Modeling and Control of Novel Variable-Shape Converters for Natural Harvesting of Ocean Wave Energy

Iowa State University, Ames IA

Investigators

Abstract

This research will contribute new knowledge related to renewable ocean wave energy harvesting, promoting both the progress of science and advancing national prosperity. Ocean wave energy converters capture wave power and convert it to electric power. The total theoretical wave energy potential is estimated to be more than the current US electric power annual needs. Complex wave energy converters are usually needed for efficient capture of wave power, and hence the cost of electric power transformed from waves is high compared to other sources of renewable energy. This award supports fundamental research to provide the knowledge needed for developing wave energy converters that produce power at a lower cost. Almost all existing wave energy converters use rigid bodies of fixed shapes (e.g., buoys). This award will develop a new variable-shape buoy wave energy converter, in which the buoy's shape changes continuously, like a jellyfish, to change the wave field around the buoy, in a favorable way, in order to increase the captured power by the unit. Therefore, results from this research will benefit the U.S. economy and society. This project links education and research, and positively impacts society via an outreach program that aims to raise the knowledge level among high school students regarding the concepts of ocean wave energy conversion. Classical rigid-buoy wave energy converters require a spring-like control force to be applied on the buoy, in addition to the damping control force that is usually obtained from the power take-off unit. This spring-like control force implies that the unit should provide reactive power; that is, it should be able to put power into the ocean at times, in order to change the buoy's position and velocity, such that more power can be harvested at other times. The equipment required to enable reactive power increases the complexity of the unit. The variable-shape buoy will enable the elimination of reactive power; the spring-like force will be obtained from the waves themselves. As the shape changes, the hydrodynamic forces on the buoy change, affecting its position, velocity, the wave field around it, and exciting a nonlinear phenomenon that is, otherwise, neglected. This nonlinear force will also be leveraged to increase the harvested energy. Preliminary analysis shows that in some cases the efficiency of the device is 1.5 times the efficiency of a fixed shape device of the same size. Some scientific questions are yet to be answered to realize the full application potential of variable-shape buoy wave energy converters. This research will fill the knowledge gap on the modeling, control and optimization of the device. Leveraging nonlinear hydrodynamic forces, this research will develop the optimal control problem formulation, a framework for simultaneous optimization of the buoy's shape and control, a reinforcement learning control algorithm, and high-fidelity numerical simulations for the device. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.