# Specific Modeling Issues on an Adaptive Winglet Skeleton
## 1 Introduction  
The long experience gained by an extended Italian group on morphing, developed from more than 20 years of activity in international contexts, led to the ambitious aim of proposing a project concerning the design and realization of a complete morphing wing implementing different kinds of devices in its basic geometry. The occasion matured within the CS2 GRA frame, as Leonardo S.P.A. (Aircraft Division) issued a call for proposals on several topics, among which the abovementioned subjects [1]. CIRA, University of Napoli, and Politecnico di Milano took charge of designing and realizing four different adaptive prototypes to be installed on a single wing: a winglet, an adaptive trailing edge, and an adaptive leading edge plus an adaptive wingtip, respectively. The project did rely at awide extent on the further development of numerical capabilities particularly suited for morphing system design, on the wake of the developed expertise. Kinematic systems differ from compliant morphing systems, as their basic architecture is almost an extension of standard devices already placed on any kind of aircraft, such as flap, slats, and so on, while the latter tries to modify the inner structure of the reference craft to make it suitably deformable [2; 3; 4; 5; 6]. In both cases, however, the need of assigning further macroscopic degrees of freedom to the target structure, imposes the creation of high-nodal density models [7]. They have to consider the deployment of a more complex and articulated structural outline, an immediate consequence of the additional mobility and the increased number of parts. These kinds of models have been reported in the literature to be characterized by a certain behavior with respect to further increase of their density [8; 9; 10; 11]. As the number of nodes and elements increase, or conversely, the mesh step decreases, certain singularities are shown that turn on the debate among the researchers about the fact they are actual index of a physical behavior or instead are simply linked to some mathematical issue [12]. The fact is, revealing the point deformation in a very limited geometry domain is a true challenge considering that standard sensors, even when miniaturized, only produce information along a certain area and do not have the capability of providing point information. Of course, this can be limitedly true for displacements, while they may have a dramatic impact on strain detection [13; 14]. In light of these considerations, the paper herein presented reports some significant experiences that the authors believe to be interesting to discuss, concerning specifically the increasingly higher modal density mesh effects on the structural response. This goal had an even more significance, because of the possibility of attaining a wide database of experimental output, as the target element did undergo an extensive test campaign. As introduced, lab acquisitions were not expected to allow a deeper correlation among experimental and numerical data, but it was considered that could at least make a base of reference, even for further activities. As part of the Clean Sky 2 program, CIRA is the leader of the AIRGREEN2 project in the REG-IADP platform whose leader is Leonardo S.p.A. (Aircraft Division). The AIRGREEN2 project began in November 2015 and will end in 2023. The main purpose of the project is the development and validation of technologies suitable for the wing of the future regional aircraft of LDO and related demonstrators up to, for some of them, validation by experimentation in flight. The technological strands that characterize the AIRGREEN2 project are:  
Innovative wing structure (design, manufacturing and testing): innovative composite design, repair, structural health monitoring, LRI (liquid resin infusion) processes and AFP (automatic fiber placement) [15; 16].