Modelling and numerical / experimental investigation of granular cargo shift in maritime transportation

Abstract

The study of granular materials (powders, sands, grains, metal ore etc.) should be a topic of greatinterest in naval architecture, since cargo shift represents a major hazard for ship safety and probably the most common cause of capsize of large ships. Despite though its great importance, the behaviour of granular cargos transported by sea has not been sufficiently investigated yet from a theoretical perspective. As a result, international regulations governing the procedures of loading and stowage of bulky cargos, while continuously updated and improved, remain mainly empirical.In the current Thesis, a micro-scale modelling approach is presented, aimed to develop capabilityfor simulating the dynamic behaviour of granular materials having physical properties conforming tothose of bulky cargos commonly transported through the sea, inside ship holds. The well-stablishedmethod of “Molecular Dynamics” is employed for modelling particles’ interactions and for predictingmacroscopic features of the excited granular material behaviour. The algorithm is further combined with standard models of ship motion, in order to understand the interplay of granular material flow with vessel motion.At the first stage, “dry” granular materials comprised of spherical particle and affected by nonlinearfrictional forces are employed. Later, a number of improvements are incorporated, to bring themodel closer to reality, by introducing the effect of environmental humidity and also the irregularity in particles’ shape. To discern qualitatively different patterns of behaviour, a variety of materials and filling ratios have been examined. Moreover, to improve performance, the computational algorithm was parallelized for Graphical Processing Unit (GPU) implementation and the merit of it was properly evaluated.Characteristic simulation results of a 2D rectangular scaled barge, partly filled with bulky cargoand vibrated in roll, sway and heave are included in the Thesis. The barge is, either, forced to oscillate in a prescribed motion; or is free to move under the effect of wave loads and her cargo’s occasional fluid-like movement. Critical parameter values where cargo shift is initiated are identified. The intention has been to maintain the excitation amplitudes and frequencies close to realistic open sea conditions although the scaling problem is in itself a major scientific challenge.Judging from the qualitative character of the obtained results and also from comparisons of somekey findings with experimental results, it appears that the described simulation model has goodpotential to evolve into a useful and practical computational tool for the investigation of stability of ships carrying solid cargos in bulky form.