diff --git a/component_failure_modes_definition/component_failure_modes_definition.tex b/component_failure_modes_definition/component_failure_modes_definition.tex index 90001a0..7b968c2 100644 --- a/component_failure_modes_definition/component_failure_modes_definition.tex +++ b/component_failure_modes_definition/component_failure_modes_definition.tex @@ -2,7 +2,8 @@ \abstract{ This chapter defines what is meant by the terms components, component fault modes and `unitary~state' component fault modes. The application of Bayes theorem in current methodologies, and -the unsuitability of the `null hypothesis' or p value statistical approach. +the suitability of the `null hypothesis' or `P' value statistical approach +ar discussed. Mathematical constraints and definitions are made using set theory. } @@ -19,12 +20,12 @@ Using these failure modes we can build a `failure model' from the bottom-up. Traditional static fault analysis methods work from the top down. They identify faults that can occur in a system, and then work down to see how they could be caused. Some apply statistical tequniques to -determine the likelyhood of component failures causing specific system level errors (see Bayes theorem \ref{bayes}). +determine the likelihood of component failures causing specific system level errors (see Bayes theorem \ref{bayes}). Another top down technique is ato apply cost benifit analysis to determine which faults are the highest priority to fix\cite{FMEA}. The aim of this study is to produce complete failure -models of safety critical systems from the bottom-up +models of safety critical systems from the bottom-up, starting, where possible with known component failure modes. @@ -33,7 +34,7 @@ starting, where possible with known component failure modes. It is helpful here to define some terms, `system', `functional~group', `component', `base~component' and `sub-system'. A System, is really any coherent entity that would be sold as a safety critical product. -A sub-system is a system that is part of some larger system. +A sub-system is a part of some larger system. For instance a stereo amplifier separate is a sub-system. The whole Sound System, consists perhaps of the following `sub-systems': CD-player, tuner, amplifier~separate, loudspeakers and ipod~interface. @@ -43,18 +44,23 @@ CD-player, tuner, amplifier~separate, loudspeakers and ipod~interface. %and breaks it down. A sub-system will be composed of component parts, which -may themselves be sub-systems. However each `component part' -will have a fault/failure behaviour and it should -always be possible to obtain a set of failure modes -for each `component'. +may themselves be sub-systems. + +Eventually by a recursive downwards process we would be able to identify +sub-systems built from base component parts. +Each `component part' +will have a known fault/failure behaviour. +That is to say, each base component has a set of known +ways in which it can fail. If we look at the sound system again as an example; the CD~player could fail in serveral distinct ways, no matter what has happened to it or has gone wrong inside it. - +A top down approach has an intrinsic problem in that we cannot guess +every possible failure mode at the SYSTEM level. Using the reasoning that working from the bottom up forces the consideration of all possible -component failures (which can be missed in a top~down approach) +component failures (which could be missed in a top~down approach) we are presented with a problem. Which initial collections of base components should we choose ? For instance in the CD~player example; to start at the bottom; we are presented with @@ -92,8 +98,8 @@ Currently this sort of information is generally only available for generic comp %At higher levels of analysis, functional~groups are pre-analysed sub-systems that interact to %erform a given function. -\vspace{0.3cm} -%\begin{table}[p] +%\vspace{0.3cm} +\begin{table}[p] \begin{tabular}{||l|l||} \hline \hline {\em Definition } & {\em Description} \\ \hline System & A product designed to \\ @@ -113,10 +119,11 @@ Failure mode & of a `Failure Mode Group' \\ \hline Base Component & Any bought in component, which \\ & hopefully has a known set of failure modes \\ \hline \hline -\label{tab:def} + \end{tabular} -%\end{table} -\vspace{0.3cm} +\label{tab:def} +\end{table} +%\vspace{0.3cm} \section{A UML Model of terms introduced} @@ -130,43 +137,54 @@ Base Component & Any bought in component, which \\ \end{figure} The diagram in figure \ref{fig:fmmd_uml} -shows the relationships between the terms defined in table \ref{tab:def}. +shows the relationships between the terms defined in table \ref{tab:def} as classes in a UML model. We can start with the functional group. This is a minimal collection of components that perform a simple given function. For our audio separates rig, this could be the compoents that supply power to the laser diode. -From the `Functional Group we can now collect -all the `failure modes of the `components, and -produce a `Failure Mode Group. This -has a reference to the `Functional Group, and is a collection +From the `Functional~Group' we can now collect +all the `failure modes of the `components', and +produce a `Failure~Mode~Group'. This +has a reference to the `Functional~Group', and is a collection of `failure modes. -By analysing the effects of the failure modes in the `Failure Mode Group' +By analysing the effects of the failure modes in the `Failure~Mode~Group' we can determine the failure mode behaviour of the functional group. This failure mode behaviour is a collection of derived failure modes. We can now consider the Functional group as a component now, because we have a set of failure modes for it. -We can term this set of failure modes a sub-system. -Note that this is recursive. We can build functional groups using sub-systems +\subsection{Sub-System Class Definition} +A sub-system can now be defined by the classes used to create it, and +its set of derived failure modes. + +Note that the UML model is recursive. We can build functional groups using sub-systems as components. This UML model naturally therefore, forms a hierarchy of failure mode analysis, which has a one top level entry, that being the SYSTEM. The TOP level entry will determine the failure modes for the product/system under analysis. - +\subsection{Refining the UML model to use inheritance} We can refine this model a little by noticing that a system is merely the top level sub-system. We can thus have System inherit sub-system. A derived failure mode, is simply a failure mode at a higher level of analysis it can therefore inherit `failure\_mode'. -The modified UML diagram using inheritance is figure \ref{fig:fmmd_uml2} +The modified UML diagram using inheritance is figure \ref{fig:fmmd_uml2}. \begin{figure}[h] \centering - \includegraphics[width=350pt,bb=0 0 680 500,keepaspectratio=true]{component_failure_modes_definition/fmmd_uml2.jpg} - % fmmd_uml.jpg: 680x500 pixel, 72dpi, 23.99x17.64 cm, bb=0 0 680 500 - \caption{UML respresentation of Failure Mode Data types} + \includegraphics[width=350pt,bb=0 0 877 675,keepaspectratio=true]{./fmmd_uml2.jpg} + % fmmd_uml2.jpg: 877x675 pixel, 72dpi, 30.94x23.81 cm, bb=0 0 877 675 + \caption{UML Representation of Failure Mode Data Types} \label{fig:fmmd_uml2} \end{figure} +% +% \begin{figure}[h] +% \centering +% \includegraphics[width=350pt,bb=0 0 680 500,keepaspectratio=true]{component_failure_modes_definition/fmmd_uml2.jpg} +% % fmmd_uml.jpg: 680x500 pixel, 72dpi, 23.99x17.64 cm, bb=0 0 680 500 +% \caption{UML respresentation of Failure Mode Data types} +% \label{fig:fmmd_uml2} +% \end{figure} \subsection{Unitary State Component Failure Mode sets} @@ -181,7 +199,7 @@ Having a set of failure modes where $N$ modes could be active simultaneously would mean having to consider $2^N$ failure mode scenarios. % Should a component be analysed and simultaneous failure mode cases exit, -the combinations could be represented by a new failure modes, or +the combinations could be represented by new failure modes, or the component should be considered from a fresh perspective, perhaps considering it as several smaller components within one package. @@ -239,7 +257,7 @@ the failure mode set is not unitary~state and does not exist in the family of se \subsection{Component Failure Modes and Statistical Sample Space} - +%\paragraph{NOT WRITTEN YET PLEASE IGNORE} A sample space is defined as the set of all possible outcomes. When dealing with failure modes, we are not interested in the state where the compoent is working perfectly or `OK' (i.e. operating with no error). @@ -254,6 +272,7 @@ is therefore $$ F = \Omega(K) \backslash OK $$ \subsection{Bayes Theorem} + \paragraph{NOT WRITTEN YET PLEASE IGNORE} \label{bayes} Describe application - likely hood of faults being the cause of symptoms - probablistic approach - no direct causation paths to the higher~abstraction fault mode. @@ -271,6 +290,7 @@ to %unitary~state set family. \subsection{Tests of Hypotheses and Significance} +\paragraph{NOT WRITTEN YET PLEASE IGNORE} Linked in with Bayes theorem Accident analysis plane crashes and faults etc