Abstract

A new simplified and practical methodology for the calculation of the equilibrium scour morphology in the clear-water regime is proposed using the bed shear stress amplification as a surrogate for the scour depth. With gradually decreasing scour depth increments, the morphology of the sandy bed is calculated iteratively with a CFD model using a relatively short computational time frame. For both the initial flat bed and the calculated scoured bed, a detailed analysis of the pressure field around the pile was carried out taking into account three-dimensional hydrodynamic phenomena such as upstream pressure and downstream suction.

Introduction

A transition towards renewable energy resources is crucial in the strategy to reduce global warming. To achieve this challenge, the demand for Offshore Wind Turbines (OWT) is rapidly increasing. The wind velocity is steadier and more persistent on offshore sites, where large wind farms can be built for efficient wind harvesting. However, offshore structures are exposed to a continuously changing marine environment with wind, waves, currents and morphological seabed changes. Scour might pose a real threat to the serviceability and stability of offshore structures, because the embedment length of piled foundations can be significantly reduced when exposed to large currents. Hence, it is essential that the effects of scour on the dynamic performance and the geotechnical stability of the foundation of OWT is fully understood and considered in detail. Only a few studies (e.g. Mayall et al., 2020; Al-Hammadi and Simons, 2019) investigate the effects that scour, or scour protection, have on the dynamic performance of OWT. Moreover, to the authors' knowledge, no study has been published regarding the dynamic foundation performance from the long-term perspective for scoured monopiles. To this end, the present study contributes with two important inputs needed for the analysis of the foundation of OWT: the equilibrium scour morphology and the pressure field around the pile.

This content is only available via PDF.
You can access this article if you purchase or spend a download.