Numerical Modeling of Released Subsea Buoyancy Module for Reliable Prediction of its Trajectory and Velocity Using Transient CFD Analysis for Risk Assessment

Abstract

Buoyancy modules are widely used in offshore and subsea fields, such as on pipelines, risers, umbilicals, and ROVs, etc. in operation and installation. Accidental release of subsea buoyancy modules due to broken or damaged parts may pose a potential risk and hazard to offshore vessels, floating platforms and risers & surrounding umbilicals. A released buoyancy module rises and may collide with any floating structures or pipes above it. For offshore and subsea field development, it is important to assess such potential risk to offshore vessels, floating platforms, and risers & umbilicals around them. Accurate prediction of the trajectory and the impact speed of the released buoyancy module is the key component for risk assessment in offshore and subsea field development. This paper presents a Computational Fluid Dynamics (CFD) solution for prediction of the trajectory and velocity of the released buoyancy modules from subsea. Six Degree of Freedom (DOF) rigid body motion of buoyancy module is modeled using an efficient moving mesh approach in transient CFD simulation. The effect of ocean currents at different water depths is considered in the motion of buoyancy modules. This methodology has potential applications in many areas, such as, offshore vessel and floating platform protection, riser and umbilical protection, offshore and subsea field planning and layout, etc. This transient CFD approach has been successfully implemented on typical buoyancy modules and demonstrated effect of ocean currents on the trajectory of the buoyancy modules. Hydrostatic forces, 6DOF motion and the velocities of the buoyancy module were predicted with different ocean current velocities. The approach proposed in this paper captures the physics of released buoyance module in transient CFD and provides a practical tool for determining the trajectory and velocity of the released buoyancy modules from subsea and quantifying the risk for such an event. It can potentially be used for assessing the risk to offshore vessels and floating platforms, risers and umbilicals, as well as for offshore and subsea field planning and layout.