追波中航走船の操縦運動と横揺れとの連成挙動について

抄録

In this paper, the emphasis is laid upon yaw-sway-roll-rudder coupled motion of a container ship in following seas.
We take the case that the component of ship speed in the direction of wave propagation is equal to the wave celerity, i. e., the encounter frequency is nil. The linearized equations of sway, yaw and roll coupled motion in still water are generalized to use by adding the terms. of wave exciting forces.
The hydrodynamic force coefficients varying with ship's relative position to wave system, are obtained by captive model tests in regular following waves generated by means of a wave making board. Using the experimental results, dynamic stability of a ship in following seas is discussed.
It reveals the possibility and physical mechanism of an unstable yaw-roll behavior due to the fact that :
1) the wave exciting yaw moment acts as a negative restoring moment ;
2) hydrodynamic forces acting upon a ship in following seas give less damping compared with in still water ;
3) small metacentric height encourages a heavy yaw-roll coupling.
However, such unstable behavior in following seas can be stabilized by adding an adequate control parameters of autopilot steering system.