Assessment of Methods for Short-Term Extreme Value Analysis of Riser Collision

Risers are commonly arranged as clusters with relatively small spacing due to economic necessity. As a consequence, collision between risers becomes an essential problem. This study presents a comprehensive assessment of various methods for riser collision probability analysis. A pair of tandem arrangement risers subjected to combined current and wave loads is modelled. Three hours short-term simulation is performed in order to obtain the time history samples for the collision probability analysis. The wake effect due to the presence of the upstream riser is considered. The shortest distance between risers is calculated at each time step. Four methods for estimation of the extreme value distribution, e.g. Gumbel probability paper method, Weibull based method, average conditional exceedance rate method and moment based Hermit method, are presented, and the results obtained from different methods are compared and discussed.