Characterisation and Improvement of Aerodynamic Vibration in Modern Composite Rigging

Abstract This study addresses the effects that wind-induced vibration has on composite rigging shrouds as well as the development of engineered dampeners to mitigate the identified effects. The research considered monolithic and bundled multiple-body shroud architectures, representing the two carbon-fibre based alternatives available in current composite rigging. Indeed, the literature suggests wide range of situations where vortex-induced-vibrations can affect rigging stays, yet yacht rigging experiments remain to be conducted. Consequently, wind tunnel testing, on-site measurements, and laboratory tests were performed to characterise the rigging vibration and dampening properties. The first output of the investigation evaluated through field velocity measurements in wind tunnel the turbulence intensity at the trailing edge of vibrating shrouds. Results depicted how the flow turbulence in resonating situations can be triple to that of the shroud when static. Secondly, testing with an excitation device provided the damping response of shrouds with different constructions. These tests quantified the motion amplitude of resonating shrouds as well as the inherent damping properties. Additional tests were performed on the same specimens following the installation of custom external damping devices to mitigate the vibration. Results showed how cables with varying constructions can attenuate the vibration up to 63% faster, whereas the dampeners were proven to provide significant reductions both in the resonance amplitude and damping time. Finally, onsite measurements were performed to quantify the vibration phenomenon and the performance of the dampeners in a real yachting situation. These results provide novel findings on the aerodynamics and vibration characteristics of modern composite riggings, and may be applicable to racing yachts and superyachts. Keywords vibration; rigging; carbon fibre; damping; aerodynamics; wind tunnel; vortex shedding