Study on the collision probability of vertical risers considering the wake interference effect

Abstract

This paper develops a model to predict the collision probability of risers. Considering the wake interference effect, a dual-riser model is built based on the vector form intrinsic finite element. The central difference method is employed to obtain the dynamic responses of risers. Then, an analytical geometry-based procedure is established to identify a minimum distance from the displacement response in a duration. A random sample of the minimum distance is obtained based on a series of repeated such processes. Further, the collision probability is predicted from this random sample utilizing the probability paper method and the least-squares fitting method. Finally, the effects of critical parameters (i.e., initial spacing, top tension factor (TTF), reduced velocity) on the collision probability of two vertical risers arranged tandem are investigated. Results show that the collision probability is considerably underestimated without considering the wake interference effect. Moreover, an increase in TTF of the upstream riser (URTTF) or a decrease in that of the downstream riser (DRTTF) is more feasible to reduce the collision probability. For every 0.1 increases in URTTF, the collision probability drops by 2 orders of magnitude. For every 0.1 decreases in DRTTF, the collision probability drops by 1-2 orders of magnitude.