Aase Reyes

Purpose: This paper addresses the influence of the main bulb’s parameters of a containership on heave and pitch RAO for head waves.Design/methodology/approach: To obtain the RAO curves, these parameters are scattered over the design space through latin hypercube sampling (LHS), where different bulb designs are obtained using the free form deformation (FFD) technique. Linear RAO curves are calculated based on numerical software, split into various frequency intervals and assessed according to six evaluation parameters.Findings: The findings show that maximum, minimum and average values of the RAO curve are useful indicators to study the RAO of a ship. Average values of the curve are reduced more than 6% for heave and over 24% for pitch with respect to a vessel with a conventional bulbous bow. The best designs concentrate the volume around the mid-lower part of the bulb, whilst the worst designs concentrate the bulb volume towards the upper part of the bulb.Originality/value: In the literature, we get an overview of the influence of different bows on seakeeping. However, the influence of the bulb or large variations of the bow in a parametric way have not been studied yet. Since most of these parameters are derived from the RAO curve and ship motions, this paper focuses on studying the RAO curve for heave and ship motions of a bulbous bow containership. The objective is to minimize the RAO values of the curves so that most derived parameters reduce their values as well.

A sandwich structure is a composite material consisting of thin skins encapsulating a cellular core. Such structures have proven to be excellent energy absorbents and are frequently found in various types of protection. Even so, few studies exist in the open literature on the response of the core material itself under extreme loadings such as blast and impact. Since a blast load is usually accompanied by numerous fragments, it is important to understand and be able to predict the ballistic impact resistance of the often highly inhomogeneous cellular core materials in design. In this study, the ballistic impact response of an aluminium foam with a complex cell structure has been investigated both experimentally and numerically. First, an extensive material test program involving compression tests on cubic specimens loaded in the thickness direction of the foam was carried out to reveal the mechanical properties of the material. In addition, several of the specimens were scanned before testing using X-ray Micro Computed Tomography (XRMCT) to map the multi-scale topology and morphology of the material. These data were later analysed to extract density-variation plots in many different material orientations. Second, ballistic impact tests were conducted using a gas gun where rigid spheres were launched towards aluminium foam plates, and the ballistic limit velocity and curve of the foam material were established. Finally, numerical simulations of both the material tests and the ballistic impact tests were carried out using LS-DYNA and different modelling approaches based on the XRMCT data. It will be shown that, independent of the modelling strategy applied, good agreement between the experimental impact tests and the numerical predictions can be obtained. However, XRMCT data are important if the final goal is to numerically optimise and improve the behaviour of inhomogeneous foams with respect to energy absorption, thermal isolation, or similar properties.

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading.