High-Fidelity Modeling for Installation of Subsea Structures in the Splash Zone

subsea manifold

3D Computational Domain including Detailed Geometry of a Subsea Manifold

Lowering subsea structures and equipment into the splash zone is a critical part of offshore installation campaigns. In preparation, engineering teams perform many installation analyses to ensure sufficient crane capacity, clearance and accessibility, structural integrity, and equipment/structure stability. Traditional low-fidelity approaches rely on simplified formulations or empirical equations; some consist of model tests to determine wave loads on structures. But these traditional approaches cannot simulate wave-structure interaction nor the dynamic stress and deformation of structure/equipment due to wave slamming. And hence the accuracy is always a key concern.

The challenges of simulating this operation arise from the complex geometry of the subsea structure and equipment, complex flow field around the structure and equipment, and the wave slamming and wave-structure interactions. A high-fidelity simulation approach is clearly needed.

To that end, I am co-presenting a paper at the 2014 Offshore Technology Conference (OTC) in Houston, TX on May 5th that leverages Fluid-Structure Interaction (FSI) to predict wave-induced motions, wave loads, dynamic stresses, and deformation of structures in the splash zone during installation. This approach combines transient multiphase computational fluid dynamics (CFD), including dynamic mesh motion, with transient nonlinear computational structural dynamics, including tension forces in nonlinear flexible slings. The method has been successfully implemented for lowering a subsea manifold in splash zone. The dynamic stresses obtained using this approach can be used to quantify fatigue damage in every component on the structure/equipment due to wave loads in the splash zone during installation.

pressure contours manifold

Pressure Contours and the Free Surface when the Manifold is Passing Through the Splash Zone 

Contours of von Mises Stress on Manifold

Contours of von Mises Stress on Manifold

Time History of Fluid Forces on Manifold

Time History of Fluid Forces on Manifold

Last year at the International Conference on Ocean, Offshore and Arctic Engineering (OMAE), I co-authored another novel approach in which the time domain diffraction simulation (ANSYS Aqwa) is coupled with multiphase CFD simulation (ANSYS Fluent) to model installation of subsea equipment/structure in the splash zone (OMAE2013-11569). The transient CFD model with rigid body motion for the equipment/structure calculates added masses, forces and moments on the equipment/structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation. As a continuation of this work, I will present a follow-up paper at OMAE 2014 to demonstrate the advantage of this coupled CFD-diffraction analysis for installation of suction pile in splash zone (OMAE2014-23225).

Schematic of two-way Coupled Transient CFD and Diffraction Analysis

Schematic of two-way Coupled Transient CFD and Diffraction Analysis

If you plan to attend these conferences, be sure to mark these dates on your calendar:

Fluid-Structure Interaction: Lowering Subsea Structure / Equipment in Splash Zone During Installation
OTC
Monday, May 5th,  9:53 – 10:14 a.m.

A Parametric Study of Wave-Structure Interaction Using the Coupled Transient CFD and Diffraction Methodology
OMAE
Monday, June 9th, 4:00 – 6:00 p.m.