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Über dieses Buch

Ernst G. Frankel This book has its origin in lecture notes developed over several years for use in a course in Systems Reliability for engineers concerned with the design of physical systems such as civil structures, power plants, and transport vehicles of all types. Increasing public concern with the reliability o~ systems for reasons of human safety, environmental protection, and acceptable ir. vestment risk limitations has resulted in an increasing interest by engineers in the formal applica~i0n of reliability theory to e~gineering desian. At the same time there is a demand for more effective approaches to the des~gn of procedures for the operation and use of man-made syste~s and more meaningful assessment of the risks intr)duction and use of such a system poses both when operating as designed and when operating at below design performance. The purpose of the book is to provide a sound, yet practical, introduction to reliability analysis and risk assessment which can be used by professionals in engineering, planning, management, and economics to improve the design, operation, and risk assessment of systems of interest. The text should be useful for students in many disciplines and is designed for fourth~year undergraduates or first-year graduate students. I would like to acknowledge the help of many of my graduate students who contributed to the development of this book by offering comments and criticism. Similarly I would like to thank Mrs.

Inhaltsverzeichnis

Frontmatter

Preface

Abstract
This book has its origin in lecture notes developed over several years for use in a course in Systems Reliability for engineers concerned with the design of physical systems such as civil structures, power plants, and transport vehicles of all types. Increasing public concern with the reliability of systems for reasons of human safety, environmental protection, and acceptable investment risk limitations has resulted in an increasing interest by engineers in the formal application of reliability theory to engineering design. At the same time there is a demand for more effective approaches to the design of procedures for the operation and use of man-made systems and more meaningful assessment of the risks introduction and use of such a system poses both when operating as designed and when operating at below design performance.
Ernst G. Frankel

1.0. Introduction

Abstract
The world we live in is imperfect and we increasingly have to live with failure of many of our traditional as well as advanced mechanical, electrical, structural, as well as economic and social systems. The reason often is not insufficiency of concept, design, or operational standards used in the system, but the fact that little or no consideration has been given to the desired reliability, availability, and maintainability of the system in its conception, design, and operation. It is not only that we often expect too much, but that we are ignorant of the actual operating environment and required performance imposed on a system. Little or no consideration is usually given to the basic fact that “nothing is perfect”, and the system’s design as well as operating conditions are subject to many deviations and uncertainties. It is therefore necessary to assign inherent or potential imperfections to systems so as to achieve desired performance.
Ernst G. Frankel

2.0. Fundamental Concepts

Abstract
The reliability of a system and the risk of failure of a system are complementary concepts. The reliability of a system is the probability that the system will not fail during a specified time period under given operation conditions, while the risk of failure is the probability that the system will fail during that period and operating conditions. Failure is a probabilistic event, and may occur as a result of inherent defects in the system, wear and tear, or imposition of unexpected internal or external factors. It may be the result of faulty design, insufficient maintenance, faulty operation, natural catastrophies, or other factors. Most systems interact with and are affected by other systems which may induce conditions or factors which increase the risk of or actually cause failure of the system.
Ernst G. Frankel

3.0. Assessment of Reliability Function

Abstract
In the previous section, the reliability of a system was expressed in precise probabilistic terms. However, no indication was given on how to find the appropriate reliability function for a real component or system. There are two different approaches to this problem. Either the reliability function can be estimated from curve-fitting the failure data obtained from extensive life testing or it may be hypothesized to be a certain parameterized function (as was done for the mechanical system discussed in the previous section) with the parameters estimated via statistical sampling techniques. Below will be given an example of each of these approaches. However, it must be realized that these examples just give a taste of the methodology available and that reference to one of the standard statistics tests should be made prior to any testing for reliability assessment.
Ernst G. Frankel

4.0. Reliability of Series and Parallel Systems

Abstract
Now that techniques for determining the reliability of a component or system have been discussed, the effect of combining components in series or in parallel redundant groups should be considered. First, series systems will be discussed.
Ernst G. Frankel

5.0. Failure Mode and Effects Analysis — Fault Tree Analysis

Abstract
The purpose of failure mode and effects analysis is to identify the different failures and modes of failures that can occur at the component, subsystem, and systems level and to evaluate the direct and consequential effects of these failures. It involves a formal analysis to determine the effect of subsystem, component, or part failure on system performance or the ability to meet performance requirements or objectives. Such an analysis is usually performed upstream during the conceptual or development phases of a system, to assure that all possible modes of failure have been considered and that the proper design and/or operating provisions have been incorporated to eliminate the potential or cause for the failure or that the magnitude and effect of the failure mode have been reduced to an acceptable level.
Ernst G. Frankel

6.0. Multivariable Probability Distributions and Stochastic Processes

Abstract
Up to this point, the reliability of a system has been determined by use of simple probability concepts and logical arguments. However, for more complex systems, especially those that are maintained, the more powerful techniques of stochastic process theory will be necessary in order to obtain effective solutions. Before discussing stochastic processes though, it may be useful to review multivariable probability distributions.
Ernst G. Frankel

7.0. Testing for Markov Properties

Abstract
Most of the reliability models discussed in this book assume that the systems under consideration exhibit stationary Markov properties. To test whether this assumption is valid or not requires the use of various Chi Square and maximum likelihood statistical techniques. In this section much of the theory for testing Markov properties will be developed for Markov chains. Methods for extending the theory for continuous time parameter Markov processes will be mentioned. In particular, methods will be provided to estimate the transition probabilities from data, to test whether the transition probabilities indicate that the system is stationary, Markovian, or statistically independent, to test whether two processes are identical and to test whether the data is from a system with specific transition probabilities.
Ernst G. Frankel

8.0. The Generalized Failure Process for Nonmaintained Systems

Abstract
Now it is time to apply the theory of Markov processes to systems in order to obtain their reliability. The general approach will be to model the systems as a Poisson failure process, and then use the Markov matrices developed by the model to determine system reliability.
Ernst G. Frankel

9.0. Analysis of Maintained Systems

Abstract
Maintained systems consist of components, some or all of which can be maintained. Similarly the assemblage of components is assumed maintainable. Maintenance comprises different types of actions designed to:
1.
Monitor performance or conditions of components of systems
 
2.
Adjust and calibrate components or systems
 
3.
Perform preventative repairs
 
4.
Perform scheduled repairs
 
5.
Perform complete overhauls
 
6.
Perform casualty repairs
 
For the purpose of our analysis it is convenient to divide maintenance into
a.
Monitoring and calibration normally done without shutting down a system.
 
b.
Preventative repairs done intermittently but not necessarily scheduled.
 
c.
Scheduled repairs performed at preplanned intervals and involving planned maintenance actions.
 
d.
Overhauls which involve a complete systems repair and may include large-scale component replacement. Overhauls may or may not be scheduled. They can be performed as part of a plan or as a result of unexpected casualties.
 
e.
Casualty repairs are defined as repairs required to put a system or component back into operation after an unexpected breakdown.
 
Ernst G. Frankel

10.0. Strategies for Repair Policies

Abstract
Before discussing optimization of system operation with respect to resources (weight, volume, cost, etc.), it might be interesting to consider come of the aspects of the variables affecting operational inputs. When discussing the expected time mij, a system finds itself in a certain state j given it was initially in state i then we may define a ratio mij/t = proportion of time before absorption system finds itself in state j given initially in state i where t = MTBF.
Ernst G. Frankel

11.0. Effects of Component Interaction

Abstract
In previous chapters the overall reliability of hypothetical complex systems has been derived on the assumption of complete independence of component failure rates. In situations where the system comprises mechanical, thermal, hydraulic, chemical, etc., components, it is found that although these methods are mathematically correct, they do not yield the actual reliability observed in practice. Intuitively, it might appear that this poor correlation is because the model is not a good functional representation of the real system. Although this may, on occasion, be a possible reason, further analysis may show that the model is correct; but that the assumption of independence of components was unjustified. It can readily be shown that in systems where components are reduced by wear, chemical reaction, environmental attack, etc., or where component subsystems share a component medium, interaction will invariantly exist. This often results in a change of component failure distribution and may also greatly affect optimum maintenance and replacement scheduling. Because of this, the failure distribution observed in the single component life test is not applicable and must be modified.
Ernst G. Frankel

12.0. Application of Fault Tree and Other Network Techniques

Abstract
As discussed before, fault tree analysis is a technique by which many events affecting a system which interact to produce other events, and ultimately system failure, can be related using simple logical relationships as part of a tree network structure. The logical relationships define the interaction of the events and allow the methodical construction of the fault tree structure. As noted, a fault tree usually starts with a top event, which, is incurred as a result of the occurrence of primary events which in turn are caused by secondary, lower order and command events. A simple example of an on-line redundant system is shown in Figure 12.1.
Ernst G. Frankel

13.0. Reliability and Risk in Perspective

Abstract
All systems, natural or man-made, are subject to failure. We have discussed methods of analysis of failure phenomena and approaches which may help in the design of more reliable systems. Man plays an important role both in the design and use of systems and contributes to the failure of both natural and man-made systems. On the other hand nature may also cause failure, through natural events or interactive factors. The nature of failures varies widely as do the causes of failure events and the events leading to failures. Man’s contributions to the failure of systems involves
1.
conception or misconception of system requirements, capability, or environment
 
2.
design deficiencies and erroneous assumptions
 
3.
faulty construction, manufacture, erection and installation
 
4.
mistakes in the methods or procedures of operation
 
5.
control and management of the system.
 
Ernst G. Frankel

Backmatter

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