Benchmark on the prediction of whipping response of a warship model in regular waves

Results

are presented of a benchmark study organised by the Marstruct Virtual Institute on motion and global wave loads on a warship model in regular waves. The aim of the study is the quantification of the uncertainty in numerical whipping predictions. Nine institutions participated in the benchmark with 6 codes, quantifying the hydroelastic responses. The seakeeping methods employed include non-linear strip theory, 3D boundary element method formulated in frequency and time domain, and computational fluid dynamics (CFD). Euler and Timoshenko beams are used for modelling the hull girder stiffness. Experimentally based methods, CFD and momentum theories are employed for calculating slamming loads. The study encompasses a comparison of wet natural frequencies of ship vertical flexural vibration, vertical ship motions, vertical wave bending moments and whipping bending moments at midships. Wave-induced and whipping responses are analysed for regular head waves of different steepness and for two ship speeds. For most comparisons, experimental results are available from previously performed and published model-scale experiments on a Canadian Patrol Frigate. Frequency-independent model error, which is commonly used for uncertainty quantification of rigid body seakeeping responses is extended to quantify uncertainties in whipping bending moments. It is found that fully coupled CFD and finite element method (FEM) provide results consistent with measurements, but such simulations are prohibitively computationally expensive and the interpretation of results can be challenging. The combination of the potential theory seakeeping method with correction based on CFD-FEM simulation for limiting number of cases is a promising alternative.