Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The failure of many System of Systems (SoS) enterprises can be attributed to the inappropriate application of traditional Systems Engineering (SE) processes within the SoS domain, because of the mistaken belief that a SoS can be regarded as a single large, or complex, system. SoS Engineering (SoSE) is a sub-discipline of SE; Risk Management and Modelling and Simulation (M&S) are key areas within SoSE, both of which also lie within the traditional SE domain. Risk Management of SoS requires a different approach to that currently taken for individual systems; if risk is managed for each component system then it cannot be assumed that the aggregated affect will be to mitigate risk at the SoS level. A literature review was undertaken examining three themes: (1) SoS Engineering (SoSE), (2) M&S and (3) Risk. Theme 1 of the literature provided insight into the activities comprising SoSE and its difference from traditional SE with risk management identified as a key activity. The second theme discussed the application of M&S to SoS, providing an output, which supported the identification of appropriate techniques and concluding that, the inherent complexity of a SoS required the use of M&S in order to support SoSE activities. Current risk management approaches were reviewed in theme 3 as well as the management of SoS risk. Although some specific examples of the management of SoS risk were found, no mature, general approach was identified, indicating a gap in current knowledge. However, it was noted most of these examples were underpinned by M&S approaches. It was therefore concluded a general approach SoS risk management utilising M&S methods would be of benefit. In order to fill the gap identified in current knowledge, this research proposed a new model based approach to Risk Management where risk identification was supported by a framework, which combined SoS system of interest dimensions with holistic risk types, where the resulting risks and contributing factors are captured in a causal network. Analysis of the causal network using a model technique selection tool, developed as part of this research, allowed the causal network to be simplified through the replacement of groups of elements within the network by appropriate supporting models. The Bayesian Belief Network (BBN) was identified as a suitable method to represent SoS risk. Supporting models run in Monte Carlo Simulations allowed data to be generated from which the risk BBNs could learn, thereby providing a more quantitative approach to SoS risk management. A method was developed which provided context to the BBN risk output through comparison with worst and best-case risk probabilities. The model based approach to Risk Management was applied to two very different case studies: Close Air Support mission planning and the Wheat Supply Chain, UK National Food Security risks, demonstrating its effectiveness and adaptability. The research established that the SoS SoI is essential for effective SoS risk identification and analysis of risk transfer, effective SoS modelling requires a range of techniques where suitability is determined by the problem context, the responsibility for SoS Risk Management is related to the overall SoS classification and the model based approach to SoS risk management was effective for both application case studies.

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This thesis is focused on the dynamics and control of nonlinear engineering systems. A developed approach is applied to three specific problems: suppression of torsional vibrations occurring in a drill-string, lateral vibrations on an unbalanced rotor and vibrational energy extraction from rotating pendulum systems. The first problem deals with drill-string torsional vibrations while drilling, which is conducted in the experimental drilling rig developed at University of Aberdeen. A realistic model of the experimental setup is then constructed, taking into account the dynamics of the drill-string and top motor. Physical parameters of the experimental drilling rig are estimated in order to calibrate the model to ensure the correspondence of the research results to the experimental conditions. Consequently, a control method is introduced to suppress torsional and stick-slip oscillations exhibited in the experimental drilling rig. The experimental and numerical results considering delay of the actuator are shown to be in close agreement, including the success of the controller in significantly reducing the vibrations. In the second problem a soft impact oscillator approach is used to study the dynamics of the asymmetric Jeffcott rotor. A realistic model of the experimental setup is developed, taking into account an asymmetric physical configuration in rotor part as well as snubber rig. Several experimental bifurcation diagrams are conducted with different conditions in range around the grazing point. Experimental and numerical results based on the proposed model are compared and shown to be in close agreement. The last problem relates to initiating and maintaining the rotational motion of a parametric pendulum as an energy harvesting system. Several possible control methods to initiate and maintain the rotational motion of a harmonically-excited pendulum are proposed and then verified experimentally. The time-delayed feedback method is shown to maintain quite well the rotational motion of a sinusoidally excited parametric pendulum, even in the presence of noise. A control method for the wave-excited pendulum system is then suggested and tested in order to increase the probability of its rotational motion. This proposed control method succeeds in significantly raising the probability of rotational motion of the wave-excited pendulum.

The fuel systems fitted to the current generation of civil transport aircraft are rather complicated, due to the presence of multiple tanks, pumps, valves and complex pipeline systems. During fuel transfer between the tanks, when controlling the aircraft centre of gravity or engine feed and refuel operations, a number of pumps and valves are involved resulting in complex pressure and flow interactions. In order to minimise the pressure surges during sudden system changes and flow overshoot during fuel transfer and refuelling, different motor drive system control strategies have been investigated. It is proposed that the current control method of electrically driven centrifugal-type pumps could be replaced by improved open and closed loop strategies where the flow overshoot can be minimised and pressure surges reduced. Steady-state and dynamic models of an AC induction motor drive and typical aircraft fuel system pipework components have been developed. The validation of these models has been performed using experimental data obtained from a fuel test rig constructed at the University of Bath using water as the working fluid. The simulation results have been shown to agree well with those from experimentation. In addition, the induction motor has been modelled based on its physical properties using the Finite Element Method software MEGA. The investigated fuel system has been described in linear terms and its behaviour has been identified. It is shown that the system dynamic behaviour can be controlled/improved using well established closed loop proportional-integral control. An open loop technique of simultaneous pump and valve control has been proposed and validated using experimental results, resulting in a reduction of both the transient pressure surges and flow overshoot during sudden valve closures, showing significant performance improvements. Improved closed loop control strategies for the pump drive system have also been developed in simulation. These are based on adaptive proportional-integral-derivative and fuzzy logic control strategies.

by Lau Wai Kwong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 99-102). / Abstract --- p.ii / Acknowledgements --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Limitations of the Mobile Computing Environments --- p.2 / Chapter 1.2 --- Applications of Transaction Replication in Mobile Environments --- p.5 / Chapter 1.3 --- Motivation for Transaction Replication in Mobile Environments --- p.5 / Chapter 1.4 --- Major Simulation Results --- p.6 / Chapter 1.5 --- Roadmap to the Thesis --- p.7 / Chapter 2 --- Previous and Related Research --- p.8 / Chapter 2.1 --- File Systems --- p.8 / Chapter 2.1.1 --- Management of Replicated Files --- p.8 / Chapter 2.1.2 --- Disconnected Operations --- p.10 / Chapter 2.2 --- Database Management --- p.12 / Chapter 2.2.1 --- Data Replication Schemes --- p.12 / Chapter 2.2.2 --- Cache Invalidation and Query Processing --- p.15 / Chapter 2.2.3 --- Transaction Management in Mobile Environments --- p.17 / Chapter 3 --- System Model and Assumptions --- p.21 / Chapter 3.1 --- System Architecture --- p.21 / Chapter 3.2 --- Transaction and Data Model --- p.23 / Chapter 3.3 --- One-copy Serializability --- p.25 / Chapter 3.4 --- Assumptions --- p.27 / Chapter 4 --- Transaction Replication in a Mobile Environment --- p.29 / Chapter 4.1 --- Read-only Public Transactions --- p.30 / Chapter 4.1.1 --- Data Broadcasting --- p.31 / Chapter 4.1.2 --- Cache Update --- p.33 / Chapter 4.1.3 --- Cache Miss --- p.36 / Chapter 4.1.4 --- Execution of Read-only Public Transactions --- p.37 / Chapter 4.2 --- R/W Public Transactions --- p.39 / Chapter 4.3 --- Correctness Argument --- p.41 / Chapter 4.3.1 --- Correctness Proof --- p.43 / Chapter 4.4 --- Extension to Support Partition Failures --- p.47 / Chapter 5 --- Design and Implementation of the Simulation --- p.49 / Chapter 5.1 --- CSIM Language --- p.49 / Chapter 5.2 --- Simulation Components --- p.50 / Chapter 5.2.1 --- Fixed Network --- p.50 / Chapter 5.2.2 --- Mobile Host --- p.50 / Chapter 5.2.3 --- Wireless Channel --- p.51 / Chapter 5.2.4 --- Database and Transactions --- p.52 / Chapter 5.3 --- A Lock-based Scheme --- p.53 / Chapter 5.4 --- Graphing ...........、 --- p.54 / Chapter 6 --- Results and Analysis --- p.55 / Chapter 6.1 --- Results Dissection --- p.55 / Chapter 6.2 --- Performance of the Scheme --- p.56 / Chapter 6.2.1 --- Parameters Setting --- p.56 / Chapter 6.2.2 --- Experiments and Results --- p.59 / Chapter 6.3 --- Comparison with the Lock-based Scheme --- p.78 / Chapter 6.3.1 --- Parameters Setting --- p.79 / Chapter 6.3.2 --- Experiments and Results --- p.80 / Chapter 7 --- Conclusions and Future Work --- p.93 / Chapter 7.1 --- Conclusions --- p.93 / Chapter 7.2 --- Future Work --- p.94 / Chapter A --- Implementation Details --- p.96 / Bibliography --- p.99

Bibliography: p. 281-289. Electronic publication; Full text available in PDF format; abstract in HTML format. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Robert W. Ashton, William B. Maier II. Includes bibliographical references (p. 83-84). Also available online.