Master-Arbeit Univ. St. Gallen, 2006.

Thesis (M. Arch.)--University of Hong Kong, 2004. / Includes special report study entitled: Automated construction process in the information age. Also available in print.

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 87-90).

Thesis (Ocean E)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1981. / Supervised by J. Kim Vandiver. Includes bibliographical references (p. 169-175).

Thèse d'Etat--Paris I, 1994.

This research has arisen from recent changes in attitudes to offshore safety. To help demonstrate structural safety to the Health and Safety Executive, operators are increasingly using structural system reliability assessments. While significant developments have been achieved in this area, there are still a number of uncertainties associated with such assessments. Unresolved technical issues also introduce significant variability in the results. The aim of this project is to develop a framework for system reliability, which will set a basis for moving towards more consistent reliability assessments. An extensive review study was undertaken first to establish the state of the art in the area of structure system reliability analysis of offshore structures. Based on the findings of this study, a generic system reliability framework was developed which was then developed further for specific application to fixed offshore platforms. These initial studies identified some of the key technical issues that required further investigation. The subsequent offshore application and sensitivity study, using a representative fixed platform model, concentrated on these issues and in particular on the effects of foundation parameters on ultimate strength and their interaction with other key parameters in determining the resistance function. The effect of foundation parameters and different modelling methods on system strength and reliability of fixed offshore platforms, which has largely been neglected in the past, was also investigated. The response surface methodology was developed for system reliability assessment of offshore structures incorporating the effect of foundation reliability. The findings were then used to revise the framework and provide more comprehensive account of key steps in the process of system reliability assessment. Some guidelines on the application of the response surface technique to fixed platform assessment were developed. In addition, an initial screening tool was also proposed for assessing the level of complexity required for the resistance model of the reliability assessment. The presentation of the reliability framework provides a comprehensive account of the various steps, methods and decisions associated with system reliability analysis. The framework, which can be used in both the design and reassessment of structures, can provide a basis for moving towards more consistent reliability assessments. Recommendations on areas that require further research are also presented.

No description available.

Container-ships are vessels possessing an internal structure that facilitates the handling of containerised cargo. At each port along the journey of a container-ship, containers destined for that port are unloaded, and some containers destined for subsequent ports are loaded. Determining a viable configuration of containers that facilitates this unloading and loading, in a cost-effective way, constitutes the deepsea container-ship stowage problem. The work of determining a stowage configuration for a container-ship, on leaving a port, is performed by human stowage planners. The success of a configuration requires consideration of many factors. These factors include whether the configuration contravenes ship stability, minimises the physical costs of handling the containers, and takes into account expected container loads at subsequent ports. Further complications arise from the existence of hazardous cargo that must be segregated from other cargo and the ship's crew, and from the need to handle containers of non-standard dimensions. Stowage planners must work under strict time constraints, and are limited in the number of stowage configurations that they can consider. This real-world problem seems to be one that would benefit from automation through the application of artificial intelligence. Although many decision support systems exist that automate the time-consuming calculations for ship stability, little work has been published in the area of full automation of stowage planning. Authors proposing full automation have correctly identified the salient features of the problem, but have allowed the array-like nature of spaces within containerised vessels to entirely dictate their approach to addressing the placements of specific containers to specific locations. To enable the implementation of these approaches, excessively large search spaces are pruned through the removal of important features of the problem, rendering the solutions not commercially viable. By concentrating solely on the specific placements of containers, these authors have not recognised how human planners solve the problem. The author of this thesis approaches the container-ship stowage problem from a knowledge engineer's perspective. In the proposed approach, 'intelligence' is provided through the application of the findings of a knowledge elicitation exercise and a systems analysis of the work of human planners. The assumed heuristics inherent in their use of documents are highlighted. This thesis reports on the results of the analysis of the processes employed by a stowage planner. Explanations are provided of how these results allow the problem to be decomposed into subproblems. An implementation of the approach described would determine good, although not necessarily optimum, solutions to the entire problem in a commercially viable duration of time. Further, this approach allows many more stowage configurations to be considered than would be possible for a human planner. The work contained within this thesis demonstrates the feasibility and benefits of such an implementation. The last chapter contains, in addition to a full and detailed list of conclusions made during the research, a summary of some of those areas that still require further work.

Aços de alta resistência mecânica, aspergidos termicamente, são os materiais mais adequados para garantir o bom desempenho de certos componentes de plataformas offshore, expostos a situações severas de carregamento em água do mar. A literatura apresenta vários estudos relativos ao efeito combinado entre esforços mecânicos e o meio agressivo, em aços de alta resistência, entretanto, poucos avaliam o desempenho desses aços aspergidos metalicamente. A susceptibilidade à corrosão sob tensão e à corrosão-fadiga, de um aço de alta resistência mecânica aspergido termicamente, empregado em componentes de plataformas offshore, foi avaliada mediante as técnicas de ensaio de tração com baixa taxa de deformação, ensaio de fadiga por flexão em três pontos e metalografia da fratura. Os ensaios foram realizados em água do mar sintética ao potencial de corrosão e à um potencial catódico, utilizando-se amostras de aço revestidas termicamente com zinco e alumínio pelo processo de aspersão com plasma spray. O comportamento de amostras ensaiadas ao ar foi usado como parâmetro para avaliação do desempenho do aço em água do mar. Os resultados obtidos indicam que o aço revestido é susceptível à corrosão sob tensão e à corrosão fadiga em água do mar, sendo que o mecanismo de fragilização envolve a ruptura prematura dos revestimentos e a participação do hidrogênio.

Os aços inoxidáveis super duplex são materiais relativamente recentes no âmbito industrial, porém seu uso vem crescendo constantemente. Isso se deve a sua excelente combinação de resistência mecânica e resistência a corrosão, incentivando o seu uso em ambientes agressivos. Porém, esse material é suscetível ao hidrogênio fazendo com que seu uso seja limitado em condições onde pode haver permeação de hidrogênio, como é o caso da proteção catódica. O entendimento do processo de fragilização nessa classe de aço trata-se de um desafio tecnológico, especificando sua condição de uso para evitar colapso estrutural. O material estudado trata-se do aço UNS S32760 hidrogenado em três diferentes potenciais catódicos, com o objetivo de compreender melhor o comportamento do material com a absorção de hidrogênio e, também, relacionar os resultados com especificações de uso já existentes. Os corpos de prova hidrogenados foram submetidos a ensaio de baixa taxa de deformação tornando possível a obtenção de parâmetros como tensão máxima, elongação e redução de área na região de fratura. Avaliações macroestruturais e microestruturais foram realizadas com o objetivo de identificar os micromecanismos de fratura. Além disso, para melhor compreensão dos mecanismos de fratura, estas foram observadas através de microscopia eletrônica de varredura para avaliar a influência da proteção catódica. A soma das análises realizadas tornou possível concluir que o aço inoxidável super duplex UNS S32760 já apresenta mecanismos de fragilização em potenciais de -800mVECS em desacordo com algumas especificações existentes. À medida que o potencial aplicado se torna mais catódico, o hidrogênio exerce maior influência no material, entretanto em potenciais extremamente elevados a identificação do fenômeno de fragilização se torna problemática, já que a redução de área e trincas na superfície não são facilmente identificáveis. / Super duplex stainless steel is a modern material in the industry, but its use is gradually increasing. This is due to its excellent blend of mechanical and corrosion properties pushing its use in aggressive environments. However, this material is sensitive to hydrogen making its use limited in environments where the hydrogen permeation can take place, such as in cathodic protection. The understanding of the embrittlement process in class of steels is a technological challenge, specifying the correct use condition to avoid possible structural collapse. The material studied was the UNS S32760 steel hydrogenate in three different cathodic potential, with the aim to better understand the behavior of this material with absorbed hydrogen and, also, connect the results with current standards. The specimens with hydrogen were evaluated in a slow strain rate test making it possible to obtain parameters as maximum stress, elongation and area reduction in the fracture. Macrostructures and microstructures evaluations have been made with the aim to identify the fracture micromechanisms. Furthermore, to obtain a better understanding of the fracture mechanism, the fracture surfaces have been observed with scanning electron microscope to evaluate the influence of the cathodic protection. The sum of all analysis realized make possible to conclude than the super duplex stainless steel UNS S32760 presents embrittlement phenomena at potential of -800mVECS in discordance with some standards currently in use. As the applied potential become more cathodic, the hydrogen acts more influence in material, however in extremely high potentials the recognition of embrittlement phenomena becomes difficult to evaluate, since the area reduction and cracks in the surface are not easily distinguished.