Session: 10-02-02 Bucket Foundations and Suction Piles

Submission Number: 181828

Development of a New Capacity Envelope for a Shared Suction Anchor for Ulsan Floating Offshore Wind Energy Farms 

With the development of floating offshore wind farms, research on shared anchors for cost reduction is being actively conducted. The objective of this study is to develop a capacity envelope for a shared suction anchor applicable to the Ulsan floating offshore wind energy farms. In this study, an IEA 22 MW wind turbine and a semi-submersible platform employing Concrete Filled Double Skin technology were used. Also, unlike the catenary mooring system that secures restoring force through suspended weight, this study used an upward restoring mooring system designed to minimize the footprint. Therefore, due to the significant increase in anchor uplift force caused by the buoyancy generating the restoring force, a suction anchor with superior vertical bearing capacity was adopted. A fully coupled load analysis under DLC 6.1 conditions was performed, and anchor forces were derived according to DNV-RP-E303. A 3-line shared anchor layout, considering economic efficiency, was used. Considering the anchor-mooring line configuration, the maximum horizontal force and the combined vertical force were calculated as the horizontal and vertical design loads of the shared anchor, respectively. Based on the vertical and horizontal bearing capacities determined according to the Offshore Wind Accelerator, the dimensions of the suction anchor were established. The anchor dimensions were 10 m in diameter and 30 m in length. To satisfy the design pressure calculated from the combined penetration suction pressure and seawater pressure according to DNVGL-RP-C202, the anchor wall thickness (50 mm) and 36 longitudinal stiffeners (200 mm × 20 mm) were arranged to provide buckling strength. A large deformation numerical analysis using the Coupled Eulerian-Lagrangian method in ABAQUS/Explicit was performed to derive the capacity envelope of the designed shared anchor. To minimize boundary effects, the soil domain was set to 15 times the anchor diameter in width and 2.5 times in length, with a 15 m void layer placed above the soil. The soil adjacent to the anchor was finely meshed into 200 mm × 200 mm elements, modeling the soil with approximately one million EC3D8R elements and the anchor with about 20,000 R3D4 elements. A friction coefficient of 0.5 was applied between the suction anchor and the soil. The soil’s yield function was modeled using the Mohr-Coulomb model, and a user subroutine was implemented to represent the soil behavior with linearly increasing shear strength with depth. Symmetric boundary conditions were applied to account for the supporting effects of the surrounding soil not included in the model. Specifically, a local cylindrical coordinate system was established at the center of the soil, and radial displacement was constrained at the lateral nodes on the soil boundary. Longitudinal displacement was restrained at the bottom nodes of the remaining soil. To simulate the seawater pressure acting on the upper soil and the initial equilibrium state of the soil, initial stresses varying with depth were defined in the first load step. Simultaneously, gravity was applied to the soil and seawater pressure was imposed as distributed load on the upper soil to achieve the initial equilibrium state. In the second load step, forced displacements corresponding to uplift angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90° were applied individually at the anchor point. Based on displacement velocity convergence from the analysis results, a forced displacement of 100 mm/s was used. The reaction forces obtained at the anchor point were considered as the bearing capacities, from which horizontal-vertical bearing capacity curves were derived for each uplift angle. Subsequently, curve fitting was performed to determine the coefficients of the capacity envelope equation satisfying the derived bearing capacities. The validity of the anchor design in this study was verified by comparing the derived capacity envelope with the design loads.

FUNDING

This research was funded by the Korea Energy Technology Evaluation and Planning and the Korea Ministry of Trade, Industry and Energy (MOTIE) (Nos. 20213000000030, RS-2023-00238996, RS-2024-00450063, and RS-2025-25450859) and by the Korea Ministry of Oceans and Fisheries (MOF) (No. RS-2025-02220608).

Presenting Author: 윤호진 : 인하대학교

Presenting Author Biography: Mr. Hojin Yoon is currently pursuing his Master’s degree in the field of offshore Ocean Engineering and Naval Architecture, with a focus on foundation design for floating offshore wind turbines (FOWTs). His research specializes in suction anchor design, Coupled Eulerian–Lagrangian (CEL) analysis, and the concept of shared anchoring systems to improve mooring efficiency and structural stability in floating offshore environments. His current work involves the application of the CEL technique to simulate large-deformation interactions between the soil and anchor structure during installation and in-service loading.

Authors:

Hojin Yoon Inha University
Kyung-Tae Bae Daewoo E&C
Joonmo Choung Inha University