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Title: Model-based global assessment of ocean thermal energy conversion (OTEC) power potential.
Creator: Rauchenstein, Lindy, Hanson, Howard P., VanZwieten, James H., Dhanak, Manhar R., Graduate College
Date Issued: 2011-04-08
PURL: http://purl.flvc.org/fcla/dt/3170913
Subject Headings: Ocean thermal power plants, Solar energy, Continental margins
Format: Document (PDF)

Title: Design and testing of an untethered vertically ascending profiler for use in measuring near-surface turbulence.
Creator: Bogin, Jeffrey Isaac., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: The Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum...
Show moreThe Vertically Ascending Micro-scale Profiler, or VAMP, has been designed, constructed, and tested to be used in conjunction with FAU's Turbulence Package in order to collect vertical turbulence profiles close to the free surface. Unique to VAMP is that it has been specifically designed as an untethered ascending profiler. Examination of turbulence data collected using VAMP shows that the measured shear spectrum and the turbulent kinetic energy dissipation closely matches the Nasmyth Spectrum. Data processing techniques made it possible to filter out motion generated by surface wave action, which allowed VAMP to collect data at depths as shallow as the troughs of the surface waves. VAMP can be launched, deployed several times, and recovered all within a thirty minute time frame by a crew of four.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/13020
Subject Headings: Turbulence--Measurement, Surface waves (Oceanography)
Format: Document (PDF)

Title: Experimental Investigation of Skin Friction Drag Reduction on a Flat Plate using Microbubbles.
Creator: Grabe, Zachary A., Dhanak, Manhar R., Florida Atlantic University
Abstract/Description: A microbubble generation system has been designed, constructed, and tested in a circulating water tunnel. A 1.0 m long flat plate was subjected to a flow where the Reynolds number ranged from ReL = 7.23x 10^5 - 1.04 x 10^6. Bubble diameters and skin friction measurements were studied at various airflow rates and water velocities. Bubbles were produced by forcing air through porous plates that were mounted flush with the bottom of the test plate. Once emitted through the plates, the bubbles...
Show moreA microbubble generation system has been designed, constructed, and tested in a circulating water tunnel. A 1.0 m long flat plate was subjected to a flow where the Reynolds number ranged from ReL = 7.23x 10^5 - 1.04 x 10^6. Bubble diameters and skin friction measurements were studied at various airflow rates and water velocities. Bubbles were produced by forcing air through porous plates that were mounted flush with the bottom of the test plate. Once emitted through the plates, the bubbles traveled downstream in the boundary layer. The airflow rate and water velocity were found to have the most significant impact on the size of the bubbles created. Skin friction drag measurements were recorded in detail in the velocity and airflow rate ranges. The coefficient of skin friction was determined and relationships were then established between this coefficient and the void ratio.
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Date Issued: 2007
PURL: http://purl.flvc.org/fau/fd/FA00012523
Subject Headings: Frictional resistance (Hydrodynamics), Drag (Aerodynamics), Skin friction (Aerodynamics), Fluid mechanics
Format: Document (PDF)

Title: An experimental investigation of the performance of a series of propellers for a human powered underwater vehicle.
Creator: Heeb, Karl Von., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: Designing a propeller for optimum performance on a human powered underwater vehicle presents a significant engineering challenge. The propeller must be highly efficient to utilize the inherently low power output of a human. Also, the propeller must be correctly matched to the maximum sustainable torque of the propulsor. This thesis experimentally investigates a minimum induced loss propeller design program and its application to a human powered underwater vehicle. The design program is based...
Show moreDesigning a propeller for optimum performance on a human powered underwater vehicle presents a significant engineering challenge. The propeller must be highly efficient to utilize the inherently low power output of a human. Also, the propeller must be correctly matched to the maximum sustainable torque of the propulsor. This thesis experimentally investigates a minimum induced loss propeller design program and its application to a human powered underwater vehicle. The design program is based on the vortex theory of propellers. The work includes experimental measurements of the velocity and rotational rate of three propellers designed with the minimum induced loss propeller design program. This positively verifies the output of the design algorithm. Also, the research, through the use of an underwater ergometer, determines the maximum power and torque sustainable by a human pedaling underwater. Final results of the research show that the design algorithm overestimates the blade section angles by 25% because the design program neglects the influence of the wake of the vehicle.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15078
Subject Headings: Propellers, Submersibles, Underwater propulsion
Format: Document (PDF)

Title: Subsurface flow generated by a steady wind stress applied at the water surface.
Creator: Gurfinkiel, Lionel., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: A turbulent water current induced by winds, through a friction force at the sea surface and subjected to the Coriolis force in shallow water was studied. A Large Eddy Simulation model developed by Zikanov et al. is used to solve the Navier-Stokes equations. To define the bottom boundary condition, a drag coefficient parameter, based on the ideas of Csanady, is used to evaluate the shear stress at the bottom. To find a suitable bottom boundary condition for this LES simulation, several cases...
Show moreA turbulent water current induced by winds, through a friction force at the sea surface and subjected to the Coriolis force in shallow water was studied. A Large Eddy Simulation model developed by Zikanov et al. is used to solve the Navier-Stokes equations. To define the bottom boundary condition, a drag coefficient parameter, based on the ideas of Csanady, is used to evaluate the shear stress at the bottom. To find a suitable bottom boundary condition for this LES simulation, several cases were considered with change in drag coefficient property. The effect of variation in the depth of the water column was also considered. Variation in surface deflection of the current, variation of the mass flux and distribution of eddy viscosity with depth of the water column are determined. The cases are compared with the case of a deep water column. Numerical results are also compared with field observations.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/13030
Subject Headings: Ocean-atmosphere interaction--Mathematical models, Turbulence, Wind waves--Mathematical models
Format: Document (PDF)

Title: Sound generated due to vortical flow past a forward facing step.
Creator: Gundlapalli, Ravishankar., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: The sound field associated with the motion of 2-dimensional finite core vortex past a forward facing step is obtained. A numerical scheme using Contour Dynamics technique and incompressible, inviscid equations of motion is developed to determine the evolution of the structure of the vortex, its path over the step and the radiated sound. An appropriate low-frequency Green's function is derived and the expression for the far field acoustic pressure as formulated by Mohring is used. The vortex...
Show moreThe sound field associated with the motion of 2-dimensional finite core vortex past a forward facing step is obtained. A numerical scheme using Contour Dynamics technique and incompressible, inviscid equations of motion is developed to determine the evolution of the structure of the vortex, its path over the step and the radiated sound. An appropriate low-frequency Green's function is derived and the expression for the far field acoustic pressure as formulated by Mohring is used. The vortex structure evolves in the non-uniform flow in the vicinity of the step and under certain conditions is found to undergo significant deformation of its core structure. The far field acoustic pressure is found to be a strong function of vortex motion in the vicinity of the step. Results for the vortex trajectory and the associated acoustic pressure are presented for a variety of flow parameters.
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Date Issued: 1992
PURL: http://purl.flvc.org/fau/fd/FADT14825
Subject Headings: Underwater acoustics, Vortex-motion, Eddies, Hydrodynamics
Format: Document (PDF)

Title: Thermocline tracking using an upgraded ocean explorer autonomous underwater vehicle.
Creator: Clabon, Mathieu., Florida Atlantic University, Dhanak, Manhar R.
Abstract/Description: This thesis addresses the problem of tracking a thermocline---a layer of water showing an intense vertical temperature gradient---with an Autonomous Underwater Vehicle (AUV). One of Florida Atlantic University's Ocean Explorer (OEX) AUV has been upgraded, as part of the work described here, by integration of a standard and convenient software interface, and used in several thermocline survey experiments aimed at gathering oceanographic data relevant to thermoclines. A tool that simulates the...
Show moreThis thesis addresses the problem of tracking a thermocline---a layer of water showing an intense vertical temperature gradient---with an Autonomous Underwater Vehicle (AUV). One of Florida Atlantic University's Ocean Explorer (OEX) AUV has been upgraded, as part of the work described here, by integration of a standard and convenient software interface, and used in several thermocline survey experiments aimed at gathering oceanographic data relevant to thermoclines. A tool that simulates the longitudinal motion of the OEX through a water slice, whose temperature map is read using a simulated temperature and depth sensor, has been developed. Using this tool and information from at-sea experiments, several control methods for the OEX to track a thermocline were analyzed. In particular, two different algorithms were implemented and tested by simulation. Overall, two control algorithms have been validated, and it will soon be possible to provide the AUV with a thermocline tracking capability.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/13025
Subject Headings: Thermoclines (Oceanography), Oceanographic submersibles--Computer simulation, Underwater navigation
Format: Document (PDF)

Title: Simulations and feedback control of nonlinear coupled electromechanical oscillators for energy conversion applications.
Creator: Psarrou, Dimitrios., Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This thesis discusses the coupling of a mechanical and electrical oscillator, an arrangement that is often encountered in mechatronics actuators and sensors. The dynamics of this coupled system is mathematically modeled and a low pass equivalent model is presented. Numerical simulations are then performed, for various input signals to characterize the nonlinear relationship between the electrical current and the displacement of the mass. Lastly a framework is proposed to estimate the mass...
Show moreThis thesis discusses the coupling of a mechanical and electrical oscillator, an arrangement that is often encountered in mechatronics actuators and sensors. The dynamics of this coupled system is mathematically modeled and a low pass equivalent model is presented. Numerical simulations are then performed, for various input signals to characterize the nonlinear relationship between the electrical current and the displacement of the mass. Lastly a framework is proposed to estimate the mass position without the use of a position sensor, enabling the sensorless control of the coupled system and additionally providing the ability for the system to act as an actuator or a sensor. This is of value for health monitoring, diagnostics and prognostics, actuation and power transfer of a number of interconnected machines that have more than one electrical system, driving corresponding mechanical subsystems while being driven by the same voltage source and at the same time being spectrally separated and independent.
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Date Issued: 2011
PURL: http://purl.flvc.org/FAU/3320109
Subject Headings: Renewable energy sources, Mechatronics, Nonlinear theories, Oscillators, System analysis
Format: Document (PDF)

Title: Automated Launch and Recovery of an Autonomous Underwater Vehicle from an Unmanned Surface Vessel.
Creator: Sarda, Edoardo I, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Research on collaboration among unmanned platforms is essential to improve the applications for autonomous missions, by expanding the working environment of the robotic systems, and reducing the risks and the costs associated with conducting manned operations. This research is devoted to enable the collaboration between an Unmanned Surface Vehicle (USV) and an Autonomous Underwater Vehicle (AUV), by allowing the first one to launch and recover the second one. The objective of this...
Show moreResearch on collaboration among unmanned platforms is essential to improve the applications for autonomous missions, by expanding the working environment of the robotic systems, and reducing the risks and the costs associated with conducting manned operations. This research is devoted to enable the collaboration between an Unmanned Surface Vehicle (USV) and an Autonomous Underwater Vehicle (AUV), by allowing the first one to launch and recover the second one. The objective of this dissertation is to identify possible methods to launch and recover a REMUS 100 AUV from a WAM-V 16 USV, thus developing this capability by designing and implementing a launch and recovery system (LARS). To meet this objective, a series of preliminary experiments was first performed to identify two distinct methods to launch and recover the AUV: mobile and semi-stationary. Both methods have been simulated using the Orcaflex software. Subsequently, the necessary control systems to create the mandatory USV autonomy for the purpose of launch and recovery were developed. Specifically, a series of low-level controllers were designed and implemented to enable two autonomous maneuvers on the USV: station-keeping and speed & heading control. In addition, a level of intelligence to autonomously identify the optimal operating conditions within the vehicles' working environment, was derived and integrated on the USV. Lastly, a LARS was designed and implemented on the vehicles to perform the operation following the proposed methodology. The LARS and all subsystems developed for this research were extensively tested through sea-trials. The methodology for launch and recovery, the design of the LARS and the experimental findings are reported in this document.
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Date Issued: 2016
PURL: http://purl.flvc.org/fau/fd/FA00004631, http://purl.flvc.org/fau/fd/FA00004631
Subject Headings: Underwater acoustic telemetry., Fuzzy systems., Nonlinear control theory., Adaptive signal processing., Oceanographic submersibles--Automatic control., Submersibles--Control systems.
Format: Document (PDF)

Title: Analysis of Turbulence Observed in the Florida Current using an ADCP.
Creator: Denton, John E., Dhanak, Manhar, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The observation of turbulence in the Florida Current is presented with the use of velocity measurements collected with an Acoustic Doppler Current Profiler (ADCP). The research is conducted through application of the theories of Taylor and Kolmogorov and related derivations, and processing tools of MATLAB software to this Eulerian observation of flow [1]. The velocity profile of the Florida Current is deduced in terms of its turbulent character with shear, acceleration, gradient, Reynolds...
Show moreThe observation of turbulence in the Florida Current is presented with the use of velocity measurements collected with an Acoustic Doppler Current Profiler (ADCP). The research is conducted through application of the theories of Taylor and Kolmogorov and related derivations, and processing tools of MATLAB software to this Eulerian observation of flow [1]. The velocity profile of the Florida Current is deduced in terms of its turbulent character with shear, acceleration, gradient, Reynolds Number, Reynolds Stress, Welch power spectrum density of current velocity, wavenumbers of Taylor’s hypothesis and Kolmogorov, wavenumber spectrum, eddy diameters, diapycnal diffusivity, and the Richardson Number. Processing methods are validated with results of other research conducted in the Florida Current with the use of a Multi-Scale Profiler, and an Advanced Microstructure Profiler for determination of shear, dissipation, diffusivity, and estimates of turbulent eddy diameters based on Taylor’s Hypothesis [1][4]. A spectral analysis is developed and is compared with Kolmogorov’s -5/3-Law. The process and the results of the analysis are described.
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Date Issued: 2018
PURL: http://purl.flvc.org/fau/fd/FA00013173
Subject Headings: Florida Current, Turbulence--Measurement, Underwater acoustics--Data processing, Doppler effect
Format: Document (PDF)

Title: A Low-Level USV Controller Incorporating an Environmental Disturbance Observer.
Creator: Diddams, Michael Albert, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Modeling, system identification and controller design for a 16’ catamaran is described with the objective of enhanced operation in the presence of environmental disturbances including wind, waves and current. The vehicle is fully-actuated in surge, sway and yaw degrees of freedom. Analytical and experimental system identification is carried out to create a numerical model of the vehicle. A composite system of a Multiinput multi-output Proportional-Derivative (PD) controller and a nonlinear...
Show moreModeling, system identification and controller design for a 16’ catamaran is described with the objective of enhanced operation in the presence of environmental disturbances including wind, waves and current. The vehicle is fully-actuated in surge, sway and yaw degrees of freedom. Analytical and experimental system identification is carried out to create a numerical model of the vehicle. A composite system of a Multiinput multi-output Proportional-Derivative (PD) controller and a nonlinear disturbance observer is used for station-keeping and transiting modes of operation. A waypoint transiting algorithm is developed to output heading and cross-track error from vehicle position and waypoints. A control allocation method is designed to lower azimuthing frequency and incorporate angle saturation and rate limits. Validation is achieved with improvement in simulation with the addition of the nonlinear observer.
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Date Issued: 2018
PURL: http://purl.flvc.org/fau/fd/FA00013022
Subject Headings: Unmanned surface vehicles, Environmental disturbances, Catamarans--Design and construction
Format: Document (PDF)

Title: Characterization of Internal Wave Activity in the Straits of Florida.
Creator: Tarantul Soto, Andrew, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The Gulf Stream current in the Straits is typically dominated by a strong northerly current, associated shear, and eddies. The water column also includes a prominent thermocline and periodically features internal waves centered on the upper or lower edges of the thermocline. Despite numerous previous related studies, there is limited available field data on internal waves in the Straits of Florida. Here, study and analysis of velocity, temperature and conductivity data acquired in the Straits...
Show moreThe Gulf Stream current in the Straits is typically dominated by a strong northerly current, associated shear, and eddies. The water column also includes a prominent thermocline and periodically features internal waves centered on the upper or lower edges of the thermocline. Despite numerous previous related studies, there is limited available field data on internal waves in the Straits of Florida. Here, study and analysis of velocity, temperature and conductivity data acquired in the Straits over a period of time are described, in support of identifying presence of internal waves in the flow. A systematic procedure is employed in modifying the universal Garrett- Munk spectrum for internal waves in the open ocean for application to flow in the Straits of Florida. Using this process, identified internal waves are characterized and related velocity fluctuations in the time series are isolated to facilitate consideration of their correlations with simultaneously observed magnetic fields.
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Date Issued: 2017
PURL: http://purl.flvc.org/fau/fd/FA00005946
Subject Headings: Dissertations, Academic -- Florida Atlantic University, Florida, Straits of, Gulf Stream (Fla.), Internal waves.
Format: Document (PDF)

Title: Empirical Analysis of the Dissipated Acoustic Energy in Wave Breaking.
Creator: Francke, Kristina, Dhanak, Manhar, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: In this research an attempt is made at explaining the physical processes behind energy dissipation during wave breaking, through spectral analysis of the resulting sound. The size of an air bubble can be directly linked to the frequency of the sound that is heard using the simple harmonic solution to the Rayleigh–Plesset equation. It indicates the inverse relationship between frequency and bubble size. And this relationship has been used to identify wave breaking in general [MANASSEH 2006]....
Show moreIn this research an attempt is made at explaining the physical processes behind energy dissipation during wave breaking, through spectral analysis of the resulting sound. The size of an air bubble can be directly linked to the frequency of the sound that is heard using the simple harmonic solution to the Rayleigh–Plesset equation. It indicates the inverse relationship between frequency and bubble size. And this relationship has been used to identify wave breaking in general [MANASSEH 2006]. Now this research goes a step farther and looks at how the frequency spectrum of the sound changes with time, in an effort to understand the general pattern and from that to deduce an empirical equation that describes the breaking down of turbulence during a wave breaking event. Two main processes have been identified, with the second process having three main indicators that are necessary to evidence wave breaking. The first process is a near instantaneous shattering of the initial air bubble into much smaller metastable bubbles of a size that appears to be common for all waves independent of wave height. Then in the second process, the bubbles continue to break down following a recognisable pattern.
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Date Issued: 2020
PURL: http://purl.flvc.org/fau/fd/FA00013504
Subject Headings: Waves, Energy dissipation, Spectral analysis, Fluid dynamics, Acoustic energy
Format: Document (PDF)

Title: Electromagnetic field emissions from underwater power cables.
Creator: DiBiasio, Christopher, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This study is performed as a partial aid to a larger study that aims to determine if electromagnetic fields produced by underwater power cables have any effect on marine species. In this study, a new numerical method for calculating magnetic fields around subsea power cables is presented and tested. The numerical method is derived from electromagnetic theory, and the program, Matlab, is implemented in order to run the simulations. The Matlab code is validated by performing a series of tests...
Show moreThis study is performed as a partial aid to a larger study that aims to determine if electromagnetic fields produced by underwater power cables have any effect on marine species. In this study, a new numerical method for calculating magnetic fields around subsea power cables is presented and tested. The numerical method is derived from electromagnetic theory, and the program, Matlab, is implemented in order to run the simulations. The Matlab code is validated by performing a series of tests in which the theoretical code is compared with other previously validated magnetic field solvers. Three main tests are carried out; two of these tests are physical and involve the use of a magnetometer, and the third is numerical and compares the code with another numerical model known as Ansys. The data produced by the Matlab code remains consistent with the measured values from both the magnetometer and the Ansys program; thus, the code is considered valid. The validated Matlab code can then be implemented into other parts of the study in order to plot the magnetic field around a specific power cable.
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Date Issued: 2014
PURL: http://purl.flvc.org/fau/fd/FA00004277, http://purl.flvc.org/fau/fd/FA00004277
Subject Headings: DIstributed generation of electric power, Electromagnetic interference, Electromagnetic theory, Ocean energy resources -- Environmental aspects
Format: Document (PDF)

Title: Flow Control Through Geometric Modifications to Improve Airfoil/Hydrofoil Performance.
Creator: Ni, Zao, Dhanak, Manhar, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Geometric modification as the most effective passive flow control method has recently received wide attention due to its enormous potential in enhancing performance characteristics of airfoils or hydrofoils without expensive manufacturing and maintenance cost. Two primary passive flow control modifications, known as leading-edge tubercles and internal slots and their applications in airfoils/hydrofoils have been investigated in this dissertation. For the hydrofoil, since free surface effects...
Show moreGeometric modification as the most effective passive flow control method has recently received wide attention due to its enormous potential in enhancing performance characteristics of airfoils or hydrofoils without expensive manufacturing and maintenance cost. Two primary passive flow control modifications, known as leading-edge tubercles and internal slots and their applications in airfoils/hydrofoils have been investigated in this dissertation. For the hydrofoil, since free surface effects cannot be neglected, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil has been studied as well. In the theoretical approach aspect, an empirically-based model based on an iteration scheme has been proposed for predicting the lift coefficients of twisted airfoils with leading-edge tubercles by using experimental data for untwisted airfoils. With both numerical and experimental investigations, this dissertation has discussed the application of a custom optimized-design internal slot on a NACA 634-021 airfoil blade to allow ventilation of flow through the slot from the pressure side to the suction side of the blade, in support of delaying flow separation, and stall. The combined effect of an internal slot in an airfoil and transverse leading-edge tubercles on its performance has been further studied both numerically and experimentally. Moreover, performance of a NACA 634-021 hydrofoil in motion under and in close proximity of a free surface for a large range of AoAs has been studied. Lift and drag coefficients of the hydrofoil at different submergence depths are investigated both numerically and experimentally. The results of the numerical study are in good agreement with the experimental results. The agreement confirms the new finding that for a submerged hydrofoil operating at high AoAs close to a free surface, the interaction between the hydrofoil-motion induced waves on the free surface and the hydrofoil results in mitigation of the flow separation characteristics on the suction side of the foil and delay in stall, and improvement in hydrofoil performance. A similarly submerged hydrofoil with a custom-designed internal slot has further been studied. The performance characteristics of the slotted hydrofoil in the presence of the free surface are investigated both numerically and experimentally.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013248
Subject Headings: Hydrofoils, Aerofoils, Performance, Flow control
Format: Document (PDF)

Title: A Deep Learning Approach To Target Recognition In Side-Scan Sonar Imagery.
Creator: Einsidler, Dylan, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Automatic target recognition capabilities in autonomous underwater vehicles has been a daunting task, largely due to the noisy nature of sonar imagery and due to the lack of publicly available sonar data. Machine learning techniques have made great strides in tackling this feat, although not much research has been done regarding deep learning techniques for side-scan sonar imagery. Here, a state-of-the-art deep learning object detection method is adapted for side-scan sonar imagery, with...
Show moreAutomatic target recognition capabilities in autonomous underwater vehicles has been a daunting task, largely due to the noisy nature of sonar imagery and due to the lack of publicly available sonar data. Machine learning techniques have made great strides in tackling this feat, although not much research has been done regarding deep learning techniques for side-scan sonar imagery. Here, a state-of-the-art deep learning object detection method is adapted for side-scan sonar imagery, with results supporting a simple yet robust method to detect objects/anomalies along the seabed. A systematic procedure was employed in transfer learning a pre-trained convolutional neural network in order to learn the pixel-intensity based features of seafloor anomalies in sonar images. Using this process, newly trained convolutional neural network models were produced using relatively small training datasets and tested to show reasonably accurate anomaly detection and classification with little to no false alarms.
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Date Issued: 2018
PURL: http://purl.flvc.org/fau/fd/FA00013025
Subject Headings: Deep learning, Sidescan sonar, Underwater vision
Format: Document (PDF)

Title: GENERATIVE ADVERSARIAL NETWORK DATA GENERATION FOR THE USE OF REAL TIME IMAGE DETECTION IN SIDE-SCAN SONAR IMAGERY.
Creator: McGinley, James Patrick, Dhanak, Manhar, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: Automatic target recognition of unexploded ordnances in side scan sonar imagery has been a struggling task, due to the lack of publicly available side-scan sonar data. Real time image detection and classification algorithms have been implemented to combat this task, however, machine learning algorithms require a substantial amount of training data to properly detect specific targets. Transfer learning methods are used to replace the need of large datasets, by using a pre trained network on...
Show moreAutomatic target recognition of unexploded ordnances in side scan sonar imagery has been a struggling task, due to the lack of publicly available side-scan sonar data. Real time image detection and classification algorithms have been implemented to combat this task, however, machine learning algorithms require a substantial amount of training data to properly detect specific targets. Transfer learning methods are used to replace the need of large datasets, by using a pre trained network on the side-scan sonar images. In the present study the implementation of a generative adversarial network is used to generate meaningful sonar imagery from a small dataset. The generated images are then added to the existing dataset to train an image detection and classification algorithm. The study looks to demonstrate that generative images can be used to aid in detecting objects of interest in side-scan sonar imagery.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013394
Subject Headings: Sidescan sonar, Algorithms, Machine learning
Format: Document (PDF)

Title: HYDRODYNAMIC PERFORMANCE OF AN UNMANNED CATAMARAN VEHICLE IN HEAD SEAS.
Creator: Prasad, Bijoy, Dhanak, Manhar, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: This study analyzes the hydrodynamic performance of an advanced catamaran vehicle using computational fluid dynamics (CFD) simulations and experimental testing data in support of system identification and development of a physics-based control system for unmanned surface vehicle (USV) operations in coastal waters. A series of steps based on increasing complexity are considered sequentially in this study. First the steady flow past the static vehicle, then the vehicle with a fixed orientation...
Show moreThis study analyzes the hydrodynamic performance of an advanced catamaran vehicle using computational fluid dynamics (CFD) simulations and experimental testing data in support of system identification and development of a physics-based control system for unmanned surface vehicle (USV) operations in coastal waters. A series of steps based on increasing complexity are considered sequentially in this study. First the steady flow past the static vehicle, then the vehicle with a fixed orientation advancing in calm water, and finally the vehicle moving with two degrees of freedom (DOF) in calm water as well as head seas. The main objective of the study is to assess the role of general multiphase unsteady Reynolds Averaged Navier Stokes (RANS) as a predictive tool for the hydrodynamic performance of an USV. A parametric analysis of the vehicle performance at different Froude number and wave steepness in shallow waters is conducted. The characteristics of the wave resistance, heaving and pitching motion, wave-hull interactions, and free surface flow patterns are investigated. The study will aid in the design of a robust physics-based control system for the vehicle and provide a tool for prediction of its performance.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013404
Subject Headings: Catamarans, Computational fluid dynamics, Water waves
Format: Document (PDF)

Title: Tidal Power Arrays and the Coriolis Force with Array Design Considerations.
Creator: Miglietta, Victoria, Dhanak, Manhar, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: Tidal currents are a renewable energy resource and the work presented is in the field of harnessing tidal currents for electrical power generation. The main objective of the research is to provide information on rotational flow effects, caused by the spinning of the earth, around obstacles on the sea floor, in support of developing robust design of an underwater turbine array. This research looks at a gravity based linear array, a single turbine deep, with its largest dimension several...
Show moreTidal currents are a renewable energy resource and the work presented is in the field of harnessing tidal currents for electrical power generation. The main objective of the research is to provide information on rotational flow effects, caused by the spinning of the earth, around obstacles on the sea floor, in support of developing robust design of an underwater turbine array. This research looks at a gravity based linear array, a single turbine deep, with its largest dimension several kilometers long. The primary goal is to model a Taylor column above a linear array. The Taylor column has closed streamlines or stagnant flows inside of it and the flows around the column accelerate asymmetrically. The layout design of the array is intended to minimize the effect of the stagnant flows by predicting the location where closed streamlines could develop. The design is for the array and not for a turbine. Also, the locations where the energetic flows through the array have the longest periods are identified. Numerical modeling with ANSYS Fluent failed repeatedly to accurately model rotational effects around an obstacle with a minimal relative current so as to form a Taylor column. Instead, Johnson’s (1982) analytical solutions for quasigeostrophic flows over elongated topography are used to study how the blocking parameter influences streamlines with changes in velocity typical of a tidal change. The streamlines illustrate the location over an array where the flows are accelerated and also where closed streamlines form.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013399
Subject Headings: Coriolis force, Tidal power, Renewable energy resources, Hydraulic turbines
Format: Document (PDF)

Title: caHydrodynamic analysis of flapping foils for the propulsion of near surface under water vehicles using the panel method.
Creator: Bustos, Julia, Ananthakrishnan, Palaniswamy, Dhanak, Manhar R., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the...
Show moreThis thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the case of a deeply submerged hydrofoil followed by the case where it is located in shallow water depth or near the free surface. In the second case, the presence of the free surface and wave effects are taken into account, specifically at high and low frequencies and small and large amplitudes of flapping. The objective is to determine the thrust and efficiency of the flapping –foils under the influence of added effects of the free surface. Results show that the free-surface can significantly affect the foil performance by increasing the efficiency particularly at high Frequencies.
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Date Issued: 2015
PURL: http://purl.flvc.org/fau/fd/FA00004351, http://purl.flvc.org/fau/fd/FA00004351
Subject Headings: Aerodynamics -- Mathematical models, Fluid mechanics, Naval architecture, Ships -- Aerodynamics, Steering gear
Format: Document (PDF)

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