A need exists to develop a non-destructive testing technique that can identify
the formation and propagation of diagonal tension cracks in conventionally
steel reinforced concrete deck girder (RCDG) highway bridges in the State of
Oregon. Such a technique could be included into a structural health
monitoring (SHM) system installed on...
Normal gait of human is believed to be an adapted motor control result of optimal behavior of individual. Normal gait would be altered by aging or injury without being perceived. Subtle changes in gait which is not easy to detect, can cause many serious problems including joint pains and even...
Extending the flight time of an autonomous unmanned air vehicle by soaring is
considered. A suboptimal controller is developed and successful static soaring is
demonstrated with a 6 degree of freedom glider model. Altitude gain rates of between
¼ and ½ m/s are achieved with this simple implementation.
A hybrid...
For piezoelectric stack (PZT) driven droplet generator, the driving waveform
and driving frequency effect on liquid filament shape and droplet characteristics have
been experimentally studied. The experimental study was based on a PZT driven
droplet generator with known geometric design parameters and working fluid
properties. A lumped-element-model (LEM) constructed to...
Droplet formation from a flexible nozzle plate driven by a prescribed-waveform excitation of a piezoelectric is numerically investigated using a computational fluid dynamics (CFD) model with the VOF method. The droplet generator with a flexible nozzle plate, which is free to vibrate due to the pressure acting on the plate,...
Two-phase gas-liquid flows in microscale fractal-like branching channel flow networks were experimentally studied to assess the validity of existing void fraction correlations and flow regimes based on superficial gas and liquid velocities. Void fractions were assessed using two different methods. First, void fraction data were acquired using a High-Speed-High-Resolution (HSHR)...
The thermal wave technique has been explored for the use of liquid thermal conductivity measurement and flow property diagnostics in this dissertation. For liquid thermal conductivity measurements, an experimental technique based on the thermal wave approach is developed. A stainless steel strip functions as both a heating element and a...
A one-dimensional numerical model has been developed to study diabatic and adiabatic
flow boiling in microchannels. This model accounts for developing flow effects and
variable property effects. The model uses correlations for void fraction and two-phase
multipliers found in the literature. The model has been used to study the performance...
A hypothesis used to explain the relationship between timber harvesting
and landslides is that tree roots add mechanical support to soil, thus increasing
soil strength. Upon harvest, the tree roots decay which reduces soil strength and
increases the risk of management -induced landslides. The technical literature
does not adequately support...
Risk is a crucial decision factor besides traditional cost and performance during collaborative decision making in a distributed environment. Three main challenges exist: 1) stakeholders' different perspectives and/or diverse cultures can lead to inconsistent risk probability evaluations; 2) risk consequence is hard to be quantified in concrete unit; 3) risk...
At the start of the 21st century much of the focus of aircraft design has been turned to unmanned aerial vehicles (UAVs) which generally operate at much lower speeds in higher risk areas than manned aircraft. One subset of UAVs are Micro Air Vehicles (MAVs) which usually are no larger...
An experimental study was performed to investigate the effect of
flow channel geometry on fully developed turbulent flow in "clean" rod
bundle flow channels. This information was sought to obtain a better
understanding of crossflow mixing between rod bundle subchannels. The
experiments were performed in water with a Reynolds number...
Ever since composite laminate technology was introduced into the aerospace and automotive industry, there has been a need to fully understand the damage progression experienced by composite laminated plates in the presence of a notch. While numerous research studies have been conducted on this matter when subjected to in-plane loads,...
This study investigates the hydrodynamic characteristics of droplet impinging on heated surfaces using High Speed High Resolution (HSHR) imaging and evaluates the effect of surface temperature and using water and a nanofluid on a polished and a nano-structured surface. Three types of surfaces are used in the
study: polished silicon,...
Many animals detect prey or enhance their locomotion with information from hair-like receptors that are activated by local fluid flows. The utility of biological hair receptors has motivated the design of artificial hair sensors (AHS) for flow control applications where aerodynamic or hydrodynamic forces play a significant role in the...
The use of autonomous robots in complex exploration tasks is rapidly increasing. Indeed, robots can provide speed and cost effectiveness in many tasks, as well as allow operation in environments that are hostile to humans. In this dissertation we: 1) provide two adaptive navigation algorithms; 2) develop a coordination mechanism;...
In granular or fibrous materials, in which the dimensions of the internal
structure can be of the same order of magnitude as major flaws or holes, classical
elasticity theory does not consistently provide accurate models of the large stress
gradients that may develop. With the incorporation of additional rotational degrees...
This thesis addresses Micro Aerial Vehicle (MAV) control by leveraging learning based techniques to improve robustness of the control system. Applying classical control methods to MAVs is a difficult process due to the complexity of the control laws with fast and highly non-linear dynamics. These methods are mostly based on...
Sprawled-posture insects exhibit a remarkable ability to rapidly run in a stable manner
over complex terrain, a feat that has yet to be equaled by man-made legged robots.
Recent experimental results suggest that these insects may employ a hierarchical
control structure, in which locomotion performance emerges from a combination of...
Many engineering devices and propulsion systems suffer from undesirable effects of cavitation; such as degradation in the efficiency of pumps and turbines, generation of noise and vibration on ship propeller, increased drag and erosion of propeller blade, etc.
In spite of decades of research on this problem, detailed study of...
Since the Industrial Revolution, automated systems have increasingly become a part of everyday life. Automated systems range in scale and scope from simple assists to complete robotic replacements. Inexpensive integrated circuits, sensors and microprocessors have allowed automated systems to become smaller, cheaper and more prevalent. Identifying appropriate opportunities for automation,...
The optimal design technique for minimum power loss in
traction drive continuously variable transmissions is
developed. The mathematical model is developed to
evaluate the traction force and torque in traction drive
contact. Kinematic analysis of general traction drive
contact is conducted to find the best configuration for
minimum power loss....
Currently, the temporal arc distribution across the ingot during the vacuum arc remelting (VAR) process is not a known or monitored parameter. It is has previously been shown that arcs can spatially constrict during VAR, and this constriction can lead to undesired defects in the material. Additionally, correct accounting for...
Wave dispersion and fracture are phenomena that involve. mechanisms triggered at the scale of a material's internal structure. Experiments were performed with a candidate material to judge the hypothesis that wave dispersion measurements can be used to nondestructively predict fracture strength. Wood-based particleboard was chosen as the candidate material because...
Control issues are investigated for a parafoil and payload system with left and right parafoil brakes used as the control mechanism. It is shown through dynamic modeling and simulation that parafoil and payload systems can exhibit two basic modes of lateral control, namely, roll and skid steering. Using a small...
Biological organisms, phenomena and strategies, herein referred to as biological systems, provide a rich set of analogies that can be used to inspire engineering innovation. Biologically-inspired, or biomimetic, designs are publicly viewed as creative and novel solutions to human problems. Moreover, some biomimetic designs have become so commonplace that it...
Fractal-like branching microchannel flow networks have been found to improve wall temperature uniformity and decrease both pressure drop and flow power compared to arrays of straight microchannels. The present study seeks to maximize the benefits of fractal-like branching channels by means of a gradient-based optimization algorithm. The algorithm identifies the...
Two-phase flow in a fractal-like branching microchannel heat sink may have
enhanced heat transfer capabilities over single phase flow in the same branching
channel network. In order to exploit this potential, a complete understanding
of flow boiling in this geometry is required. The fractal-like geometry is similar
to that of...
A number of computational tools now exist to aid in developing conceptual solutions based on a functional description of a design problem. A key limitation of these tools is the way results are organized for presentation to the user. In general, results are an undifferentiated mass of potential solutions. Analysis...
Technologies such as avionics and power electronics are driving the demand for thermal management schemes towards high heat fluxes and low surface temperatures. Typically, these applications require the dissipation of heat fluxes in the rage of 100-1000 W/cm² while maintaining surface temperatures lower than about 85 °C. Phase-change heat transfer...
Development of a performance analysis for propeller type wind
turbines is presented. The analysis uses a strip theory approach
that includes tip-loss and blade interference. A comparison is
presented between analysis and test data. The comparison indicates
that the analysis predicts wind turbine performance to an accuracy
that is within...
While the locomotion performance of legged robots over flat terrain or known obstacles has improved over the past few decades, they have yet to equal the performance of their animal counterparts over variable terrain. This work analyzes a multi-legged reduced order model of cockroach locomotion on variable slopes which will...
A unique channel surface enhancement technique via diffusion-bonding a layer of conductive fine wire mesh onto the heating wall was developed and used to experimentally study flow boiling enhancement in parallel microchannels. Each channel was 1000 μm wide and 510 μm high. A dielectric working fluid, HFE 7000, was used...
Jets in crossflow are used in a wide range of engineering applications and have been studied for more than 60 years. The transversal penetration and structure of a jet placed in a crossflow is known to be strongly three-dimensional. It is believed that, by using a pulsed jet inclined in...
While many organizations claim to "put safety first," safety is rarely considered early in the design process when system-level architectural decisions are made. Instead, system design follows an abstraction-to-detail process to first meet functional and then performance requirements. Following this process, safety assurance occurs in the later stages of design...
A gap exists in the methods used in industry and available in academia that prevents customers and engineers from having a voice when considering engineering risk appetite in the dynamic shaping of early-phase conceptual design trade study outcomes. Current methods used in Collaborative Design Centers either collect risk information after...
Engineers have long been inspired by nature's flyers. Such animals navigate complex environments gracefully and efficiently by using a variety of evolutionary adaptations for high-performance flight. Biologists have discovered a variety of sensory adaptations that provide flow state feedback and allow flying animals to feel their way through flight. A...
Dynamic modeling of the atmospheric flight mechanics of a projectile equipped with an uncontrolled internal rotating disk is investigated and a modified projectile linear theory is established. It is shown through modeling of this type of projectile that several coefficients of the epicyclic dynamics are altered, leading to changes in...
This work proposes a framework of concept generation and evaluation that takes into consideration the benefit of creativity and innovation in current market trends. By educating engineers in how to increase creativity in concept design and assess it quantitatively, the next generation of designers will be a step ahead of...
Cavitation instabilities in elastic-plastic solids under spherically-symmetric and axisymmetric loadings were investigated using the finite element method. Both quasi-static and dynamic analyses were used to solve these problems. In the quasi-static analyses, we investigated a cavitation instability in elastic/perfectly-plastic, linear hardening elastic-plastic, power hardening elasticplastic, and constrained silver materials. Here,...
Material failures in heat exchangers are often
closely tied to events associated with the conditions
of service and operating parameters. These events can
generally be attributed to adverse load application and
higher than optimum operating temperatures that could
lead to changes in the microstructure of the materials
and fatigue failure...
Impact point dispersion of a direct fire rocket can be drastically reduced with a ring of appropriately sized lateral pulse jets coupled to a trajectory tracking flight control system. The system is shown to work well against uncertainty in the form of initial off-axis angular velocity perturbations as well as...
The problem of simple mathematical models of laminar natural convective
flow within a long vertical parallel-plate channels and circular tubes kept at
uniformly heated walls is revisited to seek a clear physical understanding of heat
transfer mechanisms. A series solution method to analyze the fully developed flow
and an integral...
This dissertation approaches the problem of how to design process
measurements by identifying process attributes which are common to all product
development processes. By classifying the generic attributes of a product
development process and their relationships, a framework is established which
gives definition and context to individual measurements. At the...
Silver interlayers between maraging steel base metal were examined to evaluate mechanisms leading to ductile failure in constrained thin metals. The constraint of the maraging steel base metal during uniaxial testing of constrained thin silver results in a large hydrostatic tension component, a small von Mises effective stress, and negligible...
Uncontrolled direct fire rockets exhibit high impact point dispersion, even at relatively short range, and as such have been employed as area weapons on the battlefield. In order to reduce the dispersion of a direct fire rocket, feedback control is employed to fire short-duration solid rocket pulses mounted near the...
Monitoring, diagnosis and prediction of failures play key roles in automatic supervision of machine tools. They have received much attention because of the potential for reduced maintenance expenses, down time, and an increase in the equipment utilization level. At present, signal analysis techniques are predominantly used. But methods involving system...
Heat transfer and fluid mechanical behavior of water
flowing horizontally in vertically-narrow rectangular
channels was studied in this work. Friction factor and
Nusselt number variations were determined experimentally
for four different wall heating conditions, and for aspect
ratios(height to width) of 5, 4, 3, 2, and 1. Wall
heating conditions...
Predictions of mechanical collisions between two bodies frequently cannot be completed by the impulse-momentum equation together with a complete description of the motion of the system at the initial contact. Additional account must be taken of the deformations and frictional interaction induced by the impulsive reaction force, where the bodies...
A computational model for a resonantly coupled alpha free-piston Stirling cooler
is presented. The cooler consists of two isothermal working spaces for compression and
expansion connected by a regenerator consisting of a stack of narrow parallel channels.
The regenerator is assumed to have a linear temperature distribution along its axial...
There are many options available when selecting a computational model for
two-phase flows. It is important to understand all the features of the model
selected, including when the model is appropriate and how using it may affect
your results. This work examines how volume displacement effects in two-phase
Eulerian-Lagrangian models...
Improvement of manufacturing productivity is dependent on the successful
automation of manufacturing processes, the success of which is based in turn upon
the availability of information which describes the state of manufacturing operations.
Acoustic Emission (AE) signals related to the cutting process and tool wear have
been recently applied to...
An Engineering Decision Support System, EDSS, was developed using Bayesian mathematics which incorporates knowledge and confidence components observed in alternative-criterion pair decision making. The separation of knowledge and confidence has been previously unaccounted for in decision-making methods. EDSS provides decision support to individuals or teams which must make choices between...
Design of commercial aircraft structure, composed of composite material, requires the
prediction of failure loads given large scale damage. In particular, a fuselage of
graphite/epoxy lamination was analyzed for damage tolerance given a standard large
crack that severed both skin and internal structure. Upon loading, a zone of damage is...
The compressive behavior of continuous fiber composites is not as well
understood as their tensile behavior because research and industrial applications have until
recently focused on the latter. Furthermore, most theoretical and experimental studies on
the compression of composites have examined the case of unidirectional specimens with
fibers along the...
Part I discusses the development of an aluminum-magnesium-silicon alloy that may combine strength, extrudability, favorable corrosion resistance with low cost and scrap compatibility. The first part of the study determined the effects of small composition, heat treatment and mechanical processing changes on the ambient temperature tensile properties of the alloy....
With the rapid increase of the world energy demand and
consumption, the method and techniques to analyze, improve
and optimize energy conversion systems have to deal not only
with direct fuel exergy (energy) consumption, but also with
other resources, which have associated exergy consumptions,
and with environmental impacts, such as...
The self-interstitial defect is commonly regarded as important in regulating diffusion
in silicon. A review of the literature reveals that the scientific bases for invoking the
self-interstitial defect are weak, while an alternate defect, the vacancy cluster, has been
largely ignored. One argument which has been used to establish dominance...
The objective of this work was to develop a method for determining stochastic loads on horizontal axis wind turbine blades. Stochastic loads caused by wind turbulence are a major consideration in designing for long life, cost effective wind turbines. The rotor blades are of particular concern because the blades are...
A continuous process for the production of ceramic materials has been studied.
This method reacted metal and oxidizer in a diffusionally controlled process,
demonstrated by reacting a magnesium particle stream and hot water vapor. Many small
rich hydrogen/air diffusion flames provide an atmosphere of hot water vapor, hydrogen,
and nitrogen...
Mechanical behavior of Nb-Ti superconducting composites with copper matrices have
been studied experimentally and theoretically.
Experimental work includes extensive measurements of Cu/Nb-Ti composite system.
Techniques for fine fiber testing and composite wire measurement have been developed.
Experimental parameters examined in this research include geometry, hardness, Young's
modulus, Poisson's ratio, yield...
Characterization of local boiling trends, in addition to the typically reported area-averaged trends, is essential for the robust design and implementation of phase change technologies to sensitive heat transfer applications such as electronics cooling. Obtaining the values of heat fluxes corresponding to locally varying surface temperatures has been a challenge...
The engineering design process and the advancement of future computer-aided-design systems need new design aids to be used during the conceptual design phase. This design phase is where information gathering and understanding of the problem are developed, analyzed and broken into small more manageable elements. These elements consist of customer...
This thesis presents an effective control design methodology using a one-step-ahead prediction adaptive control law and an adaptive control law based on a Lyapunov function. These control law were applied to a highly maneuverable high performance aircraft, in particular, a modified F/A-18. An adaptive controller is developed to maneuver an...
In mining and mineral processing, compressive loading is often encountered
during the comminution of ore bearing minerals and in the wear resistant materials
used in the comminution circuit. A common thread joining many of the materials that
are primarily used under compressive loading is the presence of a high modulus...
Coal continues to be burned by direct combustion in packed or moving bed in
small size domestic furnaces, medium size industrial furnaces, as well as small power
stations. Recent stringent restrictions on exhaust emissions call for a better
understanding of the process of combustion of coal in beds.
The present...
Polymeric composites exhibit time-dependent behavior, which raises a concern
about their long term durability and leads to a viscoelastic study of these materials.
Linear viscoelastic analysis has been found to be inadequate because many polymers
exhibit nonlinear viscoelastic behavior. Classical laminate theory is commonly used in
the study of laminated...
Even though the elastic deformations that occur during the
impact of colliding bodies may be small in comparison to their actual
dimensions, they play an important role in mechanical collisions.
During the time the bodies are in contact, elastic, friction, and inertia
properties combine to produce a complex variation of...
The Lyapunov direct method is utilized to determine the
robustness bounds for nonlinear, time-variant uncertainies
p[subscript i]. Determination of the robustness bounds consists of two
principal steps: (i) generation of a Lyapunov function and
(ii) determination of the bounds based on the generated
Lyapunov function. Presently in robustness investigations,
a...
When trace quantities of an alkali element are added to a flame,
its optical and electrical properties change significantly. Addition of
alkali seed to both premixed and diffusion flames has been used in the
development of two new techniques, one for flame temperature measurement
and the other for enhanced mixing....
Porous media flows are encountered in many natural and man-made systems such as gas adsorption, filtration, heat exchangers, combustion, catalytic reactors and groundwater hydrology. This study experimentally investigates these flows as function of pore Reynolds number, Re[subscript pore]. The pore Reynolds number is based on the porous bed hydraulic diameter,...
In current practice, design documentation often fails
to support the activities of design understanding,
communication, and redesign. A Design History Tool has been
developed to improve current design documentation. This
tool is a computerized design history that represents and
plays back important information generated during the
process of designing a...
The application of laser generated ultrasonics was first
demonstrated in the mid-seventies and has shown good potential
when applied to isotropic materials. However, its use with
composite materials is still in the early stages of development.
This study explores the potential for application of laser
generated Rayleigh and Lamb waves...
Bidirectional reflectance is a fundamental property
used for the analysis of radiative heat transfer. It is a
form of reflectivity in which the spectral and directional
dependencies of both the beam incident on a surface and the
beam reflected from the surface are specified.
A new system has been designed...
The development of modern industries calls for the
robotic manipulators with high speed and accurate tracking
performance. Many authors have paid attention to robust
control of robotic manipulators; however, only few authors
have also considered the control problem of manipulators
with power limitation.
In this dissertation, the robotic manipulator is...
Algorithms for analyzing laser interferometry
signals were developed and adopted to the computer based
processing of small displacement measurements. These
methods, matrix operation approach and fixed parameters
approach, are based on signal phase calculation and are
able to replace complex fringe counting electronic
circuits. The matrix operation provides an approach...
In this paper, a numerical method is used to predict
the response of an elastic body during a collision in which
both normal and tangential impulses are important. Results
are compared with those from simplified prediction
procedures, which stem from the assumptions that the energy-returning
capacity of the normal deformation...
Combustive Synthesis or Self-Propagating High-Temperature
Synthesis (SHS), is an energy-efficient combustion
method of producing metallic, ceramic and composite
materials from their constituent powders.
This thesis presents the results of an experimental and
numerical evaluation of the propagation velocity for the SHS
solid-solid reaction of titanium and carbon, as well as...
This study presents the results of an experimental investigation
of wood combustion. Variables chosen for investigation
were fuel feed rate, fuel moisture content,
fuel particle size, excess air, fraction and temperature of
under-fire air. Data recorded during the experiments included
the composition and temperature of the combustion
products in the...
A system which allows the computer to capture sketches
made by a mechanical designer is described. The system not
only recognizes basic features as they are sketched, but it
also reasons the spatial relationships between features and
builds a high level abstract representation (feature model)
of the artifact. The temporal...
The objective of this investigation is the development
of improved techniques for the estimation of robustness for
dynamic systems with structured uncertainties, a problem
which was approached by application of the Lyapunov direct
method. This thesis considers the sign properties of the
Lyapunov function derivative integrated along finite intervals
of...
This thesis presents a model of legged locomotion in
which position and velocity of body are directly controlled
by positions and velocities of feet. One central
relationship between foot acceleration, leg stroke and body
velocity is developed. Procedures for determining all
parameters of a step sequence including periods of constant...
Self-propagating high-temperature synthesis (SHS) is a new
method of producing advanced ceramic materials and offers an
attractive alternative to conventional methods of materials
processing.
An experimental investigation was carried out to determine
the SHS reaction wave propagation speed in a vertical cylindrical
compact made from a mixture of titanium and...
Control of high-speed, light-weight robotic manipulators is a challenge because of their special dynamic characteristics. In this work, a two-stage control algorithm for the position control of flexible manipulators is proposed. First, the more complex, flexible robot system is replaced by a simplified hypothetical rigid body system (HRRA) with off-line...
In this dissertation, a group of vehicle dynamics simulation tools is developed with two primary goals: to accurately represent vehicle behavior and to provide insight that improves the understanding of vehicle performance. Three tools are developed that focus on tire modeling, vehicle modeling and lap time simulation.
Tire modeling is...
This thesis presents the results of an experimental
and analytical study of single-port buoyant turbulent jets
discharged into shallow water. The experimental results
include the measured downstream dilution, centerline
concentration and trajectory. Independent parameters
considered were Froude number, submerged depth, discharge
angle and velocity ratio.
Results indicate that decreasing the...
This experiment is concerned with sampling submicrometer
particles in near sonic and supersonic flows.
The study employed a high volume condensation aerosol
generator to produce stearic acid particles having a
geometric mean diameter of 0.8 μm and a geometric
standard deviation of 1.28. The aerosol was diluted
with dry air...
In this work, flow through synthetic arrangements of contacting spheres is studied
as a model problem for porous media and packed bed type flows. Direct numerical
simulations are performed for moderate pore Reynolds numbers in the range,
10 ≤ Re ≤ 600, where non-linear porescale flow features are known to...
In-situ vapor extraction is performed by applying a pressure differential across a hydrophobic porous membrane that forms a wall of the channel as a means of reducing the local quality of flow boiling within the channel. As the local quality is reduced, the heat transfer capability can be improve while...
Development of variable speed horizontal axis wind turbines has resulted in a need for an analysis code with a rotor speed degree-of-freedom. This study develops a five degree-of-freedom time domain computer code that evaluates blade and rotor, mean and cyclic loads with nonlinear aerodynamics together with atmospheric turbulence as a...
Freezing is one of the important technologies for preservation of foods.
In this project, using surimi as a food model, thermophysical properties of frozen
foods were evaluated and the freezing process was simulated using a finite
element package.
To measure temperature-dependent thermal conductivity, a line-source
probe system was used. Effects...