Session: 09-07-02 Tidal & Current Energy I

Submission Number: 181934

Numerical Prediction of the Dynamic Response of a Current Turbine Under Extreme Sea Condition 

This study conducts a numerical investigation of the motion response and mooring line behavior of a current turbine subjected to combined wave–current loading, with the objective of evaluating its stability and safety under extreme sea conditions. The hydrodynamic properties, including the frequency-dependent added mass corresponding to the six degrees of freedom motions of the current turbine, are determined using ANSYS AQWA. The drag coefficients associated with both translational and rotational motions are estimated through numerical simulations of STAR-CCM+. The dynamic response of the current turbine is analyzed using OrcaFlex, which employs the finite element method to compute mooring line tension. The mooring system, featuring mooring lines 140 m in length, is configured for a water depth of 100 m. The current conditions considered in this study ranges from of 0.5 m/s to 1.5 m/s. Irregular waves are modeled using the JONSWAP spectrum. Two extreme sea states are analyzed: the first represents the 50-year return period, with a significant wave height of 12 m and a peak period of 14.5 s; the second represents the 100-year return period, with a significant wave height of 15.1 m and a peak period of 16.3 s. Numerical results reveal that, in terms of motion response, the investigated range of current velocity leads to a mean surge displacement ranging from −19.29 m to −14.13 m, a submerged depth ranging from −75.03 m to −73.16 m, and a mean pitch angle ranging from −7.86° to −3.76°. Regarding the mooring line behavior, the studied current velocity range results in a mean mooring line tensions ranging from 0.036 MN to 0.205 MN, a mooring line elongation ranging from 0.001 m to 3.905 m, and a mooring line angle ranging from 8.84° to 10.86°. These results demonstrate that current velocity has a significant influence on the mean dynamic response of the current turbine. The mooring line tension increases from 0.477 MN for the 50-year return period case to 0.644 MN for the 100-year return period case, the mooring line elongation increases from 9.12 m to 12.29 m, and the mooring line angle increases from 1.50° to 3.15°. The mean values of the motion response and mooring line behavior are mainly influenced by current velocity rather than wave conditions. In contrast, the amplitude values are mainly governed by wave effects. The surge, submergence depth, and pitch motions are primarily affected by wave conditions, whereas both wave and current effects contribute significantly to the variations in mooring line tension, elongation, and mooring angle. Under the most severe condition, the maximum mooring line tension is 0.644 MN, far below the breaking strength of 6.4 MN.

Presenting Author: Chih Chen Pi Department of Engineering Science and Ocean Engineering, National Taiwan University

Presenting Author Biography: Master Program of Engineering Science and Ocean Engineering, National Taiwan University (2025-)
Bachelor of Department of Civil Engineering, National Chung Hsing University (2021-2025)
Research on Wind Technology

Authors:

Chih Cheng Hsu Department of Engineering Science and Ocean Engineering, National Taiwan University
Chih Chen Pi Department of Engineering Science and Ocean Engineering, National Taiwan University
Shiu Wu Chau Department of Engineering Science and Ocean Engineering, National Taiwan University