Validation of Numerical Predictions of the Impact Forces and Hydrodynamics of a Deep-V Planing Hull

Abstract

Abstract : The focus of this paper is to describe and document a recent effort to assess these numerical codes for the prediction of deep-V planing craft hydrodynamic forces and moments and evaluate how well NFA models the complex multiphase flows associated with high Froude number flows, specifically the formation of the spray sheet. This detailed validation effort was composed of three parts. The first part focused on assessing the codes' ability to predict pressures on the surface of a 10 degree deadrise wedge during impact with an undisturbed free surface. Detailed comparisons of NFA to pressure gauges show that NFA accurately predicted pressures during the slamming event. Comparisons of experimental measurements with LAMP predictions showed fairly good agreement, though LAMP tends to overpredict pressures. The second part examines the codes' ability to match sinkage, trim and resistance from Fridsma's experiments performed on constant deadrise planing hulls. Results show good agreement between NFA and experimentally measured values, as well as values calculated using Savitsky's parametric equations. Fairly good agreement was shown between LAMP and experimental values as well, with trim predictions matching well and heave tending to be over-predicted. The final part of the validation study focused on assessing how the codes' ability to accurately model the complex multiphase flow associated with high Froude number flows, specifically the formation of the spray sheet. 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. Though LAMP was not used to model the complex flow, it accurately predicted the model heave and trim. Overall these three validation studies provide a detailed assessment on the current capabilities of NFA and LAMP to predict the hydrodynamics of a deep-V planing hull.