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- 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
-
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
-
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)
- Title
- Investigation of debonding and crack kinking in foam core sandwich beams.
- Creator
- Prasad, Srinivas., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Debond failures in structural sandwich may lead to severe reductions in load-bearing capability of the structure because of impartial transfer of shear and tensile forces between facing and core due to the lack of interfacial bonding. Analysis of interfacial bonding in sandwich specimens subjected to transverse tensile and shear forces is presented. Stress intensity factors computed based on the near-tip displacement field are related to experimental crack growth observation on the sandwich...
Show moreDebond failures in structural sandwich may lead to severe reductions in load-bearing capability of the structure because of impartial transfer of shear and tensile forces between facing and core due to the lack of interfacial bonding. Analysis of interfacial bonding in sandwich specimens subjected to transverse tensile and shear forces is presented. Stress intensity factors computed based on the near-tip displacement field are related to experimental crack growth observation on the sandwich beams with aluminum skins on a wide range of PVC foam cores. Experimentally it was found that the crack tends to grow at the interface between the bondline and core as opposed to skin/bondline interface. In shear dominated fields, a pre-existing flow tended to deflect into the core rather than grow along the interface. The tendency for kinking and the direction of the kink is examined experimentally and analyzed using the finite element method.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14861
- Subject Headings
- Finite element method, Sandwich construction, Diffusion bonding (Metals), Fracture mechanics
- Format
- Document (PDF)
- Title
- Investigation of debonding failures in sandwich constructions.
- Creator
- Sendlein, Lyle Scott., Florida Atlantic University, Merry, Stephanie L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Debonding failure of cored marine composite materials is investigated. A new test method that subjects the bond line between the core and the face sheets to a shear stress singularity is presented and studied analytically by laminated beam shear deformation theory, numerically by the finite element method, and experimentally with specimens of glass/polyester face sheets on balsa wood or PVC core sandwich beams.
- Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14519
- Subject Headings
- Mobile communication systems--Design, Wireless communication systems--Technological innovations, Cellular telephones--Design
- Format
- Document (PDF)
- Title
- Synchronous spatial array processing for underwater vehicle tracking.
- Creator
- Normand, Olivier., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Navigation of Unmanned Underwater Vehicles (UUVs) is commonly assisted in confined areas by acoustic positioning systems. The Department of Ocean Engineenng at Florida Atlantic University is developing an altemative system based on submerged modems. This thesis describes an optimal target location estimation technique using a multi-channel spatial receiver array (Millscross) used as a development tool combined with a synchronous modem and transponder network mounted on buoys and UUVs. The...
Show moreNavigation of Unmanned Underwater Vehicles (UUVs) is commonly assisted in confined areas by acoustic positioning systems. The Department of Ocean Engineenng at Florida Atlantic University is developing an altemative system based on submerged modems. This thesis describes an optimal target location estimation technique using a multi-channel spatial receiver array (Millscross) used as a development tool combined with a synchronous modem and transponder network mounted on buoys and UUVs. The Millscross provides a reference to evaluate the performance of the navigation estimator. Spatial array principles are used to develop decoding and beamforming techniques to process modem messages, enabling the end user (the UUV) to estimate in real-time its own position and navigate in space. A simulation was used to compare actual results with theory and determine the processing and decoding algorithms. These algorithms were then applied to real data to estimate the target position (direction of arrival and geodetic coordinates).
Show less - Date Issued
- 2002
- PURL
- http://purl.flvc.org/fcla/dt/12917
- Subject Headings
- Underwater navigation, Underwater acoustics, Signal processing--Digital techniques
- Format
- Document (PDF)
- Title
- Stress intensity factors and weight functions for surface cracks using boundary/finite element alternating methods.
- Creator
- Mu, Ruijia., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In the present investigation, the boundary/finite element alternating methods are used to evaluate the stress intensity factors and weight functions for surface crack problems. For two dimensional problems, Westergaard stress functions are used to find the analytical solutions for an infinite plate with an embedded crack, subjected to crack face tractions, and the boundary element method for the numerical solution. The stress intensity factors and weight functions for an arbitrary plate with...
Show moreIn the present investigation, the boundary/finite element alternating methods are used to evaluate the stress intensity factors and weight functions for surface crack problems. For two dimensional problems, Westergaard stress functions are used to find the analytical solutions for an infinite plate with an embedded crack, subjected to crack face tractions, and the boundary element method for the numerical solution. The stress intensity factors and weight functions for an arbitrary plate with an edge crack subjected to mixed mode loads are obtained by the alternating technique. For three dimensional problems, an elliptical coordinate system and the gravity potential functions are used to derive the three dimensional analytical solutions for an infinite solid with an embedded crack. The analytical solutions are derived for the cases of shear tractions and normal tractions, separately, by assuming that the tractions are symmetric about both the major and minor axes. Superposition gives the general solutions. The analytical solutions and the finite element method, in conjunction with alternating technique, are used to evaluate the stress intensity factors for a solid with a semi-elliptical surface crack, subjected to arbitrary loads. A general approach to evaluate the weight functions for a two dimensional plate with a three dimensional semi-elliptical surface crack is formulated. Numerical examples are evaluated using the formulation developed in the present investigation. The results show good agreement with those from classical solutions. The convergence characteristics of the alternating methods are also discussed. Finally, the formulation is applied to welded plate T-joints with edge/semi-elliptical surface cracks, subjected to three point bending, to obtain stress intensity factors.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/12319
- Subject Headings
- Fracture mechanics, Finite element method--Data processing, Materials--Fatigue, Strains and stresses
- Format
- Document (PDF)
- Title
- Structural intensity measurements in thick structures.
- Creator
- Vallory, Joelle., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Structural intensity is propagated through a thick structure by both in-plane and out-of-plane (transverse) waves. These waves propagate at different phase speeds and therefore it is important to distinguish the components of the structural intensity associated with each wave type. To show the presence of these different wave components, experimental results are performed on a thick beam. Using a frequency-wavenumber analysis, the different waves and contributions to the structural intensity...
Show moreStructural intensity is propagated through a thick structure by both in-plane and out-of-plane (transverse) waves. These waves propagate at different phase speeds and therefore it is important to distinguish the components of the structural intensity associated with each wave type. To show the presence of these different wave components, experimental results are performed on a thick beam. Using a frequency-wavenumber analysis, the different waves and contributions to the structural intensity are identified. The significance of the contributions to the structural intensity are a function of both frequency and thickness of the structure. Using simulated measurements on a thick L-shaped plate, the relative importance between the in-plane and out-of-plane contributions to structural intensity as a function of frequency and thickness is demonstrated. It is shown that in-plane wave contributions increase in importance as frequency or thickness increases.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14697
- Subject Headings
- Structural dynamics, Noise, Vibration
- Format
- Document (PDF)
- Title
- Study of edge effects in laminated sandwich specimens.
- Creator
- Mankuzhy, Pradeep Prabhakaran., Florida Atlantic University, Merry, Stephanie L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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Different methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a...
Show moreDifferent methods have been employed to calculate the interlaminar stresses and to study the edge effect in a laminated sandwich specimens under uniaxial tension. However, Finite Element Analysis and Force Balance Method produced stress values which disagreed in both magnitude and sign, a controversy which exists in the case of composite laminates also. Experimental methods, photoelastic coating method and strain gaging, were attempted to obtain the strain distribution on the top surface of a sandwich specimen in three point bending. However, these conventional methods failed to show the sharp strain gradient that exists near the free edge. The Force Balance Method was simplified for sandwich specimens by considering the face laminate as a homogeneous and orthotropic material with averaged properties. Simplified expressions were also obtained for calculating the boundary layer thickness. The boundary layer thickness was found to vary linearly with core thickness for the cases considered.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14523
- Subject Headings
- Sandwich construction--Fatigue, Composite materials, Strains and stresses, Structural analysis (Engineering)
- Format
- Document (PDF)
- Title
- Subsurface structure of an atmospherically forced water column in littoral waters.
- Creator
- Chernys, Michael., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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The developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the...
Show moreThe developing subsurface structure of a shallow sub-tropical water column during the passage of cold low-pressure atmospheric front is characterized through synoptic and in-situ observations during the passage of three separate fronts over South Florida. Subsurface distribution of current, salinity, temperature, density and dissipation rates were examined using an autonomous underwater vehicle (AUV), ship-based instruments, moored instruments and an Ocean Surface Current Radar (OSCR) as the fronts passed through the region. Airfoil shear probes mounted in a package on the nose of the AUV were used to measure the level and distribution of small-scale turbulence in the water column and to estimate the in-situ dissipation rate of turbulent kinetic energy. Prevailing meteorological conditions were determined from two NOAA C-MAN stations and, for two of the experiments, from a local Air Sea Interaction Spar buoy (ASIS). The first atmospheric front examined was in December 1998. A significant 10°C drop in air temperature was recorded. The AUV carried out several pre-programmed surveys over a 6-day period. A turbulent kinetic energy dissipation rates of O(10-6W/kg) were observed in the water column during the passage of the front. Fetch-limited, offshore, wind-induced surface and subsurface currents were identified during the passage of the front on April 9, 2000. As the winds increased in magnitude and shifted direction, a change in surface current was apparent in the OSCR observations. A bottom-mounted ADCP and an AUV-mounted ADCP both recorded distinct corresponding contributions to the subsurface current due to the winds. Clockwise rotation of the current profile in the water column, consistent with wind-generated currents, was observed. A third low-pressure cold front passed through the region on April 18 an 19, 2000. AUV surveys were carried out as the front passed over the region for 19 hours within a 24-hour period. Dissipation rates reached O(10 -6W/kg) during the period of the survey and decreased to O(10 -8W/kg) subsequently. The distribution of dissipation rate appeared to agree with the characteristic log law for wind-induced turbulence at the start of the passage of the front, but was significantly higher subsequently and more dependent on the combination of convective fluxes and wind stress.
Show less - Date Issued
- 2002
- PURL
- http://purl.flvc.org/fau/fd/FADT12001
- Subject Headings
- Turbulence--Measurement, Oceanographic submersibles
- Format
- Document (PDF)