## 5 Results
### Fourth Level  
After collecting the optimal compliant structure solutions of different wing sections in the spanwise direction, the three-dimensional finite element model of the complete morphing leading edge device is generated. The model generation is based on Abaqus CAE coupled with the CST representation of the wing, via a Python interface. Abaqus is used to perform nonlinear stress analyses, verify the structural integrity of the final configuration under actuation and pressure loads, and finally evaluate the aeroelastic effects due to the wing-box interaction. The complete model consists of a total of 20 compliant ribs connected to the stringers that are tied to the flexible skin. A full integration of stringers into the internal layers of the skin is assumed. This solution acts to minimize the local stiffness in the chord-direction introduced by the stringers, which provides a more localized actuation of the skin. It results in a more diffuse deformation and a reduction in the skin local waviness. The skin is divided into additional sections to avoid excessive discontinuities in the skin lamination. The smoother thickness distribution in the chordwise direction is also used to reduce the strain concentrations along the skin. Such regions are more representative of a technologically feasible solution, which can be developed when considering a smoother thickness variation due to a more progressive ply drop-off in the lamination of the skin. Constant layups are assumed in the span direction. The input actuation is introduced through a rotation of 80 deg of a shaft connected to all of the compliant ribs by a rigid kinematic chain. The aerodynamic loads are applied to the skin surface, while considering the pressure coefficient distributions of Figure 11. Pressures are applied once the final deflection has been achieved by a multi-step nonlinear analysis. The model consists of 73,822 elements: 67,600 linear 4-node shell (S4) elements for the skin modeling (46,306 for the external skin and 21,294 for the stringers) and 6222 linear 2-node beam (B31) elements for modeling the compliant ribs. As far as the skin is concerned, the element's typical size in the high curvature nose region is approximately 5 mm, whereas in the other regions, where the curvature variation is less significant, it is equal to 15 mm. Three-dimensional stress analyses are based on the same solver used during the third level of optimization. The static implicit nonlinear multi-step analyses are performed by the Abaqus Standard-Implicit code. The stress field inside the compliant ribs is shown in Figure 19, and it is lower than the considered material strength, and, under the maximum actuation level, it perfectly matches the values computed during the third level of optimization. Figure 19: Stress distribution inside the compliant ribs at the wing tip (**a**) and wing root (**b**). The comparison between the target aerodynamic shape and the skin deformation is shown in Figure 20. The corresponding three-dimensional \(LSE\) value is equal to 5.32 mm. No anticlastic phenomena due to the actuation loads are observable, and the final solution shows a good shape quality that is not affected by any skin-waviness phenomena. Once the actuation shaft achieved the maximum droop nose configuration, the aerodynamic loads were not so important as to implicate a significant variation in the final shape. The highest deviations are detected in the nose regions where the skin is less supported and provides a lower relative bending stiffness. The undeformed and maximum droop nose configuration are also given in Figure 21, which provides the strain distribution in the outermost layer of the skin. The strains show a very constant distribution in the spanwise direction, and the maximum strain value perfectly matches the skin structural constraints imposed in the first level of optimization.