229 publications from this institution
Extending the operating lifetime of ageing technical systems is of great interest for industrial applications. Life extension requires identifying and selecting decision alternatives which allow for a safe and economic operation of the system beyond its design lifetime. This article proposes a dynamic Bayesian network for assessing the life extension of ageing repairable systems. The main objective of the model is to provide decision support based on the system performance during a finite time horizon, which is defined by the life extension period. The model has three main applications: (i) assessing and selecting optimal decision alternatives for the life extension at present time, based on historical data; (ii) identifying and minimizing the factors that have a negative impact on the system performance; and (iii) reassessing and optimizing the decision alternatives during operation throughout the life extension period, based on updating the model with new operational data gathered. A case study illustrates the application of the model for life extension of a real firewater pump system in an oil and gas facility. The case study analyzes three decision alternatives, where preventive maintenance and functional test policies are optimized, and the uncertainty involved in each alternative is computed.
A Dynamic Positioning (DP) system enables vessels and rigs to accurately maintain a predetermined position and heading or track. It enables precise operations under harsh environmental conditions. DP is used for a variety of purposes; however, the role of the DP operator (DPO) is considered the same regardless of type of operation: to monitor and keep the vessel in position. Some of the decisions that the DPO makes are safety critical, for example, decisions about the set-up of the system can prevent the vessel from colliding with an offshore oil and gas platform. Applied cognitive task analysis (ACTA) is performed to analyze how the different operational settings influence the role and decision-making of the DPO. Two DPOs with experience from five different operation types were interviewed. The results from the ACTA for the different operation types are compared with respect to technical steps, cues, the cognitive steps and components, actions, and decisions. The contextual factors are evaluated using an adapted version of Rasmussen's dynamic safety model. The results of the comparison are used to evaluate the current role of the DPO, in light of the DP system and different DP operations. Recommendations for the improvement of safety, the design of the DP system, training and set-up of DP operations are formulated.