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- Title
- The prediction of dislocation generation during gallium arsenide crystal growth.
- Creator
- Liu, Ping., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Thermal stresses are induced by temperature variations in gallium arsenide(GaAs) crystal growth. The thermal stresses cause plastic deformations by dislocation and dynamic interaction in the crystal. In this study, firstly the temperature distribution in the Czochralski technique (CZ) growth of GaAs crystal is obtained according to the Jordan model. Secondly a visco-plastic response function for the GaAs crystal is developed from the Haasen model. Finally a nonlinear finite element model is...
Show moreThermal stresses are induced by temperature variations in gallium arsenide(GaAs) crystal growth. The thermal stresses cause plastic deformations by dislocation and dynamic interaction in the crystal. In this study, firstly the temperature distribution in the Czochralski technique (CZ) growth of GaAs crystal is obtained according to the Jordan model. Secondly a visco-plastic response function for the GaAs crystal is developed from the Haasen model. Finally a nonlinear finite element model is employed to simulate the dislocation generation during CZ growth of GaAs crystal.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14780
- Subject Headings
- Gallium arsenide semiconductors, Dislocations in crystals, Crystal growth
- Format
- Document (PDF)
- Title
- A perturbation method for the vibration analysis of beams and plates with free-layer damping treatments.
- Creator
- Shen, Sueming, Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The feasibility of using structural modification techniques to determine the effect of added viscoelastic damping treatments on the modal properties of a distinct eigenvalue system and a degenerate system is investigated. Linear perturbation equations for the changes introduced into the system eigenproperties are derived and applied to several examples involving the flexural vibration of beams and square plates with varying degrees of damping treatment. Both large and small perturbations are...
Show moreThe feasibility of using structural modification techniques to determine the effect of added viscoelastic damping treatments on the modal properties of a distinct eigenvalue system and a degenerate system is investigated. Linear perturbation equations for the changes introduced into the system eigenproperties are derived and applied to several examples involving the flexural vibration of beams and square plates with varying degrees of damping treatment. Both large and small perturbations are considered. An FEM code has been developed to compute the dynamic system parameters which are subsequently used in an iterative method to determine the modal properties. The perturbation approach described can accommodate temperature and frequency-dependent material properties, and the procedures involved are illustrated in the examples considered. Results obtained for these examples are compared with those available from closed form or finite element solutions, or from experiments. Excellent agreement of the results of the present method with those of other contemporary methods demonstrates the validity, overall accuracy, efficiency and convergence rate of this technique. The perturbation approach appears to be particularly well suited for systems with temperature and frequency dependent material properties, and for design situations where a number of damping configurations must be investigated.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/12239
- Subject Headings
- Girders--Vibration, Plates (Engineering)--Vibration, Perturbation (Mathematics), Damping (Mechanics)
- Format
- Document (PDF)
- Title
- pH determination of concrete pore water by a leaching technique for various concrete mixtures.
- Creator
- Sitton, Izic., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A pH determination technique of concrete pore water by means of leaching OH- ions from powdered samples was developed. This method was then evaluated in terms of sample size, extent of dilution, leaching period, the type of leaching, calcium hydroxide error, and titration scatter. Based upon variations of the above parameters it was concluded that a maximum amount of hydroxide ions was released into solution for samples with the smallest particle size within a 24 hours static leaching period....
Show moreA pH determination technique of concrete pore water by means of leaching OH- ions from powdered samples was developed. This method was then evaluated in terms of sample size, extent of dilution, leaching period, the type of leaching, calcium hydroxide error, and titration scatter. Based upon variations of the above parameters it was concluded that a maximum amount of hydroxide ions was released into solution for samples with the smallest particle size within a 24 hours static leaching period. A 50ml dilution volume proved optimum with regard to filtration and titration. Under the above circumstances calcium hydroxide dissolution did not seem to pose a significant source of error. Furthermore, repeatability of the measurements was good and titration scatter was determined to be about 0.05 pH units. This method was used to determine the pH of samples containing different amounts of fly ash or silica fume additions as well as plain cement (control) samples. A drop in OH- concentration, that is pH, was detected with increasing pozzolanic addition. The results are discussed with the context of the degree of corrosion mitigation afforded by these pozzolans.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/15364
- Subject Headings
- Concrete--Corrosion, Seawater corrosion, Concrete--Testing, Leaching
- Format
- Document (PDF)
- Title
- On the topic of Aerosol Generation and Propagation.
- Creator
- Schreck, Jesse H., Verma, Siddhartha, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
In this research, three methods of aerosol generation, and their subsequent propagation, are investigated experimentally. These experiments provided insight into the potential risk aerosol can have pertaining to the spread of infectious disease such as COVID – 19. The first of which investigated an alternative generation route that may exist given the discovery of small numbers of viable viruses in urine and stool samples. Flushing biomatter can lead to the aerosolization of micro-organisms;...
Show moreIn this research, three methods of aerosol generation, and their subsequent propagation, are investigated experimentally. These experiments provided insight into the potential risk aerosol can have pertaining to the spread of infectious disease such as COVID – 19. The first of which investigated an alternative generation route that may exist given the discovery of small numbers of viable viruses in urine and stool samples. Flushing biomatter can lead to the aerosolization of micro-organisms; thus, there is a likelihood that bioaerosols generated in public restrooms may pose a concern for the transmission of COVID-19, especially since these areas are relatively confined, experience heavy foot traffic, and may suffer from inadequate ventilation. The results indicate that the particular designs tested in the study generate a large number of droplets in the size range 0.3 𝜇𝑚 – 3 𝜇𝑚, which can reach heights of at least 1.52 m. This highlights the need for incorporating adequate ventilation in the design and operation of public spaces, which can help prevent aerosol accumulation in high occupancy areas and mitigate the risk of airborne disease transmission. Secondly, experiments were conducted to evaluate the effectiveness of facial coverings at various distances around a simulated cough. These concluded that due to the gaps along the seal of a face mask, aerosols can escape 360° around a coughing individual. In the final portion of the thesis study, an experimental method was developed and conducted to break up a droplet via mechanical excitation. The results of these experiments showed that when a droplet is placed on a vibrating string, the droplet can be broken into many secondary droplets which is analogous to one speaking or singing thus providing insight as to how vocal cords can generate respiratory aerosols.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013685
- Subject Headings
- Aerosols, Communicable diseases--Transmission, COVID-19
- Format
- Document (PDF)
- Title
- MICROALGAE HARVESTING IN A MICROFLUIDIC CENTRIFUGAL SEPARATOR FOR ENHANCED BIOFUEL PRODUCTION.
- Creator
- Kavosi, Mohammadhassan, Kim, Myeongsub, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
Among various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting efficiency, making such a fuel less competitive. To increase the separation efficiency of microalgae from cultivation solution, an orbital microchannel was utilized that enabled the isolation of biofuel-algae particles from the...
Show moreAmong various sources for biofuels, microalgae provide at least three-orders-of-magnitude higher production rate of biodiesel at a given land area than conventional crop-based methods. However, microalgal biodiesel still suffers from significantly lower harvesting efficiency, making such a fuel less competitive. To increase the separation efficiency of microalgae from cultivation solution, an orbital microchannel was utilized that enabled the isolation of biofuel-algae particles from the effluent. The results obtained showed that the separation efficiency in the microfluidic centrifugal separator can be as high as 76% within a quick separation time of 30 seconds. Multiple parameters of algae behaviors and separation techniques such as initial concentration, pH and temperature were studied and manipulated to achieve better efficiencies. It was found that changing these factors altered the separation efficiency by increasing or decreasing flocculation, or “clumping” of the microalgae within the microchannels. The results suggested that an acidic condition would enhance the separation efficiency since in a basic environment, large flocs of microalgae would block and hinder the separation process. Furthermore, a hot temperature solution (around 33 °C) yielded to a higher separation efficiency. The important characteristics of the separator geometry and the infusion rate on algae separation were also very effective in the separation process. This study revealed that there is an opportunity to improve the currently low efficiency of algae separation in centrifugal systems using much smaller designs in size, ensuring a much more efficient algae harvesting.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013745
- Subject Headings
- Microfluidics, Biofuels, Microalgae, Biodiesel fuels, Separation (Technology)
- Format
- Document (PDF)
- Title
- TRAJECTORY PLANNING WITH DYNAMICS-AWARE PARABOLIC BLENDS.
- Creator
- Moscicki, Travis, Ellenrieder, Karl von, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
This thesis presents the concept of dynamics-aware parabolic blends for an unmanned surface vehicle. Typically, trajectory generation techniques consider only kinematic constraints on a vehicle. By transforming the equations of motion for a surface vehicle to the body fixed frame, the dynamical constraints on the system are more intuitively integrated into the trajectory generator, when compared to working in the Earth fixed frame. Additionally, the accelerations, velocities, and positions...
Show moreThis thesis presents the concept of dynamics-aware parabolic blends for an unmanned surface vehicle. Typically, trajectory generation techniques consider only kinematic constraints on a vehicle. By transforming the equations of motion for a surface vehicle to the body fixed frame, the dynamical constraints on the system are more intuitively integrated into the trajectory generator, when compared to working in the Earth fixed frame. Additionally, the accelerations, velocities, and positions generated by the parabolic blend algorithm are incorporated into the dynamic equations of motion for the vehicle to provide the feedforward control input of a two degree of freedom control law. The feedback control input of the two degree of freedom scheme is an integral sliding mode control law, which tracks the error between the vehicle state and the desired states generated by the novel parabolic blend technique. The approach is numerically validated through simulation, where the described control law demonstrates a 71.93% reduction in error when compared to a standard proportional-derivative control law subjected to the same desired trajectory. Furthermore, on water experiments were performed using both a proportional-derivative control law and an integral sliding mode control law. Both showed the ability to track the proposed parabolic blend approach.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013748
- Subject Headings
- Unmanned vehicles, Trajectories
- Format
- Document (PDF)
- Title
- Non-Invasive Measurement Methods for Transient Flows in Wind Tunnels.
- Creator
- Marcheggiani, Joseph P., Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
A non-invasive transient state measurement method for wind tunnels would be very valuable as an experimental tool. Traditional measurement techniques for transient flows, e.g., hot wire anemometry, require sensors that are placed in the flow. Alternatively, particle image velocimetry (PIV) may be used to measure transient flows non intrusively, but applying PIV requires sensors that are expensive, and it may take months to process the data. The non-invasive measurement techniques considered...
Show moreA non-invasive transient state measurement method for wind tunnels would be very valuable as an experimental tool. Traditional measurement techniques for transient flows, e.g., hot wire anemometry, require sensors that are placed in the flow. Alternatively, particle image velocimetry (PIV) may be used to measure transient flows non intrusively, but applying PIV requires sensors that are expensive, and it may take months to process the data. The non-invasive measurement techniques considered in this thesis utilize sensors that are imbedded into the wall of a wind tunnel, or the response of a Kevlar walled wind tunnel to obtain the pressure time histories of a transient flow. These measurements are suitable and accurate for analyzing steady state flows but the feasibility of using them on time varying flows has yet to be explored. If this method proves possible, it would be very beneficial even if it is less accurate than current invasive methods because it would give results in real time. This thesis investigates a simple transient flow of the startup vortex of an airfoil caused by a step change in angle of attack. Based on thin airfoil theory, two models of an airfoil were created. It was determined that the response of a Kevlar wall can measure the unsteady lift of an airfoil.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013837
- Subject Headings
- Wind tunnels, Transient flow (Aerodynamics), Measurement, Sensors
- Format
- Document (PDF)
- Title
- THE IMPACT CORROSION HAS ON THE DEGRADATION OF MECHANICAL PROPERTIES OF CARBON STEEL REBARS IN HIGH PERFORMANCE CONCRETE.
- Creator
- Rosa-Pagan, Angel R., Presuel-Moreno, Francisco, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
A significant amount of reinforced concrete structures in the USA are reaching the design life span of 50 years. Degradation of these infrastructure due to corrosion presents an economical, safety and quality of life challenge for our society. Being able to study and determine the conditions of our infrastructure, perform maintenance before failure and predict failure before occurrence has become critical for our society and our way of life. This study was performed to add to existing...
Show moreA significant amount of reinforced concrete structures in the USA are reaching the design life span of 50 years. Degradation of these infrastructure due to corrosion presents an economical, safety and quality of life challenge for our society. Being able to study and determine the conditions of our infrastructure, perform maintenance before failure and predict failure before occurrence has become critical for our society and our way of life. This study was performed to add to existing research in the understanding of the relationships between the corrosion current of the embedded carbon steel rebars in reinforced concrete, rebar mass loss due to corrosion and the degradation of the mechanical properties of the carbon steel embedded in high performance concrete structures. The study also aimed to study the influence of different independent variables such as the chloride solution reservoir size and the concrete composition of the prepared specimens for the study. Specimens for the study were prepared by embedding three carbon steel size #4 rebars in blocks of high performing concrete with different admixture to enhance their performance against corrosion. To initiate corrosion specimens were exposed to accelerated chloride transport method (electromigration). To accelerate corrosion some samples were selected for anodic polarization and additional electromigration. After corrosion initiation, the rebars Open Circuit Potential (OCP) and corrosion current (Icorr) were periodically measured using a galvanostat device from April 2017 to August 2021. The OCP average values showed that all the rebars considered in this study were in active corrosion. Faraday’s law was used to determine the rebar calculated mass loss from the measured corrosion current and the elapse time between measurements. The rebar mass loss was in turn used to model the loss of the physical properties of the rebar (yield strength, ultimate strength, and ultimate strain) using (Vanama & Ramakrishnan, 2020) model. Analysis of these parameters results showed a direct relationship between the measured corrosion current and the calculated mass loss of the corroding rebar. The study also showed a direct relationship between the calculated mass loss of the corroding rebar and the degradation of the physical properties of the rebar.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013843
- Subject Headings
- Corrosion, Reinforced concrete--Deterioration, Carbon steel, High strength concrete
- Format
- Document (PDF)
- Title
- DESIGN & DEVELOPMENT OF A SECURE SELF-LEVELING WIRELESS RECHARGING PLATFORM FOR AN AERIAL DRONE ON AN UNMANNED SURFACE VESSEL.
- Creator
- McKinney, Adriana, Dhanak, Manhar, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The Design and Development of an automated recharging station for an aerial drone, onboard a small, unmanned surface vessel, is described. Drones require a landing surface that is level within five degrees of the surrounding terrain for repeated reliable landing and takeoff. System constraints and at-sea application necessitate a compact, lightweight, and secure solution. A passive self-leveling platform and an accompanying automated parallel-pusher drone restraint mechanism have been...
Show moreThe Design and Development of an automated recharging station for an aerial drone, onboard a small, unmanned surface vessel, is described. Drones require a landing surface that is level within five degrees of the surrounding terrain for repeated reliable landing and takeoff. System constraints and at-sea application necessitate a compact, lightweight, and secure solution. A passive self-leveling platform and an accompanying automated parallel-pusher drone restraint mechanism have been designed and fabricated to aid in achieving a level landing surface and holding the drone in place while it charges. The self-leveling mechanism has been analyzed and subjected to initial laboratory tests. The testing of the drone restraint mechanism to verify its weight capacity and closing time, and the integration of the platform with a custom conductive contact wireless charging pad are identified as future work. The resulting cohesive unit will be tested for performance optimization and implementation onboard the unmanned surface vehicle.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013869
- Subject Headings
- Drone aircraft, Drone aircraft--Control systems--Design and construction, Drone aircraft--Automatic control
- Format
- Document (PDF)
- Title
- Bio-Inspired Modified Turbulent Boundary Layers.
- Creator
- French, Stone A., Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The reduction of drag and sound pressure levels (SPL) are desirable traits in many fluidics’ applications ranging from high-speed transportation to energy generation. Inspiration has been found in some species of owls that possess boundary layer control surface treatments on their wings that appear to reduce SPL while in flight. This modification of the flow over the wings is known as the development of a modified boundary layer (MBL). Virginia Tech is working in collaboration with Florida...
Show moreThe reduction of drag and sound pressure levels (SPL) are desirable traits in many fluidics’ applications ranging from high-speed transportation to energy generation. Inspiration has been found in some species of owls that possess boundary layer control surface treatments on their wings that appear to reduce SPL while in flight. This modification of the flow over the wings is known as the development of a modified boundary layer (MBL). Virginia Tech is working in collaboration with Florida Atlantic University to investigate this reduction in SPL experimentally but requires the assistance of RANS simulation to obtain drag results. This thesis investigates the drag effects of the rod style geometries being evaluated at VT to mimic the MBL of an owl. In doing this it was found that the height of the rods has a direct correlation with the amount of drag induced by the presence of the rods in the flow field.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013826
- Subject Headings
- Turbulent boundary layer, Sound pressure, Biomimicry, Drag (Aerodynamics)
- Format
- Document (PDF)
- Title
- An Analysis of the Surface Pressure Spectra in a Fluid Flow with a Zero-Pressure Gradient Turbulent Boundary Layer.
- Creator
- Balestrieri, Frank, Glegg, Stewart, Florida Atlantic University, Department of Ocean and Mechanical Engineering, College of Engineering and Computer Science
- Abstract/Description
-
The objective of this thesis is to review recently developed empirical and analytical models for the surface pressure and wavenumber spectra for fully developed boundary layers to highlight the effect of assumptions about the turbulence length scales and show how the effects of mean flow Reynolds number has on the spectra shape. The Goody model is used as a reference model to compare the spectra shape as it characterizes the basic physical features of the wall-pressure spectrum under a zero...
Show moreThe objective of this thesis is to review recently developed empirical and analytical models for the surface pressure and wavenumber spectra for fully developed boundary layers to highlight the effect of assumptions about the turbulence length scales and show how the effects of mean flow Reynolds number has on the spectra shape. The Goody model is used as a reference model to compare the spectra shape as it characterizes the basic physical features of the wall-pressure spectrum under a zero-pressure gradient turbulent boundary layer and scales as a function of Reynolds number. The turbulence length scales of the comparison models are modified to observe the effects on the shape of the spectra. A new model is also considered that also scales as a function of Reynolds number and is compared to the Goody model.
Show less - Date Issued
- 2021
- PURL
- http://purl.flvc.org/fau/fd/FA00013816
- Subject Headings
- Turbulent boundary layer, Turbulence
- Format
- Document (PDF)
- Title
- Electrochemical intercalation of lithium-ion into carbon fibers prepared from synthetic cellulose precursor.
- Creator
- Kashauer, Robert Lewis., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A number of fibrous carbon materials have been investigated as intercalation host materials. Commercially available rayon fiber (synthetic cellulose) based carbon fibers were synthesized for use as anode material in lithium-ion batteries. The effects of oxidation and carbonization temperature, heating ramp rate, soak time and gaseous atmosphere during thermal treatment on the electrochemical performance of the carbon fibers were studied. Intercalation/deintercalation experiments were...
Show moreA number of fibrous carbon materials have been investigated as intercalation host materials. Commercially available rayon fiber (synthetic cellulose) based carbon fibers were synthesized for use as anode material in lithium-ion batteries. The effects of oxidation and carbonization temperature, heating ramp rate, soak time and gaseous atmosphere during thermal treatment on the electrochemical performance of the carbon fibers were studied. Intercalation/deintercalation experiments were performed to evaluate the electrochemical performance of the carbon fibers. The highest reversible capacity and lowest irreversible capacity loss were obtained for carbon fibers carbonized at 1100C at a ramp rate of 10C/min held at soak times of 1 and 5 hours. Electrolyte containing 1M LiPF6 in 70/30 v/o EC:DMC proved to be most suitable for these carbon fiber materials. The influence of electrolyte composition (solvent and salt) on the reversible and irreversible capacities as well as on the intercalation/deintercalation potential profile were also studied.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/15452
- Subject Headings
- Carbon fibers, Lithium cells, Electrolytes
- Format
- Document (PDF)
- Title
- Embrittlement susceptibility of corroded pre-stressing steel in concrete during cathodic polarization.
- Creator
- Poeydomenge, Arnaud., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Experiments and analyses were performed to better define the limits of concern regarding hydrogen embrittlement in association with application of cathodic protection to prestressed concrete. To accomplish this, prestressed concrete specimens were locally corroded to different levels by anodic polarization and then polarized to -1.30 V SCE. A procedure of examination was developed using strain gauges to determine the level of prestrain. Relatively few brittle failures of wires resulted due,...
Show moreExperiments and analyses were performed to better define the limits of concern regarding hydrogen embrittlement in association with application of cathodic protection to prestressed concrete. To accomplish this, prestressed concrete specimens were locally corroded to different levels by anodic polarization and then polarized to -1.30 V SCE. A procedure of examination was developed using strain gauges to determine the level of prestrain. Relatively few brittle failures of wires resulted due, at least in part, to a relatively low prestrain of the pretensioned tendons. A model was developed which, coupled with data from parallel research, permitted definition of the minimum cross section for brittle failure as a function of the magnitude of prestrain and corrosion morphology of the wire. These results were tabulated in a format that can be used during field inspection to identify structural elements for which fracture could occur upon application of cathodic protection.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/15417
- Subject Headings
- Prestressed concrete--Corrosion, Cathodic protection, Prestressed concrete--Embrittlement, Prestressed steel construction
- Format
- Document (PDF)
- Title
- Efficient leeway drift prediction.
- Creator
- Lee, Yanhua., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Search and rescue of crafts in distress on the sea surface require the capability to accurately predict the drift of target craft in a short time. A nonlinear mathematical model (original model) has been developed as a tool for the study of the boat drift. Wind load computation considers the wind gradient and the vessel geometry. The current loads include form and friction drag. From the numerical evaluations, the effects of various environmental and vehical parameters on drift are properly...
Show moreSearch and rescue of crafts in distress on the sea surface require the capability to accurately predict the drift of target craft in a short time. A nonlinear mathematical model (original model) has been developed as a tool for the study of the boat drift. Wind load computation considers the wind gradient and the vessel geometry. The current loads include form and friction drag. From the numerical evaluations, the effects of various environmental and vehical parameters on drift are properly accounted for. Simplification of the original model results in a model which is computationally 60 times faster, so-called version 1, without losing much accuracy. In order to meet the needs of two minute prediction for practical implementation, a further simplified model, version 2, was developed from version 1. It is found that the computing speed can be improved one hundred times, and this will facilitate the practical implementation of FAU model in search planning.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14499
- Subject Headings
- Search and rescue operations--Mathematical models, Ocean currents--Mathematical models, Winds--Speed--Mathematical models
- Format
- Document (PDF)
- Title
- Electrochemical impedance spectroscopy of nickel-hydrogen and silver oxide-metal hydride secondary batteries.
- Creator
- Nechev, Kamen S., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Full nickel-hydrogen (Ni-H2) boilerplate batteries were cycled and impedance measurements were made at different states-of-charge (SOC), electrolyte concentrations and charge/discharge rates. Experiments were conducted on cells containing new and cycled (11,000 cycles) electrodes. Additionally, an EIS study of Ni-H2 flightweight IPV satellite cells was performed. A number of experiments were conducted on silver oxide-metal hydride batteries. The interest was focused on both negative and...
Show moreFull nickel-hydrogen (Ni-H2) boilerplate batteries were cycled and impedance measurements were made at different states-of-charge (SOC), electrolyte concentrations and charge/discharge rates. Experiments were conducted on cells containing new and cycled (11,000 cycles) electrodes. Additionally, an EIS study of Ni-H2 flightweight IPV satellite cells was performed. A number of experiments were conducted on silver oxide-metal hydride batteries. The interest was focused on both negative and positive electrodes and upon the system itself. This work was preliminary and aided in describing the general performance of the battery. For analysis, the data was fitted to an equivalent electrical circuit using the Nonlinear Least Squares Method (NLSM). The correlation between theoretical and empirical data was sufficiently good.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14958
- Subject Headings
- Nickel-hydrogen batteries, Electrodes, Nickel, Impedance spectroscopy, Electrochemical analysis, Electric batteries--Electrodes
- Format
- Document (PDF)
- Title
- Effect of strain rate and temperature on the stress corrosion cracking tendency of engineering alloys in acidified seawater.
- Creator
- Kundalgurki, Srivatsa G., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The stress corrosion cracking (SCC) tendencies of several engineering alloys were studied in an acidified seawater environment as a function of applied strain rate and electrolyte temperature. The selected alloys included austenitic stainless steels 304L, 316L, 904L and A-286 (an iron-based superalloy at two heat treatments yielding ultimate tensile strengths of 130 and 200 ksi), Inconel 718 (220 ksi ultimate tensile strength) and Hastelloys C-22 and C-276. The slow strain rate test technique...
Show moreThe stress corrosion cracking (SCC) tendencies of several engineering alloys were studied in an acidified seawater environment as a function of applied strain rate and electrolyte temperature. The selected alloys included austenitic stainless steels 304L, 316L, 904L and A-286 (an iron-based superalloy at two heat treatments yielding ultimate tensile strengths of 130 and 200 ksi), Inconel 718 (220 ksi ultimate tensile strength) and Hastelloys C-22 and C-276. The slow strain rate test technique was used to evaluate the SCC strain rate dependency of each alloy at extension rates of 4.7 x 10^-6, 4.7 x 10^-4 and 4.7 x 10^-3 mm/sec. The effect of electrolyte temperature was evaluated at 38C and 60C at a single extension rate of 4.7 x 10^-5 mm/sec. Control specimens were tested in a laboratory air environment at an extension rate of 4.7 x 10^-5 mm/sec. Various mechanical parameters of the specimens tested in the corrosive medium were compared with those of control specimens to quantify the degree of cracking. Fractographic evidence of SCC was obtained using scanning electron microscopy (SEM). An attempt was made to correlate SCC tendency with the alloy's passivation kinetics and microstructure. Atmospheric exposure testing was performed in a simulated space shuttle launch pad environment for selected alloys.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/14853
- Subject Headings
- Alloys--Stress corrosion, Stress corrosion, Sea-water corrosion
- Format
- Document (PDF)
- Title
- Influence of direct electrical current upon specific volume of mortar in sea water.
- Creator
- Le Floch, Anne., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Hollow, cylindrical mortar specimens of 0.4 water-cement ratio were prepared without reinforcement and exposed to flowing natural sea water for periods up to one year. Direct currents of 2, 10 and 50 mA were impressed between a mixed metal-oxide titanium substrate electrode positioned within each of these two zones, with a different electrolyte supply and exhaust for the cylinder core and exterior surface. Linear expansion of the specimens was evaluated as a function of exposure duration from...
Show moreHollow, cylindrical mortar specimens of 0.4 water-cement ratio were prepared without reinforcement and exposed to flowing natural sea water for periods up to one year. Direct currents of 2, 10 and 50 mA were impressed between a mixed metal-oxide titanium substrate electrode positioned within each of these two zones, with a different electrolyte supply and exhaust for the cylinder core and exterior surface. Linear expansion of the specimens was evaluated as a function of exposure duration from the output of embedded strain gages and from dimensional measurement of cylinder length and diameter. It was found that expansion of specimens exposed to direct current exceeded baseline ones (no current). Also, the expansion was anisotropic in that different magnitudes and trends were apparent for the diameter versus length directions. The expansion under free exposure (no current) was determined to be a function of specimen size and of the direction of measurement relative to the cast specimen face.
Show less - Date Issued
- 1995
- PURL
- http://purl.flvc.org/fcla/dt/15214
- Subject Headings
- Concrete--Deterioration, Concrete--Corrosion, Seawater corrosion, Cathodic protection
- Format
- Document (PDF)
- Title
- Influence of chlorides and surface condition on pitting potential of high performance reinforcing steel.
- Creator
- Leroux, Virginie Edwige., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In order to identify the influence of chlorides and surface finish on pitting potential of high performance reinforcing steel, cyclic polarization scans were performed on types 304, 2201 and 3Cr12 stainless steels and MMFX-II in simulated pore solution to which chloride was incrementally added. Furthermore, the surface condition was investigated with regard to the pitting potential. Pitting potential distributions versus the chloride content and surface finish were obtained. Pitting...
Show moreIn order to identify the influence of chlorides and surface finish on pitting potential of high performance reinforcing steel, cyclic polarization scans were performed on types 304, 2201 and 3Cr12 stainless steels and MMFX-II in simulated pore solution to which chloride was incrementally added. Furthermore, the surface condition was investigated with regard to the pitting potential. Pitting potential distributions versus the chloride content and surface finish were obtained. Pitting resistance was lowered as chloride was added and as the surface became rougher. Furthermore, a critical chloride to hydroxide ratio as a function of potential was determined for each material. Finally, according to the results of this study, the MMFX reinforcing steel was considered to have a corrosion performance close to that of Type 2201 stainless steel for bridge use. MMFX-II specimens with a polished surface exhibited more positive pitting potentials than did ones with an as-received finish.
Show less - Date Issued
- 2004
- PURL
- http://purl.flvc.org/fcla/dt/13103
- Subject Headings
- Reinforcing bars--Corrosion, Steel, Structural--Corrosion, Chlorides
- Format
- Document (PDF)
- Title
- Influence of weld profile on the thickness-fatigue life relationship for welded Tee specimens.
- Creator
- Wang, Qingmin., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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An experimental investigation was performed to determine the stresses at the weld toe for a group of welded Tee specimens of API 2H Grade 42 steel with thicknesses ranging from 12.7 to 101.6 mm and weld profiles conforming to the American Welding Society Code--AWS Basic, Alternate #1 and Alternate #2. The objective was to improve the understanding of the interactive weld profile - plate thickness effect on fatigue behavior. A finite element technique was employed to compute the stress...
Show moreAn experimental investigation was performed to determine the stresses at the weld toe for a group of welded Tee specimens of API 2H Grade 42 steel with thicknesses ranging from 12.7 to 101.6 mm and weld profiles conforming to the American Welding Society Code--AWS Basic, Alternate #1 and Alternate #2. The objective was to improve the understanding of the interactive weld profile - plate thickness effect on fatigue behavior. A finite element technique was employed to compute the stress gradient along and perpendicular to the plate surface. A parametric equation of SCF as a function of weld toe radius and included angle was derived based upon the finite element analysis. The results indicate that the thickness effect can be partially reduced by using an improved weld profile which reduces the stress concentration at the weld toe.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14563
- Subject Headings
- Welded joints--Fatigue
- Format
- Document (PDF)
- Title
- Karhunen-Loeve decomposition for non stationary propulsor flow noise.
- Creator
- Kersulec, Jean-Luc., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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The aim of this thesis is to develop a theory for non stationary propulsor flow noise. The model which is proposed is based on Amiet's paper "Acoustic Radiation from an Airfoil in a Turbulent Stream" [1], which describes broad band noise when a simple model of airfoil interacts with a turbulent flow, under the assumption of stationarity. The Karhunen-Loeve method provides a set of modes which describe the turbulent flow without the assumption of stationarity. A method is described to obtain...
Show moreThe aim of this thesis is to develop a theory for non stationary propulsor flow noise. The model which is proposed is based on Amiet's paper "Acoustic Radiation from an Airfoil in a Turbulent Stream" [1], which describes broad band noise when a simple model of airfoil interacts with a turbulent flow, under the assumption of stationarity. The Karhunen-Loeve method provides a set of modes which describe the turbulent flow without the assumption of stationarity. A method is described to obtain broad band noise calculations when the mean turbulent flow varies with time and produces non stationary turbulence. A comparison of the numerical results obtained with the results from the paper of reference [1] shows the characteristics of time varying sound radiation. The various mathematical formulae will give a starting point to the analysis of real time varying flows, which are not considered in this thesis.
Show less - Date Issued
- 2005
- PURL
- http://purl.flvc.org/fcla/dt/13233
- Subject Headings
- Aerodynamic noise, Turbulence, Aerofoils, Unsteady flow (Aerodynamics), Nonlinear control theory, Differential equations, Nonlinear
- Format
- Document (PDF)
