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A Symmetric Homophily-preserving Opinion Diffusion Model
Prokop, Aleš ; Koutecký, Martin (advisor) ; Talmon, Nimrod (referee)
We define and study a symmetric homophily-preserving opinion diffusion model on clusters of voters. This model is symmetric, which means that clusters of voters influence each other. The model is also homophily-preserving, meaning when a voter changes their opinion, their neighborhood also changes, which is a frequently observed property of social sites. We present properties of the diffusion model, such as convergence, ϵ-convergence for some types of graphs, and polyhedral description of the set of fixed points, as well as generalizations on graphs with weighted edges and directed graphs and their properties. We provide the definition of the threshold diffusion process. We study fixed points of the diffusion and threshold diffusion process. We also provide a program for experimentation on our model. 1
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Numerical simulation of oil flow in the gearbox
Činčár, Vojtěch ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
Component design, subsequent functional verification and possible optimization are an integral part of any production process. Based on increasing customer requirements, the aim is to achieve the smallest possible dimensions and the lowest possible price, while maintaining safety. Incorporating both aspects can be achieved using advanced computational approaches, while this work focuses on the area of flow simulation. Specifically, it deals with the analysis of oil flow in a railway vehicle gearbox using computational fluid dynamics or CFD. The flow simulations were performed using ParticleWorks software, which works with the semi-implicit moving particle method MPS, whose suitability was verified by short analysis works. By monitoring the flow in the workspace, the geometry of the gearbox housing was first verified. However, the critical areas are the bearings whose lubrication quality was analysed using a series of computational models that included the service conditions that may occur. In addition to summarizing the overall evaluation, the paper concludes by outlining a possible suggestion for the potential improvement of bearing distribution and lubrication quality.
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Influence of bevel gear modifications on the transmission error
Martinka, Tomáš ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This diploma thesis deals with the problem of transmission error in gears with a specific focus on bevel gears with straight teeth. The course of the transmission error and especially its peak value (PPTE) directly affects the noise of the transmissions and thus the noise of the entire gear device. In the long term, therefore, one of the main goals in the field of gear manufacturing and application is to reduce the value of PPTE. In this work, the influence of the modification of a specific bevel gear on the resulting static transmission error (STE) under static conditions is investigated. One way to modify a gear is to use a macrogeometric approach, where it is possible to adjust the number of teeth, gear modulus, gear engagement angle, and other factors that further affect the size of the gear and can significantly affect the resulting forces in the gearing. which can further lead to the impossibility of installation in the existing equipment and therefore this approach must be taken into account when designing the equipment. Another possibility is a microgeometric approach, which, with sufficient load-bearing capacity of the equipment components, will allow the assembly of gears in existing equipment while maintaining the original dimensions of the gears. The research of this thesis includes the definition and classification of gears based on the relative angle of the axes of rotation of the wheel and pinion, the geometry of the teeth and the pitch and the shape of the control curve of the teeth. Another area of focus of the research is the definition of the transmission error and the effects of its course on the noise of equipment equipped with transmissions. The practical part of this work is focused on the comparison of the course of the STE detected by the finite element method (FEM) in the program Ansys Workbench 2022/R2, into which individual variants of the gear models with applied adjustments were exported in the STEP format. and further modified in the Space Program Claim. The work is focused on investigating the effect of the size of a short height modification for multiple load moments, the effect of tooth height modification, the effect of shape modification and the effect of wheel axial position deviation on STE. The results of the analysis of the individual variants are compared based on the course of the results of the transmission errors with regard to the maximum contact stress of the flanks of the engaging teeth and the maximum stress in the heel of the tooth.
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Injection System with Pressure Accumulator for Vehicles of NRMM Category
Pavlík, Martin ; Prokop, Aleš (referee) ; Dundálek, Radim (advisor)
This bachelor thesis deals with the common-rail system in NRMM diesel engines and its application mainly in tractors. In the research part of the thesis is given a division of the system, a description of used components with an explanation of their function and furthermore examples of the manufacturing companies of these components. The second part of the thesis focuses on the components currently used in designs of fuel systems for specific machines. The parts of the tractors fuel system are presented in the thesis. Injection pressures were measured from data of sensor located on the high-pressure rail. The final part of the thesis focuses on produced pollutants while combustion process, the Stage V emission standard, emission reduction methods and the effect of alternative propulsion on the NRMM.
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Hybrid and Electric Powertrains of the Trucks
Mrkva, Filip ; Řehák, Kamil (referee) ; Prokop, Aleš (advisor)
This bachelor's thesis deals with current trends in construction of electrified powertrains of trucks. Individual concepts are described and divided according to the arrangement and degree of electrification of the drive. Based on the most actual information from the manufacturers' websites, the parameters of the components used in real vehicles equipped with alternative powertrains are analysed. Real powertrains are evaluated in terms of usability in operation, operating costs, and environmental friendliness. Advantages and disadvantages of hybrid, battery and hydrogen trucks compared to conventional vehicles with internal combustion engines are discussed. Furthermore, the direction in which the discussed branch of the automotive industry will continue to develop is mapped, as well as the most significant obstacles and challenges associated with it. As part of the work, battery cars with an integrated electric axle were evaluated as the most promising for a relatively simple drive design, easy charging, and sufficient range for many applications. Key problems in the developing electric vehicle industry were also pointed out, which are mainly the low energy density of battery and hydrogen cells together with the energy-demanding production of batteries.
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Design of a parking brake for vehicles powered by an electric motor
Kolčava, Jiří ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This diploma thesis deals with issues in the field of latch parking brakes, specifically the control mechanism. The key element of the work was the structural design of this mechanism, which converts the rotary movement of the electric motor into the translational movement of the control member enabling the latch to be inserted and extended from the latch wheel. The research part describes the main components of the mechanism and a description of individual types of control. This is followed by the creation of four conceptual designs and the selection of the optimal solution using the method of weighted coefficients. The structural part contains analytical strength calculations of the chosen conceptual design, including the solution of the kinematics of the mechanism. This part also deals with the analysis of the torque from the activation spring depending on the rotation of the crank mechanism and the subsequent optimization of the electric motor. In the end, the analytical strength calculations of selected structural units are verified by FEM analysis to confirm the functionality of the mechanism.
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Digital twin
Kopeček, Pavel ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This thesis deals with the issue related to digital twin technology, which is developing during the current 4th industrial revolution primarily based on digitization across industries and in the near future, if properly applied, can be one of the core elements of most industrial processes. A digital twin represents a virtual representation of a physical object (machines, functional components, for example, within cars or even a part of the human body), with which it transmits information to each other in the form of data important for the target functions of the digital twin through the created communication channel. With the use of the obtained data, the control algorithm of this technology and through simulation models contained in the virtual space of the digital twin, this technology enables real-time work, the purpose of which is to perform an analysis of the operational state for the purpose of its evaluation, correction or, using the so-called "what-if" analyses, even its prediction, with the aim of achieving the most efficient use of real objects during their entire life cycle (production process of the object, operation and maintenance of the object, disposal of the object). The main outputs of this work are, from a research point of view, the performance of a critical evaluation of the current state of the application of digital twins within the industrial world and the creation of a digital twin creation algorithm, from a practical point of view, the creation of selected input 3D analyzes (simulation models) and the creation of a reduced ROM model for the purpose of creating basic building blocks for a digital twin of two-stage train transmission. For the practical part the Ansys Workbench system package and a relatively new system for calculating dynamic tasks called Ansys Motion were used.
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Computational Modelling of the Transmission Dynamic Behaviour
Švub, Pavel ; Řehák, Kamil (referee) ; Prokop, Aleš (advisor)
This thesis focuses on constructing a computational model of a gearbox using Matlab software, with the main objective of analysing the dynamic loads that occur during gearbox operation. The thesis examines the most important sources of dynamic forces in gear mechanisms, such as gear backlash, gear mesh stiffness, bearing stiffness, and shaft stiffness. Furthermore, it provides an overview of basic mathematical models used for modelling the dynamics of gear transmissions. Based on these findings, a custom model of a two-shaft gearbox is developed, which also allow gear shifting. Synchronization with a flexibly limited force is utilized for gear shifting. This model is then subjected to various loading conditions to monitor the response of individual components, including gear forces, bearing loads, and the magnitude of transmission error.
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Computational Modeling of Dynamic Behaviour of Tractor
Hejčl, Pavel ; Řehák, Kamil (referee) ; Prokop, Aleš (advisor)
This work deals with the assessment of the effects of a rear-mounted mower on tractor dynamics. The first part summarizes knowledge of the used tractor suspension variants and their various modifications. Furthermore, the current possibilities for simulating the dynamics of tractors and the construction of the rear three-point hitch are described. The main part of the work is devoted to the assembly of the multibody model of the tractor with the rear-mounted mower. The correctness of the assembly of the virtual tractor prototype is verified by comparison with the technical experiment on the real tractor. The validated model is further used to analyse various well-defined steady-state and transient driving conditions typical of this set.
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Numerical simulation of oil flow in bearing housing
Zogata, Filip ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This thesis is concerned with the development of a computational model of the bearing node, since in the development of a synchronous generator, great emphasis is placed on the proper design of the bearing node, as this complex component has a direct effect on the overall efficiency of the generator. A large number of engineering experiments need to be used to test on the physical model, but it is also necessary to test using the numerical model, as the production of the prototype itself for testing is very costly, and therefore it is advisable to verify the prototype itself before production by a series of numerical simulations. Another important feature is the possibility to investigate even unfavourable or even extreme conditions, which are already very difficult, sometimes impossible, to test physically in the laboratory, and these numerical simulations can be divided according to several parameters, but in the field of bearing nodes we mainly encounter structural, dynamic, temperature or flow problems. This thesis in particular is focused on establishing a basic overview of computational fluid dynamics in the oil flow domain, while this knowledge is used in practice, as another objective is to develop a numerical model of lubrication of the aforementioned bearing node. However, this is a very complex problem, and therefore a study is first carried out to investigate the key components, and only by gradually adding different elements is the numerical model created in the Particleworks software environment, while a sensitivity study is carried out focusing on particle size. Subsequently, the individual partial results are summarized in the conclusion of this paper.
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