Nonlinear indicial functions for modelling aeroelastic forces of bluff bodies

This study introduces a novel time-domain model of nonlinear indicial functions to capture the amplitude dependency of self-excited forces in aeroelastic instabilities, including flutter, vortex-induced vibration (VIV), and unsteady galloping. The model aims to reproduce the nonlinear aerodynamic forces that arise from large-amplitude oscillations causing variations in the transient wind angle of attack. The model assumes that the decay coefficients in the indicial functions can be taken as nonlinear functions of the transient angle of attack induced by the body motion, enabling the incorporation of both amplitude dependency and memory effect within a simple time-domain model. The proposed model is experimentally validated considering an unsteady galloping test of an elastically supported rectangular 2:1 cylinder sectional model.