Hybrid Modelling for Dynamic Reliability Assessments in Subsea Oil and Gas Processing Systems
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Traditional reliability methods such as fault tree analysis and reliability block diagrams were not designed to account for the complex dynamic behavior of most industrial systems. These traditional reliability methods make simplifications in the modelling of many engineering systems, by assuming static operational and environmental conditions. Therefore, they are not able to account for the influence of the dynamics of the operations, environment or interactions between components of the system over the failure rates or degradation process of these, neither for the reciprocal influence of the failures and degradation processes over the process and system performance. For this purpose, dynamic reliability has been conceived as an extension of traditional reliability methods, by combining these with process modelling, automation and the theory of dynamic systems. This thesis focuses in hybrid modelling, as a mean to approach dynamic reliability problems. In hybrid modelling, the problem is described as dependent processes that are modelled separately and then coupled by means of shared variables, describing the dynamic behavior of the system in terms of deterministic physical laws and stochastic models describing failures and/or degradation processes. Driven by the goal in the oil and gas industry of finding new solutions for moving entire topside processing facilities to the seabed, a separator case study is presented, exploring the potential of hybrid models and demonstrating the modelling and simulations procedure and characteristics. The dynamic hybrid model of the case study is constructed using Simulink® as a tool for conducting simulations. Discussions about the modelling procedure and the hybrid model capabilities are included, pointing at the potential and challenges or drawbacks. The results show that hybrid models allow to integrate systems design with reliability analysis, from early stages of new technology development, giving a mean to find optimal solutions regarding safety, cost and performance, while providing confidence in the qualification of such technology. Dynamic reliability assessments are meant to fill the areas in which the traditional methods fall short, complementing these rather than replacing them.