MATHEMATICAL MODELS OF HYDRO- OR AERO-DYNAMIC FORCES ACTING ON SHIP MOVING IN AN OBLIQUE DIRECTION WITH FLUIDDYNAMIC CONCEPTS

When advancing slowly, a ship's motion is strongly affected by existing external forces, such as wind forces, resulting in drifting at angles that vary from small to large. When simulating maneuvering in wind, the hydrodynamic lateral force Y, the yaw moment N and the longitudinal force X vary with the ship's drift angle, and the aerodynamic forces vary with wind direction. These forces should all be describable by simple and accurate mathematical models covering all ranges of drift angle and wind direction. It is desirable, too, that the mathematical model be a physical model based on hydrodynamics or aerodynamics. This paper separates fluid force from ideal force (Munk moment), lift and induced drag forces due to viscosity, cross flow drag force, and frictional drag forces. As a result, it develops a mathematical model that describes the X, Y and N components of the fluid dynamic forces acting on the ship.