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Vibration at turning
Procházka, Luděk ; Kolář, Ladislav (referee) ; Fiala, Zdeněk (advisor)
This thesis deals with vibration which occurs during the cutting process in turning. It describes vibration, types of vibration and its causes. It also provides a basic description of the turning technology. The main part of the thesis is a description of self-excited vibrations, an unwanted phenomena in the turning process, which needs to be eliminated or reduced. The experimental section of the thesis aims to measure natural frequencies of the machine-tool-workpiece system and to create a stability diagram for this process.
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Increasing resistance to self-excited oscillations in CNC machine tools for machining non-rotating workpieces
Prchalová, Michaela ; Pavlík, Jan (referee) ; Marek, Jiří (advisor)
The Master’s Thesis is focused on increasing resistance to self-excited oscillations in CNC machine tools for machining non-rotating workpieces. The main goal of the thesis is to perform a system analysis of the solved problematics and justification of the chosen way of solving the assigned task. Another goal of this thesis is to perform an analysis of the current state of science and technology in the specified problematics. Based on the analysis of the current state, a proposal for the methodology of prediction of self-excited oscillations for a specified type of machine was made, including recommendations for future users on how to proceed. The whole thesis is based on a real problem occurring during machining of a structurally difficult workpiece.
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STABILITY ANALYSIS OF CUTTING PROCESS OF MACHINE TOOL WITH RESPECT TO CHATTER
Vetiška, Jan ; Marek, Jiří (referee) ; Singule, Vladislav (referee) ; Březina, Tomáš (advisor)
The thesis deals with building and utilization of mechatronic models which are based on modeling of system of rigid and flexible bodies. Such models are then used for analysis of behavior of complex systems, for instance machine tools. The work is concentrated on analysis of self-excitation of a machine tool. The appearance of the self-excitation during the machining may be influenced by several methods described in the work. The evaluation of the appearance of the self-excitation is analyzed via so called lobe diagram. It is necessary to know transfer function describing the impact of acting forces on the deformation of the system (machine tool in this case) for compilation of the lobe diagram. The whole structure of the model shows compliant behavior which dramatically influences the transfer function thus the approach to the modeling of mechanical parts as flexible bodies is proposed. There are created models of modally reduced flexible bodies based on modified CAD models which have same modal properties as non-reduced FEM models up to the maximal excitation frequency. The reduced models have significantly lower number of degrees of freedom and it is possible to work with them in multi-body simulation tools and at the same time they contain the information about the deformations. The work utilizes Graig-Bamton method which is implemented to the ANSYS. The whole model is consequently built and analyzed in ADAMS. It is possible to export the linearized model of the system in form of state matrices which are used for writing of the transfer function. The conditions of stability of the machining process are then evaluated via the lobe diagram. The proposed thesis presents the modeling of mechatronic systems with stiff and rigid bodies. The approach may be used for analysis of machining tools as well as for development of advanced mechatronic systems with active damping, etc.
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Application of Fluid-structure Interaction on Oscillating Human Vocal Folds
Meisner, Patrik ; Švancara, Pavel (referee) ; Hájek, Petr (advisor)
The presented thesis is involved in the biomechanics of phonation. The aim of the thesis is to set a fluid-structure interaction between the vocal folds and air flow when the pressure from lungs reaches the physiological values. In the expected outcome the self-oscillating vocal folds should be observable with characteristics shape-shift from convergent to divergent. In theory part of the thesis is described Anatomy of the vocal tract, physiology of the human phonation, research of computational simulations, experiments and visualisation methods are described in the theory part of the thesis. In the second part, setup of computational simulation with the finite element method is presented. Besides of the fluid-structure interaction the acoustical model is set. Achieved results are presented and compared to the results in literature. Displacements are evaluated from the structural model and pressures, velocities and flow velocities are evaluated from fluid model, so as acoustics results.
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Computational modeling of noise emitted by tram wheel during cornering
Motyka, Jakub ; Fiedler, Robert (referee) ; Švancara, Pavel (advisor)
This thesis deals with computational modeling of curve squeal noise phenomena which occurs during cornering tight curves by trams. Lateral creep between rail and wheel and slip-stick phenomena leads to self-excited vibrations of the wheel which, therefore, emits unpleasant high-pitched noise. Two FEM models in frequency domain are carried out. First model is based on prestressed modal analysis. Due to unsymmetric stiffness matrix, unstable eigenvalues can occur. It is assumed that self-excited vibrations occurs on frequencies corresponding to that eigenvalues. Second model uses harmonic response analysis. It examines vibrations of the wheel excited by lateral creep force acting in contact region. This force is obtained externally by simple time-domain model. Results from harmonic response are used consequently for noise radiation computation.
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Design of a two-axis multi-spindle lathe carriage
Sedlář, Jiří ; Štěpánek, Vojtěch (referee) ; Hadraba, Petr (advisor)
This diploma thesis deals with the design of a two-axis multi-spindle lathe carriage. In the first part, there is made a research, and its aim is to find possible variants of design solutions. After the best rated variant was selected, the thesis further continues with the necessary technical calculations of the main design nodes such as a synchronous servomotor, ball screw, linear guide and bearing. The design itself was carried out with regard to calculations and the resulting model was examined in terms of dynamic stability. The subject of examination was to find the natural frequencies of the assembly and to determine the amplitudes of the oscillations which arise from the harmonic excitation force. Finally, Lobe diagrams for grooving and longitudinal turning operations were drawn.
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Increasing resistance to self-excited oscillations in CNC machine tools for machining non-rotating workpieces
Prchalová, Michaela ; Pavlík, Jan (referee) ; Marek, Jiří (advisor)
The Master’s Thesis is focused on increasing resistance to self-excited oscillations in CNC machine tools for machining non-rotating workpieces. The main goal of the thesis is to perform a system analysis of the solved problematics and justification of the chosen way of solving the assigned task. Another goal of this thesis is to perform an analysis of the current state of science and technology in the specified problematics. Based on the analysis of the current state, a proposal for the methodology of prediction of self-excited oscillations for a specified type of machine was made, including recommendations for future users on how to proceed. The whole thesis is based on a real problem occurring during machining of a structurally difficult workpiece.
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Application of Fluid-structure Interaction on Oscillating Human Vocal Folds
Meisner, Patrik ; Švancara, Pavel (referee) ; Hájek, Petr (advisor)
The presented thesis is involved in the biomechanics of phonation. The aim of the thesis is to set a fluid-structure interaction between the vocal folds and air flow when the pressure from lungs reaches the physiological values. In the expected outcome the self-oscillating vocal folds should be observable with characteristics shape-shift from convergent to divergent. In theory part of the thesis is described Anatomy of the vocal tract, physiology of the human phonation, research of computational simulations, experiments and visualisation methods are described in the theory part of the thesis. In the second part, setup of computational simulation with the finite element method is presented. Besides of the fluid-structure interaction the acoustical model is set. Achieved results are presented and compared to the results in literature. Displacements are evaluated from the structural model and pressures, velocities and flow velocities are evaluated from fluid model, so as acoustics results.
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Design of a two-axis multi-spindle lathe carriage
Sedlář, Jiří ; Štěpánek, Vojtěch (referee) ; Hadraba, Petr (advisor)
This diploma thesis deals with the design of a two-axis multi-spindle lathe carriage. In the first part, there is made a research, and its aim is to find possible variants of design solutions. After the best rated variant was selected, the thesis further continues with the necessary technical calculations of the main design nodes such as a synchronous servomotor, ball screw, linear guide and bearing. The design itself was carried out with regard to calculations and the resulting model was examined in terms of dynamic stability. The subject of examination was to find the natural frequencies of the assembly and to determine the amplitudes of the oscillations which arise from the harmonic excitation force. Finally, Lobe diagrams for grooving and longitudinal turning operations were drawn.
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Computational modeling of noise emitted by tram wheel during cornering
Motyka, Jakub ; Fiedler, Robert (referee) ; Švancara, Pavel (advisor)
This thesis deals with computational modeling of curve squeal noise phenomena which occurs during cornering tight curves by trams. Lateral creep between rail and wheel and slip-stick phenomena leads to self-excited vibrations of the wheel which, therefore, emits unpleasant high-pitched noise. Two FEM models in frequency domain are carried out. First model is based on prestressed modal analysis. Due to unsymmetric stiffness matrix, unstable eigenvalues can occur. It is assumed that self-excited vibrations occurs on frequencies corresponding to that eigenvalues. Second model uses harmonic response analysis. It examines vibrations of the wheel excited by lateral creep force acting in contact region. This force is obtained externally by simple time-domain model. Results from harmonic response are used consequently for noise radiation computation.
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