Adaptive time step in simulation of progressive flooding

•New method for use of an adaptive time step in simulation of progressive flooding of ships.•Method has been tested with various complex flooding scenarios.•Use of an adaptive time step decreases computation time without losing accuracy of results.

Time accurate simulation of progressive flooding inside a ship often requires a short time step. However, after the initial phases, as the flooding progresses to undamaged compartments, the flow rates decrease and much longer time step could be used. Yet the collapsing of non-watertight structures may cause additional phases of fast flooding, where a shorter time step is required. In this paper the use of an adaptive time step in flooding simulation is discussed, and a new approach to this problem is presented. The time step is automatically adjusted during the simulation on the basis of the maximum absolute velocity of the free surface levels in the flooded compartments. The method is tested with small case studies, presenting typical flooding conditions in passenger ships.