TECNALIA approach to Multiphysics Analysis in Offshore Wind and its application to IEA Wind OC5 phase II project

Germán Pérez, Josean Galván, Ińigo Mendikoa, Miren J. Sanchez, Carlos A. Garrido


A Floating Offshore Wind Turbine (FOWT) consists of a number of subsystems including the floating support structure (hull structure and tower), the turbine rotor-nacelle assembly (RNA) and control system, as well as the station keeping system including mooring system and anchoring systems.
The numerical simulation tools for calculating motion and dynamics of FOWT are still under development. For the purpose of motion and load calculations in the multiphysics analysis, modeling of a FOWT can be divided into the following areas: hull, flexibility of the tower, station keeping system, rotor-nacelle assembly and control system.
This presentation describes the key issues and characteristics of the main FOWT subsystems relevant to multiphysics analyses. Representative coupling effects between the components of the FOWT are also identified.
TECNALIA has been working on different floating offshore wind projects, developing aerodynamic and hydrodynamic coupled tools and also has participated in the OC5 project for the benchmark of those coupled tools
A brief description of each model will be shown, discussing different approaches for time domain simulations and coupling effects that can be used. It is recommended that the approach selected for the numerical analysis is verified by model testing, full-scale testing, or the use of a different analytical approach.
Numerical simulations of a design load case set, combining various environmental conditions, is necessary for certification, so the work presented is a key part of the substructure development. Depending on specific floating concept the design load cases selection may be key for correct global performance assessment.


As a first step, a set of simplified, unidirectional load cases is chosen in order to compare the performance of the models presented in this document.
The code validation methodology is performed as follows: (i) create a model, (ii) choose dataset for comparison, (iii) calibration of hydrodynamic model using decay tests, current - only tests, code-to-code comparison and wave - only tests, (iv) validation from code-to-experiment comparison and (v) verification from code -to-code comparison.
For numerical models calibration and validation, down scaled model test campaign data was used. The experimental results have been compared with computations and deliver in general good correspondence.


Here a brief summary is provided of some results relevant to the coupled dynamics numerical tools from the OC5 phase II project. The floating system considered consisted of the NREL 5MW wind turbine installed on a tri-column semi-submersible structure.
Moreover, TECNALIA and NAUTILUS perform their own model test campaign and coupled numerical model calibration, validation and verification. Results for linked tool between FAST and Orcaflex are shown in this presentation also for the NAUTILUS test campaign.


A wide range of numerical tools are used for floating substructure design and optimization by OC5 participants. The comparison will be useful for a better understanding of turbine dynamics and modeling techniques, and validation of codes results.
The calibration, validation and verification methodology of these numerical tools will be presented. As part of this process, selection of design load cases is a key decision for floating offshore wind concept assessment and computational time consumption. This will also be discussed in the results presentation.


The numerical tools are qualified to some extent for use in the design of floating 5MW wind turbine substructures. In general they are in reasonable agreement with measurements for normal operating conditions, however in transient and more adverse conditions they do not satisfactorily predict extreme loads.
The way of simulating coupling effects is highly dependent on the actual tools and analysis approaches employed in multiphysics analyses. Recommendations for optimal multiphysic analysis will be provided, as well as future work for improving computational calculations.
The work presented is aligned with the Joint Industry Project for floating offshore wind dynamic simulations, coordinated by DNVGL and with the participation of TECNALIA as technology partner of NAUTILUS.