Development of analytical methods for fuselage design: validation by means of finite element analyses

The paper presents the results of a set of finite element analyses (FEAs) carried out to support the development of an integrated design procedure that, based on semi-empirical and analytical methods, is capable of defining generic fuselage sections of a transport aircraft. The procedure, which is implemented in a structural optimization code, defines a structure that, compliant with durability and damage tolerance requirements, is characterized by a post-critical behaviour of the stiffened panels and by a design of the frames that takes the frame flexibility and the presence of the floor beams into account. FEAs, carried out on a reference configuration defined by the optimization code, are used to acquire a deeper knowledge of the advantages and disadvantages of the analytical approach in the design of complex structures subjected to realistic load cases. In particular, the influence of the actual frame flexibility on the distribution of the skin shear flow induced by the frame is evaluated; moreover, the effects on the stress distribution in skin and frames, caused by the presence of the stringers, and of the stiffness concentration introduced by the floor beam are addressed. Finite element method results demonstrate the effectiveness of the analytical model of the flexible frame in evaluating the shear flow that a single loaded frame transfers to the skin and highlight the effects of the presence of adjacent loaded frames. By means of geometrically non-linear FEAs, the effects of the stringers on the stress distribution of a pressurized cylinder are evaluated, as well as the magnitude and extension of the perturbation introduced by the floor beams.