Browsing by Subject "Lagrangian"

Now showing 1 - 3 of 3
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    Data Driven Approach To Vehicle Emissions Reduction
    (2016-12) Kotz, Andrew
    Anthropogenic climate change and air pollution resulting from vehicle emissions are major issues facing society. Recent research and government regulations have focused on reducing these emissions through efficiency improvements, advanced aftertreatment technology and ever-tighter regulations. However, despite these advances vehicles still exhibit high emissions during actual use as compared to laboratory or certification testing. Using modern data collection techniques, I identified that electrification and hybridization of transit buses can reduce vehicle power consumption by up to 72% under “real-world” driving conditions, thus decreasing vehicle CO2 emissions. To illustrate the process behind vehicle data collection and offer a use-case for future vehicle connectivity, I discuss the development of a novel mass-based automatic passenger counter to provide a more accurate, lower-cost passenger counting method which can be retrofitted on existing transit buses. Initial results indicate this new passenger counting technology has an accuracy of 97%, however miscounts occur during times when the bus is kneeling, leaving an opportunity for future research. Using measurements from standard exhaust sensors I revealed that NOx emissions of 2013 model year (MY) transit buses were 3-9 times the federal test procedure (FTP) certification limit under “real-world” driving conditions while complying with all regulated standards. To help identify the systematic and physical causes for these high NOx emissions I developed a novel spatial emissions mapping technique called Lagrangian Hotspot Analysis, which used connected vehicle technology to identify spatial influences on vehicle emissions. Results indicate that a hotspot located in the vicinity of a bus stop and intersection had an emissions rate of roughly 3.3 times that of the route average, with these high emissions being attributed to the long idle periods and slow speeds. Instances of cold start and uphill accelerations were also found to increase NOx emissions. Finally, I compared a 2013MY and 2015MY conventional diesel bus to evaluate technology improvements between the generations with the key finding that NOx emissions from the 2015MY bus are reduced by 80% compared to the 2013MY. Further, the NOx emissions were lower than the FTP cycle limit under real-world driving. After the 2013MY bus was updated with the emissions aftertreatment technology of the 2015MY bus, I observed the same NOx reduction in the 2013MY bus. I attribute this reduction to increases in urea consumption through optimization of urea dosing strategy. Such findings imply that certification NOx levels are possible under real-world driving and that upgrading existing buses with modern aftertreatment systems can provide substantial NOx reductions.
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    Euler-Lagrangian simulations of turbulent bubbly flow.
    (2011-03) Mattson, Michael David
    A novel one-way coupled Euler-Lagrangian approach, including bubble-bubble collisions, coalescence and variable bubble radius, was developed in the context of simulating large numbers of cavitating bubbles in complex geometries using direct numerical simulation (DNS) and large-eddy simulation (LES). This dissertation i) describes the development of the Euler-Lagrangian approach, ii) outlines the novel bubble coalescence model derived for this approach and iii) describes simulations performed of bubble migration in a turbulent boundary layer, bubble coalescence in a turbulent pipe ow and cavitation inception in turbulent flow over a cavity. The coalescence model uses a hard-sphere collision model is used and determines coalescence stochastically. The probability of coalescence is computed from a ratio of coalescence timescales, which are dynamically determined from the simulation. Coalescence in a bubbly, turbulent pipe ow (Re#28; = 1920) in microgravity was simulated with conditions similar to experiments by Colin et al. [1] and excellent agreement of bubble size distribution was obtained. With increasing downstream distance, the number density of bubbles decreases due to coalescence and the average probability of coalescence decreases due to an increase in overall bubble size. The Euler-Lagrangian approach was used to simulate bubble migration in a turbulent boundary layer (420 < Re#18; < 1800). Simulation parameters were chosen to match Sanders et al. [2], although the Reynolds number of the simulation is lower than the experiment. The simulations show that bubbles disperse away from the wall as observed experimentally. Mean bubble diffusion and profiles of bubble concentration are found to be similar to the passive scalar results, except very near the wall. The carrier-fluid acceleration was found to be the reason for moving the bubbles away from the wall. The one-way coupled Euler-Lagrangian approach was applied to simulate the experiment of cavitating turbulent ow over a cavity by Liu and Katz [3]. The classical Rayleigh-Plesset equation is integrated using adaptive time-stepping to accurately and efficiently solve for the change of the bubble radius over time. The one-way coupled Euler-Lagrangian model predicts cavitation inception at the trailing edge of the cavity and also in the vortices shed from the leading edge, in qualitative agreement with experiment.
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    Lagrangian spheres, symplectic surfaces and the symplectic mapping class group.
    (2012-07) Wu, Weiwei
    Given a Lagrangian sphere in a symplectic 4-manifold (M, &omega) with b=1, we find embedded symplectic surfaces intersecting it minimally. When the Kodaira dimension &kappa of (M, &omega) is -&infin, this minimal intersection property turns out to be very powerful for both the uniqueness and existence problems of Lagrangian spheres. On the uniqueness side, for a symplectic rational manifold and any class which is not characteristic, we show that homologous Lagrangian spheres are smoothly isotopic, and when the Euler number is less than 8, we generalize Hind and Evans' Hamiltonian uniqueness in the monotone case. On the existence side, when &kappa=-&infin, we give a characterization of classes represented by Lagrangian spheres, which enables us to describe the non-Torelli part of the symplectic mapping class group.