Aircraft Ditching Simulations within a Multi-disciplinary Aircraft Design Process Chain

Abstract

In the design and certification process of new aircraft the structural capacity to withstand dynamic fluid loading as experienced during ditching, i.e. a controlled emergency landing on water, must be demonstrated. In recent aircraft development programmes hi-fidelity numerical analyses are increasingly complementing or replacing experimental studies. However, a realistic simulation of the complex loading conditions at the interface between aircraft body and the free water surface for models including aerodynamic as well as hydrodynamic loads is very challenging. Over the last years a ditching process chain has been developed at DLR based on the VPS software. In this process the structural model is based on a classical Finite Element (FE) approach while the fluid domain is modelled using the Smoothed Particle Hydrodynamics (SPH) method. Within the EC funded project SMAES (Smart Aircraft in Emergency Situations, 2011- 2014) DLR and the ESI Group collaborated to enhance the VPS capabilities by modelling strategies for the fluid domain to significantly improve the efficiency and robustness of the simulation process. Further improvements could be achieved by using the VPS Multi-Model Coupling feature for coupled FE-SPH analyses to separate the simulation of the structural model with small elements and corresponding small timesteps from the time consuming SPH simulation, which allows significantly larger timesteps. Taking advantage of the afore mentioned improvements, first ditching simulations with full flexible aircraft models could be performed from the impact with the free water surface until the end of the landing phase (~2 seconds in real time). To automatically set up generic full aircraft FE models a process chain based on the CPACS (Common Parameterized Aircraft Configuration Schema) aircraft data description format is applied. The parameters for FE-SPH fluid structure interaction relies on a comprehensive method validation using experimental data on panel level. In this presentation the state of the art of full aircraft ditching simulation using VPS with the focus on its application within a DLR multi-disciplinary aircraft design process chain will be presented. Simulation results aim to show the influence of local deformations at the lower fuselage panel compared to a reference simulation with a rigid aircraft models during ditching. This comparison includes modelling and computational aspects. Next steps towards a more simulation-based certification process are discussed.