Rigid Body Water Impact Experimental Tests and Numerical Simulations Using SPH Method

Statistics show that emergency ditching and water impacts in emergency are likely to have tragic consequences. Most of the passive safety devices developed for aircraft crashworthiness is designed for ground impacts. Loads, when impacting a solid or a soft surface, are rather different and therefore energy absorption devices developed for ground impact are usually not effective during a water impact and specific devices must be developed. In 2005, a Group for Aeronautical Research and Technology in Europe (GARTEUR), the AG15, was established to improve the SPH method for application to helicopter ditching. In this framework, water impact drop tests, using a triangular cross-section specimen were carried out at Politecnico di Milano in order to collect reliable data for numerical models validation. Impact decelerations and pressures were measured. A pressure transducer suitable to measure impact pressures was developed. Hence, the numerical model was worked out adopting the SPH method to model the fluid region. Applications of the SPH method to water impact analysis are not common because of SPH model instability in unbounded regions. The conditions for SPH model stability were investigated and the accuracy of the overall model was evaluated referring to the data collected in the tests. Eventually, a close experimental-numerical correlation was obtained and guidelines for further investigations were drawn.