A Detailed Validation of Numerical Flow Analysis (NFA) to Predict the Hydrodynamics of a Deep-V Planing Hull

Abstract

The focus of this paper is to describe and document the recent effort to validate the computer code Numerical Flow Analysis (NFA) for the prediction of hydrodynamic forces and moments associated with deep-V planing craft. This detailed validation effort was composed of three parts. The first part focuses on assessing NFA’s ability to predict pressures on the surface of a 10 degree deadrise wedge during impact with an undisturbed free surface. Detailed comparisons to pressure gauges are presented for two different drop heights, 6 inches and 10 inches. Results show NFA accurately predicted pressures during the slamming event. The second part examines NFA’s ability to match sinkage, trim and resistance from experiments performed on constant deadrise planing hulls, detailed in Fridsma (1969). Simulations were preformed on two 20 degree deadrise hullforms of varying length to beam ratios (4 and 5) over a range of speed-length ratios (2, 3, 4, 5, and 6 knots-ft -1/2). Results show good agreement with experimentally measured values, as well as values calculated using Savitsky’s parametric equations, detailed in Savistsky (1964). The final part of the validation study focused on assessing how well NFA was able to accurately model the complex multiphase flow associated with high Froude number flows, specifically the formation of the spray sheet. NFA simulations of a planing hull fixed at various angles of roll (0 degrees, 10 degrees, 20 degrees, and 30 degrees) were compared to experiments from Judge (2012). Comparisons to underwater photographs illustrate NFA’s ability to model the formation of the spray sheet and the free surface turbulence associated with planing boat hydrodynamics.