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Tractor cabin skelet optimization
Saňák, Stanislav ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This thesis addresses the issue associated with the design of the tractor cabin frame. Agricultural machinery, including tractors, is utilized for work in highly challenging conditions such as fields or forest terrains, characterized by uneven, hilly, and often unpaved surfaces. Working in such extremely hazardous environments poses a significant challenge, especially for the operators of these machines. It is very common for drivers to lose control of the vehicle while navigating such terrain, resulting in the tractor tipping over on its side or roof, and in worse cases, experiencing repeated rollovers due to inertia. In such situations, the presence of a protective frame around the tractor cabin is the only possible means of crew rescue. However, the rollover of such a vehicle imposes extreme stress on the cabin frame due to the weight of the tractor and often its cargo. Historically, rollovers have been the leading cause of accidents resulting in fatalities of tractor crews, which prompted the establishment of standards aimed at reducing this type of accident. Tractors are tested against these critical situations to ensure the maximum possible crew safety. Nowadays, every manufactured tractor must comply with these tests. Since these tests are of a destructive nature, it is more cost-effective and time-efficient to first conduct tests using numerical simulations, within which the tractor cabin is optimized to successfully pass the given tests. The actual test is then performed on the final, already optimized cabin frame. In this study, a numerical simulation using the finite element method was conducted on the tractor cabin skeleton for the ROPS (Roll-Over Protective Structure) test, which simulates the tractor overturning. Based on the simulation results, optimizations were made to the cabin that were necessary to pass this test, which consists of several load cases. The optimized cabin frame was subsequently subjected to a basic dynamic analysis (modal analysis). This analysis identified the natural frequencies of the cabin that could be excited in the event of typical excitations acting on this structure (road surface irregularities, vibrations from the engine unit, and so on). Finally, based on real values obtained from experimental measurements, a harmonic analysis was performed. This analysis monitored the response of the frame to excitations corresponding to actual excitations from the engine unit.
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Analysis of Modal Shapes and Natural Frequencies of Real-Shaped Vocal Fold
Horčic, Václav ; Švancara, Pavel (referee) ; Hájek, Petr (advisor)
This bachelor's thesis deals with the modal analysis of a model based on a 3D scan of the human vocal cords. This is a model solved by the finite element method, where the value of the first natural frequency roughly corresponds to the value of the fundamental frequency of female vocal folds. The research part of the thesis is devoted to an overview of finite element models of the geometry of the vocal cords, which is followed by a brief description of the anatomy and physiology of the human speech system together with the theory of the formation of the human voice. The finite element model is created using a 3D scan of the vocal folds in the commercial program ANSYS Workbench, in which it is solved by the finite element method.
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Reduction of vibration and noise at passenger car interior
Patočka, Pavel ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
This thesis addresses the issue of reducing vibrations and noise in the interiors of passenger vehicles, which is commonly tackled today by additional soundproofing using vibration-damping and sound-absorbing materials. In the research part of this thesis, besides methods for measuring vibrations and noise, the properties and application methods of these materials are described in detail. As the name of these materials suggests, their main goal is to dampen vibrations and absorb sound. Their principle, in simple terms, consists of converting mechanical or sound energy into another form of energy (most commonly thermal energy). However, the application of these materials to a structure affects its modal properties, including natural frequencies and mode shapes. To further investigate the influence on natural frequencies and mode shapes after applying vibration-damping material to a structure, both numerical and experimental modal and harmonic analyses of a simple metal sheet sample were conducted. The benefits of vibration-damping and sound-absorbing materials in terms of additional vehicle soundproofing were evaluated based on a road test conducted under real operating conditions.
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Topological optimisation of the turbocharger electric actuator bracket
Směšný, Jan ; Kudláček, Petr (referee) ; Novotný, Pavel (advisor)
Topology optimization utilizes mathematical methods to develop the most efficient components in terms of mechanical properties and weight. Nowadays, it is a commonly used tool for designing components not only in the automotive, aerospace, and space industries. This work deals with the topological optimization of a metal bracket used to attach an electric actuator to a turbocharger. The turbocharger assembly is subjected to external influences, the most significant of which are vibrations from the engine. The program Ansys Workbench was used for modal and topology optimization calculations. The goal of the optimization was to minimize weight and maximize the natural frequency. The optimization takes into account a simple manufacturing method using conventional techniques (shearing & bending), which will remain the same for the optimized component. Additional care is taken to ensure, that the natural frequency of the bracket-actuator system is above the excitation frequency from the engine. The final optimization revealed that by appropriately removing material, the component's weight can be reduced by 22% without significantly degrading its dynamic properties.
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Modal Analysis of the Classical Guitar Bridge
Ondečko, Adam ; Votava, Tomáš (referee) ; Hájek, Petr (advisor)
The bachelor thesis deals with the determination of the natural freqvencies and mode shapes of a classical guitar bridge and their influence on the function of the guitar. The function of the guitar is described by the oscillations of the individual oscillators: the strings, the air in the cavity of the guitar, the top and bottom plates, and then by their oscilation as a system. In the bachelor's thesis the roles of the guitar bridge are discussed and the different types of guitar bridges are presented. In the thesis, the guitar bridge is considered as a separate component and as part of the guitar's top plate. The mode shapes and natural freqvencies are obtained using modal analysis with the use of computational modelling using the finite element method. The natural freqvencies are determined for 2 types of guitar bridges, the effect of the guitar bridge on the mode shapes and natural freqvencies of the guitar top plate is further evaluated. The natural freqvencies of the classical guitar bridge affect the tone quality and the duration of oscilation of the string. Tones close to the natural freqvencies of the guitar bridge sound louder and last shorter amount of time than the others. The guitar bridge changes the stiffness of the top plate and thus influences its mode shapes and freqvencies.
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Harmonic Analysis of the Double Bass Bridge
Čalkovský, Lukáš ; Votava, Tomáš (referee) ; Hájek, Petr (advisor)
This bachelor's thesis focuses on the research of string instruments and their mechanical properties. It explores the double bass bridge and its importance. On a model created in the SolidWorks program, modal analysis was performed using the ANSYS software, which determined the frequencies and shapes of the individual modes. Harmonic analysis was also performed and analysed. Part of the investigation was to analyze the possible cause of the formation of so-called wolf tones. The double bass bridge does not exhibit any special characteristics in the double bass range, so it is not the cause of this anomaly.
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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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