Wind Loads On Offshore Structures

Abstract

A review of the state of the art of wind design procedures for offshore structures indicated that wind/wave interactions were not taken into account. In hurricane conditions, large amplitude waves may cause cyclic loading on the platform due to the wind flowing between the waves and the platform deck. Also, the waves induce velocities which are not currently considered by designers when they formulate a design velocity profile. In order to model the problem a trochoidal wave with a 60 foot amplitude and 720 foot wavelength was chosen along with a 180’ X 180’ X 18’ platform deck. Wind tunnel models were then built using a scale of 1:500. Velocity profiles above the waves were determined in both uniform and simulated atmospheric boundary layer approach flows. Lift forces on the model platform were then measured in the uniform flow. Experimental velocity perturbations were compared with a linear perturbation solution and a 4th order perturbation solution. It was concluded that the instantaneous velocity field above a wavy surface could be modeled as the sum of the reference velocity profile and the induced perturbation velocity profile with an increase inaccuracy of up to 33% over current mode 1 s. This could increase the accuracy of the dynamic pressure prediction by as much as 77% in the lower layers.