From e1461615d7706e09c031549303717b12a415b228 Mon Sep 17 00:00:00 2001 From: Robin Clark Date: Sat, 12 May 2012 11:14:48 +0100 Subject: [PATCH] moar --- submission_thesis/CH4_FMMD/copy.tex | 8 +++++++- submission_thesis/CH6_Evaluation/copy.tex | 6 ++++-- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/submission_thesis/CH4_FMMD/copy.tex b/submission_thesis/CH4_FMMD/copy.tex index 8d2a921..6c9f1d7 100644 --- a/submission_thesis/CH4_FMMD/copy.tex +++ b/submission_thesis/CH4_FMMD/copy.tex @@ -170,7 +170,8 @@ To look in detail at half a million fault~scenarios is obviously impractical. % Requirements for an improved methodology The deficiencies identified in the % current methodologies are used to establish criteria for an improved methodology. -\paragraph{Reasoning distance - complexity and reach-ability.} +\paragraph{Reasoning distance - complexity and reachability.} +\label{sec:rd} Tracing a component level failure up to a top level event, without the rigour accompanying state explosion, involves working heuristically. A base component failure will typically be conceptually removed by several stages from a top level event. @@ -192,6 +193,11 @@ from the base component failure to the system level event. The reasoning distance serves to show that when the causes of a top level event are completely determined, a large amount of work not typical of heuristic or intuitive interpretation is required. + +Reasoning distances will be large for complicated systems, and this is therefore a weakness in both +FMEA and FTA type analyses. This concept is developed further to create a metric for comparing +complexities from FMEA and FMMD analysis in section~\ref{sec:cc}. + % could have a chapter on this. % take a circuit or system and follow all the interactions % to the components that cause the system level event. diff --git a/submission_thesis/CH6_Evaluation/copy.tex b/submission_thesis/CH6_Evaluation/copy.tex index 5fe006b..165f047 100644 --- a/submission_thesis/CH6_Evaluation/copy.tex +++ b/submission_thesis/CH6_Evaluation/copy.tex @@ -1,7 +1,7 @@ \section*{Metrics} \section{Defining the concept of `comparison~complexity' in FMEA} - +\label{sec:cc} % % DOMAIN == INPUTS % RANGE == OUTPUTS @@ -17,11 +17,13 @@ we could stipulate that every failure mode must be checked for effects against all the components in the system. We could term this `rigorous~FMEA'~(RFMEA). The number of checks we have to make to achieve this, gives an indication of the complexity of the task. +This is described in section~\ref{sec:rd}, where the reasoning distance, or complexity to +analyse a single FMEA failure scenario, is given in equation \ref~{eqn:complexity}. + % We could term this `comparison~complexity', as the number of paths between failure modes and components necessary to achieve RFMEA for a given system/functional~group. - % (except its self of course, that component is already considered to be in a failed state!). % Obviously, for a small number of components and failure modes, we have a smaller number