Modelling strategies for numerical simulation of aircraft ditching

Ditching, which is a controlled landing of an airplane on water, is an emergency condition to be investigated in order to improve the aircraft global crashworthiness. The complex hydrodynamic phenomena involved in ditching events are difficult to simulate and the accuracy of the results depends on the capability to reproduce the forces related to the interaction of the fuselage with the water surface. In the first part of the paper, the vertical impact on water of a rigid sphere is analysed using the explicit solver LS-DYNA in order to compare different modelling strategies. Four models of the fluid domain are presented: Lagrangian, arbitrary Lagrangian-Eulerian, smoothed particle hydrodynamics and hybrid Lagrangian-smoothed particle hydrodynamics. In the second part, the ditching of a scaled simplified airplane is simulated considering two different models for the water region. Experimental data from the literature are used to validate the simulations. The analysis, where the water and the air are modelled with the arbitrary Lagrangian-Eulerian method, shows a better correlation with the experimental data because this formulation can reproduce the suction force which acts on the fuselage and affects significantly the ditching dynamics.