WINDOPT: An Optimization Tool for Floating Support Structures for Deep Water Wind Turbines

Abstract

An integrated design tool for optimization of a floating wind turbine support structure of the spar buoy type, including mooring system and power takeoff cable, is described in this paper. The program utilizes efficient design tools for analysis of mooring system forces and vessel motions, and combines this with a gradient method for solution of non-linear optimization problems with arbitrary constraints. The objective function to be minimized is the spar buoy cost, and the mooring line and cable costs. Typical design requirements that may be included as constraints are: mooring line load limitations and minimum fatigue life, cable curvature radius, cable tension, tower top acceleration, and vessel motion and inclination. The spar buoy is modelled as composed of a set of cylindrical sections with different mass, buoyancy and cost properties, where each section is assumed to have a uniform mass distribution. It is assumed that a representative initial cost figure is available, and that it can be scaled in proportion with material mass. A simple relationship between mass and geometrical properties is proposed for both massive and thin walled tubular sections. Examples are included to demonstrate the various aspects of the optimization approach, including different parameterizations of the spar buoy.