Shape: A 3D Modeling Tool for Astrophysics

We present a flexible interactive 3D morpho-kinematical modeling application for astrophysics. Compared to other systems, our application reduces the restrictions on the physical assumptions, data type and amount that is required for a reconstruction of an object's morphology. It is one of the first publicly available tools to apply interactive graphics to astrophysical modeling. The tool allows astrophysicists to provide a-priori knowledge about the object by interactively defining 3D structural elements. By direct comparison of model prediction with observational data, model parameters can then be automatically optimized to fit the observation. The tool has already been successfully used in a number of astrophysical research projects.Comment: 13 pages, 11 figures, accepted for publication in the "IEEE Transactions on Visualization and Computer Graphics

Convection and chemistry effects in CVD: A 3-D analysis for silicon deposition

The computational fluid dynamics code FLUENT has been adopted to simulate the entire rectangular-channel-like (3-D) geometry of an experimental CVD reactor designed for Si deposition. The code incorporated the effects of both homogeneous (gas phase) and heterogeneous (surface) chemistry with finite reaction rates of important species existing in silane dissociation. The experiments were designed to elucidate the effects of gravitationally-induced buoyancy-driven convection flows on the quality of the grown Si films. This goal is accomplished by contrasting the results obtained from a carrier gas mixture of H2/Ar with the ones obtained from the same molar mixture ratio of H2/He, without any accompanying change in the chemistry. Computationally, these cases are simulated in the terrestrial gravitational field and in the absence of gravity. The numerical results compare favorably with experiments. Powerful computational tools provide invaluable insights into the complex physicochemical phenomena taking place in CVD reactors. Such information is essential for the improved design and optimization of future CVD reactors

Visually accurate multi-field weather visualization

Journal ArticleWeather visualization is a difficult problem because it comprises volumetric multi-field data and traditional surface-based approaches obscure details of the complex three-dimensional structure of cloud dynamics. Therefore, visually accurate volumetric multi-field visualization of storm scale and cloud scale data is needed to effectively and efficiently communicate vital information to weather forecasters, improving storm forecasting, atmospheric dynamics models, and weather spotter training. We have developed a new approach to multi-field visualization that uses field specific, physically-based opacity, transmission, and lighting calculations per-field for the accurate visualization of storm and cloud scale weather data. Our approach extends traditional transfer function approaches to multi-field data and to volumetric illumination and scattering

Ignition of Deflagration and Detonation Ahead of the Flame due to Radiative Preheating of Suspended Micro Particles

We study a flame propagating in the gaseous combustible mixture with suspended inert particles. The gas is assumed to be transparent for the radiation emitted by the combustion products, while particles absorb and re-emit the radiation. Thermal radiation heats the particles, which in turn transfer the heat to the surrounding gaseous mixture by means of heat conduction, so that the gas temperature lags that of the particles. We consider different scenarios depending on the spatial distribution of the particles, their size and the number density. In the case of uniform distribution of the particles the radiation causes a modest increase of the temperature ahead of the flame and the corresponding increase of the flame velocity. The effects of radiation preheating is stronger for a flame with smaller normal velocity. In the case of non-uniform distribution of the particles, such that the particles number density is smaller just ahead of the flame and increases in the distant region ahead of the flame, the preheating caused by the thermal radiation may trigger additional independent source of ignition. This scenario requires the formation of a temperature gradient with the maximum temperature sufficient for ignition in the region of denser particles cloud ahead of the advancing flame. Depending on the steepness of the temperature gradient formed in the unburned mixture, either deflagration or detonation can be initiated via the Zeldovich's gradient mechanism. The ignition and the resulting combustion regimes depend on the temperature profile which is formed in effect of radiation absorption and gas-dynamic expansion. In the case of coal dust flames propagating through a layered dust cloud the effect of radiation heat transfer can result in the propagation of combustion wave with velocity up to 1000m/s and can be a plausible explanation of the origin of dust explosion in coal mines.Comment: 45 pages, 14 figures. Accepted for publication Combustion and Flame 29 June 201

Atmospheric cloud representation methods in computer graphics: A review

Cloud representation is one of the important components in the atmospheric cloud visualization system. Lack of review papers on the cloud representation methods available in the area of computer graphics has directed towards the difficulty for researchers to understand the appropriate solutions. Therefore, this paper aims to provide a comprehensive review of the atmospheric cloud representation methods that have been proposed in the computer graphics domain, involving the classical and the current state-of-the-art approaches. The reviewing process was conducted by searching, selecting, and analyzing the prominent articles collected from online digital libraries and search engines. We highlighted the taxonomic classification of the existing cloud representation methods in solving the atmospheric cloud-related problems. Finally, research issues and directions in the area of cloud representations and visualization have been discussed. This review would be significantly beneficial for researchers to clearly understand the general picture of the existing methods and thus helping them in choosing the best-suited approach for their future research and development

Analysis of a hydrogen fueled internal combustion engine

Thesis (Master)--Izmir Institute of Technology, Energy Engineering, Izmir, 2005Includes bibliographical references (leaves: 58-60)Text in English; Abstract: Turkish and Englishxi, 60 leavesIn the history of internal combustion engine development, hydrogen has been considered at several phases as a substitute to hydrocarbon-based fuels. Starting from the 70.s, there have been several attempts to convert engines for hydrogen operation.Together with the development in gas injector technology, it has become possible to control precisely the injection of hydrogen for safe operation. Since the fuel cell needs certain improvements before it is widely used in vehicles, the conventional internal combustion engine is to play an important role in the transition. This study examines the performance characteristics and emissions of a hydrogen fueled conventional spark sparkignition engine. Slight modifications are made for hydrogen feeding which do not change the basic characteristics of the original engine. Comparison is made between the gasoline and hydrogen operation and engine design changes are discussed. Certain remedies to overcome the backfire phenomena are attempted

Principles and applications of CVD powder technology

Chemical vapor deposition (CVD) is an important technique for surface modification of powders through either grafting or deposition of films and coatings. The efficiency of this complex process primarily depends on appropriate contact between the reactive gas phase and the solid particles to be treated. Based on this requirement, the first part of this review focuses on the ways to ensure such contact and particularly on the formation of fluidized beds. Combination of constraints due to both fluidization and chemical vapor deposition leads to the definition of different types of reactors as an alternative to classical fluidized beds, such as spouted beds, circulating beds operating in turbulent and fast-transport regimes or vibro-fluidized beds. They operate under thermal but also plasma activation of the reactive gas and their design mainly depends on the type of powders to be treated. Modeling of both reactors and operating conditions is a valuable tool for understanding and optimizing these complex processes and materials. In the second part of the review, the state of the art on materials produced by fluidized bed chemical vapor deposition is presented. Beyond pioneering applications in the nuclear power industry, application domains, such as heterogeneous catalysis, microelectronics, photovoltaics and protection against wear, oxidation and heat are potentially concerned by processes involving chemical vapor deposition on powders. Moreover, simple and reduced cost FBCVD processes where the material to coat is immersed in the FB, allow the production of coatings for metals with different wear, oxidation and corrosion resistance. Finally, large-scale production of advanced nanomaterials is a promising area for the future extension and development of this technique

Combustion Characteristics of Waste Tyre Pyrolysis Fuel as Industrial Burner Fuel

This study examined the potential of using waste tyre pyrolysis fuel oil as an industrial burner fuel. The combustion characteristics of tyre-derived fuel (TDF) oil were evaluated using Cuenod NC4 forced draught oil burner equipped with a built-in fuel atomizer and an onboard control system. TDF oil obtained from a local waste tyre treatment facility was blended with petroleum diesel (DF) at TDF volumetric concentration of 40% (TDF40), which was tested against pure petroleum diesel and refined modified tyre-derived fuel (TDF*). Critical combustion parameters such as thermal power output, fuel consumption, flame stability, flue gas temperature, and emissions were investigated to evaluate the performance of the combustion equipment. Using DF as a reference fuel, it was observed that TDF40 required high air-to-fuel ratio (AFR) in order to produce a stable flame with high flame temperature and less emissions. TDF* produced a reasonably stable flame with less sulphur dioxide emissions compared to TDF40; however, its specific fuel consumption (SFC) was higher than that of DF. It was also discovered that the burner’s SFC was higher when fuelled with TDF40. Total contamination and viscosity of TDF oil contribute significantly to the flow characteristics of the fuel, resulting in reduced pressure and subsequently poor fuel atomization. Rapid soot formation at atomizer nozzle was also observed when the burner was fuelled with TDF40. TDF oil and its derivatives (TDF*) produce SO2, NO2 and CO emission levels higher than the acceptable limits as prescribed by the European Air quality standard (EU2015/2193). It was concluded that TDF oil could be used as a potential industrial burner fuel if diluted with petroleum diesel fuel at TDF volumetric concentration of <40% or any ratio that could adjust the viscosity level below 5.3 cSt. Fuel preheating and multistage filtration system are also recommended to reduce total contamination and water levels in the fuel mixture. Exhaust gas scrubbing is recommended due to significantly high sulphur oxide emission in the flue gas

Combustion Characteristics of Methane, Ethane, Propane, and Butane Blends Under Conditions Relevant of a Dual-Fuel Diesel and Natural Gas Engine

As natural gas production infrastructure is already in place in most of the world and will continue expanding for the foreseeable future, natural gas is an alternative to traditional liquid petroleum fuels in heavy-duty engines. Dedicated natural gas or dual-fuel diesel-natural gas heavy-duty engines are alternatives to diesel-only power generation equipment. One challenge is the large variation in the natural gas composition available for such applications, which is known to significantly affect engine’s combustion characteristics and the emissions composition. As the literature on dual-fuel combustion under low load engine operating conditions that use more realistic natural gas mixtures (i.e., mixtures that, in addition of methane (C1;the most abundant natural gas component), also contain ethane (C2), propane (C3), and butane (C4)) is limited, this study evaluated the combustion characteristics of a variety of C1-C4 mixtures using three different experimental platforms: a 4.5-L 4-cylinder heavy-duty production diesel engine modified for dual-fuel diesel-natural gas engine operation, a prototype 1.125-L single-cylinder engine with extended optical access that was based on the same production diesel engine, and a laminar flame burner. Experiments in the heavy-duty production engine under low load dual-fuel diesel-natural gas operating conditions (6 bar break mean effective pressure at 1000 RPM, 1000 bar diesel injection pressure, and 40% diesel substitution ratio) showed that gas composition affected the diesel fuel ignition delay and combustion phasing, which are known to affect both engine performance and emissions. As in-cylinder pressure correlated with the autoignition temperature of the gaseous mixture, mixtures with higher C2-C4 content produced the best engine performance and emissions compared to using 100% C1, suggesting that the addition of C2-C4 content benefits low load dual-fuel combustion. For example, brake specific carbon dioxide and nitrogen oxides emissions reduced up to 6.6% and 20%, respectively. In addition, gas mixtures containing C3 and C4 reduced the brake specific carbon dioxide equivalent by up to 50 g/kWh compared to the C1-only case. Experiments in the prototype single cylinder optical engine employed imaging diagnostics to better understand the C1-C4 effects observed in the production engine experiments. High boost and high intake temperature were used to create in-cylinder conditions similar to those in the production engine at the start of combustion. To enhance the visual differences between the natural gas components, only one component was used at a time instead of a multicomponent mixture as in the production engine experiments, and difficulties in accurately controlling the C4 flow resulted in using only C1-C3. Experiments were performed at similar low load dual fuel operating conditions (~ 6.6 bar indicated mean effective pressure at 1000 RPM, 500 bar diesel injection pressure, and ~ 63% diesel substitution ratio), using both traditional and advanced diesel injection timing (i.e., conventional mixing-controlled compression ignition or MCCI compared to reactivity-controlled compression ignition or RCCI). Natural luminosity data showed that C3 RCCI had a more advanced combustion phasing despite an increased ignition delay and higher spatially-integrated natural luminosity compared to C1 RCCI and C2 RCCI. An earlier premixed combustion and a smaller phasing difference between the apparent heat release and spatially-integrated natural luminosity was seen for MCCI compared to RCCI. The results suggested that the C1-C3 content indeed affected the diesel gas mixing and stratification of the low load dual-fuel operation, hence the differences in engine performance and emissions observed in the production engine experiments. As a result, the findings in this study can be used for modeling the dual-fuel combustion of C1-C4 blends and can help industry in utilizing more efficiently natural gas with higher C2-C4 content