Session: 09-02-06 Wind Energy: Dynamic Analysis II

Submission Number: 181674

Numerical Investigation on Natural Frequency Phenomena for a 4.2 Mw Offshore Wind Turbine Suction Bucket Using Bladed System Code 

Accelerating climate change highlights the need for large scale deployment of low carbon generation. Offshore wind is a strong candidate due to high capacity factors and proximity to coastal load centers. In the Republic of Korea, policy targets an expansion of renewables by 2030. From an LCOE perspective, larger turbine ratings and broader offshore siting are key measures. Larger turbines on complex seabeds raise requirements for structural reliability and resonance margins. Careful dynamic assessment is therefore essential for safe and economical operation.

Foundation induced seabed scour critically affects the system’s dynamic characteristics. Scour reduces lateral and rotational soil stiffness. The coupled tower, substructure, soil system then shows lower natural frequencies and a longer structural period. Frequency spacing from rotor induced 1P and 3P excitations and from wave loading bands can shrink. Responses may grow and fatigue damage may accelerate. Soil and structure interaction modeling that represents scour progression is thus required for reliable dynamic evaluation across design, installation, operation, and life extension.

This study examines a Unison 4.2 MW offshore wind turbine in the coastal waters off Gunsan, Republic of Korea. An integrated Bladed model of the tower, substructure, and soil is constructed. Scour induced stiffness loss is represented by lumped parameter springs. Time history simulations use representative scour depths and mean wind conditions. Displacement, velocity, acceleration, force, and moment responses are evaluated at several elevations along the tower to identify spatial sensitivity and to inform monitoring and retrofit strategies.

A modal sensitivity analysis is also conducted. Six variables are scaled across multiple scour stages. Geometry includes tower diameter, wall thickness, and height. Material properties include density, Young’s modulus, and shear modulus. In total, 150 eigen analyses are performed. The study maps the relative influence of geometry and material on frequency shifts under scour and identifies combinations that most reduce resonance margins.

Presenting Author: Junyoung Lee Chung-Ang University

Presenting Author Biography: Junyoung Lee is an M.S. candidate in Mechanical Engineering at Chung-Ang University, Republic of Korea. His research focuses on offshore wind turbine dynamics and foundation–structure interaction. He develops Bladed-based integrated models of 4–20 MW turbines and studies 1P/3P resonance margins, scour-induced stiffness degradation, and suction-bucket foundations using Winkler/p-y formulations. He also uses SCADA, CFD, and FEM to calibrate modal properties and validate design envelopes. At the conference, he will present a numerical investigation of natural-frequency behavior of a 4.2-MW OWT supported by a suction-bucket foundation, highlighting implications for structural reliability and design.

Authors:

Junyoung Lee Chung-Ang University
Dongho Cho Korea Electric Power Corporation
Jaeho Jeong Chung-Ang University