Application of the finite element method to predict the crashworthy response of a metallic helicopter under floor structure onto water.

Abstract

Helicopters are seen by the petroleum industry as the only viable way of transportation between on and offshore platforms. At present, there exists no certification requirement to ensure a high level of survivability in the event of a water impact. Within the literature, there exists a body of information related to the post crash analysis of accident data, which supports the finding that a conventional metallic under floor design performs poorly during a water impact, in relation to the transmission of water pressure and the absorption of energy. In order to characterise this behaviour, this paper concerns the crashworthiness of helicopters on water for an impact speed of 8 m s−1, for a simple box-beam construction that is common to metallic helicopters. A complete section-by-section analysis of a component floor will be presented, which has been compared both quantatively and qualitatively with the results provided by the finite element code, LS-DYNA3D. Comparisons will be made to collapsed frame height, as well as to detailed measurements for skin deflection. The main areas of good and poor agreement are discussed and conclusions drawn on the validity of the simulations, with a view for developing a practical methodology for fluid–structure interactions. This paper discusses the recommendations for design changes that could potential improve the level of crashworthiness currently offered, through the careful redesign of frames and joints, in order to allow for progressive collapse and sustained energy absorption. This paper concludes with a recommendation that a next generation design must incorporate a passive dual role capability that can cater for both hard and soft surface impacts, by being able to degrade its localised strength depending upon the type of surface encountered.