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On finite element modelling in time reversal problems
Mračko, Michal ; Kober, Jan ; Kolman, Radek ; Převorovský, Zdeněk ; Plešek, Jiří ; Masák, Jan ; Kruisová, Alena
In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or other acoustic emission sources in bodies and structures. As it is known, a classical explicit integration scheme - central difference is reversible. The central difference scheme as a time integrator is widely used for linear and nonlinear finite element analyses and it is also implemented in commercial and open-source finite element software. In the paper properties of the explicit FEM in time reversal problems are studied and analysed. We use the standard Galerkin FEM formulation with linear shape functions, one-point Gauss integration and lumped mass matrix. Loading by the Ricker pulse was applied for modelling of the acoustic source in an elastic square domain. A special attention is paid to the choice of boundary conditions in reverse problem which keep the reversibility of problems of interest. Finally, we show the quality of refocusing of the original acoustic source.
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Greep analysis of-piece of the steam distributor
Gabriel, Dušan ; Masák, Jan ; Plešek, Jiří
The finite element analysis of the steam distributor of the CHEMOPETROL heating plant T200 was analyzed under creep conditions. Material properties were described by the probabilistic exponential model with damage. The purpose of the analysis was to compare the original version and the proposed design modification applied to one of T-pieces of the distributor when the original contact algorithm was employed to simulate the interaction between the collar and the pipe.
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Creep analysis of HP inner casing DSPWR – contact task
Kopačka, Ján ; Masák, Jan ; Gabriel, Dušan ; Plešek, Jiří
The report summarizes results of the 3rd stage of the creep analysis of Doosan Škoda Power high-pressure inner casing. An analysis of the high-pressure inner casing is carried out with respect to the contact boundary conditions in the division plane and the use of a complex creep material model. The results of the PMD contact analysis are compared to the measured values and also compared with the ANSYS program where the Norton-Bailey model of creep was used.
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Explicit dynamic finite element analysis of a firing pin assembly
Mochar, Dominik ; Gabriel, Dušan ; Masák, Jan ; Kopačka, Ján ; Kolman, Radek ; Plešek, Jiří ; Hynek, P. ; Vtípil, J.
In this paper, explicit dynamic finite element analysis of a firing pin assembly was performed. Two different geometries of the firing pin were considered using the finite element software PMD and Abaqus. For both variants there was evaluated a stress distribution at the critical point of a tested component, that is going to be later used for a fatigue analysis of the firing pin.
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Special eigenvalue problems for symmetric sparse matrices related to electronic structure calculations
Novák, Matyáš ; Tůma, Miroslav (advisor) ; Plešek, Jiří (referee)
Ab-initio methods for calculating electronic structure represent an important field of material physics. The aim of this theses - within the project focused on developing the new method for calculating electronic states in non-periodic structures based on density functional theory, pseudopotentials, and finite elements methods - is to convert Kohn-Sham equations into the form suitable for discretisation, to suggest apropriate method for solving generalized eigenproblem resulting from this discretisation and to implement an eigenvalue solver (or to modify existing one). The thesis describes a procedure for converting the many-particle Schrödinger equation into generalized rank-k-update eigenvalue problem and discusses various methods for its solution. Eigensolver Blzpack, which makes use of the block Lanczos method, has been modified, integrated into the Sfepy framework (a tool for the finite element method calculation) and resulting code has been successfully tested.
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Dispersion properties of finite element method: review
Kolman, Radek ; Okrouhlík, Miloslav ; Plešek, Jiří ; Gabriel, Dušan
Review of the dispersion properties of plane square bilinear finite element used in plane elastic wave propagation problems is presented. It is assumed the grid (spatial) dispersion analysis and, further, the temporal-spatial dispersion analysis for explicit direct time integration based on the central difference method. In this contribution, the dispersion surfaces, polar diagrams and error dispersion graphs for bilinear finite element are depicted for different Courant numbers in explicit time integration. Finally, recommendation for setting the mesh size and the time step size for the explicit time integration of discretized equations of motion by the bilinear finite element method is provided.
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Night Sky on Mobile Device
Plešek, Jan ; Dittrich, Petr (referee) ; Koutný, Jiří (advisor)
p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo} This thesis describes concept and implementation of the application designed to observate the night sky in the simple and intuitive way using the concept of augmented reality. Based on the brief specification of the most widespread mobile operation systems, the iOS system was chosen as the implementation platform. The thesis describes methods to calculate the position of celestial objects based on the data gathered from GPS module, magnetometer and accelerometer. Stars, planets and other objects are rendered by the stereographic projection. The user can see celestial objects trough the mobile device display and control the direction of the view by positioning and turning the device. The application could be used for quick orientation in night sky during astronomical observation or educational purposes.
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