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FLOW CONTROL OF TANDEM CYLINDERS USING PLASMA ACTUATORS
Title
FLOW CONTROL OF TANDEM CYLINDERS USING PLASMA ACTUATORS.
Creator
Larsen, Jonah, Bhattacharya, Samik, University of Central Florida
Abstract / Description
The flow over a set of tandem cylinders at a moderate Reynolds numbers (Re), and with different separation lengths has been studied. Two dimensional (2D) and three-dimensional (3D) plasma actuators were used to control the flow over the leading cylinder to change the vortex shedding, and subsequently the flow on the second cylinder. The 3D plasma actuator was segmented along the length of the cylinder with a spacing of ? = 4 while the 2D actuator simply ran straight down the span of the...
Show moreThe flow over a set of tandem cylinders at a moderate Reynolds numbers (Re), and with different separation lengths has been studied. Two dimensional (2D) and three-dimensional (3D) plasma actuators were used to control the flow over the leading cylinder to change the vortex shedding, and subsequently the flow on the second cylinder. The 3D plasma actuator was segmented along the length of the cylinder with a spacing of ? = 4 while the 2D actuator simply ran straight down the span of the cylinder. Particle image velocimetry (PIV) measurements were used to investigate the flow along the central plane in the wake of the cylinders. The image pairs were processed into velocity grids which were then averaged. Plots of the shear, vorticity, and turbulent kinetic energy were created. These plots are used to understand how the character of vortex shedding from the upstream cylinder changes the same from the downstream one.
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Date Issued
2018
Identifier
CFH2000425, ucf:45872
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH2000425
Compiler Design of a Policy Specification Language for Conditional Gradual Release
Title
Compiler Design of a Policy Specification Language for Conditional Gradual Release.
Creator
Kashyap Harinath, Manasa, Leavens, Gary, Turgut, Damla, Wang, Liqiang, University of Central Florida
Abstract / Description
Securing the confidentiality and integrity of information manipulated by computer software is an old yet increasingly important problem. Current software permission systems present on Android or iOS provide inadequate support for developing applications with secure information flow policies. To be useful, information flow control policies need to specify declassifications and the conditions under which declassification must occur. Having these declassifications scattered all over the program...
Show moreSecuring the confidentiality and integrity of information manipulated by computer software is an old yet increasingly important problem. Current software permission systems present on Android or iOS provide inadequate support for developing applications with secure information flow policies. To be useful, information flow control policies need to specify declassifications and the conditions under which declassification must occur. Having these declassifications scattered all over the program makes policies hard to find, which makes auditing difficult. To overcome these challenges, a policy specification language, 'Evidently' is discussed that allows one to specify information flow control policies separately from the program and which supports conditional gradual releases that can be automatically enforced. I discuss the Evidently grammar and modular semantics in detail. Finally, I discuss the implementational details of Evidently compiler within the Xtext language development environment and the implementation's enforcement of policies.
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Date Issued
2018
Identifier
CFE0007205, ucf:52274
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007205
Feasability analysis of ramp control systems, a simulation approach
Title
Feasability analysis of ramp control systems, a simulation approach.
Creator
Popkin, Henry Allen, Klee, Harold, Engineering
Abstract / Description
Florida Technological University College of Engineering Thesis; The ever increasing traffic congestion being experienced on urban freeways has caused attention to be focused on methods for improving traffic operations on these facilities. The reduction or elimination of freeway congestion can be handled in two basic ways: 1) by increasing the freeway's capacity defined as the number of vehicles per unit time that can pass a given point in one lane of the freeway multiplied by the number of...
Show moreFlorida Technological University College of Engineering Thesis; The ever increasing traffic congestion being experienced on urban freeways has caused attention to be focused on methods for improving traffic operations on these facilities. The reduction or elimination of freeway congestion can be handled in two basic ways: 1) by increasing the freeway's capacity defined as the number of vehicles per unit time that can pass a given point in one lane of the freeway multiplied by the number of lanes on the freeway, or 2) by decreasing the traffic loads imposed on these freeways. Monumental costs and adverse public relations are involved in the construction of either new freeways or additional lanes in urban areas to increase freeway capacity. Due to these factors, the move in recent years has been toward decreasing traffic loads to accomplish the goals of reduction or elimination of freeway congestion. In an effort to combat the freeway congestion, traffic researchers have devoted much time and effort to the theoretical and practical aspects of systems in which controlled access is utilized to prevent or reduce congestion caused by traffic demands in excess of freeway operational capacity. Such systems perform the function of 'freeway surveillance and control'. An important aspect of these systems is the control mechanism used for the regulation of the ramp traffic to the freeway. This topic of ramp metering is the subject of this report.
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Date Issued
1975
Identifier
CFR0003522, ucf:52998
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFR0003522
ON THE NATURE OF THE FLOW IN A SEPARATED ANNULAR DIFFUSER
Title
ON THE NATURE OF THE FLOW IN A SEPARATED ANNULAR DIFFUSER.
Creator
Dunn, Jason, Kapat, Jayanta, University of Central Florida
Abstract / Description
The combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are...
Show moreThe combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are two diffusion processes in the combustor-diffuser system: The flow first exits the compressor into a pre-diffuser, or compressor discharge diffuser. This diffuser is responsible for a majority of the pressure recovery. The flow then exits the pre-diffuser by a sudden expansion into the dump diffuser. The dump diffuser comprises the majority of the losses, but is necessary to reduce the fluid velocity within acceptable limits for combustion. The topic of active flow control is gaining interest in the industry because such a technique may be able to alleviate some of the requirements of the dump diffuser. If a wider angle pre-diffuser with separation control were used the fluid velocity would be slowed more within that region without significant losses. Experiments were performed on two annular diffusers to characterize the flow separation to create a foundation for future active flow control techniques. Both diffusers had the same fully developed inlet flow condition, however, the expansion of the two diffusers differed such that one diffuser replicated a typical compressor discharge diffuser found in a real machine while the other would create a naturally separated flow along the outer wall. Both diffusers were tested at two Reynolds numbers, 5x104 and 1x105, with and without a vertical wall downstream of the exit to replicate the dump diffuser that re-directs the flow from the pre-diffuser outlet to the combustor. Static pressure measurements were obtained along the OD and ID wall of the diffusers to determine the recovered pressure throughout the diffuser. In addition to these measurements, tufts were used to visualize the flow. A turbulent CFD model was also created to compare against experimental results. In the end, the results were validated against empirical data as well as the CFD model. It was shown that the location of the vertical wall was directly related to the amount of separation as well as the separation characteristics. These findings support previous work and help guide future work for active flow control in a separated annular diffuser both computationally and experimentally.
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Date Issued
2009
Identifier
CFE0002953, ucf:47944
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002953
REDUCTION OF VORTEX-DRIVEN OSCILLATIONS IN A SOLID ROCKET MOTOR COLD FLOW SIMULATION THROUGH ACTIVE CONTROL
Title
REDUCTION OF VORTEX-DRIVEN OSCILLATIONS IN A SOLID ROCKET MOTOR COLD FLOW SIMULATION THROUGH ACTIVE CONTROL.
Creator
Ward, Jami, Leonessa, Alexander, University of Central Florida
Abstract / Description
Control of vortex-driven instabilities was demonstrated via a scaled-down, cold-flow simulation that modeled closed-end acoustics. When vortex shedding frequencies couple with the natural acoustic modes of a choked chamber, potentially damaging low-frequency instabilities may arise. Although passive solutions can be effective, an active control solution is preferable. An experiment was performed to demonstrate an active control scheme for the reduction of vortex-driven oscillations. A non...
Show moreControl of vortex-driven instabilities was demonstrated via a scaled-down, cold-flow simulation that modeled closed-end acoustics. When vortex shedding frequencies couple with the natural acoustic modes of a choked chamber, potentially damaging low-frequency instabilities may arise. Although passive solutions can be effective, an active control solution is preferable. An experiment was performed to demonstrate an active control scheme for the reduction of vortex-driven oscillations. A non-reacting experiment using a primary flow of air, where both the duct exit and inlet are choked, simulated the closed-end acoustics. Two plates, separated by 1.27 cm, produced the vortex shedding phenomenon at the chamber's first longitudinal mode. Two active control schemes, closed-loop and open-loop, were studied via a cold-flow simulation for validating the effects of reducing vortex shedding instabilities in the system. Actuation for both control schemes was produced by using a secondary injection method. The actuation system consisted of pulsing compressed air from a modifed, 2-stroke model airplane engine, controlled and powered by a DC motor. The use of open-loop only active control was not highly effective in reducing the amplitude of the first longitudinal acoustic mode, near 93 Hz, when the secondary injection was pulsed at the same modal frequency. This was due to the uncontrolled phasing of the secondary injection system. A Pulse Width Modulated (PWM) signal was added to the open-loop control scheme to correct for improper phasing of the secondary injection flow relative to the primary flow. This addition allowed the motor speed to be intermittently increased to a higher RPM before returning to the desired open-loop control state. This proved to be effective in reducing the pressure disturbance by approximately 46%. A closed-loop control scheme was then test for its effectiveness in controlling the phase of the secondary injection. Feedback of the system's state was determined by placing a dynamic pressure transducer near the chamber exit. Closed-loop active control, using the designed secondary injection system, was proven as an effective means of reducing the problematic instabilities. A 50% reduction in the FFT RMS amplitude was realized by utilizing a Proportional-Derivative controller to modify the phase of the secondary injection.
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Date Issued
2006
Identifier
CFE0000920, ucf:46728
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000920
QOS IN COGNITIVE PACKET NETWORKS: ADAPTIVE ROUTING, FLOW AND CONGESTION CONTROL
Title
QOS IN COGNITIVE PACKET NETWORKS: ADAPTIVE ROUTING, FLOW AND CONGESTION CONTROL.
Creator
Su, Pu, Gelenbe, Erol, University of Central Florida
Abstract / Description
With the emergence of various applications that have different Quality of Service (QoS) requirements, the capability of a network to support QoS becomes more and more important and necessary. This dissertation explores QoS in Cognitive Packet Networks (CPN) by using adaptive routing, flow and congestion control. We present a detailed description and analysis of our proposed routing algorithms based on single and multiple QoS constraints. An online estimation of packet loss rate over a path is...
Show moreWith the emergence of various applications that have different Quality of Service (QoS) requirements, the capability of a network to support QoS becomes more and more important and necessary. This dissertation explores QoS in Cognitive Packet Networks (CPN) by using adaptive routing, flow and congestion control. We present a detailed description and analysis of our proposed routing algorithms based on single and multiple QoS constraints. An online estimation of packet loss rate over a path is introduced. We implement and evaluate the adaptive routing scheme in an experimental CPN test-bed. Our experiments support our claims that the users can achieve their desired best-effort QoS through this routing scheme. We also propose a QoS-based flow and congestion control scheme that is built in the transport layer and specially designed to work with CPN to support users' QoS while remaining friendly to TCP. Theoretical models and experimental analysis are presented. Finally we experimentally demonstrate that the proposed flow and congestion control scheme can effectively control the input flows, react to the congestion and work with our proposed adaptive routing scheme to achieve users' QoS.
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Date Issued
2005
Identifier
CFE0000813, ucf:46685
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000813