Modeling of Ground Vibration Testing for Highly Flexible Aircraft

Abstract

A modeling procedure is presented for analysis of Ground Vibration Testing (GVT) of highly flexible aircraft. The work was motivated by the fact that such aircraft typically operate with large deformation in various flight conditions, so that a linear theory cannot correctly predict the aeroelastic behavior. Because one would want the shape of the aircraft in the GVT configuration to closely mimic that of the actual flying aircraft, a nonlinear theory is required for the GVT as well. As a first step, a bungee formulation for GVT is derived by an augmented Lagrangian method and is incorporated into a geometrically-exact, intrinsic, finite element representation of interconnected beams. The geometric constraints imposed by bungee cords make the system statically indeterminant, which causes their strain-displacement relations to appear in the formulation. Numerical simulations of the dynamics of rigid bodies and highly flexible beams suspended by bungee cords are presented for both static and dynamic behavior with eigenanalysis about the static equilibrium state. This analysis also provides information about coupling of the lowest elastic modes with the GVT rigid-body modes. The GVT parameters should be chosen in such a way that GVT modes dominated by rigid-body motion are separated enough to lead to a close approximation of the modal frequencies dominated by structural deformation for free-free boundary conditions.