Determination of aerodynamic damping of twin cables in wet conditions through passive-dynamic wind tunnel tests

Moderate amplitude cable vibrations continue to be reported on the cable-stayed Øresund Bridge, despite the presence of helical fillets and dampers. The vibrations are particularly notable in wet conditions, which would suggest a form of rain-wind induced vibrations (RWIV). A statistical operational modal analysis of the monitored vibrations revealed, in certain conditions and for specific wind velocities, the presence of negative aerodynamic damping.To investigate the observed aerodynamic damping of the twin cable arrangement further, a series of 1:2.3 scale passive-dynamic wind tunnel tests was performed at the DTU/FORCETechnology ClimaticWind Tunnel facility in Kgs.

Lyngby, Denmark. Tests were performed for both dry and wet conditions, with and without helical fillets. The specific relative cable-wind angle tested was identified as critical from the aforementioned full-scale monitoring of the bridge cables. For the wet tests, the twin cable surfaces were treated in order to obtain uniform upper and lower water rivulets.

The interaction between water rivulets, surface properties and the flow was found to govern the activation of the RWIV mechanism. The resulting aerodynamic damping from wet passive-dynamic wind tunnel tests showed the effect of the helical fillets in preventing the occurrence of negative aerodynamic damping, contrary to the plain cables. © 2013 Taylor & Francis Group, London, UK.