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- Title
- An investigation of the acoustic field in wedge-shaped scale models of continental shelf regions.
- Creator
- House, Ian Geoffrey., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions....
Show moreThe acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions. One such assumption is to model a region of the ocean as a water column overlying a planar sloping bottom. To test the accuracy of these theories model scale measurements of the acoustic field under highly controlled conditions have been undertaken in this study. Two experiments were performed on models with a sloping bottom. The first model consisted of a fast fluid bottom, and the second model consisted of a thin epoxy layer, to model a sediment, overlying a concrete layer, which modelled the substrate rock. The measurements performed included pulse, CW traverse, and depth profile measurements in both the across slope and down slope directions, in order to demonstrate the three dimensional features of the field. The features of the results are discussed and where possible are compared with existing theories. The results indicated that the three dimensional propagation effects in a fluid bottom wedge are described accurately by a theoretical model which uses an effective depth correction. No three dimensional theory was available for the shear wave supporting bottom case but the fluid bottom theory was found to provide accurate predictions. Down slope propagation over a shear wave supporting bottom was also shown to be accurately predicted using a two dimensional finite element parabolic equation code.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/12284
- Subject Headings
- Underwater acoustics--Measurement, Ocean bottom, Continental shelf
- Format
- Document (PDF)
- Title
- The effects of substrate, surface finish, flow rate and exposure duration on calcareous deposits.
- Creator
- Mantel, Katherine Elizabeth., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The effect of substrate finish and composition, flow rate and exposure duration on the composition, morphology and protective properties of calcareous deposits formed during cathodic polarization of several steels in seawater has been investigated. The current density behaviour of the scale formation in conjunction with morphology and composition characteristics indicated that the substrate finish and composition did not influence the nucleation or growth of the deposit. The results strongly...
Show moreThe effect of substrate finish and composition, flow rate and exposure duration on the composition, morphology and protective properties of calcareous deposits formed during cathodic polarization of several steels in seawater has been investigated. The current density behaviour of the scale formation in conjunction with morphology and composition characteristics indicated that the substrate finish and composition did not influence the nucleation or growth of the deposit. The results strongly suggest a relationship between electrolyte velocity, current density behaviour and morphology. With increased flow and consequent higher current density requirements, results indicated a low nucleation rate of CaCO3. The current density behaviour and composition of the calcareous deposit revealed a growth progression of a Mg rich film formed in the first few minutes, followed by an increasingly uniform surface coverage by CaCO3 in the form of aragonite.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14575
- Subject Headings
- Steel--Cathodic protection, Calcium carbonate
- Format
- Document (PDF)
- Title
- A combined FEM-fracture mechanics analysis approach for I.C. packages.
- Creator
- Renavikar, Ajit Anand., Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A study of the stress distribution in and fracture behavior of the hermetic glass seal in a typical Integrated Circuit package is presented herein. Finite Element Analysis and Fracture Mechanics approaches were found effective for this investigation. A prescribed load or displacement applied at the tip of the lead protruding from the package causes high stresses at the lead-glass interface, which can lead to cracking and fracture of the seal. An approach for finding the value of the allowable...
Show moreA study of the stress distribution in and fracture behavior of the hermetic glass seal in a typical Integrated Circuit package is presented herein. Finite Element Analysis and Fracture Mechanics approaches were found effective for this investigation. A prescribed load or displacement applied at the tip of the lead protruding from the package causes high stresses at the lead-glass interface, which can lead to cracking and fracture of the seal. An approach for finding the value of the allowable load or displacement applicable at the lead tip is discussed. A correlation with a standard crack shape is presented for the 3-D model of the package. An extension of the problem revealing the effects of crack propagation on the stress intensity factor for the glass material is presented in later chapters. The J-integral method from Fracture Mechanics is found to be extremely useful for this investigation. A decline in the stress intensity factor with crack growth was observed from this study.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14511
- Subject Headings
- Integrated circuits--Fracture, Fracture mechanics, Finite element method, Electronics--Materials--Fatigue
- 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
- The de-Dopplerization of acoustic signatures.
- Creator
- Mouches, Jean-Marc., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
When acoustic measurements of moving vehicles are made by a stationary observer, the Doppler shift has two detrimental effects on the interpretation of the data. The spectra are smeared by the change in Doppler factor during the vehicle pass by, and the motion induced phase shift in the signals causes errors. The measured signals can be corrected back to source time if a moving time delay correction is applied. However, when the signals are sampled digitally this time delay correction...
Show moreWhen acoustic measurements of moving vehicles are made by a stationary observer, the Doppler shift has two detrimental effects on the interpretation of the data. The spectra are smeared by the change in Doppler factor during the vehicle pass by, and the motion induced phase shift in the signals causes errors. The measured signals can be corrected back to source time if a moving time delay correction is applied. However, when the signals are sampled digitally this time delay correction requires an estimate to be made of the signal level between samples. This can be achieved by using a digital filter with time varying coefficients which estimates the signal from at least two adjacent samples. Results of both numerical simulations and real applications of this technique will be given.
Show less - Date Issued
- 1988
- PURL
- http://purl.flvc.org/fcla/dt/14489
- Subject Headings
- Doppler effect, Signal processing
- Format
- Document (PDF)
- Title
- A comparison of a special purpose processor with a general purpose processor and a numerical approach in generating helicopter dynamics equations.
- Creator
- Ravichandran, S., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Presently three schemes are used to generate the governing equations of motion. These schemes are: (1) general purpose processors such as REDUCE, MACSYMA and MAPLE, (2) a special purpose symbolic processor DEHIM--Dynamic Equations for Helicopter Interpretive Models and (3) completely numerical approaches such as AGEM--Automatic Generation of Equations of Motion. With REDUCE as a representative multipurpose processor in scheme 1, comparative aspects of these three schemes have been studied by...
Show morePresently three schemes are used to generate the governing equations of motion. These schemes are: (1) general purpose processors such as REDUCE, MACSYMA and MAPLE, (2) a special purpose symbolic processor DEHIM--Dynamic Equations for Helicopter Interpretive Models and (3) completely numerical approaches such as AGEM--Automatic Generation of Equations of Motion. With REDUCE as a representative multipurpose processor in scheme 1, comparative aspects of these three schemes have been studied by applying them to the same set of problems. These problems range from a linear model of a single blade with one degree of freedom to a mildly nonlinear three-bladed rotor model with several degrees of freedom. The derivation process includes the nonlinear equations and the perturbed linear equations about a user-supplied equilibrium state in a rotating frame and then the multiblade equations, which represent transformation into a nonrotating frame using multiblade coordinates. (Abstract shortened with permission of author.)
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14517
- Subject Headings
- Algebra--Computer programs, Helicopters--Dynamics
- Format
- Document (PDF)
- Title
- A computer aided process planning application using data management software.
- Creator
- Linn, Patrick Michael., Florida Atlantic University, Han, Chingping (Jim), College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The future of manufacturing industry is extending from the high profile systems like CAD and CAM, to a system that provides real time knowledge towards the manufacturing process. Computer Aided Process Planning (CAPP) is such a system. The computer provides the CAPP system a means to store and search previously developed process plans to find a similar process for a current part. In this research a CAPP application was developed using dBase IV, to provide a link between manufacturing process...
Show moreThe future of manufacturing industry is extending from the high profile systems like CAD and CAM, to a system that provides real time knowledge towards the manufacturing process. Computer Aided Process Planning (CAPP) is such a system. The computer provides the CAPP system a means to store and search previously developed process plans to find a similar process for a current part. In this research a CAPP application was developed using dBase IV, to provide a link between manufacturing process plans and engineering data. The relational database used provides an effective way to manage and manipulate manufacturing process information. The application uses engineering and manufacturing data from Curt G. Joa, Inc., to verify its operation. The development of the application, its corresponding computer programs, and literature survey are discussed in this thesis.
Show less - Date Issued
- 1992
- PURL
- http://purl.flvc.org/fcla/dt/14882
- Subject Headings
- Production planning--Data processing, Manufacturing processes--Automation
- Format
- Document (PDF)
- Title
- A critical evaluation of current demand determination methods for cathodic protection retrofits of offshore structures.
- Creator
- Lemieux, Edward John., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Development of a baseline design protocol for cathodic protection retrofits of offshore structures is becoming an increasingly important topic in light of the large number of structures operating beyond their original cp system design life. One of the critical steps in this development is determination of the total anode mass which is required to continue sufficient cathodic protection for which structure current demand must be established. Three current demand determination methods were...
Show moreDevelopment of a baseline design protocol for cathodic protection retrofits of offshore structures is becoming an increasingly important topic in light of the large number of structures operating beyond their original cp system design life. One of the critical steps in this development is determination of the total anode mass which is required to continue sufficient cathodic protection for which structure current demand must be established. Three current demand determination methods were investigated including the Gaussian ammeter, the Potential method, which utilizes the driving potential and anode resistance in its current calculation, and the IR Drop method. To this end, three anodes were deployed at the Naval Research Laboratory, Key West, Fl., and current output determinations were made upon these. Each of the three current measurement methods was evaluated on the basis of accuracy, reliability and feasibility in field use.
Show less - Date Issued
- 1997
- PURL
- http://purl.flvc.org/fcla/dt/15503
- Subject Headings
- Cathodic protection, Offshore structures, Ocean currents
- Format
- Document (PDF)
- Title
- An evaluation of the certainty of system performance measures generated by the South Florida Water Management Model.
- Creator
- Trimble, Paul Joseph., Florida Atlantic University, Scarlatos, Panagiotis (Pete) D., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The South Florida Water Management Model was developed to evaluate proposed alternatives for the south Florida regional hydrologic system. The degree of certainty of the computed system performance measures is required to correctly apply these measures for evaluation and selection of appropriate water resources policies and investments. Initially, a sensitivity matrix is defined which summarizes the model output sensitivity to incremental changes of key parameters. The method of singular...
Show moreThe South Florida Water Management Model was developed to evaluate proposed alternatives for the south Florida regional hydrologic system. The degree of certainty of the computed system performance measures is required to correctly apply these measures for evaluation and selection of appropriate water resources policies and investments. Initially, a sensitivity matrix is defined which summarizes the model output sensitivity to incremental changes of key parameters. The method of singular value decomposition is applied to the sensitivity matrix to better understand relations between parameters and output variables. Finally, parameter uncertainty is compared to that of total predictive uncertainty of the system performance measures.
Show less - Date Issued
- 1995
- PURL
- http://purl.flvc.org/fcla/dt/15200
- Subject Headings
- Hydrologic models, Water conservation--Florida, Water supply--Florida, Water quality management--Florida, South Florida Water Management District
- Format
- Document (PDF)
- Title
- An expert system for the selection and design of retaining walls.
- Creator
- Lee, Sunghoon., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This thesis presents a procedure for the selection and design of retaining walls using an expert system. The selection part is formulated in the form of production rules by OPS5, a programming language for production systems, and the design part is written in the procedural language, BASIC. Nine different types of retaining walls are incorporated in the knowledge base of the selection part, and three types of walls in the design part of the expert system. The selection and design parts are...
Show moreThis thesis presents a procedure for the selection and design of retaining walls using an expert system. The selection part is formulated in the form of production rules by OPS5, a programming language for production systems, and the design part is written in the procedural language, BASIC. Nine different types of retaining walls are incorporated in the knowledge base of the selection part, and three types of walls in the design part of the expert system. The selection and design parts are combined using OPS5 support routines.
Show less - Date Issued
- 1989
- PURL
- http://purl.flvc.org/fcla/dt/14542
- Subject Headings
- Retaining walls, Expert systems (Computer science)
- Format
- Document (PDF)
- Title
- An experimental study of vortex response during cutting by a blade or cylinder.
- Creator
- Krishnamoorthy, Srikanth., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An experimental study of the vortex response to interaction with and cutting by a thin flat plate or circular cylinders of various diameters has been performed. The direction of motion of the flat plate (or circular cylinder) is normal to the vortex axis in the experiments. The vortex is generated by withdraw of fluid at an orifice at the bottom of an "inner cylinder" immersed in a rectangular tank, and the flow field is visualized with both water soluble and immiscible dyes. In the...
Show moreAn experimental study of the vortex response to interaction with and cutting by a thin flat plate or circular cylinders of various diameters has been performed. The direction of motion of the flat plate (or circular cylinder) is normal to the vortex axis in the experiments. The vortex is generated by withdraw of fluid at an orifice at the bottom of an "inner cylinder" immersed in a rectangular tank, and the flow field is visualized with both water soluble and immiscible dyes. In the experiments with circular cylinders, the bending of the vortex is compared to computational predictions from [15], and the mechanism of subsequent breakup of the vortex as it gets closer to the cylinder is studied. The vortex is observed to bend farther without breakup for larger forward speeds of the circular cylinder. Very little bending is observed when the vortex interacts with the flat plate, except for angles of attack exceeding the stall limit Following cutting of the vortex by the flat plate or circular cylinder, a vortex shock is observed to form and propagate up the vortex axis. No vortex shock is observed on the opposite side of the blade. The various forms of these vortex shocks have been photographed, and they appear very similar to travelling vortex breakdowns. The propagation speed of the shocks is compared to an analytical solution for instantaneous vortex cutting by a flat plate of zero thickness.
Show less - Date Issued
- 1993
- PURL
- http://purl.flvc.org/fcla/dt/14977
- Subject Headings
- Vortex-motion, Blades--Noise, Cylinders, Rotors (Helicopters), Helicopters--Noise
- Format
- Document (PDF)
- Title
- An evaluation on two plastic materials for Vo's ankle implant.
- Creator
- Paul, Jetro., Florida Atlantic University, Han, Chingping (Jim), College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The purpose of this study is to evaluate two plastic materials, PMMA and UHMWPE, by using a material testing device "Robotic arch cycle motor" to imitate a normal body weight of 150 lbs. on Vo's artificial ankle implant. In this experiment, there are 82 sets of a three hours for UHMWPE, and 34 sets for PMMA have been applied to these materials with maintaining of 165 lbs. or 110% of a normal body weight person. In addition, timer, saline solution 0.5%, and thermometer are employed to set up a...
Show moreThe purpose of this study is to evaluate two plastic materials, PMMA and UHMWPE, by using a material testing device "Robotic arch cycle motor" to imitate a normal body weight of 150 lbs. on Vo's artificial ankle implant. In this experiment, there are 82 sets of a three hours for UHMWPE, and 34 sets for PMMA have been applied to these materials with maintaining of 165 lbs. or 110% of a normal body weight person. In addition, timer, saline solution 0.5%, and thermometer are employed to set up a vivo human environment to maxim the accuracy dada collection. Number of cycles is recorded by computer and to be converted to the lifetime of Vo's ankle implant. The result shows that UHMWPE has a greater performance of 0.0176in in Vo's artificial ankle implant than PMMA.
Show less - Date Issued
- 2001
- PURL
- http://purl.flvc.org/fcla/dt/12853
- Subject Headings
- Ankle--Effect of implants on, Artificial joints, Polymethylmethacrylate
- Format
- Document (PDF)
- Title
- An experimental and analytical investigation of viscoelastic pipe-soil interaction.
- Creator
- Ahn, Woo-Suk., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An overview of the current issues of HDPE pipe-soil systems is followed by a comprehensive literature review addressing current specifications, design methods, and relevant research projects. The following experimental tasks are described: (i) environmental stress cracking resistance (modified AASHTO M294), (ii) creep (10,000 hour parallel plate loading at super ambient temperatures), (iii) performance of buried pipes, subjected to live loading in a soil chamber, and (iv) field monitoring....
Show moreAn overview of the current issues of HDPE pipe-soil systems is followed by a comprehensive literature review addressing current specifications, design methods, and relevant research projects. The following experimental tasks are described: (i) environmental stress cracking resistance (modified AASHTO M294), (ii) creep (10,000 hour parallel plate loading at super ambient temperatures), (iii) performance of buried pipes, subjected to live loading in a soil chamber, and (iv) field monitoring. The findings include (i) satisfactory short-term environmental stress cracking resistance, (ii) temperature-dependency of the flexural modulus, (iii) the evidence of transition between slow crack growth and rapid crack propagation due to imperfect installation, and (iv) high load carrying capacity for the properly installed pipe in uniform backfill, showing an over-deflection failure mode with top flattening. The analytical investigations are as follows: (i) Bidirectional shift-constructed master curve, based on accelerated creep test values for long-term modulus prediction that showed good agreement with the Arrhenius equation-based analysis, (ii) Development of a seven-degree Voigt-Kelvin viscoelastic model based on the bidirectional shift-constructed master curve for analytical prediction of the long-term modulus, (iii) Comparison of two-dimensional and three-dimensional harmonic FEM analyses with the measured response of pipe-soil interaction, that demonstrated the analytical predictability of the pattern of deformation and stress distribution, and (iv) Determination of axial stress distribution along the pipe in non-uniform backfill condition, evaluated by approximate analysis based on finite differencing the deflection profile obtained from the assembly of individual finite segments/sections. This overcomes the limitation of the harmonic FEM analysis for pipe-soil interaction involving non-uniform soil conditions longitudinally and/or varying soil thickness circumferentially. The findings include (i) importance of axial stress contribution at failure, (ii) top flattening failure mode due to over-deflection preceding buckling or yielding, and (iii) critical adverse effect of the non-uniform backfill condition that can lead to joint opening, localized buckling, liner tearing/debonding, or cracking. The work has "spin off" applications to the coastal and offshore environments for sewage outfalls, marine pipelines etc.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/12550
- Subject Headings
- Soil-structure interaction, Pipe, Plastic--Testing, Underground pipelines
- Format
- Document (PDF)
- Title
- An experimental investigation of the design and performance of small-diameter tunnel thrusters.
- Creator
- Whitney, James Walter, Jr., Florida Atlantic University, Smith, Samuel M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Maneuvering thrusters can provide small underwater vehicles with the ability to dynamically control position at low speeds. However, the successful implementation of these thrusters requires an understanding of their dynamic response, as well as a design which meets the specified design requirements. This thesis experimentally investigates the design and dynamic performance of small diameter tunnel thrusters for two small autonomous underwater vehicles. A systematic series of dynamic...
Show moreManeuvering thrusters can provide small underwater vehicles with the ability to dynamically control position at low speeds. However, the successful implementation of these thrusters requires an understanding of their dynamic response, as well as a design which meets the specified design requirements. This thesis experimentally investigates the design and dynamic performance of small diameter tunnel thrusters for two small autonomous underwater vehicles. A systematic series of dynamic experiments were conducted with three working tunnel thruster prototypes that fulfill the operating and design constraints of these vehicles. The results from these experiments are shown to provide an accurate representation of the overall performance and thrust capability of the thrusters tested. Experimental data is compared with simulations utilizing a recently proposed thruster model, and the ability of the model to predict the dynamic response is discussed.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/15555
- Subject Headings
- Submersibles--Equipment and supplies, Oceanographic submersibles--Design
- Format
- Document (PDF)
- Title
- A numerical study of bluff body aerodynamics by vortex method.
- Creator
- He, Fusen., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Vortex methods are grid-free; therefore, their use avoids a number of shortcomings of Eulerian, grid-based numerical methods for solving high Reynolds number flow problems. These include such problems as poor resolution and numerical diffusion. In vortex methods, the continuous vorticity field is discretized into a collection of Lagrangian elements, known as vortex elements. Vortex elements are free to move in the flow field which they create. The velocity field induced by these vortex...
Show moreVortex methods are grid-free; therefore, their use avoids a number of shortcomings of Eulerian, grid-based numerical methods for solving high Reynolds number flow problems. These include such problems as poor resolution and numerical diffusion. In vortex methods, the continuous vorticity field is discretized into a collection of Lagrangian elements, known as vortex elements. Vortex elements are free to move in the flow field which they create. The velocity field induced by these vortex elements is a solution to the Navier-Stokes equation, and in principle the method is suitable for high Reynolds number flows. In this dissertation, viscous vortex element methods are studied. Some modifications are developed. Discrete vortex element methods have been used to solve the Navier-Stokes equations in high Reynolds number flows. Globally satisfactory results have been obtained. However, computed pressure fields are often inaccurate due to the significant errors in the surface vorticity distribution. In addition, different ad hoc assumptions are often used in different proposed algorithms. In the present study, improvements are made to better represent the near-wall vorticity when obtaining numerical solutions for the Navier-Stokes equations. In particular, we split the boundary vortex sheet into two parts at each time step. One part remains a vortex sheet lying on the boundary of the solid body, and the other enters into the flow field as a free vortex element with a uniformly distributed vorticity. A set of kinematic relationships are used to determine the two appropriate portions of the split, and the position of the vortex element to be freed at the time of release. Another improvement is to include the nonlinear acceleration terms in the governing equations near the solid boundary when evaluating the surface pressure distribution. The aerodynamic force coefficients can then be obtained by summing up the pressure forces. By comparing the computed surface vorticities, surface pressures and aerodynamics force coefficients with existing numerical/experimental data in the cases of viscous flow around a circular cylinder, an aerofoil, and a bridge deck section, it is shown that the present approach is more accurate in modelling the flow features and force coefficients without making different ad hoc assumptions for different geometries. The computation is efficient. It can be useful in the study of the unsteady fluid flow phenomenon in practical engineering problems.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/12574
- Subject Headings
- Vortex-motion, Fluid mechanics, Viscous flow
- Format
- Document (PDF)
- Title
- A numerical study of fuselage scattering effects on rotor noise.
- Creator
- Atalla, Noureddine., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
This thesis considers the effect of scattering on the sound radiation from rotating sources. The study is carried out using a combined numerical implementation of ray acoustics and the paraxial ray approximation. A detailed description of the theoretical background to these methods is presented, along with a description of their numerical implementation. Application of the method to classical problems is considered to prove the accuracy and the power of the approach. Application of the method...
Show moreThis thesis considers the effect of scattering on the sound radiation from rotating sources. The study is carried out using a combined numerical implementation of ray acoustics and the paraxial ray approximation. A detailed description of the theoretical background to these methods is presented, along with a description of their numerical implementation. Application of the method to classical problems is considered to prove the accuracy and the power of the approach. Application of the method to some typical problems involving scattering of noise from propellers and rotors is presented. It is found that for impulsive acoustic signatures the scattering effects are important especially in the sideline direction from a helicopter fuselage. The effects of sharp edges on the steady loading noise from tilt-rotor configurations indicates that there is a new mechanism for generating impulsive acoustic signatures caused by scattering by sharp edges of the fuselage. The acoustic signatures generated by this mechanism can appear very similar to other types of impulsive source generated by aerodynamic interactions on the blade and therefore must be important. This type of source can be eliminated if the fuselage has rounded edges. Flow effects on scattering problems have also been considered. It was shown that the flow causes a modification and displacement of the lobes of the directivity pattern and the shadow zone, which can be important at Mach numbers greater than 0.2. The main conclusion of this thesis is that scattering effects cannot be ignored for highly directional rotating sources next to rigid scattering objects as is always the case for propellers and helicopters rotors.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/12276
- Subject Headings
- Sound-waves--Scattering, Rotors--Noise
- Format
- Document (PDF)
- Title
- An object-oriented model for a manufacturing resource planning system.
- Creator
- Kastritis, Karen Mary., Florida Atlantic University, Han, Chingping (Jim), Fernandez, Eduardo B., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
Manufacturing Resource Planning systems are functionally complex systems. In providing effective resource management tools, they support the integration of a wide variety of complex functions. These systems also undergo frequent changes as business needs change. For these reasons, analysis techniques which provide methods to create clear, flexible systems must be sought. Object oriented analysis is such a technique. This thesis presents the development of an object oriented model for a...
Show moreManufacturing Resource Planning systems are functionally complex systems. In providing effective resource management tools, they support the integration of a wide variety of complex functions. These systems also undergo frequent changes as business needs change. For these reasons, analysis techniques which provide methods to create clear, flexible systems must be sought. Object oriented analysis is such a technique. This thesis presents the development of an object oriented model for a Manufacturing Resource Planning system (MRPII). It will be shown that the use of objects and object oriented techniques to model complex systems such as MRPII results in system models which are more easily understood and more flexible to change than other more conventional representations. Future research may include the formal design and implementation of the model. The flexibility of the implemented system could then be compared to the level of flexibility of a non-object based system.
Show less - Date Issued
- 1996
- PURL
- http://purl.flvc.org/fcla/dt/15288
- Subject Headings
- Manufacturing processes, Manufacturing resource planning, Production management--Data processing, Object-oriented programming (Computer science)
- Format
- Document (PDF)
- Title
- GALLOPING OF AN ELASTICALLY SUPPORTED BLUFF BODY IN TURBULENT FLOW.
- Creator
- Li, Qiang, Florida Atlantic University, Lin, Y. K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The phenomenon of flow-induced vibration is found in many engineering systems. The fluid flow generates forces on the structure that cause motion of the structure. In turn, the structural motion changes the angle of attack between the flow and the structure, hence the forces on the structure. Furthermore, turbulence generally exists in a natural fluid flow; namely, the fluid velocity contains a random part. Thus, the problem is formulated as a nonlinear system under random excitations. This...
Show moreThe phenomenon of flow-induced vibration is found in many engineering systems. The fluid flow generates forces on the structure that cause motion of the structure. In turn, the structural motion changes the angle of attack between the flow and the structure, hence the forces on the structure. Furthermore, turbulence generally exists in a natural fluid flow; namely, the fluid velocity contains a random part. Thus, the problem is formulated as a nonlinear system under random excitations. This thesis is focused on one type of motion known as galloping. A mathematical model for the motion of an elastically supported square cylinder in turbulent flow is developed. The physical nonlinear equation is converted to ideal stochastic differential equations of the Ito type using the stochastic averaging method. The probability density for the motion amplitude and the values for the most probable amplitudes are obtained for various mean flow velocities and turbulence levels.
Show less - Date Issued
- 1987
- PURL
- http://purl.flvc.org/fcla/dt/14361
- Subject Headings
- Random vibration--Mathematical models, Turbulence, Fluid dynamics
- Format
- Document (PDF)
- Title
- Galvanic anode cathodic protection (CP) retrofit upon offshore pipelines: An analytical model for CP potential profiles.
- Creator
- Pierson, Patrick Robert., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
An analytical model for cathodic protection (CP) attenuation along a one-dimensional structure such as a pipeline is developed in terms of non-dimensional polarization and, alternately, cathode potential. The derivation is based upon the fundamental principle that (1) potential is, in fact, the potential difference across the metal/electrolyte interface, (2) an assumption of a linear potential and current density relationship, and (3) the treatment of Galvanic anodes as spherical current...
Show moreAn analytical model for cathodic protection (CP) attenuation along a one-dimensional structure such as a pipeline is developed in terms of non-dimensional polarization and, alternately, cathode potential. The derivation is based upon the fundamental principle that (1) potential is, in fact, the potential difference across the metal/electrolyte interface, (2) an assumption of a linear potential and current density relationship, and (3) the treatment of Galvanic anodes as spherical current sources. The resulting expression characterizes the distribution of protection in terms of physical design variables and electrochemical properties of the cathode. Polarization is presented graphically in terms of two parameters which are comprised of the aforementioned variables and make for a novel method of analysis. Two sample pipeline CP systems are analyzed by this method, one of which is an existing design and the other a hypothetical design used to illustrate the effect of the varying parameters. Some sample anode life calculations based upon the analytical model are performed, and a method for correcting the model for the existence of a non-spherical bracelet anode is proposed. It is concluded that electrolyte resistance (or alternately anode resistance) is of greater importance in all practical Galvanic CP attenuation calculations than is the metallic (Ohmic) resistance.
Show less - Date Issued
- 1998
- PURL
- http://purl.flvc.org/fcla/dt/15581
- Subject Headings
- Petroleum pipelines--Cathodic protection, Natural gas pipelines--Cathodic protection
- Format
- Document (PDF)
- Title
- Frequency-time spectral analysis of helicopter turbulence and response in forward flight.
- Creator
- Vellathottam, George V., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
The atmospheric turbulence that a blade station experiences is called blade-fixed turbulence. It can qualitatively differ from the conventional body-fixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,-elocity, which causes fore-and-aft motions of the blade station through the turbulence waves. A closed-form solution of a frequency-time spectrum for the dominant vertical turbulence velocity at an arbitrary blade station is dc,...
Show moreThe atmospheric turbulence that a blade station experiences is called blade-fixed turbulence. It can qualitatively differ from the conventional body-fixed turbulence such as experienced by an element of the body or fuselage. This difference is due to the rotational ,-elocity, which causes fore-and-aft motions of the blade station through the turbulence waves. A closed-form solution of a frequency-time spectrum for the dominant vertical turbulence velocity at an arbitrary blade station is dc,·eloped. This solution makes it possible to explain qualitatively the turbulence cllcrgy transfer due to rotational velocity from the low-frequency region (< 1P or 1/ rcv.) to the high-frequency(> 1P) region with the occurrence of spectral peaks and split peaks at 1P /2, 1P, 3P /2, 2P etc. Comparison of blade responses to bladeand body-fixed turbulence is also presented over a comprehensive range of turbulcuce scale length and advance ratio; the comparison covers frequency-time spectra, correlations including standard deviations, and average threshold-crossing rates of a flapping blade. A major contribution is to formulate both the cyclostationary turbulence and blade response by the frequency-time spectra, which predict simultaneously the time- ancl frequency-dependent characteristics such as the energy culltained in the frequency and time intervals. For low-altitude and low-advanceratio flights, such as nap-of-the earth or NOE flights, rotational velocity effects on turbulence modeling qualitatively affect the prediction of turbulence ancl response statistics.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/14683
- Subject Headings
- Turbulence, Rotors (Helicopters)
- Format
- Document (PDF)