Fast time domain evaluation of Anti-Roll Tank and ship coupling using non-linear retardation functions

Anti-Roll Tanks (ART) have been used for more than a century to damp the roll motion of ships. These devices exist in various configurations, passively and actively controlled. All versions rely on resonant water motions in a chamber which, by essence, is a very non-linear process. To account for these non-linearities, several approaches have been proposed, where the most recent and complete one is the direct coupling of time domain seakeeping codes with a CFD models of the ART. However, this approach comes at the price of relatively high computation effort. This is in contradiction with the need for long simulations to establish the effects of the non-linearities in the ART reaction forces on extreme events. To reduce the computation costs of a direct simulation, a new technique is proposed which uses retardation functions based on harmonic ART response data. The technique proposed here uses a family of retardation functions with a Hilbert transform method for time dependent interpolations to capture the non-linearity in the response of the tank as a function of excitation amplitude.