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The modal damping ratio analysis of the mechanical part using the OMA method
Sodomka, Tomáš ; Lošák, Petr (referee) ; Houfek, Lubomír (advisor)
In one of the first hours of study at the Institute of Mechanics of Bodies, Mechatronics and Biomechanics, the author of this work received three basic recommendations regarding measurement: 1) Do not measure! 2) If you measure, do not repeat the measurement!! 3) If you repeat the measurement, do not compare the measurements!!! However, this thesis boldly violates all three recommendations. In the introductory theoretical part, it briefly introduces the vibration of multi-degree of freedom damped systems and describes experimental ways of determining the modal damping. It also summarizes the Operational Modal Analysis (OMA) approach, explains the principle of the FDD method, and introduces EFDD (Enhanced Frequency Domain Decomposition) method which allows to determine not only natural frequencies and shapes as FDD does, but also modal damping of the shapes. A script in Matlab environment for processing vibrations using EFDD method is one of the thesis outputs. The script is first tested by computational model, where a model system with known damping is tested and damping is determined by the script. Subsequently, the work moves to the actual measurement of the real system - a bonded bar which is analysed by Experimental Modal Analysis and OMA, while the second variant uses commercial EFDD method (Brüel a Kjr company) and programmed script. In the conclusion of the thesis the damping results are compared to each other. The diploma thesis continues in Ing. M. Pop’s thesis – Modal Analysis Experimental Method Verification. From this work a part of measured data is taken. Specific cases of data use are always listed in the appropriate section of the text.
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Navier-Stokesova equation - solution of the real liquid
Krausová, Hana ; Čermák, Libor (referee) ; Fialová, Simona (advisor)
This thesis deals with the Navier-Stokes equations for real, compressible fluid with first and second viscosity. The method of expansion into a series of eigenmodes of vibration is chosen to solve the Navier-Stokes equations. The general relations of the expansion coefficients and the eigenmode shapes are given for 1D-, 2D- and 3D-flows. The specific formulae of eigenmodes of vibration are determined only for 1D-flow. The final form of the pressure function is analysed using Matlab software.
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Design of test rig for long-term testing of couplings intended for railroad applications
Machálek, Ondřej ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
The master thesis deals with design of test rig for long-term testing of coupling appointed to railway vehicles. At first, there is made a brief research which is related to railway coupling used for transmitting a torque. This is followed by an analysis of the most used power devices to derive real loads conditions of tested couplings. There is chosen the most appropriate conception based on made analysis and it is followed by the description of designed components. There is made a verification of modal properties non-purchased components which is necessary part of the thesis. Numerical modal analysis was performed in ANSYS Workbench software. In the end of the thesis there are included stress-strain analysis of the chosen designed components.
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NVH parameters determination of gearbox housing
Belák, Kristián ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This master’s thesis deals with determination of NVH parameters of the gearbox housing. Introductory part is focused on the necessary theoretical knowledge. Subsequently, it contains the modal analysis with the computational and experimental approach, which are being compared to each other. In the case of the computational approach, analysis of the influence of bolt pretension on the modal properties is also involved. The thesis continues with the harmonic analysis with the computational and experimental approach, including their mutual comparison. Based on these analyses, design modifications for improvement of the NVH parameters are designed at the end of the thesis, which are being compared to each other and to the original geometry, using the computational approach.
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Design apparatus for measuring geometric accuracy of machine tools
Holcman, David ; Marek, Tomáš (referee) ; Holub, Michal (advisor)
This bachelor’s work deals with modern methods of geometric accuracy measurement of machine tools, modal analysis and definition of demands on used agents during the measurement process. A part of this work is dedicated to description of numerical finite element method, which is the cornerstone of ascertaining the natural frequencies by a software program. In the closing part the appropriate adjustments of minimisation of influence on measurement are suggested.
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NVH parameter determinantion of plate
Bouchner, Michal ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
The aim of this thesis is examination and verification of numeric model for solving acoustics and vibration problems. Specifically, we are speaking about cast iron plate machined from gearbox. Main objectives of this work is set of experimental and numerical analysis at this simplified part with follow-up numerical model, where same analyses examining not only structure, but especially acoustic space around were performed. Due to this we were able to compare data between experimental and numerical analyses and to be able to prove or disprove functionality and limitation of numerical model.
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Vibrations at machining of metals
Fiala, Zdeněk ; Polzer, Aleš (referee) ; Píška, Miroslav (advisor)
The diploma work deals with a mathematical description of vibration and its generation when machining. Moreover, some techniques of modal parameters measurement in the theoretical part are included. The practical part is designed and based on the measured natural frequencies of the machine with specific tool and materials. In conclusion, a lobe diagram stability for semiautomatic lathe SPN 12 CNC and selected machining operation is specified by means of apparatus.
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Simulation anlysis of turbocharger vibrations
Valo, Lukáš ; Lošák, Petr (referee) ; Březina, Lukáš (advisor)
The master thesis deals with computational modeling of a turbocharger vibrations and and assessment of influnce of passive dynamic vibration absorber on vibrations of actuator bracket. The use of dynamic vibration absorber was summarized in the research study. The analysis were performed using finite element method in ANSYS. Several computational models of turbocharger were created with different ways of modeling bolted joints between turbocharger parts. Modal analysis of each model was performed and the results were compared. For the selected model, the response to the kinematic excitation from the internal combustion engine for two load conditions was calculated using harmonic analysis. A simple model of vibration dynamic absorber was applied to the turbocharger model with reduced degrees of freedom and its influnce on vibrations of actuator bracket was investigated. Significant decrease of the maximum acceleration amplitude was achieved in a given frequency range when absorber parameters were optimized.
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Design of modern speaker body with usage of new technology
Kůst, Martin ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This diploma thesis deals with the analysis and design optimization of a speaker cabinet (enclosure) produced by the additive technology of 3D sand printing. The introductory part is devoted to the theory, both in the field of noise, vibration and the method of their calculations, as well as the theory of speakers and their systems. Numerical and experimental modal analysis is performed, which were compared to determine the mechanical properties of the new material, including material damping. This is followed by experimental and numerical harmonic analysis, with output in the form of a numerical model describing the behaviour of the structure during its excitation. The data are compared with a modal analysis of the internal acoustic space and the critical shapes and their frequencies are determined. At the end of the work, construction modifications are proposed to increase the rigidity of enclosures, the influence of which is evaluated on the created numerical models.
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Dynamic analysis of structure loaded seismic loads
Janošková, Lenka ; Nevařil, Aleš (referee) ; Vlk, Zbyněk (advisor)
In this diploma thesis the seismic load on two different models is solved – the first model is a beam hall and the second model is a multistory building. The calculation of seismic load was performed according to standard ČSN EN 1998-1 (Eurocode 8) using the response spectrum analysis and the method of equivalent static forces (substi-tute load). For the combination of seismic responses in different directions are used SRSS and CQC rules. Models and calculations were solved in a student’s version of program RFEM 4.10 (Ing. Software Dlubal, s.r.o.). The comparison of mentioned methods in each models, also the comparison of combinative rules in calculation and the final evaluation of seismic responses on both of models are the subject of this thesis.
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