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- Title
- ACCELERATED LIFE TESTING OF SUBSEA EQUIPMENT UNDER HYDROSTATIC PRESSURE.
- Creator
-
Thiraviam, Amar Raja, Malone, Linda, University of Central Florida
- Abstract / Description
-
Accelerated Life Testing (ALT) is an effective method of demonstrating and improving product reliability in applications where the products are expected to perform for a long period of time. ALT accelerates a given failure mode by testing at amplified stress level(s) in excess of operational limits. Statistical analysis (parameter estimation) is then performed on the data, based on an acceleration model to make life predictions at use level. The acceleration model thus forms the basis of...
Show moreAccelerated Life Testing (ALT) is an effective method of demonstrating and improving product reliability in applications where the products are expected to perform for a long period of time. ALT accelerates a given failure mode by testing at amplified stress level(s) in excess of operational limits. Statistical analysis (parameter estimation) is then performed on the data, based on an acceleration model to make life predictions at use level. The acceleration model thus forms the basis of accelerated life testing methodology. Well established accelerated models such as the Arrhenius model and the Inverse Power Law (IPL) model exist for key stresses such as temperature and voltage. But there are other stresses like subsea pressure, where there is no clear model of choice. This research proposes a pressure-life (acceleration) model for the first time for life prediction under subsea pressure for key mechanical/physical failure mechanisms. Three independent accelerated tests were conducted and their results analyzed to identify the best model for the pressure-life relationship. The testing included material tests in standard coupons to investigate the effect of subsea pressure on key physical, mechanical, and electrical properties. Tests were also conducted at the component level on critical components that function as a pressure barrier. By comparing the likelihood values of multiple reasonable candidate models for the individual tests, the exponential model was identified as a good model for the pressure-life relationship. In addition to consistently providing good fit among the three tests, the exponential model was also consistent with field data (validation with over 10 years of field data) and demonstrated several characteristics that enable robust life predictions in a variety of scenarios. In addition the research also used the process of Bayesian analysis to incorporate prior information from field and test data to bolster the results and increase the confidence in the predictions from the proposed model.
Show less - Date Issued
- 2010
- Identifier
- CFE0003411, ucf:48422
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003411
- Title
- FLAME-TURBULENCE INTERACTION FOR DEFLAGRATION TO DETONATION.
- Creator
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Chambers, Jessica, Ahmed, Kareem, University of Central Florida
- Abstract / Description
-
Detonation is a high energetic mode of pressure gain combustion that exploits total pressure rise to augment high flow momentum and thermodynamic cycle efficiencies. Detonation is initiated through the Deflagration-to-Detonation Transition (DDT). This process occurs when a deflagrated flame is accelerated through turbulence induction, producing shock-flame interactions that generate violent explosions and a supersonic detonation wave. There is a broad desire to unravel the physical mechanisms...
Show moreDetonation is a high energetic mode of pressure gain combustion that exploits total pressure rise to augment high flow momentum and thermodynamic cycle efficiencies. Detonation is initiated through the Deflagration-to-Detonation Transition (DDT). This process occurs when a deflagrated flame is accelerated through turbulence induction, producing shock-flame interactions that generate violent explosions and a supersonic detonation wave. There is a broad desire to unravel the physical mechanisms of turbulence induced DDT. For the implementation of efficient detonation methods in propulsion and energy applications, it is crucial to understand optimum turbulence conditions for detonation initiation. The study examines the role of turbulence-flame interactions on flame acceleration using a fluidic jet to generate turbulence within the reactant flow field. The investigation aims to classify the turbulent flame dynamics and temporal evolution of the flame stages throughout the turbulent flame regimes. The flame-flow interactions are experimentally studied using a detonation facility and high-speed imaging techniques, including Particle Image Velocimetry (PIV) and Schlieren flow visualization. Flow field measurements enable local turbulence characterization and analysis of flame acceleration mechanisms that result from the jet�s high level of turbulent transport. The influence of initial flame turbulence on the turbulent interaction is revealed, resulting in higher turbulence generation and overall flame acceleration. Turbulent intensities are classified, revealing a dynamic fluctuation of flame structure between the thin reaction zone and the broken reaction regime throughout the interaction.
Show less - Date Issued
- 2016
- Identifier
- CFH2000024, ucf:45578
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000024
- Title
- Influence of Transverse Slot Jet on Premixed Flame Acceleration.
- Creator
-
Tarrant, Dylan, Ahmed, Kareem, Bhattacharya, Samik, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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This work aims to identify the key flow parameters that influence flame acceleration in a semi-confined square channel. A transverse fluidic jet was used as an active flow blockage mechanism and to introduce turbulence into the propagating flame. Three experimental parameters were used to examine the relative influence of (1) mixture reactivity defined here as system equivalence ratio (SER), (2) jet mixture composition (JMC), and the momentum ratio (MR) on the acceleration of laminar premixed...
Show moreThis work aims to identify the key flow parameters that influence flame acceleration in a semi-confined square channel. A transverse fluidic jet was used as an active flow blockage mechanism and to introduce turbulence into the propagating flame. Three experimental parameters were used to examine the relative influence of (1) mixture reactivity defined here as system equivalence ratio (SER), (2) jet mixture composition (JMC), and the momentum ratio (MR) on the acceleration of laminar premixed methane flame. High-speed PIV and schlieren photography were utilized to characterize the instantaneous flow-field conditions throughout the flame-jet interaction. Using these diagnostic techniques, flame front positions and local velocity vector fields have been spatially and temporally resolved. Changes in flame properties including flame structure, velocity, and vorticity were tracked as a function of time. Stoichiometric equivalence ratios were more effective in the production of vorticity and the promotion of flame acceleration. The stoichiometric condition accelerated the flame to the highest final flame velocity of the three parameters examined. Different compositions of the jet mixture demonstrated that the flame acceleration is primarily affected by the jet turbulence and not on the reactivity of the jet compositions. Out of the three parameters examined, the momentum ratio parameter had the least amount of influence on the flow field and flame acceleration. The increase of 33 % in the momentum ratio had negligible effect in the final flame front velocity and implies that the jet turbulence is the main driving mechanism for flame acceleration.
Show less - Date Issued
- 2018
- Identifier
- CFE0007255, ucf:52186
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007255
- Title
- ACADEMIC ACCELERATION IN FLORIDA ELEMENTARY SCHOOLS: A SURVEY OF ATTITUDES, POLICIES, AND PRACTICES.
- Creator
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Guilbault, Keri, Bozeman, William, University of Central Florida
- Abstract / Description
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The focus of this research was to provide recent descriptive information about acceleration policies and practices in Florida elementary schools. District, school, and personal demographic variables were investigated to determine the extent to which they affected school-based acceleration options provided for students. Also, school district policies were examined to determine which types of research-based acceleration options were more frequently used and what procedures were in place to...
Show moreThe focus of this research was to provide recent descriptive information about acceleration policies and practices in Florida elementary schools. District, school, and personal demographic variables were investigated to determine the extent to which they affected school-based acceleration options provided for students. Also, school district policies were examined to determine which types of research-based acceleration options were more frequently used and what procedures were in place to guide the decision-making process. Results from this study indicated that extant acceleration policies only included grade skipping and limited procedures for referral, screening and decision-making in the schools. The most common types of acceleration offered in Florida elementary schools were subject acceleration in the Language Arts and Mathematics provided outside of the regular classroom, continuous progress, and curriculum compacting. The most frequently selected reason for not accelerating a student listed by both school principals and district administrators of gifted education programs was concern over a studentÃÂ's social and emotional development. No relationship was found to exist between schoolsÃÂ' or principalsÃÂ' personal demographic variables and types of acceleration offered in elementary schools. No relationship was found between elementary school principalsÃÂ' knowledge of gifted learners and the types of acceleration implemented in their schools.
Show less - Date Issued
- 2009
- Identifier
- CFE0002969, ucf:47988
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002969
- Title
- Accelerated Life Model with Various Types of Censored Data.
- Creator
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Pridemore, Kathryn, Pensky, Marianna, Mikusinski, Piotr, Swanson, Jason, Nickerson, David, University of Central Florida
- Abstract / Description
-
The Accelerated Life Model is one of the most commonly used tools in the analysis of survival data which are frequently encountered in medical research and reliability studies. In these types of studies we often deal with complicated data sets for which we cannot observe the complete data set in practical situations due to censoring. Such difficulties are particularly apparent by the fact that there is little work in statistical literature on the Accelerated Life Model for complicated types...
Show moreThe Accelerated Life Model is one of the most commonly used tools in the analysis of survival data which are frequently encountered in medical research and reliability studies. In these types of studies we often deal with complicated data sets for which we cannot observe the complete data set in practical situations due to censoring. Such difficulties are particularly apparent by the fact that there is little work in statistical literature on the Accelerated Life Model for complicated types of censored data sets, such as doubly censored data, interval censored data, and partly interval censored data.In this work, we use the Weighted Empirical Likelihood approach (Ren, 2001) to construct tests, confidence intervals, and goodness-of-fit tests for the Accelerated Life Model in a unified way for various types of censored data. We also provide algorithms for implementation and present relevant simulation results.I began working on this problem with Dr. Jian-Jian Ren. Upon Dr. Ren's departure from the University of Central Florida I completed this dissertation under the supervision of Dr. Marianna Pensky.
Show less - Date Issued
- 2013
- Identifier
- CFE0004913, ucf:49613
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004913
- Title
- Use of Accelerated Calcite Precipitation Method to Investigate Calcium Carbonate Precipitation from Recycled Concrete for Drainage System Applications.
- Creator
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McCulloch, Toni, Nam, Boo Hyun, Chopra, Manoj, Arboleda Monsalve, Luis, An, Jin Woo, Filler, Dennis, University of Central Florida
- Abstract / Description
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Recycled concrete aggregate (RCA) is a sustainable construction material that is a viable option for use in drainage systems by replacing virgin aggregate. Replacing virgin aggregate with RCA is beneficial from both economic and environmental perspectives. However, the use of RCA as pipe backfill materials may cause a long-term performance issue such as potential clogging due to fines accumulation and calcite precipitation on filter fabric. Previous studies investigated the long-term...
Show moreRecycled concrete aggregate (RCA) is a sustainable construction material that is a viable option for use in drainage systems by replacing virgin aggregate. Replacing virgin aggregate with RCA is beneficial from both economic and environmental perspectives. However, the use of RCA as pipe backfill materials may cause a long-term performance issue such as potential clogging due to fines accumulation and calcite precipitation on filter fabric. Previous studies investigated the long-term performance of RCA regarding flow rate. Therefore, this study investigated calcite precipitation potential of RCA. The Accelerated Calcite Precipitation (ACP) procedure was devised and used to estimate (")life-time(") calcite precipitation of RCA for French Drains. The ACP procedure was studied further and improved to optimize the calcite precipitation procedure. The enhanced method was used to compare the calcite precipitation of limestone and RCA samples - sources with varying chemistry and history. Key findings are (1) the clogging due to calcite precipitation of RCA is not as significant as clogging due to the existing and/or accumulated fines, (2) the calcite precipitation can be increased with a temperature of 75(&)deg;C and 17-hour heating time, and (3) the potential for calcite precipitation from RCA is not as significant as limestone for Type I underdrain gradation.
Show less - Date Issued
- 2018
- Identifier
- CFE0007321, ucf:52132
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007321
- Title
- Predictive modeling for assessing the reliability of bypass diodes in Photovoltaic modules.
- Creator
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Shiradkar, Narendra, Sundaram, Kalpathy, Schoenfeld, Winston, Atia, George, Abdolvand, Reza, Xanthopoulos, Petros, University of Central Florida
- Abstract / Description
-
Solar Photovoltaics (PV) is one of the most promising renewable energy technologies for mitigating the effect of climate change. Reliability of PV modules directly impacts the Levelized Cost of Energy (LCOE), which is a metric for cost competitiveness of any energy technology. Further reduction in LCOE of PV through assured long term reliability is necessary in order to facilitate widespread use of solar energy without the need for subsidies. This dissertation is focused on frameworks for...
Show moreSolar Photovoltaics (PV) is one of the most promising renewable energy technologies for mitigating the effect of climate change. Reliability of PV modules directly impacts the Levelized Cost of Energy (LCOE), which is a metric for cost competitiveness of any energy technology. Further reduction in LCOE of PV through assured long term reliability is necessary in order to facilitate widespread use of solar energy without the need for subsidies. This dissertation is focused on frameworks for assessing reliability of bypass diodes in PV modules. Bypass diodes are critical components in PV modules that provide protection against shading. Failure of bypass diode in short circuit results in reducing the PV module power by one third, while diode failure in open circuit leaves the module susceptible for extreme hotspot heating and potentially fire hazard. PV modules, along with the bypass diodes are expected to last at least 25 years in field. The various failure mechanisms in bypass diodes such as thermal runaway, high temperature forward bias operation and thermal cycling are discussed. Operation of bypass diode under shading is modeled and method for calculating the module I-V curve under any shading scenario is presented. Frameworks for estimating the diode temperature in field deployed modules based on Typical Meteorological Year (TMY) data are developed. Model for predicting the susceptibility of bypass diodes for thermal runaway is presented. Diode wear out due to High Temperature Forward Bias (HTFB) operation and Thermal Cycling (TC) is studied under custom designed accelerated tests. Overall, this dissertation is an effort towards estimating the lifetime of bypass diodes in field deployed modules, and therefore, reducing the uncertainty in long term reliability of PV modules.
Show less - Date Issued
- 2015
- Identifier
- CFE0006001, ucf:51023
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006001
- Title
- Characterization of Fast Flames for Turbulence-Induced Deflagration to Detonation Transition.
- Creator
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Chambers, Jessica, Ahmed, Kareem, Kapat, Jayanta, Kassab, Alain, University of Central Florida
- Abstract / Description
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One of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are...
Show moreOne of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, chemiluminescence, and Schlieren measurements. The investigation classifies the fast flame propagation modes at various regimes. The study further examines the conditions for a turbulent fast flame at the boundary of transitioning to quasi-detonation. The evolution of the flame-compressibility interactions for this turbulent fast flame is characterized. The local measured turbulent flame speed is found to be greater than the Chapman(-)Jouguet deflagration flame speed which categorizes the flame to be at the spontaneous transition regime and within the deflagration-to-detonation transition runaway process.
Show less - Date Issued
- 2018
- Identifier
- CFE0006985, ucf:51642
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006985
- Title
- IS PERCEIVED INTENTIONALITY OF A VIRTUAL ROBOT INFLUENCED BY THE KINEMATICS?.
- Creator
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Sasser, Jordan, McConnell, Daniel S., University of Central Florida
- Abstract / Description
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Research has shown that in Human-Human Interactions kinematic information reveals that competitive and cooperative intentions are perceivable and suggests the existence of a cooperation bias. The present study invokes the same question in a Human-Robot Interaction by investigating the relationship between the acceleration of a virtual robot within a virtual reality environment and the participants perception of the situation being cooperative or competitive by attempting to identify the...
Show moreResearch has shown that in Human-Human Interactions kinematic information reveals that competitive and cooperative intentions are perceivable and suggests the existence of a cooperation bias. The present study invokes the same question in a Human-Robot Interaction by investigating the relationship between the acceleration of a virtual robot within a virtual reality environment and the participants perception of the situation being cooperative or competitive by attempting to identify the social cues used for those perceptions. Five trials, which are mirrored, faster acceleration, slower acceleration, varied acceleration with a loss, and varied acceleration with a win, were experienced by the participant; randomized within two groups of five totaling in ten events. Results suggest that when the virtual robot's acceleration pattern were faster than the participant's acceleration the situation was perceived as more competitive. Additionally, results suggest that while the slower acceleration was perceived as more cooperative, the condition was not significantly different from mirrored acceleration. These results may indicate that there may be some kinematic information found in the faster accelerations that invoke stronger competitive perceptions whereas slower accelerations and mirrored acceleration may blend together during perception; furthermore, the models used in the slower acceleration conditions and the mirrored acceleration provide no single identifiable contributor towards perceived cooperativeness possibly due to a similar cooperative bias. These findings are used as a baseline for understanding movements that can be utilized in the design of better social robotic movements. These movements would improve the interactions between humans and these robots, ultimately improving the robot's ability to help during situations.
Show less - Date Issued
- 2019
- Identifier
- CFH2000524, ucf:45668
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000524
- Title
- Shifted Plastic Hinge Column Connections Using Grouted Sleeves for Accelerated Bridge Construction.
- Creator
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Al-Jelawy, Haider, Mackie, Kevin, Gou, Jihua, Chopra, Manoj, University of Central Florida
- Abstract / Description
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Accelerated bridge construction (ABC) is being increasingly used in new bridge construction and repair. ABC typically requires prefabricated elements joined with mechanical couplers. Grouted sleeves (GSs) offer good construction tolerances and load transfer between precast elements. However, previous research identified some performance issues with precast columns employing GS connections for seismic regions. Therefore, there is a need to develop improved connection details. This research...
Show moreAccelerated bridge construction (ABC) is being increasingly used in new bridge construction and repair. ABC typically requires prefabricated elements joined with mechanical couplers. Grouted sleeves (GSs) offer good construction tolerances and load transfer between precast elements. However, previous research identified some performance issues with precast columns employing GS connections for seismic regions. Therefore, there is a need to develop improved connection details. This research consists of three components; testing of six large-scale precast reinforced concrete column models, a series of individual component tests on GS bar splices, and analytical studies. Large-scale, precast column models were designed and experimentally tested using a shifted plastic hinge (SPH) concept to minimize the damage in the capacity-protected elements and retain the column ductility. The column testing matrix considered aspect ratio, moment gradient, and splicing details. Column models were tested in an upright cantilever configuration under quasi-static cyclic load. Results showed that SPH can be used for both flexural and flexural-shear columns. Two types of component tests were performed: tensile tests to quantify the tensile behavior of the splices, and strain penetration tests to quantify the slip at the sleeve ends. The tests were used to obtain constitutive models for the bond-slip behavior of the GS splices.Results showed that GS splices developed the full ultimate stress of the spliced bars and that the slip at sleeve ends can considerably influence the global behavior of the precast columns. The analytical models were developed in OpenSees using fiber-based beams models and they incorporated the calibrated bond-slip models of GS splices. The large-scale column tests were simulated and compared with respective experimental results. Analytical results showed that the developed models were able to mimic the column behavior and can be used for analysis of GS precast columns.
Show less - Date Issued
- 2017
- Identifier
- CFE0006851, ucf:51739
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006851
- Title
- Nonlinear Dynamics in Multimode Optical Fibers.
- Creator
-
Eftekhar, Mohammad Amin, Christodoulides, Demetrios, Amezcua Correa, Rodrigo, Li, Guifang, Kaup, David, University of Central Florida
- Abstract / Description
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Multimode optical fibers have recently reemerged as a viable platform for addressing a number of long-standing issues associated with information bandwidth requirements and power-handling capabilities. The complex nature of heavily multimoded systems can be effectively exploited to observe altogether novel physical effects arising from spatiotemporal and intermodal linear and nonlinear processes. Here, we have studied nonlinear dynamics in multimode optical fibers (MMFs) in both the normal...
Show moreMultimode optical fibers have recently reemerged as a viable platform for addressing a number of long-standing issues associated with information bandwidth requirements and power-handling capabilities. The complex nature of heavily multimoded systems can be effectively exploited to observe altogether novel physical effects arising from spatiotemporal and intermodal linear and nonlinear processes. Here, we have studied nonlinear dynamics in multimode optical fibers (MMFs) in both the normal and anomalous dispersion regimes. In the anomalous dispersion regime, the nonlinearity leads to a formation of spatiotemporal 3-D solitons. Unlike in single-mode fibers, these solitons are not unique and their properties can be modified through the additional degrees of freedom offered by these multimoded settings. In addition, soliton related processes such as soliton fission and dispersive wave generation will be also drastically altered in such multimode systems. Our theoretical work unravels some of the complexities of the underlying dynamics and helps us better understand these effects. The nonlinear dynamics in such multimode systems can be accelerated through a judicious fiber design. A cancelation of Raman self-frequency shifts and Blue-shifting multimode solitons were observed in such settings as a result of an acceleration of intermodal oscillations. Spatiotemporal instabilities in parabolic-index multimode fibers will also be discussed. In the normal dispersion regime, this effect can be exploited to generate an ultrabroad and uniform supercontinuum that extends more than 2.5 octaves. To do so, the unstable spectral regions are pushed away from the pump, thus sweeping the entire spectrum. Multimode parabolic pulses were also predicted and observed in passive normally dispersive tapered MMFs. These setting can obviate the harsh bandwidth limitation present in single-mode system imposed by gain medium and be effectively used for realizing high power multimode fiber lasers. Finally, an instant and efficient second-harmonic generation was observed in the multimode optical fibers. Through a modification of initial conditions, the efficiency of this process could be enhanced to a record high of %6.5.
Show less - Date Issued
- 2018
- Identifier
- CFE0007399, ucf:52063
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007399
- Title
- Ultra-High Performance Concrete for Precast Seismic Bridge Column Connection.
- Creator
-
Chan, Titchenda, Mackie, Kevin, Catbas, Necati, Chopra, Manoj, Bai, Yuanli, University of Central Florida
- Abstract / Description
-
Accelerated bridge construction (ABC) utilizes prefabricated bridge elements constructed off-site, delivered, and assembled on-site to expedite construction time and reduce traffic disruption. ABC has been increasingly used for super- and sub-structure elements in low seismic regions. However, its application in medium and high seismic regions remain limited, particularly for precast columns where connections typically coincide with plastic hinge (PH) regions. Ultra-high performance concrete ...
Show moreAccelerated bridge construction (ABC) utilizes prefabricated bridge elements constructed off-site, delivered, and assembled on-site to expedite construction time and reduce traffic disruption. ABC has been increasingly used for super- and sub-structure elements in low seismic regions. However, its application in medium and high seismic regions remain limited, particularly for precast columns where connections typically coincide with plastic hinge (PH) regions. Ultra-high performance concrete (UHPC), characterized by high compressive and tensile strength, and superior bond properties, is a potential material that can mitigate PH damage and enhance load transfer. This research proposes a new and simple damage tolerant precast column connection for use in medium and high seismic regions. The connection laps the column longitudinal reinforcement with footing dowels using a short splice length, a practical concrete cover, no shear reinforcement, and the shifted PH concept to prevent footing damage. Two 0.42-scale precast columns with different shear span ratios were tested under reversed cyclic loading to investigate the proposed connection relative to previously tested cast-in-place specimens. Results showed the connection performed well in shear, developed column longitudinal bars, shifted PH formation above the UHPC connection, and exhibited high lateral capacity and ductility. Twenty-seven pullout and lap splice beams were tested to study the bond of reinforcement in UHPC under different parameters and stress states. Results indicated significant bond strength improvement and splice length reduction compared with conventional concrete. The pullout specimens were simulated using the OpenSees framework to propose reinforcing steel in UHPC bond-slip models where existing studies in the literature were limited. The models were incorporated into the numerical modeling of the precast columns using one-dimensional fiber-section and two-dimensional plane stress nonlinear analyses. Results from the two modeling methods showed good agreement with the experiments, with the calibrated bond-slip models providing a good representation of load transfer in the connection.
Show less - Date Issued
- 2019
- Identifier
- CFE0007610, ucf:52534
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007610
- Title
- STRATEGICALLY MINDED: DYNAMIC ANALYSIS OF STRATEGIC FLIGHT BAT MANEUVERS.
- Creator
-
Kasprzyk, Marie, Jayasuriya, suhada, University of Central Florida
- Abstract / Description
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Digital recordings of three different species of bats were studied in this thesis to determine the forces and moments that were experienced throughout the bat's flight. The recordings were also studied to determine the pursuit strategies that were most effective for the bat to quickly capture its prey. A pursuit strategy is a strategic way to travel that will allow a pursuer to capture/approach their target the quickest. Therefore when a bat utilizes a particular pursuit strategy, it will...
Show moreDigital recordings of three different species of bats were studied in this thesis to determine the forces and moments that were experienced throughout the bat's flight. The recordings were also studied to determine the pursuit strategies that were most effective for the bat to quickly capture its prey. A pursuit strategy is a strategic way to travel that will allow a pursuer to capture/approach their target the quickest. Therefore when a bat utilizes a particular pursuit strategy, it will adjust its position/ direction vector in a particular way that will allow it to approach its target very quickly. Data was collected directly from the video by manual collection utilizing Microsoft Visual Studio to extract frames, collect and record the data. This research was conducted to determine when throughout the flight the bat would experience significant forces and moments. The location and magnitude of the forces were reported along with an explanation of why the bat was experiencing a peak at each specific time. The forces and moments that the bat experienced thought-out the flight pursuit were calculated by relative velocity and acceleration calculations. In all four scenarios the bat experienced forces in relation to rotating its body about its center of mass. Forces were specifically seen when the bat periodically began to rotate its body before the final plunge to capture its prey. Prey avoidance and pursuit strategies were also studied and observed in this thesis which included the constant bearing and the constant absolute target direction. The intent was to determine which pursuit strategy bats use to quickly capture their prey. The constant bearing strategy is utilized to pursue prey moving along a smooth path, on the other hand the Constant Absolute Target Direction (CATD) pursuit strategy is utilized to capture erratically moving prey. For most of the bats analyzed, it was seen that the CATD strategy proved to be the preferred pursuit strategy. CATD was not only adequate for analyzing the pursuit of erratically moving prey but also worked well when analyzing the pursuit of prey that remained stationary. It cannot be fully concluded that bats utilize the CATD strategy to successfully capture erratically flying prey. The angle remains relatively constant but does not exhibit a zero change in angle as by definition. The large forces experienced by the bat were seen when the bat began to rotate its body about its pitch axis or when the bat made a large turn. Moments were seen specifically when the bat began to bank into its last and final turn towards its target.
Show less - Date Issued
- 2013
- Identifier
- CFH0004418, ucf:45108
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004418
- Title
- An Examination of the Algebra 1 Achievement of Black and Hispanic Student Participants in a Large Urban School District's Mathematics Intervention Program.
- Creator
-
Bronson, Elethia, Taylor, Rosemarye, Baldwin, Lee, Storey, Valerie A., Andreasen, Janet, University of Central Florida
- Abstract / Description
-
The mathematics achievement gap between Black and White as well as Hispanic and White students has been well documented nationwide and in the school district of study. Much has been written in observance of the achievement gap, yet markedly less research has focused on practices and interventions that have improved mathematics performance for Black and Hispanic students. Consequently, this study examined the Algebra 1 achievement (indicated by student scale scores on the Florida Standards...
Show moreThe mathematics achievement gap between Black and White as well as Hispanic and White students has been well documented nationwide and in the school district of study. Much has been written in observance of the achievement gap, yet markedly less research has focused on practices and interventions that have improved mathematics performance for Black and Hispanic students. Consequently, this study examined the Algebra 1 achievement (indicated by student scale scores on the Florida Standards Assessments Algebra 1 End-of-Course exam) of Black and Hispanic students participating in a mathematics intervention program as compared to the Algebra 1 achievement of their similar non-participating peers in one large urban school district. Descriptive statistics and inferential statistical analysis via the one-way ANOVA and the independent samples t-test were utilized. Further quantitative analysis was conducted focusing on the mean scale score differences among intervention program participants in varying course structures, summer days attended, and school socioeconomic status. The study found that Black and Hispanic 7th grade program participants significantly outperformed their similar non-participating 7th grade peers and non-participating Black and Hispanic 9th grade students. No statistically significant differences were found among program participants who attended the summer preview camp for different numbers of days. Black and Hispanic intervention program participants enrolled in a double-block Algebra 1 course numerically outscored their single-period program peers overall and when disaggregated by race/ethnicity and prior year achievement level. The findings indicate the intervention program has the potential to improve Algebra 1 achievement and increase access to advanced-level mathematics for Black and Hispanic students. This study contributes to the scant literature on successful mathematics intervention programs targeting Black and Hispanic students. Studying the implementation of the program in schools demonstrating success could provide insight, enabling other schools to replicate an environment where Black and Hispanic secondary mathematics learners thrive.
Show less - Date Issued
- 2018
- Identifier
- CFE0007393, ucf:52073
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007393
- Title
- The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
- Creator
-
Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
- Abstract / Description
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Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of...
Show moreFuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications.Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work.Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states.In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests.The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 (-) 5 nm and 20 (-) 150 nm size, respectively, that did not change size or shape when incorporated into the membranes.At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
Show less - Date Issued
- 2012
- Identifier
- CFE0004789, ucf:49731
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004789