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Articles 1 - 4 of 4
Full-Text Articles in Engineering
A Reinforcement Learning Approach To Spacecraft Trajectory Optimization, Daniel S. Kolosa
A Reinforcement Learning Approach To Spacecraft Trajectory Optimization, Daniel S. Kolosa
Dissertations
This dissertation explores a novel method of solving low-thrust spacecraft targeting problems using reinforcement learning. A reinforcement learning algorithm based on Deep Deterministic Policy Gradients was developed to solve low-thrust trajectory optimization problems. The algorithm consists of two neural networks, an actor network and a critic network. The actor approximates a thrust magnitude given the current spacecraft state expressed as a set of orbital elements. The critic network evaluates the action taken by the actor based on the state and action taken. Three different types of trajectory problems were solved, a generalized orbit change maneuver, a semimajor axis change maneuver, …
Measurement Of Stresses And Their Effect On Transport In Thin Film Battery Electrodes, Subhajit Rakshit
Measurement Of Stresses And Their Effect On Transport In Thin Film Battery Electrodes, Subhajit Rakshit
Dissertations
At the moment, there is a significant push towards environmentally friendly energy production and gasoline-free transportation technologies. As a result, there is a renewed interest in energy storage devices such as lithium-ion batteries which will play a key role in providing energy storage capability for these applications. However, the current battery technology is reaching its limits and may not meet future energy storage demands. The increased demand and the limited lithium reserves in geographically remote areas of the earth will lead to higher cost of Li. The alternative battery technologies, such as sodium-ion batteries, are promising due to their low …
Development Of Heat Transfer Correlations For Low-Reynolds Numbers, Flows In Horizontal Circular Pipes, Latif Eyada Ibraheem
Development Of Heat Transfer Correlations For Low-Reynolds Numbers, Flows In Horizontal Circular Pipes, Latif Eyada Ibraheem
Dissertations
Turbulent flows are intrinsic to most fluid-based engineering systems, including internal combustion engines. In these devices, mixing, scalar transport and heat transfer are both critical for proper operation and challenging to model. In previous work, Kreun et al. [1] modeled a pre-heated intake manifold of a Diesel engine for cold-start simulations. Accurately predicting the heat transfer at the intake port proved to be a challenging task. Existing heat transfer correlations yielded predictions which were (at best) within 20% of the measured values. The discrepancy was attributed to a mismatch between the range of applicability of existing heat transfer models and …
Epitaxial Growth Of Iii-Nitride Nanostructures And Their Optoelectronic Applications, Moab Rajan Philip
Epitaxial Growth Of Iii-Nitride Nanostructures And Their Optoelectronic Applications, Moab Rajan Philip
Dissertations
Light-emitting diodes (LEDs) using III-nitride nanowire heterostructures have been intensively studied as promising candidates for future phosphor-free solid-state lighting and full-color displays. Compared to conventional GaN-based planar LEDs, III-nitride nanowire LEDs exhibit numerous advantages including greatly reduced dislocation densities, polarization fields, and quantum-confined Stark effect due to the effective lateral stress relaxation, promising high efficiency full-color LEDs. Beside these advantages, however, several factors have been identified as the limiting factors for further enhancing the nanowire LED quantum efficiency and light output power. Some of the most probable causes have been identified as due to the lack of carrier confinement in …