Abstract

Aircraft emergency water landings (ditching) are uncommon but remain an ever-present possibility. Therefore, crashworthiness standards as part of the Federal Aviation Regulations demand such situations to be accounted for during the certification phase. The criteria require aircraft to prove its ability to survive ditching and be able to float after impact for a duration long enough for the passengers to be rescued. In emergency scenarios, it is preferred to choose an open body of water as the landing location as opposed to hard terrain. It would be prohibitively expensive to test impacts of this nature to cover all required certification cases. The data collection can also be a tedious process. Due to these hindrances, performing numerical validation of aircraft water ditching (fluid-solid) interactions has become more important than ever. In case of hard terrain impact, most of the energy is absorbed by the frame of an aircraft. However, in water impacts, the initial load is distributed over the skin. As a result, the ability of an aircraft to withstand crash becomes dependent on the strength of the shear panels to allow an effective transfer of impact energy to damage-absorbing members and mechanisms before failling. Large full-scale simulations to capture the structural response of an aircraft under severe impact loading however can be computationally intensive. This work focusses on comparative analysis of numerical strategies for assessing fluid-structural Interactions. Two of the methods considered are Lagrangian, and Arbitrary Lagrangian and Eulerian (ALE) schemes.

For preliminary validations, the experimental studies performed by other research groups have been used to investigate the effect of mesh refinement and computational time on the Lagrangian and ALE schemes. These simulations will provide a basis for selecting the right formulations when developing fluid-solid interactive models for aerospace applications. Based on the results of the studies conducted, the most computationally efficient scheme was then used to perform the simulations of an aircraft fuselage section when impacting water in an emergency landing situation. The fuselage model used in this project was pre-validated against a rigid terrain experimental drop test before it was applied to the ditching studies. Overall, this investigation aims at assessing advanced modeling techniques and approaches that can pave the way for analysis-assited water impact certification and, ultimately, certification by analysis.

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