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Abstract Easily portable, small-sized ocean wave energy converters (WECs) may be used in many situations where large-sized WEC devices are not necessary or practical. Power maximization for small-sized WECs amplifies challenges that are not as difficult with large-sized devices, especially tuning the device’s natural frequency to match the wave frequency and achieve resonance. In this study, power maximization is performed for a small-sized, two-body attenuator WEC with a footprint constraint of about 1m. A thin, submerged tuning plate is added to each body to increase added mass without significantly increasing hydrostatic stiffness in order to reach resonance. Three different body cross-section geometries are analyzed. Device power absorption is determined through time domain simulations using WEC-Sim with a simplified two-degree-of-freedom (2DOF) model and a more realistic three-degree-of-freedom (3DOF) model. Different drag coefficients are used for each geometry to explore the effect of drag. A mooring stiffness study is performed with the 3DOF model to investigate the mooring impact. Based on the 2DOF and 3DOF power results, there is not a significant difference in power between the shapes if the same drag coefficient is used, but the elliptical shape has the highest power after assigning a different approximate drag coefficient to each shape. The mooring stiffness study shows that mooring stiffness can be increased in order to increase relative motion between the two bodies and consequently increase the power.
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Hierarchical control of a park of floating oscillating water column wave energy converters
—Ocean wave energy is a renewable energy which remains costly for large-scale electricity generation. Although the oscillating water column (OWC) wave energy converter (WEC) is a promising device type with a rectifying air turbine and generator which convert alternating airflow induced by the water motion into kinetic energy then to electric energy, there are still several challenges to overcome to achieve commercial energy production. A first step is deploying multiple devices close to each other in WEC parks, to save cost associated with mooring lines and power transmission cables and a second step is applying control at each stage of energy conversion to increase the electric energy output of the devices and ensure a safe operation. Herein, we first present a state-space model of a park of seven hydrodynamically interacting floating OWC WECs in all degrees of freedom with nonlinear PTO dynamics and a shared, quasi-static mooring model. The electric power flow is modeled by considering the conversion losses from the AC generators over a DC link, including a storage unit to the grid connection. Secondly, the OWC WEC park is expressed from a higher hierarchical level as an automaton driven by discrete events. Finally, we use a standard supervisory control approach to enable different local control schemes to ensure a save operation of the individual WEC and the park. The supervisor has good adaptability potential for different WECs and the incorporation of safety mechanisms.
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- Award ID(s):
- 1711859
- PAR ID:
- 10298877
- Date Published:
- Journal Name:
- Proceedings of the European Wave and Tidal Energy Conference
- ISSN:
- 2309-1983
- Page Range / eLocation ID:
- 2103-1 to 2103-10
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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- The DOI is not currently available.
