Finite element model update of a very flexible wing using ground vibration testing data

ifasd2024 Tracking Number 79

Ground vibration testing (GVT) is typically conducted on an aircraft where the structure is supported using a suspension setup that emulates the free-flying aircraft. When the structure is very flexible, it is challenging to find a suspension system that can support the structure without influencing its dynamic response. This study investigates the computational and experimental techniques required to conduct such a GVT on a very flexible aircraft (VFA) and update its finite element model (FEM). There are two main challenges associated with conducting GVT on a VFA. The first is the measurement of the low frequencies (<1.0 Hz) related to the test structure. The second is the practical challenge of obtaining a soft enough suspension to minimize the interaction between the suspension-related modes and the aircraft’s elastic modes. For VFA, decoupling of the suspension and airframe modes is typically not feasible. This requires accounting for the suspension in the FEM, which can be achieved by characterizing the suspension upfront as an isolated component and accounting for it in the FEM. GVT was conducted on a VFA using the methodology developed by Sharqi and Cesnik1, which is based on performing GVT in various deformed shapes representative of the vehicle’s free-flight behavior. A FEM updating methodology developed by the authors2 was then demonstrated numerically and on simple slender beams. A validation of the methodology was conducted on a scale model with the representative dynamics of a solar-powered flying wing. The final paper will provide details on the GVT and FEM updating conducted on the aircraft and discuss the importance of the suspension setup in such an experiment. A free-free GVT on a VFA is a substantial effort that requires more resources than a conventional GVT on a relatively rigid (or moderately flexible) structure. This work will detail the process of performing GVT on a VFA with the suspension model included and removing it once the FEM is successfully updated. This results in a FEM that is dynamically representative of the actual test structure, bypassing the need for an expensive, if even practical, free-free GVT.