Abstract
Finding new ways to enhance the production of kelp is useful for aquaculture and atmospheric carbon capture practices. Kelp aquaculture has significant potential to become a carbon-neutral source for biofuels. Upwelling, which increases kelp growth, is a process that draws cold, nutrient rich waters from deeper in the ocean towards the photic zone where kelp is grown. Waves provide an on-site, renewable energy source to power upwelling devices. Several studies have shown that upwelling can increase kelp biomass by up to four times original growth rates.
The UNH Wave Powered Water Pump (WPWP) is an upwelling device designed specifically for use in kelp aquaculture. The point absorber style device is formed of two main floating bodies: the float buoy and the spar buoy. The float buoy is designed to follow the vertical motion of the waves, while the spar buoy is designed to maintain a steadier position in the vertical direction. By utilizing the relative motion between the spar buoy and float buoy, a piston pump draws deeper water in on an upstroke and sends the cold water to the surface on a downstroke. The piston pump motion is tied to the float buoy motion, and two one-way check valves control the flow direction. A system of hoses attached to the pump extend the pump’s inlet and outlet.
A numerical model of the WPWP can predict pump flow rates in various wave conditions, and guide design decisions to increase efficiency of the hydraulic Power Take Off (PTO). To create a numerical model, several open-source software codes were utilized, including: meshmagick, Capytaine, and WEC-Sim. A simplified CAD model of the WPWP’s features was first created in SolidWorks and then transformed into a finite element mesh using meshmagick. Next, Capytaine utilized the geometric mesh information to determine the hydrodynamic characteristics of the WPWP. These hydrodynamic characteristics indicate that the potential for relative motion in heave is high, which is the desired design goal. The hydrodynamic and hydrostatic characteristics were added to the NREL Reference Model 3 (RM3) WEC-Sim model. Additional changes were made to the RM3, by modifying the PTO to represent the single piston pump design of the WPWP. The model was run in wave conditions reflective of a summertime deployment near Appledore Island, Maine. These conditions were chosen because the team aims to conduct field experiments to validate the model in summer of 2022.
Preliminary results of the numerical model indicate that a maximum pumping rate of ten gallons per minute may be achieved which is similar to the estimated rate extrapolated from limited deployment data from April of 2021. Additionally, the simulated flow results show the one-way check valves operate as expected, where when one is experiencing flow, the other is closed. Future work involves validating the model by simulating several different ocean wave conditions, and conducting field experiments.
This work is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Water Power Technologies Office (WPTO) Award Number DE-EE0009450.