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Title: Characterization of mechanical properties in nanoparticle reinforced hybrid carbon fiber composites using photoluminescence piezospectroscopy.
Creator: Jahan, Sanjida, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, University of Central Florida
Abstract / Description: Carbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved...
Show moreCarbon fiber composites have become popular in aerospace structures and applications due to their light weight, high strength, and high performance. Hybrid carbon fiber reinforced polymer (HCFRP) composites with alumina nanoparticles reinforcement display improved material properties such as fracture toughness, resistance to crack propagation and improved fatigue life. However, homogeneous dispersion of nanoscale materials in the matrix is important for even distribution of the improved properties. Implementing silane coupling agents (SCAs) improves dispersion by acting as a bridge between organic and inorganic materials, which increases interfacial strength and decreases sedimentation by bonding the particulate filler to the fiber reinforcement. This research is aimed at quantifying the improvement in dispersion of nanoparticles and elucidating the effects on the mechanical property of HCFRP samples through the novel use of photoluminescent characteristic peaks emitted by the alumina reinforcement particles. Photo-luminescene emission from secondary reinforcement particles of alumina embedded within the hybrid carbon fiber composites is leveraged to reveal microstructural effects of functionalization and particle weight fraction as it relates to overall composite mechanics.6, 9 and 12 weight percentage of alumina particle loading with Reactive Silane Coupling Agents, Non-reactive Silane Coupling Agent surface treatments and untreated condition are investigated in this research. Uniaxial tensile tests were conducted with measurements using piezospectroscopy (PS) and concurrent digital image correlation (DIC) to quantify the mechanical property and load distribution between the carbon fiber/epoxy and the reinforcing nanoparticles. The piezospectroscopic data were collected in an in-situ configuration using a portable piezospectroscopy system while the sample was under tensile load. Photoluminescence results show the dispersion and sedimentation behavior of the nanoparticles in the material for different surface treatment and weight percentage of the alumina nanoparticles. The piezospectroscopic maps capture and track the residual stress and its change under applied load. The results reveal the effect of varying particle loading on composite mechanical properties and how this changes with different functionalization conditions. The role of the particles in load transfer in the hybrid composite is further investigated and compared with theory. This work extends the capability of spectroscopy as an effective non-invasive method to study, at the microstructural level, the material and manufacturing effects on the development of advanced composites for applications in aerospace structures and beyond.
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Date Issued: 2017
Identifier: CFE0006886, ucf:51715
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006886

Title: VARIATION OF GEOTECHNICAL STRENGTH PROPERTIES WITH AGE OF LANDFILLS ACCEPTING BIOSOLIDS.
Creator: Pinapati, Kishore, Chopra, Manoj, University of Central Florida
Abstract / Description: The solid portion of waste disposal, known as Municipal Solid Waste (MSW) can be landfilled. Landfilling has proved to be a safe, sanitary and economical method of disposal. A by-product from wastewater treatment plants called biosolids is sometimes co-disposed along with MSW in landfills. Recent work at the University of Central Florida has focused on the behavior of the mixture of MSW and biosolids. As an increased amount of waste accumulates in these landfills, it creates a new problem &...
Show moreThe solid portion of waste disposal, known as Municipal Solid Waste (MSW) can be landfilled. Landfilling has proved to be a safe, sanitary and economical method of disposal. A by-product from wastewater treatment plants called biosolids is sometimes co-disposed along with MSW in landfills. Recent work at the University of Central Florida has focused on the behavior of the mixture of MSW and biosolids. As an increased amount of waste accumulates in these landfills, it creates a new problem – the geotechnical stability of landfills. In current literature, classical geotechnical testing methods have been followed to find the strength properties of these landfill materials. Furthermore, geotechnical methods of slope stability analyses have been employed to determine the stability of landfill slopes. As these materials have a high organic content, their strength properties may potentially change with time because of the decay of the organic materials. In the present work, an attempt is made to monitor the change in the geotechnical strength properties of the landfill materials as a function of time. Direct shear tests used for soil testing, with some modifications, were performed on cured compost samples of MSW mixed with biosolids. Geotechnical strength properties of these cured samples were compared to those of an artificially prepared mixture of MSW and biosolids, from the published literature. In addition, direct shear tests are also performed to find the interface properties of a geonet with the cured samples to check the role of a geonet in reinforcing the landfill slopes. A slope stability analysis software SLOPE/W is used to analyze the stability of the landfills. Cohesion is observed to decrease with time while the friction angle increases with time. Stability (the factor of safety against failure) of landfill slopes increases with time due to increased effective stresses and increased friction angle, as the organic material decays. This may result in additional subsidence but an increase in the effective shear strength with time. Based on the interface test results and subsequent slope stability analyses, it is found that the inclusion of a geonet improves the slope stability of a landfill. This could be a potential benefit to the landfill as reinforcement if properly placed. Based on the slope stability analysis on landfills with different slopes, it is concluded that the slope stability of a landfill is improved by keeping the slopes less steep.
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Date Issued: 2006
Identifier: CFE0000919, ucf:46758
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000919

Title: An Application of Operant Conditioning in an Organizational Setting.
Creator: Knight, Patricia J., Burroughs, Wayne A., Social Sciences
Abstract / Description: Florida Technological University College of Social Sciences Thesis
Date Issued: 1974
Identifier: CFR0012665, ucf:53134
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFR0012665

Title: INVESTIGATION OF GROUND PENETRATING RADAR FOR DETECTION OF LEAKING PIPELINES UNDER ROADWAY PAVEMENTS AND DEVELOPMENT OF FIBER-WRAPPING REPAIR TECHNIQUE.
Creator: Suarez, Pedro, Kuo, Shiou-San, University of Central Florida
Abstract / Description: Nowadays, it has become a common practice to observe urban roadways undergo severe distress characterized by substantial depressions. In some cases, these pavement depressions are caused by leakages in the connecting joints of sewage pipelines laid beneath the roadway pavement. Manual inspection of pipe leakages has become costly and complex since sewage pipes with relative small diameters do not allow inspection from inside and digging may be required. On the other hand, pipes with large...
Show moreNowadays, it has become a common practice to observe urban roadways undergo severe distress characterized by substantial depressions. In some cases, these pavement depressions are caused by leakages in the connecting joints of sewage pipelines laid beneath the roadway pavement. Manual inspection of pipe leakages has become costly and complex since sewage pipes with relative small diameters do not allow inspection from inside and digging may be required. On the other hand, pipes with large diameters, in which inspection can be made from pipe interior, inspector can not remain inside of the pipe for long periods of time because of toxic fumes. In order to overcome this problem, a geophysical technique known as ground penetrating radar (GPR) has been proposed as a candidate to detect the leakages. GPR is a nondestructive reflection technique, which uses high frequency electromagnetic waves to acquire subsurface information. GPR contributes to detect leaks in sewer pipes either by detecting underground voids surrounding the faulty pipe, or by detecting anomalies in the depth of the pipe as the radar propagation velocity varies due to the saturation of the soil near the leak. Once the leakage is detected, on site-repair technique to restore the damaged pipe is not an easy task. In this study, fiber reinforced polymer (FRP) composite created by saturating a fiber sheet with an epoxy resin matrix is proposed to be applied in several layers of overlay to the faulty structure surface. This fiber sheet is typically made of carbon or glass and saturated with the chemical resin matrix and makes the repaired structure even stronger than originally constructed. For the last twenty years, FRP has been used to repair and strengthen concrete columns by employing a practice known as "fiber wrapping technique". This method involves the wrapping of unidirectional fiber composite sheets around concrete columns. FRP wrapping approach can be extended to sewage pipelines for repairing and strengthening the distressed pipeline. The purpose of this study is to detect leakages in sewer pipelines using GPR, and develop an on-site fiber-wrapping technique for repairing and strengthening sewage pipes. In detecting sewer leakages, one case study is presented. The case involves the use of GRP for leakage detection in a sewer pipeline overlaid by flexible pavement that already shows signs of subsidence. Moreover, in developing a repair technique, a gypsum cement mold wrapped with carbon fiber composite material is placed around a large-scale faulty pipe joint, and tested using a MTS servo-controlled hydraulic actuator. In addition, both free ends of the pipes are capped and filled with water to determine the effectiveness of the technique in stopping leaks along the repaired joint. During the GPR survey performed in the area of study, no clear indications of leakages were observed along the buried sewer pipeline. This lack of traceable signals from the subsurface was the result of the significant attenuation of the radar signal with depth that made impossible to discern effectively any anomaly along the designated pipeline. Although different antennas having center frequencies of 300 and 80 MHz were used and a variety of settings on the GPR unit were tried, the buried pipeline was barely detectable. Nevertheless, signal reflections generated by buried pipelines in other areas such as stormwater pipes on UCF campus and drainage pipelines at road side of University Boulevard were clearly detected, which makes to believe that the significant attenuation of the radar signal at the area of study is due to the extreme high conductivity of soils which have been severely contaminated by the leakage of sewage from the distressed pipeline. In contrast, favorable results were obtained in the development of the repair technique since the two-component system, Hydro-stone Gypsum Cement and FRP composite material, wrapped around the faulty joint effectively increased its structural capacity even higher than the pipe original strength.
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Date Issued: 2004
Identifier: CFE0000290, ucf:46215
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000290

Title: Guided Autonomy for Quadcopter Photography.
Creator: Alabachi, Saif, Sukthankar, Gita, Behal, Aman, Lin, Mingjie, Boloni, Ladislau, Laviola II, Joseph, University of Central Florida
Abstract / Description: Photographing small objects with a quadcopter is non-trivial to perform with many common user interfaces, especially when it requires maneuvering an Unmanned Aerial Vehicle (C) to difficult angles in order to shoot high perspectives. The aim of this research is to employ machine learning to support better user interfaces for quadcopter photography. Human Robot Interaction (HRI) is supported by visual servoing, a specialized vision system for real-time object detection, and control policies...
Show morePhotographing small objects with a quadcopter is non-trivial to perform with many common user interfaces, especially when it requires maneuvering an Unmanned Aerial Vehicle (C) to difficult angles in order to shoot high perspectives. The aim of this research is to employ machine learning to support better user interfaces for quadcopter photography. Human Robot Interaction (HRI) is supported by visual servoing, a specialized vision system for real-time object detection, and control policies acquired through reinforcement learning (RL). Two investigations of guided autonomy were conducted. In the first, the user directed the quadcopter with a sketch based interface, and periods of user direction were interspersed with periods of autonomous flight. In the second, the user directs the quadcopter by taking a single photo with a handheld mobile device, and the quadcopter autonomously flies to the requested vantage point.This dissertation focuses on the following problems: 1) evaluating different user interface paradigms for dynamic photography in a GPS-denied environment; 2) learning better Convolutional Neural Network (CNN) object detection models to assure a higher precision in detecting human subjects than the currently available state-of-the-art fast models; 3) transferring learning from the Gazebo simulation into the real world; 4) learning robust control policies using deep reinforcement learning to maneuver the quadcopter to multiple shooting positions with minimal human interaction.
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Date Issued: 2019
Identifier: CFE0007774, ucf:52369
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007774

Title: ULTRA-HIGH PERFORMANCE FIBER REINFORCED CONCRETE IN BRIDGE DECKAPPLICATIONS.
Creator: Xia, Jun, Mackie, Kevin, University of Central Florida
Abstract / Description: The research presented in this dissertation focuses on the material characterization of ultrahigh performance fiber reinforced concrete (UHP-FRC) at both the microscopic and macroscopic scales. The macroscopic mechanical properties of this material are highly related to the orientation of the steel fibers distributed within the matrix. However, the fiber orientation distribution has been confirmed to be anisotropic based on the flow-casting process. The orientation factor and probability...
Show moreThe research presented in this dissertation focuses on the material characterization of ultrahigh performance fiber reinforced concrete (UHP-FRC) at both the microscopic and macroscopic scales. The macroscopic mechanical properties of this material are highly related to the orientation of the steel fibers distributed within the matrix. However, the fiber orientation distribution has been confirmed to be anisotropic based on the flow-casting process. The orientation factor and probability density function (PDF) of the crossing fiber (fibers crossing a cutting plane) orientation was obtained based on theoretical derivations and numerical simulations with respect to different levels of anisotropy and cut planes oriented arbitrarily in space. The level of anisotropy can be calibrated based on image analysis on cut sections from hardened UHP-FRC prisms. Simplified equations provide a framework to predict the mechanical properties based on a single fiber-matrix interaction rule selected from existing theoretical models. Along with the investigation of the impacts from different curing methods and available post-cracking models, a versatile parameterized uniaxial stress-strain constitutive model was developed and calibrated. The constitutive model was implemented in a finite element analysis software program, and the program was utilized in the preliminary design of moveable bridge deck panels made of passively reinforced UHP-FRC. This deck system was among the several alternatives to replace the problematic steel grid decks currently in use. Based on experimental investigations of the deck panels, failure occurred largely in shear rather than flexure during bending tests. However, this shear failure is not abrupt and usually involves large deformation, large sectional rotation, and wide shear cracks before loss of load-carrying capacity. This particular shear failure mode observed was further investigated numerically and experimentally. Three-dimensional FEM models with the ability to reflect the interaction between rebar and concrete were created in a commercial FEM software to investigate the load transfer mechanism before and after bond failure. Small-scale passively reinforced prisms were tested to verify the conclusions drawn from simulation results. In an effort to improve the original design, several shear-strengthened deck panels were tested and evaluated for effectiveness. Finally, methods and equations to predict the ultimate shear capacity were calibrated. A two-dimensional frame element based complete moveable bridge finite element model was built for observation of bridge system performance. The model contained the option to substitute any available deck system based on a subset of pre-calibrated parameters specific to each deck type. These alternative deck systems include an aluminum bridge deck system and a glass fiber reinforced plastic (GFRP) deck system. All three alternatives and the original steel grid deck system were evaluated based on the global responses of the moveable bridge, and the advantages and disadvantages of adopting the UHP-FRC deck system are quantified.
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Date Issued: 2011
Identifier: CFE0003721, ucf:48803
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003721

Title: Development and Characterization of Nanoparticlee Enhancements in Pyrolysis-Derived High Temperature Composites.
Creator: McKee, James, Gou, Jihua, Kapat, Jayanta, Xu, Chengying, University of Central Florida
Abstract / Description: Thermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because...
Show moreThermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because they are not capable of supporting larger structures. The limitations of polymer reinforced composites have limited their entry into these applications, except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These materials have been successfully demonstrated their utility in extreme environments, such as spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited their use to similarly high performance applications where the costs are justifiable. Previous work by others with (")fuzzy fiber(") composites have shown that aligned carbon nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To this end vertically aligned CNTs were studied for their potential use, but found to be difficult to process with current conventional techniques. A composite material comprised of basalt, a relatively new reinforcing fiber, and phenolic, which has been used in high-temperature applications with great success was made to attempt to create a new material for these applications. To further improve upon the favorable properties of the resulting composite, the composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel technique was also developed to promote in-situ carbon nanotube growth of the resulting basalt-carbon composite without using a monolithic piece of cured phenolic resin in place of the standard aromatic hydrocarbon-catalyst precursor. The in-situ growth of carbon nanotubes (CNTs) was explored as their thermal stability and effectiveness in improving performance has been previously demonstrated when used as a resin additive. The specimens were examined with SEM, EDS, and TGA to determine the effects of both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the parameters of CVD processing. Additional testing would also show that the growth behavior of the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is a threshold temperature necessary to facilitate the availability of catalysts from within the basalt fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the newly formed composite with a high degree of thermal stability, making the new materials potentially usable in applications such as turbines, in addition to large-scale thermal protection systems.
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Date Issued: 2013
Identifier: CFE0005380, ucf:50458
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005380

Title: Role of Force Resultants Interaction on Fiber Reinforced Concrete.
Creator: Chan, Titchenda, Mackie, Kevin, Catbas, Necati, Makris, Nicos, University of Central Florida
Abstract / Description: Ultra-high performance concrete (UHPC) is a recently developed concrete gaining a lot of interest worldwide, and a lot research has been conducted to determine its material properties. UHPC is known for its very high strength and high durability. Association Francaise de Genie Civil (AFGC) has defined UHPC as a concrete exhibiting compressive strength greater than 150 MPa (22 ksi). To utilize the full compressive strength of UHPC, complementary tension reinforcement is required. A recent...
Show moreUltra-high performance concrete (UHPC) is a recently developed concrete gaining a lot of interest worldwide, and a lot research has been conducted to determine its material properties. UHPC is known for its very high strength and high durability. Association Francaise de Genie Civil (AFGC) has defined UHPC as a concrete exhibiting compressive strength greater than 150 MPa (22 ksi). To utilize the full compressive strength of UHPC, complementary tension reinforcement is required. A recent research study to find light weight yet high strength alternative deck systems for Florida movable bridges demonstrated that a composite UHPC and high strength steel (HSS) reinforcement deck system is a viable alternative. However, failure modes of the deck system observed during experimental testing were shear failures rather than flexural failures. Interestingly, the shear failures were ductile involving large deformations and large sectional rotations.The purpose of this research is to quantify the sensitivity of UHPC structural member mechanical response to different shear and normal stress demands, and investigate the underlying failure modes. An experimental investigation on small-scale prisms without reinforcement, prisms reinforced with ASTM Grade 60 steel, and prisms reinforced with high strength steel was carried out to capture load-deflection behavior as well as modes of failure of the UHPC specimens. Numerical analysis based on modified compression field theory (MCFT) was developed to verify experimental results at the section level, and further verification using continuum methods was performed using MCFT/DSFM (disturbed stress field method) based finite element analysis software (VecTor2).Results from the numerical analysis could reasonably predict the load-displacement as well as the failure modes of the experimental specimens. Obvious flexural failure was observed on unreinforced UHPC specimens where wide crack opening gradually widened at the bottom fiber of the concrete to the loading position. Whereas UHPC-Grade 60 steel specimens experienced ductile flexural failure with similar wide crack opening after the rebar yielded. On the other hand, UHPC-MMFX specimens largely failed in shear from a diagonal tension crack and crush of concrete top fiber.
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Date Issued: 2014
Identifier: CFE0005471, ucf:50394
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005471

Title: Characterization of Impact Damage and Fiber Reinforced Polymer Repair Systems for Metallic Utility Poles.
Creator: Johnson, Cara, Mackie, Kevin, Tatari, Mehmet, Chopra, Manoj, University of Central Florida
Abstract / Description: Previous studies have demonstrated that the behavior of ber reinforced polymers(FRPs) bonded to metallic utility poles are governed by the following failure modes; yieldingof the metallic substrate, FRP tensile rupture, FRP compressive buckling, and debonding ofFRP from the substrate. Therefore, an in situ method can be devised for the repair of utilitypoles, light poles, and mast arms that returns the poles to their original service strength.This thesis investigates the eect of damage due to...
Show morePrevious studies have demonstrated that the behavior of ber reinforced polymers(FRPs) bonded to metallic utility poles are governed by the following failure modes; yieldingof the metallic substrate, FRP tensile rupture, FRP compressive buckling, and debonding ofFRP from the substrate. Therefore, an in situ method can be devised for the repair of utilitypoles, light poles, and mast arms that returns the poles to their original service strength.This thesis investigates the eect of damage due to vehicular impact on metallic poles,and the eectiveness of externally-bonded FRP repair systems in restoring their capacity.Damage is simulated experimentally by rapid, localized load application to pole sections,creating dents ranging in depth from 5 to 45% of the outer diameter. Four FRP compositerepair systems were selected for characterization and investigation due to their mechani-cal properties, ability to balance the system failure modes, and installation eectiveness.Bending tests are conducted on dented utility poles, both unrepaired and repaired.Nonlinear nite element models of dented and repaired pole bending behavior aredeveloped in MSC.Marc. These models show good agreement with experimental results,and can be used to predict behavior of full-scale repair system. A relationship between dentdepth and reduced pole capacity is developed, and FRP repair system recommendations arepresented.
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Date Issued: 2013
Identifier: CFE0004697, ucf:49872
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004697

Title: A REINFORCEMENT LEARNING TECHNIQUE FOR ENHANCING HUMAN BEHAVIOR MODELS IN A CONTEXT-BASED ARCHITECTURE.
Creator: Aihe, David, Gonzalez, Avelino, University of Central Florida
Abstract / Description: A reinforcement-learning technique for enhancing human behavior models in a context-based learning architecture is presented. Prior to the introduction of this technique, human models built and developed in a Context-Based reasoning framework lacked learning capabilities. As such, their performance and quality of behavior was always limited by what the subject matter expert whose knowledge is modeled was able to articulate or demonstrate. Results from experiments performed show that subject...
Show moreA reinforcement-learning technique for enhancing human behavior models in a context-based learning architecture is presented. Prior to the introduction of this technique, human models built and developed in a Context-Based reasoning framework lacked learning capabilities. As such, their performance and quality of behavior was always limited by what the subject matter expert whose knowledge is modeled was able to articulate or demonstrate. Results from experiments performed show that subject matter experts are prone to making errors and at times they lack information on situations that are inherently necessary for the human models to behave appropriately and optimally in those situations. The benefits of the technique presented is two fold; 1) It shows how human models built in a context-based framework can be modified to correctly reflect the knowledge learnt in a simulator; and 2) It presents a way for subject matter experts to verify and validate the knowledge they share. The results obtained from this research show that behavior models built in a context-based framework can be enhanced by learning and reflecting the constraints in the environment. From the results obtained, it was shown that after the models are enhanced, the agents performed better based on the metrics evaluated. Furthermore, after learning, the agent was shown to recognize unknown situations and behave appropriately in previously unknown situations. The overall performance and quality of behavior of the agent improved significantly.
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Date Issued: 2008
Identifier: CFE0002466, ucf:47715
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002466

Title: Decision-making for Vehicle Path Planning.
Creator: Xu, Jun, Turgut, Damla, Zhang, Shaojie, Zhang, Wei, Hasan, Samiul, University of Central Florida
Abstract / Description: This dissertation presents novel algorithms for vehicle path planning in scenarios where the environment changes. In these dynamic scenarios the path of the vehicle needs to adapt to changes in the real world. In these scenarios, higher performance paths can be achieved if we are able to predict the future state of the world, by learning the way it evolves from historical data. We are relying on recent advances in the field of deep learning and reinforcement learning to learn appropriate...
Show moreThis dissertation presents novel algorithms for vehicle path planning in scenarios where the environment changes. In these dynamic scenarios the path of the vehicle needs to adapt to changes in the real world. In these scenarios, higher performance paths can be achieved if we are able to predict the future state of the world, by learning the way it evolves from historical data. We are relying on recent advances in the field of deep learning and reinforcement learning to learn appropriate world models and path planning behaviors.There are many different practical applications that map to this model. In this dissertation we propose algorithms for two applications that are very different in domain but share important formal similarities: the scheduling of taxi services in a large city and tracking wild animals with an unmanned aerial vehicle.The first application models a centralized taxi dispatch center in a big city. It is a multivariate optimization problem for taxi time scheduling and path planning. The first goal here is to balance the taxi service demand and supply ratio in the city. The second goal is to minimize passenger waiting time and taxi idle driving distance. We design different learning models that capture taxi demand and destination distribution patterns from historical taxi data. The predictions are evaluated with real-world taxi trip records. The predicted taxi demand and destination is used to build a taxi dispatch model. The taxi assignment and re-balance is optimized by solving a Mixed Integer Programming (MIP) problem.The second application concerns animal monitoring using an unmanned aerial vehicle (UAV) to search and track wild animals in a large geographic area. We propose two different path planing approaches for the UAV. The first one is based on the UAV controller solving Markov decision process (MDP). The second algorithms relies on the past recorded animal appearances. We designed a learning model that captures animal appearance patterns and predicts the distribution of future animal appearances. We compare the proposed path planning approaches with traditional methods and evaluated them in terms of collected value of information (VoI), message delay and percentage of events collected.
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Date Issued: 2019
Identifier: CFE0007557, ucf:52606
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007557

Title: Complementary Layered Learning.
Creator: Mondesire, Sean, Wu, Annie, Wiegand, Rudolf, Sukthankar, Gita, Proctor, Michael, University of Central Florida
Abstract / Description: Layered learning is a machine learning paradigm used to develop autonomous robotic-based agents by decomposing a complex task into simpler subtasks and learns each sequentially. Although the paradigm continues to have success in multiple domains, performance can be unexpectedly unsatisfactory. Using Boolean-logic problems and autonomous agent navigation, we show poor performance is due to the learner forgetting how to perform earlier learned subtasks too quickly (favoring plasticity) or...
Show moreLayered learning is a machine learning paradigm used to develop autonomous robotic-based agents by decomposing a complex task into simpler subtasks and learns each sequentially. Although the paradigm continues to have success in multiple domains, performance can be unexpectedly unsatisfactory. Using Boolean-logic problems and autonomous agent navigation, we show poor performance is due to the learner forgetting how to perform earlier learned subtasks too quickly (favoring plasticity) or having difficulty learning new things (favoring stability). We demonstrate that this imbalance can hinder learning so that task performance is no better than that of a sub-optimal learning technique, monolithic learning, which does not use decomposition. Through the resulting analyses, we have identified factors that can lead to imbalance and their negative effects, providing a deeper understanding of stability and plasticity in decomposition-based approaches, such as layered learning.To combat the negative effects of the imbalance, a complementary learning system is applied to layered learning. The new technique augments the original learning approach with dual storage region policies to preserve useful information from being removed from an agent's policy prematurely. Through multi-agent experiments, a 28% task performance increase is obtained with the proposed augmentations over the original technique.
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Date Issued: 2014
Identifier: CFE0005213, ucf:50626
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005213

Title: Fiber-Reinforced Polymer (FRP) Composites in Retrofitting of Concrete Structures: Polyurethane Systems Versus Epoxy Systems.
Creator: El Zghayar, Elie, Mackie, Kevin, Catbas, Necati, Chopra, Manoj, University of Central Florida
Abstract / Description: Fiber reinforced polymer (FRP) composites have been of interest to the structural engineering society since the earliest days of FRP composites industry. The use of such systems has been implemented in both new construction and for repair and rehabilitation of existing structures. Since the 1980s, researchers have developed a significant body of knowledge to use FRP composites in infrastructure applications; however, most of this established knowledge was concentrated on the use of...
Show moreFiber reinforced polymer (FRP) composites have been of interest to the structural engineering society since the earliest days of FRP composites industry. The use of such systems has been implemented in both new construction and for repair and rehabilitation of existing structures. Since the 1980s, researchers have developed a significant body of knowledge to use FRP composites in infrastructure applications; however, most of this established knowledge was concentrated on the use of traditional epoxy (EP) systems (epoxy matrix FRPs and epoxy adhesives). FRP composites with polyurethane (PU) matrices and adhesives have recently attracted the attention of a few researchers due to their potential advantages in constructibility and mechanical properties. The deployment of these systems is currently limited by a lack of knowledge on mechanical and durability performance. The objective of this research is to quantify the mechanical behavior of PU composites utilized in externally-bonded repair of common flexural and flexural-axial reinforced concrete systems. In addition, the mechanical performance, strength, and failure modes are compared directly with an epoxy-based composite by subjecting reinforced concrete specimens utilizing each of the matrix types (EP and PU) to the same protocols. The study presented therefore allows an objective comparison (advantages and disadvantages) between the two composite system used for repair and rehabilitation of concrete infrastructure. An experimental research program was designed with different length scales. Small-scale experiments were utilized to characterize the component level properties of the materials and bond to concrete, which include the flexural behavior as well as the pure shear behavior. The results of these small scale experiments were used to calibrate analytical models of the interface behavior between FRP laminate and concrete, and paved the way for the next level of the research which studied the behavior of each composite system at larger scales. The large scale experiments included flexural retrofitting of reinforced concrete girders and retrofitting of circular columns using FRP laminates. The large-scale experimental specimens were mechanically damaged prior to FRP repair and testing, making the testing more appropriate compared to common practice of repairing undamaged specimens.
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Date Issued: 2015
Identifier: CFE0005942, ucf:50820
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005942

Title: Mechanical Study on Edge-Oxidized Graphene Oxide (EOGO) Reinforced Concrete.
Creator: Khawaji, Mohammad, Nam, Boo Hyun, Chopra, Manoj, Zaurin, Ricardo, Kwok, Kawai, University of Central Florida
Abstract / Description: It is known that graphene oxide (GO) has superior mechanical properties and can enhance mechanical properties of cement composites. However, Hummer produced conventional GOs have been limited to small-scale specimens (e.g., cement paste and mortar) and applications to concrete have not been implemented due to their high cost and large volume of concrete. Edge-oxidized graphene oxide (EOGO) is a low-cost, carbon-based nanomaterial produced by a mechanochemical process with ball milling and a...
Show moreIt is known that graphene oxide (GO) has superior mechanical properties and can enhance mechanical properties of cement composites. However, Hummer produced conventional GOs have been limited to small-scale specimens (e.g., cement paste and mortar) and applications to concrete have not been implemented due to their high cost and large volume of concrete. Edge-oxidized graphene oxide (EOGO) is a low-cost, carbon-based nanomaterial produced by a mechanochemical process with ball milling and a non-toxic oxidizing agent. The low cost (less than $50/kg) of EOGO enables its use in bulk-scale concrete materials/structures, which is a prerequisite for the field implementation. In this study, EOGO was applied to macroscopic concrete to investigate mechanical and workability performance of EOGO reinforced concrete. Interestingly, it was observed that the addition of EOGO to normal concrete increases concrete slump, which opposes the conventional GO study on cement paste. To maximize the benefits of the improved workability, EOGO was then applied to fiber reinforced concretes (FRCs) to compensate their low workability. Two different types of fibers were used, including basalt and steel fibers. The results indicated that EOGO is not effective in basalt fiber reinforced concrete (BFRC) perhaps due to the high absorption of basalt fibers. However, adding EOGO to steel fiber reinforced concrete (SFRC) exhibited significant enhancement in workability and strength compared with control specimens. Subsequently, the effect of EOGO on flexural fatigue behavior of cement composite mixtures (cement mortar and concrete) was investigated. The flexural fatigue results show that adding EOGO to cement composites enhances flexural fatigue performance. Lastly, the impact of EOGO on pavement structure was investigated based on Mechanistic-Empirical Design Guide (MEPDG). The results show EOGO significantly extends service life and minimizes the required thickness of surface layer.
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Date Issued: 2019
Identifier: CFE0007826, ucf:52821
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007826

Title: Experimental study and modeling of mechanical micro-machining of particle reinforced heterogeneous materials.
Creator: Liu, Jian, Xu, Chengying, An, Linan, Gordon, Ali, Bai, Yuanli, Gong, Xun, University of Central Florida
Abstract / Description: This study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized...
Show moreThis study focuses on developing explicit analytical and numerical process models for mechanical micro-machining of heterogeneous materials. These models are used to select suitable process parameters for preparing and micro-machining of these advanced materials. The material system studied in this research is Magnesium Metal Matrix Composites (Mg-MMCs) reinforced with nano-sized and micro-sized silicon carbide (SiC) particles.This research is motivated by increasing demands of miniaturized components with high mechanical performance in various industries. Mg-MMCs become one of the best candidates due to its light weight, high strength, and high creep/wear resistance. However, the improved strength and abrasive nature of the reinforcements bring great challenges for the subsequent micro-machining process.Systematic experimental investigations on the machinability of Mg-MMCs reinforced with SiC nano-particles have been conducted. The nanocomposites containing 5 Vol.%, 10 Vol.% and 15 Vol.% reinforcements, as well as pure magnesium, are studied by using the Design of Experiment (DOE) method. Cutting forces, surface morphology and surface roughness are characterized to understand the machinability of the four materials. Based on response surface methodology (RSM) design, experimental models and related contour plots have been developed to build a connection between different materials properties and cutting parameters. Those models can be used to predict the cutting force, the surface roughness, and then optimize the machining process.An analytical cutting force model has been developed to predict cutting forces of Mg-MMCs reinforced with nano-sized SiC particles in the micro-milling process. This model is different from previous ones by encompassing the behaviors of reinforcement nanoparticles in three cutting scenarios, i.e., shearing, ploughing and elastic recovery. By using the enhanced yield strength in the cutting force model, three major strengthening factors are incorporated, including load-bearing effect, enhanced dislocation density strengthening effect and Orowan strengthening effect. In this way, the particle size and volume fraction, as significant factors affecting the cutting forces, are explicitly considered. In order to validate the model, various cutting conditions using different size end mills (100 (&)#181;m and 1 mm dia.) have been conducted on Mg-MMCs with volume fraction from 0 (pure magnesium) to 15 Vol.%. The simulated cutting forces show a good agreement with the experimental data. The proposed model can predict the major force amplitude variations and force profile changes as functions of the nanoparticles' volume fraction. Next, a systematic evaluation of six ductile fracture models has been conducted to identify the most suitable fracture criterion for micro-scale cutting simulations. The evaluated fracture models include constant fracture strain, Johnson-Cook, Johnson-Cook coupling criterion, Wilkins, modified Cockcroft-Latham, and Bao-Wierzbicki fracture criterion. By means of a user material subroutine (VUMAT), these fracture models are implemented into a Finite Element (FE) orthogonal cutting model in ABAQUS/Explicit platform. The local parameters (stress, strain, fracture factor, velocity fields) and global variables (chip morphology, cutting forces, temperature, shear angle, and machined surface integrity) are evaluated. Results indicate that by coupling with the damage evolution, the capability of Johnson-Cook and Bao-Wierzbicki can be further extended to predict accurate chip morphology. Bao-Wierzbiki-based coupling model provides the best simulation results in this study. The micro-cutting performance of MMCs materials has also been studied by using FE modeling method. A 2-D FE micro-cutting model has been constructed. Firstly, homogenized material properties are employed to evaluate the effect of particles' volume fraction. Secondly, micro-structures of the two-phase material are modeled in FE cutting models. The effects of the existing micro-sized and nano-sized ceramic particles on micro-cutting performance are carefully evaluated in two case studies. Results show that by using the homogenized material properties based on Johnson-Cook plasticity and fracture model with damage evolution, the micro-cutting performance of nano-reinforced Mg-MMCs can be predicted. Crack generation for SiC particle reinforced MMCs is different from their homogeneous counterparts; the effect of micro-sized particles is different from the one of nano-sized particles.In summary, through this research, a better understanding of the unique cutting mechanism for particle reinforced heterogeneous materials has been obtained. The effect of reinforcements on micro-cutting performance is obtained, which will help material engineers tailor suitable material properties for special mechanical design, associated manufacturing method and application needs. Moreover, the proposed analytical and numerical models provide a guideline to optimize process parameters for preparing and micro-machining of heterogeneous MMCs materials. This will eventually facilitate the automation of MMCs' machining process and realize high-efficiency, high-quality, and low-cost manufacturing of composite materials.
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Date Issued: 2012
Identifier: CFE0004570, ucf:49196
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004570

Title: Reproductive life history and signal evolution in a multi-species assemblage of electric fish.
Creator: Waddell, Joseph, Crampton, William, Fedorka, Kenneth, Quintana-Ascencio, Pedro, Stoddard, Philip, University of Central Florida
Abstract / Description: Animals that co-occur in sympatry with multiple closely-related species use reproductive mate attraction signals not only to assess the quality of a potential conspecific mate (sexual selection), but also to discriminate conspecifics from heterospecifics (species recognition). However, the extent to which sexual selection and species recognition may interact, or even conflict, is poorly known. Neotropical electric fish offer unrivaled opportunities for understanding this problem. They...
Show moreAnimals that co-occur in sympatry with multiple closely-related species use reproductive mate attraction signals not only to assess the quality of a potential conspecific mate (sexual selection), but also to discriminate conspecifics from heterospecifics (species recognition). However, the extent to which sexual selection and species recognition may interact, or even conflict, is poorly known. Neotropical electric fish offer unrivaled opportunities for understanding this problem. They generate simple, stereotyped mate attraction signals that are easy to record and quantify, and that are well-understood from the neurobiological perspective. Additionally, they live in electrically-crowded environments, where multiple congeners live and reproduce in close proximity. This dissertation reports an investigation of electric signal diversity and reproductive life history in a nine-species assemblage of the electric fish genus Brachyhypopomus from the upper Amazon. A year-long quantitative sampling program yielded a library of electric signal recordings from (>)3,000 individuals and an accompanying collection of preserved specimens from which suites of informative life history traits were measured. These data were used to understand basic reproductive biology, and to describe sexually dimorphic and interspecific diversity in electric signals. By integrating approaches from ecology, physiology, and evolutionary biology, novel perspectives are provided on: 1. how sexual selection and species recognition interact to shape signal diversity and the occupation of signal space in multi-species animal communities; 2. how extreme seasonal variation in Amazonian ecosystems influences trade-offs in the allocation of reproductive resources (-) including mate attraction signals, and; 3. how environmental variation shapes general life-history traits in a diverse tropical animal assemblage.
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Date Issued: 2017
Identifier: CFE0006925, ucf:51689
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006925

Machine Learning (2)	+ -
Reinforcement (2)	+ -
Age (1)	+ -
Alumina reinforcement (1)	+ -
Animal tracking (1)	+ -

Basalt Fiber (1)	+ -
Basalt fiber (1)	+ -
Biosolids (1)	+ -
Brachyhypopomus (1)	+ -
CNF (1)	+ -
CNT (1)	+ -
CVD (1)	+ -
Communication (1)	+ -
Compost (1)	+ -
Contexts (1)	+ -
CxBR (1)	+ -
Decision making (1)	+ -
Deep Reinforcement Learning (1)	+ -
Distribution prediction (1)	+ -
Edge-oxidized graphene oxide (EOGO) (1)	+ -
Electric organ (1)	+ -
Electrogenesis (1)	+ -
Electroreception (1)	+ -
Evolutionary Computation (1)	+ -
FRP (1)	+ -
Fiber Reinforced Composites (1)	+ -
Fiber Reinforced Polymers (1)	+ -
Fiber Reinforced Polymers FRP Composites Retrofit Polyurethane Epoxy Bond Debond ACI440 Beam Column Experimental Lap Shear Flexure (1)	+ -
Fiber reinforced concrete (1)	+ -
Flexural behavior (1)	+ -

University of Central Florida (15)	+ -
Chopra, Manoj (4)	+ -
Mackie, Kevin (4)	+ -
Bai, Yuanli (2)	+ -
Catbas, Necati (2)	+ -

Gou, Jihua (2)	+ -
Sukthankar, Gita (2)	+ -
Xu, Chengying (2)	+ -
Aihe, David (1)	+ -
Alabachi, Saif (1)	+ -
An, Linan (1)	+ -
Behal, Aman (1)	+ -
Boloni, Ladislau (1)	+ -
Burroughs, Wayne A. (1)	+ -
Chan, Titchenda (1)	+ -
Crampton, William (1)	+ -
El Zghayar, Elie (1)	+ -
Fedorka, Kenneth (1)	+ -
Gong, Xun (1)	+ -
Gonzalez, Avelino (1)	+ -
Gordon, Ali (1)	+ -
Hasan, Samiul (1)	+ -
Jahan, Sanjida (1)	+ -
Johnson, Cara (1)	+ -
Kapat, Jayanta (1)	+ -
Khawaji, Mohammad (1)	+ -
Knight, Patricia J. (1)	+ -
Kuo, Shiou-San (1)	+ -
Kwok, Kawai (1)	+ -
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