The motions of the model were recorded using the Qualisys system
andwere tracked by 3 reflection balls and 8 cameras. The reflection balls
are installed on top of the tower as shown in Fig. 5. By hammering test,
the natural frequencies of the first and second flexible modes of the
tower were found to be around 7 Hz and 19 Hz in model scale, which
is much higher than the wave frequency range (around 0.3 Hz – 1 Hz)
and the lowfrequency range related to the horizontal resonantmotions
of themoored structure which is around 0.07 Hz. Hence, the tower was
modeled as a rigid structure