Coupled roll and directional stability characteristics of surface ships.

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Author
Logsdon, Mary J.
Date
1992-06Advisor
Healey, Anthony J.
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Show full item recordAbstract
The problem of roll, sway and yaw motions of surface ships is considered. A
mathematical model is developed which consists of the nonlinear maneuvering equations
and incorporates cross coupling between sway force, yaw moment and the roll angle induced
during a steady turn. The hydrodynamic derivatives and coefficients of a typical container
ship were used as the base-line study model. The coupled system of nonlinear algebraic
equations is formulated and solved to predict the steady state roll angle, sway velocity and
turning rate as a function of the rudder angle. The results are then compared to that of the
decoupled systems currently employed. A local perturbation is implemented in the vicinity
of the above steady states to investigate dynamic stability of motion. Sensitivity analysis with
respect to important design parameters such as speed loss during turning, approach speed,
transverse metacentric height and trim is performed. Results demonstrate the significance
of the coupling between roll, sway and yaw and the need to incorporate similar studies in
the ship design and analysis process.