Optimal Cyclic Control of a Structurally Constrained Morphing Energy-Harvesting Kite Using an Experimentally Validated Simulation Model

Abstract

This work presents an experimentally validated dynamic model, control trajectory optimization methodology, and representative simulation results for a morphing underwater kite. Morphing, defined as real-time modification of the kite’s geometry to either curtail structural loading or enhance power generation, is motivated by the fact that the optimal design of an energy-harvesting kite is highly sensitive to flow speed and tether length, particularly in the presence of structural limitations that render load curtailment necessary at high flow speeds and short tether lengths. To achieve morphing behavior, an inboard Fowler flap (capable of modifying the chord and camber of an inboard wing section) was employed in tandem with a symmetric aileron bias, enabling simultaneous control over both the wing’s overall lift coefficient and center of lift without requiring the mechanical complexity associated with span morphing. The effects of these morphing parameters were integrated into an existing dynamic simulation framework, and experiments were conducted using a customized scaled tow testing setup to refine and experimentally validate the simulation model. Following the refinement of this model, a morphing trajectory optimizer was designed to optimize the morphing input trajectories over a spooling cycle using flow data from the previous cycle. Finally, using the refined simulation model and multicycle controller, simulations of large-scale kites operating in a realistic flow environment were conducted. In these simulations, a kite capable of morphing was shown to generate between 8.1% and 25.3% more energy than non-morphing kite designs.