Methodologies for virtual sensing applied to aeronautical and ship structures

In this thesis the problem of achieving a full, experimentally based, representation of the load and elastic deflection response of aeronautical and ship structures is concerned by the development of numerical procedures and their assessment via related experimental activities. The objective is to provide reliable estimations of elastic deflections and external forces throughout the structure using noisy pointwise measurements. This issue is critical for some important structural engineering applications such as Structural Health Monitoring and Condition-Based Maintenance. The most important tools generally used for this purpose (e.g., Kalman filter) have been first reviewed, pointing strengths and critical issues out. Then, an approach based on an optimal second-order natural observer has been proposed also integrating this with signal processing approaches like discrete wavelet transform and finite-element component analysis approaches like dynamics condensation. The developed and integrated numerical framework was finally applied to the state estimation of two specific structures, namely, an aircraft and surface vessel operating under unsteady environmental conditions featured by wind gust or sea waves, respectively. More in detail, a scaled physical model of a fast catamaran, tested in the towing-tank, and a numerical model of a flexible aircraft were studied as significant test cases for assessing the introduced methodologies. Both the structures involved are interesting in their respective research fields. The accurate and complete estimation of the structural dynamics behavior of the fast catamaran is particularly interesting since in real world it might be exposed to critical slamming phenomena on the wetdeck region. The experimental set-up and in particular the choice of the structural measurements were crucial to have a minimum but reliable database for the reconstruction of the structural deflection field. By applying the above methodologies, it was also possible to provide a deeper insight relative to violent fluid-structure interaction phenomena and to evaluate possible fatigue-life reduction for components where direct monitoring was not possible. The other case study consists of an aircraft research model that experiences a particular kind of instability involving both aeroelasticity and flight dynamics. In such aeronautical application, the structural measurements are virtually obtained by means of simulations based on a flight dynamics and aeroelasticity toolbox developed for the present purpose and featured by an accurate description of the coupling caused by aerodynamic and inertial forces. This case has been performed to investigate numerically the technique proposed in this thesis by integrating the methodology with multi-resolution analysis.