Session: 09-01-08: Offshore Wind Energy - Hydrodynamics 2

Paper Number: 105875

105875 - Numerical Investigation of Sloshing Inside a Column of the Oc4 Floating Offshore Wind Turbine 

Sloshing is the fluctuation of liquid in a partially filled tank due to external excitation, which is widely present in the field of ocean engineering. Violent sloshing in a tank can induce significant loads on the supporting structure, which may cause damage to structural integrity and affect the dynamic responses of the structure when it is afloat in waves. Nowadays, floating offshore wind turbines (FOWT) with multiple-column designs have become increasingly popular in the exploitation of the abundant wind resources in far offshore areas with water depth of over 50 metres. These structures are usually ballasted with water in the cylindrical columns for stability purposes. In some designs, a concentric cylindrical base column with a larger diameter than that of the main column is attached to the bottom of the latter to provide additional damping. However, sloshing in such a cylindrical tank with a base column and its impacts on the responses of the FOWT have been rarely studied.

In the present work, sloshing in one of the three columns of the widely known OC4 DeepCwind semi-submersible FOWT is investigated numerically by using an open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The base column is fully filled with water while the upper column is only partially filled. A sinusoidal translational motion with predefined excitation parameters including amplitude and frequency is imposed to the tank to simulate the surge response of the FOWT in waves while the coupling effect of the tank and the wave is not considered at present. A reference model of an ordinary cylindrical tank without the base column is also set up so that the effects of the base column on its sloshing responses can be assessed. The excitation parameters are varied and a series of motion amplitudes and frequencies is simulated. Results are compared and analysed in various aspects, including the variation of free surface elevation and the sloshing force exerted upon either the upper column or the base column with respect to the excitation amplitude and frequency. The flow field inside the tank is also visualised to help understand the sloshing mechanism when the base column is present. This study will serve as the basis for future coupled analysis of sloshing and FOWT responses in waves.

Presenting Author: Yuanchuan Liu Ocean University of China

Presenting Author Biography: Dr Yuanchuan Liu is currently an associate professor at Ocean University of China in Qingdao, China. He received his PhD degree at University of Strathclyde, UK in 2018 and worked as a postdoc for two years at OUC before he was offered his present position. His recent research interests include coupled analysis of floating offshore wind turbines and layout optimisation of offshore wind farms.

Authors:

Renjie Zhang Ocean University of China
Yuanchuan Liu Ocean University of China
Liang Li Ocean University of China