## 5 Adaptive Wing Design and Manufacturing
### Adaptive Wing Structural Analysis (FEA)  
The structural modeling of the prototype wing is accomplished by using the finite element method (FEM) and ANSYS software. This section describes the selection of the element types, the FEM solid modeling, the part connection, the mesh generation, and the boundary conditions. The most commonly used element type in aerospace is two-dimensional (2D), as the industry is mostly dealing with thin-walled structures. Almost every main structural part can be modeled using this type of element. One-dimensional-type elements on the other hand also have applications for connecting beam-like structures [26; 27]. Two-dimensional-type elements are generally chosen for the design of thin-walled structures such as the polymer skin for the wing considered here. The thicknesses of the other parts in the wing box could also be reduced and modeled with 1D-type elements, but for the spars, it was determined that they be modeled using 2D-type elements to obtain more accurate results in the bending responses. The last sets of structural parts are the ribs, which are used to increase the torsional stiffness of the wing structure and to stabilize the skin panels. The resultant stress levels on the ribs, except for the concentrated stresses around the fasteners, are assumed to be very low compared to the stresses on the spars and the skin [28]. Hence, 1D-type elements were assigned to the ribs.  
Figure 15: Adaptive wing prototype based on the S45 structure, spanwise view: (**a**) two actuators support ribs, (**b**) three skin support ribs, (**c**) front spar, and (**d**) rear spar.  
The modeling of the structural parts was conducted by generating surfaces. First, the geometrical model of the composite skin was generated. Second, the surfaces representing the wing box were generated. Third, the ribs were generated in three sections by location. The first section was located at the leading edge section up to the location of the first spar. The second section was located in between the two spars. The last portion starts at the second spar and continues until the trailing edge.  
The spar and rib surfaces can be meshed using a meshing technique called 'Iso-Meshing', whereas complex surfaces such as the skin and the wing box can be meshed using the 'Paver Meshing' method [29; 30]. The Iso-Meshing method creates elements that have the same angles between edges, but Paver Meshing only keeps the global element edge length defined for the meshing approximately the same, and then, it creates non-symmetrical elements.  
There were two sets of connections for the wing. The first one was the connection between the spars and the skin, and the second one was the connection between the ribs and the skin. All the necessary edges for the defined connection sets have been associated with the related surface. The resulting geometry is shown in Figure 16.  
The purpose of the FE model property updating is to integrate the components of a structure model and their properties. A wing mesh model becomes a structure composed of spars, ribs, and skin, which has specific mechanical properties, material properties, and other information, in addition to the geometrical information. Shape optimization is solved at each iteration. The mesh and the FE model are updated at the same time in the process of the optimization iterations, causing a new round of meshing and physical property loading.  
The FE methodology presented in this section allows (i) the generation of the FE model through a CATIA design template. The template interface can achieve rapid model modifications and improvements. (ii) It allows the mesh segmentation of the spars, ribs, and skin, which are divided and meshed separately inside the FE model. (iii) The FE properties and model analysis are loaded on the wing structure after iteration.  
The FE model developed in this section was manufactured in-house and is presented in Section 5.3.  
Figure 16: Mesh generation of the adaptive wing: (a) top view and (b) isometric view.