Long-term reliability analysis of wave energy converters

Due to the highly stochastic nature of the ocean environment, offshore structures need to be designed to withstand widely varying forces without compromising performance. In particular, wave energy converters (WECs) are devices that aim to capture power from incoming waves while remaining structurally intact for a planned deployment period. The structural integrity of these WECs comes into question if the device encounters a rare and violent sea state. This study analyzes different techniques used to derive long-term loads for two wave energy devices. In addition, comparisons are made between the methods in terms of efficiency and accuracy. For one device, called Reference Model 3 (RM3), a binning scheme is utilized over all sea states to predict long-term loads using direct integration. It is found that the selected binning grid is too coarse for a fair comparison to be made to the results from another method, the environmental contour method. For the second device, a centipod model, parametric fitting is employed to describe the metocean wave data as well as for short-term extreme response distributions obtained from WEC response simulation. The long-term response predictions from the different methods are shown to be reasonably consistent with each other in terms of accuracy and uncertainty estimates. Direct integration over all sea states and the use of Monte Carlo simulations lead to consistent prediction of rare long-term loads as long as the discretization of the metocean data (in the integration) is fine enough. Additionally, in direct integration, increasing the number of simulations around sea states with high expected loads decreases the long-term response variability and helps to yield consistent and accurate results.Civil, Architectural, and Environmental Engineerin