A stochastic model for railway track asset management

The determination of the strategy to ensure that the geometry for railway track is kept within acceptable limits, in a cost effective manner, is a complex process. It requires the simultaneous consideration of the activities which govern inspection, maintenance and renewal. In addition to this the geometry degradation process is dependent upon the maintenance history. The condition where the track geometry is shown to have deteriorated to a level where intervention is required can be improved using a tamping machine. Tamping is carried out by a special train which measures the geometry of the rails, predicts the correction needed, lifts the rails to the required position, inserts tines into the ballast either side of the sleepers and packs the ballast such that the correct rail position is attained. Whilst improving the geometry this process has the disadvantage that it also breaks the ballast which accelerates the track geometry degradation and reduces the time between interventions. This paper describes a modelling process to predict the state of the track geometry given any specified asset management strategy. It is based on the Petri net method and in addition to predicting the track condition over time it can also compute the expected whole life costs. By varying the parameters which govern the inspection, maintenance and renewal of the ballast as the most cost effective means to achieve the required level of performance can be predicted

A reliability-based approach to mission planning in multi-platform phased missions

Many systems perform phased missions consisting of several distinct, sequential phases. Mission success depends on the successful completion of all mission phases. Increasingly, for example in military theatre, platforms operating phased missions are required to collaborate in order to achieve an overall mission objective, with specific platform phases containing specific tasks that contribute to that objective. Particularly, but not exclusively, in the case of autonomous vehicles, the calculation of phase and mission failure probabilities can be used to assist in making decisions on the future course of a mission. This paper describes how this decision making process can be implemented

A comparison of modelling approaches for the time-limited dispatch (TLD) of aircraft

The time-limited dispatch (TLD) of aircraft allows operators to efficiently meet certification requirements. In order to display that these requirements are met it is necessary to model the aircraft systems to which TLD is being applied. Currently variations of fault tree analysis and Markov analysis are commonly used. However, in order to apply either of these methods a number of assumptions are made in order to assist in the analysis. Monte Carlo simulation (MCS) is presented here as an alternative method of demonstrating the required level of system reliability. A simple system is analysed using a time-weighted average approach, a reduced fault state Markov approach and a MCS approach. MCS is seen to offer benefits when modelling the application of TLD to a simple system that could also be seen in the modelling of the application of TLD to real aircraft systems

A comparison of modelling approaches for the time-limited dispatch (TLD) of aircraft

The time-limited dispatch (TLD) of aircraft allows operators efficiently to meet certification requirements. In order to show that these requirements are met it is necessary to model the aircraft systems to which TLD is being applied. Currently, variations of fault tree analysis and Markov analysis are commonly used. However, in order to apply either of these methods, a number of assumptions are made to assist in the analysis. Monte Carlo simulation (MCS) is presented here as an alternative method of demonstrating the required level of system reliability. A simple system is analysed using a time-weighted average approach, a reduced fault state Markov approach, and an MCS approach. MCS is seen to offer benefits when modelling the application of TLD to a simple system that could also be seen in the modelling of the application of TLD to real aircraft systems

The safe dispatch of aircraft with known faults

Time-limited dispatch (TLD) allows the dispatch of aircraft with faults present in their control systems for limited time periods. In order for TLD to be applied to an aircraft system it is first necessary to demonstrate that the relevant safety and certification requirements are being met by modelling the system in question. To do this existing modelling techniques use variations of fault tree analysis and Markov analysis with various simplifying assumptions, made to assist in the analytical process. Monte Carlo simulation is presented here as an alternative method of analysis, which can deal well with the potential difficulties that may present themselves when modelling TLD, such as the complex architectures of aircraft systems and dependencies that are introduced when applying TLD. In this paper a simple example system is introduced and the application of TLD to it is modelled using the existing variation of Markov analysis and a Monte Carlo simulation technique. The results obtained using the different techniques are seen to differ and a number of reasons are suggested for this difference

The safe dispatch of aircraft with known faults

Time-limited dispatch (TLD) allows the dispatch of aircraft with faults present in their control systems for limited time periods. In order for TLD to be applied to an aircraft system it is first necessary to demonstrate that the relevant safety and certification requirements are being met by modelling the system in question. To do this existing modelling techniques use variations of fault tree analysis and Markov analysis with various simplifying assumptions, made to assist in the analytical process. Monte Carlo simulation is presented here as an alternative method of analysis, which can deal well with the potential difficulties that may present themselves when modelling TLD, such as the complex architectures of aircraft systems and dependencies that are introduced when applying TLD. In this paper a simple example system is introduced and the application of TLD to it is modelled using the existing variation of Markov analysis and a Monte Carlo simulation technique. The results obtained using the different techniques are seen to differ and a number of reasons are suggested for this difference

Aircraft safety modeling for time-limited dispatch

This paper offers an alternative method of modeling the Time-Limited Dispatch (TLD) of aircraft. Existing methods involve the use of fault tree analysis and Markov analysis with various simplifying assumptions. Monte Carlo simulation (MCS) is the suggested alternative, which overcomes the problems associated with the other techniques, such as dependencies between basic events (fault tree analysis) or huge number of system states (Markov analysis). The results obtained from the analysis of a simple example are compared for the existing modeling approaches and MCS. MCS is seen to have potential advantages, especially when modeling TLD for large, full scale systems

A reliability-based prognostics framework for railway track management

Railway track geometry deterioration due to traffic loading is a complex problem with important implications in cost and safety. Without appropriate maintenance, track deterioration can lead to severe speed restrictions or disruptions, and in extreme cases, to train derailment. This paper proposes a physics-based reliability-based prognostics framework as a paradigm shift to approach the problem of railway track management. As key contribution, a geo-mechanical elastoplastic model for cyclic ballast settlement is adopted and embedded into a particle filtering algorithm for sequential state estimation and RUL prediction. The suitability of the pro- posed methodology is investigated and discussed through a case study using published data taken from a laboratory simulation of train loading and tamping on ballast carried out at the University of Nottingham (UK)

An information theoretic approach for knowledge representation using Petri nets

A new hybrid approach for Petri nets (PNs) is proposed in this paper by combining the PNs principles with the foundations of information theory for knowledge representation. The resulting PNs have been named Plausible Petri nets (PPNs) mainly because they can handle the evolution of a discrete event system together with uncertain (plausible) information about the system using states of information. This paper overviews the main concepts of classical PNs and presents a method to allow uncertain information exchange about a state variable within the system dynamics. The resulting methodology is exemplified using an idealized expert system, which illustrates some of the challenges faced in real-world applications of PPNs

Meeting the duty? An explorative study of four Welsh local authority looked-after children’s education (LACE) teams and views of their interventions from looked-after young people

Almost a decade ago, Berridge, Dance, Beecham and Field (2008, p.49) noted a worrying absence of research into the UK picture of education support teams in terms of their organisational structure and priorities. This thesis represents an original contribution to knowledge in regard to the educational support provided for Looked-After Children in Wales. The overall sample (n=28) comprised four Looked After Children Education (LACE) coordinators, seven LACE team practitioners and seventeen young people with looked-after status, aged 14-16 years old, from across four local authorities in south Wales. This qualitative research is informed by constructionist ontology and is positioned within an interpretivist framework. Data were subjected to a coding framework and thematic analysis. The research yields useful insights with some clear implications for policy and practice. It has sought to address that void and add to a slowly growing knowledge base as little is known about the ways in which LACE Coordinators and their team practitioners interpret and enact relevant policy in their day to day work. Research findings include: The LACE team relationships with young people being described by workers were typically in administrative and procedural terms; LACE practitioners’ support typically lasts for an hour, once a week, and which was described by some young people as of welcome but limited value. Thus, the perennial discourse of ‘low attainment’ that surrounds looked-after children might be more aptly be re-cast as ‘low investment’ by the state, national and local; LACE practitioners’ described their work practice as a specialist knowledge area, but also disclosed how their knowledge and expertise was often undervalued or rejected by other external practitioners; young people’s identities appeared to be fashioned, by LACE practitioners, through occupational assumptions derived from a broader public welfare child discourse. In contrast the young people’s own identities did not coalesce with the perceptions of LACE practitioners. Instead, their comments indicated a more ‘normalised’, non-stigmatised, and pragmatic but also care (as affect) related sense of self. The thesis has argued that there needs to be a new framework that unites the way workers understand looked-after children and the relationships that will optimise meaningful achievement