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Title: Development of 3D Vision Testbed for Shape Memory Polymer Structure Applications.
Creator: Thompson, Kenneth, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: As applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo...
Show moreAs applications for shape memory polymers (SMPs) become more advanced, it is necessary to have the ability to monitor both the actuation and thermal properties of structures made of such materials. In this paper, a method of using three stereo pairs of webcams and a single thermal camera is studied for the purposes of both tracking three dimensional motion of shape memory polymers, as well as the temperature of points of interest within the SMP structure. The method used includes a stereo camera calibration with integrated local minimum tracking algorithms to locate points of interest on the material and measure their temperature through interpolation techniques. The importance of the proposed method is that it allows a means to cost effectively monitor the surface temperature of a shape memory polymer structure without having to place intrusive sensors on the samples, which would limit the performance of the shape memory effect. The ability to monitor the surface temperatures of a SMP structure allows for more complex configurations to be created while increasing the performance and durability of the material. Additionally, as compared to the previous version, both the functionalities of the testbed and the user interface have been significantly improved.
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Date Issued: 2015
Identifier: CFE0005893, ucf:50860
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005893

Title: Deposition Thickness Modeling and Parameter Identification for Spray Assisted Vacuum Filtration Process in Additive Manufacturing.
Creator: Mark, August, Xu, Yunjun, Gou, Jihua, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: To enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer...
Show moreTo enhance mechanical and/or electrical properties of composite materials used in additive manufacturing, nanoparticles are often time deposited to form nanocomposite layers. To customize the mechanical and/or electrical properties, the thickness of such nanocomposite layers must be precisely controlled. A thickness model of filter cakes created through a spray assisted vacuum filtration is presented in this paper, to enable the development of advanced thickness controllers. The mass transfer dynamics in the spray atomization and vacuum filtration are studied for the mass of solid particles and mass of water in differential areas, and then the thickness of a filter cake is derived. A two-loop nonlinear constrained optimization approach is used to identify the unknown parameters in the model. Experiments involving depositing carbon nanofibers in a sheet of paper are used to measure the ability of the model to mimic the filtration process.
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Date Issued: 2015
Identifier: CFE0005974, ucf:50788
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005974

Title: Optimal Switch Timing for Piezoelectric-Based Semi-Active Vibration Reduction Techniques.
Creator: Kelley, Christopher, Kauffman, Jeffrey, Das, Tuhin, Xu, Yunjun, University of Central Florida
Abstract / Description: Semi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every...
Show moreSemi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every displacement extrema. Due to the complexity of analyzing a system with discrete switches, these control laws were developed based on intuition. The few analyses that attempt to determine an optimal switching law mathematically only evaluate the system at resonance. This thesis investigates the effects of switch timing on vibration reduction and the frequency dependence of the optimal switch timing control law. Regardless of the switch timing, sensing uncertainties, noise, and modeling errors can cause the switches to occur away from the designed moment. Thus, this work also quantifies the expected degradation in vibration reduction performance due to variations in the designed switch time. Experimental, numerical, and analytical solutions agree that the optimal switch timing of these semi-active techniques depends on frequency. A closed-form solution for the optimal switch timing is derived in terms of well-known, non-dimensional parameters.
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Date Issued: 2016
Identifier: CFE0006336, ucf:51555
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006336

Title: A New Path Planning Guidance Law For Improved Impact Time Control of Missiles and Precision Munitions.
Creator: Snyder, Mark, Qu, Zhihua, Haralambous, Michael, Xu, Yunjun, University of Central Florida
Abstract / Description: A new missile guidance law is proposed for the control of impact time which provides an improved time-to-go calculation by removing error due to trajectory curvature and also provides a family of trajectories for trajectory planning purposes. Unlike conventional optimal guidance laws, the proposed law is non explicit in time-to-go and the linearization of the engagement kinematics in order to gain a closed form solution is not necessary.
Date Issued: 2016
Identifier: CFE0006398, ucf:51506
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006398

Title: A multi-scale approach to study Solid Oxide Fuel Cells: from Mechanical Properties and Crystal Structure of the Cell's Materials to the Development of an Interactive and Interconnected Educational Tool.
Creator: Aman, Amjad, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description: Solid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system...
Show moreSolid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system performance, and studies related to reliability, robustness and durability. The goal of this dissertation is to further the understanding of the mechanical properties and crystal structure of materials used in the cathode and electrolyte of solid oxide fuel cells, as well as to report on the development of a supplementary educational tool that could be used in course related to fuel cells. The first part of the dissertation relates to the study of LaCoO3 based perovskites that are used as cathode material in solid oxide fuel cells and in other energy-related applications. In-situ neutron diffraction of LaCoO3 perovskite during uniaxial compression was carried out to study crystal structure evolution and texture development. In this study, LaCoO3 was subjected to two cycles of uniaxial loading and unloading with the maximum stress value being 700-900 MPa. The in-situ neutron diffraction revealed the dynamic crystallographic changes occurring which is responsible for the non-linear ferroelastic deformation and the appearance of hysteresis in LaCoO3. At the end of the first cycle, irreversible strain was observed even after the load was removed, which is caused by non-recoverable domain reorientation and texture development. At the end of the second cycle, however, no irreversible strain was observed as domain reorientation seemed fully recovered. Elastic constants were calculated and Young's modulus was estimated for LaCoO3 single crystals oriented along different crystallographic directions. The high temperature mechanical behavior study of LaCoO3 based perovskites is also of prime importance as solid oxide fuel cells operate at high temperatures. Incidentally, it was observed that as opposed to the behavior of most materials, LaCoO3 exhibits stiffening between 700 oC to 900 oC, with the Young's modulus going from a value of ~76 GPa at room temperature to ~120 GPa at 900 oC. In-situ neutron diffraction, XRD and Raman spectroscopy were used to study structural changes occurring in the material as it was heated. The results from these experiments will be discussed.The next portion of the dissertation will focus on electrolytes. Numerical simulation was carried out in order to predict the non-linear load-stress relationship and estimation of biaxial flexure strength in layered electrolytes, during ring-on-ring mechanical testing.Finally, the development of an interactive and inter-connected educational software is presented that could serve as a supplementary tool to teach fuel cell related topics.
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Date Issued: 2016
Identifier: CFE0006436, ucf:51467
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006436

Title: Approximated Control Affine Dynamics Mode For an Agricultural Field Robot Considering Wheel Terrain Interaction.
Creator: Menendez-Aponte, Pablo, Xu, Yunjun, Lin, Kuo-Chi, Moslehy, Faissal, University of Central Florida
Abstract / Description: As populations and the demand for higher crop yields grow, so to does the need forefficient agricultural wheeled mobile robots. To achieve precise navigation through a fieldit is desirable that the control system is designed based on an accurate dynamic model. Inthis paper a control affine model for a custom designed skid-steer differential drive wheeledmobile robot is found. The Terramechanic wheel terrain interaction is adopted and modifiedto consider wheels with a torus geometry. Varying...
Show moreAs populations and the demand for higher crop yields grow, so to does the need forefficient agricultural wheeled mobile robots. To achieve precise navigation through a fieldit is desirable that the control system is designed based on an accurate dynamic model. Inthis paper a control affine model for a custom designed skid-steer differential drive wheeledmobile robot is found. The Terramechanic wheel terrain interaction is adopted and modifiedto consider wheels with a torus geometry. Varying slip ratios and slip angles are consideredin the terrain reaction forces, which is curve-fitted using a nonlinear least squares approachsuch that the achieved model is control affine. The parameters in the proposed model isidentified through an extended Kalman filter so that the state variables in the model arematched. Both simulation and experiments in a commercial farm validated the proposedmodel and the identification approach.
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Date Issued: 2016
Identifier: CFE0006480, ucf:51410
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006480

Title: Geolocation of Diseased Leaves in Strawberry Orchards for a Custom-Designed Octorotor.
Creator: Garcia, Christian, Xu, Yunjun, Lin, Kuo-Chi, Kauffman, Jeffrey, University of Central Florida
Abstract / Description: In recent years, technological advances have shown a strive for more automated processes in agriculture, as seem with the use of unmanned aerial vehicles (UAVs) with onboard sensors in many applications, including disease detection and yield prediction. In this thesis, an octorotor UAV is presented that was designed, built, and flight tested, with features that are custom-designed for strawberry orchard disease detection. To further automate the disease scouting operation, geolocation, or the...
Show moreIn recent years, technological advances have shown a strive for more automated processes in agriculture, as seem with the use of unmanned aerial vehicles (UAVs) with onboard sensors in many applications, including disease detection and yield prediction. In this thesis, an octorotor UAV is presented that was designed, built, and flight tested, with features that are custom-designed for strawberry orchard disease detection. To further automate the disease scouting operation, geolocation, or the process of determining global position coordinates of identified diseased regions based on images taken, is investigated. A Kalman filter is designed, based on a linear measurement model derived from an orthographic projection method, to estimate the target position. Simulation, as well as an ad-hoc experiment using flight data, is performed to compare this filter to the extended Kalman filter (EKF), which is based on the commonly used perspective projection method. The filter is embedded onto a CPU board for real-time use aboard the octorotor UAV, and the algorithm structure for this process is presented. In the later part of the thesis, a probabilistic data association method is used, jointly with a proposed logic-based measurement-to-target correlation method, to analyze measurements of different target sources and is incorporated into the Kalman filter. A simulation and an ad-hoc experiment, using video and flight data acquired aboard the octorotor UAV with a gimballed camera in hover flight, are performed to demonstrate the effectiveness of the algorithm and UAV platform.
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Date Issued: 2016
Identifier: CFE0006305, ucf:51597
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006305

Title: Dynamic Modeling of Autorotation for Simultaneous Lift and Wind Energy Extraction.
Creator: Mackertich, Sadaf, Das, Tuhin, Moslehy, Faissal, Xu, Yunjun, University of Central Florida
Abstract / Description: The goal of this thesis is to develop a multi-body dynamics model of autorotation with the objective of studying its application in energy harvesting. A rotor undergoing autorotation is termed an Autogyro. In the autorotation mode, the rotor is unpowered and its interaction with the wind causes an upward thrust force. The theory of an autorotating rotorcraft was originally studied for achieving safe flight at low speeds and later used for safe descent of helicopters under engine failure. The...
Show moreThe goal of this thesis is to develop a multi-body dynamics model of autorotation with the objective of studying its application in energy harvesting. A rotor undergoing autorotation is termed an Autogyro. In the autorotation mode, the rotor is unpowered and its interaction with the wind causes an upward thrust force. The theory of an autorotating rotorcraft was originally studied for achieving safe flight at low speeds and later used for safe descent of helicopters under engine failure. The concept can potentially be used as a means to collect high-altitude wind energy. Autorotation is inherently a dynamic process and requires detailed models for characterization. Existing models of autorotation assume steady operating conditions with constant angular velocity of the rotor. The models provide spatially averaged aerodynamic forces and torques. While these steady-autorotation models are used to create a basis for the dynamic model developed in this thesis, the latter uses a Lagrangian formulation to determine the equations of motion. The aerodynamic effects on the blades that produce thrust forces, in-plane torques, and out-of-plane torques, are modeled as non-conservative forces within the Lagrangian framework. To incorporate the instantaneous aerodynamic forces, the above-mentioned spatial averaging is removed. The resulting model is causal and consists of a system of differential equations. To investigate the dynamics under energy-harvesting operation, an additional in-plane regenerative torque is added to simulate the effect of a generator. The aerodynamic effects of this regenerative braking is incorporated into the model. In addition, the dynamic model relaxes assumptions of small flapping angles, and the periodic flapping behavior of the blades are naturally generated by the dynamics instead of assuming Fourier expansions. The dynamic model enables the study of transients due to change in operating conditions or external influences such as wind speeds. It also helps gain insight into force and torque fluctuations.Model verification is conducted to ensure that the dynamic model produces similar steady-operating conditions as those reported in prior works. In addition, the behavior of autorotation under energy harvesting is evaluated. The thesis also explores the viability of achieving sufficient lift while extracting energy from prevailing winds. A range of regenerative torques are applied to determine the optimal energy state. Finally, a complete high-altitude energy harvesting system is modeled by incorporating a tether utilizing a catenary model. Overall, the thesis lends support to the hypothesis that a tethered autogyro can support its weight while harvesting energy from strong wind-fields, when augmented with appropriate control systems.
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Date Issued: 2016
Identifier: CFE0006138, ucf:51173
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006138

Title: Mission Analysis for Pico-Scale Satellite Based Dust Detection in Low Earth Orbits.
Creator: Belli, Jacob, Xu, Yunjun, Lin, Kuo-Chi, Bradley, Eric, University of Central Florida
Abstract / Description: A conceptual dust detection mission, KnightSat III, using pico-scale satellites is analyzed. The purpose of the proposed KnightSat III mission is to aid in the determination of the size, mass, distribution, and number of dust particles in low earth orbits through a low cost and flexible satellite or a formation of satellites equipped with a new dust detector. The analysis of a single satellite mission with an on-board dust detector is described; though this analysis can easily be extended to...
Show moreA conceptual dust detection mission, KnightSat III, using pico-scale satellites is analyzed. The purpose of the proposed KnightSat III mission is to aid in the determination of the size, mass, distribution, and number of dust particles in low earth orbits through a low cost and flexible satellite or a formation of satellites equipped with a new dust detector. The analysis of a single satellite mission with an on-board dust detector is described; though this analysis can easily be extended to a formation of pico-scale satellites. Many design aspects of the mission are discussed, including orbit analysis, power management, attitude determination and control, and mass and power budgets. Two of them are emphasized. The first is a new attitude guidance and control method, and the second is the online optimal power scheduling. It is expected that the measurements obtained from this possible future mission will provide insight into the dynamical processes of inner solar system dust, as well as aid in designing proper micro-meteoroid impact mitigation strategies for future man-made spacecraft.
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Date Issued: 2013
Identifier: CFE0004813, ucf:49728
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004813

Title: Manufacturing of Single Solid Oxide Fuel Cells.
Creator: Torres-Caceres, Jonathan, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description: Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials...
Show moreSolid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable.The goal of the research is to optimize and simplify the production of single SOFCs using high performance ceramics. This includes the use of 8mol% Y2O3-ZrO2 (YSZ) and 10mol% Sc2O3-1mol%CeO2-ZrO2 (SCSZ) layered electrolytes which purport higher conductivity than traditional pure YSZ electrolytes. Prior to printing the electrodes onto the electrolyte, the cathode side of the electrolyte was coated with 20mol% Gd2O3-CeO2 (GDC). The GDC coating prevents the formation of a nonconductive La2Zr2O7 pyrochlore layer, which forms due to the interdiffusion of the YSZ electrolyte ceramic and the (La0.6Sr0.4)0.995Fe0.8Co0.2O3 (LSCF) cathode ceramic during sintering. The GDC layer was deposited by spin coating a suspension of 10wt% GDC in ethanol onto the electrolyte. Variation of parameters such as time, speed, and ramp rate were tested. Deposition of the electrodes onto the electrolyte surface was done by screen printing. Ink was produced using a three roll mill from a mixture of ceramic electrode powder, terpineol, and a pore former. The pore former was selected based on its ability to form a uniform well-connected pore matrix within the anode samples that were pressed and sintered. Ink development involved the production of different ratios of powder-to-terpineol inks to vary the viscosity. The different inks were used to print electrodes onto the electrolytes to gauge print quality and consistency. Cells were produced with varying numbers of layers of prints to achieve a desirable thickness. Finally, the densification behaviors of the major materials used to produce the single cells were studied to determine the temperatures at which each component needs to be sintered to achieve the desired density and to determine the order of electrode application, so as to avoid over-densification of the electrodes. Complete cells were tested at the National Energy Technology Laboratory in Morgantown, WV. Cells were tested in a custom-built test stand under constant voltage at 800(&)deg;C with 3% humidified hydrogen as the fuel. Both voltage-current response and impedance spectroscopy tests were conducted after initial startup and after 20 hours of operation. Impedance tests were performed at open circuit voltage and under varying loads in order to analyze the sources of resistance within the cell. A general increase in impedance was found after the 20h operation. Scanning electron micrographs of the cell microstructures found delamination and other defects which reduce performance. Suggestions for eradicating these issues and improving performance have been made.
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Date Issued: 2013
Identifier: CFE0004946, ucf:49641
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004946

Title: Bio-Inspired Cooperative Optimal Trajectory Planning for Autonomous Vehicles.
Creator: Remeikas, Charles, Xu, Yunjun, Kassab, Alain, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: With the recent trend for systems to be more and more autonomous, there is a growing need for cooperative trajectory planning. Applications that can be considered as cooperative systems such as surveying, formation flight, and traffic control need a method that can rapidly produce trajectories while considering all of the constraints on the system. Currently most of the existing methods to handle cooperative control are based around either simple dynamics and/or on the assumption that all...
Show moreWith the recent trend for systems to be more and more autonomous, there is a growing need for cooperative trajectory planning. Applications that can be considered as cooperative systems such as surveying, formation flight, and traffic control need a method that can rapidly produce trajectories while considering all of the constraints on the system. Currently most of the existing methods to handle cooperative control are based around either simple dynamics and/or on the assumption that all vehicles have homogeneous properties. In reality, typical autonomous systems will have heterogeneous, nonlinear dynamics while also being subject to extreme constraints on certain state and control variables. In this thesis, a new approach to the cooperative control problem is presented based on the bio-inspired motion strategy known as local pursuit. In this framework, decision making about the group trajectory and formation are handled at a cooperative level while individual trajectory planning is considered in a local sense. An example is presented for a case of an autonomous farming system (e.g. scouting) utilizing nonlinear vehicles to cooperatively accomplish various farming task with minimal energy consumption or minimum time. The decision making and trajectory generation is handled very quickly while being able to consider changing environments laden with obstacles.
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Date Issued: 2013
Identifier: CFE0005053, ucf:49978
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005053

Title: Synthesis, Processing and Characterization of Polymer Derived Ceramic Nanocomposite Coating Reinforced with Carbon Nanotube Preforms.
Creator: Yang, Hongjiang, Gou, Jihua, Xu, Yunjun, Lin, Kuo-Chi, University of Central Florida
Abstract / Description: Ceramics have a number of applications as coating material due to their high hardness, wear and corrosion resistance, and the ability to withstand high temperatures. Critical to the success of these materials is the effective heat transfer through a material to allow for heat diffusion or effective cooling, which is often limited by the low thermal conductivity of many ceramic materials. To meet the challenge of improving the thermal conductivity of ceramics without lowering their performance...
Show moreCeramics have a number of applications as coating material due to their high hardness, wear and corrosion resistance, and the ability to withstand high temperatures. Critical to the success of these materials is the effective heat transfer through a material to allow for heat diffusion or effective cooling, which is often limited by the low thermal conductivity of many ceramic materials. To meet the challenge of improving the thermal conductivity of ceramics without lowering their performance envelope, carbon nanotubes were selected to improve the mechanical properties and thermal dispersion ability due to its excellent mechanical properties and high thermal conductivity in axial direction. However, the enhancements are far lower than expectation resulting from limited carbon nanotube content in ceramic matrix composites and the lack of alignment. These problems can be overcome if ceramic coatings are reinforced by carbon nanotubes with good dispersion and alignment. In this study, the well-dispersed and aligned carbon nanotubes preforms were achieved in the form of vertically aligned carbon nanotubes (VACNTs) and Buckypaper. Polymer derived ceramic (PDC) was selected as the matrix to fabricate carbon nanotube reinforced ceramic nanocomposites through resin curing and pyrolysis. The SEM images indicates the alignment of carbon nanotubes in the PDC nanocomposites. The mechanical and thermal properties of the PDC nanocomposites were characterized through Vickers hardness measurement and Thermogravimetric Analysis. The ideal anisotropic properties of nanocomposites were confirmed by estimating the electrical conductivity in two orthogonal directions.
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Date Issued: 2014
Identifier: CFE0005446, ucf:50385
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005446

Title: Online Path Planning and Control Solution for a Coordinated Attack of Multiple Unmanned Aerial Vehicles in a Dynamic Environment.
Creator: Vega-Nevarez, Juan, Qu, Zhihua, Haralambous, Michael, Xu, Yunjun, University of Central Florida
Abstract / Description: The role of the unmanned aerial vehicle (UAV) has significantly expanded in the military sector during the last decades mainly due to their cost effectiveness and their ability to eliminate the human life risk. Current UAV technology supports a variety of missions and extensive research and development is being performed to further expand its capabilities. One particular field of interest is the area of the low cost expendable UAV since its small price tag makes it an attractive solution for...
Show moreThe role of the unmanned aerial vehicle (UAV) has significantly expanded in the military sector during the last decades mainly due to their cost effectiveness and their ability to eliminate the human life risk. Current UAV technology supports a variety of missions and extensive research and development is being performed to further expand its capabilities. One particular field of interest is the area of the low cost expendable UAV since its small price tag makes it an attractive solution for target suppression. A swarm of these low cost UAVs can be utilized as guided munitions or kamikaze UAVs to attack multiple targets simultaneously. The focus of this thesis is the development of a cooperative online path planning algorithm that coordinates the trajectories of these UAVs to achieve a simultaneous arrival to their dynamic targets. A nonlinear autopilot design based on the dynamic inversion technique is also presented which stabilizes the dynamics of the UAV in its entire operating envelope. A nonlinear high fidelity six degrees of freedom model of a fixed wing aircraft was developed as well that acted as the main test platform to verify the performance of the presented algorithms
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Date Issued: 2012
Identifier: CFE0004613, ucf:49925
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004613

Title: On RADAR DECEPTION, AS MOTIVATION FOR CONTROL OF CONSTRAINED SYSTEMS.
Creator: Hajieghrary, Hadi, Jayasuriya, Suhada, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description: This thesis studies the control algorithms used by a team of ECAVs (Electronic Combat Air Vehicle) to deceive a network of radars to detect a phantom track. Each ECAV has the electronic capability of intercepting the radar waves, and introducing an appropriate time delay before transmitting it back, and deceiving the radar into seeing a spurious target beyond its actual position. On the other hand, to avoid the errors and increase the reliability, have a complete coverage in various...
Show moreThis thesis studies the control algorithms used by a team of ECAVs (Electronic Combat Air Vehicle) to deceive a network of radars to detect a phantom track. Each ECAV has the electronic capability of intercepting the radar waves, and introducing an appropriate time delay before transmitting it back, and deceiving the radar into seeing a spurious target beyond its actual position. On the other hand, to avoid the errors and increase the reliability, have a complete coverage in various atmosphere conditions, and confronting the effort of the belligerent intruders to delude the sentinel and enter the area usually a network of radars are deployed to guard the region. However, a team of cooperating ECAVs could exploit this arrangement and plans their trajectories in a way all the radars in the network vouch for seeing a single and coherent spurious track of a phantom. Since each station in the network confirms the other, the phantom track is considered valid. This problem serves as a motivating example in trajectory planning for the multi-agent system in highly constrained operation conditions. The given control command to each agent should be a viable one in the agent limited capabilities, and also drives it in a cumulative action to keep the formation.In this thesis, three different approaches to devise a trajectory for each agent is studied, and the difficulties for deploying each one are addressed. In the first one, a command center has all information about the state of the agents, and in every step decides about the control each agent should apply. This method is very effective and robust, but needs a reliable communication. In the second method, each agent decides on its own control, and the members of the group just communicate and agree on the range of control they like to apply on the phantom. Although in this method much less data needs to communicate between the agents, it is very sensitive to the disturbances and miscalculations, and could be easily fell apart or come to a state with no feasible solution to continue. In the third method a differential geometric approach to the problem is studied. This method has a very strong backbone, and minimizes the communication needed to a binary one. However, less data provided to the agents about the system, more sensitive and infirm the system is when it faced with imperfectionalities. In this thesis, an object oriented program is developed in the Matlab software area to simulate all these three control strategies in a scalable fashion. Object oriented programming is a naturally suitable method to simulate a multi-agent system. It gives the flexibility to make the code more close to a real scenario with defining each agent as a separated and independent identity. The main objective is to understand the nature of the constrained dynamic problems, and examine various solutions in different situations. Using the flexibility of this code, we could simulate several scenarios, and incorporate various conditions on the system. Also, we could have a close look at each agent to observe its behavior in these situations. In this way we will gain a good insight of the system which could be used in designing of the agents for specific missions.
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Date Issued: 2013
Identifier: CFE0004857, ucf:49683
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004857

Title: A Lab-Scale Experimental Framework for Studying the Phenomenon of Autorotation.
Creator: Rimkus, Sigitas, Das, Tuhin, Xu, Yunjun, Simaan, Marwan, University of Central Florida
Abstract / Description: While wind energy has emerged as a popular source of renewable energy, the traditional wind turbine has an inherent limitation, namely that it only generates power in the presence of sufficiently high and consistent wind speeds. As a result, wind farms are typically built in areas with a high probability of the required wind speeds, which are geographically sparse. One way of overcoming this drawback is to tap into the energy available in winds at high altitudes which are not only consistent...
Show moreWhile wind energy has emerged as a popular source of renewable energy, the traditional wind turbine has an inherent limitation, namely that it only generates power in the presence of sufficiently high and consistent wind speeds. As a result, wind farms are typically built in areas with a high probability of the required wind speeds, which are geographically sparse. One way of overcoming this drawback is to tap into the energy available in winds at high altitudes which are not only consistent and of high magnitude, but also globally pervasive. An airborne wind energy device based upon the phenomenon of autorotation could potentially be used to exploit the abundance of wind of energy present at high altitudes.The work in this thesis first presents our study of a tethered-airfoil system as a candidate airborne wind energy (AWE) system. A mathematical model was used to show the feasibility of energy capture and the stability of the device in a wind field. Subsequently, the research identified the principle of autorotation to be better suited for high altitude energy harvesting. To this end, the thesis first presents a theoretical basis of the principle of autorotation, which is developed from existing models in literature. The model was adapted to predict aerodynamic conditions when used for harvesting energy. Encouraging simulation results prompted the main emphasis of this thesis, namely design of an experimental framework to corroborate the theory. Several experiments were devised to determine basic performance characteristics of an autogyro rotor and the data from each experiment is presented. A lab-scale experimental setup was developed as part of this thesis. The setup, consisting of a flapping-blade autogyro rotor and sensors, was used to acquire preliminary aerodynamic performance data. It is envisioned that refinements to this setup will ultimately provide a means of directly comparing analytical and experimental data. In this regard, we provide conclusions and make comments on improvements for future experiments.
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Date Issued: 2014
Identifier: CFE0005239, ucf:50593
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005239

Title: Vision-Based Sensing and Optimal Control for Low-Cost and Small Satellite Platforms.
Creator: Sease, Bradley, Xu, Yunjun, Lin, Kuo-Chi, Bradley, Eric, University of Central Florida
Abstract / Description: Current trends in spacecraft are leading to smaller, more inexpensive options whenever possible. This shift has been primarily pursued for the opportunity to open a new frontier for technologies with a small financial obligation. Limited power, processing, pointing, and communication capabilities are all common issues which must be considered when miniaturizing systems and implementing low-cost components. This thesis addresses some of these concerns by applying two methods, in attitude...
Show moreCurrent trends in spacecraft are leading to smaller, more inexpensive options whenever possible. This shift has been primarily pursued for the opportunity to open a new frontier for technologies with a small financial obligation. Limited power, processing, pointing, and communication capabilities are all common issues which must be considered when miniaturizing systems and implementing low-cost components. This thesis addresses some of these concerns by applying two methods, in attitude estimation and control. Additionally, these methods are not restricted to only small, inexpensive satellites, but offer a benefit to large-scale spacecraft as well.First, star cameras are examined for the tendency to generate streaked star images during maneuvers. This issue also comes into play when pointing capabilities and camera hardware quality are low, as is often the case in small, budget-constrained spacecraft. When pointing capabilities are low, small residual velocities can cause movement of the stars in the focal plane during an exposure, causing them to streak across the image. Additionally, if the camera quality is low, longer exposures may be required to gather sufficient light from a star, further contributing to streaking. Rather than improving the pointing or hardware directly, an algorithm is presented to retrieve and utilize the endpoints of streaked stars to provide feedback where traditional methods do not. This allows precise attitude and angular rate estimates to be derived from an image which, with traditional methods, would return large attitude and rate error. Simulation results are presented which demonstrate endpoint error of approximately half a pixel and rate estimates within 2% of the true angular velocity. Three methods are also considered to remove overlapping star streaks and resident space objects from images to improve performance of both attitude and rate estimates. Results from a large-scale Monte Carlo simulation are presented in order to characterize the performance of the method.Additionally, a rapid optimal attitude guidance method is experimentally validated in a ground-based, pico-scale satellite test bed. Fast slewing performance is demonstrated for an incremental step maneuver with low average power consumption. Though the focus of this thesis is primarily on increasing the capabilities of small, inexpensive spacecraft, the methods discussed have the potential to increase the capabilities of current and future large-scale missions as well.
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Date Issued: 2013
Identifier: CFE0005249, ucf:50603
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005249

Title: PROCESSING AND CHARACTERIZATION OF MULTIFUNCTIONAL THERMOPLASTIC NANOCOMPOSITE FILMS.
Creator: Wang, Xin, Gou, Jihua, Challapalli, Suryanarayana, Xu, Yunjun, University of Central Florida
Abstract / Description: Nanoparticles reinforced polymer composite films have been widely studied for their enhanced mechanical, electrical and thermal properties compared with host polymer matrix. However, most research was conducted on incorporation of nanoparticles in polymer films to improve single property and there is a lack of research on the multifunctional polymer nanocomposite films. In this work, a scalable and continuous spray deposition process was developed for the production of nanoparticles...
Show moreNanoparticles reinforced polymer composite films have been widely studied for their enhanced mechanical, electrical and thermal properties compared with host polymer matrix. However, most research was conducted on incorporation of nanoparticles in polymer films to improve single property and there is a lack of research on the multifunctional polymer nanocomposite films. In this work, a scalable and continuous spray deposition process was developed for the production of nanoparticles reinforced multifunctional thermoplastic nanocomposite films. This process is capable of making a thin sheet of thermoplastic nanocomposites with high nanoparticle loadings. The smallest thickness can be 40um.The objective of this study is to design and optimize the thermoplastic nanocomposite films by utilizing nanoclay and helical carbon nanotube for multifunctional application: a) high electrical conductivity and thermal stability. Helical carbon nanotube paper based thermoplastic polyurethane nanocomposite films have been studied. The electrical conductivity and thermal stability of nanocomposite films increase a lot due to the incorporation of helical carbon nanotube paper with high electrical and thermal conductivity. The peculiar helical configuration of carbon nanotubes could greatly improve the interfacial bonding between carbon nanotubes and polymer matrix. b)High wear resistance and thermal stability. A nanoclay reinforced thermoplastic polyurethane nanocomposite coating was applied on the surface of leather. Due to the high hardness and thermal stability of nanoclay, the leather coated with nanocomposite film showed an improvement of wear resistance and thermal stability.
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Date Issued: 2014
Identifier: CFE0005734, ucf:50105
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005734

Title: Navigation of an Autonomous Differential Drive Robot for Field Scouting in Semi-structured Environments.
Creator: Freese, Douglas, Xu, Yunjun, Lin, Kuo-Chi, Kauffman, Jeffrey L., Behal, Aman, University of Central Florida
Abstract / Description: In recent years, the interests of introducing autonomous robots by growers into agriculture fields are rejuvenated due to the ever-increasing labor cost and the recent declining numbers of seasonal workers. The utilization of customized, autonomous agricultural robots has a profound impact on future orchard operations by providing low cost, meticulous inspection. Different sensors have been proven proficient in agrarian navigation including the likes of GPS, inertial, magnetic, rotary...
Show moreIn recent years, the interests of introducing autonomous robots by growers into agriculture fields are rejuvenated due to the ever-increasing labor cost and the recent declining numbers of seasonal workers. The utilization of customized, autonomous agricultural robots has a profound impact on future orchard operations by providing low cost, meticulous inspection. Different sensors have been proven proficient in agrarian navigation including the likes of GPS, inertial, magnetic, rotary encoding, time of flight as well as vision. To compensate for anticipated disturbances, variances and constraints contingent to the outdoor semi-structured environment, a differential style drive vehicle will be implemented as an easily controllable system to conduct tasks such as imaging and sampling.In order to verify the motion control of a robot, custom-designed for strawberry fields, the task is separated into multiple phases to manage the over-bed and cross-bed operation needs. In particular, during the cross-bed segment an elevated strawberry bed will provide distance references utilized in a logic filter and tuned PID algorithm for safe and efficient travel. Due to the significant sources of uncertainty such as wheel slip and the vehicle model, nonlinear robust controllers are designed for the cross-bed motion, purely relying on vision feedback. A simple image filter algorithm was developed for strawberry row detection, in which pixels corresponding to the bed center will be tracked while the vehicle is in controlled motion. This incorporated derivation and formulation of a bounded uncertainty parameter that will be employed in the nonlinear control. Simulation of the entire system was subsequently completed to ensure the control capability before successful validation in multiple commercial farms. It is anticipated that with the developed algorithms the authentication of fully autonomous robotic systems functioning in agricultural crops will provide heightened efficiency of needed costly services; scouting, disease detection, collection, and distribution.
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Date Issued: 2018
Identifier: CFE0007401, ucf:52743
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007401

Title: AUTONOMOUS ROBOTIC GRASPING IN UNSTRUCTURED ENVIRONMENTS.
Creator: Jabalameli, Amirhossein, Behal, Aman, Haralambous, Michael, Pourmohammadi Fallah, Yaser, Boloni, Ladislau, Xu, Yunjun, University of Central Florida
Abstract / Description: A crucial problem in robotics is interacting with known or novel objects in unstructured environments. While the convergence of a multitude of research advances is required to address this problem, our goal is to describe a framework that employs the robot's visual perception to identify and execute an appropriate grasp to pick and place novel objects. Analytical approaches explore for solutions through kinematic and dynamic formulations. On the other hand, data-driven methods retrieve grasps...
Show moreA crucial problem in robotics is interacting with known or novel objects in unstructured environments. While the convergence of a multitude of research advances is required to address this problem, our goal is to describe a framework that employs the robot's visual perception to identify and execute an appropriate grasp to pick and place novel objects. Analytical approaches explore for solutions through kinematic and dynamic formulations. On the other hand, data-driven methods retrieve grasps according to their prior knowledge of either the target object, human experience, or through information obtained from acquired data. In this dissertation, we propose a framework based on the supporting principle that potential contacting regions for a stable grasp can be foundby searching for (i) sharp discontinuities and (ii) regions of locally maximal principal curvature in the depth map. In addition to suggestions from empirical evidence, we discuss this principle by applying the concept of force-closure and wrench convexes. The key point is that no prior knowledge of objects is utilized in the grasp planning process; however, the obtained results show thatthe approach is capable to deal successfully with objects of different shapes and sizes. We believe that the proposed work is novel because the description of the visible portion of objects by theaforementioned edges appearing in the depth map facilitates the process of grasp set-point extraction in the same way as image processing methods with the focus on small-size 2D image areas rather than clustering and analyzing huge sets of 3D point-cloud coordinates. In fact, this approach dismisses reconstruction of objects. These features result in low computational costs and make it possible to run the proposed algorithm in real-time. Finally, the performance of the approach is successfully validated by applying it to the scenes with both single and multiple objects, in both simulation and real-world experiment setups.
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Date Issued: 2019
Identifier: CFE0007892, ucf:52757
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007892

Title: Nonlinear Control Synthesis for Facilitation of Human-Robot Interaction.
Creator: Ding, Zhangchi, Behal, Aman, Pourmohammadi Fallah, Yaser, Haralambous, Michael, Boloni, Ladislau, Xu, Yunjun, University of Central Florida
Abstract / Description: Human-robot interaction is an area of interest that is becoming increasingly important in robotics research. Nonlinear control design techniques allow researchers to guarantee stability, performance, as well as safety, especially in cases involving physical human-robot interaction (PHRI). In this dissertation, we will propose two different nonlinear controllers and detail the design of an assistive robotic system to facilitate human-robot interaction. In Chapter 2, to facilitate physical...
Show moreHuman-robot interaction is an area of interest that is becoming increasingly important in robotics research. Nonlinear control design techniques allow researchers to guarantee stability, performance, as well as safety, especially in cases involving physical human-robot interaction (PHRI). In this dissertation, we will propose two different nonlinear controllers and detail the design of an assistive robotic system to facilitate human-robot interaction. In Chapter 2, to facilitate physical human-robot interaction, the problem of making a safe compliant contact between a human and an assistive robot is considered. Users with disabilities have a need to utilize their assistive robots for physical interaction during activities such as hair-grooming, scratching, face-sponging, etc. Specifically, we propose a hybrid force/velocity/attitude control for our physical human-robot interaction system which is based on measurements from a force/torque sensor mounted on the robot wrist. While automatically aligning the end-effector surface with the unknown environmental (human) surface, a desired commanded force is applied in the normal direction while following desired velocity commands in the tangential directions. A Lyapunov based stability analysis is provided to prove both convergence as well as passivity of the interaction to ensure both performance and safety. Simulation as well as experimental results verify the performance and robustness of the proposed hybrid force/velocity/attitude controller in the presence of dynamic uncertainties as well as safety compliance of human-robot interactions for a redundant robot manipulator.Chapter 3 presents the design, analysis, and experimental implementation of an adaptive control enabled intelligent algorithm to facilitate 1-click grasping of novel objects by a robotic gripper since one of the most common types of tasks for an assistive robot is pick and place/object retrieval tasks. But there are a variety of objects in our daily life all of which need different optimal force to grasp them. This algorithm facilitates automated grasping force adjustment. The use of object-geometry free modeling coupled with utilization of interaction force and slip velocity measurements allows for the design of an adaptive backstepping controller that is shown to be asymptotically stable via a Lyapunov-based analysis. Experiments with multiple objects using a prototype gripper with embedded sensing show that the proposed scheme is able to effectively immobilize novel objects within the gripper fingers. Furthermore, it is seen that the adaptation allows for close estimation of the minimum grasp force required for safe grasping which results in minimal deformation of the grasped object.In Chapter 4, we present the design and implementation of the motion controllerand adaptive interface for the second generation of the UCF-MANUSintelligent assistive robotic manipulator system. Based on usability testingfor the system, several features were implemented in the interface thatcould reduce the complexity of the human-robot interaction while alsocompensating for the deficits in different human factors, such as WorkingMemory, Response Inhibition, Processing Speed; , Depth Perception, SpatialAbility, Contrast Sensitivity. For the controller part, we designed severalnew features to provide the user has a less complex and safer interactionwith the robot, such as `One-click mode', `Move suggestion mode' and`Gripper Control Assistant'. As for the adaptive interface design, wedesigned and implemented compensators such as `Contrast Enhancement',`Object Proximity Velocity Reduction' and `Orientation Indicator'.
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Date Issued: 2019
Identifier: CFE0007798, ucf:52360
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007798

Robotics (3)	+ -
SOFC (3)	+ -
optimal control (3)	+ -
vibration reduction (3)	+ -
Computer Vision (2)	+ -

CubeSat (2)	+ -
Fuel Cells (2)	+ -
Grasping (2)	+ -
Optimal trajectory design (2)	+ -
Robust Control (2)	+ -
Shape Memory Polymer (2)	+ -
Solid Oxide Fuel Cells (2)	+ -
Testbed (2)	+ -
UAV (2)	+ -
additive manufacturing (2)	+ -
attitude control (2)	+ -
autogyro (2)	+ -
autorotation (2)	+ -
cooperative control (2)	+ -
missile (2)	+ -
robust control (2)	+ -
trajectory planning (2)	+ -
virtual motion camouflage (2)	+ -
wind energy (2)	+ -
3D printing (1)	+ -
A Smart UAV Platform for Railroad Inspection (1)	+ -
Adaptive Control (1)	+ -
Aerodynamics (1)	+ -
Agriculture (1)	+ -
Agriculture Ground Robot (1)	+ -

University of Central Florida (50)	+ -
Xu, Yunjun (50)	+ -
Lin, Kuo-Chi (20)	+ -
Das, Tuhin (11)	+ -
Gou, Jihua (10)	+ -

Behal, Aman (8)	+ -
Haralambous, Michael (6)	+ -
Kauffman, Jeffrey (5)	+ -
Orlovskaya, Nina (5)	+ -
Qu, Zhihua (4)	+ -
Boloni, Ladislau (3)	+ -
Cho, Hyoung (3)	+ -
Kauffman, Jeffrey L. (3)	+ -
Song, Sang-Eun (3)	+ -
Aman, Amjad (2)	+ -
Bradley, Eric (2)	+ -
Challapalli, Suryanarayana (2)	+ -
Chen, Quanfang (2)	+ -
Chew, Phyekeng (2)	+ -
Defterli, Sinem (2)	+ -
Elgohary, Tarek (2)	+ -
Kassab, Alain (2)	+ -
Li, Ni (2)	+ -
Lopp, Garrett (2)	+ -
Mark, August (2)	+ -
Moslehy, Faissal (2)	+ -
Pourmohammadi Fallah, Yaser (2)	+ -
Thompson, Kenneth (2)	+ -
Torres-Caceres, Jonathan (2)	+ -
Wang, Xin (2)	+ -

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