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Aircraft Ditching Numerical Simulation

Climent, Hector and Benitez, Luis and Rueda, Fernando and Toso-Pentecote, Nathalie (2006) Aircraft Ditching Numerical Simulation. In: ICAS 2006. ICAS 2006, 2006-09-03 - 2006-09-08, Hamburg, Germany.

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Abstract

Ditching is an aircraft emergency condition that ends with the planned impact of the aircraft with water. Three main phases have to be analyzed during ditching: • Aircraft conditions before impact • Structural response during the impact • Subsequent floatation This paper is mainly devoted to the second phase (i.e. the impact with water). During this phase, the high pressures developed by the impact with water of the sliding aircraft may cause rupture of the structure, jeopardizing the required safe evacuation of crew and passengers. The classical approach to ditching has been the use of model ditching test under several ditching scenarios. By these means, the global behavior of the model is assessed and extrapolated to the real aircraft size in order to define the optimum ditching conditions. In addition, the model is instrumented with pressure transducers that in turn are used to compute loads on the structure. Nevertheless, the increase of computer power and reliability of numerical models makes it possible to perform ditching numerical simulations. For the cases with vertical-velocity only (i.e. helicopters) this is particularly true and large advances has been made in recent years. The use of techniques like Smooth Particle Hydrodynamics (SPH) has proven to be very effective in vertical impacts in which good correlations have been demonstrated with tests including full-scale tests. The cases with combined vertical speed and horizontal speed (i.e. aircraft) are significantly more difficult. The pressures produced by the water on the aircraft structure may be either positive (over pressures) or negative (suction) and the SPH technique with the available constitutive laws is not able to properly represent suction forces. Hence, more sophisticated techniques are needed (i.e. CFD). A hybrid approach that combines model test with sophisticated numerical simulation techniques has been followed at EADS-CASA to address these problems. First a detailed explicit Finite Element (FE) model of the structure is prepared and impacted a water block model. Then a complete series of model ditching tests is used to derive critical load cases in the structure. The FE model, the ditching tests and the procedure to pass from rigid mock-up pressures to real size flexible aircraft will be described in the paper as well as the structural response to these loads. The paper will end with lessons learned and suggested ways of improvement for future ditching analyses.

Document Type:Conference or Workshop Item (Paper)
Title:Aircraft Ditching Numerical Simulation
Authors:
AuthorsInstitution or Email of Authors
Climent, HectorEADS-CASA
Benitez, LuisEADS-CASA
Rueda, FernandoIDOM
Toso-Pentecote, NathalieUNSPECIFIED
Date:2006
Journal or Publication Title:ICAS 2006
Status:Published
Keywords:crashworthiness, safety, ditching, model test, water pressure
Event Title:ICAS 2006
Event Location:Hamburg, Germany
Event Type:international Conference
Event Dates:2006-09-03 - 2006-09-08
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:Aircraft Research
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Structures & Materials
Location: Stuttgart
Institutes and Institutions:Institute of Structures and Design > Structural Integrity
Deposited By: Nathalie Toso
Deposited On:20 Nov 2006
Last Modified:09 Feb 2012 17:50

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