Ensuring damage-free emergency sea landing of airplanes and helicopters

The proper prediction of the stress endured by an aircraft during “ditching” (sea landing) is crucial to guarantee its resistance and ensure safety of passengers and crew. Unfortunately, due to the extreme violence and briefness of this stress and to the numerous physical phenomena involved, experimental testing is particularly complex. Subject to time and financial constraints, numerical simulation is therefore essential.

Your application

Aircrafts, such as airplanes and helicopters, are often required to fly over large areas of water and must therefore be able to ditch (i.e. land on the sea) in an emergency. Manufacturers are required to guarantee the integrity of the aircraft and the safety of passengers and crew during ditching and the subsequent flotation. To meet this ambitious challenge, appropriate structural sizing is essential.

The physical phenomena involved in ditching are complex and varied: aerodynamics, hydrodynamics, structural… For example, during the approach phase when the pitch angle is low, air flow plays an essential role: the free surface of water is deformed by the air cushion that forms between the fuselage and the water. Such surface deformation strongly affects the stress endured by the aircraft during impact. Swell is also one of the main factors to consider: aircraft hitting the crest or trough of a wave is subject to totally different hydrodynamic loads.
To properly account for all relevant phenomena, one must resort to CFD software able to handle each of the physical phenomena involved: diphasic flows (air and water), large distortion of free surface, compressibility, swell generation and propagation, fluid-structure coupling, etc.

Our solution

SPH-flow software is a diphasic particle-based solver. Its Lagrangian approach allows violent flows involving extensive free surface deformation to be modelled. Moreover, the use of adaptive particle refinement enables accuracy to be improved at specific locations around the fuselage. In the current context, it allows very localized pressure impacts to be captured without increasing computation costs. These essential capabilities make SPH-flow the perfect CFD solver for ditching simulation.
Furthermore, SPH-flow uses coupling modules with different solid mechanics solvers (such as EDF Code_Aster and 3DS SIMULIA Abaqus). Fluid-structure simulation opens up the possibilities of studying aircraft structure distortions.
Nextflow Software has developed considerable expertise in ditching simulation in partnership with Dassault Aviation and Airbus Helicopters. This skill has been further reinforced by strong experience gained in related studies, such as spaceship boosters falling in the sea or lifeboat and container dropping.

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