AN OPEN SOURCE FINITE ELEMENT CODE FOR STRUCTURAL DYNAMIC RESPONSE OF OFFSHORE WIND TURBINES

Resumo

The wind energy potential of the Brazilian Exclusive Economic Zone (EEZ) is significant,
with a shallow continental shelf and extremely favorable wind speed in the northeast region. The
exploration of offshore wind energy emerges as an alternative for the growing energy demand of the
country, as well as for renewable energy requirements. Offshore wind turbines are slender structures,
subjected continuously to dynamic actions mainly from wind and sea. Therefore, these structures
demand an accurate prediction of eigenvalues to avoid mechanical resonance concerning loading
spectra. This paper presents a study of natural modes in NREL Phase 2 offshore wind turbine, as well
as the steps required for the development of an open-source finite element solution in Python. The
computational solution developed in this paper considers both fluid-structure (FSI) and soil-structure
(SSI) interactions in tridimensional models. This code is embedded in SALOME preprocessor as a
plugin. This plugin extends the preprocessing capabilities of SALOME to a complete code for modal
analysis of offshore wind turbines. The blades, hub, tower, and monopile are discretized using DKT
shell elements. The nacelle is modeled using tetrahedral elements. FSI is evaluated using additional
masses, and Winkler springs define SSI. Comparisons between the proposed plugin and ANSYS
simulations present errors inferior to 1%. Case studies were made, similar to those found in literature,
considering elastic or rigid supports, and additional fluid masses, or neglecting FSI. The results confirm
that both SSI and FSI are required for accurate modeling and ignoring these effects might lead to
divergences that compromise the prediction of offshore wind turbine behavior.