On the excitation mechanisms of rain-wind induced vibration of cables: Unsteady and hysteretic nonlinear features

Models for simulating rain-wind induced vibrations (RWIVs) are proposed that capture often ignored basic excitation mechanisms involving unsteady aerodynamics and hysteretic nonlinearity. The need for these features becomes important since the conventional quasi-steady (QS) theory based model cannot account for these aerodynamic features adequately due to the absence of any consideration of the fluid memory effects. In light of this shortcoming, a semi-empirical model parallel to Scanlan's analysis framework for simulating self-excited forces on bridge decks is developed to take into account the unsteadiness, whereas an optimally-chosen higher-order (nonlinear) polynomial with the Moore-Penrose pseudoinverse identification scheme is exploited for capturing the hysteretic nonlinearity. Parameters related to unsteadiness and nonlinearity in these models are derived from the mapping of pressure field and attendant measured integrated loads on an oscillating cable-rivulet section model. Numerical examples with unsteady and hysteretic nonlinear features are illustrated based on models derived from wind-tunnel data. In addition, the higher-order spectrum is utilized to analyze nonlinear coupling features in RWIV. These models and observations of RWIV promise to serve as building blocks for a holistic model for RWIV as additional research is carried out to further refine the role of each feature and how these can be combined.