A time domain maneuvering simulation of an IACC class yacht suitable for the analysis of unsteady upwind sailing and tacking is presented. The simulation code (RODAN) considers motions in six degrees of freedom. The hydrodynamic and aerodynamic loads are calculated primarily with unsteady potential theory supplemented by empirical models. The hydrodynamic model includes the effects of incident waves. Control of the rudder is provided by a simple feedback autopilot which is tuned to mimic human steering.
The hydrodynamic models are based on the superposition of force components. The components fall into two groups, those which the yacht will experience in calm water, and those due to incident waves. The calm water loads include double body maneuvering loads hydrostatic loads, free surface radiation loads, and viscous/residual loads. Incident wave components include Froude-Krylov and diffraction loads.
The double body maneuvering loads are calculated with an unsteady panel code which treats the instantaneous geometry of the yacht below the undisturbed free surface.
The Groude-Krylov pressures are integrated over the surface defined by the panel code. The free surface radiation loads are calculated via convolution of impulse response functions derived from seakeeping strip theory. The diffraction loads are also derived from strip theory. The viscous are residual loads are based upon empirical estimates.
The aerodynamic models are based on a database of steady state sail coefficients. Dynamic effects are modeled by using the instantaneous incident wind velocity and direction as the independent variables for the sail load contribution of each of several chordwise strips. The sail coefficient database was calculated numerically with potential methods and simple empirical viscous corrections. Additional aerodynamic load calculations are made to determine the parasitic drag of the rig and hull.