Fluid-Structure Interaction: Lowering Subsea Structure / Equipment in Splash Zone During Installation

Abstract

Successful installation of subsea structures and equipment is critical for offshore campaigns in development of deep-water fields. This paper presents a novel approach using Fluid-Structure Interaction (FSI) to predict wave induced motions, wave loads, dynamic stresses and deformation of subsea structure and equipment in the splash zone during installation. This approach combines transient multiphase CFD simulation including dynamic mesh motion with transient nonlinear Computational Structural Dynamics including tension forces in non-linear flexible slings. This proposed approach has been successfully implemented for lowering of a subsea manifold in splash zone during installation. This paper has many potential applications, such as, installation of manifold, subsea tree, PLET/PLEM, suction pile, pump station, or other subsea structure and equipment. In this coupled FSI approach, pressure loads on the structure due to wave slamming from CFD model is mapped to FEA model of structure-sling assembly, which provides motion and deformation to CFD model. The results clearly show the advantage of this FSI approach to capture the coupled physics of wave slamming and its interaction with the structure and subsequent motions of structure which is being lowered in the splash zone that other approaches cannot capture. Structural integrity of the subsea structure and equipment as well as the sling forces is well evaluated and predicted with this approach. Traditional approaches for prediction of the motions and loads of subsea structure/equipment during installation rely on simplified formulations or empirical equations or model test to determine the wave loads on structures. It cannot simulate wave-structure interaction, nor the dynamic stress and deformation of structure/equipment due to wave-structure interaction. The approach proposed in this paper provides a state-of-the-art FSI tool which enhances understanding wave-structure interaction in splash zone during installation. The dynamic stress obtained by using this approach can be used for quantifying fatigue damage of every component on the structure/equipment due to wave loads in splash zone during installation.