Dynamic interaction of catenary risers with the seafloor

It is the purpose of this study to quantify the sea-bottom soil reaction effect on the dynamics of a Steel Catenary Riser by incorporating the soil reaction forces into the theoretical model of the dynamic equilibrium system. The calculations for the soil reaction forces have been performed quasi-statically, assuming specified embedment depths and trenching geometries. The plane stresses of the soil are determined with the aid of the commercial Geotechnical software, Phase2. Accordingly, the stresses are integrated around the arched riser–soil contact surface for the derivation of vertical soil reaction forces that resist to the penetration of the riser. These force-values are introduced in the nonlinear dynamic model as concentrated loads which are applied at the touchdown point (TDP). Several tests cases of top end harmonic excitations have been performed, aiming to investigate the effect of the TDP soil reaction on the various dynamic parameters which are responsible for fatigue damage.

► The seafloor soil reaction effect on the dynamics of a SCR is quantified.
► The associated soil reaction forces are obtained through the geotechnical approach.
► Valid assumptions are made to consider the uncertainties involved with the trenched soil.
► The soil reaction forces are incorporated into the dynamic model to produce an integrated numerical tool.
► The importance of the soil reaction during downstroke to riser's global dynamics is highlighted and discussed.