Numerical simulation of a submerged wave energy converter under irregular wave conditions

A submerged wave energy converter point absorber, which will be further referred to as TWED (Torres Wave Energy Device) has been analyzed and studied under irregular wave conditions. A non-linear time domain numerical model of the TWED floater movement has been implemented in Simulink®. In a previous paper, the numerical model was exploited to test the sensibility of the TWED performance to changes in some variables under regular waves: linear generator damping constant, floater diameter, depth, bearing frictions and vertical drag coefficients. In this paper, the TWED is optimized for maximum energy production in real wave climate. To obtain the average wave performance of the converter, a 44 year series of data record at a point near the Cantabrian Coast has been used. The objective functions have been the Average Absorbed Power, AAP, and the sea-state generator linear damping constant variable, K. After the optimization, the full time series of AAP was obtained and from it, several statistics analysis for AAP and K were carried out for different time intervals (complete series, yearly series, and monthly series) in order to study the variability of K and AAP. In addition, an evaluation of the TWED behavior in a sea state in the Operation Limit has been studied. The studies showed that the instantaneous absorbed power in a sea state could be as much as 20 times higher than the mean absorbed power, while the performance in irregular waves is lower, around 70 % less than that of regular waves.