Adaptative structures: the key for future airship certification
Creators: name:  Y. GOURINAT 
name:   L. CHRISTON 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: STRUCTURES
MATERIALS
STRUCTURAL DYNAMICS

description: In the context of aerospace structural durability, the active and passive control of flexible structures is a major challenge in which recent improvments have been realized in the frame of solid dynamics. A series of computations and tests in the field of Generalized Predictive Control (GPC) and Structural Health Monitoring (SHM) for aircraft and rotorcraft structures, associated with new cellular and entangled materials have been performed. These developments provide new scientific bases which presently clearly allow the perspective of operational and certified airship, for freight and passengers. The main lock, which - until now - has compromised the certification of large airships, is the dynamic control of very large structures. Indeed, the concept of a rigid airship can only be relative, and history shows that all large balloons have been destroyed for dynamic reasons (gust, landing, turbulence). The active control already applied to convertible helicopters, combined with specific materials with high entropy and the temporal prediction of loads and their transient and cyclic repercussions are considerable advances. This whole process is made possible by the emergence of high-level numerical and analytical models, integrating shell-fluid interactions and geometric and mechanical non-linearities, and also predictive gust turbulence measures with Lidars, commonly projected for Flying Wing control in ground effect and low Mach regimes. Thus, the algorithms developed for fly-by-wire flight controls implemented in aircraft and launchers now make it possible to build and qualify a very large airship. Concerning the active control, the present capability of thermodynamic models of membrane-beam in internal aeroacoustic and external fluid interaction integration in digital flight controls make possible the active structural stabilisation of the dynamic shapes. The stake is here the integration of full-authority for servoing in strongly nonlinear large structures. That was initiated in dynamic buckled and unstable shells, and the emergence of complete models and control chain with global meta-modes similar to the ones used on telescope mirrors to compensate the atmospheric turbulence provides robust algorithms for these flexible structures. Precisely, hybrid models with Lagrangian representation of Reissner Shells (with U, V, W local deflections in main curvature axes) coupled with Eulerian parametrization of the fluid (?p pressure local fluctuation) lead to explicit mass [M] and static [K] matrix, and explicit [Z] impedance hybrid matrix. The major challenge is obviously the rectangular coupling block in each dynamic matrix. In addition, the integration of non-linear dissipative internal materials previously developped for noise control in shells and the external 3D observation for load anticipation authorize now the truncation of gusts, shocks and resonances in real time, for safety, comfort and performance purpose. As for the flying wing, the initial integration of digital flight control is mandatory to make the airship feasible, but the recent scientific and technological realizations open that perspective. The mastery of the very particular rheology of hydrogen or helium has also been significantly improved on one hand in the field of numerical codes, and on the other hand in the field of Froude similarity shell granular media material approaches. Last but not least, these evolutions are scientifically mature and it is possible to envisage to implement these processes in the certification rules themselves for large airships, in accordance with the airworthiness authorities, the architects and the operators.