The application of advanced hydrodynamic analyses in ship design

Abstract

Recent advances in computational hydrodynamics offer the opportunity to incorporate more accurate analyses earlier in the ship design process. In particular, significant work has been conducted towards the prediction of nonlinear wave-induced motions and loads in the time domain. Seakeeping analysis has traditionally been incorporated late in the design process, using parametrics and two-dimensional linear strip theory methods in the frequency domain. Model testing, due to its relative expense, is incorporated even later in the process. As a result, seakeeping performance is often evaluated after, rather than during, each stage of ship design. Serious problems, particularly in structural loading, may not be discovered until late in the process. This research investigates the applicability of nonlinear time domain predictions to ship design. A method for incorporating time domain analyses of motions and loads in early design is proposed. Several hulls are tested in the frequency and time domains in moderate to severe seas. The first set of hulls are mathematically defined, derived from the well-known Wigley Seakeeping Hull, with variations in flare, tumblehome, and waterline entrance both above and below the calm waterline. A Very Large Crude Carrier, representative of many commercial hulls, is also analyzed. The nonlinear motions and loads differ substantially from linear predictions, especially in critical operating conditions. The nonlinear methods also predict significant variations in performance due to flare and tumblehome, which are not adequately observed with linear theory. Despite increased preparation complexity and computation times, and requirements for validation, time domain methods should be incorporated in early design. Detailed analyses of hull concepts may then be conducted much sooner, reducing the economic and schedule impact of any necessary changes.