A Critical Assessment of Potential Flow Models for Ship Seakeeping

Many studies on the seakeeping problem of ships based on potential flow models have been performed by applying Rankine panel methods (RPMs) both in frequency domain and more recently in time domain to capture some nonlinear effects. Most analyses have treated slender ships and suggested some improvements of the estimation accuracy at least for slender ships and for the global hydrodynamic forces and ship motions. However, it is not clear whether the methods are effective also for blunt ships and for the estimation of local forces or not. Full comparison between different computation methods especially for blunt ships and for local physical values is necessary, and this may lead us to a critical assessment of potential flow models for ship seakeeping. We present results for systematic experiments for a Series-60 (Cb = O.8) measuring global hydrodynamic forces and local radiation/diffraction waves at the same time. Numerical calculations by strip method, Green function method (GFM), frequency domain RPM and time-domain RPM are compared with experiments. Based on this comparison, we attempt a evaluation of performances of the seakeeping codes. A key issue in the discussion is whether only viscous CFD codes may be capable of capturing local flow details at the bow of blunt ships.