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 Title
 A study of Compressive Sensing for application to Structural Health Monitoring.
 Creator

Ganesan, Vaahini, Das, Tuhin, Kauffman, Jeffrey, Raghavan, Seetha, University of Central Florida
 Abstract / Description

One of the key areas that have attracted attention in the construction industry today is Structural Health Monitoring, more commonly known as SHM. It is a concept developed to monitor the quality and longevity of various engineering structures. The incorporation of such a system would help to continuously track health of the structure, indicate the occurrence/presence of any damage in real time and give us an idea of the number of useful years for the same. Being a recently conceived idea,...
Show moreOne of the key areas that have attracted attention in the construction industry today is Structural Health Monitoring, more commonly known as SHM. It is a concept developed to monitor the quality and longevity of various engineering structures. The incorporation of such a system would help to continuously track health of the structure, indicate the occurrence/presence of any damage in real time and give us an idea of the number of useful years for the same. Being a recently conceived idea, the state of the art technique in the field is straight forward  populating a given structure with sensors and extracting information from them. In this regard, instrumenting with too many sensors may be inefficient as this could lead to superfluous data that is expensive to capture and process.This research aims to explore an alternate SHM technique that optimizes the data acquisition process by eliminating the amount of redundant data that is sensed and uses this sufficient data to detect and locate the fault present in the structure. Efficient data acquisition requires a mechanism that senses just the necessary amount of data for detection and location of fault. For this reason Compressive Sensing (CS) is explored as a plausible idea. CS claims that signals can be reconstructed from what was previously believed to be incomplete information by Shannon's theorem, taking only a small amount of random and linear non  adaptive measurements. As responses of many physical systems contain a finite basis, CS exploits this feature and determines the sparse solution instead of the traditional least  squares type solution. As a first step, CS is demonstrated by successfully recovering the frequency components of a simple sinusoid. Next, the question of how CS compares with the conventional Fourier transform is analyzed. For this, recovery of temporal frequencies and signal reconstruction is performed using the same number of samples for both the approaches and the errors are compared. On the other hand, the FT error is gradually minimized to match that of CS by increasing the number of regularly placed samples. Once the advantages are established, feasibility of using CS to detect damage in a single degree of freedom system is tested under unforced and forced conditions. In the former scenario, damage is indicated when there is a change in natural frequency of vibration of the system after an impact. In the latter, the system is excited harmonically and damage is detected by a change in amplitude of the system's vibration. As systems in real world applications are predominantly multiDOF, CS is tested on a 2DOF system excited with a harmonic forcing. Here again, damage detection is achieved by observing the change in the amplitude of vibration of the system. In order to employ CS for detecting either a change in frequency or amplitude of vibration of a structure subjected to realistic forcing conditions, it would be prudent to explore the reconstruction of a signal which contains multiple frequencies. This is accomplished using CS on a chirp signal.Damage detection is clearly a spatiotemporal problem. Hence it is important to additionally explore the extension of CS to spatial reconstruction. For this reason, mode shape reconstruction of a beam with standard boundary conditions is performed and validated with standard/analytical results from literature. As the final step, the operation deflection shapes (ODS) are reconstructed for a simply supported beam using CS to establish that it is indeed a plausible approach for a less expensive SHM. While experimenting with the idea of spatiotemporal domain, the mode shape as well as the ODS of the given beam are examined under two conditions  undamaged and damaged. Damage in the beam is simulated as a decrease in the stiffness coefficient over a certain number of elements. Although the range of modes to be examined heavily depends on the structure in question, literature suggests that for most practical applications, lower modes are more dominant in indicating damage. For ODS on the other hand, damage is indicated by observing the shift in the recovered spatial frequencies and it is confirmed by the reconstructed response.
Show less  Date Issued
 2014
 Identifier
 CFE0005334, ucf:50520
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005334
 Title
 Energy Harvesting toward the Vibration Reduction of Turbomachinery Blades via Resonance Frequency Detuning.
 Creator

Hynds, Taylor, Kauffman, Jeffrey, Das, Tuhin, Raghavan, Seetha, University of Central Florida
 Abstract / Description

Piezoelectricbased energy harvesting devices provide an attractive approach to powering remote devices as ambient mechanical energy from vibrations is converted to electrical energy. These devices have numerous potential applications, including actuation, sensing, structural health monitoring, and vibration control  the latter of which is of particular interest here. This work seeks to develop an understanding of energy harvesting behavior within the framework of a semiactive technique...
Show morePiezoelectricbased energy harvesting devices provide an attractive approach to powering remote devices as ambient mechanical energy from vibrations is converted to electrical energy. These devices have numerous potential applications, including actuation, sensing, structural health monitoring, and vibration control  the latter of which is of particular interest here. This work seeks to develop an understanding of energy harvesting behavior within the framework of a semiactive technique for reducing turbomachinery blade vibrations, namely resonance frequency detuning. In contrast with the bulk of energy harvesting research, this effort is not focused on maximizing the power output of the system, but rather providing the low power levels required by resonance frequency detuning. The demands of this technique dictate that harvesting conditions will be far from optimal, requiring that many common assumptions in conventional energy harvesting research be relaxed.Resonance frequency detuning has been proposed as a result of recent advances in turbomachinery blade design that have, while improving their overall efficiency, led to significantly reduced damping and thus large vibratory stresses. This technique uses piezoelectric materials to control the stiffness, and thus resonance frequency, of a blade as the excitation frequency sweeps through resonance. By detuning a structure's resonance frequency from that of the excitation, the overall peak response can be reduced, delaying high cycle fatigue and extending the lifetime of a blade. Additional benefits include reduced weight, drag, and noise levels as reduced vibratory stresses allow for increasingly light blade construction.As resonance frequency detuning is most effective when the stiffness states are well separated, it is necessary to harvested at nominally open and shortcircuit states, corresponding to the largest separation in stiffness states. This presents a problem from a harvesting standpoint however, as open and shortcircuit correspond to zero charge displacement and zero voltage, respectively, and thus there is no energy flow. It is, then, desirable to operate as near these conditions as possible while still harvesting sufficient energy to provide the power for stateswitching. In this research a metric is developed to study the relationship between harvested power and structural stiffness, and a key result is that appreciable energy can be harvested far from the usual optimal conditions in a typical energy harvesting approach. Indeed, sufficient energy is available to power the onblade control while essentially maintaining the desired stiffness states for detuning. Furthermore, it is shown that the optimal switch in the control law for resonance frequency detuning may be triggered by a threshold harvested power, requiring minimal onblade processing. This is an attractive idea for implementing a vibration control system onblade, as size limitations encourage removing the need for additional sensing and signal processing hardware.
Show less  Date Issued
 2015
 Identifier
 CFE0005811, ucf:50039
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005811
 Title
 Decentralized Power Management in Microgrids.
 Creator

Bhattacharjee, Amit, Das, Tuhin, Simaan, Marwan, Kassab, Alain, University of Central Florida
 Abstract / Description

A large number of power sources, operational in a microgrid, optimum power sharing andaccordingly controlling the power sources along with scheduling loads are the biggest challenges in modern power system. In the era of smart grid, the solution is certainly not simple paralleling. Hence it is required to develop a control scheme that delivers the overall power requirements while also adhering to the power limitations of each source. As the penetration of distributed generators increase and...
Show moreA large number of power sources, operational in a microgrid, optimum power sharing andaccordingly controlling the power sources along with scheduling loads are the biggest challenges in modern power system. In the era of smart grid, the solution is certainly not simple paralleling. Hence it is required to develop a control scheme that delivers the overall power requirements while also adhering to the power limitations of each source. As the penetration of distributed generators increase and are diversified, the choice of decentralized control becomes preferable. In this work, a decentralized control framework is conceived. The primary approach is taken where a small hybrid system is investigated and decentralized control schemes were developed and subsequently tested in a hardware in the loop in conjunction with the hybrid power system setup developed at the laboratory. The control design approach is based on the energy conservation principle. However, considering the vastness ofthe real power network and its complexity of operation along with the growing demand ofsmarter grid operations, called for a revamp in the control framework design. Hence, in thelater phase of this work, a novel framework is developed based on the coupled dynamicalsystem theory, where each control node corresponds to one distributed generator connectedto the microgrid. The coupling topology and coupling strengths of individual nodes aredesigned to be adjustable. The layer is modeled as a set of coupled differential equationsof preassigned order. The control scheme adjusts the coupling weights so that steady stateconstraints are met at the system level, while allowing flexibility to explore the solutionspace. Additionally, the approach guarantees stable equilibria during power redistribution.The theoretical development is verified using simulations in matlab simulink environment.
Show less  Date Issued
 2014
 Identifier
 CFE0005465, ucf:50386
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005465
 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 multiagent 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 multiagent 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.
Show less  Date Issued
 2013
 Identifier
 CFE0004857, ucf:49683
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0004857
 Title
 A LabScale 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 tetheredairfoil 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 labscale experimental setup was developed as part of this thesis. The setup, consisting of a flappingblade 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.
Show less  Date Issued
 2014
 Identifier
 CFE0005239, ucf:50593
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005239
 Title
 An Introductory Study of The Dynamics of Autorotation for Wind Energy Harvesting.
 Creator

Salih, Bilal, Das, Tuhin, Kassab, Alain, Kauffman, Jeffrey, University of Central Florida
 Abstract / Description

Wind turbines have been used for decades to harvest wind energy. They are suitable only to work on close to ground, and have several drawbacks that are related to the availability of the wind and the amount of extracted power compared with the cost of construction. On the other hand, there is an abundant wind power that is available at high altitudes. The wind jet streams at high elevations 8 ? 12 kms are pervasive and persistent, and can potentially produce immense wind energy. Even at...
Show moreWind turbines have been used for decades to harvest wind energy. They are suitable only to work on close to ground, and have several drawbacks that are related to the availability of the wind and the amount of extracted power compared with the cost of construction. On the other hand, there is an abundant wind power that is available at high altitudes. The wind jet streams at high elevations 8 ? 12 kms are pervasive and persistent, and can potentially produce immense wind energy. Even at moderate elevations of 4 ? 5 kms, wind power densities are much higher than on ground and more consistent. Consequently, in this thesis research, we investigate the topic of harvesting energy from high altitudes. First, we provide a comprehensive review of two existing theoretical methods that are proposed for airborne wind energy harvesting, the tethered airfoil, and the static autogyro. The latter approach has inherent advantages that warrant further investigation. Autorotation is a wellknown phenomenon where a rotor sustains its angular velocity and maintains significant lift in the presence of strong aerodynamic forces and torques generated by interaction with a strong wind field. Autorotation has been researched in the context of free descent of helicopters but has not been considered for energy harvesting. Existing models have mainly focused on statics analysis. In this research, we propose a simple dynamic model of the Autogyro, with the goal of ultimately realizing an Autorotation Energy System (AES). The focus of our work is to provide a preliminary dynamic analysis of autorotation, which is largely absent in current literature, to explore the possibility of using autorotation for designing a multipurpose system that can simultaneously fly at high altitudes and generate energy from the wind. The proposed preliminary dynamic model is used to generate a simulation platform, which is used to explore the autogyros rudimentary maneuvers. Extensive simulation results are provided to evaluate the dynamic performance of AES. Energy harvesting analyses and results are also presented. It is expected that the results will guide the choice of actuations and control that will be necessary for generating combined autorotation and powered flights that would be net energy generating or energy efficient. The research will be relevant for both tethered and untethered AES and could also be incorporated into multirotor based UAVs such as quadrotors.
Show less  Date Issued
 2014
 Identifier
 CFE0005245, ucf:50597
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005245
 Title
 Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems.
 Creator

Groves, Curtis, Kassab, Alain, Das, Tuhin, Kauffman, Jeffrey, Moore, Brian, University of Central Florida
 Abstract / Description

Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data...
Show moreSpacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data. Quantifying the uncertainty in analytical predictions is imperative to the success of any simulationbased product. The method could provide an alternative to traditional (")validation by test only(") mentality. This method could be extended to other disciplines and has potential to provide uncertainty for any numerical simulation, thus lowering the cost of performing these verifications while increasing the confidence in those predictions.Spacecraft requirements can include a maximum airflow speed to protect delicate instruments during ground processing. Computational Fluid Dynamics can be used to verify these requirements; however, the model must be validated by test data. This research includes the following three objectives and methods. Objective one is develop, model, and perform a Computational Fluid Dynamics analysis of three (3) generic, nonproprietary, environmental control systems and spacecraft configurations. Several commercially available and open source solvers have the capability to model the turbulent, highly threedimensional, incompressible flow regime. The proposed method uses FLUENT, STARCCM+, and OPENFOAM. Objective two is to perform an uncertainty analysis of the Computational Fluid Dynamics model using the methodology found in (")Comprehensive Approach to Verification and Validation of Computational Fluid Dynamics Simulations("). This method requires three separate grids and solutions, which quantify the error bars around Computational Fluid Dynamics predictions. The method accounts for all uncertainty terms from both numerical and input variables. Objective three is to compile a table of uncertainty parameters that could be used to estimate the error in a Computational Fluid Dynamics model of the Environmental Control System /spacecraft system.Previous studies have looked at the uncertainty in a Computational Fluid Dynamics model for a single output variable at a single point, for example the reattachment length of a backward facing step. For the flow regime being analyzed (turbulent, threedimensional, incompressible), the error at a single point can propagate into the solution both via flow physics and numerical methods. Calculating the uncertainty in using Computational Fluid Dynamics to accurately predict airflow speeds around encapsulated spacecraft in is imperative to the success of future missions.
Show less  Date Issued
 2014
 Identifier
 CFE0005174, ucf:50662
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005174
 Title
 Energyoptimal Guidance of an AUV Under Flow Uncertainty and FluidParticle Interaction.
 Creator

De Zoysa Abeysiriwardena, Demuni Singith, Das, Tuhin, Kumar, Ranganathan, Elgohary, Tarek, Behal, Aman, University of Central Florida
 Abstract / Description

The work presented gives an energyoptimal solution to the guidance problem of an AUV. The presented guidance methods are for lower level control of AUV paths, facilitating existing global planning methods to be carried out comparatively more efficiently. The underlying concept is to use the energy of fluid flow fields the AUVs are navigating to extend the duration of missions. This allows gathering of comparatively more data with higher spatiotemporal resolution. The problem is formulated...
Show moreThe work presented gives an energyoptimal solution to the guidance problem of an AUV. The presented guidance methods are for lower level control of AUV paths, facilitating existing global planning methods to be carried out comparatively more efficiently. The underlying concept is to use the energy of fluid flow fields the AUVs are navigating to extend the duration of missions. This allows gathering of comparatively more data with higher spatiotemporal resolution. The problem is formulated for a generalized two dimensional uniform flow field given a fixed final time andfree end states. This allows the AUVs to navigate to certain spatial positions while maintaining the required temporal resolution of each segment of its mission. The simplistic way the problem is posed allows an analytical closed form solution of the EulerLagrange equations. Two dimensional thrust vectors are obtained as optimal control inputs. The control inputs are then incorporated into afeedback structure, allowing the particle to navigate in the presence of disturbance in the flow field. Further, the work also explores the influence of fluidparticle interaction on the control cost and behavior of the particle. The concept of changing the cost weights of the optimal cost formulation in situ has been introduced. Potential applications of the present concept are explored through anobstacle avoidance scenario. The optimal guidance methods are then adapted to nonuniform flow fields with quadratic and discontinuous spatial variation being the primary focus.
Show less  Date Issued
 2018
 Identifier
 CFE0007169, ucf:52282
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0007169
 Title
 Transient CFD analysis of autorotation using hybrid LES and adaptive mesh morphing techniques.
 Creator

Coronado Domenge, Patricia, Das, Tuhin, Kassab, Alain, Kumar, Ranganathan, Leishman, J., Bhattacharya, Aniket, University of Central Florida
 Abstract / Description

LargeEddy Simulation (LES) based turbulence modeling is a developing area of research in FluidStructure Interaction (FSI). There is considerable scope for further scientific research in this field and this dissertation aims to extend it to the study of flowinduced motion. The emphasis of this work is on autorotation, an important category of flowinduced motion that is commonly seen in energy applications such as wind turbines and in aviation applications such as the autogyro. In contrast...
Show moreLargeEddy Simulation (LES) based turbulence modeling is a developing area of research in FluidStructure Interaction (FSI). There is considerable scope for further scientific research in this field and this dissertation aims to extend it to the study of flowinduced motion. The emphasis of this work is on autorotation, an important category of flowinduced motion that is commonly seen in energy applications such as wind turbines and in aviation applications such as the autogyro. In contrast to existing works on FSI that typically assume prescribed motion of structures in a flow field, this research develops LES based FSI studies for largescale flowinduced motions as seen in autorotation. The uniqueness of the formulation and modeling approach lies in the development of a numerically stable computational scheme that incorporates a moving and morphing mesh structure. The method is first demonstrated for the autorotation of a square flat plate and then extended to a rotor structure similar to that of a helicopter.In order to simulate an autorotating square flat plate, a coupled Computational Fluid Dynamics (CFD)  Rigid Body Dynamics (RBD) model is proposed, employing the delayeddetachededdy simulation (DDES) and the Smagorinsky turbulence models to resolve subgridscale stresses (SGS). The plate is allowed to spin freely about its center of mass. Computational results are compared to experimental measurements and Reynolds Average NavierStokes (RANS) simulations found in the literature. When compared to RANS, the results from the LES models provide better predictions of the pressure coefficient. Moreover, LES accurately captures the transient behavior of the plate, and close correspondence is found between the predicted and measured moment coefficients. The qualitative prediction of vortex structures and the quantitative computation of pressure coefficients are in good agreement with experimental results. Hybrid models, such as improved DelayedDetachedEddy Simulation (iDDES), are shown to provide very similar results to those of pure LES. Therefore hybrid models are found to be a good alternative to use for the simulation of FSI in autorotation, saving valuable computational time . The iDDES method combines both RANS and LES, dividing the flow domain into LES far away from a solid wall and RANS near a solid wall, overcoming the computational costs of pure LES.Encouraging results from this effort prompted the extension to a realistic scenario, namely the autorotation of a flappingblade rotor in a prevailing wind field. A coupled CFD  Multi Body Dynamics (MBD) model is developed to study the complex FSI of an autorotating 3blade rotor, similar to that of a helicopter, employing the iDDES turbulence model. In addition to the rotor being allowed to spin freely about its axis, each of the individual blades is free to rotate about hinges at the root. This adds degrees of freedom to the kinematics of the rotor and necessitates localized mesh morphing around the blades to capture the FSI with accuracy. The model is validated against experimental data and shows excellent agreement. The experimental apparatus consists of a flapping blade rotor and a fixture used to mount it at different angles of incidence with respect to the wind field. The rotor is instrumented with a DC motor that is operated in generator mode. The setup is dualpurpose, providing speed measurement using the motor's backemf and regenerative braking by varying the current draw. Overall, the presented research can help obtain accurate values of aerodynamic parameters at a high spatial resolution that would be otherwise difficult to acquire in experiments. Ultimately this approach can be a cost effective means of aerodynamic modeling in applications involving large scale FSI.
Show less  Date Issued
 2016
 Identifier
 CFE0006088, ucf:50952
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006088
 Title
 Stability and Control in Complex Networks of Dynamical Systems.
 Creator

Manaffam, Saeed, Vosoughi, Azadeh, Behal, Aman, Atia, George, Rahnavard, Nazanin, Javidi, Tara, Das, Tuhin, University of Central Florida
 Abstract / Description

Stability analysis of networked dynamical systems has been of interest in many disciplines such as biology and physics and chemistry with applications such as LASER cooling and plasma stability. These large networks are often modeled to have a completely random (Erd\"osR\'enyi) or semirandom (SmallWorld) topologies. The former model is often used due to mathematical tractability while the latter has been shown to be a better model for most real life networks.The recent emergence of cyber...
Show moreStability analysis of networked dynamical systems has been of interest in many disciplines such as biology and physics and chemistry with applications such as LASER cooling and plasma stability. These large networks are often modeled to have a completely random (Erd\"osR\'enyi) or semirandom (SmallWorld) topologies. The former model is often used due to mathematical tractability while the latter has been shown to be a better model for most real life networks.The recent emergence of cyber physical systems, and in particular the smart grid, has given rise to a number of engineering questions regarding the control and optimization of such networks. Some of the these questions are: \emph{How can the stability of a random network be characterized in probabilistic terms? Can the effects of network topology and system dynamics be separated? What does it take to control a large random network? Can decentralized (pinning) control be effective? If not, how large does the control network needs to be? How can decentralized or distributed controllers be designed? How the size of control network would scale with the size of networked system?}Motivated by these questions, we began by studying the probability of stability of synchronization in random networks of oscillators. We developed a stability condition separating the effects of topology and node dynamics and evaluated bounds on the probability of stability for both Erd\"osR\'enyi (ER) and SmallWorld (SW) network topology models. We then turned our attention to the more realistic scenario where the dynamics of the nodes and couplings are mismatched. Utilizing the concept of $\varepsilon$synchronization, we have studied the probability of synchronization and showed that the synchronization error, $\varepsilon$, can be arbitrarily reduced using linear controllers.We have also considered the decentralized approach of pinning control to ensure stability in such complex networks. In the pinning method, decentralized controllers are used to control a fraction of the nodes in the network. This is different from traditional decentralized approaches where all the nodes have their own controllers. While the problem of selecting the minimum number of pinning nodes is known to be NPhard and grows exponentially with the number of nodes in the network we have devised a suboptimal algorithm to select the pinning nodes which converges linearly with network size. We have also analyzed the effectiveness of the pinning approach for the synchronization of oscillators in the networks with fast switching, where the network links disconnect and reconnect quickly relative to the node dynamics.To address the scaling problem in the design of distributed control networks, we have employed a random control network to stabilize a random plant network. Our results show that for an ER plant network, the control network needs to grow linearly with the size of the plant network.
Show less  Date Issued
 2015
 Identifier
 CFE0005834, ucf:50902
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005834
 Title
 ProbabilisticBased Computing Transformation with Reconfigurable Logic Fabrics.
 Creator

Alawad, Mohammed, Lin, Mingjie, DeMara, Ronald, Mikhael, Wasfy, Wang, Jun, Das, Tuhin, University of Central Florida
 Abstract / Description

Effectively tackling the upcoming (")zettabytes(") data explosion requires a huge quantum leapin our computing power and energy efficiency. However, with the Moore's law dwindlingquickly, the physical limits of CMOS technology make it almost intractable to achieve highenergy efficiency if the traditional (")deterministic and precise(") computing model still dominates.Worse, the upcoming data explosion mostly comprises statistics gleaned from uncertain,imperfect realworld environment. As such...
Show moreEffectively tackling the upcoming (")zettabytes(") data explosion requires a huge quantum leapin our computing power and energy efficiency. However, with the Moore's law dwindlingquickly, the physical limits of CMOS technology make it almost intractable to achieve highenergy efficiency if the traditional (")deterministic and precise(") computing model still dominates.Worse, the upcoming data explosion mostly comprises statistics gleaned from uncertain,imperfect realworld environment. As such, the traditional computing means of firstprinciplemodeling or explicit statistical modeling will very likely be ineffective to achieveflexibility, autonomy, and human interaction. The bottom line is clear: given where we areheaded, the fundamental principle of modern computing()deterministic logic circuits canflawlessly emulate propositional logic deduction governed by Boolean algebra()has to bereexamined, and transformative changes in the foundation of modern computing must bemade.This dissertation presents a novel stochasticbased computing methodology. It efficientlyrealizes the algorithmatic computing through the proposed concept of Probabilistic DomainTransform (PDT). The essence of PDT approach is to encode the input signal asthe probability density function, perform stochastic computing operations on the signal inthe probabilistic domain, and decode the output signal by estimating the probability densityfunction of the resulting random samples. The proposed methodology possesses manynotable advantages. Specifically, it uses much simplified circuit units to conduct complexoperations, which leads to highly area and energyefficient designs suitable for parallel processing.Moreover, it is highly faulttolerant because the information to be processed isencoded with a large ensemble of random samples. As such, the local perturbations of itscomputing accuracy will be dissipated globally, thus becoming inconsequential to the final overall results. Finally, the proposed probabilisticbased computing can facilitate buildingscalable precision systems, which provides an elegant way to tradeoff between computingaccuracy and computing performance/hardware efficiency for many realworld applications.To validate the effectiveness of the proposed PDT methodology, two important signal processingapplications, discrete convolution and 2D FIR filtering, are first implemented andbenchmarked against other deterministicbased circuit implementations. Furthermore, alargescale Convolutional Neural Network (CNN), a fundamental algorithmic building blockin many computer vision and artificial intelligence applications that follow the deep learningprinciple, is also implemented with FPGA based on a novel stochasticbased and scalablehardware architecture and circuit design. The key idea is to implement all key componentsof a deep learning CNN, including multidimensional convolution, activation, and poolinglayers, completely in the probabilistic computing domain. The proposed architecture notonly achieves the advantages of stochasticbased computation, but can also solve severalchallenges in conventional CNN, such as complexity, parallelism, and memory storage.Overall, being highly scalable and energy efficient, the proposed PDTbased architecture iswellsuited for a modular vision engine with the goal of performing realtime detection, recognitionand segmentation of megapixel images, especially those perceptionbased computingtasks that are inherently faulttolerant.
Show less  Date Issued
 2016
 Identifier
 CFE0006828, ucf:51768
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006828
 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. Vibrationtoelectricity energy harvesting techniques have been investigated extensively for use in sensors embedded in structures or in hardtoreach 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. Vibrationtoelectricity energy harvesting techniques have been investigated extensively for use in sensors embedded in structures or in hardtoreach 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 vibrationbased 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 lowenergy chaotic oscillations onto larger trajectory orbits more suitable for energy harvesting.The periodic perturbationbased 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 benchtop experiment using MATLAB and LabVIEW FPGA. In conclusion, this work discusses the limitations for widescale use and addresses areas of further work; both with respect to chaotic energy harvesting and parallel advances required within the field as a whole.
Show less  Date Issued
 2017
 Identifier
 CFE0006878, ucf:51718
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006878
 Title
 Large Eddy Simulations with a Tabulated Conditional Moment Closure Moment Closure Model for Turbulent Premixed Combustion with Heat Loss.
 Creator

Velez, Carlos, Vasu Sumathi, Subith, Martin, Scott, Kassab, Alain, Das, Tuhin, University of Central Florida
 Abstract / Description

The Tabulated Premixed Conditional Moment Closure (TPCMC) method has been shown to provide the capability to predict turbulent, premixed methane flames with detailed chemistry and reasonable run times in a RANS/URANS adiabatic environment. Here the premixed TPCMC method is extended in a Large Eddy Simulation (LES) framework for nonadiabatic premixed flames, allowing heat loss to occur in the mixture before, during and after combustion. It is proposed that the LES framework is a more...
Show moreThe Tabulated Premixed Conditional Moment Closure (TPCMC) method has been shown to provide the capability to predict turbulent, premixed methane flames with detailed chemistry and reasonable run times in a RANS/URANS adiabatic environment. Here the premixed TPCMC method is extended in a Large Eddy Simulation (LES) framework for nonadiabatic premixed flames, allowing heat loss to occur in the mixture before, during and after combustion. It is proposed that the LES framework is a more suitable representation for both chemical and turbulent scales in premixed combustion. By resolving the high energy turbulent scales and modeling the small scale turbulence, it is expected that the resolution of the turbulence and transient effects are better captured in a LES framework leading to better predictions of the mixing rate and consequently the reaction rate, which is the main focus and source of error in combustion modeling. The LES TPCMC model is implemented using the open source CFD software OpenFOAM for its open access to C++ source code and large library of turbulence and thermophysical models. The proposed model validated with PIV and Raman measurements of a turbulent, enclosed reacting flame of a single jet and backward facing step geometry. The DLR data sets provide both unity (E.g.Methane) and nonunity (E.g. Hydrogen) Lewis number fuels, allowing for the proposed numerical model to be validated against both unity and nonunity Lewis # flames. Velocity, temperature and major/minor species are compared to the experimental data. Once validated, this model is intended to be useful for designing lean premixed combustors for gas turbines which operate primarily in the corrugated premixed combustion regime, where chemical and turbulent time scales are of the same order requiring adequate models for their interaction.LES results match the experimental data better than the Reynolds Averaged NavierStokes (RANS/URANS) solution and is able to better resolve the transient features of the flame with an increase in run time of only 50 %, when compared to URANS.
Show less  Date Issued
 2015
 Identifier
 CFE0006234, ucf:51058
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006234
 Title
 Six Degree of Freedom Dynamic Modeling of a High Altitude Airship and Its Trajectory Optimization Using Direct Collocation Method.
 Creator

PierreLouis, Pradens, Xu, Yunjun, Lin, KuoChi, Das, Tuhin, University of Central Florida
 Abstract / Description

The long duration airborne feature of airships makes them an attractive solution for many military and civil applications such as longendurance surveillance, reconnaissance, environment monitoring, communication utilities, and energy harvesting. To achieve a minimum energy periodic motion in the air, an optimal trajectory problem is solved using basic direct collocation methods. In the direct approach, the optimal control problem is converted into a nonlinear programming (NLP). Pseudo...
Show moreThe long duration airborne feature of airships makes them an attractive solution for many military and civil applications such as longendurance surveillance, reconnaissance, environment monitoring, communication utilities, and energy harvesting. To achieve a minimum energy periodic motion in the air, an optimal trajectory problem is solved using basic direct collocation methods. In the direct approach, the optimal control problem is converted into a nonlinear programming (NLP). Pseudoinverse and several discretization methods such as Trapezoidal and HermiteSimpson are used to obtain a numerical approximated solution by discretizing the states and controls into a set of equal nodes. These nodes are approximated by a cubic polynomial function which makes it easier for the optimization to converge while ensuring the problem constraints and the equations of motion are satisfied at the collocation points for a defined trajectory. In this study, direct collocation method provides the ability to obtain an approximation solution of the minimum energy expenditure of a very complex dynamic problem using Matlab fmincon optimization algorithm without using Himiltonian function with Lagrange multipliers. The minimal energy trajectory of the airship is discussed and results are presented.
Show less  Date Issued
 2017
 Identifier
 CFE0006779, ucf:51822
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0006779
 Title
 Planning and Control of Swarm Motion as Continua.
 Creator

Rastgoftar, Hossein, Jayasuriya, Suhada, Das, Tuhin, Xu, Chengying, Qu, Zhihua, Simaan, Marwan, University of Central Florida
 Abstract / Description

In this thesis, new algorithms for formation control of multi agent systems (MAS) based on continuum mechanics principles will be investigated. For this purpose agents of the MAS are treated as particles in a continuum, evolving in an nD space, whose desired configuration is required to satisfy an admissible deformation function. Considered is a specific class of mappings that is called homogenous where the Jacobian of the mapping is only a function of time and is not spatially varying. The...
Show moreIn this thesis, new algorithms for formation control of multi agent systems (MAS) based on continuum mechanics principles will be investigated. For this purpose agents of the MAS are treated as particles in a continuum, evolving in an nD space, whose desired configuration is required to satisfy an admissible deformation function. Considered is a specific class of mappings that is called homogenous where the Jacobian of the mapping is only a function of time and is not spatially varying. The primary objectives of this thesis are to develop the necessary theory and its validation via simulation on a mobileagent based swarm test bed that includes two primary tasks: 1) homogenous transformation of MAS and 2) deployment of a random distribution of agents on to a desired configuration. Developed will be a framework based on homogenous transformations for the evolution of a MAS in an nD space (n=1, 2, and 3), under two scenarios: 1) no interagent communication (predefined motion plan); and 2) local interagent communication. Additionally, homogenous transformations based on communication protocols will be used to deploy an arbitrary distribution of a MAS on to a desired curve. Homogenous transformation with no communication: A homogenous transformation of a MAS, evolving in an R^n space, under zero inter agent communication is first considered. Here the homogenous mapping, is characterized by an n x n Jacobian matrix Q(t) and an n x 1 rigid body displacement vector D(t), that are based on positions of n+1 agents of the MAS, called leader agents. The designed Jacobian Q(t) and rigid body displacement vector D(t) are passed onto rest of the agents of the MAS, called followers, who will then use that information to update their positions under a predefined motion plan. Consequently, the motion of MAS will evolve as a homogenous transformation of the initial configuration without explicit communication among agents. Homogenous Transformation under Local Communication: We develop a framework for homogenous transformation of MAS, evolving in R^n, under a local inter agent communication topology. Here we assume that some agents are the leaders, that are transformed homogenously in an nD space. In addition, every follower agent of the MAS communicates with some local agents to update its position, in order to grasp the homogenous mapping that is prescribed by the leader agents. We show that some distance ratios that are assigned based on initial formation, if preserved, lead to asymptotic convergence of the initial formation to a final formation under a homogenous mapping.Deployment of a Random Distribution on a Desired Manifold: Deployment of agents of a MAS, moving in a plane, on to a desired curve, is a task that is considered as an application of the proposed approach. In particular, a 2D MAS evolution problem is considered as two 1D MAS evolution problems, where x or y coordinates of the position of all agents are modeled as points confined to move on a straight line. Then, for every coordinate of MAS evolution, bulk motion is controlled by two agents considered leaders that move independently, with rest of the follower agents motions evolving through each follower agent communicating with two adjacent agents.
Show less  Date Issued
 2013
 Identifier
 CFE0004915, ucf:49640
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0004915
 Title
 Differential Games for MultiAgent Systems under Distributed Information.
 Creator

Lin, Wei, Qu, Zhihua, Simaan, Marwan, Haralambous, Michael, Das, Tuhin, Yong, Jiongmin, University of Central Florida
 Abstract / Description

In this dissertation, we consider differential games for multiagent systems under distributed information where every agent is only able to acquire information about the others according to a directed information graph of local communication/sensor networks. Such games arise naturally from many applications including mobile robot coordination, power system optimization, multiplayer pursuitevasion games, etc. Since the admissible strategy of each agent has to conform to the information...
Show moreIn this dissertation, we consider differential games for multiagent systems under distributed information where every agent is only able to acquire information about the others according to a directed information graph of local communication/sensor networks. Such games arise naturally from many applications including mobile robot coordination, power system optimization, multiplayer pursuitevasion games, etc. Since the admissible strategy of each agent has to conform to the information graph constraint, the conventional game strategy design approaches based upon Riccati equation(s) are not applicable because all the agents are required to have the information of the entire system. Accordingly, the game strategy design under distributed information is commonly known to be challenging. Toward this end, we propose novel openloop and feedback game strategy design approaches for Nash equilibrium and noninferior solutions with a focus on linear quadratic differential games. For the openloop design, approximate Nash/noninferior game strategies are proposed by integrating distributed state estimation into the openloop globalinformation Nash/noninferior strategies such that, without global information, the distributed game strategies can be made arbitrarily close to and asymptotically converge over time to the globalinformation strategies. For the feedback design, we propose the best achievable performance indices based approach under which the distributed strategies form a Nash equilibrium or noninferior solution with respect to a set of performance indices that are the closest to the original indices. This approach overcomes two issues in the classical optimal output feedback approach: the simultaneous optimization and initial state dependence. The proposed openloop and feedback design approaches are applied to an unmanned aerial vehicle formation control problem and a multipursuer singleevader differential game problem, respectively. Simulation results of several scenarios are presented for illustration.
Show less  Date Issued
 2013
 Identifier
 CFE0005025, ucf:49991
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005025
 Title
 Decentralized Power Management and Transient Control in Hybrid Fuel Cell UltraCapacitor System.
 Creator

Madani, Seyed Omid, Das, Tuhin, Kassab, Alain, Lin, KuoChi, Simaan, Marwan, University of Central Florida
 Abstract / Description

Solid Oxide Fuel Cells (SOFCs) are considered suitable for alternative energy solutions due to advantages such as high efficiency, fuel flexibility, tolerance to impurities, and potential for combined cycle operations. One of the main operating constraints of SOFCs is fuel starvation, which can occur under fluctuating power demands. It leads to voltage loss and detrimental effects on cell integrity and longevity. In addition, reformer based SOFCs require sufficient steam for fuel reforming to...
Show moreSolid Oxide Fuel Cells (SOFCs) are considered suitable for alternative energy solutions due to advantages such as high efficiency, fuel flexibility, tolerance to impurities, and potential for combined cycle operations. One of the main operating constraints of SOFCs is fuel starvation, which can occur under fluctuating power demands. It leads to voltage loss and detrimental effects on cell integrity and longevity. In addition, reformer based SOFCs require sufficient steam for fuel reforming to avoid carbon deposition and catalyst degradation. Steam to carbon ratio (STCR) is an index indicating availability of the steam in the reformer. This work takes a holistic approach to address the aforementioned concerns in SOFCs, in an attempt to enhance applicability and adaptability of such systems. To this end, we revisit prior investigation on the invariant properties of SOFC systems, that led to prediction of fuel utilization U and STCR in the absence of intrusive and expensive sensing. This work provides further insight into the reasons behind certain SOFC variables being invariant with respect to operating conditions. The work extends the idea of invariant properties to different fuel and reformer types.In SOFCs, transient control is essential for U, especially if the fuel cell is to be operated in a dynamic loadfollowing mode at high fuel utilization. In this research, we formulate a generalized abstraction of this transient control problem. We show that a multivariable systems approach can be adopted to address this issue in both time and frequency domains, which leads to input shaping. Simulations show the effectiveness of the approach through good disturbance rejection. The work further integrates the aforementioned transient control research with system level control design for SOFC systems hybridized with storage elements. As opposed to earlier works where centralized robust controllers were of interest, here, separate controllers for the fuel cell and storage have been the primary emphasis. Thus, the proposed approach acts as a bridge between existing centralized controls for single fuel cells to decentralized control for power networks consisting of multiple elements. As a first attempt, decentralized control is demonstrated in a SOFC ultracapacitor hybrid system. The challenge of this approach lies in the absence of direct and explicit communication between individual controllers. The controllers are designed based on a simple, yet effective principle of conservation of energy. Simulations as well as experimental results are presented to demonstrate the validity of these designs.
Show less  Date Issued
 2014
 Identifier
 CFE0005524, ucf:50305
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005524
 Title
 Modeling and Contour Control of MultiAxis Linear Driven Machine Tools.
 Creator

Zhao, Ran, Lin, KuoChi, Xu, Chengying, Bai, Yuanli, Das, Tuhin, An, Linan, University of Central Florida
 Abstract / Description

In modern manufacturing industries, many applications require precision motion control of multiagent systems, like multijoint robot arms and multiaxis machine tools. Cutter (end effector) should stay as close as possible to the reference trajectory to ensure the quality of the final products. In conventional computer numerical control (CNC), the control unit of each axis is independently designed to achieve the best individual tracking performance. However, this becomes less effective when...
Show moreIn modern manufacturing industries, many applications require precision motion control of multiagent systems, like multijoint robot arms and multiaxis machine tools. Cutter (end effector) should stay as close as possible to the reference trajectory to ensure the quality of the final products. In conventional computer numerical control (CNC), the control unit of each axis is independently designed to achieve the best individual tracking performance. However, this becomes less effective when dealing with multiaxis contour following tasks because of the lack of coordination among axes. This dissertation studies the control of multiaxis machine tools with focus on reducing the contour error. The proposed research explicitly addresses the minimization of contour error and treats the multiaxis machine tool as a multiinputmultioutput (MIMO) system instead of several decoupled singleinputsingleoutput (SISO) systems. New control schemes are developed to achieve superior contour following performance even in the presence of disturbances. This study also extends the applications of the proposed control system from plane contours to regular contours in R3. The effectiveness of the developed control systems is experimentally verified on a micro milling machine.
Show less  Date Issued
 2014
 Identifier
 CFE0005287, ucf:50552
 Format
 Document (PDF)
 PURL
 http://purl.flvc.org/ucf/fd/CFE0005287