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Articles 1 - 8 of 8
Full-Text Articles in Engineering
Rotor Position And Vibration Control For Aerospace Flywheel Energy Storage Devices And Other Vibration Based Devices, B. X. S. Alexander
Rotor Position And Vibration Control For Aerospace Flywheel Energy Storage Devices And Other Vibration Based Devices, B. X. S. Alexander
ETD Archive
Flywheel energy storage has distinct advantages over conventional energy storage methods such as electrochemical batteries. Because the energy density of a flywheel rotor increases quadratically with its speed, the foremost goal in flywheel design is to achieve sustainable high speeds of the rotor. Many issues exist with the flywheel rotor operation at high and varying speeds. A prominent problem is synchronous rotor vibration, which can drastically limit the sustainable rotor speed. In a set of projects, the novel Active Disturbance Rejection Control (ADRC) is applied to various problems of flywheel rotor operation. These applications include rotor levitation, steady state rotation …
Convolutional Coded Generalized Direct Sequence Spread Spectrum, Madan Venn
Convolutional Coded Generalized Direct Sequence Spread Spectrum, Madan Venn
ETD Archive
In this thesis we investigate the worst-case performance of coded ordinary and coded generalized direct sequence spread spectrum (DSSS) systems in a communication channel corrupted by an unknown and arbitrary interfering signal of bounded power. We consider convolutional codes with Viterbi decoding in order to compare the performance of coded ordinary and coded generalized DSSS systems. For the generalized DSSS system, we use a pulse stream of +1,-1 and 0 as the spreading sequence, which is different from ordinary DSSS system which uses the typical sequence with pulse values of +1 and -1. A C program for performing Monte-Carlo simulations …
High Intensity Laser Power Beaming For Wireless Power Transmission, Daniel Edward Raible
High Intensity Laser Power Beaming For Wireless Power Transmission, Daniel Edward Raible
ETD Archive
This paper describes work supporting the development of a high intensity laser power beaming (HILPB) system for the purpose of wireless power transmission. The main contribution of this research is utilizing high intensity lasers to illuminate vertical multi-junction (VMJ) solar cells developed by NASA-GRC. Several HILPB receivers are designed, constructed and evaluated with various lasers to assess the performance of the VMJ cells and the receiver under a variety of conditions. Several matters such as parallel cell back-feeding, optimal receiver geometry, laser wavelength, non-uniform illumination and thermal effects at high intensities are investigated. Substantial power densities are achieved, and suggestions …
A Wrapper-Based Approach To Sustained Time Synchronization In Wireless Sensor Networks, Dheeraj Reddy Bheemidi
A Wrapper-Based Approach To Sustained Time Synchronization In Wireless Sensor Networks, Dheeraj Reddy Bheemidi
ETD Archive
Time synchronization is an important service for wireless sensor network applications. Nodes in the network stay synchronized by exchanging periodic messages that carry local timestamps. Several algorithms have been proposed in the literature that are suited to different kinds of application scenarios. A common problem across these time synchronization algorithms is that the energy cost of message exchange is high. In fact, the cost of radio communication far outstrips the cost of performing local operations on the processor. If the message exchanges were stopped, nodes will fall out of sync, and may no longer be able to meet application requirements. …
A Sensor Network System For Monitoring Short-Term Construction Work Zones, Manohar Bathula
A Sensor Network System For Monitoring Short-Term Construction Work Zones, Manohar Bathula
ETD Archive
Safety hazards encountered near construction work zones are high, both in number and in the kind. There is a need to monitor traffic in such construction zones in order to improve driver and vehicle safetyIn the past traffic monitoring systems were built with high cost equipment such as inductive plates, video cameras etc. These solutions are too cost{prohibitive and invasive to be used in the large. Wireless sensor networks provide an opportunity space that can be used to address this problem. This thesis specifically targets temporary or short-term construction work zones. We present the design and implementation of a sensor …
Dspace Implementation Of A Generalized Method Of Harmonic Elimination For Pwm Boost Type Rectifier Under Unbalanced Operating Conditions, Ke Chen
ETD Archive
In this thesis, the implementation of a generalized method of harmonic elimination for the PWM boost type rectifier under severe fault conditions in the power system is presented. This method has been implemented by using DSPACE RT1104 digital control system. Control loop has been designed for real-time DC link voltage regulation. The simulation and experimental results verify the feasibility of the control scheme for input-output harmonic elimination. With the proposed method, unity power factor can be achieved as well as low-order harmonic elimination. High quality input and output waveforms of the three-phase PWM boost type rectifier are obtained under extremely …
A Novel Cascaded Multilevel Converter, Rajmohan Rangarajan
A Novel Cascaded Multilevel Converter, Rajmohan Rangarajan
ETD Archive
A novel cascaded multilevel converter is proposed in this thesis. The thesis proposes to produce more voltage levels from fewer H-bridges in a cascaded multilevel converter. The converter uses fewer H-bridges and the proposed switching scheme renders more voltage level in the staircase waveform with equal steps. Since the resulting voltage levels are equal, the angles are determined for the complete elimination of more unwanted harmonics. The implementation of the switching scheme, in single and three-phase configurations were simulated with Ansoft Simplorer♭ and the frequency spectrum of the resulting waveform and its total harmonic distortion are shown to verify the …
Byzantine Fault Tolerance For Nondeterministic Applications, Bo Chen
Byzantine Fault Tolerance For Nondeterministic Applications, Bo Chen
ETD Archive
The growing reliance on online services accessible on the Internet demands highly reliable system that would not be interrupted when encountering faults. A number of Byzantine fault tolerance (BFT) algorithms have been developed to mask the most complicated type of faults - Byzantine faults such as software bugs,operator mistakes, and malicious attacks, which are usually the major cause of service interruptions. However, it is often difficult to apply these algorithms to practical applications because such applications often exhibit sophisticated non-deterministic behaviors that the existing BFT algorithms could not cope with. In this thesis, we propose a classification of common types …