Use of petrinets for solution of a stern gland optimal inspection interval problem

Abstract

Petrinets are a useful tool for graphical and mathematical modelling of complex systems as it greatly simplifies the study of the dynamic behaviour of such systems. It is therefore not surprising that it finds its utility in a vast variety of applications. However, its use in analysis of mechanical systems is limited. The limitation in its applicability to mechanical system stems from the fact that most of the mechanical system components, in a race towards failure, follow a non-exponential failure time distribution where the 'age memory' of the component plays a significant role. The paper discusses a method to circumvent the above limitations by use of a 'method of stages' that can be used to model the wear process as well as exploit the memory less property of various exponentially distributed transition stages and simplify retention of the age memory of the non-exponential process that it models. Application of petrinets for evaluation of various stage probabilities on a sample problem of stern gland of a ship is discussed and results compared with the analytical approach.