, Gabriela ; Přidalová, Kateřina (referee) ; Macháček, Mikuláš (advisor)
My diploma thesis consist in creating short videos. I have been interviewing important Czech graphic designers of an older generatin and I've been interested in socio-historical background which a profession of graphic design had before Velvet revolution and before new media coming. The project got a name Graphic Design Talks. The videos are put on Facebook with other information about each designer. I would like to continue interviewing new deigners add new videos even after I finish my study.
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What was/is the meaning of independent publications in countries with a totalitarian regimes?
Demovičová, Barbora ; Čumlivski,, Jan (referee) ; Macháček, Mikuláš (advisor)
Is it important that a graphic designer/art student expresses their opinion on the society and world around them through their work? How can a graphic designer influence social situation, the community in which they live, or other events? What is the role of civic protest and activism? What is the relationship between art and politics? What is the political power of the art? Researching the role of political art, independent publishing, civic actions and comparing the public protests in the past with protests today lead to creating a self-published independent publication reflecting current issues in Slovakia. Focus on Slovak society came after the murder of investigative journalist Ján Kuciak and his fiancée Martina Kušnírová resulting in a wave of public protests and formation of new government of Slovak Republic. This publication is mix of hope for change, idealism, and later scepticism and frustration. This publication is comprised of author’s personal texts and interviews with different persons working in various fields, for example with investigative journalist Marek Vagovič, sociologist and one of the leaders of Velvet Revolution Fedor Gál, publisher and owner of samizdat library Libri Prohibiti Jiří Gruntorád, or Slovak artists Peter Kalmus and Miroslav Cipár.
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Lifetime measurement of current carriers in silicon solar cells structures
Macháček, Martin ; Hégr, Ondřej (referee) ; Boušek, Jaroslav (advisor)
This thesis deals with a lifetime measurement of current carriers in silicon solar cell structures. In the first chapter there is a description of several recombination models and their participation at a final effective lifetime value. By using these recombination models in a computer simulation it is possible to receive approximate evaluation of some important silicon solar cell structure parameters. The PC1D simulation program was used for this thesis. For the lifetime measurement of real test-wafers two methods were used: QSSPC (quasi-steady-state photoconductance) and MW-PCD (microwave photoconductance decay). There is a detail description of these methods, used measurements machines and differences between both of them in the chapter four. The main objective of the thesis is mentioned in the last chapter, which is mainly focused on a chemical passivation of silicon wafers and deals with a problem of post-passivation wafer cleaning. There are three passivation techniques mentioned: the iodine in ethanol solution, the iodine and polymer in ethanol solution and the quinhydron in methanol solution. In two cases a results, that are adequate to return the tested wafers in the manufacture process, were achieved.
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The Lucy Collective - Women Of History, Women Of Fiction
Franková, Anna ; Herout,, Adam (referee) ; Macháček, Mikuláš (advisor)
This project is a prototype of a database-driven website with user-editable content The Lucy Collective – Women Of History. This site will collect information about historical women and links to sources related to them, and serve as a "first-step" resource for educators, creators, and other people interested in the topic. The prototype's main goal is to present the intended structure, useability, and design of the final website, and serve as a basis for building the final working version.
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Low Budget Publications
Bařina, Karel ; Hanzalová, Markéta (referee) ; Macháček, Mikuláš (advisor)
Artist’s book named „For example like this“ should be a guide for design beginners as well as for advanced graphic designers. The book is adressing problems and ambiguities around designing a publication which designers often have to deal with and which shouldn’t be forgotten. It is also a guide in the case that a designer chooses to craft a book on his/her own.
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The Magazine
Drinková, Kristína ; Macháček, Adam (referee) ; Macháček, Mikuláš (advisor)
By this bachelor work I try to design a visual line of the independent online FAVU "magazine", which is to communicate information about events in studios, exhibitions, about students and lectures in a consistent form.
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