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- Title
- Simulation, control and optimization of underwater vehicle performance.
- Creator
- Zipf, David Glenn., Florida Atlantic University, Dunn, Stanley E., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This project addresses the simulation, control and optimization of underwater vehicle performance. An analytical model of underwater vehicle motion has been developed. This model is based on a set of six degree of freedom nonlinear differential equations of motion. These equations incorporate inertial, hydrodynamic, hydrostatic, gravity and thruster forces to define the vehicle's motion. The forces are calculated and the equations of motion solved using a finite difference method of...
Show moreThis project addresses the simulation, control and optimization of underwater vehicle performance. An analytical model of underwater vehicle motion has been developed. This model is based on a set of six degree of freedom nonlinear differential equations of motion. These equations incorporate inertial, hydrodynamic, hydrostatic, gravity and thruster forces to define the vehicle's motion. The forces are calculated and the equations of motion solved using a finite difference method of integration. An automatic closed loop control strategy has been developed and integrated into the motion model. The controller determines control plane deflection and thruster output based on sensor provided input, maneuver request and control gain constants. The motion model simulates the effects of these controller requests on the vehicle motion. The controller effects are analyzed and an optimal set of control gains is determined. These optimal gains are determined based on a quantitative comparison of a pre-defined Performance Index (PI) function. The PI is a function of critical performance values, i.e., energy consumption, and user defined weighted constants. By employing an iteration technique the PI is minimized to provide an optimal set of control gains.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14534
- Subject Headings
- Oceanographic submersibles--Automatic control, Oceanographic submersibles--Simulation methods, Vehicles, Remotely piloted
- Format
- Document (PDF)
- Title
- Feasibility of using carbon fiber reinforced plastic tendons in prestressed concrete Double-Tee bridge system.
- Creator
- Zhuang, Ming., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
One of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete...
Show moreOne of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete bridge structures. Besides investigating durability of CFC cables and pretensioned concrete beams with CFC cables in adverse environments (alkali and seawater), flexure and shear tests were performed on single Double-Tee beams, together with service load behavior, fatigue strength and ultimate load capacity tests on a half scale model Double-Tee girder bridge system prestressed with CFC cables. Exposure to seawater and alkali environments has no adverse effect on the strength of the CFRP tendons as well as the pretensioned beams with CFRP. Based on the flexural strength tests on Double-Tee beams, the bond between CFRP tendons and concrete is satisfactory. The Double-Tee bridge system exhibited good fatigue resistance and adequate ductility under ultimate load conditions. The ultimate load capacity of the bridge is approximately three times the service load corresponding to two HS20-44 trucks and equals 2.4 times the first crack load. Finite element analyses were carried out to predict elastic deformations and collapse load of the Double-Tee bridge prestressed with CFC cables. Feasibility of using CFC cables in bridge structures is assessed based on the experimental and analytical parameters such as deflections, strains, crack distributions and crack widths.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/12465
- Subject Headings
- Carbon fibers, Composite construction, Fiber reinforced plastics, Bridges, Iron and steel, Reinforced concrete construction, Prestressed concrete construction
- Format
- Document (PDF)
- Title
- Finite element modeling for dislocation generation in semiconductor crystals grown from the melt.
- Creator
- Zhu, Xinai., Florida Atlantic University, Tsai, Chi-Tay, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Dislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs and InP-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs and InP...
Show moreDislocations in Gallium Arsenide (GaAs) and Indium Phosphide (InP) single crystals are generated by excessive stresses that are induced during the crystal growth process, and the fabrication and packaging of microelectronic devices/circuits. The presence of dislocations has adverse effects on the performance, lifetime and reliability of the GaAs and InP-based devices/circuits. It is well known that dislocation density can be significantly reduced by doping impurity atoms into the GaAs and InP crystal and/or decreasing the thermal stresses in these crystals during their growth process. In order to reduce the dislocation density generated in the GaAs and InP crystals, the influence of crystal growth parameters and doping impurity atoms on the dislocations reduction in GaAs and InP crystals has to be understood. Therefore, a transient finite element model was developed to simulate the dislocation generation in GaAs and InP crystals grown from the melt. A viscoplastic constitutive equation that couples a microscopic dislocation density with a macroscopic plastic deformation is employed to formulate this transient finite element model, where the dislocation density is considered as an internal state variable and the doping impurity is represented by a drag-stress in this constitutive model. GaAs and InP single crystals grown by the vertical gradient freeze (VGF) process were adopted as examples to study the influences of doping impurity and growth parameters on dislocations generated in these grown crystal. The calculated results show that doping impurity can significantly reduce dislocation generation and produces low-dislocation-density or dislocation free GaAs and InP single crystals. It also shows that the dislocations generated in GaAs and InP crystals increase as the crystal diameter and imposed temperature gradient increase, but do not change or increase slightly as the crystal growth rate increases. Therefore, this finite element model can be effectively used by crystal growers to select acceptable levels of doping impurity, crystal diameter, temperature gradient, and growth rate to produce the lowest dislocation density in GaAs and InP crystals through a thorough numerical investigation using this developed finite element model.
Show less - Date Issued
- 2004
- PURL
- http://purl.flvc.org/fcla/dt/12072
- Subject Headings
- Dislocations in crystals, Gallium arsenide semiconductors, Indium phosphide, Metal crystals--Growth
- Format
- Document (PDF)
- Title
- Deterministic, stochastic and convex analyses of one- and two-dimensional periodic structures.
- Creator
- Zhu, Liping., Florida Atlantic University, Lin, Y. K., Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The periodic structures considered in the dissertation are one-dimensional periodic multi-span beams, and two-dimensional periodic grillages with elastic interior supports. The following specific topics are included: (1) Deterministic Vibration--Exact solutions are obtained for free vibrations of both multi-span beams and grillages, by utilizing the wave propagation concept. The wave motions at the periodic supports/nodes are investigated and the dispersion equations are derived from which...
Show moreThe periodic structures considered in the dissertation are one-dimensional periodic multi-span beams, and two-dimensional periodic grillages with elastic interior supports. The following specific topics are included: (1) Deterministic Vibration--Exact solutions are obtained for free vibrations of both multi-span beams and grillages, by utilizing the wave propagation concept. The wave motions at the periodic supports/nodes are investigated and the dispersion equations are derived from which the natural frequencies of the periodic structures are determined. The emphasis is placed on the calculation of mode shapes of both types of periodic structures. The general expressions for mode shapes with various boundary conditions are obtained. These mode shapes are used to evaluate the exact dynamic response to a convected harmonic loading. (2) Stochastic Vibration--A multi-span beam under stochastic acoustic loading is considered. The exact analytical expressions for the spectral densities are derived for both displacement and bending moment by using the normal mode approach. Nonlinear vibration of a multi-span beam with axial restraint and initial imperfection are also investigated. In the latter case, the external excitation is idealized as a Gaussian white nose. An expression for the joint probability density function in the generalized coordinates is obtained and used to evaluate the mean square response of a multi-span beam system. (3) Convex Modeling of Uncertain Excitation Field--It is assumed that the parameters of the stochastic excitation field are uncertain and belong to a multi-dimensional convex set. A new approach is developed to determine the multi-dimensional ellipsoidal convex set with a minimum volume. The most and least favorable responses of a multi-span beam are then determined for such a convex set, corresponding to a stochastic acoustic field. The procedure is illustrated in several examples.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/12366
- Subject Headings
- Grillages (Structural engineering), Girders--Vibration, Wave-motion, Theory of, Vibration
- Format
- Document (PDF)
- Title
- Development of an integrated computational tool for design and analysis of composite turbine blades under ocean current loading.
- Creator
- Zhou, Fang., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A computational tool has been developed by integrating National Renewable Energy Laboratory (NREL) codes, Sandia National Laboratories' NuMAD, and ANSYS to investigate a horizontal axis composite ocean current turbine. The study focused on the design, analysis, and life prediction of composite blade considering random ocean current, cyclic rotation, and hurricane-driven ocean current. A structural model for a horizontal axis FAU research OCT blade was developed. Following NREL codes were used...
Show moreA computational tool has been developed by integrating National Renewable Energy Laboratory (NREL) codes, Sandia National Laboratories' NuMAD, and ANSYS to investigate a horizontal axis composite ocean current turbine. The study focused on the design, analysis, and life prediction of composite blade considering random ocean current, cyclic rotation, and hurricane-driven ocean current. A structural model for a horizontal axis FAU research OCT blade was developed. Following NREL codes were used: PreCom, BModes, ModeShape, AeroDyn and FAST. PreComp was used to compute section properties of the OCT blade. BModes and ModeShape calculated the mode shapes of the blade. Hydrodynamic loading on the OCT blade was calculated by modifying the inputs to AeroDyn and FAST. These codes were then used to obtain the dynamic response of the blade, including blade tip displacement, normal force (FN) and tangential force (FT), flap and edge bending moment distribution with respect to blade rotation.
Show less - Date Issued
- 2013
- PURL
- http://purl.flvc.org/fcla/dt/3362582
- Subject Headings
- Structural dynamics, Fluid dynamics, Marine turbines, Mathematical models, Turbines, Blades, Design and construction
- Format
- Document (PDF)
- Title
- Determination of probability density from statistical moments by neural network approach.
- Creator
- Zheng, Zhiyin., Florida Atlantic University, Cai, Guo-Qiang, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
It is known that response probability densities, although important in failure analysis, are seldom achievable for stochastically excited systems except for linear systems under additive excitations of Gaussian processes. Most often, statistical moments are obtainable analytically or experimentally. It is proposed in this thesis to determine the probability density from the known statistical moments using artificial neural networks. A multi-layered feed-forward type of neural networks with...
Show moreIt is known that response probability densities, although important in failure analysis, are seldom achievable for stochastically excited systems except for linear systems under additive excitations of Gaussian processes. Most often, statistical moments are obtainable analytically or experimentally. It is proposed in this thesis to determine the probability density from the known statistical moments using artificial neural networks. A multi-layered feed-forward type of neural networks with error back-propagation training algorithm is proposed for the purpose and the parametric method is adopted for identifying the probability density function. Three examples are given to illustrate the applicability of the approach. All three examples show that the neural network approach gives quite accurate results in comparison with either the exact or simulation ones.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/15330
- Subject Headings
- Distribution (Probability theory), Moments method (Statistics), Estimation theory, Structural failures--Investigation, Neural networks (Computer science)
- Format
- Document (PDF)
- Title
- Dynamic modeling of two layered stratification.
- Creator
- Zhang, Yaodong., Florida Atlantic University, Scarlatos, Panagiotis (Pete) D., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
In this thesis, a two-dimensional in the vertical plane numerical model has been developed for simulation of the free surface and density interface profiles due to a wind shear stress applied on a stratified water body, such as lake or reservoir. The results agreed qualitatively and quantitatively with our experimental results, as well as with the work of other researchers. A computer algorithm is established that can be used to estimate the shear stress along the interface and the velocity...
Show moreIn this thesis, a two-dimensional in the vertical plane numerical model has been developed for simulation of the free surface and density interface profiles due to a wind shear stress applied on a stratified water body, such as lake or reservoir. The results agreed qualitatively and quantitatively with our experimental results, as well as with the work of other researchers. A computer algorithm is established that can be used to estimate the shear stress along the interface and the velocity field throughout the water body. The model can be applied for prediction of wind-induced mixing processes in elongated lakes or reservoirs.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/14809
- Subject Headings
- Upwelling, Turbulence, Density currents
- Format
- Document (PDF)
- Title
- Modeling of bracelet anodes and anode arrays for pipeline CP systems.
- Creator
- Zhang, Xiaolin., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Two models for pipeline bracelet anodes depletion with time were analyzed: one with uniform corrosion and the other with localized corrosion. The potential of the pipeline was determined to become more positive with time due to corrosion of the anode. The pipeline protected by the anode with localized corrosion had more a positive potential than the one protected by the anode with uniform corrosion. A method based upon the equations of Sunde was developed for determining resistance of linear...
Show moreTwo models for pipeline bracelet anodes depletion with time were analyzed: one with uniform corrosion and the other with localized corrosion. The potential of the pipeline was determined to become more positive with time due to corrosion of the anode. The pipeline protected by the anode with localized corrosion had more a positive potential than the one protected by the anode with uniform corrosion. A method based upon the equations of Sunde was developed for determining resistance of linear and rectangular anode arrays. Accuracy of this approach was evaluated using Boundary Element Modeling (BEM). The difference between the two methods was defined as Error. A corrected function of Sunde's equation was developed in order to get a more accurate resistance of a 1 x N anode array. The influence on resistance of a M x N (M < N) anode array of anode size, separation distance and array number was analyzed. Error increased with increasing anode size and decreased with increasing number of anodes and separation distance. The application and limitations of commonly used anode resistance formulas are discussed.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/13087
- Subject Headings
- Pipelines--Cathodic protection, Corrosion and anti-corrosives, Underwater pipelines, Anodes
- Format
- Document (PDF)
- Title
- Stochastic earthquake ground motion modeling.
- Creator
- Zhang, Ruichong., Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A model for earthquake ground motion is developed in this dissertation using principles of geophysics and stochastics. The earth is idealized as being composed of horizontally stratified layers, with uniform physical properties for each layer. The seismic source is assumed to be the result of shear dislocation propagating on a fault line, which is further discretized into a series of point sources at equal intervals. The fundamental problem of the ground motion in a layered medium due to a...
Show moreA model for earthquake ground motion is developed in this dissertation using principles of geophysics and stochastics. The earth is idealized as being composed of horizontally stratified layers, with uniform physical properties for each layer. The seismic source is assumed to be the result of shear dislocation propagating on a fault line, which is further discretized into a series of point sources at equal intervals. The fundamental problem of the ground motion in a layered medium due to a point source at a given source location is first considered. The governing equations of three-dimensional wave motion in a uniform layer are presented and solved in both Cartesian and cylindrical coordinates. Wave propagation in a multi-layered medium is then analyzed in detail, in which the wave scattering matrices are introduced so that stability and accuracy in numerical calculation can be guaranteed. A detailed review of the mechanism of seismic point source is also provided. Based on the fundamental solution for a point source, an earthquake model is constructed by superposing the solutions associated with a series of point sources along a line which are activated sequentially at random times. Statistical characteristics of earthquake ground motion is then obtained by applying a generalized version of the random-pulse-train theory and its evolutionary spectral representation. Finally the effects of uneven interface on the earthquake ground motion is also analyzed using a first-order perturbation approach.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/12290
- Subject Headings
- Earth movements, Earthquakes, Stochastic processes
- Format
- Document (PDF)
- Title
- The development and application of a numerical model for predicting the frequency response of the seabed from vertical profiles of sediment impedance.
- Creator
- Zhang, Jian Long., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Interaction of normal incidence, wideband acoustic pulses with seabed is investigated to determine the acoustic frequency ranges that provide the most information about the sediment structure. An exact numerical model is developed for calculating the frequency response and impulse response of the seabed from an impedance profile of a sediment core. A database of impedance profiles from several ocean environments were studied to describe the shapes of commonly found impedance changes. The...
Show moreInteraction of normal incidence, wideband acoustic pulses with seabed is investigated to determine the acoustic frequency ranges that provide the most information about the sediment structure. An exact numerical model is developed for calculating the frequency response and impulse response of the seabed from an impedance profile of a sediment core. A database of impedance profiles from several ocean environments were studied to describe the shapes of commonly found impedance changes. The impulse response of the seabed is convolved with acoustic pulses to generate synthetic acoustic returns. The synthetic profiles are studied to determine the effect of operating frequency and bandwidth on resolution and on the accuracy of measuring impedance changes. This thesis explains why inversion procedures have failed to generate vertical impedance profiles of the seabed from normal incidence reflection data. The results of this work provide guidelines for selecting subbottom profiler array sizes and operating frequencies for quantitative sediment studies, and for subsampling cores.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/15293
- Subject Headings
- Marine sediments--Acoustic properties, Seismic reflection method
- Format
- Document (PDF)
- Title
- Transport and dispersion of fire extinguishing agents downstream from clutter elements of aircraft engine nacelles.
- Creator
- Zbeeb, Khaled., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The combination of highly turbulent airflow, flammable fluids, and numerous ignition sources makes aircraft engine nacelles a difficult fire zone to protect. Better understanding of nacelle air flow and how it influences the spread of fires and fire extinguishing agents is needed to improve the efficiency of fire suppression. The first objective was to establish a CFD model for a flow field test section to analyze the transport and dispersion of fire extinguishing agents in the presence of...
Show moreThe combination of highly turbulent airflow, flammable fluids, and numerous ignition sources makes aircraft engine nacelles a difficult fire zone to protect. Better understanding of nacelle air flow and how it influences the spread of fires and fire extinguishing agents is needed to improve the efficiency of fire suppression. The first objective was to establish a CFD model for a flow field test section to analyze the transport and dispersion of fire extinguishing agents in the presence of various clutter elements. To validate the use of the CFD model, the simulation results of the CFD model were compared to the experimental data and they show an agreement with the experimental data. The second objective was to present parametric studies to show the effects of the coflow speed, turbulence intensity and agent droplet size on the transport and dispersion of the agent particles downstream from the clutter elements.
Show less - Date Issued
- 2009
- PURL
- http://purl.flvc.org/FAU/186687
- Subject Headings
- Airplanes, Nacelles, Safety measures, Airplanes, Fires and fire prevention, Fire extinguishing agents, Testing, Airplanes, Fluid dynamics, Mathematical models
- Format
- Document (PDF)
- Title
- Investigation of trapped vortex combustion using hydrogen-rich fuels.
- Creator
- Zbeeb, Khaled., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The combustion process of a fuel is a challenging subject when it comes to analyze its performance and resultant emissions. The main task of this study is to optimize the selection of a hydrogen-rich fuel based on its performance and emissions. Computational Fluid Dynamics analysis is performed to test the combustion performance and emissions from the vortex trapped combustor when natural gas fuel (methane) is replaced with renewable and alternative fuels such as hydrogen and synthesis gas....
Show moreThe combustion process of a fuel is a challenging subject when it comes to analyze its performance and resultant emissions. The main task of this study is to optimize the selection of a hydrogen-rich fuel based on its performance and emissions. Computational Fluid Dynamics analysis is performed to test the combustion performance and emissions from the vortex trapped combustor when natural gas fuel (methane) is replaced with renewable and alternative fuels such as hydrogen and synthesis gas. Correlation graphs for the trapped vortex combustor performance and NOx, CO, and CO2 emissions for various types of fuels with different compositions and heat of combustion values were established. Methane, Hydrogen and 10 different syngas fuels were analyzed in this study using computational fluid dynamics numerical method. The trapped vortex combustor that represents an efficient and compact combustor for flame stability was investigated. The TVC consists of a fore body and two after body disks . These components are all encircled with a Pyrex tube. The purpose of the after body disks is to create the vortex wakes that will enhance the combustion process and minimize the NOx emissions. The TVC CFD model was validated by comparing the CFD model results using propane fuel with existing experimental results that were established in Rome, Italy. The static temperature distribution and NOx, CO emissions, combustor efficiency and total pressure drop results of the three dimensional CFD model were similar to the experimental data. Effects of H2/CO and H2/CH4 ratios and the mass fraction of each constituent of syngas fuels and Hydrogen-Methane fuel mixture on the TVC performance and emissions were investigated., Moreover, the fuel injector Reynolds number and Lower heating values for Methane, Hydrogen and 10 syngas fuels on the TVC performance and emissions were also investigated. Correlation plots for the NOx, CO and CO2 emissions versus the fuel injector Reynolds number and low heating value were established. These correlation curves can be used as a fair design diagram to optimize the fuel selection process for aerospace and electrical power plant applications.
Show less - Date Issued
- 2011
- PURL
- http://purl.flvc.org/FAU/3334096
- Subject Headings
- Hydrogen as fuel, Research, Combustion chambers, Vortex-motion, Fluid dynamics
- Format
- Document (PDF)
- Title
- Electrochemical double-layer capacitors utilizing low surface area graphite fibers.
- Creator
- Zawacki, David Isaiah., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Electrochemical double-layer capacitors were constructed using low surface area carbon fibers that are commercially available. The fibers were made from polyacrylonitrile (PAN) and pitch and vary from low (LC = 14A, d002 = 3.54A) to high (LC = 169A, d002 = 3.40A) crystallinity. High energy densities (up to 7.83 Wh/kg) were obtained by electrochemically intercalating HSO4- ions between the graphene planes of the carbon fibers. The intercalation process was strongly influenced by the...
Show moreElectrochemical double-layer capacitors were constructed using low surface area carbon fibers that are commercially available. The fibers were made from polyacrylonitrile (PAN) and pitch and vary from low (LC = 14A, d002 = 3.54A) to high (LC = 169A, d002 = 3.40A) crystallinity. High energy densities (up to 7.83 Wh/kg) were obtained by electrochemically intercalating HSO4- ions between the graphene planes of the carbon fibers. The intercalation process was strongly influenced by the crystallinity of the carbon fiber and by the precursors from which the fiber was manufactured. All the pitch fibers had a higher structural order and a higher carbon content than the PAN fibers. A total of 10 capacitors were constructed. Nine of these were constructed from fibers that were electrochemically activated and one was constructed from fiber as received. 38 w/o sulfuric acid was used as the electrolyte for each of these capacitors. Performance of the capacitors decreased as the structural order and carbon content of the fibers decreased.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/15427
- Subject Headings
- Capacitors, Electric double layer, Graphite fibers
- Format
- Document (PDF)
- Title
- Response analysis of structures including effects of soil-structure interaction.
- Creator
- Yu, Jun., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The objective of the study is to determine the structural response to external force and earthquake excitations with consideration of soil-structure interaction. The physical model concerned herein is an N-story building on a rigid or flexible foundation embedded in a layered soil medium. In this substructure approach, the soil medium and the structure are treated as one-dimensional waveguides and their motions are characterized as wave scattering. To include effects of soil-structure...
Show moreThe objective of the study is to determine the structural response to external force and earthquake excitations with consideration of soil-structure interaction. The physical model concerned herein is an N-story building on a rigid or flexible foundation embedded in a layered soil medium. In this substructure approach, the soil medium and the structure are treated as one-dimensional waveguides and their motions are characterized as wave scattering. To include effects of soil-structure interaction, the foundation response is expressed as a summation of influence functions, which are defined as the response to a simple stress distribution over the contact surface between the soil and foundation. The analysis, therefore, is carried out without solving integral equations. The coupling effect is recovered by using equilibrium, compatibility and reciprocal conditions. As a result, the structural response solution is expressed in terms of parameters of a seismic source and external excitations, and can be used in a statistical analysis if uncertainties of these parameters are taken into account.
Show less - Date Issued
- 1995
- PURL
- http://purl.flvc.org/fcla/dt/12425
- Subject Headings
- Soil-structure interaction, Earthquake engineering, Structural dynamics, Foundations
- Format
- Document (PDF)
- Title
- Numerical path integration of stochastic systems.
- Creator
- Yu, Jinshou., Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The present dissertation is focused on the numerical method of path integration for stochastic systems. The existing procedures of numerical path integration are re-examined. A comparison study is made of the results obtained using various interpolation schemes. The amounts of computation time and relative accuracies of the existing procedures are tested with different mesh sizes and different time step sizes. A new numerical procedure based on Gauss-Legendre integration formula is proposed,...
Show moreThe present dissertation is focused on the numerical method of path integration for stochastic systems. The existing procedures of numerical path integration are re-examined. A comparison study is made of the results obtained using various interpolation schemes. The amounts of computation time and relative accuracies of the existing procedures are tested with different mesh sizes and different time step sizes. A new numerical procedure based on Gauss-Legendre integration formula is proposed, which requires no explicit numerical interpolation. The probability evolution is represented in terms of the transition probabilities among Gauss points in various sub-intervals. Each transition probability is assumed to be Gaussian, and it can be obtained from the moment equations. Gaussian closure is used to truncate the moment equations in the case of a nonlinear system. The computation parameters of the new procedure, such as size of time-step and number of sub-intervals, can be determined in a systematic manner. The approximate Gaussianity of the transition probability obtained from the moment equations is first tested by comparing it with the simulation results, from which a proper time-step size is selected. The standard deviation of the transition probability in each direction of the state space can then be obtained from the moment equations, and is used to determine the size of the sub-intervals in that direction. The new numerical path integration procedure is applied to several one-dimensional and two-dimensional stochastic systems, for which the responses are homogeneous Markov processes. It is shown that the new procedure is not only accurate and efficient, but also numerically stable and highly adaptable. The new procedure is also applied to a nonlinear stochastic system subjected to both sinusoidal and random excitations. The system response in this case is a non-homogeneous Markov process. The algorithm is adapted for this case, so that re-computation of the transition probability density at every time step can be avoided.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/12506
- Subject Headings
- Stochastic systems, Numerical integration, Markov processes
- Format
- Document (PDF)
- Title
- Experimental and Modeling Study of Chloride Ingress into Concrete and Reinforcement Corrosion Initiation.
- Creator
- Yu, Hui, Hartt, William H., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Effects of reinforcement and coarse aggregate on chloride ingression into concrete and reinforcement corrosion initiation have been studied with experimental and modeling (finite element method) analyses. Once specimens were fabricated and exposed to a chloride solution, various experimental techniques were employed to determine the effect of reinforcement and coarse aggregate on time-to-corrosion and chloride ingress and concentration at corrosion locations. Model analyses were performed to...
Show moreEffects of reinforcement and coarse aggregate on chloride ingression into concrete and reinforcement corrosion initiation have been studied with experimental and modeling (finite element method) analyses. Once specimens were fabricated and exposed to a chloride solution, various experimental techniques were employed to determine the effect of reinforcement and coarse aggregate on time-to-corrosion and chloride ingress and concentration at corrosion locations. Model analyses were performed to verify and explain the experimental results. Based upon the results, it was determined that unexpectedly higher chloride concentrations were present on the top of the rebar trace than that to the side at the same depth and an inverse concentration gradient (increasing [Cl-] with increasing depth) occurred near the top of rebars. Also, coarse aggregate volume profile in close proximity to the rebar and spatial distribution of these aggregates, in conjunction with the physical obstruction afforded by reinforcement to chloride flow, complicates concrete sampling for Cl- intended to define the critical concentration of this species to initiate corrosion. Modeling analyses that considered cover thickness, chloride threshold concentration, reinforcement size and shape, and coarse aggregate type and percolation confirmed the experimental findings. The results, at least in part, account for the relatively wide spread in chloride corrosion threshold values reported in the literature and illustrate that more consistent chloride threshold concentrations can be acquired from mortar or paste specimens than from concrete ones.
Show less - Date Issued
- 2007
- PURL
- http://purl.flvc.org/fau/fd/FA00012582
- Subject Headings
- Reinforced concrete construction--Corrosion, Chlorides--Diffusion rate, Composite reinforced concrete, Concrete--Chemical resistance
- Format
- Document (PDF)
- Title
- Design and analysis of an ocean current turbine performance assessment system.
- Creator
- Young, Matthew T., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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This thesis proposes a sensor approach for quantifying the hydrodynamic performance of Ocean Current Turbines (OCT), and investigates the influence of sensor-specific noise and sampling rates on calculated turbine performance. Numerical models of the selected sensors are developed, and then utilized to add stochastic measurement error to numerically-generated, non-stochastic OCT data. Numerically-generated current velocity and turbine performance measurements are used to quantify the relative...
Show moreThis thesis proposes a sensor approach for quantifying the hydrodynamic performance of Ocean Current Turbines (OCT), and investigates the influence of sensor-specific noise and sampling rates on calculated turbine performance. Numerical models of the selected sensors are developed, and then utilized to add stochastic measurement error to numerically-generated, non-stochastic OCT data. Numerically-generated current velocity and turbine performance measurements are used to quantify the relative influence of sensor-specific error and sampling limitations on sensor measurements and calculated OCT performance results. The study shows that the addition of sensor error alters the variance and mean of OCT performance metric data by roughly 7.1% and 0.24%, respectively, for four evaluated operating conditions. It is shown that sensor error results in a mean, maximum and minimum performance metric to Signal to Noise Ration (SNR) of 48.6% and 6.2%, respectively.
Show less - Date Issued
- 2012
- PURL
- http://purl.flvc.org/FAU/3359164
- Subject Headings
- Marine turbines, Mathematical models, Fluid dynamics, Structural dynamics, Stochastic processes, Rotors, Design and construction, Testing
- Format
- Document (PDF)
- Title
- ACOUSTIC EMISSIONS TESTING AS A NONDESTRUCTIVE MONITOR OF CONCRETE CRACKING DUE TO REINFORCING BAR CORROSION.
- Creator
- YOUNG, JAMES DANIEL., Florida Atlantic University, Dunn, Stanley E., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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Steel reinforced concrete specimens of loaded and unloaded configuration were placed in contact with seawater in a state of accelerated corrosion. They were simultaneously monitored for acoustic emission and the results were analyzed in an evaluation of the use of acoustic emission as a nondestructive monitor of corrosion induced cracking. It was shown that, in a laboratory environment, counts and amplitude information are sensitive indicators of the levels of cracking within the concrete...
Show moreSteel reinforced concrete specimens of loaded and unloaded configuration were placed in contact with seawater in a state of accelerated corrosion. They were simultaneously monitored for acoustic emission and the results were analyzed in an evaluation of the use of acoustic emission as a nondestructive monitor of corrosion induced cracking. It was shown that, in a laboratory environment, counts and amplitude information are sensitive indicators of the levels of cracking within the concrete specimen; and thereby the degree of corrosion damage may be inferred. Analytical models applicable to the representation of acoustic emission amplitude distribution are discussed also.
Show less - Date Issued
- 1982
- PURL
- http://purl.flvc.org/fcla/dt/14141
- Subject Headings
- Reinforced concrete--Cracking, Reinforced concrete--Corrosion, Acoustic emission testing
- Format
- Document (PDF)
- Title
- MODEL EXPERIMENTS FOR 3-DIMENSIONAL PROPAGATION CHARACTERISTICS IN A WEDGE-SHAPED OCEAN.
- Creator
- Yoon, Jong Rak, 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 theoretical solution for acoustic propagation in a wedge-shaped ocean with ideal pressure-release boundaries predicts a well-defined beam which diverges as the energy propagates out towards deep water. Outside of the beam, shadow zones are formed, and the beam's spatial extent is determined by the lowest mode of propagation. The purpose of the experimental results presented here is to check the theoretical analyses, as part of an ongoing investigation into three dimensional propagation in...
Show moreThe theoretical solution for acoustic propagation in a wedge-shaped ocean with ideal pressure-release boundaries predicts a well-defined beam which diverges as the energy propagates out towards deep water. Outside of the beam, shadow zones are formed, and the beam's spatial extent is determined by the lowest mode of propagation. The purpose of the experimental results presented here is to check the theoretical analyses, as part of an ongoing investigation into three dimensional propagation in the ocean environment, and to investigate further the propagation characteristics of this type. It has been found that for downslope propagation, the spatial characteristics of the field in a direction parallel to the shore line are in good agreement with the theoretical solution and the azimuthal extent of the beam depends on the wedge angle and frequency.
Show less - Date Issued
- 1987
- PURL
- http://purl.flvc.org/fcla/dt/14387
- Subject Headings
- Underwater acoustics
- Format
- Document (PDF)
- Title
- Measurement of source height on moving highway vehicles.
- Creator
- Yoon, Jong Rak, 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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A measurement method for the equivalent noise source height of an arbitrary distribution of moving noise sources is developed to investigate the highway vehicle equivalent source heights which are currently used by the FHWA for noise barrier design. The study is intended to provide information required to improve this noise barrier design code. The equivalent point source position is defined for an arbitrary distribution of acoustic sources above a reflecting plane and a method for its...
Show moreA measurement method for the equivalent noise source height of an arbitrary distribution of moving noise sources is developed to investigate the highway vehicle equivalent source heights which are currently used by the FHWA for noise barrier design. The study is intended to provide information required to improve this noise barrier design code. The equivalent point source position is defined for an arbitrary distribution of acoustic sources above a reflecting plane and a method for its measurement using a microphone array is developed. The normalized errors of the measured equivalent source heights are defined including the effects of background noise, the geometric near field, source size, and source directionality. Normalized errors of the measured source heights obtained by a numerical simulation for each parameter lead to optimization of the microphone spacing and to the design of an array of microphones which give the equivalent source height as a function of frequency. The method is then applied to the measurement of the equivalent source height of stationary loudspeakers and is shown to give results which are consistent with theoretical predictions. The effect of the Doppler frequency shift of moving vehicles is investigated using a loudspeaker mounted on the roof of a moving car. If the speed of a moving noise source is less than 97 kph, the error due to the Doppler frequency shift was found to be negligible. Results of measurement on highway vehicles show that the noise source heights for heavy trucks and for automobiles are different from those used currently by the FHWA.
Show less - Date Issued
- 1990
- PURL
- http://purl.flvc.org/fcla/dt/12247
- Subject Headings
- Traffic noise--Mathematical models, Traffic noise--Measurement--Mathematical models, Noise barriers--Mathematical models
- Format
- Document (PDF)