Trident Scholar Abstracts 2013

Matthew Paul Christian
Midshipman First Class
United States Navy

Numerical Model for Predicting and Managing Heat Dissipation from a Neural Probe

Stimulating neural probes are used in an effort to better understand neural pathways.  Current designs with light as a stimulating impulse externally couple the light into the probe.  Relocating the light source to the probe tip would improve the flexibility of the technique; however, this approach would generate heat within the embedded probe.  Minor temperature excursions can easily damage tissues under study, creating inaccurate results and/or damaging the tissue.  A model has been created using COMSOL for the thermal effects of these heated probes in the brain. The model includes blood perfusion and metabolic processes.  The model was used to investigate the effect of different geometric parameters on the temperature excursion as well as the effect of injecting saline solution through the probe to determine if active cooling is a feasible concept in the context of microneural probes.  It was observed that the maximum temperature change decreases with insertion depth and decreases as the heated area of the probe is increased.  The model was also used to study the effect of extending the probe beyond the heated region.  This resulted in a significant reduction in temperature excursion. The model has been experimentally validated through physical tests using an Agar gel as a neural tissue simulant.

In this research, fiber Bragg grating (FBG) optical temperature sensors are used for structural health monitoring of composite materials. The specific goal is to detect the thermal response of a composite to high energy radiation incident on the surface of a composite structure. The unique optical characteristics of FBG sensors permit rapid detection of highly localized temperature gradients in a host structure, making FBGs well-suited for this application.

However, since the FBG sensors respond to axial strain in the optical fiber, any structural strain experienced by the composite is also detected. Thus the embedded FBG sensors respond to the mechanical strain in addition to any thermal effects. Consequently, this research has focused both on identifying the unique characteristics of each response and on developing feasible methods to isolate the thermal response from the strain response. This ensures that any response to mechanical strain does not mask the response to a temperature gradient present on the composite surface. The test specimen built for this work is a three-dimensional array of FBG temperature sensors embedded in a carbon/epoxy composite structure.

There are two techniques used to isolate the thermal and strain responses in this research. First, the embedded three-dimensional FBG array is an architectural strategy that incorporates both in-plane and through-thickness sensor arrays. This architectural component exploits the spatial differences between the temperature profile and the strain profile in a composite structure. Second, an accompanying signal processing scheme is used to interpret and identify each response. Both techniques will be presented, and the degree to which this strategy increases the functionality of FBG temperature sensors in mechanically strained composite structures will be assessed. Finally, opportunities for continued research in this topic area will be discussed.

In the western North Pacific Ocean, tropical cyclone (TC) hazards, including strong winds, storm surge, high waves, and heavy rainfall threaten archipelagos, densely crowded coastlines, and naval forces ashore and afloat. To accurately forecast TC track, intensity, and radii of 34-, 50-, and 64-kt winds out to 120 hours, meteorologists at the Joint Typhoon Warning Center (JTWC) must start from a thorough understanding of the TC’s current structure. To accomplish this mission, they rely heavily upon satellite observations, particularly measurements in the water vapor (WV) and infrared (IR) channels on geostationary satellites. Unlike their counterparts in the Atlantic basin, however, JTWC forecasters do not have an aircraft reconnaissance program to take in-situ measurements of TCs. Therefore, it is critical to develop products that identify key TC structures in geostationary satellite data and track them over time, as these data are often the only real-time information available to the forecasters.

This project examined satellite brightness temperatures in the WV and IR channels in typhoon-strength TCs during the 2012 season to first identify the eye, eyewall, and deep convection, and then to investigate the evolution of those features over time. The eye radius, which fluctuates as the tropical cyclone undergoes internal cycles, including eyewall replacement, was defined in this study as the location of the steepest gradient in two satellite products: (1) IR brightness temperatures, and (2) the difference in brightness temperatures between WV and IR channels. The eyewall, which contains the strongest winds and deepest convective clouds, was defined in this study as the location of the radial minimum IR brightness temperatures, indicating the tallest and coldest clouds, as well as the location of the radial maximum WV-IR brightness temperature differences, indicating the location of deepest convection. The TC intensity was found to be moderately negatively correlated with infrared brightness temperatures, and moderately positively correlated with WV-IR brightness temperature differences, especially during challenging-to-predict periods of intensification or decay. In addition to the eye and eyewall radii, outward propagating convective waves were identified in both WV and IR data. These waves had similar phase speed and wavelength as those found by other recent studies to be relevant to dynamical processes that control the tropical cyclone, offering another potentially useful tool to identify and predict TC structural changes.

FACULTY ADVISORS
CDR Elizabeth R. Sanabia, USN (PMP)
Assistant Professor Bradford S. Barrett
Oceanography Department

EXTERNAL COLLABORATORS
Jeffrey D. Hawkins, Naval Research Laboratory, Monterey, CA
Christopher S. Velden, Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin-Madison

Christopher Dean Galvin
Midshipman First Class
United States Navy

Unmanned vehicles have established an important place in the modern battlefield. They play a key role in intelligence and surveillance while not putting human lives in harm’s way. The United States Navy recognizes this, has created The Navy Unmanned Surface Vessel (USV) Master Plan, which lists autonomous launch and recovery (L&R) as a key challenge.
A necessary enabling technology is the ability to automatically identify L&R sites from sensor data. This project focuses on the identification of suitable docking sites from three dimensional LiDAR scans. A LiDAR, or Light Detection and Ranging, sensor is a sensor that collects range images from a rotating array of vertically aligned lasers.
Our solution leverages open source C++ code from Point Cloud Library—“a standalone, large scale, open project for 2D/3D image and point cloud processing.” Given a LiDAR point cloud our identification algorithm proceeds as follows. First the RANSAC algorithm is used to isolate horizontal planar surfaces that may belong to the dock. Then using all the points that are not part of the planar surface, Euclidean Cluster Recognition is used to isolate clusters that could be potential vertical pilings. Bayes’ Theorem is used to compute the probability that each cluster matches the characteristics of piling. For each candidate piling, the origin of that cluster is compared to the location of the target dock’s planar surface. The dock can be identified by the relation of the pilings location to the dock’s planar surface. The final output of the algorithm will be a sub-set of points, isolated from the original cloud, that are hypothesized to correspond to the dock.

FACULTY ADVISOR
Associate Professor Joel M. Esposito
Weapons and Systems Engineering Department

  
Jennifer Lynn Jones
Midshipman First Class
United States Navy

An Evaluation of the Corrosion and Mechanical Performance of Interstitially Surface Hardened Stainless Steel

A surface hardening technique called “interstitial hardening” has been developed to introduce interstitial carbon atoms into stainless steel surfaces without the formation of carbides. Surface hardening of machine elements such as impellors or fasteners would improve performance regarding cavitation and galling resistance, and has intensified interest in this process.
The interstitial hardening technique involves an activation step where the protective oxide film is removed from the surface in order to allow appreciable diffusion of the interstitial atom into the material at temperatures below which precipitate phases will form. Commercial processes have been developed to do this using halogen gases or plasma. However, there remains a need to characterize and validate the specific performance characteristics of the hardened materials. The stability of the hardened surface and the reproducibility of the process on various substrates need to be verified. In particular, the process parameters for which the corrosion resistance of the stainless steel is retained, rather than degraded, is of particular interest for marine applications.
This project incorporated experimental testing conducted on 316L stainless steel that has been surface hardened using available commercial techniques, using both carbon and nitrogen as the interstitial atom. The hardness and thickness of the surface hardened layer is characterized and compared using metallography and microhardness profiling. The corrosion performance of the hardened surface is assessed using electrochemical potentiodynamic testing to determine the pitting potential in 3.5 wt. % NaCl solution. Corrosion fatigue and slow strain rate testing of untreated, hardened and damaged, hardened surfaces exposed to ASTM seawater is conducted. Finally, critical galling stresses are determined and compared. Post-test examination of damage attempts to identify mechanisms of material failure and characterize how corrosion-assisted cracks initiate and grow in surface-hardened materials.

FACULTY ADVISORS
Associate Professor Michelle G. Koul
Associate Professor Joel J. Schubbe
Mechanical Engineering Department

College graduates in the United States tend to have significantly higher earnings and higher labor participation rates than their counterparts with only high school degrees. Yet despite the rising importance of college education, there is growing concern that many college entrants are unprepared to succeed in undergraduate studies, contributing to higher drop-out rates and weaker performance among students pursuing bachelor’s degrees. One approach in addressing this problem has been to select certain students into pre-college programs to give them a better chance to succeed in college. This paper examines the returns to participation in pre-college remedial education after controlling for intrinsic student ability.
We used a large cross-sectional dataset of students from the graduating classes of 1988 – 2011 from the U.S. Naval Academy, categorizing students into those who have attended a pre-college program such as the Naval Academy Prep School, a foundation school, or another college prior to the Naval Academy, and those entering directly from high school. Using a combination of propensity score matching and regression discontinuity to mitigate selection bias, we determine the empirical relationships between assignment to a post-secondary education program and future success in college.
Results show that pre-college programs have positive returns to graduation rates across the board. However, in terms of course grades, results indicate that the cohort of prep school students perform better than their direct entry counterparts only in their first semester. This is followed by no returns, and in some cases negative returns, to the prep school programs in subsequent semesters when considering a range of outcome variables. Moreover, the cohort that attends pre-college programs tends to graduate with a significantly lower overall class rank. This study provides insights into how pre-college programs can be reshaped to enhance the future performance of their participants.

FACULTY ADVISORS
Associate Professor Ahmed Rahman
Associate Professor Katherine A. Smith
Economics Department

  
Nicholas Robert LaSalle
Midshipman First Class
United States Navy

Study of Passive Flow Control of Ship Air Wakes

Helicopter flight operations on naval vessels are limited to specific flight envelopes to ensure the safety of the pilot and aircraft. These flight envelopes are developed based upon helicopter operating capabilities and the impact of air wakes on the aircraft. Since Naval Academy training vessels, known as YPs, have similar superstructure and deck configurations as a modern cruiser or destroyer, comparisons can be made between YP air wakes and those of larger naval surface ships. A dedicated YP has been modified with a flight deck and hanger structure to create an air wake similar to that of a modern destroyer.
This project examines the effects of passive flow control techniques aimed at reducing the impact of ship air wakes on naval rotary wing aircraft flight operations. Passive flow control techniques such as fences and deflectors around the hanger face and flight deck could potentially alter air wake flow structures and help control the severity of the ship air wake. For this investigation, notched fences have been placed along the top and sides of the hanger face, angled aft at 30 degrees to vertical, and along the starboard flight deck, angled out board.
Air wake data is collected in-situ onboard YP 676, from a 4% scale wind tunnel ship model, and from computational fluid dynamics (CFD) simulations. In-situ measurements are compared with wind tunnel and CFD results to validate the accuracy of the simulations and to quantify any alterations in the air wake and its associated flow structures. Data collected from this investigation should provide a method for investigating how to decrease the impact of air wakes on rotary wing aircraft.

FACULTY ADVISORS
CAPT Murray R. Snyder, USN (Ret.)
Dr. Hyung S. Kang
Aerospace Engineering Department

The ability to accurately combine energy from multiple low power beams on a specific target is critical to making directed energy weapons effective and practical. At the United States Naval Academy Directed Energy Research Center, a project is underway to develop a three beam combining system that employs fast steering mirrors (FSMs) for pointing and jitter control of individual beams. In the previous work, an adaptive H-infinity optimal controller has been developed to control a single beam using a beam position detector for feedback.
This project will apply the H-infinity adaptive controller to the multiple-beam combining system in a multiple-input, multiple-output feedback control environment. Instead of using a position detector, a high-speed video camera will be employed to provide centroid estimation and feedback for pointing control algorithms.

FACULTY ADVISORS
CAPT R. Joseph Watkins, USN (PMP)
Mechanical Engineering Department

Professor Richard T. O'Brien, Jr.
Weapons and Systems Engineering Department

Associate Professor Tae W. Lim
Aerospace Engineering Department

  
Peter Albert Roemer
Midshipman First Class
United States Navy

Stochastic Modeling of the Persistence of HIV: Early Population Dynamics

Mathematical modeling of biological systems is crucial to effectively and efficiently developing treatments for medical conditions that plague humanity. Systems of differential equations are the traditional tools used to theoretically describe the spread of disease within the body. In this project we consider the dynamics of the Human Immunodeficiency Virus (HIV) in vivo during the initial stages of infection.
Both mathematical and biological results support the idea that contact with the HIV retrovirus does not automatically imply permanent infection. Given factors such as the CD4+ T-cell growth rate, infection rate, and viral clearance rate, it is possible to correctly predict the end viral state in a deterministic model. While this is useful, such a model lacks the randomness inherent in physical processes and parameter estimation. To account for this, our project examines both discrete and continuous stochastic models for the early stages of HIV infection. These models are crafted using the knowledge of biological interactions and fundamental mathematical principles.
We also examine the well-known three-component deterministic model in greater detail, proving existence and uniqueness of the solutions. Furthermore, we prove that solutions remain biologically meaningful, i.e., are positivity preserving, and perform a thorough stability analysis for the equilibrium states of the system. Finally, we develop two new stochastic models and obtain extensive numerical results to measure the probability of infection given the transmission of the virus to a new individual. To simulate the dynamics of the virus, we employ a number of computational methods for ordinary and stochastic differential equations, including Runge-Kutta methods and the Euler-Maruyama scheme.

FACULTY ADVISORS
Assistant Professor Mrinal Raghupathi
Assistant Professor Stephen D. Pankavich
Mathematics Department

  
Andrew Jeffrey Rydalch
Midshipman First Class
United States Navy

Andrew Christopher Tresansky
Midshipman First Class
United States Navy

High Energy Lasers (HEL) are being developed as potential Directed Energy Weapons for the U.S. Navy. In order to best employ this technology, the effect of these HELs on materials needs to be understood. There have been extensive studies on the effects of lasers on materials, as well as the modeling of these effects but this research focuses on the irradiance and wavelength regime of current interest to the U.S. Navy.

Using material property inputs determined using Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR) a physics-based computer model was developed using COMSOL. The model is used to predict the temperature field, heat affected zone and through thickness drilling that HEL irradiation causes in polymer and composite materials.

Since laser heating causes ablation, material removal had to be included in the model. Material removal in the model was accomplished by actuating the material properties of ablated nodes to make them behave as if they had been removed. This was done by using Heaviside functions to actuate the material property functions over experimentally determined ablation temperature ranges. Material removal is usually accomplished by remeshing after each time step and removing ablated nodes, which creates complex topographies and is computationally expensive.

The model was validated by experiments in the USNA Directed Energy Research Center An easy to model polymer, PMMA, and more complicated carbon fiber composite were irradiated with an IPG Photonics fiber coupled laser. Front face, rear face, and internal temperatures were recorded and the burn rate was measured. The model predictions were compared to the experimental data and a sensitivity analysis was conducted on the model. The model was then iterated to higher accuracy by improving the mesh density, material properties and model geometry. Moving forward, this model could be expanded to incorporate multi-physics to more fully describe the effects of HEL on materials as well as on structures yielding predictions with even greater accuracy.

FACULTY ADVISORS
Associate Professor Peter J. Joyce
Associate Professor Joshua J. Radice
CAPT R. Joseph Watkins, USN (PMP)
Mechanical Engineering Department

EXTERNAL COLLABORATORS
Dr. Robert Cozzens, Naval Research Laboratory
Dr. Christopher Lloyd, Naval Surface Warfare Center Dahlgren

Tidal turbines utilize the kinetic energy of water resulting from ocean tidal flows to generate power. This type of power generation is a potential source of clean, reliable renewable energy. However, the technology is still being developed. The effects of unsteady flow conditions, specifically surface waves, on tidal turbines have not been completely analyzed. This Trident project examines the effects of waves on the performance characteristics of a model horizontal axis tidal turbine selected by the Department of Energy and designed by the National Renewable Energy Laboratory (NREL).

The performance characteristics of a 1/25th scale model horizontal axis tidal turbine were tested under unsteady flow conditions. The experiments were conducted in the large tow tank facility at the United States Naval Academy Hydromechanics Laboratory. Parameters including wave height, wave length and tow speed for the experiment were scaled to properly model flow conditions that a horizontal axis tidal turbine was expected to experience at a full scale. Two different experiments were conducted. First, turbine rotational speed, torque and thrust were measured for unsteady flow conditions characterized by a range of incoming waves. Wave types were varied to represent different flow conditions. Turbine performance characteristics, including thrust and power coefficients, were obtained as functions of rotor tip speed ratio for the unsteady flow conditions tested. Power generation was also presented as a function of wave phase. All measurements were taken at a 700 Hz sampling rate as the waves passed over the turbine. The data were used to analyze the effects of waves on turbine performance. The second experiment involved a detailed fluid flow survey in the near wake of the turbine for one of the waves utilized in the first experiment. Fluid flow was measured using Acoustic Doppler Velocimeters sampling at 200 Hz. The results of this experiment provided a characterization of velocity fields in the near wake of the turbine, necessary information for the placement of multiple turbines in a larger array. The results of this project have potential for application in the civilian sector and U.S. Navy power generation.

FACULTY ADVISORS
Assistant Professor Luksa Luznik
Professor Karen A. Flack
Mechanical Engineering Department