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978-3-8439-1549-6, Reihe Informationstechnik
Automatic Design of IMA-Based Systems
169 Seiten, Dissertation Universität Stuttgart (2013), Softcover, B5
During the last years, the integrated modular avionics (IMA) design philosophy became widely established at aircraft manufacturers, resulting in more and more hardware equipment being replaced by generic avionics computers. With the ever-increasing amount of functional capabilities of avionics systems, the complexity of designing such a system has increased equally; the safety evaluation of design candidates is further complicated by the possibility and necessity of multiple avionics functions sharing hardware components.
This thesis presents a computer-aided design method for avionics that (1) allows to evaluate an avionics architecture using objective quality criteria, in particular regarding its safety, and (2) enables the engineer to rapidly modify an architecture and re-evaluate it, thus aiding in the thorough exploration of the design space. Based on these steps, (3) an automated determination of the optimal architecture is possible, and was realised as a quite sophisticated software prototype.
In the main part of this thesis, we explain the metamodel used to formally represent those aspects of avionics systems that are necessary for the purpose. We present our safety evaluation algorithm, its failure model, its mathematical basis, how typical avionics structures are modelled, and how the algorithm computes system failure probabilities and minimal cut sets from the model. We show a generic cost computation algorithm for the metamodel. And we will explain in detail the automatic design algorithm, which utilises safety and cost evaluation as optimisation objectives in a genetic algorithm in order to determine an optimal and safe architecture for a given system. Among other things, the algorithm is able to automatically determine the optimal redundancy of functions and their interconnection, the interfaces of IMA computers, the optimal allocation of functions to the hardware, the signal routing and the placement of components and cables in the aircraft.
An evaluation of the approach was conducted for several example systems, demonstrating that it is able to cope with a wide range of problem aspects and to produce a correspondingly wide range of architectures. The algorithm's performance was even analysed for a fly-by-wire flight control system of a general aviation aircraft, which constitutes a challenging and realistically-sized optimisation problem; with some guidance by the user, optimal results were obtained even in this complex case.