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.
Development of alternative freshwater via desalination can address water scarcity and security. Meanwhile, sustainable renewable energy sources are critical to economically achieve seawater desalination. Marine renewable energy has tremendous potential to power the blue economy and is co-located with seawater. This study proposes an ocean wave powered reverse osmosis desalination system, which consists of an oscillating surge wave energy converter with a piston pump and a reverse osmosis desalination module with an accumulator on the shore. Seawater can be pressurized by the oscillating surge wave energy converter and pumped to the reverse osmosis desalination module as feed where it then produces permeate that is free of undesired molecules and larger particles. Numerical models considering potential flow theory of the wave energy converter and solution-diffusion theory of the reverse osmosis membrane were established. A 1:10 scaled prototype was designed, fabricated and tested in a wave tank based on the Froude scaling law. Comprehensive wave tank tests were implemented, characterized, and analyzed considering the water-energy nexus. Scaled tests resulted in the minimal specific energy consumption of 0.44 kWh/m3 under regular wave (wave period Ts = 4s /wave height Hs = 10 cm) with the corresponding optimal recovery ratio of 32%.
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