Wave-Energy Device Control and Simulation Tools

Friday, February 24, 2017 - 2:30pm
3110 Etcheverry Hall
Nathan Tom, Ph.D.

Research Engineer

National Renewable Energy Laboratory, Golden, CO


E-201 Ocean Engineering Seminar Series, Spring 2017


2:00 - 2:30pm Beverages & Refreshments

2:30 - 4:00pm Seminar


Dr. Tom will speak on his recent work on balancing power absorption against structural loading for a novel bottom-fixed oscillating surge wave-energy converter, in both regular- and irregular-wave environments. The power-to-load ratio will be evaluated using pseudo-spectral control to determine the optimum power-takeoff (PTO) torque based on a multi-term objective function. This work has attempted to extend the pseudo-spectral optimal control problem to not just maximize the time-averaged absorbed power, but also include measures for the surge foundation force and PTO torque in the optimization. The objective function can now include potentially three competing terms that the optimizer must balance. Separate penalty weights are attached to the surge foundation force and PTO control torque so as to tune the optimizer performance to emphasize either power absorption or load shedding. To better model the pitch equation of motion, derived from linear hydrodynamic theory, a quadratic viscosity-based torque has been included in the system dynamics. However, to continue the use of quadratic programming solvers, an iteratively obtained linearized drag coefficient is utilized so as to provide good accuracy in the predicted pitch motion. Furthermore, his analysis has begun to consider the use of non-ideal PTO units to more accurately evaluate controller performance. The PTO efficiency is not directly included in the objective function but rather the penalty weights are utilized to limit the PTO torque amplitudes, thereby reducing the losses resulting from the bi-directional energy flow through a non-ideal PTO. Results from pseudo-spectral control show that shedding a portion of the available wave energy can lead to greater reductions in structural loads, peak-to-average power ratio, and reactive power requirement.



Dr. Nathan Tom received his Ph.D. in the fall of 2013 from the Ocean Engineering group in the Department of Mechanical Engineering of UC Berkeley and is currently a staff engineer at the National Renewable Energy Laboratories (NREL) based in Colorado. He also received his M.S. (2009) and B.S. (2011) degrees from the ME department of UCB. Dr. Tom currently works on a laboratory directed R&D project that focuses on the design of wave energy converters with actuated geometry. He also has assisted in the development of WEC-Sim (Wave Energy Converter Simulator) through a collaborative effort with Sandia National Laboratories. Previously, he was the recipient of the 2013 Ocean, Offshore, and Arctic Engineering “Subrata Chakrabarti Young Professional Award.”


Hosted by: Prof. R. W. Yeung (rwyeung@berkeley.edu), 6135 Etcheverry Hall