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Doctoral Thesis
DOI
https://doi.org/10.11606/T.18.2013.tde-26032013-104724
Document
Author
Full name
Wellison José de Santana Gomes
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2013
Supervisor
Committee
Beck, André Teófilo (President)
Leonel, Edson Denner
Rochinha, Fernando Alves
Sagrilo, Luis Volnei Sudati
Trindade, Marcelo Areias
Title in Portuguese
Otimização de riscos sob processos aleatórios de corrosão e fadiga
Keywords in Portuguese
Confiabilidade estrutural
Otimização de risco
Otimização estrutural
Polinômios de caos
Abstract in Portuguese
Processos aleatórios de corrosão e fadiga reduzem lentamente a resistência de estruturas e componentes estruturais, provocando um aumento gradual nas probabilidades de falha. A gestão do risco de falha de componentes sujeitos a corrosão e/ou fadiga é feita através de políticas de inspeção, manutenção e substituição, atividades que implicam em custos, mas visam manter a confiabilidade em níveis aceitáveis, enquanto o componente permanecer em operação. Aparentemente, os objetivos economia e segurança competem entre si, no entanto, a redução de recursos para inspeção e manutenção pode levar a maiores e crescentes probabilidades de falha, implicando em maiores custos esperados de falha, ou seja, maior risco. A otimização de risco estrutural é uma formulação que permite equacionar este problema, através do chamado custo esperado total. Nesta Tese, a otimização de risco é utilizada no intuito de encontrar políticas ótimas de inspeção e manutenção, isto é, quantidades de recursos a serem alocadas nestas atividades que levem ao menor custo esperado total possível. Os processos de corrosão e fadiga são representados através de modelos em polinômios de caos, construídos de maneira inédita, com base em dados experimentais ou observados da literatura. Com base nestes modelos, os problemas de otimização de risco envolvendo processos de fadiga e corrosão são resolvidos para diferentes configurações de custos de falha e de inspeções. Verifica-se que as políticas ótimas de inspeção, manutenção e substituição podem ser bastante diferentes para configurações de custo distintas, e que a determinação destas políticas é bastante desafiadora, devido, dentre outros fatores, à grande quantidade de mínimos locais do problema de otimização em questão, causadas por descontinuidades e oscilações da função custo esperado total.
Title in English
Risk optimization under random corrosion and fatigue processes
Keywords in English
Polynomial chaos
Risk optimization
Structural optimization
Structural reliability
Abstract in English
Random corrosion and fatigue processes reduce slowly but gradually the resistance of structures and mechanical components, leading to gradual increase in failure probabilities. Risk management for mechanical components subject to corrosion and fatigue is made by means of policies of inspection, maintenance and substitution. These activities imply costs, but are made to maintain the reliability at acceptable levels, while the component remains in operation. Apparently, economy and safety are competing objectives; however, reduction in inspection and maintenance spending may lead to larger failure probabilities, increasing expected costs of failure (risk). Risk optimization allows one to solve this problem, by means of the so-called total expected cost. In this Thesis, risk optimization is used in order to find the best inspection and maintenance policy, i.e., the proper amount of resources to allocate to such activities in order to obtain minimum total expected cost. Corrosion and fatigue are modeled by means of polynomial chaos expansions, using a novel approach developed herein and experimental or observed data obtained from the literature. These models are employed within two risk optimization problems, solved for different failure and inspection cost configurations. Results show that the optimal policies of inspection, maintenance and replacements can be very different, for different cost configurations, and that the solution of the associated risk optimization problems is a very challenging task, due to the large number of local minima, caused by discontinuities and fluctuations in the total expected costs.
 
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Publishing Date
2013-03-28
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • BECK, A. T., e Gomes, W. J. S. Stochastic Fracture Mechanics Using Polynomial Chaos [doi:10.1016/j.probengmech.2013.04.002]. Probabilistic Engineering Mechanics [online], 2013, vol. 34, p. 26-39.
  • Gomes, W. J. S., and Beck, André T. Optimal Inspection and Design of Onshore Pipelines Under External Corrosion Process. Structural Safety, 2014.
  • Gomes, W. J. S., BECK, A. T., and Haukaas, T. Optimal Inspection Planning for Onshore Pipelines Subject to External Corrosion [doi:10.1016/j.ress.2013.04.011]. Reliability Engineering & Systems Safety [online], 2013, p. 18-27.
  • Gomes, W. J. S., BECK, A. T., e Ávila S. Jr., Claudio R. Modeling Random Corrosion Processes via Polynomial Chaos Expansion. Journal of the Brazilian Society of Mechanical Sciences and Engineering , 2012, vol. 34NSpe, p. 561-568.
  • Gomes, W.J.S., e BECK, A. T. Representação de Processos de Corrosão e Fadiga Utilizando Polinômios de Caos. Cadernos de Engenharia de Estruturas , 2011, vol. 13, p. 81-84.
  • Gomes, Wellison José de Santana, and BECK, A. T. Global structural optimization considering expected consequences of failure and using ANN surrogates [doi:10.1016/j.compstruc.2012.10.013]. Computers & Structures [online], 2013, vol. 126, p. 56-68.
  • Gomes, W. J. S., and BECK, A. T. Optimal Inspection of Onshore Pipelines Subject to External Corrosion [doi:10.3303/CET1333139]. In PHM - Prognostics and System Health Management Conference, Milão, Italia, 2013. Chemical Engineering Transactions. : AIDIC, 2013.
  • Gomes, W. J. S., e BECK, A. T. Optimization of a Transmission Line Tower under Random Wind Loads Considering Expected Consequences of Failure. In International Symposium on Solid Mechanics - MecSol2013, Porto Alegre, 2013. Proceedings of the 4th International Symposium on Solid Mechanics.Porto Alegre : UFRGS, 2013.
  • Gomes, W. J. S., e BECK, A. T. Optimization of Inspection Intervals for Corroding Pipelines. In 11th International Conference on Structural Safety and Reliability - ICOSSAR, Nova York, 2013. Safety, Reliability Risk and Life-Cycle Performance of Structures and Infrastructures., 2013.
  • Gomes, W. J. S., e BECK, A. T. Random Crack Propagation using Polynomial Chaos. In 11th International Conference on Structural Safety and Reliability - ICOSSAR, Nova York, 2013. Safety, Reliability Risk and Life-Cycle Performance of Structures and Infrastructures., 2013.
  • Gomes, W. J. S., e BECK, A. T. Structural Optimization under Uncertainties using Artificial Neural Network Surrogates. In 11th International Conference on Structural Safety and Reliability - ICOSSAR, Nova York, 2013. Safety, Reliability Risk and Life-Cycle Performance of Structures and Infrastructures., 2013.
  • Gomes, W.J.S., e BECK, A. T. Optimization of Transmission Line Steel Towers Under Random Wind Loads. In 10th World Conference on Computational Mechanics, São Paulo, 2012. Book of Abstracts: 10th World Congress on Computational Mechanics.São Paulo : Soma, 2012. Resumo.
  • Gomes, W.J.S., Silva Jr., C.R.A., e BECK, A. T. Modeling Random Corrosion Processes via Polynomial Chaos Expansion. In Uncertainties 2012: First International Symposium on Uncertainty Quantification and Stochastic Modeling, Maresias, São Sebastião, 2012. Proceedings of the 1st International Symposium on Uncertainty Quantification and Stochastic Modeling.São Carlos, SP : Editora Cubo, 2012.
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