Validation of Numerical Methods for Multi-terrain Impact Simulations of a Crashworthy Composite Helicopter Subfloor

Helicopters typically operate over a large variety of terrains. Designing a crashworthy subfloor that can perform efficiently in most impact environments requires the use of accurate simulation tools with a good confidence in the modeling approach and the representation of the soft surfaces. The present work investigates the accuracy of the most commonly used equations of state to numerically model water with explicit Finite Element and Smoothed Particle Hydrodynamics methods. Both analytical and numerical investigations indicated that the Smoothed Particle Hydrodynamics method together with the Murnaghan equation of state provide the best compromise between accuracy and efficiency in predicting the dynamics of a structure impacting onto water. The modeling approach also showed superior accuracy to the more common Finite Element method in representing a soft ground like soil. Based on the use of trapezoidal energy absorbing elements, a composite subfloor was then designed and simulations using the previously validated technique indicated its good crashworthy potential in impact situations over different surfaces.