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Title: Weight function approach for stress analysis of the surface crack in a finite plate subjected to nonuniform stress fields.
Creator: Jani, Jayant Shivkumar., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The effects of various nonuniform stress fields on the stress intensity factors for the semi-elliptic surface crack (three-dimensional problem) in a finite plate are determined using the weight function approach. The formulation satisfies the linear elastic fracture mechanics criteria and the principle of conservation of energy. Based on the knowledge of stress intensity solutions for the reference load/stress system, the expression for the crack opening displacement function for the surface...
Show moreThe effects of various nonuniform stress fields on the stress intensity factors for the semi-elliptic surface crack (three-dimensional problem) in a finite plate are determined using the weight function approach. The formulation satisfies the linear elastic fracture mechanics criteria and the principle of conservation of energy. Based on the knowledge of stress intensity solutions for the reference load/stress system, the expression for the crack opening displacement function for the surface crack is derived. Using the crack opening displacement function and the reference stress intensity factor, the three-dimensional weight functions and subsequently the stress intensity solutions for the surface crack subjected to nonuniform stress fields are derived. The formulation is then applied to determine the effects of linear, quadratic, cubic, and pure bending stress fields on the stress intensity factor for the surface crack in a finite plate. In the initial stage of the study a two-dimensional problem of an edge-crack emanating from the weld-toe in a T-joint is considered. The effect of parameters such as plate thickness, weld-toe radius, and weld-flank angle on the stress intensity factor for an edge-crack is studied. Finite element analyses of the welded T-joints are performed to study the effects of plate thickness, weld-toe radius and the weld-flank angle on the local stress distribution. The ratio of plate thickness to weld-toe radius ranging from 13.09 to 153.93, and the weld-flank angles of 30, 45, and 60 degrees are considered in the analyses. Based on the results from FEM analyses, a parametric equation for the local stress concentration factor and a polynomial expression for the local stress distribution across the plate thickness are derived using the method of least squares and the polynomial curve-fitting technique.
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Date Issued: 1990
PURL: http://purl.flvc.org/fcla/dt/12254
Subject Headings: Strains and stresses, Plates (Engineering), Fracture mechanics
Format: Document (PDF)

Title: Wave attenuation by rigid and flexible-membrane submerged breakwaters.
Creator: Harris, Lee Errol., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This research investigates the use of rigid and flexible-membrane submerged breakwaters for wave energy attenuation. A comprehensive review of breakwater design criteria and previous research on submerged breakwaters is included. Physical model laboratory studies conducted by the author and other researchers are investigated as a means for obtaining formulations for wave transmission coefficients. The mechanisms by which waves are attenuated and break are analyzed using video photography of...
Show moreThis research investigates the use of rigid and flexible-membrane submerged breakwaters for wave energy attenuation. A comprehensive review of breakwater design criteria and previous research on submerged breakwaters is included. Physical model laboratory studies conducted by the author and other researchers are investigated as a means for obtaining formulations for wave transmission coefficients. The mechanisms by which waves are attenuated and break are analyzed using video photography of the wave tank tests. The primary objective of this doctoral research was to determine and compare the wave attenuation of non-conventional rigid and flexible-membrane type submerged breakwaters. Physical model tests were performed using the wave tank facilities at Florida Institute of Technology located in Melbourne, Florida. Six different breakwater cross-sections used were: (1) rectangular, (2) triangular, (3) P.E.P.-$Reef\sp{TM}$, (4) single sand-filled container, (5) three stacked sand-filled containers, and (6) one single water-filled container. The first three breakwater units were rigid (or monolithic), and the last three units are flexible-membrane breakwater units. All six units tested had the same height, length (longshore), and base width (cross-shore), with different cross-sections and shapes, and were composed of different materials. A new classification scheme was developed for breakwaters and artificial reefs, based on water depth, structure height, and wave heights. The wave-structure interaction resulting in the wave breaking on the submerged breakwaters was documented, and the observations were analyzed. Wave transmission coefficients were computed for the six different breakwater models tested, and comparisons between the different models were made. Conclusions regarding the primary factors affecting the effectiveness of rigid and flexible-membrane submerged breakwaters were developed, as were recommendations for further research.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12468
Subject Headings: Breakwaters, Water waves
Format: Document (PDF)

Title: Visualization of buried objects in three-dimensional acoustic data acquired by a buried object scanning sonar.
Creator: Tellier, Arnaud Marc., Florida Atlantic University, Schock, Steven G., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The common approach for finding objects buried under the seabed is to use a single channel chirp reflection profiler. Reflection profiles lack information on target location, geometry and size. This thesis investigates methods for visualizing buried objects in noisy 3D acoustic data acquired by a small aperture scanning sonar. Various surface and volume rendering methods are tested with synthetic datasets containing fluid loaded spheres and with experimental data acquired with a 4-by-8 planar...
Show moreThe common approach for finding objects buried under the seabed is to use a single channel chirp reflection profiler. Reflection profiles lack information on target location, geometry and size. This thesis investigates methods for visualizing buried objects in noisy 3D acoustic data acquired by a small aperture scanning sonar. Various surface and volume rendering methods are tested with synthetic datasets containing fluid loaded spheres and with experimental data acquired with a 4-by-8 planar hydrophone array towed over buried objects with various aspects and size. The Maximum Intensity Projection is the best of the tested methods for real-time visualization of the data where a global overview of the targets is needed. A surface rendering technique such as the Marching Cubes is useful for offline measurement of the geometry and size of buried objects selected by the operator.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/15682
Subject Headings: Three-dimensional display systems, Sonar, Sound-waves--Scattering, Computer graphics
Format: Document (PDF)

Title: Viscosity correction for breathing gas mixtures measured via a laminar flow element.
Creator: Signo, Barbara., Florida Atlantic University, Moslemian, Davood, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: To minimize previously observed inaccuracies in the measurement of the flow rates of breathing gas mixtures, errors in the measurement of the pressure differential across the LFE with short diffusers using high frequency response pressure transducers were ruled out. A Laminar Flow Element was calibrated with air, nitrogen, and helium at various pressure and temperature conditions. The feasibility of using the Universal Calibration Curve determined from atmospheric air data to estimate the...
Show moreTo minimize previously observed inaccuracies in the measurement of the flow rates of breathing gas mixtures, errors in the measurement of the pressure differential across the LFE with short diffusers using high frequency response pressure transducers were ruled out. A Laminar Flow Element was calibrated with air, nitrogen, and helium at various pressure and temperature conditions. The feasibility of using the Universal Calibration Curve determined from atmospheric air data to estimate the flow rate of other gases at hyperbaric conditions was evaluated. The viscosity values of pure gases calculated by theoretical methods were compared to the viscosity values estimated by using the Universal Calibration Curve Viscosity Iteration method. Using flowrate calibration data for the gas mixtures of interest, the viscosity values for these gas mixtures were estimated. These viscosity values were then compared to the corresponding viscosity values calculated by theoretical methods. The Universal Calibration Curve obtained by fitting flowrate calibration data of air flowing at STP can be used to estimate the flow of other gases flowing at hyperbaric pressures.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/14981
Subject Headings: Viscosity, Gases--Viscosity, Flow meters, Gas flow--Measurement
Format: Document (PDF)

Title: Vibrational power flow in thick connected plates.
Creator: McCollum, Michele D., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The total vibrational power flow in connected plate structures is investigated using an analytical "Power Flow" approach. The effects of shear and rotary inertia on the flexural wave transmission and the influence of in-plane wave generation at structural discontinuities are included in the analytical model. In formulating a Power Flow model, the structure is divided into substructures whose responses may be determined analytically to obtain expressions for the input and transfer mobilities...
Show moreThe total vibrational power flow in connected plate structures is investigated using an analytical "Power Flow" approach. The effects of shear and rotary inertia on the flexural wave transmission and the influence of in-plane wave generation at structural discontinuities are included in the analytical model. In formulating a Power Flow model, the structure is divided into substructures whose responses may be determined analytically to obtain expressions for the input and transfer mobilities of the substructures. For the case of plate-type structures joined along a line, the mobilities are functions of both frequency and space. The power transmission between the individual plate substructures is then written as a function of these mobility expressions. The structure of concern in this dissertation consists of two plates connected in an L-configuration. In obtaining the expressions for the mobilities, the vibrational response of the individual plates is determined by solving the appropriate equations of motion. In this study the antisymmetric (flexural) motion is described using Mindlin's (1951) thick plate approximation to the three-dimensional equations of motion. The applicability of this thick plate formulation is limited to frequencies below the frequency of the first antisymmetric mode of thickness-shear vibration of the plate. The symmetric (in-plane) motion of the plates is described using the generalized theory of plane stress which neglects the direct coupling of the in-plane motion with the thickness vibration modes, and is therefore valid only for frequencies which are lower than the frequency of the first mode of pure thickness vibration of the plate. The results for the power transmission in the L-plate obtained using the Power Flow formulation are verified at high frequencies by comparison with the results obtained using the Statistical Energy Analysis (SEA) technique. The SEA formulation for the L-plate is based on Mindlin's equations for flexural motion and the theory of generalized plane stress for in-plane vibration. The results of the Power Flow formulation are verified at low frequencies by the results obtained using a Finite Element model of the L-shaped plate.
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Date Issued: 1988
PURL: http://purl.flvc.org/fcla/dt/11929
Subject Headings: Plates (Engineering)--Vibration
Format: Document (PDF)

Title: Vibration tailoring of inhomogeneous beams and circular plates.
Creator: Pentaras, Demetris., Florida Atlantic University, Elishakoff, Isaac, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The vibrational behavior of inhomogeneous beams and circular plates is studied, utilizing the semi-inverse method developed by I. Elishakoff and extensively discussed in his recent monograph (2005). The main thread of his methodology is that the knowledge of the mode shape is postulated. The candidate mode shapes can be adopted from relevant static, dynamic or buckling problems. In this study, the exact mode shapes are sought as polynomial functions, in the context of vibration tailoring, i.e...
Show moreThe vibrational behavior of inhomogeneous beams and circular plates is studied, utilizing the semi-inverse method developed by I. Elishakoff and extensively discussed in his recent monograph (2005). The main thread of his methodology is that the knowledge of the mode shape is postulated. The candidate mode shapes can be adopted from relevant static, dynamic or buckling problems. In this study, the exact mode shapes are sought as polynomial functions, in the context of vibration tailoring, i.e. designing the structure that possesses the pre-specified value. Apparently for the first time in the literature, several closed-form solutions for vibration tailoring have been derived for vibrating inhomogeneous beams and circular plates. Twelve new closed-form solutions for vibration tailoring have been derived for an inhomogeneous polar orthotropic plate that is either clamped or simply supported around its circumference. Also, the vibration tailoring of a polar orthotropic circular plate with translational spring is analyzed. There is considerable potential of utilizing the developed method for design of functionally graded materials.
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Date Issued: 2006
PURL: http://purl.flvc.org/fcla/dt/13344
Subject Headings: Acoustical engineering, Plates (Engineering)--Vibration--Mathematical models, Buckling (Mechanics), Structural analysis
Format: Document (PDF)

Title: VIBRATION ANALYSIS OF RECTANGULAR PLATES UNDER FLUID LOADING.
Creator: LEE, TZER CHIA., Florida Atlantic University, Dunn, Stanley E., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: An energy method is presented for predicting the natural frequencies, radiation loss factor and system loss factor of simply supported rectangular plates under fluid loading. Both bare plates and plates with complete damping treatments are considered. Results obtained using the method developed are compared with two other theories. The agreement is generally good. The study points out the need for detailed analyses of plate vibration patterns and their associated radiation output under...
Show moreAn energy method is presented for predicting the natural frequencies, radiation loss factor and system loss factor of simply supported rectangular plates under fluid loading. Both bare plates and plates with complete damping treatments are considered. Results obtained using the method developed are compared with two other theories. The agreement is generally good. The study points out the need for detailed analyses of plate vibration patterns and their associated radiation output under various plate boundary conditions. There also exists a need for carefully conducted experimental work to verify the applicability of the current theory.
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Date Issued: 1981
PURL: http://purl.flvc.org/fcla/dt/14086
Subject Headings: Plates (Engineering)--Vibration
Format: Document (PDF)

Title: Validation of numerical modelling for long range acoustic propagation.
Creator: Riley, Joseph M., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Laboratory scale measurements were conducted to validate numerical prediction models used to predict the acoustic field in a shallow water ocean environment. Experimental measurements were conducted in a range independent environment which included the effects of shear in marine sediments and in a depth varying range dependent environment. Good agreement between the experimental measurements and the numerical prediction codes were obtained using optimized values for the input parameters of...
Show moreLaboratory scale measurements were conducted to validate numerical prediction models used to predict the acoustic field in a shallow water ocean environment. Experimental measurements were conducted in a range independent environment which included the effects of shear in marine sediments and in a depth varying range dependent environment. Good agreement between the experimental measurements and the numerical prediction codes were obtained using optimized values for the input parameters of the environmental model. In comparing experimental measurements to the numerical prediction codes it became apparent that the codes were very sensitive to the input parameters describing the bottom boundary of the ocean waveguide.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/14819
Subject Headings: Acoustical engineering, Underwater acoustics, Marine sediments
Format: Document (PDF)

Title: THE USE OF COMPUTER SIMULATION TECHNIQUES IN THE DESIGN OF SHIP CHANNEL WIDTH (PORT, HARBOR, TAMPA).
Creator: THOMAS, CLINTON WILLIAM., Florida Atlantic University, Lin, Newman K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This report presents a detailed approach to the problem of determining expected shipping delays that are caused by inadequate channel width. Data collection and analysis is accomplished for the shipping industry of Tampa Bay, Florida. Historical data and cargo projection are used to develop the expected shipping traffic density and distribution for the year 2000. An overview of a computer model that simulates the shipping traffic and accounts for delays due to channel width is presented. A...
Show moreThis report presents a detailed approach to the problem of determining expected shipping delays that are caused by inadequate channel width. Data collection and analysis is accomplished for the shipping industry of Tampa Bay, Florida. Historical data and cargo projection are used to develop the expected shipping traffic density and distribution for the year 2000. An overview of a computer model that simulates the shipping traffic and accounts for delays due to channel width is presented. A sensitivity analysis performed on the model to determine the effect each input variable has on shipping delays. The results are presented in the form of shipping delay curves for seven types of vessels over a range of channel widths.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14287
Subject Headings: Shipping--Simulation methods, Channels (Hydraulic engineering)--Design and construction--Simulation methods, Shipping--Florida--Tampa Bay
Format: Document (PDF)

Title: A unified theory of coordination for robotic mechanisms with general parallel or hybrid structures.
Creator: Ling, Shou-Hung., Florida Atlantic University, Huang, Ming Z., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A well designed robot manipulator should have adequate workspace and good static-dynamic performance. It is well known that serial manipulators, while compared to similar size parallel ones, have larger workspace. However, due to their cantilever-like structure, the serial manipulators suffer from the disadvantage of having relatively poor static-dynamic performance. Contrarily, for fully parallel manipulators the good static-dynamic performance comes from the sacrifice of the workspace....
Show moreA well designed robot manipulator should have adequate workspace and good static-dynamic performance. It is well known that serial manipulators, while compared to similar size parallel ones, have larger workspace. However, due to their cantilever-like structure, the serial manipulators suffer from the disadvantage of having relatively poor static-dynamic performance. Contrarily, for fully parallel manipulators the good static-dynamic performance comes from the sacrifice of the workspace. Therefore, manipulators with more general geometries, in particular those with both the serial and the parallel modules, namely the hybrid manipulators, have attracted much of the research attention in robotics recently. While it can be asserted that kinematic theories and techniques are well established for fully serial-chain manipulators, the same assertion cannot be made when they are considered in the above general context. The research described in this dissertation is an undertaking toward the establishment of a general theory of coordination for robotic mechanisms with general parallel or hybrid structures. The scope of this research is concentrated in the kinematics aspect of the aforementioned class of robot manipulators with the main emphasis on the velocity (instantaneous) kinematics. A kinestatic approach, which is based on screw system theory, is adopted in this dissertation. This kinestatic approach leads to the establishment of a fundamental theorem, dubbed as the Parallel Manipulator Coordination Theorem, which integrates the idea of parallel and serial manipulators. Furthermore, the theorem enables us to develop an analysis strategy for systematic formulation and characterization of robotic mechanisms with general parallel (non-redundant) and hybrid geometries. The analysis strategy entails constraints, statics, velocity, and singularity considerations. One distinct advantage of using the screw system theory as the analysis tool is that it facilitates the analysis in a fashion that physical meanings are preserved through out the derivation. The very aspect of preserving the physical meaning distinguishes this method from other algebraically-based and numerically-based methods. An intelligent fault-tolerant system has been studied at the end. The technique and conclusions from the study of parallel manipulator modules have been used to analyze the proposed design.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/12385
Subject Headings: Manipulators (Mechanism), Robotics, Kinematics, Screws, Theory of
Format: Document (PDF)

Title: Ultimate load, creep, shrinkage, and reliability studies of a precast single cell segmental bridge with external post-tensioning.
Creator: Murugesh, Ganapathy., Florida Atlantic University, Reddy, Dronnadula V., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This dissertation is a study of a 1:3.5 scale model of an externally post-tensioned single cell segmental bridge model of the Long Key bridge. The behavior of the bridge system was evaluated in terms of deflections, strains, joint openings, etc. under static and ultimate load conditions. The precast segmental bridge was cast, assembled, and tested at the Department of Ocean Engineering, Florida Atlantic University for AASHTO HS20-44 truck loadings at typical locations. The study addressed the...
Show moreThis dissertation is a study of a 1:3.5 scale model of an externally post-tensioned single cell segmental bridge model of the Long Key bridge. The behavior of the bridge system was evaluated in terms of deflections, strains, joint openings, etc. under static and ultimate load conditions. The precast segmental bridge was cast, assembled, and tested at the Department of Ocean Engineering, Florida Atlantic University for AASHTO HS20-44 truck loadings at typical locations. The study addressed the joint opening behavior and the response of external tendons during service and ultimate load levels. The analytical nonlinear behavior of the bridge upto the ultimate load level has been predicted using a finite element software PCFRAME developed at University of California, Berkeley. Creep and shrinkage strains were predicted using computer program CRACK developed at University of Calgary, Canada. Creep and shrinkage coefficients evaluated from short term tests, were used in predicting the long term behavior. A method for reliability analysis of post-tensioned segmental bridges has also been presented for serviceability and ultimate limit state conditions.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/14709
Subject Headings: Precast concrete construction--Testing, Post-tensioned prestressed concrete construction--Testing, Bridges, Concrete--Models
Format: Document (PDF)

Title: TWO DIMENSIONAL FLOW WITHIN A TRIANGULAR OSCILLATING CRACK (TURBULENCE, VORTEX STREET, TRANSITION FLOW, MIXING).
Creator: KIM, SOO YONG., Florida Atlantic University, Tennant, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The transition of two dimensional flow within a crack with oscillating wall is studied experimentally to establish the role of the parameters involved. Multiple instabilities in the fluid are produced by the motion of the oscillating wall. For a better understanding of the flow structure and displaying in the whole flow field at a time, flow visualization was used. Frequency, amplitude, and crack width were systematically varied. The present study shows that, in general, the frequency and...
Show moreThe transition of two dimensional flow within a crack with oscillating wall is studied experimentally to establish the role of the parameters involved. Multiple instabilities in the fluid are produced by the motion of the oscillating wall. For a better understanding of the flow structure and displaying in the whole flow field at a time, flow visualization was used. Frequency, amplitude, and crack width were systematically varied. The present study shows that, in general, the frequency and crack width play a role in the transition process at low frequencies of oscillations. However, amplitude becomes progressively important at its higher range. Results also show that the flow changes its character approximately after a Reynolds number 11420. After that the transition process continues until the Reynolds number 34322 which is the upper limit of variation of frequency (Reynolds number) in the present study.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14312
Subject Headings: Fluid dynamics, Flow visualization
Format: Document (PDF)

Title: A TURBULENCE CURRENT METER DESIGN, CONSTRUCTION AND USE.
Creator: KIDERA, EDWARD HENRY, IV., Florida Atlantic University, Tennant, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The...
Show moreThe objectives of this investigation were - 1) design and build a turbulence current meter capable of measuring velocity fluctuations in a geophysical scale flow and 2) the measurement of such flow including subsequent analysis of near bottom turbulence. An unique device capable of sensing velocity fluctuations in the region 25cm above the bottom was constructed based on concepts original to the study of turbulence. A review of previous equipment and research is included for a comparison. The instrument's usefulness was illustrated in the open channel flow of a tidal estuary by its ability to detect the horizontal velocity field. The data obtained for the turbulence shows large variation in velocity of the lateral component on the order of 50-75% of the "mean" current speed. Digital filtering of the data reveals distinct structures of high energy, intermittent in their nature and analogous to "bursting". The energy spectrum of the longitudinal component follows the predicted slope of -1 for over two decades (.01 to 1.3 + Hz).
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Date Issued: 1978
PURL: http://purl.flvc.org/fcla/dt/13943
Subject Headings: Turbulence--Measurement, Water current meters
Format: Document (PDF)

Title: Trim analysis by shooting and finite elements and Floquet eigenanalysis by QR and subspace iterations in helicopter dynamics.
Creator: Achar, Nagari Shriranga., Florida Atlantic University, Gaonkar, Gopal H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The trim analysis for the initial state and control inputs that satisfy response periodicity and flight conditions, and the Floquet eigenanalysis for a few largest eigenvalues of the Floquet transition matrix (FTM) are investigated. In the trim analysis, the convergence of Newton iteration is investigated in computing the periodic initial state and control inputs sequentially and in parallel. The trim analysis uses the shooting method and two h-versions of temporal finite element methods, one...
Show moreThe trim analysis for the initial state and control inputs that satisfy response periodicity and flight conditions, and the Floquet eigenanalysis for a few largest eigenvalues of the Floquet transition matrix (FTM) are investigated. In the trim analysis, the convergence of Newton iteration is investigated in computing the periodic initial state and control inputs sequentially and in parallel. The trim analysis uses the shooting method and two h-versions of temporal finite element methods, one based on displacement formulation and the other on mixed formulation of displacements and momenta. In each method, both the sequential and in-parallel schemes are used, and the resulting nonlinear equations are solved by damped Newton iteration with an optimally selected damping parameter. The reliability of damped Newton iteration, including earlier-observed divergence problems, is quantified by the maximum condition number of the Jacobian matrices of the iterative scheme. For illustrative purposes, rigid flap-lag and flap-lag-torsion models based on quasisteady aerodynamics are selected. Demanding trim analysis conditions are included by considering advance ratios or dimensionless flight speeds twice as high as those of current helicopters. Concerning the Floquet eigenanalysis, the feasibility of using the Arnoldi-Saad method, one of the emerging subspace iteration methods, is explored as an alternative to the currently used QR method, which is not economical for partial eigenanalysis. The reliability of the Arnoldi-Saad method is quantified by the eigenvalue condition numbers and the residual errors of the eigenpairs. In the three trim analysis methods, while the optimally selected damping parameter provides almost global convergence, the in-parallel scheme requires much less machine time than the conventional sequential scheme; both schemes have comparable reliability of the Newton iteration without and with damping. The Arnoldi-Saad method takes much less machine time than the QR method with comparable reliability.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12297
Subject Headings: Helicopters--Dynamics, Helicopters--Handling characteristics, Stability of helicopters--Mathematical models
Format: Document (PDF)

Title: Trajectory control of a new class of CNC machine tools.
Creator: Xiu, Daoxi., Florida Atlantic University, Masory, Oren, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: One emerging application of parallel manipulators is to use them as CNC (Computerized Numerical Controlled) machine tools and recently several prototypes of such CNC machines have been developed, all based on hexapod machine--a type of parallel manipulators similar to a Stewart platform. The goal of this research is to develop an effective control scheme, cross-coupling control, for this type of CNC machine tools, which will reduce the contouring errors and thus further enhance their...
Show moreOne emerging application of parallel manipulators is to use them as CNC (Computerized Numerical Controlled) machine tools and recently several prototypes of such CNC machines have been developed, all based on hexapod machine--a type of parallel manipulators similar to a Stewart platform. The goal of this research is to develop an effective control scheme, cross-coupling control, for this type of CNC machine tools, which will reduce the contouring errors and thus further enhance their advantages. This dissertation describes the research work as follows. Firstly. based on the analysis of the kinematics and dynamics, a PID (Proportional-Integral-Derivative) controller was designed for each leg of the hexapod CNC machine. Secondly, real-time contour error models were developed and verified to determine not only for the calculation of the contour errors of the hexapod CNC machine but also for the general case of any machine tools. Thirdly, the contour errors of the hexapod CNC machine were investigated for a conventional PID controller. The results indicate that the accuracy of the hexapod machine is better than the conventional CNC machine tools even for mismatched axes and load exertion. Finally, a cross-coupling control scheme was proposed for the purpose to enhance the contour accuracy of this new type of hexapod CNC machine tools. A cross-coupling controller design for a 2-DOF platform was performed to provide the guidelines. Then, a cross-coupling controller for the new type of hexapod CNC machine tools was designed by feeding back the contour error to each axis. The efficiency of the proposed cross-coupling controller was verified through simulations. The result shows that the proposed cross-coupling controller is very effective in reducing the contouring errors. While cross-coupling controllers were originally proposed for conventional CNC machine tools, this research is the first attempt of expanding this concept to the new type of hexapod CNC machine tools.
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Date Issued: 1998
PURL: http://purl.flvc.org/fcla/dt/12576
Subject Headings: Machine-tools--Numerical control, Manipulators (Mechanism), PID controllers
Format: Document (PDF)

Title: Trailing edge noise propagation through a cascade of blades.
Creator: Roy, Charlie Desire., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Aircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It...
Show moreAircraft engine fan trailing edge noise prediction is very challenging. To achieve a better understanding of the physics of the propagation problem, the fan has been modeled as an infinite cascade of blades and acoustic monopoles and dipoles have been placed at the trailing edges. The flow has been computed using the Transonic Small Disturbance equation. As soon as the critical Mach number is exceeded by the free stream, a supersonic region that joins two consecutive blades appears. It completely blocks the sound and limits the study to entirely subsonic flow. In this type of flow, a sound propagation simulator has been implemented. The linearized form of Howe's equation is solved by a high frequency method. The ray caustic problem which causes regular ray tracing failure is fixed by interpolating the field on a preset grid. Results are compared with the analytical solution in uniform flow and computations in realistic flow are presented.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/12990
Subject Headings: Trailing edges (Aerodynamics), Blades, Turbulent boundary layer
Format: Document (PDF)

Title: Tool wear monitoring using artificial neural networks.
Creator: Kurapati, Venkatesh., Florida Atlantic University, Masory, Oren, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: An on-line scheme for monitoring tool wear in unmanned machining operations using artificial neural networks (ANNs) is proposed. Various configurations of ANNs are studied to increase the accuracy of tool wear estimation. With this aim three configurations of the ANNs namely, an ANN without memory, an ANN with one phase memory, and an ANN with two phase memory are considered. Each ANN is trained to associate an input vector which consists of values of cutting conditions, with an output vector...
Show moreAn on-line scheme for monitoring tool wear in unmanned machining operations using artificial neural networks (ANNs) is proposed. Various configurations of ANNs are studied to increase the accuracy of tool wear estimation. With this aim three configurations of the ANNs namely, an ANN without memory, an ANN with one phase memory, and an ANN with two phase memory are considered. Each ANN is trained to associate an input vector which consists of values of cutting conditions, with an output vector containing flank wear as a single output. The training data and evaluation data is generated using the popular analytical tool wear model. The performance of all the ANNs are compared by considering four different cases of evaluation data. The proposed scheme of tool wear modeling using ANNs is easily extendible to include other cutting parameters and can be implemented in real-time.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/14868
Subject Headings: Neural networks (Computer science), Flexible manufacturing systems, Power tools, Machine tools--Data processing
Format: Document (PDF)

Title: THREE-DIMENSIONAL PHOTOELASTIC STRESS ANALYSIS OF A METAL-TO-METAL CONTACT BOLTED FLANGE.
Creator: Mahfuz, Hassan, Florida Atlantic University, Case, Robert O., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Three-dimensional photoelastic stress analysis techniques are used to determine the stress distribution in a metal-to-metal contact bolted flange. The flange belongs to a thin-walled stage support casing of a jet aircraft engine. Of special interest is the state of stress experienced at flange separation due to axial and bending loads during severe in-flight maneuvering. Details of model development, data collection and discussion of results for the stresses in the bolts and in the vicinity...
Show moreThree-dimensional photoelastic stress analysis techniques are used to determine the stress distribution in a metal-to-metal contact bolted flange. The flange belongs to a thin-walled stage support casing of a jet aircraft engine. Of special interest is the state of stress experienced at flange separation due to axial and bending loads during severe in-flight maneuvering. Details of model development, data collection and discussion of results for the stresses in the bolts and in the vicinity of the flange are presented.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14319
Subject Headings: Strains and stresses, Photoelasticity, Materials--Testing
Format: Document (PDF)

Title: A three-dimensional finite element model for the biomechanical analysis of total ankle replacement.
Creator: Vo, Ha Van., Florida Atlantic University, Han, Chingping (Jim), College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The artificial ankle joint implant has been developed since 1970 after the relatively successful total hip and knee arthroplasty. The main goal of ankle replacement is to eliminate pain and preserve joint motion. Unfortunately, total ankle replacement (TAR) has not been effective as implant of other joints. Recently, published studies of early series showed that the newer second-generation ankle prosthesis have been improved with time. However, only one of the three current ankle designs is...
Show moreThe artificial ankle joint implant has been developed since 1970 after the relatively successful total hip and knee arthroplasty. The main goal of ankle replacement is to eliminate pain and preserve joint motion. Unfortunately, total ankle replacement (TAR) has not been effective as implant of other joints. Recently, published studies of early series showed that the newer second-generation ankle prosthesis have been improved with time. However, only one of the three current ankle designs is allowed by FDA to be used widely in the U.S. This study provides a new ankle design with an advanced approach in designs, biomechanical rationale, and implantation using finite element method (FEM). The new ankle prosthesis in designed to be optimal in terms of ultimate stress, implant parameter that correlating with minimal bone removal using finite element model created from CT scan. In addition, its implantation is less invasive and traumatic compared to the current TAR with longer expecting service life time. Case study showed that the thickness meniscus of the new ankle design obtained from FEM is well within the recommendation ranges by the expert in the ankle joint implantation field.
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Date Issued: 2003
PURL: http://purl.flvc.org/fcla/dt/12052
Subject Headings: Ankle--Effect of implants on, Artificial joints, Ankle--Mechanical properties, Finite element method
Format: Document (PDF)

Title: Thickness and weld profile effects upon the fatigue crack development in sea water.
Creator: Li, Yong., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This research investigated the plate thickness and weld profile effects upon fatigue of structural steel in sea water. Specific attention was focused on the initiation and propagation behavior of fatigue cracks formed at the toe of different profiled welds and varied plate thicknesses. It was shown that the initiation life was reduced as the thickness increased. The improved weld profile increased the crack initiation life. Analysis of the fatigue data indicated that the Initiation Life to...
Show moreThis research investigated the plate thickness and weld profile effects upon fatigue of structural steel in sea water. Specific attention was focused on the initiation and propagation behavior of fatigue cracks formed at the toe of different profiled welds and varied plate thicknesses. It was shown that the initiation life was reduced as the thickness increased. The improved weld profile increased the crack initiation life. Analysis of the fatigue data indicated that the Initiation Life to Failure Life Ratio Ni/Nf appeared to be greater for the improved weld profile than for the AWS Basic weld profile. The improved weld profile prolonged the propagation life Np. The thickness factor influenced the propagation life Np for the improved weld profile, but the trend was uncertain for the basic weld profile.
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Date Issued: 1989
PURL: http://purl.flvc.org/fcla/dt/14532
Subject Headings: Steel, Structural--Fatigue
Format: Document (PDF)

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