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- Title
- Optimal Attitude Control Management for a Cubesat.
- Creator
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Develle, Michael, Xu, Yunjun, Lin, Kuo-Chi, Chew, Phyekeng, University of Central Florida
- Abstract / Description
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CubeSats have become popular among universities, research organizations, and government agencies due to their low cost, small size, and light weight. Their standardized configurations further reduce the development time and ensure more frequent launch opportunities. Early cubesat missions focused on hardware validation and simple communication missions, with little requirement for pointing accuracy. Most of these used magnetic torque rods or coils for attitude stabilization. However, the...
Show moreCubeSats have become popular among universities, research organizations, and government agencies due to their low cost, small size, and light weight. Their standardized configurations further reduce the development time and ensure more frequent launch opportunities. Early cubesat missions focused on hardware validation and simple communication missions, with little requirement for pointing accuracy. Most of these used magnetic torque rods or coils for attitude stabilization. However, the intrinsic problems associated with magnetictorque systems, such as the lack of three-axis control and low pointing accuracy, make them unsuitable for more advanced missions such as detailed imaging and on-orbit inspection. Three-axis control in a cubesat can be achieved by combining magnetic torque coils with other devices such as thrusters, but the lifetime is limited by the fuel source onboard. To maximize the missionlifetime, a fast attitude control management algorithm that could optimally manage the usage of the magnetic and thruster torques is desirable. Therefore, a recently developed method, the B-Spline-augmented virtual motion camouflage, is presented in this defense to solve the problem. This approach provides results which are very close to those obtained through other popular nonlinear constrained optimal control methods with a significantly reduced computational time.Simulation results are presented to validate the capabilities of the method in this application.
Show less - Date Issued
- 2011
- Identifier
- CFE0004099, ucf:49102
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004099
- Title
- Process Optimization Towards the Development of an Automated CNC Monitoring System for a Simultaneous Turning and Boring Operation.
- Creator
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Hernandez, Manuel, Xu, Chengying, Chew, Phyekeng, Xu, Yunjun, University of Central Florida
- Abstract / Description
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Manufacturing operations generate revenue by adding value to material through machine work and the cost associated with part production hinders the maximum profit available. In order to remain competitive, companies invest in research to maximize profit and reduce waste of manufacturing operations. This results in cheaper products for the customer without sacrificing quality. The purpose of this research was to identify machine settings of an Okuma LC 40 Turning Center and optimize the cost...
Show moreManufacturing operations generate revenue by adding value to material through machine work and the cost associated with part production hinders the maximum profit available. In order to remain competitive, companies invest in research to maximize profit and reduce waste of manufacturing operations. This results in cheaper products for the customer without sacrificing quality. The purpose of this research was to identify machine settings of an Okuma LC 40 Turning Center and optimize the cost of machining in terms of tool cost and energy consumption while maintaining part quality at a productive cycle time. Studying the relationship between energy consumption, tool life, and cycle time with the speed and feed settings through statistical Analysis of Variance (ANOVA) method will allow the production plant to make profitable financial decisions concerning simultaneous turning operation of forged chrome-alloy steel. The project was divided into three phases; the first phase began with a literature survey of sensors used in current manufacturing research and the adaptation of our sensors to the Okuma LC 40 turning center. Then, phase II used design of experiments to identify spindle speed and feedrate settings that optimize multiple responses related to the turning process. The result was a saving in energy consumption (kWh) by 11.8%, a saving in cutting time by 13.2% for a total cost reduction from $1.15 per tool pass to $1.075 per tool pass. Furthermore, this work provides the foundation for phase III to develop an intelligent monitoring system to provide real-time information about the state of the machine and tool. For a monitoring system to be implemented in production, it should utilize cost effective sensors and be nonintrusive to the cutting operation.
Show less - Date Issued
- 2012
- Identifier
- CFE0004278, ucf:49510
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004278
- Title
- Electrohydrodynamic Manipulation of Liquid Droplet Emulsions in a Microfluidic Channel.
- Creator
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Wehking, Jonathan, Chew, Phyekeng, Chen, Quanfang, Chen, Ruey-Hung, University of Central Florida
- Abstract / Description
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This work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by...
Show moreThis work specifically aims to provide a fundamental framework, with some experimental validation, for understanding droplet emulsion dynamics in a microfluidic channel with an applied electric field. Electrification of fluids can result in several different modes of electrohydrodynamics (EHD). Several studies to date have provided theoretical, experimental, and numerical results for stationary droplet deformations and some flowing droplet configurations, but none have reported a method by which droplets of different diameters can be separated, binned and routed through the use of electric fields. It is therefore the goal of this work to fill that void and report a comprehensive understanding of how the electric field can affect flowing droplet dynamics.This work deals with two primary models used in electrohydrodynamics: the leaky dielectric model and the perfect dielectric model. The perfect dielectric model assumes that fluids with low conductivities do not react to any effects from the small amount of free charge they contain, and can be assumed as dielectrics, or electrical insulators. The leaky dielectric model suggests that even though the free charge is minimal in fluids with low conductivities, it is still is enough to affect droplet deformations. Finite element numerical results of stationary droplet deformations, implemented using the level set method, compare well both qualitatively (prolate/oblate and vortex directions), and quantitatively with results published by other researchers. Errors of less than 7.5% are found when comparing three-dimensional (3D) numerical results of this study to results predicted by the 3D leaky dielectric model, for a stationary high conductivity drop suspended in a slightly lower conductivity suspending medium. Droplet formations in a T-junction with no applied electric field are adequately predicted numerically using the level set finite element technique, as demonstrated by other researchers and verified in this study. For 3D models, droplet size is within 6%, and droplet production frequency is within 2.4% of experimental values found in the microfluidic T-junction device. In order to reduce computational complexity, a larger scale model was solved first to obtain electrical potential distributions localized at the channel walls for the electrode placement configurations.Droplet deceleration and pinning is demonstrated, both experimentally and numerically, by applying steep gradients of electrical potential to the microchannel walls. As droplets flow over these electrical potential ``steps," they are pinned to the channel walls if the resulting electric forces are large enough to overcome the hydrodynamic forces. A balance between four dimensionless force ratios, the electric Euler number (Eu_e - ratio of inertial to electric forces), Mason number (Ma - ratio of viscous to electric forces), electric pressure (Ps - ratio of upstream pressure forces to electric forces), and the electric capillary number (Ca_e - ratio of electric to capillary forces) are used to quantify the magnitudes of each of these forces required to pin a droplet, and is consistent with a cubic dependency on the drop diameter. For larger drop diameters, effects of hydrodynamic forces become more prominent, and for smaller droplets, a greater electric forces is required due to the proximity of the droplet boundary with reference to the electrified channel wall. Droplet deceleration and pinning can be exploited to route droplets into different branches of a microfluidic T-junction. In addition, using steep electrical potential gradients placed strategically along a microchannel, droplets can even be passively binned by size into separate branches of the microfluidic device. These characteristics have been identified and demonstrated in this work.
Show less - Date Issued
- 2013
- Identifier
- CFE0005071, ucf:49950
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005071
