Seat Design Influence on Occupant Injury Criteria During Tsunami Lifeboat Water Entry: An ALE Fluid-Structure Interaction Approach

A drop test simulation model of a tsunami lifeboat was developed using a HYBRID III dummy to represent the occupant. A two-stage simulation was conducted: the first stage determined the acceleration response of the lifeboat hull upon water impact, and the second stage used this response to define the platform motion for investigating occupant response under two seat geometries. Occupant safety was assessed using the Combined Acceleration Response (CAR) Index and Combined Dynamic Response Ratio (CDRR). Results show that the HYBRID III dummy can capture occupant motion and impact kinematics during the drop test, and that dummy-derived acceleration, rather than seat-node acceleration, should be used to determine the CAR Index, since the dummy exhibited larger acceleration than the seat. Between the two proposed seat geometries, seat type-1 showed superior performance compared to seat type-2, with lower acceleration in most axes. An ergonomic seat design may therefore reduce the risk of occupant injury by lowering the acceleration response during water entry. Nevertheless, both seat designs satisfied the applicable IMO safety thresholds and are considered suitable for the tsunami lifeboat.