Current Issues and Challenges in the Reliability and Maintenance of Complex Systems

With the rising demands in improvement of deliveries to reduction of cost, there is an increasing pressure from operational managers to reduce cost and improve reliability and increase availability of production systems, air travel , rail travel , space and all mechanised systems. This has put a challenge on maintenance and reliability engineers worldwide who face a gargantuan task of improving their skill sets and analytical abilities to deepen the knowledge curve in order to keep their organisation the leader in the cost, quantity and quality. Let us examine some basics which can help us get more inspiration. From an engineering point of view we need to get back to our Math. We as engineers need to value the math involved in all the production systems we work with. So since reliability is a relative concept we have to delve deeper using five concepts

1. A stochastic model

2. Maintenance of complex systems.

3. Stochastic methods in software engineering

4. Computational methods and simulation in reliability and maintenance

5. Maintenance management systems

We will just see in brief some concepts of the above

1. A stochastic model.

A stochastic model looks at using statistical and probability methods for predicting reliability and maintenance techniques for predicting fatigue crack growth, fatigue crack propagation, linearizing time transformations, physics of failure, reliability analysis via corrections, rational based failure modelling. This involves a large part from the amount of data available to apply this model. There fore the diagram gives a fair idea to the amount of data collection required to build a model for predicting reliability.

All these subjects provide a wealth of tools for the reader to introspect and apply to the systems he is tasked for maintaining in his plan. But it obviously involves a task in collecting data to select an appropriate method for analysis.

2. Maintenance of complex systems.

A complex system, sets of machines to maintain is the most dread factor for a maintenance engineer like the task to maintain the aircraft in the picture. The parts and each part failure can cause a huge loss which is Multi million kroner cost of purchase + million kroner cost of pilot and multi million kroner ordnance . Its a big challenge to maintain such a complex piece of equipment especially when you have a a big installation of such complex equipment running simultaneously or squadrons of aircraft. Mr Frank Van der Duyn Schouten from CentER for Economic Research, School of Management and Economics, Tilburg University, 5000 LE Tilburg, The Netherlands in his thesis Maintenance policies for multi component systems suggests using applied probability theory, renewal theory and markov decision theory which he suggests as an idea for making a model and supports a solution in understanding the procedures to support complex maintenance management decision problems.

3.Stochastic methods in software engineering

Software reliability engineering has become an increasingly important part of software development and software acquisition as the dependence of society on software has become virtually universal.

Software reliability engineering is a rapidly spreading practice for software based systems for asserting reliability techniques. We use the term "software-based" because the real interest is in reliability of total systems, which may have both hardware and software components. Clearly, there is no such thing as a pure software system; some sort of computing logic (hardware) is always needed to execute a program. Software reliability engineering is an important subset of the larger domain of software engineering. It has four significant defining characteristics:

1. Setting quantitative reliability objectives in such a way that customer satisfaction with the product will be maximized if they are met ,

2. Engineering the product and the development process to meet the objectives,

3. Focusing development and test on the highest-use and most critical operations,

4. testing components and the system to meet the objectives

4. Computational methods and simulation in reliability and maintenance

5. Maintenance management systems

The maintenance management system supports the associated maintenance process. The management system cannot therefore be implemented effectively until the process has been mapped out and modelled. Business process analysis can be used to provide a model of the business process. For the maintenance process, the maintenance model identifies all activities required to satisfy the maintenance objectives and their relationship to other parts of the business.Most important is to have a clear description of the maintenance process which is widely understood and accepted throughout the company. The maintenance activities can be described in as much detail as required, but always keeping a transparent relationship with the process to which they belong. Thus maintenance activities can always be seen in context of their contribution to overall business objectives.The maintenance business model must fulfill many criteria. It must serve a "top down" purpose and thus be directly related to a higher-level "Operations" business model: maintenance must be seen as part of the larger picture. Yet it must also be "bottom up": maintenance engineers must be able to recognise their own tasks within it. Most importantly in the context of this paper: it must be capable of acting as the starting point for the development of the maintenance management system.The development of a business model is the first and possibly the hardest single step in the development of a management system. The business model acts as the framework within which the activities are defined, including a description of their logical sequences and their interrelationships with other activities and other processes.

Generically, the maintenance process can be described using a

PLAN -SCHEDULE - EXECUTE - ANALYZE - IMPROVE loop.

• Plan. All five stages are self-evidently essential to an effective management system. However, the course is set in the planning stage. It ensures that policies and strategies are consistent with those in the rest of the company and with the corporate objectives. It sets the targets and identifies the resources to be made available. It identifies what needs to be achieved in the years ahead.

• Schedule. Scheduling sets when things get done. It deals with clash avoidance, efficient use of resources and minimizing any effects on availability in order to meet contractual production requirements.

• Execution. This is the (only) stage when field activities take place. In this stage the physical implementation of planned and scheduled activities takes place. It is the part of the process which yields the return in the form of product, where most of the resources are consumed, and also where the biggest (physical) risks are encountered.

• Analyse. This stage is where all the results obtained during execution are examined and performance analysed. Aim of the analysis stage is firstly to compare performance against plan, and secondly to point the way to do better than the plan.

• Improvement. The final stage (before feedback to the first two) is improvement in which remedies or improvements are proposed and justified.This stage is also where the capacity to react to new challenges and opportunities is established. The improvement stage and the planning stage are closely linked, as improvements are selected by methods very similar to the ones by which the original plans were made.

The Management System

The purpose of a management system is to ensure that the process activities are performed in a manner which meets agreed customer requirements. The system also provides a basis (benchmark) to facilitate improvement.

In general, management systems should cover the following aspects.

1. the description of the process, activities and tasks designed to meet corporate and customer requirements with performance measurement and feedback systems to enable control and continuous improvement.

2. policies, standards and procedures related to the process and activities;

3. controls appropriate to the risks and critical activities of the process;

4. an organisational structure that matches the process, with tasks and responsibilities defined for each critical activity;

5. a description of the main competencies required from staff to supervise and carry out the activity/task;

6. information and data systems to enable control and improvement

Measuring Performance of the Management System

Without appropriate measurements, no activity can be managed properly.Such measurements can be performed using performance indicators. Performance indicators are comparative quantitative measures of actual events, set against previously projected measures of those events, which additionally provide a qualitative indication of future projected performance based on current achievement. Performance indicators should only be defined for the critical activities in the process. The process of comparison incorporates an original projection, a current measure and a quantitative measure of variation between the two. The process of comparison implies:

1. the validity of the original projection;

2. a requirement to control the outcome;

3. an expected deviation from the original projection;

4. an ability to forecast and to alter current events to reduce deviations;

5. that the measure will indicate the action required to do this

The most significant point about good performance indicators, therefore,is that they are useful in indicating future action. Their primary role is nothing to do with gathering historical data as such.Performance indicators are generally designed to measure business process and activities performance in terms of:

1. Effectiveness (an attribute indicating that the products meet specified fit for purpose requirements);

2. Efficiency (an attribute indicating that the products are produced with minimum use of resources);

3. Flexibility (effective and efficient in face of change).

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