A large share of global shipped tonnage concerns dry bulk materials, which are typically unloaded from ships using large mechanical grabs, a slow process with long waiting times and high emissions. This process can be modelled and its performance improved using the Discrete Element Method (DEM). While such research has been performed for materials like iron ore or coal, no accurate and efficient material model exists for coarse limestone, a coarse material that is difficult to penetrate and for which large improvements in handling efficiency are expected, reducing waiting times and emissions. Previous research using a material model with two-spherical particles focused on the penetration resistance of limestone and experimentally determined various characteristics of limestone, but with a computational time of 18 days did not result in a feasible full-scale material model . Particle shape-related characteristics like interlocking and dilatancy are expected to influence the bulk material behaviour of limestone, to be taken into account when making a numerical model.

A numerical model is to be created in order to evaluate and improve the grab performance in limestone. Using the state of the art experimental results as a basis, additional experimental setups were designed to determine additional material and particle characteristics, like coefficients of sliding friction, the Angle of Repose (AoR). A method was set up to classify the particle shape. Degrading particles showed that the particle roundness (angularity) influences a particle’s frictional behaviour (and thus AoR). Full-scale experiments were performed in-situ using a full-sized grab.

A DEM material model of limestone is created based on a smaller-scale lifting cylinder (AoR) setup and a full-scale grab setup. Ten different particle shapes are modelled using 5-spherical particles fitted to particle templates, while discarding the PSD. The model is first calibrated for the small-scale setup. These settings are then verified and optimised for the full-scale setup, with the optimised model coarse-grained with a factor of ×1.5, resulting in a calculation time of 3 hours and a standard deviation of 1.8% of the mean. The model accurately represents payload, knife penetration, and knife path.

Design improvements are modelled. Analysis showed that small design improvements are possible, increasing the grab performance significantly. The thesis showed that it is possible to make an efficient material model which accurately represents the coarse material by using multi-spherical particles reflecting the material’s particle shape distribution and calibrated based on a lifting cylinder (AoR) and full-scale (payload, knife path, penetration) experiment. The selection of particle shapes allows for accurate modelling of interlocking and dilatancy in a computationally efficient material model.