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The dynamic characteristics of check valve
Pavlík, Václav ; Dokoupil, Pavel (referee) ; Habán, Vladimír (advisor)
This master´s thesis provides an overview of all designs of check valves, their usage and typical features. Main purpose of this work is to clear up the phenomenon of check valve slam and the other problems that occur during transients. The check valve slam was measured at the test rig in the hydraulic laboratory. For unsteady flow evaluation after pump shut down was used Gibson method. The dynamic characteristic was possible to create by results from this method. It was achieved without impact of the speed of sound in the fluid. This work also contains 2D transient CFD calculations, which was used for evaluation of the hydrodynamic torque acting on the hinge pin. This approach provides an option to calculate wide range of cases at the expense of not entirely exact geometry. The main contribution of the theoretical study at the beginning of this thesis is its entireness. It might give an important clue when right valve is selecting. For good choice of valve might be helpful to use dynamic characteristics in this thesis presented. Mentioned characteristics were created by new way and its background is in measurements and simplified CFD calculations.
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High pressure hydraulics in agricultural machinery
Pavlík, Václav ; Kárník, Jan (referee) ; Soukup, Lubomír (advisor)
This bachelor thesis provides an overview of the most used ways of converting kinetic energy into pressure energy and the other way around by using hydrostatic converters. It is focused on the issue of high-pressure hydraulic mechanisms in agricultural machinery. In the next section I focused on getting an overview of the function of sophisticated hydraulic systems in current tractors and calculation of heat losses of lifting weight by front three-point hitch. For solving was used Bernoulli equation for real flow in pipes.
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Formation and evolution of dynamical binaries
Pavlík, Václav ; Šubr, Ladislav (advisor) ; Heyrovský, David (referee)
The aim of this work is the study of hard binary stars in the star cluster and their time of life before they crossed the energetic boundary, which separates the soft and hard binaries. We used our own method of identification of binary stars within the model of star cluster which is based on the given positions, velocities and masses of stars. This method uses three main criteria -- the proximity of two stars, the time that this pair was found together and negative total energy. The results that we obtained using our algorithm helped us to determie more precise boundary between the hard and soft binary than the analytical estimates based on the evaluation of the typical kinetic energy of the free stars within the cluster. We also studied the lifetime of the binaries before they become hard and we reached a correspondence with the results of Tanikawa et al. (2011), who studied similar topic. Due to a large set of numerical realizations, which we analysed, we got better statistics than previous works. We also found that the examined lifetime of binaries seems to be represented by exponential distribution. For better analysis of this distribution it would be necessary to use about five times higher time resolution than we worked with.
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Perturbed stellar motion in dense star clusters
Pavlík, Václav ; Šubr, Ladislav (advisor) ; Davies, B. Melvyn (referee) ; Portegies Zwart, Simon (referee)
Star clusters are thought to be the birthplaces of stars as well as the building blocks of galaxies. They typically consist of thousands to millions of stars bound together by self-gravity. These systems evolve on the scale of Myr to Gyr, there- fore, it is impossible for us to see any change in their global evolution even within hundreds of human lifetimes. Although the equations of motion of stars in a star cluster are simple New- tonian, it is impossible to predict precisely history of any star within them to any point in the future. Therefore, we may either compare the observations of different star clusters at different age, we may invent theoretical approaches and analytical predictions, or we must follow their evolution numerically (e.g. with direct N-body integrators) which is the main focus of my research and this thesis. First, we follow the evolution of star clusters in general while coming up with a novel method to estimate their characteristic timescale (i.e. the time of core collapse) based on global parameters. The core collapse is directly linked to the formation of hard binary stars, thus, we focus on their analysis as well. We also follow several recent observational results: (i) ALMA observations of the Serpens South star-forming region indicate that star clusters are born mass...
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Modelling the Orion Nebula Cluster
Pavlík, Václav ; Šubr, Ladislav (advisor)
Title: Modelling the Orion Nebula Cluster Author: Václav Pavlík Department: Astronomical Institute of the Charles University Supervisor: doc. RNDr. Ladislav Šubr, Ph.D. (Astronomical Institute of the Charles University) Abstract: Young star clusters are widely discussed from the point of view of their evolution and structure. In this work we focused our attention on studying a typical representative of these objects - the Orion Nebula Cluster (ONC, M 42) - based on the observational data, including their confrontation with N- body models from Šubr et al. (2012). These numerical models were inspired by the recently proposed evolutionary scenario, according to which the star clusters begin their evolution from very dense initial conditions. From the analysis of the X-ray sources we revealed that the ONC is likely to be rotationally symmetric in the inner area (� 0.7 pc). Further analysis including also optical and IR observational data led us to the conclusion that the ONC is elongated from the North-East to the South-West on large scales (up to 2 pc). We also compared radial profiles of different mass groups of stars and we discovered a possibly inverse mass segregation between stars with masses in the interval (1 ; 5) M⊙ and the stars less massive than 0.5 M⊙ in the range from 0.5 pc to 1.5 pc. This...
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Perturbed stellar motion in dense star clusters
Pavlík, Václav ; Šubr, Ladislav (advisor) ; Davies, B. Melvyn (referee) ; Portegies Zwart, Simon (referee)
Star clusters are thought to be the birthplaces of stars as well as the building blocks of galaxies. They typically consist of thousands to millions of stars bound together by self-gravity. These systems evolve on the scale of Myr to Gyr, there- fore, it is impossible for us to see any change in their global evolution even within hundreds of human lifetimes. Although the equations of motion of stars in a star cluster are simple New- tonian, it is impossible to predict precisely history of any star within them to any point in the future. Therefore, we may either compare the observations of different star clusters at different age, we may invent theoretical approaches and analytical predictions, or we must follow their evolution numerically (e.g. with direct N-body integrators) which is the main focus of my research and this thesis. First, we follow the evolution of star clusters in general while coming up with a novel method to estimate their characteristic timescale (i.e. the time of core collapse) based on global parameters. The core collapse is directly linked to the formation of hard binary stars, thus, we focus on their analysis as well. We also follow several recent observational results: (i) ALMA observations of the Serpens South star-forming region indicate that star clusters are born mass...
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The Evaluation of quality of conserved fodder and recommendations of conservation technology improvement in selected farm
PAVLÍK, Václav
The aim of this thesis was to assess the quality of preserved forage in various ways of preserving silage. Sensory evaluation of the fermentation process and laboratory evaluation was used to assess the quality of legume-based silages in various preservation technologies. In addition, forage preservation in silage pressing technology was compared with and without additive (Silafor 2000 Plus). The literature review shows the importance of feed conservation, basic methods of conservation of forage, botanical composition of forage crops, conservation principles and their processes. The following are the advantages and disadvantages of preservation processes. In total, 3 ways of preservation of legume-free mixture - baling of foil, silage trough and silage bag - were evaluated. The evaluation of the results of the technology was based on the best results of the method of preservation in the bag, the preservation in the pit, the package using adiditive and the lower quality preservation of the package without additive. The forage quality was also significantly influenced by the proportion of oats in the mixture and the phenophase of the harvest.
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Modelling the Orion Nebula Cluster
Pavlík, Václav ; Šubr, Ladislav (advisor)
Title: Modelling the Orion Nebula Cluster Author: Václav Pavlík Department: Astronomical Institute of the Charles University Supervisor: doc. RNDr. Ladislav Šubr, Ph.D. (Astronomical Institute of the Charles University) Abstract: Young star clusters are widely discussed from the point of view of their evolution and structure. In this work we focused our attention on studying a typical representative of these objects - the Orion Nebula Cluster (ONC, M 42) - based on the observational data, including their confrontation with N- body models from Šubr et al. (2012). These numerical models were inspired by the recently proposed evolutionary scenario, according to which the star clusters begin their evolution from very dense initial conditions. From the analysis of the X-ray sources we revealed that the ONC is likely to be rotationally symmetric in the inner area (� 0.7 pc). Further analysis including also optical and IR observational data led us to the conclusion that the ONC is elongated from the North-East to the South-West on large scales (up to 2 pc). We also compared radial profiles of different mass groups of stars and we discovered a possibly inverse mass segregation between stars with masses in the interval (1 ; 5) M⊙ and the stars less massive than 0.5 M⊙ in the range from 0.5 pc to 1.5 pc. This...
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Modelování Velké mlhoviny v Orionu
Pavlík, Václav ; Šubr, Ladislav (advisor) ; Jungwiert, Bruno (referee)
Title: Modelling the Orion Nebula Cluster Author: Václav Pavlík Department: Astronomical Institute of the Charles University Supervisor: doc. RNDr. Ladislav Šubr, Ph.D. (Astronomical Institute of the Charles University) Abstract: Young star clusters are widely discussed from the point of view of their evolution and structure. In this work we focused our attention on studying a typical representative of these objects - the Orion Nebula Cluster (ONC, M 42) - based on the observational data, including their confrontation with N- body models from Šubr et al. (2012). These numerical models were inspired by the recently proposed evolutionary scenario, according to which the star clusters begin their evolution from very dense initial conditions. From the analysis of the X-ray sources we revealed that the ONC is likely to be rotationally symmetric in the inner area (� 0.7 pc). Further analysis including also optical and IR observational data led us to the conclusion that the ONC is elongated from the North-East to the South-West on large scales (up to 2 pc). We also compared radial profiles of different mass groups of stars and we discovered a possibly inverse mass segregation between stars with masses in the interval (1 ; 5) M⊙ and the stars less massive than 0.5 M⊙ in the range from 0.5 pc to 1.5 pc. This...
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The comparison of different technologies of bulky fodder crop conservation
PAVLÍK, Václav
This bachelor thesis deals with comparison of various technologies for roughages preservation. Roughages represent a great part of basic ration for farm animals. The introductory part of this thesis deals with the importance of preservation itself and the basic ways of roughages preservation. Several processes, principles and technologies of preservation by dry curing process and silage are also described here. Further, the thesis lists advantages and disadvantages of individual preservation technologies and silage additives. The second part of the thesis is focused on observing and sensory evaluation of fodder quality within various ways of preservation - silage in silage mangers, silage in bags, wrapped silage bays and bales of hay. Are designed appropriate progresses preservation bulky forage for farm animals in a companies with different volume of production. As suitable way of conservation it´s a conservation by silage in a sac and in round packaging or by high pressure stamping hay into a round packages.
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