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Articles 1  30 of 986
FullText Articles in Engineering
Modeling And Control Of Magnetic Gear Dynamics In A Wind Turbine Drivetrain, Danielle Vournas
Modeling And Control Of Magnetic Gear Dynamics In A Wind Turbine Drivetrain, Danielle Vournas
Dissertations and Theses
This thesis looks at the modeling and simulation of linear and nonlinear magnetic gear dynamics in a wind turbine drivetrain. The objective is to lay the groundwork for analysis, modeling and optimization of control structures focused on poleslip prevention. A classical mechanical twomass torsion spring model is used as the basis for developing the dynamic system equations and Simulink models. The wind turbine torque input to the low speed rotor is modeled as a disturbance input, the generator torque is modeled as a controlled input, and the highspeed rotor speed is the only measured output. The nonlinear dynamics are linearized ...
Thermal Bending, Buckling And PostBuckling Analysis Of Unsymmetrically Laminated Composite Beams With The Effects Of Moisture And Geometric Imperfections, Claudia Barreno
Dissertations and Theses
This thesis is concerned with the analytical study of the thermal bending, buckling, and postbuckling of unsymmetrically laminated composite beams with imperfection under hygrothermal effects. Three different boundary conditions will be considered on this study. The nonlinear governing partial differential equations are derived by taking into account the vonKarman geometrical nonlinearity for an imperfect unsymmetrical laminated composite beam. Classical beam theory (CBT) as well as first order shear deformation theory (FSDT) will be used. The effects of temperature, angle of orientation, moisture variations, imperfection, and geometrical parameters, will be evaluated and discussed. Two different laminated composite laminates will be considered ...
Hybrid Structural Composites With Energy Harvesting Capabilities, Simon Furnes
Hybrid Structural Composites With Energy Harvesting Capabilities, Simon Furnes
Dissertations and Theses
Hybrid materials have received significant interest due to the potential enhancements they provide over traditional materials such as sensing, actuating, energy scavenging, thermal management, and vibration damping. While traditional materials can be utilized for either one of these functions or loadbearing, the hybrid materials are superior as they allow combination of a wide array of functionalities whilst being suitable for loadbearing purposes.
The goal of this thesis is to elucidate the synergistic effects of hybridization of two piezoelectric materials; zinc oxide nanowires (ZnO NWs) and thin film of lead zirconium titanate (PZT) on the mechanical and energy harvesting of beams ...
Multimode Nonlinear Vibration Analysis Of Stiffened Functionally Graded Double Curved Shells In A Thermal Environment, Boutros Azizi
Multimode Nonlinear Vibration Analysis Of Stiffened Functionally Graded Double Curved Shells In A Thermal Environment, Boutros Azizi
Dissertations and Theses
The motivation of the current work is to develop a multimodal analysis of the nonlinear response of stiffened double curved shells made of functionally graded materials under thermal loads. The formulation is based on the first order shear deformation shell theory in conjunction with the von Kármán geometrical nonlinear straindisplacement relationships. The nonlinear equations of motion of stiffened double curved shell based on the extended Sanders’s theory were derived using Galerkin’s method. The resulting system of infinite nonlinear ordinary differential equations, that includes both cubic and quadratic nonlinear terms, was solved using a nonlinear dynamic software XPPAUT to ...
A VolumeForce Synthetic Disturbance Approach For HighFidelity Of Unsteady Fluid Structure Interactions, Marina Kazarina
A VolumeForce Synthetic Disturbance Approach For HighFidelity Of Unsteady Fluid Structure Interactions, Marina Kazarina
Dissertations and Theses
The purpose of this dissertation is to analyze the momentum source model, for generating synthetic vortical disturbance field in numerical simulations of unsteady fluidstructure interactions, access limitations of this approach, to find requirements for the computational domain, space and time resolution, and apply this model to investigate selected physical problems. For this reason a comprehensive parametric study of volumeforce based method of generating spectral synthetic turbulence inside the computational domain is conducted first. The method is then extended to synthesize turbulence with arbitrary energy spectrum. The synthetic turbulence is generated through momentum source terms in NavierStokes equations, and the developed ...
Modeling Vertical Migration Of Cyanobacteria And Zooplankton, Corina Christina Mae Overman
Modeling Vertical Migration Of Cyanobacteria And Zooplankton, Corina Christina Mae Overman
Dissertations and Theses
Cyanobacteria, also known as bluegreen algae, often cause harmful algal blooms and release toxic substances that can harm humans and other animals. Accurately modeling these phytoplankton is a step towards predicting, preventing, and controlling such blooms. Cyanobacteria and zooplankton species are known to migrate vertically in the water column on a daily cycle. Capturing this behavior is one aspect of correctly modeling their dynamics. Here, several models of cyanobacteria vertical movement were tested in proofofconcept models before being applied to data from field studies. These models included both continuum and particletracking frameworks. Four continuumframework models of cyanobacteria vertical migration were ...
Sensory Relevance Models, Walt Woods
Sensory Relevance Models, Walt Woods
Dissertations and Theses
This dissertation concerns methods for improving the reliability and quality of explanations for decisions based on Neural Networks (NNs). NNs are increasingly part of stateoftheart solutions for a broad range of fields, including biomedical, logistics, userrecommendation engines, defense, and selfdriving vehicles. While NNs form the backbone of these solutions, they are often viewed as "black box" solutions, meaning the only output offered is a final decision, with no insight into how or why that particular decision was made. For highstakes fields, such as biomedical, where lives are at risk, it is often more important to be able to explain a ...
Feasibility Of Circular Orbits For Proximity Operations In Strongly Perturbed Environments Around Uniformly Rotating Asteroids, Nicholas Peter Liapis
Feasibility Of Circular Orbits For Proximity Operations In Strongly Perturbed Environments Around Uniformly Rotating Asteroids, Nicholas Peter Liapis
Dissertations and Theses
Asteroids have been mapped and observed since 1801 when an Italian astronomer Guiseppe Piazzi discovered Ceres (Serio, Manara, & Sicoli, 2002). Since then, asteroids have been growing in popularity throughout the scientific community because they are thought to hold the information we need to understand how the solar system developed and why life exists on earth, as well as potential precious resources. This research studies different types of orbits that have been performed to date around asteroids and how they can be reworked to require less control effort. Different types of missions that have been sent to asteroids are discussed, as ...
Nonlinear Estimation And Control Methods For Mechanical And Aerospace Systems Under Actuator Uncertainty, Krishna Bhavithavya Kidambi
Nonlinear Estimation And Control Methods For Mechanical And Aerospace Systems Under Actuator Uncertainty, Krishna Bhavithavya Kidambi
Dissertations and Theses
Air flow velocity field control is of crucial importance in aerospace applications to prevent the potentially destabilizing effects of phenomena such as cavity ow oscillations, flow separation, flowinduced limit cycle oscillations (LCO) (flutter), vorticity, and acoustic instabilities. Flow control is also important in aircraft applications to reduce drag in aircraft wings for improved flight performance. Although passive flow control approaches are often utilized due to their simplicity, active flow control (AFC) methods can achieve improved flight performance over a wider range of timevarying operating conditions by automatically adjusting their level of control actuation in response to realtime sensor measurements. Although ...
Drafting In SelfTimed Circuits, Christopher Lee Cowan
Drafting In SelfTimed Circuits, Christopher Lee Cowan
Dissertations and Theses
Intervals between data items propagating in selftimed circuits are controlled by handshake signals rather than by a clock. In many selftimed designs, a trailing data item will catch up with a leading item or token, even when it trails by thousands of gate delays. This effect, called "drafting," can be seen in many of the selftimed designs, e.g., GasP, Mousetrap, Click, and Micropipeline. The purpose of this dissertation is to reveal the circuit mechanism of drafting in selftimed circuits typically used in FIFO stages. Drafting is usually considered to be incidental to the operation of selftimed circuits since interval ...
LargeScale Der Aggregations Of Electric Water Heaters And Battery Inverter Systems, Kevin Marnell
LargeScale Der Aggregations Of Electric Water Heaters And Battery Inverter Systems, Kevin Marnell
Dissertations and Theses
Distributed energy resources like residential electric water heaters and residential battery inverter systems offer a small amount of change to the grid individually. When aggregated however, these assets can cause major effects to the electric grid. Aggregating these resources allows them to take on generatorlike functions with the ability to increment power and decrement power.
The Western Energy Imbalance Market is an energy market offering 15 minute and 5 minute markets for energy transactions between balancing areas. Generation assets make increment and decrement bids. Traditionally the only entrants to this market have been large scale generators and large scale assets ...
Benefits Of Additional Runway Crossings On Parallel Runway Operations, Sergio Ezequiel Taleisnik
Benefits Of Additional Runway Crossings On Parallel Runway Operations, Sergio Ezequiel Taleisnik
Dissertations and Theses
As the air transportation industry expands, airports face numerous challenges to manage the increasing traffic. Among these problems, runway crossings are a considerable source of ground traffic inefficiency and risk. Building endaround taxiways are the only strategy to avoid crossings, but these are not always feasible, and therefore airport planners must find alternatives. This study consisted of a simulation over an airport that currently requires a vast amount of its arrivals to go through runway crossings in order to reach the apron; the airport simulation software utilized was the Total Airspace and Airport Modeler (TAAM). The process began with a ...
Prediction Of Noise Associated With An Isolated Uav Propeller, Samuel O. Afari
Prediction Of Noise Associated With An Isolated Uav Propeller, Samuel O. Afari
Dissertations and Theses
The emergent field of interest in the Urban Air Mobility community is geared towards a world where aerial vehicles are commonplace. This poses the problem of the effects of the radiated noise. The present research presents an indepth analysis of the noise generation mechanism of a propeller as a mode of propulsion of the said aerial vehicles. Numerical simulation utilizing a Hybrid LargeEddy Simulation (LES) coupled with Unsteady ReynoldsAveraged NavierStokes (RANS) solver, is adopted on an isolated propeller modeled from the commercial DJI Phantom II 9450 propeller. The SpalartAllmaras one equation turbulence model with rotation/curvature correction is used. The ...
Spacecraft Trajectory Planning For Optimal Observability Using AnglesOnly Navigation, Francisco José Franquiz
Spacecraft Trajectory Planning For Optimal Observability Using AnglesOnly Navigation, Francisco José Franquiz
Dissertations and Theses
This work leverages existing techniques in anglesonly navigation to develop optimal range observability maneuvers and trajectory planning methods for spacecraft under constrained relative motion. The resulting contribution is a guidance method for impulsive rendezvous and proximity operations valid for elliptic orbits of arbitrary eccentricity.
The system dynamics describe the relative motion of an arbitrary number of maneuvering (chaser) spacecraft about a single noncooperative residentspaceobject (RSO). The chaser spacecraft motion is constrained in terms of the 1) collision bounds of the RSO, 2) maximum fuel usage, 3) eclipse avoidance, and 4) optical sensor field of view restrictions. When more than one ...
Aggregation Of Electric Water Heaters For Peak Shifting And Frequency Response Services, Thomas Leighton Clarke
Aggregation Of Electric Water Heaters For Peak Shifting And Frequency Response Services, Thomas Leighton Clarke
Dissertations and Theses
The increased penetration of renewable energy sources poses new challenges for grid stability. The stochastic and uncontrollable generation of solar and wind power cannot be adjusted to match the load profile, and the transition away from traditional synchronous generators is reducing the grid capacity to arrest and recover from frequency disturbances.
Additionally, the distributed nature of many renewable energy sources makes centralized control of generation more complicated. The traditional power system paradigm balances the supply and demand of electricity on the grid by regulating generation. As this becomes more difficult, one alternative is to adjust the load instead. This is ...
Uhf And Microwave PhaseModulated Scattering Array, Nasr Nomas Hussein Alkhafaji
Uhf And Microwave PhaseModulated Scattering Array, Nasr Nomas Hussein Alkhafaji
Dissertations and Theses
This dissertation investigates the use an array of active nonlinear elements, with particular emphasis on controlling distortion products generated by nonlinear elements in space rather than using conventional ways such as transmission lines, waveguides, and power dividers and combiners. The nonlinear elements are made of assemblies of antennas and electronic switches, called modulated scatterers (MSs). These socalled MSs elements are utilized in a wide variety of applications such as radio frequency identification (RFID) systems, microwave imaging, InternetofThings sensors, etc. However, no research work has been reported in the literature regarding exploiting and controlling several distortion products generated by MSs at ...
Analytical And Numerical Modeling Of Long Term Changes To Tides, Storm Surge, And Total Water Level Due To Bathymetric Changes And Surge Characteristics, Ramin Familkhalili
Analytical And Numerical Modeling Of Long Term Changes To Tides, Storm Surge, And Total Water Level Due To Bathymetric Changes And Surge Characteristics, Ramin Familkhalili
Dissertations and Theses
Natural and local anthropogenic changes in estuaries (e.g., sealevel rise, navigation channel construction and loss of wetlands) interact with each other and produce nonlinear effects. There is also a growing recognition that tides in estuaries are not stationary. These factors together are changing the estuarine water level regime, however the implications for extreme water levels remain largely unknown. Changes over the past century in many estuaries, such as channel deepening and streamlining for navigation have significantly altered the hydrodynamics of long waves, often resulting in amplified tides (a ~85% increase in Wilmington, NC since 1900) and storm surge in ...
Seismic Performance Of Substandard Reinforced Concrete Bridge Columns Under SubductionZone Ground Motions, Alvaro Francisco Lopez Ibaceta
Seismic Performance Of Substandard Reinforced Concrete Bridge Columns Under SubductionZone Ground Motions, Alvaro Francisco Lopez Ibaceta
Dissertations and Theses
A large magnitude, long duration subduction earthquake is impending in the Pacific Northwest, which lies near the Cascadia Subduction Zone (CSZ). Great subduction zone earthquakes are the largest earthquakes in the world and are the sole source zones that can produce earthquakes greater than M8.5. Additionally, the increased duration of a CSZ earthquake may result in more structural damage than expected. Given such seismic hazard, the assessment of reinforced concrete substructures has become crucial in order to prioritize the bridges that may need to be retrofitted and to maintain the highway network operable after a major seismic event. Recent ...
Very High Frequency Bipolar Junction Transistor Frequency Multiplier Drive Network Design And Analysis, Daniel Dale Schaeffer
Very High Frequency Bipolar Junction Transistor Frequency Multiplier Drive Network Design And Analysis, Daniel Dale Schaeffer
Dissertations and Theses
The function of a frequency multiplier is verbatim  a frequency multiplier is a circuit that takes a signal of particular frequency at the input and produces harmonic multiples of the input signal's frequency at the output. Their use is widespread throughout history, primarily in the application of frequency synthesis. When implemented as a part of a large system, a chain of multipliers can be used to synthesize multiple reference signals from a single highperformance reference oscillator.
Frequency multiplier designs use a variety of nonlinear devices and topologies to achieve excitation of harmonics. This thesis will focus on the design ...
Experimental And Computational Analysis Of A 3d Printed Wing Structure, Aryslan Malik
Experimental And Computational Analysis Of A 3d Printed Wing Structure, Aryslan Malik
Dissertations and Theses
Correct prediction of aeroelastic response is a crucial part in designing flutter or divergence free aircrafts within a designated flight envelope. The aeroelastic analysis includes specifically tailoring the design in order to prevent flutter (passive control) or eliminate it by applying input on control surfaces (active control). Highfidelity models such as coupled Computational Fluid Dynamics (CFD)  Computational Structural Dynamics (CSD) can obtain full structural and aerodynamic behavior of a deformable aircraft. However, these models are so large that pose a significant challenge from the control systems design perspective. Thus, the development of an aeroelastic modeling software that can be used ...
Adaptive Commanding Of Control Moment Gyroscopes With Backlash, Justin G. Bourke
Adaptive Commanding Of Control Moment Gyroscopes With Backlash, Justin G. Bourke
Dissertations and Theses
The existence of backlash in mechanical systems provides significant challenges when attempting to control these systems to a high degree of precision. The imperfect meshing of gear or belt teeth deteriorates the performance of position controllers and tracking of small commands, producing unacceptable steadystate offsets, increased rise and settling times. Agile spacecraft often use control moment gyroscopes (CMGs) equipped with gear trains to efficiently provide torque for the fine attitude adjustments used in docking and precision stabilization maneuvers. A theoretical examination and a practical model is developed to study the effectiveness of both proportionalintegral (PI) and model referencing adaptive controllers ...
Development Of Robust Control Laws For Disturbance Rejection In Rotorcraft Uavs, Johannes Verberne
Development Of Robust Control Laws For Disturbance Rejection In Rotorcraft Uavs, Johannes Verberne
Dissertations and Theses
Inherent stability inside the flight envelope must be guaranteed in order to safely introduce private and commercial UAV systems into the national airspace. The rejection of unknown external wind disturbances offers a challenging task due to the limited available information about the unpredictable and turbulent characteristics of the wind. This thesis focuses on the design, development and implementation of robust control algorithms for disturbance rejection in rotorcraft UAVs. The main focus is the rejection of external disturbances caused by wind influences. Four control algorithms are developed in an effort to mitigate wind effects: baseline nonlinear dynamic inversion (NLDI), a wind ...
Cfd Study Of TaylorLike Vortices In Swirling Flows, Sattar Panahandehgar
Cfd Study Of TaylorLike Vortices In Swirling Flows, Sattar Panahandehgar
Dissertations and Theses
Swirling flows are complex fluid motions that appear in various natural phenomena and manmade devices. Numerous engineering applications such as turbomachinery, jet engine combustion chambers, mixing tanks and industrial burners involve swirling flows. This wide range of applications is due to unique characteristics offered by swirling flows such as increase in mixing rate, heat transfer rate and wall shear stress. In this study the axisymmetric swirling flow behavior in the context of a hybrid rocket engine have been analyzed. While modeling the flow inside a cylindrical chamber using CFD, a similarity with the Taylor vortices instability has been observed. Similar ...
A Behavioral Research Model For Small Unmanned Aircraft Systems For Data Gathering Operations, Paul Leonard Myers Iii
A Behavioral Research Model For Small Unmanned Aircraft Systems For Data Gathering Operations, Paul Leonard Myers Iii
Dissertations and Theses
According to Hitlin (2017) of the Pew Research Center, only 8% of U.S. citizens own an unmanned aircraft. Additionally, regarding feelings if U.S. citizens saw an unmanned aircraft flying close to where they live, 26% say they would be nervous, 12% feel angry, and 11% are scared. As of March 9, 2018, there were 1,050,328 U.S. small unmanned aircraft system (sUAS) registrations compared to 947,970 November 29, 2017. While sUAS use has increased in the U.S., it has lagged when compared to other items for personal use available to U.S. citizens as ...
Space Image Processing And Orbit Estimation Using Small Aperture Optical Systems, David Zuehlke
Space Image Processing And Orbit Estimation Using Small Aperture Optical Systems, David Zuehlke
Dissertations and Theses
Anglesonly initial orbit determination (AIOD) methods have been used to find the orbit of satellites since the beginning of the Space Race. Given the ever increasing number of objects in orbit today, the need for accurate space situational awareness (SSA) data has never been greater. Small aperture (< 0:5m) optical systems, increasingly popular in both amateur and professional circles, provide an inexpensive source of such data. However, utilizing these types of systems requires understanding their limits. This research uses a combination of image processing techniques and orbit estimation algorithms to evaluate the limits and improve the resulting orbit solution obtained using small aperture systems. Characterization of noise from physical, electronic, and digital sources leads to a better understanding of reducing noise in the images used to provide the best solution possible. Given multiple measurements, choosing the best images for use is a nontrivial process and often results in trying all combinations. In an effort to help autonomize the process, a novel “observability metric” using only information from the captured images was shown empirically as a method of choosing the best observations. A method of identifying resident space objects (RSOs) in a single image using a gradient based search algorithm was developed and tested on actual space imagery captured with a small aperture optical system. The algorithm was shown to correctly identify candidate RSOs in a variety of observational scenarios.
Hypervelocity Impact Analysis Of Hybrid Nanocomposite Sensors For Inflatable Space Structures, Yachna Gola
Hypervelocity Impact Analysis Of Hybrid Nanocomposite Sensors For Inflatable Space Structures, Yachna Gola
Dissertations and Theses
Future space exploration requires easytotransport, and easytobuild and deploy space habitats. NASA and Bigelow Aerospace have collaborated so that human habitation can be made safe and easy with inflatable space habitats (Litteken, 2017). One of the biggest threats faced by these structures in outer space is impact damage by micrometeoroid orbital debris (MMOD) traveling at velocities as high as 15 km/s (Lemmens, Krag, Rosebrock, & Carnelli, 2013). This work presents fabrication and testing of hybrid nanocomposites with carbon nanotubes (CNT) and coarse graphene nanoplatelets (GNP) as fillers and flexible epoxy matrix, that are proposed to be used for sensing the ...
Preliminary Test Predictions For Scale RamAir Parachute Testing, Christian A. Guzman Zurita
Preliminary Test Predictions For Scale RamAir Parachute Testing, Christian A. Guzman Zurita
Dissertations and Theses
The present thesis proposes a preliminary analysis to predict the aerodynamic performance for experimental tests of ramair parachutes in a wind tunnel. A scaled experimental test setup is developed for determining the aerodynamic coefficients of lift (𝐶𝐿) and drag (𝐶𝐷) conducted in a wind tunnel. Additionally, a CFD approach where a steadystate parachute shape defined based on experiments, photographs, and literature, is presented. The accuracy of the simulation depends considerably on the ability to resolve the canopy geometry. Therefore, a CAD geometry generation is implemented for flexible control of the canopy structure by implementing design parameters, e.g., chord, span ...
LowTipSpeed HighTorque Proprotor Noise Approximation For Design Cycle Analysis, Xavier G. Santacruz
LowTipSpeed HighTorque Proprotor Noise Approximation For Design Cycle Analysis, Xavier G. Santacruz
Dissertations and Theses
Noise reduction in aviation would enable urban missions that cannot be own with current generation helicopters because of their noisiness. This goal can be achieved by using electric motors as they are quieter and can produce higher torque at lower RPMs. Therefore, a proprotor system can be designed to exploit this characteristic potentially abating noise levels. This research performed noise approximations included with rotor aerodynamics for a single, electricdriven, hovering proprotor by creating a code meant to be used in design cycle analysis. The approximation was based on geometry by using the blade element momentum theory, and calculating the pressure ...
Covering Shock Wave Induced Interfacial Mixing: Numerical Study And A Control Primer, Erik S. Proaño
Covering Shock Wave Induced Interfacial Mixing: Numerical Study And A Control Primer, Erik S. Proaño
Dissertations and Theses
This document is aiming toward deepening the understanding of the phenomena of mixing and the effect of the initial conditions in the cylindrical & spherical RichtmyerMeshkov and RayleighTaylor Instabilities. This work is focused on identifying the most energetic structures of the ow in order to define a reduced order model intended for modeling the evolution of the mixing layer after reshocking the density interface. Initially, Simulations are implemented for the two dimensional case of a cylindrical shock wave convergently approaching an initially wavelike perturbed density discontinuity formed by a target of Sulfur Hexauoride immersed into unshocked air with Atwood number of 0.67. The perturbation is varied by setting different values for the wave amplitude and wavenumber; the amplitude and wavenumber effects on latetime mixing are studied separately and then such perturbation features are coupled together in the analysis of single and multimode welldefined cylindrical perturbations. The simulation data is then utilized as a mechanism for obtaining a model equation intended to predict the mixing layer evolution using a Proper Orthogonal Decomposition. The ultimate goal of the POD is to model the evolution after reshock which has been the main issue to be tackled ...
Optimal Battery Weight Fraction For Serial Hybrid Propulsion System In Aircraft Design, Tsz Him Yeung
Optimal Battery Weight Fraction For Serial Hybrid Propulsion System In Aircraft Design, Tsz Him Yeung
Dissertations and Theses
This thesis focuses on electric propulsion technology associated with serial hybrid power plants most commonly associated with urban air mobility vehicles. While closed form analytical solutions for parallel hybrid aviation cases have been determined, optimized serial hybrid power plants have not seen the same degree of fidelity. Presented here are the analytical relationships between several preliminary aircraft design objectives and the battery weight fraction. These design objectives include aircraft weight, range, operation cost, and carbon emissions. The relationships are based on a serial hybrid electric propulsion architecture from an energy standpoint, and can be applied to hybrid aircraft of different ...