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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