Development of a dynamic calculation tool forsimulation of ditching

Sammanfattning: The present document is the final master thesis report written by Marc PILORGET,student at SUPAERO (home institution) and KTH (Royal Institute of Technology,Exchange University). This six months internship was done at DASSAULT AVIATION(Airframe engineering department) based in Saint-Cloud, France. It spanned from the 5thof July to the 23rd of December. The thesis work aims at developing an SPH (SmoothParticle Hydrodynamics) calculation method for ditching and implementing it in the finiteelement software ELFINI® developed by DASSAULT. Ditching corresponds to a phasewhen the aeroplane is touching the water. The problematic of ditching has always beenan area of interest for DASSAULT and the whole aeronautical industry. So far, only testsand simple analytical calculations have been performed. Most of the work was carried bythe NACA (National Advisory Committee for Aeronautics) in the late 70's. However in thepast decade, a new method for fluid-structure coupling problems has been developed. Itis called SPH. The basic principle is the following: the domain is represented by means ofparticles and each particle of fluid is treated separately and submitted to the Navier-Stokes equations. The particle is influenced by the neighbouring particles with a weightfunction depending on the distance between the two particles. Particles are also placed atthe interface solid-fluid: they are called limit particles. The final purpose of this SPHmethod is to access to the structural response of an aircraft when ditching. The crucialinterest of such a method compared to methods used so far is the absence of mesh. Theanalysis of large deformation problems by the finite element method may require thecontinuous remeshing of the domain to avoid the breakdown of the calculation due toexcessive mesh distortion. When considering ditching or other large deformationsproblems, the mesh generation is a far more time-consuming task than the constructionand solution of a discrete set of equations. For DASSAULT-AVIATION, the long termobjective is to get a numerical tool able to model ditching. The SPH method is used tosolve the equations for the fluid and is coupled with a finite element method for thestructure. So far, the compressible solver for 2D geometries has been implemented.Tests are going to be performed to ensure the program’s robustness. Then theincompressible solver for 2D geometries will be studied both theoretically andnumerically.