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Title: SMART MATERIAL ACTUATION AND MORPHING FOR UNMANNED AIRCRAFT SYSTEMS.
Creator: Da Silva Lima, Caio H, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: The intent of this thesis is to outline the design, analysis, and characterization of an axially compressed piezocomposite actuator and, in particular, to determine the correlation and accuracy of two models used to predict deflection of an axially compressed piezocomposite bimorph. Restrictions in material properties lead to vehicle inefficiencies caused by the discontinuous geometry of deflected control surfaces in unmanned aircraft systems. This performance disadvantage in discrete control...
Show moreThe intent of this thesis is to outline the design, analysis, and characterization of an axially compressed piezocomposite actuator and, in particular, to determine the correlation and accuracy of two models used to predict deflection of an axially compressed piezocomposite bimorph. Restrictions in material properties lead to vehicle inefficiencies caused by the discontinuous geometry of deflected control surfaces in unmanned aircraft systems. This performance disadvantage in discrete control surfaces is caused in part by the sharp edges that are formed when the surface is pivoted. Flow continuity over the body of a vehicle is important in minimizing the effects of drag and, in turn, increasing aerodynamic performance. An efficient alternative to discrete control surface actuation is axially compressed piezocomposite actuation which could potentially improve the efficiency of the vehicle in all environments. Bimorph performance in angular deflection and displacement for the PA16N and MFC-M8528-P1 piezocomposites is analyzed using a Classical Laminate Plate Theory (CLPT) model and an Elastica model. Model accuracy is verified through experimental testing of a PA16N bimorph. CLPT model is shown to be accurate to within .05 mm and Elastica model is shown to be accurate to within .04 mm for axial forces below 30 N. Correlation between the mathematical models is confirmed. Experimental results for the PA16N show that a 30 N compression force applied to the bimorph can increase the maximum displacement by approximately 2.5 times the original displacement.
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Date Issued: 2016
Identifier: CFH2000095, ucf:45563
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000095

Title: The Effect of Martensite-Fractions Assumptions In Shape Memory Alloy Springs.
Creator: Vazquez, Christian, Kauffman, Jeffrey L., Das, Tuhin, Kwok, Kawai, University of Central Florida
Abstract / Description: This research addresses various models of a spring-mass system that uses a spring made of a shape memory alloy (SMA). The system model describes the martensite fractions, which are values that describe an SMA's crystalline phases, via differential equations. The model admits and this thesis contrasts two commonly used but distinct assumptions: a homogeneous case where the martensite fractions are constant throughout the spring's cross section, and a bilinear case where the evolution of the...
Show moreThis research addresses various models of a spring-mass system that uses a spring made of a shape memory alloy (SMA). The system model describes the martensite fractions, which are values that describe an SMA's crystalline phases, via differential equations. The model admits and this thesis contrasts two commonly used but distinct assumptions: a homogeneous case where the martensite fractions are constant throughout the spring's cross section, and a bilinear case where the evolution of the martensite fractions only occurs beyond some critical radius. While previous literature has developed a model of the system dynamics under the homogeneous assumption using the martensite-fractions differential equations, little research has focused on the dynamics when considering the bilinear case, especially using the differential equations. This thesis models the system dynamics under both the homogeneous and bilinear assumptions and determines if the bilinear case is an improvement over the homogeneous case. The research develops a numerical approach of the system dynamics for both martensite-fractions assumptions. For various initial displacements and temperatures, plotting the resulting displacement, velocity, and martensite fractions over time determines the coherence of the assumptions. Not only did the bilinear assumption offer more reasonable plots, but the homogeneous assumption delivered bizarre results for certain temperatures and initial displacements. For future research, a fully nonlinear case can replace the homogeneous and bilinear assumptions. Additionally, future research can utilize other martensite-fractions evolution models, as opposed to differential equations.
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Date Issued: 2018
Identifier: CFE0007381, ucf:52742
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007381

Title: Spatial and Temporal Compressive Sensing for Vibration-based Monitoring: Fundamental Studies with Beam Vibrations.
Creator: Ganesan, Vaahini, Das, Tuhin, Kauffman, Jeffrey L., Raghavan, Seetha, University of Central Florida
Abstract / Description: Vibration data from mechanical systems carry important information that is useful for characterization and diagnosis. Standard approaches rely on continually streaming data at a fixed sampling frequency. For applications involving continuous monitoring, such as Structural Health Monitoring (SHM), such approaches result in high data volume and require powering sensors for prolonged duration. Furthermore, adequate spatial resolution, typically involves instrumenting structures with a large...
Show moreVibration data from mechanical systems carry important information that is useful for characterization and diagnosis. Standard approaches rely on continually streaming data at a fixed sampling frequency. For applications involving continuous monitoring, such as Structural Health Monitoring (SHM), such approaches result in high data volume and require powering sensors for prolonged duration. Furthermore, adequate spatial resolution, typically involves instrumenting structures with a large array of sensors. This research shows that applying Compressive Sensing (CS) can significantly reduce both the volume of data and number of sensors in vibration monitoring applications. Random sampling and the inherent sparsity of vibration signals in the frequency domain enables this reduction. Additionally, by exploiting the sparsity of mode shapes, CS can also enable efficient spatial reconstruction using fewer spatially distributed sensors than a traditional approach. CS can thereby reduce the cost and power requirement of sensing as well as streamline data storage and processing in monitoring applications. In well-instrumented structures, CS can enable continuous monitoring in case of sensor or computational failures. The scope of this research was to establish CS as a viable method for SHM with application to beam vibrations. Finite element based simulations demonstrated CS-based frequency recovery from free vibration response of simply supported, fixed-fixed and cantilever beams. Specifically, CS was used to detect shift in natural frequencies of vibration due to structural change using considerably less data than required by traditional sampling. Experimental results using a cantilever beam provided further insight into this approach. In the experimental study, impulse response of the beam was used to recover natural frequencies of vibration with CS. It was shown that CS could discern changes in natural frequencies under modified beam parameters. When the basis functions were modified to accommodate the effect of damping, the performance of CS-based recovery further improved. Effect of noise in CS-based frequency recovery was also studied. In addition to incorporating damping, formulating noise-handling as a part of the CS algorithm for beam vibrations facilitated detecting shift in frequencies from even fewer samples. In the spatial domain, CS was primarily developed to focus on image processing applications, where the signals and basis functions are very different from those required for mechanical beam vibrations. Therefore, it mandated reformulation of the CS problem that would handle related challenges and enable the reconstruction of spatial beam response using very few sensor data. Specifically, this research addresses CS-based reconstruction of deflection shape of beams with fixed boundary conditions. Presence of a fixed end makes hyperbolic terms indispensable in the basis, which in turn causes numerical inconsistencies. Two approaches are discussed to mitigate this problem. The first approach is to restrict the hyperbolic terms in the basis to lower frequencies to ensure well conditioning. The second, a more systematic approach, is to generate an augmented basis function that will combine harmonic and hyperbolic terms. At higher frequencies, the combined hyperbolic terms will limit each other's magnitude, thus ensuring boundedness. This research thus lays the foundation for formulating the CS problem for the field of mechanical vibrations. It presents fundamental studies and discusses open-ended challenges while implementing CS to this field that will pave way for further research.
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Date Issued: 2017
Identifier: CFE0007120, ucf:51954
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007120

Title: Piezoresistive Behavior of Carbon Nanopaper Polymer Composites for Strain Sensing.
Creator: Beyrooti, Jayden, Kwok, Kawai, Gou, Jihua, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Carbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to...
Show moreCarbon nanopapers made of carbon nanotubes (CNTs) or carbon nanofibers (CNFs), possess unique electrical, thermal and mechanical properties and when integrated with a polymer matrix, can become a multifunctional composite capable of strain sensing and heat actuation. Smart structures such as these can be used in many applications including deployable space structures, human motion detection, and structural health monitoring as flexible, sensitive and stable strain sensors in addition to providing electrical heat actuation for the shape memory effect in polymers. This study focuses on strain sensing capabilities by developing a numerical model to predict piezoresistive behavior. The piezoresistive effect is a change in resistivity of a conductive network when a deformation is applied. This allows strain to be determined by simply measuring the electrical resistance. An equivalent resistor network can be formed to represent the fiber network. The proposed 2D model generates randomly oriented fibers inside a unit cell, determines their intersection points, and creates a mesh of the network for finite element analysis. Electrical conductivity is found for the initial and deformed fiber states by determining the current through the network for a known voltage. A piezoresistivity experimental study is conducted to investigate the strain sensing abilities of this material and validate model results. This simple model provides an initial framework that can be developed in future work. Despite its 2D nature, the model captures the governing mechanisms of piezoresistivity to a certain extent.
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Date Issued: 2019
Identifier: CFE0007788, ucf:52353
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007788

Title: Design and Structural Analysis of Morphing Wings.
Creator: Fernandez, Nicholas, Bhattacharya, Samik, Kauffman, Jeffrey L., Orlovskaya, Nina, University of Central Florida
Abstract / Description: Many natural flyers and marine swimmers can morph their wings during a number of unsteady maneuverings. With such wing morphing they are able to control the unsteady aerodynamic forces. A number of man-made flyers, such as unmanned aerial vehicles and micro air vehicles, fly in comparable Reynolds number range, but they are yet to acquire similar morphing capabilities as natural flyers or swimmers. Moreover, the knowledge of fluid structural interaction (FSI) of such morphing wings is not...
Show moreMany natural flyers and marine swimmers can morph their wings during a number of unsteady maneuverings. With such wing morphing they are able to control the unsteady aerodynamic forces. A number of man-made flyers, such as unmanned aerial vehicles and micro air vehicles, fly in comparable Reynolds number range, but they are yet to acquire similar morphing capabilities as natural flyers or swimmers. Moreover, the knowledge of fluid structural interaction (FSI) of such morphing wings is not well developed. Hence there is a need to investigate the FSI of morphing wings. In this thesis, a morphing wing was designed and its FSI was investigated. The wing was designed with the help of advanced 3D printing and the morphing capabilities utilized servo driven actuators. The design enabled the wing to execute spanwise bending, twisting and combined bending and twisting during a number of unsteady maneuverings. In the present work, the effect of gradual acceleration on the resultant unsteady forcing was investigated. FEA simulations were performed in order to gauge the response of the wing in different scenarios. A flat plate wing was towed in a 6-m-long towing tank and force data was collected using a 6-dof force sensor. With this method of morphing, future experiments can be performed for different unsteady cases. The analysis performed in this thesis will also be helpful in understanding more complex FSI problems applicable to morphing wings.
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Date Issued: 2019
Identifier: CFE0007802, ucf:52338
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007802

Title: Vibration Reduction of Mistuned Bladed Disks via Piezoelectric-Based Resonance Frequency Detuning.
Creator: Lopp, Garrett, Kauffman, Jeffrey L., Das, Tuhin, Xu, Yunjun, University of Central Florida
Abstract / Description: Recent trends in turbomachinery blade technology have led to increased use of monolithically constructed bladed disks (blisks). Although offering a wealth of performance benefits, this construction removes the blade-attachment interface present in the conventional design, thus unintentionally removing a source of friction-based damping needed to counteract large vibrations during resonance passages. This issue is further exacerbated in the presence of blade mistuning that arises from small...
Show moreRecent trends in turbomachinery blade technology have led to increased use of monolithically constructed bladed disks (blisks). Although offering a wealth of performance benefits, this construction removes the blade-attachment interface present in the conventional design, thus unintentionally removing a source of friction-based damping needed to counteract large vibrations during resonance passages. This issue is further exacerbated in the presence of blade mistuning that arises from small imperfections from otherwise identical blades and are unavoidable as they originate from manufacturing tolerances and operational wear over the lifespan of the engine. Mistuning is known to induce vibration localization with large vibration amplitudes that render blades susceptible to failure induced by high-cycle fatigue. The resonance frequency detuning (RFD) method reduces vibration associated with resonance crossings by selectively altering the blades' structural response. This method utilizes the variable stiffness properties of piezoelectric materials to switch between available stiffness states at some optimal time as the excitation frequency sweeps through a resonance. For a single-degree-of-freedom (SDOF) system, RFD performance is well defined. This research provides the framework to extend RFD to more realistic applications when the SDOF assumption breaks down, such as in cases of blade mistuning. Mistuning is inherently random; thus, a Monte Carlo analysis performed on a computationally cheap lumped-parameter model provides insight into RFD performance for various test parameters. Application of a genetic algorithm reduces the computational expense required to identify the optimal set of stiffness-state switches. This research also develops a low-order blisk model with blade-mounted piezoelectric patches as a tractable first step to apply RFD to more realistic systems. Application of a multi-objective optimization algorithm produces Pareto fronts that aid in the selection of the optimized patch parameters. Experimental tests utilizing the academic blisk with the optimized patches provides validation.
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Date Issued: 2018
Identifier: CFE0007488, ucf:52639
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007488

Title: High Temperature Mechanics of Aerospace Ceramic Composites Characterized via Synchrotron Radiation.
Creator: Manero, Albert, Raghavan, Seetha, Kauffman, Jeffrey L., Gou, Jihua, University of Central Florida
Abstract / Description: This research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine...
Show moreThis research investigates the mechanics of complex aerospace material systems designed for extreme environments. Ceramics and ceramic matrix composites (CMCs) provide highly sought-after capabilities including the potential to withstand extreme temperatures and heat fluxes, severe oxidation and mechanical stresses. Two important material systems form the basis of the scope for this effort: i) thermal barrier coatings (TBCs) on Ni-superalloys that have enabled dramatic increases in turbine inlet temperatures exceeding 1100(&)deg;C; and ii) ceramic matrix composites that have shown capability and promise for hypersonic applications beyond 1300(&)deg;C. Understanding the mechanical and material properties of these materials as they evolve with temperature and load requires in-situ measurements under realistic representative environments, and from these measurements life expectancy and failure mechanisms can be more completely elucidated.In this work, TBCs representative of typical jet engine turbine blade coatings, comprised of a Yttria-stabilized zirconia top coat and NiCoCrAlY bond coat deposited on an IN 100 superalloy substrate were studied. Particular interest was given to the thermally grown oxide (TGO) that develops between the top layer and the bond coat that has a major influence on TBC durability. The oxide scale's development is linked to the typical failure mechanisms observed in application for aircraft engines, and the influence of internal cooling has been shown to vary the behavior and evolution over its lifetime. Tubular specimens coated via electron beam physical vapor deposition (EB-PVD) were investigated with hard synchrotron X-rays at Argonne National Laboratory's Advanced Photon Source, while subjected to realistic mechanical and thermal loading representative of the engine environment. A multi-variable investigation was conducted to determine the influence and magnitude of internal flow cooling, external applied force loading, and thermal exposure in cyclical application. The superposition of all these variables together creates variation spatially across in service turbine blades. Lattice strains for the axial and radial directions were resolved for the YSZ top coat layer and the internal thermally grown oxide scale. The findings revealed that during sufficiently high axial loading the strain condition for both the thermally grown oxide and top coat layers may be reversed in direction, and demonstrated how the internal flow and applied mechanical loading produce opposing effects while showing the magnitude of each variable. This reversal of the strain direction is known to contribute to the failure mechanics in the system. This discovery shows that with increased internal cooling to critical zones that experience higher mechanical loads, it is possible to tune the response of the system and prevent the reversal from compressive to tensile strains (in the axial direction). The impact of the results has the potential to be used in design for enhanced durability of the multi-layer coatings.Ceramic matrix composites are identified to comprise the next generation of turbine blades and high temperature parts. All oxide ceramic matrix composites were investigated for the influence of micro-structure variations and processing on the mechanics of the system. Isolation techniques of the all alumina composite by means of synchrotron diffraction and tomography presented a novel non-destructive method for evaluating the constituent's properties and evolution. The study successfully revealed how variations in grain size and elastic modulus result in a complex strain states. Further tomographical analysis identified system mechanics influenced by porosity and processing effects. CMCs with an yttria based environmental barrier coating were investigated for comparison to uncoated parts to further capture the in service condition, and revealed considerations for how to improve the durability of the inter-laminar strength of environmental barrier coatings interface. Together the research conducted has contributed to the high temperature aerospace materials' community, and the experimental work taken strides to provide validation and support future numerical simulation for developing better lifetime modeling. Resulting high temperature mechanics' information has the potential to enhance the design of aerospace components for substantial increases in durability. The outcomes from this work can be leveraged to continue advancing material characterization for aerospace material systems under complex and extreme environments.
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Date Issued: 2016
Identifier: CFE0006836, ucf:51794
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006836

Title: Continuous Oscillation: Vibrational Effects and Acceptable Frequency Ranges of Small Bore Piping in Field Applications.
Creator: Kasprzyk, Marie, Kauffman, Jeffrey L., Bai, Yuanli, Gordon, Ali, University of Central Florida
Abstract / Description: In turbomachinery, a common failure mode is cracking of welds at the equipment and piping connection point. Each incidence of these cracks causes a forced shutdown to perform repairs that cost millions of dollars. This type of failure is predominately seen in small bore piping, which has a nominal diameter of 2 inches and smaller. This thesis addresses the failure prediction analysis of small bore piping, specifically in turbomachinery applications. Performing failure analysis to predict the...
Show moreIn turbomachinery, a common failure mode is cracking of welds at the equipment and piping connection point. Each incidence of these cracks causes a forced shutdown to perform repairs that cost millions of dollars. This type of failure is predominately seen in small bore piping, which has a nominal diameter of 2 inches and smaller. This thesis addresses the failure prediction analysis of small bore piping, specifically in turbomachinery applications. Performing failure analysis to predict the potential cracking of welds will allow for replacement of the piping during a planned shutdown which in the long term saves money due to costs such as expediting materials, overtime pay, and extended downtime. This analysis uses real-world applications of a chemical plant in Louisiana. The piping analyzed was connected to centrifugal compressors. The data used from these pieces of equipment included the material of construction, the piping schedule, lengths, nominal diameter, and running speeds. Based on research that shows welding the connection point with a full penetration weld greatly increases the life expectancy of the connection, this thesis uses full penetration welds in the analysis. The piping was analyzed using the software ANSYS to perform a finite element analysis, specifically examining the stress due to the induced harmonic forces. It is a common fact that having fewer supports on a vibrating pipe induces greater stresses and strains on the weld connections. Supports installed 12" from the equipment only show one to two ranges of frequencies to avoid compared to the longer piping which has four to five ranges of unacceptable frequencies. Tables are developed to relay acceptable frequencies based on observed stresses of the welds in the model.
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Date Issued: 2017
Identifier: CFE0006749, ucf:51862
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006749

Title: Development and Implementation of a Streamlined Process for the Creation and Mechanization of Negative Poisson's Ratio Meso-Scale Patterns.
Creator: Shuler, Matthew, Gordon, Ali, Kauffman, Jeffrey L., Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be...
Show moreThis thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be developed in order to confer transformative thermomechanical responses to structures where transverse expansion is more desirable than contraction. For example, materials at high temperature. Additionally, patterns that take into account manufacturing limitations, while maintaining the properties characteristically attached to negative Poisson's Ratio materials, are ideal in order to utilize the potential of NPR structures. A novel NPR pattern is developed, numerically analyzed, and optimized via design of experiments. The parameters of the meso-structure are varied, and the bulk response is studied using finite element analysis (FEA). The candidate material for the study is Medium-Density Fiberboard (MDF). This material is relevant to a variety of applications where multiaxial stresses, particularly compressive, lead to mechanical fatigue. Samples are fabricated through a laser cutting process, and a comparison is drawn through the use of experimental means, including traditional tensile loading tests and digital image correlation (DIC). Various attributes of the elasto-plasticity responses of the bulk structure are used as objectives to guide the optimization process.
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Date Issued: 2017
Identifier: CFE0006795, ucf:51830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006795

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: Flutter Stability of Shrouded Turbomachinery Cascades with Nonlinear Frictional Damping.
Creator: Torkaman, Alex, Kauffman, Jeffrey L., Kapat, Jayanta, Raghavan, Seetha, Mackie, Kevin, University of Central Florida
Abstract / Description: Prediction of flutter in shrouded turbomachinery cascades is difficult due to i) coupling of aerodynamic drivers and structural dynamics of the cascade through shrouds, and ii) presence of nonlinear dry friction damping as a result of relative motion between adjacent shrouds. An analytical framework is developed in this dissertation to determine flutter stability of shrouded cascades with consideration of friction damping. This framework is an extension to the well-established energy method,...
Show morePrediction of flutter in shrouded turbomachinery cascades is difficult due to i) coupling of aerodynamic drivers and structural dynamics of the cascade through shrouds, and ii) presence of nonlinear dry friction damping as a result of relative motion between adjacent shrouds. An analytical framework is developed in this dissertation to determine flutter stability of shrouded cascades with consideration of friction damping. This framework is an extension to the well-established energy method, and it includes all contributing factors affecting stability of the cascade such as aerodynamic excitation and the stabilizing effects of dry friction damping caused by nonlinear contact forces between adjacent blades. This framework is developed to address a shortcoming in current analytical methods for flutter assessment in the industry. The influence of dry friction damping is typically not included due to complexity associated with nonlinearity, leading to uncertainty about exact threshold of flutter occurrence. The new analytical framework developed in this dissertation will increase the accuracy of flutter prediction method that is used for design and optimization of gas turbines.A hybrid time-frequency-time domain solution method is developed to solve aeroelastic equations of motion in both fluid and structural domains. Solution steps and their sequencing are optimized for computational efficiency with large scale realistic models and analytical accuracy in determining nonlinear friction force. Information exchange between different domains is used to couple aerodynamic and structural solutions together for a comprehensive and accurate analysis of shrouded cascade flutter problem in presence of nonlinear friction.Example application to a shrouded IGT blade shows that the influence of nonlinear friction damping in flutter suppression of an aerodynamically unstable cascade is significant. Comparison with engine test data shows that at observed vibration amplitudes in operation friction damping is sufficient to overcome aerodynamic excitation of this aerodynamically unstable cascade, resulting in overall cascade stability.
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Date Issued: 2018
Identifier: CFE0007379, ucf:52077
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007379

Title: Seismic Response of Moment Resisting Frames Coupled with Rocking Walls.
Creator: Aghagholizadeh, Mehrdad, Makris, Nicos, Catbas, Necati, Mackie, Kevin, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: This study investigates the inelastic response of yielding structures coupled with rocking walls. This topic is of major significance in the design of tall moment-resisting buildings, since during recent major earthquakes several tall, moment-resisting frames that had been designed in an accordance to the existing seismic code provisions, exhibited a weak-story failure. Utilization of this structural system can help reducing maximum story drifts, prevents weak story failure and minimize...
Show moreThis study investigates the inelastic response of yielding structures coupled with rocking walls. This topic is of major significance in the design of tall moment-resisting buildings, since during recent major earthquakes several tall, moment-resisting frames that had been designed in an accordance to the existing seismic code provisions, exhibited a weak-story failure. Utilization of this structural system can help reducing maximum story drifts, prevents weak story failure and minimize residual deformation of the structure. This study first examines different configurations of both stepping rocking walls and pinned rocking walls that have been reported in the literature.Next, effect of additional vertical tendons or vertical damping devices in maximum response of the system is investigated. This research first derives the nonlinear equations of motion of a yieldingoscillator coupled with a rocking wall and the dependability of the one-degree of freedom idealization is validated against the nonlinear time-history response analysis of a 9-story moment-resisting frame coupled with a rocking wall. This research finally concludes that, stepping wall suppresses peak and permanent displacements, with the heavier wall being most effective. In contrast, the pinned rocking wall increases in general the peak inelastic displacements and the permanent displacements. While, the coupling of weak building frames with rocking walls is an efficient strategy that controls inelastic deformations by enforcing a uniform interstory-drift distribution, therefore, avoiding mid-story failures, the study shows that even for medium-rise buildings the effect of vertical tendons on the inelastic structural response is marginal, except for increasing the vertical reactions at the pivoting points of the rocking wall. Additionally, The SDOF idealization presented in this study compares satisfactory with finite-element analysis of a 9-story steel SAC building coupled with a stepping rocking wall; therefore, the SDOF idealization can be used with confidence for preliminary analysis and design.
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Date Issued: 2018
Identifier: CFE0007301, ucf:52157
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007301

Title: Load Estimation, Structural Identification and Human Comfort Assessment of Flexible Structures.
Creator: Celik, Ozan, Catbas, Necati, Yun, Hae-Bum, Makris, Nicos, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Stadiums, pedestrian bridges, dance floors, and concert halls are distinct from other civil engineering structures due to several challenges in their design and dynamic behavior. These challenges originate from the flexible inherent nature of these structures coupled with human interactions in the form of loading. The investigations in past literature on this topic clearly state that the design of flexible structures can be improved with better load modeling strategies acquired with reliable...
Show moreStadiums, pedestrian bridges, dance floors, and concert halls are distinct from other civil engineering structures due to several challenges in their design and dynamic behavior. These challenges originate from the flexible inherent nature of these structures coupled with human interactions in the form of loading. The investigations in past literature on this topic clearly state that the design of flexible structures can be improved with better load modeling strategies acquired with reliable load quantification, a deeper understanding of structural response, generation of simple and efficient human-structure interaction models and new measurement and assessment criteria for acceptable vibration levels. In contribution to these possible improvements, this dissertation taps into three specific areas: the load quantification of lively individuals or crowds, the structural identification under non-stationary and narrowband disturbances and the measurement of excessive vibration levels for human comfort. For load quantification, a computer vision based approach capable of tracking both individual and crowd motion is used. For structural identification, a noise-assisted Multivariate Empirical Mode Decomposition (MEMD) algorithm is incorporated into the operational modal analysis. The measurement of excessive vibration levels and the assessment of human comfort are accomplished through computer vision based human and object tracking, which provides a more convenient means for measurement and computation. All the proposed methods are tested in the laboratory environment utilizing a grandstand simulator and in the field on a pedestrian bridge and on a football stadium. Findings and interpretations from the experimental results are presented. The dissertation is concluded by highlighting the critical findings and the possible future work that may be conducted.
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Date Issued: 2017
Identifier: CFE0006863, ucf:51752
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006863

Title: Structure-preserving finite difference methods for linearly damped differential equations.
Creator: Bhatt, Ashish, Moore, Brian, Choudhury, Sudipto, Gurel, Basak, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Differential equations (DEs) model a variety of physical phenomena in science and engineering. Many physical phenomena involve conservative or dissipative forces, which manifest themselves as qualitative properties of DEs that govern these phenomena. Since only a few and simplistic models are known to have exact solutions, approximate solution techniques, such as numerical integration, are used to reveal important insights about solution behavior and properties of these models. Numerical...
Show moreDifferential equations (DEs) model a variety of physical phenomena in science and engineering. Many physical phenomena involve conservative or dissipative forces, which manifest themselves as qualitative properties of DEs that govern these phenomena. Since only a few and simplistic models are known to have exact solutions, approximate solution techniques, such as numerical integration, are used to reveal important insights about solution behavior and properties of these models. Numerical integrators generally result in undesirable quantitative and qualitative errors . Standard numerical integrators aim to reduce quantitative errors, whereas geometric (numerical) integrators aim to reduce or eliminate qualitative errors, as well, in order to improve the accuracy of numerical solutions. It is now widely recognized that geometric (or structure-preserving) integrators are advantageous compared to non-geometric integrators for DEs, especially for long time integration.Geometric integrators for conservative DEs have been proposed, analyzed, and investigated extensively in the literature. The motif of this thesis is to extend the idea of structure preservation to linearly damped DEs. More specifically, we develop, analyze, and implement geometric integrators for linearly damped ordinary and partial differential equations (ODEs and PDEs) that possess conformal invariants, which are qualitative properties that decay exponentially along any solution of the DE as the system evolves over time. In particular, we derive restrictions on the coefficient functions of exponential Runge-Kutta (ERK) numerical methods for preservation of certain conformal invariants of linearly damped ODEs. An important class of these methods is shown to preserve the damping rate of solutions of damped linear ODEs. Linearly stability and order of accuracy for some specific cases of ERK methods are investigated. Geometric integrators for PDEs are designed using structure-preserving ERK methods in space, time, or both. These integrators for PDEs are also shown to preserve additional structure in certain special cases. Numerical experiments illustrate higher order accuracy and structure preservation properties of various ERK based methods, demonstrating clear advantages over non-structure-preserving methods, as well as usefulness for solving a wide range of DEs.
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Date Issued: 2016
Identifier: CFE0006832, ucf:51763
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006832

Title: Chaotification as a Means of Broadband Vibration Energy Harvesting with Piezoelectric Materials.
Creator: Geiyer, Daniel, Kauffman, Jeffrey L., Das, Tuhin, Moslehy, Faissal, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description: Computing advances and component miniaturization in circuits coupled with stagnating battery technology have fueled growth in the development of high efficiency energy harvesters. Vibration-to-electricity energy harvesting techniques have been investigated extensively for use in sensors embedded in structures or in hard-to-reach locations like turbomachinery, surgical implants, and GPS animal trackers. Piezoelectric materials are commonly used in harvesters as they possess the ability to...
Show moreComputing advances and component miniaturization in circuits coupled with stagnating battery technology have fueled growth in the development of high efficiency energy harvesters. Vibration-to-electricity energy harvesting techniques have been investigated extensively for use in sensors embedded in structures or in hard-to-reach locations like turbomachinery, surgical implants, and GPS animal trackers. Piezoelectric materials are commonly used in harvesters as they possess the ability to convert strain energy directly into electrical energy and can work concurrently as actuators for damping applications. The prototypical harvesting system places two piezoelectric patches on both sides of the location of maximum strain on a cantilever beam. While efficient around resonance, performance drops dramatically should the driving frequency drift away from the beam's fundamental frequency. To date, researchers have worked to improve harvesting capability by modifying material properties, using alternative geometries, creating more efficient harvesting circuits, and inducing nonlinearities. These techniques have partially mitigated the resonance excitation dependence for vibration-based harvesting, but much work remains.In this dissertation, an induced nonlinearity destabilizes a central equilibrium point, resulting in a bistable potential function governing the cantilever beam system. Depending on the environment, multiple stable solutions are possible and can coexist. Typically, researchers neglect chaos and assume that with enough energy in the ambient environment, large displacement trajectories can exist uniquely. When subjected to disturbances a system can fall to coexistent lower energy solutions including aperiodic, chaotic oscillations. Treating chaotic motion as a desirable behavior of the system allows frequency content away from resonance to produce motion about a theoretically infinite number of unstable periodic orbits that can be stabilized through control. The extreme sensitivity to initial conditions exhibited by chaotic systems paired with a pole placement control strategy pioneered by Ott, Grebogi, and Yorke permits small perturbations to an accessible system parameter to alter the system response dramatically. Periodic perturbation of the system trajectories in the vicinity of isolated unstable orbit points can therefore stabilize low-energy chaotic oscillations onto larger trajectory orbits more suitable for energy harvesting.The periodic perturbation-based control method rids the need of a system model. It only requires discrete displacement, velocity, or voltage time series data of the chaotic system driven by harmonic excitation. While the analysis techniques are not fundamentally limited to harmonic excitation, this condition permits the use of standard discrete mapping techniques to isolate periodic orbits of interest. Local linear model fits characterize the orbit and admit the necessary control perturbation calculations from the time series data.This work discusses the feasibility of such a method for vibration energy harvesting, displays stable solutions under various control algorithms, and implements a hybrid bench-top experiment using MATLAB and LabVIEW FPGA. In conclusion, this work discusses the limitations for wide-scale use and addresses areas of further work; both with respect to chaotic energy harvesting and parallel advances required within the field as a whole.
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Date Issued: 2017
Identifier: CFE0006878, ucf:51718
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006878

Title: Timoshenko Beam Viscous Damping Model for Spacecraft Cabling Dynamics.
Creator: McPherson, Brandi, Kauffman, Jeffrey L., Bai, Yuanli, Song, Sang-Eun, University of Central Florida
Abstract / Description: With the increasing data handling and power requirements of today's spacecraft, accurately modeling the effects of cabling on spacecraft structural dynamics has become an increasingly important part of the design process. During testing, spacecraft cabling produces a damping effect on the system dynamics; however, current models often overpredict this response in higher frequency modes and produce unrealistic damping values. Previous models incorporated structural and viscous damping terms...
Show moreWith the increasing data handling and power requirements of today's spacecraft, accurately modeling the effects of cabling on spacecraft structural dynamics has become an increasingly important part of the design process. During testing, spacecraft cabling produces a damping effect on the system dynamics; however, current models often overpredict this response in higher frequency modes and produce unrealistic damping values. Previous models incorporated structural and viscous damping terms into Euler-Bernoulli and shear beams; this thesis presents a viscous damping model for Timoshenko beams that can accurately capture the effects of both spacecraft wiring and harnesses during the design phase. Damping in built-up structures shows a weak frequency-dependence; therefore, it is of interest to develop a combination of damping terms and coefficients that provide approximately frequency-independent modal damping. Where previous work included a rotation-based damping term to Euler-Bernoulli beam equations to produce frequency-independent damping, this thesis includes higher-order derivative damping terms to characterize their motion. Because Timoshenko beams account for the effects of both transverse shear and rotary inertia, it is of interest to characterize the damping coefficients using these parameters. Finally, deformed beam shapes were studied to further characterize each damping term as a physical dissipative mechanism.
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Date Issued: 2017
Identifier: CFE0006764, ucf:51851
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006764

Title: Bio-Inspired Visual Servo Control of a Picking Mechanism in an Agricultural Ground Robot.
Creator: Defterli, Sinem, Xu, Yunjun, Kauffman, Jeffrey L., Lin, Kuo-Chi, Song, Sang-Eun, Zheng, Qipeng, University of Central Florida
Abstract / Description: For a recently constructed disease detection agricultural ground robot, the segregation of unhealthy leaves fromstrawberry plants is a major task of the robot's manipulation subsystem in field operations. In this dissertation, the motion planning of a custom-designedpicking mechanism in the ground robot's subsystem is studied in two sections. First, a set of analytical, suboptimal semi-analyticaland numerical algorithms are studied to solve the inverse kinematics problem of the handling...
Show moreFor a recently constructed disease detection agricultural ground robot, the segregation of unhealthy leaves fromstrawberry plants is a major task of the robot's manipulation subsystem in field operations. In this dissertation, the motion planning of a custom-designedpicking mechanism in the ground robot's subsystem is studied in two sections. First, a set of analytical, suboptimal semi-analyticaland numerical algorithms are studied to solve the inverse kinematics problem of the handling mechanism in firmcircumstances. These premeditated approaches are built on the computation of the joint variables by an identified 3Dposition data of the target leaf only. The outcomes of the three solution algorithms are evaluated in terms of the performanceindexes of energy change and the CPU time cost. The resultant postures of the mechanism for different target pointlocations are observed both in simulations and the hardware experiments with each IK solution. Secondly, after the manipulation task of the mechanism via the proposed inverse kinematicalgorithms is performed, some compensation may be needed due to the sudden and unpredicted deviation of the targetposition under field conditions.For the purpose of finding optimal joint values under certain constraints, a trajectory optimization problem in image-based visual servoing method via the camera-in-handconfiguration is initiated when the end-effector is in the close proximity of the target leaf. In this part of the study, a bio-inspired trajectory optimization problem in image-basedvisual servoing method is constructed based on the mathematical model derived from the prey-predatorrelationships in nature. In this biological phenomenon, the predator constructs its path in a certain subspace whilecatching the prey. When this motion strategy is applied to trajectory optimization problems, it causes a significantreduce in the computation cost since it finds the optimum solution in a certain manifold. The performance of the introducedbio-inspired trajectory optimization in visual servoing is validated with the hardware experiments both in laboratory settings and in fieldconditions.
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Date Issued: 2018
Identifier: CFE0007170, ucf:52247
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007170

Turbomachinery (2)	+ -
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1 inch diameter (1)	+ -
2 inch diameter (1)	+ -
20 (1)	+ -

350 Hz (1)	+ -
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Analysis of manipulators (1)	+ -
Autonomous ground vehicle (1)	+ -
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Bio-inspired motion strategies (1)	+ -
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Carbon Nanomaterials (1)	+ -
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Delay coordinate embedding (1)	+ -
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Earthquake Engineering (1)	+ -
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Kauffman, Jeffrey L. (17)	+ -
University of Central Florida (17)	+ -
Das, Tuhin (4)	+ -
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