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Title: Integrated simulator of JIT manufacturing process.
Creator: Li, Shuanghu., Florida Atlantic University, Mazouz, Abdel Kader, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The main objective of this research is to develop an integrated simulator which would perform as a decision support system of a Just-in-Time manufacturing process. It would permit a process designer or manufacturing engineer with no simulation expertise to define the process variables, then run the simulation program. A secondary objective is to combine in one system the key functions required by a manufacturing engineer or manager, such as the operational (real time), statistical, and...
Show moreThe main objective of this research is to develop an integrated simulator which would perform as a decision support system of a Just-in-Time manufacturing process. It would permit a process designer or manufacturing engineer with no simulation expertise to define the process variables, then run the simulation program. A secondary objective is to combine in one system the key functions required by a manufacturing engineer or manager, such as the operational (real time), statistical, and financial aspects. And also makes those function modules easy to understand and user-friendly. The integrated simulator can use animation to visualize an actual production line. A case study has been developed to verify and validate the work done.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/14800
Subject Headings: Just-in-time systems--Computer simulation, Manufacturing processes--Automation, Simulation methods--Computer programs
Format: Document (PDF)

Title: Interlaminar crack propagation in thick composite shells.
Creator: Ozdil, Feridun., Florida Atlantic University, Carlsson, Leif A., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Delamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional...
Show moreDelamination growth has been investigated as a potential failure mechanism for filament-wound composite cylinders used for offshore and underwater structures. Analysis and experiments on DCB, ENF, and MMB beam fracture specimens machined from angle-ply laminate panels and filament-wound composite cylinders are presented. Bending analysis of beam fracture specimens machined from flat panels and composite cylinders was derived from first order shear deformation theory and one-dimensional expressions obtained from laminated plate and shell theories. For the DCB specimens, elastic foundation effects were modeled. Experiments on flat, glass/polyester laminate beam specimens considered [0]6, [+/-30]5 and [+/-45] 5 lay-ups with mid-plane delaminations. Experiments on beam specimens machined from composite cylinders were conducted on [+/- q ]6 and [+/- q ]12 lay-ups with mid-surface delaminations where q = 30 degrees, 55 degrees and 85 degrees. For all lay-ups and specimen configurations, beam model predictions of compliance were in good agreement with experimental data over the range of laminate thicknesses, ply angles, and crack lengths examined. Fracture toughness for delamination propagation was examined for flat glass/polyester panels and glass/epoxy cylinders. The initiation value of mode II fracture toughness, GIIc, was much larger than the initiation value of mode I fracture toughness GIc. The initiation value of mixed mode fracture toughness, Gc, increased with decreased ratio GI/GII and increased ply angle q . Debonding of transversely oriented fiber bundles was observed as a major crack arrest and fracture resistance mechanism for the flat, glass/polyester angle-ply laminates. Bridging by interlaced fiber bundles and crack jumping to another interface contributed to crack arrest and limited the growth in the curved, glass/epoxy angle-ply laminates. For all lay-ups, the crack propagated in a non-uniform manner across the width of the specimen as explained by elastic coupling effects in the laminate beams of the cracked region.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/12588
Subject Headings: Laminated materials, Shells (Engineering), Composite materials
Format: Document (PDF)

Title: Interaction of acoustic waves generated by coupled finite fluid-loaded plates.
Creator: Kaina, Rachid., Florida Atlantic University, Cuschieri, Joseph M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The response of fluid-loaded plates has been extensively studied in the past. However, most of the work deals with either infinite plates or finite plates with particular boundary conditions and the results are generally presented only in the limit of small wavelengths compared with the dimensions of the plates. Furthermore, the problem of coupled finite plates where both the acoustic interaction and structural interaction are included in the solution has not been considered. In this...
Show moreThe response of fluid-loaded plates has been extensively studied in the past. However, most of the work deals with either infinite plates or finite plates with particular boundary conditions and the results are generally presented only in the limit of small wavelengths compared with the dimensions of the plates. Furthermore, the problem of coupled finite plates where both the acoustic interaction and structural interaction are included in the solution has not been considered. In this dissertation the response of two coupled finite plates set in two alternative configurations is considered. The plates are simply supported on two edges, with arbitrary boundary conditions on the remaining two edges. The solutions obtained for the response of the plates include both the structural interaction at the common junction and the acoustic interaction due to the scattered pressure from each of the two plates. The results are presented in terms of the vibrational power flow into and out of each plate component. The solution is based on a formulation developed in the wavenumber domain combined with the Mobility Power Flow method. Using this approach, different substructural elements coupled under different boundary conditions to form a complex global structure can be considered. The detailed spatial and temporal scales of the structure response are not lost when using this method. In obtaining the solution for the scattering from the fluid-loaded plates, a modal decomposition in the direction normal to the simply supported edge is used. A spatial Fourier-transform decomposition is used in the other direction. Due to the finiteness of the plate, eight unknowns parameters are obtained in the transformed result. The solution for these eight unknown parameters is obtained from the boundary conditions and the condition that the response must remain finite. Two analytical approaches are used to solve the final plate integral equation. The first approach consists of an approximation method which obtains a solution based on the solution of the corresponding infinite plate problem. The second approach is a more accurate solution based on the Projection Method for the solution of integral equations. Both of the approaches used in the solution provide accurate predictions at high frequencies. At low frequencies especially for low structural damping or for heavy fluid loading, only the Projection Method gives reliable results. This is attributed to the fact that at low frequencies, the influence of the edges of the plates on the scattering is significant. The overall results obtained from this analysis indicate that the fluid loading and the plate characteristics have a significant influence on the acoustic scattering properties, especially in the case of heavy fluid loading. The application of the method to coupled fluid-loaded plates indicates that the junction enhances the scattering properties. The acoustical interaction between the coupled plates increases the contribution to scattering from subsonic wavenumber components. In the absence of the interaction, only supersonic wavenumbers contribute to the scattering. Inclusion of acousticlal interaction requires both supersonic and subsonic components. The significance of the contribution from the subsonic wavenumber components is dependent on the type of the fluid loading.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12341
Subject Headings: Finite element method, Plates (Engineering), Acoustic emission, Sound--Transmission
Format: Document (PDF)

Title: Interaction of vortex sheet with a finite vortex.
Creator: Viswanathan, K. S., Florida Atlantic University, Dhanak, Manhar R., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is...
Show moreThe rollup of a vortex sheet of elliptic span loading in the presence of a vortex of finite core size is studied in the Trefftz plane. The vorticity in the finite vortex is taken to be uniform and sign opposite to that of the sheet and the flow is assumed to be inviscid and incompressible. A numerical scheme is developed to determine the evolution of (a) the finite vortex using the Contour Dynamics technique, (b) the vortex sheet using an algorithm developed by Krasny. The interaction is shown to substantially affect the development of the vortex sheet rollup. The vortex sheet undergoes significant deformation at the rolling up tip region due to its devouring the vortex patch as well as due to the formation of secondary rollup features on the sheet. These features are believed to be important in inhibiting rollup considerably. The interaction is quantified by using a criterion developed to measure the extent of the tip vortex rollup and its characteristics are studied for a range of flow parameters. The strength of the rolling up tip region of the vortex sheet is found to be highly dependent on the location and the vorticity in the finite vortex.
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Date Issued: 1994
PURL: http://purl.flvc.org/fcla/dt/15048
Subject Headings: Turbulence, Whirlwinds, Vortex-motion, Wakes (Aerodynamics)
Format: Document (PDF)

Title: Influences of chlorides, pH and surface films on the corrosion of reinforcing steel in alkaline solutions.
Creator: Sundaresan, Raman., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The objective of this study was to determine the influences of chlorides, pH and surface films on the corrosion of reinforcing steel in alkaline solutions. Anodic and linear polarization experiments were conducted on 1018 steel specimens exposed to these environments. The results indicate that there is a threshold amount of [Cl-] beyond which passivity is compromised. The i-passive in the electrolyte of pH 12.24 was approximately 0.01 of that in the electrolyte of pH 10.13. At least a one day...
Show moreThe objective of this study was to determine the influences of chlorides, pH and surface films on the corrosion of reinforcing steel in alkaline solutions. Anodic and linear polarization experiments were conducted on 1018 steel specimens exposed to these environments. The results indicate that there is a threshold amount of [Cl-] beyond which passivity is compromised. The i-passive in the electrolyte of pH 12.24 was approximately 0.01 of that in the electrolyte of pH 10.13. At least a one day period was necessary for the effect of the excess crystals of Ca(OH)2 to be felt. Corrosion rates of specimen with a Ca(OH)2 surface film were lower than without this film. [Cl-] /[OH-] in the range 2.5 to 3.5 appeared to be the threshold for breakdown of passivity.
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Date Issued: 1989
PURL: http://purl.flvc.org/fcla/dt/14520
Subject Headings: Reinforced concrete--Corrosion, Steel--Corrosion, Corrosion and anti-corrosives
Format: Document (PDF)

Title: Investigation of carbon dioxide transport in life support helmets.
Creator: Camperman, John Michael., Florida Atlantic University, Tennant, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: This research explores carbon dioxide transport in life support helmet annular space using new theoretical and experimental techniques. Increased transport from next generation helmets is necessary to allow reduction of fresh gas flow and associated noise. Conventional helmet noise interferes with communications and some underwater helmets even approach hearing threshold shift levels. Helmet flow is three dimensional, unsteady, and turbulent; this research is the first known effort to...
Show moreThis research explores carbon dioxide transport in life support helmet annular space using new theoretical and experimental techniques. Increased transport from next generation helmets is necessary to allow reduction of fresh gas flow and associated noise. Conventional helmet noise interferes with communications and some underwater helmets even approach hearing threshold shift levels. Helmet flow is three dimensional, unsteady, and turbulent; this research is the first known effort to identify the fundamental mechanisms of CO2 transport. An analytical model is developed which predicts average inhaled CO2 concentration for generic helmet geometry using a mixing volume approach. The model includes sensitivity to supply flow, breath rate, metabolic CO2 production, inhalation and exhalation mixing volumes, and breathing symmetry. Numerical sensitivity analysis using the model indicates optimum design paths. Nominal head-helmet-lung geometry is identified. An experimental nominal model was developed which supports inhaled concentration measurements with air-CO2 or water-dye as working fluids. Water modeling provides flow visualization which is used to identify complex convective and turbulent CO2 transport mechanisms. Correlation of water-dye and air-CO2 results indicates conditions when molecular diffusion of CO2 is significant. The research was directed primarily toward diving helmets but is applicable to spacesuit and firefighter helmets, as well as any situation involving mass transport in a periodic mixing chamber. New analytical and experimental models are substantially more accurate than the conventional steady state helmet mixing model, and provide direction for improved helmet design.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/12432
Subject Headings: Deep diving--Equipment and supplies, Deep diving--Physiological aspects, Carbon dioxide, Underwater physiology
Format: Document (PDF)

Title: HYDRODYNAMIC LOADS ON OFFSHORE STRUCTURES DURING SUBSEA BLOWOUTS.
Creator: RAJIV, PAKANATI V. S., Florida Atlantic University, Su, Tsung-Chow, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The plume resulting from a subsea well blowout alters the environmental loading on a floating platform which is directly above the well. Horizontal ocean currents deflect the plume and may create a more severe loading on the structure. During the early stages of a blowout the "starting plume" induces forces of a different magnitude on the structure. A preliminary experimental study, investigating the transient loads induced by starting plumes and the effects of currents on blowout plumes, was...
Show moreThe plume resulting from a subsea well blowout alters the environmental loading on a floating platform which is directly above the well. Horizontal ocean currents deflect the plume and may create a more severe loading on the structure. During the early stages of a blowout the "starting plume" induces forces of a different magnitude on the structure. A preliminary experimental study, investigating the transient loads induced by starting plumes and the effects of currents on blowout plumes, was conducted. The results of the experiments showed that the forces involve significant fluctuations which are quite different from the average values. The normal forces induced by starting plumes were slightly greater. Horizontal currents caused an increase in the moment acting on the structure. This is of considerable importance as moments, when coupled with the situation of flooded decks and compartments, may cause the structure to sink.
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Date Issued: 1985
PURL: http://purl.flvc.org/fcla/dt/14267
Subject Headings: Offshore structures--Hydrodynamics--Experiments
Format: Document (PDF)

Title: IDENTIFICATION OF DISTRIBUTED STATIC LOADINGS ON BEAMS.
Creator: Shen, Sueming, Florida Atlantic University, Stevens, Karl K., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The problem of identification. of distributed static loadings of a one-dimensional beam is considered. All response experimental data were derived from computer simulations. True response data yield highly accurate identification of the resultant forces; the identification is, however, very sensitive to errors in the response data. The results of the experimental data are accurate within a small range of error.
Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14322
Subject Headings: Mechanics, Applied, Statics
Format: Document (PDF)

Title: INFLUENCE BY CALCAREOUS DEPOSITS ON FATIGUE CRACK CLOSURE IN STEEL.
Creator: LEE, AI-KUO., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: A model for calcareous deposit induced fatigue crack closure has been previously reported based upon the criterion that the deposit thickness within the crack equals or exceeds one-half the minimum crack opening displacement. In the present paper an expanded and refined model is proposed by considering (1) compaction of calcareous deposits during the closure period of the stress cycle and (2) the relationship between R ratio and threshold stress intensity range. Compression tests upon...
Show moreA model for calcareous deposit induced fatigue crack closure has been previously reported based upon the criterion that the deposit thickness within the crack equals or exceeds one-half the minimum crack opening displacement. In the present paper an expanded and refined model is proposed by considering (1) compaction of calcareous deposits during the closure period of the stress cycle and (2) the relationship between R ratio and threshold stress intensity range. Compression tests upon calcareous films grown on steel surfaces have been performed, and these reveal the change in deposit thickness as a function of stress. The implications of these models to calcareous deposit induced fatigue crack closure are discussed in terms of mechanical and electrochemical parameters.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14315
Subject Headings: Steel--Fatigue, Steel--Corrosion
Format: Document (PDF)

Title: Experimental studies on flexural behavior of CFRP retrofitted concrete members.
Creator: Raghavachary, Sowrirajan., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The flexural behavior of rectangular concrete beams strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) laminates was studied by varying the number of plates bonded to their bottom tensile face. The increases in strength and stiffness of the beams provided by the bonded plates, over control beam without CFRP plates, were evaluated. Failure loads of the beams were determined by the ACI strain compatibility method using a FORTRAN software developed for this purpose. The...
Show moreThe flexural behavior of rectangular concrete beams strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) laminates was studied by varying the number of plates bonded to their bottom tensile face. The increases in strength and stiffness of the beams provided by the bonded plates, over control beam without CFRP plates, were evaluated. Failure loads of the beams were determined by the ACI strain compatibility method using a FORTRAN software developed for this purpose. The predicted collapsed load agrees reasonably well with the actual failure load. Precracked solid and voided slab bridge models retrofitted with varying number of CFRP laminates were used to evaluate their contribution to the flexural resistance. The increases in strength and stiffness of the retrofitted slabs were based on the deflections, strains and crack patterns at ultimate load. Theoretical analyses to predict the load-deflection behavior of the precracked sections were performed using PCFRAME software. The predicted values agree reasonably well with the experimental results.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/15120
Subject Headings: Fiber reinforced plastics, Reinforced concrete, Fiber, Bridges, Concrete, Prestressed concrete, Concrete beams--Fatigue
Format: Document (PDF)

Title: Experimental and Modeling Study of Chloride Ingress into Concrete and Reinforcement Corrosion Initiation.
Creator: Yu, Hui, Hartt, William H., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Effects of reinforcement and coarse aggregate on chloride ingression into concrete and reinforcement corrosion initiation have been studied with experimental and modeling (finite element method) analyses. Once specimens were fabricated and exposed to a chloride solution, various experimental techniques were employed to determine the effect of reinforcement and coarse aggregate on time-to-corrosion and chloride ingress and concentration at corrosion locations. Model analyses were performed to...
Show moreEffects of reinforcement and coarse aggregate on chloride ingression into concrete and reinforcement corrosion initiation have been studied with experimental and modeling (finite element method) analyses. Once specimens were fabricated and exposed to a chloride solution, various experimental techniques were employed to determine the effect of reinforcement and coarse aggregate on time-to-corrosion and chloride ingress and concentration at corrosion locations. Model analyses were performed to verify and explain the experimental results. Based upon the results, it was determined that unexpectedly higher chloride concentrations were present on the top of the rebar trace than that to the side at the same depth and an inverse concentration gradient (increasing [Cl-] with increasing depth) occurred near the top of rebars. Also, coarse aggregate volume profile in close proximity to the rebar and spatial distribution of these aggregates, in conjunction with the physical obstruction afforded by reinforcement to chloride flow, complicates concrete sampling for Cl- intended to define the critical concentration of this species to initiate corrosion. Modeling analyses that considered cover thickness, chloride threshold concentration, reinforcement size and shape, and coarse aggregate type and percolation confirmed the experimental findings. The results, at least in part, account for the relatively wide spread in chloride corrosion threshold values reported in the literature and illustrate that more consistent chloride threshold concentrations can be acquired from mortar or paste specimens than from concrete ones.
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Date Issued: 2007
PURL: http://purl.flvc.org/fau/fd/FA00012582
Subject Headings: Reinforced concrete construction--Corrosion, Chlorides--Diffusion rate, Composite reinforced concrete, Concrete--Chemical resistance
Format: Document (PDF)

Title: FATIGUE BEHAVIOR OF JOINTS IN PRECAST PRESTRESSED CONCRETE DOUBLE TEE BRIDGE SYSTEM.
Creator: RAO, VENKATESWARA B., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The feasibility of the use of double-tee beams in a bridge system is examined by conducting tests on a 1:3.5 scale model of a two-span transversely and longitudinally post-tensioned continuous double-tee beam system. Constant amplitude fatigue loading was applied on the model at typical locations simulating HS 20-44 AASHTO truck loading. The behavior of the bridge system was evaluated in terms of deflections, wheel load distributions, crack growth and patterns with increasing number of cycles...
Show moreThe feasibility of the use of double-tee beams in a bridge system is examined by conducting tests on a 1:3.5 scale model of a two-span transversely and longitudinally post-tensioned continuous double-tee beam system. Constant amplitude fatigue loading was applied on the model at typical locations simulating HS 20-44 AASHTO truck loading. The behavior of the bridge system was evaluated in terms of deflections, wheel load distributions, crack growth and patterns with increasing number of cycles of fatigue loading. A finite element analysis of the bridge system was done using plate and beam elements and results compared with experimental values.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14332
Subject Headings: Prestressed concrete beams--Fatigue, Bridges, Concrete--Joints
Format: Document (PDF)

Title: FATIGUE CRACK DEVELOPMENT IN CATHODICALLY POLARIZED WELDED STEEL IN SEAWATER.
Creator: WEHLING, CHRISTOPHER MARK., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The fatigue crack growth behavior of welded ABS DH32 steel spec~mens cathodically polarized to -1.00 volt (Cu-CuS04) and subjected to bending fatigue of nominal stress + 69 MN/m^2 (+- 10 ksi) in seawater was investigated. Small non-propagating surface cracks with lengths up to 4.93 mm formed in the specimens. There were no s~gns of failure after 36 x 10^6 cycles when the experiment was terminated. Comparison of this test with similar freely corroding and -0.85 volt (Cu-CuS04) tests indicated...
Show moreThe fatigue crack growth behavior of welded ABS DH32 steel spec~mens cathodically polarized to -1.00 volt (Cu-CuS04) and subjected to bending fatigue of nominal stress + 69 MN/m^2 (+- 10 ksi) in seawater was investigated. Small non-propagating surface cracks with lengths up to 4.93 mm formed in the specimens. There were no s~gns of failure after 36 x 10^6 cycles when the experiment was terminated. Comparison of this test with similar freely corroding and -0.85 volt (Cu-CuS04) tests indicated that -1.00 volt (Cu-CuS04) cathodic protection is conducive to arrestment of small fatigue cracks. This suggests that modest cathodic over-protection of steel in seawater may beneficial.
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Date Issued: 1981
PURL: http://purl.flvc.org/fcla/dt/14091
Subject Headings: Steel--Fatigue
Format: Document (PDF)

Title: Fabrication and characterization of copper/molybdenum coatings on carbon fibers by electrodeposition.
Creator: Maucione, Luke J., Florida Atlantic University, Lipka, Stephen M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The codeposition of a smooth and uniform coating of copper and molybdenum was successfully achieved on T-650 carbon fiber. The effect of various plating parameters on the electrodeposition of copper and molybdenum such as plating bath chemistry, current density, and pulse frequency were studied. By adjusting the aforementioned variables, qualitative and quantitative analysis was conducted to evaluate the deposit smoothness, uniformity, and wetting characteristics. Qualitative analysis of the...
Show moreThe codeposition of a smooth and uniform coating of copper and molybdenum was successfully achieved on T-650 carbon fiber. The effect of various plating parameters on the electrodeposition of copper and molybdenum such as plating bath chemistry, current density, and pulse frequency were studied. By adjusting the aforementioned variables, qualitative and quantitative analysis was conducted to evaluate the deposit smoothness, uniformity, and wetting characteristics. Qualitative analysis of the deposits were made using scanning electron microscopy and energy dispersive spectroscopy. Quantitative analysis of the deposit coating was conducted using inductively coupled plasma chemical analysis, dewetting tests, X-ray diffraction, transmission electron microscopy, and auger electron spectroscopy. Based on the results, a plating line was designed and constructed for the continuous deposition of copper and molybdenum onto carbon fiber tows.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/15124
Subject Headings: Composite materials, Alloy plating, Metallic composites, Molybdenum alloys
Format: Document (PDF)

Title: FATIGUE OF HIGH STRENGTH LOW-ALLOY STEELS IN NATURAL SEA WATER.
Creator: KRISHNAKUMAR, RENGAN., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: The fatigue response of selected high strength low alloy steels, that are under consideration for future offshore structural applications, was investigated. Freely corroding and cathodically polarized experiments were conducted under conditions relevant .to these applications. Cathodic polarization experiments involved testing of A537 Direct Quenched (A537 DQ) steel at different potentials in the -0.80 V to -1.10 V (SCE) range. The damage to freely corroding high strength steel was more than...
Show moreThe fatigue response of selected high strength low alloy steels, that are under consideration for future offshore structural applications, was investigated. Freely corroding and cathodically polarized experiments were conducted under conditions relevant .to these applications. Cathodic polarization experiments involved testing of A537 Direct Quenched (A537 DQ) steel at different potentials in the -0.80 V to -1.10 V (SCE) range. The damage to freely corroding high strength steel was more than on structural steel for calculations based on the Wirsching wide band spectrum. Polarization to -0.80 V (SCE) improved the fatigue life of A537 DQ steel over the freely corroding life. A definite conclusion with regard to the influence of different levels of cathodic polarization on the fatigue life of the steel investigated can not not be drawn based on the results from this study due to data variability.
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Date Issued: 1987
PURL: http://purl.flvc.org/fcla/dt/14374
Subject Headings: Steel--Fatigue, Seawater
Format: Document (PDF)

Title: Experimental and theoretical characterization of near-threshold fatigue crack growth for high strength steels in seawater.
Creator: Yang, Jingjun., Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Near-threshold fatigue crack growth rate data were generated for six high strength steels at stress ratios of 0.5 and 0.8 under different environmental conditions, which included air, freely corroding in seawater, and cathodically polarized in seawater to -0.80v, -0.95v and -1.10v (vs SCE). The influence of stress ratio, loading frequency, magnitude of cathodic polarization and initial DeltaK on fatigue crack growth behavior for these high strength steels was experimentally characterized. The...
Show moreNear-threshold fatigue crack growth rate data were generated for six high strength steels at stress ratios of 0.5 and 0.8 under different environmental conditions, which included air, freely corroding in seawater, and cathodically polarized in seawater to -0.80v, -0.95v and -1.10v (vs SCE). The influence of stress ratio, loading frequency, magnitude of cathodic polarization and initial DeltaK on fatigue crack growth behavior for these high strength steels was experimentally characterized. The results disclosed general trends of fatigue crack growth under conditions relevant to offshore structure applications and circumscribed variables that are primarily influential with regard to service performance. The rate controlling processes and cracking mechanisms of near-threshold fatigue crack growth, particularly under cathodic polarization in seawater, were also studied in conjunction with crack mouth opening displacement measurements, fractographic observation and crack profile examination. The data and observations suggest that calcareous deposit induced closure was the rate-controlling factor for near-threshold fatigue crack growth under cathodic polarization in seawater although the cracking involved a brittle failure mechanism as a result of hydrogen embrittlement. With different FCGR determining procedures which included natural K-decreasing, enhanced K-decreasing, natural K-increasing and constant DeltaK, the FCGR under cathodic polarization in seawater was found to be time-dependent and, as such, was not a unique function of DeltaK but depended upon K-history or experimental procedures. These observations were consistent with results of a theoretical analysis which involved kinetics modeling of the interaction between fatigue crack growth and calcareous deposit thickening. The model also predicted the existence of an upper limit transition DeltaK, DeltaK Upp/T, between the Paris and threshold regions and it was found that the predicted DeltaK Upp/T was in agreement with the experimental one. The basis for applying this critical parameter (DeltaK Upp/T) to offshore structure designs was addressed in conjunction with experimental results.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/12410
Subject Headings: Seawater corrosion, Steel--Fatigue, Steel--Fracture, Corrosion and anti-corrosives
Format: Document (PDF)

Title: Experimental and theoretical studies of cryogenic sealing.
Creator: Jia, Lin X., Florida Atlantic University, Chow, Wen L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Funded by NASA Kennedy Space Center, this research project was to solve the liquid hydrogen leakage problem in the cryogenic system of Columbia space shuttle. A contracting-expanding self-sealing (CESSC) device was developed by making use of the thermal contraction ratio of dissimilar metals. A research cryostat providing with a high pressure and variable temperature test chamber was built to leak check the cryogenic fittings. A cryogenic research laboratory for the project was established in...
Show moreFunded by NASA Kennedy Space Center, this research project was to solve the liquid hydrogen leakage problem in the cryogenic system of Columbia space shuttle. A contracting-expanding self-sealing (CESSC) device was developed by making use of the thermal contraction ratio of dissimilar metals. A research cryostat providing with a high pressure and variable temperature test chamber was built to leak check the cryogenic fittings. A cryogenic research laboratory for the project was established in the Department of Mechanical Engineering, Florida Atlantic University. Both NASA KC126 fitting and the CESSC fitting were tested in the cryogenic testing system. A theoretical approach was also attempted to study the cryogenic leaking phenomenon. A finite element code was developed to simulate the thermal contraction for different CESSC designs. The ANSYS code was also used for the same purpose. The CESSC fittings were successfully used in the space program as well as in the superconducting projects. The principle of the CESSC seal has been extended to solve a variety of problems in cryogenic field.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12448
Subject Headings: Sealing (Technology), Low temperature research
Format: Document (PDF)

Title: FLIGHT TESTS OF AN OPEN LOOP HIGHER HARMONIC CONTROL SYSTEM ON AN S-76A HELICOPTER.
Creator: WALSH, DAVID M., Florida Atlantic University, Goankar, Gopal, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: Flight tests of an open loop higher harmonic vibration control system were conducted on an S-76A helicopter during the early part of 1985. This paper discusses the design, conduct and results of those tests. The flight tests included evaluations of Higher Harmonic Control (HHC) inputs in the longitudinal, lateral and collective axes at varying amplitudes and phases. These flight tests have demonstrated the feasibility of HHC on a medium size, high speed helicopter. Significant vibration...
Show moreFlight tests of an open loop higher harmonic vibration control system were conducted on an S-76A helicopter during the early part of 1985. This paper discusses the design, conduct and results of those tests. The flight tests included evaluations of Higher Harmonic Control (HHC) inputs in the longitudinal, lateral and collective axes at varying amplitudes and phases. These flight tests have demonstrated the feasibility of HHC on a medium size, high speed helicopter. Significant vibration reductions throughout the aircraft were demonstrated at forward speeds up to 150 knots. The capability of HHC to reduce vibrations was also demonstrated at varying rotor speeds and during maneuvers. Structural data obtained during testing, showed a general increase in control system loads during HHC operation. However, no loads were above structural limits and it appears that a control system could be designed with sufficient strength to accept all HHC loads.
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Date Issued: 1986
PURL: http://purl.flvc.org/fcla/dt/14341
Subject Headings: Vibration (Aeronautics), Helicopters
Format: Document (PDF)

Title: Feasibility of using carbon fiber reinforced plastic tendons in prestressed concrete Double-Tee bridge system.
Creator: Zhuang, Ming., Florida Atlantic University, Arockiasamy, Madasamy, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: One of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete...
Show moreOne of the major problems the construction industry faces today is corrosion of reinforcing and prestressing steel, which significantly affects the durability of concrete structures. Fiber reinforced plastics (FRPs) are highly regarded as prospective replacement for steel in prestressed concrete structures under corrosive environment. This investigation was conducted to establish the feasibility of using Carbon Fiber Composite (CFC) cables as reinforcing/prestressing elements in concrete bridge structures. Besides investigating durability of CFC cables and pretensioned concrete beams with CFC cables in adverse environments (alkali and seawater), flexure and shear tests were performed on single Double-Tee beams, together with service load behavior, fatigue strength and ultimate load capacity tests on a half scale model Double-Tee girder bridge system prestressed with CFC cables. Exposure to seawater and alkali environments has no adverse effect on the strength of the CFRP tendons as well as the pretensioned beams with CFRP. Based on the flexural strength tests on Double-Tee beams, the bond between CFRP tendons and concrete is satisfactory. The Double-Tee bridge system exhibited good fatigue resistance and adequate ductility under ultimate load conditions. The ultimate load capacity of the bridge is approximately three times the service load corresponding to two HS20-44 trucks and equals 2.4 times the first crack load. Finite element analyses were carried out to predict elastic deformations and collapse load of the Double-Tee bridge prestressed with CFC cables. Feasibility of using CFC cables in bridge structures is assessed based on the experimental and analytical parameters such as deflections, strains, crack distributions and crack widths.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12465
Subject Headings: Carbon fibers, Composite construction, Fiber reinforced plastics, Bridges, Iron and steel, Reinforced concrete construction, Prestressed concrete construction
Format: Document (PDF)

Title: High performance and robust control.
Creator: Xu, Min., Florida Atlantic University, Smith, Samuel M., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description: It is desirable to have robust high performance nonlinear control with a model-free design approach for the real time automatic control of practical industrial processes. The field has seen the application of Sliding Mode Controllers (SMCs). SMCs are nonlinear robust controllers, however most design approaches related to SMCs are model-based approaches. PID controllers and some Fuzzy Logic Controllers (FLCs) are model-free controllers, however their robustness is not integrated into their...
Show moreIt is desirable to have robust high performance nonlinear control with a model-free design approach for the real time automatic control of practical industrial processes. The field has seen the application of Sliding Mode Controllers (SMCs). SMCs are nonlinear robust controllers, however most design approaches related to SMCs are model-based approaches. PID controllers and some Fuzzy Logic Controllers (FLCs) are model-free controllers, however their robustness is not integrated into their design parameters directly. This dissertation presents two new types of robust high performance nonlinear controllers with model-free design approaches. One introduces fuzzy logic to a model-free SMC which is a simple saturation function incorporating three design parameters. Due to the interpolative nature of fuzzy control, a TSK type FLC with the model-free SMCs as its rule's consequents will produce a controller with a nonlinear sliding curve and a nonlinear boundary layer. We call this controller a Fuzzy Sliding Controller (FSC). The other uses a new type of Variable Structure Controller (VSC), which intentionally switches from one controller to another controller during a step response. In conventional approaches to VSC, the control surface does not change its shape during a step response. The new type of VSC intentionally changes the shape of the control surface during the step response. This technique is analogous to that technique employed in image processing called "morphing" where a given image gradually changes over time to the image of a different entity. In order to avoid confusion with the conventional approach to a VSC, we use the term "Morphological" Controller (MC) for the VSC of the new type. The performance and robustness with respect to parameter variations, disturbances and slow sample rates of the proposed controllers are studied in detail with a DC motor and an Inverted Pendulum System. As a means to verify the proposed controllers in practical cases, we design the model-free SMC, the FSC and the MC for the highly nonlinear and uncertain dynamics of an Autonomous Underwater Vehicle, Ocean Voyager II. It is shown that the proposed controllers are high performance and high robustness controllers.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12446
Subject Headings: Nonlinear control theory, Automatic control, Feedback control systems, Feedforward control systems
Format: Document (PDF)

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