Numerical simulations of a 15MW wind turbine on a concrete TLP with rigid pipe tendons

Abstract

In this work, we analyze the stability of a concrete TLP platform with a square hull, designed for a 15 MW wind turbine. We verify the natural frequencies in the different degrees of freedom (DOFs) and two ultimate state design load cases (DLC) via two independent models, one in HAWC2+WAMIT from DTU and one in Orcaflex+AQWA from Bluenewables (BN). The decay tests show that the platform eigenfrequencies are outside of the main wave excitation range, and that the models predict the same natural periods within ±5%, with a maximum deviation 20% for the roll period (2.4 s vs. 2.23 s). In the ultimate load states (DLC 1.6 and 6.1), the platform motions are mainly driven by the wind and wave forcing. A small resonance is observed for the pitch motion, driven by the aerodynamic loads, and for the surge, driven by the difference-frequency components of the second-order wave excitation force. The tendons tension reaches a maximum of Nmax = 30 MN for DLC 6.1 (HS = 10.9 m, TP = 14.0 s, Vref = 42.3 m s−1). In both DLC 6.1 and DLC 1.6 the tendons are far from the compression limit, with a safety margin of ≈ 8 MN for the analyzed test cases.