Wave energy conversion using fluidic flexible matrix composite power take-off pumps

Abstract

Fluidic flexible matrix composites (F2MCs) are composite tubes that consist of multiple layers of oriented, high performance fibers, such as carbon, precisely placed in a flexible matrix resin to form high-mechanical advantage actuators and variable stiffness materials. Unique to the F2MC tube is its ability to generate high pressures and volume change with a small external load as a result of the stiff reinforcement fiber orientation in the wall of the tube and the soft supporting elastomer. When a load is applied to the tubes, the volume of the F2MC tube is reduced and fluid is forced out of the tube by the reinforcing fibers. This is the first reported research on the design, fabrication, and characterization of F2MC tubes as power take-off (PTO) mechanisms for ocean wave energy conversion where the heaving motion of a floating body in waves provides the axial load that drives fluid through the pumps. An analytical model is developed to predict the performance of F2MC pumps in a variety of test conditions, and 1/50th scale F2MCs pumps are tested in a water basin. The scaled pumps are mechanically cycled between 0 Hz and 2 Hz at up to 17 percent strain replicating ocean waves of varying period and amplitude. Instantaneous input mechanical power and output fluid power values are calculated from force, velocity, pressure, and flow rate measurements, and the actuator efficiency is subsequently determined and compared with the prediction of the analytical model. At 1/50th scale, a maximum power conversion efficiency of 40 percent is obtained for a single pump and a peak output power of 0.21 W is recorded. At full scale, the predicted peak output power is 180 kW, suggesting that F2MC pumps are a promising class of fluid power take-off (PTO) mechanisms for ocean wave energy conversion, representing a substantial improvement over hydraulic cylinders.