Abstract
From September 20 to October 12, 2021 physical model tests of the HiSeas OWC-WEC were conducted at the Offshore Technology Research Center (OTRC) in College Station, Texas. The goal of the model test program was to measure the performance of the WEC in a range of regular and irregular wave conditions so that the data could be used for validating a numerical model of the WEC hydromechanics. The tests were conducted at a scale of 1:35 and Froude scaling was applied. The measurements included oscillating water column elevation, air pressure in the oscillating water column chamber, WEC motions, and mooring tension. The physical model of the WEC was provided to the OTRC by HiSeas Energy.
A WEC-Sim model of the oscillating water column device was constructed using boundary element method code WAMIT and mass/inertia estimates provided by HiSeas. Two versions of the WEC-Sim model were constructed: one with a simplified spring-damper PTO capable of delivering reactive power, and a second modeling a passive orifice to be tuned to experimental results described above. The results of the modeling demonstrate that while controllers with reactive power can significantly increase mechanical power capture, the PTO must be carefully co-designed to ensure that this benefit is economically translated to electrical power capture. In the orifice model, the drag coefficients in heave, surge, and pitch were adjusted along with the effective orifice diameter to match observed dynamics in free-decay tests. The most impactful tuning parameter was effective orifice diameter, implying that viscous effects of the oscillating flows were significant. The model matches power well except in regular waves near resonance and at low frequencies in irregular seas, both of which suggest limitations in the accuracy of the boundary element method code.