This work uses sparse arrays of ocean wave buoys to create a linear reconstruction of the sea surface and provide deterministic wave predictions at a future time and nearby position (i.e., within a few wavelengths). The predictions are constrained to be within the statistics of recently observed waves. This recently established method is applied in post-processing at two distinct projects related to 1) a wave energy converter and 2) an offshore wind platform. The conditions range from scale-model tank testing to an operational open-ocean wind farm. Relative to a conventional statistical forecasting with random waves, the method achieves at least 60% improvement in prescribing the next several waves arriving at a given target location. Work is ongoing to implement this method in realtime, using radio modems to transmit raw motion data (5 Hz sampling) from the buoy array to a central node that continually updates a 30-second prediction window with less than 1-second latency. The deterministic wave predictions can be used to improve control strategies for platforms at sea, with improvements in efficiency and reductions in dynamic loads.

As wave energy conversion technology advances, recharge of autonomous underwater vehicles has emerged as a promising application for this at-sea power. We bring together an interdisciplinary team to create a simulation framework linking hydrodynamic modeling, autonomous docking and navigation algorithms, and a power tracking model to better understand how a full wave energy converter–autonomous underwater vehicle system could be modeled. A floating point absorber wave energy converter is modeled and analyzed under various wave conditions. We incorporate three different dock designs, using the modeled dock motion and simulated wave-induced currents to test our autonomous docking algorithm. We couple the output of this algorithm to the hydrodynamic model to simulate autonomous docking. This shows that docking with a floating third body is successful in most sea states, while a dock rigidly mounted to the wave energy converter presents difficulty for autonomous docking. Finally, we incorporate a power model to better understand the feasibility and capabilities of a wave energy converter–underwater vehicle system in simulated wave environments. This shows that this system is comfortably supported in the majority of sea states, and provides an estimate of the on-board power storage required to maximize vehicle mission time.

Heave plates are one approach to generating the reaction force necessary to harvest energy from ocean waves. In a Morison equation description of the hydrodynamic force, the components of drag and added mass depend primarily on the heave plate oscillation. These terms may be parameterized in three ways: (1) as a single coefficient invariant across sea state, most accurate at the reference sea state, (2) coefficients dependent on the oscillation amplitude, but invariant in phase, that are most accurate for relatively small amplitude motions, and (3) coefficients dependent on both oscillation amplitude and phase, which are accurate for all oscillation amplitudes. We validate a MATLAB model for a two-body point absorber wave energy converter against field data and a dynamical model constructed in ProteusDS. We then use the MATLAB model to evaluate the effect of these parameterizations on estimates of heave plate motion, tension between the float and heave plate, and wave energy converter electrical power output. We find that power predictions using amplitude-dependent coefficients differ by up to 30% from models using invariant coefficients for regular waves ranging in height from 0.5 to 1.9 m. Amplitude- and phase-dependent coefficients, however, yield less than a 5% change when compared with coefficients dependent on amplitude only. This suggests that amplitude-dependent coefficients can be important for accurate wave energy converter modeling, but the added complexity of phase-dependent coefficients yields little further benefit. We show similar, though less pronounced, trends in maximum tether tension, but note that heave plate motion has only a weak dependence on coefficient fidelity. Finally, we emphasize the importance of using experimentally derived added mass over that calculated from boundary element methods, which can lead to substantial under-prediction of power output and peak tether tension.