A Computationally Efficient Method for Nonlinear Multihull Seakeeping.

Abstract

A method for predicting the large amplitude motions of multihull vessels in a computationally efficient and robust manner has been developed and demonstrated. The present theory utilizes frequency domain hydrodynamic coefficients that include hull interactions in the radiation problem and a body-exact solution of the time-varying hydrostatic and Froude-Krylov forces in the time-domain. The theory and computational tool have been developed with a stated objective of supporting multihull design optimization, which requires extremely fast and stable computations that can accurately assess the seakeeping measure of merit in a relative sense. Higher fidelity tools can be used subsequent to a converged design to obtain a more accurate assessment of seakeeping performance. The contribution of this work to the general body of knowledge is in the development of a theory that captures hull interaction effects at lower ship speeds, where interaction effects are likely, while retaining the numerical efficiency of strip theory. A far-field approximation is invoked, whereby the radiated waves from one demi-hull appear as incident waves to another demi-hull. Comparisons of the present theory to model test data and 3D computations have shown fairly good agreement for some ship designs and, while capturing correct trends, relatively poor agreement for other ship designs. Agreement is generally better for multihulls that are long and slender with demi-hull separation greater than two times the demi-hull beam.