Events

ECE Doctor of Philosophy Dissertation Defense By: Bentolhoda Jafary

Topic: Reliability and Maintenance Modeling of Systems Subject to Positive and Negatively Correlated Component Failure Location: Lester W. Cory Conference Room, Science & Engineering Building (SENG), Room 213A ABSTRACT: Modern society increasingly depends on engineered systems in diverse fields such as defense, communication, and healthcare. Both the reliability and maintainability of these systems is therefore paramount. Past research had developed models to identify optimal periodic maintenance policies such as those that minimize cost or maximize availability. However, these maintenance policies may be suboptimal when the components of a system are subject to correlated or dependent failure. Moreover, the vast majority of past research on correlated and dependent failure is focused on positive correlation and dependence, yet negative correlation and dependence are also important to the design of resilient systems. To address these limitations, this dissertation makes several modeling and methodological contributions in the context of a variety of system and software reliability and maintenance contexts, including binary state systems, consecutive k-out-of-n: failed systems composed of multi-state components, and a software computation subject to checkpointing operations. Primary contribution include: (i) models and methods to quantify the impact of correlated failures on maintenance models in order to identify optimal maintenance intervals despite correlated failures and (ii) efficient methods to obtain algebraic expressions with explicit correlation parameters as well as exact numerical methods for the reliability of systems composed of non-identical components and arbitrary combinations of nonidentical positive and negative correlations between the failures of the components. NOTE: All ECE Graduate Students are ENCOURAGED to attend. All interested parties are invited to attend. Open to the public. Advisor: Dr. Lance Fiondella Committee Members: Dr. Hong Liu and Dr. Liudong Xing, Department of Electrical & Computer Engineering, UMass Dartmouth; Dr. Donghui Yan, Department of Mathematics, UMass Dartmouth; Dr. Mark White, NASA Jet Propulsion Laboratory *For further information, please contact Dr. Lance Fiondella at 508.999.8596, or via email at lfiondella@umassd.edu.

ECE Master of Science Thesis Defense By: Nicholas J. Vincelette

Topic: Doppler Properties of Acoustic Scattering from Ocean-Like Surfaces Location: Lester W. Cory Conference Room, Science & Engineering Building (SENG), Room 213A Abstract: In SONAR systems and underwater acoustic communications, acoustic signals that propagate in the ocean are scattered in different directions, when they encounter the air-water interface. Since the ocean surface is a dynamic boundary, the scattering process is time dependent and will result in the signal spectrum experiencing Doppler broadening. The focus of this research is on the scattering of longitudinal waves from ocean-like surfaces. Since the air-water interface is a soft boundary, the scattering of transverse waves, also known as shear waves, may be ignored. For the purpose of clarity, this study will focus on one-dimensional ocean-like surfaces. The study will investigate the effect of long surfaces waves (>> acoustic wavelength) on acoustic scattering. The study will also investigate the impact of acoustic wave frequency on the scattering process. By modeling the scattering from dynamic ocean-like surfaces that have varying harmonics and time-dependent phase, one is able to investigate the Doppler properties of the scattered signal, which is critical in many sonar and acoustic communication applications. Coherence times of the scattered signals, which is used as a measure of Doppler broadening, are estimated for different ocean surface conditions. The project’s ultimate goal is to incorporate these factors in a rigorous study of the Doppler spectral properties of the scattered waves. NOTE: All ECE Graduate Students are ENCOURAGED to attend. All interested parties are invited to attend. Open to the public. Advisor: Dr. Dayalan P. Kasilingam Committee Members: Dr. David A. Brown and Dr. Paul J. Gendron, Department of Electrical & Computer Engineering, UMASS Dartmouth and Dr. Raymond N. Laoulache, College of Engineering, UMASS Dartmouth *For further information, please contact Dr. Dayalan P. Kasilingam at 508.999.8534, or via email at dkasilingam@umassd.edu.

Department of Fisheries Oceanography-PhD Dissertation Defense-Sean Lucey

The School for Marine Science and Technology Department of Fisheries Oceanography PhD Dissertation Defense "Improving the Ecosystem Modeling Toolbox with an Open Source Mass Balance Model" by Sean Lucey Advisor: Steven Cadrin, SMAST, University of Massachusetts Dartmouth Committee: Gavin Fay, SMAST, University of Massachusetts Dartmouth Sarah Gaichas, Northeast Fisheries Science Center Michael Fogarty, Northeast Fisheries Science Center Monday, August 26, 2019 10:00 am SMAST East, Rooms 101/102 836 S. Rodney French Blvd, New Bedford Abstract: Ecosystem-based Fisheries Management (EBFM) is a holistic, place-based approach to managing living marine resources. In order for it to be successful we need to improve our understanding of species interactions and other ecosystem processes. One way that can be achieved is through the use of ecosystem models. Ecosystem models are a mathematical representation of the complex and sometimes chaotic living world. Ecosystem models encompasses a wide range of approaches to understanding that world. One useful suite of models are known as mass balance models. Mass balance models describe the flow of energy through the system and are adapt at identifying direct and indirect impacts of management decision on the system. This approach has been popularized by the software package Ecopath with Ecosim. In the Northeast United States there have been numerous studies using the Ecopath with Ecosim software, the most notable being the Energy Analysis and Modeling eXercise (EMAX) conducted by the Northeast Fisheries Science Center. While this package has many strengths, it is also very difficult for practitioners to customize without help from the developers and can suffer from a lack of reproducibility. Here I describe an open source alternative version of the mass balance algorithms called Rpath. Rpath is written using a combination of R and C++ with the majority of the code readily accessible to be modified by practitioners. The new package is further expanded to serve as an operating model in a closed-loop management strategy evaluation process. As part of this functionality, the model can be paused after each time step to evaluate an external model which then modifies the Rpath model parameters before the original model resumes. The closed-loop simulation is demonstrated on the EMAX version of Georges Bank, a region of the Northeast US Continental Shelf Large Marine Ecosystem that has distinct physical and oceanographic properties that make it ideally suited for place-based management. The EMAX version of Georges Bank is too aggregated to be useful for management. Therefore a more disaggregated version was developed that also includes better resolution of fishing fleets, making the model much more useful in a management context. This new version will be available for future management strategy evaluation processes utilizing the capabilities of Rpath, thus improving the ecosystem modeling toolbox. For additional information, please contact Sue Silva at s1silva@umassd.edu.

ECE Master of Science Thesis Defense By: Matthew D. Tidwell

Topic: Designing Linear FM Active Sonar Waveforms for Continuous Line Source Transducers to Maximize The Fisher Information at a Desired Bearing Location: Lester W. Cory Conference Room, Science & Engineering Building (SENG), Room 213A ABSTRACT: Several authors previously found that echolocating animals aim their sonar beam to place the target of interest slightly off the main beam axis. Analysis found the animals' beam aiming strategy maximized the Fisher Information (FI) about the target bearing encoded in the frequency spectrum of the received echoes by the transmitter's frequency dependent beampatterns. This thesis reverses the focus from analysis to synthesis. We present design methods to maximize the FI of the bearing estimate at a desired angle using linear frequency modulated (LFM) waveforms transmitted by a continuous line source (CLS) transducer. If the bandwidth of the transmitted chirp is sufficiently small relative to the center frequency, the angle maximizing the bearing FI is solely determined by the center frequency. The center frequency is shown to place a null in the transducer's beampattern at the target's angular location or, equivalently, the target's angular location places a null in the received echo at the corresponding center frequency. This maximizes the waveform's relative variation resulting in favorable auto-correlation properties. Increasing bandwidth increases robustness to target bearing mismatch at the cost of decreased precision at the target's true angular location. NOTE: All ECE Graduate Students are ENCOURAGED to attend. All interested parties are invited to attend. Open to the public. Advsior: Dr. John R. Buck Committee Members: Dr. Dayalan P. Kasilingam, Department of Electrical & Computer Engineering, UMASS Dartmouth and Dr. Mary H. Johnson, Naval Undersea Warfare Center *For further information, please contact Dr. John R. Buck at 508.999.9237, or via email at jbuck@umassd.edu.

Department of Estuarine and Ocean Sciences-MS Thesis Defense-Kathryn Tremblay

The School for Marine Science and Technology Department of Estuarine and Ocean Sciences MS Thesis Defense "Hypoxia and Upselling on the Northern New Jersey Coast" by Kathryn Noel Tremblay Advisor Wendell Brown SMAST, University of Massachusetts Dartmouth Committee James Bisagni, SMAST, University of Massachusetts Dartmouth Josh Kohut, Rugers University Steven Lentz, Woods Hole Oceanographic Institution Wednesday, August 28, 2019 10:30 am SMAST East, Rooms 101/102 836 S. Rodney French Blvd, New Bedford Abstract: Historical evidence shows that areas of hypoxia are co-located with upwelling events along the New Jersey (NJ) coast during summer. These events, which tend to occur near bathymetric highs within 30 km of the coast, are known to be forced by sustained northward winds that drive the Ekman transport of coastal waters seaward. The observed hypoxia is a condition in which dissolved oxygen levels have dropped below 5.0 mg/L based on criteria set by New Jersey Water Quality Standards. Since 2011, Slocum glider AUVs (autonomous underwater vehicle) have been used to measure the dissolved oxygen (DO) and other water properties along the NJ coast during summer. Here we use the September 2013 glider RU28 data, buoy-winds, satellite sea surface temperatures (SST), and high frequency (HF) radar-derived surface currents to assess the potential for upwelling and hypoxia along the northern New Jersey coast. The sub-surface measurements from the glider, which zig-zagged along most of the NJ coast, measured the lowest temperature and dissolved oxygen in our northern study region. We find that a sustained northward wind during September is accompanied by surface ocean temperature decreases indicating upwelling. Water mass analysis suggests that that near-by Mid Atlantic Bight Cold Pool water mass is just offshore in deeper water and mixing within the area of upwelling and hypoxia. For additional information, please contact Sue Silva at s1silva@umassd.edu

Department of Estuarine and Ocean Sciences-PhD Proposal Defense by Alan Austin

The School for Marine Science and Technology Department of Estuarine and Ocean Sciences PhD Proposal Defense "Linkage between tidal exchange and water quality in a temperate (Pleasant Bay, Massachusetts, USA) and sub-tropical (Cananéia, São Paulo, Brazil) estuary." by Alan Austin Advisors: Brian Howes, SMAST Miles Sundermeyer, SMAST Marcelo Dottori, University of São Paulo Committee: John Ramsey, Applied Coastal Tuesday, September 3, 2019 2:00 pm SMAST West, Room 204 706 S. Rodney French Blvd, New Bedford Abstract: Better understanding of water quality dynamics in relation to estuarine circulation can help solve issues related to eutrophication, navigational practices and sea level rise. This dissertation will identify circulation features and water quality dynamics within the Pleasant Bay estuary in Cape Cod, Massachusetts, USA, and the Cananéia estuarine system in São Paulo, Brazil. The goal of this research is to quantify circulation and water quality changes within Pleasant Bay in connection with major inlet configurations and cross-compare features between it and Cananéia, a sub-tropical lagoonal estuary in Brazil. Questions addressed in this research include: 1. What are the circulation patterns within Pleasant Bay and what role do they play in the water quality observations? 2. How much does the tidal circulation and flushing rate within Pleasant Bay vary as the inlet opening locations change over time and what are the associated changes in water quality? 3. What are the current circulation features within Cananéia in both the dry and wet seasons and how do they relate to seasonal differences in water quality within the estuary? To answer the above questions, hydrodynamic and water quality data will be collected in both systems, and a numerical model constructed to understand how water quality and circulation features within the two estuaries depend on their respective natural and anthropogenic environmental forcing conditions. The calibration and validation of both models will rely on the field measurements as well as historical data. For additional information, please contact Sue Silva at s1silva@umassd.edu.