A Safety Analysis via Minimal Path Sets Detection for Object-Oriented Models

A new method is developed that integrates safety analysis with multi-domain object-oriented modelling. This is the contribution aimed by this paper. First, it recaps the basics of object-oriented modelling. Then, a model of a safety relevant aircraft system, a stabiliser trim system, is established using component models from generic libraries that are supplemented with failure behaviour. Next, a generic method is developed that automatically detects the minimal path sets of a technical system based on the corresponding object-oriented model, thus performing a safety analysis. Techniques from graph theory are adopted for computational efficiency and feasibility of the method. The minimal path sets detection method is exemplified by means of the established realistic system model

Generator Power Optimisation for a More-Electric Aircraft by Use of a Virtual Iron Bird

A prodedure is developed to minimise the generator design power within the electric power system of a future more-/ all-electric aircraft. This allows to save weight on the generators and on other equipment of the electic power system. Execution of the optimisation procedure by hand demonstrates the complexity of the problem. An automation of the process shows the capabilities of integrated modelling, simulation and optimisation tools

Friction Estimation for Torque Control of Electro-Mechanical Flight Surface Actuation

Electro-mechanical actuation (EMA) is pursued for primary flight control of future commercial aircraft. This technology is expected to save effort and related cost of manufacture and maintenance. Primary flight control EMAs will be typically designed to have a high gear ratio between the motor and surface. This involves significant inertia and friction torques that must be handled by the actuator controller. The friction can vary substantially, since the actuators are exposed to changing loads and a wide temperature range. This paper describes a state observer that estimates an EMA’s friction. It is assumed to include a static and a viscous share. The observer is employed for an adaptive concept of surface torque control. The described concept has been investigated by means of simulation, test rig experiments are being prepared

Multi-Objective Controller Optimization and Robustness Analysis by the Example of Electro-Mechanical Flight Surface Actuation

In this paper the adaption of the software environment ’Multi-Objective Parameter Synthesis’ (MOPS) for controller gain optimization is presented. The definition of the optimization criteria, as well as their implementation to the optimization environment are shown. Worst-case searches are conducted to evaluate the effect of uncertainties on the control loop’s performance and stability. The methodology of this controller optimization and robustness analysis are demonstrated by means of the torque control for electro-mechanical flight surface actuation. This technology is pursued for future commercial aircraft

Sensorimotor Experience Influences Recovery of Forelimb Abilities but Not Tissue Loss after Focal Cortical Compression in Adult Rats

Sensorimotor activity has been shown to play a key role in functional outcome after extensive brain damage. This study was aimed at assessing the influence of sensorimotor experience through subject-environment interactions on the time course of both lesion and gliosis volumes as well as on the recovery of forelimb sensorimotor abilities following focal cortical injury. The lesion consisted of a cortical compression targeting the forepaw representational area within the primary somatosensory cortex of adult rats. After the cortical lesion, rats were randomly subjected to various postlesion conditions: unilateral C5–C6 dorsal root transection depriving the contralateral cortex from forepaw somatosensory inputs, standard housing or an enriched environment promoting sensorimotor experience and social interactions. Behavioral tests were used to assess forelimb placement during locomotion, forelimb-use asymmetry, and forepaw tactile sensitivity. For each group, the time course of tissue loss was described and the gliosis volume over the first postoperative month was evaluated using an unbiased stereological method. Consistent with previous studies, recovery of behavioral abilities was found to depend on post-injury experience. Indeed, increased sensorimotor activity initiated early in an enriched environment induced a rapid and more complete behavioral recovery compared with standard housing. In contrast, severe deprivation of peripheral sensory inputs led to a delayed and only partial sensorimotor recovery. The dorsal rhizotomy was found to increase the perilesional gliosis in comparison to standard or enriched environments. These findings provide further evidence that early sensory experience has a beneficial influence on the onset and time course of functional recovery after focal brain injury

Automated safety analysis by minimal path set detection for multi-domain object-oriented models

A method called DMP for Detection of the Minimal Path set of any fault-tolerant technical system, the system being represented as a multi-domain object-oriented model, is described, exemplified and substantiated in this article. Thus, by use of DMP, a safety analysis of the system is automatically performed. DMP employs simulation of normal behaviour, degradation and failure of a system. In essence, it is a state space simulation. The state space, in this context, denotes the set of combinations of intact and failed components of a system to be examined for detection of its minimal path set. Without any reduction technique, the size of a system’s state space grows exponentially with the number of its components. In order to render the DMP method feasible, the object structure of the system model is represented as a graph. Evaluation of the graph reduces the size of the state space and hence the number of simulations required

Virtual Iron Bird - A Multidisciplinary Modelling and Simulation Platform for New Aircraft System Architectures

The concept of a Virtual Iron Bird for the modelling of aircraft system architectures is presented. This platform can be used to evaluate and assess more-electric aircraft system configurations by simulations. For these purposes an object-oriented model library is set up by use of the modern multi-physical modelling language Modelica. Besides the design of the library, an inverse modelling approach is shown allowing to analyse the behaviour and power consumption of aircraft systems. In order to determine accuracy estimates of the overall results, Monte Carlo simulations of uncertainty models are performed, which identify the statistical distributions of the results and assessment criteria

Integrierte Sicherheits- und Zuverlässigkeits-Analysemethoden für die Entwicklung von Flugzeugsystemen mithilfe multi-physikalischer, objekt-orientierter Modelle

Safety and reliability are essential in commercial air transport. Therefore, safety assessment is an inherent part of the aircraft systems development process. Operational reliability has to be considered for economic reasons. Most of the state-of-the-art methods for safety and reliability analysis employ a binary representation of the system. One of these is fault tree analysis (FTA), a manual method that is still common today. Conducting safety or reliability analysis by means of FTA involves considerable effort. In addition, because of the binary, non-physical approach, such analysis tools remain uncoupled to other engineering tools. Nowadays, a multi-domain object-oriented approach has become the state-of-the-art in physical modelling and simulation. Such an approach enables an intuitive method of modelling, in which the objects, their boundaries and interconnections correspond to real existing components. This thesis contributes to the field of model-based methods for system safety and reliability analysis. Here, the most important innovation is that the proposed methods suit multi-domain object-oriented modelling based on differential-algebraic equations. Search techniques and algorithms founded on graph theory were devised in order to minimise the computing effort for conducting an analysis. The proposed methods enable establishing multi-disciplinary engineering tools for the conceptual design of fault-tolerant systems. The aim is improvement of system development and safety assessment processes.Sicherheit und Zuverlässigkeit sind für den kommerziellen Betrieb von Verkehrsflugzeugen essenziell. Aus diesem Grund ist die Bewertung der Sicherheit ein fester Bestandteil im Entwicklungsprozeß von Flugzeug-Bordsystemen. Aus wirtschaftlichen Gründen wird außerdem die Zuverlässigkeit d.h. operationelle Verfügbarkeit berücksichtigt. Die meisten gegenwärtigen Methoden für Sicherheits- und Zuverlässigkeits-Analyse erfordern eine binäre Darstellung (Boolesches Modell) des Systems. Eine dieser Methoden ist die Fehlerbaumanalyse (fault tree analysis - FTA), eine manuelle Methode, die gegenwärtig noch weit verbreitet ist. Die Durchführung einer Sicherheits- oder Zuverlässigkeits-Analyse mithilfe der FTA ist aufwändig. Außerdem sind wegen des binären, nicht-physikalischen Modellansatzes die entsprechenden Analysewerkzeuge nicht mit anderen Ingenieurswerkzeugen gekoppelt. Im Bereich der physikalischen Modellierung und Simulation ist ein objekt-orientierter Ansatz heutzutage Stand der Technik. Dieser Ansatz ermöglicht ein intuitives Vorgehen bei der Modellierung technischer Systeme, da Modellobjekte, deren Grenzen und Verbindungen realen Komponenten entsprechen. Diese Dissertation leistet einen Beitrag auf dem Gebiet modellbasierter, automatischer Methoden für Sicherheits- und Zuverlässigkeits-Analyse. Die wesentliche Neuerung ist, dass die beschriebenen Methoden für den multi-physikalischen objekt-orientierten Modellansatz, der auf Differenzial- und algebraischen Gleichungen basiert, entwickelt worden sind. Der mit der Durchführung von Analysen verbundene Rechenaufwand wird mithilfe weiterentwickelter Suchmethoden und Algorithmen aus dem Bereich der Graphentheorie minimiert. Die beschriebenen Methoden bilden eine Grundlage für fortschrittliche, multi-disziplinäre Ingenieurswerkzeuge, die in der Entwicklung sicherheitskritischer, ausfalltoleranter Systeme angewendet werden können. Das Ziel ist eine Verbesserung der Entwicklungs- und Sicherheitsanalyse-Prozesse

Incorporation of Reliability Analysis Methods with Modelica

A novel method is being developed to combine tech-niques of safety and reliability analysis with the Modelica language, which is now widely used for the modelling and simulation of technical systems. The new method allows to perform reliability calcu-lations based on the system model that is created and used for simulation studies. The reliability analysis procedure is started “at the push of a button” and de-termines the so called minimum path sets and the failure probability of a system automatically. The incorporated reliability computation methods are realised initially by a new modelling and analysis tool supporting concept design studies of aircraft on-board electric power systems

Automated Safety Analysis by Minimal Path Set Detection for Multi-Domain Object-Oriented Models

This paper describes, exemplifies and substantiates a method for detection of the minimal path set of any fault-tolerant technical system that is represented as a multi-domain object-oriented model. Thus, the method automatically performs a safety or reliability analysis of the system