Modeling of Riser Response for DP Control

Abstract

The present paper is concerned with modeling of riser response to static and dynamic loading. Focus is on top and bottom angles which are of crucial importance, e.g., during drilling and workover operations. Parametric studies are performed for a representative deep-water riser configuration. The relationship between surface floater motion and angle responses is investigated. In a wider context, the possibility of reducing the maximum response levels by dynamic positioning of the floater is the main objective. It is illustrated by a numerical simulation of the system behavior how the response relations obtained herein can be utilized for such a purpose. Generally, minimization of one of the riser end angles by adjusting the vessel position can only take place at the cost of increasing the other one. Hence, an optimum position should be defined by considering both angles but with different weight functions. An attractive approach is to determine these weights as functions of the respective reliability indices for each of the two angles. The viability of this scheme is also explored by numerical simulation for the same example riser configuration.