CFD Verification and validation (V & V) studies are conducted using both single-and two-phase flow solvers for the high-speed stepped planing hulls, which provides the assessment of their capability for design and identification of issues for the further experimental and CFD research. The hydrostatic analysis supports previous studies in showing the importance and sensitivity of the results regarding the hydrostatic setup. Setting by displacement and LCG is the best, but more accurate documentation of the static sinkage and trim is required. The intervals of V & V are somewhat larger for stepped vs. un-stepped hulls, but nonetheless reasonable. The force and moment analysis shows the distributions of the pressure vs. frictional resistance, longitudinal distributions of the lift force and balance of the pressure vs. frictional vs. weight pitch moments. The flow features on the bottom (i.e., stagnation, pressure, and spray areas), ventilated cavity and wake region are better resolved by the two-phase than the single-phase flow solver. The cavity shows air inflow from the side at the step and airflow ejected at the cavity reattachment. The predicted cavity size is larger for two-than for single phase flow, and the Lee (2014) empirical formula lies between them. Porpoising instability is predicted by both two-phase flow solvers, and it is shown that the heave and pitch natural period decrease with forward speed. Overall, the results from both codes and for both single- and two-phase are found to be sufficiently accurate to be used for design similarly to what was previously concluded by the same authors in case of un-stepped planing hulls.
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