  This paper presents a structured power and energy-flow-based qualitative
modelling approach that is applicable to a variety of system types including
electrical and fluid flow. The modelling is split into two parts. Power flow is
a global phenomenon and is therefore naturally represented and analysed by a
network comprised of the relevant structural elements from the components of a
system. The power flow analysis is a platform for higher-level behaviour
prediction of energy related aspects using local component behaviour models to
capture a state-based representation with a global time. The primary
application is Failure Modes and Effects Analysis (FMEA) and a form of
exaggeration reasoning is used, combined with an order of magnitude
representation to derive the worst case failure modes. The novel aspects of the
work are an order of magnitude(OM) qualitative network analyser to represent
any power domain and topology, including multiple power sources, a feature that
was not required for earlier specialised electrical versions of the approach.
Secondly, the representation of generalised energy related behaviour as
state-based local models is presented as a modelling strategy that can be more
vivid and intuitive for a range of topologically complex applications than
qualitative equation-based representations.The two-level modelling strategy
allows the broad system behaviour coverage of qualitative simulation to be
exploited for the FMEA task, while limiting the difficulties of qualitative
ambiguity explanation that can arise from abstracted numerical models. We have
used the method to support an automated FMEA system with examples of an
aircraft fuel system and domestic a heating system discussed in this paper.
