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Proposal of shaft alignment method for small rotors using digital image correlation
Hrůza, Vlastimil ; Pokorný, Jan (referee) ; Ščerba, Bořek (advisor)
The presented thesis deals with the design of a method for aligning small rotors, for which commonly available methods are not suitable. This is due to space restrictions around the coupling, which often do not allow installation of conventional alignment systems on the shafts. The proposed method therefore utilizes non-contact measurement of the surface of the shafts using digital image correlation (DIC). Calculation of misalignment and corrective moves is based on fitting the points measured on individual shafts with cylinders and evaluating the mutual position of their axes. To determine the area of applicability of the proposed method, sensitivity analysis was performed, which showed that the method gives good results for surface-accurate shafts with a uniformly applied speckle pattern for DIC measurement. Validation of the method was then carried out by measuring on a designed test rig using a commonly available laser alignment system. The validation measurement proved the functionality of the method and confirmed the conclusions of the sensitivity analysis.
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Automation of video extensometers using artificial intelligence
Leinweber, Vít ; Adamec, Tomáš (referee) ; Ščerba, Bořek (advisor)
This thesis deals with the automation of the use of video extensometers using artificial intelligence methods, specifically the implementation of a suitable algorithm for the recognition of the type of sample to be measured and the placement of a suitable software tool in the correct position on the sample in real-time. The theoretical part of the thesis describes digital image correlation, computer vision with a focus on object recognition, and machine learning with a focus on deep convolutional neural networks and their architectures for object detection. Based on the findings from the theoretical part of the work, the YOLOv8 algorithm is chosen as the most suitable algorithm for classifying the type of sample and determining its location in real-time. In the practical part of the thesis, a dataset containing three types of samples is created using the database of video extensometer manufacturer. The dataset is extended with images containing samples to be detected and augmented. The selected algorithm is trained, optimized, and tested using the created dataset. A genetic algorithm and a random search of the hyperparameter space are used in the optimization process. The best trained models of the YOLOv8 algorithm are compared with each other on two test sets and the best one is selected. Furthermore, the work with this algorithm as a detector integrated into the corresponding software for working with video extensometers is described. Finally, a method for correcting the effect of potential misalignment of samples in the images entering the detector is proposed.
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Determination of residual stresses by hole-drilling method considering finite body boundaries
Began, Jakub ; Ščerba, Bořek (referee) ; Halabuk, Dávid (advisor)
The diploma thesis analyses the impact of the finite dimensions of a body on residual stresses by means of the hole-drilling method which was derived for bodies of dimensions large enough not to affect the measurement. To assess the impact of the finite dimensions of a body on measured residual stresses, a computational model simulating the hole drilling method was created using the finite element method. The assumptions made during the creation of the computational model included a desired geometric shape and an uniform residual stresses along the depth of the drilled hole. The computational model was subsequently parameterised so that it could be used to simulate different combinations of the finite dimensions of a body, whose impact on measured residual stresses was analysed. In the next part of the thesis, the impact of the biaxiality of residual stresses on the accuracy of their measurement was assessed. Subsequently, three correction algorithms were proposed to minimise the errors of measured residual stresses caused by the finite dimensions of a body. The first correction algorithm is supposed to correct calibration coefficients, the second one to correct input strains, and the third one to correct the assessed residual stresses. In the last part of the thesis, the individual correction algorithms were tested and compared. The outcomes of the diploma thesis suggest the possibility to correct the errors in the analysed residual stresses due to finite dimensions of a body, on the condition of a desired geometric shape and an uniform stresses along the depth of the drilled hole.
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Use of the DIC method in solving basic problems of solid mechanics
Hrůza, Vlastimil ; Pokorný, Jan (referee) ; Ščerba, Bořek (advisor)
This bachelor’s theses deals with the solution of basic problems of solid mechanics using digital image correlation. The research part of the thesis presents some of the optical methods used for deformation measurement, digital image correlation in particular, whose history, principles, limitations and utilizations are described in detail. In the practical part of the theses, three experiments are carried out, which are then evaluated using digital image correlation and the results are compared with the created computational models. In the first experiment, strain on the tensile test specimens with notches is measured, the second experiment is focused on measuring strain when bending curved beams and in the final experiment, natural frequency of a fork produced by 3D printing is determined.
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Optical measurement of crack length utilizing the DIC method
Dziubek, Jan ; Halabuk, Dávid (referee) ; Ščerba, Bořek (advisor)
The thesis deals with the measurement of crack length using digital image correlation. The theoretical part of the thesis presents the method of digital image correlation, crack problems, and also introduces conventional methods for measuring crack length. There are currently no universal procedures in the field of crack length measurement using DIC. Different authors have only proposed different procedures to find the crack tip. Three different methods are used to determine the crack length using digital image correlation. Use of the edge detection method in the displacement field, the inflection point search method and the deformation threshold method. The aim of this work is to describe and compare these approaches.
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Napjatostně deformační analýza mostu v Třineckých železárnách
Ščerba, Bořek ; Skalka, Petr (referee) ; Fuis, Vladimír (advisor)
The bachelor thesis analyses stress and deformation of the truss construction. The first point of the thesis is a research, which includes obtaining information about the construction, for exemple dimensions, loads, purpose, history etc. Then, calculation models are created considering a different level of simplification. Two analytical models are crutial for the thesis – one statically determinate and the other statically indeterminate. They are used for analysing two different loads applied to the construction using methods of solid mechanics – it’s own weight and its own weight in combination with a weight of a vehicle that is driving through. Afterwards, the statically inderteminate model is verified using finite element method (FEM).
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Influence of setting and configuration of straightening machine on results of simulation of cross-roll straightening
Ščerba, Bořek ; Petruška, Jindřich (referee) ; Návrat, Tomáš (advisor)
Analytical methods or implicit finite element method (FEM) with beam elements to model straightened bar were used to analyze straightening process in multi-staggered cross-roll straighteners up to now. These are effective but require certain simplifications. Aim of this thesis is to create an explicit FEM model allowing usage of solid elements for circular bar without disproportional increase of computational time. This may lead to deeper understanding of the straightening process. The model is to be verified using straightening tables and then used to quantify influence of rollers configuration on results of the straightening process.
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Comparative analysis of the effect of nonlinearities on the lumbar segment stress/strain of the spine after correction of spondylolisthesis
Holá, Lucia ; Ščerba, Bořek (referee) ; Vosynek, Petr (advisor)
This final thesis focuses on the stress-strain analysis of the physiological, postoperative and degenerative state of the lumbar spine segment. The aim of this thesis is to implement nonlinear material characteristics into previously made computational models and to compare these two models. The solution is performed by computational modeling using the finite element method. The geometry model was made by modification of the previous model of geometry. The group of degenerative state models comprises of three different levels of spondylolisthesis, according to Myereding’s classification. Based on the performed analysis, it was found that the increasing severity of spondylolisthesis, as well as the change in material definition plays a huge role in the stress development in the intervertebral discs and in the vertebrae. The total deformation of the spine segment increases with the use of nonlinear material characteristics, as well as with the increasing variability from the physiological state. However, the stress distribution in the intervertebral disc decreases with the use of nonlinear material characteristics and in case of the vertebral stress distribution increases, unlike in the linear material models. The biggest similarity with the physiological state of the lumbar spine segment was found in the postoperative state using the spinal implants.
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Analysis of the influence of the fixation setting of the fusion of the spinal vertebrae on the resulting correction of scoliosis
Kopecký, Tomáš ; Ščerba, Bořek (referee) ; Vosynek, Petr (advisor)
This bachelor's thesis deals with the numerical modeling of the spine with an established fixation device under three types of loading, with three types of connection between the last element of the fixator and its guiding rod. The thesis describes the creation of the spine and fixator models, as well as the setting of loading conditions. Three loading states are monitored, in both directions: flexion/extension, lateral bending in both directions, and axial rotation in both directions. Furthermore, the implementation of three types of connections for all these loadings is described. In the first case, the entire fixator is immovable, in the second case, the last element of the fixator can move along the axis of the spine, and in the last case, it can also rotate in all three directions. The evaluation and subsequent comparison of deformation in the direction of the spine axis are the outputs of this thesis. The final evaluation is that the displacement occurring is on the order of tenths of millimeters.
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