We present a model for the fast evaluation of the total drag of ship hulls operating in both wet and dry transom stern conditions, in calm or wavy water, based on the combination of an unsteady semi-Lagrangian potential flow formulation with fully nonlinear free-surface treatment, experimental
correlations, and simplified viscous drag modeling. The implementation is entirely based on open source libraries. The spatial discretization is solved using a streamline upwind Petrov‐Galerkin stabilization of an iso-parametric, collocation based, boundary element method, implemented
using the open source library deal.II. The resulting nonlinear differential-algebraic system is integrated in time using implicit backward differentiation formulas, implemented in the open source library SUNDIALS. The Open CASCADE library is used to interface the model directly with computer-aided
design data structures. The model accounts automatically for hulls with a transom stern, both in wet and dry regimes, by using a specific treatment of the free-surface nodes on the stern edge that automatically detects when the hull advances at low speeds. In this case, the transom stern is
partially immersed, and a pressure patch is applied on the water surface detaching from the transom stern, to recover the gravity effect of the recirculating water on the underlying irrotational flow domain. The parameters of the model used to impose the pressure patch are approximated from
experimental relations found in the literature. The test cases considered are those of the U.S. Navy Combatant DTMB-5415 and the National Physical Laboratory hull. Comparisons with experimental data on quasi-steady test cases for both water elevation and total hull drag are presented and discussed.
The quality of the results obtained on quasi-steady simulations suggests that this model can represent a promising alternative to current unsteady solvers for simulations with Froude numbers below 0.35.
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boundary element method;
unsteady nonlinear free surface
Document Type: Research Article
SISSA—International School for Advanced Studies, Trieste, Italy
Publication date: March 1, 2017
This article was made available online on January 6, 2017 as a Fast Track article with title: "Wet and Dry Transom Stern Treatment for Unsteady and Nonlinear Potential Flow Model for Naval Hydrodynamics Simulations ".
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The Journal of Ship Research is a quarterly publication providing highly technical papers on applied research in hydrodynamics, propulsion, ship motions, structures, and vibrations. While the Journal requires that papers present the results of research that advances ship and ocean science and engineering, most contributions bear directly on other disciplines, such as civil and mechanical engineering, applied mathematics, and numerical analysis. High quality papers are contributed from the U.S., Canada and overseas, with representation from established authorities as well as new researchers.
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