Conferences, Lectures, & Seminars
Events for November
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Gravity Currents Propagating Over an Array of Bottom Obstacles
Wed, Nov 11, 2009 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
George Contantinescu Associate Professor Department of Civil and Environmental EngineeringIIHR-Hydroscience and EngineeringUniversity of IowaIowa City, IA 52242 Highly resolved 3-D Large Eddy Simulation (LES) is used to study the interaction between a lock-exchange gravity current with a large volume of release and an array of bottom-mounted large-scale obstacles in the form of 2-D dunes or square ribs. The study of the interaction between a gravity current and an array of obstacles is important for many practical applications. For example, arrays of obstacles are often used as protective measures on the hilly terrains and on the skirts of the mountains to stop or slow down gravity currents in the form of powder-snow avalanches. Even if they do not arrest the flow, the retarding obstacles reduce the impact of the avalanche with the buildings situated downstream of the obstacles. The temporal variation of the impact forces on the obstacles is analyzed. This information is needed for the design of the retarding obstacles. Additionally, simulation results are used to understanding how this variation is related to the passage of the backward propagating hydraulic jumps and the different flow structures that develop within the flow. The loose bed surface over which the gravity current propagates in the environment is often not flat. Bed forms, typically in the form of ripples, dunes or anti-dunes are present at the seafloor or river bed. The presence of large-scale bedforms provides an additional mechanism for energy dissipation and can substantially modify the capacity of a compositional gravity current to entrain sediment with respect to the case of a flat bed. LES is used to understand how the shape and the relative size of the large-scale obstacles (roughness elements) affect the front velocity, the structure of the current, the energy balance, the bed shear distributions and sediment entrainment capacity of the current as it propagates over a loose bed. Finally, scale effects are investigated between Reynolds numbers at which most of the laboratory studies are conducted (Re~104)
Location: Stauffer Science Lecture Hall, Rm 100
Audiences: Everyone Is Invited
Contact: April Mundy
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Gas-Phase Nanomaterials Synthesis and In-Situ Laser-Based Diagnostics
Wed, Nov 18, 2009 @ 03:30 PM - 04:30 PM
Aerospace and Mechanical Engineering
Conferences, Lectures, & Seminars
Stephen D. Tse Associate Professor Department of Mechanical and Aerospace Engineering Rutgersthe State University of New Jersey Piscataway, NJ sdytse@rci.rutgers.edu Gas-phase synthesis of materials has demonstrated a history of scalability and offers the potential for high-volume commercial production, at reduced costs. Flame synthesis of ceramic oxide nanoparticles and semiconducting metal-oxide nanostructures will be discussed. Plasma synthesis affords the synthesis of non-oxide materials, such as Group III-Nitride nanopowders, which will be discussed. Al2O3 and TiO2 nanoparticles are produced from corresponding organometallic vapor precursors using an axisymmetric stagnation-point premixed flat flame impinging on a cooled substrate under uniform electric field application. Other nanostructures, such as WO2.9 nanowires, ZnO nanoribbons, and MO2 nanoplates are also synthesized, whereby growth occurs by the vapor-solid mechanism, with local gas-phase temperature and chemical species strategically specified at the substrate for self-synthesis. Finally, cubic-BN and cubic-GaN nanopowders (which are especially attractive for photonic and structural applications) are synthesized using a plasma process, for subsequent consolidation into bulk nanomaterials. Laser-based spectroscopy is utilized to characterize the gas-phase flow field (e.g. temperature, species concentrations). Additionally, a novel technique of using Raman spectroscopy to diagnose nanoparticle presence and characteristics (in aerosol form) during synthesis has been applied. This technique serves as a sensitive and reliable way to characterize particle composition and crystallinity (e.g. anatase versus rutile) and delineate the phase conversion of nanoparticles as they evolve in the flow field.
Location: Stauffer Science Lecture Hall, Rm 100
Audiences: Everyone Is Invited
Contact: April Mundy