On The Long-Term Reliability Analysis Of A Point Absorber Wave Energy Converter

Of interest in this study is the long-term response and performance of a two-body wave point absorber ("Reference Model 3"), which serves as a wave energy converter (WEC). In a previous study, the short-term uncertainty in this device's response was studied for an extreme sea state. We now focus on the assessment of the long-term response of the device where we consider all possible sea states at a site of interest. We demonstrate how simulation tools may be used to evaluate the long-term response and consider key performance parameters of the WEC device, which are the heave and surge forces on the power take-off system and the power take-off extension. We employ environmental data at a designated deployment site in Northern California. Metocean information is generated using approximately 15 years of data from this site (National Data Buoy Center site no. 46022). For various sea states, a selected significant wave height and peak period are chosen to describe representative conditions. Then, using a public-domain simulation tool (Wave Energy Converter Simulator or WECSim), we generate various short-term time-domain response measure for these sea states. Distribution fits to extreme response statistics are generated, for each bin that represents a cluster of sea states, using the open-source toolbox, WDRT (WEC Design Response Toolbox). Long-term distributions for each response variable of interest are estimated by weighting short-term distributions by the likelihood of the sea states; from these distributions, the 50-year response can be derived. The 50 year response is also estimated using an approximate but more efficient inverse reliability approach. Comparisons are made between the two approaches.