Luisa Boni

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

Abstract 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.

Solar sail structural analysis via improved finite element modeling

Despite the existence of many studies about the structural analysis of a square solar sail, the need for obtaining reliable numerical results still poses a number of practical issues to be solved. The aim of this paper is to propose a new method that improves the existing analysis techniques. In this sense, the solar sail is modeled using distributed sail-boom connections, and its structural behavior in free flight is studied, using the inertia relief method, at different incidence angles of the incoming solar radiation. The proposed approach is able to circumvent the onset of numerical convergence problems by means of suitable strategies. A nonlinear analysis is carried out starting from an initial geometrical configuration in which the whole solar sail is perturbed using a linear combination of the first global buckling modes, obtained with a static eigenvalue analysis. Key points of the procedure are the application of a correct sail pre-stress, a clever choice of the type of elements to be used in the finite element analysis and the use of a suitable mesh refinement. The performance of the new approach have been successfully tested on square solar sails with side length varying from relatively small to medium-to-large sizes, in the range of 10–100 m. A detailed analysis is presented for a reference 20 m × 20 m square solar sail, where the paper shows that the suggested procedure is able to guarantee accurate results without the need of additional stabilization technique. In particular, the vibration global mode shapes and frequencies of the solar sail are correctly described even in presence of unsymmetrical loading conditions. In other terms, the numerical analysis is completed without any convergence problem and any disturbing local modes.

Experimental Tests and Numerical Analyses of Fiber Metal Laminate Panels under Shear Load with Bonded Window Frame

Experimental and numerical activities have been developed to investigate the behavior of Fiber metal laminates (FML) shear loaded panels having a bonded window frame. Both static and fatigue tests have been carried out at the Department of Aerospace Engineering of Pisa on 10 panels manufactured by Alenia Aeronautica, in the context of the DIALFAST (Development of Innovative and Advanced Laminates for Future Aircraft Structures) project, co-funded by the European Commission within the Sixth Framework Programme. In addition to technological problems, the tested specimens represent very critical components, involving fundamental aspects of the structural design of fuselage panels; in particular, the primary interest to exploit the postbuckling behavior of FML components, as commonly applied in conventional aluminum alloy fuselage structures, is associated with the effort of making reinforced holes which do not alter significantly the stress distribution of the main body of the panel. Detailed finite element analyses, performed by means of the ABAQUS V 6.5 package, have been used to investigate the panel response during testing. The numerical results have shown a very good agreement with the experimental data, thus revealing an effective instrument to study the behavior of a postbuckled shear panel, in presence of the neutral hole issue.

Finite element analysis of solar sail force model with mission application

A finite element approach is used to calculate the components of forces and moments acting on a square solar sail at a sun-sail distance equal to one astronomical unit. The model takes into account the deformation effect induced by the solar radiation pressure, where the incidence of the reflected photons changes as a function of the local orientation of the sail surface. Assuming a specular reflection model, the analysis shows that the maximum value of the transversal thrust component takes place when the solar zenith angle is about 36°, which is in accordance with the result available for a classical flat solar sail. Notably, the modulus of the moment due to the solar radiation pressure takes its maximum value approximately at the same (solar zenith) angle.