Current Search: Department of Ocean and Mechanical Engineering (x)
View All Items
(521 - 540 of 676)
Pages
- Title
- High-speed acoustic communication in shallow water using spatio-temporal adaptive array processing.
- Creator
- Beaujean, Pierre-Philippe, Florida Atlantic University, LeBlanc, Lester R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A novel method of achieving stable high-speed underwater acoustic communication with a fairly low-complexity of implementation is proposed. The proposed approach is to split the space and time processing into two separate sub-optimal processes. As a result, processing complexity is significantly reduced and the instabilities associated with large tap vectors at large time-frequency spread products are reduced. The proposed space-time signal processing method utilizes a different beamformer...
Show moreA novel method of achieving stable high-speed underwater acoustic communication with a fairly low-complexity of implementation is proposed. The proposed approach is to split the space and time processing into two separate sub-optimal processes. As a result, processing complexity is significantly reduced and the instabilities associated with large tap vectors at large time-frequency spread products are reduced. The proposed space-time signal processing method utilizes a different beamformer optimization strategy compared to the time domain optimization strategy. This allows to separately adjust the adaptation parameters for the spatial and temporal characteristics of the signal, which have vastly different requirements. The time domain signal is subject to variations in phase that require rapid filter updates whereas the directional characteristics of the signal do not vary appreciably over the message length and do not require a rapid adaptation response. The proposed method allows for high-speed underwater acoustic communication in very shallow water using coherent modulation techniques, and offers a series of unique features: significant reduction of the signal-to-noise and interference ratio (SNIR), improvement of the bandwidth efficiency by reduction of the forward-error coding redundancy requirements, real-time evaluation of the time-spread by Doppler spread product (BL) and channel stability estimate. Experimental results demonstrate that stable acoustic communication can be achieved at rates of 32000 bits per second at a distance of 3 km, in 40 feet of water and in sea-state 2 conditions. Fast and slow fading properties of the channel are measured, as the BL product can vary by a decade in 116 ms, and by two decades within minutes, from 0.001 to 0.1. The real-time analysis shows a strong correlation between time spread, Doppler spread, spatial coherence of the acoustic channel and communication performance. Overall, this research provides more scientific and experimental ground to understand the limitations of multi-channel adaptive receiver techniques in terms of stability, hardware requirements and channel tracking capability.
Show less - Date Issued
- 2001
- PURL
- http://purl.flvc.org/fcla/dt/11952
- Subject Headings
- Underwater acoustic telemetry, Adaptive signal processing
- Format
- Document (PDF)
- Title
- Heating, venting and aerosol particles dynamics in a vacuum clean chamber: An analytical investigation.
- Creator
- Li, Jiyue., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
It is empirically observed and broadly used in the semiconductor manufacturing industry that the clean environment of in-vacuum processing can be enhanced through heating from outside the clean chamber. This paper reports an analytical investigation of this problem and presents the results that confirm the speeding effects of changing the temperature gradient at one end of the clean chamber on venting the aerosol particles from inside the clean chamber. First, a mathematical frame for the...
Show moreIt is empirically observed and broadly used in the semiconductor manufacturing industry that the clean environment of in-vacuum processing can be enhanced through heating from outside the clean chamber. This paper reports an analytical investigation of this problem and presents the results that confirm the speeding effects of changing the temperature gradient at one end of the clean chamber on venting the aerosol particles from inside the clean chamber. First, a mathematical frame for the basic problem is formulated and then various analytical techniques are employed to reduce a set of coupled nonlinear partial differential equations to linear equations, and finally, numerical results are obtained from explicit, analytical formulas.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14524
- Subject Headings
- Clean rooms--Heating and ventilation
- Format
- Document (PDF)
- Title
- Lifeline structures under earthquake excitations.
- Creator
- Reddy, Kondakrindhi Praveen., Florida Atlantic University, Yong, Yan, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An analytical method is proposed for the response analysis of lifeline structures subjected to earthquake excitations. The main feature of the approach is to consider the vibrational motion as a result of the wave motion in a waveguide-like lifeline structure. Based on the theory of wave propagation, scattering matrices are derived to characterize the wave propagation in individual segments and wave reflections and transmissions at supports and boundaries. Response solution is derived in a...
Show moreAn analytical method is proposed for the response analysis of lifeline structures subjected to earthquake excitations. The main feature of the approach is to consider the vibrational motion as a result of the wave motion in a waveguide-like lifeline structure. Based on the theory of wave propagation, scattering matrices are derived to characterize the wave propagation in individual segments and wave reflections and transmissions at supports and boundaries. Response solution is derived in a closed form, suitable for stochastic analysis when the input is an earthquake excitation. A space-time earthquake ground motion model that accounts for both coherent decay and seismic wave propagation is used to specify motions at supports. The proposed technique can be used to obtain lifeline structural response accurately and determine the correlation between any two locations in an effective manner. The computational aspects of its implementation are also discussed. Numerical examples are presented to illustrate the application and efficiency of the proposed analytical scheme.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14898
- Subject Headings
- Artificial intelligence, Fuzzy logic, Neural networks (Computer science), Pavements--Skid resistance
- Format
- Document (PDF)
- Title
- Mobility power flow (MPF) approach applied to fluid-loaded shells with ring discontinuities.
- Creator
- McCain, Thomas Scott., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The vibrational and acoustic characteristics of fluid-loaded, cylindrical shells with single or multiple, aperiodically-spaced ring discontinuities are studied using an approach based on the mobility power flow (MPF) method and a hybrid numerical/analytical method for the evaluation of the velocity Green's function of the shell. The discontinuities are associated with internal structures coupled to the shell via ring junctions. The approach is a framework allowing alternative shell and/or...
Show moreThe vibrational and acoustic characteristics of fluid-loaded, cylindrical shells with single or multiple, aperiodically-spaced ring discontinuities are studied using an approach based on the mobility power flow (MPF) method and a hybrid numerical/analytical method for the evaluation of the velocity Green's function of the shell. The discontinuities are associated with internal structures coupled to the shell via ring junctions. The approach is a framework allowing alternative shell and/or internal structure models to be used. The solution consists of the net vibrational power flow between the shell and internal structure(s) at the junction(s), the shell's velocity Green's function, and the far-field acoustic pressure. Use of the MPF method is advantageous because the net power flow solution can be used as a diagnostic tool in ascertaining the proper coupling between the shell and internal structure(s) at the junction(s). Results are presented for two canonical problems: an infinite, thin cylindrical shell, externally fluid-loaded by a heavy fluid, coupled internally to: (1) a single damped circular plate bulkhead, and (2) a double bulkhead consisting of two identical damped circular plates spaced a shell diameter apart. Two excitation mechanisms are considered for each model: (1) insonification of the shell by an obliquely-incident, acoustic plane wave, and (2) a radial ring load applied to the shell away from the junction(s). The shell's radial velocity Green's function and far-field acoustic pressure results are presented and analyzed to study the behavior of each model. In addition, a comparison of these results accentuates the qualitative difference in the behavior between the single and multiple junction models. When multiple internal structures are present, the results are strongly influenced by inter-junction coupling communicated through the shell and the fluid. Results are presented for circumferential modes n = 0 & 2. The qualitative differences in the results for modes n = 0 and n = 2 (indicative of all modes n > 0ified in the far-field acoustic pressure and velocity Green's function response with the characteristics of the shell and internal plate bulkhead. The results for the single junction model demonstrate the significance of the shell's membrane waves on the reradiation of acoustic energy from the shell; however, when multiple junctions are present, inter-junction coupling results in a significant broad acoustic scattering pattern. Using the results and analysis presented here, a better understanding can be obtained of fluid-loaded shells, which can be used to reduce the strength of the acoustic pressure field produced by the shell.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/12490
- Subject Headings
- Shells (Engineering)--Vibration, Cylinders--Vibration, Fluid dynamics, Sound--Transmission
- Format
- Document (PDF)
- Title
- Modal analysis of plates with uncertain properties: Theory and applications.
- Creator
- Wu, Jingshu., Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This dissertation is concerned with modal analysis of plates with properties which vary over the structures. The uncertain geometric and material parameters are treated as random fields which are discretized over individual regions by using a local averaging technique. These discretized properties are then combined with a random perturbation procedure based upon traditional finite element methods. The result is a stochastic finite element method (SFEM) program for modal analysis of plates....
Show moreThis dissertation is concerned with modal analysis of plates with properties which vary over the structures. The uncertain geometric and material parameters are treated as random fields which are discretized over individual regions by using a local averaging technique. These discretized properties are then combined with a random perturbation procedure based upon traditional finite element methods. The result is a stochastic finite element method (SFEM) program for modal analysis of plates. This SFEM method is applied to two problems areas. The first application is to provide a new approach for modal analysis of printed circuit boards wherein the circuit board is modeled as an elastic plate with random spatial variation of its properties. The SFEM program is used to predict the effect of this variation on the natural frequencies and mode shapes of the board. Predicted results are compared with those obtained from modal testing of a circuit board. It is shown that variations between the measured and predicted modal parameters can be accounted for by small random variations in the board properties. This approach offers a simple, realistic, and cost-effective way for prediction of board modal properties. The second application is on vibration control of plates by application of surface viscoelastic damping treatments. Existing works generally treat the geometric and material properties of the damping layer as deterministic parameters, although uncertainties in the values of these parameters are commonplace. No work has been done regarding surface damping treatments with uncertain properties. In this thesis, the modal properties of plates with random spatial variation of the damping layer properties are investigated. The effects of this variation on the system natural frequencies, modal loss factors, and mode shapes are calculated by the SFEM program developed. Results are presented for a cantilever aluminum plate with complete PVC surface damping treatment with uncertain properties. In the SFEM modeling of both PC boards and plates with surface damping treatments, the effects on the system eigenvalues/eigenvectors of the correlation distance of the random property field, the correlation constant between the random fluctuations, and the magnitude of the random property variations, are investigated.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/12335
- Subject Headings
- Modal analysis, Stochastic processes, Finite element method, Plates (Engineering)--Testing
- Format
- Document (PDF)
- Title
- Mode I interlaminar fracture toughness of interleaved graphite/epoxy.
- Creator
- Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Mode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material...
Show moreMode I interlaminar fracture toughness, G IC, of interleaved graphite/epoxy has been investigated with DCB specimens, beam theory, and finite element analysis. Finite element modeling aimed to investigate the influence of interleaf thickness on compliance and energy release rate and possible mixed mode loading in the case of asymmetric interfacial crack. Another objective was to compute crack tip yield zone dimensions as a function of thickness and elastic properties of the interleaf material. The analysis is correlated with experiments. Thermoplastic interleaves enhanced G IC to a great extent. The toughness increased sharply with film thickness to a maximum at 16 mu m and decreased for the thicker interleaves. On the other hand, inadequate adhesion preempted the toughness potential of thermoset interleaves.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14682
- Subject Headings
- Laminated materials--Testing, Fracture mechanics, Strength of materials
- Format
- Document (PDF)
- Title
- Microcomputer and exsysp based expert system for selection and design of retaining structures.
- Creator
- Sinha, Anuradha., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The automation of retaining structure selection and design by utilizing artificial intelligence tools is presented herein. The study involved the development of a microcomputer based expert system, RESTEX (REtaining STructure EXpert). The modules of the expert systems RETAININGEARTH, with M.1 knowledge base, and REFLEXYS have been updated and the resulting RESTEX modules are written in C using Exsys Professional for high speed and efficient utilization of memory. RESTEX is an interactive menu...
Show moreThe automation of retaining structure selection and design by utilizing artificial intelligence tools is presented herein. The study involved the development of a microcomputer based expert system, RESTEX (REtaining STructure EXpert). The modules of the expert systems RETAININGEARTH, with M.1 knowledge base, and REFLEXYS have been updated and the resulting RESTEX modules are written in C using Exsys Professional for high speed and efficient utilization of memory. RESTEX is an interactive menu-driven system consisting of modules for Structure Selection, Preliminary Design, Soils Classification, Stability Analysis, and Reinforcement Design. The system is capable of performing selection, analysis, and design of gravity walls, cantilever walls, counterfort walls, reinforced earth, gabion, cantilever and anchored sheet piles.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14937
- Subject Headings
- Precast concrete construction--Fatigue, Post-tensioned prestressed concrete construction--Fatigue, Bridges, Box girder, Strains and stresses
- Format
- Document (PDF)
- Title
- Modeling of a storm water system: Village of Tequesta level of service study.
- Creator
- Sharp, Wayne Andrew., Florida Atlantic University, Scarlatos, Panagiotis (Pete) D., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The Village of Tequesta typifies an older storm water system. The infrastructure for the system has not kept up with development within the community. The design was for the conditions at the time of initial development. The levels of services provided are pertinent to establishing a direction and long term goals under current conditions. The existing seven and a half miles of conduit was modeled for a 25 year 24 hour storm. The rainfall amount simulated for the Tequesta area is 10.48 inches...
Show moreThe Village of Tequesta typifies an older storm water system. The infrastructure for the system has not kept up with development within the community. The design was for the conditions at the time of initial development. The levels of services provided are pertinent to establishing a direction and long term goals under current conditions. The existing seven and a half miles of conduit was modeled for a 25 year 24 hour storm. The rainfall amount simulated for the Tequesta area is 10.48 inches within a tidal area. The effects of the tide and the conditions of the conduit system lead to a realization that surface drainage is deeply affected by the tidal ranges associated with storm events.
Show less - Date Issued
- 2000
- PURL
- http://purl.flvc.org/fcla/dt/15773
- Subject Headings
- Storm sewers--Florida--Tequesta, Drainage--Florida--Tequesta, Storm water retention basins--Florida--Tequesta
- Format
- Document (PDF)
- Title
- Modeling and control of the "C-Plane" ocean current turbine.
- Creator
- VanZwieten, James H., Florida Atlantic University, Driscoll, Frederick R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The "C-Plane" is a submerged ocean current turbine that uses sustained ocean currents to produce electricity. This turbine is moored to the sea floor and is capable of changing depth, as the current profile changes, to optimize energy production. A 1/30th scale physical prototype of the C-Plane is being developed and the analysis and control of this prototype is the focus of this work. A mathematical model and dynamic simulation of the 1/30th scale C-Plane prototype is created to analyze this...
Show moreThe "C-Plane" is a submerged ocean current turbine that uses sustained ocean currents to produce electricity. This turbine is moored to the sea floor and is capable of changing depth, as the current profile changes, to optimize energy production. A 1/30th scale physical prototype of the C-Plane is being developed and the analysis and control of this prototype is the focus of this work. A mathematical model and dynamic simulation of the 1/30th scale C-Plane prototype is created to analyze this vehicle's performance, and aid in the creation of control systems. The control systems that are created for this prototype each use three modes of operation and are the Mixed PID/Bang Bang, Mixed LQR/PID/Bang Bang, and Mixed LQG/PID/Bang Bang control systems. Each of these controllers is tested using the dynamic simulation and Mixed PID/Bang Bang controller proves to be the most efficient and robust controller during these tests.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/12980
- Subject Headings
- Marine turbines--Automatic control, Ocean energy resources, Marine turbines--Mathematical models
- Format
- Document (PDF)
- Title
- Estimation of cross range dimensions from a single beam forward look SONAR.
- Creator
- Park, Joseph C., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A computer algorithm is developed to provide real-time cross range spatial quantization for a single beam forward look SONAR similar in operation to a typical sidescan SONAR. This involves the computer simulation of return time signals generated by scanning a surface profile. The time signals are normalized with respect to the scanning altitude to simulate the application of a time varying gain, and then are used as input to the surface estimation algorithm. The algorithm requires two time...
Show moreA computer algorithm is developed to provide real-time cross range spatial quantization for a single beam forward look SONAR similar in operation to a typical sidescan SONAR. This involves the computer simulation of return time signals generated by scanning a surface profile. The time signals are normalized with respect to the scanning altitude to simulate the application of a time varying gain, and then are used as input to the surface estimation algorithm. The algorithm requires two time signals acquired from adjacent scanning positions and solves a stereoscopic geometry in arriving at the surface estimate. Final estimates have an error of less than 1% in target height determination within a set range of operation.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14501
- Subject Headings
- Sonar--Computer simulation, Signal processing--Computer simulation, Underwater acoustics--Computer simulation
- 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
- APPLICATION OF A MICROPROCESSOR TO ACOUSTIC DATA SAMPLING AND MANAGEMENT TASKS (AS APPLIED TO MANGANESE NODULE MINING).
- Creator
- MURPHY, DAVID PAUL, JR., Florida Atlantic University, Davidson, J. Blaine, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Methods of collecting information about the deep ocean sediments are considered. A compact, flexible data collection and management system based on microprocessor technology is developed. The hardware of the system is detailed and a typical software operating system is presented which controls sensor operations, stores temporary data and communicates with a shipboard computer system.
- Date Issued
- 1979
- PURL
- http://purl.flvc.org/fcla/dt/13987
- Subject Headings
- Microprocessors, Marine sediments--Sampling, Manganese nodules
- Format
- Document (PDF)
- Title
- Computation of hydrodynamic coefficients and determination of dynamic stability characteristics of an underwater vehicle including free surface effects.
- Creator
- Saout, Olivier., Florida Atlantic University, Ananthakrishnan, Palaniswamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The inviscid hydrodynamic coefficients of an underwater vehicle (Ocean EXplorer), including the nonlinear effects of the wave surface, are computed using a boundary-integral method. A mixed Eulerian-Lagrangian formulation (Longuet-Higgins and Cokelet, 1976) is used for the treatment of nonlinear free-surface conditions. The algorithm is validated using the work-energy theorem (Yeung, 1982) and experimental data. Results, in the form of free-surface elevations and hydrodynamic coefficients,...
Show moreThe inviscid hydrodynamic coefficients of an underwater vehicle (Ocean EXplorer), including the nonlinear effects of the wave surface, are computed using a boundary-integral method. A mixed Eulerian-Lagrangian formulation (Longuet-Higgins and Cokelet, 1976) is used for the treatment of nonlinear free-surface conditions. The algorithm is validated using the work-energy theorem (Yeung, 1982) and experimental data. Results, in the form of free-surface elevations and hydrodynamic coefficients, are obtained for a range of body geometries and maneuvers. The open-loop dynamics of underwater vehicles are then investigated by solving the 3DOF rigid-body equations of motion (OXY plane). The advantages and possible usage of the developed methodology for the design and control of underwater vehicles, as well as topics for further research, are addressed in the conclusion chapter of the thesis.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/12981
- Subject Headings
- Hydrodynamics, Oceanographic submersibles, Water waves
- Format
- Document (PDF)
- Title
- Compression failure of sandwich specimens with and without face/core debonds.
- Creator
- Vadakkeveedu, Vinod P., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The objective of this thesis is to report on an experimental study on the compressive behavior of foam cored sandwich composite specimens with and without face/core debond. A test fixture was designed which enables a precisely machined sandwich specimen instrumented with back-to-back strain gages to be loaded in edgewise compression. Tests were conducted on specimens without implanted face/core interface debonds over a range of core densities and gage lengths. The experimentally determined...
Show moreThe objective of this thesis is to report on an experimental study on the compressive behavior of foam cored sandwich composite specimens with and without face/core debond. A test fixture was designed which enables a precisely machined sandwich specimen instrumented with back-to-back strain gages to be loaded in edgewise compression. Tests were conducted on specimens without implanted face/core interface debonds over a range of core densities and gage lengths. The experimentally determined compression strengths and failure modes were compared to closed-form predictions and finite element analysis. Specimens with an implanted through-the-width face/core debond were also tested and mechanism of failure was analyzed using finite element analysis. Good agreement between collapse loads predicted using geometrically nonlinear analysis and experimentally measured strengths was observed.
Show less - Date Issued
- 2003
- PURL
- http://purl.flvc.org/fcla/dt/13047
- Subject Headings
- Sandwich construction, Strains and stresses, Structural analysis (Engineering)
- Format
- Document (PDF)
- Title
- Computations of normal vortex interaction with blades and circular cylinders.
- Creator
- Yalamanchili, Ramakrishna., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A numerical model for the simulation of three-dimensional normal blade-vortex interaction has been developed to study the bending and variation of core radius of the vortex due to the influence of the blade and the subsequent unsteady force on the blade. For thin blades, a procedure to enable instantaneous cutting of the vortex has been employed to study the vortex response to cutting. The vortex is represented by a filament model which includes axial flow within the core and non-uniform core...
Show moreA numerical model for the simulation of three-dimensional normal blade-vortex interaction has been developed to study the bending and variation of core radius of the vortex due to the influence of the blade and the subsequent unsteady force on the blade. For thin blades, a procedure to enable instantaneous cutting of the vortex has been employed to study the vortex response to cutting. The vortex is represented by a filament model which includes axial flow within the core and non-uniform core area. The vortex is convected with self-induced velocities given by the Biot-Savart line integral, and the effect of the cylinder is obtained using a vortex sheet panel method. The governing equations for the vortex axial velocity have a form similar to that of the one-dimensional gas dynamics equations and admit "shock-like" discontinuities. The results indicate that the amount of vortex bending due to interaction with the blade is primarily dependent on the ratio of blade thickness T to ambient vortex core radius sigma o, although for a given amount of bending of the vortex axis, increase in cylinder forward speed results in a decrease in vortex core radius. For blades with T/sigma o < 0(1), very little bending is observed for attack angles under the stall limit. In the case of vortex cutting by a blade, vortex shocks and expansion waves are observed to propagate on the vortex axis away from the blade.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14985
- Subject Headings
- Helicopters, Blades--Noise, Rotors (Helicopters), Vortex-motion
- Format
- Document (PDF)
- Title
- Computed tomographic measurements of void fraction and modeling of the flow in bubble columns.
- Creator
- Kumar, Sailesh B., Florida Atlantic University, Moslemian, Davood, Dudukovic, M. P., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the...
Show moreA complete understanding of the gas-liquid two phase flow in bubble columns is required for the development of reliable models for scale-up of these multiphase reactors. Although several models have been proposed to describe the hydrodynamics. lack of adequate experimental data has hindered meaningful evaluation of model parameters and model predictions. The Computer Automated Radioactive Particle Tracking ( CARPT) facility that was implemented earlier has provided interesting results on the recirculation patterns of the liquid phase. The technique has provided quantitative information on liquid velocities and turbulence parameters as well. In addition to these hydrodynamic parameters the measurement of void fraction is also important. To complement the capabilities of CARPT a scanner for ;-ray Computed Tomography (CT) was implemented to quantify the local void fraction and its distribution in two phase flow systems. The automated scanner is capable of imaging flows in test sections between 0.02.5 m and 0..15 m in diameter at different elevations above the distributor. The scanner makes use of the same detectors used in the CARPT facility and with the use of a specially designed moving collimator provides a spatial resolution of about 5 mm. A non-conventional algorithm based on maximum likelihood principles called the E-M algorithm was used for imagw reconstruction. Long scanning times are required leading to time averaged density profiles. Although the system is only capable of providing time averaged void fraction distributions. it can provide unique information concerning the structure of two phase flow. The system performance was evaluated by identifying the sources of errors in measurement and their bounds. The capabilities of the scanner for imaging void fraction distribution was demonstrated both qualitatively and quantitatively. Fse of existing radiation detectors and the associated signal processing and data acquisition system helped in reducing the cost of the system. The scanner was utilized to quantify the local void fraction and its distribution in bubble columns of five diameters (0.10. 0.14, 0.19, 0.26. 0.30 m internal diameter) and at four superficial gas velocities. The effect of various operating parameters such as column diameter, superficial gas velocity. the type of distributor. the static liquid height and some changes in the physical properties of the liquid phase were studied. For the first time a comprehensive characterization of the void fraction in an air water bubble column using a non-invasive technique was achieved. The experimental data obtained using CARPT and CT under identical operating conditions was used for developing a methodology for scale-up of bubble columns using a one dimensional model for liquid recirculation. Successful scale-up of liquid hydrodynamics using a one dimensional model requires an adequate closure scheme for the Reynolds shear stress. The existing correlations for the prescription of the eddy viscosity or the mixing length scale are demonstrated to be applicable only for a limited range of conditions. and consequently cannot be used for scale-up predictions. A method for estimating the mixing length scale has been explored and an attempt at unifying a wide range of data available in the literature within the pun·iew of the method has been made. The futility of such an attempt is attributed to the non-reproducibility of the flow in different laboratories and the conasequent lack of data obtained under identical conditions. It is demonstrated, however, that scale-up based on the mixing length distribution is possible when it is obtained from a consistent set of data for liquid velocity and gas void fraction profiles. Using the present method for prescribing the mixing length scale. model predictions for scale-up compare satisfactorily for the data that was obtained as part of this research. The achievement was that the turbulence length scale estimated in one column diameter was successfully used in predicting the liquid velocities in larger diameter columns.
Show less - Date Issued
- 1994
- PURL
- http://purl.flvc.org/fcla/dt/12384
- Subject Headings
- Two-phase flow, Hydrodynamics, Bubble chambers, Tomography, Emission
- Format
- Document (PDF)
- Title
- Control of response of tall multi-story buildings under wind excitation.
- Creator
- Qiu, Xin., Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Theoretical investigation is carried out into the extent to which floor accelerations of a wind-excited tall building can be reduced by increasing damping in those components in a building which are generally regarded to be non-structural elements, and by using active control. The wind loads are modeled as stochastic processes, which are correlation-stationary in time. Only the drag wind forces are considered in the analyses. The spectral densities and cross-spectral densities of two commonly...
Show moreTheoretical investigation is carried out into the extent to which floor accelerations of a wind-excited tall building can be reduced by increasing damping in those components in a building which are generally regarded to be non-structural elements, and by using active control. The wind loads are modeled as stochastic processes, which are correlation-stationary in time. Only the drag wind forces are considered in the analyses. The spectral densities and cross-spectral densities of two commonly used models, proposed by Davenport and by Simiu, are compared. The Davenport spectrum is used in the numerical calculation for illustration purposes. Several structural models are discussed: an ideal spatially periodic model, an ideal piece-wise spatially periodic model, a nominal spatially periodic model with random disorder in periodicity, and an ideal spatially periodic model equipped with an active mass damper control system. The problems are formulated using the transfer matrix approach in the frequency domain. Analytical solutions are obtained for the spectral densities and the mean-square values of the floor accelerations and those of the active control force. Numerical examples are given for illustration.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/12495
- Subject Headings
- Tall buildings--Aerodynamics, Wind-pressure, Damping (Mechanics)
- Format
- Document (PDF)
- Title
- Control design for highly maneuverable autonomous underwater vehicles.
- Creator
- Poirrier, Ronald., Florida Atlantic University, Leonessa, Alexander, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Accurate Autonomous Underwater Vehicles positioning requires an appropriate control design which takes into account the nonlinear coupling between the different degrees of freedom. Assuming a vehicle equipped with two side-thruster modules including two tunnel thrusters each, the control problem will be split into an outer control loop handling the motion of the vehicle, and an inner control loop designed to track the thrust commanded to each thruster. A multivariable Lyapunov function based...
Show moreAccurate Autonomous Underwater Vehicles positioning requires an appropriate control design which takes into account the nonlinear coupling between the different degrees of freedom. Assuming a vehicle equipped with two side-thruster modules including two tunnel thrusters each, the control problem will be split into an outer control loop handling the motion of the vehicle, and an inner control loop designed to track the thrust commanded to each thruster. A multivariable Lyapunov function based approach, characterized by robustness properties with respect to parametric uncertainties and linearly bounded control output, will be proposed for the outer-loop and simulation results will be discussed. Regarding the low-level control framework, the performance of nine different controllers including conventional PI, sliding mode fuzzy controllers, and adaptive schemes such as model reference and sliding mode adaptive controllers, will be compared through theoretical derivations and experimental results. Such a comparison will show the advantages of the adaptive schemes in terms of tuning, robustness, and tracking performances.
Show less - Date Issued
- 2001
- PURL
- http://purl.flvc.org/fau/fd/FADT12777
- Subject Headings
- Submersibles--Automatic control, Oceanographic submersibles
- Format
- Document (PDF)
- Title
- Creep and shrinkage effects on integral abutment bridges.
- Creator
- Munuswamy, Sivakumar., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Integral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and...
Show moreIntegral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and statical indeterminacy of the structure introduce time-dependent variations in the redundant forces. An analytical model and numerical procedure to predict instantaneous linear behavior and non-linear time dependent long-term behavior of continuous composite superstructure are developed in which the redundant forces in the integral abutment bridges are derived considering the time-dependent effects. The redistributions of moments due to time-dependent effects have been considered in the analysis. The analysis includes nonlinearity due to cracking of the concrete, as well as the time-dependent deformations. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) models for creep and shrinkage are considered in modeling the time dependent material behavior. The variations in the material property of the cross-section corresponding to the constituent materials are incorporated and age-adjusted effective modulus method with relaxation procedure is followed to include the creep behavior of concrete. The partial restraint provided by the abutment-pile-soil system is modeled using discrete spring stiffness as translational and rotational degrees of freedom. Numerical simulation of the behavior is carried out on continuous composite integral abutment bridges and the deformations and stresses due to time-dependent effects due to typical sustained loads are computed. The results from the analytical model are compared with the published laboratory experimental and field data. The behavior of the laterally loaded piles supporting the integral abutments is evaluated and presented in terms of the lateral deflection, bending moment, shear force and stress along the pile depth.
Show less - Date Issued
- 2004
- PURL
- http://purl.flvc.org/fau/fd/FADT12067
- Subject Headings
- Bridges--Abutments, Concrete--Creep, Concrete--Expansion and contraction
- Format
- Document (PDF)
- Title
- DEVELOPMENT OF A TWO-DIMENSIONAL LINEAR STATIC FINITE ELEMENT PROGRAM FOR A DESKTOP MICROCOMPUTER.
- Creator
- SCHWEET, RICHARD RAYMOND., Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The finite element method is widely used in many areas of engineering and applied science, including structures, fluids, heat transfer, and electromagnetism. Several commercial programs exist which have extensive capabilites in these areas, but they usually require special training and mainframe computers to use. This creates a series of problems in an engineering organization because of the inefficiencies of timeshared computer systems and remote processing. These problems result in poor...
Show moreThe finite element method is widely used in many areas of engineering and applied science, including structures, fluids, heat transfer, and electromagnetism. Several commercial programs exist which have extensive capabilites in these areas, but they usually require special training and mainframe computers to use. This creates a series of problems in an engineering organization because of the inefficiencies of timeshared computer systems and remote processing. These problems result in poor productivity of the analyst. This work demonstrates the feasibility of using a desktop microcomputer to perform finite element structural analysis. A program is developed which is capable of solving two-dimensional linear static problems using truss, beam and plane stress elements. The program includes extensive pre- and post-processing capabilities and graphic displays. It allows problems with up to 500 degrees-of-freedom to be solved within a few hours and requires only about one-half hour of instruction to use. The program theory, a user's manual, and verification problems are presented.
Show less - Date Issued
- 1984
- PURL
- http://purl.flvc.org/fcla/dt/14225
- Subject Headings
- Microcomputers--Programming, Electronic data processing--Engineering
- Format
- Document (PDF)
