heal.abstract |
Present thesis attempts an introduction to machine learning methodologies. This introduction is attempted along with the creation of a dynamic probabilistic predictive model which simulates deterioration trends. The general approach for such a model is a risk-based approach. Risk can be useful for decision making, as it considers the expected value of the degree of impact. The implementation of such a model is achieved through a dynamic probabilistic graphical model, namely a dynamic Bayesian belief network. Dynamic Bayesian networks are a powerful tool for risk modeling and for creating prediction models. The graphical representation of Bayesian networks makes them understandable and accessible even to non-familiar researchers or maritime executives. The above methodology is implemented on the lubrication of marine diesel engine, namely the main engine of large commercial vessels. Studies show that there are enough motivating reasons for this specific focus, as lubrication failures are the most significant cause of damage, both in number and average cost. Meanwhile, considering a risk-based approach for machinery systems constitutes a challenge, since they are not widely adopted.
Thus, a dynamic Bayesian network is developed which simulates deterioration of engine components, oil degradation, and the off-line condition monitoring technique of oil analysis along with subsequent maintenance and repairs. Oil analysis is introduced to the system as the most common condition monitoring technique for marine engine lubrication. Additionally, an effective modeling of dependencies among lubricant properties, lubrication system parameters, failure mechanisms and failing components must be produced in order to achieve realistic simulations. Real data and respective analysis, along with expert elicitation and literature references are utilized for achieving model quantification. A variety of oil analysis interval schemes are defined, and a decision upon the most beneficial scheme follows, based on risk comparison. Matlab programming is used, along with the Bayes Net toolbox libraries, for producing the code of the model. |
en |