put proof for comparison equations in
PLT
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PNG_DIA = circuit1_dag.png mvampcircuit.png pd.png invamp.png shared_component.png tree_abstraction_levels.png
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PNG_DIA = circuit1_dag.png mvampcircuit.png pd.png invamp.png shared_component.png tree_abstraction_levels.png three_tree.png
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@ -813,7 +813,7 @@ This can be simplified if we can determine the total number of failure modes in
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equation~\ref{eqn:rd} becomes $$ RD(fg) = fT.(|fg|-1).$$
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\pagebreak[4]
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\subsection{Reasoning Distance Examples}
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\subsection{Reasoning Distance Examples}(c-1)
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The potential divider discussed in section~\ref{potdivfmmd} has a four failure modes and two components and therefore has an $RD$ of 4.
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$$RD(potdiv) = \sum_{n=1}^{2} |2|.(|1|) = 4 $$
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@ -823,5 +823,96 @@ having 3 failure modes each, we would have an $RD$ of
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$$RD(fictitious) = \sum_{n=1}^{81} |3|.(|80|) = 19440 .$$
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This would be the polynomial ($O(N^2)$) result of applying FMEA rigorously (we could term this
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Rigorous FMEA (RFMEA).
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\pagebreak[4]
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\subsection{Using the concept of Reasoning Distance to compare RFMEA with FMMD}
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\begin{figure}
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\centering
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\includegraphics[width=400pt,keepaspectratio=true]{./three_tree.png}
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% three_tree.png: 851x385 pixel, 72dpi, 30.02x13.58 cm, bb=0 0 851 385
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\caption{FMMD Hierarchy with $(|fg| = 3) \wedge (|fm(c)| = 3)$}
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\label{fig:three_tree}
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\end{figure}
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Because components have variable numbers of failure modes,
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and {\fgs} have variable numbers of components it is difficult to
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come up with a general formula for comparing the number of checks to make for
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RFMEA and FMMMD.
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If we were to create an example by fixing the number of components in a {\fg}
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and the number of failure modes per component, we can derive formulae
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to represent the number of checks to make.
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Consider $k$ to be the number of components in a {\fg} (i.e. $k=|fg|$),
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$f$ is the number of failure modes per component (i.e. $f=|fm(c)|$), and
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$L$ to be the number of levels in the hierarchy of an FMMD analysis.
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We can represent the number of failure scenarios to check in an FMMD
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with equation~\ref{eqn:anscen}.
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\begin{equation}
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\label{eqn:anscen}
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\sum_{n=0}^{L} {k}^{n}.k.f.(k-1)
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\end{equation}
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The thinking behind equation~\ref{eqn:anscen}, is that for each level of analysis -- counting down from the top --
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there are ${k}^{n}$ {\fgs} within each level; we need to apply RFMEA to each {\fg} on the level.
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The number of checks to make for RFMEA is number of components $k$ multiplied by the number of failure modes $f$
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checked against the remaining components in the {\fg} $(k-1)$.
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If, for the sake of example we fix the number of components in a {\fg} to three and
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the number of failure modes per component to three, an FMMD hierarchy
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would look like figure~\ref{fig:three_tree}.
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\subsection{Worked Example}
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Using the diagram in figure~\ref{fig:three_tree}, we have three levels of analysis.
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Starting at the top, we have a {\fg} with three derived components, each of which has
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three failure modes.
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Thus the number of checks to make in the top level is $3^0.3.2.3=18$.
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On the level below that, we have three {\fgs} each with a
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an identical number of checks, $3^1.3.2.3=56$.{\fg}
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On the level below that we have nine {\fgs}, $3^2.3.2.3=168$.
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Adding these together gives $242$ checks to make to perform RFMEA \textbf{within}
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{\fgs}.
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If we were to take the system represented in figure~\ref{fig:three_tree}, and
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apply RFMEA on it as a whole system, we can use equation~\ref{eqn:rd},
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$ RD(fg) = \sum_{n=1}^{|fg|} |fm(c_n)|.(|fg|-1)$, where $|fg|$ is 27, $fm(c_n)$ is 3
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and $(|fg|-1)$ is 26.
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This gives:
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$ RD(fg) = \sum_{n=1}^{27} |3|.(|27|-1) = 2106$
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In order to get general equations with which to compare RFMEA with FMMD
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we can re-write equation~\ref{eqn:rd} in terms of the number of levels
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in an FMMD hierarchy. The number of components in is number of components
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in a {\fg} raised to the power of the level plus one.
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Thus we re-write equation~\ref{eqn:rd} as:
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\begin{equation}
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\label{eqn:fmea_state_exp21}
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\sum_{n=1}^{k^{L+1}}.(k^{L+1}-1).f \; , % \\
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%(N^2 - N).f
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\end{equation}
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or
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\begin{equation}
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\label{eqn:fmea_state_exp22}
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k^{L+1}.(k^{L+1}-1).f \;. % \\
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%(N^2 - N).f
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\end{equation}
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We can now use equation~\ref{eqn:anscen} and \ref{eqn:fmea_state_exp22} to compare (for fixed sizes of $|fg|$ and $|fm(c)|$)
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the two approaches, for the work required to perform rigorous checking.
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\subsection{Exponential squared to Exponential}
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can I say that ?
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\end{document}
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