Simulation of Fluid Circulation Using Modern Computational Methods

V této bakalářské práci je řešen modelový problém simulace proudění tekutin za pomoci systému TKSL. V práci jsou popsané rovnice definující proudění tekutin, jejich převod do tvaru vhodného pro řešení, jejich výpočet pomocí základních schém metody konečných diferencí v systému TKSL a porovnání tohoto řešení s řešením pomocí explicitní MacCormackovy metody.In this bachelor's thesis a model problem of a fluid flow simulation is solved using TKSL system. The thesis describes the equations defining the fluid flow, their transformation into the form suitable for solution, their calculation using the basic schemes of finite difference method in TKSL system and comparation of this solution with one using explicit MacCormack method.

High Load-Induced Birefringence of PMMA Investigated in VIS/NIR Spectral Range

In the paper, we present the results of an investigation of polymethylmetacrylate’s birefringence induced due to applying high-load. The stress-induced birefringence of the polymethylmetacrylate samples was experimentally investigated by an apparatus combining an in-house made plane polariscope with a machine for fatigue testing of materials. A halogen lamp was used as the source of white light. The polariscope’s basis was formed by two sets of plane polarizers, one designed for visible (470-750) nm and another one for near-infrared (900-1800) nm spectral range, respectively. The investigated sample was placed between the polarizers and light that passed through the polariscope was collected by an optical fiber connected to an appropriate optical spectral analyzer. The spectra of transmitted light were measured as a function of load and their analysis provided information on the load-induced birefringence of the investigated polymethylmetacrylate samples

Prediction of Multiple Time Series at Stock Market Trading

V diplomové práci je uveden všeobecný postup používaný pro předpověď časových řad, jejich rozdělení, základní charakteristiky a základní statistické metody pro jejich předpovídaní. Spomenuty jsou také neuronové sítě a jejich dělení s ohledem na vhodnost k předpovídaní časových řad. Je navrhnut a implementován program pro predikci vývoje více časových řad při burzovním obchodování, kterého základem je model flexibilního neuronového stromu, kterého struktura je optimalizována pomocí imunitního programování a parametry pomocí modifikované verze simulovaného žíhání anebo pomocí optimalizace hejnem částic. Program je nejdříve testován na schopnosti předpovídat jednoduché časové řady a nakonec je testována jeho schopnost předpovídat více časových řad.The diploma thesis comprises of a general approach used to predict the time series, their categorization, basic characteristics and basic statistical methods for their prediction. Neural networks are also mentioned and their categorization with regards to the suitability for prediction of time series. A program for the prediction of the progress of multiple time series in stock market is designed and implemented, and it's based on a model of flexible neuron tree, whose structure is optimized using immune programming and parameters using a modified version of simulated annealing or particle swarm optimization. Firstly, the program is tested on its ability to predict simple time series and then on its ability to predict multiple time series.

Changes of the Magnetic Properties during Heat Treatment in AISI 304

The aim of this study was to evaluate changes of the magnetic properties during heat treatment in austenitic stainless steel AISI 304. Investigated changes were caused by plastic deformation in material. Specific composition of alloying elements in austenitic stainless steels has got influence on their deformation behavior. Samples were heat treated before measurement of magnetic properties in different intervals of temperatures. The first series of measurements has shown, that it is necessary to make more precise analysis of temperature intervals in the second part of experiment. For verification of structural changes in material there was used hardness test Vickers method and observation by light optical microscope. There was proven that AISI 304 is slightly magnetic after cold forming, although in general it is considered as non-magnetic

Magnesium Alloys Based Composites

Metal matrix composites (MMCs) based on magnesium alloys are excellent candidates for engineering light structure materials, and have great potential in automotive, high performance defence and aerospace applications. In spite of relatively high number of papers dealing with microstructure and mechanical properties of MMCs based on Mg alloys, the deformation mechanisms and other physical properties of these materials are not known enough.The objective of this chapter is to reveal influence of various reinforcement types on the mechanical and physical behaviour of composites in which various magnesium alloys were reinforced with short alumina (Saffil®) fibres and/or SiC and Si particles.JRC.F.4-Safety of future nuclear reactor

Internal Friction in Magnesium Alloys and Magnesium Alloys- Based Composites

In practice, some problems connected with undesirable mechanical vibrations or interruption of acoustic bridges may be solved using high damping materials. Especially, transport industry needs high damping light materials with proper mechanical properties. Magnesium alloys and magnesium alloys‐based metal matrix composites may be considered as materials exhibiting such behaviour. Damping of mechanical vibrations and their conversion to the heat (internal friction) is conditioned by the movement and redistribution of various defects in the crystal lattice. Generally, internal friction depends on the material microstructure and conversely changes in the material microstructure may be studied using the internal friction measurements. The strain amplitude‐dependent internal friction was investigated at room temperature in commercially available Mg alloys and Mg alloys‐based composites with the aim to identify changes in the microstructure invoked by thermal and mechanical loading. The temperature‐dependent internal friction indicated the following effects: (a) mechanisms connected with dislocations and grain boundaries in the microcrystalline pure Mg, (b) precipitation and phase transformations in alloys and (c) generation as well as relaxations of thermal stresses in composites. The internal friction was measured in the bending mode in two frequency regions: I.: units and tens of Hz and II.: units of kHz

The Effect of Surface Treatment on Corrosion Resistance of Austenitic Biomaterial

This paper focuses on the effect of surface treatment (grinding, electrochemical polishing) on the corrosion resistance of AISI 316L, a Cr-Ni-Mo low-carbon austenitic surgical stainless steel, in a physiological solution at the temperature of 37 °C. The influence of a surface defect and of sensitization by heat treatment on the corrosion behaviour of electrochemically polished surface is also studied. The evaluation is based on the results of cyclic potentiodynamic polarization tests and on the microscopic observation of specimen surfaces after performed tests. The analysis of cyclic potentiodynamic curves showed the highest pitting corrosion resistance of electrochemically polished specimens regardless of the previous sensitization. The as-received specimen showed the highest susceptibility to pitting, which was microscopically confirmed. Based on the performed experiments we can conclude that electrochemical polishing is an efficient chemical surface treatment to increase the resistance of AISI 316L to pitting corrosion; the resistance to pitting corrosion of electrochemically polished surface can by markedly decreased by the presence of mechanical defects; the as-received surface and the ground surface showed lower resistance to pitting corrosion than electrochemically polished ones; sensitization induced by heat treatment (700 °C/10 hours) does not decrease resistance to pitting corrosion

CHARACTERIZATION OF PRECIPITATES FORMED IN THE ALUMINUM ALLOY WITH ANTIMONY

The aim of the article was to identify and characterize the precipitates formed in the aluminum alloys with the addition of antimony. The performed investigation was on the casting aluminium alloy based on ENAC-AlMg5Si2Mn (ENAC-51500) used in the automotive industry with the addition of antimony in an amount of 0.2 % for the first sample and 1.2 % for the second one. The main research technique was scanning electron microscopy, in order to evaluate the morphology and precipitates in the investigated samples, the backscattered electrons were used. Performed research allowed to determine the effect of the addition of antimony on the morphology of formed precipitates