Seismic risk analysis of wind turbine support structures - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 720

resents specifi c combinations of the earthquake characteristics and the
collection of all bins captures all possible characteristics. We use 20 repre-
sentative ground motion records from each bin. It is noteworthy that
selected ground motions are recorded at the surface. For the purpose of
these dynamic analyses, we transfer the recorded ground motions to the
depth of the soil mass base using the continuous solution to the wave equa-
tion (Roesset and Whitman, 1969). We idealize the soil profi le as a system
of homogeneous, visco-elastic sublayers of infi nite horizontal extent and the
shear waves are considered to propagate vertically. Also, to account for the
nonlinearity of the soil, we use an equivalent linear procedure developed
by Idriss and Seed (1968).
The aerodynamics of the turbine is simulated by the support of FAST.
We use FAST to simulate the wind turbine and produce the time history of
the forces at the top of the tower due to the wind and the operation of the
turbine. The time history of wind loading used as an input for FAST is
generated using TurbSim. The result of this simulation is the operational
loading on the tower, which is used in the fi nite element model of the
support structure as an external loading in addition to wave and current
loading. Figure 26.1 shows a schematic representation of how FAST and
ABQAUS are combined to model the dynamic behavior of a wind turbine
system.

Wind

Rotor mass

Aerodynamics

A 1

H 1

H H

Configuration in FAST

A 2

Wave & current

H 2

H 3

A 3

Earthquake

Configuration in ABAQUS

26.1 Schematic representation of an offshore wind turbine model in
FAST and ABAQUS.