|
|
Research on the load-carrying capacity of lubricating film in rolling bearings
Šmíd, David ; Čermák, Jan (referee) ; Omasta, Milan (advisor)
This diploma thesis deals with the problem of sudden contamination of the elastohydrodynamic contact by solid particles and their influence on parameters affecting the lubricating film, such as surface texture and real film thickness, especially for line contact. The contact is operated under conditions corresponding to the operation of the main wind turbine bearings, with measurable parameters supported by optical observations. The main effort of this work is to relate the influence of the flow of solid particles in the lubricant to the parameters determining the lubrication regime. For the experiments, a taper-on-disc device was constructed to simulate linear contact. Using this device, the effects of different solid particles on the damage of a sample (roughness parameters Ra and Rq) with linear contact and the influence of this altered structure on the lubricating film thickness (hmin) are experimentally described. These remarks are partially compared with the effect of particles on point contact. The result of this paper is a better understanding of the solid particle flow in the Hertzian contact region and clarification of the influence of this flow on the surface structure and associated lubricating film thickness, especially for linear contact.
|
|
|
Concentration of grease constituents in the EHD contact and its surroundings
Palán, Miroslav ; Čermák, Jan (referee) ; Košťál, David (advisor)
The thesis focused on the study of the effect of thickener particle size and speed on the concentration of grease particles (thickener and base oil) in the contact and its close surroundings. The calibration images were taken on a sandwich module and the experiments were carried out in a ball-on-disk configuration. The distribution of particles in the grease was investigated by fluorescence microscopy, which allows separate observation of the individual particles. The results showed that the particle size of the thickener fundamentally affects its concentration in and around the contact. The larger particle size is found in the lubricant, the higher is it concentration in the contact. The work also shows the effect of changing the velocity on the change in concentration of the individual components and the connection of the transition velocity with the distribution of the components. The work gives a new perspective on the behavior of greases and provide useful knowledge for the development and optimization of greases for different applications.
|
|
|
Analysis of the Problem of a Cyclic Pursuit
Kučerová, Vendula ; Tomášek, Petr (referee) ; Čermák, Jan (advisor)
This bachelor's thesis analyzes the problem of cyclic pursuit. It deals with the characterization of cyclic pursuit problems and describes how the theory of differential equations is employed in this area. The formulation of a mathematical model is emphasized, followed by its exact solution and further analysis supported by graphical visualization of the obtained solutions.
|
|
|
Positioning device for light microscope
Materna, Jan ; Čermák, Jan (referee) ; Vlach, Radek (advisor)
The thesis deals with the design and implementation of a device prototype enabling biaxial tilt and rotation of a sample examined with an inverted light microscope. This device is also adapted for remote control. The work first focuses on the research of possible solutions and then on the design of the entire device, including motorization, control, power supply or working with samples.
|
|
|
.
Průša, David ; Žižková, Nikol (referee) ; Čermák, Jan (referee) ; Šuhajda, Karel (advisor)
In construction practice, microwave radiation is widely used for drying building materials, remediating damp masonry or sterilizing biotic pests that have invaded building structures. Another, albeit less frequent, use may be, for example, in accelerating the solidification of materials and components, where the time required to obtain the handling strength is reduced due to the effect of microwave radiation. The available scientific and technical literature indicates that some materials, such as brick elements, do not change their physical and mechanical properties when exposed to microwave radiation for moisture remediation, although this has not yet been sufficiently verified, and, in contrast, that there is a significant change in properties when microwave radiation is used to accelerate the setting of fresh mixtures, such as those containing a cementitious binder matrix. This thesis builds on many years of research in the area, complements and refines existing information, provides new insights into the mechanical and physical properties of commonly available building materials that have been exposed to controlled microwave radiation, and compares them with reference values. It also provides an opportunity for further experiments that can build on this research. The experimental research was conducted on two independent sets of samples. The first experiment was carried out on a set of clay brick samples, using tests according to European standards, and focused on the effect of microwave radiation on compressive strength and water absorption. The experimental specimens were exposed to moisture followed by exposure to microwave radiation for drying and then compared with reference specimens. The data from these experiments suggest that microwave radiation can be used for the rehabilitation of brick elements and there is no significant change in the resulting mechanical properties with respect to the initial condition. The second experiment was carried out on a set of concrete mixtures, where the curing process was accelerated using microwave radiation, and the mechanical and physical properties obtained were compared with those of reference specimens. The data from this experiment suggest that microwave radiation can be used to accelerate the curing of concrete specimens, thereby obtaining the handling strength in a relatively short time, but a reduction in the resulting strength can be expected compared with reference specimens.
|
|
| |
|
|
Specific Bellman's Lost in a Forest Problem analysis
Žůrek, Daniel ; Čermák, Jan (referee) ; Hoderová, Jana (advisor)
This thesis focuses on the analysis of a selected Bellman problem known as "Lost in a Forest." Initially, it defines and presents some auxiliary theorems important for finding the shortest escape path. The main part of the thesis focuses on the construction and analysis of escape paths in various types of forests. The thesis thoroughly examines the shortest escape path in an infinite strip of forest with unit width. The results of this thesis provide new insights into the optimization of escape paths and offer formal proofs confirming that Zalgaller's path is the shortest possible escape path in the given context. Additionally, the thesis addresses the solution for a rectangular forest with an obstacle, bringing new ideas to this area.
|
|
|
Distribution of grease in rolling bearing
Hynek, Jakub ; Čermák, Jan (referee) ; Šperka, Petr (advisor)
The work deals with the issue of grease distribution in a rolling bearing. Grease lubricated ball bearing in this way often experience the problem of starvation, when the contact area is not sufficiently supplied with lubricant, which leads to bearing failure. In general, this is a very complex and comprehensive topic. Specifically, the description of the effect of selected parameters on the distribution of grease in the rolling bearing was solved. The evaluation took place on the contact surfaces of the inner and outer ring and bearing balls. The average film thickness in selected areas at the point of contact and in front of it were evaluated. The method for observation was fluorescence microscopy. The effects of the percentage filling of the bearing with grease, the speed, the material and the design of the cage on the distribution and distribution of the grease on the bearing surfaces are described in the thesis. The result is information about the distribution of the grease on the raceways and balls of the bearing and their immediate surroundings. It was shown that the new experimental approach used makes it possible to evaluate the amount of grease available for bearing lubrication in a real configuration.
|
|
|
Study of the thermal insulation effect of thermally reflective insulations
Skříček, Darek ; Vala, Jiří (referee) ; Čermák, Jan (referee) ; Šťastník, Stanislav (advisor)
The dissertation on the topic Study of the thermal insulation effect of thermally reflective insulations is focused on the issue of measuring the thermal resistance R of thermoreflective insulations and determining the most suitable layer with the best thermal insulation properties. By measuring thermoreflective insulations on the Hot-Box measuring chamber, it was proven that higher values of thermal resistance R are always achieved with aluminum foil, which has the highest possible reflection of the radiant component of heat, i.e. the lowest possible emissivity on the surface. For this reason, the reflectance was measured on the Mid-IR Integrat IR ™ measuring apparatus. To study the thermal insulation effect of thermoreflective insulations, ten samples of these insulations with different compositions of aluminum and bubble foils are used to measure the insulation properties. The suitability of using thermoreflective insulation for building insulation was proven by measuring these foils.
|
|
|
How Language and Nation Interwine: Changes in the Language of Australian Literature from 1830 up to the Present
Císlerová, Magdalena ; Čermák, Jan (advisor) ; Willoughby, Louisa (referee) ; Horáková, Martina (referee)
While previous research has explored the relationship between national identity and language in Australia, it has not been examined on language data through history. This dissertation thus aims to trace linguistic manifestations of emerging local identity on a corpus of canonical Australian literature from 1830 up to the present. The corpus is divided into four periods based on the stages of development of postcolonial Englishes as per Schneider's Dynamic model (2007). The central hypothesis is that local identity manifests linguistically in an increased presence of the vernacular and domestic frames of reference in periods of heightened nationalism. Consequently, the nature of this study is interdisciplinary, combining linguistics with literary and cultural studies to offer a complex picture of the relationship between language and identity via a quantitative as well as qualitative analysis. The quantitative analysis concentrates on keywords, exploring both keywords generated from the corpus, using an analogically created corpus of British literature as reference, and culturally significant keywords, following Wierzbicka's (1997) theory of every culture having a set of keywords that reflect its core values. The generated lists reflect the socio-historical and cultural context, revealing common...
|
guest ::
