Approved for public release; distribution is unlimited / The Cellular Automata (CA) method is based on the idea that the macroscopic behavior of a system can be captured by using simple local rules running at a microscopic level. In other words, a system can be modeled by means of simple local rules that govern the behavior of the whole system. In this thesis a local CA rule set is introduced and a methodology is developed to model physical systems that are governed by one and two dimensional wave equations. One dimensional systems are also successfully modeled by using CA and FEM techniques working as coupled, whereas two dimensional systems could only be modeled in an error margin due to the variation of the introduced time scaling factor when external forces are involved. Also, the applicability of the CA method to fracture mechanics problems is investigated. / Outstanding Thesis

The low Reynolds number aerodynamics of the flapping wing Micro-Air Vehicle (MAV) developed at NPS by Max Platzer and Kevin Jones was studied numerically. The dynamic mesh simulation model of the full multi-wing configuration, which consists of a fixed wing and a pair of aft position, opposed pitch/ plunge flapping wings was developed using an advanced CFD code that is available commercially. The unsteady flow fields, wake structures and forces were determined by solving the incompressible Navier-Stokes equations, and the results were compared to past experimental observations. The results were encouraging and provided impetus for future computational optimization studies on the NPS flapping wing MAV.

This thesis explains the methodologies that predict the trajectory and accuracy of an unguided, indirect-fire launched projectile in predicted fire. The trajectory is the path that a projectile travels to the impact point, while the accuracy is the measurement of the deviation of the impact point from the target. In addition, this thesis describes, the methodology for calculating the various factors such as drag and drift in the trajectory calculation. A three degree of freedom model will be compared to a five degree of freedom model. With an accurate trajectory prediction, it is possible to calculate the delivery accuracy in a predicted fire, which does not have cumulative error corrections associated with the registration or adjusted fire. The delivery accuracies that are considered in this thesis are; 1) Mean Point of Impact (MPI) that are related to aiming errors and 2) Precision errors that are related to the dispersion caused by ballistics effect. Finally, the trajectory and accuracy estimates are compared with NATO Armament Ballistics Kernel (NATO) and Joint Weapons Accuracy Model (JWAM) respectively, and the differences are of the order of 4 percent.

The Pulse Detonation Engine offers the Department of Defense a new low cost, light weight, and efficient solution to supersonic flight on many of its small airborne platforms. In the past, both liquid fuel and gaseous fuel designs have been partially developed and tested. Several aspects of these configurations have led to the need for the development of a new design, in particular the reduction of total pressure losses, and the removal of auxiliary oxygen system previously required to initiate a detonation wave in fuel-air mixtures within practical distances. Furthermore, higher repetition rates are required for practical thrust levels, as well as the use of liquid fuels, as these are more attractive due to their higher energy densities. A new PDE configuration was designed to operate on the liquid fuel, JP-10. The fuel injection system was characterized using laser diagnostics so that the fuel injection strategy could be optimized for the specified operating conditions. The timing parameters for the fuel-air injection profile were characterized as well in order to deliver the desired amount and duration. This was a concurrent effort with computational simulations of the internal flow paths, design/integration of a novel transient plasma ignition system, and ongoing developments of a performance measurement test rig. / US Navy (USN) author.

No description available.

<p>Non reparative solutions to damaged or impaired sensory systems have proven highly effective in many applications but are generally underutilized. For auditory disorders, traditional reparative solutions such as hearing aids and implant technology are limited in their ability to treat neurological causes of hearing loss. A method to provide auditory information to a user via the lingual nerve is proposed. The number of mechanoreceptors in the tongue exceeds the number of inner hair cells in the cochlea and the dynamic range of neurons in both systems is comparable suggesting that the achievable throughput of information in the lingual nerve is comparable to that of the auditory nerve. This supports the feasibility of transmitting audio information to the brain via the lingual nerve. Using techniques implemented in similar successful technology, the achievable throughput of the dorsal surface of the tongue using existing stimulation methods without additional innovation was estimated to be as high as 1,800 bits per second for an experienced user, in the same range required by many audio codecs used for spoken language. To make a more accurate estimation of achievable throughput, devices were developed to stimulate the tongue electrically, and an experiment to map the sensitivity of the tongue to a form of electrotactile stimulus was performed. For the population tested, discrimination ability of the tongue varied greatly. For all participants estimates for the immediately achievable throughput for the surface of the tongue was sufficient to communicate basic phonetic information to the participant. The estimated throughput for an experienced user was estimated to be as high as 1,400 bits per second. Lingual sensitivity maps were generated that will allow researchers and developers to manufacture electrode arrays that can reliably stimulate lingual nerve endings in a discriminatory manner. In another study we tested the feasibility of sending audio information to a person via the tongue. Preliminary data are presented on participants in a learning study that were able to discern stimuli generated from recorded voices, supporting our hypothesis on immediately achievable throughputs.

This thesis describes the development of grid generation and numerical methods for predicting the flow in variable geometry, positive displacement screw machines. It has been shown, from a review of available literature, that the two main approaches available to generate deforming grids for the CFD analysis of 3D transient flow in screw machines are algebraic and differential. Grids that maintain the cell count and connectivity, during solution, provide the highest accuracy and customised grid generation tools have the capability to accommodate large mesh deformations. For the analysis of screw rotors with a variable lead or varying profile, these techniques are suitable but are required to be developed further with new procedures that can define the three dimensional variation of geometry of the rotors onto the computational grid. An algebraic grid generation method was used for deforming grid generation of variable lead and varying profile rotors. Functions were developed for correlating a specified lead variation along the rotor axis with the grid spacing. These can be used to build a continuously variable lead with linear, quadratic or higher order functions. For variable profile rotors, a novel approach has been developed for three dimensional grid structuring. This can be used to specify a continuously variable rotor profile, a variable lead, and both internal and external rotor engagement, thus making it possible to generate rotor domains with conical and variable lead geometries. New grid distribution techniques were developed to distribute boundary points on the rotors from the fixed points on the rack and the casing. These can refine the grid in the region of interlobe leakage gaps between the rotors, produce a one to one connected interface between them and improve the cell quality. Inflation layers were applied and tested for mesh refinement near the rotor boundaries. Case studies have been presented to validate the proposed grid generation techniques and the results have been compared with experimental data. Simulated results agreed well with measured data and highlighted the conditions where deviations are highest. Results with variable geometry rotors showed that they achieve steeper internal pressure rise and a larger discharge port area could be used. With variable lead rotors the volumetric efficiency could be improved by reducing the sealing line length in the high pressure zone. Calculations with inflation layers showed that local velocities were better predicted but there was no substantial influence on the integral performance parameters.

<p> Interest in thermoelectric devices (TEDs) for waste-heat recovery applications has recently increased due to a growing global environmental consciousness and the potential economic benefits of increasing cycle efficiency. Unlike conventional waste-heat recovery systems like the organic Rankine cycle, TEDs are steady-state, scalable apparatus that directly convert a temperature difference into electricity using the Seebeck effect. The benefits of TEDS, namely steady-state operation and scalability, are often outweighed by their low performance in terms of thermal conversion efficiency and power output. To address the issue of poor device performance, this dissertation takes a multi-faceted approach focusing on device modeling, analysis and design and material processing.</p><p> First, a complete one-dimensional thermal resistance network is developed to analytically model a TED, including heat exchangers, support structures and thermal and electrical contact resistances. The purpose of analytical modeling is twofold: to introduce an optimization algorithm of the thermoelectric material geometry based upon the realized temperature difference to maximize thermal conversion efficiency and power output; and to identify areas within the conventional TED that can be restructured to allow for a greater temperature difference across the junction and hence increased performance. Additionally, this model incorporates a component on the numerical resolution of radiation view factors within a TED cavity to properly model radiation heat transfer. Results indicate that geometric optimization increases performance upwards of 30% and the hot-side ceramic diminishes realized temperature difference. The resulting analytical model is validated with published numerical and comparable analytical models, and serves as a basis for experimental studies.</p><p> Second, an integrated thermoelectric device is presented. The integrated TED is a restructured TED that eliminates the hot-side ceramic and directly incorporates the hot-side heat exchanger into the hot-side interconnector, reducing the thermal resistance between source and hot-side junction. A single-state and multi-stage pin-fin integrated TED are developed and tested experimentally, and the performance characteristics are shown for a wide range of operating fluid temperatures and flow rates. Due to the eliminated to thermal restriction, the integrated TED shows unique performance characteristics in comparison to conventional TED, indicating increased performance.</p><p> Finally, a grain-boundary engineering approach to material processing of bulk bismuth telluride (Bi₂Te₃) is presented. Using uniaxial compaction and sintering techniques, the preferred crystallographic orientation (PCO) and coherency of grains, respectively, are controlled. The effect of sintering temperature on thermoelectric properties, specifically Seebeck coefficient, thermal conductivity and electrical resistivity, are determined for samples which exhibited the highest PCO. It is shown the performance of bulk Bi₂Te₃ produced by the presented method is comparable to that of nano-structured materials, with a maximum figure of merit of 0.40 attained at 383 K.</p>

Next generation small satellites, also known as nanosatellites, have masses significantly lower than traditional satellites. Including the propellant mass, the total mass of a nanosatellite is often in the range of 1 to 4 $kg$. These satellites are being developed for numerous applications related to research, defense, and industry. Since their popularity began in the early 2000's, limitations on the downscaling of propulsion systems has proven to be problematic. Due to this, the vast majority of nanosatellite missions have limited lifespans of 90-120 days in low Earth orbit before they reenter the Earth's atmosphere. Although satellites on this scale have little available space for instrumentation, the development in the fields of microsensors, microelectronics, micromachinery, and microfluidics has increased the capabilities of small satellites tremendously. With limited options for primary propulsion and attitude control, nanosatellites would benefit greatly from the development of an inexpensive and easily implemented propulsion system. This work focuses on the development of an additively manufactured chemical propulsion system suitable for nanosatellite primary propulsion and attitude control. The availability of such a propulsion system would allow for new nanosatellite mission concepts, such as deep space exploration, maneuvering in low gravity environments, and formation flying. Experimental methods were used to develop a dual mode microthruster design which can operate in either low impulse, pseudo-monopropellant mode, or high impulse, bipropellant mode. Through the use of a homogeneous catalysis scheme for gas generation, nontoxic propellants are used to produce varying levels of thrust suitable for application in nanosatellite propulsion. The use of relatively benign propellants results in a system which is safe and inexpensive to manufacture, store, transport, and handle. In addition to these advantages, the majority of the propulsion system, including propellant storage, piping, manifolding, reaction chambers, and nozzles can be 3D printed directly into the nanosatellite chassis, further reducing the overall cost of the system. This work highlights the selection process of propellants, catalysts, and nozzle geometry for the propulsion system. Experiments were performed to determine a viable catalyst solution, validate the gas generation scheme, and validate operation of the system.

This research is focused on the performance evaluation of micro Combined Heat and Power (mCHP) systems based on modern prime mover technologies using both theoretical and experimental analysis. Estimations of the environmental and economic impact associated with their deployment in residential conditions were also carried out. Experimental work was performed on assessing the dynamic and steady-state performance of the 1 kWe Stirling based mCHP system (Whispergen), the 0.75 kWe Proton Exchange Membrane Fuel Cell (PEMFC, PA Hilton Ltd) and the 5.5 kWe Internal Combustion Engine (ICE) based mCHP (Dachs). Results obtained from experiments (such as partial efficiencies, nominal capacities etc.) were fed directly in a theoretical model. Primary energy requirements corresponding to average UK domestic conditions were simulated based on real life technical data. All theoretical work was conducted using EnergyPlus building simulation tool in which the operation of several hydronic heating systems was modelled. Furthermore, attained experimental data and previously published research results were used to validate the theoretical modelling process. Several operating strategies of the Stirling based mCHP unit were simulated in order to determine the regime which offers highest reduction in carbon emissions and household expenditures. In addition, variations in a number of parameters that significantly affect the performance of the system were investigated including energy consumption profiles, occupancy characteristics, dwelling thermal requirements, domestic hot water tank volume, etc). For the optimum performance strategy, several configurations of co-generation systems with nominal capacity in the range from 1 to 3 kWe were simulated. All simulated mCHP scenarios were compared against a conventional heating equipment. Finally, the advantages of a mass installation on a district level, consisting of 60, 120 and 240 dwellings and utilising a mixture of different mCHP units (ICE, Stirling, PEMFC), were estimated.