Session: Hydrodynamic and Coupled Analyses-1

Paper Number: 164818

164818 - Efficient Structural Assessment Approaches for the Design of Floating Offshore Wind Turbine Substructures 

Abstract: 

Floating offshore wind substructures face highly dynamic environmental conditions, leading to non-linear loading mostly influenced by wind turbine control strategies and mooring systems. Consequently, structural assessments of floating wind substructures must be conducted in the time domain for fatigue and ultimate limit states to ensure accuracy as designs progress through to detailed stages. This study examines three time-domain structural assessment approaches: Direct Load Generation, Load Reconstruction and Response Reconstruction, applied to the VolturnUS-S with the IEA15MW wind turbine, subject to a simplified set of design load cases. The approaches are compared based on fatigue damage and ultimate structural stress level. Whilst Direct Load Generation offers the highest accuracy with any substructure and in any condition, Load and Response Reconstruction approaches reduce computational and storage needs, maintaining high accuracy in most conditions, which is achieved through corresponding unit load precomputation stages.

Load Reconstruction involves automated precomputations of hydrodynamic pressure transfer functions for panels in the frequency domain, used in subsequent reconstructions based on time-domain coupled simulation results. This method is especially suitable for substructures with dynamically excited vibration modes, as the pressure reconstruction is followed by either a quasistatic or dynamic finite-element structural analysis.

Response Reconstruction is the fastest approach and is achieved through precomputation of partial structural responses for unit loads, unit motions and unit waves in the frequency domain. Subsequently, the combined detailed time-domain structural response is reconstructed using the coupled simulation results. The method avoids the sometimes prohibitive computational cost associated with load mapping as well as the finite-element analysis at each time step.

This study provides practical guidance for selecting structural assessment approaches, based on the structural arrangement, computational efficiency and design phase needs.

Presenting Author: Imanol Touzon DNV

Presenting Author Biography: Imanol Touzón received the M.Sc. degree in Industrial Engineering: intensification on Mechanical Design, from the University of Basque Country, in 2010 and a PhD in Industrial Engineering in 2021.
Since then he has worked in R&D projects for technology development of floating offshore renewables, combining it with several years in the industry, designing structures for floating offshore wind and wave energy conversion.
His experience lays on development of wave-structure interaction numerical models of floating platforms, mooring and umbilical cable design, control strategies and applied engineering project proposal definition. He is currently part of the Renewables and Ocean Structures team at DNV-Digital Solutions.

Authors:

Imanol Touzon DNV
Won Ho Lee DNV
Renata M. Grabowsky Nunes DNV
Jens Eftang DNV