Keywords: design conceptualisation, aeronautic structures, wireframe primitives, quad-mapped mesh, CAD/CAE tool.

The design conceptualisation is a critical phase during which several important decisions concerning geometrical shapes, functions, materials and manufacturing processes are taken with a strong impact on the final product and its cost [1]. During this phase it is very important to rapidly analyze and compare several design solutions in order to identify the most promising one.

In the aeronautical field the conceptual development of the product has some peculiarities that differentiate it from other sectors. The use of a not completely formalized sketch as a conceptualisation tool is not sufficient, in fact, in a context where, since the very early phases of the design process, some important valuations concerning aerodynamics, lightness and structural strength of the aeronautic product have to be carried out [2,3].

In this paper a methodology aiming at rapidly performing the parametric geometric modelling of the structural scheme of an aeronautical concept is developed. This structural scheme is represented by a quad-mapped mesh of the aeronautical structure, complete with loads, materials and constraints. An original framework of two and three-dimensional high-level primitives, typical for an aeronautical structure, is firstly identified. For each primitive a set of modifiable dimensional parameters is identified. This parametric definition together with the identification of a hierarchy (or relationship of dependences) among the primitives guarantees the automatic propagation of the modifications. Each change made in an instance must cause its variation and the ones relative to all the other entities dependent on it by a propagation process aiming at the automatic regeneration of the whole mesh. In this way several structural concepts can be efficiently modelled and modified during the very early phases of the design process.

The quad-mapped mesh of the aeronautical concept consists mostly of quad elements that are quadrilateral shaped elements with four nodes. Another requisite for the mesh of the aeronautical concept is to be a mapped mesh that is a mesh restricted in terms of the element shape it contains and of the mesh pattern. A quad mapped mesh must contain quadrilateral elements which are located so that a regular pattern, with obvious rows of elements, can be identified. In order to generate a mapped quad-mesh a suitable meshing procedure is here proposed. Moreover, this procedure must guarantee a one-to-one correspondence between mesh elements belonging to adjacent instances.

The methodology here proposed has been implemented in a CAD/CAE tool, called MeshFEM, developed using the C++ and Matlab languages and the VTK library for the three-dimensional graphic visualization. Once the mesh is generated a data file is written, in the NASTRAN format, as output.

1

W. Hsu, I.M.Y. Woon, "Current research in the conceptual design of mechanical products", Computer-Aided Design, 30(5), 377-389, 1998. doi:10.1016/S0010-4485(97)00101-2

2

"Engineering Design Handbook. Helicopter Engineering. Part One. Preliminary Design", Army Materiel Command Alexandria, Virginia, 30 August 1974.

3

C. Matthews, "Aeronautical Engineer's Data Book", Butterworth-Heineman, Oxford, 2001.

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