TOWARDS THE GLOBAL ANALYSIS OF SOIL AND RISER INTERACTION USING A DEGRADATION SOIL MODEL

Resumo

In offshore industry as water depth gets deeper, the prediction of riser loads gets more complex, due to
issues such as its interaction with seabed. The touchdown point (TDP) – where the riser touches the seabed for the
first time – is a hot spot where the interaction is intense, and good predictions of TDP response is critical to the
assessment of steel catenary riser (SCR) fatigue life. Therefore, the soil model plays an important role, because
simplified models can overestimate the SCR curvature at TDP. Different types of soil have been studied from
linear to nonlinear springs to represent the seabed. Nonetheless, linear springs cannot represent the real soil
behavior, thus research focuses on P-y curves based in pipe-soil experimental results. Two models became widely
studied: the non-degradation and degradation models. The former has been applied in general software analysis,
but the degradation model has not. The degradation model is based on plastic soil deformation under cyclic loads,
and it has other features such as consideration of soil- water mixing, erosion, and soil consolidation, which can
drive the riser-soil separation and trench formation. The purpose of this article is to describe the implementation
of a soil-riser interaction model considering degradation effects [1] on the in-house time domain global analysis
software SITUA-Prosim. Two case studies are presented to validate the model and the proposed algorithm.