Reduced-order model for ship motions incorporating a volume-based calculation of body-nonlinear hydrostatic and Froude-Krylov forces

Abstract

The theoretical background of a fast time-domain simulation tool for ship motion in waves, commonly referred to as SimpleCode, is reviewed. The tool implements a body-nonlinear formulation for the hydrostatic and Froude-Krylov forces with the instantaneous submerged volume and centroid of sections along the ship's length. Other forces are approximated by ODE (ordinary differential equation) like polynomials. SimpleCode implements a six degrees of freedom (DOF) solver as well two 3-DOF solvers: one for vertical plane motions (heave, roll, and pitch) and another for horizontal plane motions (surge, sway, and yaw). While the initial objective of the tool was limited to the statistical validation of extrapolation methods, it was later extended to other applications and is considered to be a general reduced-order numerical model (ROM) of ship motions in waves. The SimpleCode has been used for the development and statistical validation of the EPOT and split-time methods and for the identification of extreme response events in a multi-fidelity seakeeping analysis.