# Browsing by Subject "Engineering, Mechanical"

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Item Open Access A Nonlinear Harmonic Balance Solver for an Implicit CFD Code: OVERFLOW 2(2009) Custer, Chad H.A National Aeronautics and Space Administration computational fluid dynamics code, OVERFLOW 2, was modified to utilize a harmonic balance solution method. This modification allows for the direct calculation of the nonlinear frequency-domain solution of a periodic, unsteady flow while avoiding the time consuming calculation of long physical transients that arise in aeroelastic applications.

With the usual implementation of this harmonic balance method, converting an implicit flow solver from a time marching solution method to a harmonic balance solution method results in an unstable numerical scheme. However, a relatively simple and computationally inexpensive stabilization technique has been developed and is utilized. With this stabilization technique, it is possible to convert an existing implicit time-domain solver to a nonlinear frequency-domain method with minimal modifications to the existing code.

This new frequency-domain version of OVERFLOW 2 utilizes the many features of the original code, such as various discretization methods and several turbulence models. The use of Chimera overset grids in OVERFLOW 2 requires care when implemented in the frequency-domain. This research presents a harmonic balance version of OVERFLOW 2 that is capable of solving on overset grids for sufficiently small unsteady amplitudes.

Item Open Access Adaptive Control of an Optical Trap for Single Molecule and Motor Protein Research(2007-12-13) Wulff, Kurt DThis research presents the development of an advanced, state-of-the-art optical trap for use in biological materials and nanosystems investigation. An optical trap is an instrument capable of manipulating microscopic particles using the inherent momentum of light. First introduced by Askin et al., the single beam gradient optical trap is capable of generating small forces (~1-100 pN) in a noninvasive manner. As a result, the optical trap is often used to manipulate biological specimen. This research presents the process for the construction of a custom optical trap, the methods to build a controllable optical trap through a traditional fixed gain controller as well as an adaptive controller, and also enables the application of torque to trapped particles. A method of using adaptive techniques for system identification and calibration is also presented. This research has the potential to use forces and torques to affect our understanding of the mechanics of single molecules and motor proteins. This instrument provides a more precise means of manipulating biological specimen as well as a tool for nanofabrication and has the potential to expand the knowledge base of DNA, chromosomes, biomotors, motor proteins, reversible polymers, and can be used to control chemical reactions. The research presented here documents the creation of an optical trap that is sensitive for applications requiring precise displacements and forces, adaptable to a variety of current and future research applications, and useable by anyone interested in researching micro- and nanosytems.Item Open Access An Integrated Online Path Planning and Control Approach for Robotic Sensor Networks(2010) Zhang, GuoxianThis dissertation addresses an information-driven sensor path planning problem which has various applications such as robot cleaning, environment monitoring, and manufacturing. Information-driven sensor path planning is concerned with planning the measurements of a sensor or a sensor network in order to support sensing objectives, such as target detection, classification and localization, based on prior information. When the sensor's field-of-view or visibility region is bounded, the sensor's position and orientation determine what targets can be measured at any given time. Therefore, the sensor path must be planned in concert with the measurement sequence. When sensors are installed on robotic platforms and are deployed in an obstacle-populated environment, the sensor path must also avoid collisions between the platform and the obstacles or other robotic sensors. Addressing this sensor path planning problem, this dissertation first presents a general and systematic approach for deriving information value functions that represent the expected utility of sensor decisions in a canonical sensor planning problem. The resulting information functions and search strategies are compared through extensive numerical simulations involving direct-search, alert-confirm, task-driven, and log-likelihood-ratio search strategies, and the maximum a-posteriori, maximum-likelihood,

and Neyman-Pearson decision rules. After that a novel off-line information roadmap method is developed to navigate single robotic sensor in which obstacles, targets, sensor's platform and field of view are represented as closed and bounded subsets of an Euclidean workspace. The information roadmap is sampled from a normalized information theoretic metric that favors samples with a high value of information in configuration space. Finally, when multiple robotic sensors are deployed in the workspace, and information of the workspace such as geometry, location, and prior measurements on targets and obstacles can become available online, another novel sensor path planning method, named information potential method, is proposed to take into account the new information obtained over time. Targets with high information value tend to have high probability to be measured by the robotic sensor network. A hybrid control system is utilized to coordinate and control each robotic sensor in the network to detect and measure obstacles and targets in the workspace. The potential function is also utilized to generate the milestones in a local probabilistic roadmap method to help robotic sensors escape their local minima.

The proposed methods are applied to a landmine classification problem to plan the path of a robotic sensor network in which each robot is equipped with a ground-penetrating radar. Other sensors, such as infrared sensors on unmanned aerial vehicles (UAVs), are utilized a priori for target detection and cursory classification. In the off-line sensor path planning applications for a single robotic sensor, experiments show that paths obtained from the information roadmap exhibit a classification efficiency significantly higher than that of existing robot motion strategies. Also, the information roadmap can be used to deploy non-overpass capable robots that must avoid targets as well as obstacles. Then in the multiple online robotic sensor network path planing applications, experiments show that path obtained from the information potential method takes advantages of the online information and coordination among robotic sensors, and the results show that the information potential method outperforms other strategies such as rapidly-exploring random trees and classical potential field methods that does not take target information value into account.

Item Open Access Control and Optimization of Track Coverage in Underwater Sensor Networks(2007-12-14) Baumgartner, Kelli A. CrewsSensor network coverage refers to the quality of service provided by a sensor network surveilling a region of interest. So far, coverage problems have been formulated to address area coverage or to maintain line-of-sight visibility in the presence of obstacles (i.e., art-gallery problems). Although very useful in many sensor applications, none of the existing formulations address coverage as it pertains to target tracking by means of multiple sensors, nor do they provide a closed-form function that can be applied to the problem of allocating sensors for the surveilling objective of maximizing target detection while minimizing false alarms. This dissertation presents a new coverage formulation addressing the quality of service of sensor networks that cooperatively detect targets traversing a region of interest, and is readily applicable to the current sensor network coverage formulations. The problem of track coverage consists of finding the positions of*n*sensors such that the amount of tracks detected by at least*k*sensors is optimized. This dissertation studies the geometric properties of the network, addressing a deterministic track-coverage formulation and binary sensor models. It is shown that the tracks detected by a network of heterogeneous omnidirectional sensors are the geometric transversals of non-translates families of disks. A novel methodology based on cones and convex analysis is presented for representing and measuring sets of transversals as closed-form functions of the sensors positions and ranges. As a result, the problem of optimally deploying a sensor network with the aforementioned objectives can be formulated as an optimization problem subject to mission dynamics and constraints. The sensor placement problem, in which the sensors are placed such that track coverage is maximized for a fixed sensor network, is formulated as a nonlinear program and solved using sequential quadratic programming. The sensor deployment, involving a dynamic sensor network installed on non-maneuverable sonobuoys deployed in the ocean, is formulated as an optimization problem subject to inverse dynamics. Both a finite measure of the cumulative coverage provided by a sensor network over a fixed period of time and the oceanic-induced current velocity field are accounted for in order to optimize the dynamic sensor network configuration. It is shown that a state-space representation of the motions of the individual sensors subject to the current vector field can be derived from sonobuoys oceanic drift models and obtained from CODAR measurements. Also considered in the sensor model are the position-dependent acoustic ranges of the sensors due to the effects from heterogenous environmental conditions, such as ocean bathymetry, surface temporal variability, and bottom properties. A solution is presented for the initial deployment scheme of the non-maneuverable sonobuoys subject to the ocean's current, such that sufficient track coverage is maintained over the entire mission. As sensor networks are subject to random disturbances due to unforseen heterogenous environmental conditions propagated throughout the sensors trajectories, the optimal initial positions solution is evaluated for robustness through Monte Carlo simulations. Finally, the problem of controlling a network of maneuverable underwater vehicles, each equipped with an onboard acoustic sensor is formulated using optimal control theory. Consequently, a new optimal control problem is presented that integrates sensor objectives, such as track coverage, with cooperative path planning of a mobile sensor network subject to time-varying environmental dynamics.Item Open Access Coupled-Mode Flutter for Advanced Turbofans(2010) Clark, Stephen ThomasIn the vast majority of measured turbomachinery blade flutter occurrences, the response occurs predominately in a single mode. The primary reason for this single-mode flutter is that for turbomachinery applications the combination of high mass ratio, high solidity, and large natural frequency separation results in only slight mode coupling.

The increased importance of fuel efficiency is driving the development of improved turbofans and open-rotor fans. These new designs use fewer blades and will incorporate composite materials or hollowed airfoils in their fan blade designs. Both of these design changes result in lower mass ratio, lower solidity fan blades that may cause multi-mode flutter, rather than single-mode flutter as seen on traditional fan blades. Thus, a single mode flutter design analysis technique may not be adequate. The purpose of this study is to determine initial guidelines for deciding when a coupled-mode analysis is necessary.

The results of this research indicate that mass ratio, frequency separation, and solidity have an effect on critical rotor speed. Further, guidelines were developed for when a multi-mode flutter analysis is required. These guidelines define a critical mass ratio that is a function of frequency separation and solidity. For blade mass ratios lower than this critical value, a multi-mode flutter analysis is required. Finally, the limitations of aerodynamic strip-theory have been revealed in a three-dimensional coupled-mode flutter analysis.

Item Open Access Design with Constructal Theory: Steam Generators, Turbines and Heat Exchangers(2010) Kim, Yong SungThis dissertation shows that the architecture of steam generators, steam turbines and heat exchangers for power plants can be predicted on the basis of the constructal law. According to constructal theory, the flow architecture emerges such that it provides progressively greater access to its currents. Each chapter shows how constructal theory guides the generation of designs in pursuit of higher performance. Chapter two shows the tube diameters, the number of riser tubes, the water circulation rate and the rate of steam production are determined by maximizing the heat transfer rate from hot gases to riser tubes and minimizing the global flow resistance under the fixed volume constraint. Chapter three shows how the optimal spacing between adjacent tubes, the number of tubes for the downcomer and the riser and the location of the flow reversal for the continuous steam generator are determined by the intersection of asymptotes method, and by minimizing the flow resistance under the fixed volume constraints. Chapter four shows that the mass inventory for steam turbines can be distributed between high pressure and low pressure turbines such that the global performance of the power plant is maximal under the total mass constraint. Chapter five presents the more general configuration of a two-stream heat exchanger with forced convection of the hot side and natural circulation on the cold side. Chapter six demonstrates that segmenting a tube with condensation on the outer surface leads to a smaller thermal resistance, and generates design criteria for the performance of multi-tube designs.

Item Open Access Development of a State-of-the-Art Atomic Force Microscope for Improved Force Spectroscopy(2008-11-19) Rivera, MonicaThis research describes the development of a state-of-the-art atomic force microscope (AFM) for improved force spectroscopy. Although the AFM has been used extensively in this field of research, the performance of the instrument has been limited by inefficient operation techniques, incorrect experimental assumptions, and inadequate controller design. This research focuses on overcoming these deficiencies by providing precise control over the instrument for specialized research in a manner that is conducive to the natural science researcher.

To facilitate this research, a custom, multi-axis AFM system was constructed. The instrument was designed primarily for AFM-based force spectroscopy and as a result a substantial amount of research focused on the development of a wide variety of approach/retraction methods for the instrument. Defining research in this area included the development of methods to minimize potentially damaging compressive forces, form polymer bridges at different tip-sample gap widths, produce clean, deconvoluted force-extension curves, and limit single molecule force spectroscopy pulling geometry errors. In an effort to increase the efficiency of the instrument, the programs developed during this research were fully automated, allowing autonomous operation of the instrument for long periods of time. To compliment the data collection programs, both manual and automated analysis programs with force-volume imaging capabilities were also developed.

By studying the AFM from a dynamic systems, measurements, and controls approach, the resulting controllers were tailored to meet the process requirements of the intended applications. In doing so, the sensitivity of the instrument was improved for applications of interest. By incorporating control over the environment, contact force, loading rate, and pulling angle, the research has increased the accuracy of the AFM such that molecules and receptor-ligand binding events can be investigated with greater detail. Furthermore, the incorporation of a graphical user interface and automated data collection and analysis tools has made the AFM a more user-friendly, efficient instrument for the natural science researcher.

Item Open Access Development of an Efficient Design Method for Non-synchronous Vibrations(2008-04-24) Spiker, Meredith AnneThis research presents a detailed study of non-synchronous vibration (NSV) and the development of an efficient design method for NSV. NSV occurs as a result of the complex interaction of an aerodynamic instability with blade vibrations. Two NSV design methods are considered and applied to three test cases: 2-D circular cylinder, 2-D airfoil cascade tip section of a modern compressor, and 3-D high pressure compressor cascade that encountered NSV in rig testing. The current industry analysis method is to search directly for the frequency of the instability using CFD analysis and then compare it with a fundamental blade mode frequency computed from a structural analysis code. The main disadvantage of this method is that the blades' motion is not considered and therefore, the maximum response is assumed to be when the blade natural frequency and fluid frequency are coincident. An alternate approach, the enforced motion method, is also presented. In this case, enforced blade motion is used to promote lock-in of the blade frequency to the fluid natural frequency at a specified critical amplitude for a range of interblade phase angles (IBPAs). For the IBPAs that are locked-on, the unsteady modal forces are determined. This mode is acceptable if the equivalent damping is greater than zero for all IBPAs. A method for blade re-design is also proposed to determine the maximum blade response by finding the limit cycle oscillation (LCO) amplitude. It is assumed that outside of the lock-in region is an off-resonant, low amplitude condition. A significant result of this research is that for all cases studied herein, the maximum blade response is not at the natural fluid frequency as is assumed by the direct frequency search approach. This has significant implications for NSV design analysis because it demonstrates the requirement to include blade motion. Hence, an enforced motion design method is recommended for industry and the current approach is of little value.Item Open Access Effect of van der Waals forces on Retilce Nonflatness in Extreme Ultraviolet Lithography(2010) Gajendran, HarishankerDue to the increasing cost of the enhancement techniques in current projection lithographic techniques and the required time in developing new technology's

as feasible manufacturing technology, EUVL is considered as the leading candidate for production of 45 nm node and less. In EUVL, mask is held electrostatically against chuck. This electrostatic chucking process affects the nonflatness of the mask due to contact interaction and the voltage force between the mask and chuck. A fundamental understanding of chucking phenomenon is required to realize the SEMI P37 and SEMI P40 stringent flatness requirements.

The primary challenge is to understand and characterize the ability of electrostatic chucking phenomenon to acheive consistent and reliable shapes of chucked masks.

The objective of this thesis is to study the effect of initial nonflatness of mask and chuck, chucking voltage, chuck and mask dimension and gravity on the final nonflatness of the mask A finite element model of the mask and chuck with initial nonflat surface is developed. To predict the final nonflatness of the mask frontside with nm accuracy, the contact interaction between mask and chuck is modeled using van der Waals forces. These results are compared with penalty method for the runtime and accuracy of results

Item Open Access Flutter and Forced Response of Turbomachinery with Frequency Mistuning and Aerodynamic Asymmetry(2008-04-25) Miyakozawa, TomokazuThis dissertation provides numerical studies to improve bladed disk assembly design for preventing blade high cycle fatigue failures. The analyses are divided into two major subjects. For the first subject presented in Chapter 2, the mechanisms of transonic fan flutter for tuned systems are studied to improve the shortcoming of traditional method for modern fans using a 3D time-linearized Navier-Stokes solver. Steady and unsteady flow parameters including local work on the blade surfaces are investigated. It was found that global local work monotonically became more unstable on the pressure side due to the flow rollback effect. The local work on the suction side significantly varied due to nodal diameter and flow rollback effect. Thus, the total local work for the least stable mode is dominant by the suction side. Local work on the pressure side appears to be affected by the shock on the suction side. For the second subject presented in Chapter 3, sensitivity studies are conducted on flutter and forced response due to frequency mistuning and aerodynamic asymmetry using the single family of modes approach by assuming manufacturing tolerance. The unsteady aerodynamic forces are computed using CFD methods assuming aerodynamic symmetry. The aerodynamic asymmetry is applied by perturbing the influence coefficient matrix. These aerodynamic perturbations influence both stiffness and damping while traditional frequency mistuning analysis only perturbs the stiffness. Flutter results from random aerodynamic perturbations of all blades showed that manufacturing variations that effect blade unsteady aerodynamics may cause a stable, perfectly symmetric engine to flutter. For forced response, maximum blade amplitudes are significantly influenced by the aerodynamic perturbation of the imaginary part (damping) of unsteady aerodynamic modal forces. This is contrary to blade frequency mistuning where the stiffness perturbation dominates.Item Open Access Information-driven Sensor Path Planning and the Treasure Hunt Problem(2008-04-25) Cai, ChenghuiThis dissertation presents a basic information-driven sensor management problem, referred to as treasure hunt, that is relevant to mobile-sensor applications such as mine hunting, monitoring, and surveillance. The objective is to classify/infer one or multiple fixed targets or treasures located in an obstacle-populated workspace by planning the path and a sequence of measurements of a robotic sensor installed on a mobile platform associated with the treasures distributed in the sensor workspace. The workspace is represented by a connectivity graph, where each node represents a possible sensor deployment, and the arcs represent possible sensor movements. A methodology is developed for planning the sensing strategy of a robotic sensor deployed. The sensing strategy includes the robotic sensor's path, because it determines which targets are measurable given a bounded field of view. Existing path planning techniques are not directly applicable to robots whose primary objective is to gather sensor measurements. Thus, in this dissertation, a novel approximate cell-decomposition approach is developed in which obstacles, targets, the sensor's platform and field of view are represented as closed and bounded subsets of an Euclidean workspace. The approach constructs a connectivity graph with observation cells that is pruned and transformed into a decision tree, from which an optimal sensing strategy can be computed. It is shown that an additive incremental-entropy function can be used to efficiently compute the expected information value of the measurement sequence over time. The methodology is applied to a robotic landmine classification problem and the board game of CLUE$^{\circledR}$. In the landmine detection application, the optimal strategy of a robotic ground-penetrating radar is computed based on prior remote measurements and environmental information. Extensive numerical experiments show that this methodology outperforms shortest-path, complete-coverage, random, and grid search strategies, and is applicable to non-overpass capable platforms that must avoid targets as well as obstacles. The board game of CLUE$^{\circledR}$ is shown to be an excellent benchmark example of treasure hunt problem. The test results show that a player implementing the strategies developed in this dissertation outperforms players implementing Bayesian networks only, Q-learning, or constraint satisfaction, as well as human players.Item Open Access Mechanical and Tribological Study of a Stimulus Responsive Hydrogel, pNIPAAm, and a Mucinous Glycoprotein, Lubricin(2009) Chang, Debby Pei-ShanFriction is the resistive force that arises when two contacting surfaces move relative to each other. Frictional interactions are important from both engineering and biological perspectives. In this research I focus on the fundamental understanding of friction on polymeric and biological surfaces in aqueous environments. First, I examine the frictional properties of a stimulus-responsive hydrogel, poly-N-isopropylacrylamide (pNIPAAm), to understand how different phase states affect its tribological properties. My measurements indicate that gels in a collapsed conformation at low shear rates, exhibit significantly larger friction than swollen gels. These differences arise from changes in surface roughness, adhesive interactions, and chain entanglements of the gel surfaces associated with the phase transition. Importantly, I show that the changes in friction, triggered by an external stimulus, are reversible.

Second, I examine details of the boundary lubrication mechanism involved in mediating friction and wear in diarthrodial joints. Specifically, I looked at the constituents of the synovial fluid, lubricin and hyaluronic acid (HA) and examined their interactions on model substrates, (1) to determine the effect of surface chemistry on adsorption using surface plasmon resonance (SPR), and (2) to study normal force interactions between these surfaces using colloidal probe microscopy (CPM). I found that lubricin is highly surface-active, adsorbed strongly onto hydrophobic, hydrophilic and also collagen surfaces. Overall, lubricin develops strong repulsive interactions. This behavior is in contrast to that of HA, which does not adsorb appreciably, nor does it develop significant repulsive interactions. I speculate that in mediating interactions at the cartilage surface, an important role of lubricin is one of providing a protective coating on cartilage surfaces that maintains the contacting surfaces in a sterically repulsive state.

Item Open Access On the stability of swarm consensus under noisy control(ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control, DSCC 2011, 2011-12-01) Rogers, B; Fricke, GK; Garg, DPRepresentation of a swarm of independent robotic agents under graph-theoretic constructs allows for more formal analysis of convergence properties. We consider the local and global convergence behavior of an N-member swarm of agents in a modified consensus problem wherein the connectivity of agents is governed by probabilistic functions. The addition of a random walk control ensures ε-stability of the swarm consensus. Simulation results are given to show the rate of convergence to consensus and planned experiments are described. Copyright © 2011 by ASME.Item Open Access Optimization of the Aerodynamics of Small-scale Flapping Aircraft in Hover(2008-06-27) Lebental, SidneyFlapping flight is one of the most widespread mean of transportation. It is a complex unsteady aerodynamic problem that has been studied extensively in the past century. Nevertheless, by its complex nature, flapping flight remains a challenging subject. With the development of micro air vehicles, researchers need new computational methods to design these aircrafts efficiently.

In this dissertation, I will present three different methods of optimization for flapping flight with an emphasis on hovering with each their advantages and drawbacks. The first method was developed by Hall et al. It is an extremely fast and powerful three-dimensional approach. However, the assumptions made to develop this theory limit its use to lightly loaded wings. In addition, it only models the motion of the trailing edge and not the actual motion of the wing.

In a second part, I will present a two-dimensional unsteady potential method. It uses a freely convected wake which removes the lightly loaded restriction. This method shows the existence of an optimal combination of plunging and pitching motion. The motion is optimal in the sense that for a required force vector, the aerodynamic power is minimal.

The last method incorporates the three-dimensional effects. These effects are especially important for low aspect ratio wings. Thus, a three-dimensional unsteady potential vortex method was developed. This method also exhibits the presence of an optimal flapping/pitching motion. In addition, it agrees really well with the two previous methods and with the actual kinematics of birds during hovering flapping flight.

To conclude, some preliminary design tools for flapping wings in forward and hovering flight are presented in this thesis.

Item Open Access Probabilistic Modeling of Decompression Sickness, Comparative Hydrodynamics of Cetacean Flippers, Optimization of CT/MRI Protocols and Evaluation of Modified Angiocatheters: Engineering Methods Applied to a Diverse Assemblage of Projects(2010) Weber, Paul WilliamThe intent of the work discussed in this dissertation is to apply the engineering methods of theory/modeling, numerics/computation, and experimentation to a diverse assemblage of projects. Several projects are discussed: probabilistic modeling of decompression sickness, comparative hydrodynamics of cetacean flippers, optimization of CT/MRI protocols, evaluation of modified catheters, rudder cavitation, and modeling of mass transfer in amphibian cone outer segments.

The first project discussed is the probabilistic modeling of decompression sickness (DCS). This project involved developing a system for evaluating the success of decompression models in predicting DCS probability from empirical data. Model parameters were estimated using maximum likelihood techniques, and exact integrals of risk functions and tissue kinetics transition times were derived. Agreement with previously published results was excellent including maximum likelihood values within one log-likelihood unit of previous results and improvements by re-optimization, mean predicted DCS incidents within 1.4% of observed DCS, and time of DCS occurrence prediction. Alternative optimization and homogeneous parallel processing techniques yielded faster model optimization times. The next portion of this project involved investigating the nature and utility of marginal decompression sickness (DCS) events in fitting probabilistic decompression models to experimental dive trial data. Three null models were developed and compared to a known decompression model that was optimized on dive trial data containing only marginal DCS and no-DCS events. It was found that although marginal DCS events are related to exposure to decompression, empirical dive data containing marginal and full DCS outcomes are not combinable under a single DCS model; therefore, marginal DCS should be counted as no-DCS events when optimizing probabilistic DCS models with binomial likelihood functions. The final portion of this project involved the exploration of a multinomial DCS model. Two separate models based on the exponential-exponential/linear-exponential framework were developed: a trinomial model, which is able to predict the probabilities of mild, serious and no-DCS simultaneously, and a tetranomial model, which is able to predict the probabilities of mild, serious, marginal and no-DCS simultaneously. The trinomial DCS model was found to be qualitatively better than the tetranomial model, for reasons found earlier concerning the utility of marginal DCS events in DCS modeling.

The next project discussed is comparative hydrodynamics of cetacean flippers. Cetacean flippers may be viewed as being analogous to modern engineered hydrofoils, which have hydrodynamic properties such as lift coefficient, drag coefficient and associated efficiency. The hydrodynamics of cetacean flippers have not previously been rigorously examined and thus their performance properties are unknown. By conducting water tunnel testing using scale models of cetacean flippers derived via computed tomography (CT) scans, as well as computational fluid dynamic (CFD) simulations, a baseline work is presented to describe the hydrodynamic properties of several cetacean flippers. It was found that flippers of similar planform shape had similar hydrodynamic performance properties. Furthermore, one group of flippers of planform shape similar to modern swept wings was found to have lift coefficients that increased with angle of attack nonlinearly, which was caused by the onset of vortex-dominated lift. Drag coefficient versus angle of attack curves were found to be less dependent on planform shape. Larger cetacean flippers were found to have degraded performance at a Re of 250,000 compared to flippers of smaller odontocetes, while performance of larger and smaller cetacean flippers was similar at a swim speed of 2 m/s. Idealization of the planforms of cetacean flippers was found to capture the relevant hydrodynamic effects of the real flippers, although unintended consequences such as the lift curve slope changing from linear to nonlinear were sometimes observed. A numerical study of an idealized model of the humpback whale flipper showed that the leading-edge tubercles delay stall compared to a baseline (no tubercle) flipper because larger portions of the flow remaining attached at higher angles of attack.

The third project discussed is optimization of CT/MRI protocols. In order to optimize contrast material administration protocols for Computed Tomography (CT) and Magnetic Resonance Imaging (MRI), a custom-built physiologic flow phantom was constructed to model flow in the human body. This flow phantom was used to evaluate the effect of varying volumes, rates, and types of contrast material, use of a saline chase, and cardiac output on aortic enhancement characteristics. For CT, reducing the volume of contrast material decreased duration peak enhancement and reduced the maximum value of peak enhancement. Increasing the rate of contrast media administration increased peak enhancement and decreased duration of peak enhancement. Use of a saline chase resulted in an increase in peak enhancement. Peak aortic enhancement increased when reduced cardiac output was simulated. For MRI, when the same volume of contrast material was injected at the same rate, the type of contrast material used has a significant effect on the greatest peak signal intensity and duration peak signal intensity. A higher injection rate of saline chaser is more advantageous than a larger volume of saline chaser to increase the peak aortic signal intensity using low contrast material doses. Furthermore, for higher volumes of contrast material, the effect of increasing the volume of saline chaser makes almost no difference while increasing the rate of injection makes a significant difference. When a saline chaser with a high injection rate is used, the dose of the contrast material may be reduced by 25-50% and more than 86% of the non-reduced dose peak aortic enhancement will be attained.

The next project discussed is evaluation of modified angiocatheters. In this study, a standard peripheral end hole angiocatheter was compared to those modified with side holes or side slits by using experimental techniques to qualitatively compare the contrast material exit jets, and by using numeric techniques to provide flow visualization and quantitative comparisons. A Schlieren imaging system was used to visualize the angiocatheter exit jet fluid dynamics at two different flow rates, and a commercial computational fluid dynamics (CFD) package was used to calculate numeric results for various catheter orientations and vessel diameters. Experimental images showed that modifying standard peripheral intravenous angiocatheters with side holes or side slits qualitatively changed the overall flow field and caused the exiting jet to become less well-defined. Numeric calculations showed that the addition of side holes or slits resulted in a 9-30% reduction of the velocity of contrast material exiting the end hole of the angiocatheter. With the catheter tip directed obliquely to the wall, the maximum wall shear stress was always highest for the unmodified catheter and always lowest for the 4 side slit catheter. Modified angiocatheters may have the potential to reduce extravasation events in patients by reducing vessel wall shear stress.

The next project discussed involves studying the effect of leading-edge tubercles on cavitation characteristics for marine rudders. Three different rudders were constructed and tested in a water tunnel: baseline, 3-tubercle leading edge, and 5-tubercle leading edge. In the linear (non-stall) regime, tubercled rudders performed equally to the smooth rudder. Hydrodynamic stall occurred at smaller angles of attack for the tubercled rudders than for the smooth rudder. When stall did occur, it was more gradual for the tubercled rudders, whereas the smooth rudder demonstrated a more dramatic loss of lift. At lower Re, the tubercled rudders also maintained a higher value of lift post-stall than the smooth rudder. Cavitation onset for the tubercled rudders occurred at lower angles of attack and higher values of cavitation number than for the smooth rudder, but cavities on the tubercled rudders were localized in the slots as opposed to the smooth rudder where the cavity spread across the entire leading edge.

In the final project discussed, modeling of mass transfer in amphibian cone outer segments, a detailed derivation of a simplified (continuum, one-dimensional) mathematical model for the radio-labeled opsin density profile in the amphibian cone outer segment is presented. This model relies on only one free parameter, which was the mass transfer coefficient between the plasmalemma and disc region. The descriptive equations were nondimensionalized, and scale analysis showed that advective effects could be neglected as a first approximation for early times so that a simplified system could be obtained. Through numeric computation the solution behavior was found to have three distinct stages. The first stage was marked by diffusion in the plasmalemma and no mass transfer in the disc region. The second stage first involved the plasmalemma reaching a metastable state whereas the disc region density increased, then involved both the plasmalemma and disc regions increasing in density with their distributions being qualitatively the same. The final stage involved a slow relaxation to the steady-state solution.

Item Open Access Recording Information into DNA(2009) Tanner, Maria ElisaThe objective of this research is to develop the concept of "genetic memory", the storage of information into genetic material, through the demonstration of the feasibility and benefits of recording the time-history of one or more environmental state variables into genetic material. First, the amount of information that could be stored into non-coding DNA using a lossy mechanism such as regulated diffusion is determined by developing a mathematical model. Next, a mechanism through which this concept of sensing, recording, and storing information on the nanoscale could be accomplished is proposed.

In conjunction with DNA, which is the actual means of storing information, the proposed approach for the realization of genetic memory also uses thermosensitive liposomes as a means of sensing state variables and acting as a valve to transport and release the DNA in response to the appropriate stimuli. Each variant of thermally sensitive liposomes contains a unique DNA sequence that serves as an identifier. Upon release, the DNA encounters ligase, ATP, and other cofactors and binds - preserving a record of the stimulus experienced by the liposomes. Liposomes, through careful design, can be developed to have unique transition temperatures at which the permeability rate of the contents encapsulated by the liposome increases. It is only at or above this transition temperature that a liposome will become porous.

Through modeling and experimentation, the feasibility of the liposome/DNA system as a mechanism for information storage is successfully demonstrated.

Item Open Access Techniques to Assess Acoustic-Structure Interaction in Liquid Rocket Engines(2008-04-25) Davis, Robert BenjaminAcoustoelasticity is the study of the dynamic interaction between elastic structures and acoustic enclosures. In this dissertation, acoustoelasticity is considered in the context of liquid rocket engine design. The techniques presented here can be used to determine which forcing frequencies are important in acoustoelastic systems. With a knowledge of these frequencies, an analyst can either find ways to attenuate the excitation at these frequencies or alter the system in such a way that the prescribed excitations do result in a resonant condition. The end result is a structural component that is less susceptible to failure. The research scope is divided into three parts. In the first part, the dynamics of cylindrical shells submerged in liquid hydrogen (LH_{2}) and liquid oxygen (LOX) are considered. The shells are bounded by rigid outer cylinders. This configuration gives rise to two fluid-filled cavities: an inner cylindrical cavity and an outer annular cavity. Such geometries are common in rocket engine design. The natural frequencies and modes of the fluid-structure system are computed by combining the rigid wall acoustic cavity modes and the*in vacuo*structural modes into a system of coupled ordinary differential equations. Eigenvalue veering is observed near the intersections of the curves representing natural frequencies of the rigid wall acoustic and the*in vacuo*structural modes. In the case of a shell submerged in LH_{2}, system frequencies near these intersections are as much as 30% lower than the corresponding*in vacuo*structural frequencies. Due to its high density, the frequency reductions in the presence of LOX are even more dramatic. The forced responses of a shell submerged in LH_{2}and LOX while subject to a harmonic point excitation are also presented. The responses in the presence of fluid are found to be quite distinct from those of the structure*in vacuo*. In the second part, coupled mode theory is used to explore the fundamental features of acoustoelastic systems. The result is the development of relatively simple techniques that allow analysts to make informed decisions concerning the importance of acoustic-structure coupling without resorting to more time consuming and complex methods. In this part, a new nondimensional parameter is derived to quantify the fundamental strength of a particular acoustic-structure interaction irrespective of material and fluid properties or cavity size. It is be shown that, in some cases, reasonable approximations of the coupled acoustic-structure frequencies can be calculated without explicit knowledge of the uncoupled component mode shapes. Monte Carlo simulations are performed to determine the parameter values over which the approximate coupled frequency expressions are accurate. General observations concerning the forced response of acoustoelastic systems are then made by investigating the response of a simplified two mode system. The third part of this research discusses the implementation of a component mode synthesis (CMS) technique for use with geometrically complex acoustoelastic systems. The feasibility of conceptually similar techniques was first demonstrated over 30 years ago. Since that time there have been remarkable advancements in computational methods. It is therefore reasonable to question the extent to which CMS remains a computationally advantageous approach for acoustoelastic systems of practical interest. This work demonstrates that relative to the most recent release of the popular finite element software package, ANSYS, CMS techniques have a significant computational advantage when the forced response of an acoustoelastic system is of interest. However, recent improvements to the unsymmetric eigensolver available in ANSYS have rendered CMS a less efficient option when calculating system frequencies and modes. The CMS technique is then used to generate new results related to geometrically complex acoustoelastic systems.Item Open Access The Design Of A Nanolithographic Process(2007-07-02) Johannes, Matthew StevenThis research delineates the design of a nanolithographic process for nanometer scale surface patterning. The process involves the combination of serial atomic force microscope (AFM) based nanolithography with the parallel patterning capabilities of soft lithography. The union of these two techniques provides for a unique approach to nanoscale patterning that establishes a research knowledge base and tools for future research and prototyping.To successfully design this process a number of separate research investigations were undertaken. A custom 3-axis AFM with feedback control on three positioning axes of nanometer precision was designed in order to execute nanolithographic research. This AFM system integrates a computer aided design/computer aided manufacturing (CAD/CAM) environment to allow for the direct synthesis of nanostructures and patterns using a virtual design interface. This AFM instrument was leveraged primarily to study anodization nanolithography (ANL), a nanoscale patterning technique used to generate local surface oxide layers on metals and semiconductors. Defining research focused on the automated generation of complex oxide nanoscale patterns as directed by CAD/CAM design as well as the implementation of tip-sample current feedback control during ANL to increase oxide uniformity. Concurrently, research was conducted concerning soft lithography, primarily in microcontact printing (ÂµCP), and pertinent experimental and analytic techniques and procedures were investigated.Due to the masking abilities of the resulting oxide patterns from ANL, the results of AFM based patterning experiments are coupled with micromachining techniques to create higher aspect ratio structures at the nanoscale. These relief structures are used as master pattern molds for polymeric stamp formation to reproduce the original in a parallel fashion using µCP stamp formation and patterning. This new method of master fabrication provides for a useful alternative to conventional techniques for soft lithographic stamp formation and patterning.Item Open Access The Effect of Wing Damage on Aeroelastic Behavior(2009) Conyers, Howard J.Theoretical and experimental studies are conducted in the field of aeroelasticity. Specifically, two rectangular and one cropped delta wings with a hole are analyzed in this dissertation for their aeroelastic behavior.

The plate-like wings are modeled using the finite element method for the structural theory. Each wing is assumed to behave as a linearly elastic and isotropic, thin plate. These assumptions are those of small-deflection theory of bending which states that the plane sections initially normal to the midsurface remain plane and normal to that surface after bending. The wings are modeled in low speed flows according to potential flow theory. The potential flow is governed by the aerodynamic potential equation, a linear partial differential equation. The aerodynamic potential equation is solved using a distribution of doublets that relates pressure to downwash in the doublet lattice method. A hole in a wing-like structure is independently investigated theoretically and experimentally for its structural and aerodynamic behavior.

The aeroelastic model couples the structural and aerodynamic models using Lagrange's equations. The flutter boundary is predicted using the V-g method. Linear theoretical models are capable of predicting the critical flutter velocity and frequency as verified by wind tunnel tests. Along with flutter prediction, a brief survey on gust response and the addition of stores(missile or fuel tanks) are examined.