The Impact of Platform Motion on the Aerodynamic Characteristics of
Floating Offshore Wind Turbine Arrays
Abstract
To harness wind energy resources from the ocean, floating offshore wind
turbines (FOWTs) are gaining increasing attention within the industry.
In this paper, the impact of platform motion on the aerodynamic
characteristics of the FOWT array is numerically investigated. A
high-fidelity numerical tool with the Computational Fluid Dynamics (CFD)
method is further developed based on the open-source CFD toolbox
OpenFOAM by coupling the Actuator Line Model (ALM). The FOWT arrays
consisting of three semi-submersible platforms and NREL 5 MW turbines
with different arrangements based on tandem and staggered layouts are
simulated, and their dynamic response and wake interactions are analysed
under regular wave conditions. Results show that in gridded layouts, the
downstream turbine experiences the most significant wind velocity
reduction due to wake interference, compared with the staggered layouts.
In the most common scenarios, the capacity factor of the total system of
a tandem layout is 50%, while it is 92% for the staggered layouts. It
is also found that whether the third downstream turbine is fixed or not
has a minor influence on the time-averaged power output. However, the
motion of the turbine, due to the floating platform, significantly
influences power fluctuation. In gridded layouts, the downstream FOWT
can have up to 25% higher fluctuation amplitude than fixed one, while
for staggered layouts, this can reach 80% in the most critical case. It
is also observed that strong wind turbulence reduces the impact of
platform motion on power fluctuations, especially for the third turbine.
By analysing the power output and the platform motion, it is found that
the pitch and surge motion of the present OC4 platform have an opposite
influence on the power output. Thus, a coupled model considering both
degrees of freedom is necessary.