EXPERIMENTAL AND NUMERICAL STUDY ON THE COMPARISON OF POINT-ABSORBER WAVE ENERGY CONVERTERS

Abstract

The objective of this thesis is to investigate how buoy geometry affects the performance of point absorber wave energy converters. Five different buoy geometries were designed, each with the same initial diameter and total height. These models were then tested using the same experimental conditions. The experimental phase was conducted in a lab scale wave tank and involved the use of a LVDT sensor to measure buoy displacement, wave height gauges to measure water height, and a high-speed camera to record the experiments. The models were tested completely perpendicular to the water as well as at different angles with the water. ANSYS AQWA was used for numerical analysis of the buoys. The buoy models were modeled perpendicular to the water using the wave conditions that were recorded in the wave tank as well as the wave conditions that were recorded at Jennette’s Pier (Nags Head, NC) over five days. AQWA wave tank simulations output graphs depicting amplitude, radiation forces and gravitational forces for each buoy while the environmental simulations focused on amplitude only. Buoyancy forces were calculated for each model (perpendicular to the water only). The experimental results showed the overall trend that as angle of inclination increased, the buoy amplitude would decrease. The most likely reason why the ranges decreased as the angle of inclination increased was because as the LVDT sensor was inclined, the shield of the sensor began acting as an inclined plane creating friction between the sensor shield and armature. One model consistently outperformed the other models in both the wave tank and environmental simulations. The wave tank simulations also suggested a correlation between volume and buoy amplitude. There were differences between the experimental results and numerical wave tank results. This could have been because of friction between the sensor armature and shield, irregular wave shapes in the wave tank, certain parts not modeled in AQWA, and negative damping values in AQWA. Further studies into buoy geometry in point absorbers should examine performance changes when changing materials to examine the relationship between mass and buoy performance more thoroughly.