Comparison of Recent Parametric Trenched and Partially Embedded/ Spanning Pipelines With DNV-RP-F109 Load Reduction Design Curves

An extensive series of 2D CFD analyses of subsea pipelines with parametrically varying seabed profiles have been performed in the past two years. These cases feature variations on wave and current flow conditions with pipeline partial embedment or spanning which extend beyond the range of conditions which have been published to date. This paper presents a comparison of the reduction factors calculated from this work with DNV-RP-F109 load factors and previous published research. At present, the DNV-RP-F109 partial embedment / trenched pipeline load reduction factors are applied in both absolute stability analysis and also as a reduction factor on hydrodynamic force-time histories used in dynamic stability analysis. The suitability of this load factor reduction for dynamic stability analysis will also be considered. In addition, a limited number of cases have been constructed in 3D which provide some initial insights into the variation of hydrodynamic loads across a pipeline span as a function of finite span length, enabling the validity of applying the 2D DNV load reduction factors across a 3D span to be considered. The 3D cases also consider inclined attack angles, and the effect they have on hydrodynamic forces across a span.