Dissertationen zum Thema „Prehľad“

Táto diplomová práca sa zaoberá prieskumom a taxonómiou sieťových forenzných nástrojov. Popisuje základné informácie o sieťovej forenznej analýze, vrátane procesných modelov, techník a zdrojov dát používaných pri forenznej analýze. Ďalej práca obsahuje prieskum existujúcich taxonómií sieťových forenzných nástrojov vrátane ich porovnania, na ktorý naväzuje prieskum sieťových forenzných nástrojov. Diskutované sieťové nástroje obsahujú okrem nástrojov spomenutých v prieskume taxonómií aj niektoré ďalšie sieťové nástroje. Následne sú v práci detailne popísané a porovnané datasety, ktoré sú podkladom pre analýzu jednotlivými sieťovými nástrojmi. Podľa získaných informácií z vykonaných prieskumov sú navrhnuté časté prípady použitia a nástroje sú demonštrované v rámci popisu jednotlivých prípadov použitia. Na demonštrovanie nástrojov sú okrem verejne dostupných datasetov použité aj novo vytvorené datasety, ktoré sú detailne popísane vo vlastnej kapitole. Na základe získaných informácií je navrhnutá nová taxonómia, ktorá je založená na prípadoch použitia nástrojov na rozdiel od ostatných taxonómií založených na NFAT a NSM nástrojoch, uživateľskom rozhraní, zachytávaní dát, analýze, či type forenznej analýzy.

This thesis investigates the laminar flame speed of C₁-C₃ alkanes and their binary mixtures at conditions of interest in natural gas based gas turbines viz. high temperature, pressure and dilution. Laminar flame speed has been found useful not only for validating chemical kinetics mechanisms but also for developing empirical scaling laws for practical combustion systems. The thesis addresses the lack of laminar flame speed data of C₁-C₃ alkanes at preheat (300-650 K), pressure (1-10 atm) and significant oxidizer dilution (15-21 vol% O₂). Over 400 measurements are reported over a wide range of conditions along with comparison to predictions from leading chemical mechanisms. Unstretched flame speed measurements were performed using a modified Bunsen flame technique based on reaction zone area from chemiluminescence imaging, whereas the strain sensitivity measurements were performed using a bluff-body stabilized stagnation flame with high resolution PIV. These measurements are used to: (i) discern the uncertainties associated with the measurements, (ii) understand the effect of fuel mixture and vitiation on flame speed, and (iii) validate the performance of the leading chemical kinetics mechanisms. Extensive testing shows the unstretched flame speed measurements from the modified Bunsen technique are reasonably accurate. Vitiation studies for methane and propane flames at high preheat show the reduction in flame speed results primarily from the thermal effect of the diluent and that the relative change in flame speed from the undiluted mixture is well correlated to the fractional change in the adiabatic flame temperature over a range of conditions. Significant difference in the measured and predicted flame speeds were observed for rich, atmospheric pressure, propane and lean, high pressure, methane/ethane mixtures with dilution. This highlights possible avenues for improvements in the chemical kinetics mechanisms. Systematic errors were also identified in the Bunsen flame measurements at certain conditions, such as for rich flames with dilution, indicating a need for better understanding of the Bunsen flame technique at these conditions. The difference in the measured and predicted flame speed does not show any clear correlation with the flame height or the strain sensitivity of the mixture. Finally previously proposed mixing rules for estimating flame speed of fuel mixtures from pure fuel components are shown to be reasonably accurate over a range of pressure, reactant temperature and dilution conditions.

La vitesse de flamme laminaire représente une grandeur physique clé à mesurer car elle permet d'obtenir des données fondamentales sur la réactivité, la diffusivité et l'exothermicité du carburant. Elle est également un des paramètres utilisés pour le développement et la validation des mécanismes réactionnels détaillés ainsi que pour la modélisation de la combustion turbulente. Bien que cette grandeur physique ait fait l'objet de nombreuses études expérimentales depuis plusieurs décennies, sa méconnaissance sur des carburants multi-composant dans des conditions haute-pression et haute-température similaires à celles existantes dans les chambres de combustion reste un sujet d'actualité pour les industriels des secteurs automobile et aéronautique. Au cours de cette thèse, un brûleur de configuration bec Bunsen fonctionnant avec un prémélange gazeux combustible/air a été conçu pour produire une flamme laminaire à pression élevée tout en permettant la mesure par voie optique de la vitesse de flamme laminaire de carburants multi-composant (kérosène, biocarburants de seconde génération...). La mesure est basée sur la détection du contour de flamme par diverses diagnostics optiques comme la chimiluminescence OH*, la PLIF-OH et la PLIF-acétone/aromatique. En premier lieu, les mélanges de carburants purs gazeux (CH4) ou liquide (acétone) avec de l'air ont été étudiés pour valider le brûleur expérimental et la méthodologie de mesure de la vitesse de flamme laminaire par voie optique. Les évolutions de la vitesse de flamme laminaire pour des carburants de type kérosène (composants purs, surrogate LUCHE et Jet A-1) en fonction de la pression, température de préchauffage et richesse ont été ensuite étudiées et comparées avec des simulations numériques utilisant un mécanisme réactionnel détaillé. La dernière partie de la thèse est consacrée à l'étude de l'influence des composés oxygénés présents dans un biocarburant de seconde génération de type d'essence sur la vitesse de flamme laminaire. Après avoir mesuré la vitesse de flamme laminaire de différentes molécules oxygénées, les effets d'addition de ces composés oxygénés dans le carburant ont été quantifiés
Laminar flame speed is one of the key parameters for understanding reactivity, diffusivity and exothermicity of fuels. It is also useful to validate both the kinetic chemical mechanisms as well as turbulent models. Although laminar flame speeds of many types of fuels have been investigated over many decades using various combustion methodologies, accurate measurements of laminar flame speeds of multicomponent liquid fuels in high-pressure and high-temperature conditions similar to the operating conditions encountered in aircraft/automobile combustion engines are still required. In this current study, a high-pressure combustion chamber was specifically developed to measure the laminar flame speed of multicomponent liquid fuels such as kerosene and second generation of biofuels. The architecture of the burner is based on a preheated premixed Bunsen flame burner operated in elevated pressure and temperature conditions. The optical diagnostics used to measure the laminar flame speed are based on the detection of the flame contour by using OH* chemiluminescence, OH- and acetone/aromatic- Planar laser induced fluorescence (PLIF). The laminar flame speed of gaseous CH4/air and acetone/air premixed laminar flames were first measured for validating the experimental setup and the measurement methodologies. Then, the laminar flame speeds of kerosene or surrogate fuels (neat kerosene compounds, LUCHE surrogate kerosene and Jet A-1) were investigated and compared with simulation results using detailed kinetic mechanisms over a large range of conditions including pressure, temperature and equivalence ratio. The last part of the thesis was devoted to study the effect of oxygenated compounds contained in the second generation of biofuels on the laminar flame speeds. After measuring the laminar flame speeds of various oxygenated components present in partially hydro-processed lignocellulosic biomass pyrolysis oils, the effect of these oxygenates on the flame speeds of these fuels were quantitatively investigated

The Master´s thesis focuses on the possibilities of using MAG welding on carbon steel 1.1221(C60E) without using preheating. It researches the effect of basic welding parameters on the final characteristics with the goal being to find a welding seam without defects, without using preheating.

En vanlig orsak till brott i svetsade kolstålskonstruktioner kan härledas till små sprickbildningar som uppstår i svetsgodset eller det område av grundmaterialet som har påverkats strukturellt av energin från svetsprocessen, även kallad HAZ. Dessa sprickor uppstår ofta timmar eller dagar efter avslutad svetsning och beror på en kombination av väte, en hård och spröd mikrostruktur och närvaro av spänningar. För att undvika dessa sprickor kan man förvärma materialet innan svetsning. Den förhöjda arbetstemperaturen ger en långsammare svalning vilken minskar risken för martensitbildning och låter väte diffundera ut från svetsförbandets kritiska delar. Det finns olika beräkningsmodeller för att räkna ut den förvärmningstemperatur som krävs för att motverka dessa sprickor. De flesta av dem är grafiska men försök har gjorts att översätta dessa till matematiska algoritmer. Beräkningsmodellerna kan ge väldigt varierande temperaturer och olika modeller kan anses vara bäst tillämpade till olika stål. I denna rapport har det undersökts vilken beräkningsmodell som är bäst lämpad för konstruktionsstålet S355J2. Modellerna som har använts är den matematiska CET, de grafiska CEIIW och CEN samt matematiska tolkningar av de två sistnämnda. Utvärderingen har gjorts genom att svetsa upp prover på plåtar med en godstjocklek på 30 mm med en stegvis ökande förhöjd arbetstemperatur. Dessa prover har sedan genomgått både oförstörande och förstörande provning för att undersöka hur sprickbenägna de är. En analys av svetsförbandets mikrostruktur har också genomförts för att identifiera de mest kritiska zonerna. Det visade sig att de matematiska tolkningarna av de grafiska metoderna skiljde sig såpass mycket från sina grafiska motsvarigheter att de inte kan rekommenderas för användning. Det visade sig även att det inte fanns en beräkningsmodell av ursprungsmodellerna som var bäst lämpad för S355J2 utan valet berodde helt och hållet på vilken sträckenergi som användes då modellerna tar olika mycket hänsyn till denna. För en sträckenergi på över 1,6 kJ/mm rekommenderas CET-metoden som beräknade en temperatur som gav goda materialparametrar. För sträckenergier under 0,9 kJ/mm beräknar ingen metod en tillräckligt hög temperatur, men CEIIW är den som beräknar den högsta förhöjda arbetstemperaturen och rekommenderas därför för användning. Man bör dock ha i åtanke att den inte var tillräckligt hög och bör därför ses som en lågt räknad rekommendation. Mellan 0,9 kJ/mm och 1,6 kJ/mm har inga prover svetsats men rekommendationen är att använda sig av CET-metoden då den är enkel och beräknar högst temperatur. Vad det gäller svetsförbandets kritiska zoner så visade det sig att korntillväxtzonen var området där vätesprickor har störst förutsättningar för att uppstå.
One of the most common causes of failure in welded carbon steel constructions can be traced to small cracks that occur in the weld metal or in the area of the base metal that has been affected structurally by the energy from the welding process, also known as HAZ. These cracks can occur hours or days after the welding is completed and do so due to a combination of hydrogen that has penetrated the metal during the weld process, a hard and brittle microstructure and tensile stresses acting on the weld. A method to avoid these cracks is to preheat the material before welding. The increased temperature results in a slower cooling which reduces the risk of a martensitic microstructure and allow hydrogen to diffuse out of the most critical zones of the welded joint. There are many different methods for calculating the preheat temperature needed to counter these cracks. Most of them are solved graphically but attempts have been made to translate them into mathematical algorithms to facilitate calculations. The outcome of the methods may vary and different methods can be considered to be best applied to various steel. The purpose of this study is to investigate which method is best suited to determine the preheat temperature to eliminate the risk of hydrogen cracking for the structural steel S355J2. The methods used in this study was the mathematical CET, the graphic CEIIW and CEN and mathematical interpretations of the latter two. The evaluation was made by welding samples of plates with a thickness of 30 mm and with an incrementally increased preheat temperature. These samples were then subjected to both non-destructive and destructive testing to examine how prone they were to crack. An analysis of the weld microstructure was also conducted to identify the most critical zones. It turned out that the mathematical interpretations of the graphic methods differed so much from their graphical equivalent that they can not be recommended for use. It was also found that none of the original methods can be said to be best suited for S355J2 but the choice depended entirely on the heat input. For a heat input over 1.6 kJ/mm it is recommended to use the CET-method which estimated a temperature that gave good material parameters. For a heat input below 0.9 kJ/mm no method calculates a sufficiently high temperature, but the CEIIW-method is calculating the highest temperature and is therefore recommended for use. However, one should keep in mind that it was not sufficient and should therefore be seen as a conservative recommendation. No samples were welded between 0.9 kJ/mm and 1.6 kJ/mm but the recommendation is to use the CET- method because it is simple and calculates the maximum temperature. It was also found that the coarse grain zone was the area where hydrogen cracking is most likely to occur.

Coal derived synthetic gas (syngas) fuel is a promising solution for today s increasing demand for clean and reliable power. Syngas fuels are primarily mixtures of H2 and CO, often with large amounts of diluents such as N2, CO2, and H2O. The specific composition depends upon the fuel source and gasification technique. This requires gas turbine designers to develop fuel flexible combustors capable of operating with high conversion efficiency while maintaining low emissions for a wide range of syngas fuel mixtures. Design tools often used in combustor development require data on various fundamental gas combustion properties. For example, laminar flame speed is often an input as it has a significant impact upon the size and static stability of the combustor. Moreover it serves as a good validation parameter for leading kinetic models used for detailed combustion simulations. Thus the primary objective of this thesis is measurement of laminar flame speeds of syngas fuel mixtures at conditions relevant to ground-power gas turbines. To accomplish this goal, two flame speed measurement approaches were developed: a Bunsen flame approach modified to use the reaction zone area in order to reduce the influence of flame curvature on the measured flame speed and a stagnation flame approach employing a rounded bluff body. The modified Bunsen flame approach was validated against stretch-corrected approaches over a range of fuels and test conditions; the agreement is very good (less than 10% difference). Using the two measurement approaches, extensive flame speed information were obtained for lean syngas mixtures at a range of conditions: 1) 5 to 100% H2 in the H2/CO fuel mixture; 2) 300-700 K preheat temperature; 3) 1 to 15 atm pressure, and 4) 0-70% dilution with CO2 or N2. The second objective of this thesis is to use the flame speed data to validate leading kinetic mechanisms for syngas combustion. Comparisons of the experimental flame speeds to those predicted using detailed numerical simulations of strained and unstrained laminar flames indicate that all the current kinetic mechanisms tend to over predict the increase in flame speed with preheat temperature for medium and high H2 content fuel mixtures. A sensitivity analysis that includes reported uncertainties in rate constants reveals that the errors in the rate constants of the reactions involving HO2 seem to be the most likely cause for the observed higher preheat temperature dependence of the flame speeds. To enhance the accuracy of the current models, a more detailed sensitivity analysis based on temperature dependent reaction rate parameters should be considered as the problem seems to be in the intermediate temperature range (~800-1200 K).

This diploma thesis focuses on implementation issues of ADS-B in the airspace of Czech republic and Europe. Our introduction contains a review of necessity of this system and describes ADS-B. The next part addresses the legislation of this system in detail, also sums up the state of its implementation and the plan of implementation. Our conclusion shows the problems connected with the system , offers their solution and views for the future.

The master‘s thesis deals with the influence of the thermal cycle of welding with preheat on castings made of grey cast iron to change the hardness. The thesis deals with the classification of graphitic cast irons, their structure, properties and influences they have on the formation and transformation of the structure. Emphasis is placed on chemical composition and structure stability at elevated temperatures. The practical part deals with the investigation of the effects of casting repair on the decrease of hardness measured in the foundry Heunisch Brno.

碩士
國立中興大學
精密工程學系所
102
Due to high-tech products day by day tired progress requirements for product weight, close to compact size to facilitate easy to carry, so thin demand for high-quality steel increased rapidly. Nozzle is a thin plate steel manufacturing segment after the manufacturing process high-temperature fluid liquid steel, slag, and add gas additive, in the crucible or converter add to the tools necessary process, but also to ensure the smooth progress of the foundation smelting. To prolong the life of the Melting Nozzle to reduce production costs, improve economic efficiency principles efforts. China Steel Corporation (CSC) are manufactured in the preheating process the Melting Nozzle, that material properties due to heat and excessive expansion, leading to the Melting Nozzle cannot afford to 1300℃ High temperature and cracked the urgent need for research to explore the factors that reduce its life. Therefore, this study using the finite element analysis method for high temperature preheat the Melting Nozzle and support with thermal insulation materials simulate the stress-strain analysis. Obtained the preheat Melting Nozzle, and the nozzle support whit internal insulation materials to withstand high temperature stress and strain of the situation. To explore the role of reason in the preheat Melting Nozzle, and select the preferred nozzle material, thereby improving the Melting Nozzle life.

碩士
國立交通大學
機械工程學系
99
This research used a 30kW-generator in Taiwan Sugar swine farm in Taichung to collect data for the long-term electricity generation. This study is an continous effort of Lin’s work [3], which carried out the electricity generation project by using 60% methane concentration of biogas in a small swine farm in Miaoli. This experimental study, using 73% methane concentration of biogas, consisted of three parts. Firstly, investigate the effect of biogas supply rate together with the different excess air ratios on generator performance. Secondly, make a comparison with Lin’s results. Finally, apply a waste heat recovery system to preheat the inlet gas under different temperatures and analyze the preheating influence on the generator performance. In the present study, the maximum power generation is 26.7kW occurred at biogas flow rate of 260L/min, whereas the maximum thermal efficiency and methane consumption ratio are 27% and 96.03% at biogas flow rate of 200L/min. The power generation in the present work is higher than one in Lin’s one [3], except the region around λ (excess air ratio) < 0.85. However, the thermal efficiency increases with the increasing methane concentration just in the region of λ>0.95, while on the relatively rich side (λ<0.95), there is no benefit. The improvement by preheating inlet gas is obvious when excess air ratio is relatively high, such as λ>1.3.

Casting is a substantial part of modern manufacturing and production, typically used in the production of aluminum alloys. The high pressure die casting process is extremely suitable for mass production. Due to the high volume, wasted time and resources during the production cycle become more significant. Aluminum die castings require the die to be at elevated temperatures to produce acceptable castings. When the inner surfaces of a die are cold, the outer shell of the casting will cool too rapidly, and solidification of the outer shell occurs before the aluminum has time to uniformly fill the cavities. Therefore, without the die being within the proper temperature range, the castings produced will have significant issues in porosity and casting incompleteness. Furthermore, stresses are introduced to the casting surfaces when warm-up shots are used to raise the temperature prior to production. In the present work, research is conducted on designing a heating method for a casting die used in the manufacturing of an automotive transmission intermediate plate. An electric, short wave infrared heating system is simple and effective for the purpose. By utilizing an electric infrared heater in combination with a flat mirror reflector, the aluminum high pressure die casting die was heated to 300 ◦C surface temperature within 30 minutes. Further research can be done to optimize heat flux distribution and minimize energy consumption.