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Space mission design
Koziel, David ; Navrátil, Jan (referee) ; Zikmund, Pavel (advisor)
In this work, there are basic laws and knowledge relating to space flights into an orbit around the Earth. Also, there are instructions for beginners, who want to work with the GMAT program (General Mission Analysis Tool), which is the program used for designing space missions. In the final part of the work, there is also a use of the program demonstrated on a specific mission of a satellite (CubeSat) into the Geostationary Earth Orbit. In this section, there is a described method of work, individual relevant functions of the program and possibilities, and a way of work in it. Finally, graphical and data outputs of the simulation are evaluated. Therefore, the output of the work is complex characteristics of the basics of problems of space mission design and a brief GMAT software guide, which could be used in the future to teach.
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Dynamic characteristics obtained from solution of simple vocal folds models
Kubíček, Radek ; Švancara, Pavel (referee) ; Hájek, Petr (advisor)
Bachelor’s thesis concerns the biomechanics of voice and its aim is to obtain dynamic characteristics of simple analytical and numerical vocal folds models. Thesis includes main theories of voice production and thorough analysis of the widest used computational models. Essential is an anatomical and physiological introduction including basic pathologies. Behaviour of computational models mentioned in the bibliographic research is demonstrated by the dynamics characteristics gained by modal analysis and by the solid mechanics equation solution. Eigenfrequencies come under range from literature. The aim of thesis is comparison of analytical and numerical solution and particular computational models.
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Optimization of Modal Damping of Blades in High Pressure Stages of Steam Turbine
Lošák, Petr ; Malenovský, Eduard (advisor)
Steam turbine rotor is a very complicated assembly, typically consists of several rotor rows. Due to design limitations and increasing demands on the efficiency of the steam turbines, it is practically impossible to avoid all of the resonant states. The significant vibrations can occur, for example, due to passing resonance state during turbine start up or run out. In the worst case the turbine operates state is close to the resonance state of the rotor row. This leads to the significant oscillation of the bladed disk, and may results in the blade (or blade to disk joints) high cycle fatigue. These parts are highly loaded components and any cracks are unacceptable. Therefore it is absolutely necessary to damp vibration by using, for example, passive damping elements. The damping element analyzed in this thesis is a strap with an isosceles trapezoidal cross section, which is placed in the circumferential dovetail groove in the blade segmental shrouding. The sliding between the contact surfaces leads to the dissipation of energy which causes decreasing of undesirable vibrations. The main aim is to design the optimal dimensions of the strap cross-section with a view to the most effective damping of vibration for a particular turbine operating state. Considered bladed disk has 54 blades which are coupled in 18 packets by segmental shrouding. The damping element is paced in circumferential dovetail groove created in the shrouding. This type of damping element is suitable especially for damping vibrations in the axial direction and only with the mode shape with the nodal diameters. The modal properties of the bladed disk are influenced by the sliding distance. Since the friction force depends on centrifugal force acting on the damping element and on the angle of the side walls of the strap and groove, the sliding distance can be influenced by the damping element dimensions. During the optimization process the best possible size of middle width, height and angle of damping element cross-section is searched. The strap weight, contact area size and flexural stiffness of damping element can be influenced by these parameters. Their change has also impact on the size of the contact pressure and thus on the size of relative motion as well. As stated previously, the damping efficiency is influenced by the relative motion between the damping element and shrouding. Numerical simulation in time domain is very time-consuming, especially for systems containing nonlinearities. In order to verify dynamic behavior of the computational model with the passive friction element in numerical simulations, the simplified model is created. The model is created in the ANSYS environment. The main requirement imposed on this model is to have as small number of degrees of freedom as possible, so the time needed to perform the simulation is reduced to a minimum. To satisfy this requirement the simplified model is a cantilever beam with rectangular cross section. The dovetail groove is created in this model in longitudinal direction. In this groove is damping element. In addition to damping element dimensions optimization, the influence of each design variable on model dynamic behavior is studied. The results are verified experimentally. Experiment also shows other interesting results that confirm the damping element influence on the modal characteristics. The gained knowledge is used to optimize the dimensions of the damping element in the model of the bladed disk.
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Optimization of Modal Damping of Blades in High Pressure Stages of Steam Turbine
Lošák, Petr ; Zeman,, Vladimír (referee) ; Pešek, Luděk (referee) ; Kellner,, Josef (referee) ; Malenovský, Eduard (advisor)
Steam turbine rotor is a very complicated assembly, typically consists of several rotor rows. Due to design limitations and increasing demands on the efficiency of the steam turbines, it is practically impossible to avoid all of the resonant states. The significant vibrations can occur, for example, due to passing resonance state during turbine start up or run out. In the worst case the turbine operates state is close to the resonance state of the rotor row. This leads to the significant oscillation of the bladed disk, and may results in the blade (or blade to disk joints) high cycle fatigue. These parts are highly loaded components and any cracks are unacceptable. Therefore it is absolutely necessary to damp vibration by using, for example, passive damping elements. The damping element analyzed in this thesis is a strap with an isosceles trapezoidal cross section, which is placed in the circumferential dovetail groove in the blade segmental shrouding. The sliding between the contact surfaces leads to the dissipation of energy which causes decreasing of undesirable vibrations. The main aim is to design the optimal dimensions of the strap cross-section with a view to the most effective damping of vibration for a particular turbine operating state. Considered bladed disk has 54 blades which are coupled in 18 packets by segmental shrouding. The damping element is paced in circumferential dovetail groove created in the shrouding. This type of damping element is suitable especially for damping vibrations in the axial direction and only with the mode shape with the nodal diameters. The modal properties of the bladed disk are influenced by the sliding distance. Since the friction force depends on centrifugal force acting on the damping element and on the angle of the side walls of the strap and groove, the sliding distance can be influenced by the damping element dimensions. During the optimization process the best possible size of middle width, height and angle of damping element cross-section is searched. The strap weight, contact area size and flexural stiffness of damping element can be influenced by these parameters. Their change has also impact on the size of the contact pressure and thus on the size of relative motion as well. As stated previously, the damping efficiency is influenced by the relative motion between the damping element and shrouding. Numerical simulation in time domain is very time-consuming, especially for systems containing nonlinearities. In order to verify dynamic behavior of the computational model with the passive friction element in numerical simulations, the simplified model is created. The model is created in the ANSYS environment. The main requirement imposed on this model is to have as small number of degrees of freedom as possible, so the time needed to perform the simulation is reduced to a minimum. To satisfy this requirement the simplified model is a cantilever beam with rectangular cross section. The dovetail groove is created in this model in longitudinal direction. In this groove is damping element. In addition to damping element dimensions optimization, the influence of each design variable on model dynamic behavior is studied. The results are verified experimentally. Experiment also shows other interesting results that confirm the damping element influence on the modal characteristics. The gained knowledge is used to optimize the dimensions of the damping element in the model of the bladed disk.
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The Influence of Passive Safety Features During Vehicle Collisions with Pedestrians
Mrázek, Jan ; Vémola, Aleš (referee) ; Tokař, Stanislav (advisor)
This thesis deals with the influence of passive safety features during vehicle collisions with pedestrians. The first part focuses on introducing the basic components of active and passive vehicle safety. The second part deals with construction and usage of modern components of passive safety during vehicle collisions with pedestrians. A comparing situation model of vehicle collisions with pedestrian is introduced in the third part for which a simulation programme has been used. At the close of this part there is a result synthesis of these model situations. The last part deals with the possibility of increasing pedestrian safety.
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Computational simulation of cross-roll leveling of rods
Benešovský, Marek ; Vrbka, Jan (referee) ; Petruška, Jindřich (advisor)
Final thesis describes two variants of computational models to simulate cross-roll leveling of rods, which are based on the Lagrangian approach to describe the continuum. Implementation of both variants was performed in ANSYS software, and their main difference lies in the choice of the type of elements for the discretization. An integral part of this thesis is the description of the principle, which is an evaluation of the curvature of the rod after completion of the simulation leveling. In the other part of the work are presented the results, which are then compared with realized experiment and simulation algorithm for cross-roll leveling based on the Euler approach. The final part is dedicated to the optimal settings of the leveller.
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Simulation of the sound transfer via human ear
Hájek, Petr ; Švancara, Pavel (referee) ; Pellant, Karel (advisor)
The presented thesis concerns the biomechanics of hearing. The main aim of this work is the determination of so called corrections which allow for the comparison of synthetic audiograms and measured audiograms. With these corrections we attempt to overcome the discrepancy that exists between the computational modelling and audiological measurement. The discrepancy lies in a fact that the computational modelling usually simulates the sound coming from a free eld to the external auditory canal, while audiological measurement is realized by audiological headphones, whether the auditory system is healthy or injured. Then corrections adjust the computational model so that the obtained result is comparable to audiological measurement. In this work is also addressed the influence of stapes kinematics to the excitation of basilar membrane. The movement of stapes consists of piston-like movement and rocking movement. The computational simulation shows which movement is more signicant for the excitation of basilar membrane and how this effect can be used in otosurgery, in particular, for type IV of tympanoplasty.
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Computational modelling of noise inside cabin of aircraft VUT 100 Cobra
Prnka, Jiří ; Houfek, Lubomír (referee) ; Švancara, Pavel (advisor)
This master’s thesis deals with the computational simulation of low-frequency noise inside the cabin of small commercial airplane VUT 100 Cobra. For this low-frequncy range deterministic methods: Final Element Method (FEM) and Boundary Element Method (BEM) are used for simulation of the dynamic behaviour of the object. FEM has been used to compute eigenmodes and eigenfrequences of the structure of the aeroplane cabin and of the acoustic space inside cabin. Then response to harmonic excitation of engine represented by unit forces in place of contact has been computed. Obtained velocities on the surface of the cabin are then used as the basis for the noise calculation inside the cabin using BEM. After that effect of some construction modifications on sound level inside cabin are evaluated by computational modelling.
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Computational simulation of leveling of non-circular rods
Stráník, Radim ; Návrat, Tomáš (referee) ; Petruška, Jindřich (advisor)
This bachelor’s thesis illustrates the principle of straightening rolled through long table roll straightening machines using repeated plastic deformation, based on Eulerian description of the material flow. Thesis describes the program on computational simulation process straightening rods and extends it an easy to use input module for entering non-circular cross-section rods. At the end of the discussion also introduces the optimal settings for all input parameters to achieve best results.
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Computational Simulations in Automotive Safety
Krkoška, Kamil ; Svída, David (referee) ; Ramík, Pavel (advisor)
The goal of this bachelor thesis is to build up a compact overview of recent development in automotive safety, concrete methods and results reached in this branch. Here are briefly described solutions for improvement of active and passive safety and next is explained testing of these systems in crash tests and assessment of these tests by using biomechanical limits. Attention is also given to the usage and benefit of computational simulations. Next are described procedures of simulations and also software used for these simulations. Then there are mentioned examples of successful applications of computational simulations.
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