  This paper discusses a framework to design elements of the plant and control
systems for floating offshore wind turbines in an integrated manner using
linear parameter-varying models. Multiple linearized models derived from
aeroelastic simulation software in different operating regions characterized by
the incoming wind speed are combined to construct an approximate low-fidelity
model of the system. The combined model is then used to generate open-loop,
optimal control trajectories as part of a nested control co-design strategy
that explores the system's power production and stability using the platform
pitch tilt as a proxy in the context of crucial plant and control design
decisions. The radial distance between the central and outer columns and the
diameter of the outer columns of the semisubmersible platform are the plant
design variables. The platform stability and power production are studied for
different plant design decisions. The effect of plant decisions on subsequent
power production and stability response of the floating wind turbine is
quantified in terms of the levelized cost of energy. The results show that the
inner-loop constraints and the plant design decisions affect the turbine's
power and, subsequently, the cost of the system.
