|
|
Losses in induction machines supplied by a frequency converter
Lípa, Miroslav ; Vítek, Ondřej (referee) ; Bárta, Jan (advisor)
Diplomová práce se zabývá měřením asynchronního motoru se dvěma různými zdroji napájení, a to s frekvenčním měničem a generátorem. Tyto dva zdroje napájení byly následně simulovány pomocí metody konečných prvků a porovnány. První kapitola se zabývá popisem asynchronního stroje napájeného frekvenčním měničem a také doporučenými úpravami pro tento druh napájení, aby se předešlo co nejvíce nežádoucím jevům. Druhá kapitola se věnuje ztrátám asynchronního stroje. Třetí kapitola popisuje přístup k měření a vyhodnocování harmonických ztrát způsobených napájením z měniče a také standardizovaný přístup podle mezinárodních norem. Druhá polovina třetí kapitoly také popisuje výpočetní analýzu, která je v této práci použita ve formě analýzy konečných prvků. Nakonec jsou popsány nejistoty měření při použití standardní metody vstup-výstup. Ve čtvrté kapitole je představeno modelování v softwaru ANSYS MAXWELL, kde je nejprve popsána tvorba modelu specifikovaného stroje, poté jeho simulace se sinusovým napájením, a v druhé polovině je vysvětlena simulace s PWM napájením a jak bylo PWM replikováno pomocí naměřených průběhů. V páté kapitole jsou prezentovány všechny výsledky měření s vyhodnocením. Na konci kapitoly je uvedeno srovnání simulace a měření a jeho nedostatečná přesnost.
|
|
|
Design and analsysis of magnetic bearing
Kyanka, Radim ; Ctibor, Jiří (referee) ; Rúra, Dávid (advisor)
The master thesis is focused on literature research and description of magnetic bearings in order to create a design model of a stand for demonstration of magnetic levitation. The simulated model is developed using the finite element method. It also discusses the advantages and disadvantages along with a comparison with conventional bearings in drives. Analytical design is discussed here, which is also simplified and neglects several parasitic effects. These analyses are then discussed. The main part of thesis containe design and calculation for an 8-pole active radial heteropolar magnetic bearing. The result of the design is then applied to the realization of the demonstrator.
|
|
|
Počítačové modelování tepelného namáhání skleněné tabule při gravírování laserem
ZOUBEK, Tomáš
Computer modelling is often used to understand the nature or behaviour of physical phenomena. In this work, a three-dimensional computer model was created from a 25x30x4 mm (width x height x thickness) glass plate on which twenty dots with a radius of 371.54 ?m were burned using a laser engraving process. The distance between the dots was 1.25 mm. A computer simulation of the thermal stress of the laser engraving process was carried out on this model. The input parameters used were the laser travel time between points (0,5 s^(-1)), the duration of the laser discharge (0,5 s^(-1)), the laser power (30 W), the laser intensity and the laser density over a given area (given by equation 11), the heat flux coefficient of the glass sheet (5,7 Wm^(-2)K^(-1)) and the function controlling the firing of the laser beam at specific points and times (equations 5.4 and 5.5). The simulation was carried out for two variants that differed in the order of the fired points. For the first variant, the points were fired chronologically from left to right in rows, whereas for the second variant the points were fired in the order 1, 3, 5, 11, 13, 15, 7, 9, 17, 19, 2, 4, 12, 14, 6, 8, 10, 16 and 20. The second variant proved to be more optimal for the geometry and material studied. It resulted in less thermal stress, as lower temperatures were achieved with a defined laser beam, and at the same time there was a greater time delay between processes stressing the same locations.
|
|
|
Design and assessment of the load-bearing part of the reinforced concrete structure
Tihelka, Marek ; Lagiň, Juraj (referee) ; Kostiha, Vojtěch (advisor)
The aim of the bachelor thesis is the design and assessment of a reinforced concrete foundation structure of a sports hall. The proposed solution is a monolithic foundation slab. The design software SCIA Engineer 22.0 was used to determine the reactions acting on the slab and slab internal forces. The reactions were also verified by manual calculations. The slab was assessed for ultimate and serviceability limit state and designed by hand. This work also includes design of reinforced concrete monolithic column. A drawing documentation was also prepared for both reinforced concrete slab and column.
|
|
|
Using optimization methods to design machine parts
Kubrický, Daniel ; Pokorný, Přemysl (referee) ; Zeizinger, Lukáš (advisor)
This bachelor thesis describes using structural optimization methods to design machine parts. In the first part of the thesis, a description of the current state of knowledge of the optimization process was made together with its theoretical background. In the second part of the thesis, a static analysis and topology optimization or Generative design was developed using the example of a bell crank in six commercial software. In the third part, the resulting models of each software were compared with each other, and the results were compared using the von Mises maximum stress criterion and the overall model deformation. Finally, this work was concluded with an evaluation of the use of the structural optimization software.
|
|
|
Porušování jemnozrnného cementového kompozitu v blízkosti rozhraní plniva a matrice
Vyhlídal, Michal ; Kabele,, Petr (referee) ; Profant, Tomáš (referee) ; Keršner, Zbyněk (advisor)
The Interfacial Transition Zone (ITZ) between the aggregate grain/reinforcement bar and the matrix is considered to be the weakest element in cementitious composites and is, according to some authors, directly responsible for the nonlinear (more precisely, quasi-brittle) behavior of the composites. The aim of this work is verification of the generally accepted paradigm of the weakest element by means of fracture experiments and corresponding numerical simulations. In the experimental part, in addition to traditional fracture tests, modern methods of 3D scanning, scanning electron microscopy, chemical analysis using an electron microprobe and nanoindentation were used. In the numerical part, models based on generalized linear elastic fracture mechanics as well as modern models intended for the simulation of cement composites, namely crack band model with smeared cracks and the Microplane model, were used. Based on the results, the numerical part was complemented by the Cohesive Zone Material model simulating the behavior of the interface. All results are discussed and put into context with already published work. The main conclusion of the work is that the properties of the ITZ do not have such an influence on the behavior of cement composites as the adhesion between the inclusion and the ITZ, i.e. the matrix.
|
|
|
Stress-strain analysis of skull implant with fixators
Machala, Karel ; Votava, Tomáš (referee) ; Marcián, Petr (advisor)
A skull implant with fixators is used for the reconstruction of a damaged area of the skull, where a defect has occurred due to traumatic injury or disease. Nowadays, the production of a skull implant is preoperatively planned and employs modern technologies to achieve a patient-specific, customized approach. However, the manufacturing process of accurately fitting skull implants is associated with the challenge of achieving geometric precision and potential complications. The mechanical behaviour of the skull implant within the defect is a crucial factor that influences its functionality. This bachelor's thesis presents a comparison of distinct models of skull implant geometry at the interface between the implant and bone tissue, based on stress-strain analysis. Stress-strain states are determined using computational modelling utilizing the finite element method. Three variations of skull geometry models with the skull implant, considering different interfaces between the implant and bone tissue, were analysed. Additionally, for result comparison, a reference model of a skull without a defect was solved and analysed. The values of implant displacement were higher in cases where a gap was created at the interface between the implant and bone tissue. The stress values on the fixators were higher for the model variations with a gap created at the interface between the implant and bone tissue.
|
|
|
Stress-strain analysis of the process of continuous steel casting
Cabaj, Gabriel ; Petruška, Jindřich (referee) ; Návrat, Tomáš (advisor)
The thesis is focused on the development of a computational model for determination of stress and strain of a round billet in the process of continuous steel casting. The supplied material characteristics, the geometry of the continuous casting machine and the temperature distribution in the billet are applied as input data for stress and strain analysis. The computational model based on the finite element method is developed in the commercial software ANSYS. The thesis can be divided into three parts. The first part includes background information related to the continuous casting of steel and a research analysis of the computational modeling of this process. The second part describes the development of the planar and three-dimensional computational model in detail. Finally, the obtained stress and strain results are analyzed and general conclusions, and recommendations for further development are proposed.
|
|
| |
|
|
Asynchronous time integration while achieving zero interface energy
Dvořák, Radim ; Kolman, Radek ; Falta, J. ; Neühauserová, M.
This contribution deals with an asynchronous direct time integration of the finite-element model. The proposed method is applied to the phenomenon of wave propagation through an elastic linear continuum. The numerical model is partitioned into individual subdomains using the domain decomposition method by means of localized Lagrange multipliers. For each subdomain, different time discretizations are used. No restrictions for relation between subdomain’s time steps are imposed. The coupling of the subdomains is forced by an acceleration continuity condition. Additionally, we use the a posteriori technique to also provide the displacement and velocity continuity at the interfaces, and hence we obtain exact continuity of all three kinematic fields. The proposed method is experimentally validated using the modified SHPB (split Hopkinson pressure bar) setup.
|
guest ::
