Extreme behavior prediction of vortex-induced vibrations

Abstract

Vortex-Induced Vibration (VIV) can pose a serious design threat for offshore structures, especially slender cylindrical deepwater structure like a spar. Numerous studies have been conducted in developing prediction models for cylindrical bodies under uniform or sheared current and/ or regular wave conditions. However more research needs to be done for bodies subject to a combination of currents and random waves. This suggests that statistical models are needed to help characterize the vortex-induced motion behavior. In the present study, datasets obtained from tests carried out in the Offshore Technology Research Center (OTRC) at Texas A&M University investigating a towed flexible cylinder has been considered. This data has been analyzed using a new statistical approach that requires knowledge of the correlation structure of the response data. An analytical form of the autocorrelation function is suggested and investigated herein. The behavior of the cylinder in terms of the displacement response above a given threshold level is examined, since this is of much interest to the offshore engineers. The results from the prediction model are compared with those from the measured data to validate the accuracy of the model. The results indicate that the approach is viable. The predicted values are quite close to the measured values for low thresholds. But as the threshold is increased, due to the lack of data from the experiments, the predicted values have a tendency of overestimating the displacement, although the difference between the measured and predicted values is not much.