Thesis (M.S.)--Ohio University, June, 1995. / Title from PDF t.p.

Thesis (Ph. D.)--University of Hong Kong, 1991. / Photocopy typescript.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Dr. Swaminathan, Madhavan; Committee Member: Dr. Chatterjee, Abhijit; Committee Member: Dr. Lim, Sungkyu. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xii, 132 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 123-128).

In this thesis, an IGBT-based DC/DC converter employing an internal inductor-capacitor-inductor (LCL) passive circuit is investigated in DC grid under fault conditions. It is concluded that a range of converter parameters exist which will give DC fault current magnitudes close to rated currents. Steady state and transient fault responses are investigated in depth. The converter is modelled on PSCAD platform under fault operation and the simulation results verify the analytical studies. LCL DC hub is an extension of DC/DC converter to multiple ports with capability of limiting the propagation of DC faults in a DC grid. Analytical mathematical equations for steady state fault currents are derived. A state space model of the hub is introduced for transient fault study. The hub is able to interconnect multiple DC cables at different voltage levels and act as DC substation for DC grid. The designed hub also has the ability to maintain the current within the order of its rated value without additional protection even for the worst case fault. The analytical study results are confirmed by detailed simulation on PSCAD. Based on the good performance of the LCL DC hub under DC faults, a DC grid topology with protection system employing LCL DC hub is proposed and investigated in this thesis. The advantage and feasibility of this method in DC fault protection is investigated based on the developed grid model. The DC grid protection systems are proposed and analysed in depth under several DC fault scenarios. The PSCAD simulation results under a range of DC fault scenarios on various locations are shown. These results confirm significance of the proposed DC grid protection system and advantages of this proposed topology in fault isolation.

In product design, tolerances are specified due to the inherent variabilities of manufacturing processes. Tolerance specifications have significant implications on the quality and cost of the product. For proper tolerance specification, tolerance analysis must be performed. Prototyping is the the only method available for the analysis of the product geometric variations. For the automation of the analysis procedure, the part tolerance information must be represented in a format suitable for computer interpretation. Previously proposed tolerance representation schemes have suffered either from inadequate variational coverage or departure from the established ANSI tolerancing standards. Toward this end, a tolerance representation scheme capable of modeling the range of tolerances defined in the ANSI Y14.5 standard in a format suitable for automated tolerance analysis has been proposed. One unique feature of this representation scheme is the use of B-splines for the modeling of form variations. The representation scheme can also take into account the distribution characteristics of the manufacturing processes used to enable statistical tolerance analysis. To provide an accurate characterization of the variational form characteristics of the manufactured part features, the use of process capability templates was introduced. For assembly tolerance analysis, a relative positioning scheme capable of modeling the interaction between mating splines was developed to propagate the individual part variations within the assembly. This enabled the tolerance stackup on the assembly design function(s) to be computed automatically without the need to formulate any tolerance functions. A prototype software, written in the C++ programming language and running from within CATIA, has been developed to demonstrate the integration of the above concepts. / Ph. D.

A systematic optimization method for generating the tolerance chart of a machining part and a computer program to implement this method have been developed. The developed method consists of four major components: the representation scheme for the machining sequence of the part, the algorithm for the identification of tolerance chains, the optimization model for tolerance allocation, and the calculation technique for working dimensions. The tree representation is utilized for capturing the relationships of the machining sequence. Based on this representation scheme, an automated algorithm for identifying the tolerance chains of blueprint dimensions and stock removals is developed. The optimization model consists of two stages: primary and secondary tolerance allocation. The primary stage deals with the optimization of the tolerances of the working dimensions affecting the blueprint dimensions, while the secondary stage deals with the optimization of those tolerances affecting the stock removals. For calculating the working dimensions, a new method is developed to determine the signs of the working dimensions in the tolerance chains automatically. The software is developed using the C programming language. The computerized optimization method has been tested on two examples. In both cases, better results were found when compared to those obtained by a manual method or other optimization approaches. / Master of Science

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Ma thèse s'intègre dans un contexte de développement d'une cotation fonctionnelle dans un environnement de CAO 3D chez Snecma, acteur majeur dans le monde de la propulsion aéronautique et spatiale. Les objectifs de ces travaux de recherches sont variés et suivent une logique de maîtrise de la géométrie sur tout le cycle de conception / contrôle / fabrication, notamment par le déploiement de la cotation ISO.Dans un premier temps une définition fonctionnelle ISO est proposée pour des pièces de formes complexes qui composent une turbo-machine, tout en considérant les problèmes liés au contrôle en métrologie automatique et sans contact. Cette définition nécessite quelques mises à jour des normes actuelles. Une autre difficulté fut de répondre aux demandes industrielles dans leur globalité en considérant les différents types de pièces des moteurs.Une seconde partie importante du travail consiste à développer des outils de contrôle et d'analyse de surfaces 3D complexes en vue d'une meilleure connaissance de leur géométrie en séparant les défauts locaux et globaux, qui n’ont pas le même impact fonctionnel.Une troisième partie consiste à développer une stratégie de transfert de fabrication 3D sur des pièces complexes usinées sur des montages 6 points en considérant les problèmes d’orientation des surfaces.L’ensemble des travaux permet de garantir le respect, sur des pièces de formes complexes, des exigences fonctionnelles de la définition jusqu’à la pièce usinée grâce au déploiement des normes ISO de cotation.Ces travaux ont abouti à une publication au CIRP CAT 2014 en Chine, le développement en interne Snecma d’un outil de quantification des défauts globaux/locaux, une volonté forte de développer un outil générique de transfert 3D basé sur le travail réalisé, deux distinctions créativité Snecma dont une classé seconde sur toutes les créativités 2013 et un changement de grande ampleur dans la méthode de contrôle des spécifications de forme de profils d’aube. / My PhD thesis is integrated into a context of functional dimensioning development in a 3D CAD environment at Snecma, a major player in the aerospace propulsion world. The objectives of this research work are varied but follow one goal: mastery quality geometry throughout the design, control and manufacturing cycle, by the deployment of the ISO standards of tolerancing.At first a functional definition ISO is proposed for parts with complex shapes that make up a turbo-machine while considering issues related to metrology and automatic control without contact. This definition requires some updates of existing standards. Another problem was to meet industrial demands in their entirety by considering the various types of engine parts.A second important part of the work is to develop control and analyze tools for complex 3D shapes for a better understanding of their geometry by separating local and global faults, which do not have the same functional impact.A third part develops a 3D manufacturing transfer strategy on complex workpieces on mounting “6 points” by considering the surface orientation problems.All work ensures compliance of functional requirements, on parts with complex shapes, from definition to the workpiece through the deployment of ISO standards of tolerancing.This work led to a publication in CIRP CAT 2014 China, a Snecma internal development of a quantification tool of global / local defects, a strong wich to develop a 3D transfer generic tool based on the work done, two awards Snecma creativity with one ranked second in 2013 on all the awards and a major change in the control method of form profiles specifications.

To ensure that a system is robust and will continue operation even when facing disruptive or traumatic events, we have created a methodology for system architects and designers which may be used to locate risks and hazards in a design and enable the development of more robust and resilient system architectures. It uncovers design vulnerabilities by conducting a complete exploration of a systems’ component operational state space by observing the system from multi-dimensional perspectives and conducts a quantitative design space analysis by means of probabilistic risk assessment using Bayesian Networks. Furthermore, we developed a tool which automated this methodology and demonstrated its use in an assessment of the OCTT PHM communication system architecture. To boost the robustness of a wireless communication system and efficiently allocate bandwidth, manage throughput, and ensure quality of service on a wireless link, we created a wireless link management architecture which applies sensor fusion to gather and store platform networked sensor metrics, uses time series forecasting to predict the platform position, and manages data transmission for the links (class based, packet scheduling and capacity allocation). To validate our architecture, we developed a link management tool capable of forecasting the link quality and uses cross-layer scheduling and allocation to modify capacity allocation at the IP layer for various packet flows (HTTP, SSH, RTP) and prevent congestion and priority inversion. Wireless sensor networks (WSN) are vulnerable to a plethora of different fault types and external attacks after their deployment. To maintain trust in these systems and increase WSN reliability in various scenarios, we developed a framework for node fault detection and prediction in WSNs. Individual wireless sensor nodes sense characteristics of an object or environment. After a smart device successfully connects to a WSN’s base station, these sensed metrics are gathered, sent to and stored on the device from each node in the network, in real time. The framework issues alerts identifying nodes which are classified as faulty and when specific sensors exceed a percentage of a threshold (normal range), it is capable of discerning between faulty sensor hardware and anomalous sensed conditions. Furthermore we developed two proof of concept, prototype applications based on this framework. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2013.