Secure and authenticated data communication in wireless sensor networks

© 2015 by the authors; licensee MDPI, Basel, Switzerland. Securing communications in wireless sensor networks is increasingly important as the diversity of applications increases. However, even today, it is equally important for the measures employed to be energy efficient. For this reason, this publication analyzes the suitability of various cryptographic primitives for use in WSNs according to various criteria and, finally, describes a modular, PKI-based framework for confidential, authenticated, secure communications in which most suitable primitives can be employed. Due to the limited capabilities of common WSN motes, criteria for the selection of primitives are security, power efficiency and memory requirements. The implementation of the framework and the singular components have been tested and benchmarked in our tested of IRISmotes

Resilience – a prerequisite for autonomous shipping?

Resilience Engineering is discussed as a method to analizse risks and opportunities of autonomous ships during their design phase to ensure a safe and efficient introduction into the maritime domain. Scenarios of various autonomity level are discussed and presented in the context of a systematic display of the system-of-system of maritime transport

Model updating strategy for structures with localised nonlinearities using frequency response measurements

This paper proposes a model updating strategy for localised nonlinear structures. It utilises an initial finite-element (FE) model of the structure and primary harmonic response data taken from low and high amplitude excitations. The underlying linear part of the FE model is first updated using low-amplitude test data with established techniques. Then, using this linear FE model, the nonlinear elements are localised, characterised, and quantified with primary harmonic response data measured under stepped-sine or swept-sine excitations. Finally, the resulting model is validated by comparing the analytical predictions with both the measured responses used in the updating and with additional test data. The proposed strategy is applied to a clamped beam with a nonlinear mechanism and good agreements between the analytical predictions and measured responses are achieved. Discussions on issues of damping estimation and dealing with data from amplitude-varying force input in the updating process are also provided

Measurement of FRFs and Modal Identification In Case of Correlated Multi-Point Excitation

The modal identification of large and dynamically complex structures often requires a multi-point excitation. Sine sweep excitation runs are applied when it is necessary to concentrate more energy on each line of the frequency spectrum. The conventional estimation of FRFs from multi-point excitation requires uncorrelated excitation signals. In case of multi-point (correlated) sine sweep excitation, several sweep runs with altered excitation force patterns have to be performed to estimate the FRFs. An alternative way, which offers several advantages, is to process each sine sweep run separately. The paper first describes the conventional method for FRF estimation in case of multi-point excitation, followed by two alternative methods applicable in case of correlated excitation signals. Both methods generate a virtual single-point excitation from a single run with multi-point excitation. In the first method, an arbitrary structural point is defined as a virtual driving point. This approach requires a correction of the modal masses obtained from modal analysis. The second method utilizes the equality of complex power to generate virtual FRFs along with a single virtual driving point. The computation of FRFs and the modal identification using virtual single-point excitation are explained. It is shown that the correct set of modal parameters can be identified. The application of the methods is elucidated by an illustrative analytical example. It could be shown that the separate evaluation of symmetric and anti-symmetric multi-point excitation runs yield obviously better and more reliable results compared to the conventional method. In addition, the modal analysis of the separate symmetric and anti-symmetric excitation runs is easier, since the stabilization diagrams are easier to interpret. The described methods were successfully applied during the Ground Vibration Tests on Airbus A380 and delivered excellent results. The methods are highly advantageous and may thus be established as a new standard procedure for testing aerospace structures

Korrektur von Parameter-Fehlern in strukturdynamischen FE-Modellen mit Hilfe experimenteller Frequenzgänge

Die Qualität eines strukturdynamischen Finite Elemente Modells hängt vor allem von der Wiedergabe des dynamischen Verhaltens der zu reproduzierenden Teststruktur ab. Um die Güte eines mathematischen Modells beurteilen zu können, werden Daten aus Schwingungsuntersuchungen (Frequenzgangsfunktionen und Modaldaten) genutzt. Liefert eine Korrelation zwischen Analyse- und Testmodell unbefriedigende Ergebnisse, d.h. die Abweichungen zwischen den Meßdaten und dem mathematischen Modell sind zu groß, wird eine Korrektur des Rechenmodells erforderlich. Es müssen Modifikationen vorgenommen werden, die die Modellparameter (z.B. E-Modul oder Dichte eines Balkens) oder unter Umständen auch die Idealisierung (Element-Typ) und Diskretisierung (Netzdichte) betreffen. In den letzten Jahren wurden Computergestützte Korrekturverfahren (engl.: Computational Updating (CMU) methods) entwickelt und erfolgreich angewendet, mit dem Ziel, die FE-Modellparameter automatisch zu korrigieren und dadurch die Diskrepanzen zwischen dem mathematischen Modell und den Testdaten zu verringern. Das populärste Computergestützte Korrekturverfahren macht von der schrittweise linearisierten inversen Sensivitätsmethode Gebrauch. Das Verfahren erlaubt dem Nutzer als fehlerhaft angenommene Massen- und Steifigkeitsparameter zur Korrektur freizugeben, um die Abweichung zwischen analytischen und gemessenen ungedämpften Eigenfrequenzen und/oder Eigenformen zu minimieren. Das Verfahren verwendet für die Anpassung ausschließlich die mittels einer experimentellen Modalanalyse (EMA) aus Schwingungsversuchsdaten identifizierten Modalparameter (Eigenfrequenzen und Eigenformen). Eine gleichzeitige Anpassung von Massen-, Steifigkeits- und Dämpfungsparametern ist mit diesem Verfahren nicht möglich. Im Vortrag wird ein neues Computergestütztes Korrekturverfahren vorgestellt mit dem es möglich ist, sowohl physikalische Massen- und Steifigkeitsparameter als auch modale Dämpfungsparameter zu korrigieren. Das Verfahren basiert auf der schrittweise linearisierten inversen Sensitivitätsmethode und nutzt Frequenzgangsfunktionen an den Resonanzstellen. Die Effektivität des entwickelten Verfahrens wird an einer Benchmark Teststruktur aufgezeigt