The relationship between variations of the atmospheric electric field in the southern polar region and thunderstorm activity

Observations of the atmospheric, near-surface vertical electric field component E-z have been carried out at the Russian-Antarctic station, Vostok, since 1998 under the framework of a cooperative Russian-Australian project. Only data satisfying "fair weather" conditions are selected for the subsequent analyses. Behavior of E-z field at Vostok station is compared with thunderstorm occurrence determined from a network of ELF magnetic field measurements in April 1998 and with simultaneous VLF emission measurements at Halley Bay (Antarctica). We find no correlation between the 5 min averages of E-z and the lightning flashes intensity or between E-z and VLF emissions, although significant correlation between E-z and VLF emissions is observed in particular cases. The same statistical results have been obtained from a comparison of hourly averaged values. Moreover, even the mean diurnal variation of electric field derived for 10 fine weather days in April 1998 turned out to be inconsistent with the mean diurnal variation of the lightning flashes for the same days. Reasons of these inconsistencies are discussed

<i>Preface</i><br> An introduction to the 1st European Space Weather Week (ESWW)

International audienc

Development of a test planning methodology for performing experimental model validation of bolted flanges

This work presents a strategy for testing and validating structures connected together with bolted joints, which are the most common components in mechanical structures. Considering the great number of coupled mechanical structures and research studies on this subject, the authors focused this research work on bolted flanges of aircraft engine casings. In fact, the coupling of engine casings is generally obtained by a large number of joints which assure the correct sealing at the flanges’ interfaces. From a finite element (FE) modelling perspective, joints are often modelled by either rigid connections or springs, otherwise incurring a very expensive computational time. This modelling approach is not a problem when dealing with low amplitude levels of vibrations. For higher levels of vibrations, joints and flanges cannot be considered rigidly connected and that exerted flexibility at the joints’ area can determine nonlinear dynamic behaviour. This work aims to study the dynamic behaviour of bolted flanges by using modal testing performed under controlled response amplitude. Two test structures, (1) a simple bolted flange test case and (2) a sector of a Rolls-Royce aero-engine casing, are tested under high level of vibrations. Both test structures are modelled by FE method, and nonlinear elements are used for modelling the flanges’ interfaces so as to perform prediction of nonlinear responses. These predictions are eventually correlated with the measured data.</p