S. Casey – Masters Thesis, Oregon State University, June 2013
Hydraulic power take-off (PTO) systems have been implemented in several wave energy converter (WEC) designs in recent years. Two popular hydraulic PTO configurations coupled to a point absorber hydrodynamic model are simulated in waves representative of an energetic sea state likely to be found in deep waters off the coast of Oregon. The first hydraulic PTO configuration is a passive system tuned to the dominant forcing period of the sea state. The second system is an actively controlled hydraulic PTO topology tracking an optimal power absorption trajectory. A linear quadratic tracking controller is developed to follow the reference trajectory and performs well despite the nonlinear elements of the system dynamics. Simulation results of the system dynamics are presented for both models. A loading analysis is conducted and loading distributions of the two systems in irregular waves are compared. The distributions show the active system to have a larger variability in loading, while the distributions of the passive system indicate more frequent mean loading components. Parameters of the passive system components are varied in order to understand the effect on power output and loading.