Seakeeping Theory

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Seakeeping Theory

Fossen, Thor I.

The study of ship dynamics has traditionally been covered by two main theories: maneuvering and seakeeping. This chapter presents the seakeeping theory in equilibrium axes {s} and shows how the time‐domain solution known as the Cummins equation can be transformed to body‐fixed axes {b}. Different principles for the computation of the hydrodynamic coefficients can be used. The main tool is potential theory where it is assumed that the flow is constant, irrotational and incompressible such that time becomes unimportant. In order to evaluate the potentials a boundary value problem needs to be solved. The chapter derives the kinematics needed to transform the equations of motion from the seakeeping reference frame {s} to the body‐fixed reference frame {b} and the NED reference frame {n}. The time‐domain models are useful both for simulation and control systems design. Fluid memory effects and wave force terms are kept from the seakeeping theory.

fluid mechanics; hydrodynamics; kinematics; motion control; ships