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Summary of unconventional aircraft concepts
Nečas, David ; Šošovička, Róbert (referee) ; Lajza, Ondřej (advisor)
This bachelor´s thesis deals with civil aircrafts of unconventional conceptions, which got into serial production. The thesis will be divided according to categories of aircrafts, whereas in every category with the exception of large transport aircrafts one conventional and two unconventional aircrafts will be specified for comparing various properties. Military aircraft will be mentioned only marginally because of the representative of significant unconventional conception.
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The effect of surface modification of acetabular cup on friction coefficient of hip implant
Cahová, Aneta ; Valena, Martin (referee) ; Nečas, David (advisor)
This bachelor’s thesis is focused on limited longevity of hip joint replacements. In order to extend the longevity of replacements effect of microtexture application on surface of artificial acetabulum cup on coefficient of friction was investigated. Attention was paid to composition of model synovial fluid and geometry and layout of texture. For joint simulation, a pendulum hip joint simulator was employed. In first part three femoral heads, two acetabulum cups and five fluids were tested, respectively two heads, four acetabulum cups and one fluid in second part. Significant effect of fluid composition and geometry and layout of texture was observed during measurement. Compared smooth and textured cup the highest decline of friction was 78 %. Results can be used for further research of micortextures. Friction reduction and prolonging lifespan of implants may eventually improve life quality of many patients.
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Analysis of friction of hip joint replacements with modification of surface topography
Němeček, Daniel ; Quinn, Cheney (referee) ; Nečas, David (advisor)
Hip endoprosthesis introduces an effective treatment for patients suffering from advanced stages of hip degeneration. Despite the advancements made in recent years, limited longevity negatively affects the application of this technology in young patients. The main mechanism which causes limited longevity is wear, which depends on the friction and lubrication of the joint. This thesis aims to observe the effect of a textured surface on a UHMWPE polyethylene cup combined with a smooth femoral head as a solution, which may reduce the friction and wear of the contact surfaces. Two textured cups and three smooth femoral heads were used in the experiment (ceramic, metal, oxinium). The results showed that the textured surface has a positive effect on both reducing friction and providing more stability with the use of synovial fluid. A significant reduction in friction is observed for the surface with smaller dimples rather than for the surface with larger ones. Specifically, the combination of a ceramic femoral head and a finely dimpled surface resulted in the reduction of friction by 66 %. Attention was also paid to the effect of the load on the hip. In most cases, the load did not significantly impact the results. It can be assumed that reducing the friction at the joint leads to the reduction of the rate of wear, thus increasing the implant longevity.
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An investigation of lubrication of knee joint replacement
Sýkora, Tomáš ; Horák, Zdeněk (referee) ; Nečas, David (advisor)
This diploma thesis deals with an experimental analysis of knee joint replacement lubrication. The experiments were realized at a knee joint simulator which can apply conditions according to certain standard and survey the phenomena by using fluorescence microscopy. The aim of thesis is to clarify the influence of particular components of synovial fluid on the lubrication process. The intensity of fluorescence expresses dimensionless parameter of a lubrication film thickness. There was a fundamental study with mineral oils before the experiments with the synovial fluid. The study allows to have a look at contact transformation during walk. Results are shown in graphs as dependency of intensity on time, including pictures showing phenomena in the contact zone. Experiment results show that protein -globulin creates a layer on the surface. There is albumin on the layer and it makes the lubricating film thicker. The protein interaction is supported by hyaluronic acid and fosfolipids which stabilizes the created structure. According to lubrication is behaviour of film related to a complex structure of synovial fluid. Thesis gives more information about behaviour of synovial fluid and can be used for future development of knee replacements.
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Bearings for space
Vavřík, Petr ; Nečas, David (referee) ; Košťál, David (advisor)
Currently, space satellites in orbit are required to operate reliably for more than 10 years. This places high demands on the satellite's tribological systems, which must function properly in the hostile space environment for this period. This bachelor thesis deals with the description of suitable bearings and their lubrication for space applications. Lubrication regimes are described at the outset. Then, space factors affecting the proper operation of tribological systems are summarized. The largest part is devoted to the description of the most used bearings and lubricants. The thesis concludes with the design of suitable bearings and their lubrication for the satellite reaction wheel.
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Stress strain analysis of the femur based on the CT data collection
Nečas, David ; Marcián, Petr (referee) ; Vosynek, Petr (advisor)
The area of clinical biomechanics is a rapidly growing engineering discipline in the world of today. This master's thesis is concerned with the stress-strain analysis of human femoral neck. In the first place it emphasizes the creation of computational model, especially the model of bone material, because of its high level of inhomogeneity. The creation of the computational model has been tested using several software packages, which are often mentioned in connection with the biomechanical tasks. The latter part of the thesis contains finite element method analysis for several material models, which are based on extensive analysis of relations used to transfer the information from computed tomography data to material model properties. Subsequently, the realization of experimental measurement is described. The final part of the thesis contains evaluated results obtained from the FEM analysis, which are also compared with the experiment.
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The effect of proteins on friction of artificial articular cartilage
Plachý, Tomáš ; Nečas, David (referee) ; Rebenda, David (advisor)
This bachelor thesis deals with the influence of the composition of synovial fluid on the coefficient of friction of artificial cartilage. The effect of protein concentration and their combination with other components of synovial fluid on the coefficient of friction of CD hydrogels simulating artificial cartilage is observed. All experiments were performed at a constant load of 10 N, speed 10 mm / s, temperature 37 ° C. In experiments investigating the effect of a combination of hyaluronic acid and phospholipids together with proteins, concentrations corresponding to a healthy individual were used. In experiments where the effect of the proteins themselves and their own combinations was investigated, concentrations corresponding to both a healthy individual and patients with advanced osteoarthritis or patients with aseptic release of the prosthesis were used. The work shows that when using the proteins alone, or their combination, there is a decrease in concentration of friction coefficient with increasing concentration. However, if hyaluronic acid alone or phospholipids alone is added to the protein, the coefficient of friction increases. The reduction occurs only after the addition of the combination of acid and phospholipid.
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Experimental rig for study of lubricant film in compliant contact of oil seal using fluorescence technique
Michalec, Michal ; Nečas, David (referee) ; Dočkal, Kryštof (advisor)
The thesis deals with design of the device that is used for observation of lubricant film thickness in line, compliant contact of rotary lip seal. The problem is, that with use of components made from standard materials, it is not possible to look inside their contact. Therefore, it is necessary to replace one body by optical transparent material, that will allow the insight into the contact using existing equipment, which is fluorescence microscope. In theoretical part are described issues of lubrication and observing method of fluorescence. Based on findings, there was designed a device allowing observation of lubricant behaviour. The last part of thesis describes modified design of existing equipment and individual components in detail. Functionality of designed experimental rig was verified by experiments using of R834/80 mineral oil.
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The design of eye-lens simulator
Špaček, Matěj ; Rebenda, David (referee) ; Nečas, David (advisor)
The aim of this bachelor thesis is a design of an eye-lens simulator. Tribometer module in pin-on-ring configuration was designed to allow direct observation of a contact zone. The survey of existing tribometers was conducted as a part of the thesis, based on which, three concept solutions were suggested. Final solution of the module was chosen and designed based on the concepts. The apparatus enables to simulate conditions of real human eye so it could contribute to a contact lens research and eye lubrication solution development.
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Lubricant film formation in compliant contact
Jaroš, Tomáš ; Čermák, Jan (referee) ; Nečas, David (advisor)
This diploma thesis deals with the study of film formation in compliant contact. Primary attention is dedicated to the influence of the entrainment speed and slide-to-roll ratio (SRR) on the central film thickness. Based on a research study of the available experimental methods, the fluorescence microscopy was used to achieve the aim of the work. Experiments were realized in ball-on-disk configuration. Firstly, a validation of the method was performed where the solid contact of the ceramic ball and the glass disk was analyzed. Since the measured values were in a good agreement with the theoretical prediction, a ball of NBR rubber material, which is commonly used for production of lip seals and o-rings, was subsequently used. The experimental measurements were performed under pure rolling and rolling/sliding conditions when the entrainment speeds varied in the range from 10 to 400 mm / s. A constant load of 0.2 N was applied. The measured data were then compared to the theoretical predictions for compliant contacts. The results showed that the thickness of the lubricating film gradually increases with increasing entrainment speed, which corresponds to theoretical assumption. Against expectations, evident influence of SRR on the film formation has been observed. In the last part of the thesis the measured data are confronted with previously published studies. Finally, some limitations of this study are discussed and recommendations for further improvement of the used experimental method are suggested.
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