A mixed mode function - boundary element method for very large floating structure - water interaction systems excited by airplane landing impacts

Abstract

This thesis develops a mixed mode function – boundary element method (BEM) to analyze the dynamics of an integrated airplane – floating structure – water interaction system subject to airplane landing impacts.

The airplane and the floating structure are treated as two solid substructures of which the motions are represented by their respective modal functions. The landing gear system of the airplane is modelled with a few linear spring – damper units connecting the airplane and the floating structure. The water is assumed to be inviscid and incompressible and the fluid motion is irrotational. Under a linear potential theory, the motion of the fluid is governed by the Laplace equation and the related boundary conditions. A linearised composite free surface boundary condition and an undisturbed far field (infinity) radiation condition are considered. The Green function, or kernel, of BEM formulation is a fundamental solution of the Laplace equation assuming an infinite fluid domain. The motion of the floating structure and the surrounding fluid are coupled through the wetted surface interface conditions. The coupled equations of the airplane, the floating structure and the surrounding fluid are solved using a step by step time integration procedure based
on the Newmark assumptions.

A FORTRAN program MMFBEP is written to implement the proposed numerical method. A few examples are completed to validate the mathematical model and the developed computer code. In comparing the available numerical and experimental results reported in the literature, sound agreements are reached.

It is hoped that the developed method and computer code may be further improved and modified to provide an engineering tool for the dynamic design of Very Large Floating Structures (VLFS).

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