Time simulation of manoeuvring and seakeeping assessments using a unified mathematical model

The formulation of traditional seakeeping and calm water manoeuvring theories usually preclude any study in which the manoeuvring and seakeeping performance of a ship interact as observed, for example, during the turning of a ship in a seaway or during operation in following seas. Recently, a unified mathematical model [1] has been proposed which encapsulates the traditional theories, yet is applicable to the more general study of a ship manoeuvring in a seaway. The arbitrary nature of ship motions excited by random waves dictates that this model uses convolution type expressions in the formulation of the hydrodynamic forces and moments acting on the ship. In the limiting cases, the unified mathematical model has been shown to reduce to the traditional models of seakeeping and calm water manoeuvring. This paper describes the implementation of the unified mathematical model in the form of a time simulation, and presents comparisons with the traditional theories of seakeeping and calm water manoeuvring. This demonstrates that, given the correct data, linear manoeuvring and seakeeping performances can be investigated using a single mathematical model. For illustrative purposes, preliminary results for a Mariner type ship performing circle and zig-zag manoeuvres in a seaway are presented. This investigation also includes a time simulation representation of excitation components. This is achieved by representing the instantaneous underwater shape of the hull using quadrilateral panel elements and summing contributions of the fluid actions on each panel. Results obtained for the Mariner ship type are presented with reference to linear and non-linear effects.