View All Items
(21 - 40 of 102)
Pages
- Title
- Enhancing Cognitive Algorithms for Optimal Performance of Adaptive Networks.
- Creator
-
Lugo-Cordero, Hector, Guha, Ratan, Wu, Annie, Stanley, Kenneth, University of Central Florida
- Abstract / Description
-
This research proposes to enhance some Evolutionary Algorithms in order to obtain optimal and adaptive network configurations. Due to the richness in technologies, low cost, and application usages, we consider Heterogeneous Wireless Mesh Networks. In particular, we evaluate the domains of Network Deployment, Smart Grids/Homes, and Intrusion Detection Systems. Having an adaptive network as one of the goals, we consider a robust noise tolerant methodology that can quickly react to changes in...
Show moreThis research proposes to enhance some Evolutionary Algorithms in order to obtain optimal and adaptive network configurations. Due to the richness in technologies, low cost, and application usages, we consider Heterogeneous Wireless Mesh Networks. In particular, we evaluate the domains of Network Deployment, Smart Grids/Homes, and Intrusion Detection Systems. Having an adaptive network as one of the goals, we consider a robust noise tolerant methodology that can quickly react to changes in the environment. Furthermore, the diversity of the performance objectives considered (e.g., power, coverage, anonymity, etc.) makes the objective function non-continuous and therefore not have a derivative. For these reasons, we enhance Particle Swarm Optimization (PSO) algorithm with elements that aid in exploring for better configurations to obtain optimal and sub-optimal configurations. According to results, the enhanced PSO promotes population diversity, leading to more unique optimal configurations for adapting to dynamic environments. The gradual complexification process demonstrated simpler optimal solutions than those obtained via trial and error without the enhancements.Configurations obtained by the modified PSO are further tuned in real-time upon environment changes. Such tuning occurs with a Fuzzy Logic Controller (FLC) which models human decision making by monitoring certain events in the algorithm. Example of such events include diversity and quality of solution in the environment. The FLC is able to adapt the enhanced PSO to changes in the environment, causing more exploration or exploitation as needed.By adding a Probabilistic Neural Network (PNN) classifier, the enhanced PSO is again used as a filter to aid in intrusion detection classification. This approach reduces miss classifications by consulting neighbors for classification in case of ambiguous samples. The performance of ambiguous votes via PSO filtering shows an improvement in classification, causing the simple classifier perform better the commonly used classifiers.
Show less - Date Issued
- 2018
- Identifier
- CFE0007046, ucf:52003
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007046
- 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.
Show less - Date Issued
- 2018
- Identifier
- CFE0007170, ucf:52247
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007170
- Title
- Coordinated Optimal Power Planning of Wind Turbines in an Offshore Wind Farm.
- Creator
-
Vishwakarma, Puneet, Xu, Yunjun, Kapat, Jayanta, Kauffman, Jeffrey, Behal, Aman, University of Central Florida
- Abstract / Description
-
Wind energy is on an upswing due to climate concerns and increasing energy demands on conventional sources. Wind energy is attractive and has the potential to dramatically reduce the dependency on non-renewable energy resources. With the increase in wind farms there is a need to improve the efficiency in power allocation and power generation among wind turbines. Wake interferences among wind turbines can lower the overall efficiency considerably, while offshore conditions pose increased...
Show moreWind energy is on an upswing due to climate concerns and increasing energy demands on conventional sources. Wind energy is attractive and has the potential to dramatically reduce the dependency on non-renewable energy resources. With the increase in wind farms there is a need to improve the efficiency in power allocation and power generation among wind turbines. Wake interferences among wind turbines can lower the overall efficiency considerably, while offshore conditions pose increased loading on wind turbines. In wind farms, wind turbines' wake affects each other depending on their positions and operation modes. Therefore it becomes essential to optimize the wind farm power production as a whole than to just focus on individual wind turbines. The work presented here develops a hierarchical power optimization algorithm for wind farms. The algorithm includes a cooperative level (or higher level) and an individual level (or lower level) for power coordination and planning in a wind farm. The higher level scheme formulates and solves a quadratic constrained programming problem to allocate power to wind turbines in the farm while considering the aerodynamic effect of the wake interaction among the turbines and the power generation capabilities of the wind turbines. In the lower level, optimization algorithm is based on a leader-follower structure driven by the local pursuit strategy. The local pursuit strategy connects the cooperative level power allocation and the individual level power generation in a leader-follower arrangement. The leader, could be a virtual entity and dictates the overall objective, while the followers are real wind turbines considering realistic constraints, such as tower deflection limits. A nonlinear wind turbine dynamics model is adopted for the low level study with loading and other constraints considered in the optimization. The stability of the algorithm in the low level is analyzed for the wind turbine angular velocity. Simulations are used to show the advantages of the method such as the ability to handle non-square input matrix, non-homogenous dynamics, and scalability in computational cost with rise in the number of wind turbines in the wind farm.
Show less - Date Issued
- 2015
- Identifier
- CFE0005899, ucf:50896
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005899
- Title
- Spectrally Uniform Frames and Spectrally Optimal Dual Frames.
- Creator
-
Pehlivan, Saliha, Han, Deguang, Mohapatra, Ram, Sun, Qiyu, Tatari, Mehmet, University of Central Florida
- Abstract / Description
-
Frames have been useful in signal transmission due to the built in redundancy. In recent years, theerasure problem in data transmission has been the focus of considerable research in the case theerror estimate is measured by operator (or matrix) norm. Sample results include the characterizationof one-erasure optimal Parseval frames, the connection between two-erasure optimal Parsevalframes and equiangular frames, and some characterization of optimal dual frames.If iterations are allowed in...
Show moreFrames have been useful in signal transmission due to the built in redundancy. In recent years, theerasure problem in data transmission has been the focus of considerable research in the case theerror estimate is measured by operator (or matrix) norm. Sample results include the characterizationof one-erasure optimal Parseval frames, the connection between two-erasure optimal Parsevalframes and equiangular frames, and some characterization of optimal dual frames.If iterations are allowed in the reconstruction process of the signal vector, then spectral radiusmeasurement for the error operators is more appropriate then the operator norm measurement.We obtain a complete characterization of spectrally one-uniform frames (i.e., one-erasure optimalframes with respect to the spectral radius measurement) in terms of the redundancy distributionof the frame. Our characterization relies on the connection between spectrally optimal frames andthe linear connectivity property of the frame. We prove that the linear connectivity property isequivalent to the intersection dependence property, and is also closely related to the well-knownconcept of k-independent set. For spectrally two-uniform frames, it is necessary that the framemust be linearly connected. We conjecture that it is also necessary that a two-uniform frame mustbe n-independent. We confirmed this conjecture for the case when N = n+1, n+2, where N is thenumber of vectors in a frame for an n-dimensional Hilbert space. Additionally we also establishseveral necessary and sufficient conditions for the existence of an alternate dual frame to make the iterated reconstruction to work.
Show less - Date Issued
- 2013
- Identifier
- CFE0005111, ucf:50747
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005111
- Title
- META-RAPS: PARAMETER SETTING AND NEW APPLICATIONS.
- Creator
-
Hepdogan, Seyhun, Whitehouse, Gary, University of Central Florida
- Abstract / Description
-
ABSTRACT Recently meta-heuristics have become a popular solution methodology, in terms of both research and application, for solving combinatorial optimization problems. Meta-heuristic methods guide simple heuristics or priority rules designed to solve a particular problem. Meta-heuristics enhance these simple heuristics by using a higher level strategy. The advantage of using meta-heuristics over conventional optimization methods is meta-heuristics are able to find good (near optimal)...
Show moreABSTRACT Recently meta-heuristics have become a popular solution methodology, in terms of both research and application, for solving combinatorial optimization problems. Meta-heuristic methods guide simple heuristics or priority rules designed to solve a particular problem. Meta-heuristics enhance these simple heuristics by using a higher level strategy. The advantage of using meta-heuristics over conventional optimization methods is meta-heuristics are able to find good (near optimal) solutions within a reasonable computation time. Investigating this line of research is justified because in most practical cases with medium to large scale problems, the use of meta-heuristics is necessary to be able to find a solution in a reasonable time. The specific meta-heuristic studied in this research is, Meta-RaPS; Meta-heuristic for Randomized Priority Search which is developed by DePuy and Whitehouse in 2001. Meta-RaPS is a generic, high level strategy used to modify greedy algorithms based on the insertion of a random element (Moraga, 2002). To date, Meta-RaPS had been applied to different types of combinatorial optimization problems and achieved comparable solution performance to other meta-heuristic techniques. The specific problem studied in this dissertation is parameter setting of Meta-RaPS. The topic of parameter setting for meta-heuristics has not been extensively studied in the literature. Although the parameter setting method devised in this dissertation is used primarily on Meta-RaPS, it is applicable to any meta-heuristic's parameter setting problem. This dissertation not only enhances the power of Meta-RaPS by parameter tuning but also it introduces a robust parameter selection technique with wide-spread utility for many meta-heuristics. Because the distribution of solution values generated by meta-heuristics for combinatorial optimization problems is not normal, the current parameter setting techniques which employ a parametric approach based on the assumption of normality may not be appropriate. The proposed method is Non-parametric Based Genetic Algorithms. Based on statistical tests, the Non-parametric Based Genetic Algorithms (NPGA) is able to enhance the solution quality of Meta-RaPS more than any other parameter setting procedures benchmarked in this research. NPGA sets the best parameter settings, of all the methods studied, for 38 of the 41 Early/Tardy Single Machine Scheduling with Common Due Date and Sequence-Dependent Setup Time (ETP) problems and 50 of the 54 0-1 Multidimensional Knapsack Problems (0-1 MKP). In addition to the parameter setting procedure discussed, this dissertation provides two Meta-RaPS combinatorial optimization problem applications, the 0-1 MKP, and the ETP. For the ETP problem, the Meta-RaPS application in this dissertation currently gives the best meta-heuristic solution performance so far in the literature for common ETP test sets. For the large ETP test set, Meta-RaPS provided better solution performance than Simulated Annealing (SA) for 55 of the 60 problems. For the small test set, in all four different small problem sets, the Meta-RaPS solution performance outperformed exiting algorithms in terms of average percent deviation from the optimal solution value. For the 0-1 MKP, the present Meta-RaPS application performs better than the earlier Meta-RaPS applications by other researchers on this problem. The Meta-RaPS 0-1 MKP application presented here has better solution quality than the existing Meta-RaPS application (Moraga, 2005) found in the literature. Meta-RaPS gives 0.75% average percent deviation, from the best known solutions, for the 270 0-1 MKP test problems.
Show less - Date Issued
- 2006
- Identifier
- CFE0001206, ucf:46949
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001206
- Title
- CIRCUIT DESIGN AND RELIABILITY OF A CMOS RECEIVER.
- Creator
-
Yang, Hong, Yuan, Jiann, University of Central Florida
- Abstract / Description
-
This dissertation explores CMOS RF design and reliability for portable wireless receivers. The objective behind this research is to achieve an increase in integration level, and gain more understanding for RF reliability. The fields covered include device, circuit and system. What is under investigation is a multi-band multi-mode receiver with GSM, DCS-1800 and CDMA compatibility. To my understanding, GSM and CDMA dual-mode mobile phones are progressively investigated in industries, and few...
Show moreThis dissertation explores CMOS RF design and reliability for portable wireless receivers. The objective behind this research is to achieve an increase in integration level, and gain more understanding for RF reliability. The fields covered include device, circuit and system. What is under investigation is a multi-band multi-mode receiver with GSM, DCS-1800 and CDMA compatibility. To my understanding, GSM and CDMA dual-mode mobile phones are progressively investigated in industries, and few commercial products are available. The receiver adopts direct conversion architecture. Some improved circuit design methods are proposed, for example, for low noise amplifier (LNA). Except for band filters, local oscillators, and analog-digital converters which are usually implemented by COTS SAW filters and ICs, all the remaining blocks such as switch, LNA, mixer, and local oscillator are designed in MOSIS TSMC 0.35ìm technology in one chip. Meanwhile, this work discusses related circuit reliability issues, which are gaining more and more attention. Breakdown (BD) and hot carrier (HC) effects are important issues in semiconductor industry. Soft-breakdown (SBD) and HC effects on device and RF performance has been reported. Hard-breakdown (HBD) effects on digital circuits have also been investigated. This work uniquely address HBD effects on the RF device and circuit performance, taking low noise amplifier and power amplifier as targets.
Show less - Date Issued
- 2004
- Identifier
- CFE0000212, ucf:46259
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000212
- Title
- SUB-OPTIMAL ULTRA-WIDE BAND RECEIVERS.
- Creator
-
Bhuvanendran, Nilesh, Lei Wei, Dr, University of Central Florida
- Abstract / Description
-
Ultra-wide Band (UWB) has sparked a lot of interest lately from theindustry and academia. The growing capacity of the wireless industry is requires a new communication system that satis¯es the high data rate which does not interfere with existing RF systems. UWB promises to be this new technology. UWB also promises low power, low cost and °exibility. The UWB Channel opens up a huge new wireless channel with Giga Hertz Capacities as well as the highest spatial capacities measured in...
Show moreUltra-wide Band (UWB) has sparked a lot of interest lately from theindustry and academia. The growing capacity of the wireless industry is requires a new communication system that satis¯es the high data rate which does not interfere with existing RF systems. UWB promises to be this new technology. UWB also promises low power, low cost and °exibility. The UWB Channel opens up a huge new wireless channel with Giga Hertz Capacities as well as the highest spatial capacities measured in bits per hertz per square meter. When properly implemented UWB channel can share spectrum with traditional radio systems without causing harmful interference. In this thesiswe studied and compared several reduced complexity sub-optimal Ultra-Wide Band receivers. These receivers include auto correlation receiver, the square value detector and the absolute value detector are studied. We consider OOK and PPM modulation schemes. We examine these schemes and the receivers on Gaussian and UWB indoor channels. We compare the performance with optimal receivers.A transmitter receiver system using 0.1us pulses implemented usingexisting hardware. A packet consisting of 24 bits were transmitted and the received signal could be veri¯ed in real time using a vector signal analyzer. The results show sub-optimal receivers provide a better trade off between robust,complexity and performance.
Show less - Date Issued
- 2004
- Identifier
- CFE0000106, ucf:46186
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000106
- Title
- NEW OPTIMAL HIGH EFFICIENCY DSP-BASED DIGITAL CONTROLLER DESIGN FOR SUPER HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MOTOR.
- Creator
-
zhao, limei, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly...
Show moreThis dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly efficient digital controller. However, there are still challenges for such super high-speed controller design because of its stability, high-speed, variable speed operation, and required efficiency over a wide speed range. Currently, limited research, and no commercial experimental analysis, is available concerning such motors and their control system design. The stability of a super high-speed PMSM is an important issue particularly for open-loop control, given that PMSM are unstable after exceeding a certain applied frequency. In this dissertation, the stability of super high-speed PMSM is analyzed and some design suggestions are given to maximize this parameter. For ordinary motors, the V/f control curve is a straight line with a boost voltage because the stator resistance is negligible and only has a significant effect around the DC frequency. However, for the proposed super high-speed PMSM the situation is quite different because of the motor's size. The stator resistance is quite large compared with the stator reactive impedance and cannot be neglected when employing constant a V/f control method. The challenge is to design an optimal constant V/f control scheme to raise efficiency with constant V/f control. In the development, test systems and prototype boards were built and experimental results confirmed the effectiveness of the dissertation system.
Show less - Date Issued
- 2005
- Identifier
- CFE0000856, ucf:46651
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000856
- Title
- THE RELATIONSHIP BETWEEN MILLENNIALS' ATTITUDES TOWARDS THE UNITED STATES AND THEIR GOALS AND PERSONAL CONSTRUCTS.
- Creator
-
Hernandez, Angelica M, Negy, Charles, University of Central Florida
- Abstract / Description
-
The purpose of this study was to examine various aspects of Millennials' attitudes related to their beliefs about the United States and in the context of their personal, career, and family goals and ethnic identity. Another purpose of this study was to determine if selected personality variables would predict attitudes toward the United States. It was found that Millennials who held positive attitudes toward the United States in terms of being a viable country for them also had relatively...
Show moreThe purpose of this study was to examine various aspects of Millennials' attitudes related to their beliefs about the United States and in the context of their personal, career, and family goals and ethnic identity. Another purpose of this study was to determine if selected personality variables would predict attitudes toward the United States. It was found that Millennials who held positive attitudes toward the United States in terms of being a viable country for them also had relatively clear and developed personal, career, and family goals. Moreover, three personality variables - resiliency, optimism, and (inversely) cynicism significantly contributed to Millennials' views of the United States. Last, ethnic identity - strong feelings of attachment and loyalty to one's ethnicity - correlated in various ways with both attitudes toward the United States and the belief that the United States is oppressive toward minorities. Those observed correlations varied depending on the specific ethnicity (non-Hispanic Whites who strongly identified with their ethnicity were less likely to consider the United States a discriminatory country toward minorities, whereas Hispanics, African Americans, and Asian Americans who identified strongly with their ethnicity were more likely to view the United States as oppressive toward minorities. More research is recommended to clarify and elucidate some of the obtained findings in this study.
Show less - Date Issued
- 2018
- Identifier
- CFH2000327, ucf:45750
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000327
- Title
- A MODEL OF LOW-RISK PIRACY.
- Creator
-
Camilo, Amil, Burguet, Roberto, University of Central Florida
- Abstract / Description
-
Heterogeneous consumers make the decision to buy a durable good or to download a replica, and a monopolist chooses to price and protect their intellectual property in the form of an authentication cost. An optimal price and authentication cost is derived, and shown to be higher than the efficient outcome for a uniform distribution of consumers. The optimal selection of price and protection are shown to be commensurate with his authenticating technology, and the searching ability of consumers....
Show moreHeterogeneous consumers make the decision to buy a durable good or to download a replica, and a monopolist chooses to price and protect their intellectual property in the form of an authentication cost. An optimal price and authentication cost is derived, and shown to be higher than the efficient outcome for a uniform distribution of consumers. The optimal selection of price and protection are shown to be commensurate with his authenticating technology, and the searching ability of consumers. As an extension, a layout for a monopolist problem where consumers have different searching abilities is shown to be indistinct from a homogeneous case when consumers are uniformly distributed.
Show less - Date Issued
- 2019
- Identifier
- CFH2000495, ucf:45647
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000495
- Title
- IMITATING INDIVIDUALIZED FACIAL EXPRESSIONS IN A HUMAN-LIKE AVATAR THROUGH A HYBRID PARTICLE SWARM OPTIMIZATION - TABU SEARCH ALGORITHM.
- Creator
-
Husk, Evan, Gonzalez, Avelino, University of Central Florida
- Abstract / Description
-
This thesis describes a machine learning method for automatically imitating a particular person's facial expressions in a human-like avatar through a hybrid Particle Swarm Optimization - Tabu Search algorithm. The muscular structures of the facial expressions are measured by Ekman and Friesen's Facial Action Coding System (FACS). Using a neutral face as a reference, the minute movements of the Action Units, used in FACS, are automatically tracked and mapped onto the avatar using a hybrid...
Show moreThis thesis describes a machine learning method for automatically imitating a particular person's facial expressions in a human-like avatar through a hybrid Particle Swarm Optimization - Tabu Search algorithm. The muscular structures of the facial expressions are measured by Ekman and Friesen's Facial Action Coding System (FACS). Using a neutral face as a reference, the minute movements of the Action Units, used in FACS, are automatically tracked and mapped onto the avatar using a hybrid method. The hybrid algorithm is composed of Kennedy and Eberhart's Particle Swarm Optimization algorithm (PSO) and Glover's Tabu Search (TS). Distinguishable features portrayed on the avatar ensure a personalized, realistic imitation of the facial expressions. To evaluate the feasibility of using PSO-TS in this approach, a fundamental proof-of-concept test is employed on the system using the OGRE avatar. This method is analyzed in-depth to ensure its proper functionality and evaluate its performance compared to previous work.
Show less - Date Issued
- 2012
- Identifier
- CFH0004286, ucf:44949
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004286
- Title
- OPTIMAL INVESTMENT STRATEGIES USING MULTI-PROPERTY COMMERCIAL REAL ESTATE: ANALYSIS OF PRE/POST HOUSING BUBBLE.
- Creator
-
Kundiger, Kyle, Frye, Melissa, University of Central Florida
- Abstract / Description
-
This paper analyzes theperformance of five commercial real estate property types (office, retail, industrial, apartment, and hotel) between 2000 and 2012 to determine the U.S. housing crisis'simpact on Real Estate investing. Under the concept of Modern Portfolio Theory, the data was analyzed using investment analysis programs to determine correlation, risk/return characteristics, and trade-offs (Sharpe ratio) as well as the optimal allocation among the individual property types. In light of...
Show moreThis paper analyzes theperformance of five commercial real estate property types (office, retail, industrial, apartment, and hotel) between 2000 and 2012 to determine the U.S. housing crisis'simpact on Real Estate investing. Under the concept of Modern Portfolio Theory, the data was analyzed using investment analysis programs to determine correlation, risk/return characteristics, and trade-offs (Sharpe ratio) as well as the optimal allocation among the individual property types. In light of the results, each property type plays a different role in investment strategies in various economic cycles. Some assets are attractive solely based onpotential return, or risk for return tradeoffs; however, through diversification, other property types play valuable roles in hedging risk on investors' target returns.
Show less - Date Issued
- 2012
- Identifier
- CFH0004296, ucf:44935
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004296
- Title
- EFFICIENCY IMPROVEMENT TECHNIQUES FOR HIGH VOLTAGE CAPACITOR CHARGING METHODS.
- Creator
-
Islas, Michael, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
The goal of this thesis is to design and fabricate a DC-to-DC converter for use in high-voltage capacitor charging applications. The primary objectives include increasing the efficiency and reducing the cost of traditional methods used for this application. Traditional methods were not designed specifically for high-voltage capacitor charging and were thus very primitive and exhibited lower efficiency. Prior methods made use of a high voltage power supply and a current limiting resistor or...
Show moreThe goal of this thesis is to design and fabricate a DC-to-DC converter for use in high-voltage capacitor charging applications. The primary objectives include increasing the efficiency and reducing the cost of traditional methods used for this application. Traditional methods were not designed specifically for high-voltage capacitor charging and were thus very primitive and exhibited lower efficiency. Prior methods made use of a high voltage power supply and a current limiting resistor or control scheme. The power supply would often only operate efficiently at a single voltage value and would thus function poorly over a range used in charging a capacitor. The resistor would also dissipate a fair amount of power, also limiting efficiency. This design makes use of a traditional flyback topology utilizing a controller developed specifically for this application, centering the design approach on the LT3750. Hence, taking full advantage of the efficiency improving control scheme it provides. Additionally, through the use of advanced techniques to eliminate noise and power losses, the efficiency may be significantly improved. A detailed theoretical analysis of the charger is also presented. The analysis will then be applied to optimization techniques to select ideal component values to meet specific design specifications. In this research, a specifically designed and developed prototype will be used to experimentally verify the theoretical work and optimization techniques.
Show less - Date Issued
- 2009
- Identifier
- CFE0002899, ucf:48025
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002899
- Title
- ADAPTIVE EFFICIENCY OPTIMIZATION FOR DIGITALLY CONTROLLED DC-DC CONVERTERS.
- Creator
-
AL-HOOR, WISAM, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
The design optimization of DC-DC converters requires the optimum selection of several parameters to achieve improved efficiency and performance. Some of these parameters are load dependent, line dependent, components dependent, and/or temperature dependent. Designing such parameters for a specific load, input and output, components, and temperature may improve single design point efficiency but will not result in maximum efficiency at different conditions, and will not guarantee improvement...
Show moreThe design optimization of DC-DC converters requires the optimum selection of several parameters to achieve improved efficiency and performance. Some of these parameters are load dependent, line dependent, components dependent, and/or temperature dependent. Designing such parameters for a specific load, input and output, components, and temperature may improve single design point efficiency but will not result in maximum efficiency at different conditions, and will not guarantee improvement at that design point because of the components, temperature, and operating point variations. The ability of digital controllers to perform sophisticated algorithms makes it easy to apply adaptive control, where system parameters can be adaptively adjusted in response to system behavior in order to achieve better performance and stability. The use of adaptive control for power electronics is first applied with the Adaptive Frequency Optimization (AFO) method, which presents an auto-tuning adaptive digital controller with maximum efficiency point tracking to optimize DC-DC converter switching frequency. The AFO controller adjusts the DC-DC converter switching frequency while tracking the converter minimum input power point, under variable operating conditions, to find the optimum switching frequency that will result in minimum total loss and thus the maximum efficiency. Implementing variable switching frequencies in digital controllers introduces two main issues, namely, limit cycle oscillation and system instability. Dynamic Limit Cycle Algorithms (DLCA) is a dynamic technique tailored to improve system stability and to reduce limit cycle oscillation under variable switching frequency operation. The convergence speed and stability of AFO algorithm is further improved by presenting the analysis and design of a digital controller with adaptive auto-tuning algorithm that has a variable step size to track and detect the optimum switching frequency for a DC-DC converter. The Variable-Step-Size (VSS) algorithm is theoretically analyzed and developed based on buck DC-DC converter loss model and directed towered improving the convergence speed and accuracy of AFO adaptive loop by adjusting the converter switching frequency with variable step size. Finally, the efficiency of DC-DC converters is a function of several variables. Optimizing single variable alone may not result in maximum or global efficiency point. The issue of adjusting more than one variable at the same time is addressed by the Multivariable Adaptive digital Controller (MVAC). The MVAC is an adaptive method that continuously adjusts the DC-DC converter switching frequency and dead-time at the same time, while tracking the converter minimum input power, to find the maximum global efficiency point under variable conditions. In this research work, all adaptive methods were discussed, theoretically analyzed and its digital control algorithm along with experimental implementations were presented.
Show less - Date Issued
- 2009
- Identifier
- CFE0002838, ucf:48072
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002838
- Title
- Multi-level Optimization and Applications with Non-Traditional Game Theory.
- Creator
-
Yun, Guanxiang, Zheng, Qipeng, Boginski, Vladimir, Karwowski, Waldemar, Yong, Jiongmin, University of Central Florida
- Abstract / Description
-
We study multi-level optimization problem on energy system, transportation system and information network. We use the concept of boundedly rational user equilibrium (BRUE) to predict the behaviour of users in systems. By using multi-level optimization method with BRUE, we can help to operate the system work in a more efficient way. Based on the introducing of model with BRUE constraints, it will lead to the uncertainty to the optimization model. We generate the robust optimization as the...
Show moreWe study multi-level optimization problem on energy system, transportation system and information network. We use the concept of boundedly rational user equilibrium (BRUE) to predict the behaviour of users in systems. By using multi-level optimization method with BRUE, we can help to operate the system work in a more efficient way. Based on the introducing of model with BRUE constraints, it will lead to the uncertainty to the optimization model. We generate the robust optimization as the multi-level optimization model to consider for the pessimistic condition with uncertainty. This dissertation mainly includes four projects. Three of them use the pricing strategy as the first level optimization decision variable. In general, our models' first level's decision variables are the measures that we can control, but the second level's decision variables are users behaviours that can only be restricted within BRUE with uncertainty.
Show less - Date Issued
- 2019
- Identifier
- CFE0007881, ucf:52758
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007881
- Title
- STRESS SHIELDING MINIMIZED IN FEMORAL HIP IMPLANTS: A FINITE ELEMENT MODEL OPTIMIZED BY VIRTUAL COMPATIBILITY.
- Creator
-
feldt, christian, Chew, Larry, University of Central Florida
- Abstract / Description
-
Bone mechanics and traditional implant materials produce a recurring problem for patients of total hip arthroplasty (THA): the bone is "shielded" from the loading it has become accustomed to over many years of development. Bone adheres to what is called "Wolff's Law", meaning it is an adaptive structure which adjusts its geometry based on the loads experienced over its life. As the new femoral hip implant transmits reduced stresses to the remaining bone, bone tissue atrophies at the interface...
Show moreBone mechanics and traditional implant materials produce a recurring problem for patients of total hip arthroplasty (THA): the bone is "shielded" from the loading it has become accustomed to over many years of development. Bone adheres to what is called "Wolff's Law", meaning it is an adaptive structure which adjusts its geometry based on the loads experienced over its life. As the new femoral hip implant transmits reduced stresses to the remaining bone, bone tissue atrophies at the interface, permitting loosening of the implant, pain, and thereby obliging additional surgery to correct the issue. In the present work, a methodology is endeavored for creating an innovative design for femoral hip implants. The approach uncouples the finite element implant model from the bone model, in order to focus solely on expected behavior within the implant while considering the varying material behavior in unique directions and locations. The implant's internal geometry is optimized in order to better match typical, intact bone conditions. The eventual design reduces extreme changes in stresses within remnant bone such that the implant will remain implanted for greater periods of time without additional surgical attention.
Show less - Date Issued
- 2011
- Identifier
- CFE0004051, ucf:52891
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004051
- Title
- MULTI-OBJECTIVE OPTIMIZATION FOR HEAVY EARTHMOVING CONSTRUCTION EQUIPMENT MANAGEMENT BASED ON TIME, COST, AND POLLUTANT EMISSIONS.
- Creator
-
Alshboul, Odey, Tatari, Omer, Al-Deek, Haitham, Abou-Senna, Hatem, Awad, Amro, University of Central Florida
- Abstract / Description
-
Earthmoving activity is considered a significant activity in the construction project. The cost of earthmoving activity in the construction projects in some cases reaches about 30% of the overall cost of the project. Moreover, heavy equipment selection needs to be utilized in this activity, such as trucks and excavators. Such equipment emits a huge amount of carbon that has a negative effect on environmental dimensions. A mathematical model to optimize all design variables (i.e., capacity,...
Show moreEarthmoving activity is considered a significant activity in the construction project. The cost of earthmoving activity in the construction projects in some cases reaches about 30% of the overall cost of the project. Moreover, heavy equipment selection needs to be utilized in this activity, such as trucks and excavators. Such equipment emits a huge amount of carbon that has a negative effect on environmental dimensions. A mathematical model to optimize all design variables (i.e., capacity, number, and speed) related to this equipment is urgently required to prevent these negative impacts. The proposed model offers a genetic algorithm-based optimization technique for earthmoving activity. The model has four main phases: (1) define all related decision variables for earthmoving equipment, (2) detect all related constraints that impact the optimization model, (3) derive the mathematical optimization model, and (4) apply the multi-objective genetic algorithms. The optimization approach is utilized to minimize the cost and duration of the earthmoving activity, along with reducing the carbon emissions and fuel consumption. A case study is applied to test and validate the addressed model. Optimization outputs have proven the model efficiency in saving substantial cost and time compared to the actual results. The results of the case study show that the innovative and original contribution of the created mathematical optimization model. These unique and new competencies are anticipated to support contractors and construction management engineers to minimize time and cost associated with earthmoving activities.
Show less - Date Issued
- 2019
- Identifier
- CFE0007598, ucf:52518
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007598
- Title
- Optimization of Process Parameters for Faster Deposition of CuIn1-xGaxS2 and CuIn1-xGaxSe2-ySy Thin Film Solar Cells.
- Creator
-
Kaul, Ashwani, Dhere, Neelkanth, Heinrich, Helge, Kar, Aravinda, Chow, Lee, Sundaram, Kalpathy, University of Central Florida
- Abstract / Description
-
Thin film solar cells have the potential to be an important contributor to the world energy demand in the 21st century. Among all the thin film technologies, CuInGaSe2 (CIGS) thin film solar cells have achieved the highest efficiency. However, the high price of photovoltaic (PV) modules has been a major factor impeding their growth for terrestrial applications. Reduction in cost of PV modules can be realized by several ways including choosing scalable processes amenable to large area...
Show moreThin film solar cells have the potential to be an important contributor to the world energy demand in the 21st century. Among all the thin film technologies, CuInGaSe2 (CIGS) thin film solar cells have achieved the highest efficiency. However, the high price of photovoltaic (PV) modules has been a major factor impeding their growth for terrestrial applications. Reduction in cost of PV modules can be realized by several ways including choosing scalable processes amenable to large area deposition, reduction in the materials consumption of active layers, and attaining faster deposition rates suitable for in-line processing. Selenization-sulfurization of sputtered metallic Cu-In-Ga precursors is known to be more amenable to large area deposition. Sputter-deposited molybdenum thin film is commonly employed as a back contact layer for CIGS solar cells. However, there are several difficulties in fabricating an optimum back contact layer. It is known that molybdenum thin films deposited at higher sputtering power and lower gas pressure exhibit better electrical conductivity. However, such films exhibit poor adhesion to the soda-lime glass substrate. On the other hand, films deposited at lower discharge power and higher pressure although exhibit excellent adhesion show lower electrical conductivity. Therefore, a multilayer structure is normally used so as to get best from the two deposition regimes. A multi-pass processing is not desirable in high volume production because it prolongs total production time and correspondingly increases the manufacturing cost. In order to make manufacturing compliant with an in-line deposition, it is justifiable having fewer deposition sequences. Thorough analysis of pressure and power relationship of film properties deposited at various parameters has been carried out. It has been shown that it is possible to achieve a molybdenum back contact of desired properties in a single deposition pass by choosing the optimum deposition parameters. It is also shown that the film deposited in a single pass is actually a composite structure. CIGS solar cells have successfully been completed on the developed single layer back contact with National Renewable Energy Laboratory (NREL) certified device efficiencies (>)11%. The optimization of parameters has been carried out in such a way that the deposition of back contact and metallic precursors can be carried out in identical pressure conditions which is essential for in-line deposition without a need for load-lock. It is know that the presence of sodium plays a very critical role during the growth of CIGS absorber layer and is beneficial for the optimum device performance. The effect of sodium location during the growth of the absorber layer has been studied so as to optimize its quantity and location in order to get devices with improved performance. NREL certified devices with efficiencies (>)12% have been successfully completed.
Show less - Date Issued
- 2012
- Identifier
- CFE0004559, ucf:49261
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004559
- Title
- MULTIOBJECTIVE DESIGN OPTIMIZATION OF GAS TURBINE BLADE WITH EMPHASIS ON INTERNAL COOLING.
- Creator
-
Nagaiah, Narasimha, Geiger, Christopher, Nazzal, Dima, Reilly, Charles, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
In the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are time-consuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to...
Show moreIn the design of mechanical components, numerical simulations and experimental methods are commonly used for design creation (or modification) and design optimization. However, a major challenge of using simulation and experimental methods is that they are time-consuming and often cost-prohibitive for the designer. In addition, the simultaneous interactions between aerodynamic, thermodynamic and mechanical integrity objectives for a particular component or set of components are difficult to accurately characterize, even with the existing simulation tools and experimental methods. The current research and practice of using numerical simulations and experimental methods do little to address the simultaneous (")satisficing(") of multiple and often conflicting design objectives that influence the performance and geometry of a component. This is particularly the case for gas turbine systems that involve a large number of complex components with complicated geometries.Numerous experimental and numerical studies have demonstrated success in generating effective designs for mechanical components; however, their focus has been primarily on optimizing a single design objective based on a limited set of design variables and associated values. In this research, a multiobjective design optimization framework to solve a set of user-specified design objective functions for mechanical components is proposed. The framework integrates a numerical simulation and a nature-inspired optimization procedure that iteratively perturbs a set of design variables eventually converging to a set of tradeoff design solutions. In this research, a gas turbine engine system is used as the test application for the proposed framework. More specifically, the optimization of the gas turbine blade internal cooling channel configuration is performed. This test application is quite relevant as gas turbine engines serve a critical role in the design of the next-generation power generation facilities around the world. Furthermore, turbine blades require better cooling techniques to increase their cooling effectiveness to cope with the increase in engine operating temperatures extending the useful life of the blades.The performance of the proposed framework is evaluated via a computational study, where a set of common, real-world design objectives and a set of design variables that directly influence the set of objectives are considered. Specifically, three objectives are considered in this study: (1) cooling channel heat transfer coefficient, which measures the rate of heat transfer and the goal is to maximize this value; (2) cooling channel air pressure drop, where the goal is to minimize this value; and (3) cooling channel geometry, specifically the cooling channel cavity area, where the goal is to maximize this value. These objectives, which are conflicting, directly influence the cooling effectiveness of a gas turbine blade and the material usage in its design. The computational results show the proposed optimization framework is able to generate, evaluate and identify thousands of competitive tradeoff designs in a fraction of the time that it would take designers using the traditional simulation tools and experimental methods commonly used for mechanical component design generation. This is a significant step beyond the current research and applications of design optimization to gas turbine blades, specifically, and to mechanical components, in general.
Show less - Date Issued
- 2012
- Identifier
- CFE0004495, ucf:49282
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004495
- Title
- Optimization of Ocean Thermal Energy Conversion Power Plants.
- Creator
-
Rizea, Steven, Ilie, Marcel, Bai, Yuanli, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
A proprietary Ocean Thermal Energy Conversion (OTEC) modeling tool, the Makai OTEC Thermodynamic and Economic Model (MOTEM), is leveraged to evaluate the accuracy of finite-time thermodynamic OTEC optimization methods. MOTEM is a full OTEC system simulator capable of evaluating the effects of variation in heat exchanger operating temperatures and seawater flow rates. The evaluation is based on a comparison of the net power output of an OTEC plant with a fixed configuration. Select...
Show moreA proprietary Ocean Thermal Energy Conversion (OTEC) modeling tool, the Makai OTEC Thermodynamic and Economic Model (MOTEM), is leveraged to evaluate the accuracy of finite-time thermodynamic OTEC optimization methods. MOTEM is a full OTEC system simulator capable of evaluating the effects of variation in heat exchanger operating temperatures and seawater flow rates. The evaluation is based on a comparison of the net power output of an OTEC plant with a fixed configuration. Select optimization methods from the literature are shown to produce between 93% and 99% of the maximum possible amount of power, depending on the selection of heat exchanger performance curves. OTEC optimization is found to be dependent on the performance characteristics of the evaporator and condenser used in the plant. Optimization algorithms in the literature do not take heat exchanger performance variation into account, which causes a discrepancy between their predictions and those calculated with MOTEM. A new characteristic metric of OTEC optimization, the ratio of evaporator and condenser overall heat transfer coefficients, is found. The heat transfer ratio is constant for all plant configurations in which the seawater flow rate is optimized for any particular evaporator and condenser operating temperatures. The existence of this ratio implies that a solution for the ideal heat exchanger operating temperatures could be computed based on the ratio of heat exchanger performance curves, and additional research is recommended.
Show less - Date Issued
- 2012
- Identifier
- CFE0004430, ucf:49343
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004430
