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Title: DSP IMPLEMENTATION OF DC VOLTAGE REGULATION USING ADAPTIVE CONTROL FOR 200 KW 62000 RPM INDUCTION GENERATOR.
Creator: Elkhomri, Othman, Wu, Thomas, University of Central Florida
Abstract / Description: The thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship...
Show moreThe thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship has been modeled using adaptive control technique to vary the gains automatically at any load condition. The adaptive control technique has been successfully generalized for real time DSP implementation to regulate the DC voltage for high speed induction generators rated from 5 kW to 200 kW.
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Date Issued: 2006
Identifier: CFE0001076, ucf:46787
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001076

Title: EXPERIMENTS IN POOL BOILING HEAT TRANSFER AND NUCLEATIONDYNAMICS OF HIGH PRESSURE REFRIGERANTS.
Creator: Joo, Daniel, Kumar, Ranganathan, University of Central Florida
Abstract / Description: A high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable...
Show moreA high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable of studying the physics and thermodynamics of refrigerants under nucleate pool boiling. The main objective of this experiment was the design of the experimental setup. Various designs were tested and validated, of which all incorporated a pressure resistant chamber constructed out of aluminum and glass viewing ports. Design parameters such as the heating element thickness were verified using a transient FEA thermal model. This model, which was developed in ANSYS, verified that this design would be able to capture the thermal response of the thermochromatic liquid crystals. This analysis concluded that a negligible error of 0.02°C is expected due to transient effects. Difficulties were encountered during early stages of development; most notable were imaging limitations such as low camera frame-rates and poor resolution. Since a TLC technique was used to measure the temperature of the boiling surface, a camera system fast enough to capture the thermal response was needed. At bubble frequencies of 30 nucleations per second, it was necessary for the camera to have much higher frame rates. Through the use of two synchronized cameras, the surface temperature, position, size and shape of the bubbles were recorded simultaneously. Two camera systems were designed and tested. The first system consisted of a high speed CMOS camera capable of capturing 1,000 frames per second, and an RBG CCD color camera capable of 30 Frames per second. However, this system was limited the slow frame rate and low resolution of the RBG camera. The second system used two high resolution and fast shutter speed cameras, which were able to capture fast bubble nucleations. This method required the assumption that under constant operating conditions, the path of one bubble was identical to the next. This method was tested utilizing the high speed camera, and was shown that there was less than a .04% deviation from the path any bubble to that of the next. Detailed analysis of nucleating surface temperatures using thermochromatic liquid crystal technique and temporal-temperature response under various heat flux and at 813.6kPa (118Psia) and 882.5kPa (128Psia) was performed. It is seen that temperature distribution is quite varied in each case. At high pressures the size of nucleation site decreases, giving rise to an increase in the surface temperature. Bubble growth is also analyzed through the use of high speed cameras and compared to temperature distributions. Simultaneous temperature and bubble size measurements provided a correlation between bubble growth and heat transfer. Boiling parameters such as bubble frequency, bubble size, and contact area are also analyzed. From the surface temperature plots, the local and average heat transfer coefficients were calculated as a function of time and bubble dynamics.
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Date Issued: 2006
Identifier: CFE0001489, ucf:47106
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001489

Title: SUPER HIGH-SPEED MINIATURIZED PERMANENT MAGNET SYNCHRONOUS MOTOR.
Creator: Zheng, Liping, Sundaram, Kalpathy, University of Central Florida
Abstract / Description: This dissertation is concerned with the design of permanent magnet synchronous motors (PMSM) to operate at super-high speed with high efficiency. The designed and fabricated PMSM was successfully tested to run upto 210,000 rpm The designed PMSM has 2000 W shaft output power at 200,000 rpm and at the cryogenic temperature of 77 K. The test results showed the motor to have an efficiency reaching above 92%. This achieved efficiency indicated a significant improvement compared to commercial...
Show moreThis dissertation is concerned with the design of permanent magnet synchronous motors (PMSM) to operate at super-high speed with high efficiency. The designed and fabricated PMSM was successfully tested to run upto 210,000 rpm The designed PMSM has 2000 W shaft output power at 200,000 rpm and at the cryogenic temperature of 77 K. The test results showed the motor to have an efficiency reaching above 92%. This achieved efficiency indicated a significant improvement compared to commercial motors with similar ratings. This dissertation first discusses the basic concept of electrical machines. After that, the modeling of PMSM for dynamic simulation is provided. Particular design strategies have to be adopted for super-high speed applications since motor losses assume a key role in the motor drive performance limit. The considerations of the PMSM structure for cryogenic applications are also discussed. It is shown that slotless structure with multi-strand Litz-wire is favorable for super-high speeds and cryogenic applications. The design, simulation, and test of a single-sided axial flux pancake PMSM is presented. The advantages and disadvantages of this kind of structure are discussed, and further improvements are suggested and some have been verified by experiments. The methodologies of designing super high-speed motors are provided in details. Based on these methodologies, a super high-speed radial-flux PMSM was designed and fabricated. The designed PMSM meets our expectation and the tested results agree with the design specifications. 2-D and 3-D modeling of the complicated PMSM structure for the electromagnetic numerical simulations of motor performance and parameters such as phase inductors, core losses, rotor eddy current loss, torque, and induced electromotive force (back-EMF) are also presented in detail in this dissertation. Some mechanical issues such as thermal analysis, bearing pre-load, rotor stress analysis, and rotor dynamics analysis are also discussed. Different control schemes are presented and suitable control schemes for super high- speed PMSM are also discussed in detail.
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Date Issued: 2005
Identifier: CFE0000762, ucf:46562
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000762

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.
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Date Issued: 2005
Identifier: CFE0000856, ucf:46651
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000856

Title: Design of Low-Capacitance Electrostatic Discharge (ESD) Protection Devices in Advanced Silicon Technologies.
Creator: Dong, Aihua, Sundaram, Kalpathy, Fan, Deliang, Gong, Xun, Wei, Lei, Salcedo, Javier, University of Central Florida
Abstract / Description: Electrostatic discharge (ESD) related failure is a major IC reliability concern and this is particularly true as technology continues shrink to nano-metric dimensions. ESD design window research shows that ESD robustness of victim devices keep decreasing from 350nm bulk technology to 7nm FinFET technologies. In the meantime, parasitic capacitance of ESD diode with same It2 in FinFET technologies is approximately 3X compared with that in planar technologies. Thus transition from planar to...
Show moreElectrostatic discharge (ESD) related failure is a major IC reliability concern and this is particularly true as technology continues shrink to nano-metric dimensions. ESD design window research shows that ESD robustness of victim devices keep decreasing from 350nm bulk technology to 7nm FinFET technologies. In the meantime, parasitic capacitance of ESD diode with same It2 in FinFET technologies is approximately 3X compared with that in planar technologies. Thus transition from planar to FinFET technology requires more robust ESD protection however the large parasitic capacitance of ESD protection cell is problematic in high-speed interface design. To reduce the parasitic capacitance, a dual diode silicon controlled rectifier (DD-SCR) is presented in this dissertation. This design can exhibit good trade-offs between ESD robustness and parasitic capacitance characteristics. Besides, different bounding materials lead to performance variations in DD-SCRs are compared. Radio frequency (RF) technology is also demanded low capacitance ESD protection. To address this concern, a ?-network is presented, providing robust ESD protection for 10-60 GHz RF circuit. Like a low pass ? filter, the network can reflect high frequency RF signals and transmit low frequency ESD pulses. Given proper inductor value, networks can work as robust ESD solutions at a certain Giga Hertz frequency range, making this design suitable for broad band protection in RF input/outputs (I/Os). To increase the holding voltage and reduce snapback, a resistor assist triggering heterogeneous stacking structure is presented in this dissertation, which can increase the holding voltage and also keep the trigger voltage nearly as same as a single SCR device.
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Date Issued: 2018
Identifier: CFE0007172, ucf:52251
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007172

Title: Intrinsic Modulation Response Modeling and Analysis for Lithographic Vertical-Cavity Surface-Emitting Lasers.
Creator: Li, Mingxin, Deppe, Dennis, Fathpour, Sasan, Wu, Shintson, Malocha, Donald, University of Central Florida
Abstract / Description: Vertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using...
Show moreVertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using lithographic approach are demonstrated to overcome the limitations of oxide VCSELs, in which an intra-cavity phase shifting mesa is applied to define the device size and provide optical mode and electrical current confinement instead of an oxide aperture. A newly developed model of intrinsic modulation response is proposed and analyzed to focus on the thermal limit of the modulation speed of VCSELs. The results show that both the temperature dependent differential gain and stimulated emission rate impact laser speed and the stimulated emission rate dominates the speed limit. Thermal limits of modulation response are compared for oxide and lithographic VCSELs for various sizes. The results predict that the intrinsic modulation response can be significantly increased by using lithographic VCSELs due to low thermal resistance and reduced mode volume while maintaining high efficiency. The intrinsic bandwidth could exceed 100 GHz for a 2-?m-diameter lithographic VCSEL. Combined with low electrical parasitics, it is expected to produce over 100 Gb/s data rate from a single directly modulated laser. VCSELs designed for high speed are discussed and their characteristics are demonstrated.
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Date Issued: 2016
Identifier: CFE0006346, ucf:51556
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006346

Title: Cryogenic performance projections for ultra-small oxide-free vertical-cavity surface-emitting lasers.
Creator: Bayat, Mina, Deppe, Dennis, Li, Guifang, Schoenfeld, Winston, Lyakh, Arkadiy, University of Central Florida
Abstract / Description: Small-sized vertical-cavity surface-emitting laser (VCSEL) may offer very low power consumption along with high reliability for cryogenic data transfer. Cryogenic data transfer has application in supercomputers and superconducting for efficient computing and also focal plane array cameras operating at 77 K, and at the lower temperature of 4 K for data extraction from superconducting circuits. A theoretical analysis is presented for 77 K and 4 K operation based on small cavity, oxide-free...
Show moreSmall-sized vertical-cavity surface-emitting laser (VCSEL) may offer very low power consumption along with high reliability for cryogenic data transfer. Cryogenic data transfer has application in supercomputers and superconducting for efficient computing and also focal plane array cameras operating at 77 K, and at the lower temperature of 4 K for data extraction from superconducting circuits. A theoretical analysis is presented for 77 K and 4 K operation based on small cavity, oxide-free VCSEL sizes of 2 to 6 (&)#181;m, that have been shown to operate efficiently at room temperature. Temperature dependent operation for optimally-designed VCSELs are studied by calculating the response of the laser at 77 K and 4 K to estimate their bias conditions needed to reach modulation speed for cryogenic optical links. The temperature influence is to decrease threshold for reducing temperature, and to increase differential gain for reducing temperature. The two effects predict very low bias currents for small cavity VCSELs to reach needed data speed for cryogenic optical data links. Projections are made for different cavity structures (half-wave cavity and full-wave cavity) shown that half-wave cavity structure has better performance. Changing the number of top-mirror pairs has also been studied to determine how cavity design impacts speed and bit energy. Our design and performance predictions paves the way for realizing highly efficient, ultra-small VCSEL arrays with applications in optical interconnects.
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Date Issued: 2019
Identifier: CFE0007782, ucf:52330
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007782

Title: Design of Novel Devices and Circuits for Electrostatic Discharge Protection Applications in Advanced Semiconductor Technologies.
Creator: Wang, Zhixin, Liou, Juin, Gong, Xun, Yuan, Jiann-Shiun, Jin, Yier, Vinson, James, University of Central Florida
Abstract / Description: Electrostatic Discharge (ESD), as a subset of Electrical Overstress (EOS), was reported to be in charge of more than 35% of failure in integrated circuits (ICs). Especially in the manufacturing process, the silicon wafer turns out to be a functional ICs after numerous physical, chemical and mechanical processes, each of which expose the sensitive and fragile ICs to ESD environment. In normal end-user applications, ESD from human and machine handling, surge and spike signals in the power...
Show moreElectrostatic Discharge (ESD), as a subset of Electrical Overstress (EOS), was reported to be in charge of more than 35% of failure in integrated circuits (ICs). Especially in the manufacturing process, the silicon wafer turns out to be a functional ICs after numerous physical, chemical and mechanical processes, each of which expose the sensitive and fragile ICs to ESD environment. In normal end-user applications, ESD from human and machine handling, surge and spike signals in the power supply, and wrong supplying signals, will probably cause severe damage to the ICs and even the whole systems. Generally, ESD protections are evaluated after wafer and even system fabrication, increasing the development period and cost if the protections cannot meet customer's requirements. Therefore, it is important to design and customize robust and area-efficient ESD protections for the ICs at the early development stage. As the technologies generally scaling down, however, ESD protection clamps remain comparable area consumption in the recent years because they provide the discharging path for the ESD energy which rarely scales down. Diode is the most simple and effective device for ESD protection in ICs, but the usage is significantly limited by its low turn-on voltage. MOS devices can be triggered by a dynamic-triggered RC circuit for IOs operating at low voltage, while the one triggered by a static-triggered network, e.g., zener-resistor circuit or grounded-gate configuration, provides a high trigger voltage for high-voltage applications. However, the relatively low current discharging capability makes MOS devices as the secondary choice. Silicon-controlled rectifier (SCR) has become famous due to its high robustness and area efficiency, compared to diode and MOS. In this dissertation, a comprehensive design methodology for SCR based on simulation and measurement are presented for different advanced commercial technologies. Furthermore, an ESD clamp is designed and verified for the first time for the emerging GaN technology.For the SCR, no matter what modification is going to be made, the first concern when drawing the layout is to determine the layout geometrical style, finger width and finger number. This problem for diode and MOS device were studied in detail, so the same method was usually used in SCR. The research in this dissertation provides a closer look into the metal layout effect to the SCR, finding out the optimized robustness and minimized side-effect can be obtained by using specific layout geometry. Another concern about SCR is the relatively low turn-on speed when the IOs under protection is stressed by ESD pulses having very fast rising time, e.g., CDM and IEC 61000-4-2 pulses. On this occasion a large overshoot voltage is generated and cause damage to internal circuit component like gate oxides of MOS devices. The key determination of turn-on speed of SCR is physically investigated, followed by a novel design on SCR by directly connecting the Anode Gate and Cathode Gate to form internal trigger (DCSCR), with improved performance verified experimentally in this dissertation. The overshoot voltage and trigger voltage of the DCSCR will be significantly reduced, in return a better protection for internal circuit component is offered without scarifying neither area or robustness. Even though two SCR's with single direction of ESD current path can be constructed in reverse parallel to form bidirectional protection to pins, stand-alone bidirectional SCR (BSCR) is always desirable for sake of smaller area. The inherent high trigger voltage of BSCR that only fit in high-voltage technologies is overcome by embedding a PMOS transistor as trigger element, making it highly suitable for low-voltage ESD protection applications. More than that, this modification simultaneously introduces benefits including high robustness and low overshoot voltage.For high voltage pins, however, it presents another story for ESD designs. The high operation voltages require that a high trigger voltage and high holding voltage, so as to reduce the false trigger and latch-up risk. For several capacitive pins, the displacement current induced by a large snapback will cause severe damage to internal circuits. A novel design on SCR is proposed to minimize the snapback with adjustable trigger and holding voltage. Thanks to the additional a PIN diode, the similar high robustness and stable thermal leakage performance to SCR is maintained. For academic purpose of ESD design, it is always difficult to obtain the complete process deck in TCAD simulation because those information are highly confidential to the companies. Another challenge of using TCAD is the difficulty of maintaining the accuracy of physics models and predicting the performance of the other structures. In this dissertation a TCAD-aid ESD design methodology is used to evaluate ESD performance before the silicon shuttle.GaN is a promising material for high-voltage high-power RF application compared to the GaAs. However, distinct from GaAs, the leaky problem of the schottky junction and the lack of choice of passive/active components in GaN technology limit the ESD protection design, which will be discussed in this dissertation. However, a promising ESD protection clamp is finally developed based on depletion-mode pHEMT with adjustable trigger voltage, reasonable leakage current and high robustness.
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Date Issued: 2015
Identifier: CFE0006060, ucf:50989
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006060

Title: HIGH-SPEED MODELOCKED SEMICONDUCTOR LASERS AND APPLICATIONS IN COHERENT PHOTONIC SYSTEMS.
Creator: Lee, Wangkuen, Delfyett, Peter, University of Central Florida
Abstract / Description: 1.55-µm high-speed modelocked semiconductor lasers are theoretically and experimentally studied for various coherent photonic system applications. The modelocked semiconductor lasers (MSLs) are designed with high-speed (>5 GHz) external cavity configurations utilizing monolithic two-section curved semiconductor optical amplifiers. By exploiting the saturable absorber section of the monolithic device, passive or hybrid mode-locking techniques are used to generate short optical pulses with...
Show more1.55-µm high-speed modelocked semiconductor lasers are theoretically and experimentally studied for various coherent photonic system applications. The modelocked semiconductor lasers (MSLs) are designed with high-speed (>5 GHz) external cavity configurations utilizing monolithic two-section curved semiconductor optical amplifiers. By exploiting the saturable absorber section of the monolithic device, passive or hybrid mode-locking techniques are used to generate short optical pulses with broadband optical frequency combs. Laser frequency stability is improved by applying the Pound-Drever-Hall (PDH) frequency stabilization technique to the MSLs. The improved laser performance after the frequency stabilization (a frequency drifting of less than 350 MHz), is extensively studied with respect to the laser linewidth (~ 3 MHz), the relative intensity noise (RIN) (< -150 dB/Hz), as well as the modal RIN (~ 3 dB reduction). MSL to MSL, and tunable laser to MSL synchronization is demonstrated by using a dual-mode injection technique and a modulation sideband injection technique, respectively. Dynamic locking behavior and locking bandwidth are experimentally and theoretically studied. Stable laser synchronization between two MSLs is demonstrated with an injection seed power on the order of a few microwatt. Several coherent heterodyne detections based on the synchronized MSL systems are demonstrated for applications in microwave photonic links and ultra-dense wavelength division multiplexing (UD-WDM) system. In addition, efficient coherent homodyne balanced receivers based on synchronized MSLs are developed and demonstrated for a spectrally phase-encoded optical CDMA (SPE-OCDMA) system.
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Date Issued: 2007
Identifier: CFE0001703, ucf:47326
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001703

Title: Investigation of infrared thermography for subsurface damage detection of concrete structures.
Creator: Hiasa, Shuhei, Catbas, Necati, Tatari, Omer, Nam, Boo Hyun, Zaurin, Ricardo, Xanthopoulos, Petros, University of Central Florida
Abstract / Description: Deterioration of road infrastructure arises from aging and various other factors. Consequently, inspection and maintenance have been a serious worldwide problem. In the United States, degradation of concrete bridge decks is a widespread problem among several bridge components. In order to prevent the impending degradation of bridges, periodic inspection and proper maintenance are indispensable. However, the transportation system faces unprecedented challenges because the number of aging...
Show moreDeterioration of road infrastructure arises from aging and various other factors. Consequently, inspection and maintenance have been a serious worldwide problem. In the United States, degradation of concrete bridge decks is a widespread problem among several bridge components. In order to prevent the impending degradation of bridges, periodic inspection and proper maintenance are indispensable. However, the transportation system faces unprecedented challenges because the number of aging bridges is increasing under limited resources, both in terms of budget and personnel. Therefore, innovative technologies and processes that enable bridge owners to inspect and evaluate bridge conditions more effectively and efficiently with less human and monetary resources are desired. Traditionally, qualified engineers and inspectors implemented hammer sounding and/or chain drag, and visual inspection for concrete bridge deck evaluations, but these methods require substantial field labor, experience, and lane closures for bridge deck inspections. Under these circumstances, Non-Destructive Evaluation (NDE) techniques such as computer vision-based crack detection, impact echo (IE), ground-penetrating radar (GPR) and infrared thermography (IRT) have been developed to inspect and monitor aging and deteriorating structures rapidly and effectively. However, no single method can detect all kinds of defects in concrete structures as well as the traditional inspection combination of visual and sounding inspections; hence, there is still no international standard NDE methods for concrete bridges, although significant progress has been made up to the present.This research presents the potential to reduce a burden of bridge inspections, especially for bridge decks, in place of traditional chain drag and hammer sounding methods by IRT with the combination of computer vision-based technology. However, there were still several challenges and uncertainties in using IRT for bridge inspections. This study revealed those challenges and uncertainties, and explored those solutions, proper methods and ideal conditions for applying IRT in order to enhance the usability, reliability and accuracy of IRT for concrete bridge inspections. Throughout the study, detailed investigations of IRT are presented. Firstly, three different types of infrared (IR) cameras were compared under active IRT conditions in the laboratory to examine the effect of photography angle on IRT along with the specifications of cameras. The results showed that when IR images are taken from a certain angle, each camera shows different temperature readings. However, since each IR camera can capture temperature differences between sound and delaminated areas, they have a potential to detect delaminated areas under a given condition in spite of camera specifications even when they are utilized from a certain angle. Furthermore, a more objective data analysis method than just comparing IR images was explored to assess IR data. Secondly, coupled structural mechanics and heat transfer models of concrete blocks with artificial delaminations used for a field test were developed and analyzed to explore sensitive parameters for effective utilization of IRT. After these finite element (FE) models were validated, critical parameters and factors of delamination detectability such as the size of delamination (area, thickness and volume), ambient temperature and sun loading condition (different season), and the depth of delamination from the surface were explored. This study presents that the area of delamination is much more influential in the detectability of IRT than thickness and volume. It is also found that there is no significant difference depending on the season when IRT is employed. Then, FE model simulations were used to obtain the temperature differences between sound and delaminated areas in order to process IR data. By using this method, delaminated areas of concrete slabs could be detected more objectively than by judging the color contrast of IR images. However, it was also found that the boundary condition affects the accuracy of this method, and the effect varies depending on the data collection time. Even though there are some limitations, integrated use of FE model simulation with IRT showed that the combination can be reduce other pre-tests on bridges, reduce the need to have access to the bridge and also can help automate the IRT data analysis process for concrete bridge deck inspections. After that, the favorable time windows for concrete bridge deck inspections by IRT were explored through field experiment and FE model simulations. Based on the numerical simulations and experimental IRT results, higher temperature differences in the day were observed from both results around noontime and nighttime, although IRT is affected by sun loading during the daytime heating cycle resulting in possible misdetections. Furthermore, the numerical simulations show that the maximum effect occurs at night during the nighttime cooling cycle, and the temperature difference decreases gradually from that time to a few hours after sunrise of the next day. Thus, it can be concluded that the nighttime application of IRT is the most suitable time window for bridge decks. Furthermore, three IR cameras with different specifications were compared to explore several factors affecting the utilization of IRT in regards to subsurface damage detection in concrete structures, specifically when the IRT is utilized for high-speed bridge deck inspections at normal driving speeds under field laboratory conditions. The results show that IRT can detect up to 2.54 cm delamination from the concrete surface at any time period. This study revealed two important factors of camera specifications for high-speed inspection by IRT as shorter integration time and higher pixel resolution.Finally, a real bridge was scanned by three different types of IR cameras and the results were compared with other NDE technologies that were implemented by other researchers on the same bridge. When compared at fully documented locations with 8 concrete cores, a high-end IR camera with cooled detector distinguished sound and delaminated areas accurately. Furthermore, indicated location and shape of delaminations by three IR cameras were compared to other NDE methods from past research, and the result revealed that the cooled camera showed almost identical shapes to other NDE methods including chain drag. It should be noted that the data were collected at normal driving speed without any lane closures, making it a more practical and faster method than other NDE technologies. It was also presented that the factor most likely to affect high-speed application is integration time of IR camera as well as the conclusion of the field laboratory test.The notable contribution of this study for the improvement of IRT is that this study revealed the preferable conditions for IRT, specifically for high-speed scanning of concrete bridge decks. This study shows that IRT implementation under normal driving speeds has high potential to evaluate concrete bridge decks accurately without any lane closures much more quickly than other NDE methods, if a cooled camera equipped with higher pixel resolution is used during nighttime. Despite some limitations of IRT, the data collection speed is a great advantage for periodic bridge inspections compared to other NDE methods. Moreover, there is a high possibility to reduce inspection time, labor and budget drastically if high-speed bridge deck scanning by the combination of IRT and computer vision-based technology becomes a standard bridge deck inspection method. Therefore, the author recommends combined application of the high-speed scanning combination and other NDE methods to optimize bridge deck inspections.
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Date Issued: 2016
Identifier: CFE0006323, ucf:51575
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006323

Title: Ignition Studies of Oxy-Syngas/CO2 Mixtures Using Shock Tube for Cleaner Combustion Engines.
Creator: Barak, Samuel, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
Abstract / Description: In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume...
Show moreIn this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios (?), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio (?), hydrogen to carbon monoxide, from 0.25, 1.0 and 4.0. The study was performed at 1.61-1.77 atm and a temperature range of 1006-1162K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed non-homogeneous combustion in the system, however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.
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Date Issued: 2018
Identifier: CFE0006974, ucf:52909
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006974

Title: MEASUREMENTS IN AIR-WATER BUBBLY FLOW THROUGH A VERTICAL NARROW HIGH-ASPECT RATIO CHANNEL.
Creator: Patrick, Benjamin, Kumar, Ranganathan, University of Central Florida
Abstract / Description: Two-Phase bubbly flows are encountered in a wide range of industrial applications, particularly where phase changes occur as seen in high performance heat exchangers and boiling reactors for power generation. These flows have been extensively studied in channels with circular geometries using air-water flows, though little data exists for flows through narrow rectangular channels. Measurements in thin geometries are particularly challenging since large bubbles bridge the gap, and it is...
Show moreTwo-Phase bubbly flows are encountered in a wide range of industrial applications, particularly where phase changes occur as seen in high performance heat exchangers and boiling reactors for power generation. These flows have been extensively studied in channels with circular geometries using air-water flows, though little data exists for flows through narrow rectangular channels. Measurements in thin geometries are particularly challenging since large bubbles bridge the gap, and it is difficult to compare point measurements with photographic techniques. The objective of this study is to explore the abilities of hot-film anemometry and high speed photography for taking measurements in a narrow vertical rectangular channel for a range of volume fractions, with particular attention on the narrow dimension. Hot-film anemometry (HFA) is a measurement technique originally developed for the measurement of fluid velocities, but has since been found to have applications for broader measurements in multiphase flow. With the sensor operating on the principle of heat loss, the method takes advantage of the differing abilities of the phases to transport heat, with each phase leaving its own signature in the signal response. The linchpin of this method lies in the ability to accurately distinguish between the two phases within the signal, and to execute this operation, various algorithms and techniques have been developed and used with some success for a wide range of flow conditions. This thesis is a study of the various methods of analysis such as amplitude threshold for triggering, and small slope threshold for finely tuning the edges of the bubble interactions, and demonstrates the capabilities of the hot-film sensor in a narrow rectangular vertical duct with a high aspect ratio. A vertical acrylic test section was fabricated for the purposes of this study, inset with a rectangular channel 38.1mm in width and 3.125mm in depth. Experiments were conducted for volume fractions ranging from 2% to 35%, which remained within the limits of the bubbly flow regime, but ranged from small uniform bubbles to larger bubbles coalescing into a transition regime. The hot-film signal was analyzed for void fraction, bubble speed, and bubble size. An in- depth study of the various methods of phase discrimination was performed and the effect of threshold selection was examined. High-speed video footage was taken in conjunction with the anemometer data for a detailed comparison between methods. The bubble speed was found to be in close agreement between the HFA and high-speed video, staying within 10% for volume fractions above 10%, but still remaining under a 30% difference for even as low as the 2% volume fraction, where measurements have been found to be historically difficult. The trends with volume fraction between the HFA and high-speed results were very similar. A correlation for narrow rectangular channels employing a simple drift flux model was found to compare with the void fraction data where appropriate. Good agreement was found between the methods using a hybrid phase discrimination technique for the HFA data for the void fraction and bubble speed results, with the high-speed video results showing a slight over-estimation in regards to the bubble size.
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Date Issued: 2011
Identifier: CFE0004006, ucf:49185
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004006

ESD (2)	+ -
high speed (2)	+ -
high speed modulation (2)	+ -
Air-Water Flow (1)	+ -
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Infrared thermography (1)	+ -
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University of Central Florida (12)	+ -
Deppe, Dennis (2)	+ -
Gong, Xun (2)	+ -
Kumar, Ranganathan (2)	+ -
Sundaram, Kalpathy (2)	+ -

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