Variable kinematic 1D, 2D and 3D Models for the Analysis of Aerospace Structures

The aerospace structure design is one of the most challenging field in the mechanical engineering. The advanced structural configurations, introduced to satisfy the weight and strength requirements, require advanced analysis techniques able to predict complex physical phenomena. Finite Element Method, FEM, is one of the most used approach to perform analyses of complex structures. The use of FEM method allows the classical structural models to be used to investigate complex structures where a close form solution is not available. The FEM formulation can be easily implemented in automatic calculation routines therefore this approach can take advantage of the improvements of computers. In the last fifty years many commercial codes, base on FEM, has been developed and commercialized, as examples it is possible to refer to Nastran R by MSC or Abaqus R by Dassault Systémes. All the commercial codes are based on classical structural models. The beam model are based on Euler-Bernoulli or Timoshenko theories while two-dimensional models deal with Kirchhoff or Mindlin theories. The limitations introduced by the kinematic assumptions of such theories make the FEM elements based oh these models inef- fective in the analysis of advanced structures. The physical phenomena introduced by composite and smart materials, multi-field application and unconventional loads configurations can not be investigated using the classical FEM models, where the only solution improvement can be reached by refining the mesh and increasing the number of degrees of freedom. This scenario makes the development of advanced structural models very attractive in the structural engineering. With the development of new materials and structural solutions, a number of new structural models have been introduced in order to perform an accurate design of advanced structures. Classical structural model have been im- proved introducing more refined kinematics formulation. One- and two- dimensional models are widely used in aerospace structure design, the limitations introduced by the classical models have been overcame by introducing refined kinematic formulations able to deal with the complexities of the problems. On the other hand, while in the classical models each point is characterized by 3 translations and 3 rotations, the use of advanced models with complex kinematic introduces a number of complication in the analysis of complex geometries, in fact is much more difficult to combine models with different kinematics. The aim of this thesis is to develop new approaches that allow different kinematic models to be used in the same structural analysis. The advanced models used in the present thesis have been derived using the Carrera Unified Formulations, CUF. The CUF allows any structural model do be derived by means of a general formulation independent from the kinematics assumed by the theory. One-, two- and three- dimensional models are derived using the same approach. These models are therefore combined together using different techniques in order to perform structural analysis of complex structures. The results show the capabilities of the present approach to deal with the analysis of typical complex aerospace structure. The performances of variable kinematics models have been investigated and many assessment have been proposed. This walled structure, reinforced structure and composite and sandwich material have been con- sidered. The advanced models introduced in this thesis have been used to perform static, dynamic and aeroelastic analysis in order to highlight the capabilities of the approach in different field. The results show that the present models are able to provide accurate results with a strong reduction in the computational cost with respect classical approaches.