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

Submission Number: 181272

Fully Coupled Load-Stress Analysis Through Hydroqus-OpenFAST Integration 

To design a floating offshore wind turbine (FOWT), it is essential to perform an integrated load analysis (ILA) in the time domain and validate both motion and structural responses. Such ILAs are primarily conducted using OpenFAST and OrcaFlex. However, these programs treat the substructure as a rigid body, making it impossible to capture its structural response. To evaluate structural response, one must perform a separate finite element analysis (FEA) in software such as Abaqus using the ILA results. This approach is one-way coupled, requiring artificial boundary conditions for the finite element model, which can lead to structural responses that deviate from reality. To address this issue, an integrated load–stress analysis based on HydroQus, a hydrodynamic force computation plug-in for Abaqus, has been developed. The authors’ HydroQus enables Abaqus, which traditionally could not compute hydrodynamic forces, to apply them in real time—thus allowing fully coupled load–stress analysis using finite element models. While HydroQus can provide near-realistic real-time stress responses, it was initially limited to parked turbine conditions because it did not consider the aerodynamic loads acting on the rotor–nacelle assembly (RNA). To overcome this limitation, the authors developed a coupled HydroQus–OpenFAST framework. In this framework, OpenFAST serves as an aero-servo-elastic solver for the RNA and tower, transmitting the tower-base loads to HydroQus. HydroQus then combines these loads with the computed hydrodynamic forces and transfers them to Abaqus, which solves for the motion of the floating structure. The computed motions are subsequently sent back from HydroQus to OpenFAST, and this iterative exchange is repeated at each Abaqus time increment. As a result, fully coupled load–stress analysis under realistic operating conditions of the turbine becomes possible. Following this methodology, a load–stress analysis was performed on an FOWT composed of the IEA 15 MW wind turbine, the VolturnUS semi-submersible platform, and three catenary mooring lines. The design load case (DLC) applied in the analysis corresponded to DLC 1.6, representing an ultimate limit state under power production conditions. The forthcoming results include both conventional ILA outputs (e.g., motion histories and mooring tensions) and unique HydroQus-based outputs such as real-time stress histories. The proposed load–stress analysis technique is expected to enable highly reliable structural design for next-generation FOWTs.

Presenting Author: Dong Ho Yoon Inha University

Presenting Author Biography: DongHo Yoon is a Ph.D. student in the Department of Naval Archtecture and Ocean Engineering at Inha University, South Korea. He has been studying load-stress analysis of floating offshore wind turbine.

Authors:

Dong Ho Yoon Inha University
Joonmo Choung Inha University