Simulation of helicopter under-floor structure impact on water

An arbitrary Langrangian-Eulerian formulation was used to simulate numerically the vertical impact on water of part of a conventional helicopter under-floor metallic structure. The analysis was performed for crashworthiness assessment purposes. Two impact velocities were investigated: 8 m/s and 12 m/s. An investigation of the size and boundary conditions of the water volume necessary to simulate realistically the impact on water was performed. The results showed good agreement with the ones based on the work done by Von Karman [8] in investigation of the impact of seaplane floats during landing. It was concluded that, in this sort of impact, the water plays a relevant role in absorbing the airframe kinetic energy. It was verified that, within the first 2 milliseconds after impact, the energy transferred to the water was of the same order as the energy absorbed by the structure. The results showed that the conventional under-floor structure performs poorly with respects to energy absorption in the water crash when compared with a crash on a rigid surface. Within the response time considered, approximately 55% less energy was absorbed by the system in the water impact.