Mechanical Engineering Commons^™

Concurrent Spatial Mapping Of The Viscoelastic Behavior Of Heterogeneous Soft Materials Via A Polymer-Based Microfluidic Device, Wenting Gu

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation presents a novel experimental technique, namely concurrent spatial mapping (CSM), for measuring the viscoelastic behavior of heterogeneous soft materials via a polymer-based microfluidic device. Comprised of a compliant polymer microstructure and an array of electrolyte-enabled distributed resistive transducers, the microfluidic device detects both static and dynamic distributed loads. Distributed loads deform the polymer microstructure and are recorded as resistance changes at the locations of the transducers.

The CSM technique identifies the elastic modulus of soft materials by applying a precisely controlled indentation depth using a rigid probe to a sample placed on the device. The spatially-varying elastic modulus …

A Hybrid Position Feedback Controller For Bistable Structures, Mehmet R. Simsek

Mechanical & Aerospace Engineering Theses & Dissertations

Bistability is the property of structures showing the ability to attain two statically stable states. Due to dynamic and static advantages such as no energy demand at stable positions and providing higher deflections compared to a monostable structure, bistability may be appealing in control surface design for aircraft structures and load alleviation for wind turbine blades. The dynamics of bistable structures is nonlinear because of the snap-through occurring during the cross-well oscillation between two stable states. A new control strategy called hybrid position feedback control is developed based on the conventional positive position control to exploit linear dynamics of bistable …

Thin Film Studies Toward Improving The Performance Of Accelerator Electron Sources, Md Abdullah Al Mamun

Mechanical & Aerospace Engineering Theses & Dissertations

Future electron accelerators require DC high voltage photoguns to operate beyond the present state of the art to conduct new experiments that require ultra-bright electron beams with high average current and higher bunch charge. To meet these demands, the accelerators must demonstrate improvements in a number of photogun areas including vacuum, field emission elimination in high voltage electrodes, and photocathodes. This dissertation illustrates how these improvements can be achieved by the application of suitable thin-films to the photogun structure for producing ultra-bright electron beams.

This work is composed of three complementary studies. First, the outgassing rates of three nominally identical …

Experimental Investigation Of Turbulent Structures And Non-Equilibrium Effects In Axial Wake Vortices Via Particle Image Velocimetry, Jeffry William Ely

Mechanical & Aerospace Engineering Theses & Dissertations

Vortices are a common phenomenon in fluid flows that arise as kinetic energy dissipates into heat via viscous interaction. They arise naturally at large scales in the form of dust devils, tornadoes, and as a counter-rotating vortex pair in the wake of aircraft. It is important to understand the conditions leading to their formation, their duration, and their dissipation in order to forecast or prevent undesirable effects. Among these deleterious effects is a decrease in safety of aircraft operations in the wake of other aircraft, an extremely common situation at airports around the world. A large number of mathematical models …

Secondary Electron Emission From Plasma Processed Accelerating Cavity Grade Niobium, Miloš Bašović

Mechanical & Aerospace Engineering Theses & Dissertations

Advances in the particle accelerator technology have enabled numerous fundamental discoveries in 20th century physics. Extensive interdisciplinary research has always supported further development of accelerator technology in efforts of reaching each new energy frontier.

Accelerating cavities, which are used to transfer energy to accelerated charged particles, have been one of the main focuses of research and development in the particle accelerator field. Over the last fifty years, in the race to break energy barriers, there has been constant improvement of the maximum stable accelerating field achieved in accelerating cavities. Every increase in the maximum attainable accelerating fields allowed for higher …

Dynamic Project Time And Cost Evaluation Under The Combined Influence Of Contract, Quality, And Uncontrollable Change, Thomas V. Hammock

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation proposes a method that quantifies the dynamics caused by disruptions due to multiple changes that can occur during the progression of a large scale project. To begin, equations consisting of multiple parallel event sequences are derived that define the relationship between individual process events and the final project completion time. Matrix notation and a precedence matrix concept are used in this derivation to produce equations that are best suited for computer programming applications. This relationship is the foundation upon which the equations are built to calculate the variation impact on each event of a large scale project. Pursuing …

Multiple Point Constraint (Mpc)-Based Variable Node Super-Element, Mohamad Eftekharjoo

Mechanical & Aerospace Engineering Theses & Dissertations

The multiple point constraint (MPC)-based variable node element is introduced in this study to handle mismatched meshes between sub-domains in finite element analysis. The MPC-variable node element is a collection of a group of elements. The compatibility condition along the interface boundary is imposed along the edge of these elements through Lagrange multipliers. The Elimination method is then used to remove the effects of the dependent nodes in these elements to produce a single MPC-based variable node element. The derived variable node elements are applied to solve two plane strain problems in order to validate the accuracy of the proposed …

Achieving Wing-Like Structural Response With Piezocomposite Unimorph Thin Plates, Francis Hauris

Mechanical & Aerospace Engineering Theses & Dissertations

This research investigates the geometric parameters that structurally influence static and dynamic bending and twisting of a wing-like plate when actuated with a surface-bonded piezoelectric material. The plate is parameterized using a finite element model that is validated by comparison with known analytical solutions. The geometric parameters analyzed for static and dynamic analysis are: the aspect ratio, actuator position, actuator angle, thickness-ratio of the active piezocomposite to the inactive substrate, and portion of the fixed end of the cantilevered structure that is fixed in the chordwise direction. For harmonically actuated cases, the resonant flapping frequency is also examined. Performance metrics …

Constrained Discrete Phase Control Of A Heaving Wave Energy Converter In Irregular Seas Using Reinforcement Learning, Praveen D. Malali

Mechanical & Aerospace Engineering Theses & Dissertations

Designed for offshore deployment in irregular seas, the point absorber wave energy conversion (WEC) system is promisingly attractive amongst the currently available WEC technologies. The effectiveness of phase control when applied to a heaving point absorber through a hydraulic power take-off (PTO) system is systematically investigated in both regular and irregular waves. For this purpose, two phase control accumulators are utilized in the hydraulic PTO system. Simulations are performed in MATLAB® using the Cummins equation to model the dynamics of the heaving point absorber in the time domain.

For a given sea state, the opening instant of the control valves …

Nano Scale Mechanical Analysis Of Biomaterials Using Atomic Force Microscopy, Diganta Dutta

Mechanical & Aerospace Engineering Theses & Dissertations

The atomic force microscope (AFM) is a probe-based microscope that uses nanoscale and structural imaging where high resolution is desired. AFM has also been used in mechanical, electrical, and thermal engineering applications. This unique technique provides vital local material properties like the modulus of elasticity, hardness, surface potential, Hamaker constant, and the surface charge density from force versus displacement curve. Therefore, AFM was used to measure both the diameter and mechanical properties of the collagen nanostraws in human costal cartilage. Human costal cartilage forms a bridge between the sternum and bony ribs. The chest wall of some humans is deformed …

Characteristics Of Laser-Induced Plasma Flame Kernel Formation And Evolution, Wilmer Flores

Mechanical & Aerospace Engineering Theses & Dissertations

With increasing interest to engineer more efficient combustion engines, the use of laser induced ignition demonstrates to be a compelling alternative to the conventional electric spark plug. The benefits greatly outweigh those found in a conventional electric spark motor whereas research shows improvements in reduced energy consumption and harmful emissions. In addition, the ability to divert the laser beam and its reliability are advantages. Laser-based ignition is capable of generating a plasma for combustion in versatile surroundings where ignition is desired. Laser induced ignition of methane-air was investigated under diverse flow and mixture conditions. To perform this experiment three air/fuel …

Triboelectric Solar Generator Concept And Experimental Research, Elias Yazdanshenas

Mechanical & Aerospace Engineering Theses & Dissertations

In this thesis, a novel concept, a triboelectric solar generator (TSG ), is proposed for generation of high voltage direct current (HVDC) electricity from solar radiation. An experimental investigation was conducted to prove the concepts of charge generation through the triboelectric effect and charge transmission using semiconductors. The triboelectric effect, also known as the contact electrification, is a well-known physical phenomenon that electrostatic charges are generated by rubbing dissimilar materials. However, traditional triboelectric generators had never been commercialized due to their poor power output. Physically, it is due to the difficulty of charge transmission from insulators, which generate charges. The …

Development Of Analytical Sensitivity Analysis For Ahp Applications, Marie L. Ivanco

Mechanical & Aerospace Engineering Theses & Dissertations

Decision makers often face complex problems, which can seldom be addressed without the use of structured analytical models. Mathematical models have been developed over the last 50 years to streamline and facilitate decision making activities. The Analytic Hierarchy Process constitutes one of the most utilized Multi-Criteria Decision Analysis Methods. While AHP has been thoroughly researched and applied, the method still shows limitations in terms of integrating profile disparities of Subject Matter Experts (SMEs). This thesis develops an analytical sensitivity analysis method for AHP based on local partial derivatives to address these limitations. Four examples are presented to demonstrate and validate …

Validation Of Open Chain Model During Kinematic Analysis Of Joint Mobilization Of The Foot: An In Vitro Study, Anthony Ross Mcnally

Mechanical & Aerospace Engineering Theses & Dissertations

Joint mobilization techniques have been shown to improve dorsiflexion range of motion after ankle injury in multiple in vivo studies; however, the underlying arthrokinematic effects of this treatment still require clarification. Therefore, the purpose of this preliminary study was to determine the viability of an open kinetic chain in vitro model for applying Maitland Grade III anterior/posterior joint mobilizations to the talocrural joint while examining the osteokinematic and arthrokinematic changes at the talocrural, subtalar and hindfoot joints. Three fresh frozen cadaver lower legs had Maitland Grade III anterior-to-posterior joint mobilization applied to the talocrural joint in 2 sessions of 200 …

Design Of Timing Circuit For Fuel Injection Conversion And Development Of Laboratory To Analyze Engine Performance Using A Dynamometer, Aditi Jayram Limaye

Mechanical & Aerospace Engineering Theses & Dissertations

A fundamental facility was built to analyze some of the basic parameters involved in engine performance, namely torque and power output of the engine. One of the objectives was to convert a carbureted engine into a fuel injection or (Fl) engine. This was achieved by designing and creating a timing circuit that is required to trigger the electronic fuel injector or (EFI). The facility was designed around a dynamometer and a fuel delivery system; that provided a specialized tool to analyze engines and injectors.

The results from the carbureted experiments and the FI experiments were compared to the rated specifications …

Isogeometric Analysis For Electromagnetism, Tahsin Khajah

Mechanical & Aerospace Engineering Theses & Dissertations

The combination of numerical analysis with the scanning technology has been seeing increased use in many research areas. There is an emerging need for high-fidelity geometric modeling and meshing for practical applications. The Isogeometric Analysis (IGA) is a comprehensive computational framework, which integrates geometric modeling and meshing with analysis. Different from other existing numerical methods, the IGA can generate analysis ready models without loss of geometrical accuracy. In IGA, the continuity and the quality of a solution can be conveniently controlled and refined. These features enable IGA to integrate modeling, analysis, and design in a unified framework, the root idea …

Implementation Of Analytical Fatigue Models Into Opensim To Predict The Effects Of Fatigue On Anterior Cruciate Ligament Loading, Michael A. Samann

Mechanical & Aerospace Engineering Theses & Dissertations

The anterior cruciate ligament (ACL) provides stability to the knee joint while performing activities such as a side step cut. Neuromuscular fatigue, a reduction in muscle force producing capabilities, alters lower extremity mechanics while performing a side step cut and may increase the risk of ACL injury, particularly in females. Musculoskeletal modeling allows for the measurement of muscle forces, which are difficult to measure in-vivo. Therefore, musculoskeletal modeling, may improve our understanding of the effects of neuromuscular fatigue on muscle force production and loading of the ACL. Therefore, the purpose of this study was to develop a musculoskeletal model which …

State Variable Model For Unsteady Two Dimensional Axial Vortex Flow With Pressure Relaxation, Mazin Mohammed Elbakri Abuharaz

Mechanical & Aerospace Engineering Theses & Dissertations

This research has utilized a state variable model for unsteady two dimensional axial vortex flows experiencing non-equilibrium pressure gradient forces. The model was developed successfully using perturbed radial and azimuthal momentum equations and a pressure Poisson's equations. Three main regions of the axial vortex flow were highlighted in this study including: a laminar core region, a non-equilibrium pressure envelope, and an outer potential vortex.

Linear stability theory was utilized to formulate the model and the perturbation functions were assumed to be of the Fourier type. The flow parameters considered were the Reynolds numbers, ranging between 6,000 and 14,000, and a …

System Identification Of An Autonomous Surface Vehicle, Christopher John Cook

Mechanical & Aerospace Engineering Theses & Dissertations

The modeling and system identification of a small pontoon based marine craft, without rudder control, in a controlled environment. Old Dominion University's autonomous surface vehicle was modeled using the Observer/Kalman System Identification method. The experimental position data was collected using a laser positioning system along with Arduino based sensors on board the boat to collect the motor speeds of the dual outboard motors. The data was then compiled using the System/ Observer/Controller Identification Toolbox to derive a dynamic model that is capable of providing path estimation and prediction information to the autonomous robotic system.

Fluid-Structure Interaction Modeling Of A F/A-18 Twin-Tail Buffet Using Non-Linear Eddy Viscosity Models, Ahmed M. Nagib M. Elmekawy

Mechanical & Aerospace Engineering Theses & Dissertations

When turbulent flow generates unsteady differential pressure over an aircraft's structure, this may generate buffeting, a random oscillation of the structure. The buffet phenomenon is observed on a wide range of fighter aircraft, especially fighters with twin-tail. More research is needed to better understand the physics behind the vortical flow over a delta wing and the subsequent tail buffet.

This dissertation reports the modeling and simulation of a steady-state one-way fluid-structure interaction for the tail buffet problem observed on a F/A-18 fighter. The time-averaged computational results are compared to available experimental data. Next, computations are extended to simulate an unsteady …

Role Of Surface Chemistry In Nanoscale Electrokinetic Transport, Secuk Atalay

Mechanical & Aerospace Engineering Theses & Dissertations

This dissertation work presents the efforts to study the electrofluidics phenomena, with a focus on surface charge properties in nanoscale systems with the potential applications in imaging, energy conversion, ultrafiltration, DNA analysis/sequencing, DNA and protein transport, drug delivery, biological/chemical agent detection and micro/nano chip sensors.

Since the ion or molecular or particle transport and also liquid confinement in nano-structures are strongly dominated by the surface charge properties, in regards of the fundamental understanding of electrofluidics at nanoscale, we have used surface charge chemistry properties based on 2-pK charging mechanism. Using this mechanism, we theoretically and analytically showed the surface charge …

Design And Implementation Of Software For Technological Forecasting And Modeling Technological Obsolescence, Gershom Kwaku Obeng

Mechanical & Aerospace Engineering Theses & Dissertations

In a world that is highly infused with technology, it is important that an organization knows how many resources such as manpower, equipment, and funding are needed at what time so that the organization does not suffer unnecessary risks. It is also important to know when to replace equipment. After examining different methods of forecasting, it was determined that manipulation of growth curves was the best way to determine the likelihood of device failure at a specific time. An approach in engineering economics was used to estimate the cost due to the failure of various devices or groups of devices. …

Micro-Scale Dielectric Spectroscopy Of Biological Cells, Arindam Ghosh

Mechanical & Aerospace Engineering Theses & Dissertations

In recent years microfluidics has become one of the most commonly used tools to investigate cellular biology and to provide a platform for novel biomedical devices. Electrical Impedance Spectroscopy (EIS) was formulated as a non-invasive and label-fi.ee method to investigate the dielectric and the structural properties of materials. Since the early 20th century, EIS and Dielectric Spectroscopy have been applied to measure the dielectric properties of biological cells and tissues. Information about the cell membrane, cytoplasm and the nucleus can be extracted by dielectric spectroscopy. This thesis focuses on the applicability of the analytical models, in particular the Maxwell-Wagner Interfacial …

Theory Of Constraints Project Management In A Manufacturing Environment, Shihching Kraft

Mechanical & Aerospace Engineering Theses & Dissertations

The following thesis covers the concepts of Theory of Constraints (TOC) Project Management. Introduced by Eliyahu M. Goldratt in I 984, TOC is a management philosophy that focuses on the use of critical chain project management to prioritize everyday tasks in a company. In TOC Project Management, there is always at least one resource constraint that limits the speed at which projects are completed. TOC management philosophy also recognizes that most projects in the manufacturing industry face unknown schedule delays that could cause projects to be completed late or over the planned budget. During project plan creation, plans are developed …

Development And Assessment Of An In-Situ Load System, Kenneth Toro

Mechanical & Aerospace Engineering Theses & Dissertations

The In-situ Load System (ILS) was designed at NASA Langley Research Center (LaRC) to perform multi-component check loads on a force balance at a test facility. The ILS is designed to allow a force balance to be placed at off nominal orientations, while maintaining an applied load in the gravitational direction. This allows for multicomponent loads to be applied to a balance as a function of balance orientation and ILS configuration. The system is designed to be used in conjunction with a facilities existing pitch and roll control systems.

The ILS was modified to provide higher load ranges than those …

Static And Vibration Analyses, And Sensitivity Analysis Of Stepped Beams Using Singularity Functions, Carla Rocio Davila

Mechanical & Aerospace Engineering Theses & Dissertations

This thesis intends to prove that singularity functions can be used to perform static and vibration analyses and their sensitivity analysis of stepped beams subjected to various support constraints. Specifically, this thesis develops formulations using singularity functions for static and vibration analyses of a simply-supported, a roller­ supported, and a spring-supported stepped beam. The Static and Vibration Sensitivity Analysis formulations are derived for the simply-supported beam to show the feasibility of this approach. The techniques presented in this thesis can be extended to various other supports constraints such as a middle support, and spring support or any other variation of …

Field Emission Studies Toward Improving The Performance Of Dc High Voltage Photoelectron Guns, Mahzad Bastaninejad

Mechanical & Aerospace Engineering Theses & Dissertations

Field emission is the main mechanism that prevents DC high voltage photoemission electron guns from operating at the very high bias voltages required to produce low emittance beams. Gas conditioning is shown to eliminate field emission from cathode electrodes used inside DC high voltage photoelectron guns. Measurements and simulation results indicate that gas conditioning eliminates field emission from cathode electrodes via two mechanisms: sputtering and implantation, with the benefits of implantation reversed by heating the electrode. The field emission characteristics of 5 stainless steel electrodes varied significantly upon the initial application of voltage but improved to nearly the same level …

Subtalar Joint Instability: Diagnosis And Conservative Treatment, Julie Choisne

Mechanical & Aerospace Engineering Theses & Dissertations

Subtalar instability may be caused by various ligamentous injuries. Combined instability at the ankle and subtalar joint is not adequately diagnosed. Further, isolated subtalar instability is usually misdiagnosed which may lead to long term damage to the joint. Developing a non-invasive and clinically practical tool to diagnose subtalar joint instability would be an important asset. The ability of an ankle brace, a common treatment for hindfoot instability, to promote stability for the subtalar joint was not well established. The purposes of this study were to 1) assess the kinematics of the subtalar, ankle, and hindfoot in the presence of isolated …

Preliminary Development Of A Subject Specific Finite Element Model Of The Hindfoot, Liang Dong

Mechanical & Aerospace Engineering Theses & Dissertations

The human hindfoot is a complex structure and its medical treatment can vary from patient to patient. If physicians have access to a patient specific computer model, the optimal treatment option can be explored on the model before preforming it on the patient. The purpose of this study was to create a quasi-static finite element model and to show the stress contour in the cartilage between the bones. Ankle joint contact pressure was collected on one cadaver limb with a 40 lbs ( 178 N) axial load applied and tendon loads applied to simulate the ratio of tendon loading during …

Multi-Objective Preliminary Design Optimization Of Planing Craft Using Differential Evolution And Artificial Networks, Robert Eugene Weidman

Mechanical & Aerospace Engineering Theses & Dissertations

The differential evolution (DE) algorithm is an evolutionary algorithm that has been utilized as a metaheuristic optimizer in the last few years. A recently developed multi-objective version of DE is utilized in this research in order to optimize the preliminary design of planing craft. The craft performance is evaluated using the planing hull preliminary design software PHAST. The optimization problem objectives are the craft acquisition cost and the overall measure of effectiveness; the latter comprises various performance aspects: ride quality, transportability, payload, and mobility. Static stability and operating constraints are also considered. Each of the aforementioned four measures of effectiveness …