Role of initial particle deposition in collapse dynamics and deposition morphology of submarine granular flows using CFD-DEM coupling method

Submarine landslides represent a significant marine geohazard, making it essential to understand their underlying dynamics. Initial deposition plays a crucial role in determining the flow behavior and ultimate runout distance of submarine granular materials. Despite the importance of particle interactions, especially considering the wide range of particle sizes involved, their impact on submarine landslide dynamics has not been thoroughly explored. In this study, we employ a three-dimensional coupled CFD-DEM method to simulate the collapse of granular columns under varying initial deposition conditions, aiming to uncover the dynamic characteristics of submarine landslides at the particle scale. Our findings reveal that initial depositions with a higher concentration of larger particles at the top lead to their upward migration toward the upper and frontal regions of the flow, while smaller particles tend to settle at the base. This enhances the overall mobility of the landslide. Notably, initial depositions with larger aspect ratios result in greater particle segregation and more efficient conversion of initial potential energy into vertical kinetic energy. This segregation extends the range of kinetic energy variation, reduces energy dissipation through horizontal velocity, and ultimately increases the runout distance. Moreover, the presence of an ambient fluid significantly prolongs the duration of movement compared to dry cases, although it results in a shorter final runout distance. These insights provide a deeper understanding of the mechanics governing submarine landslides and highlight the critical role of initial deposition conditions in shaping their behavior.