Trident Scholar Abstracts 2017

Benjamin H. Bailin
Midshipman First Class
United States Navy

On the Effects of Unsteady Flow Conditions on the Performance of a Cross Flow Hydrokinetic Turbine

Hydrokinetic turbines convert the energy of flowing water into usable electricity. Axial flow and cross flow turbines are the most common forms of hydrokinetic turbine, however cross flow turbine performance and the impact of surface waves are not well understood. Tests were conducted to observe the effects of waves on the performance characteristics of a cross flow turbine promulgated by the Department of Energy’s Reference Model Project, specifically Reference Model 2.

Testing of a 1:6 scale model was conducted in the large towing tank in the Hydromechanics Laboratory. The scale model turbine had a 1.075 m diameter and blades with a height of 0.807 m and a NACA 0021 cross section. Baseline (no wave) turbine performance was compared to published data on the same model turbine. Additionally, tests were conducted with incident waves, which were scaled to be large enough to create a shear in velocity across the span of the turbine. Tests were also conducted at various turbine depths and various tow speeds which resulted in a range of Reynolds numbers.

The average turbine performance characteristics improved slightly as depth decreased due to acceleration of the constricted flow near the surface. Waves did not significantly change the performance of the turbine when averaged over of an entire cycle and several wave periods. This was the case even though the test waves created a velocity shear across the entire span of the blade. The waves were found to impart cyclic signatures in the torque measurement which may have consequences for instantaneous blade loading and power output from the device.

A computational model was developed to predict turbine performance and compares favorably to the experiment at peak turbine performance. However, the model does not accurately predict the correct power at off peak conditions

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The ability of a helicopter to hover and takeoff/land vertically makes it uniquely suited for many different missions. However, its relatively low forward flight speed has led to a focus on developing helicopters with significantly higher velocity ceilings. A criteria of high-speed helicopters is a rotor system with high efficiency in both hover and forward flight, but traditional design choices (i.e., blade twist) that increase the efficiency of one flight condition often degrade the efficiency of the other. While active systems, such as blade morphing or shape shifting rotor blades, have potential to alter loading distribution between flight conditions, these structures can add unwanted weight and complexity to the aircraft. Another solution to achieving twist rate changes could be through the use of passive aerodynamic design: circulation control using leading-edge protuberances.

The inspiration for the use of protuberances stems from the leading-edge of the pectoral flipper on the humpback whale which, despite its large size, has exceptional maneuverability (i.e., small turning radius) among other whale species. Protuberances of various amplitude and wavelength geometries have previously been evaluated on an assortment of lifting surfaces, such as airfoils, wings, helicopter blades, and wind and tidal turbines. Those studies found increases in performance, especially in off-design conditions, most likely due to delayed stall through a mechanism similar to vortex generators. However, there is a dearth of information on how protuberance amplitude and frequency affect the formation and strength of these streamwise vortices, as well as the effect these vortices have on the loading distribution and circulation trailed into the wake.

This project utilized thrust and torque measurements and high-resolution particle image velocimetry (PIV) measurements to analyze performance and wake characteristics of rotors with 2 leading-edge protuberances. Four modified blades, with sinusoidal leading-edges of various amplitudes and wavelengths, were compared to a fifth baseline design. At lower thrust conditions, the baseline and modified blades had similar power requirements. However, as thrust increased, the modified blades required additional power compared to the baseline; this power increase was directly related to protuberance amplitude, while wavelength had a minimal effect. The baseline and low amplitude blades produced similar flow fields: a concentrated tip vortex and a less turbulent wake sheet. Conversely, the higher amplitude blades produced a significantly more turbulent wake sheet and less coherent tip vortices that dissipated quickly. The higher amplitude blades created more uniform (and more ideal) inflow across the rotor disk, but the generation of vortices along these blades most likely contributed to their greater power requirements.

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In this research, we explore a novel approach to measuring the susceptibility of smartphone unlock authentication to shoulder surfing attacks. We have created a series of video recordings where researchers enter authentication sequences into mobile devices (e.g. PINs, graphical patterns with lines, and graphical patterns without lines) in a controlled setting. These videos are designed to simulate shoulder surfing settings under varied attack conditions. Camera angles have been selected to mimic the locations where observational attacks may take place. Participants have taken the survey and played the role of attackers, viewing video-recorded footage of PIN and graphical pattern authentication input with various camera angles, hand positions, phone sizes, and authentication length and strength. In this study, we recruited 94 midshipmen participants as well as 1164 more respondents via Amazon Mechanical Turk, an online service to recruit survey participants. Based on the collected data, for example, measurements of the success rate of an attack and the recording methodology developed, we provide insight into the factors of mobile unlock authentication which best and least resist shoulder surfing attacks, as well as examine scenarios where weaknesses may occur. There are significant differences in success rates between the different authentication types. For PINs with a single view, the average success rate is 23.04%. The pattern with lines authentication has more than triple the success rate with a single view at 72.44%. The goal of this research is to identify more effective guidance for mobile device users to avoid observational attacks. We also aim to advance the methodologies used to measure the shoulder surfing attack surfaces where baselines of comparisons to preexisting systems (e.g. PINs and patterns) are not standardized. Utilizing the methodology and recordings, other researchers may build upon this approach to analyze future systems and replicate our results.

FACULTY ADVISOR
Assistant Professor Adam J. Aviv
Computer Science Department

External Collaborator
Associate Professor Ravi Kubar
Information Science Department, University of Maryland - Baltimore County

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Ethan W. Doherty
Midshipman First Class
United States Navy

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Proteins are biopolymers that perform a myriad of functions in living cells. These functions are determined by each protein’s three-dimensional structure. Current knowledge of protein folding principles provides a partial understanding of the thermodynamic factors that drive protein structure, folding, and stability, sufficient to allow proteins to be treated as templates for design and engineering. This project used protein engineering to explore protein structure and folding mediated by interactions with metal ions. As a proof of principle, experiments were undertaken that aimed to re-engineer staphylococcal nuclease to contain a metal ion-dependent switch that exhibits a loss of structure in the absence of a specific metal ion but recovers its native fold in the presence of that ion. Spectroscopic methods were used to monitor structural changes between the metal-free and the metal-bound protein. Changes in the protein’s amino acid sequence were introduced systematically to create nickel (II) binding sites based on a naturally occurring high-affinity nickel site. The site was comprised of four amino acid side chains that coordinated the metal ion. Several iterations of candidate proteins, each containing a putative nickel binding site comprised of 2-4 residues, and of reference proteins lacking this site were designed, produced, and characterized spectroscopically. From each of the protein iterations, information was obtained about the refolding process, including the effects of steric constraints, protein oligomerization, and protein thermodynamics. Proteins with fewer substitutions were more effective at maintaining their structure due to a reduced thermodynamic penalty.

FACULTY ADVISORS
Professor Jamie L. Schlessman
Chemistry Department

Associate Professor Carl E. Mungan
Physics Department

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Ψ  Christopher L. Panuski
Midshipman First Class
United States Navy

Development of a Mechanically Mediated RF-to-Optical Transducer

Detection and transmission of weak radio-frequency (RF) signals poses a significant challenge for modern electronic systems, in which lossy copper wires and thermal noise can corrupt sensitive information. Conversion, or “transduction” of these signals into the optical domain, however, enables enhanced detection sensitivity as well as long distance, low-loss transmission in optical fibers. Mechanically mediated transduction architectures, which rely upon the coupling of electronic and optical signals to a common mechanical oscillator, have sparked recent research interest for this application due to their ability to efficiently couple signals of drastically different frequencies. Recent advances in photonic integrated circuits (PICs), which enable the manufacture of complex optical circuits, have demonstrated the potential to integrate mechanical resonators into optical designs, and therefore serve as an ideal platform for transducer development.

Here, extending upon previous work on sensitive optomechanical interactions, we explore a novel, fully integrated technique for RF-to-optical transduction. In the proposed system, an RF signal displaces a coupled mechanical resonator placed within the evanescent field of an optical waveguide. This resulting displacement subsequently induces an optical phase shift due to the resonator’s proximity to the underlying optical waveguide. Placing this “phase shifter” within an interferometer enables sensitive optical phase detection, thus completing the conversion from an RF to an optical signal. To quantify the expected device performance, a theoretical model was developed and evaluated based upon the results of computational finite element simulations. A complete fabrication cycle was then conducted at the Naval Research Laboratory’s Nanoscience Institute, which yielded devices for experimental verification of these conclusions and enabled a proof-of-concept implementation of the proposed architecture. This research thus provides a complete theoretical, computational, and experimental characterization of a novel scheme for RF-to-optical transduction which may have future applications for enhanced sensing and for fundamental research into coherent quantum state transfer.

FACULTY ADVISORS
Associate Professor R. Brian Jenkins
Electrical and Computer Engineering Department

Associate Professor Deborah M. Mechtel
Electrical and Computer Engineering Department

Associate Professor Carl E. Mungan
Physics Department

Professor Nicholas J. Frigo
Physics Department

External Collaborator
Dr. Marcel Pruessner
Naval Research Laboratory

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Experiments involving heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) produce the hottest matter known to humans, approximately 100,000 times hotter than the center of the Sun or 7 trillion degrees Celsius. In these collisions, the nucleons melt into their constituent quarks and gluons for approximately 10 yoctoseconds (1E-23 seconds). As the collision system expands and cools, the quarks and gluons combine into particles via a process called “hadronization” and subsequently stream out into the detectors. Detailed studies of these produced particles can yield information about the properties of the medium in which they were produced. Some of the produced particles, known collectively as “resonances,” have lifetimes comparable to the lifetime of the collision medium itself. More specifically, comparative studies of the relative production of short-lived resonances and possible modifications of their properties by medium effects may provide information about the conditions present in and lifetime of the collision medium.

In this project, we utilize data from 24.4 million collisions of copper nuclei at center-of-mass energies of 200 GeV per nucleon pair collected by the Solenoidal Tracker At RHIC (STAR) detector to reconstruct decays of the doubly-charged Delta baryon resonance and its anti-particle. Fits to the invariant mass distribution of Delta candidates are performed as functions of transverse momentum and collision centrality and properties of the Delta resonances are extracted statistically. Specifically we look at the mass, the width, and the yield of this resonance. Comparisons of our results with previous studies from proton on proton collisions and deuteron on gold nucleus collisions, as well as with model calculations, may provide deeper insight into effects present in the collision medium as well as the lifetime of the medium itself.

FACULTY ADVISOR
Associate Professor Richard A. Witt
Physics Department

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James P. Talisse
Midshipman First Class
United States Navy

Algebraic Structure of Dynamical Systems

A dynamical system is a mathematical object which describes the motion of a set of points over time. Dynamical systems can be used to study differential equations, cryptography, computer science, and even biology. Viewed as a purely mathematical object, one can ask questions about the behavior of the dynamical system based on the structure of algebraic objects associated with it. In this project we study two algebraic objects, centralizers and topological full groups, associated to symbolic dynamical systems. The centralizer group tells us about the symmetries a system possesses. Results relating to the centralizer historically have indicated that the more complex the dynamical system is, captured by the Topological Entropy, the more structure its centralizer has. Similarly, low complexity systems have been shown to have very simple centralizers. This seems to suggest that one can recover information about the dynamical system based upon its centralizer group. In particular, if a system is known to have a certain centralizer group, we might want to draw conclusions about the complexity of the system. In this project we present a class of high complexity systems which have a very rigid centralizer, which shows the relationship is more subtle than may have been originally thought.

We also study the topological full group of a dynamical system. This group completely defines the system up to time reversal. We apply numerical estimates to draw conclusions about the algebraic properties of this group. In particular, we seek to know when the topological full group of a dynamical system is amenable. Amenability is an algebraic property that can be thought of as having a probability measure on G. This measure would answer the question: given a subset A of G, what is the probability that a random element of G is in A? We apply Grigorchuk’s amenability criterion to answer this question.

Both these results provide us with information about the algebraic structure of dynamical systems. If we know certain information about the different groups associated with a dynamical system, we can make conclusions about the system itself. As such, questions about dynamical systems can now become questions about algebra, and vice versa. These results mostly reveal the structure of symbolic dynamical systems and address the fundamental question of mathematics about what is possible. However, our construction of a positive entropy system with trivial centralizer can be interpreted as the existence of an information channel with positive capacity that cannot be encrypted with substitution ciphers.

FACULTY ADVISOR
Assistant Professor Kostya Medynets
Mathematics Department

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Thomas J. Wilson
Midshipman First Class
United States Navy

Modeling the Effects of Meteorological Conditions on the Neutron Flux

The neutron background at sea level is seen to vary by as much as 20% within a 24 hour period. These short term variations are primarily driven by environmental factors. Radiation sensors detect a signal in a noisy background, so the variation of the background must be understood for sensors to be effective. Neutron sensors are used in the search for transported materials that can be used to make a nuclear weapon. The purpose of this project was to develop a statistical model that predicts environmental neutron background as a function of five meteorological variables: inverse barometric pressure, temperature, local humidity, precipitation, and cloud cover. Neutron data were collected using moderated 3He neutron detection systems located in Annapolis, MD. Data collected using a large neutron sensor in Annapolis show the neutron background varying from 13,000 counts per hour to 9,000 counts per hour, a 20% variation, over five months of data collection with large variation between days. Meteorological data were collected with two commercially available weather stations in Annapolis, MD along with sensors installed at a nearby airport. Synchronization of the weather and neutron data was an important part of this study and dictated the time interval that could be chosen for the modeling process. Linear autoregression was used to estimate the effects of the meteorological variables on neutron flux while accounting for the correlation among errors at previous time intervals. The dominant variable of the model was inverse barometric pressure with a contribution an order of magnitude larger than any other variable’s contribution. The resulting model can predict neutron background with errors of a predictable magnitude. This approach to background correction provides an independent means of normalizing neutron sensor data to a constant background level, whereas traditional means of background correction rely on recent count history - with no assurance that recent changes observed are based on background alone. When implemented, this approach will support optimal performance of alarm algorithms, improved sensor effectiveness, and higher likelihood of interdicting the illicit trafficking of Special Nuclear Material out of regulatory control.

FACULTY ADVISORS
Professor Svetlana Avramov-Zamurovic
Weapons and Systems Engineering Department

Assistant Professor Marshall G. Millett
Mechanical Engineering Department

VADM Charles J. Leidig, USN (Ret.)
Corbin A. McNeill Chair of Engineering

Professor Martin E. Nelson (Emeritus)
Mechanical Engineering Department

LT Kayla J. Barron
Superintendent's Office

Assistant Professor Douglas N. VanDerwerken
Mathematics Department