Session: 06-02-01 Coastal Engineering I

Paper Number: 124789

124789 - Scour Assessment and Prediction Around Jack-Up Footings in Wave-Current Conditions 

Scouring around jack-up footings exposed to marine hydrodynamics is one of the main concerns for foundation failures during drilling operations. The assessment and prediction of the scour processes are critical for designing erosion protection measures and robust jack-up footings. However, the guidelines and practical tools for the scour assessment and prediction around jack-ups are still lacking due to the complex nature of scour processes in the marine environment and the unique design of each spud can footing.

In this study, we aim to investigate the scour processes around different designs of spud cans subjected to currents, waves, and combined waves and currents using a fully coupled hydrodynamic and morphological computational fluid dynamics (CFD) model to propose guidelines and practical tools for the scour assessment and prediction. In this model, the incompressible flow is simulated by solving the Reynolds-averaged Navier-Stokes (RANS) equations with a two-equation turbulence model for closure. The seabed topography evolution stems from the bed load transportation and suspended load concentration driven by the incoming flows. The sediment continuity (Exner) equation is solved for updating the seabed elevation, where a physics-based sand slide model is employed herein to ensure the local bed angle does not exceed the angle of repose.

We first validate this CFD model against the laboratory experiments for scour development around spud cans exposed to various currents and co-directional as well as orthogonal wave-current conditions. The equilibrium scour depth for the spud can models with different penetration depths in two medium-scale hydraulic flumes are compared with the numerical results. The empirical formulae proposed in the experimental study for predictions of the equilibrium scour depth and the characteristic time scale of scour are then revisited and examined. Subsequently, we apply this model to study the scour development and backfilling of scour holes around typical spud cans under various types and magnitudes of marine hydraulic load. The scour mechanisms are revealed for spud cans with different shapes and penetration depths. Moreover, empirical models for the scour predictions around jack-up footings in wave-current conditions are derived. Consequently, the proposed formulae allow for a reliable evaluation of the scour potential and development before the drilling operations or during an incident review.

This study provides insights into the scour development and mechanisms around jack-up footings in different hydrodynamic climates. The powerful CFD model and the novel prediction formulae yield effective practical tools and guidelines for scour assessments, protection system designs, and scour-friendly jack-up designs.

Presenting Author: Zhengyu Hu National University of Singapore

Presenting Author Biography: Zhengyu Hu is a Ph.D. candidate from the Department of Civil and Environmental Engineering at the National University of Singapore. His research interests lie in the area of wave-structure-seabed interactions. Much of his work is improving the understanding, design, and performance of coastal structures in water waves.

Authors:

Zhengyu Hu National University of Singapore
Yuzhu Li National University of Singapore
Okky Purwana Geo Oceanics