References

In this presentation we consider a generic airship [3] which can be modelled by an ellipsoid. When the structure is rigid, the flow around the airship is axisymmetrical (unsymmetrical instabilities are omitted). Two cases of small perturbations can be discussed without loosing the benefit of the axisymmetry. • The rigid modelling of the structure. As far as no instability are developed, one can use a Fourier decomposition. But this can be done if we neglect the coupling between the harmonics due to the non linear term (convective term). This is performed from a linearisation of the flow model in the vicinity of the steady axisymmetrical solution. Thus, one can deduce the expressions of the aerodynamical coefficients with respect to the various parameters. In a second step, one can write the dynamic response of the structure, in the linear framework assuming that the steady state approximation is valid. • The flexible modelling. The dynamic behaviour of the stucture is modelled using a basis of eigenmodes which are computed using a finite element code for shells. The coupling between the fluid and the structure is taken into account by an Euler-Lagrange formulation. The mapping which transforms the fluid domain is then linearized and this enables to avoid the remeshin