Numerical simulation of flexible aircraft structures under ditching loads

Abstract

Aircraft certification requires demonstrating an aircraft’s structural capacity to withstand hydrodynamic loads as experienced during an emergency landing on water known as ditching. Currently employed means to analyze ditching comprise comparison with previously certified aircraft, sub-scale experimental testing, and semi-analytical as well as uncoupled computational methods; all of these are subject to simplifications that limit their predictability and accuracy. Therefore, there is the motivation to employ advanced, coupled numerical simulations to enhance the analysis capabilities. This paper presents a numerical simulation approach combining Smoothed Particle Hydrodynamics and Finite Element method, which permits investigating the structural behavior under ditching loads within one simulation. Comprehensive validation studies based on comparison with experimental results from novel guided ditching experiments of generic panels in aeronautical design have been undertaken and high accuracy has been achieved regarding acting force and strain time histories. Additionally, the profound analysis of the structural behavior of flexible panels allows assessing the main mechanisms that cause the acting hydrodynamic loads to increase significantly when the structure is being deformed. Presented results extend the fundamental knowledge in this field. The validated simulation approach is finally applied to analyze the structural behavior of a detailed stringer-frame-reinforced panel representing a generic aircraft bottom fuselage structure. Comparison between the structural behavior of the generic panels and the aft fuselage structure is established. Furthermore, conclusions with regard to ditching simulations involving larger or even full aircraft structures are drawn.