Thesis (PH.D.) -- Syracuse University, 2006 / "Publication number AAT 3242502."

<p> Numerical investigations of an optimized thin airfoil with a passive and an active flow control device (riblets and rotary cylinder) have been performed. The objectives of the thesis were to investigate the tip vortices reduction using riblets and decrease in flow separation, using a rotary cylinder for improved lift-to-drag ratio. The investigations has application potentials in improving performances of Micro Air Vehicles (MAVs). The airfoil has a chord length of 19.66 cm and a span of 25 cm. with the free stream mean velocity was set at 20 m/s. The Reynolds number was calculated as 3 &times; 10⁴. Investigations with base model of the airfoil have shown flow separation at approximately 85% chord length at an angle of attack of 17 degrees. For investigation using passive flow control device, i.e. riblets, investigations were performed for different radial sizes but at a fixed location. It was found that with 1 mm radial size riblet, the tip vortices were reduced by approximately 95%, as compared to the baseline model. Although negligible lift-to-drag improvement was seen, a faster dissipation rate in turbulent kinetic energy was observed. Furthermore, investigations were carried out using the active flow control device. The rotary cylinder with a 0.51 cm in diameter was placed slightly downstream of the location of flow separation, i.e. at x/c = 0.848. Investigations were performed at different cylinder's rotations, corresponding to different tangential velocities of being higher than, equal to and less than the free stream mean velocity. Results have shown approximately 10% improvement in lift to drag ratio when the tangential velocity is near the free stream mean velocity. Further investigation may include usage of the riblets and the rotary cylinder combined, to increase the stability as well as the lift-to-drag ratio of the MAVs.</p>

<p> Future nuclear arms-control agreements may call for reductions of the total number of nuclear weapons and warheads in the world arsenals. Such agreements would require new trusted verification mechanisms to confirm that items presented to inspectors are nuclear warheads and not spoofs. Proliferation and national security concerns require, however, that inspectors gain no warhead design information through this process. To address this paradox, considerable efforts have been directed towards the development of "information barriers." These barriers consist of automated measurement systems that process sensitive information but only display the results of internal analysis in a binary valid/invalid manner. These systems are, by their nature, at risk of electronic tampering and snooping &ndash; and their trusted implementation has so far proved extremely difficult to realize. </p><p> This thesis takes radically different directions to address this challenge. It demonstrates new approaches to information protection and trusted instruments for nuclear warhead verification that are based on the cryptographic concepts of zero-knowledge proofs and physically unclonable functions. </p><p> To the author's knowledge, this thesis provides the first demonstration of a zero-knowledge physical measurement technique. Using fast neutron differential radiography and superheated emulsion detectors, such a technique can show two objects have identical geometry and opacity to 14-MeV neutrons without revealing what these properties are. This zero-knowledge feature no longer holds when the objects compared are significantly different. Such a technique could form the basis of a template-matching verification system that could confirm the authenticity of nuclear weapons without sharing any secret design information. </p><p> The thesis then introduces and demonstrates key elements of an optical physical unclonable function sensitive to neutrons and based on superheated emulsions. Such sensors are unique objects that cannot be cloned or simulated. The data they produce are a function of both their internal disordered structure and the physical quantity they measure. Due to their sensitivity against any structural variation, including through neutron irradiation, it is possible to show that they &ndash; or the data they have recorded -- have not been tampered with. Such sensors could be used by adversarial parties in sensitive facilities without the risk of being compromised.</p><p>

<p> This dissertation presents a data assimilation method for estimating the physical drivers of the Earth's ionosphere layer through the combination of Global Navigation Satellite System based (GNSS) ionospheric density measurements, Fabry-Perot interferometer (FPI) neutral wind measurements and several empirical models. The main contributions include: 1) Kalman filtering for multi-observation ingestion and multi-state estimation, 2) ingestion of FPI neutral wind measurements, 3) spherical harmonic basis functions for global electric potential estimation and 4) a study of storm-time ion drifts using globally ingested data. </p><p> The thermosphere is a region of Earth's atmosphere (80-1000 km) that contains a balance of particle density and solar ionizing radiation such that an ionosphere can form. During geomagnetic storm events, the ionosphere can be disturbed causing abrupt redistribution of the ionospheric plasma. These disruptions can cause blackouts for radio wave-based communications and navigation systems. Understanding what causes the ionosphere to change is therefore necessary as society becomes more dependent on navigation and communication technologies. </p><p> The first step in understanding the ionosphere is to quantify its physical drivers. Measurements of the ionosphere are limited both spatially and temporally because the region is so vast. Models, on the other hand, provide our best understanding and capability to simulate the ionosphere and its drivers but often fall short in capturing certain phenomena during severe geomagnetic storms. In this work, a data assimilation algorithm called Estimating Model Parameters from Ionospheric Reverse Engineering (EMPIRE) is further developed to combine both measurements and simulation data sets for estimating ionospheric drivers globally. EMPIRE ingests ionosphere plasma density rate measurements and subtracts model simulation results to produce an observation of the difference between measurements and simulation. EMPIRE then fits basis functions which represent physical drivers to the measurement-simulation discrepancy. The mapping from observation to physical driver happens using the ion continuity governing equation as a model. </p><p> The EMPIRE algorithm was originally developed in 2009 to perform regional data assimilation and used only plasma density measurements. In this work, EMPIRE is modified to use a Kalman filter so measurements and models can be ingested in an efficient and systematic manner. Direct physical driver measurements are provided by FPI neutral wind measurements using the newly developed Kalman filter. This thesis demonstrates the first ever use of FPIs and plasma density measurements in a data assimilative environment. Next, EMPIRE is modified to estimate coefficients to spherical harmonic basis functions rather than power series basis functions. Spherical harmonic functions allow EMPIRE to provide global estimates because they are continuous and orthogonal on a spherical domain (such as Earth). A study is then conducted to ingest global plasma density rate measurements and neutral winds to estimate ion drifts across the globe.</p><p>

<p> Numerical investigations of flow past rotating circular cylinders with and without wires wrapped on the surface of the cylinder were studied using Computational Fluid Dynamics (CFD). The flow characteristics such as flow separation, shedding of the primary and secondary vortices, and drag coefficients were investigated. The software STAR CCM+ from Siemens PLM was used in all investigations. Three-dimensional Unsteady Reynolds Average Navier Stokes (URANS) equations were utilized. The free stream mean velocity was constant at 10 m/sec, which corresponded to an approximate Reynolds number based on cylinder&rsquo;s diameter of 32,000. The results are presented for cylinders with and without wires at varying rotation rates &alpha; of 0, 0.5, and 1. This is represented by &alpha;, the ratio of the tangential velocity at the cylinder to that of the free stream velocity of the flow. As the rotation rate increased from 0 to 1, the drag coefficient for the smooth rotating cylinder reduced, while the drag coefficient for the wire-wrapped cylinder increased. The wire-wrapped cylinder produced significantly higher lift when compared with the corresponding value for the smooth cylinder. Increasing the rotation rate increases the lift and lift to drag ratio.</p><p>

<p> Combustion in scramjet engines is faced with the limitation of brief residence time in the combustion chamber, requiring fuel and preheated air streams to mix and ignite in a matter of milliseconds. Accurate predictions of autoignition times are needed to design reliable supersonic combustion chambers. Most efforts in estimating non-premixed autoignition times have been devoted to hydrogen-air mixtures. The present work addresses hydrocarbon-air combustion, which is of interest for future scramjet engines. </p><p> Computation of ignition in supersonic flows requires adequate characterization of ignition chemistry and description of the flow, both of which are derived in this work. In particular, we have shown that activation energy asymptotics combined with a previously derived reduced chemical kinetic mechanism provides analytic predictions of autoignition times in homogeneous systems. Results are compared with data from shock tube experiments, and previous expressions which employ a fuel depletion criterion.</p><p> Ignition in scramjet engines has a strong dependence on temperature, which is found by perturbing the chemically frozen mixing layer solution. The frozen solution is obtained here, accounting for effects of viscous dissipation between the fuel and air streams. We investigate variations of thermodynamic and transport properties, and compare these to simplified mixing layers which neglect these variations. Numerically integrating the mixing layer problem reveals a nonmonotonic temperature profile, with a peak occurring inside the shear layer for sufficiently high Mach numbers.</p><p> These results will be essential in computation of ignition distances in supersonic combustion chambers.</p><p>

The thermal protection system (TPS) represents the greatest risk factor after propulsion for any transatmospheric mission (Dr. Charles Smith, NASA ARC). Any damage to the TPS leaves the space vehicle vulnerable and could result in the loss of human life as happened in the Columbia accident. Aboard the current Space Shuttle Orbiters no system exists to notify the astronauts or ground control if the thermal protection system has been damaged. Through this research, a proof-of-concept monitoring system was developed. The system has two specific applications for thermal protection systems: (1) Improving models used to predict thermal and mechanical response of TPS materials, and (2) Self-diagnosing damage within regions of the TPS and communicating the damage to the appropriate personnel over a potentially unstable network. Mechanical damage is among the most important things to protect the TPS against. Methods to detect the primary types of mechanical damage suffered by thermal protection systems have been developed. Lightweight, low-power sensors were developed to detect any cracks in small regions of a TPS. Implementation of a network of these sensors within 10's to 1000's of regions will eventually provide high spatial resolution of damage detection; allowing for detection of holes in the TPS. Also important in thermal protection material development is to know the ablation rates and time/temperature response of the materials. A new type of sensor has been developed to monitor temperature at different depths within thermal protection materials. The signals being transmitted through the sensors can be multiplexed to allow for mechanical damage and temperature to be monitored using the same sensor.

We exploit novel modeling techniques to investigate the micromechanics of the organ of Corti (OC). Our first aim was to confirm that the tunnel of Corti (ToC) can sustain fluid wave propagation, as this may provide physiological grounds for the explanation of the cochlear amplifier by non-classical cochlear models. The experimental evidence is that OHC contraction induces oscillatory flow in the tunnel of Corti. The question we address is whether this oscillatory flow is produced by an actual fluid wave traveling in the ToC or is merely an oscillating flow with no spatial phase change. We hypothesize that the pillar cells must not present a significant barrier to flow into the tunnel of Corti if the latter can support sustainable traveling fluid waves in response to outer hair cell motion. We use both analytical and numerical models to investigate this hypothesis. The numerical model consists of a realistic three dimensional finite element model of ToC in the middle turn of the gerbil cochlea. The analytical estimates and numerical calculations give similar estimates for the impedance of the pillar cells to fluid flow into the tunnel of Corti. We conclude that the row of pillar cells does not significantly impede fluid exchange between ToC and the space of Nuel. The wavelength of the resulting fluid wave launched into the tunnel is 0.9 mm, which is similar, but somewhat larger, than the wavelength estimated for the classical traveling wave. We also found that this fluid wave propagates at least 1 wavelength before being significantly attenuated. Our results support the hypothesis that there is an additional source of longitudinal coupling, provided by the tunnel of Corti, as required in non-classical models of the cochlear amplifier. Our second aim was to assess the influence of the interstitial microfluid flow on the micromechanics of the organ of Corti. For this purpose, a finely resolved short section of the cochlea was simulated to study the fluid-elastic interaction. A modal analysis of the section was performed with and without cochlear fluid and the modal results were interpreted as the limiting case of wave propagation. The analysis results suggest that: (1) The long wave response is similar to the classical OC motion, with both arcuate and pectinate regions of the basilar membrane moving in phase and a pivoting of arch of Corti about the inner pillar foot. In this mode, however, the two inner rows of OHCs bend radially in phase while moving out of phase with the outermost row of OHCs. (2) The resonant response of the short cochlea section is characterized by a complex fluid-structure interaction mode, where the two regions of the basilar membrane move out of phase and fluid is moved between the tunnel of Corti, the interstitial spaces between the OHCs, and the outer tunnel. The outer hair cell rows move all in phase following the radial flow direction. A significant fluid motion was observed between the cylindrical cellular structures of the OC as the result of the structural displacement. This indicates that the flow of interstitial fluid avoids overpressuring the OC, and is responsible for driving cellular movements. (3) In both the long and short wave cases, fluid is squeezed radially, back and forth in the subtectorial space as a result of the bending motion of the reticular lamina in the region above the OHC heads. This causes a compression and expansion of the subtectorial space. This motion is consistent with experimentally observed motion during electrical stimulation experiments. Finally, we have developed a method to analyze periodic fluid-elastic waveguides with complex geometries, such as the cochlea. The method is a hybrid numerical-analytical based on the Floquet theory. We apply the method to two and three dimensional waveguides. We present and discuss the details of the method.

<p>Turbomachinery flow fields are inherently unsteady and complex which makes the related CFD analyses computationally intensive. Physically based preliminary design tools are desirable for parametric studies early in the design stage, and to provide deep physical insight and a good starting point for the later CFD analyses. Four analytical/semi-analytical models are developed in this study: 1) a generalized flat plate cascade model for investigating the unsteady aerodynamics of a blade row with non-uniformly spaced blades; 2) a multistage interaction model for investigating rotor-stator interactions; 3) an analytical solution for quantifying the impeller wake convection and pressure wave propagating between a centrifugal compressor impeller and diffuser vane; and 4) a semi-analytical model based Lifting line theory for unified propeller and horizontal-axis turbine optimization. Each model has been thoroughly validated with existing models. </p><p> With these models, non-uniformly spaced blade rows and vane clocking are investigated in detail for their potential use as a passive control technique to reduce forced response, flutter and aeroacoustic problems in axial compressors. Parametric studies with different impeller blade numbers and back sweep angles are conducted to investigate their effect on impeller wake and pressure wave propagation. Results show that the scattered pressure waves with high circumferential wave numbers may be an important excitation source to the impeller as their amplitude grows much faster as they travel inwardly than the lower order primary pressure waves. Detailed analysis of Lifting line theory reveals the mathematical and physical equivalence of Lifting line models for propellers and horizontal-axis turbines. With a new implementation, the propeller optimization code can be used for horizontal-axis turbine optimization without any modification. The newly developed unified propeller and horizontal-axis turbine optimization code based on lifting line theory and interior point method has been shown to be a very versatile tool with the capability of hub modelling, working with non-uniform inflow and including extra user specified constraints. </p>

<p> Unmanned aerial vehicles are quickly becoming a significant and permanent feature in today's world of aviation. Amongst the various types of UAVs, a popular type is the quadcopter. Also referred to as a quadrotor, this rotor craft's defining feature is that it has four propellers. While its use is common in the hobbyist community, this aircraft's use within industry is blooming. </p><p> Presented are the efforts to design and implement a controller for a BeagleBone based quadcopter. As part of this effort, characteristics of the quadcopter were experimentally determined. These characteristics consist of physical properties of the quadcopter, such as the moments of inertia, the motor performance characteristics, and variance within its sensors. A model was then created and implemented within a MATLAB environment to simulate the flight of the quadcopter. With a simulated environment created, a controller was designed to control the flight of the quadcopter and a Kalman Filter was implemented to filter a sensor input. These designs were then verified in the simulated environment.</p>