Hydrogen-powered engines have been gaining increasing interest due to the global concerns of the effects of hydrocarbon combustion on climate change. Gas turbines are suitable for operation on hydrogen fuel. This thesis reports the results of investigations of the special requirements of the fuel controller for a hydrogen gas turbine. In this investigation, a digital fuel controller for a hydrogen-fueled modified Pratt and Whitney PT6A-20 turboprop engine was successfully designed and implemented. Included in the design are safety measures to protect the operating personnel and the engine. A redundant fuel control is part of the final design to provide a second method of managing the engine should there be a malfunction in any part of the primary controller. Parallel to this study, an investigation of the existing hydrogen combustor design was performed to analyze the upper stability limits that were restricting the operability of the engine. The upstream propagation of the flame into the premixer, more commonly known as a flashback, routinely occurred at 150 shaft horsepower during engine testing. The procedures for protecting the engine from a flashback were automated within the fuel controller, significantly reducing the response time from the previous (manual) method. Additionally, protection measures were added to ensure the inter-turbine temperature of the engine did not exceed published limits. Automatic engine starting and shutdown procedures were also added to the control logic, minimizing the effort needed by the operator. The tested performance of the engine with each of the control functions demonstrated the capability of the controller. Methods to generate an engine-specific fuel control map were also studied. The control map would not only takes into account the operability limits of the engine, but also the stability limits of the premixing devices. Such a map is integral in the complete design of the engine fuel controller. / Master of Science

In this dissertation, experimental data was used to investigate the influence of a nearby mast structure on the striking distance to a lightning rod. The results of this research helped identify and understand the impact of different factors such as stroke polarity, lightning rod height, striking distance to the ground, lateral distance from the lightning stroke to an adjacent mast, and height of the adjacent mast on the striking distance of a lightning rod. Moreover, a system identification methodology was employed for the development and validation of striking distance models from experimental work performed at the Mississippi State University High Voltage Laboratory. Striking distance models were obtained to represent the striking distance to the ground, striking distance to an isolated lightning rod, and striking distance to a lightning rod in the presence of an adjacent mast. In the case of the striking distance to the ground the system identification approach was used for the extraction of the parameters of the black-box model proposed. From the results the relationship between the striking distance to ground and the leader voltage were obtained for both polarities of the lightning stroke. The system identification approach was then expanded to obtain the models for the striking distance to the lightning rod. The system identification approach was used to evaluate different mathematical models based on the ones found in the literature. The models were trained on experimental data, their quality evaluated, and the best model was selected for both positive and negative polarity. Furthermore, the model for negative polarity was evaluated against data from real lightning conditions in order to corroborate the model extrapolation capability. Building on the success obtained on the cases of the striking distance to the ground and to an isolated lightning rod the focus was turned to expanding the models to incorporate the influence of an adjacent mast. Models for positive and negative polarity were obtained and the quality of the equations was evaluated.

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Present trends in communication links between devices have opted for wireless instead of wired solutions. As a consequence, unlicensed bands have seen a rise in the interference level as more and more devices are introduced into the market place that take advantage of these free bands for their communication needs. Under these conditions, the receiver's ability to recognize and identify the presence of interference becomes increasingly important. In order for the receiver to make an optimal decision on the signal-of-interest, it has to be aware of the type (modulation) of interference as well as how the received signals are affected (channel) by these impediments in order to appropriately mitigate them. This dissertation addresses the blind (unaided) identification of the signal modulations and the channel in a Multiple Input Multiple Output (MIMO) system. The method presented herein takes advantage of the modulation induced periodicities of the signals in the system and uses higher-order cyclostationary statistics to extract the signal and channel unknowns. This method can be used to identify more signals in the system than antenna elements at the receiver (overloaded case). This dissertation presents a system theoretic analysis of the problem as well as describes the development of an algorithm that can be used in the identification of the channel and the modulation of the signals in the system. Linear and non-linear receivers are examined at the beginning of the manuscript in order to review the a priori information that is needed for each receiver configuration to function properly. / Ph. D.

Stepped hull forms are hulls with a vertical step in the hull bottom to improve performance at top speed. Stepped hulls are well documented anecdotally and scientifically to improve calm water performance at high speeds, but commonly demonstrate dangerous and unexpected dynamic instabilities during initial trials. These hulls also operate practically in waves, but their performance characteristics in waves are not well understood and rarely evaluated prior to full scale trials. To expand the scientific understanding of stepped hull performance, a systematic set of experiments and Reynolds Averaged Navier Stokes (RANS) computational fluid dynamics (CFD) simulations are used to evaluate the calm water performance, dynamic stability, and regular head wave response of two stepped hull models. Calm water experiments on two stepped hull models at varying displacement, longitudinal center of gravity location and forward speed offer data which can be used in the design to interpolate hull performance throughout expected operating conditions. CFD simulations in calm water are validated using the experimental results and numerical modeling approaches for stepped hull simulations are recommended. The calm water dynamic stability of both stepped hulls is investigated experimentally and numerically and procedures to evaluate the dynamic stability using both approaches are recommended. The performance of both stepped hulls in regular head waves is studied through experiments, which are used to validate CFD simulations of the hull in regular waves. System identification is used on five calm water CFD simulations to identify a reduced order model for the prediction of stepped hull response in waves. / Doctor of Philosophy / Boats designed specifically for high-speed operations, like military patrol craft, can often achieve higher top speeds when small vertical steps are added to the bottom of the hull. When a step is introduced, the back portion of the hull bottom is raised above the forward portion of the hull bottom to allow air underneath the hull at high speeds. When designed properly, a stepped hull can be safely operated by experienced and unexperienced users at higher speeds than conventional hulls. However, when the steps are not designed well a boat can be dangerous to operate, suffering from unexpected phenomena like end swapping (where the boat violently rotates from bow to stern) when beginning a turn. Unfortunately, it is currently difficult to predict how a stepped hull will behave during the early stages of the design. Builders often rely on full-scale prototype trials to assess the performance and safety of their designs, which is an expensive process. In this work, experimental tests (on small scale models) and computer simulations were performed on two stepped hull models in calm water and in waves to establish techniques to predict performance and safety without a full-scale prototype. The experiments were used to compare the performance of two geometries and assess the accuracy of computer simulation predictions. The computer simulations were found to predict the stepped hull performance accurately enough to be used in design prior to prototyping. Procedures are recommended to evaluate the safety of a stepped hull through experiments and computer simulations. Evaluation of hull safety through computer simulations or experiments offers the opportunity to reduce danger to test personnel during full scale trials and minimize the need for expensive design modifications after construction of the first prototype. The performance of the two hull designs in waves were studied experimentally, through computer simulation, and through a simplified method informed by computer simulations. The development of a simplified method to evaluate stepped hull performance in waves offers the opportunity for designers to consider performance in waves earlier in the design for a lower cost than previously available.

Yes / This paper presents an investigation into the development of an intelligent active vibration control (AVC) system. Evolutionary Genetic algorithms (GAs) and Adaptive Neuro-Fuzzy Inference system (ANFIS) algorithms are used to develop mechanisms of an AVC system, where the controller is designed on the basis of optimal vibration suppression using the plant model. A simulation platform of a flexible beam system in transverse vibration using finite difference (FD) method is considered to demonstrate the capabilities of the AVC system using GAs and ANFIS. MATLAB GA tool box for GAs and Fuzzy Logic tool box for ANFIS function are used for AVC system design. The system is then implemented, tested and its performance assessed for GAs and ANFIS based design. Finally a comparative performance of the algorithm in implementing AVC system using GAs and ANFIS is presented and discussed through a set of experiments.

Proper mathematical models of structures are beneficial for designers and analysts. The accuracy of the results is essential. Therefore, verification and/or correction of the models is vital. This can be done by utilizing experimental results or other analytical solutions. There are different methods of generating the accurate mathematical models. These methods range from completely analytically derived models, completely experimentally derived models, to a combination of the two. These model generation procedures are called System Identification. Today a popular method is to create an analytical model as accurately as possible and then improve this model using experimental results. This thesis provides a review of System Identification methods as applied to vibrating structures. One simple method and three more complex methods, chosen from current engineering literature, are implemented on the computer. These methods offer the capability to correct a discrete (for example, finite element based) model through the use of experimental measurements. The validity of the methods is checked on a two degree of freedom problem, an eight degree of freedom example frequently used in the literature, and with experimentally derived vibration results of a free-free beam. / Master of Science

System identification deals with the problem of building mathematical models of dynamical systems based on observed data from the systems. Most of the conventional techniques of system identification, in general, require some amount of a priori knowledge about the structure of the systems. Also, they are only useful either with linear or linearized systems. There are numerous control principles working nicely in industry. However, they are less effective for MIMO systems or complex nonlinear systems. The need to control, in a better way, increasingly complex dynamical systems under significant uncertainty has made the need for new methods quite apparent. This thesis investigates different approaches for identification and control of complex nonlinear systems using neural networks. For system identification and control, ANN properties of generalization and their capability of extracting complex relationships among inputs presented to them are useful. Two different techniques, called whole region method (WRM) and the separate regions method (SRM) technique, have been developed and applied to two classes of nonlinear systems. Different connectionist control techniques such as adaptive control and neuro-PID control have been developed and applied to the robotic manipulators. / Master of Science