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This study examines, both experimentally and numerically, the collapse process of a submerged granular column in loose packing, with an emphasis on the effects of the grain size and the initial aspect ratio of the granular column. A two-phase flow continuum model, developed based on the rheological characteristics of solid-water mixtures, is used to perform the numerical simulations. Two particle sizes representing very fine particles and coarse particles are examined in this study. The two-phase flow model is validated and verified by comparing with the measured characteristics of the collapse process. Compared to the collapse of a granular column of coarse particles, the runout distance of a granular column with very fine particles is longer and the spread velocity is higher. Based on the two-phase flow simulation results supported by the experimental results, critical initial aspect ratios are identified to classify the types of the initial collapse process and the final deposit morphology, and the empirical expressions are provided to describe the changes of the runout distance, collapse duration, final deposition height, and spread velocity with the initial aspect ratio. A phenomenon similar to the so-called Kelvin-Helmholtz instability can be observed in both the experiment and the simulation at the later stage of the collapse, which causes the formation of several vortexes in the two-phase flow during the collapse process. The presence of these vortexes is responsible for the pressure drop on the bed after the passage of the flow front and the wavy feature on the final deposit morphology. [ABSTRACT FROM AUTHOR]

A complicated coupling system performs fuel filling operation of a ship on the sea that involves tank sloshing and filling impact. This research elaborated on the sloshing load and flow characteristics of the variable mass tank and revealed its physical process through numerical simulations to provide safety assurance for fuel filling. First, this work clarified the difference between the numerical theory of variable mass tank sloshing and that of ordinary sloshing. On this foundation, a numerical model was developed for a three-dimensional variable mass tank sloshing. In addition, the model was validated by comparing the results of the previous experiments. Second, the sloshing pressure and internal free surface of the tank were monitored by numerical simulations. At the same time, a series of sensitivity analyses were carried out against the sloshing period, filling rate, and sloshing amplitude. Finally, the baffle was added to the sloshing tank to study the influence of internal barrier structure on the sloshing flow and pressure characteristics. The following conclusions were obtained from this work: Fuel filling caused an increase in liquid mass, suppressing sloshing and increasing the tank load. Overall, the sloshing load increased with the filling rate. Moreover, the impact of internal barrier structure on sloshing is discussed in this study, and it was discovered that the sloshing effect could be efficiently suppressed by the barrier structure. [ABSTRACT FROM AUTHOR]