Damage assessment of a free-fall dropped object on sub-seabed in offshore operation

Copyright © 2015 by the International Society of Offshore and Polar Engineers (ISOPE). This paper presents the damage assessment of a free-fall dropped object on the seabed. The damage of a dropped object totally depends on the relationship of impact energy and the soil strength at the mudline. In this study, first, unexpected dropping scenarios were assumed varying the relevant range of the impact velocity, structure geometry at the impact moment and soil strength profile along the penetration depth. Theoretical damage assessments were then undertaken for a free-fall dropped event with a fixed final embedment depth of structure. This paper also describes the results from three-dimensional large deformation finite element (LDFE) analysis undertaken for the validation purpose. The analyses were carried out using the Coupled Eulerian-Lagrangian approach, modifying the simple elastic-perfectly plastic Tresca soil model. The validation exercises of each dropped scenario show a good agreement and the present numerical approach is capable of predicting the behavior of a free-fall dropped object.