Semi-Markov and delay time models of maintenance

Choi, KM

Abstract

This thesis is concerned with modelling inspection policies of facilities which
Qraduallv deteriorate in time. The context of inspection policies lends itself readily to
probabilistic modelling. Indeed, many of the published theoretical models to be found
in the literature adopt a Markov approach, where states are usually 'operating', 'operating
but fault present', and 'failed'. However, most of these models fail to discuss the 'fit' of
the model to data,a nd virtually no exampleso f actual applications or case-studiesa re to
be found.
hi a series of recent papers dating from 1984, a robust approach to solve these
problems has been introduced and developed as the Delay Time Model (DTM). The
central concept for this model is the delay time, h, of a fault which is the time lapse
from when a fault could first be noticed until the time when its repair can be delayed no
longer because of unacceptable consequences. The bottle neck in delay time modelling
is how to estimate the delay time distribution parameters. Two methods for estimating
these parameters have been developed. namely the subjective method and the objective
method.
Markov models have the advantage of an extensive body of theory. 'fliere are,
however. difficulties of definition, measurement, and calculation when applying Markov
models to real-world situations within a maintenance context. Indeed. this problem has
motivated the current research which ainis to explore the two modelling methodologies
in cases where comparison is valid, and also to gain an insight as to how robust Markov
inspection models can be as decision-aids where Markovian properties are not strictly
satisfied. It Nvill be seen that a class of inspection problems could be solved by a serni-
Markov model using the delay time concept. In this thesis, a typical senii-i%Ia, rkov
inspection model based upon the delay time concept is presented for a complex
repairable systein that may fail during the course of its service lifetime and the results
are compared. Finally, a case study of the senii-Markov inspection model and the delay
time model is discussed.

Citation

Choi, K. (1997). Semi-Markov and delay time models of maintenance. (Thesis). University of Salford, UK

• Thesis Type: Thesis
• Deposit Date: Jun 29, 2009
• Publicly Available Date: Jun 29, 2009
• Additional Information: Additional Information : PhD supervisor: Professor A. H. Christer