The aim of this study is to estimate the mean annual power absorption of a selection of eight Wave Energy Converters (WECs) with different working principles. Based on these estimates a set of power performance measures that can be related to costs are derived. These are the absorbed energy per characteristic mass [kWh/kg], per characteristic surface area [MWh/m 2 ], and per root mean square of Power Take Off (PTO) force [kWh/N]. The methodology relies on numerical modelling. For each device, a numerical Wave-to-Wire (W2W) model is built based on the equations of motion. Physical effects are modelled according to the state-of-the-art within hydrodynamic modelling practise. Then, the W2W models are used to calculate the power matrices of each device and the mean annual power absorption at five different representative wave sites along the European Coast, at which the mean level of wave power resource ranges between 15 and 88 kW per metre of wave front. Uncertainties are discussed and estimated for each device.Computed power matrices and results for the mean annual power absorption are assembled in a summary sheet per device. Comparisons of the selected devices show that, despite very different working principles and dimensions, power performance measures vary much less than the mean annual power absorption. With the chosen units, these measures are all shown to be of the order of 1.

New results from the most recent work within the Norwegian Joint Industry Project (JIP) “Higher Order Wave Load Effects on Large Volume Structures” are presented. A nonslender theoretical model is validated from experiments for two fixed, vertical cylinders with different diameter/peak wavelength ratios. A combination of complete diffraction first-order simulations, sum and difference frequency second-order simulations, and third-order FNV (Faltinsen, Newman, and Vinje, nonlinear long wave model) is implemented in order to develop a simplified and robust ringing load model for a large range of cylinder diameter/peak wavelength ratios. Results from the full diffraction second-order analysis show a significant reduction of second-order loads compared to pure FNV in the wavelength range relevant for ringing loads. The results show improved correspondence with high-frequency experimental loads compared with the unmodified FNV. Results for different cylinder peak wavelength ratios are presented, including validation against experiments. In addition, a few simplified response simulations are carried out demonstrating significant improvements with the modified FNV model.

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In this paper, a joint distribution of all relevant environmental parameters used in design of offshore structures including directional components is presented, along with a novel procedure for dependency modelling between wind and wind sea. Probabilistic directional models are rarely used for response calculation and reliability assessments of stationary offshore structures. However, very few locations have the same environment from all compass directions in combination with a rotationally symmetric structure. The scope of this work is to present a general environmental joint distribution with directional descriptions for long term design of stationary offshore structures such as offshore wind turbines. Wind, wind sea and swell parameters will be investigated for a chosen location in the central North Sea.

The design process for offshore wind turbines includes a fatigue life evaluation of the structure with the relevant environmental conditions at the specified wind farm location. Such analyses require long-term distributions of the environmental parameters including their correlation. In general, the significant wave height, wave peak period and mean wind speed are the most important parameters for describing offshore environmental conditions. However, due to the low side-to-side damping level of offshore bottom-fixed wind turbines, wave directions misaligned with the wind direction may excite low-damped vibrational modes. As a consequence, the accumulated fatigue damage in the wind turbine foundation may change, compared to collinear wind and waves. In the current work, an extension to the three-parameter environmental joint probability distribution is presented, with the resulting distribution being a function of the significant wave height, peak period of the total sea, mean wind speed and the wave directional offset compared to the mean wind heading i.e. the wind-wave misalignment. The sea states within a 1-year return period for Dogger Bank are presented, as well as the 10- and 50-year environmental contour lines and extreme wind-wave misalignment angles.