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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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Analysis of the effect of damping on the magnitude of the response during dynamic headlamp excitation
Lukáš, Jan ; Biskup, Martin (referee) ; Vosynek, Petr (advisor)
The aim of the submitted diploma thesis is the magnitude determination of the headlamp response to the dynamic excitation. Currently it is necessary to measure this response, because it is one of the assessed criteria of quality of the headlamp. When comparing results of the experimental measurement and the computational modelling, a good consensus of resonant frequencies is observed, but there are significant differences in acceleration amplitudes. The cause of this is the variable damping value. The theoretical part of the thesis deals with polymeric materials, basics of oscillation and damping. It serves to understand the mechanisms, which influence the results of the experimental measurement. The practical part is dedicated to the procedure of the computational modelling and the experimental measurement implementation. The analysis of the experimental measurement results leads to an ascertainment of nonlinearities, which influence the headlamp behaviour. The results of a sensitivity analysis of the computational modelling are used to create curves, on the basis of which the damping is estimated. The inclusion of the estimated damping into computational modelling leads to reduction of the compared differences of the acceleration amplitudes. The conclusion of the thesis contains the recommendation for the damping determination during the computational modelling of the headlamp.
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Experimental determination of the liquid influence on an oscillating body
Grešáková, Kristýna ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
Damping and natural frequency of a vibrating body or a system is not easy to estimate during the design phase of~project. If the body is submerged in water, estimating becomes even more complicated. This~work focuses on experimental determination of the liquid influence on an oscillating body. The~presented modal analysis was executed on two bodies when being surrounded by air, but~also when gradually and fully submerged in water using two reservoirs with different dimensions. The collected data was analyzed with a suggested hybrid method, which determined the damping ratio and the natural frequency. Added mass was calculated employing the Ansys software. Part of the presented work focuses on the selection of a suitable time window for the Fourier transform.
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Verification of geometry influence on dynamic properties of immersed body
Černý, Tomáš ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
Immersion of the body into the fluid creates additional effects which must be considered when designing the machines. Additional effects from the fluid influence the dynamic properties of the body. In this work the decrease of the natural frequency and the increase of the damping ratio during the gradual immersion of the body into the fluid are investigated. Diploma thesis is based on an experiment, which is performed on a series of flat strip steel components of various widths. The first three bending and first three torsion shapes of the free-hanging body are examined. Emphasis is placed on the influence of part width. In the next phase of the experiment, the influence of the proximity of the solid wall to the dynamic properties of the cantilever beam is examined. Further, the determination of the added density from the fluid is performed by modal analysis using the ANSYS software.
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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.
|
|
|
Analysis of the effect of damping on the magnitude of the response during dynamic headlamp excitation
Lukáš, Jan ; Biskup, Martin (referee) ; Vosynek, Petr (advisor)
The aim of the submitted diploma thesis is the magnitude determination of the headlamp response to the dynamic excitation. Currently it is necessary to measure this response, because it is one of the assessed criteria of quality of the headlamp. When comparing results of the experimental measurement and the computational modelling, a good consensus of resonant frequencies is observed, but there are significant differences in acceleration amplitudes. The cause of this is the variable damping value. The theoretical part of the thesis deals with polymeric materials, basics of oscillation and damping. It serves to understand the mechanisms, which influence the results of the experimental measurement. The practical part is dedicated to the procedure of the computational modelling and the experimental measurement implementation. The analysis of the experimental measurement results leads to an ascertainment of nonlinearities, which influence the headlamp behaviour. The results of a sensitivity analysis of the computational modelling are used to create curves, on the basis of which the damping is estimated. The inclusion of the estimated damping into computational modelling leads to reduction of the compared differences of the acceleration amplitudes. The conclusion of the thesis contains the recommendation for the damping determination during the computational modelling of the headlamp.
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|
|
Verification of geometry influence on dynamic properties of immersed body
Černý, Tomáš ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
Immersion of the body into the fluid creates additional effects which must be considered when designing the machines. Additional effects from the fluid influence the dynamic properties of the body. In this work the decrease of the natural frequency and the increase of the damping ratio during the gradual immersion of the body into the fluid are investigated. Diploma thesis is based on an experiment, which is performed on a series of flat strip steel components of various widths. The first three bending and first three torsion shapes of the free-hanging body are examined. Emphasis is placed on the influence of part width. In the next phase of the experiment, the influence of the proximity of the solid wall to the dynamic properties of the cantilever beam is examined. Further, the determination of the added density from the fluid is performed by modal analysis using the ANSYS software.
|
|
|
Experimental determination of the liquid influence on an oscillating body
Grešáková, Kristýna ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
Damping and natural frequency of a vibrating body or a system is not easy to estimate during the design phase of~project. If the body is submerged in water, estimating becomes even more complicated. This~work focuses on experimental determination of the liquid influence on an oscillating body. The~presented modal analysis was executed on two bodies when being surrounded by air, but~also when gradually and fully submerged in water using two reservoirs with different dimensions. The collected data was analyzed with a suggested hybrid method, which determined the damping ratio and the natural frequency. Added mass was calculated employing the Ansys software. Part of the presented work focuses on the selection of a suitable time window for the Fourier transform.
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