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Title: Influence of Voids on Water Uptake in Polymer Panels.
Creator: Abdelmola, Fatmaelzahraa, Carlsson, Leif A., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The influence of voids on the moisture uptake of epoxy has been studied. Specimens with void contents from 0 to about 50% were prepared. Void geometry and content were analyzed using microscopy and density methods. Void containing dry samples were characterized by Differential Scanning Calorimetry and Dynamic-Mechanical Analysis which verified consistency of chemistry of the epoxy network. The moisture uptake of specimens immersed in distilled water at 40 °C was monitored. The rate of...
Show moreThe influence of voids on the moisture uptake of epoxy has been studied. Specimens with void contents from 0 to about 50% were prepared. Void geometry and content were analyzed using microscopy and density methods. Void containing dry samples were characterized by Differential Scanning Calorimetry and Dynamic-Mechanical Analysis which verified consistency of chemistry of the epoxy network. The moisture uptake of specimens immersed in distilled water at 40 °C was monitored. The rate of absorption and saturation moisture content increased with increasing void content. The moisture uptake of void-free and void containing specimens was non-Fickian. The Langmuir model provided good fits to the experimental results for specimens with low to medium void content, although the moisture uptake of the high void content specimens showed substantial deviations from the Langmuir diffusion model. The moisture diffusivity agreed reasonably with predications from the Maxwell inclusion model over a range of void contents from 0 to 50%. The state of sorbed water was examined using mass balance calculations and DSC analysis. Only 6-8% of the void volume is occupied by water at saturation. Absorbed water may be classified as free and bound water. For void-free specimens, only bound water was found. The medium and high void content specimens contained water in three states: free water, freezable bound water, and non-freezable bound water. The DSC results show that the proportions of free water and freezable bound water increase with increasing void content, while the content of non-freezable bound water decreased. Moisture induced swelling decreased with increasing void content. The swelling is attributed to the content of non-freezable bound water.
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Date Issued: 2018
PURL: http://purl.flvc.org/fau/fd/FA00013137
Subject Headings: Polymers--Absorption and adsorption, Epoxy resins, Water
Format: Document (PDF)

Title: Trim analysis by shooting and finite elements and Floquet eigenanalysis by QR and subspace iterations in helicopter dynamics.
Creator: Achar, Nagari Shriranga., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The trim analysis for the initial state and control inputs that satisfy response periodicity and flight conditions, and the Floquet eigenanalysis for a few largest eigenvalues of the Floquet transition matrix (FTM) are investigated. In the trim analysis, the convergence of Newton iteration is investigated in computing the periodic initial state and control inputs sequentially and in parallel. The trim analysis uses the shooting method and two h-versions of temporal finite element methods, one...
Show moreThe trim analysis for the initial state and control inputs that satisfy response periodicity and flight conditions, and the Floquet eigenanalysis for a few largest eigenvalues of the Floquet transition matrix (FTM) are investigated. In the trim analysis, the convergence of Newton iteration is investigated in computing the periodic initial state and control inputs sequentially and in parallel. The trim analysis uses the shooting method and two h-versions of temporal finite element methods, one based on displacement formulation and the other on mixed formulation of displacements and momenta. In each method, both the sequential and in-parallel schemes are used, and the resulting nonlinear equations are solved by damped Newton iteration with an optimally selected damping parameter. The reliability of damped Newton iteration, including earlier-observed divergence problems, is quantified by the maximum condition number of the Jacobian matrices of the iterative scheme. For illustrative purposes, rigid flap-lag and flap-lag-torsion models based on quasisteady aerodynamics are selected. Demanding trim analysis conditions are included by considering advance ratios or dimensionless flight speeds twice as high as those of current helicopters. Concerning the Floquet eigenanalysis, the feasibility of using the Arnoldi-Saad method, one of the emerging subspace iteration methods, is explored as an alternative to the currently used QR method, which is not economical for partial eigenanalysis. The reliability of the Arnoldi-Saad method is quantified by the eigenvalue condition numbers and the residual errors of the eigenpairs. In the three trim analysis methods, while the optimally selected damping parameter provides almost global convergence, the in-parallel scheme requires much less machine time than the conventional sequential scheme; both schemes have comparable reliability of the Newton iteration without and with damping. The Arnoldi-Saad method takes much less machine time than the QR method with comparable reliability.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12297
Subject Headings: Helicopters--Dynamics, Helicopters--Handling characteristics, Stability of helicopters--Mathematical models
Format: Document (PDF)

Title: Hybrid telemanipulation simulation for mission rehearsal and intervention.
Creator: Agba, Emmanuel I., Florida Atlantic University, Wong, Tin-Lup, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A "hybrid" telerobotic simulation system that is suitable for telemanipulation rehearsal, operator training, human factors study and operator performance evaluation has been developed. The simulator also has the capabilities for eventual upgrade for supervisory control. It is capable of operation in the conventional rate-control, master/slave control and a data driven preprogrammed mode of operation. It has teach/playback capability which allows an operator to generate joint commands for real...
Show moreA "hybrid" telerobotic simulation system that is suitable for telemanipulation rehearsal, operator training, human factors study and operator performance evaluation has been developed. The simulator also has the capabilities for eventual upgrade for supervisory control. It is capable of operation in the conventional rate-control, master/slave control and a data driven preprogrammed mode of operation. It has teach/playback capability which allows an operator to generate joint commands for real time teleoperation. For high-level task execution, the operator selects a specific task from a set of menu options and the simulator automatically generates the required joint commands. The simulator was developed using a three dimensional graphic model of an increasingly popular manipulator, TITAN 7F. A closed-form solution for inverse kinematics of the manipulator was found. Degeneracies from inverse kinematics solutions were observed to exist for certain arm configurations, although the manipulator can physically attain such configurations. An approach based on known facts about the manipulator geometry and physical constraints coupled with heuristics was used to generate physically attainable joint solutions from the inverse kinematics. The conditions that cause solution degeneracy were demonstrated to be related to singularity conditions. A novel object interaction detection strategy was implemented for more realistic telemanipulation. The object detection technique was developed based on the use of superellipsoid, which has a convenient inside-outside function for interference testing. The manipulator, with its end-effector and payloads, if any, were modeled as superquadric ellipsoids. A systematic way of determining transformation matrices between the superquadric manipulator links was developed. The interaction detection technique treats both moving and stationary objects in a consistent manner and has proved to be easy to implement and optimize for real-time applications. The feature has been applied for the simulation of pick-and-place operations and collision detection. It is also used to provide visual feedback as a low-cost force reflection and can be interfaced with a bilateral controller for force reflection simulation.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/12278
Subject Headings: Manipulators (Mechanism), Remote control, Vehicles, Remotely piloted, Remote submersibles
Format: Document (PDF)

Title: An experimental and analytical investigation of viscoelastic pipe-soil interaction.
Creator: Ahn, Woo-Suk., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: An overview of the current issues of HDPE pipe-soil systems is followed by a comprehensive literature review addressing current specifications, design methods, and relevant research projects. The following experimental tasks are described: (i) environmental stress cracking resistance (modified AASHTO M294), (ii) creep (10,000 hour parallel plate loading at super ambient temperatures), (iii) performance of buried pipes, subjected to live loading in a soil chamber, and (iv) field monitoring....
Show moreAn overview of the current issues of HDPE pipe-soil systems is followed by a comprehensive literature review addressing current specifications, design methods, and relevant research projects. The following experimental tasks are described: (i) environmental stress cracking resistance (modified AASHTO M294), (ii) creep (10,000 hour parallel plate loading at super ambient temperatures), (iii) performance of buried pipes, subjected to live loading in a soil chamber, and (iv) field monitoring. The findings include (i) satisfactory short-term environmental stress cracking resistance, (ii) temperature-dependency of the flexural modulus, (iii) the evidence of transition between slow crack growth and rapid crack propagation due to imperfect installation, and (iv) high load carrying capacity for the properly installed pipe in uniform backfill, showing an over-deflection failure mode with top flattening. The analytical investigations are as follows: (i) Bidirectional shift-constructed master curve, based on accelerated creep test values for long-term modulus prediction that showed good agreement with the Arrhenius equation-based analysis, (ii) Development of a seven-degree Voigt-Kelvin viscoelastic model based on the bidirectional shift-constructed master curve for analytical prediction of the long-term modulus, (iii) Comparison of two-dimensional and three-dimensional harmonic FEM analyses with the measured response of pipe-soil interaction, that demonstrated the analytical predictability of the pattern of deformation and stress distribution, and (iv) Determination of axial stress distribution along the pipe in non-uniform backfill condition, evaluated by approximate analysis based on finite differencing the deflection profile obtained from the assembly of individual finite segments/sections. This overcomes the limitation of the harmonic FEM analysis for pipe-soil interaction involving non-uniform soil conditions longitudinally and/or varying soil thickness circumferentially. The findings include (i) importance of axial stress contribution at failure, (ii) top flattening failure mode due to over-deflection preceding buckling or yielding, and (iii) critical adverse effect of the non-uniform backfill condition that can lead to joint opening, localized buckling, liner tearing/debonding, or cracking. The work has "spin off" applications to the coastal and offshore environments for sewage outfalls, marine pipelines etc.
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Date Issued: 1998
PURL: http://purl.flvc.org/fcla/dt/12550
Subject Headings: Soil-structure interaction, Pipe, Plastic--Testing, Underground pipelines
Format: Document (PDF)

Title: Fatigue modeling of composite ocean current turbine blade.
Creator: Akram, Mohammad Wasim, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and...
Show moreThe success of harnessing energy from ocean current will require a reliable structural design of turbine blade that is used for energy extraction. In this study we are particularly focusing on the fatigue life of a 3m length ocean current turbine blade. The blade consists of sandwich construction having polymeric foam as core, and carbon/epoxy as face sheet. Repetitive loads (Fatigue) on the blade have been formulated from the randomness of the ocean current associated with turbulence and also from velocity shear. These varying forces will cause a cyclic variation of bending and shear stresses subjecting to the blade to fatigue. Rainflow Counting algorithm has been used to count the number of cycles within a specific mean and amplitude that will act on the blade from random loading data. Finite Element code ANSYS has been used to develop an S-N diagram with a frequency of 1 Hz and loading ratio 0.1 Number of specific load cycles from Rainflow Counting in conjunction with S-N diagram from ANSYS has been utilized to calculate fatigue damage up to 30 years by Palmgren-Miner's linear hypothesis.
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Date Issued: 2010
PURL: http://purl.flvc.org/FAU/2867332
Subject Headings: Turbines, Blades, Materials, Fatigue, Marine turbines, Mathematical models, Structural dynamics, Composite materials, Mathematical models, Sandwich construction, Fatigue
Format: Document (PDF)

Title: Semi-Autonomous Control of Robotic Arm with Haptic Feedback and Closed Loop Force Controller.
Creator: Al-Saidi, Mostapha, Engeberg, Erik, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: This thesis presents the work done to deliver a robotic system that provides assistance to operators at nuclear waste cleaning facilities. The work done to deliver such system was focused on robotic control and tactile sensing abilities. Haptic feedback mechanism was also added to the system to convey information for the operator. First chapter of the thesis introduces the goals and objectives of this project as well as a detailed literature review on the subsystems used. Second chapter...
Show moreThis thesis presents the work done to deliver a robotic system that provides assistance to operators at nuclear waste cleaning facilities. The work done to deliver such system was focused on robotic control and tactile sensing abilities. Haptic feedback mechanism was also added to the system to convey information for the operator. First chapter of the thesis introduces the goals and objectives of this project as well as a detailed literature review on the subsystems used. Second chapter presents previous work done in the area of soft robotics. Such work proved important as the haptic feedback mechanism utilizes a soft robotic armband. Third chapter introduces phase one of the main project. This chapter justifies the use of the selected robots and introduces the concept of adding tactile abilities to the robotic hand used. Chapter four introduces phase two of the project that focused on improving phase one system via a new tactile sensor.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013353
Subject Headings: Robotics, Haptic devices, Actuators, Tactile sensors
Format: Document (PDF)

Title: Mechanical characterization of woven fabric composite materials.
Creator: Alif, Nidal M., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The mechanical behavior of woven fabric composites is presented in this study through modeling of the elastic properties and experimental studies on the failure behavior and fracture analysis. A two-dimensional laminate theory based elastic model for the prediction of the elastic constants of satin weave fabric composites is developed. The predicted elastic constants are compared with results from other models and correlated with the experimental data. An experimental study is presented on...
Show moreThe mechanical behavior of woven fabric composites is presented in this study through modeling of the elastic properties and experimental studies on the failure behavior and fracture analysis. A two-dimensional laminate theory based elastic model for the prediction of the elastic constants of satin weave fabric composites is developed. The predicted elastic constants are compared with results from other models and correlated with the experimental data. An experimental study is presented on mechanical response in tension, compression and shear and on damage development in tension of two woven fabric composite systems viz. carbon/epoxy and glass/epoxy. Damage inspection of the carbon/epoxy composite under tension revealed that the initial failure was cracking of pure matrix regions followed by transverse bundle cracking. Fill/warp debonding and longitudinal splits of the fill bundles occurred close to ultimate failure of the composite. The glass/epoxy composite displayed damage in the form of fill/warp debonding and longitudinal splits, but no transverse yarn cracking. Interlaminar fracture behavior of a five-harness satin orthogonal woven fabric carbon/epoxy composite laminate loaded in mode I, mode II and mixed mode has been investigated. Special emphasis was put on microscopic details of crack growth, and their relation to the fracture resistance. For all fracture mode combinations it was found that crack growth occurred in a nonplanar region of topology determined by the weave pattern and relative positioning of the plies adjacent to the crack plane. The woven fabric structure constrains fiber bridging, but partial debonding of transversely oriented fiber bundles led to occasional crack branching, stick-slip behavior leading to variations in the mode I fracture resistance. Slow stable crack growth occurred in the mode I and mode II fracture specimens prior to unstable fracture and resulted in nonlinear load-displacement response.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12481
Subject Headings: Composite materials--Mechanical properties, Textile fabrics--Mechanical properties, Elastic fabrics
Format: Document (PDF)

Title: Digital acoustic communications using decision directed learning.
Creator: Alleyne, Jochen Raoul, Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This document serves as a dissertation for the Doctor of Philosophy in Ocean Engineering degree at Florida Atlantic University's Department of Ocean Engineering. This dissertation documents the design, development, and performance analysis of an acoustic receiver system that incorporates a decision directed learning filter for acoustic multi-phase shift keying signals. The system makes use of advanced signal processing, inclusive of spatial diversity and decision directed learning techniques...
Show moreThis document serves as a dissertation for the Doctor of Philosophy in Ocean Engineering degree at Florida Atlantic University's Department of Ocean Engineering. This dissertation documents the design, development, and performance analysis of an acoustic receiver system that incorporates a decision directed learning filter for acoustic multi-phase shift keying signals. The system makes use of advanced signal processing, inclusive of spatial diversity and decision directed learning techniques in order to decode digital acoustic data. Error correcting techniques are also employed as well as methods of analyzing the efficiency of the system.
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Date Issued: 2001
PURL: http://purl.flvc.org/fcla/dt/11951
Subject Headings: Underwater acoustic telemetry, Digital communications, Acoustic filters
Format: Document (PDF)

Title: Flow visualization of the ventilated cavities generated by a surface piercing propeller.
Creator: Altamirano, Luis., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: In the present study, 3 wake parameters are semi-automatically measured in 63 composite-labeled images of a surface piercing propeller tested at yaw angles 0-30 degrees, pitch angles 0-15 degrees, propeller immersion ratios of 0.33 and 0.50 and scaled advance ratios 0.656-1.927. A fourth wake parameter is measured in four composite labeled images of yaw angles 0-30 degrees, pitch angle 0 degrees, immersion ratios of 0.33 and 0.50 and scaled advance ratios 1.363-1.927. Measurements are plotted...
Show moreIn the present study, 3 wake parameters are semi-automatically measured in 63 composite-labeled images of a surface piercing propeller tested at yaw angles 0-30 degrees, pitch angles 0-15 degrees, propeller immersion ratios of 0.33 and 0.50 and scaled advance ratios 0.656-1.927. A fourth wake parameter is measured in four composite labeled images of yaw angles 0-30 degrees, pitch angle 0 degrees, immersion ratios of 0.33 and 0.50 and scaled advance ratios 1.363-1.927. Measurements are plotted against propeller's angular position. Major findings include the behavior of wake parameters as the values of scaled advance ratio, yaw angle, pitch angle, and immersion ratio vary.
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Date Issued: 2010
PURL: http://purl.flvc.org/FAU/1927299
Subject Headings: Ships, Hydrodynamics, Ship propulsion
Format: Document (PDF)

Title: Nonlinear control of an unmanned amphibious vehicle.
Creator: Alvarez, Jose L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The DUCKW-Ling is an 8.3 foot long, amphibious water plane area twin hull (SWATH) concept vehicle which is propelled by a pair of crawler tracks on land and dual propellers when water-borne. In its operational zone, the vehicle's dynamics change dramatically as it transitions from being completely water-borne and buoyancy supported to being completely land-borne and track supported. In the water environment, a cascaded, first-order sliding mode controller was used to control the surge and...
Show moreThe DUCKW-Ling is an 8.3 foot long, amphibious water plane area twin hull (SWATH) concept vehicle which is propelled by a pair of crawler tracks on land and dual propellers when water-borne. In its operational zone, the vehicle's dynamics change dramatically as it transitions from being completely water-borne and buoyancy supported to being completely land-borne and track supported. In the water environment, a cascaded, first-order sliding mode controller was used to control the surge and heading of the vehicle, and was capable of having a faster response when compared to using a proportional controller. Additionally, field trials of the DUKW-Ling show the capability of the vehicle to navigate and track predetermined waypoints in both terrestrial and aquatic terrains. In the transitional zone, the electric motor current from the tracks was used as the feedback mechanism to adequately actuate the propellers and tracks in the system as the dynamics of the vehicle change.
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Date Issued: 2013
PURL: http://purl.flvc.org/fcla/dt/3362334
Subject Headings: Nonlinear control theory, Feedback control systems, Motor vehicles, Amphibious, Design and construction, Adaptive signal processing
Format: Document (PDF)

Title: Bulk diffusion of high performance concrete specimens exposed to different levels of sodium chloride and seawater.
Creator: Arias, Wendy J., Presuel-Moreno, Francisco, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The purpose of this study was to investigate the performance to chloride penetration of specimens made with three base compositions (three different supplementary cementitious materials) and water to cementitious ratios of 0.35, 0.41, or 0.47. The specimens were subjected to bulk diffusion test or full immersion. The mixes were exposed to 0.1 M, 0.6 M, or 2.8 M sodium chloride solution for different periods of time. Also, partially immersed specimens were exposed to indoor and outdoor...
Show moreThe purpose of this study was to investigate the performance to chloride penetration of specimens made with three base compositions (three different supplementary cementitious materials) and water to cementitious ratios of 0.35, 0.41, or 0.47. The specimens were subjected to bulk diffusion test or full immersion. The mixes were exposed to 0.1 M, 0.6 M, or 2.8 M sodium chloride solution for different periods of time. Also, partially immersed specimens were exposed to indoor and outdoor exposures (tidal, splash, barge). Chloride concentration profiles were obtained and the apparent diffusion coefficient was calculated. The skin effect was found only on some chloride profiles exposed to 0.1 M sodium chloride solution. The chloride binding capacity was calculated; specimens with 20% Fly Ash and 8% Silica Fume had the highest binding capacity (70.99%). The apparent diffusivity coefficient was found to be dependent on the curing regime as well as the water to cement ratio. The correlation between effective resistivity and apparent diffusion coefficient was determined.
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Date Issued: 2014
PURL: http://purl.flvc.org/fau/fd/FA00004076, http://purl.flvc.org/fau/fd/FA00004076
Subject Headings: Bulk solids flow, Concrete -- Corrosion, Concrete, Effect of salt on, Reinforced concrete -- Deterioration, Sustainable construction
Format: Document (PDF)

Title: Design and finite element analysis of an ocean current turbine blade.
Creator: Asseff, Nicholas S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A composite 3 meter ocean current turbine blade has been designed and analyzed using Blade Element Theory (BET) and commercial Finite Element Modeling (FEM) code, ANSYS. It has been observed that using the numerical BET tool created, power production up to 141 kW is possible from a 3 bladed rotor in an ocean current of 2.5 m/s with the proposed blade design. The blade is of sandwich construction with carbon fiber skin and high density foam core. It also contains two webs made of S2-glass for...
Show moreA composite 3 meter ocean current turbine blade has been designed and analyzed using Blade Element Theory (BET) and commercial Finite Element Modeling (FEM) code, ANSYS. It has been observed that using the numerical BET tool created, power production up to 141 kW is possible from a 3 bladed rotor in an ocean current of 2.5 m/s with the proposed blade design. The blade is of sandwich construction with carbon fiber skin and high density foam core. It also contains two webs made of S2-glass for added shear rigidity. Four design cases were analyzed, involving differences in hydrodynamic shape, material properties, and internal structure. Results from the linear static structural analysis revealed that the best design provides adequate stiffness and strength to produce the proposed power without any structural failure. An Eigenvalue Buckling analysis confirmed that the blade would not fail from buckling prior to overstressed laminate failure if the loading was to exceed the Safety Factor.
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Date Issued: 2009
PURL: http://purl.flvc.org/FAU/221944
Subject Headings: Marine turbines, Mathematical models, Fluid dynamics, Structural dynamics, Composite materials, Mathematical models
Format: Document (PDF)

Title: A numerical study of fuselage scattering effects on rotor noise.
Creator: Atalla, Noureddine., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This thesis considers the effect of scattering on the sound radiation from rotating sources. The study is carried out using a combined numerical implementation of ray acoustics and the paraxial ray approximation. A detailed description of the theoretical background to these methods is presented, along with a description of their numerical implementation. Application of the method to classical problems is considered to prove the accuracy and the power of the approach. Application of the method...
Show moreThis thesis considers the effect of scattering on the sound radiation from rotating sources. The study is carried out using a combined numerical implementation of ray acoustics and the paraxial ray approximation. A detailed description of the theoretical background to these methods is presented, along with a description of their numerical implementation. Application of the method to classical problems is considered to prove the accuracy and the power of the approach. Application of the method to some typical problems involving scattering of noise from propellers and rotors is presented. It is found that for impulsive acoustic signatures the scattering effects are important especially in the sideline direction from a helicopter fuselage. The effects of sharp edges on the steady loading noise from tilt-rotor configurations indicates that there is a new mechanism for generating impulsive acoustic signatures caused by scattering by sharp edges of the fuselage. The acoustic signatures generated by this mechanism can appear very similar to other types of impulsive source generated by aerodynamic interactions on the blade and therefore must be important. This type of source can be eliminated if the fuselage has rounded edges. Flow effects on scattering problems have also been considered. It was shown that the flow causes a modification and displacement of the lobes of the directivity pattern and the shadow zone, which can be important at Mach numbers greater than 0.2. The main conclusion of this thesis is that scattering effects cannot be ignored for highly directional rotating sources next to rigid scattering objects as is always the case for propellers and helicopters rotors.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/12276
Subject Headings: Sound-waves--Scattering, Rotors--Noise
Format: Document (PDF)

Title: Local buckling and debond propagation in sandwich columns and panels.
Creator: Aviles, Francis., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite...
Show moreThe local buckling failure mechanism and subsequent debond propagation in sandwich columns and panels with composite face sheets containing a face-to-core debond is experimentally, analytically, and numerically analyzed. The experimental investigation is based on a comprehensive test program to examine local buckling failure and fracture toughness of sandwich specimens consisting of glass/epoxy face sheets over various density PVC foams and a balsa wood core. Elastic foundation and finite element models are developed for prediction of the local buckling load of sandwich columns and panels containing an implanted debond at the face/core interface. Nonlinear finite element analysis was conducted to investigate debond propagation in the post-buckling region. Overall, model predictions were in agreement with experimental results. The buckling load was found to decrease with reduced face sheet stiffness, reduced core modulus, and increased debond length. Sandwich panels with circular debonds were more resistant to local buckling than those with square debonds of the same characteristic size. Circular debonds of 50 mm diameter and square debonds of 45 mm side length established the threshold for local buckling failure. Nonlinear finite element analysis of debonded sandwich columns and panels showed that the major crack displacement is opening (mode I). The tendency of the crack tip to first open and then close after buckling of the face sheet is believed to be due to the formation of an eccentric load path at the onset of buckling. The fracture mechanics analysis of debonded sandwich panels showed that the energy release rate is much higher in the direction perpendicular to the applied load than along the loading direction, and exceeds the measured toughness value in the transverse direction. This explains the experimental observation that a debond embedded in a sandwich panel tends to propagate in the transverse direction.
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Date Issued: 2005
PURL: http://purl.flvc.org/fau/fd/FADT12123
Subject Headings: Buckling (Mechanics), Sandwich construction, Fracture mechanics, Diffusion bonding (Metals), Strength of materials
Format: Document (PDF)

Title: Coating selection process for Gulf Stream hydroturbines.
Creator: Bak, Andrew Spicer., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The study addresses the coating selection for a proposed placement of a hydroturbine into the Gulf Stream. The turbine will generate energy in a similar manner to a wind turbine. The effects of biofouling and corrosion in the current project are assessed. A review of different types of traditional paint coatings is given, as well as the option for a copper-nickel alloy. Testing that should be undertaken for the coating selection is described in detail. Coating considerations are offered and...
Show moreThe study addresses the coating selection for a proposed placement of a hydroturbine into the Gulf Stream. The turbine will generate energy in a similar manner to a wind turbine. The effects of biofouling and corrosion in the current project are assessed. A review of different types of traditional paint coatings is given, as well as the option for a copper-nickel alloy. Testing that should be undertaken for the coating selection is described in detail. Coating considerations are offered and discussed. Design considerations and modifications are also offered.
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Date Issued: 2009
PURL: http://purl.flvc.org/FAU/368607
Subject Headings: Hydraulic turbines, Materials, Testing, Coatings, Thermal properties, Protective coatings
Format: Document (PDF)

Title: Initiation and propagation of corrosion in dry-cast reinforced concrete pipes.
Creator: Balasubramanian, Hariharan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This study investigates corrosion initiation and propagation in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. Potential, LPR and EIS measurements were carried out. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values, which suggest mass transfer limitations. So far these specimens show no visual signs of corrosion such as cracks or corrosion products with one exception; where corrosion products...
Show moreThis study investigates corrosion initiation and propagation in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. Potential, LPR and EIS measurements were carried out. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values, which suggest mass transfer limitations. So far these specimens show no visual signs of corrosion such as cracks or corrosion products with one exception; where corrosion products have reached the surface. Moreover, the apparent corrosion rate values obtained suggest high corrosion rate. No crack appearance so far, could be explained by the high porosity of the specimens; the corrosion products are filling these pores. It is speculated that although, there might be mass transfer limitations present, the current demanded by the anode is being balanced by a larger cathode area due to macrocell effects, since the high moisture conditions likely reduced the concrete resistivity and increased the throwing power.
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Date Issued: 2013
PURL: http://purl.flvc.org/fcla/dt/3362341
Subject Headings: Concrete, Deterioration, Tubular steel structures, Deterioration, Pipelines, Design and construction, Concrete construction, Corrosion and anti-corrosives
Format: Document (PDF)

Title: INITIATION AND PROPAGATION OF CORROSION IN DRY-CAST REINFORCED CONCRETE PIPES WITH ENVIRONMENTAL EFFECTS.
Creator: Balasubramanian, Hariharan, Presuel-Moreno, Francisco, Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This research was conducted to better understand the corrosion propagation stage on dry-cast reinforced concrete pipes (DCRCPs) while exposed to high moisture conditions and chlorides. Corrosion initiation and propagation were studied in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. All specimens were subjected to accelerated chloride transport by the application of an electric field. Corrosion of the steel wire mesh initiated after a few days to a few...
Show moreThis research was conducted to better understand the corrosion propagation stage on dry-cast reinforced concrete pipes (DCRCPs) while exposed to high moisture conditions and chlorides. Corrosion initiation and propagation were studied in instrumented specimens obtained from segments of dry-cast reinforced concrete pipes. All specimens were subjected to accelerated chloride transport by the application of an electric field. Corrosion of the steel wire mesh initiated after a few days to a few months rather than several years. The specimens were then transferred to high moisture environments (immersed in water, high humidity and/or covered with wet sand) during the corrosion propagation stage. Reinforcement potentials, linear polarization resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) measurements were carried out periodically. During the propagation stage in different exposures, reinforcement eventually reached negative potentials values (< –-0.55 Vsce), which suggest mass transfer limitations. These specimens showed no visual signs of corrosion such as cracks or corrosion products except the ones exposed to high humidity and laboratory environments; where some corrosion products have reached the concrete surface. Moreover, the apparent corrosion rate values obtained suggest high corrosion rates. No crack appearance on specimens exposed to other conditions could be explained by the porosity of the specimens; the corrosion products moved into saturated pores. It is speculated that although there might be mass transfer limitations present, the current demanded by the anode is being balanced by a larger cathode area due to macrocell effects since the high moisture conditions likely reduced the concrete resistivity and increased the throwing power. The corrected polarization resistance (Rc) was calculated by subtracting the solution resistance from the apparent polarization resistance measured. The Rc values measured over time were used to obtain the calculated mass loss (using Faraday’s Law). Most specimens were forensically analyzed and the measured mass loss compared to the calculated mass loss. The forensic examination includes the measurement of the actual corroding areas. The measured corroding areas were used to obtain corrosion current density (icorr) values. A comparison was made of the calculated corrosion current densities obtained using the linear polarization resistance method (LPR) and the extrapolation method from cyclic polarization tests. It was evident that most of the specimens’ corrosion rates were significantly high. The corrosion products filled the wet-pores inside the concrete and provide an explanation for no cracks or corrosion bleed outs being visually observed on the specimens.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013182
Subject Headings: Reinforced concrete, Corrosion, Environmental effects
Format: Document (PDF)

Title: SORPTIVITY, RESISTIVITY AND POROSITY OF CONCRETE CONTAINING SUPPLEMENTARY CEMENTITIOUS MATERIALS.
Creator: Barman, Sanjoy, Presuel-Moreno, Francisco, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
Abstract/Description: Supplementary cementitious materials (SCMs), are beneficial when used as partial replacement of cement in concrete mixtures for coastal concrete structures, blended with Portland cement (binary or ternary mixes), i.e., high-performance concrete provides improved properties when exposed to marine harsh environment. In order to characterize selected durability properties of different concrete mixtures, a testing program was established. The intent of this study consists of testing 10cm diameter...
Show moreSupplementary cementitious materials (SCMs), are beneficial when used as partial replacement of cement in concrete mixtures for coastal concrete structures, blended with Portland cement (binary or ternary mixes), i.e., high-performance concrete provides improved properties when exposed to marine harsh environment. In order to characterize selected durability properties of different concrete mixtures, a testing program was established. The intent of this study consists of testing 10cm diameter x 20cm long concrete specimens prepared with a range of different mix designs. 1) to evaluate the rate of water absorption due to capillary suction, referred to as sorptivity, 2) to evaluate the concrete surface resistivity, 3) to evaluate and compare the total porosity of specimens with different mixes, and 4) to obtain correlations between resistivity and sorptivity. All of these experimental tests were carried out according to ASTM International Standards (Sorptivity, Porosity) and Florida Method of Test (Resistivity). The tests were performed on concrete samples at various ages. Moreover, The results provided a fast and reasonable approximation of the concrete durability over time. Ordinary portland cement was partially replaced with supplementary cementitious materials including: fly ash (20%), silica fume (8%) and blast furnace slag (50%). These SCMs are highly effective in creating more durable concrete design mixtures. The water-to-cementitious (w/cm) ratios of 0.41 and 0.35 were investigated. The concrete that contains pozzolanic materials has demonstrated progress in extending the time for initiation of corrosion. The test results obtained indicate that the concurrent inclusion of fly ash and silica fume greatly reduced water penetration. The mixes containing slag also showed lower porosity and water absorption result, when compared to specimens containing fly ash only. Ternary concrete mixtures specimens showed much higher surface resistivity values than binary mixture specimens. These results suggest that reducing w/cm ratio, adding SCMs to concrete mixtures improved the concrete durability. The possibilities for the risks of corrosion initiation would be minimized (delayed) by prescriptive and then performance-based concrete blends with SCM materials optimized for service exposure in aggressive environments.
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Date Issued: 2020
PURL: http://purl.flvc.org/fau/fd/FA00013633
Subject Headings: Fly ash, High performance concrete, Porosity, Silica fume, Slag
Format: Document (PDF)

Title: Hydrodynamic functions of the wing-shaped heads of hammerhead sharks.
Creator: Barousse, Julien., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The hydrodynamics of three different shark heads: Eusphyra blochii (Winghead shark), Carcharhinus acronotus (Blacknose shark) and Sphyrna tiburo (Bonnethead shark) were investigated. Force transducer measurement was used to explore how the cephalofoil (wing-shaped head) affects maneuverability and efficiency. As the dynamic behavior of maneuvering wings differs from that of the steady state motion, experiments have been conducted to simulate: 1) steady-state (no yaw motion) constant velocity...
Show moreThe hydrodynamics of three different shark heads: Eusphyra blochii (Winghead shark), Carcharhinus acronotus (Blacknose shark) and Sphyrna tiburo (Bonnethead shark) were investigated. Force transducer measurement was used to explore how the cephalofoil (wing-shaped head) affects maneuverability and efficiency. As the dynamic behavior of maneuvering wings differs from that of the steady state motion, experiments have been conducted to simulate: 1) steady-state (no yaw motion) constant velocity swimming, 2) constant forward velocity with yawing motion of the head and 3) turning maneuvers. Different range of velocities, angle of attack, yaw frequency and yaw amplitude were tested. Drag and lift coefficients were calculated and compared. The lift coefficient of Winghead shark is much higher compared to the other sharks. The lift-to-drag ratio showed that the Winghead shark has a hydrodynamic advantage compared to Blacknose shark and Bonnethead shark.
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Date Issued: 2009
PURL: http://purl.flvc.org/FAU/2795459
Subject Headings: Aquatic animals (Physiology), Adaptation (Biology), Sharks, Locomotion, Predation (Biology)
Format: Document (PDF)

Title: Dynamic stall effects on hingeless rotor stability with experimental correlation.
Creator: Barwey, Dinesh., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The effects of dynamic stall, lift, drag and pitching moment on the aeroelastic stability of hingeless rotors are predicted. The emphasis is on correlating the predictions with the measured lag-damping levels of a three-bladed model rotor operated in an untrimmed mode. The correlation covers a wide range of test conditions for several values of rotor speed, collective pitch angle, shaft-tilt angle and advance ratio. The database includes cases that vary from near zero-thrust conditions in...
Show moreThe effects of dynamic stall, lift, drag and pitching moment on the aeroelastic stability of hingeless rotors are predicted. The emphasis is on correlating the predictions with the measured lag-damping levels of a three-bladed model rotor operated in an untrimmed mode. The correlation covers a wide range of test conditions for several values of rotor speed, collective pitch angle, shaft-tilt angle and advance ratio. The database includes cases that vary from near zero-thrust conditions in hover to highly stalled forward-flight conditions with dimensionless speed or advance ratios as high as 0.55 and shaft angles as high as 20$\sp\circ$. The aerodynamic representation is based on the ONERA dynamic stall models comprising virtually independent unified lift, drag and pitching-moment models. The nonlinear equations of blade motion and stall dynamics are perturbed about a periodic forced response, and the damping is evaluated by Floquet analysis. The extensive correlation study, based on a rigid-blade flap-lag analysis, demonstrates the viability of Floquet analysis in predicting lag-mode damping under dynamically stalled forward-flight conditions. It also demonstrates the limitations of the linear and quasisteady stall aerodynamic theories. In comparison to these theories, the theory with dynamic stall lift and quasisteady stall drag qualitatively improves the correlation and is viable over the entire range of the database. Addition of dynamic stall drag provides further quantitative improvement. Also presented is a comparative study of two dynamic stall drag models: circulation-like drag variables incorporating unsteady air-velocity variations and conventional drag-coefficient variables. While the formulation with drag coefficients exhibits computational sensitivity to convergence with respect to blade discretization for some isolated cases, the formulation with circulation-like drag variables removes this sensitivity and is computationally robust. The investigation concludes with an elastic blade analysis that includes blade flexibility in lag bending, flap bending and torsion as well as root-flexure elasticity. This analysis shows increasing sensitivity to structural refinements in blade and root-flexure modeling, and this sensitivity increases with increasing pitch setting. Correlation and parametric studies show that the root-flexure elasticity introduces significant bending-torsion couplings that have considerable impact on the stability of a rotor for which the root-flexure is soft, and the blade is stiffer in comparison with the root. This research is expected to serve as a reference comparison with other correlations based on different approaches of modeling dynamic stall and the elasticity of hingeless rotor blades and root-flexure.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12288
Subject Headings: Rotors--Dynamics, Stalling (Aerodynamics), Lift (Aerodynamics)
Format: Document (PDF)

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