Master thesis is dealing with the issue of condensate creation and removal from the Nesher Ramle steam turbine during start-up and steady state. At the beginning a preliminary calculation of heat balance and the turbine itself is done. It is followed by description and design of drainage system supplemented by calculation of the steam flow through the orifices. Steam flow calculation was done via S. D. Morris, Pavelek with Kalčík and Ambrož, all three methods were compared. The main goal is the theoretical calculation of the amount of condensate created during start-up which is influenced by its initial state from which it is started. Three default states are considered, cold, warm and hot. In the last chapter the comparison of theoretical calculation with the measured data on real turbine is done and it is supported by the evaluation of the data from the measurement of the steam turbine at steady state on maximum power and half power. From the steady state analysis, percentage of water flow to expander from the total amount of condensate formed in the turbine were obtained.

The master thesis "Upgrading of Jindřichov na Moravě and Branná Railway Stations" deals with designing new platforms that are suitable for people with reduced mobility in accordance with applicable laws and standards. Platforms with the platform edge height of 550 millimetres above the top of rail were designed. The speed limit was increased from the original 40 km/h up to 50 km/h. Moreover, the thesis design reconstruction of railway superstructure and railway substructure and deal with the drainage system.

The master thesis "Upgrading of Jeseník Railway Stations" deals with designing new platform that is suitable for people with reduced mobility in accordance with applicable laws and standards. Platform with the platform edge height of 550 millimetres above the top of rail were designed. The speed limit was increased. Moreover, the thesis design reconstruction of railway superstructure and railway substructure and deal with the drainage system.

The task of the thesis is to propose an adjustment to the railway station Březová nad Svitavou with regard to the introduction of the remote control of security device and explore the possibility of building a new railway stop that would be located closer to downtown. The aim is mutual comparison of elaborated variants. Work includes design of new platforms meet the conditions for safe access for people with limited mobility, next adjustment are adjustment of the geometric parameters of the track superstructure and substructure, including system of drainage station.

The aim of this Master’s thesis is to design a steam condensing turbine with three bleeds. First, a heat balance of the steam cycle is calculated, followed by thermodynamic and stress calculation of the turbine blading and design of a gland steam system and drain system. A price proposal is suggested for the given steam turbine. In the end, a design drawing of the steam turbine is constructed.

No description available.

The aviation environment holds challenging application constraints for efficient hydraulic system noise reduction devices. Besides strong limits on component weight and size, high safety and reliability standards demand simple solutions. Hence, basic silencers like inline expansion chambers and Helmholtz-Resonators are state-of-the-art aboard commercial aircrafts. Unfortunately, they do not meet today’s noise attenuation aims regarding passenger comfort and equipment durability. Significant attenuation performance is expected from active concepts that generate anti-phase noise. However, such concepts remain a long term approach unless related costs, e.g. due to additional power allocation and real-time control equipment can be avoided. In this paper an active fluid borne noise attenuation concept is discussed that accounts for the mentioned constraints. An aircraft hydraulic pump is considered as main noise source. The active attenuator is an in-house rotary valve design. The basic feature is a known direct shaft coupling principle of pump and rotary valve, so no speed/ frequency control of the valve and no separate power supply are required. The common-shaft principle is further simplified here and proposed as integral feature of future “smart pumps”.

<div>Pavement drainage systems are one of the key drivers of pavement function and longevity, and effective drain maintenance can significantly extend a pavement's service life. Maintenance of these drains, however, is often hampered by the challenge of locating the drains. Ground Penetrating Radar (GPR) typically offers a rapid and effective method to detect these underground targets. However, typical detection schema that rely upon the observation of the hyperbolic return from a GPR scan of a buried conduit still tend to miss many of the older drains beneath pavements as they may be partially or fully filled with sediment and/or may be fabricated from clay or other earthen materials, yielding a return signal that is convolved with significant background noise. </div><div><br></div><div>To manage this challenge, this work puts forward an improved background noise and clutter reduction method to enhance the target signals in what amounts to a constructed environment that tends to have more consistent subsurface properties than one might encounter in a general setting. Within this technique, two major algorithms are employed. Algorithm 1 is the core of this method, and plays the role of reducing background noise and clutter. Algorithm 2 is supplementary, and helps eliminate anomalous discontinuous returns generated by the equipment itself, which could otherwise lead to false detection indications in the output of Algorithm 1. Instead of traditional 2-D GPR images, the result of the proposed algorithms is a 1-D plot along the survey line, highlighting a set of “points of interest” that could indicate buried drain locations identified at any given GPR operating frequency. Subsurface exploration using two different operating frequencies, 900 MHz and 400 MHz herein, is then employed to further enhance detection confidence. Points of interest are ultimately coded to define the confidence of the detection. Comparing the final result of proposed algorithms with the original GPR images, the improved algorithm is demonstrated to provide significantly improved detection results, and could potentially be applied to similar problems in other contexts.</div><div><br></div><div>Besides the background reduction methods, a group of simulations performed using GPRMAX2D software are examined to explore the influence of road cross-section designs on sub-pavement drainage conduit GPR signatures, and evaluate the effectiveness of alternate GPR antennae configurations in locating these buried conduits in different ground conditions. Two different models were explored to simulate conduit detection. In addition, different pipe and soil conditions were modeled, such as pipe size, pipe material, soil moisture level, and soil type. Four different quantitative measurements are used to analyze GPR performance based on different key factors. The four measurements are 1) signal to background ratio (SBR) in dB; 2) signal to receiver noise ratio (SNR) in dB; 3) signal energy in Volts; and 4) average signal band power in Watts.</div><div><br></div><div>The water and clay content of subsurface soil can significantly influence the detection results obtained from ground penetrating radar (GPR). Due to the variation of the material properties underground, the center frequency of transmitted GPR signals shifts to a lower range as wave attenuation increases. Examination of wave propagation in the subsurface employing an attenuation filter based on a linear system model shows that received GPR signals will be shifted to lower frequencies than those originally transmitted. The amount of the shift is controlled by a wave attenuation factor, which is determined by the dielectric constant, electric conductivity, and magnetic susceptibility of the transmitted medium. This work introduces a receiver-transmitter-receiver dual-frequency configuration for GPR that employs two operational frequencies for a given test - one higher and one slightly lower - to take advantage of this phenomenon to improve subpavement drain detection results. In this configuration, the original signal is transmitted from the higher frequency transmitter. After traveling through underground materials, the signal is received by two receivers with different frequencies. One of the receivers has the same higher center frequency as the transmitter, and the other receiver has a lower center frequency. This configuration can be expressed as Rx(low-frequency)-Tx(high-frequency)-Rx(high-frequency) and was applied in both laboratory experiments and field tests. Results are analyzed in the frequency domain to evaluate and compare the properties of the signal obtained by both receivers. The laboratory experiment used the configuration of Rx(400MHz)-Tx(900MHz)-Rx(900MHz). The field tests, in addition to the configuration used in the lab tests, employed another configuration of Rx(270MHz)-Tx(400MHz)-Rx(400MHz) to obtain more information about this phenomenon. Both lab and field test results illustrate the frequency-shift phenomenon described by theoretical calculations. Based on the power spectrum for each signal, the lower frequency antenna typically received more energy (higher density values) at its peak frequency than the higher frequency antenna.</div>

No description available.

High electron mobility transistors (HEMTs) realized using AlxGa1-xN/GaN are relatively new technology which is prominent for high-speed and high-power applications. Some of the main problems with this technology were identified as dynamic RDSon, current collapse and threshold voltage instabilities due to the off-state stress. What was less investigated is the effect of the off-state stress on the leakage current at lower voltages. In this work, multiple devices with various initial leakage currents are stressed at different stress conditions (drain voltage, temperature, duration) and the development of drain-source on-state resistance (RDSon), threshold voltage (Vth) and drain-source leakage current (IDSS) after stress are tracked. It was found out that devices with initially higher leakage exhibit higher RDSon and Vth before stress, which simulations attributed to the higher Al mole fraction in the back-barrier or less unintentional doping in the channel layer. During the off-state stress (VDS = 900 V), the leakage current shortly rises and then sharply drops, presumably because of the charge redistribution in the back-barrier. After the stress, no larger changes were observed for RDSon and Vth , but they were for the leakage current i.e., initially low leakage devices had post-stress leakage increase, while initially high leakage devices had post-stress leakage decrease. This is assumed to be caused by the charge redistribution. Parasitic capacitance measurements showed the rise of the pre-stress input, output and reverse transfer capacitances with the pre-stress leakage, which could presumably be explained by higher Al mole fraction inducing more charges in the channel layer, deeming higher Al mole fraction in the back-barrier as a main assumed cause for all the observed effects. After the stress, capacitance changes were tentatively explained by the charge redistribution in the back-barrier. Finally, high temperature was shown to significantly reduce the observed long time to recovery. However, more measurements are needed to further observe this influence. Additionally, more experiments (e.g., on wafer, G-ω measurement, etc.) are needed in general to further investigate the mechanisms behind these memory effects. / Transistorer med extra hög elektronmobilitet, sk HEMT-ar (high electron mobility transistor) kan fabriceras med hjälp av materialen galliumnitrid (GaN) och aluminium-galliumnitrid (AlxGa1-xN). GaN HEMT-ar lämpar sig mycket väl för kraftkomponenter för höga frekvenser. Några av problemen med denna nya teknologi är hög resistans mellan ”drain” och ”source”, RDSon, reduktion av mättnadsströmmen (”current collapse”) och instabiliteter hos styrets tröskelspänning (Vth) när komponenterna stressas i avslaget tillstånd. Mindre känt är effekterna av stress för en avslagen komponent på läckströmmen (IDSS) vid låga påkänningar. I detta arbete har komponenter med varierande läckströmmar utsatts för olika typer av stress, t ex drain-spänning och höjd temperatur under olika långa tider samtidigt som parametrarna RDSon, Vth och IDSS har uppmätts. Det kunde noteras att komponenter med initialt högre läckströmmar hade högre RDSon och Vth innan de utsattes för stress, vilket med hjälp av simuleringar kunde visas bero på högre Al-molfraktion i skiktet under AlxGa1-xN-lagret, alternativt lägre dopning i kanal-lagret. Vid stress (VDS = 900 V) med komponenterna i avslaget tillstånd ökade läckströmmen kortvarigt för att sedan minska, troligtvis beroende på att laddningar omfördelas i lagret under kanal-skiktet. Efter stress sågs inte några större förändringar hos RDSon och Vth , men förändringar syntes på läckströmmen: komponenter med initialt låga läckströmmar visade ökning av läckströmmen efter stress, medan komponenter med initialt höga läckströmmar visade en post-stress minskning av läckström. Detta antas bero på den nämnda omfördelningen av laddningar djupare ner i komponenterna. Mätningar av parasitisk kapacitans visade på en ökning av pre-stress in- och ut-kapacitanserna (Ciss, Coss) samt ”gate-drain”-kapacitansen som funktion av pre-stress läckströmmar. Detta kan möjligtvis förklaras av att en högre andel Al inducerar mer laddningar i kanalen, vilket indikerar att högre Al-molfraktion i skiktet under kanal-lagret är orsaken till många av de effekter som setts. Kapacitansförändringar efter stress förklaras troligen av att laddningarna i detta lager återgår. Till sist noteras också att hög temperatur tydligt reducerade den långa tiden som komponenterna behövde för att återhämta sig. Det var också tydligt att mer mätningar är nödvändiga för att ytterligare säkerställa de uppmätta förändringarna, t ex mätningar av G-ω på icke kapslade chips, skulle kunna öka förståelsen för dessa minneseffekter.