Aerospace Engineering Commons^™

Processing Of Zrb2-Zrc-Zrxsiy Ceramic By Reactive Metal Penetration, Nischel B. Maheswaraiah

Open Access Theses & Dissertations

The processing of ZrB2-ZrC-ZrxSiy composite by reactive metal penetration was investigated as a successor to the ZrB2-SiC composites for hypersonic vehicles application, which cannot be used for extended time at temperatures greater than 1600C due to formation of SiO and CO gases. Zirconium (Zr), zirconium disilicide (ZrSi2), and boron carbide (B4C) were reacted in graphite crucibles for 60, 120, 180, and 240 minutes. Microscopy and x-ray diffraction (XRD) deduced the formation of a heterogeneous microstructure of ZrB2-ZrC-ZrxSiy precipitates surrounded by a solidified Zr-Si melt. Unreacted boron carbide was observed in samples held at 1860C for 60 minutes and 120 minutes, …

Analysis Of The Theta-D Filter As Applied To Hit-To-Kill Interceptors And Satellite Orbit Determination, Michael W. Dancer

Masters Theses

"When designing feedback control systems, there is often a need for estimation methods that provide system information that is not readily available via sensors placed within the system. In many cases a sensor that measures a particular system state either does not exist or is prohibitively expensive. In addition, all realistic systems contain some degree of nonlinearity. This thesis focuses on two such cases: missile guidance with bearings-only measurements and GPS satellite orbit determination. In each case, a new nonlinear filter, the [theta]-D method, is used and evaluated for its performance in providing the necessary estimation. To aid the filter …

Studies Of Dynamic Crack Propagation And Crack Branching With Peridynamics, Youn Doh Ha, Florin Bobaru

Department of Engineering Mechanics: Faculty Publications

In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement (m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons.We also analyze the influence of the particular shape of themicro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well …

Low-Thrust Control Of Orbital Elements, Nathan Harl

Doctoral Dissertations

"This dissertation presents a method for controlling the orbital elements of a spacecraft using continuous low-thrust systems. The method involves the use of a general performance index, which is designed to minimize the difference between the instantaneous orbital elements of a spacecraft and some desired set of orbital elements. Due to the generality of the controller design, the resultant controller can be applied to a wide variety of scenarios about various bodies in space. To minimize the designed performance index, a shooting method and a Sequential Quadratic Programming algorithm are utilized and compared.

The primary application of the general controller …

Fusion Of Imprecise Qualitative Information, Florentin Smarandache, Xinde Li, Xianzhong Dai, Jean Dezert

Branch Mathematics and Statistics Faculty and Staff Publications

In this paper, we present a new 2-tuple linguistic representation model, i.e. Distribution Function Model (DFM), for combining imprecise qualitative information using fusion rules drawn from Dezert-Smarandache Theory (DSmT) framework. Such new approach allows to preserve the precision and efficiency of the combination of linguistic information in the case of either equidistant or unbalanced label model. Some basic operators on imprecise 2-tuple labels are presented together with their extensions for imprecise 2-tuple labels. We also give simple examples to show how precise and imprecise qualitative information can be combined for reasoning under uncertainty. It is concluded that DSmT can deal …

Fusion Of Sources Of Evidence With Different Importances And Reliabilities, Florentin Smarandache, Jean Dezert, J.M. Tacnet

Branch Mathematics and Statistics Faculty and Staff Publications

This paper presents a new approach for combining sources of evidences with different importances and reliabilities. Usually, the combination of sources of evidences with different reliabilities is done by the classical Shafer’s discounting approach. Therefore, to consider unequal importances of sources, if any, a similar reliability discounting process is generally used, making no difference between the notion of importance and reliability. In fact, in multicriteria decision context, these notions should be clearly distinguished. This paper shows how this can be done and we provide simple examples to show the differences between both solutions for managing importances and reliabilities of sources. …

Microstructure Investigation Of Al-Rich Titanium Aluminum Alloys, David Pham

Open Access Theses & Dissertations

The microstructures of Ti-Al alloys with 70-80 wt% Al were investigated. Aluminum wire (99.999%) and TiH₂ powder (99.7%) were used to produce the sample compositions inside a vertical tube furnace at 1600^oC in an Ar atmosphere. Argon is purified through a dehumidification and deoxidation system. Magnesium perchlorate Mg(ClO₄)₂ acts as a desiccant and titanium sponge pulls oxygen from the Ar in furnaces operating at 800^oC and 750^oC. X-ray diffraction and an optical microscope are used to identify phases and compositions

An Investigation On Pulsing Performance Of Mn Class Bi-Propellant Thrusters, Carlos Francisco Gomez

Open Access Theses & Dissertations

With the advancement of technology and machining methods, considerable attention has been focused in manufacturing micro thrusters for micro spacecraft applications (Yetter et al, 2003). Micro propulsion systems are currently being investigated for Miniature Kill Vehicles (MKV) and Micro Satellite Systems (MSS) with an emphasis in reducing weight and cost but without affecting performance. Reducing the weight seems practical when reducing the size of the propulsion system, but problems are encountered with system design.

In addition, propulsion requirements strongly influence choice in propellant and complexity. A thorough understanding of stabilizing thrust levels and the ability to control the propulsion system …

Constrained Optimal Orbit Design For Earth Observation, Sharon D. Vtipil

Mechanical & Aerospace Engineering Theses & Dissertations

The purpose of this dissertation is to demonstrate use requirements for a satellite observation mission can be used to determine a constrained optimal orbit based on observation site requirements, observation condition restraints, and sensor characteristics. The typical Earth observation satellite is first designed according to an appropriate orbit; then the observation requirements are used to develop a target schedule. The new design process outlines the development of the appropriate orbit by incorporating user requirements at the forefront of mission planning, not after an orbit has been selected. This research shows how to map the user requirements into constraints for the …

Analysis Of Wake Vortices Of A Medium Range Twin-Propeller Military Cargo Aircraft Using Statistically Designed Experiments, Burhan Sahin

Mechanical & Aerospace Engineering Theses & Dissertations

An experimental study was initiated to analyze the trajectories of the streamwise vortices behind the wing tip and flap of a medium range and propeller driven twin-engine military cargo aircraft. The model used for the experimental study was a generic, high wing and half model of a propeller driven aircraft and mounted within Old Dominion University's Low Speed Wind Tunnel where the wind tunnel flow speed was set to constant value of 9 m/sec. The main purpose of the study was to reach regression models for the motion and vorticity strength of both vortices under varying factors such as angle …

Solution Approximation For Atmospheric Flight Dynamics Using Volterra Theory, Ashraf Mohammed Kandeel Omran

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation introduces a set of novel approaches in order to facilitate and enrich Volterra theory as a nonlinear approximation technique for constructing mathematical solutions from the governing relationships describing aircraft dynamic behavior. These approaches reconnect Volterra theory and flight mechanics research, which has not been addressed in the technical literature for over twenty years. Volterra theory is known to be viable in modeling weak nonlinearities, but is not particularly well suited for directly describing high performance aircraft dynamics. In order to overcome these obstacles and restrictions of Volterra theory, the global Piecewise Volterra Approach has been developed. This new …

Active Control Of Shocks And Sonic Boom Ground Signal, Bedri Yagiz

Mechanical & Aerospace Engineering Theses & Dissertations

The manipulation of a flow field to obtain a desired change is a much heightened subject. Active flow control has been the subject of the major research areas in fluid mechanics for the past two decades. It offers new solutions for mitigation of shock strength, sonic boom alleviation, drag minimization, reducing blade-vortex interaction noise in helicopters, stall control and the performance maximization of existing designs to meet the increasing requirements of the aircraft industries. Despite the wide variety of the potential applications of active flow control, the majority of studies have been performed at subsonic speeds. The active flow control …

Investigation Into Contact Resistance And Damage Of Metal Contacts Used In Rf-Mems Switches, Kevin W. Gilbert

Theses and Dissertations

This research examines the physical and electrical processes involved in lifecycle failure of Microelectromechanical (MEMS) Radio-Frequency (RF) cantilever beam ohmic contact switches. Failures of these switches generally occur at the contact, but complete details of performance of microcontacts are difficult to measure and have not been previously reported. This study investigated the mechanics of microcontact behavior by designing and constructing a novel experimental setup. Three representative contact materials of varying microstructure (Au, Au5%Ru, Au4%V₂O₅) were tested and parameters of contact during cycling were measured. The Au4%V₂O₅, a dispersion strengthened material developed at …

Fatigue Behavior Of An Advanced Sic/Sic Composite At Elevated Temperature In Air And In Steam, Devon T. Christensen

Theses and Dissertations

The fatigue behavior of an advanced Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1200 ˚C in laboratory air and in steam environments. The composite consisted of a SiC matrix reinforced with Boron Nitride (BN) coated Hi-Nicalon fibers woven into eight-harness-satin (8HS) weave plies. Tensile stress-strain behavior and tensile properties were also evaluated at 1200 ˚C. Tension-tension fatigue tests were conducted in both laboratory air and in steam at 1200 ˚C at frequencies of 0.1 Hz, 1.0 Hz, and 10 Hz. The tension-tension fatigue tests had a ratio of minimum stress to maximum stress of R = …

Flow Visualization Study Of Passive Flow Control Features On A Film-Cooled Turbine Blade Leading Edge, Daniel R. Carroll

Theses and Dissertations

A flow visualization study was conducted on a model of a film-cooled turbine blade leading edge in a closed-loop water channel at Re_D = 30k. The model consisted of an 8.89 cm diameter half-cylinder with flat afterbody joined at the ninety degree point. A single radial coolant hole (d_c / D = 0.054) drilled 21.5° from the stagnation line, angled 20° to the surface and 90° to the flow direction generated a coolant jet transverse to the freestream. Water channel testing assessed the hydrodynamic effects of 16 passive flow control features, to include a variety of …

Discrete Film Cooling In A Rocket With Curved Walls, Jonathan F. Mccall

Theses and Dissertations

This study quantified the effects of discrete wall-based film cooling in a rocket with curved walls. Simulations and experiments showed decreasing with wall radius of curvature, holding jet diameter constant, improves net heat flux reduction (NHFR) and adiabatic effectiveness (η) for 90˚ compound injected cylindrical jets, though η is reduced at the highest curvature. NHFR and η improved further with a high favorable stream-wise pressure gradient (K=2.1x10^-5) at all tested blowing ratios, but were affected little by a high density ratio (DR=1.76) using carbon dioxide as the coolant. Experiments were run at a Reynolds number of 31K and …

Laser-Induced Fluorescence And Synthetic Jet Fuel Analysis In The Ultra Compact Combustor, Aaron C. Drenth

Theses and Dissertations

The Ultra-Compact Combustor (UCC) is currently under investigation at the Air Force Institute of Technology (AFIT) and Air Force Research Laboratory’s Propulsion Directorate. The combustor is a small-scale, axi-symmetric, atmospheric pressure, laboratory combustor with an outer circumferential cavity in which the flame is stabilized by a highly accelerated swirled flow. UCCs will enable aero gas turbine reheat cycle engines and significantly shorten conventional aero gas turbine engines. The experiments of this work utilized the AFIT small-scale combustion diagnostics facility, investigating a sector model of the UCC. The research objectives were to perform an addition to the COAL lab laser diagnostic …

Flow Measurements Using Particle Image Velocimetry In The Ultra Compact Combustor, Levi M. Thomas

Theses and Dissertations

Velocity measurements were performed using the Particle Image Velocimetry (PIV) technique on the Ultra Compact Combustor (UCC) test rig at the Air Force Institute of Technology (AFIT). Velocity patterns and time-averaged turbulence statistics were calculated for data taken with the UCC burning hydrogen fuel in the straight cavity vane and curved cavity vane configurations. The equivalence ratio was varied from 0.7 to 1.5, while the ratio of cavity air to main air was varied from 5% to 20% in testing performed on the straight vane configuration. Spanwise velocity was observed to decrease linearly with distance from the cavity vane over …

Avoiding Overrun Accidents On Contaminated Runways, Nihad E. Daidzic

Aviation Department Publications

No abstract provided.

Simulation, Synthesis, And Characterization Of Hydrogels And Nanocomposite Gels., Kamleshkumar J. Suthar

Dissertations

Stimuli-responsive gels are three-dimensional, cross-linked polymeric materials that undergo large physical change in response to the environmental stimuli, like temperature, pH, electrical potential, and irradiation. Ferrogels are colloidaldispersion of magnetic nanoparticles in the hydrogel network. The magnetic nanoparticles are attached to the polymeric network by different adhesive forces; as a result, it becomes sensitive to the applied magnetic field.

The main objective of this research is the simulation, synthesis, and characterization of the hydrogel and ferrogel. Simulation of the hydrogel response was performed for various environmental stimuli using a multiphysics finite element analysis software, COMSOL. The pH and electrical response …

Removal Of Biofilm Through Controlled Cavitation, Mathew Chackalackal Mathew

Master's Theses - Daytona Beach

Human kind is poised to take the next "giant step" in space exploration, the manned mission to Mars, among other things. But before any plans for such long term habitation on an alien planet, there has to be consideration towards prevention and removal of bacterial contamination. Bacterial contamination or rather degradation of materials was considered of negligible importance. Bacterial degradation can be serious for long-term manned space mission, more so because there is no way to obtain quick replacements. For such conditions, a new innovative way of bacterial removal has been proposed wherein the bacteria is removed with no damage …

An Autonomous Unmanned Aerial Vehicle-Based Imagery System Development And Remote Sensing Images Classification For Agricultural Applications, Yiding Han

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This work concentrates on the topic of remote sensing using a multispectral imag-ing system for water management and agriculture applications. The platform, which is alight-weight inexpensive runway-free unmanned aerial vehicle (UAV), namely, AggieAir, ispresented initially. A major portion of this work focuses on the development of a light-weight multispectral imager payload for the AggieAir platform, called GhostFoto. Theimager is band-recongurable, covering both visual red, green, and blue (RGB) and nearinfrared (NIR) spectrum, and interfaced with UAV on-board computer. The developmentof the image processing techniques, which are based on the collected multispectral aerialimages, is also presented in this work. One application …

Spatial Instability Of Electrically Driven Jets With Finite Conductivity And Under Constant Or Variable Applied Field, Saulo Orizaga, Daniel N. Riahi

Applications and Applied Mathematics: An International Journal (AAM)

We investigate the problem of spatial instability of electrically driven viscous jets with finite electrical conductivity and in the presence of either a constant or a variable applied electric field. A mathematical model, which is developed and used for the spatially growing disturbances in electrically driven jet flows, leads to a lengthy equation for the unknown growth rate and frequency of the disturbances. This equation is solved numerically using Newton’s method. For neutral temporal stability boundary, we find, in particular, two new spatial modes of instability under certain conditions. One of these modes is enhanced by the strength Ω of …

Grating Lobe Reduction In Aperiodic Linear Arrays Of Physically Large Antennas, William C. Barott, Paul G. Steffes

Publications

We present performance bounds obtained from the optimization of the sidelobe levels of aperiodic linear arrays. The antennas comprising these arrays are large compared to the distance between neighboring antennas, a case not addressed in previously published work. This optimization is performed in pattern-space and is applicable over a wide range of scan angles. We show that grating lobes can be suppressed even when the elemental antennas are several wavelengths in size, provided that the ratio of the antenna size to the average spacing between the antenna center-points does not exceed 80%.

Effects Of Delamination On Composite Sandwich Structures Under Static And Fatigue Loading, Eugene Everett Eswonia

Master's Theses

This thesis will present the experimental and numerical analysis of composite sandwich structures under monotonic and fatigue loading. The sandwich skins were made of fiberglass and the core used was a closed cell PVC foam. Initial delaminations were introduced into the sandwich structures during manufacturing to see the effect of delamination size on the ultimate strength and monotonic fracture. Fiberglass rods, called shear keys, added to the foam core to determine whether or not they increased the strength of the test specimens. Furthermore, shear key locations were also varied and their effects noted. The fixed rate static behavior for all …

A Domain-Specific Design Tool For Verifying Spacecraft System Behavior, Sravanthi Venigalla

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

In this report we present a graphical tool, Behavioral Analysis of Spacecraft Systems (BASS), that can be used by spacecraft designers to perform system-level behavioral analysis of small satellites. The domain-specific spacecraft meta-model is created in the visual modeling tool Generic Modeling Environment (GME) such that spacecraft designs created using the meta-model appear familiar to the spacecraft designers. Users can model scenarios that are to be verified for the design in BASS. The graphical models are assigned formal semantics facilitating the creation of formally verifiable spacecraft models. The C++ application that translates the modeling objects to equivalent mathematical representation of …

Embedded Spacecraft Thermal Control Using Ultrasonic Consolidation, Jared W. Clements

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Research has been completed in order to rapidly manufacture spacecraft thermal control technologies embedded in spacecraft structural panels using ultrasonic consolidation. This rapid manufacturing process enables custom thermal control designs in the time frame necessary for responsive space. Successfully embedded components include temperature sensors, heaters, wire harnessing, pre-manufactured heat pipes, and custom integral heat pipes. High conductivity inserts and custom integral pulsating heat pipes were unsuccessfully attempted. This research shows the viability of rapid manufacturing of spacecraft structures with embedded thermal control using ultrasonic consolidation.

The Part Count Tool (Pact) For Concept Selection, Tarang Parashar, Katie Grantham Lough, Robert B. Stone

Engineering Management and Systems Engineering Faculty Research & Creative Works

This paper presents a part count tool that automates the consideration of manufacturing cost during the conceptual design phase by predicting part count for a particular product concept. with an approximate number of parts per product in the conceptual design phase, the designer can estimate the cost associated with the product. on the basis of the cost, the designer can make changes according to budget requirements. the part count tool will also aid in ranking the design concepts by number of components for a product. This tool utilizes existing automated concept generation algorithms to generate the design concepts. It extracts …

Interim Access To The International Space Station, Tyson Karl Smith

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This thesis evaluates mission scenarios using the existing Evolved Expendable Launch Vehicles for delivering the Crew Exploration Vehicle to the International Space Station. The Space Shuttle is scheduled to retire in the year 2011 and the Ares I is being developed to replace it. With its current schedule, the earliest that the Ares I will become fully operational is 2016. The configurations in this thesis are presented to narrow the gap in which the USA does not have direct access to the International Space Station. They also present "buy down" options for the USA human space operations, if the current …

The Potential Of Cubesat Networks, Robert J. Twiggs

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint presentation created by Professor Bob Twiggs titled "The Potential of CubeSat Networks" from November 17, 2009.