Galloping Stability Criterion for 3-DOF Coupled Motion of an Ice-Accreted Conductor

Abstract

This study presents an analytical galloping stability criterion for a three-degree-of-freedom (3-DOF) coupled motion of an ice-accreted conductor by using the eigenvalue perturbation method. To compare the validity of this theory with the classical Den Hartog and Nigol galloping mechanism as well as numerical method, an aeroelastic model of a six-bundled conductor with D-shape ice coating was investigated using a wind tunnel test under different attack angles, wind velocities, and conductor vertical to rotational natural frequency ratios. The experimental results show that wind velocity and frequency ratio have significant effects on galloping initiation characteristics. Under a wind attack azimuth of 70°, vertical galloping enhances with increasing wind velocity for conductor with a low frequency ratio but vanishes for high frequency ratio at high wind velocity. Test results under wind azimuth of 85° indicate that torsional galloping seems more prone to be excited when the vertical natural frequency is smaller than the rotational one. The classical Den Hartog and Nigol galloping theories are unable to explain some experimental galloping phenomena, while the proposed 3-DOF galloping stability criterion can give reasonable predictions of galloping occurrences consistent with all experiment observations. Comparisons between the analytical model and numerical method also show good agreements in galloping initiation predictions, suggesting the proposed 3-DOF galloping stability criterion is reasonable.